T,~~~~~o LECTURES ON THE APPLICATIONS OF CHEMISTRY AND GEOLOGY TO AGRICULTURE.' The profit of the earth is for all: the king himself is served by the field."'-Ewcles. v. 9. BY JAS. F. W. JOHNSTON, M.A., F.R.SS. L. & E., FELLOW OF THE GEOLOGICAL AND CHEMICAL SOCIETIES, Honorary Member of the Royal Agricultural Society, Foreign Member of the Royal Swedish Academy of Agriculture, &c. &c; Chemist to the Agricultural Chemistry Association of Scotland, and Reader in Chemistry and Mineralogy in the University of Durham. NEW EDITION, WITH AN APPENDIX, CONTAINING SUGGESTIONS FOR EXPERIMENTS IN PRACTICAL AGRICULTITRB. NEW YORK: C. M. SAXTON, AGRICULTURAL BOOK PUBLISHERS No. 123 FULTON STREET. 1851. TO THR VENERABLE CHARLES THORP, D.D. F.R.S., &c., &c., ARCHDEACON OF DURHAM, AND WARDEN OF THE UNIVERSITY OP DURHAM. MY DEAR SIR,I cannot more appropriately dedicate the following Lectures than to the head of the University with which I am officially connected, and within the walls of which the earlier Lectures were first delivered. In publishing this Volume I am only endeavouring to follow out the enlightened intentions of yourself and the other Founders of the University of Durham, who have contributed so largely of their fortune and their influence foi the promotion and diffusion of sound and useful learning. That you have-so long and so successfully laboured to carry these intentions into effect, is another reason why I desire to dedicate my work especially to you. I need scarcely add how much pleasure it affords me to embrace this public opportunity of testifying my own-personal regard and esteem. Believe me, my dear Sir, With much respect, Your obedient humble servant, JAMES F. W. JOHNSTON. PREFACE. THE First Part of the following Lectures was addressed to a Society~ of practical agriculturists, most of whom possessed no knowledge whatever of scientific Chemistry or Geology. They commence, therefore, with the discussion of those elementary principles which are necessary to a proper understanding of each branch of the subject. Every thing in such Lectures, which is not-or may not be-easily understood by those to whom they are addressed, is worse than useless. It has been my wish, therefore, to employ no scientific terms, and to refierto no philosophical principles, which I have not previously explained. To many who may take up the latter portions cfthe work, some points may appear obscure or difficult to be f;lly understood; such persons will, I hope, do me the justice to begin at the beginning, and to blame the Author only when that which is necessary to the understanding of the later is not to be found in the earlier Lectures. For the sake of clearness, I have, in the following pages, divided the subject intofour Parts-the study of each preceding Part preparing the way for a complete understanding of those which follow. Thus, Part I. is devoted to the organic elements and parts of plants, the nature and sources of these elements, and to an explanation of the mode in which they become converted into the substance of plants;-Part II., to the inorganic elements of plants, comprehending the study of the soils from which these elements are derived, and * The Durham County Agricultural Society, and the Members of the Durham Farmers' Club. Vi PREFACE. the general relations of geology to agriculture;-Part III., to the various methods, mechanical and chemical, by which the soil may be improved, and especially to the nature of manures, by which soils are made more productive, and the amount of vegetable produce increased;-and Part IV., to the results of vegetation, to the kind and value of the food produced under different circumstances, and its relation to the growth and feeding of cattle, and to the amount and quality of dairy produce. By this method I have endeavoured, to ascend from the easy to the apparently difficult; and I trust that the willing and attentive reader will find no difficulty in keeping by my side during the entire ascent. The Author has much pleasure in now presenting these Lectures to the public in a complete form. He has only to express a hope that the delay which has occurred in the publication of the latter part of the work has enabled him to render it more useful, and therefore more worthy of the public approbation. NOTE.-The rapid sale of a large impression having rendered a second edition of the first and second Parts necessary before the entire completion of the work, such alterations, corrections, and additions only have been made as could be introduced without altering the original paging of the work. Several oversights, however, have been corrected, and some omissions supplied, which presented themselves in the earlier edition. CONTENTS. PART X. ON THE ORGANIC CONSTITUENTS OF PLANTS. LECTURE I. IMPORTANCE OF AGRICULTURE..ntroduction................. p.11 Hydrogen, its properties and' relations to Different kinds and states of matter.....21 vegetable life.............. p. 2 Carbon, its properties and relations to ve- i Nitrogen, its properties and relations to getable life..................... 23 vegetable life..................26 Oxygen, its properties and relations to ve- Rewards of study.........27 getable life......4............. LECTURE II. CHARACTERISTIC PROPERTIES OF ORGANIC SUBSTANCES. Characteristic properties of organic sub- On the constitution of the atmosphere....31 stances................ 2......28 IThe nature and laws of chemical combiRelative proportions of organic ele'ments..29 nation.....2...... 32 Of the form or state of combination in Of water, and itsrelations tovegetable life..36 which the organic elements enter into Of the cold produced by the evaporation and minister to the growth of plants......31 of water, and its influence on vegetation..43 LECTURE III. CARBONIC AND OXALIC ACIDS, THEIR PROPERTIES AND RELATIONS. Carbonic acid, its properties and relations Light carburetted hydrogen, the gas of to vegetable life....................45 marshes and of coal mines.....49 Oxalic acid, its properties and relations to Ammonia, its properties and relations to vegetablevegetable life................. v. 50 Carbonic oxide, its constitution -and pro- Nitric acid, its constitution and properties..56 perties..........***......a48 Questions to be considered.............57 LECTURE IV. SOURCE OF THE ORGANIC ELEMENTS OP PLANTS. Source of the carbon of plants............. 58 Form in which the nitrogen enters into Form in which carbon enters into thecir- the circulation of plants... 68 culation of plants................ 63 Absorption of ammonia by plants...... 70 Source of the hydrogen of plants......... 64 -Absorption of nitric acid by plants....... 72 Source of the oxygenof plants............ 66 Conclusions................. 74 Source of the nitrogen of plants..........ib. LECTURE V. HOW DOES THE FOOD ENTER INTO THE CIRCULATION OF PLANTS? General structure of plants, and of their Functions of the leaves.................. 89 several parts.........................75 Functions of the bark....................96 The functions of the root........ 76 Circumstances by which the functions of The course of the sap......... 85,the various parts of plants are modified.. 97 Functions of the stem8............... 88 Effects of marling..................,101 CONTENTS OF PART 1. LECTURE VI. SUBSTANCES OF WHICH PLANTS CHIEFLY CONSIST. Woody fibre or lignin-its constitution Of the fermentation of starch and sugar, and properties................p. 103 and of the relative circumstances under Starch-its constitution and properties....106 which cane and grape sugars generally Gum-its constitution and properties.....108 occur in nature................p. 115 Of Sugar-its varieties and chemical con. Of substances which contain nitrogen.stitution.................. 109 Gluten,.vegetable albumen, and diastase.116 Mutual relations of woody fibre, starch, Vegetable Acids.-Acetic acid, oxalic acid, gum, and sugar....................111 tartaric acid, citric acid, malic acid.....121 Mutual transformations of woody fibre, General observations on the substances starch, gum, and sugar..............112 of which plants chiefly consist..........126 LECTURE VII. CHEMICAL CHANGES BY WHICH THE SUBSTANCES OF WHICH PLANTS CHIEFLY CONSIST ARE FORMED FROM THOSE ON WHICH THEY LIVE. Chemical changes which take place du- Of the chemical changes between the ring germination, and during the devel- opening of the flower and the ripening opement of the first leaves and roots....130 oftlhe fruit or seed.......139 Of the chemical changes from the for- Of the chemical changes which take place mation of the true leaf to the expansion after the ripening of the fruit and seed.. 143 of the flower..........................134 Of the rapidity with which these changes On the production of oxalic acid in the take place, and the circumstances by leaves and stems of plants.*........ 137 which they are promoted............... b. LECTURE VIII. HOW THE SUPPLY OF FOOD FOR PLANTS IS KEPT UP IN THE GENERAL VEGETATION OF THE GLOBE. Of the proportion of their carbon which Of the supply of ammonia to plants..... 156 plants derive from the atmosphere......145 Of the supply of nitric acid to plants.....159 Of the relation which the quantity of car- Theory of the action of nitric acid and bon extracted by plants from the air, ammonia......163 bears to the whole quantity contained Comparative influence of nitric acid and in the atmosphere..................147 of ammonia in different climates.......166 How the supply of carbonic acid in the Stimulating influence ofthese compounds ab. atmosphere is renewed and regulated. 148 Concluding observations regarding the eneral conclusions in relation thereto... 155 organic constituents of plants........16 ] rai a monsiteso pa t..................... PARtT XX. ON THE INORGANIC ELEMENTS OF PLANTS. LECTURE IX. INORGANIC CONSTITUENTS OF VEGETABLE SUBSTANCES. Of the relative proportions of inorganic Of those compounds of the inorganic ele. matter in vegetable substances.......p. 178 ments which enter directly into the Kind of inorganic matter found in plants.. 180 circulation or exist in the substance Of the several elementary bodies usually and ash of plants...............183 met with in the ash of plants...........182 LECTURE X. INORGANIC CONSTITUENTS OF PLANTS CONTINUED. Inorganic constituents of plants continued.200 To what extent do the crops most usualTabular view of the constitution of the ly cultivated exhaust the soil of inorcompounds of the inorganic elements ganic vegetable food.................220 above described....................214 Of the alleged constancy of the inorganic On the relative proportions of the differ- constituents of plants, in kind and ent inorganic compounds present in quantity.....2.........2.........2.. the ash of plants........... 216 LECTURE XI. NATURE AND ORIGIN OF SOILS. Of the organic matter in the soil......229 On the general structure of the earth's General constitution of the earthy part of crust................................237 the soil.............................230 Relative positions and peculiar characOf the classification of soils from their ters of the several strata......'......239 chemical constituents.............232 Classification of the stratified rocks, their Of the distinguishing characters of soils extent, and the agricultural relations of and subsoils............... 235 the soils derived from them..........241 Of the general origin of soils......... 236 LECTURE XII. COMPOSITION OF THE GRANITIC ROCKS, AND OF THEIR CONSTITUENT MINERALS. Composition of the granitic rocks...... 257 Of the occurrence of such accumulations Of the degradation of the granitic rocks, in Great Britain, and of their influence and of the soils formed from them...260 in modifying the character of the soil..270 Of the trap rocks, and the soils formed Itow far these accumulations of drift infrom them..........263 terfere with the general deductions of Of superficial accumulations of foreign AgriculturalGeology...............272 materials, and of the means by which Of superficial accumulations of peat..... 275 they have been transported............266 LECTURE XIII. EXACT CHEMICAL CONSTITUTION OF SOILS. Of the exact nature of the organic con- I Of the exact chemical constitution of stituents of soils, and of the mode of certain soils, and of the results to be separating them.......277 deduced from them...................282 Of the exact chemical constitution of Of the physical properties of soils..290 the earthy part of the soil............281 Conclusion................297 PART III. ON THE IMPROVEMENT OF THE SOIL BY MECHANICAL AND CHEMICAL MEANS. LECTURE XIV. THE QUALITIES OF; THE SOIL MAY BE CHANGED BY ART. Connection between the kind of soil and Of the theory ofsprings........p. 312 the kind of plants that grow upon it.p. 304 Qf ploughing and subsoiling.........318 Of draining, and its effects..............306 Of deep-ploughing and trenching......321 Practical effects of draining............311 Improvement of the soil by mixing.....323 LECTURE XV. IMPROVEMENT OF THE SOIL BY CHEMICAL MEANS. Of saline manures...............,327 Use of common salt........ *....* 345 Theory of the action of potash and soda.328 Chlorides of calcium and magnesium...347 Sulphates of potash, soda, magnesia, and Phosphate of lime and earth of bones...348 lime (gypsum)................ 331 Silicates of potash and soda........349 Theory, of the action of these sulphates..332 Salts of ammonia...............ib. Nitrates of potash and soda............335 Of mixed saline manures............352 Effect of these nitrates on the quantity Wood ashes..........................ib. of various crops.....................336 Use of kelp................355 Effect of the nitrates on the quality of Straw ashes.......................356 the crop............... 339 Turf-peat or Dutchashes............359 Cases in which they have failed..;....341 Crushed granites and lavas......... 361 Theory of the action of these nitrates.. 343 Results of experiments with mixed maSpecial effects of the nitrates of potash nures.......... 362 and soda.............,...344 LECTURE XVI. OF THE USE OF LIME AS A MANURE. Of the composition of common and Ought lime to be applied in large doses magnesian lime-stones...........364 at distant intervals, or in smaller quanOf the burning and slaking of. lime....366 tities more frequently repeated I.....383 Changes. which the, hydrates'of lime Form and state of combination inwhich and magnesia undergo by prolonged lime ought to be applied to the land....386 exposure to the air..............367 Use and advantage of the compost form.388 States of chemical combination in which When ought lime to be applied I..... 389 lime may be applied to the land.......369 Of the effects produced by lime upon Of the various natural forms in which the land and upon the crops..........390 carbonate of lime is applied to the land.370 Circumstances by which the effects of Effects of marl, and of the coral, shell, lime are modified...................393 and lime-stone sands upon the soil....374 Effects of an overdose of lime..........395 Of the use of chalks, as a manure.......375 Length of time during which lime acts..396 Is lime indispensable to the fertility of' Of the sinking of lime into the soil......397 the soil?................... 377 Why liming must be repeated......398 States of combination in which lime ex- Theory of theaction of lime...........400 ists in the soil............., 379 Of lime as the food of plants..........ib. Of the quantity of lime which ought to The chemical action of lime is exerted' be added to the soil.................381 chiefly on the organic matter of the soil.401 CONTENTS OF PART III. Of the forms in which organic matter Of the comparative utility of burned and usually exists in the soil, and the cir unburned lime.................p. 408 cumstances under which its decom- Action of lime on organic substances, position may take place...........p. 401 which contain nitrogen...... 409 General action of alkaline substances How these chemical changes directly upon organic matter...............403 benefit vegetation..............412 Special effects of caustic lime upon the Why lime must be kept near the surface.ib. several varieties of organic matter in Action of lime upon the inorganic or the soil....................... 404 mineral matter of the soil...........413 Action of mild (or carbonate of) lime Action of lime on animal and vegetable upon the vegetable matter of the life.....,.............415 soil...................406 Use of silicate of lime..................416' LECTURE XVII. OF ORGANIC MANURES. Of green manuring or the application of Improvement of the soil by laying down vegetable matter in a green state......417 to grass................. 424 Important practical results obtained by Improvement of the soil by the planting green manuring.......... 418 of trees........................429 Of the plants which in different soils Of the use of sea-weed as a manure.....431 and climates are employed for green Of manuring with dry vegetable submanuring.................419 stances.............................. 433 Will green manuring alone prevent land Use of rape-dust......................434 from becoming exhausted........421 Use of decayed vegetable matter as a Of the practice of green manuring.....422 manure...............436 Of natural manuring with recentvegeta- Use of charred vegetable matters-soot, ble matter...................... b. &c., as manures...................437 Weight of roots left in the soil by the Of the theoretical value of different different grasses and clovers...........423 vegetable substances as manures.....440 LECTURE XVIII. ANIMAL MANURES. Of flesh, blood, and skin................443 Of solid animal manures-night soil, Of wool, woollen rags, hair, and horn...445 the dung of the cow, the horse, the Of the composition of bones............446 sheep, and the pig............. 465 On what does the fertilizing action of Of the quantity of manure produced bones depend'........447 from the same kind of food by the Of the application of bone-dust to pas- horse, the cow, and the sheep.......468 ture lands 451 Of the relative fertilizing values of difOf animal charcoal, the refuse of the su- ferent animal excretions.............469 gar refineries, and animalized carbon..452 Influence of circumstances on the qualiOf fish, fish refuse, whale blubber, and ty of animal manures........ 470 oil........................ 453 Of the changes which the food underRelative fertilizing value of the animal goes in passing through the bodies of manures already described.........454 animals..............;.. 472 Of the droppings of fowls-pigeons' Of farm-yard manure, and the loss it un. dung and guano..... 456 dergoes by fermenting..............474 Results of experiments with guano......459 Of top-dressing with fermenting maOf liquid animal manures-the urine of nures..............................477 man, of the cow, the horse, the Of eating off with shee...............478 sheep, and the pig.................460 Of the improvement of the soil by irriOf the waste of liquid manure-of urate gation.............................479 and of sulphated urine..............463 PA R' ZIV. vi THE PRODUCTS OF THE SOIL, AND THEIR USE IN THE FEEDING OF ANIMALS. LECTURE XIX. OF THE PRODUCE OF THE SOIL. Of the maximum or greatest possible and Of the composition of rye, and the effect the average or actual produce of the of different manures upon its composiland......p. 487 tion...................p. 510 Of the circumstances by which the pro- Composition of rice, Indian corn, and duce of food is affected-climate, sea- buck-wheat..........................511 son, soil, &c......................... 488 On the alleged general effect of different Influence on the mode of culture on the manures in modifying the amount of produce of food..........;....... 490 gluten and albumen in wheat, barley, Of the theory of the rotation of crops.... 492 oats, and rye............... 513 Why land becomes tired of clover...... 494 Composition of peas, beans, and vetches. 515 Of the theory of fallows............... 495 Effect of soils and manures on the quality Of wheat and wheaten flour............. 498 of peas and beans................... 518 Of the composition of, wheaten flour.... 499 Of the composition of potatoes, and the Of the influence of soil and climate on effect of circumstances in modifying the composition of wheaten flour...-... 501 their composition.... 620 Influence of variety of seed, of mode of Of the composition of the turnip, the caculture, of time of cutting, and of special rot, the beet, andl the parsnip.......... 523 manures on the composition of wheat. 502 Of the composition of the green stems of Of the effects of germination and of bak- peas, vetches, clover, spurry, and ing upon the flour of wheat........... 504 buck-weat.............. 525 Of the supposed relation between the per- Of the composition of the grasses when centage of gluten in flour, and the made into hay.................... 526 weight of bread obtained from it...... 507 Of hemp, line, rape, and other oil-bearing Of the composition of barley, and the in- seeds......... 528 fluence of different manures upon the General differences in composition among relative proportions of its several con- the different kinds of vegetable food... 529 stituents....................... 508 Average composition and produce of nuEffect of malting upon barley........... 509 tritive matter per acre, by each of the Of the composition of oats, and effect of usually cultivated crops............... 530 manures in modifying that composition. 510 LECTURE XX. OF MILK AND ITS PRODUCTS. Of the properties and composition of Of the separation and measurement of milk.. 533 cream-the galactometer-the compoOf the circumstances by which the corn sition of cream, and the preparation of position or quality of milk is modified. 534 cream cheese.................... 547 Of the circumstances which affect the Of the separation of butter by churning quantity of the milk.................. 540 orotherwise......................... 549 Of the mode of separating and estimating Of the composition of butter............ 551 the several constituents of milk....... 542 Of the average quaniity of butter yielded Ofthe sugar of milk, and of the acid of by milk and cream, and of the yearly milk or lactic acid.................... 543 produce of a cow................... 552 Of the mutual relations which exist be- Of the circumstances which affect the tween lactic acid and the cane, grape, quality of butter........... 553 and milk sugars............ 544 Of the fatty substances of which butter Of the souring and preserving of milk... 546 consists, and of the acid of butter (buty CONTENTS OF PART IV. ric acid), and the capric and caproic Of the average quantity of cheese yielded acids..................p. 557 by different varieties of milk, and of Of casein or the curd of milk and its pro- the produce of a single cow..........p. 580 perties............................... 561 Of the fermented liquor from milk, and of Of the relations of casein to the sugars milk vinegar 581 and fats............... 562 Of the composition of the saline constituOf the rancidity and preservation of butter 563 ents of milk........................... ib, Of the natural and artificial curdling of Purposes served by milk in the animal milk................................. 566 economy............................ 582 Of the preparation of rennet......... 567 On the churning of milk in the French Theory of the action of rennet.......... 569 churn................................ ib. Of the circumstances by which the quali- Quantity of milk and butter yielded by ty of cheese is affected................ 573 Ayrshire cows....................... 583 Circumstances under which cheese of Profit of making butter and cheese comdifferent qualities may be obtained from pared with that of selling the milk..... 584 the same milk........................ 575 LECTURE XXI. OPl TtIE FEEDING OF ANIMALS, AND THE PURPOSES SERVED BY THE FOOD. Of the substances of which the parts of l Kind and quantity of additional food reanimals consist....................... 586 quired by a pregnant animal.......... 604 Whence does the body obtain these sub- Kind and quantity of additional food restances 3 are they contained in the quired by amilking animal........... 605 food?.., 589 Influence of size, condition, warmth, exOf the respiration of animals, and of the ercise, and light on the quantity offood purposes served by the starch, gum, necessary to make up for the natural and suaar contained in vegetable food.. 591 waste.................. 607 Of the origin and purposes served by the Influence of the form or state in which fat of animals........................ 594 the food is given on the quantity reOf the natural waste of the parts of the quired by an animal............... 611 body in a full-grown animal........... 597 Influence of soil and culture on the nutriOf the kind and quantity of food necessa- tive value of agricultural produce... 612 ry to make up for the natural waste in Car. we correctly estimate the feeding the body of a full-grown animal....... 59S properties of different kindsof produce The health of an animal can be sustained under all circumstances............ 613 only by a mixed food..O.. C. GOC Effect of different modes of feeding on Of the kind and quantity of additional the manure and on the soil.......... 615 food required by the fattening animal.. 60. Summary of the views illustrated in this Kind and quantity of additional food re. lecture.......................... 617 quired by a growing animal........... 602 Concluding section................ 619 APPENDXX. L Suggestions for experiments in VIII. Results of experiments in practi practical agriculture..............p. 1 cal agriculture made in 1842II. Effect of sudden alternations of B. Experiments on potatoestemperature.............. 11 1. Those of Mr. Campbell, of II. Results of experiments in practical Craigie.............. p. 47:agriculture made during the spring 2. Those of Mr. Fleming, of and summer of 1841- Barochan....... 47 to 51 AtAske Hall........................13 C. Experiments upon barley....51 At Erskine,............... 16 D. Experiments upon oatsAt Barochan —- 1IThose of Lord Blantyre....52 1L On hay...............17 2. Those of Mr. Fleming.....53 2. On winter rye.......... 18 E. Experiments upon wheat3. On wheat................. 19 1. Those of Lord Blantyre..... 53 4. On potatoes..,..............20 2. Those of Mr. Flemiig.....54 5. On moss oats.,.:............. 21 3. Those of Mr. Burnet, ofGad6, On oatsi with sulphate and ni girth...............ib trate of soda, as a top.dressing.22 F. Experiments upon pasture and 7. On peas and beans,with sulphate other grasses- of soda..................... 23 1. Those of Mr. Alexander.....55 8. On nitrate of soda as a top-dress- 2. Those of Mr. Fleming.......56 ing for gooseberry and currant 3. Those ofMr.Campbell,of sla.ib. bushes............ 23 G. Experiments upon mixed crops IV. Suggestions for comparative ex- by Mr. Alexander............57 periments with guano and other H. Experiments upon beansmanures............... 24 1. Those of Mr. Alexander....ib. V. Of the examination and analysis of 2. Those of Lord Blantyre.....ib. soils.............................27 I. Effect of the top-dressings apDetermination of the physical pro- plied in 1841 upon the crop perties of the soil.............. ib. of 1842................... 58 Of the organic matter present in II. Remarks upon the experiments the soil..........................29 of 1842...... ib. Of the soluble saline matter in the A. The experiments on turnips...59 soil....31 B. The experiments on potatoes..64 Determination of the quantity of C. The experiments on barley....67 the several constituents of the D. The experiments on oats.......ib. soluble saline matter.............33 E. The experiments on wheat....68 Of the insoluble earthy matter of F. The experiments on grass....71 the soil....37 G. The experiments on mixed VI. Different theories of the action of crops.................. 73 gypsum.......................39 H. The experiments on beans....ib. VII. Suggestions for experiments with IX. Results of additional experiments the silicates of potash and soda...40 made in 1842...............75 VIII. Results of experiments in practical Remarks on these experiments...78 agriculture made in 1842- X. Experiments in practical agriculA. Experiments on turnips- ture made in 1843 by Mr. 1. Made at Lennox Love.......42 Fleming, of Barochan2. Made at Barochan.....43 to 46 1. With guano upon potatoes...83 3. Made at Southbar............46 2. On hay.....................85 4. Made at Muirkirk......... ib. 3. On oats.....................86 5. Effectofgypsum on the tur- 4. On turnips......... 87 nip crop............. 47 Remarks on these experiments...89 LECTURES ON THE APPLICATIONS OF CHEMISTRY AND GEOLOGY TO AGRICULTURE. TIart K. ON THE ORGANIC ELEMENTS OF PLANTS. LECTURE I. Importance of Agriculture-Relation of the growth of food to the population of Great BritainRecent progress and prospects of English Agriculture-Application of Chemical and Geo. logical Science to the art of culture-to the improvement of soils-the rotation of cropsthe application of manures, &c.-Outline of the Course of Lectures-Number and nature of the elementary bodies-The organic elements Carbon, Hydrogen, Oxygen, and Nitro gen, their properties and their relations to vegetable life. WERrF I about to address you in a single or detached Lecture only, I should think it my duty to select some one branch of the art of culture for special illustration, and without much introductory matter to proceed at once to the exposition of the principle or principles on which it depended. As the present, however, is only the first of a Series of Lectures I hope to have the honor of delivering to you, I may be permitted to introduce my subject with a few prefatory remarks, which will here find their appropriate place. In regard to the importance of Agriculture it may appear superfluous in me to address you. That art on which a thousand millions of men are dependent for their very sustenance-in the prosecution of which nine-tenths-of the fixed capital of all civilized nations is embarked-and probably two hundred millions of men expend their daily toil-that art must confessedly be the most important of all; the parent and precursor of all other arts. In every country then, and at every period, the investigation of the principles on which the rational practice of this art is founded, ought to have commanded the principal attention of the greatest minds. To what other object could they have been more beneficially directed? But there are periods in the history of every country when the study of Agriculture becomes more urgent, and in that country acquires a vastly superior importance. When a tract of land is thinly peopled, like the newly settled districts of North America, New Holland, or New Zealand, a very defective system of culture will produce food enough not only for the wants of the inhabitants, but for the partial supply of other countries also. But when the population becomes more dense, the same imperfect or sluggish system will no longer suffice. The land must be better tilled, its special qualities and defects must be studied, and means must gradually be adopted for extracting the maximum produce from every portion susceptible of cultivation. The British islands are in this latter condition. Agriculture now is of vastly more importance to us as a nation, than it was towards the close even of the last century. In 1780, the island of Great Britain contained about 9 millions of inhabitants; it now contains nearly 20. The land has not increased in quantity, but the consumption of food has probably more than doubled. The importation from abroad has not increased to any important extent; by improved management, therefore, the same area of land has been caused to yield a double produce. But the population will continue to increase; can we expect that the food raised from the land will continue to increase in the same ratio? ~2 ON IMPROVEMENTS IN AGRICULTURE. This is an important question, to which we can give only an imperfect and somewhat unsatisfactory answer. The superficial area of Great Britain comprises about 57 millions of acres, of which 34 millions are in cultivation, about 13 millions are incapable of culture, and the remaining 10 millions are waste lands susceptible of improvement. The present population, therefore, is supported by the produce of 34 millions of acres, or every 34 acriss raises food -for about 20 people.. Suppose the 10 millions.of acres which are susceptible of improvement to be brought into such a state of culture as to maintain an equal proportion-the most favourable supposition-they would raise food for an additional population of about 6' millions, or would keep Great Britain independent of any large and constant foreign supply till the number of its inhabitants amounted to: 26 millions. But at the present rate of increase this will take place in about 20 years,* so that by 1860, unless some general improvement take place in the agriculture of the country, the demands of the population will have completely overtaken the productive powers of the land.' But though we cannot say how far the fertility of the soil may be increased, or how long it may be able to keep a-head: of the growing numbers of the people, we have our own past experience, the example of other countries, and the indications of theory, all concutrring to'persuade us that the limit of its productive powers can neither be predicted nor foreseen. If.we glance at the history of British agriculture-during the last half century-from the introduction of the green crop system or the alternate husbandry from Flanders'into Norfolk, up to the present time-we find the results of each successive improvement more remarkable than the former. The use of lime, a more general drainage of the soil, the invention of improved ploughs and other agricultural implements, as well as the introduction of better and more economical modes ofusing them, the application of bone manure, and more recently of thorough draining and subsoil ploughing, have all tended not only to the raising.of crops at a less cost, but in far greater abundance, and; on spots which our forefathers considered wholly unfit for the growth of corn. T:he result of each new improvement, I have said, has seemed more astonishing than the former.. For after a waste piece of land has been brought into an average state of productiveness, we are not prepared for any great improvement upon it by new labours; nor could we readily, believe that, half'a century after such land had been in culture, its produce or its value should at once be doubled, by a'better draining, a deeper ploughing, or by sprinkling on its surface a small quantity of a saline substance imported from a foreign country, Yet the exampleof the Chinese shows us that the productive powers of the soil are not to be easily estimated. Nothing repays the labours of the husbandman more fully than the willing soil-nothing is more grateful for his attention, or offers surer rewards to patient industry, or to renewed attempts at improvement. In China we see a people whom we call semi-barbarians, multiplying within their own limits till their numbers are almost incredible; For more precise data and calculations see Porter's Progress of the Nation. PROSPECTS OF SCIENTIFIC AGRICULTURE. 13 practising from the most remote ages, and in the most skilful manner, various arts which the progress of modern science has but recently introduced into civilized Europe; cultivating their soil with the most assiduous labour, and stimulating its fertility by means which we have hitherto neglected, despised, or been wholly ignorant of-but which the discoveries of the present time are pointing out as best fitted to secure the amplest harvests-and have thus been enabled to compel their limited soil to yield a sufficient sustenance to its almost unlimited population.* Experience and example, therefore, encourage us to look forward to still further improvements in the art of culture, and, independent of such as may-be derived from purely mechanical principles, theoretical cnemistry seems to point out the direction in which important advances of another kind may reasonably be anticipated. The Chinese are said to be not only familiar with the relative value and efficiency of the various manures, but also to understand how to prepare and apply without loss that which is best fitted to stimulate and support each kind of plant. How far this statement is exaggerated we are unable at present to determine, but it is in this direction that chemistry appears likely to promote the advance of European agriculture. The practical farmer already rejoices in having in one ton of bone dust the equivalent of 14 tons of farm-yard manure; some of the most skilful living chemists predict that methods will hereafter be discovered for compressing into a still less bulky form the substances required by plants, and that we shall live to see extensive manufactories established for the preparation of these condensed manures.f An intelligent correspondent reminds me that the agricultural skill of the Chinese is questioned by recent writers on the customs of that country. This doubt is founded chiefly on the rudeness of their agricultural implements and the scarcity of cattle, whether horses or cows, among them. But in this densely peopled country the hoe they employ serves the purpose of every other implement (Davis's' China, ii. 282), and where the place of cattle is supplied by an equivalent number of men, there can be no comparative want of valuable manure. The population of China, however, is probably not so dense in all the provinces as it has hitherto been supposed. Many writers have estimated the entire population at 300 millions, while recent statists reduce it to 175 millions. Taking even the higher-estimate, the population is not more dense than in England and Holland-the area of China proper being 1,200,000 square miles, or eight times that of France. It is considerably less dense, indeed, if we take into account the number of horses and cattle which in Europe are reared and fed on the produce of the land. We may hereafter expect more accurate information, however, especially regarding the interior of this interesting country.See Appendix A. t Should the opinions above expressed appear too sanguine to some, or be treated by any of my readers as merely theoretical, I would refer them to the words of Mr. Smith of Deanston, the inventor of the subsoil plough, and the introducer of the greatest practical improvement in modern agriculture. After stating that at least three:fourths of the whole arable land in the country is under very indifferent culture, chiefly from the want of complete draining and deep working, and, adverting to the increased produce it may be made to yield, he says, it is not at all improbable that Britain may become an exporting country in grain in the course of the next twenty years."-Remarks on Thorough Draining and Deep Ploughing, by James Smith, Esq., of Deanston Works, p. 22. Were the population to remain stationary, Mr. Smith may be right; at all events, this opinion shows that even practical men do not despair of attaining to a pitch of improvement in agriculture which theoretical writers dare not venture to predict. But among all persons of enlarged information a similar opinion prevails. Thus the eloquent author of a recent work on the principles of population says, "the single alteration of substituting the kitchen-garden husbandry of Flanders in our plains, and the terraced culture of Tuscany in our hills, for the present system of agricultural management, would at once double the produce of the British islands, and procure ample subsistence for twice the number of its present inhabitants."-Alison's Principles of Population, I. p. 216. These hopes are not to be rejected or suppressed; for, though they may never be fully realized, yet they are, as it were, the seeds of exertion, from which ample harvests of good may hereafter be reaped. 4 NEGLECT OF SCIENTIFIC AGRICULTURE IN —SCHOOLS. Thus much may be said in regard to the future hopes and prospects of scientific agriculture.* But how few practical men are acquainted with what is already known of the principles of the important art by which they live! Trained up in ancient methods-attached generally to conservative principles in every shape-the practical agriculturists, as a body, have always been more opposed to change than any other large class of the community. They have been slow to believe in the superiority of any methods of culture which differed from their own, from those of their fathers, or of the district in which they live-and, even when the superiority could nc longer be denied, they have been almost as slow to adopt them. But the awakening spirit of the time is making itself felt in the remotest agricultural districts; old prejudices are dying out, and the cultivators of this most ancient, most important, and noblest of all the arts, are becoming generally anxious for information, and eager for improvement.' Two circumstances have contributed to retard the approach of this better state of things. In the first place, the agricultural interest in England has hitherto expended its main strength in attempting to secure or maintain important political advantages in the state. The encouragement of experimental agriculture has been in general neglected; while the diffusion of practical knowledge has been either wholly overlooked or considered subordinate to other objects. No national efforts have been made for the general improvement of the methods of culture. While for the other important classes of the community special schools have been established, in which the elements of all the branches of knowledge most necessary for each class have been more or less completely taught, and a more enlightened, because better instructed, race of men gradually trained up, no such schools have been instituted for the benefit of the agriculturist. In our Universities, in which the holders of land, those most interested in its improvement, are nearly all educated, a lesson upon agriculture, the right arm of the State, has hitherto scarcely ever been given.$ With the practice of the art, the theory has also been Those who have access to the Journal of the Royal English Agricultural Society will find in the first number a paper by Mr. Pusey, " On the present state of the science of Agriculture in England," in which much valuable information is contained, and of a more practical kind than I have been able to introduce. This paper ought to be printed in a separate form, and circulated widely among those who are not members of the Royal English Agri cultural Society. t This opinion has been confirmed by the numerous communications I have received from all parts of the country since the publication of these Lectures was announced, and in which I am assured that the want of knowledge is generally felt, and a supply in a sufficiently elementary form desired, by all classes of ag':ulturists. I conclude, therefore, that Liebig means the following sentence to apply to hi G-erman countrymen: " What can be ex. pected from the present (generation of) farmers, which recoils with seeming distrust and aversion from all the means of assistance offered it by chemistry, and which does not understand the art of making a rational application of chemical discoveries." I do not think chemists ought in fairness to blame the practical agriculturists for not understanding the art of applying chemical discoveries to the improvement of the culture of the land. They must first know what the discoveries are; and the error has hitherto been, that no steps have been taken to diffuse this preliminary knowledge. t However satisfied young men may be to avoid the labor of additional study while at College, how many in after-life regret that their early attention had not been directed to some of those branches of knowledge which are applicable to common life. Thus the late Lord Dudley, in his letters to the Bishop of Llandaff, invariably laments, " as mistakes in ENCOURAGEMENT OF AGRICULTURAL LITERATURE. 15 neglected. Scientific men have had no inducement to devote their time and talents to a subject which held out no promise of reward, either in the shape of actual emolument or of honorary distinction. And thus has arisen the second of those circumstances, by which I consider the.approach of a better state of things to have been retardednamely, the want of an Agricultural Literature. With the exception of a small number of periodical publications, none of these even too well supported, by which attempts have been zealously made to diffuse important information among the practical farmers-it cannot be denied that the press has not been encouraged to do its utmost on behalf of agricultural knowledge in general-while the single work of Sir Humphry Davy is nearly all that chemical science has, in this country, been induced to contribute to the advancement of agricultural theory during the last forty years.* Many of you have probably read this work of Sir Humphry Davy, and are prepared to acknowledge its value. Yet how many things does ile pass over entirely, how many things leave unexplained! Since his time, not only have numerous practical observations and discoveries been made, but the entire science of animal and vegetable chemistry has been regenerated. We are not, therefore, to expect in his work a view of the present state, either of our theoretical knowledge, or of our practical agriculture. It belongs rather to the history of the progress ot knowledge, than to the condition of existing information. Hence the merits of the agricultural chemistry of Davy are not to be tried by its accordance with actual knowledge, but with what was known in 1812, when its distinguished author read his course of lectures for the last time before the Board of Agriculture. We may with certainty predict, however, that neither the practice nor the theory of agriculture will be permitted to experience in future that want of general encouragement under which during the last half his early life, his unacquaintance with the rudiments of agriculture-his ignorance of botany and geology."-(See also a note to the Review of these Letters in the Quarterly Review for December, 1840.) For this state of things we shall soon have at least a partial remedy. It is a remarkable fact that nearly all the new educational institutions of the higher class, on the Continent of Europe, of which so many have been founded within the present century, and all those which have been established in America, I believe, without exception, have incorporated into their course of general study one or more of the newer sciences. Can we have a more consentaneous and universal testimony to their value and importance than this? The University of London has been induced, by the same public demand for this species of instruction, to include Chemistry and Botany in its course of arts; and circumstances only have caused Geology to be omitted for a time. Its numerous affiliated institutions have followed its steps; and hence the Catholic College of St. Cuthbert, at Ushaw, has in this respect anticipated its Protestant neighbor at Durham. But should the agricultural interest rest satisfied with this introduction of one or two branches, suppose it generally done, into the University course of study? Many are of opinion that it ought not, and that the general interests of practical agriculture would be manifestly promoted, among other means, by the establishment of agricultural colleges, in which all the branches necessary to be known by enlightened agriculturists of every class should be specially and distinctly taught. Whether such Colleges might be beneficially annexed to the existing Universities, is a question deserving of serious consideration. The latest edition of Lord Dundonald's "Treatise on the intimate connection between Chemistry and Agriculture," which I have seen, is dated London, 1803. I should be doing injustice to a good chemist and a zealous agriculturist, were I not to direct the attention of my readers to a series of excellent articles on chemical agriculture by Dr. Madden, inserted in the numbers of the Quarterly Journal of Agriculture, for the last two years. Since the above went to press, Three Lectures on Agriculture have appeared from the pen of Dr. Daubeny, of Oxford, whose name will securer.hem an extended circulation. 16 GENERAL SCIENCE AND AGRICULTURE. century they have in England been permitted to languish. The public mind has been awakened, and the establishment of Agricultural Associations, provincial and local, are manifestations of the interest now felt upon the subject in all parts of the country. It requires only the general exhibition of such an interest, and the adoption of some general means of encouragement, to stimulate both practical ingenuity and scientific zeal to expend themselves on this most valuable branch of national industry. Science is never unwilling to lend her hand to the practical arts; on the contrary, she is ever forward to proffer her assistance, and it is not till her advances have been rejected or frequently repulsed, that she refrains from aiding in their advancement. Need I advert, in proof of this, to the unwearied labours of the vegetable physiologists-or to the many valuable observations and experiments recorded in the memoirs of scientific chemists. In these memoirs, or in professedly scientific works, such observations have not unfrequently been permitted to rest; —the public mind being unprepared either to appreciate their value or to encourage the exertions of those who were willing to give them a practical and popular form. And how numerous are the branches of science connected with this art? Need I speak of botany, which is, as it were, the foundation on which the first elements of agriculture rest; or of vegetable physiology, to the indications of which it has hitherto almost exclusively looked for improvement and increased success; or of zoology, which alone can throw light on the nature of the numerous insects that prey upon your crops, and so often ruin your hopes,-and which can alone be reasonably expected to arm you against their ravages, and instruct you to extirpate them? Meteorology among her other labours tabulates the highest, the mean, and the lowest, temperatures, as well as the quantity of rain which falls during each day and each month of the year. Do you doubt the importance of such knowledge to the proper cultivation of the land? Consider the destructive effects of a late frost in spring, or of a continued heat in summer, and your doubt' will be shaken. A wet season in our climate brings with it many evils to the practical agriculturist; but what efflct must the rain have on the soil, in countries where nearly as much falls in a month, as in England during the course of a whole year;*-where every thing soluble is speedily washed from the land, and nothing seems to be left -but a mixture of sand and travel? It may indeed be said with truth, that no department of natural science is incapable of yielding instruction-that scarcely any knowledge is superfluous-to the tiller of the soil. It is thus that all branches of human knowledge are bound together, and all the arts of life, and all the cultivators of them, mutually dependent. And it is by lending each a helping hand to the others, that the success of all is to be secured and accelerated; while with the general progress of the whole the advance of each individual is made sure. The recent contributions and suggestions of geology are the best proof of the readiness of the sciences of observation to give their aid to the promotion especially of agricultural knowledge. The geologist can best explain the immediate origin of your several soils, the cause of the * At Canton, in the month of May, the fall of rain is often as much as 20 inches. GEOLOGY CONNECTED WITH AGRICULTURE. 17 diversities which even in the same farm, it may be in the same field, they not unfrequently exhibit;* the nature and differences among your subsoils, and (he advantages you may expect from breaking them up or bringing them to the surface. Geology is essentially a popular science, and the talents of its eminent English cultivators are admirably fitted to make it still more so. Hence, a certain amount of knowledge of this science has been of late years very generally diffused, and its relations to agriculture are becoming every day better understood. The Highland Society of Scotland, among its rhany other useful exertions, has done very much to connect agriculture and geology with the sphere of its own labours, while the Journal of the Royal Agricultural Society of England manifests a similar desire on the part of that numerous and talented body, to illustrate the connection of agriculture with geology and chemistry, in the southern division of the island. That Dr. Buckland, Mr. Murchison, and Mr. De la Beche have each engaged to make a gratuitous survey of the subsoils in several extensive agricultural districts, at the request of the Council of this Society, shows that, where their services are estimated, our most eminent scientific men will not hesitate to devote them to the development of the most important branches of national industry. The time, therefore, is peculiarly favourable for the increase and diffusion of agricultural'knowledge. The growth of our population requires it-practical men are anxious to receive instruction-scientific men are eager to impart what they know, and to make new researches for the purpose of clearing up what is unknown-are we not justified, therefore, in anticipating hereafter a constant and general diffusion of light, a steady progress of agricultural improvement? Having thus glanced at the state and prospects of scientific agriculture in general, and especially of the art of culture in England, permit me to advert to a few of those questions of daily occurrence among you, to which chemistry alone can give a satisfactory answer. I shall not in this place allude to the subject of manures-which form alone an entire chapter of most recondite chemistry, and which I shall take up in its proper place, but I shall select a few isolated topics, the bearing of chemical knowledge upon which is sufficiently striking. Some soils are naturally barren, but how few of our agriculturists are able, in regard to such soils generally, to say why; how few who pos. sess the knowledge requisite for discovering the cause! Of these barren lands some may be improved so as amply to repay the outlay; some, from their locality or from otler causes, are in the present state of our knowledge irreclaimable. How important to be able to distinguish between these two cases! " I cannot refer to a plainer, more simple, or more beautiful illustration of this fact than that which is presented in a short paper by Sir John Johnstone, Bart., inserted in the Journal of the English Agricultural Society, I. p. 271, entitled "On the Application of Geology to Agriculture." See also an able paper by the Rev. Mr. Thorpe, of which a valuable report is contained in the Doncaster Chronicle of December 5th, and which will be published in the proceedings of the Geological and Polytechnic Societyof the West Riding of Yorkshire. t Journal of the Royal Agricultural Society, Report of their Council, I. p. 188. To form a just idea of the value and importance of such surveys, it is only necessary to read chap. xv., pp. 463 to 480, of Mr. De la Beche's "Geological Report on Cornwall and De von," or Professor Hitchcock's "Report on a re examination of the Economic Geology ol Massahusetts." [8 CHEMISTRY AND AGR CULTURE. Some apparently good soils are yet barren in a high degree. In endeavouring to improve such soils, practical men have no general rulethey can have none. They work in the dark-like a man who makes experiments in a laboratory, without a teacher or without a book, till, after many blunders and much expense, he discovers some fact, to himself new, but to others long known, and forming only one of many analogous facts, flowing from a common, and probably well understood,.principle. "The application of chemical tests to such a soil," says Sir Humphry Davy, i' is obvious. It must contain some noxious principle, [or be deficient in some necessary element.-J.] which may be easily discovered and probably easily destroyed. Are any of the salts of iron present, they may be decomposed by lime. Is there an excess of siliceous sand, the system of improvement must depend on the application of clay and calcareous matters. Is there a defect of calcareous matter, the remedy is obvious. Is an excess of vegetable matter indicated, it may be removed by liming, paring, and burning. Is there a deficiency of vegetable matter, it is to be supplied by manure."- [Agricultural Chemistry, Lecture I.] What was true in regard to the applications of chemistry in the time of Sir Humphry Davy is more true in a high degree of the chemistry of our time. Not only is the nature of soils better understood, but we know in many cases what a soil must contain before it will produce a given crop. Why do pine forests settle themselves on the naked and apparently barren rocks of Scotland and of Northern Europe, content if their young roots can find but a crevice in the mountain to shelter them? Why does the beech luxuriate in the alluvial soils of Southern Sweden, ef Zealand, and Continental Denmark? Why does the birch spring up from the ashes of the pine forest-why the rapid rush of delicate grass from the burned prairies of India and of Northern America? Whence comes the thick and tender sward of the mountain limestone districts-whence the gigantic wheat stalk of a virgin soil? Why do the same forest trees propagate themselves for ages on the same spots without impoverishing the soil-why do the natural grasses, the longer they are undisturbed, render the land only the more fertile? These, one would think, aie scarcely chemical questions, and yet to all of them, and to a thousand such, chemistry alone can and will give a satisfactory answer. The rotation of crops is a practical rule, the benefit of which has been proved by experience; it becomes a true philosophical principle of action, when we discover the causes from which this benefit springs. Botany has thrown considerable light, and of an interesting and important kind, upon this practice, but chemistry has fully cleared it up and established the principle. Sir Humphry Davy speaks of the use of lime. Can you explain the mysterious, and apparently fickle and diversified, agency of this sub stance in reference to vegetation? Are the advantages so frequently attendant upon its use to be ascribed to the chemical character of the soil to which it is applied, to the kind and quantity of the vegetable matter it contains, or to the geological nature of the rocks on which it rests? Are they dependent upon the drainage and exposure of the THEORETICAL KNOWLEDGE STILL VERY DEFECTIVE.'9 land-on the kind of crop to be raised-on the general climate of the district-on the maxima and minima of temperature-or on the quantity of rain which falls? So with gypsum. Why are its effects lauded in one district, doubted in another, and decried in a third! Are no rules or principles to be discovered, by which these diversified effects are to be explained, and the true purpose and fit use of these and other mineral substances clearly pointed out? Such -principles are yet to be sought for; but if sought by the way of well devised and accurately conducted experiment, they are sure to be discovered. The land is exhausted by frequent cropping. What language more familiar, what statement more true than this? Yet how few understand what exhaustion implies; how few can explain either how it takes place, by what means it can be remedied, or how, if left to herself, nature at length does apply a remedy! Have you any doubt in regard to the prevailing ignorance on this subject? To be satisfied, you have only to look with an experienced eye on the agricultural practice of the county of Durham. Are there not thousands of acres in the centre of this county which exhibit a degree of unproductiveness not natural to the soil;-which have been overcropped, and worn out, and impoverished? A soil comparatively fertile by nature has been rendered unfertile by art. That which was naturally good, has been rendered as unproductive and unprofitable as that which was naturally bad. Has this state of things arisen from ignorance, from design, or from necessity? By whichever of these it has been immediately caused, it is clear that the requisite degree of knowledge on the part of the owners of the soil would have retarded if not wholly prevented it. The same knowledge will enable them to reclaim these lands again, and gradually restore them to a more -fertile condition; for the changes which the soil undergoes in such circumstances are all chemical changes,-either in the relative quantities of the substances it contains, or in the state of combination in which they exist. The art of culture indeed is almost entirely a chemical art, since nearly all its processes are to be explained only on chemical principles. If you add lime or gypsum to your land, you introduce new chemical agents. If you irrigate your meadows, you must demand a reason from the chemist for the abundant growth of grass which follows. Do you find animal manure powerful in its action, is the effect of some permanent, while that of others is speedily exhausted?-does a mixture of animal and vegetable manure prepare the land best for certain kinds of grain?-do you employ common salt, or gypsum, or saltpetre, or nitrate of soda, with advantage?-in all these cases you observe chemical results which you would be able to control and modify did you possess the requisite chemical knowledge. It is not wonderful that even theoretical agriculturists should be far behind in the knowledge of those principles on which their most important operations depend. The greatest light has been thrown upon the art of culture by the researches of organic chemistry, a branch which may be said to have started, if not into existence, at least into a new life, within the last ten years. Every day too is adding to the number 20 OUTLINE OF THE COURSE OF LECTURES. and value of its discoveries, and the agriculturist may well be pardoned for not keeping pace with the advances of a department cf science, which even the professed and devoted chemist can scarcely overtake. I might advert also to the mechanical operations of ploughing, whether common or subsoil, of fallowing, draining, weeding, and many others, as being only so many methods by which chemical action is induced or facilitated;-to the growth of plants, and even to such observed differences as that of the relative quantity of leaves and tubers in the potatoe, and of grain and straw in our corn-fields, as interesting cases on which scientific chemistry throws a flood of light. I might shew how the feeding of your cattle and the raising and management of dairy produce are not beyond the province of chemistry, but thatthe only approach to scientific principle yet made, even in these branches of husbandry, is derived from the results of chemical research. But I do not dwell on any of these points: they will all hereafter come under our review in their appropriate order, and will afford me an opportunity of laying before you many important facts, as well as, I hope, valuable practical deductions and observations. While, however, I feel justified in saying thus much of the light which existing chemical knowledge throws on the natural processes of vegetation, and on the artificial methods of practical agriculture, I would not lead you to suppose that'our knowledge is by any means complete, that there are not many points over which much darkness still rests-that some of the theoretical views now entertained are not crude, adopted too hastily, and generalized too rapidly. But a similar confession may be made in reference to all the modern sciences of observation without diminishing'their importance or detracting from the value of the facts they embody. Human science is progressive in all its branches, and to refuse to follow the indications of existing knowledge because it is, to some extent uncertain, would be as foolish as to refuse to avail ourselves of the morning's light, because it is not equal to that of the midday sun. 1 advance, therefore, to the special object of these lectures, and I shall first present you with a rapid outline of the method which I intend to follow. It is indispensable that this method should be simple, and that every consecutive portion' should be so'fitted to: clear the way for, and thhrw light upon, what is to follow, that we may be able' to advance fronr the first rudiments to the most difficult and abstruse parts of our subject, without any chance of the illustrations'being: even difficult to comprehend. This end I do not hope perfectly to attain, but it will be my constant aim, and, with due attention oh your part, I'do not fear that we shall fail in arriving at a perfect understanding of the various points to which I shall have occasion to direct your attention. I propose, therefore, to bring before youI. The constitution of vegetable substances with the properties of the elementary and compound bodies which either enter into the substances of plants or contribute to their growth and nourishment. II. The general structure and functions of the several parts of plants ORGANIC AND INORGANIC MATTER. 2( -their mode of growth-and the manner in which their food is absorbed, changed, and converted into parts of their substance. III. The origin, nature, and principal differences of soils-with the circumstances on which their relative fertility depends, or under which it is modified. IV. The nature and differences of manures, and their mode of action, whether directly in supplying food to the plant, or indirectly in hastening and increasing their growth. V. The nature and diversities of the fbod raised as the result of culture-especially in reference to their several equivalents or powers of supporting animal life. Under this head the feeding of cattle and the variations in the quantity and quality of dairy produce, will form subjects of consideration. These different branches, I believe, comprehend the whole subject of chemical agriculture; in regard to all of them we shall derive either from chemistry or geology much important information. ~ 1. Different kinds and states of matter. All the forms of matter which present themselves to our view, whether in the solid crust of the globe on which we live, in the air which forms the atmosphere by which we are surrounded, or in the bodies of animals and plants-all are capable of being divided into the two great groups of organic and inorganic matter. The solid rocks and soils, the atmosphere, the waters of the seas and oceans, every thing which neither is nor has been the seat of life, may generally be included under the head of inorganic matter. The bodies of all living animals and plants, and their dead carcases, consist of organic or organized matter. These generally exhibit a kind of structure readily visible by the eye, as in the pores of wood, and in the fibres of hemp, or of the lean of beef,5 and are thus readily distinguished from inorganic matter, in which no such structure is observable. But in many substances of organic origin also, no structure is observable. Thus, sugar, starch, and gum, are formed i-n plants in great abundance, and yet do not present any pores or fibres; they have never been endowed with organs, yet being produced by the agency of living organs, they are included under the general name of organic matter. So when animals and plants die, their bodies undergo decay, but the matter of which they are composed is considered as of organic origin, not only as long as any traces of structure are observable, but even after all such traces have disappeared. Thus coal is a substance of organic origin, though almost all traces of the vegetable matter from which it has been derived, have been long ago obliterated. Again, heat chars and destroys wood, starch, arid gum, forming black substances totally unlike the original matter acted upon. By distillation, wood yields tar and vinegar; and by fermentation, sugar is converted first into alcohol, and then into vinegar. All substances derived from vegetable or animal products by these and similar processes are included under the general designation of organic bodies. The pores of wood and fibres and minute vessels in animals being the organs or instruments of life, the substances themselves are called organized or organic. 2 22 NUMBER OF ELEMENTARY BODIES. Now if we take a portion of almost any of those numerous forms of matter which we meet with either in the inorganic or. in the organic kingdoms, we find, that on subjecting it to certain chemical processes, it is capable of being resolved or separated into more than one substance. Thus coal when put into a gas retort is resolved into tar, coal gas, and certain other substances. Wood, when treated in the same way, yields pyroligneous acid, tar, and water, and leaves behind a residue of charcoal.'If again we subject charcoal to the action of heat (not in the open air), or to"any other process we can devise, we can never separate any thing further from it. After all our operations we obtain only charcoal. So a piece of common lead ore, when heated in a similar manner, will, if pure, give off sulphur only, and leave the lead behind, from which nothing but lead can afterwards be extracted. Thus it is evident that wood and the ore of lead differ from charcoal and metallic lead in this respect, that the former consist of more than one kind of matter, the latter of one kind of matter only. Hence charcoal and lead are called simple or elementary bodies, while wood and all other substances which are capable of being resolved into two or more different kinds of matter are called compound bodies. The diversified forms of matter which present themselves to our notice in the mineral crust of the globe, and in the organs and vessels of plants and animals, are absolutely without number. We can no more reckon them than we can the stars of heaven. Yet it is one of those results of modern chemistry which to the mind not yet familiarized with chemical discoveries appears most wonderful,-that these numberless forms of matter are capable of being resolved into, and therefore are composed or made up of, only 55* of those simple or elementary substances, the nature of which has been above explained. Occasionally these elementary substances occur in a separate state, as in native [so called when found in the malleable state,1 gold and silver, but they are generally found associated together, forming substances from which several of the 55 simple bodies may be extracted. All the material substances in nature consist of one or more of these 55 elementary bodies. This is sufficiently surprising, yet it is, if possible, still more remarkable that nearly the entire mass of every vegetable substance may be resolved into one or more of four only of these simple substances. When a portion of animal or vegetable matter is burned it either entirely disappears or leaves behind it only a small quantity of ash. Animal and vegetable oils and fats, gum, sugar, and starch, when burned, disappear entirely; a piece of wood or of lean meat leaves a small quantity of earthy (inorganic) matter behind. Now all that disappears when any portion of vegetable matter, of any kind, is burned, consists generally of three, and only in some rare cases * The names of these elementary bodies are as fotlows:-Oxygen, hydrogen, nitrogen, sulphur, selenium, phosphorus, chlorine, bromine, iodine, fluorine, carbon, boron, silicon, potassium, sodium, lithium, barium, strontium, calcium, magnesium, aluminium, glucinium, yttrium, zirconium, thorium, cerium, lanthanium, manganese, iron, cobalt, nickel, zinc.cadmium, lead, tin, bismuth, copper, uranium, mercury (quicksilver), silver, palladium, iridium, platinum, gold, osmium, titanium, tantalum (columbium>, tungsten, molybdenum, vanadium, chromium, antimony, tellurium, arsenic. PROPERTIES OF CARBON. 23 of more than four, of the elementary bodies. These four are carbon, oxygen, hydrogen, and nitrogen. With the exception of the matter it' destructible by fire (the ash), chemical analysis* has hitherto failed todetect the presence, in any notable quantity, of more than these four substances. The same remarks apply with almost equal truth to animal substances. The destructible part of these also consists of the same four elements. To the agriculturist, therefore, an acquaintance with these four constituent parts of all that lives and grows on the face of the globe is indispensable. It is impossible for him to comprehend the laws by which the operations of nature in the vegetable kingdom are conducted, nor the reason of the processes he himself adopts in order to facilitate or to modify these operations, without this previous knowledge of the nature of the elements-the raw materials as it were-out of which all the products of vegetable growth are elaborated. I shall first, therefore, exhibit to you briefly the properties of these organic constituents of plants, in order that we may be prepared for the further inquiries-by what means or in what form they enter into the circulation of plants-and how, when they have so entered, they are converted into those substances of which tihe skeleton of the plant consists or which are produced in its several organs. ~ 2. Carbon-itsproperties and relations to vegetable life. Carbon is the name given by chemists to the substance of wood charcoal in its purest form. When wood is distilled in close vessels, or burned in heaps covered over, so as to prevent the free access of air, wood charcoal is left behind. When this process is well performed, the charcoal consists of carbon with a slight admixture only of earthy and saline matters, which remain behind on burning the.charcoal in the air. Heated in the air, charcoal burns with little flame, and, with the exception of the ash which is left, entirely disappears. It is converted into a kind of air known among chemists by the name of carbonic acid, which ascends as it is formed and mingles with the atmosphere. Charcoal is light and porous, and floats upon water, but plumbago or black lead and the diamond, which are only other forms of carbon, are heavy and dense. The former is 21, and the latter 3~, times heavier than water. The diamond is the purest form of carbon, and at a high temperature it burns in the air or in oxygen gas, and, like charcoal, disappears in the state of carbonic acid gas. Of this carbon all vegetable substances contain a very large portion. It forms from 40 to 50 per cent., by weight, of all the parts of plants which are cultivated for the food of animals or of man, [that is, of these plants in their dried state.] In the economy of nature, therefore, it performs a most important part. The light porous charcoals obtained from wood [especially from the willow, the pine, and the box], and from animal substances, possess several interesting properties, which are of practical application in the art of culture. 1~. They have the power of absorbing in large quantity into their pores, the gaseous substances and vapours which exist in' Under the general name of chemical analysis are comprehended the various processes by which, as above explained, natural forms of matter may be resolved or separated into the several elements or simple substances of which they consist. 24 PROPERTIES OF OXYGEN. the atmosph.ere;* and on this property, as I shall explain hereafter, the use of charcoal powder as a manure probably in some measure depends. 2~. They also separate from water any decayed animal matters or colouring substances which it may hold in solution; hence its use in filters for purifying and sweetening impure river or spring waters, or for clarifying syrups and oils. This action is so powerful that port wine is rendered perfectly colourless by filtering through a well prepared char coal. In or upon the soil charcoal for a time will act in the same manner, will absorb from the air moisture and gaseous substances, and from tile rain and tiom flowing waters organized matters of various kinds, any of which it will be in a condition to yield to the plants which grow around it, when they are such as are likely to contribute to their growth. 3~. They have the property also of absorbing disagreeable odours in a very remarkable manner. Hence animal food keeps longer sweet when placed in contact with charcoal-hence also vegetable substances containing much water, such as potatoes, are more completely preserved by the aid of a quantity of charcoal-and hence the refuse charcoal of the sugar refiners is found to deprive night-soil of its disagreeable odour, and to convert it into a dry and portable manure. 4~. They exhibit also the still more singular property of extracting from water a portion of the saline substances they may happen to hold in solution, and thus allowing it to escape in a less impure form. The decayed (half carbonized) roots of grass, which have been long subjected to irrigation, may act in one or all of these ways on the nore or less impure water by which they are irrigated-and thus gradually arrest and collect the materials which are fitted to promote the growth of the coming crop. ~ 3. Oxygen-its properties and relations to vegetable life. Oxygen is a substance with which we are acquainted only in the gaseous or aeriform state.f By the unaided senses it cannot be distinguished from common air, being void of colour, taste and smell. But if a lighted taper be plunged into it, the flame is wonderfully increased both in size and brilliancy, and the taper burns away with great rapidity. The effect of this gas upon animal life is of a similar kind. When a living animal is introduced into a large vessel filled with oxygen, the rapidity of the circulation is increased, all the vital functions are stimulated and excited, a state of fever comes on, and after a time the animal dies. By these two characters, oxygen is distinguished from every other elernenary body. It exists in the atmosphere to the amount of 21 per cent. of its bulk, and in this state of air is necessary to the existence of animals and of plants, and to the support of combustion on the face of the globe. It exists also largely in water, every nine pounds of this liquid containing eight pounds of oxygen. Thus of ammonia they absorb 95 times their own bulk, of sulphuretted hydrogen 55 times, of oxygen 9 times, of hydrogen nearly twice their bulk, and of aqueous vapour so much as to increase their weight from 10 to 20 per cent. t In this state it is readily obtained by heating in a glass retort the red oxide of mercury of the shops, or a white salt known by the name of chlorate of potash PROPERTIES OF HYDROGEN. 25 But the quantity of this substance which is stored up in the solid rocks is still more remarkable. Nearly one-half of the weight of the solid rocks which compose the crust of our globe, of every solid substance we see around us-of the houses in which we live, and of the stones on which we tread-of the soils which you daily cultivate, and much more than one-half by weight of the bodies of all living animals and plants, consist of this elementary body oxygen, known to us, as I have already said, only in the state of a gas. It may not appear surprising that any one elementary substance should have been formed by the Creator in such abundance as to constitute nearly one-half by weight of the entire crust of our globe, but it must strike you as remarkable, that this should also be the element on the presence of which all animal life dependsand as nothing less than wonderful, that a substance which we know only in the state of thin air, should, by some wonderful mechanism, be bound up and imprisoned in stuch vast stores in the solid mountains of the globe, be destined to pervade and refresh all nature in the form of water, and to beautify and adorn the earth in the solid parts of animals and plants. But all nature is full of similar wonders, and every step you advance in the study of the principles of the art by which you live, you will not fail to mark the united skill and bounty of the same great Contriver. Oxygen gas is heavier than common air in the proportion of about 11 to 10 [its specific gravity by experiment is 1'1026, air being 1]; it is also capable of being absorbed by water to a certain extent. One hundred measures of water dissolve 69 of this gas. [De Saussure. According to Dr. Henry, 100 volumes of water absorb only 32 of oxygen.] Rain, spring, and river waters, always contain a portion of oxygen which they have derived from the atmosphere, and this oxygen, as they trickle through the soil, ministers to the growth and nourishment of plants in various ways. Some of these will be explained in a subsequent lecture. In an atmosphere of pure oxygen gas, plants refuse to vegetate, and speedily perish. ~ 4. Hydrogen-its properties and relations to vegetable life. Hydrogen is also known to us only in the state of gas, and when per fectly pure agrees with oxygen and common air in being without colour, taste, or smell. It is not known to occur in nature in a free or simple state, nor does it exist so abundantly as either carbon or oxygen. It forms a small per centage of the weight of all animal and vegetable substances, and constitutes one-ninth of the weight of water, but with the exception of coal, it does not enter as a constituent into any of the large mineral masses that exist in the crust of the globe. When a lighted taper is plunged into this gas it is immediately extinguished, but if in contact with the air the gas itself takes fire and burns with a pale yellow flame. If previously mixed with air or with oxygen gas, it kindles and burns with a loud explosion. During this combustion water is formed. [See the Second Lecture.] It does not support life, animals cease to breathe when introduced into it, and plants gradually wither and die. It is the lightest of all known substances, being about 141 times lighter than common air, so that if the stopper be removed from a bottle in which it is contained it almost imme 26 PROPERTIES OF NITROGEN. diately escapes, [its specific gravity, by experiment, is 0-0687, air being 1.] It is the element which is employed to give buoyancy to balloons; and by this great levity and its relations to flame it is readily distinguished from all other known substances. Water absorbs it only in very small quantities, 100 gallons taking up no more than about 1l gallons of hydrogen gas. But, as already observed, this gas does not exist in nature in a free state-is not necessary. therefore, to the growth of plants or animals in this state-and hence its insolubility in water is in unison with the general adaptation of every property of every body, to the health and growth of the highest orders of living beings. Hydrogen gas is readily obtained from water by putting into it a few pieces of metallic iron or zinc, and adding a little sulphuric acid (oil of vitriol). Bubbles of the gas are liberated from the surface of the metal, ascend through the water, and may be collected on the surface. ~ 5. Nitrogen-its properties and relations to vegetable life. Nitrogen is also known to us only in the form of gas. It exists in the atmosphere to the amount of 79 per cent. of its bulk. It is without colour, taste, or smell. Animals and plants die in this gas, and a taper is instantly extinguished when introduced into it; the gas itself undergoing no change. It is lighter than atmospheric air, in the proportion of 97J to 100, [its density is 0-976, air being 1.] It is an essential constituent of the air we breathe, serving to temper the ardnur with which combustion would proceed and animals live itn,ndiiuted oxygen gas. It forms a part of very many animal and of some vegetable substances, but it is not known to enter into the composition of any of the great mineral masses of which the earth's crust is made up. In coal alone, which is of vegetable origin, it has been detected to the amount of one or two per cent. It is therefore much less abundant in nature than any of the other so called organic elements-and it exhibits much less decided properties than any of them; yet we shall hereafter see that it performs certain most important functions in reference both to the growth of plants and to the nourishment of animals. One hundred volumes of water dissolve about 1i volumes of this gas.* Spring and rain waters absorb it as they do oxygen, from the atmospheric air, and bear it in solution to the roots, by which it is not unlikely that it may be conveyed directly into the circulation of plants. Such are the several elementary bodies of which the organic or desiructible part of vegetable substances is formed. With one exception they are known to us only in the form of gases; and yet out of these gases much of the solid parts of animals and of plants are made up. WVhen alone, at the ordinary temperature of the atmosphere they form invisible kinds of air; when united, they constitute those various forms of vegetable matter which it is the aim and end of the art of culture to raise with rapidity, with certainty, and in abundance. How difficult to understand the intricate processes by which nature works up these Henry De Saussure says, that pure water absorbs 4 per cent. of its bulk of this gas. REWARDS OF STUDY. 27 raw materials into her many beautiful productions-yet how interesting it must be to know her ways, how useful even partially to find them out! Permit me, in conclusion, to submit to you one reflection. We have seen that oxygen, hydrogen, and nitrogen, are all gaseous substances, which when pure are destitute of colour, taste, and smell. They cannot be distinguished by the aid of our senses. -Man in a state of nature — uneducated man-cannot discern that they are different. Yet so simple an instrument as a lighted taper at once shows them tobe totally unlike each other. This simple instrument, therefore, serves us instead of a new sense, and makes us acquainted with properties the existence of which, without such aid, we should not even have suspected. Has the Deity then been unkind to man, or stinted in his benevolence in withholding the gift of such a sense? On the contrary, he has given us an understanding which when cultivated is better than twenty new senses. The chemist in his laboratory is better armed for the investigation of nature, than if his organs of sense had been many times multiplied. Hle has many instruments at his command, each of which, like the taper, tells him of properties which neither his senses nor any other of his instruments can discover; and the further his researches are carried, the more willing does nature seem to reveal her secrets to him, and the more rapidly do his chemical senses increase. Do you think that the rewards of study and patient experimental research are confined to the laboratory of the chemist, and that the Deity will prove less kind to you, whose daily toil is in the great laboratory of nature? As yet you see but faintly the reason of many of your commonest operations, and over the results you have comparatively little control-but the light is ready to spring up, the means are within your reach-you have only to employ your minds as -liligently as you labour with your hands, and ultimate success is sure LECTURE II. Characteristic properties of organic substances-Relative proportions of organic elementsVariable proportions of inorganic elements in plants-Form in which the organic ele ments are taken up by plants-The atmosphere, its constitution and relations to vegetab}l life-Nature and laws of chemical combination-Water and its relations to vegetable life ~ 1. Characteristic 2roperties of organic substances. OF the four elementary substances described in the former lecture, the organic part of all animal and vegetable substances consists. What is understood by the term organic has also been explained. But organic substances posssess certain characters by which they are distinguished from the inorganic or dead matter of the globe, and on which their connection with the principle of life, and with the art of culture, entirely depends. These characteristic properties are chiefly the following: 1~. They are all easily decomposed or destroyed by a moderately high temperature. If wood or straw be heated in the air, as over the flame of a candle, it becomes charred, burns, and is in a great measure dissipated. So sugar and starch darken in colour when heated, blacken, and take fire. The same is true of all vegetable substances. But limestone, clay, and other earthy or stony matters, undergo no apparent change in such circumstances-they are not decomposed. 2~. When exposed to the air, especially if it be warm and moist, vegetable and animal substances putrify and decay.* They decompose of their own accord, and after a time almost entirely disappear. Such is not the case with inorganic matters. If the rocks and stones crumble, their particles may be washed away by the rains to a lower level, but they never putrify or wholly disappear. 3~. They consist almost entirely of two or more of the four organic elements only. The mineral substances we meet with on the earih's surface, and collect for our cabinets, often contain portions of many elemnentary bodies; but, with few exceptions, the organic part of all plants, that which lives and grows, contains only the four simple substances described in my former lecture. 4~. They are distinguished also by this important character, that they cannot be formed by human art. Many of the inorganic con,pounds which occur in the mineral crust of the globe can be produced by the chemist in his laboratory, and were any corresponding benefit likely to be derived from the expenditure of time and labour, there is reason to believe that, with a few exceptions, nature might be imitated in the formation of any of her mineral productions. But in regard to organic substances, whether animal or vegetable, the chemist is perfectly at fault. He can form neither woody fibre, nor sugar, nor starch, nor muscular fibre, nor any of those substances which constitute the chief bulk of animals and plants, and which serve for the food of animated beings.' For an explanation of the exact nature and end of this putrefaction, see the subsequen Lecture, " On the decay of animal and vegetable substances." PROSPECTS OF SCIENCE. 29 This is an important and striking, and is, I believe, likely to remain a permanent distinction, between most substances of organic and of inorganic origin. Looking back at the vast strides which organic chemistry has made within the last twenty years, and is still continuing to make, and trusting to the continued progress of human discovery, some sanguine chemists venture to anticipate the time when the art of man shall not only acquire a dominion over that principle of life, by the agency of which plants now grow and alone produce food for man and beast, but shall be able also, in many cases, to imitate or dispense with the operations of that principle: and to predict that the time will come when man shall manufacture by art those necessaries and luxuries for which he is now wholly dependent on the vegetable kingdom. And, having conquered the winds and the waves by the agency of steam, is man really destined to gain a victory over the uncertain seasons too? Shall he come at last to tread the soil beneath his feet as a really useless thing-to disregard the genial shower, to despise the influence of the balmy dew-to be indifferent alike to rain and drought, to cloud and to sunshine-to laugh at the thousand cares of the husbandman-to pity the useless toil and the sleepless anxieties of the ancient tillers of the soil? Is the order of nature, through all past time, to be reversed-are the entire constitution of society, and the habits and pursuits of the whole human race, to be completely altered by the progress of scientific knowledge? By placing before man so many incitements to the pursuit of knowledge, the will of the Deity is,that out 6f this increase of wisdom he should extract the means of increased happiness and enjoyment also. But set man free from the necessity of tilling the earth by the sweat of his brow, and you take from him at the same time the calm and tranquil pleasures of a country life-the innocent erjoyments of the returning seasons-the cheerful health and happiness that wait upon labour in the free air and beneath the bright sun of heaven. And for what?only to imprison him in manufactories, to condemn him to the fretful and feverish life of crowded cities. To such ends, I trust, science is not destined to lead; and he is not only unreasonably, but thoughtlessly sanguine, who would hope to derive from organic chemistry such power over dead matter as to be able to fashion it into food for living animals. With such consequences before us it seems almost sinful to wish for it. Yet, that this branch of science will lead to great ameliorations in the art of culture, there is every reason to believe. It will explain old methods-it will clear up anomalies, reconcile contradictory results by explaining the principles from which they flow-and will suggest new methods by which better, speedier, or more certain harvests may be reaped. ~ 2. Relative proportions of organic elements. Though the substance of plants consists chiefly of the four organic elements, yet these bodies enter into the constitution of vegetables in very different proportions. This fact has already been adverted to in a general manner: it will appear more distinctly by the following statement of the exact quantities of each element contained in 1000 parts by 2* 30 RELATIVE PROPERTIES OF ORGANIC ELEMENTS. weight of some of the more important kinds of vegetable substance you are in the habit of cultivating:Hay from young Clover Clover- After-math 3 mos. old. Oats. Seed. Hay. Peas. Wheat. Hay. Potatoes. Carbon.. 507 507 494 471 465 455 458 441 Hydrogen. 66 64 58 56 61 57 50 58 Oxygen. 389 367 350 349 401 431 387 439 Nitrogen. 38 22 70 24 42 34 15 12 Ash... notstated 40 28 100 31 23 90 50 1000 ooo 1000100 lOOOt1 1000T 1000* l0OOt 1000f The numbers in the above table represent the constitution of the plants and seeds, taken in the state in which they are given to' cattle or are laid up for preservation, and then dried at 230~ Fahrenheit. By this drying they lost severally as follows: 1000 parts of Potatoes.. lost... 722 parts of water ditto of Wheat.. -. 166 ditto ditto of Hay.. -.. 158 ditto ditto of Aftermath Hay -. 136 to 140 ditto ditto of Oats...-.. 151 dittc ditto of Clover Seed.... 112 ditto ditto of Peas.. -... 86 ditto In crops as they are reaped, therefore, and even as they are given for food, much water is present. When artificially dried, the carbon approaches to one-half of their weight-the oxygen to more than onethird~-the hydrogen to little more than 5 per cent.-and the nitrogen rarely to more than 2-1 per cent. These proportions are variable, but they represent very nearly the relative weights in which these elements enter into the constitution of those forms of vegetable matter which are raised in the greatest quantity for the support of animal life. But, besides the organic part, vegetable substances contain an inorganic portion, which remains behind in the forin of ash when the plant is consumed by fire, or of dust when it decomposes and disappears in consequence of natural decay. In the dried hay, oats, &c., of which the composition is represented in the above table, we see that the quantity of ash is very variable, in oats being as small as 4 per cent., while of hay every hundred pounds left 10 of ash. A similar difference is observed generally to prevail throughout the vegetable kingdom. Each variety of plant, when burned, leaves a weight of ash, more or less peculiar to itself. Herbaceous plants generally leave more than the wood of trees-and different parts of the same plant yield unlike quantities of inorganic matter.lI Boussingault Annales de Chim. et de Phys. (1838) LxvII. p. 20 to 38. t Ditto ditto (1839) LXXI. p. 113 to 136. 1 Ditto ditto (1838) LXIX. p. 356. ~ This will appear no way inconsistent with the statement in the former Lecture, that oxygen constitutes one-half by weight of all living plants, when it is recollected that of the water driven off in drying these plants eight-ninths by weight consist of oxygen, and that,600 Ibs. of grass, for example, yield only from 80 to 100 lbs. of hay. 1I Thus of the oak, the dried bark left 60 of ash-the dried leaves 53 —the dried alburnuw 4-and the dried wqod only 2 parts in a thousand of ash.-De Saussure. ON TRE CONSTITUTION OF THE ATMOSPHERE. 31 These facts are of great importance in the theory and in the enlightened practice of agriculture. They will hereafter come under special and detailed consideration, when we shall have examined the natureof the soils in which plants grow, and shall be prepared to consider the chemical nature, the source, -and the functions, of the inorganic compounds which exist in living animal and vegetable substances. ~ 3. Of the form or state of combination in "which the organic elements enter into and minister to the growth of plants. From the details already presented in the preceding Lecture, in regard to the properties of carbon and nitrogen, and the circumstances under which they are met with in nature,-it will readily occur to you that neither of these elementary bodies is likely to enter directly, or in a simple state, into the circulation of plants. The former (carbon) being a solid substance, and insoluble in water, cannot obtain admission into the pores of the roots, the only parts of the plants with which, in nature, it can come in contact. The latter (hydrogen) does not occur either in the atmosphere or in the soil in any appreciable quantity, and hence, in its simple state, forms no part of the food of plants. Oxygen and nitrogen, again, both exist in the atmosphere in the gaseous state, and the former is known to be inhaled, under certain conditions, by the leaves of plants. Nitrogen may also in like manner be absorbed by the leaves of living plants, but, if so, it is in a quantity so small as to have hitherto escaped detection. The two latter substances (oxygen and nitrogen) are also slightly soluble in water, and, besides being inhaled by the leaves, may occasionally be absorbed in minute quantity along with the water taken in by the roots. But by far the largest proportion of these two elementary bodies, and the whole of the carbon and hydrogen which find their way into the interior of plants, have previously entered into a state of mutual combination-forming what are called distinct chemical compounds. Before describing the nature and constitution of these compounds, it will be proper to explain, 1~. the constitution of the atmosphere in which plants live, and, 2~. the nature of chemical combination and the laws by which it is regulated. ~ 4. On the constitution of the atmoscphere. The air we breathe, and in which plants live, is composed principally of a mixture of oxygen and nitrogen gases, in the proportion very nearly of 21 of the former to 79 of the latter. It contains, however, as a constituent necessary to the very existence of vegetable life, a small per centage of carbonic acid. On an average this carbonic acid amounts to about! -th part* of the bulk of the air. On the shores of the sea, or of great lakes, this quantity diminishes; and it becomes sensibly less as we recede from the land. It is also less by day than by night (as 3'38 to 4'32), and over a moist than over a dry soil. The air is also imbued with moisture. Watery vapour is every where diffused through it, but the quantity varies with the season of the year, with the climate, with the nature of the locality, with its alti-' 004 per cent. The mean of 104 experiments made by Saussure at Geneva at all times of the year and of the day gave 4-15 volumes in 10000. The maximum was 5-74, and the minimum 3 15. 32 NATURE OF CHEMICAL COMBINATIC:N. tude, and with its distance from the equator. In temperate climates, it oscillates on the same spot between P and 1~ per cent. of the weight of the air; being least in mid-winter and greatest in the hot months of summer. There are also mingled with the atmosphere, traces of the vast variety of substances which are capable of rising from the surface of the earth in the form of vapour; such, for example, as are given off by decaying animal or vegetable matter-which are the produce of disease in either class of bodies-or which are evolved during the operations of nature in the inorganic kingdom, or by the artificial processes of man. Among these accidental vapours are to be included those miasmata, which, in certain parts of the world, render whole districts tnhealthy,-as well as certain compounds of ammonia, which are inferred to exist in the atmosphere, because they can be detected in rain water, or in snow which has newly fallen. In this constitution of the atmosphere we can discover many beautiful adaptations to the wants and structure of animals and plants. Tile exciting effect of pure oxygen on the animal economy is diluted by the large a(tmixture with nitrogen;-the quantity of carbonic acid present is suffcient to supply food to the plant, while it is not so great as to prove injurious to the animal;-and the watery vapour suffices to maintain the requisite moisture and flexibility of the parts of both orders of beings, without in general being in such a proportion as to prove hurtful to either. The air also, by its subtlety, diffuses itself everywhere. Into every pore of the soil it makes its way. aWhen there, it yields its oxygen or its carbonic acid to the dead vegetable matter or to the living root. A shower of rain expels the half-corrupted air, to be succeeded by a purer portion as the water retires. The heat of the sun warms the soil, and expands the imprisoned gases,-these partially escape, and are, as before, replaced by other air when the rays of the sun are withdrawn. By the action of these and other causes a constant circulation is, to a certain extent, kept up,-between the atmosphere on the surface, which plays among the leaves and stems of plants, and the air which mingles with the soil and ministers to the roots. The precise effect and the importance of this provision will demand our consideration in a future lecture. ~5. The nature and laws of chemical combination. The terms combine and combination in chemical language have a strict and precise application. If sand and saw-dust be rubbed together in a mortar they may be intimately intermingled, but by pouring water on the mass we can separate the rarticles of wood and leave tile sand unchanged behind. So if we stir uatmneal and water together, we may cause them perfectly to mix together, but by the aid of a gentle heat we can expel the water and obtain dry oatmeal in its original condition. Or, by putting salt into water, it will dissolve and disappear, and form what is called a solution, but by boiling it down, as is done in our salt-pans, the water may be entirely removed and the salt procured of the weight originally enmployeJ and possessed of its original} properties. In none of these cases lhas any chemical acticn taken place, or any CHEMIOA AL DECOMPOSITION. 33 permanent change been produced, upon any of the substances. The two former were merely mixtures. In all cases of chemical action a permanent change takes place in some of the substances employed; and this change is the result either of a chemical combination, or of a chemical decomposition. Thus when sulphur is burned in the air, it is converted into white vapours possessed of a powerful and very unpleasant odour, and which continue to be given off until the whole of the sulphur is dissipated. Here a solid substance is permanently changed into noxious vapours which disappear in the air, and this change is caused by the combination of the sulphur with the oxygen of the atmosphere. In like manner when limestone is put into a kiln and strongly heated or burned, it is changed or converted into quicklime-a substance very different in its properties from the natural limestone employed. But:lis is a case of chemical decomposition. The limestone consists of lime and carbonic acid. By the heat these are separated, the latter is driven off and the former remains in the kiln. Again, when a jet of hydrogen gas is kindled in the air or in oxygen gas, it burns with a pale yellow flame. If a cold vessel be held over this flame, it speedily becomes bedewed with moisture, and drops of water collect upon it. How remarkable the change which hydrogen undergoes during this combustion! It unites with the oxygen of the atmosphere and forms water. How different in its properties is this water from either the oxygen or the hydrogen by the union of which it is formed! The former a liquid, the latter gases; the former an enemy to all combustion, while of the latter, the one (hydrogen) burns readily, the other (oxygen) is the very life and support of combustion in all other bodies. 1~. It appears, therefore, that chemical combination or decomposition is always attended by a permanent change. 2~. That when combination takes place, a new substance is formed differing in its properties from any of those from which it was produced, or of which it consists. When two or more elementary bodies thus unite together to form a new substance, this new substance is called a chemical compound. Thus water is a compound (not a mixture) of the two elementary bodies oxygen and hydrogen. Now when such combination takes place, it is found to do so always in accordance with certain fixed laws. Thus: I. Bodies unite together only in constant and definzteproportions. We can mix together oxygen and hydrogen gases, for example, in any proportion, a gallon of the one with any number of gallons of the other, but if we burn two gallons of hydrogen gas in any greater number of gallons of oxygen, they will only consume or unite with one gallon of the oxygen, the rest of this gas remaining unchanged. A quantity of water will be formed by this union, in which the whole of the hydrogen will be contained, combined with all the oxygen that has disappeared. Under no circumstances can we burn hydrogen so as to cause it to consume more oxygen, or from a given weight of hydrogen to produce more than a known weight of water. And as oxygen is nearly sixteen times heavier than nitrogen, it is obvious that one gallon of the former is about 34 EQUIVALENT NUMBERS-ISOMERIC BODIES eight times heavier than two gallons of the latter, so that by weight these two gases, when thus burned, unite together nearly in the proportion of 1 to 8,-one pound of hydrogen forming nine pounds of water. Again, when pure carbon is burned in the air, it unites with a fixed' and constant weight of oxygen to form carbonic acid; it never unites with more, and it does not form carbonic acid when it unites with less. Now this law of fixed and definite proportions is found to hold in regard to all bodies, and in all cases of chemical combination. Thus we have seen thatBy weight. By weight. 1 of hydrogen combines with 8 of oxygen to form water. So 6 of carbon combine... 8..... carbonic oxide, and 14 of nitrogen.. 8.. nitrous oxide. Hence 1 of hydrogen, 6 of carbon, and 14 of nitrogen unite respectively with the weight (8) of oxygen. These several numbers, therefore, are said to be equivalent to each other (they are equivalent numbers). Or they represent the fixed and definite proportions in which these several substances combine together (they are definite proportionals). Some chemists consider these numbers to represent the relative weights of the atoms or smallest particles of which the several substances are made up, and hence not unfrequently speak of them as the atomic weights of these substances, or more shortly their atoms. For the sake of brevity, it is often useful to represent the simpleoor elementary bodies shortly by the initial letter of their names. Thus hydrogen is represented by H, carbon by C, and nitrogen by N, and these letters are used to denote not only the substances themselves, but that quantity which is recognised as its equivalent, proportional, or atomic weight. Thus: Equivalent Symbol. or atomic Name. weights. H denotes 1 by weight, of hydrogen. C. 6. carbon. 0.. 8.. oxygen. N.. 14*.. nitrogen. Chemical combination is expressed shortly by placing these letters in juxta-position, or sometimes in brackets, with the sign plus (-1-) between them. Thus H O or (H + 0) denotes the combination of one atom or equivalent of hydrogen with one of oxygen, that is,.water; and at the same time a weight of water (9), equal to the sum of the atomic weights (1 + 8)-of hydrogen and nitrogen. A number prefixed or appended to a symbol, denotes that so many equivalents of the substance represented by the symbol are meant, as that number expresses. Thus 2 H 0, 3 H 0, or 3 (H + O), mean two or three equivalents of water, 3 H, or H3 three equivalents of hydrogen, and 4 C or C4, 2 N or N2, four of carbon and two of nitrogen respectively. II. Not only are the quantities of the substances which unite together definite and constant, but the properties or qualities of the substances formed are in general equally so. The properties of pure water or o'' More correctly 1, 613, 8-013, and 14-19. LAW OF MULTIPLE PROPORTIONS. 35 carbonic acid are constant and invariable under whatever circumstances they may be formed, and the elements of which they consist, when they combine together in the same proportions, are never known to form any other compounds but water and carbonic acid. This law, however, though generally, is not universally true. Many substances are known which contain the same elements united together in the same proportions, and which, nevertheless, possess very different properties. Oil of turpentine and oil of lemons are in this condition. They both consist of the same elements, carbon and hydrogen, united together in the same proportions, and yet their sensible properties as well as their chemical relations* are very dissimilar. Cane sugar, starch, and gum, all of them abundant products of the vegetable kingdom, consist also of the same elements, carbon, hydrogen, and oxygen, united together in the same proportions, and may even be represented by the same formula (C,1 Ho 0,o),t and yet these substances are as unlike to each other in their properties, as many bodies are of which the chemical composition is very different. To compounds thus differing in their properties, and yet containing the same elements, in the same proportions, chemists have given the name of Isomeric bodies. I shall have occasion to make you more familiar with some of them hereafter. 30. Another important law by which chemical combinations are regulated, is known by tLe name of the law of multiple proportions. Some substances are observed to be capable of uniting together in more than one proportion. Thus carbon unites with oxygen in several proportions, forming carbonic oxide, carbonic acid, oxalic acid, &c. Now when such is the case, it is found that the quantity (the weight) of each substance which enters into the several compounds, if not actually represented by the equivalent number or atomic weight, is represented by some simple multiple of that number. Thus two equivalents of carbon unite with 2, 3, or 4 equivalents of oxygen, to form carbonic oxide, oxalic acid, and carbonic acid respectively,-while one of nitrogen unites with 1, 2, 3, 4, or 5 of oxygen to form a series of compounds, of which the last (N 05), nitric acid, is the only one I shall have frequent occasion to speak of in the present lectures. This law of multiple proportions, though of great importance in chemical theory, I do not further illustrate, as we shall have very little occasion to refer to it in the discussion of the several topics which will hereafter come before us. Having thus briefly explained the naturc and laws of chemical coin bination, I proceed to ma.ke you acquainted with those chemical compounds of the organic elements which are known or are supposed to minister to the growth of plants. The number of compounds which the four organic elements form with each other is almost endless; but of this number a very few only " By the chemical relations of a substance are meant tza effects which are produced upon it by contact with other chemical substances. t Thisformula means that starch, gum, and sugar, consist of 12 equivalents of carbon united to 10 of hydrogen and 10 of oxygen. 36 RELATIONS OF WATER TO VEGETABLE LIFE. are known to minister directly to the growth or nourishment of plants. Of these, water, carbonic acid, ammonia, and nitric acid, are the most important; but it will be necessary shortly to advert to a few others, of the occurrence or production or action of which we may hereafter have occasion to speak. ~ 6. Of water and its relations to vegetable life. Water is a compound of oxygen and hydrogen in the proportion, as already stated, of 8 of the former to 1 of the latter by weight, or of 1 volume of oxygen to 2 of hydrogen. It is more universally diffused throughout nature than any other chemical compound with which we are acquainted, performs most i-nportant functions in reference to animal and vegetable life, and is endowed with properties by which it is wouderfully adapted to the existing condition of things. We are familiar with this substance in three several states of cohesion,-in the solid form as ice, in the fluid as water, and in the gaseous as steam. At 32~ F. and at lower temperatures, it continues solid, at higher temperatures it melts and forms a liquid (water), which a 212~ F. begins to boil and is converted into steam. By this change its bulk is increased 1700 times, and it becomes nearly two-fifths lighter than common air, [common air being 1, steam is 0-62.] It therefore readily rises into and diffuses itself through the atmosphere. 1. There are only one or two circumstances in which water in tne solid form materially affects or interferes with the labours of the agriculturist. 1~. During the frost of a severe winter, the soil contracts and appears to shrink in. But the water contained in its pores freezes and expands, and the minute crystals of ice thus formed separate the particles of the soil from each other. This expansion of the water in dry soils may not be equal to the natural contraction of the soil itself, yet still it is sufficient to cause a considerable separation of the earthy particles throughout the whole frozen mass. When a milder temperature returns, and a thaw commences, the soil expands and gradually returns to its former bulk; but the outer layers thaw first, and the particles being previously separated by the crystals of ice, and now loosened by the thaw, fall off or crumble down, and thus the soil becomes exposed to the mellowing action of the atmosphere, which is enabled everywhere to pervade it. On heavy clay land this effect of the winter's frost not unfrequently proves very beneficial.* 2~. In the form of snow it has been often supposed to be beneficial to winter wheat and other crops. That a heavy fall of snow will shelter and protect the soil and crop from the destructive effects of any severe cold which may follow, there can be no doubt. It forms a light porous covering, by which the escape of heat from the soil is almost entirely prevented. It defends the young shoots also from those alternations of temperature to which the periodical return of the sun's rays continually * This alternate contraction and expansion is often injurious to the practical farmer in throwing out his winter wheat. Some varieties are said to be more thrown out than others, and this peculiarity is sometimes ascribed to the longer and stronger roots which shoot from one variety than from another; it may, however, be occasionally owing to the different nature of the soils in which the trials have been male, or when, in the same soil, to the differ. eut states of dryness at different times. ACTION AND PROPERTIES OF SNOW. 37 exposes them;* and when a thaw arrives, by slowly melting, it allows the tender herbage gradually to accustom itself to the milder atmosphere. In this manner there is no doubt that a fall of snow may often be of great service to the practical farmer. But some believe that winter wheat actually thrives under snow. On this point I cannot speak front personal knowledge, but I will here mention two facts concerning snow, which may possibly be connected with its supposed nourishing quality. In the first place, snow generally contains a certain quantity of ammonia, or of animal matter which gives off ammonia during its decay. This quantity is variable, and is occasionally so small as to be very difficult of detection. Liebig found it in the snow of the neighbourhood of Giessen, and I have this winter detected traces of it in the snow which fell in Durhamt during two separate storms. This ammonia is present in greater quantity in the first portions that fall and lie nearest the plant. Hence if the plant can grow beneath the snow, this ammonia may affect its growth; or when the first thaw comes it may descend to the root, and may there be imbibed. Rain water also contains ammonia, but when rain falls in large quantity it runs off the land, and may do less good than the snow, which lies and melts gradually. [For the properties of ammonia, see Lecture III.] Another singular property of snow is the power it possesses of absorbing oxygen and nitrogen from the atmosphere, in proportions very different from those in which they exist in the air. The atmosphere, as already stated, contains 21 per cent. of oxygen by volume (or bulk), but the air which is present in the pores of snow has been found by various observers to contain a much smaller quantity. Boussingault [Annalen der Physick (Poggendorf), xxxiv., p. 211,] obtained from air disengaged by melting snow 17 per cent. of oxygen only, and De Saussure found still less. The difficulty of respiration experienced on very high mountains has been attributed to the nature of the air liberated from snow when melted by the sun's rays. Whether the air retained among the pores of the snow, which in severe winters covers our corn-fields, be equally deficient in oxygen with that examined by Boussingault, and whether, if it be, the abundance of nitrogen can at all affect vegetation, are matters that still remain undetermined. II. In the fluid state, that of water, the agency of this compound in reference to vegetable life, though occasionally obscure, is yet everywhere discernible. Pure water is a colourless transparent fluid, destitute of either taste or' The effects of such alternations are seen on the occurrence of a night's frost in spring. If the sun's rays fall in the early morning, on a frozen shoot, it droops, withers, and blackens-it is destroyed by the frost. If the plant be in a shaded spot, where the sun does not reach it till after the whole atmosphere has been gradually heated, and the frozen tissue slowly thawed, its leaves sustain little injury, and the warmth of the sun's rays, instead of injuring, cherish and invigorate it. This effect of sudden alternations of temperature on organic matter explains many phenomena, to which it would here be out of place to advert. A thick light covering of porous earth not beaten down preserves the potatoe pit from the effects of the frost better than a solid compact coating of clay, in the same way as snow protects the herbage better than a sheet of ice; and it is because of the porosity of the covering, that ice may be preserved more effectually, and for a longer period, in a similar pit, than in many well-constructed ice-houses. t By addina two drops of sulphuric acid to four pints of snow water, evaporating to dryness, and mixing the dry mass with quicklime or caustic potash. The residual mass con. tained a brown organic matter, mixed with the sulphate of ammonia. 38 WATER NECESSARY TO LIFE-ITS SOLVENT POWER. smell. It enters largely into the constitution of all living animals and plants, and forms upwards of one half of the weight of all the newly gathered vegetable substances we are in the habit of cultivating or collecting for the use of man. [See page 30.] Not only does it enter thus largely into the constitution of all animals and plants, but in the existing economy of nature its presence in large quantities is absolutely necessary to the persistence of animal and vegetable life. In the midst of abundant springs and showers, plants shoot forth with an amazing rapidity, while they wither, droop, and die, when water is withheld. How much the manifestation of life is dependent upon its presence, is beautifully illustrated by some of the humbler tribes of plants. Certain mosses can be kel. long in the herbarium, and yet will revive again when the dried specimens are immersed in water. At Manilla a species of Lycopodium grows upon the rocks, which, though kept for years in a dried state, revives and expands its foliage when placed in water [the Spaniards call it Triste de Corazon, Sorrow of the Heart.-Burnet's Wanderings, p. 72.] Thus life lingers as it were, unwilling to depart and rejoicing to display itself again, when the moisture returns.* There are, however, three special properties of water, which are in a high degree interesting and important to the practical agriculturist, and to which I beg to direct your particular attention. These are: 1~. Its solvent power; 2~. Its affinity for certain solid substances; and, 3~. The degree of affinity by which its own elements are held together. 1~. When pure boiled water is exposed to the air, it gradually absorbs a quantity of the several gases of which the atmosphere is composed, and acquires more or less of a sparkling appearance and an agreeable taste. The air which it thus absorbs amounts to about j-rth of its own bulk, and is entirely expelled by boiling. When thus expelled, this air, like that obtained from snow, is found on examination to contain the oxygen, nitrogen, and carbonic acid in proportions very different from those in which they exist in the atmosphere. In the latter, oxygen is present to the amount of only 21 per cent. by volume, while the air absorbed by water contains 30 to 32 per cent. of the same gas. In like manner, the mean quantity of carbonic acid in the air does not exceed I -0o- th parts (0'05 per cent.) of its bulk, while that expelled from water, which has been long exposed to the air, varies from 11 to 60 ten thousand parts (0'11 to 0'6f per cent.) In some species of animals, life is in like manner suspended by the absence of water. The inhabitants of some land and even marine shells may be dried and preserved for a long time in a state of torpor, and afterwards revived by immersion in water. The Cer'thium Armatum has been brought from the Mauritius in a dry state, while snails are said to have been revived after being dried for 15 years. The vibrio tritici (a species of worm), was restored by Mr. Bauer, after an apparent death of nearly six years, by merely soaking it in water. The Furcularia Anastobea, a small microscopic animal, may be made to undergo apparent death and resuscitation many times, by alternate drying and moistening. According to Spallanzani, animalculi have been recovered by moisture, after a torpor of 27 years. These facts tend to lessen our surprise at the alleged longevity of the seeds of plants. t Of these gases when unmixed, water absorbs very different quantities. Thus 100 volumes of water at 60~ F., absorb 3-55 of oxygea, 1-53 of hydrogen, 1 47 of nitrogen, (Henry,) 106 of carbonic acid, or 7800 of ammonia. ITS AFFINITY FOR SOLID SUBSTANCES. 39 Thus when water falls in rain or trickles along the surface of the land, it absorbs these gaseous substances, carries them with it wherever it goes, conveys them to the roots, and into the circulation of plants, and thus, as we shall hereafter see, makes them all minister to the growth and nourishment of living vegetables. Again, water possesses the power of dissolving many solid substances. If sugar or salt be mixed with water in certain quantities, they speedily disappear. In like manner, many other bodies, both simple and compound, are taken up by this liquid in greater or less quantity, and can only be recovered by driving off the water, through the aid of heat. Thus it happens that the water of our springs and rivers is never pure, but holds in solution more or less of certain solid substances. Even rain water, washing and purifying the atmosphere as it descends, brings down portions of solid matter which had previously risen into the air in the form of vapour, and as it afterwards flows along or sinks into the surface of the soil, it meets with and dissolves other solid substances, the greater portion of which it carries with it wherever it enters. In this way solid substances are conveyed to the roots of plants in a fluid form, which enables them to ascend with the sap; and the supply of these naturally solid substances is constantly renewed, by the successive passage of new portions of flowing water. We shall hereafter be able to see more clearly and to appreciate more justly this beautiful arrangement of nature, as well as to understand how indispensable it is to the continued fertility of the soil. Nor is it merely earthy and saline substances which the water dissolves, as it thus percolates through the soil. It takes up also substances of organic origin, especially portions of decayed animal and vegetable matter,-such as are supposed to be capable of ministering to the growth of plants,-and brings them within reach of the roots. This solvent power of water over solid substances is increased by an elevation of temperature. Warm water, for example, will dissolve Epsom salts or oxalic acid in much larger quantity than cold water will, and the same is true of nearly all solid substances which this fluid is capable of holding in solution. To this increased solvent power of the water they absorb, is ascribed, among other causes, the peculiar character of the vegetable productions, as well as their extraordinary luxuriance, in many tropical countries. 2~. But the affinity which water exhibits for many solid substances is little less important and remarkable. When newly burned lime is thrown into a limited quantity of water the latter is absorbed, while the lime heats, cracks, swells, and finally falls to a white powder. When thus perfectly slaked, it is found to be one-third heavier than before-every three tons having absorbed one ton of water. This water is retained in a solid form, more solid than water is when in the state of ice, and it cannot be entirely separated from the lime without the application of a red heat. When you lay upon your land, therefore, four tons of slaked lime, you mix with your soil one ton of water, which the lime afterwards gradually gives up, either in whole or in part, as it combines with other substances. To this fact we shall return when we hereafter consider the various ways 40 USES OF WATERY VAPOUR IN VEGETATION. in which lime acts, when it is employed by the farmer for the purpose of improving his land. [See the subsequent lecture, " On the action of lime when employed as a manure."] For clay also, water has a considerable affinity, though by no means equal to that which it displays for quicklime. Hence, even in welldrained clay lands, the hottest summer does not entirely rob the clay of its water. It cracks, contracts, and becomes hard, yet still retains water enough to keep its wheat crops green and flourishing, when the herbage on lighter soils is drooping or burned up. A similar affinity for water is one source of the advantages which are known to follow fronm the admixture of a certain amount of vegetable matter with the soil; though, as in the case of charcoal, its porosity* is probably more influential in retaining moisture near the roots of the plants.f 3~. The degree of affinity by which the elements of water are held together, exercises a material influence on the growth and production of all vegetable substances. If I burn a jet of hydrogen gas in the air, water is formed by the union of the hydrogen with the oxygen of the atmosphere, for which it manifests on many occasions an apparently powerful affinity. But if into a vessel of water I put a piece of iron or zinc and then add sulphuric acid, the water is decomposed and the hydrogen set free, while the metal combines with the oxygen. So in the interior of plants and animals, water undergoes continual decomposition and recomposition. In its fluid state, it finds its way and exists in every vessel and in every tissue. And so slight, it would appear, in such situations, is the hold which its elements have upon each other-or so strong their tendency to combine with other substances, that they are ready to separate from each other at every impulseyielding now oxygen to one, and now hydrogen to another, as the production of the several compounds which each organ is destined to elaborate respectively demands. Yet with the same readiness do they again re-attach themselves and cling together, when new metamorphoses require it. It is in the form of water, indeed, that nature introduces the greater portion of the oxygen and hydrogen which perform so important a part in the numerous and diversified changes which take place in the interior of plants and animals. Few things are really more wonderful in chemical physiology, than the vast variety of transmutations which are continually going on, through the agency of the elements of water. III. In the state of vapour water ministers most materially to the life and growth of plants. It not only rises into the air at 212~ Fahr. when it begins to boil, but it disappears or evaporates from open vessels at almost every temperature, with a rapidity proportioned to the previous dryness of the air, and to the velocity and temperature of the atmospheric currents which pass over it. Even ice and snow are gradAffinity for water causes vegetable matter to combine chemically with it, porosity causes it merely to drink in the water mechanically, and to retain it, unchanged, in its pores. t For an exposition of the intimate relation of water to the chemical constitution of the solid parts of living vegetables, see a subsequent Lecture, " On the nature and production of the substances of which plants chiefly consist." FORMATION OF CLOUDS AMD RAIN. 41 ually dissipated in the coldest weather, and sometimes with a degree )f velocity which at first sight seems truly surprising.* It thus happens that the atmosphere is constantly impregnated with watery vapour, which in this gaseous state accompanies the air whereever it penetrates, permeates the soil, pervades the leaves and pores of plants, and gains admission to the lungs and general vascular system of animals. We cannot appreciate the influence which, in this highly comminuted form, water exercises over the general economy of organic nature. But it is chiefly when it assumes the form of rain and dew, and redescends to the earth, that the benefits arising from a previous conversion of the water into vapour become distinctly appreciable. The quantity of vapour which the air is capable of holding in suspension is dependent upon its temperature. At high temperatures, in warm climates, or in warm weather, it can sustain more-at low temperatures less. Hence when a current of comparatively warm air loaded with moisture ascends to or comes in contact with a cold mountain top, it is cooled down, is rendered incapable of holding the whole of the vapour in suspension, and therefore leaves behind in the form of a mist or cloud, a portion of its watery burden. In rills subsequently, or springs, the aqueous particles which float in the midst, re-appear on the plains beneath, bringing nourishmentf at once, and agreateful relief to the thirsty soil. So when two currents of air charged with moisture, but of unequal temperature, meet in the atmosphere, they mix, and the mixture has the mean temperature of the two currents. But air of this mean temperature is incapable of holding in suspension the mean quantity of watery vapour; hence, as before, a cloud is formed, and the excess of moisture falls to the earth in the form of rain. In descending to refresh the earth, this rain discharges in its progress another office. It washes the air as it passes thfough it, dissolving and carrying those accidental vapours which, though unwholesome to man, are yet fitted to minister to the growth of plants. The dew, celebrated through all times and in every tongue for its sweet influence, presents the most beautiful and striking illustration of the agency of water in the economy of nature. and exhibits one of those wise and bountifil adaptations, by which the whole system of things, animate and inanimate, is fitted and bound together. All bodies on the surface of the earth radiate, or throw out rays of heat, in straight lines-every warmer body to every colder; and the entire surface is itself continually sending rays upwards through the clear air into free space. Thus on the earth's surface all bodies strive, as it were, after an equal temperature (an equilibrium of heat), while * Mr. tEoward states that a circular patch of snow 5 inches in diameter lost in the month of January 150 grains of vapour between sunset and sunrise, and 56 grains more before the close of the day, when exposed to a smart breeze on a house-top. From an acre of snow this would be equal to 1000 gallons of water during the night only.-Prout's Bridgewater Treatise, p. 302; Encyclopaed. lfetreopol., art. Meteorology. In Von Wrangell's account of his visit to Siberia and the Polar sea, translated by Major Sabine (p. 390), it is stated that, in the intense cold, not only living bodies-but the very snow-smokes and fills the air with vapour. t For the nature of this nourishment see the subsequent Lectures, "On the inorgaric con stituents of plants." 42 DESCENT OF DEW.-UNIVERSAL BOUNTY OF NATURE. the surface as a whole tends gradually towards a cooler state. But while the sun shines this cooling vill not take place, for the earth then receives in general more heat than it gives off; and if the clear sky be shut out by a canopy of clouds, these will arrest and again throw back a portion of the heat, and prevent it from being so speedily dissipated. At night, then, when the sun is absent, the earth will cool the most; on clear nights also more than when it is cloudy, and when clouds only partially obscure the sky, those parts will become coolest which look towards the clearest portions of the heavens. Now when the surface cools, the air in contact with it must cool also; and like the. warm currents on the mountain side, must forsake a portion of the watery vapour it has hithetto retained. This water, like the floating mist on the hills, descends in particles almost infinitely minute. These particles collect on every leaflet, and suspend themselves from every blade of grass, in drops of " pearly dew." And mark here a beautiful adaptation. Different substances are endowed with the property of radiating their heat, and of thus becoming cool with different degrees of rapidity, and those substances which in the air become cool first, also attract first and most abundantly the particles of falling dew. Thus in the cool of a summer's evening t.he grass plot is wet, while the gravel walk is dry; and the thirsty pasture and every green leaf are drinking in the descending moisture, while the naked land and the barren highway are still unconscious of its fall. How beautiful is the contrivance by which water is thus evaporated or distilled as it were into the atmosphere-largely perhaps from some particular spots,-then diffused equably through the wide and restless air,and afterwards precipitated again in refreshing showers or in long-mysterious dews!* But how much more beautiful the contrivance, I might almost say the instinctive tendency, by which the dew selects the objects on which it delights to fall; descending first on every living plant, copiously ministering to the wants of each, and expending its superfluity only on the unproductive waste. And equally kind and bountiful, yet provident, is nature in all her operations, and through all her works. Neither skill nor materials are ever wasted; and yet she ungrudgingly dispenses her favours, apparently without measure,-and has subjected dead matter to laws which compel it to minister, and yet with a most ready willingness, to the wants and comforts of every living thing. And how unceasingly does she press this her example not only of unbounded goodness, but of universal charity-above all other men-on the attention of the tiller of the soil. Does the corn spring more freshly when scattered by a Protestant hand-are the harvests more abundant on a Catholic soil,-and does not the sun shine alike, and the dew descend, on the domains of each political party? The beauty of this arrangement appears more striking when we consider that the whole of the watery vapour in the air, if it fell at once in the form of rain, would not amount to more than 5 inches in depth on the whole surface of the globe. In England the fall of rain varies from 22 inches (London, York, and Edinburgh) to 68 (Keswick), while in some few parts of the world (St. Domingo) it amounts to as much as 150 inches. The mean fall of rain over the whole earth is estimated at 32 or 33 inches; but if we suppose it to be only 10 or 15 Inches, the water which thus falls will require to be two or three times re-distilled in the course of every year. This is exclusive of dew, which in many countries amounts to a very large quantity.-See Prout's Bridgewater Treatise, p. 309. COLD PRODUCED BY EVAPORATION, AND ITS INFLUENCE. 43 So science, from her daily converse with nature, fails not sooner or later to take her hue and colour from the perception of this universal love and bounty. Party and sectarian diffirences dwindle away and disappear from the eyes of him who is daily occupied in the conteniplation of the boundless munificence of the great Impartial; he sees himself standing in one common relation to all his fellow-men, and feels himself to be most completely performing his part in life, when he is able in any way or in any measure to contribute to the general welfare of all. It is in this sense too that science, humbly tracing the footstepe of the Deity in all his works, and from them deducing his intelligence and his universal goodness-it is in this sense, that science is of no sect, and of no party, but is equally the province, and the property, and the friend of all. ~ 7. Of the cold produced by the evaporation of water, and its influence on vegetation. Beautiful, however, and beneficent as are the provisions by which, in nature, watery vapour is made to serve so many useful purposes, there are circumstances in which, and often through the neglect of man, the presence of water becomes injurious to vegetation. The ascent of water, in the form of vapour, permits the soil to dry, and fits it for the labours of the husbandman; while its descent in dew refreshes the plant, exhausted by the heat and excitement of a long summer's day. But the same tendency to ascend in vapour, gives rise to the cold unproductive character of lands in which water is present in great excess. This character you are familiar with in what are called cold clay soils. The epithet cold, applied to such soils, though derived probably from no theoretical views, yet expresses very truly their actual condition. The surface of the fields in localities where such lands exist, is in reality less warm, throughout the year, than that of fields of a different quality, even in their immediate neighbourhood. This is readily proved, by placing the bulb of a thermometer immediately beneath the soil in two such fields, when in the hottest day a marked difference of temperature will, in general, be perceptible. The difference is dependent upon the following principle:When an open pan of water is placed upon the fire, it continues to acquire heat till it reaches the temperature of 212~ F. It then begins to boil, but ceases to become hotter. Steam, however, passes off, aid ti he water diminishes in quantity. But while the vessel remains upon the fire the water continues to receive heat from the burning fuel as it did before it began to boil. But since, as already stated, it becomes no hotter, the heat received from the fire must be carried off by the steam. Now this is universally true. Whenever water is converted into steam, the ascending vapour carries off much heat along with it. This heat is not missed, or its loss perceived, when the vapour or steam is formed over a fire; but let water evaporate in the open air from a stone, a leaf, or a field, and it must take heat with it from these objects-and the surface of the stone, the leaf, or the field, must become colder. That stone or leaf also must becor:: coldest from which the largest quantity of vapour rises. 44 WET AND COLD SOILS IMPROVED BY DRAINING. Now, let two adjoining fields be wet or moist in different degrees, that which is wettest will almost at all times give off the largest quantity of vapour, and will therefore be the coldest. Let spring arrive, and the genial sun will gently warm the earth on the surface of the one, while the water in the other will swallow up the heating rays, and cause them te re-ascend in the watery vapour. Let summer come, and while the soil of the one field rises at mid-day to perhaps 100~ F. or upwards, that of the other may, in ordinary seasons, rarely reach 80~ or 900-in wet seasons may not even attain to this temperature, and only in long droughts will derive the full benefit of the solar rays. I shall hereafter more particularly advert to the important influence which a high temperature in the soil exercises over the growth of plants, the functions of their several parts, and their power of ripening seeds-as well as to certain beautiful adaptations by which nature, when left to herself, is continually imparting to the soil, especially in northern latitudes, those qualities-which fit it for deriving the greatest possible benefit from the presence of the sun's rays. In the mean time you are willing to concede that warmth in the soil is favourable to the success of your agricultural pursuits. What, then, is the cause of the coldness and poverty, the fickleness and uncertainty of produce, in land of the kind now alluded to? It is the presence of too much water. What is the remedy? A removal of the excess of water. And how? By effectual drainage. There are other benefits to the land, which follow from this removal of the excess of water by draining, of which it would here be out of place to treat; but a knowledge of the above principle shows you that the first effect upon the soil is the same as if you were to place it in a warmer climate, and under a milder sky-where it could bring to maturity other fruits, and yield more certain crops. The application of this merely rudimentary knowledge will enable you to remove from many imlprovable spots the stigma of being poor and cold; an appellation hitherto applied to them,-not because they are by nature unproductive, but because ignorance, or indolence, or indifference, has hitherto prevented their natural capabilities from being either appreciated or made available. Note.-In reference to the supposed fertilizing effect of snow, adverted to in the above lecture, I may mention a fact observed by Heyer, and quoted by Liebig, (p. 125), that willow branches immersed in snow water put forth roots three or four times longer than when put into pure distilled water, and that the latter remained clear while the snow water became coloured. This shows that snow contains something not present in distilled water, which is capable of accelerating the growth of plants. The experiment would have been more instructive in regard to natural operations, had the effect of the snow water been cormpared with that of an equalbulk of rain water, collected under similar circumstances. LECTURE III. Carbonic and oxalic acids, their properties and relations to vegetable life-Carbonic oxide and light carburetted hydrogen, their properties and production in nature-Ammonia, its properties and relations to vegetable-life. ~ 1. Carbonic acid, its properties and relations to vegetable life. WHEN charcoal is burned in the air it combines slowly with oxygen, and is transformed into carbonic acid gas. In oxygen gas it burns more rapidly and vividly, producing the same compound. This gas is colourless, like oxygen, hydrogen, and nitrogen, but is readily distinguished from all these, by its acid taste and smell, by its solubility in water, by its great density, and by its reddening vegetable blues. Water at 60 F. and under the ordinary pressure of the atmosphere, dissolves rather more than its own bulk of this gas (100 dissolve 106), and, however the pressure may be increased, it still dissolves the same bulk. All gases diminish in bulk uniformly as the pressure to which they are subjected is increased. Thus under a pressure of two atmospheres they are reduced to one-half their bulk, of three atmospheres to onethird, and so on. When water, therefore, is saturated with carbonic acid under great pressure, as in the manufacture of soda water, though it still dissolves only its own bulk, yet it retains a weight of the gas which is proportioned to the pressure applied. For the same reason also, when the pressure is removed, as in drawing the cork from a bottle of water so impregnated, the gas expands and escapes, causing a lively effervescence, and the water retains only its own bulk at the existing pressure. This solution in water has a slightly sour taste, and reddens vegetable blues. These properties it owes to the presence of the gas, which is therefore what chemists call an acid body, and hence its name of carbonic acid. [Acids have generally a sour taste, redden vegetable blues, or combine with bases, such as lime, soda, potash, &c., to form salts.] This gas is one-half heavier than atmospheric air, its density being 1'524, and hence it may be poured through the air from one vessel to another. Hence also, when it is evolved from crevices in the earth, in caves, in wells, or in the soil, this gas diffuses itself through the atmosphere and ascends into the air, much more slowly than the elementary gases described in the previous lecture. Where it issues from the earth in large quantity, as in many volcanic districts, it flows along the surface like water, enters into and fills up cracks and hollows, and sometimes reaches to a considerable distance from its source, before it is lost among the still air. Burning bodies are extinguished in carbonic acid, and living beings, plunged into it, instantly cease to breathe. Mixed with one-ninth of its bulk of this gas the atmospheric air is rendered unfit for respiration. It is, however, the principal food of plants, being absorbed by their leaves and roots in large quantity. Hence the presence of carbonic acid in the atmosphere is necessary to the growth of plants, and they have been oh3 46 CARBONIC ACID.-EVIDENCE OF UNITY OF DESIGN. served to thrive better when the quantity of this gas in the air is considerably augmented. Common air, as has been already stated, does not contain more on an average thanu-gth of its bulk of carbonic acid, but De Saussure found that plants in the sunshine grew better when it was increased to -Lth of the bulk of the air, but beyond this quantity they were injured by its presence, even when exposed to the sun. When the carbonic acid amounted to one-half, the plants died in seven days; when it reached two-thirds of the bulk of the air, they ceased to grow altogether. In the shade any increase of carbonic acid beyond that which naturally exists in the atmosphere of our globe, was found to be injurious. These circumstances it is of importance to remember. Did the sun always shine on every part of the earth's surface, the quantity of carbonic acid in the atmosphere might probably have been increased with advantage to vegetation. But every such increase would have rendered the air less fit for the respiration of existing races of animals. -Thus we see that not only the nature of living beings, both plants and animals, but also the periodical absence of the sun's rays, have been taken into account in the present arrangement of things. In perpetual sunshine plants would flourish more luxuriantly in air containing more carbonic acid, but they would droop and die in the shade. This is one of those proofs of unity of design which occasionally force themselves upon our attention in every department of nature, and compel us to recognise the regulating superintendence of one mind. The same hand which mingled the ingredients of the atmosphere, also set the sun to rule the day only,-tempering the amount of carbonic acid to the time of his periodical presence, as well as to the nature of animal and vegetable life. Carbonic acid consists of one equivalent of carbon and two of oxygen, and is represented by CO.2 It unites with bases (potash, soda, lime, &c.), and forms compounds known by the name of carbonate. Thus pearlash is an impure carbonates of potash,-the common soda of the shops, corbonate of soda,-and limestone or chalk, carbonates of lime. From these compounds it may be readily disengaged by pouring upon them diluted muriatic or sulphuric acids. From limestone it is also readily expelled by heat, as in the common lime-kilns. During this process the limestone loses nearly 44 per cent. of its weight, [43'7 when pure and dry,] a loss which represents the quantity of carbonic acid driven off. [Hence by burning limestone on the spot where it is quarried, nearly one-half of the cost of transport is saved,] Common carbonate of lime, in its various forms of chalk, hard lime stone, or marble, is nearly insoluble in water, but it dissolves readily ia water containing carbonic acid. Thus, if a current of this gas be passed through lime-water, the liquid speedily becomes milky from the formation and precipitation of carbonate of lime, but after a short time the cloudiness disappears, and the whole of the lime is re-dissolved. The application of teat to this clear solution expels the excess of carbonic acid, and causes the carbonate of lime again to fall. By exposure to the air, we have already seen that water always absorbs a quantity of carbonic acid from the atmosphere. As it afterwards trickles through the rocks or through soil containing lime, it grad CARBONIC ACID RENDERS LIME SOLUBLE. 47 ually dissolves a portion of this earth, equivalent to the quantity of gas it holds in solution, and thus reaches the surface impregnated with calcareous matter. Or it carries it in its progress below -the surface to the roots of plants, where its earthy contents are made available, either directly or indirectly, to the promotion of vegetable growth. To the lime thus held in solution, spring and other waters generally owe their hardness, and it is the expulsion of the carbonic acid, by heat, that causes the deposition of the sediment so often observed when such waters are boiled. I propose hereafter to devote an entire lecture to the consideration of the action of lime upon land, as it is employed for agricultural purposes, but I may here remark. that this solvent action of the carbonic acid in rain water is one of the principal agents in removing the lime from your soils, and in rendering a- fresl application necessary after a certain lapse of time. It is the cause also of that deposit of calcareous matter at the mouths of drains which you not unfrequently see in localities where lime is laid abundantly upon the land. The greater the quantity of rain, therefore, which falls in a district, the less permanent will be the effects of liming the land-the sooner will it be robbed of this important element of a fertile soil. Still carbonic acid is only one of several agents which act almost unceasingly in thus removing the lime from the land, a fact I shall hereafter have occasion more fully to explain. In nature, carbonic acid is produced under a great variety of circumstances. It is given off frornthe lungs of all animals during respiration. It is formed during the progress of fermentationr Fermented liquors owe their sparkling qualities to the presence of'this gas. During the decay of animal and vegetable substances in the air, in compost heaps, or in the soil, it is evolved in great abundance. In certain volcanic countries it issues in large quantity from springs and from cracks and fissures in the surface of the earth; while the vast amount of carbon contained in the wood and coal daily consumed by burning, is carried up into the atmosphere, chiefly in the form of carbonic acid. We shall hereafter consider the relation which exists between these several sources of supply and the proportion of carbonic acid permanently present in the air and so necessary to the support of vegetable life. ~ 2. Oxalic acid, its properties and relations to vegetable life. Oxalic acid is another compound of carbon and oxygen, which, though not known to minister either to their growth or nourishment, is yet found largely in the interior of many varieties of plants. In an uncombined state it exists in the hairs of the chick pea. In combination with potash it is found in the wood sorrel (oxalis acetosella), in the common sorrel, and other varieties ofruneex,-in which it is the cause of the acidity of the leaves and stems,-in the roots of these plants also, in the leaves and roots of rhubarb, and in the roots oftormentilla, bistort, gentian, saponaria, and many others. It is this combination with potash, formerly extracted from wood sorrel-Xhich is known in commerce by the name of salt of sorrel. In combination with lime it forms the principal solid parts of 48 PROPERTIES OF OXALIC ACID. riiany lichens, especially of theparmeliee and variolarice,* some of which contain as much oxalate of lime as is equivalent to 15 or 20 parts of pure acid in 100 of the dried plant. The crystallized oxalic acid of the shops forms transparent colourless crystals, of an intensely sour taste. These crystals dissolve readily in twice their weight of cold water, and the solution, when sufficiently dilute, is agreeably acid to the taste. This acid is exceedingly poisonous. Half an ounce of the crystals is sufficient to destroy life in a very short time, and a quarter of an ounce after the lapse of a few days. It consists solely of carbon and oxygen in the proportion of two equivalents of the former to three of the latter. Its symbol is C203. It combines with bases, and forms salts which are known by the name of oxalates, and it is characterised by the readiness with which it combines with lime to form oxalate oflime. If a solution of the acid be poured into lime water, the mixture immediately becomes milky from the formation of this compound, which is insoluble in water.f It is this oxalateoflime which exists in the lichens, while oxalate of potash exists in the sorrels. Oxalic acid is one of those compounds of organic origin which we cannot form, as we can form carbonic acid by the direct union of its elements. In all our processes for preparing it artificially, we are obliged to have recourse to a substance previously organized in the living plant. It may be prepared from sugar, starch, or even from wood, by various chemical processes. The usual method is to digest potato starch with five times its weight of strong nitric acid (aquafortis), diluted with ten of water, till red fumes cease to be given off, and then to evaporate the solution. The oxalic acid separates in crystals, or, as it is usually expressed, crystallizes in the solution thus concentrated by evaporation. It is not known to exist in the soil or in the waters which reach the roots of plants. Where it is found in living vegetables, therefore, it must, like the other substances they contain, have been formed or elaborated in the interior of the plant itself. By what very simple changes the production of this acid is or may be effected, we shall see in a subsequent lecture. ~ 3. Carbonic oxide, its constitution and properties. When carbonic acid (CO2) is made to pass through a tube containing red-hot charcoal, it undergoes a remarkable change. Its gaseous form remains unaltered, but it combines with a second equivalent of carbon (becoming C2 O), which it carries offin the aeriform state. The new' The parmelia cruciata and variolaria communis are mentioned as peculiarly rich in this acid, which used to be extracted from them for sale. A species of parmelia, collected after the droughts on the sands of Persia and Georgia, contains 66 per cent. of oxalate of lime, with about 23 per cent. of a gelatinous substance similar to that obtained from Iceland moss. This lichen is used for food by the Kirghuis. A similar lichen is collected about Bagdad for a similar purpose. t Substances that are insoluble are generally without action on the animal economy, and may be introduced into the stomach without producing any injurious effect. Hence this oxalate of lime, though it contains oxalic acid, is not poisonous. Hence also, if oxalic acid be present in the stomach, its poisonous action may be taken away by causing lime water or milk of lime to be swallowed in sufficient quantity. The acid combines with the lime, as in the experiment described in the text, and forms insoluble oxalate of lime. The common magnesia of the shops will serve the same purpose, forming an insoluble oxalateofmagnesia, It is by performing experiments under circumstances where the results are visible-as in glass vessels-that we are enabled to predict the results in circumstances where the Fhenomena are not visible, and to act wi;h as much confidence as if we could reallyssee them. LIGHT CARBURETTED HYDROGEN. 49 gas thus pioducea is known by the name of carbonic oxide. It consists of one equivalent of carbon united to one of oxygen, and is represented by C2 O2, or simply CO. This gas is colourless, without taste or smell, lighter than common air, nearly insoluble in water, extinguishes flame, does not support life; burns in the air or in oxygen gas with a blue flame, and during this combustion is converted into carbonic acid. It is produced along with carbonic acid during the imperfect combustion of coals in our fires and furnaces, but is not known to oc'cur in nature, or to minister directly to the growth of plants. There exists a general relation among the three compounds of carbon and oxygen above described, to which it may be interesting to advert, in connection with the subject of vegetable physiology. This relation appears when we compare together their chemical constitution, as represented by their chemical formula:Carbonic acid consists of one of carbon and two of oxygen, or CO2.; Carbonic oxide, of one of carbon and one of oxygen, or CO; So that if carbonic acid be present in a plant, and be there deprived of one equivalent of its oxygen, by any vital action, it will be converted into carbonic oxide. Oxalic acid consists of two of carbon and three of oxygen, or C203. If we add together the formula for Carbonic acid = CO2 and Carbonic oxide = CO, we have Oxalic acid = C203. Hence this acid may be formed in the interior of plants, either by the direct union of carbonic oxide and carbonic acid, or by depriving two of carbonic acid (2COo or C.204) of one equivalent of oxygen. When in a subsequent lecture we have studied the structure and functions of the leaves of plants, we shall see how very easy it is to understand the process by which oxalic acid is formed and deposited in the interior of plants, and by which carbonic oxide also may be, and probably is, produced. ~ 4. Light carburetted hydrogen-the gas of marshes and of coal mines. During the decay of vegetable matter in moist places, or under water, a light inflammable gas is not unfrequently given off, which differs in its properties from any of those hitherto described. In summer it may often be seen rising up in bubbles from the bottom of stagnant pools and from marshy places, and may readily be collected. This gas is colourless, without taste or smell, and is little more than half the weight of common air, [its specific gravity, by experiment, is 0-5576.] A lighted taper, plunged into it, is immediately extinguished, while the gas takes fire and burns with a pale yellow flame, yielding more light, however, than pure hydrogen gas, which it otherwise resembles. Animals introduced into it, instantly cease to breathe. It consists of one equivalent of carbon (C) united to two of hydrogen (2H or H2), and is represented by CHg, When burned in the air or 80 PROPERTIES OF AMMONIA. in oxygen gas, the carbon it contains is converted into carbonic acid (CO2), and the hydrogen into water (HO). Like oxalic acid this gas cannot, by any known process, be produced from the direct union of the carbon and hydrogen of which it consists. It is readily obtained, however, by heating acetate of potash in a retort, with an equivalent proportion of caustic baryta. [Acetate of potash is prepared by pouring vinegar (acetic acid) on common pearlash and evaporating the solution.] In nature it is largely evolved in coal mines, and is the principal combustible ingredient in those explosive atmospheres which so frequently cause disastrous accidents in mining districts. This gas is also given off along with carbonic acid during the fermentation of compost heaps, or of other large collections of vegetable matter. It is said also to be generally present in well manured soils, [PERSOz, Chimie Moleculaire, p. 547,] and is supposed by many to contribute in such cases to the nourishment of plants. It is, however, very sparingly soluble in water, so that in a state of solution, it cannot enter largely into the pores of the roots, even though it be abundantly present in the soil. How far it can with propriety be regarded as a general source of food to plants, will be considered in the following lecture. ~ 5. Ammonia, its properties and relations to vegetable life. Ammonia is a compound of hydrogen and nitrogen. It is possessed of many interesting properties, and is supposed to perform a very important part in the process of vegetation. It will be proper, therefore, to illustrate its nature and properties with considerable attention. Ammonia, like the nitrogen and hydrogen of which it is composed, is a colourless gas, but, unlike its elements, is easily distinguished from all other gaseous substances by its smell and taste. It possesses a powerful penetrating odour (familiar to you in the smell of hartshorn and of common smelling salts), has a burning acrid alkaline* taste, extinguishes a lighted taper as hydrogen and nitrogen do, but does not itself take fire like the former. It instantly suffocates animals, kills living vegetables, and gradually destroys the texture of their parts. It is absorbed in large quantities by porous substances, such as charcoal-which, as already stated, absorbs 95 times its own bulk of ammoniacal gas. Porous vegetable substances in a decaying state likewise absorb it. Porous soils also, burned bricks, burned clay, and even common clay and iron ochre, which are mixed together on the surface of most of our fertile lands-all these are capable of absorbing or drinking in, and retaining within their pores, this gaseous substance, when it happens to be brought into contact with them. But the quantity absorbed by water is much greater and more surprising. If the mouth of a bottle filled with this gas be immersed in water, the latter will rush up and fill the bottle almost instantaneously and if a sufficient supply of ammonia be present, a given quantity of water will take up as much as 670 times its bulk of the gas. This solution of ammonia in water is the spirit of hartshorn of the shops. When saturated [that is, when gas is supplied till the water reThe term alkaline, as applied to taste, will be best understood by describing it as a taste imilar to that of the common soda and peariash of the shops. ITS COMBINATION WITH ACIDS. 51 fuses to take up any more,] it is lighter than pure water, [its specific gravity is 0'875, water being 1,] has the pungent penetrating odour of the gas, and its hot, burning, alkaline taste-is capable of blistering the skin., and decomposing or destroying the texture of animal and vegetable substances. You will remark here the effect which combination has in investing substances with new characters. The two gases hydrogen and nitrogen, themselves without taste or smell, and absorbed by water in minute quantity only, form by their union a compound body remarkable both for taste and smell, and for the rapidity with which water absorbs it. Ammonia possesses also alkaline properties,* it restores the blue colour of vegetable substances that have been reddened by an acid, and it combines with acid.substances to form salts. Among gaseous substances, therefore, there are some which, like carbonic acid, have a sour taste and redden vegetable blues; others which, like ammonia, have an alkaline taste and restore the blue colour; an.. a third class which, like oxygen, hydrogen, and nitrogen, are destitute of taste and do not affect vegetable colours. These last are called neut al or indifferent substances. Ammonia, as above stated, combines with acids and forms salts, which at the ordinary temperature of the atmosphere are all solid substances. Hence if carbonic acid gas be mixed with ammoniacal gas, a.white cloud is formed consisting of minute particles of solid carbonate of ammonia-the smelling salts of the shops. Hence also a feather dipped into vinegar or dilute muriatic acid (spirit of salt), and then introduced into ammoniacal gas, forms a similar white cloud, and becomes covered with a white down of solid acetate or ofmuriate of ammonia (sal ammoniac). The same appearance is readily seen by holding the feather to the mouth of a bottle containing hartshorn (liquid ammonia), from which ammoniacal gas continually escapes, and by its lightness rises into the air, and thus comes in contact with the acid upon the feathers. The fact of the production of a solid body by the union of two gases (ammonia and carbonic or muriatic acid gases) is one of a very interesting nature to the young chemist, and presents a further illustration of the changes resulting from chemical combination as explained in the previous lecture. Ammonia is little more than half the weight of common air, [more nearly three-fifths, its specific gravity being 0-59, that of air being 1,] hence when liberated on the earth's surface it readily rises into and mingles with the atmosphere. It consists of hydrogen and nitrogen united together in the proportion of three equivalents of hydrogen (3H or H3) and one of nitrogen (N), [see Lecture II,] and hence. it is represented by the symbol (N + 3H), or more shortly by NH3. 100 parts by weight contain 82A of nitrogen and 17J of hydrogen, [correctly 82-545 and 17-455 respectively.] In nature, ammonia exists in considerable quantity It is widely, In the previous lecture, the term acid was explained as applying to substances possessed of a sour taste, and capable of reddening vegetable blues or combining with bases (potash, soda, magnesia, &',.) to form salts; alkalies are such as possess an alkaline taste (see previous Note), restore the blue colour to reddened vegetable substances, or combine with acids to form salts. Of salts, nitrate of soda saltoetre (nitrate of potash), and glauber salts (sulphate of soda), are examples. 52 ITS EXISTENCE IN NATURE, AND SPECIAL PROPERTIES. almost universally, diffused, but is not known to form large deposits on any part of the earth's surface, or to enter as a constituent into any of the great mineral masses of which the crust of the globe is composed. It exists most abundantly in a state of combination-in the forms, for example, of muriate (sal ammoniac), of nitrate, and of carbonate of ammonia. It frequently escapes into the atmosphere in an uncombined state, especially where animal matters are undergoing decay, but it rarely exists in this free state for any length of time. It speedily unites with the carbonic acid of the air, with one or other of the numerous acid vapours which are continually rising from the earth, or with the nitric acid which is formed at the expense of the nitrogen and oxygen of which the atmosphere consists. The influence of ammonia on vegetation appears to be of a very powerful kind. It seems not only to promote the rapidity and luxuriance of vegetation, but to exercise a powerful control over the functions of vegetable life. In reference to the nature and extent of this action, into which we shall hereafter have occasion to inquire, there are several special properties of ammonia which it will be of importance for us previously to understand. 10. It has a powerful affinity* for acid substances. Hence the readiness with which it unites with acid vapours when it rises into the atmosphere. Hence also when formed or liberated in the soil, in the fold-yard, in the stable, or in compost heaps, it unites with such acid substances as may be present in the soil, &c. and forms saline compounds or salts. All these salts appear to be more or less influential in the processes of vegetable life. 2~. Yet this affinity is much less strong than that which is exhibited for the same acids by potash, soda, lime, or magnesia. Hence if any of these substances be mixed or brought into contact with a salt of ammonia, the acid of the latter is taken up by the potash or lime, bwhile the ammonia is separated in a gaseous state. Thus when sal ammnoniac in powder is mixed with twice its weight of quick-lime, ammnoniacal gas is liberated in large quantity. This is the method by which pure ammonia is generally prepared; and one of the many functions performed by lime when employed for the improvement of land, especially on soils rich in animal and vegetable matter, is that of decomposing the salts, especially the organic salts, of ammonia,-as will be more fhlly explained when we come to treat at length of this important part of agricultural practice.-f 3~. The salts which ammonia forms with the acids are all,:like ammonia itself, very soluble in water. Hence two consequences follow. First, that which rises into the air in the form of gas, and there combines with the carbonic or other acids, is readily dissolved, washed out By affinity is meant the tendency which bodies have to unite and to remain united or combined. Thus ammonia forms a solid substance with the vapour of vinegar the moment the two substances come into contact; they have, therefore, a strong tendency to unite, or an affinity for each other. t See Lecture XVI. "On the use of lime." Owing to this property the action of lime upon compost heaps is often injurious, by causing thb evolution of the ammonia produced during the decomposition of the animal matters they contain. This escape of ammonia, even when imperceptible by the sense of smell, is easily detected by holding over the heap a feao ther dipped in vinegar or in spirit o' salt (muriati[ acid), when white fumes are immediately perceived if ammonia be prese;. DECOMPOSES GYPSUM. 53 and brought to the earth again by the rains and dews; so that at the same time the air is purified for the use of animals, and the ammonia brought down for the use of plants. And second, whatever salts of ammonia are contained in the soil, being dissolved by the rain, are in a condition to be taken up, when wholesome, by the roots of plants; or to be carried off by the drains when injurious to vegetation. 4~. I have already alluded to the fact of this gas being absorbed by porous substances, and to its presence, in consequence, in porous soils, and in burned bricks and clay. With the purer kinds of unburned clay, however, and with the oxide of iron contained in red (or ferruginous)5 soils, ammonia is supposed to form a chemical compound of a weak nature. In consequence of its affinity or feeble tendency to combine with these substances, they attract it from the air, and from decaying animal or vegetable matters, and retain it more strongly than many porous substances can,-yet with a sufficiently feeble hold to yield it up, readily as is supposed, to the roots of plants, when their extremities are pushed forth in search of food. In this case the carbonic, acetic, and other acids given off, or supposed to be given off by the roots, exercise an influence to which more particular allusion will be made hereafter. 6~. In the state of carbonate it decomposes gypsum, forming carbonate of lime (chalk) and sulphate of ammonia.t The action of gypsum on grass lands, so undoubtedly beneficial in many parts of the world, has been ascribed to this single property; it being supposed that the sulphate of ammonia formed, is peculiarly favourable to vegetation. This question will come properly under review hereafter. I may here, however, remark that if this be the sole reason for the efficiency of gypsum, its application ought to be beneficial on all lands not already abounding either in gypsum or in sulphate of ammonia.: But if the Soils reddened by the presence of oxide of iron. t Gypsum is sulphate of lime-consisting of sulphuric acid (oil of vitriol) and quicklime. Carbonate of ammonia consists of carbonic acid and ammonia. When the two substances act upon each other in a moist state-the two acids change places-the sulphuric acid, as it were, preferring the ammonia, the carbonic acid the lime. t Liebig says-" the striking fertility of a meadow on which gypsum is strewed depends only on its fixing in the soil the ammonia of the atmosphere, which would otherwise be volatilized with the water which evaporates."-Organic Chemistry applied to Agriculture, p. 86. tJByfixing is meant the forming of sulphate with the ammonia. Rain water is supposed to bring down with it carbonate of ammonia (common smelling salts), which acts upon the sulphateoflime (gypsum) in such a way that sulphate of armmonia and carbonate of lime are produced. The carbonate of ammonia readily volatilizes or rises again into the air, the sul. phate does not-hence the use of the wordfix.] When we come to consider the subject of mineral manures in general, we shall study mnore in detail the specific action of gypsumf in promoting vegetation-a very simple calculation, however, will serve to shew that the above theory of Liebig is far from affording a satisfactory explanation of all the phenomena. Sapposing the gypsum to meet with a sufficient supply of ammonia in the soil, and that it exercises its fill influence, 100 bs. of common unburned gypsum will fix or form sulphate with nearly 20 lbs. of ammonia containing 161 Ibs. of nitrogen. One hundred weight, therefore, (1121bs.) will form as much sulphate as will contain 22.1bs. of ammonia, and if intro. duced without lose into the interior of plants will furnish them with 181 Ibs. of nitrogen. 1~. In the first volume of British Husbandry, pp. 322, 323, the following experiment is recorded: Mr. Smith, of Tunstal, near Sittingbourne, top-dressed bne portion of a field of red clover with powdered gypsum at the rate of five bushels (or four hundred weight') per acre, and compared the produce with another portion of the same field, to which no manure had been [* A ton of pure gypsum, when crushed, will yield 25 bushels. It should, however, al. ways be applied by weight.] 3* 54 MODE IN WHICH GYPSUM ACTS. results of experimental farming in this country are to be trusted, this is by no means the case. The action neither of this, nor probably of any other inorganic substance applied to the soil, is to be explained by a reference in every case to one and the same property only. 7~. The presence or evolution of ammonia in a soil containing animal and vegetable matter in a decaying state, induces or disposes this matter to attract oxygen from the air more rapidly and abundantly. The result of this is, that organic acid compounds are formed, which combine applied. The first crop was cut for hay, and the second ripened for seed. The following were the comparative results per acre: HAY CROP. SEED. STRAW. cwt. qrs. Ibs. cwt. qrs. Ibs. Gypsumed 60 3 21 22 3 12 Unmanured..... 20 0 20 5 0 0 Excess of produce.. 40 3 1 17 3 12 The excess of produce in all the three crops upon the gypsumed land is very large: let us calculate how much nitrogen this excess would contain. In a previous lecture (II. p. 30) it was stated as the result of Boussingault's analyses, that dry clover seed contained 7 per cent. of nitrogen, and the same experimenter found in the hay of red clover 1I per cent. (or 70 and 15 lbs. respectively in 1000.) The seed as it was weighed by Mr. Smith would still contain one-ninth of its weight of water, and, consequently, only 6krd per cent. of nitrogen, [see Lecture II. p. 30.] Let it be taken at 6 per cent. and let the straw be supposed to contain only 1 per cent. of nitrogen, the quantity of this element being found to diminish in the grasses after the seed has ripened, and averaging 1 per cent. in the straw of wheat, oats, and barley, the weight of nitrogen reaped inl the whole crop will then be as follows: 1. 40 cwt. of hay (4480 Ibs.) at 14 per cent. of nitrogen. contain 67 lbs. 2. 85 Ibs. of seed at 6 per cent, contain...... 5 lbs. 3. 17 cwt. 3 qrs. 12 lbs. or 2000 Ibs. of straw at 1 per cent. contain 20 Ibs, Total nitrogen in the excess of crop, 92 lbs. But, as above shewn, the five bushels or four cwt. of gypsum could fix only 90 Ibs. of am, monia-containing 74 Ibs. of nitrogen, leaving, therefore, 18 lbhs. or onefifth of the whole, to be derived from some other source. Now this result supposes that none of the gypsum or sqlphate of ammonia was carried away by the rains, but that the whole remained in the soil, and produced its greatest possible effect on the clover-and all in one season. But the effect of the gypsum does not disappear with the crop to which it is actually applied. Its beneficial action is extended to the succeeding crop of wheat, and on grass lands the amelioration is visible for a succession of years. If, then, the increased produce of a single year may contain more nitrogen than the gypsum can be supposed to yield, this substance must exercise some other influence over vegetation than is involved in its supposed action on the indefinite quantity of ammonia in the atmosphere. 2~. Again, Mr. Barnard, of Little Bordean, Hants, applied 24 cwt. per acre on two-year old sain foin, on a clayey soil. The increased produce of the first cutting was a ton per acre, and in October fully a ton, the undressed part yielding scarcely any hay at all, while the dressed part gave 1- tons. The second year no gypsum was applied. and the difference is said to have been at least as great. Supposing the increased produce in all to have been 4 tons of hay, and the nitrogen it contained to have been only one per cent.-the 4 tons-(8960 lbs.) would contain about 90 lbs. of nitrogen. But 21 cwt. would fix only 46 lbs. of nitrogen in the form of ammonia; and therefore, supposing it to have produced its maximum effect, there ffimain 44 lbs. or nearly one half of the whole, unaccountedfor by the theory. I would not be understood to place absolute reliance on the results of the above expertments; but the way in which such results may be easily applied for the purpose of testing theoretical views, will, I hope, convince the intelligent practical agriculturist how important it is, that the results of some of the experiments he is every year nmaking should be accu, rately determined by weight and measure. By this means data would gradually be accumulated, on which we might hope to found more unexceptionable explanations of the phenomena of vegetation, than the results obtained in our laboratories have hitherto enabled us to advance. In a subsequent note it will be shewn that the mode in which the nitrates of soda and potash act-in other words, the theory of their action upon vegetation —may be tested by a similar simple calculation, and the importance of precise experiments made on the farm will then still further appear. It is in the hope of inducing some of my readers to make comparative trials and publish accurate results, that I have introduced into the Appendix (No. I.) an outline of the mode in which such experiments may most usefully be performed. INFLUENCE OF AMMONIA OVER PLANTS. 55 with tde ammonia, and form ammoniacal salts. On the decomposition of these salts by lime or otherwise-the organic acids which are separated from them, are always more advanced towards that state in which they again become fit to act as food for plants. 8~. But the most interesting, and perhaps the most important property of ammonia, is one which I have already had occasion to bring under your notice, as possessed by water also, and as peculiarly fitting that fluid for the varied functions it performs in reference to vegetable life. This property is the ease with which it undergoes decomposition, either in the air, in the soil, or in the interior of plants. In the air it is diffused through, and intimately mixed with, a large excess of oxygen gas. In the soil, especially near the surface, it is also continually in contact with oxygen. By the influence of electricity in the air, and of lime and other bases in the soil, it undergoes a constant though gradual decomposition (oxidation), its hydrogen being chiefly converted into water, and a portion of its nitrogen into nitric acid.f In the interior of plants this and other numerous and varied decompositions in all probability take place. The important influence which ammonia appears to exercise over the growth of plants-the evidence for which I shall presently lay before you-is only to be explained on the supposition that numerous transformations of organic substances are effected in the interior of living vegetables-which transformations all imply the separation from each other, or the re-arrangement of the elements of which ammonia consists. In the interior of the plant we have seen that water, ever present in great abundance, is also ever ready to yield its hydrogen or its oxygen as occasion may require, while these same elements are never unwilling to unite again for the formation of water. So it is, to a certain degree, wit.h ammonia. The hydrogen it containsin so large a quantity is ready to separate itself from the nitrogen in the interior of the plant, and, in concert with the other organic elements introduced by the roots or the leaves, to aid in producing the different solid bodies of which the several parts of plants are made up. The nitrogen also becomes fixed in the coloured petals of the flowers, in the seeds, and in other parts, of which it appears to constitute a necessary ingredient-passes off in the form of new compounds, in the insensible perspiration or odoriferous exhalations of the plant,-or returning with the downward circulation, is thrown off by the root into the soil from which it was originally derived. Much obscurity still rests on the actual transformations which take place in the interior of plants, yet we shall be able in a future lecture, I hope, to arrive at a tolerably clear understanding of the general nature of many of them. Such are the more important of those properties of ammonia, to which we shall hereafter have occasion to advert. The sources, remote as well as immediate, from which plants derive this, and other compounds we have described as contributing to the nourishment and growth of plants, will be detailed in a subsequent section. Organic acids generally contain more oxygen in proportion to their carbon and hydro gen, than those which are alkaline or neutral. t It will he remembered that ammonia is represented by NH3, water by HO, and nitric acid by NOs. It is easy to see, therefore, how, by means of oxygen, ammonia should be converted into water and nitric acid, 56 PROPERTIES OF NITRIC ACID. ~ 6. Nitric acid, its constitution and properties. Vhen the nitre or saltpetre of commerce is introduced into a retorte covered with strong sulphuric acid (oil of vitriolP) and heated over a lamp or a charcoal fire, red fumes are given off, and a transparent, often brownish or reddish liquid, distils over, which may be collected in a bottle or other receiver of glass. This liquid is exceedingly acid and corrosive. In small quantity it stains the skin and imparts a yellow colour to animal and vegetable substances. In larger quantity it corrodes the skin, producing a painful sore, rapidly destroys animal and vegetable life, and speedily decomposes and oxidizest all organic substances. Being obtained.from nitre, this liquid is called nitric acid. It consists of nitrogen combined with oxygen, one equivalent of the former (N). being united to 5 of the latter (05), and is represented by NO.5. This acid contains much oxygen, as its formula indicates, and its action on nearly all organic substances depends upon the ease. with which it is decomposed, and may be made to part with a portion. of this oxygen. In nature, it never occurs in a free state; but it is found in many intertropical (hot) countries in combination with potash, soda, and lime-in the state of nitrates. It is an important character of these nitrates that, like the salts of ammonia, they are all very soluble in water. Those of soda, lime, and magnesia attract moisture frot the air, and in a damp atmosphere gradually assume the liquid form. Saltpetre is a compound of nitric acid with potash (nitrate of potash). It is met with in the surface soil of many districts in Upper India, and is separated by washing the soil and subsequently evaporating (or boiling down) the clear liquid thus obtained. When pure, it does not become moist on exposure to the air. It is chiefly used in the manufacture of gunpowder, but has also been recommended and frequently and successfully tried by the practical husbandman, as an influential agent in promoting vegetation. In combination with soda, it is found in deposits of considerable thickness in the district of Arica in Northern' Peru, from whence it is imported into this country, chiefly for the manufacture of nitric and'sulphuric acids. More recently its lower price has caused it to be extensively employed in husbandry, especially as a top-dressing for grass lands. Like the acid itself, these nitrates of potash and soda, when present in large quantities, are injurious to vegetation. This is probably one cause of the barrenness of the district of Arica in Peru, and of other countries, where in consequence of the little rain that falls, the nitrous incrustations are accumulated upon the soil. In small quantity they appear to exercise an important and salutary influence on the rapidity of growth, and on the amount of produce of many of the cultivated grasses. This salutary influence is to be ascribed, either in whole or in part, to the constitution and nature of the nitric acid which these salts contain. It * Sulphuric acid is a compound of oxygen and sulphur, which is prepared by burning sul. phur with certain precautions in large leaden chambers. It-is also obtained directly by distilling green vitriol (sulphate of iron) at a high temperature in an iron still-hence its name oil of vitriol. It is a heavy, oily, acid, and remarkably corrosive liquid. In a concentrated state it is exceedingly destructive both to animal and to vegetable life. t When a substance combines with oxygen, either in consequence of exposure to the air or in any other circumstances, s said to become oxidized. QUESTIONS TO BE CONSIDERED. 57 is chiefly with a view to the explanation I shall hereafter attempt to give of the nature of this salutary action, that I have thought it necessary here to make you acquainted with this acid compound of nitrogen and oxygen, in connection with the alkaline compound (ammonia) of the same gas with hydrogen. Having thus shortly described both the organic elements themselves, and such chemical compounds of these elements as appear to be most concerned in promoting the growth of plants, we are prepared for entering upon the consideration of several very important questions. These questions are1~. From what source do plants derive the organic elements of which they are composed? 2~. In what form do plants take them up-or what proof have we that the compounds above described really enter into plants? 3~. By what organs is the food introduced into the circulation of plants? In consequence of what peculiar structure of these several parts are plants enabled to take up the compounds by which they appear to be fed; and what are the functions of these parts, by the exercise of which the food is converted and appropriated to their own sustenance and further growth? 4~. By what chemical changes is the food assimilated by plants, that is-after being introduced into the circulation, through what series of chemical changes does it pass, before it is converted by the plant into portions of its own substance? 5~. By what natural laws or adaptations is the supply of those compounds, which are the food of plants, kept up? Animals are supported by an unfailing succession of vegetable crops,-by the operation of what invariable laws is food continually provided for plants? These questions we shall consider in succession LECTURE IV. Source of the organic elements of plants-Source of the carbon-Form in which it enters into the circulation of plants-Source of the hydrogen-Source of the oxygen-Source of the nitrogen-Form in which nitrogen enters into the circulation of plants-Absorption of ammonia and nitric acid by plants. THE first of the series of questions stated at the close of the preceding lecture, regards the source from which plants derive the organic elements of which they are composed. They are supported, it is obvious, at the conjoined expense of the earth and the air-how much do they owe to each, and for which elements are they chiefly and immediately indebted to the soil, and for which to the atmosphere? We must first consider the source of each element separately. ~ 1. Source of the carbon of plants. We have already seen reason to believe that carbon is incapable of entering directly, in its solid state, into the circulation of plants. It is generally considered, indeed, that solid substances of every kind are unfit for being taken up by the organs of plants, and that only such as are in the liquid or gaseous state, can be absorbed by the minute vessels of which the cellular substances of the roots and leaves of plants are composed. Carbon, therefore, must enter either in the gaseous or liquid form, but from what source must it be derived? There are but two sources from which it can be obtained,-the soil in which the plant grows-and the air by which its stems and leaves are surrounded. In the soil much vegetable matter is often present, and the farmer adds vegetable manure in large quantities with the view of providing food for his intended crop. Are plants really fed by the vegetable matter which exists in the soil, or by the vegetable manure that is added to it? This question has an important practical bearing. Let us, therefore, submit it to a thorough examination. 1~. We know, from sacred history, what reason and science concur in confirming, that there was a time when no vegetable matter existed in the soil which overspread the earth's surface. The first plants must have grown without the aid of either animal or vegetable matter-that is, they must have been nourished from the air. 2~. It is known that certain marly soils, raised from a great depth beneath the surface, and containing apparently no vegetable matter, will yet, without manure, yield luxuriant crops. The carbon in such cases must also have been derived from the air. 30. You know that some plants grow and increase in size when suspended in the air, and without being in contact with the soil. Youl know, also that many plants-bulbous flower roots for example -will grow and flourish in pure water only, provided they are open to the access of the atmospheric air. Seeds also will germinate, and, when duly watered, will rise into plants, though sown in substances that contain no trace of vegetable n atter. WHENCE PLANTS DERIVE THEIR CARBON. 59 Thus De Saussure found that two beans, when caused to vegetate in the open air on pounded flints, doubled the weight of the carbon they originally contained. Under similar circumstances Boussingault found the seeds of trefoil increased in weight 2^ times, and wheat gave plants equal in weight, when dry, to twice that of the original grains, [Ann. de Chim. et de Phys. Ixvii., p. 1.] The source of the carbon in all these cases cannot be doubted. 4~. When lands are impoverished, you lay them down to grass, and the longer they lie undisturbed the richer in vegetable matter does the soil become. When broken up, you find a black fertile mould where little trace of organic matter had previously existed. The same observation applies to lands long under wood. The vegetable matter increases, the soil improves, and when cleared and ploughed it yields abundant crops of corn. Do grasses and trees derive their carbon from the soil? Then, how, by their growth, do they increase the quantity of carbonaceous matter which the soil contains? It is obvious that, taken as a whole, they must draw from the air not only as much as is contained in their own substance, but an excess also, which they impart to the soil. 5~. But on this point the rapid growth of peat may be considered as absolutely conclusive. A tree falls across a little running stream, dams up the water, and produces a marshy spot. Rushes and reeds spring up, mosses take root and grow. Year after year new shoots are sent forth, and the old plants die. Vegetable matter accumulates; a bog, and finally a thick bed of peat is formed. Nor does this peat form and accumulate at the expense of one species or genus of plants only. Latitude and local situation are the circumstances which chiefly effect this accumulation of vegetable matter on the soil. In our own country, the lowest layers of peat are formed of aquatic plants, the next of mosses, and the highest of heath. In Terra del Fuego, " nearly every patch of level ground is covered by two species of plants (astelia pumila of Brown, and donatia magellanica), which, by their joint decay, compose a thick bed of elastic peat." " In the Falkland Islands, almost every kind of plant, even the coarse grass which covers the whole surface of the island, becomes converted into this'substance."* Whence have all these plants derived their carbon? The quantity originally contained in the soil is, after a lapse of years, increased ten thousand fold. Has dead matter the power of reproducing itself? You will answer at once, that all these plants must have grown at the expense of the air, must have lived on the carbon it was capable of affording them, and as they died must have left this carbon in a state un fit to nourish the succeeding races. This reasoning appears unobjectionable, and, from the entire group of %bcts, we seem justified in concluding that plants every where, and under all circumstances, derive the whole of their carbon from the atmosphere. l Darwin's Researches in Geology and Natural History, pp. 349-50. Dr. Gerville informs me that the astelia approaches more nearly te the junceae or?sh tribe, and the donalia to our rufted saxifrages, than to any other Bl'iiish:?'tts. 60 THE VEGETABLE MATTER OF THE SOIL. In certain extreme cases, as in those of plants growing in the air and in soils perfectly void of organic matter, this conclusion must be abso lutely true. The phenomena admit of no other interpretation. But is it as strictly true of the more usual forms of vegetable life, or in the ordinary circumstances in which plants grow spontaneously or are cultivated by the art of man? Has the vegetable matter of the soil no connection with the growth of the trees or herbage? —does it yield them no regular supplies of nourishment? Does nature every where form a vegetable rould on which her wild flowers nmay blossom and her primeval forests raise their lofty heads? Has the agricultural experience of all ages and of all countries led the practical farmer to imitate nature in preparing such a soil? Does nature work in vain?-is all this experience to be at once rejected? While we draw conclusions, legitimate in kind, we must be cautious how, in degree, we extend them beyond our premises. The consideration of one or two facts will shew that our general conclusion must either be modified or more cautiously expressed. 1~. It is true that plants will, in certain circumstances, grow in a soil containing no sensible quantity of organic matter-but it is also true, generally, that they do not luxuriate or readily ripen their seed in such a soil. 2~. It is consistent with almost universal observation, that the same soil is more productive when organic matter is present, than when it is wholly absent. 3~. That if the crop be carried off a field, less organic matter is left in the soil than it contained when the crop began to grow, and that by constant cropping the soil is gradually exhausted of organic matter. Now it must be granted that tillage alone, without cropping, would gradually lessen the amount of organic matter in the soil, by continually exposing it to the air and hastening its decay and resolution into gaseous substances, which escape into the atmosphere. But two years' open fallow, with constant stirring of the land, will not rob it of vegetable matter so effectually as a year of fallow succeeded by a crop of wheat. Some of the vegetable matter, therefore, which the soil contained when the seed was sown, must be carried off the field in the crop. The conclusion therefore seems to be reasonable and legitimate; that the crop which we remove from a field has not derived all its carbon directly from the air-but has extracted a portion of it immediately from the soil. It is to supply this supposed loss, that the practical farmer finds it necessary to restore to the land in the form of manure-among other substances-the carbon also of which the straw or hay had robbed the soil. But how is this reconcileable with our previous conclusion, that the whole of the carbon is derived from the air? The difficulty is of easy solution. A seed germinates in a soil in which no vegetable matter exists; it sprouts vigorously, increases then slowly, grows languidly at the expense of the air, and the plant dies stunted or immature. But in dying it imparts vegetable matter to the soil, on which the next seed thrives better -4rawing support not only from the air, but by its roots from the soil viso. The death of this second plant enriches tk, soil further, and thus, HOW THE VEGETABLE MATTER INCREASES. 61 while each succeeding plant is partly nourished by food from the earth, yet each, when it ceases to live, imparts to the soil all the carbon which during its life it has extracted from the air. Let the quantity which each plant thus returns to the soil, exceed what it has drawn from it by only one ten-thousandth of the whole, and-unless other causes intervene-the vegetable matter in the soil must increase. Thus while it is strictly true that the carbon contained in all plants has been originally derived from the air, it is not true that the whole of what is contained in any one crop we raise, is directly derived from the atmosphere —the proportion it draws from the soil is dependent upon numerous and varied circumstances. The history of vegetable growth, therefore-in so far at least as the increase of the carbon is concerned-may be thus simply stated: 10. A plant grows partly-at the expense of the soil, and partly at that of the air. When it reaches maturity, or when winter arrives, it dies. The dead vegetable matter decays, a part of it is resolved into gaseous matter and escapes into the air, a part remains and is incorporated with the soil. If that which remains be greater in quantity than that which the plant in growing derived from the soil, the vegetable matter will increase; if less, it will diminish. 2~. In warm climates the decay of dead vegetable matter is more rapid, and, therefore, the portion left in the soil will be less than in more temperate regions-in other words, the vegetable matter in the soil will increase less rapidly-it may not increase at all. 3~. As we advance into colder countries, the decay and disappearance of dead vegetable matter, in the form of gaseous substances which escape into the atmosphere, become more slow-till at length, between the parallels of 40~ and 45~, it begins to accumulate in vast quantities in favourable situations, forming peat bogs of greater or less extent. While the living plant here, as in warm climates, derives carbon both from the earth and from the air, the dead plant, during its slow and partial decay, restores little to the atmosphere, and therefore adds rapidly to the vegetable matter of the soil. 4~. Again, in one and the same climate, the decay of vegetable matter, and its conversion into gaseous substances, is more rapid in proportion to the frequency with which it is disturbed or exposed to the action of the sun and air. Hence this decay may be comparatively slow in shady woods and in fields covered by a thick sward of grass; and in such situations organic matter may accumulate, while it rapidly diminishes in an uncovered soil, or in fields repeatedly ploughed and subjected to frequent cropping.* Being thus fitted, by nature, to draw their sustenance-now from the earth, now from the air, and now from both, according as they can most readily obtain it-plants are capable of living,-though rarely a robust life,-at the expense of either. The proportion of their food which they actually derive from each source, will depend upon many circumstances-on the nature of the plant itself-on the period of its growth-on the soil in which it is planted-on the abundance of food presented to In removing a crop we take away both what the plants have received from the earth and what they have absorbed from the air-the materials, in short, intended by nature to restore the loss of vegetable matter arising from the natural decay. 62 PLANTS PARTLY SUPPORTED BY THE AIR AND BY THE SOIL. either extremity-on the warmth and moisture of the climate-on the duration and intensity of the sunshine, and other circumstances of asimilar kind-so that the only general law seems to be, that, like animals, plants have also the power of adapting themselves, to a certain extent, to the conditions in which they are placed; and of supporting life by the aid of such sustenance as may be within their reach. Such a view of the course of nature in the vegetable kingdom, is consistent, I believe, with all known facts.. And that the Deity has bountifully fitted the various orders of plants-with which the surface of the earth is at once beautified and rendered capable of supporting animal life-to draw their nourishment, in some spots more from the air, in others more from the soil, is only in accordance with the numerous provisions we everywhere perceive, for the preservation and continuance of the present condition of things. By taking a one-sided view of nature, we may arrive at startling conclusions-correct, if taken as partial truths, yet false, if advanced as general propositions-and fitted to lead into error, such as have not the requisite knowledge to enable them to judge-for themselves- or such as, doubtful of their own judgment, are willing to yield assent to the authority of a name. Of this kind appears, at first sight, to be the statement of Liebig, that "when a plant is quite matured, and when the organs by which it obtains food from the atmosphere are firmed, the carbonic acid of the soil is no further required"-and that, "during the heat of summer it derives its carbon exclusively from the atmosphere."-[Organic Chemistry applied to Agriculture, p. 48.] A little consideration will shew us that, while the proposition contained in the former quotation may be entertained and advanced as a matterof opinion-the latter is obviously incorrect. In summer, when the sun shines the brightest, and for the greatest number of hours, the evaporation from the leaves of all plants (their insensible perspiration) is the greatest-the largest supply of water, therefore, must at this season be absorbed by the roots, and transmitted upwards to the leaves.-[Lindlev's Theory of Horticulture, p. 46.]-But this water, before it enters the roots, has derived carbonic acid and other soluble substances from the air and from the soil, in as large quantity at this period as at any other during the growth of the plant; and these substances it will carry with it in its progress through the roots and the stem. Are the functions of the root changed at this stage of the plants' growth? Do they now absorb pure water only, carefully separatingand refusing to admit even such substances as are held in solution? Or do the same materials which minister to the growth of the plant in its earlier stages, now pass upwards to the leaf and return again in the course of the circulation unchanged and unemployed, to be again rejected at the roots? Does all this take place in the height of summer, while the plant is still rapidly increasing in size? The opinion is neither supported by facts nor consistent with analogy. But such an opinion,-however the words above quoted may mislead some,-is not intended to be advanced by Liebig; for, in the following page he says, that " the power which roots possess of taking up nourishment does not cease so long as nutriment is present." In summer, LEAVES AND ROOTS ABSORB CARBONIC ACID. 63 therefore, as well as in spring or in autumn, the plant must be ever absorbing nourishment by these roots, if the soil is capable of affording itand thus, in the general vegetation of the globe, the increase of carbon in growing plants must, at every season of the year, be partly derived from the vegetable matter of the soil in which they grow. ~ 2. Form in which carbon enters into the circulation of plants. Supposing it to be established that the whole of the carbon contained in plants has originally been derived from the air-we have only to inquire in what state this element exists in the atmosphere, in order to satisfy ourselves as to the form of combination in which it is and has been received into the circulation of plants. In considering the constitution of the atmosphere in the preceding lecture, it was stated that carbonic acid, a compound of carbon and oxygen, is always present in itand that, though this gas is diffused through the air in comparatively small quantity only, yet it is everywhere to be detected,-while no other compound of carbon is to be found in it in any appreciable quantity. We must conclude, therefore, that from this gaseous carbonic acid the whole of the carbon contained in plants has been prinarily derived. This conclusion is confirmed by the observation so frequently made, that the leaves of plants in sunshine absorb carbonic acid, and that plants die in an atmosphere from which this gas is entirely excluded. But we have seen reason to believe that, under existing circumstances, plants also extract a portion of the carbon they contain from the soil in which they grow. In what state or form of combination do the roots absorb carbon? The most abundant product of the decay of vegetable matter in the soil, is the same carbonic acid which plants inhale so largely from the atmosphere by their leaves. In a soil replete with vegetable matter, therefore, the roots are surrounded by an atmosphere more or less charged with carbonic acid. Hence if they are capable of inhaling gaseous substances, this gas will enter the roots in the aeriform state-if not, it must enter in solution in the water, which the roots drink in so largely, to supply the constant waste caused by the insensible perspiration of the leaves. During the early fermentation of artificial manures there is also developed in the soil a variable proportion of light carburetted hydrogen (Lecture III., p. 49), which is supposed by some to enter occasionally into the roots. That it does enter, however, is doubtful,-and we are safe, I think, in considering this compound not only as an uncertain source of the carbon of plants, but as one from which, in the most favourable circumstances, they can derive only a small supply. Thus, from the earth as from the air, the most unfailing supply of food is the gaseous carbonic acid. But as the water passes through the soil it takes up inorganic substances-potash, soda, lime, magnesia-and conveys them through the roots into the circulation of the plants. Can it refuse to take up and to perform a similar office to the soluble organic substances it meets with, as it sinks through the soil? Or do the spongioles of the roots keep a perpetual watch over the entering waters, to prevent the introduction of every soluble form rf carbon but that of carbonic acic.'f Or, supposing such 64 ROOTS ABSORB ORGANIC SUBSTANCES ALSO substances introduced into the interior of the plant, are none of them digested there and converted to the general purposes of food? A statement of two or three facts will afford a satisfactory reply to these several questions. 1~. When plants are made to grow in infusions of madder the radicle fibres are tinged of a red colour. 20. The flower of a white hyacinth becomes red after a few hours, when the earth in which it is planted is sprinkled with the juice of the phytolaca decandra (Biot). Therefore organic substances can enter into the roots, and thence into the circulation, of the plant. 3~. The colour of the madder does not usually extend upwards to the leaves and flowers of the plant. 4~. The colour imparted to the flower of the white hyacinth disappears in the sunshine in the course-of a few days. Organic colouring matters, therefore; undergo a chemical change either in the stem, in the leaf, or in the flower-some sooner, some later-and the same is probably the case with most other organic substances which gain admission into the interior of plants. 5~. Sir Humphry Davy introduced plants of mint into weak solutions of sugar, gum, jelly, the tanning principle, &c., and found that they grew vigorously in all of them. He then watered separate spots of grass with the same several solutions, and with common water, and found all to thrive more than that to which common water was applied-while those treated with sugar, gum, and gelatine grew luxuriantly.-[Davy's Agricultural Chemistry, Lecture VI.] Therefore different organic substances-being introduced into the cir culation and there changed-are converted by plants into their own substance, or act as food, and nourish the plant. We may consider it, therefore, to be satisfactorily established that, while a plant sucks in by its leaves and roots much carbon in the form of carbonic acid, it derives a variable portion of its immediate sustenance (of its carbon) from the soluble organic substances that are within reach of its roots.. This fact is never doubted by the practical husbandman. It forms the basis of many of his daily and most important operations, while the results of these operations are further proofs of the fact. The nature of the soluble substances which are formed during the decay of animal and vegetable substances-and which the roots of plants are supposed to take up-will be considered in a subsequent lecture.* ~ 3. Source of the hydrogen of plants. The source of the hydrogen of plants is less doubtful, and will require less illustration, than the source of the carbon. This elementary substance is not known to exist in nature in an uncombined state, and, therefore, it must, like carbon, enter into plants in union with some other element. 1~. Water has been already shewn to consist of hydrogen in combina*This part of the subject might have been discussed here without appearing out of place — but it will come in more appropriately, I think, when treating of the nature and mode of action of vegetable manures. SOURCE OF THE HYDROGEN OF PLANTS. 65 tion with oxygen. In the form of vapour, this compound pervades the atmosphere, and plays among the leaves of plants, while in the liquid state it is diffused through the soil, and is unceasingly drunk in by the roots of all living vegetables. In the interior of plants-at least during their growth-this water is continually undergoing decomposition, and it is unquestionably the chief source of the hydrogen which enters into the constitution of their several parts. In explaining the properties of water I have already dwelt upon the apparent facility with which its elements are capable either of separating from, or of re-uniting to, each other, in the vascular system of animals or of plants. The reason and precise results of these transformations we shall hereafter consider. 2~. In light carburetted hydrogen (CH2),-given off as already stated during the decay of vegetable matter, and said to be always present in highly manured soils, this element, hydrogen, exists to the amount of nearly one-fourth of its weight. On the extent, therefore, to which this gaseous compound gains admission into the roots of plants, will depend the supply of hydrogen which they are capable of drawing from this source. Had we satisfactory evidence of the actual absorption of this (marsh) gas by the roots or leaves of plants, in any quantity, we should have no difficulty in admitting that plants might, from this source, easily obtain a considerable supply both of carbon and of hydrogen. It would be also easy to explain how (that is, by what chemical changes,) it is capable of being so appropriated. But the extent to which it really acts as food to living vegetables is entirely unknown. 3~. Ammonia is another compound, containing much hydrogen, [its formula being NH3, or one equivalent of nitrogen and three of hydrogen,] which, as I have already stated, exercises a manifest influence on the growth of plants. If this substance enter into their circulation in any sensible quantity,-if, as some maintain, it be not only universally diffused throughout nature, but is constantly affecting, and influencing at all times, the universal functions of vegetation-there can be no doubt that the hydrogen it contains must, to an equal extent, be concerned in the production of the various organic substances which are formed or elaborated by the agency of vegetable life. How far this probable interference of the hydrogen of ammonia with the functions of the vegetable organs, will tend to explain or illustrate the influence actually exerted by this compound, we shall, by and by, more accurately inquire. In the mean time, the quantity of ammonia, which actually enters into the circulation of plants in a state of nature, is too little known, and making the largest allowance, probably too minute, to permit us to consider it as an important source of hydrogen to the general vegetation of the globe. 4~. The soluble organic substances, which enter into the circulation of plants through the roots, as shewn in the preceding section, do not consist of carbon and water only, but of combinations of carbon with hydrogen and oxygen in various proportions. From these substances, therefore, plants derive an uncertain and indefinite supply of hydrogen in a state already half-organized, and probably still more easily assimilated or converted into portions of their own substance, than when this element is combined with oxygen in the form of water. We may, therefbre, conclude generally in regard to the source of the hydrogen of plants-that though there are undoubtedly several other 66 SOURCE OF THE OXYGEN AND NITROGEN. forms of combination in which this element may enter into their circulation, in uncertain quantity-yet that all-pervading water is the main and constant source from which the hydrogen of vegetable substances is derived. ~ 4. Source of the oxygen of plants. We can at once perceive, and without difficulty, the various sources of the oxygen of plants; though it is difficult in this case also to say how much they derive from each. 1~. The water which they imbibe so largely consists in great part of oxygen, and is easily decomposed, [eight-ninths of the weight of water are oxygen.] This alone would yield an inexhaustible supply. 2~. The atmosphere contains 21 per cent. of its bulk of oxygen, and the leaves of plants in certain circumstances are known to absorb this oxygen. The air in which they live, therefore, might be another source. 3~. Carbonic acid contains 72 per cent. by weight of oxygen, and this gas is also known to be absorbed in large quantity from the atmosphere by the leaves of plants-while its solution in water is admitted readily by the roots. From any one of these sources an ample supply of oxygen might readily be obtained, and it may be considered as a proof of the vast importance of this element to the maintenance of animal and vegetable life, that it is everywhere placed so abundantly within the reach of living beings. It is from the first of these sources, however, from the water they contain, that plants are believed to derive their principal supply. The reasons on which this opinion is founded will appear when we shall have considered the functions of the several parts of plants, and the chemical changes to which the food is subjected in the course of the vegetable circulation. ~ 5. Source of the nitrogen of plants. The quantity of nitrogen present in plants is very small, compared with that of any of the other elements which enter into their constitution. Of this you will be reminded, by a reference to the analyses of hay, oats, and potatoes, exhibited in the second lecture (page 30), which shew that the nitrogen contained in these several crops, when perfectly dried at 240~ F., is respectively' 1, 2~, and 1~ per cent. In the state in which they are usually given to cattle they contain a still less per centage of nitrogen, in consequence of the quantity of water still present in them. Thus raw potatoes as they are given to cattle contain only -1 of a per cent. of nitrogen, hay 1- per cent., and oats 1,-* per cent., or a hundred pounds of each contain 5 ounces, 1 pound 5 ounces, and 1 pound 14 ounces respectively. It would appear at first sight as if this small quantity of nitrogen could be cf little importance to the plant, especially since, as we shall hereafter see, it does not enter as a constituent into those vegetable substances, such as woody fibre, starch, sugar, and gum, which plants produce in the greatest abundance, and of which their own stems and * 033, 1 29, and 1 87 per cent. -the potatoes containing also 72 per cent. of water, the hay 14, and the oats 15 per cent. QUANTITY OF NITROGEN 3N PLANTS. 67 branches chiefly consist. The same remark, however, applies to this, as to many other cases which present themselves to the chemist, during his analyses, especially of organized substances,-that those elements which are present only in small quantity are as necessary-as essential -to the constitution of the particular substance in which they occur, as other elements are of which they contain much; and that if these small quantities are removed or absent, not only are the physical and chemical properties of the substance materially altered, but it is found also to exercise a very different influence on animal and vegetable life. This latter observation will present itselfto you in a very striking light, when we come hereafter to study the nutritive properties of the several kinds of food by which animals are chiefly supported,-and shall see on what elementary body their relative nutritive properties depend, or by the amount of which their relative value appears at least to be indicated. But a consideration of the absolute quantity of nitrogen contained in an entire crop will satisfy you that though small in comparative amount, [that is, compared with the carbon and oxygen which plants contain,] this element cannot be without its due share of importance in reference to vegetable life. Hay, as above stated, contains, as it is stacked, 1* per cent. of nitrogen, or a ton of hay contains 30 Ibs. of this element. A good crop of hay, on land which is depastured during the winter, will amount to 2 or 22 tonsf per acre. Taking 2 tons as an average, the hay from one acre will contain 60 lbs. of nitrogen, or from 100 acres 6000 lbs., equal to 22 tons of nitrogen. Allowing, therefore, nothing for the aftermath, and supposing the other crops to contain no more nitrogen than the hay does, the farmer of five hundred acres will annually carry into his stack-yard at least 13 tons of nitrogen in the form of hay, straw, grain, and other produce.t Nature performs all her operations on a large scale, and the quantity of materials she employs are large in a corresponding degree. Hence, though comparatively small, the nitrogen in vegetable substances is absolutely large. You cannot suppose, when viewed in this light, that nitrogen is an element of little consequence in reference to vegetable life; or that in nature it should be so constantly and universally diffused without reference to some important end. If I may be allowed a familiar illustration of the mode in which small quantities of matter will affect the sensible properties of large masses, I would recall to your minds the effects of seasoning upon food, in imparting, when added in small quantity only, an agreeable relish to what would otherwise be In different crops of hay Boussingatlt found in three several years the following pro. portions of nitrogen:Hay, as commonly Hay dried at stacked. 280~ F. In 1836 118 1-04 of nitrogen per cent. " 1838 1.3 1-15 "' " 1839 1'5 1'3 " " Aftermath 2 4 20 "( 1 The Rev. Mr. Ogle, of Kirkley, Northumberland, informs me that some of his land near the Hall has yielded annually at this rate for 100 years, and without other manure than the droppings from the cattle which have fed upon it. I This average estimate gives but an inaccurate idea of the quantity actually contained in some species of crops. Thus red clover with the aid of gypsum will yield 3 tons of hay per acre. This hay contains more than twice the quantity of nitrogen (Boussingault) that common hay does, hence an acre of such hay would contain at least 180 lbs. of nitrogen. (See Lecture II., p. 30.) 68 THE ATMOSPHERE THE PRIMARY SOURCE OF NITROGEN. insipid. But I need not dwell on this point, since I shall hereafter Lave occasion to draw your attention to certain facts in reference to the constitution of the atmosphere, which will satisfy you that, by the agency of comparatively feeble causes, gigantic effects are continually produced in nature,-and that we can scarcely fall into a graver error in reasoning of natural processes, than by overlooking the agency of forms of matter which present themselves to our senses in minute quantity only. In reference to insect life this truth has been long established. In the coral reefs you are familiar with the wonderful results of the persevering labour of minute animals in one element. When I come to explain the nature and origin of soils, I shall have occasion to show that even the element on which you labour-the earth, on the cultivation of which your thoughts and hands are daily employed-is occasionally indebted for some of its most valuable properties to a similar agency, often unseen by you, and though working for your good, unheeded and unthought of. Whence, then, is this nitrogen derived by plants? The primary source it is not difficult to see. We can arrive at it by a train of reasoning similar'to that which led us to the atmosphere as the original source of the carbon of plants. Nitrogen does not constitute an ingredient of anv of the solid rocks,* nor do we know any other source than the atmosphere from which it can be obtained in very large quantity. It exists, as we have seen, in many vegetables, and it is more largely present in animal substances, but these organized matters must themselves have drawn this element from a foreign source, and the atmosphere is the only one from which we can fairly assume it to have been originally derived. But. though the nitrogen, like the carbon of plants, may thus be traced to the atmosphere-as its orginal source-it does not follow that this element is either absorbed directly from the air, or, in an uncombined and gaseous state. Though the leaves of trees and herbs are continually surrounded by nitrogen, the constitution of plants may be unfitted for absorbing it by their leaves. The nitrogen may not only require to be in a state of combination before it can enter into the circulation, but it may also be capable of gaining admission only by the roots. These points are considered in the following section. ~ 6. Form in which the nitrogen enters into the circulation of plants. The question as to the form in which nitrogen enters into the circulation of plants is one which at the present moment engages much attention. It will be proper, therefore, to discuss it with considerable care. 1~. It is considered an essential part of good tillage to break up and loosen the soil, in order that the air may have access to the dead vegetable matter, as well as to the living roots which descend to considerable depths beneath the surface. When rlius admitted to the roots, it is irnpossible that some of the nitrogen of the atmosphere, as well as some of its oxygen, may be directly absorbed and appropriated by the plant. To what extent this absorption of nitrogen may proceed, however, we Except coal, and coal itself is of vegetable origin. Throughout all rocks in which orranic remains are found, more or less animal matter containing nitrogen is to be met with, 5ut these remains are only accidentally present, and they must have derived their nitrogen luring life, either directly or indirectly, from the atmosphere. RAIN WATER DISSOLVES IT. 69 have as yet no experimental results from which we can form any estimate. Whether it takes place at all or not, is wholly a matter of opinion. 2~. The leaves of plants, as will be more fully explained hereafter, absorb certain gaseous substances from the atmosphere, and we might, therefore, expect that some of the nitrogen of the air would, by this channel, be admitted into their circulation. This view, however, is not confirmed by any of the experiments hitherto made with the view of investigating the action and functions of the leaves.' We are not at liberty, therefore, to assume that any of the nitrogen which plants contain has in this way been derived directly from the air. It may be the case; but it is not yet proved. 3~. There is little doubt, however, that nitrogen enters the roots of plants in a state of solution. But the quantity they thus absorb is uncertain-it is supposed to be small, and must be variable. When water is exposed to the air in an open vessel it gradually absorbs oxygen and nitrogen, though, as has been stated in a previous lecture, in proportions different from those in which they exist in the atmosphere. The whole quantity of the mixed gases thus taken up amounts to about 4 per cent. of the bclk of the water (Humboldt and Gay-Lussac), and in rain water about 2 of the whole consist of nitrogen. One hundred cubic inches of rain water, therefore, will carry into the soil about 2a inches of nitrogen gas. But in passing through the soil, the water meets with other soluble substances before it reaches the roots, especially the deep-seated roots of plants. It takes up carbonic acid, and it dissolves solid substances, and in doing so it is a property of water to give off a portion of the other gases which it had previously absorbed from -the air. But let us suppose that rain water actually takes to the roots, and carries with it into the circulation of the plant, 2 per cent. of its bulk of nitrogen, and let us calculate how much of the nitrogen it contains a crop of hay could in this way derive from the air. See subsequent lecture On the structure and functions of the several parts of plants." The experiments above referred to were made upon plants growing in close vessels, the air contained in which was measured and examined (analysed) both before the plants were introduced and after they had been some time in the vessel. In these experiments the bulk of the nitrogen present has sometimes been observed to increase, but never to diminish, in quantity. The conclusion seems satisfactory, that no nitrogen is abstracted directly from the atmosphere by the leaves of plants. Yet Boussingault' very justly remarks, that a diminution in the bulk of the nitrogen too small to be detected in the ordinary mode of making these experiments, would be sufficient to account for a considerable portion of that comparatively small quantity of nitrogen which is present in all living plants. While, therefore, we accord their due weight to these researches of the vegetable physiologists, we are not to consider them as by any means decisive of the question. With this rational and cautious conclusion, Liebig is not satisfied; he says, " We have not the slightest reason for believing that the nitrogen of the atmosphere takes partin the processes of assimilation of plants and animals; on the contrary, we know that many plants emit thae nitrogen which is absorbed by their roots either in the gaseous form or in solution in water." (p. 70.) But if they occasionally expire nitrogen by their leaves, why must this nitrogen be exactly that portion which has previously been absorbed by the roots in the uncombined state, and the quantity of which is so uncertain and so indefinite rl Boussingault details a series of experiments in the course of which he made peas, trefoil, wheat, and oats, grow in the same pure siliceous sand containing no organic matter, ant watered them with the same distilled water. The absolute quantity of nitrogen increased sensibly in the peas and trefoil during their growth; in the wheat and oats no change could be detected by analysis. from these results he is inclined to infer that the green leaves o the former have the power of sensibly absorbing nitrogen from the atmosphere, while those of the latter have not this power-at least under the circumstances in which the experiments were made. Tils conclusion, however, is not certain, as will presently be shewn —,See Amr. de Cdic,. et de PAys. lxvii. p. 1, and lxix. p. L33.] 4 70: ABSORPTION OF AMMONIA BY PLANTS. The quantity of rain that falls at York from the first of March to the middle of June-during which time the grass grows and generally ripens-is about five inches.* On a square foot, therefore, there fall 720 cubic inches of water, containing 2 per cent. of their bulk, or 14 cubic inches of nitrogen, weighing 4- grains. This gives 28 lbs. for the quantity of nitrogen thus brought to the soil over an entire acre. But if we consider how the rain falls in our climate, we cannot suppose the grass in a field to absorb by its roots, and afterwards perspire by its leaves, more than one-third of the whole. This quantity would carrywith it 9 lbs. of nitrogen into the circulation of the plants-or little more than a seventh part of the 60 lbs. which, as we have seen, are taken off the field in a crop of hay. Such a calculation as this affords at the best but a very rude approximation to the truth-it seems, however, to justify us in concluding that plants can derive from the air, and in an uncombined state, only a small portion of the nitrogen they are found to contain-and that they probably draw a larger supply from certain compounds of this elementary substance with hydrogen and oxygen-which are known to come within the reach of their roots and leaves. The most important of these compounds, and those perhaps the most extensively concerned in influencing vegetation, are ammonia and nitric acid, the properties of which have been described in the preceding lectule.t ~ 7. Absorption of ammonia by plants. Thdt ammonia enters directly into the circulation of plants is rendered probable by a variety of considerations. 1~. Thus it is found to be actually present in the juices of many plants. In that of the beet-root, and in those of the birch and maple trees, it is associated with cane sugar (Liebig.) In the leaves of the tobacco plant, and of scurvy grass, in elder flowers, and in many fungi, it is in combination with acid substances, and may be detected by mixing their juices with quick-lime.-[Schiibler Agricultur Chemie, II., p. 56.] 2~. Some plants actually perspire ammonia. Among these is the Chenopodiunm Olidum (stinking goosefoot), which is described by Sir William Hooker as "giving out a most detestable odour, compared to putrid salt fish." In the odoriferous matter given off ammonia is contained, and may be detected by putting a glass shade over the plant, and after a time introducing a feather moistened with vinegar or dilute muriatic acid.-[Chevalier Jour. de Pharm. X., p. 100.] It is also present in the odoriferous exhalations of many sweet-smelling plants and flowers.-[Schiibler, I., p. 152.] 3~. Nearly all vegetable substances, when distilled with water, yield an appreciable quantity of ammonia. Thus the leaves of hyssop, and The result of experiments made in 1834 by Prof. Phillips and Mr. Edward Gray. The mean annual fall of rain at York is about 22 inches.-(See fifth Report of the British Association, p. 173.) t It will be recollected that ammonia consists of one equivalent of nitrogen (N) united to three of hydrogen (113), being represented by NH3; and that nitric acid consists of one of nitrogen (N) and five of oxygen (05), its formula being NOs.-See Lecture III., p. 34. AMMONIA OBTAINED FROM VEGETABLES. 71 the flowers of the lime tree, yield distilled waters in which ammonia can be detected (Schiibler), the seeds of plants thus distilled yield it in abundance (Gay-Lussac), and traces of it may be found in most vegetable extracts (Liebig). 4~. Ammonia is also given off, among other products, when wood is distilled in iron retorts for the manufacture of pyroligneous acid, and by a similar treatment it may be obtained from many other vegetable substances. The above facts, however, are not to be considered as proofs that ammonia enters directly into the circulation of plants either by their roots or by their leaves. That which is associated with sugar in the beet, may have been formed by the same converting power which, in the interior of the plant, has produced the sugar from carbonic acid and water. So, that exhaled by the leaves of the goosefoot, which grows in waste places, especially near the sea, may have been produced during the upward flow of the sap or during its passage over the leaf. And we know that the nitrogen does not exist in the state of ammonia in the seeds of plants, or in wood, or in coal-though from all of them it may be obtained by the processes above described. The production of ammonia, by the agency of a high temperature, may be illustrated by a very familiar experiment often performed, though for a very different purpose. The juice and dried leaf of tobacco contain nitre (nitrate of potash) and a little ammonia. But when tobacco is burned, ammonia in sensible quantity is given off along with the smoke, chiefly in the state of carbonate of ammonia. This may be shown by bringing a lighted cigar near to reddened litmus paper, when the blue colour will be restored; or to a red rose, when the leaves will become green; or to a rod dipped in vinegar or in dilute muriatic acid, when a white cloud will appear.-[Runge, Einleitung in die technische Chemie, p. 375.] In this case a portion of the ammonia given off by the tobacco has most probably been formed during the combustion, at the expense of the nitrogen contained in the nitrate of potash which is present in the leaf. 5~. But there are other circumstances which are strongly in favour of the opinion, that ammonia not unfrequently does enter, as such, into the circulation of plants. Thus it is proved, by long experience, that plants grow most rapidly and most luxuriantly when supplied with manure containing substances of animal origin. These substances are usually applied to the roots or leaves in a state of fermentation or decay, during which they always evolve ammonia. Putrid urine and night-soil are rich in ammonia, and they are among the most efficacious of manures. This ammonia is supposed to enter into the circulation of plants along with the water absorbed by their roots, and sometimes even by the pores of their leaves. We can scarcely be said to have as yet obtained decisive proof that it does so enter, but probabilities are strongly in favour of this supposition; and when we come hereafter to consider minutely the mode in which it is likely to act, when within the plant, we shall find the probabilities derived from practical experience to be strengthened by the deductions of theory. But though the facts so long observed in reference to the action.) an 72 OTHER IMMEDIATE SOURCES OF NITROGEN. imal manures upon vegetation, justify us in believing that ammnoila actually enters into the roots, and perhaps into the leaves, of plants-we ought not hastily to conclude that all the nitrogen which plants are capable of deriving from decaying animal matter must enter into their circulation in the form of ammonia. Other soluble compounds, containing nitrogen are formed during the decay of animal substances-they actually exist largely in the liquid manures of the stable and fold-yard, and they can scarcely fail, when applied to the soil, to be to a certain extent absorbed by the roots of plants. This urea is a substance containing much nitrogen, which exists in the urine or excrements of most animals, and by its decomposition produces carbonate of ammonia. But being very soluble, this substance may enter directly into the roots, and may be there decomposed, and made to give up its nitrogen to the living plant. To other compound substances of animal origin the same observation may apply,*-so that while the fact, that animal manure in a state of fermentation is very beneficial to vegetation, may be considered as rendering it highly probable that the ammonia which such manure contains, enters directly and supplies much nitrogen to the growing plants, it must not be entirely left out of view that, in nature, a portion of the nitrogen, derived from animal substances, may be obtained immediately from other compounds in which ammonia does not exist. To what amount ammonia actually enters into the circulation of plants, or how much of the nitrogen they contain it actually supplies, we have no means of ascertaining. Were it abundantly present in the soil, its great solubility would enable it to enter, with the water absorbed by the roots, in almost unlimited quantity. In a subsequent section we shall consider the conditions under which ammonia is produced in nature, the comparative abundance in which it exists on the earth's surface, and the extent of the influence it may be' supposed to exercise on the general vegetation of the globe. ~ 8. Absorption of nitric acid by plants. 10. That ammonia is actually present in the juices of many living vegetables has been adduced, as a kind of presumptive evidence, that this compound is directly absorbed by plants. A similar presumption is offered in favour of the direct entrance of nitric acid, by its invariable presence in combination with potash, soda, lime, or magnesia, in the juices of certain common and well known plants. Thus it is said to be always contained in the juices of the tobacco plant, of the sunflower, of the goosefoot,' and of common borage. The nettle is also said to contain it, and it has been detected in the grain of barley.4 It exists probably in the juices of many other plants in which it has not hitherto' Thus it may be applied more strongly to the hippuric acid, which exists in the urine of the horse, and other herbivorous animals. Tlis acid decomposes naturally into benzoic acid and ammonia. The sweet-scented vernal-grass (Anthoxanthun Odoratum) by which hay is perfumed, owes its agreeable odour to the presence of this benzoic acid. It may, therefore, be supposed that, where cattle and horses graze, the grasses actually absorb the hippuric acid contained in the urine, which reaches their roots, decompose it as it ascends with the sap, appropriate its nitrogen, and exhale the odoriferous benzoic acid. t Chenopodium, probably in all the species of this genus.-See Liebig, p. 82.. t Grisenthwaite (New Theory of Agriculture, p. 105) says, it is always present in barley in the form of nitrate of soda. —See Appendix. ABSORPTION OF NITRIC ACID-ITS EFFECT ON VEGETATION. 73 been sought for. Were we, therefore, entitled, from the mere presence of this acid in plants, to infer that it had really entered by their roots or leaves, we should have no hesitation in drawing our conclusion. But, like ammonia, it may have been formed in the interior of the living vegetable;* and hence the fact of its presence proves nothing in regard to the state in which the nitrogen it contains entered into the circulation of the plant. 2~. But nitric acid, like ammonia, exerts a powerful influence on the growing crop, whether of corn or of grass. Animal matters, as we have seen, give off ammonia during their decay, and manures are rich and efficacious in proportion to the quantity of animal manure they contain. The crop produced also is valuable and rich in nitrogen in like proportion. Therefore, as already stated, it is inferred that ammonia enters directly into the living plant, and supplies it with nitrogen. The effect of nitric acid is similar in kind, and perhaps equal in degree. Applied to the young grass or sprouting shoots of grain, it hastens and increases their growth, it occasions a larger produce of grain, and this grain, as when ammonia is employed, is richer in gluten, and more nutritious in its qualily.t An equal breadth of the same field yields a heavier produce, and that produce, weight for weight, contains more when saltpetre or nitrate of soda have been applied in certain quantities to the young plants which grow upon it. It is reasonable to conclude, therefore, that the acid of the nitrates, in some form or other, * When the beet-root arrives at maturity, the sugar begins to diminish, and saltpetre or other nitrates to be formed, probably at the expense of the ammonia which the juice previously contained.-Decroizelles, Jour. de Phar., X., p. 42. t The analogous effects ofammoniacal manures and of the nitrates on the relative quantities of gluten and starch in grain. are shown by the following experiments: Hermbstaedt sowed equal quantities of the same wheat, on equal plots of the same ground, and manured them with equal weights of different manures. Then from 100 parts of each sample of grain produced, he obtained starch and gluten in the following proportions: Glluten. Starch. Produce. Without manure.-.... 9-2 66-7 3 fold. With vegetable manure (rotted potatoe haulm) - - -- 9-6 65 94 5 With cow dung - - 12-0 62-3 7 With pigeons' dun - - 12-2 632 9 With horse dung..... 13-7 61-64 10 With goats' dung -,. 32-9 42-4 12 " With sheep dung..... -32-9 42-8 12 With dried night-soil -.. 3314 41-44 14 With dried ox-blood.-.... 34-24 413 14 With dried human urine - - 35-1 39-3 12 "a The manures employed by Hermbstaedt are supposed, during fermentation, to evolve more ammonia in the order in which they are here placed, beginning at the top of the list; while the amount and kind of the produce obtained by the use of each, afford the chief evi. dence in favour of the opinion that this ammonia actually enters into and yields nitrogen to the plant. Mr. Hyett found in flour raised on two patches of the same land in Gloucestershire, the one dressed with nitrate of soda, the other undressed, the following proportions: Gluten. Starch. In the nitrated - - - 23-25 49-5 In the unnitrated - - 19- 55-5 And Mr. Daubeny, [Three Lectures on Agriculture, p. 76,] in flour from wheat top-dressed with saltpetre, foundIn the nitrated - - - - 15 per cent. of gluten. In the unnitrated - - 13 " " These differences are not so striking as in the case of ammonia, but they are precisely the same in kind, and lead to the same general conclusion in regard to the nature of the influence of the nitrates on vegetation. Accurate and repeated experiments on the precise effects of the nitrates are still much to be desired. [i. Schiibler. GC'-ndsdtze der Agricultur Chemie, II. p. 170.] 14 GENERAL CONCLUSIONS. is capable of entering into the circulation of living plants-and of yielding to them, in whole or in part, the nitrogen they contain. But here, again, as in the case of ammonia, we are at fault in regard to the quantity of nitrogen which plants in a state of nature actually derive from nitric acid or the nitrates. The compounds of this acid with potash, soda, lime, and magnesia (the nitrates of these substances), are all very soluble in water. The quantity of this fluid, therefore, which enters by the roots of plants, could easily convey into their circulation far more of these nitrates than would be alone sufficient to supply thb whole of the nitrogen they require-for the formation of all their parts and products. But so it might of ammonia or its salts, as has already been shown. I shall hereafter lay before you certain considerations which may probably lead us to approximate conclusions in regard to the relative influence exercised by these two compounds on the general vegetation of the globe. Conclusions.-Respecting the form in which nitrogen enters into the circulation of plants, we have therefore, I think, fairly arrived at these deductions: 1~. That the nitrogen of the atmosphere may, to a small extent, enter directly into the living vegetable either in the form of gas or in solution in water, but that supposing nitrogen to be in this way appropriated* by the plant, the quantity so taken up could form only a small quantity of that which vegetables actually contain. 2~. That ammonia is capable of entering into plants in very large quantity, and of yielding nitrogen to them, and that in European agriculture, which employs fermenting animal manure as an important means of promoting vegetable growth, it does appear to yield to cultivated plants a considerable portion of the nitrogen they contain. 3~. That nitric acid, in like manner, is capable of entering into and giving up its nitrogen to plants; and that where this acid is employed as an instrument of culture, the crops obtained owe part of their nitrogen to the quantity of this compound which has been applied to the growing plants. The same inference may fairly be drawn in regard to the effect of nitric acid-when, in the form of nitrates, it exists or is produced naturally in the soil. 4~. That other compound bodies, such as are contained in urine, or are produced during the decay of animal matter, may also enter into the circulation of plants, and yield nitrogen to promote their growth. On the whole, however, there seem strong reasons for believing that plants are mainly dependent on ammonia and nitric acid for the nitrogen they contain; and that they obtain it most readily, and with least labour, so to speak, from these compounds,-though nature has kindly fitted them for deriving a stinted supply from other sources, when these substances are not present in sufficiert abundance. How far each of these compounds is employed by nature, as an instrument in promoting the general vegetation of the globe, will be considered in a subsequent lecture. Liebig and others say that plants are incapable of appropriating or assimilating the nitro gen which enters into their circulation in the simple state. We shall constler this question hereafter. LECTURE V. How does the food enter into the circulation of plants-Structure of the several parts of plants-Functions of the root-Course of the sap-Cause of its ascent-Functions of the stem-of the leaves-and of the bark-Circumstances by which the exercise of these functions is modified. HAVING now taken a general view of the source from which plants derive the elementary substances of which their solid parts consist, and of the slates of combination in which these elements enter into the vegetable circulation,-the next step in our inquiry is-how are these substances admitted into the interior of living plants-and under what conditions or regulations? We are thus led to study the structure and functions of the several parts of plants, and the circumstances by which the exercise of these functions is observed to be modified. ~ 1. General structure of plants, and of their several parts. Plants consist essentially of three parts-the roots, the stem, and the leaves. The former spread themselves in various directions through the soil, as the latter do through the air, and the stem is dependent for its food and increase on the rapidity with which the roots shoot out and extend, and on the number and luxuriance of the leaves. We shall obtain a clearer idea of the relative structure of these several parts by first directing our attention to that of the stem. The stem consists apparently of four parts-the pith, the wood, the bark, and the medullary rays. The pith and the medullary rays, however, are similarly constituted, and are only prolongations of one and the same substance. The pith forms a solid cylinder of soft and spongy matter, which ascends through the central part of the stem, and varies in thickness with the species and with the age of the trunk or branch. The wood surrounds the pith in the form of a hollow cylinder, and is itself covered by another hollow cylinder of bark. In trees or branches of considerable age the wood consists of two parts, the oldest or heart wood, often of a brownish colour, and the newer external wood or alburnum, which is generally softer and less dense than the heart wood. The bark also is easily separated into two portions, the inner bark or liber, and the epidermis or outer covering of the tree. The pith and the bark are connected together by thin vertical columns or partitions, which intersect the wood and divide it into triangular segments. A cross section of the trunk or branch of a tree exhibits these thin columns extending in the form of rays, or like the spokes of a wheel, from the centre to the circumference. Though they form in reality thin and continuous vertical plates, yet from the appearance they present in the cross section of a piece of wood, they are distinguished by the name of medullary rays. These several parts of the stem are composed of bundles of small tubes or hollow cylindrical vessels of various sizes, and of different kinds, the structure of which it is unnecessary for us to study. They 76 STRUCTURE OF THE STEMS, ROOTS, AND LEAVES OF PLANTS. are all intended to contain liquid and gaseous substances, and to convey them in a vertical, and sometimes in a horizontal, direction. The tubes which com(pose the wood and bark are arranged vertically, as may readily be seen on examining a piece of wood even with the naked eye, and are intended to convey the sap upwards to the leaves, and downwards to the roots. Those of which the.pith and medullary plates consist are arranged horizontally, and appear to be intended to maintain a lateral intercourse between the pith and the bark —perhaps even to place the heart of the tree within the influence of the external air. The root, though prior in its origin to the stem, may nevertheless for the purpose of illustration be considered as its downward and lateral prolongation into the earth-as the branches are its upward prolongation into the air.* When they leave the lower part of the trunk of the tree, they differ little in their internal structure from the stem itself. As they taper off, however, first the heart wood, then the pith, gradually disappear, till, towards their extremities, they consist only of a soft central woody part and its covering of soft bark. These are connected with, or are respectively prolongations of,. the new wood and bark of the trunk and branches. At the extreme points of the roots the bark becomes white, soft, spongy, and full of pores and vessels. It is by these spongy extremities only, or chiefly,'that liquid and gaseous substances are capable either of entering into, or of making their escape from, the interior of the root. The branches and twigs are extensions of the trunk; and of the former, the leaves may be considered as a still further extension. Tle fibres of the leaf are minute ramifications of the woody matter of the twigs, are connected through them with the wood of the branches and stems, and from this wood receive the sap which they contain. The green part of the leaf may-be considered as a special expansion of the bark, by which it is fitted to act upon the air, in the same way as the spongy mass into which the bark is changed at the extremity of the root, is fitted to act upon the water and other substances it meets with in the soil. For as the fibres of the leaf are connected with the wood of the stem, so the green part of the leaf is connected with its bark, and from this green part the sap first begins to descend towards the root. ~ 2. The functions of the root. The position in which the roots of plants in their natural state are generally placed, has hitherto prevented their filnctions from being so accurately investigated as those of the leaves and of the stem. While, therefore, the main purposes they are intended to serve are universally The correctness of this comparison is proved by the fact that, in many trees, the branch if planted will become a root, and the root, if exposed to the air, will gradually be transformed into a branch. The banana in the forest, and the currant tree in our gardens, are familiar instances of trees spontaneously planting their branches, and causing them to perform the functions of roots. In like manner, " if the stem of a young plum or cherry-tree, or of a willow, be bent in the autumn so that one-half of the top can be laid in the earth and one-half of the root be at the same time taken carefully up-sheltered at first and afterwards gradually exposed to the cold-and if in the following year the remaining part of the top and root be treated in the same way. the branches of the top will become roots, and the iamifications of the roots will become branches, producing leaves, flowers, and fruitin due season.-[Loudon's Encyclopadia of Agriculture.] The tree is thus reversed in position,. and the roots and branches being thus mutually convertible cannot be materially unlike in general structure. ROOTS ABSORB AQUEOUS SOLUTIONS, AND OXYGEN. 77 Known and understood, the precise way in which these ends are accomplished by the roots, and the powers with which they are invested, are still to a considerable degree matters of dispute. I. It appears certain that they are possessed of the power of absorbing water in large quantity from the soil, and of transmitting it upwards to the stem. The amount of water thus absorbed depends greatly upon the nature of the soil and of the climate in which a plant grows, but much also upon the specific structure of its leaves and the extent of its foliage. II. The analogy of the leaves and young twigs would lead us to suppose that, when in a proper state of moisture, the roots should also be capable of absorbing gaseous substances from the air which pervades the soil. Experiment, however, has not yet shown this to be the case. We know, however, that they are capable of absorbing gases through the medium of water. For if the roots of a plant are placed in water containing carbonic acid in the state of solution, this gas is found gradually to disappear. It is extracted from the water by the roots. And if the water in which the roots are immersed be contained in a bottle only partially filled with the liquid, while the remainder is occupied by atmospheric air, the oxygen in this air will also slowly diminish. It will be absorbed by the roots through the medium of the water.* Again, if in the place of the atmospheric air in this bottle, carbonic acid be substituted, the plant will droop and in a few days will die. The same will take place, if instead of common air or carbonic acid. nitrogen or hydrogen gases be introduced into the bottle. The plant will not live when its roots are exposed to the sole action of any of the three. It is obvious, therefore, that the roots of plants absorb gaseous substances from the air which surrounds their roots, at least indirectly and through the medium of water. It appears also that from this air they have the power of selecting a certain portion of oxygen when this gas is present in it. Thirdly, that though they can absorb carbonic acid to a limited amount without injury to the plant, yet that a copious supply of this gas, unmixed with oxygen, is fatal to vegetable life. This deduction is confirmed by the fact that, in localities where carbonic acid ascends through fissures in the subjacent rocks and saturates the soil, the growth of grass is found to be very much retarded. And, lastly, since nitrogen is believed not to be in itself noxious to vegetable life, the death of the plant in water surrounded by this gas, is supposed to imply that the presence of oxygen is necessary about the roots of a growing and healthy plant, and that one of the special functions of the roots is constantly to absorb this oxygen. This supposition is-in accordance with the fact that, in the dark, the leaves of plants absorb oxygen from the atmosphere; for we have already seen reason to expect that, from their analogous structure, the roots and leaves in similar circumstances should perform also analogous functions. At the same time, if the roots do require the access and presence It will be recollected that water absorbs about 4 per cent. of its bulk of air from the atmosphere, of which about one-third is oxygen. If the roots extract this oxygen from the water, the latter will again drink in a fresh portion from the atmospheric air which floatt above it, 4* 78 DO SOLID SUBSTANCES ENTER THE ROOTS? of oxygen in the soil, it would further appear that those of some plants require it more than those of others; inasmuch as some genera, like the grasses, love an open and friable soil, into which the air is more completely excluded.-[Sprengel, Chemie, II., p. 337.] III. We have in a former lecture (IV. p. 64) concluded from facts there stated, that solid substances, which are soluble- in water, acconlpany this liquid when it enters into the circulation of the plant. This appears to be true both of organic and inorganic substances. Potash, soda, lime, and magnesia thus find their way into the interior of plants, as well as those substances of animal and vegetable origin to which the observations made in the fourth lecture were intended more especially to apply. Even silica,* considered to be almost insoluble in water, enters by the roots, and is found in some cases in considerable quantities in the ster. Some persons have hence been led to conclude that solid substances, undissolved, if in a minute state of division, may be drawn into the pores of the root and may then be carried by the sap upwards to the ste m. Considered as a mere question of vegetable mechanics, argued as such among physiologists, it is of little moment whether we adopt or reject this opinion. One physiologist may state that the pores by which the food enters into the roots are so minute as to baffle the powers of the best constructed microscope, and, therefore, that to no particles of solid matter can they by possibility give admission-while another may believe solid matter to be capable of a mechanical division so minute as to pass through the pores of the finest membrane. As to the mere fact itself, it matters not which is right, or which of the two we follow. The adoption of the latter opinion implies in itself merely that foreign substances, unnecessary, perhaps injurious to vegetable life, may be carried forward by the flowing juices until in some still part of the current, or in some narrower vessel, they are arrested and there permanently lodged in the solid substance of the plant. By inference, however, the adoption of this opinion implies also, that the inorganic substances found in plants,-those which remain in the form of ash when the plant is burned,-are accidental only, not essential to its constitution. For since they may have been introduced in a mere.state of minute mechanical division suspended in the sap, they ought to consist of such substances chiefly as the soil contains in the greatest abundance, and they ought to vary in kind and relative quantity with every variation in the soil. In a clay land the ash should consist chiefly of alumina,f in a sandy soil chiefly of silica. But if, as chemical inquiry appears to indicate, the nature of the ash is not accidental, but essential, and in some degree constant, even in very different soils, this latter inference is inadmissible; —-and in reasoning backwards from this fact, we find ourselves constrained to reject the opinion that substances are capable of entering into the roots of plants in a solid state-and this without reference at all to the mechanical question, as to the relative size of the pores of the spongy roots or of the particles into which solid matter may be divided. * Silica is the name given by chemists to the pure matter of flint or of rock crystal. Sand and sandstones consist almost entirely of s'lica. t Alumina is the pure earth of clay. SELECTING POWER OF THE ROOTS. 79 IV. We are thus brought to the consideration of the alleged selecting power of the roots, which, if rightly attributed to them, must be considered as one of the most important functions of which they are possessed. It is a function, however, the existence of which is disputed by many eminent physiologists. But as the adoption or rejection of it will materially influence our reasonings, as well as our theoretical views, in regard to some of the most vital processes of vegetation,-it will be proper to weigh carefully the evidence on which this power is assigned to the roots of plants. 1~. The leaves, as we shall hereafter see, possess in a high degree the power of selecting from the atmosphere one or more gaseous substances, leaving the nitrogen, chiefly, unchanged in bulk. The absorp tion of carbonic acid and the diminution of the oxygen in the experi ments above described, appear to be analogous effbcts, and would seem to imply in the roots the existence of a similar power. 2~. Dr. Daubeny found that pelargoniums, barley (hordeum vulgare), and the winged pea (lotus tetrag'onolobuts), though made to grow in a soil containing much strontia,* appeared to absorb none of this earth, foi none was found in the ash left by the stein and roots of the plant when burned. In like manner De Saussure observed that polygonum persicaria refused to absorb acetate of lime from the soil, though it freely took up common salt.-[Lindley's Theory of Horticulture, p. 19.] 3~. Plants of different species, growing in the same soil, leave, when burned, an ash which in every case contains either different substances, ortthe same substances in unlike proportions. Thus if a bean and a grain of wheat be grown side by side, the stem of the plant from the latter seed will be found to contain silica, from the former none.f 4~. But the same plant grown in soils unlike in character and composition, contains always-if they are present in the soil at all-very nearly the same kindi of earthy matters in nearly the same proportion. Thus the stalks of corn plants, of the grasses, of the bamboo, and of many others, always contain silica, in whatever soil they grow, or at least are capable of growing with any degree of luxuriance. \Vith the view of testing this point, Lampadius prepared five square patches of ground, manured them with equal quantities of a mixture of horse and cow dung, sowed them with equal measures of the same wheat, and on four of these patches strewed respectively five pounds of finely powdered quartz (siliceous sand), of chalk, of alumina, and of carbonate of magnesia, and left one undressed. The produce of seed from each, in the above order, weighed 244, 284, 264, 21A, and 20 ounces respectively. The grain, chaff, and straw, from each of the patches left nearly the same quantity of ash-the weights varying only from 3'7 to 4'08 per cent., and the roots and chaff being richest in inorganic'matter. The relative proportions of silica, alumina, lime, and magnesia, * Watered with a solution of nitrate of strontia. Strontia is an earthy substance resent bling lime, which is found in certain rocks and mineral veins, but which has not hitherto been observed in the ashes of plants. t It is not strictly correct that the bean will absorb no silica, but the quantity it will take up will be only one-thirteenth of that taken up by the wheat plant-the per centage of silica in the ash of bean straw being, according to Sprengel, only 0-22, while in wheat straw it is 2-87 per cent. Pea straw contains four times as much as that of the bean, or 0-996 per cent. t For more precise information on this point, see the subsequent lectures, " On the inor. ganic constituents of plants," (Part II.) 80 PLANTS MAY ABSORB POISONOUS SUBSTANCES. were the same in all.-[Meyen Jahresbericht, 1839, p. 1.] Provided, therefore, the substances which plants prefer be present in the soil, the kind of inorganic matter they take up, or of ash they leave, is not mate-?ially affected by the presence of other substances, even in somewhat larger quantity. These facts all point to the same conclusion, that the roots have the power of selecting from the soil in which they grow, those substances which are best fitted to promote the growth or to maintain the healthy condition of the plants they are destined to feed. 5~. It has been stated above that the roots of certain plants refuse to absorb nitrate of strontia and acetate of lime, though presented to them in a state of solution-the same is true of certain coloured solutions which have been found incapable of finding their way into the circulation of plants whose roots have been immersed in them. On the other hand, it is a matter of frequent observation that the roots absorb solutions containing substances which speedily cause the death of the plant. Arsenic, opium, salts of iron, of lead, and of copper, and many other substances, are capable of being absorbed in quantities which prove injurious to the living vegetable-and on this ground chiefly many physiologists refuse to acknowledge that the roots of plants are by nature endowed with any.definite and constant power of selection at all. But this argument is of equal force against the possession of suclh a power by animals or even by man himself; since, with our more perfect (iscriminating powers, aided by our reason too, we every day swallow with our food what is more or less injurious, and occasionally even fatal, to human life." On the whole, therefore, it appears most reasonable to conclude that the roots are so constituted as (1~) to be able generally to select from the soil, in preference, those substances which are most suitable to the nature of the plant-(20) where these are not to be met with, to admit certain others in their steadf-(3~) to refuse admission also to certain substarces likely to injure the plant, though unable to discriminate and reject every thing hurtful or unbeneficial which may be presented to them in a state of solution. The object of nature, indeed, seems to be to guard the plant against the more common and usual dangers only-not against such as rarely present themselves in the situations in which it is destined to grow, or against substances which are unlikely even to demand admission into its roots. How useless a waste of skill, if I may so speak, would it have been to endow the roots of each plant with the power of distinguishing and rejecting opium and arsenic and the thousand other poisonous substances which the physiologist can present to them, but which in a state of nature-on its natural soil and in its natural climate-the livi.ng vegetable is never destined to encounter! I may here remark that it isby no means an extraordinary power which these circumstances spem to show the roots of plants to possess. In the presence of oxygen, nitrogen, and carbornic aci.d, in equal quantities, water will prefer and will select the latter. From a mixture of lime and magnesia, acetic or sil.phuric acid will select and separate the former. Is it unreasonable to suppose the roos of plants-the organs ofa living being-to be endpwec with powers ofdiscrimitation at least as great as those possessed by dead matter? t This conclusion i notr strictly contained in the premises above stated, but the facts from which it is drawn will be fully explained in treating of the inorganic constituents of plants. It is introduced here for the purpose of giving a complete view of whpit appears to be the true powers of discrimination possessed by tlhe root. EXCRETORY POWER OF THE ROOTS. 81 V. Another function of the roots of plants, in regard to which physiologists are divided in opinion at the present day, is what is called their excretory power. 10. When barley or other grain is caused to germinate in pure chalk, acetate of lime* is uniformly found to be mixed with it after the germination is somewhat advanced (Becquerel and Mateucci, Ann. de Cheem. et de Phys., Iv., p. 310.) In this case the acetic acid must have been given off (excreted) by the young roots during the germination of the seed. This fact may be considered as the foundation of the excretory theory as it is called. This theory, supported by the high authority of Decandolle, and illustrated by the apparently convincing experiments of Macaire, (Ann. de Chim. et de Phys., lii., p. 225,) has more recently been met by counter-experiments of Braconnot, (lxxii. p. 27,) and is now in a great measure- rejected by many eminent vegetable physiologists. It may indeed be considered as quite certain that the application of this theory by Decandolle and others to the explanation of the benefits arising from a rotation of crops, is not confirmed, or proved to be correct, by any experimrents on the subject that have hitherto been published.f According to Decandolle, plants, like animals, have the power of selecting from their food, as it passes through their vascular system, such portions as are likely to nourish them, and of rejecting, by their roots, Acetate of lime is a combination of acetic acid or vinegar with lime derived from the chalk. t The discordant results of Macaire and Braconnot were as follow: 1~. Macaire observed that when plants of Chondrilla Muoralis were grown in rain water they imparted to it something of the smell and taste of opium. Braconnot confirmed this. but attributed it to wounds in the roots which allowed the proper juice of the plant to escape. He says it is almost impossible to free the young roots from the soil in which they have grown, without injuring them and causing the sap to exude. 20. Euphorbia Peplus (Petty Spurge) imparted to the water in which it grew a gummi. resinous substance of a very acrid taste. In the hands of Braconnot it yielded to the water scarcely any organic matter, and that only slightly bitterish. 3~. Braconnot washed the soil in which plants of Euphorbia Breoni and Asclepias Incar. nata were growing in pots, and obtained a solution containing earthy and alkaline salts with only a trace of organic matter. He also washed the soil in which the Poppy (Papaver Somniferum) had been grown ten years successively. The solution, besides inorganic earthy and alkaline salts, gave a considerable quantity of acetic acid (in the form of acetate of lime) and a trace of brown organic matter. He infers that these several plants do not excrete any organic matter in sufficient quantity to be injurious to themselves. i~. Macaire observed that when separate portions of the roots of the same plant of Mercu. rialis Annua were immersed in separate vessels, the one containing pure water and the other a solution of acetate of lead,-the solution of lead was absorbed by the plant,-was to be traced in every part of it, and afterwards was partially transmitted to the pure water. Bra. connot observed the same results, but he found the entrance of the lead into the second vessel to be owing to the ascent of the fluid up the outer surface of the one root and down the exterior of the other, and that, by preventing the possibility of this passage, no lead could be detected among the pure water. The conclusions of Macaire, therefore, in favour of the rotation theory of Decandolle must be considered as at present inadmissible, and we shall hereafter see reason to coincide, at least to a certain extent, in the conclusion of Braconnot, "that if these excretions (of organic matter) really take place in the natural state of the plant, they are as yet so ob scure and so little known as to justify the presumption that some other explanation -must be given of the general system ofrotation." Various illustrations have been given by different observers of this supposed excreting power of the roots. Among the most recent are those of Nietner, who ascribes the luxuriant rye crops obtained without manure after three years of clover, to the excretions of this plant in the soil, which, like those of the pea and bean to the wheat, he supposes'o be nourishing food to the rye. He also states that the beet or the turnip after tobacco has an unpleasant taste, and is scarcely eatable, which he attributes to the excretions of the tobacco plant. Meyen ascribes the effect of the clover to the green manure supplied by its roots and stubble and that of the tobacco to the undecomposed organic substances contained in the sap and substance of the roots and stems of this plant, of which so large a quantity is left behind in the field.-[Meyen's Jahresbericht, 1839, p. 5.]-These objections of Meyen are not without their weight, but we shall hereafter see that they embody only half the truth. 82 EXPERIMENTS OF DE SAUSSURE. when the sap descends, such as are unfit to contribute to their support, or would be hurtful to them if not rejected from their system. He further supposes that, after a time, the soil in which a certain kind of plant grows becomes so loaded with this rejected matter, that the same plant refuses any longer to flourish in it. And, thirdly, that though injurious to the plant from which it has been derived, this rejected matter may be wholesome food to plants of a different order, and hence the advantage to be derived from a rotation of crops. There seems no good reason to doubt that the roots of plants do at times-it may be constantly-reject organic substances from their roots. The acetic acid given off during germination, and the same acid found by Braconnot in remarkable quantity in the soil in which the poppy (papaver somninferum) has grown-may be regarded as sufficient evidence of the fact-but the quantity of such organic matter hitherto detected among what may be safely viewed as the real excretions of plants, seems by far too small to account for the remarkable natural results attendant upon a rotation of crops. The consideration of these results, as well as of the general theory of such a rotation, will form a distinct topic of consideration in a subsequent part of these lectures. I shall, therefore, only mention one or two facts which seem to me capable of explanation only on the supposition that the roots of plants are endowed with the power of rejecting, and that they do constantly reject, when the sap returns from the leaf, some of the substances which they had previously taken up from the soil. 1~. De Saussure made numerous experiments on the quantity of ash pe cent. left by the same plant at different periods of its growth. Among other results obtained by him, it appearedA. That the quantity of incombustible or inorganic matter in the different parts of the plant was different at different periods of the year. Thus the dry leaves of the horse chestnut, gathered in May, left 7'2 per cent., towards the end of July 8-4 per cent., and in the end of Septemnber 8-6 per cent. of ash; the dry leaves of the hazel in June left 6-2, and in September 7 per cent.; and those of the poplar (populus nigra) in May 6-6, and in September 9'3 per cent. of ash. These results are easily explained on the supposition that the roots continued to absorb and send up to the leaves during the whole summer the saline and earthy substances of which the ash consisted. But —. B. He observed also that the quantity of the inorganic substances in -or the ash left by-the entire plant, diminished as it approached to maturity. Thus the dry plants of the vetch, of the golden rod (solidago vulgaris), of the turnsol (helianthus annuus), and of wheat, left respectively of ash, at three different periods of their growth, [Davy's Agricultural Chemistry, Lecture III,]Before flowering. In flower Seeds ripe. per cent. per cent. per cent. Vetch.... 15 12-2 6-6 Golden rod. 9.2 5-7' 5'0 Turnsol.... 147 13-7 9 3 Wheat.... 79 5-4 3-3 This diminution in the proportion of ash, might arise either from an increase in the absolute quantity of vegetable matter in the plants ac PROPORTION OF SILICA IN THE ASH GF PLANTS. 83 csmpanying their increase in size-or from a portion of the saline and earthy matters they contained being again rejected by the roots. But if the former be the true explanation, the relative proportions of the several substances of which the ash itself consisted, in the several cases, should have been the same at the several periods when the experiments were made. But this was by no means the case. Thus, to refer only to the quantity of silica contained in the ash left by each of the above plants at the several stages of their growth, the ashes of the Before flowering. In flower. Seeds ripe. per cent. per cent. per cent. Vetch contained... 15 1' 5 1'75 Golden rod..... 1-5 1'5 3-5 Turnsol...... 1-5 1' 5 3-75 WVheat.... 12-5 26-0 51-0 If, then, the proportion of silica in the ash increased in some cases four-fold, while the whole quantity of ash left by the plant decreased, it appears evident that some part of that which existed in the plant during the earlier periods of its growth must have bee. excreted or rejected by the roots, as it advanced towards maturity. 2~. This conclusion is confirmed and carried farther by another consideration. The quantity of ash left by the ripe wheat plant, in the above experiments of De Saussure, amounted to 3-3 per cent.;-of which ash, 51 per cent., or rather more than one-half, was silica. This silica, it is believed, could only have entered into the circulation of the plant in a state of solution in water, and could only be dissolved by the agency of potash or soda. But, according to Sprengel, the potash, soda, and silica, are to each other in the grain and straw of wheat, in the proportions ofPotash. Soda. Silica. Grain.... 0225 0-24 0-4 Straw.... 020 0-29 2-87 Or, supposing the grain to equal one-half the weight of the strawtheir relative proportions in the whole plant will be nearly as 21 potash, 27 soda, 205 silica, or the weight of the silica is upwards of four times the weights of the potash and soda taken together. Now silica requires nearly half its weight of potash to render it soluble in water,* or three-fifths of its weight of a mixture of nearly equal parts of potash and soda. The quantity of these alkaline substances found in the plant, therefore, is by no means sufficient to have dissolved and brought into its circulation the whole of the silica it contains. One of two things, therefore, must have taken place. Either a portion of the potash and soda present in the plant in the earlier stages of its growth must have escaped from its roots at a later stage,f leaving the silica behind it-or the same quantity of alkali must have circulated through the plant several times-bringing in its burden of silica, depositA soluble glass may be made by melting together in a crucible for six hours 10 parts of carbonate of potash, 15 of silica, and 1 of charcoal powder. t De Saussure does not state the exact relative quantities of potash and soda at the several periods of the growth of wheat, though they appear to have gradtally diminished. It seems, indeed, to be true of many plants, that the potash and soda they contain diminishes in quantity as their age increases. Thus the weight of potash in the juice of the ripe or sweet grape, is said to be less than in the unripe or sour grape-and the leaves of the potato have been found more rich in potash before than after blossoming (Liebig). 84 CAN THE ROOTS MODIFY THE FOOD OF PLANTS? ing it in the vascular system of the plant, and again returning to the soil for a fresh supply. In either case the roots must have allowed it egress as well as ingress. But the fact, that the proportion of silica in the plant goes on increasing as it continues to grow, is in favour of the latter view-and renders it very probable that the same quantity of alkali returns again and again into the circulation, bringing with it supplies of silica and probably of other substances which the plant requires from the soil. And while this view appears to be the more probable, it also presents an. interesting illustration of what may probably be the kind of function discharged by the potash and other inorganic substances found in the substance of plants-a question we shall hereafter have occasion to consider at some length. The above considerations, therefore, to which I might add others of a similar kind, satisfy me that the roots of plants do possess the power of excreting various substances which are held in solution. by the sap on its return from the stem-and which having performed their functions in the interior of the plant are no longer fitted, in their existing condition. to minister to its sustenance or growth. Nor is it likely that this excretory power is restricted solely to the emission of inorganic substances. Other soluble matters of organic origin are, no doubt, permitted to escape into the soil-though whether of.such a kind as must necessarily be injurious to the plant from which they have been extruded, or to such a degree as alone to render a rotation of crops necessary, neither reasoning nor experiment has hitherto satisfactorily shown. VI. The roots have the power of absorbing, and in some measure of selecting, food from the soil-can they also modify or alter it as it passes through them? A colourless sap is observed to ascend through the roots. From the very extremity up to the foot of the stem a cross section exhibits little trace of colouring matter, even when the soil contains animal and vegetable substances which are soluble, and which give dark coloured solutions, [such as the liquid manure of the fold-yard.] Does such matter never enter the root? If it does, it must be speedily changed or transformed into new compounds. We have as yet too few experiments upon this subject to enable us to decide with any degree of certainty in regard to this function of the root. It is probable, however, that as the sap passes through the plant, it is constantly, though gradually, undergoing a series of changes, from the time when it first enters the root till it again reaches it. on its return from the leaf. Can we conceive the existence of any powers in the root, or in the whole plant, of a still more refined kind? The germinating seed gives off acetic acid into the soil,-does this acetic acid dissolve lime from the soil and return with it again, as some suppose (Liebig), into the circulation of the plant?" Is acetic acid produced and excreted by the seed for this very refined purpose? We have concluded that in the wheat plant the potash and soda probably go and come several times during its growth, and the ripening of its seed. Is this a contrivance of nature to' Braconnot found acetate of lime in very small quantities to be singularly hurtful to vegetarion, and acetate of magnesia a little less so. He only mentions, however, some experiments upon mercurialis annua, [Ann. de Chim. et de Phys. lxxii. p. 36,] and as Saussuro found that some plants actually refused to take it up at all, these acetates may not be equally injurious to all plants. THE SAP ASCENDS THROUGH THE WOOD. 85 make up for the scarcity of alkaline substances in the soil-or would the same mode of operation be employed if potash and soda were present in greater abundance? Or where the alkalies are present in greater abundance, might not more work be done by them in the same time,-might not the plant be built up the faster and the larger, when there were more hands, so to speak, to do the work? Is the action of inorganic substances upon vegetation to be explained by the existence of a power resident in the roots or other parts of plants, by which such operations as this are directed or superintended? There are many mysteries connected with the nature and phenomena of vegetable life, which we have been unable as yet to induce nature to reveal to us.* But the morning light is already kindling on the tops of the mountains, and we may hope that the deepest vallies will not forever remain obscure. ~ 3. The course of the sap. If the trunk of a tree be cut off above the roots, and the lower extremity be immediately plunged into a solution of madder or other colouring substances, the coloured liquid will ascend and will gradually tinge the wood. This ascent will continue till the colour can also be observed in the nerves of the leaf. If at this stage in the experiment the trunk be cut across at various heights, the wood alone will appear coloured, the bark remaining entirely untinged. But if the process be allowed still to continue when the coloured matter has reached the leaf, and after some further time the stem be cut across, the bark also will appear dyed, and the tinge will be perceptible further and further from the leaf the longer the experiment is carried on, till at length both bark and wood will be coloured to the very bottom of the sten. Or if the root of a living plant, as in the experiment of Macaire detailed in a preceding note, be immersed in a metallic solution-such as a solution of acetate of lead,-which it is capable of absorbing without immediate injury, and different portions of the plant be examined after the lapse of different periods of time,-first the stem, afterwards the leaves, then the bark of the upper part of the stem, and lastly that of the lower part of the stem, will exhibit traces of lead. These experiments show that the sap which enters by the roots ascends through the vessels of the wood, diffuses itself over the surface of leaves, and then descends by the bark to the extremities of the root. But what becomes of the sap when it reaches the root? Is it delivered into the soil, or does it recommence the same course, and again, repeatedly perhaps, circulate through the stem, leaves, and bark? This question has been partly answered by what has been stated in the preceding section. When the sap reaches the extremity of the root, it appears to give off to the soil both solid and fluid substances of a kind and The roots oftree. wxll trpvel to comparatively great distances, and in various directions, in search of water: the roots of sainfoin (Esparsette) will penetrate 10 or 12 feet through the calcareous rubbly subsoil, or down the fissures of limestone rocks on which they delight to grow. Is this the result of someperceptive power in the plant-or is it merely by accident that the roots display these tcndencieo? Those wvho are in any delgr:e acquairted with the speculations of the-German physiolo. gists of the greatest name-in regard to the soul and even the immortality of plants-will not accuse me of going very far in alluding to the possible existence of some such pereletive power in plants. Von Martins g(et rid of objectors by speaking of them as " scie:; fic eren to whom the po"eer of cormprehendaing the tr'nscec.-entc' has ~son iF-w'rled i7 t lowC- Iet.-' a See Meyen's Jahresbericht, 1839, or Sillimazna's J(c,.'nal fc- Janfzarv, I8&1, p. 17,. 86 CAPILLARY ATTRACTION. to an amount which probably differ with every species of plant. The remainder of the sap and of the substances it holds in solution must be diffused through the cellular spongy terminations of the roots, and, with the new supply of liquid imbibed from the soil, returned again to the stern with the ascending current. But what causes the sap thus to ascend and descend?. By what power is it first sucked up through the roots, and afterwards forced down again from the leaves? Several answers have been given to this question. 1~. WVhen the end of a wide tube, either of metal or of glass, is plunged into water, the liquid will rise within the tube sensibly to the same level as that at which it stands in the vessel. But if a capillary* tube be employed instead of one with a wide bore, the liquid will rise, and will permanently remain at a considerably higher level within than without the tube. The cause of this rise has been ascribed to an attraction which the sides of the tube have. for the liquid, and which is sufficiently strong to raise it and to keep it up above the proper level of the water. The force itself is generally distinguished by the name of capillary attraction. Now, the wood of a tree, as we have seen, is composed of a mass of fine tubes, and through these the sap has been said to rise by capillary attraction. But if the top of a vine be cut off when it is juicy and full of sap, the liquid will exude from the newly formed surface, and if the air be excluded, will flow for a length of time, and may be collected in a considerable quantity [Lindley's'heory of Horticulture, p. 47, note]. Such a flow of the sap is not to be accounted for by mere capillary attraction-the sides of tubes cannot draw up a fluid beyond their own extremities. 2~. To supply the defect of this hypothesis, De Saussure supposed that the fluid at first introduced by capillary attraction into the extremities of the root, was afterwards propelled upwards by the alternate contraction and expansion of the tubes of which the wood of the root and stem is composed. This alternate contraction and expansion he also supposed to be caused by a peculiar irritating property of the sap itself, which caused each successive part of the tube into which it found admission to contract for the purpose of expelling it. Mr. Knight also ascribed the ascent of the sap to a similar contraction of certain other parts of the stem. Being once raised, he supposed it to return again or descend by its own weight-but in drooping branches it is obvious that the sap must be actually driven or drawn upwards from the leaves on its return to the root. These explanations, therefore, are still unsatisfactory. 33. If one end of an open glass tube be covered with a piece of moistened bladder or oitler fine animal membrane, tied tightly over it, and a strong solution of sugar in water be then poured into the open end of the tube, so as to cover the membrane to the depth of several inches, and if the closed end be then introduced to the depth of an inch below the surface of a vessel of pure water, the water will aftei a short time pass through the bladder inwards, and:the column of liquid in the tube will increase in height. This ascent will continue, till in favourable circumGlass tubes perforated by a very fine bore, like a human hair, are called capillary tubes. Buch are those of which thermometers are usually made. CAUSE OF THE ASCENT OF THE SAP. 87 stances the fluid will reach the height of several feet, and will flow out or run over at the open end of the tube. At the same time the water in the vessel will become sweet, indicating that while so much liquid has passed through the membrane inwards, a quantity has also passed outwards, carrying sugar along with it.*' To these opposite effects Dutrochet, who first drew attention to the fact, gave the names of Endosmose, denoting the inward progress, and Exosmose, the outward progress of the fluid. He supposed them to be due to the action of two opposite currents of electricity, and he likens the phenomena observed during the circulation of the sap in plants, to the appearances presented during the above experiment. Without discussing the degree of probability which exists as to the influence of electricity in producing the phenomena of endosmose and exosmose, it must be admitted that the appearances themselves bear a strong resemblance to those presented in the absorption and excretion of fluids by the roots of plants-and point very distinctly to at least a kindred cause. Thus, if the spongy termination of the foot represent the thin porous membrane in the above experiment-the sap with which the tubes of the wood are filled, the artificial solution introduced into the experimental tube-and the water in the soil, the water or aqueous solution into which the closed extremity of the tube is introduced,-we have a series of conditions precisely similar to those in the experiment. Fluids ought consequently to enter from the soil into the roots, and thence to ascend into the stem, as in nature they appear to do. This ascent, we have said, will continue till the fluid in the tubes of the wood (the sap) is reduced to a density as low as that of the liquid entering the roots from the soil. But in a growing tree, clothed with foliage, this will never happen. The leaves are continually ekhaling aqueous vapour, as one of their constant functions, and sometimes in very large quantity. The sap, therefore, when it reaches the leaves, is concentrated or thickened, and rendered more dense by the separation of the water, so that when it descends to the root, and again begins its upward course, it will admit of large dilution before its density can be so far diminished as to approach that of the comparatively pure water which is absorbed from the soil. And this illustration of the ascent of the sap appears the more correct from the obvious purpose it points out -(in addition to others long recognised)-as served by the evaporation which is constantly taking place from the surface of the leaf. Still the cause of the ascent of the sap is not the more clear that we can imitate it in some measure by an artificial experiment. But it will be conceded by the strictest reasoners on physical phenomena, that to have obtained the command, or even a partial control, over a natural Instead of sugar, common salt, gum, or other soluble substances may be dissolved in the water introduced at first into the tube, and the denser this solution the larger the quantity of water which will enter by the membrane, and the greater the height to which the column will rise. It ceases in all cases to rise only when the portions of liquid within and without the membrane attain nearly to the same density [i. e. contain nearly the same weight of solid matter in solution.] Instead of pure water the vessel into which the extremity of the tube is plunged may also contain a weak solution of some soluble substaqce-such as lime or soda -in which case while the sugar, or salt, or gum, will pass outwards, in smaller quantity, the lime or soda will pass inwards, along with the currents of water in which they are severally dissolved. 88 DECOMPOSITION TAKES PLACE IN THE STEM. power, is a considerable step towards a clear conception of the nature of that power itself. If the phenomena of endosmose can hereafter be clearly and indubitably traced to the agency of electricity we shall have advanced still another step, and shall be enabled to devise other means by which a more perfect imitation of nature may be effected, or a more complete control asserted over the phenomena of vegetable circulation. ~ 4. Functions of the stem. The functions of the stem are probably as various as those of the root, though the circumstances under which they are performed necessarily involve these functions in considerable obscurity. The pith which forms the central part of the stem consists, as I have already stated, of tubes disposed horizontally. When a coloured fluid is permitted to enter the lower part of the stem in the experiments above described, the pith remains untinctured in the centre of the coloured wood. It does not, therefore, serve for the conveyance of the sap. Nor does it seem to be vitally necessary to the health and growth of the plant, since Mr. Knight has shown that, from the interior of many-trees, it may be removed without apparent injury, and in nature, as trees advance in age, it gradually diminishes in bulk, and in some species becomes apparently obliterated. The vessels of the wood, which surrounds the pith, perform probably both a mechanical and a chemical function. They serve to convey upwards to the leaf the various substances which enter by the roots. This is their mechanical function. But during its progress upwards, the sap appears to undergo a series of changes. When it reaches the leaves it is no longer in the state in which it ascended from the root into the stem. The difficulty of extracting the sap from the wood, at different heights, has prevented very rigorous experiments from being made on its nature and, contents at the several stages of its ascent. These it is obvious must vary with the species and age of the plant, and with the season of the year at which the experiment is made. But the general result to be drawn from such observations as have hitherto been made, is, that those substances which enter directly into the root, when mingled with such as have already passed through the circulation of the plant, undergo, during their ascent, a gradual preparation for that state in which they become fit to minister to the growth of the plant. This preparation is completed in a great measure in the leaf, though further changes still go on as the sap descends through the bark. This deduction is strengthened by the fact that gaseous substances of various kinds and in varying quantities exist in the interior of the wood of the growing plant. These gaseous subtances, according to Boucherie, are in some cases equal in bulk to one-twentieth part of the entire trunk of the tree in which they exist. They probably move upwards along with the sap, and are more or less completely discharged into the atmosphere through the pores of the leaves. That these gaseous substances not only differ in quantity, but in kind also, with the age and species of the tree, and with the season of the year, may, I think, be considered as almost amounting to a proof that they have not been inhaled directly by the roots, but are the result of chemical decompositions which FUNCTIONS OF THE STEM AND LEAVES. 89 have taken place on the stem itself, as the sap mounted upwards towards the leaves. We have seen that the roots exercise a kind of discriminating power in admitting to the circulation of the plant the various substances which are present in the soil. The vessels of the stem exhibit an analogous power of admitting or rejecting the solutions of different substances into which they may be immersed. Thus Boucherie states that, when the trunks of several trees of the same species are cut off.above the roots, and the lower extremities immediately plunged into solutions of different substances, some of these solutions will quickly ascend into and penetrate the entire substance of the tree immersed in them, while others will not be admitted at all, or with extreme slowness only, by the vessels of the stems to which they are respectively presented. On the other hand, that which is rejected by one species will be readily admitted by another. Whether this partial stoppage of, or total refusal to admit, certain substances, be a mere contractile effort on the part of the vessels, or be the result of a chemical change by which their exclusion is effected or resisted, does not as yet clearly appear. That it does not depend upon the lightness and porosity of the wood, as might be supposed, is shown- by the observation that the poplar is less easily penetrated in this way than the beech, and the willow than the pear tree, the maple, or the plane. These various functions of the woody part of the stem are performed chiefly by the newer wood or alburnum, or, as it is often called, the sap wood of the tree. As the heart wood becomes older, the tubes of which it consists are either gradually stopped up by the deposition of solid substances which have entered by the roots, or by the formation of chemical compounds, which, like concretions in the bodies of animals, slowly increase in size till the vessels become entirely closed-or they are by degrees compressed laterally by the growth of wood around them, so as to become incapable of transmitting the ascending fluids. Perhaps the result is in most cases due in part to both these causes. This more or less perfect stoppage of the oldest vessels is one reason why the course of the sap is chiefly directed through the newer tubes.* The functions of the bark, which forms the exterior portion of the stem, will be more advantageously described, after we shall have considered the purposes served by the leaves. ~ 5. Functions of the leaves. The vessels of which the sap wood is composed extend upwards into the fibres of the leaf. Through these vessels the sap ascends, and from their extremities diffuses itself over the surface of the leaf. Here it undergoes important chemical changes, the extent, if not the exact nature, of which will appear from a short description of the functions which the leaves are known or are believed to discharge. 1~. When the roots of a living plant are immersed in water, it is a ~ As the newest roots are prolongations of the newest wood, it may be supposed that the fact of these roots being the chief absorbents from the soil, is a sufficient reason why that which is absorbed by themshould also pass up through the wood with which they are most closely connected. But that the pores of the heart wood are really incapable of transmitting fluids, is shown by plunging the newly cut stem of a tree into a coloured solution-the newer wood will be dyed, while more or less of the central portion will remain unchanged. 90 ESCAPE OF WATERY VAPOUR FROM THE LEAVES. matter of familiar observation that the water gradually diminisnes in bulk, and will at length entirely disappear, even when evaporation into the air is entirely prevented. The water which thus disappears is taken up by the roots of the plant, is carried up to the leaves, is there spread out over a large surface exposed to the sun and to the air, and in the form of vapour escapes in considerable proportion through the pores of the leaves and diffuses itself through the atmosphere. The quantity of water which thus escapes from the surface of the leaves varies with the moisture of the soil, with the species of plant, with the temperature and moisture of the air, and with the season of the year. According to the experiments of Hales, it is also dependent on the presence of the sun, and is scarcely perceptible during the night. He found that a sun-flower, 3J feet high; lost from its leaves during 12 hours of one day 30, and of another day 20 ounces of water, while during a warm night, without dew, it lost only three ounces, and in a dewy night underwent no diminution in weight.* This loss of watery vapour by the leaf is ascribed to two different kinds of action. First, to a natural perspiration from the pores of the leaf, similar to the insensible perspiration which is continually proceeding from the skins of healthy animals; and second, to a mechanical evaporation like that which gradually takes place from the surface of moist bodies when exposed to hot or dry air. The relative amount of loss due to each of these two modes of action respectively, must differ very much in different species of plants, being dependent in a great measure on the special structure of the leaf. In all cases, however, the natural perspiration is believed very greatly to exceed the mere mechanical evaporation-though the results of Hales, and of other experimenters, show that both processes proceed with the greatest rapidity under the influence of a warm dry atmosphere, aided by the direct rays of the sun. Among the several purposes served by this escape of watery vapour from the surface of the leaf, it is of importance for us to notice the direct When the escape of vapour from the leaves is more rapid than the supply of water from the roots, the leaves droop, dry, and wither. Such is sometimes the case with growing crops in very hot weather, and it always happens when a twig or flower is plucked and separated from the stem or root. When thus separated the leaves still continue to give off watery vapour into the air, and consequently the sap ascends from the twig or stalk to supply the place of the water thus exhaled. But as the sap ascends it must leave the vessels empty of fluid, and air must rush in to fill the empty space. This will continue till nearly all the fluid has risen from the stem into the leaf, and the vessels of the wood are full of air. But if the stem of the twig or flower be placed in water this liquid will rise into it, air will' be excluded, and the freshness and bloom of the leaves and flowers will be longer preserved. If the water into which they are introduced contain'any substances in solution, these will rise along with the water, and will gradually make their way through all the vessels of the wood, till they can be detecled in the leaves. By this means even large trees may in a short time be saturated with saline solutions, capable of preserving them from decay. It is only necessary to cut down or saw through the tree and insert its lower extremity into the prepared solution, when the action of the sun and air upon the leaves will cause it spontaneously to ascend. Thus corrosive sublimate (the subject of Kyan's Patent) may be injected with ease, or pyroligni'e of iron, (iron dissolved in wood vinegar,) which Boucherie recommends as equally efficient and much more economical, [Ann. de Chim. et de Phys. lxxiv. p. 113.] The process is finished when the liquid is found to have risen to the leaf. Coloured solutions may in the same way be injected and the wood tinged to any required shade. One of the chief benefits attendant upon the cutting of wood in the winter, appears to be that the absence of leaves prevents the exhaustion of the sap and the ascent of air into the vessels of the wood-the oxygen of this air tending to induce decay. But the sap may be retained, and the air excluded almost as effectually, at any other season of the year, by stripping the tree of its leaves and branches a few days before it is cut down. OTHER VOLATILE SUBSTANCES EXHALED. 91 chemical influence it exercises over the growth of the plant. As the water disappears from the leaf, the roots must absorb from the soil at least an equal supply. This water brings with it the soluble substances, organic and inorganic, which the soil contains, and thus in proportion to the activity with which the leaves lose their watery vapour, will be the quantity of those substances which enter from the soil into the general circulation of the plant. This enables us to understand how substances, very sparingly soluble in water, should yet be found in the interior of plants, and in very considerable quantity, at almost every stage of their growth. 2~. Besides watery vapour, however, the leaves of nearly all plants exhale at the same time other volatile compounds in greater or less abundance. In the petals of flowers, we are familiar with such exhalations-often of an agreeable and odoriferous character. In the case of plants and trees also which emit a sensible odour, we readily recognise the fact of volatile substances being given off by the leaves. But even when the sense of smell gives us no indication of their emission from a single leaf or a single plant, the introduction of a number of such inodorous plants into the confined atmosphere of a small room after a time satisfies us that even they part with some volatile matter from their leaves, which makes itself perceptible to our imperfect organs only when in a concentrated state. The probability therefore is, that the leaves of all plants emit, along with the watery vapour which they evolve, certain other volatile substances also, though often in quantities so minute as to escape detection by our unaided senses. By the emission of these substances the plant probably relieves itself of what would prove injurious if retained, though of the chemical nature and composition of these exhalations little or nothing has yet been ascertained. 3~. If the branch of a living plant be so bent that some of its leaves can be introduced beneath the edge of an inverted tumbler full of water, and if the leaves be then exposed to the rays of the sun, bubbles of gas will be seen to form on the leaf, and gradually to rise through the water and collect in the bottom of the tumbler. If this gas be examined it will be found to be pure oxygen. If the water contain carbonic acid gas, or if during the experiment a little carbonic acid be introduced, this gas will be found gradually to disappear, while the oxygen willcontinue to accumulate. Or if the experiment be made by introducing a living plant into a large nell-glass full of commron atmospheric air, allowing it to grow there for 12 hours in the sunshine, and then examining or analysing the air contained in the glass, the result will be of a precisely similar kind. The per centage of oxygen in the air will have increased.* And if the experiment be varied by the introduction of a small quantity of carbonic acid gas into the jar, this gas will be found as before to diminish in quantity, while the oxygen increases. The conclusion drawn from these experiments, therefore, is, that the leaves of plants, when exposed to the rays of the sun, absorb carbonic acid from the air and give off pure oxygen gas. It has been already stated that the prcportion of carbonic acid present It will be remembered that atmospheric air contains about 21 per cent. of oxygen gs. 92 OXYGEN IS EMITTED DURING THE DAY, in the atmosphere is exceedingly small, [about 1-2500th of this bulksee Lecture II., p. 30;1 but if for the purpose of experiment we increase this proportion in a gallon of air to five or ten per cent., introduce a living plant into it, and expose it to the sunshine, the carbonic acid will gradually disappear as before, while the oxygen will increase. And if we analyse the air and estimate the exact bulk of each of these gases present in it at the close of our experiment, we shallfind that the oxygen has increased generally by as much as the carbonic acid has diminished. That is to say, if five cubic inches of the latter have disappeared, five cubic inches will have been added to the bulk of the oxygen. The above general conclusion, therefore, is rendered more precise by this experiment, which appears to show that under the influence of the sun's rays the leaves of plants absorb carbonic acidfrom the air, and at the same time give off AN EQUAL BULK of oxygen gas. And as carbonic acid (CO2) contains its own bulk of oxygen gas* combined with a certain known weight of carbon, it is further inferred that the oxygen agiven off by the leaves is the same which has been previously absorbed in the fiorr of carbonic acid, and therefore it is usually stated as a function of the leaves-that in the sunshine they absorb carbonic acid fromr the air, DEcoMPosE it in the interior of the leaf, retainits carbon, and again reject or emit the oxygen it contained. This conclusion presents a very simple view of the relations of oxygen and carbonic acid respectively to the living leaf in the presence of the sun, and it appears to be fairly deduced from the facts above stated. It has occasionally been observed, however, that the bulk of oxygen given of' by the leaf has not been precisely equal to that of the carbonic acid absorbed, [see Persoz, Chimrie Moleculaire, p. 54,] and hence it is also fairly concluded that a portion of the oxygen of the carbonic acid which enters the leaf is retained, and made available in the production of the various substances which are formed in the vascular system of different plants. On the other hand it is stated by Sprengel, that if compounds containing much oxygen be presented to the roots ofplants, and thus introduced into the circulation, they are also decomposed, and the oxygen they contain in part or in whole given off by the leaves, so that, under certain circumstances, the bulk of the oxygen which escapes is actually greater than that of the carbonic acid which is absorbed by the leaves. Such is the case, flr example, when the-roots are moistened with water containing carbonic, sulphuric, or nitric acids.-[Sprengel Cfienie, 1., p. 344.] It is of importance to note these deviations from apparent simplicity in the relative bulks of the two gases which are respectively given off and absorbed by all living vegetables. There are numerous cases of the formation of sutbstances in the interior of plants which theory would fail to account for with any degree of ease, were these apparent anomalies to be neglected. This will more distinctly appear when in a subsequent lecture we shall inquire how or by what chemical changes the substances which plants contain, or of which they consist, are produced from the food which they draw from the air and from the soil. * This the reader will recollect is proved by burning charcoal in a bottle of oxygen gas till combustion ceases, when nearly the whole of the oxygen is converted into carbonic acid, but without change of bulk.-See Lecture III., p. 45. AND CARBONIC ACID DURING THE NIGHT. 33 The most general and probable expression, therefore, for the function of the leaf, now under consideration, appears to be that in the sunshine the leaves absorb from the air carbonic acid, and at the same time evolve oxygen gas, the bulk of the latter gas given off being nearly equal to, that of the former which is taken in-the relative bulks of the two gases varying more or less with the species of plant, as well as with the circumstances under which it is caused or is fitted to grow.* 4~. Such is the relation of the leaf to the oxygen and carbonic acid of the atmosphere in the presence of the sun. During the night their action is reversed, they emit carbonic acid and absorb oxygen. This is proved by experiments similar to those above described. For if the plant which has remained under the bell-glass for 12 hours in the sunshine-during which time the oxygen has sensibly increased, and the carbonic acid diminished in bulk-be allowed to remain in the same air through the following night, the oxygen will be found to have decreased, while the carbonic acid will be present in larger quantity than in the evening of the previous day. The carbonic acid thus given off during the night is supposed to be partly derived from the soil through the roots, and partly from the substance of the plant itself. The oxygen absorbed either combines with the carbon of the plant to form a portion of the carbonic acid which is at the same time given off or is employed iwn producing some of the other oxidixed [containing oxygen in considerable quantity] compounds that exist in the sap. As a general rule, the quantity of carbonic acid given off during the night is far from being equal to that which is absorbed during the day. Still it is obvious that a plant loses carbon precisely in proportion to the amount of this gas given off. Hence, when the days are longest, the plant will lose the least, and where the sun is brightest it will gain the fastest; since other things being equal, the decomposition of carbonic acid proceeds most rapidly where the sky is the clearest, and the rays of the sun most powerful. Helace we see why in Northern regions, where spring, summer, and autumn are all comprised in one long day -vegetation should proceed with such rapidity. The decomposition of the carbonic acid goes on without intermission, the leaves have no night of rest, but nature has kindly provided that, where the season of warmth is so fleeting, there should be no cessation to the necessary growth of food for man and beast. This comparison of the functions performed by the leaf, during the day and night respectively, explains the chemical nature of the blanching of vegetables practised by the gardener, as well as the cause of the pale colour of plants that grow naturally in the absence of light. Wh/en exposed to the sun, the leaves of these sickly vegetables evolve oxygen, and gradually become green and healthy. Woody matter is formed, and the stems become strong and fibrous. The light of the sun, in the existing economy of nature, is indeed equally necessary to the health of plants and of animals. The former As the oxygen given off by the leaves is always the result of a chemical decomposition, by which the carbonic acid or other compound is deprived of a portion, at least, of its oxygen or de-oxidized, this function of the leaves in the presence of the.sun is often spoken of as their de-oxidizing power. 5 94 -LEAVES SOMETIMES EMIT CHLORINE. become pale and sickly, and refuse to perform their mhost important chemical functions when excluded from the light. The bloom disappears from the human cheek, the body wastes away, and the spirit sinks, when the unhappy prisoner is debarred from the sight of the blessed sun. In his system, too, the presence of light is necessary to the performance of those chemical functions on which the healthy condition of the vital fluids depends. The processes by which oxygen and carbonic acid are respectively evolved in plants have been likened by physiologists to the respiration and digestion of animals. It is supposed that when plants respire they give off carbonic acid as animals do, and that when they digest they evolve oxygen. Respiration also, it is said, proceeds at all times, digestion only in the light of the sun. Though these views are confessedly conjectural, they are founded upon striking analogies, and may reasonably be entertained as matters of opinion. 6~. Other species of decomposition also, besides that of de-oxidization, go on in the leaf, or are there made manifest. Thus when plants grow in a soil containing much common salt (chloride of sodium) or other chlorides, they have been observed by Sprengel and Meyen to evolve chloride* gas from their leaves. This takes place, however, more during the night than during the day. Some plants also give off ammonia, (Lecture IV., p. 70,) while others (crucifere), according to Dr. Daubeny, [in his Three Lectures on Agriculture, p. 59,] emit from their leaves pure nitrogen gas. The evolution of chlorine implies the previous decomposition of the chlorides, which have been absorbed from the soil; while that of nitrogen may be due to the decomposition of ammonia, of nitric acid, or of some other compound containing nitrogen, which has entered into the circulation by the roots. The exact mode and nature of the decomposition of these substances, and the purposes served by them in the vegetable economy, will come under our consideration in a subsequent lecture. The leaf has been described (p. 76) as an expansion of the bark. It consists internally of tw), layers of veins or vascular fibres laid one over the other, the upper connected with the wood-the lower with the inner bark. It is covered on both sides by a thin membrane (epidernlis), the expansion of the outer bark. This thin memrbane is studded with numerous small pores or mouths (stomata), which vary in size and in number with the nature of the plant, and with the circumstances in which it is intended to grow. It is from the pores in the upper part of the leaf that substances are supposed to be exhaled, while every thing that is inhaled enters by those which. are observed in the under side of the leaf.f This opinion, however, is not universally received, it being admitted by some that the power both of absorbing and of emitting may be possessed by the under surface of the leaf. 70. We have seen that the chief supply. of the fluids which constitute * Chlorine is a gas of a greenish yellow colour, having an unpleasant taste and a suffocating odour. When it combines with other substances it forms chlorides. It exists in, and im. parts its smell to, chloride of lime, which is employed for disinfecting purposes, and it forms upwards of half the weight of common salt. t This is illustrated by the action of a cabbage leaf on a wound. If the upper side be applied, the. sore is protected and quickly heals, while the under side draws it and produces e constant discharge. FUNCTIONS OF THE FLOWER-LEAVES. 95 the sap of plants, is derived from the soil. The under side of the leaves of plants is also supposed by some to be capable of absorbing moisture from the air, either in the form of watery vapour, or when it falls upon the leaves in the state of dew. Like the roots also they may absorb with the dew any substances the latter happens to hold in solution. And thus plants may, in some degree, be nourished by the volatile organic substances which ascend from the earth during the heat of the day, and which are again in a great measure precipitated with the evening dew. Whether the leaves ever absorb nitrogen gas from the air has not as yet been determined with sufficient accuracy. If they do, it must in general be in very small quantity only, since it has hitherto escaped detection. In like manner it is doubtful how far they regularly absorb any other substances which the air is supposed to contain. Thus it is known that nitric acid exists in the air in very minute quantity. Some chemists also believe that ammonia is extensively diffused through the atmosphere in an exceedingly diluted state. Do the leaves of plants absorb these substances? Is the absorption of them one of the constant and necessary functions of the leaves' The reply to these questions must be very uncertain, and any principle which professes to be based upon such a reply must be regarded only as a matter of opinion. 8~. The petals of flower-leaves perform a somewhat different function from those of the ordinary leaves of a plant. They absorb oxygen at all times-though more by day than by night-and they constantly emit carbonic acid. The bulk of the latter gas evolved, however, is less than that of the oxygen taken in. The absorption of oxygen gas, and the constant production of carbonic acid, is, in some flowers, so great as to cause a perceptible increase of temperature-and to this slow combustion, so to speak, the proper heat observed in the flowers of many plants has been attributed. According to some authors, the flower-leaves also emit pure nitrogen gas.-[Sprengel, Chemie, II., p. 347.] This fact has not yet been determined by a sufficient number of accurate experiments; it is in accordance, however, with the results of Boussingault, that, when a plant flowers and approaches to maturity, the nitrogen it contains becomes less. If confirmed, this evolution of nitrogen would throw an interesting light on the most advantageous employment of green crops, both for the purposes of manure and for the feeding of cattle. 9~. When the leaves of a plant begin to decay, either naturally as in autumn, or from artificial or accidental causes, they no longer absorb and decompose carbonic acid, even under the influence of the sun's rays. On the contrary, they absorb oxygen, like the petals cf the flower, new compounds are formed within their substance-their green colour disappears-they become yellow-they wither, die, and drop from the treetheir final function, as the organs of a living being, is discharged. They then undergo new changes, are subjected to a new series of influences, and are made to serve new purposes in the economy of nature. These we shall hereafter find to be no less interesting and important in reference to a further end, than are the functions of the living leaf to the growth and nourishment of the plant.-[See subsequent lecture, " On the law of the decay of organic substances."l 96 CHEMICAL FUNCTIO'' S OF THE BARK. ~ 6. Functions of the bark. The inner bark being connected with the under layer of vessels in.the leaf, receives from them the sap after it has been changed by the action of the air and light, and transmits it downwards to the root. The outer bark, especially in young twigs and in the stalks of the grasses, so closely resembles the leaves in its appearance, that we can have no difficulty in admitting that it must, not unfrequently, perform similar functions. In the Cactus, the Stapelia, and other plants which produce no true leaves, this outer bark'seems to perform all the functions which in other vegetable tribes are specially assigned to the abundant foliage. During its descent through the inner bark, therefore, the sap must in very many cases undergo chemical changes, more or less analogous to those which usually take place in the leaf. It is by means of the inner bark that the stems of trees, such as our forest and fruit trees, are enlarged by the deposition of annual layers of new wood. The woody fibre is formed or prepared in the leaf, and as the sap descends it is deposited beneath the inner surface of the inner bark. It thus happens that, as the sap descends, it is gradually deprived of the substances it held in solution when it left the leaf, and in consequence it becomes difficult to say how much of the change, which the sap is found to have undergone when it reaches the root, is due to chemical transformations produced during its descent, and how much to the deposition of the woody fibre and other matters it has parted with by the way. Among other evidences of such changes really taking place during the descent of the sap, I may mention an observation of Meyen [Jahresbericht,. 1839, p. 27], made in the course of his experiments on the reproduction of the bark of trees. In these experiments he enclosed the naked wood in strong glass tubes, and in three cases out of eight the tubes were burst and shattered in pieces. This could only have arisen from the disengagement of gaseous substances, the result of decomposition. While, therefore, such gases as enter by the roots or are evolved in the vessels of the wood during the ascent of the sap, escape by the leaf along with those which are disengaged in the leaf itself, it is probable that those which are produced as the result of changes in the bark, descend with the downward sap, and are discharged by the root.* In the bark of the root it is probable that still further changes take place-and of a kind which can only be effected during the absence of light. This is rendered probable by the fact that the bark of the root frequently contains substances which are not to be met with in any other part of the plant. Thus from the bark of the fresh root of the apple tree a substance named phloridzine, possessed of considerable medical virtues, may be readily extracted, though it does not exist' in the bark either of the stem or of the branches. In fine, as the food which is introduced into the stomachs of animals, undergoes continual and successive chemical changes during its progress through the entire alimentary canal-so, numerous phenomena indicate that the sap of plants is also subjected to unceasing transforma* Sprengel says that the stems and twigs, and the stalks of the grasses, all absorb oxygen and give off carbonic acid.-Chemie, II., p. 341. FUNCTIONS OF THE ROOT MODIFIED BY THE SOIL. 97 tions,-in the root and in the stem as well as in the leaves, —at one time in the dark, at another under the influence of the sun's rays,-exposed when in the leaf to the full action of the air,-and when in the root almost wholly secluded from its presence;-the new compounds produced in every instance being suited either to the nature of the plant or the wants and functions of that part of it in which each transformation takes place. To some of these transformations it will be necessary to advert more particularly, when we come to consider the special changes by which those substances of which plants chiefly consist, are formed out of these compounds on which they chiefly live. ~ 7. Circumstances by which the functions of the various parts of plants are modified. Plants grow more or less luxuriantly, and their several parts are more or less largely developed, in obedience to numerous and varied circumstances. I. In regard to the special functions of the root, we have already seen that the access of atmospheric air is in some cases indispensable, while in others, by shooting vertically downwards, the roots appear to shun the approach of either air or light. It is obvious also that a certain degree of moisture in the. soil, and a certain temperature, are necessary to the most healthy discharge of the functions of the root. In hot weather the plant.droops, because the roots do not absorb water from the soil with sufficient rapidity. And though it is probable that, at every temperature above that of absolute freezing, the food contained in the soil is absorbed and transmitted more or less slowly to the stem, yet it is well known that a genial warmth in the soil stimulates the roots to increased activity. The practice of gardeners in applying bottom heat in the artificial climate of the green-house and conservatory is founded on this well-known principle. But the nature of the soil in which plants grow has also much influence on the way in which the functions of the root are discharged. As a general fact this also is well known, though the special qualities of the soil on which the greater or less activity of vegetation depends, are far from being generally understood. If the soil contain a sensible quantity of any substance which is noxious to plants, it is plain that their roots will be to a certain degree enfeebled, and their functions in consequence oaly imperfectly discharged. Or if the soil be deficient either in organic food, or in one or other of those inorganic substances which the plants necessarily require for the production of their several parts, the roots cannot perform their office with any degree of efficiency. Where the necessary materials are wanting the builder must cease to work. So in a soil which contains no silica, the grain of wheat may germinate, but he stalk cannot be produced in a natural or healthy state, since silica is indispensable to its healthy construction. II. The ascent of the sap is modified chiefly by the season of the year, by the heat of the day, and by the genus and age of the plant or tree. There seems reason to believe that the plant never sleeps, that even during the winter the circulation slowly proceeds, though the first 98 ALSO THE RAPIDITY OF THE CIRCULATION. genial sunshine of the early spring stimulates it to increased activity. The general increased temperature of the air does not produce this acceleration in so remarkable a manner as the direct rays of the sun. The sap will flow and circulate on the side of a tree on which the sunshine falls, while it remains sensibly stagnant on theother. This is shown by the cutting down similar trees at more and more advanced periods of the spring, and immersing their lower extremities in coloured solutions. The wood and bark on one side of the tree will be coloured, while, on the other, both will remain unstained. If a similar difference in the comparative rapidity of the circulation on opposite sides of a trunk or branch be supposed to prevail more or less throughout the year, we can readily account for the annual layers of wood being often thicker on the one half of the circumference of the stem than on the other. The sap is generally supposed to flow most rapidly during the spring, but if trees be cut down at different seasons, and immersed as above described, the coloured solution, according to Boucherie, reaches the leaves most rapidly in the autumn.* The heat of the day, other circumstances being the same, materially affects, for the time, the rapidity of the circulation. The more rapidly watery and other vapours are exhaled from the leaves, the more quickly must the sap flow upwards to supply the waste. If on two successive days the loss by the leaves be, as in the experiment of Hales, above described, (p. 90,) as 2 to 3, the ascent of the sap must be accelerated or retarded in a similar proportion. Hence, every sensible variation in the temperature and moisture of the air, must also, to a certain extent, modify the flow of the sap; must cause a greater or less transport of that food which the earth supplies, to be carried to every part of the plant, and must thus sensibly affect the luxuriance and growth of the whole. But the persistance of the leaves is a generic character, which has considerable influence upon the circulation in the evergreens. In the pine and the holly, from which the leaves do not fall in the autumn, the sap ascends and descends during all the colder months,-at a slower rate, it is true, than in the hot days of summer, yet much more sensibly than in the oak and ash, which spread their naked arms through the wintery air. This is illustrated by the experiments of Boucherie, who has observed that in December and January the entire wood of resinous trees may be readily and thoroughly penetrated by the spontaneous ascent of saline and other solutions, into which their stems may be immersed. III. From what has just been stated, it will appear that the mechanical functions of the stem are subject to precisely the same influences as the ascent of the sap. As the tree advances in age, the vessels of the interior will become more or less obliterated, and the general course of the sap will be gradually transferred to annual layers, more and more Boucherie makes a distinction, not hitherto insisted upon by physiologists, between the circulation on the surface of the tree by which the buds and young twigs are supported, and the interior circulation, which is not perfect until a latter period of the year. Hence in the spring, though the sap is flowing rapidly through the bark and the newest wood, coloured solutions will not penetrate the interior of the tree with any degree of rapidity. In autumn, on the other hand-when the fear of approaching winter has already descended upon the bark-the time of most active circulation has only arrived for the interior layers of the older wood. It is this season consequently that he finds most favourable for impregnating the trunks of trees with those solutions which are likely to preserve them from decay.-A-lnn. de Chim. et de Phys., lxxiv., p. 135. CHEMICAL RAYS IN THE SUN-BEAM. 99 removed from the centre.- It is this transference of the vital circulation to newer and more perfect vessels that enables the tree to grow and blossom and bear fruit through so long a life. In animals the vessels are gradually worn out by incessant action. None of them, through old age, are permitted to retire from the service of the body-and the whole system must stop when one of them is incapacitated for the further performance of its appointed duties. In regard to the chemical functions of the stern, it is obvious that they are not assigned to the mere woody matter of the vessels and cells. They take place in these vessels, but the nature and extent of the chemical changes themselves must be dependent upon the quantity and kinds of matter which ascend or descend in the sap. The entire chemical functions of the plant, therefore, must be dependent upon and must be modified by the nature of the substances w'ich the soil and the air respectively present to the roots and to the leaves. IV. In describing the functions of the leaf, 1 have already had occasion to advert to the greater number of the circumstances by which the discharge of those functions is most materially affected. We have seen that the purposes served by the leaf are entirely different according as the sun is above or below the horizon; that the temperature and moisture of the air may indeed materially influence the rapidity with which its functions are discharged —but.that the light of the sun actually determines their nature. Thus the leaf becomes green and oxygen is given off in the presence of the sun, while in his absence carbonic acid is disengaged, and the whole plant is blanched. How necessary light is to the health of plants may be inferred from the eagerness with which they appear to long for it. How intensely does the sun-flower watch the daily course of the sun,-how do the countless blossoms nightly droop when he retires,-and the blanched plant strive to reach an open chink through which his'light may reach it! That the warmth of the sun has comparatively little to do with this specific action of his rays on the chemical functions of the leaf, is illustrated by some interesting experiments of Mr. Hunt, on the effct of rays of light of different colours on the growing plant. He sowed cress seed, and exposed different portions of the soil in which the seeds were germinating, to the action of the red, yellow, green, and blue rays, which were transmitted by equal thicknesses of solutions of these several colours. " After ten days, there was under the blue fluid, a crop of cress of as bright a green as any which grew in full light and far more abundant. The crop was scanty under the green fluid, and of a pale yellow, unhealthy colour. Under the yellow solution, only two or three plants appeared, but less pale than those under the green,-while beneath the red, a few more plants came up than under the yellow, though they also were of an unhealthy colour. The red anda blue bottles being now mutually transferred, the crop formerly beneath the blue in a few * A potato has been observed to grow up in quest of light from the bottom of a well twelve feet deep-and in a dark cellar a shoot of 20 feet in length has been met with, the extremity of which had reached and rested at an open window. In the leaves of blanched vegetables peculiar chemical compounds are formed. Thus in the stalk of the potato a poisonous substance called solanin is producad, which disappears again when the stalk is exposed to the light and becomes green. 100 FUNCTIONS OF TIlE C(tEEN TWIGS. days appeared blighted, while on the patch previously exposed to tlle red, some additional plants sprung up."' Besides the rays of heat and of light, the sun-beam contains what have been called chemical rays, not distinguishable by our senses, but capable of being recognized by the chemical effects they produce. These rays appear to differ in kind, as the rays of different coloured light do. It is to the action of these chemical rays on the leaf,'and especially to those which are associated with the blue light in the solar beam, that the chemical influence of the sun on the functions of the leaf is principally to be ascribed. It cannot be doubted that the warmth and moisture of a tropical climate act as powerful stimulants-assistants it may be-to the leaf, in the absorption of carbonic acid from the air, and in that rapid appropriation (assimilation) of its carbon by which the growth of the plant is hastened and promoted. But the bright sun, and especially the chemical influence of his beams, must be regarded as the main agent in the wonderful development of a tropical vegetation. Under this influence the growth by the leaves at the expense of the air must be materially increased, and the plant be rendered less dependent upon the root and the soil for the food on which it lives.t V.- The rapidity with which a plant grow s has an important influence upon the share which the bark is permitted to take in the general nourishment of the whole. The green shoot performs in some degree the functions of the leaf. In vascular plants, therefore, which in a congenial climate may almost be seen to grow, the entire rind of a tall tree may more or less effectually absorb carbonic acid from the atmosphere, during the presence of the sun. The broad leaves of the palm tree, when fully developed, render the plant in a great degree independent of the soil for organic food-and the large amount of absorbing surface in the long green tender stalks of the grasses, and of their tropical analogues, must materially contribute to the same end. Hence the proportion of organic matter derived from the air, in any crop we reap, must always be the greater the more rapid its general vegetation has been. It is a fact familiarly known to all of you, that, besides those circumstances by which we can perceive the special functions of any one organ to be modified, there are many by which the entire economy of the plant is materially and simultaneously affected. Oi this fact the practice of agriculture is founded, and the various processes adopted by the practical farmer are only so many modes by which he hopes to influLondon and Edinburgh Journal of Science, February, 1840. Might not our cheap blue glass be used with advantage in glazing hot-houses, conservatories, &c.? t The effect of continued sunshine may be often seen in our corn-fields in May, when, under the influence of propitious weather, the young plants are shooting rapidly up. When such a field is bounded by a lofty hedge running nearly north and south, the ri.ltes nearest the hedge on either side will be in the shade for nearly one-half of the day, and will invariably appear of a paler green and less healthy colour. If the hedge be studded with occasion. 1 large trees, the spots on which the shadows of those trees rest will be indicated by distinct pale green. patches stretching further into the field than the first, and sometimes even tlihn the second ridges. EFFECT OF MARLING.-REWARDS OF NATURE. 101 ence and promote the growth. of the whole plant, and the discharge of the finctions of all its parts. Though manures in the soil act immediately through the roots, they stimulate the growth of the entire plant; and though the application of a top-dressing may be supposed first to affect the leaf, yet the beneficial result of the experiment depends upon the influence which the dressing may exercise on every part of the vegetable tissue. In connection with this part of the subject, therefore, I shall only further advert to a very remarkable fact mentioned by Sprengel, which seems, if correct, to be susceptible of important practical applications. He states that it has very frequently been observed in Holstein, that if, on an extent of level ground sown with corn, some fields be marled, and others left unmarled, the corn on the latter portions will grow less luxuriantly and will yield a poorer crop than if the whole had been unmarled. Hence he adds, if the occupier of the unmarled field would not have a succession of poor crops, he must marl his land also.* Can it really be that nature thus rewards the diligent and the improver? Do the plants which grow on a soil in higher condition take from the air more than their due share of the carbonic acid or other vegetable food it may contain, and leave to the tenants of the poorer soil a less proportion than they might otherwise draw from it? How many interesting reflections does such a fact as this suggest! What new views does it disclose of the fostering care of the great Contriver-of his kind encouragement of every species of virtuous labour! Can it fail to read to us a new and special lesson on the benefits to be derived from the application of skill and knowledge to the cultivation of the soil?' Wenn nhmlich auf einer Feldflur Stiick urn Stiick gemergelt worden ist, so wachsen die Friichte auf den nicht gemergelten Feldern, auch wenn hier alle friiheren verhaltnisse ganz dic-selben bleiben, nicht mehr sogut, als ehedem; wodurch die Besitzer jener Felder, wenn sie nicht fortwahrend geringe Erndten haben wollen, genithigt sind, gleichfalls zu mergeln. Aus dieser hochst vichirien Erscheinung, die man sehr hdiufig in Holsteinschen bemerkt, &c.-Sprengel, Chemiefir Landwtirthschaft, I., p. 303. 5* LECTURE VI.'.bstances of which plants chiefly consist-Woody fibre, Starch, Gum, Sugars-Their mu. tual relations and transformations-Gluten,Vegetable Albumen, Diastase-Acetic, Tartaric, Malic, Citric, and Oxalic Acids-General observations. FROM what has been stated regarding the structure of plants, it will be Understood in what way the food is introduced into their circulation. The text inquiry appears to be how-by what chemical changes-is the food, when introduced, converted into those substances of which plants chiefly consist. But in order that we may clearly understand this point, it is necessary that we know first the nature and chemical constitution of the substances which are most largely formed from the food in the interior of the plant. To this point, therefore, I must previously direct your attention. If you were to collect all the varieties of plants which are within your reach-whether such as are cultivated and used for food-or such as grow more or less abundantly in a wild state-and were to extract their several juices, and to separate from each of these juices the chemical compounds it contains-you would gradually gather together so many different substances, all possessed of different properties, that you would scarcely be able to number them. But if at the same time you compared the weight of each substance thus collected with that of the entire plant from which it is derived, you would find also that the quantity of many of them is comparatively so minute that only a very small portion of the vital energies of the plant can be expended in producing them,-that they may be entirely neglected in a general consideration of the great products of vegetation. Thus though quinine and morphine, the active ingredients in Peruvian bark and in opium, are most interesting substances, from their effect upon the human constitution, and their use in medicine, yet they form so small a fraction of the mass of the entire trees or plants from which they are extracted, that it would be idle to attempt to convey to you any notion of the way in which plants grow and are fed, by showing you how such substances as these are produced from the food on which plants live. While, however, the examination would satisfy you that almost every species of plant produced in small quantity one or more substances peculiar to itself, you would observe, at the same time, that every plant yielded a certain quantity of two or three substances common to and produced by all, and in most cases constituting the greater portion of their bulk. Thus all trees and herbs produce wood or woody fibre, and of this substance you know that their chief bulk consists. Again, all the grains and roots you cultivate contain starch in large quantity, and the production of this starch is one of the great objects of the art of culture. The juices of trees, and of grasses, and of cultivated roots, contain sugar and gum, and sometimes in such quantity as to make their extraction a source of profit both to the grower and to the CONSTITUTION OF WOODY FIBRE. 103 manufacturer. The flour of grain contains sugar also, and along with it two other substances, in small quantity, gluten. and vegetable albumen, which are of much importance in reference to the nutritive qualities of the different varieties of flour. Sugar is also present in the juices of fruits, but it is there associated with various acid (sour) substances which disappear to a certain extent or change into sugar as the fruit ripens. Of these few substances the great bulk of vegetables of all kinds consists. They constitute nearly the whole mass of those various crops which the.art of culture studies to raise for the use of man and beast. To the study of these substances, therefore, I shall at present confine your attention, and if I shall afterwards be able to make you understand how these few compound bodies are produced in the interior of a plant from. the food it takes up, I shall succeed in conveying to you as much information in regard to this most interesting branch of our subject as will be necessary to a general explanation not only of the natural growth and increase of plants, but of the nature and efficacy of those artificial means which the practical farmer employs, in order to hasten their growth or enlarge their increase. ~ 1. Woody fibre or lignin-its constitution and properties. 10. When a portion of the stem of a herbaceous plant, or of the new ly cut wood of the trunk or branch of a tree, is reduced to small pieces, and boiled in successive portions of water and alcohol, as long.as any thing is taken up, a white fibrous mass remains, to which the name of woody fibre or lignin has been given. This substance has no taste or smell, and is perfectly insoluble in water. It is nearly identical in its chemical constitution and properties, whether it be obtained from the porous willow, or from the solid box tree, and the fibres of linen and of cotton consist essentially of the same substances. According to the analysis of Dr. Prout, this woody fibre when dried at 350~ F., consists of From Box Wood. From the Willow. Carbon..... 50-0 49-8 Hydrogen.... 555 5'58 Oxygen.... 4445 44-62 100 100 It will be recollected that water consists of oxygen and hydrogen, combined in the proportion, by weight, of 8 of the former to 1 of the latter. (See Lecture II., p. 36.) Now if the hydrogen above given be multiplied by 8, the product will be found to be almost exactly the weight of the oxygen given-since 5-55 X 8 - 44-40, and 5-58 X 8 = 44-64. In woody fibre, therefore, the hydrogen and oxygen exist in the same proportion as in water, and its composition, therefore, might be represented by Carbon..... 50'0 Water..... 50-0 100 104 COMPOSITION OF WOOD. did we not know that woody fibre, when heated or distilled, cannot be resolved into carbon (charcoal) and water alone, and, therefore, cannot be supposed to consist of these alone. It is a remarkable character of this substance, however, that these two elements, hydrogen and oxygen, exist in it in the proportions to form water, and we shall find the knowledge of this fact of great importance to us, when we come to inquire how this constituent of vegetables is formed-from the food on which they live. 2~. If a portion of the wood of a tree be dried and analyzed without being previously digested in water, alcohol, and ether, as long as any thing is taken up, the proportion of the constituents is found to vary slightly with the species of tree, but in all cases the hydrogen is in larger quantity than is necessary to form water with the oxygen they contain. Thus, according to Payen, the dry wood of the following trees consists of Ebony. Walnut. Oak. Beech. Carbon... 52-85 51-92 50'00 49-25 Hydrogen.. 600 596 6-20 6-10 Oxygen.. 41-15 42-12 43 80 44-65 100 100 100 100 The carbon in these several kinds of wood differs as much as three per cent., but in each of them the product of the hydrogen, when multi plied by 8, is considerably greater than the per centage of oxygen. 3~. When the solid substance of wood is examined under the microscope it is observed to consist of two portions or kinds of matter, that of which the original sides of the cells and tubes is composed, called the cellular matter-the true woody fibre-and of a solid substance by which the cells are internally coated and strengthened, called the incrusting matter. It is in this latter substance that the excess of hydrogen, exhibited by the preceding analysis, is supposed to exist, the true woody fibre containing always the hydrogen and oxygen in the proportions necessary to fbrm water.* Payen at first considered this incrusting matter as a peculiar substance, for which he proposed the name of sclerogene. His first mode of separating it from the cellular matter was by treating the finely rasped wood (of the oak and beech) with nitric acid, which dissolved out the incrusting matter and left the cellular matter behind. His second mode was to digest the wood with dilute sulphuric acid, by which the cellular matter was dissolved out, and the incrusting matter left. It is obvious, however, that no reliance whatever can be placed on the analyses of substances so treated, since they cannot fail to have undergone a chemical change by being exposed to the action of these strong acids. Further examination has satisfied Payen that the incrusting matter consists of at least three substances, of which one is soluble in water, alcohol, and ether, another in alcohol only, whilqthe third is insoluble in any of these liquids. They are composed, according to his analyses, of Soluble in Soluble in Insoluble. alcohol only. water and alcohol. Carbon.. 48 62-8 68-53 Hydrogen.. 6 5'9 7'04 Oxygen... 46 31-3 24-43t 100 100 100 It is impossible tq say how far the substances analysed by Payen are to be considered as pure, or as actually existing in the pores, or in the incrusting matter of the woody fibre, but it is obvious that the presence of a variable quantity of such substances will necessarily cause that excess of hydrogen, in the entire wood, which appears in the analysis of the ebony, walnut, oak, and beech woods, given in the text. That such an excess of hydrogen above what is necessary to form water with the oxygen, does exist in thel wood of most trees [1 Meyen's.ahresbericht, 1839, p. 10.i COMPOSITION OF CELLULAR MATTER. 105 It is exceedingly difficult in any case to separate the cellular from the incrusting matter of wood, so as to obtain the means of determining by analysis the exact difference in their elementary constitution. Under the impression that in very light and porous substances he should obtain the cellular matter in a purer form, Payen analysed the fibre'of cotton-the pith of the elder, the cellular substance of the cucumber, of the mushroom, and of other fungi, the spongy matter which forms the extremities of the roots of plants, and various other similar substances, and in all these varieties he found the hydrogen and oxygen to exist in the proportions to form water. The mean of his analyses was very nearly as follows-which for the purpose of comparison I shall contrast with that of Dr. Prout: Woody fibre of box and Cellular matter of vascuwillow-Dr. Prout. lar plants-Payen. Carbon.. 50 00 44-80 Hydrogen.. 555 6-20 Oxygen.. 44-45 49'0 100 100* In both these analyses the hydrogen is very nearly 8 times that of the oxygen. All these substances, therefore, may be represented by carbon and water, though the woody fibre of Dr. Prout contains 5 per cent. more carbon than the cellular matter of Payen. If we calculate the number of equivalents of each element contained in these two varietiest of vegetable fibre composed as above exhibited, we find in the one 12 of carbon, 8 of hydrogen, and 8 of oxygen; in the other, 12 of carbon, 10 of hydrogen, and 10 of oxygen. They may therefore, be conveniently represented by the following formulae: WOODY FIBRE..... by C,1 Hs C8 CELLULAR FIBRE... by C12 Ho0 Co It is not unlikely that both of these forms of matter may exist, as well in the perfect wood of trees as in the less consolidated pith of the elder, or in the fibres of cotton-and that they may occur intermingled also in varying proportions with other substances, containing hydrogen in excess.t in its natural state, is a fact to which it will be important to advert when'we consider here. after the chemical changes which the food undergoes in the interior of the plant. Meyen's Jahresbericht, 1839, p. 10. t This is done very simply by dividing the carbon by 6, and the oxygen by 8 (see page 36), thusCarbon -. 50 6 =833 which numbers 12 Hydrogen 5-55. = 5'55 are to each 8 Oxygen - 4. 45 - 8 = 55-5 ( other as 8 X The-existence of a variety of cellular fibre identical in constitution with common starch, as this of Payen is, (see subsequent section, p. 106,) was previously rendered probable by the observations of Dr. Schleiden, that the embryo of the Schotia latifolia, consisting of pores and vessels, the sides of which exhibit distinct concentric layers, is entirely soluble in water, with the exception of the outer rind; and that its solution becomes blue on the addition of iodine. It would appear as if the cellular substance were in this case wholly composed of Starch. (Poggendorf's Annalen. xliii., p. 398.) It may, however, be in such a slate of tenuity in the embryo of this plant, as to be easily changed'into starch by thle action of hot'water; and it is still by no means certain that the cellular fibre analyzed by Payen may n6t also have undergone a change by the treatment to which it was previously subjected. I am unable, however, to speak decidedly on this subject, as I have not seen the details of M. Payen's several papers. (See subsequent section, on the msutudc tranformatzow of woody fibre, starch, gum, and sugar, p. 112.) 106 PER CENTAGE OF WOODY FIBRE IN PLANTS. I have spoken of these varieties of woody fibre as constituting a large portion of the entire mass of vegetable matter produced during the growth of plants. That such is the case in the more gigantic vegetable productions, of which the great forests consist, is sufficiently evident and so far the general statement is easily seen to be correct. It is alsc true of the dried stalks of the grasses and the corn-growing plants, of which it forms nearly one-half the weight,-but in roots and some plants which are raised for food; the quantity of woody fibre, especially in the earlier stages of their growth, is comparatively small.* Thus in the beet root it forms only 3 per cent. of the whole weight when taken from the ground. If suffered to remain in the soil till it becomes old, or if the growth be very slow, the beet becomes more woody, as many other roots do, and the quantity of ligneous fibre increases. ~ 2. Starch-its constitution and properties. Next to woody fibre, starch is probably the-most abundant product of vegetation. To the agriculturist it is a substance of much more interest and importance than the woody or cellular fibre, from the value it possesses as one of the staple ingredients in the food of man and animalsand from its forming a large portion of the weight of. the various grains and roots which are the principal objects of the art of culture. 1~. When the flour of wheat, barley, oats, Indian corn, &c., is mixed up into a dough with water, and this dough washed on a linen cloth with pure water, a milky liquid passes through, from which, when set aside, a white powder gradually falls. This white powder is the starch of wheaten or other flour. 2~. When the pith of the sago palm is washed, in a similar manner, with water upon a fine sieve, a white powder is deposited by the milky liquid which passes through. This, when collected, forced through a metal sieve to granulate (or corn) it, and dried by agitation over the fire, is the sago of commerce. The following table shows the per centage of woody fibre contained in some common'lants in the green state, and when dried in the air, and at 212~: IN THE GREEN STATE. Dried in the air. Dried at 2120. Woody fibre. Water. percent. per cent, per cent, per cent. Barley straw, ripe -... 50 - - - Oat straw, do.- - 47 - Maize straw, do. 24 Stalks of the field pea - - - 10 80s Field bean straw -. 51 - - - White turnip - - - -- - 3 92 Common beet (betavulgaris) - - - 3 86 Young twigs of common furze — - 24 50 Rape straw, ripe - --- 55 12y 77 Tare straw, do. - -. 37 - - - Vetch plant(v. sativa) 4 - 42 - 0 772 Do. (v. cracca) in flower - - 5) 68 Do. (v. narbonensis) do. - - 1 80 White lupin, in flower, -.- - 7 86, Lucerne, in flower,.. - - 9 73 Rye grass, do...... - - 11 68 Red clover, do... - 7 79 White clover, do. - - - - 43 81 Trefoil (medium) do..- - - 8X 73 Sainfoin (esparsette)... 7 76 Trefoil (agrarium) in flower - - - 12 68 Do. (rubens) do. -. - - 15 60 PREPARATION AND DECOMPOSITION OF STARCH. 107 3~. When the raw potato is peeled and grated on a fine grater, and the pulp thus produced well washed with water, potato starch is obtained in the form of a fine white powder, consisting of rounded, glossy and shining particles. 4~. When the roots of the Maranta Arundinacea of'the West India Islands are grated and washed like the potatoe, they yield the arrow root of commerce. From the root of the Manioc, the cassava is procured by a similar process, and this, when dried by agitation on a hot plate, is the tapioca of the shops. By this method of drying, both sago and tapioca undergo a partial change, which will be explained in a subsequent section (see p. 113.) The substances to which these several names are given are, when pure, similar in their properties, and identical in their chemical constitution. They are all colourless, tasteless, without smell, when dry and in a dry place may be kept for any length of time without undergoing alteration, are insoluble in cold water or alcohol, dissolve readily.in boiling water, giving a solution which gelatinizes (becomes a jelly) on cooling-and in a cold solution of iodine* they all become blue. When dried at 212~, they consist, according to Dr. Prout, with whose analysis those of other chemists agree, of Carbon.... 44'0 per cent., or 12 atoms. Hydrogen.. 62 per cent., or 10 atoms. Oxygen... 49'8 per cent., or 10 atoms. 100 Starch, therefore, may be represented by the formula C 12 H I 0,0 which is identical with that deduced in the preceding section for the cellular fibre of Payen. Both substances, therefore, contain the same elements (carbon, hydrogen and oxygen), united in the same proportions, and in both, as well as in the common fibre of wood, the hydrogen and oxygen exists in the proportion to form water. That starch constitutes a large portion of the weight of grains and roots, usually grown for food, will appear from the following table, which exhibits the quantity present in 100 lbs. of each substance named: Starch per cent. Wheat flour....... 39 to 77 Rye "........ 50 to 61 Barley "...... 67 to 70 Oatmeal....... 70 to 80 Rice flour........... 84 to 85 Maize "....... 77 to 80 Buckwheat........ 52 Pea and Bean meal....... 42 to 43 Potatoes, containing 73 to 78 of water,. 13 to 15 It thus exists most largely in the seeds of plants, and in some roots. It is frequently deposited, however, among the woody fibre of certain trees, as in that of the willow, and in the inner bark of others, as in Iodine is a solid substance, of a lead-grey colour, possessed of a peculiar powerful odour, and forming when heated a beautiful violet vapour. It exists in small quantity in sea water, and in some marine plants. Its solution in water readily shows the presence of starch, by the blue colour it imparts to i;. 108 VARIETIES OF GUM. those of the beech and the pine.* Hence the readiness with which a branch of the willow takes root and sprouts, and hence also the occasional use of the inner bark of trees for food, especially in northern countries, and in times of scarcity. In some roots which abound in sugar, as in those of the beet, the turnip, and the carrot, only 2 or 3 per cent. of starch can be detected. ~ 3. Gum-its constitution and properties, The variety of gum with which we are most familiar is gum arabic, or senegal, the produce of various species of acacia, which grow in the warmer regions of Asia, Africa, and America. It exudes from the twigs and stems of these trees, and collects in rounded more or less transparent drops or tears. It is also produced in smaller quantities in many of our fruit trees, as the apple, the- plum, and the cherry; it is present in some herbaceous plants, as in the althaea and malva officinalis (common and marsh mallow); and it exists in lint, rape, and many other seeds. When treated with boiling water these plants and seeds give mucilaginous solutions. Many varieties of gum occur in nature, but they are all characterised by being insoluble in alcohol, by dissolving or becoming gelatinous in hot or cold water, and by giving mucilaginous —viscid and glutinoussolutions, which may be employed as a paste. Three distinct species of gum have been recognised by chemists: 1~. Arabin-of which gum arabic and gum senegal almost entirely consist. It is readily soluble in cold water, giving a viscid solution, usually known by the name of the mucilage of gum arabic. 20. Cerasin-which exists in the gum of the cherry-tree. It is inso luble in cold water, but dissolves readily in boiling water. When thus dissolved it may be dried without losing its solubility, and is therefore by boiling supposed to be changed into arabin. 3~. Bassorin-existing in what is called bassora gum-and forming a large portion of gum tragacanth.f It swells and becomes gelatinous in cold water, but does not dissolve in water either cold or hot. By these characters, the three kinds of gum are not only readily distinguished, but may be easily separated from each other. Thus if a native gum or an artificial mixture contain all the three, simple steeping in and subsequent washing with cold water, will separate the arabinboiling water will then take up the cerasin, and the bassorin will remain behind. These different kinds of gum all possess the same chemical constitution. According to the analyses of Mulder, they consist of Carbon... 45-10 per cent., or 12 atoms. Hydrogen.. 610 " or 10 " Oxygen... 48'80t " or 10 " 100 Its presence is readily detected in such wood by a drop of the solution of iodine-which gives a permanent blue to starch, but ts the woody fibre only a brownish stain. t This gum exists along with starch in the roots of the various species of orchis, especially of those which are used for making salep (Meyen). Berzelius Arsberdttelse, 1839, p. 443. VARIETIES AND CONSTITUTION OF SUGAR. 109 In these analyses, as in those of starch and woody fibre, we see that t1e per centage of oxygen is equal to that of the hydrogen multiplied by 8, and consequently that these two elements are, as already stated, in the proportion to form water. But we see also that the carbon is in the proportion of 12 atoms or equivalents to 10 of each of the other constituents, and therefore gum may be represented by C 1 H1 0o- 0 -a formula which is identical with that already given for starch and cellular fibre. It appears, therefore, that not only may gum, starch, and cellular fibre be represented by carbon and water, but that they all consist of carbon and the elements of water, united together in the same proportions. Gum not only exists in many seeds, and exudes as a natural product from the stems and twigs of many trees, but is also contained in the juices of many other trees, from which it is not known to exude; and in the sap of most plants it may be detected in greater or less quantity. It may be considered, indeed, as one of those substances which are produced most largely and most abundantly in the vegetable kingdom, since, as will hereafter appear, it is one of those forms of combination through which organic matter passes in the interesting series of changes it undergoes during the development and growth of the plant. ~ 4.. Of Sugar-its varieties and chemical constitution. 10. Cane Sugar.-Sugar, identical in constitution and properties with that obtained from the sugar-cane, and generally known by the name of cane-sugar, exists in the juices of many trees, plants, and roots. In the United States'of North America the juice of the maple tree is extensively collected in spring, and when boiled down yields an abundant supply of sugar. In the Caucasus that of the walnut is extracted for the same purpose. The juice of the birch also contains sugar, and it may be obtained, in lesser quantity, from the sap of many other trees. In the juice of the turnip, carrot, and beet, it is also present, and in France and Germany the latter root is extensively cultivated for the manufacture of beet sugar. In the unripe grains of corn, at the base of the flowers of many grasses and clovers when in blossom, and even in many small roots, as in that of the quicken or couch-grass (triticum repens); the presence of sugar may likewise be readily detected. Sugar is. principally distinguished by its agreeable sweet taste. When pure, it is colourless and free from smell. It dissolves readily in alcohol and in large quantity in water. The solution in water, when much sugar is present, has an oily consistence, and is known by the name of syrup. From this syrup the sugar gradually deposits itself in the form of sugar candy. If the syrup- be boiled on too hot a fire, it chars slightly, becomes discoloured, and a quantity of molasses is formed. Pure cane-sugar, free from water, consists of Carbon... 44'92 per cent., or 12 atoms. Hydrogen.. 611 " or 10 Oxygen.. 48-97 " or 10 100 If we compare these numbers with those given for starch and gum in the preceding sections, we see that they are almost identical-so that 110 CANE, GRAtE, MANNA, AND LIQUORICE SUGARS. cane-sugar also contains oxygen and hydrogen in the proportions to form water, and may likewise be represented by the formula C,2 HI O 0. 2~. Grape sugar.-In the juice of the grape a peculiar species of sugar exists, which, in the dried raisin, presents itself in the form of little rounded grains. The same kind of sugar gives their sweetness to the gooseberry, the currant; the apple, pear, plum, apricot, and most other fruits. It is also the sweet substance of the chesnut, of the brewers' wort, and of all fermented liquors, and it is the solid sugar which floats in rounded grains in liquid honey, and which increases in apparent quantity as the honey, by keeping, becomes more and more solid. Grape sugar has nearly all the sensible characters of cane sugar, with the exception of being less soluble in water and also less sweet,-2 parts of the latter imparting an equal sweetness with 5 of the former. In chemical constitution they differ considerably. Thus grape sugar dried at 250~ F., consists of Carbon... 40'47 per cent., or 12 atoms. Hydrogen.. 6-59 " or 12 " Oxygen... 52-94 " or 12 100. The oxygen here is still eight times greater than the hydrogen, and, therefore, in this variety of sugar also, these elements exist in the proportions to form water. But for every 12 equivalents of carbon, dry grape sugar contains 12 of hydrogen and 12 of oxygen. It is consecquently represented by C12 Hi2 0,2, and contains the elements of two atoms of water (H' O2) more than cane sugar.* 3~. Manna sugar, sugar of liquorice, -c.-Besides the cane and grape sugars which occur in large quantity in the juices of plants, there are other varieties which occur less abundantly, and are therefore of less interest in the study of the general vegetation of the globe. Among these is manna, which partly exudes and is partly obtained by incisions from certain species of the ash tree which grow in the warmer countries of Southern Europe (Sicily and Italy), iad in Syria and Arabia. It also exists, it is said, in the juice of the larch tree, of common celery, and of certain trees which are met with in New South Wales. Liquorice root also contains a species of black sugar, which is known in this country under the names of Spanish and Italian juice, from the countries where it is grown. In the mushroom and other fungi a colourless variety, apparently peculiar, has also been met with,-and milk owes its sweetness to a species of sugar formed in the interior of the animal along with the other substances which the milk contains. These several kinds of sugar differ more or less, not only in sensible and chemical properties, but also in chemical constitution, from the more abundant cane and grape sugars-but they form too smalJ a part of the general products of vegetation, and are of too little consequence in practiSolutions of cane and grape sugar are readily distinguished from each other by the following chemical characters:-1. 11 the solution be heated and a few drops of sulphuric acid then added, cane sugar will be decomposed, blackened, and made to fall as a black or brown powder-while a solution of grape sugar will at the most be only slightly discoloured. 2. If, instead of sulphuric acid, caustic potash be employed, the cane sugar will be unchanged, while the grape sugar will be blackened and thrown down. MUTUAL RELATIONS OF WOODY FIBRE, STARCH, GUM, ETC. ill cal agriculture to render it necessary to do more than thus shortly advert to their existence.* ~ 5. Mutual relations of woody fibre, starch, gum, and sugar. It may be interesting now to consider for a moment the mutual relations of the several substances, woody fibre, starch, gum, and sugarabove described-which occur so largely in the vegetable kingdom, and are serviceable to man for so many different purposes. These relations will be best seen on comparing the formula by which they are respectively represented. ThusWoODY FIBRE (lignin) is represented by C12 Hs O0 CELLULAR FIBRE (according to Payen) by C12 HI 01 S'TARCH (dried at 2120 F.) by C12 HI 0 o GUM (any of the 3 varieties) by C12 Hlo 01 o CANE SUGAR (free from water) by C12 H1o O1o* GRAPE SUGAR (dried at 130~ F.) by C12 Ha2 012a In these formulae we observe1~. That the eqivalents of the oxygen are equal to those of the hydrogen in all the formulae, and, therefore, that all these substances may be supposed to consist of carbon and water. 2~. The formulme for cellular fibre, starch, gum, and cane sugar, are identical. They consist of the same elements united together in the same proportions. This is one of those facts which not only appear very remarkable to the unlearned, but are scarcely capable of being clearly comprehended and explained, even by those who have most profoundly studied this branch of natural science. Starch and sugar-how different their properties! how unlike their uses! how unequal their importance to the human race! yet they consist of the same weights of the same substances, differently conjoined. The skilful architect can put together the same proportions of the same stone and cement-and the painter can combine the same colours so as to produce a thousand varied impressions on the sense of sight. In the hand of Deity matter is infinitely more plastic. At His bidding the same particles can unite in the same quantity so as to produce the most unlike impressions-and on all our senses at once. 3~. A knowledge of the above close relations in composition, among a class of substances occurring so abundantly in the vegetable kingdom, imparts a degree of simplicity to our ideas of this otherwise complicated subject. It does not appear so mysterious that we should have woody fibre, and starch, and gum, and sugar, occurring together in variable quantities, when we know that they are all made up of the same materials, in the same or nearly the same proportions-or that one of these should occasionally disappear from a plant, to be replaced in whole or in part by another. * For a list of plants from which sugar has been extracted, see Thomson's OrgaiweChemistry (1838), p. 647. t Crystallized cane sugar (sugar candy) loses 5-3 per cent. of water in favourable circumstances. This is equal to one equivalent (HO), so that if dry sugar be Ci2 Hio Olo, crystallized sugar is C i Hi Ot t —or Ci2 Hio Olo+HO, since there is no doubt that this one equivalent of the hydrogen and oxygen exists in crystallized sugar in the state of water. Jn like manner, crystallized honey or grape sugar-as it occurs in honey or in the dried grape-loses 9 per cent. of water when heated to 250~ F. This is equal to two equivalents (2O0), so that crys. tallized grape sugar is represented by C12 Hi4 014 or C12 H12 C:s+2HO. 112 MUTUAL TRANSFORMATIONS OF STARCH, GUMI ETC. A further question, however, arises in our minds. We naturally ask, -does nature, in thus removing one of these compounds, and supplying its place by another, actually form from its elements the new substance introduced4 or does she produce it by a mere change or transformation of those previously existing. A satisfactory reply to this question may be derived from the facts detailed in the following section. ~ 6. Mutual transformations of woody fibre, starch, gum, and sugar. I.-WOODY FIBRE. 1~. Action of heat.-If wood be reduced to the state of fine saw-dust, be then boiled in water to separate everything soluble, afterwards dried by a gentle heat, and then heated several times in a baker's oven, it will become hard and crisp, and may be ground in the mill into a fine meal. The powder thus obtained is slightly yellow in colour, but has a taste and smell similar to the flour of wheat; it ferments when made into a paste with yeast or leaven, and when baked gives a light homogeneous bread. Boiled with water, it yields a stiff tremulous jelly, like that from starch (Autenrieth.-Schubler, Agricultur Chemie, i., p. 224.) By the agency of heat, therefore, it appears that the woody fibre may be changed into starch. 2~. Action of sulphuric acid.-If to three parts of the sulphuric acid of the shops (oil of vitriol) one part of water be added, and a portion of delicate woody fibre be immersed in it for half a minute, and the whole then rubbed in a mortar with a few drops of a solution of iodine-the woody fibre will assume a blue colour, showing that it is in part at least changed into starch* (Schleiden). Again, if three parts of fine saw-dust or of fragments of old linen be rubbed in a mortar with four of the sulphuric acid of the shops added by degrees-it will, in a quarter of an hour, be rendered completely soluble in water. If the solution in water be freed from acid by chalk, and then evaporated, a substance resembling gum arabic is obtained (Braconnot). According to Schleiden, the fibre may be seen under the microscope gradually to change from without inwards, first into starch and then into gum. Further, if this gum be digested with a second portion of sulphuric acid diluted with 8 or 10 times its weight of water, it will be gradually converted into grape sugar or the fibre of wood or linen may be changed directly into sugar by the prolonged action of dilute sulphuric acid. 3~. Action of potash.-If saw-dust be mixed with from two to eight times its weight of hydratef of potash and as much water, and boiled till a crust forms on the surface, and if dilute sulphuric acid be then added till the whole is slightly sour, the undestroyed woody fibre will give an It will be recollected that starch is characterized by giving a blue colour with a solution of iodine (see p. 107). The simplest way of trying this experiment is, to take a quantity of clean cotton-to wet it with water, squeezing out again as much as possible-then to spread it out upon a flat dish and moisten it quickly and thoroughly with the acid diluted as above. After half a minute, add the solution of iodine, stir quickly with a glass rod, and immediately add water, when the blue compound of iodine and starch will speedily deposit itself. -(Schleiden, Pog. Annal., XlWi., p. 396.) t Hydrate of potash is the caustic substance which is obtained by boiling common pearl. ash with quick lime. ACTION OF HEAT ON STARCH, 113 instantaneous deep blue on the addition of iodine, showing that starch has been formed. Woody fibre, therefore, may be changed into starch, either by the unaided action of heat, by that of sulphuric acid, or by boiling with caustic potash,-and the starch thus produced may be further transformed, first into gum and then into grape sugar, by the prolonged action of dilute sulphuric acid, assisted by a moderate heat. II. STARCH. 1~. Action of heat.-When flour, potato, or arrow-root starch is spread out upon a tray, then introduced into an oven and gradually heated to a temperature not exceeding 300~ F., it slowly changes, acquires a yellow or brownish tint according to the temperature employed, and becomes entirely soluble in cold water. It is changed into gum. Under the names of starch-gum, or British-gum, this substance is largely manufactured in this country, and is successfully substituted for gum arabic by the calico-printers in thickening many of their colours.* The gum thus prepared not unfrequently also possesses a sweet taste, from the further change of a portion of the gum into sugar. 2~. Action of water.-When starch is dissolved in boiling water, and is then allowed to stand in the cold either in a close vessel or exposed to the air, it gradually changes into gum or sugar. The process, however, is slow, and months must elapse before the whole of the starch is thus spontaneously transformed in the presence of water (De Saussure). It takes place more rapidly when starch and water are boiled together for a length of time. 3~. Action of sulphuric acid.-From what has been already stated in regard to the action of this acid on woody fibre it will readily be supposed that native starch, of any variety, is likely to undergo transformation when subjected to its influence. In reality, if 50 parts of starch, 12 of sulphuric acid, and 139 of water be taken, and if the starch be thoroughly moistened with a portion of the water, and then poured into the mixture of the acid with the remainder of the water, and heated to 190~ F., the starch will be entirely converted into gum. By further and more prolonged heating this gum is changed into grape sugar. The gum or sugar may be obtained in a separate state by adding to the solution either chalk or lime, which will combine with and carry down the acid.t One hundred pounds of starch treated in this way will yield from 105 to 122 lbs. of dry grape sugar. The rapidity with which this transformation takes place depends partly upon the temperature and partly upon the proportion of acid employed. Thus 100 lbs. of starch mixed with 600 of water and 10 of sulphuric acid, will be converted into grape sugar by boiling for seven hours. If by increasing the pressure the temperature be raised to 250~ F., the transformation will be effected in afew minutes. With only one' During the baking of bread this conversion of starch into gum takes place to a considerable extent. Thus Vogel found that flour which contained no gum gave, when-baked, a bread of which 18 per cent., or nearly one.fifth of the whole weight consisted of gum. Thus one cf the effects of baking is to render the flour-starch more soluble, and therefore (?) more easily digestible. t It forms gypsum with it (sulphate of lime) which is a compound of lime and sulphuric acid. 114 CHANGE OF CANE INTO GRAPE SUGAR, pound of acid and the same quantity of starch and water, the change will be effected in three hours by a temperature of 230~ F. This mode of converting potato starch into grape sugar is said to be extensively practised in France, for the purpose of subsequently fermenting the sugar and converting it into brandy. III. GUM. Action of sulphuric acid.-If powdered gum arabic be rubbed in a mortar with the sulphuric acid of the shops, -a brownish solution is obtained, which, when diluted with water and treated with chalk, yields a gummy substance similar to that obtained in the same way from starch and woody fibre. Prolonged digestion with diluted acid converts a portion of this gum into sugar.-[Berzelius, Traite de Chemie, (1831), v., p. 217.] IV.-CANE SUGAR. 10. Action of heat.-When crystallized cane sugar is heated to 320~ F. it melts, and if the temperature be raised to 360~ F. it gives off two atoms of water and is changed into caramel. This caramel is an uncrystallizable sugar, which is generally present in artificial syrups, and is often of a brownish colour. It contains the elements of an atom of water less than cane sugar, and is represented by C,2 H9 09. It is not known to occur in the natural juices of plants. 2~. Action of sulphuric acid.-When cane sugar is digested with dilute sulphuric acid, aided by a gentle heat, it is rapidly converted into grape sugar. The acid of grapes (tartaric acid) and many other vegetable acids produce a similar change; It is obvious that this conversion of cane into grape sugar can only take place in the presence of water, inasmuch, as has already been shown (p. 110), grape sugar contains the elements of two atoms of water more than cane sugar, or Cane sugar. Water. Dry grape sugar. Cia H0 01 0 + 2H 0 = Ca2 H,, 0,12. We may revert now to the question with which we concluded the preceding section. Since these different substances are so closely allied in chemical constitution, and occur so often in connection with each other in the vegetable kingdom, does nature, when her purposes demand the change, actually transform them, the one into the other, in the interior of the plant? The answer may now be safely given, that she certainly does. What we can so readily perform by our rude art may be still more easily effected in the living vegetable. That which is starch or gum in one part of the plant, may become cane or grape sugar in another, and woody fibre in a third. Thus by re-arranging the same kind and quantity of the several elements, may the various and unlike forms of matter which constitute the main products of vegetation be readily produced. Still the facility is only apparent. We can assure ourselves of the fact of such conversions, because we can at will induce them. But who operates upon these substances in the interior of the plant? Whose mind and will directs these changes-prescribing when, where, and in GRAPE SUGAR ALONE FERMENTS. 115 what order they shall take place? How much depends upon the refined and little understood mechanism of the vegetable structure-how much on the living principle itself! What is this living principlehow can it direct!* ~ 7. Of the fermentation of starch and sugar-and of the relative circumstances under which cane and grape sugars generally occur in nature. It will be of use to us, in connection with the above transformations, to advert to the property possessed by starch and nearly all the known varieties of sugar of entering into fermentation iunder favourable circumstances. When flour is made into a paste with leaven or yeast it begins to rise and ferment,-sooner or later, according to the kind of flour and the quantity of ferment added. When to a decoction of malt or to a solution of starch or of cane or grape sugar in water, a portion of yeast is added, fermentation is speedily induced; and if not arrested by unfavourable circumstances it will continue until the whole of the starch or sugar disappears. In all these cases it is grape sugar alone that undergoes fermentation. [Rose, Poggen. Annal., lii., p. 297.] The starch of the moist dough or of the solution is partially transformed into grape sugar before fermentation commences. Such is the case also with the decoction of malt and with cane sugar. The fermentation commences soon after the first portion of grape sugar is formed, and proceeds more or less rapidly according as this transformation is more or less speedily effected. Hence, in the art of brewing, the necessity of cautiously regulating the temperature by'which this change of the starch and sugar is promoted and hastened. The fermentation itself is the result not of a mere transformation of one form of matter into another having the same elementary constitution, but of a decomposition of one substance into two others unlike itself either in properties or in chemical composition. The grape sugar is resolved into alcohol (spirits of wine), which remains in the liquid, and into carbonic acid, which escapes in the form of gas and causes the fermentation. Thus alcohol being represented by C4 H6 02, and carbonic acid by C02, 2 of alcohol = Ca H1 04 and 4 of carbonic acid = C4 80 make up 1 of grape sugar = C1 1Hi2 It is an interesting fact that the cane and grape sugars occur in nature in circumstances which are entirely consistent with the statement in the preceding section, regarding the action of acids on the former variety of this natural product. Fruits contain grape sugar, which increases in quantity as they ripen or'recome less sour. In the sugar cane, the beet root, and the maple and birch trees, cane sugar exists, but in their Juices no acid is associated with the sugar. On the contrary, ammonia is known to be present in most of them along with the cane sugar. Hence it is inferred, that as in our hands and in our experiments cane sugar is changed by the agency of acids into grape sugar, and "* Oanst thou by searching find out God-Canst thou find out the Almighty unto perfection V" 116 SUBSTANCES CONTAINING NITROGEN. with remarkable ease by that acid which exists in the ripe grapes so it is in the interior of plants. Where sugar occurs in connection with an acid in the juice of a plant, it is grape sugar in whole or in great part, because in the presence of an acid body cane sugar cannot permanently exist, but is gradually transformed into the sugar of grapes. It thus appears also why fruits so readily enter into fermentation, and why, even when preserved with cane sugar, they will, in consequence of the acid they retain, slowly change the latter into grape sugar, and thus induce fermentation.* ~ 8. Of substances which contain Nitrogen.-Gluten, Vegetaole Albumen, and Diastase. The substances described in the preceding sections consist of carbon, hydrogen, and oxygen only, and of them the great bulk of the vegetable productions of the globe consists. But there are certain other substances occurring along with starch and sugar, into which nitrogen enters as a constituent, and which, though not formed in the vegetable kingdom in very large quantity, are yet of such interest and importance in other respects, as to make it necessary shortly to advert to them. 1~. Gluten.-When the flour of wheat is made into a dough, and this dough is washed with water upon a fine sieve, a milky liquid passes through, from which starch gradually subsides. This has been already stated. But on the sieve, when the water ceases to go through milky, there remains a soft adherent, tenacious, and elastic substance, which can be drawn out into long strings, has scarcely any colour, taste, or smell, and is scarcely diminished by washing either with hot or with cold water. This substance is the gluten of wheat. The flour of other kinds of grain also yield it by a similar treatment, though generally in much smaller quantity. This appears from the following table:The grain of Wheat contains 8 to 35 per cent. of gluten. Rye... 9 to 13 " 1" Barley...3 to 6 " Oats... 2 to 5 " When the moist gluten is dried in the air or at the temperature of boiling water, it diminishes much in bulk, and hardens into a brittle semi-transparent yellow substance resembling horn or glue. In this state it is insoluble in water, but dissolves readily in vinegar, in alcohol either cold or hot, and in solutions containing caustic potash, or soda, [the common pearl-ash or soda of the shops boiled with quick-lime.] 2~. Vegetable Albumen.-To the white of egg the name of albumen (albus, white) has been given by chemists. It possesses the well known property of coagulating or of forming a white solid insoluble substance. when it is heated either alone or after being mixed with water. When the starch has subsided from the milky liquid which passes Milk also, in favourable circumstances, as when kept at a temperature of 100o F., u'ndergoes fermentation, and in some countries of Asia a spirituous liquor is prepared from mares' and asses' milk. In this case the milk first becomes sour, then the acid thus formed converts the milk sugar into grape sugar, and finally this sugar enters into fermlentation. This takes place more readily in consequence of the presence of tie decomposing cheesy matter (casein) of the milk-as is shown by the fact that the introduction of a small quantity of the curd of milk into a solution of grape sugar will cause it to ferment. GLUTEN, VEGETABLE ALBUMEN, AND DIASTASE. 117 through the sieve in preparing the gluten of wheat, the water-rests transparent and colourless above the white sediment. If this water be heated, it will become more or less troubled, and white films or particles will separate, which may be easily collected, and which possess all the properties of coagulated albumen, or boiled white of egg. To this substance the name of vegetable albumen has been given. When the fresh prepared gluten of wheat is boiled in alcohol a portion of albumen generally remains undissolved, showing that water does not completely wash it out from the gluten. Vegetable albumen, when fresh and moist, has neither colour, taste, nor smell, is insoluble in water or alcohol, but dissolves in vinegar and in caustic potash or soda. When dry it is brittle, more or less coloured, and opaque. In the seeds of plants, it exists only in small quantitythus the grain of Wheat contains i to 1j per cent. Rye o. 2 to 3 " Barley.. lto (Oats... to' It occurs more largely however in the fresh juices of plants, in those of cabbage leaves, turnip roots, and many others. When these juices are heated the albumen coagulates and is readily separated. Gluten and vegetable albumen appear to be as closely related as sugar and starch are to each other. Like these two substances, they consist of the same elements, united together in the same proportions, and are capable of similar mutual transformations. According to the most recent analyses, those of Dr. Scheerer, they consist of Carbon = 54-76 Hydrogen = 7-06 Oxygen - 20-06 Nitrogen - 18-12 100 When exposed to the air in a moist state these substances undergo decomposition. They ferment, emit a most disagreeable odour, and produce, among other compounds, vinegar and ammonia. The important influence which gluten and vegetable albumen are supposed to exercise over the nourishing properties of the different kinds of food in which they occur, will be considered in a subsequent part of these lectures.* 3~. Diastase.-When cold wateris poured upon barley newly malted and crushed, is permitted to remain over it for a quarter of an hour, is then poured off, filtered, evaporated to a small bulk over boiling water, again filtered if necessary, and then mixed with much alcohol, a white tasteless powder falls-to which the name of.diastase has been given. There occur in the animal kingdom-in the bodies of animals-three other forms of the substance above described under the names of gluten and vegetable albumen. These are albumen or white of egg, already mentioned,-casein, the curd of cheese,-and fibrin, the substance of the muscular fibre of animals. 1o. Casein.-When the curd of cheese is well washed with water, and then boiled in alcohol to free it from oily matter, it forms the casein of chemists. While moist it is soft and colourless, but as it dries it hardens, assumes a yellow colour, and becomes semitransparent. Even when moist it is perfectly insoluble either in cold or in hot water. It is sola6 118 PRODUCTION OF DIASTASE. If unmalted barley be so treated no diastase is obtained. This substance, therefore, is formed during the process of malting. If wheat, or barley, or potatoes, which by steeping in water yield no diastase, be made to germinate (or sprout), and be afterwards bruised and treated as above, diastase will be obtained. It is therefore produced during germination. If the shoot of a potato be cut off within half an inch of its base, this lower portion, with the part of the potato to which it is immediately attached, separated from the rest-and the three parts (the upper portion of the shoot-the lower portion with its attached fragment of potatoand the remaining mass of the potato) treated with water,-only that portion will yield diastase in which the base of the shoot is situated, When a seed sprouts, therefore, this substance is formed at the base of the germ, and there remains during its growth. If the same portion of the potato, or if the grain of barley or wheat is ble, however, in water containing vinegar, or to which a little carbonate of potash or soda has been added. It may be kept for any length of time. in a dry place, without undergoing decay. The changes undergone by old cheese are chiefly due to the oily and other substances with which the curd is mixed. It has been remarked, that when the gluten of wheat is left for a length of time in a moist state it undergoes a kind of fermentation and gradually acquires the smell and taste of cheese (Rouelle.) 2'. Fibrin.-When lean beef or mutton is long washed in water till it becomes colourless, and is then boiled in alcohol to separate the fat, a colourless, elastic, fibrous mass is obtained, which is the fibrin of chemists. In recently drawn blood it exists in the liquid state, but coagulates spontaneously when exposed to the air, and forms the greater part of the clot of blood. It dissolves in a solution of caustic potash or of nitre, and in vinegar. 3~. Albumen.-This substance in the liquid state exists in the white of egg, and in the serum of the blood. It coagulates by heating to 160~ F, or if previously mixed with water by raising to 212~ F. These three substances, in addition to their well Known sensible properties, are distinguished as follows: 1~. Liquid casein in milk, is not coagulated by heating alone-the addition of rennet orof a little acid (vinegar or spirit of salt) is necessary, when it curdles readily. 2~. Liquid albumen in white of egg, coagulates by heat, alone, as when an egg is put into hot water. 30. Liquid fibrin in the blood coagulates by mere exposure to the air, or more rapidly by agitation in contact with the air. Like starch and sugar these three substances are mutually convertible by known means. Thus fibrin, if nnboiled, dissolves by digestion at 80~ F. in a saturated solution of nitre, and acquires the properties of liquid albumen; and if to liquid albumen.a little caustic potash be added, and afterwards'much alcohol, it will be thrown town inthe form and with the properties of casein. All these substances appear to contain the same orgalc. constituents in the same proportions. Boussingault first showed the identity in chemical constitution of gluten and vegetable al. bumen.-[Pog. An., xl., p. 2.53.] Mulder afterwards proved a similar identity between vegetable albumen and the white of egg,.fibrin, and casein.-[Ann. de Chim. et. de Phys., lxv., p. 301.] Mulder supposes them to differ from each other by the presence in unlike quantities of a small admixture of sulphur, phosphorus or phosphate of lime. Those who are not familiar with the history anti with the nature of chemical research, can form no idea of the time and labour which has by different chemists been expended on this one branch. The persevering industry of Dr. Mulder, of Rotterdam, appeared to have cleared up the entire subject by'a long series of investigations and analyses,-[for an outline of.his results, see Berzelius Arsberattlese, 1839, p. 611,]-when first Vogel, then Prosper Denis, and latest Liebig and Dr. Scheerer, have arrived at different results. Our ideas are thus again unfixed, and our partial generalizations set aside. for future emendation. The analysis inserted in the text, as representing the composition of gluten and vegetable albumen, is that given by Dr. Scheerer for the purest form offibrin. I have selected it in preference to the results either of Boussingault or of Mulder. because it is the most recent, and has been obtained with a knowledge of all the previous researches,-and assuming the chemical identity of this entire group of substances, is: the most likely to represent their constitution with accuracy. It differs from the analysis of Mulder only in stating the nitrogen at 2 per cent. higher than.was done by that chemist. The recent improvements in the mode of determining the true quantity of nitrogen in organic substances, appear to justify us in expecting the result of Scheeret to be inthisrespect the more eorrect DIASTASE CHANGES STARCH INTO SUGAR. L19 examined, when the first true leaves of the plant have been fully formed and expanded, the diastase will be found to have in great part, if not entirely, disappeared. This substance, therefore, is first formed when the seed begins to sprout, performs a functior which makes its presence necessary at the base of the germ, and which function being discharged when the true leaves are formed, it then disappears. What is the nature of this temporary function, why the diastase must reside at the base of the sprout in order to discharge it, and why it should so early cease, will appear from a detail of the properties of this singular substance. Properties of diastase.-If the solution obtained from malt be digested with potato, flour, or other starch, at a temperature between 120~ and 140~ F., the latter will gradually dissolve and will form a colourless transparent solution. When this solution is carefully evaporated a yellowish white powder is obtained, perfectly soluble in water, to which the name of dextrine has been given, [because its solution turns to the right a ray of polarized light when passed through it.] This dextrine has the same composition as starch. It is merely starch changed or transformed in such a way as to become soluble in cold water,-a change analogous to that which it undergoes by simply boiling in water. But if the digestion be continued after the starch is dissolved, the solution will gradually acquire a sweet taste, and if it be now evaporated it will yield, instead of dextrine, a mixture of gum and grape sugar. And if the digestion be still further prolonged, the whole of the starch will be converted into grape sugar only.-[See above, ~ 6, p. 113.] Thus diastase (like sulphuric acid) possesses the property of transforming starch entirely-first into gum, and then into grape sugar. The intermediate stage of dextrine has not been recognized in the action of sulphuric acid, nor is it easy to arrest the action of diastase exactly at this point-the most carefully prepared dextrine always containing a mixture of gum and sugar. One part of diastase will convert into sugar 2000 parts of starch. A solution of diastase, when allowed to stand, soon undergoes decom position, and after being boiled, it has no further effect upon starch. It has not been analysed, because it is difficult to obtain it in a pure state. It contains nitrogen, however, for, when moistened and exposed to the air, it decomposes, and, among other products, yields ammonia.* The functions of diastase-one of the purposes at least for which it is produced in the living seed, and situated at the base of the germ-will now be in some measure understood. The starch in the seed is the food of the future germ, prepared and ready to minister to its wants whenever heat and moisture concur in awakening it to life. But starch is itself insoluble in water, and could not, therefore, accompany the fluid sap when it begins to move and circulate. For this reason diastase is formed at the point where the germ first issues from the mass of food. There it transforms the starch, and renders it soluble, so that the young vessels can take it up and convey it to the point of growth. When the starch is exhausted its functions cease. It is then itself transformed and It will be recollected that ammonia contains nitrogen, Lbtang represented by NH3.-See l.ecture III., p. 51. 120 ADAPTATIONS IN THE PRODUCTIONS OF DIASTASE. carried into the general circulation. Or when, as in the potato, much more starch is present than is in many cases requisite, its function ceases long before the whole of the starch disappears. Its presence is necessary only until the leaves and roots are fully formed-when the plant is enabled to provide for itself, and becomes independent of the starch of the seed. When this period arrives, therefore, the production of diastase is no longer perceived. This I have said is one of the purposes which appears to be served by diastase in the vegetable economy. That it is the only one we have no reason to believe. There may be others quite as interesting which we do not as yet understand. This is rendered more probable by the fact that the diastase contained in one pound of malted barley is capable of converting into sugar five pounds of starch.* (Liebig.) And though at the temperature at which the seed germinates, more of this substance may be necessary to transform the same weight of starch than is required in our hands, when aided by artificial heat,-yet as we never in the ordinary course of nature find, any thing superfluous or going to waste, there is reason to believe that the diastase may be intended also to contribute directly to the nourishment and growth of the plant. As it contains nitrogen, it must be derived from the gluten or vegetable albumen of the seed; and as a young plant of wheat, when already many inches from the ground, contains no more nitrogen than was originally present in-the seed itself (Boussingault), this diastase may only be ihe result of one of those transformations of which glutenf is susceptible, and by which it is rendered soluble, and capable of aiding in the production of those parts of the substance of the growving plant into which nitrogen enters as a necessary constituent. It may not be uninstructive if we pause here for a moment and consider the beauty of the arrangements we have just been describing. In passing through a new and interesting country we do not hesitate, at times, to stop and gaze, and leisurely admire. We cannot otherwise fully realize and appreciate its beauty. So in the domains of science, we cannot be ever hurrying on-we must linger occasionally, not only that we may more carefully observe, but that we may meditate and feel. You see how bountifully nature has provided in the seed for the nourishment of the young plant, how carefully the food is stored up for it, and in how imperishable a form-how safely covered also and protected from causes of decay! For hundreds of years the principle of life will lie dormant, and for as many the food will remain sound and undiminished till the time of awakening comes. Though buried deep in the earth, the seed defies the exertions of cold or rain, for the food it contains is unaffected by cold and absolutely insoluble in water. But no sooner * It is the diastase in malt which dissolves the starch of the barley in the process of brewing, but as the diastase contained in malt is sufficient to dissolve so large a.quantity of starch, it is obviously a waste of labour to malt the whole of the barley employed. One of malt to three of barley would probably be sufficient in most cases to obtain a wort containing the whole of the starch in solution. Advantage is taken of this property in the manufacture of the white beer of Louvain, and of other places in Flanders, and in Germany, where the light colour is secured by adding a large quantity of flour to a decoction of a small quantity of barley. t That diastase is merely transformed gluten we cannot say, because the exact chemical constitution of diastase is as yet unknown. VEGETABLE ACIDS. 121 is the sleeping germ recalled to life, by the access of air and warmth and duly tempered moisture, than a new agent is summoned to its aid, and the food is so changed as to be rendered capable of ministering to its early wants. The first movement of the nascent germ-(and how it moves, by what inherent or impartial force, who shall discover to us?) -is the signal for the appearance of this agent-diastase-of which, previous to germination, no trace could be discovered in the seed. At the root of the germ, where the vessels terminate in the farinaceous matter, exactly where it is wanted, this substance is to be found;-there, and there only, resolving and transforming the otherwise unavailable store of food, and preparing it for being conveyed either to the ascending sprout or to the descending root. And when the necessity for its presence ceases-when the green leaf becomes developed, and the root has fairly entered the soil-when the plant is fitted to seek food for itselfthen this diastase disappears, it undergoes itself a new conversion, and is prepared in another form to contribute tothe further increase of the plant. How beautiful and provident are all these arrangements!-how plastic the various forms of organic matter in the hands of the All-Intelligent!-how nicely adjusted in time and place its diversified changes! What an apparently lavish expenditure of forethought and kind prevision, in behalf even of the meanest plant that grows! ~ 9. Vegetable Acids.-Acetic acid, Oxalic acid, Tartaric acid, Citric acid, lialic acid. Another class of compound substances remains to be shortly consid ered,-those, namely, which possess sour or acid properties, and which are known to be present in large quantity in many plants, and more especially in the greater number of unripe fruits. They do not, taken as a whole, form any large portion of the entire produce, either of the general vegetation of the globe or of those plants which are cultivated for food; yet the growth of fruit-as in the grape, orange, and apple countries-is sufficiently extensive, and the general interest in the cultivation of fruit trees sufficiently great, to require that the nature of the substances contained in fruits, and the peculiar changes by which they are formed, should be in some measure considered and explained. I.-ACETIC ACID. Acetic acid or vinegar is the most extensively diffused, and the most largely produced, of all the organic acids. It is formed during the germination of seeds, and it exists in the juices of many plants, but it is most abundantly evolved during the fermentation, whether natural or artificial, of nearly all vegetable substances. When pure it is a colourless liquid, having a well known agreeably acid taste. It may be boiled and distilled over without being decomposed. The vinegar of the shops is generally very much diluted, but it can be prepared of such a strength as to freeze and become solid at 45~ F., and to blister the skin and produce a sore when applied to any part of the body. When mixed with water it readily dissolves lime, magnesia, alumina, &c., forming salts called acetates, which are all soluble in water, and may, therefore, be readily washed out of the soil or of compost heaps by heavy falls of rain. 122 PREPARATION OF ACETIC ACID. When perfectly free from water, acetic acid consists ofCarbon... 47'5 per cent., or 4 atoms Hydrogen.. 58 " or3 Oxygen... 46-7 " or 3 100 It is therefore represented by the formula C4 H3 03-in which, as in those given in the preceding sections for starch, sugar, &c., the numbers representing the atoms of hydrogen and oxygen are equal, and consequently these elements are in the proportion to form water. Hence, vinegar, like sugar, may be represented by carbon and water. Let us consider for a moment the several processes by which this acid is usually formed. 1~. By the distillation of wood.-This a method by which wood vinegar-often called pyroligneous acid-is prepared in large quantity. Wood which has been dried in the air is put into an iron retort and distilled. The principal products are vinegar, water, and tarry matter. The decomposition is of a complicated description, but by comparing the constitution of woody fibre with that of vinegar, we can readily see the nature of the changes by which the latter is produced. WOODY FIBRE is = Cl H8 O0 3 of VINEGAR are = C12 H9 O0 Difference = H, O; or the elements of one atom of water. One portion of the woody fibre, therefore, combines with the elements of an atom of water, obtained by the decomposition of another portion, and thus vinegar is produced. 2~. Manufacture of Vinegarfrom Cane Sugar.-It is a well known fact in domestic economy, that if cane sugar be dissolved in water, a little vinegar added to it, and the solution kept for a length of time at a moderate temperature, the whole will be converted into vinegar without any sensible fermentation. This process is frequently followed in the preparation of household vinegar, and wasformerly adopted to some extent in our chemical manufactories. It will be recollected that we re. presented CANE SUGAR by C12 Hio 0o0, while 3 of VINEGAR = C12 Hg O0 Difference H1 0; or the elements of an atom of water, which cane sugar must lose in order to be converted into vinegar. Whether the change in this instance takes place by the direct conversion of cane sugar into vinegar, or whether the former is previously transformed into grape sugar, has not been satisfactorily determined. 3~. Manufacture of Vinegar from Alcohol.-In Germany, where common brandy is cheaper than vinegar, it is found profitable to manufacture this acid from weak spirit. For this purpose it is mixed with a little yeast, and then allowed to trickle over wood shavings moistened with vinegar, and contained in a cask, the sides of which are perforated with holes for the admission of a current of air. By this method oxygen is absorbed from the air, and in 24 hours the alcohol in the spirit is converted into vinegar and -rater. TARTARIC ACID IN THE GRAPE. 123 The explanation of this process is also simple, alcohol being represented by C4 HI O0. ThusALCOHOL = C4 H6 o0 ) 2 VINEGAR C 4 H3 03 4 of OXYGEN 04 I, WAT H3 f WATER 03 Sum C4 H6 06 J t Sum = C4 Ho 0O 4~. Production of Vinegar by fermentatidn.-WVhen vegetable matters are allowed to ferment, carbonic acid is given off and vinegar is formed. In such.cases this acid is the result of a series of changes, during which that portion of the vegetable matter which has at length reached the state of vinegar has most probably passed through the several previous stages of grape, sugar, and alcohol. The carbonic acid, as has already been explained (p. 115), is given off during the fermentation of the grape sugar, and the consequent formation of alcohol. To simple transformations, similar to those above described, we can trace the origin of the vinegar which is met with in the living juices of plants, and among the products of their decay. I. —TARTARIC ACID. The grape and the tamarind owe their sourness to a peculiar acid to which the name of tartaric acid has been given. It is also present, along with other acids, in the mulberry, in the berries of the sumach (rhus coriarii), and in the sorrels, and has been extracted from the roots of the couch-grass and the dandelion. When new wine is decanted from the lees, and set aside in vats or casks, it gradually deposits a hard crust or tartar on the sidesof the vessels. This substance is known in commerce by the name of argol, and when purified is familiar to you as the cream of tartar of the shops. It is a compound of tartaric acid with potash, and from it tartaric acid is extracted for use in medicine and in the arts. The principal use of the acid is in certain processes of the calico printers. The pure acid is sold either in the form of a white powder or of transparent crystals, which are colourless, and have an agreeable acid taste. It dissolves readily in water, and causes a violent effervescence when mixed with a solution of the carbonate of potash or of soda. As it has no injurious action upon the system, it is extensively used in artificial soda powders and effervescing draughts. When added in sufficient quantity to a solution containing potash, it causes a white crystalline powder to fall, which is cream of tartar (or bitartrate of potash), and from lime water it throws down a white chalky precipitate of tartrate of lime. Both of these compounds are present in the grape. When perfectly free from water this acid consists ofCarbon... = 36-81 or 4 atoms. Hydrogen.. = 300 or 2 atoms. Oxygen... = 6019 or 5 atoms. 100 It is therefore represented by the formula C4 H2 05. If we compare the numbers by which the atoms of hydrogen and oxygen in this acid are expressed, we see that these elements are not in the proportion to form water, and that this substance, therefore, cannot, like 124 CONSTITUTION OF TARTARIC AND CITRIC ACIDS. so many of those we have hitherto had occasion to notice, be represented by carbon and the elements of water alone. It may be represented by 4 of CARBON.. = C 4 2 of WATER.. = 02 H O or, 4C+2H+30 and 3 of OXYGEN.. = 03) TARTARIC ACID = C4 HIs 05 And, though this mode of representation does not truly exhibit the constitution of the acid, inasmuch as we have no reason to believe that it really contains water as such-yet it serves to show very clearly that in the living plant this acid cannot be formed directly from carbon and the elements of water, as starch and sugar may, but that it requires also three atoms of oxygen in excess to every five of carbon and two of water. We shall, in the following lecture, see how nicely the functions of the several parts of the plant are adjusted,-at one period to the formation of this acid, and at another to its conversion into sugar during the ripening of the fruit. III. —CITRIC ACID, OR ACID OF LEMONS. This acid gives their sourness to the lemon, the lime, the orange, the cranberry, the red whortleberry, the bird-cherry, and the fruits of the dog-rose and the woody night-shade. It is also found in some roots, as in those of the dahlia pinnata, and the asarum europaum (asarrabacca), and mixed with much malic acid, in the currant, cherry, gooseberry, raspberry, strawberry, common whortleberry, and the fruit of the hawthorn. When extracted from the juice of the lemon or lime, and afterwards purified, it forms transparent colourless crystals, possessed of an agreeable acid taste; effervesces like tartaric acid with carbonate of soda, and like it, therefore, is much employed for effervescing draughts. With potash it forms a soluble salt, which is a citrate of potash, and from lime water it throws down a white, nearly insoluble, sediment of citrate of lime, which re-dissolves when the acid is added in excess. In combination with lime it exists in the tubers, and with potash in the roots, of the Jerusalem artichoke. When free from water, citric acid consists of Carbon... 4149 - 4 atoms. Hydrogen... 343 = 2 atoms. Oxygen... 55'08 4 atoms. 100 and is therefore represented by C4 H1 04. This formula differs from that assigned to the tartaric acid only in containing one atom of oxygen less, 04 instead of O5. In the citric acid, therefore, there are 2 atoms of oxygen in excess, above what is necessary to form water with the 2 of hydrogen it contains. IV.-MALIC ACID. The malic and oxalic acids are more extensively diffused in living plants than any other vegetable acids, If acetic acid be more largely CONSTITUTION OF MALIC AND OXALIC ACIDS. 125 formed in nature, it is chiefly as a product of the decomposition of organic matter, when it has already ceased to exist in, or to form part of, a living plant. Along with the citric acid, it has been already stated that the malic occurs in many fruits. It is found more abundantly, however, and is the chief cause of the sour taste, in the unripe apple, [hence its name malic acid,] the plum, the sloe, the elderberry, the barberry, the fruit of the mountain ash, and many others. It is associated with the tartaric acid in the grape and in the Agave americana. This acid is not used in the arts or in medicine, and therefore is not usually sold in the shops. It is obtained most readily, in a pure state, from.the berries of the mountain ash. It forms colourless crystals, which have an agreeable acid taste. It combines with potash, soda, lime, and magnesia, and forms malates, and, in combination with one or more of these bases, it usually occurs in the fruits and juices of plants. The malate of lime is soluble, while the citrate, as already stated, is nearly insoluble, in water. This malate exists in large quantity in the juice of the house-leek (sempervivum tectorum), in the Sedum telephium, the Arum maculatum, and many other juicy and fleshy-leaved plants. When perfectly free from water, the malic acid has exactly the same chemical constitution as the citric, and is represented by the same formula C4 H2 04. These two acids, therefore, bear the same relation to each other as we have seen that starch, gum, and sugar do. They are what chemists call isomeric, or are isomeric bodies. We cannot transform them, however, the one into the other, by any known means, though there is every reason to believe that they may undergo such transformations in the interior of living plants. Hence probably one reason also why the malic and citric acids occur associated together in so many different fruits. V.-OXALIC ACID. This acid has already been treated of, and its properties and composition detailed, in a preceding lecture (Lecture III., p. 47). It forms colourless transparent crystals, having an agreeably acid taste, and it effervesces with the carbonates of potash and soda, but on account of its poisonous qualities, it is unsafe to administer it as a medicine. It occurs in combination with potash in the sorrels, in rhubarb, and in the juices of many lichens. Those lichens which incrust the sides of rocks and trees, not unfrequently contain half their weight of this acid in combination with lime. It can be formed artificially by the action of nitric acid on starch, sugar, gum, and many other organic substances. When perfectly free from water, oxalic acid contains no hydrogen; but consists ofCarbon... 33-75 - 2 atoms Oxygen... 6625= 3 " 100 and it is represented by C2 O3. When heated with strong sulphuric acid, it is decomposed and resolved into gaseous carbonic acid (CO,) and carbonic oxide (CO) in equal volumes. This change is easily understood since CO, - CO = C o 03. 6* 126 STARCH CONVERTED INTO WOODY FIBRE. ~ 10. General observations on the substances of which plants chiefly consist. It may be useful here shortly to review the most important facts and conclusions which have been adverted to in the present lecture. 1~. The great bulk of plants consists of a series of substances capable of being represented by, and consequently of being formed in nature from, carbon and the elements of water only. Such are woody fibre, starch, gum, and the several varieties of sugar (p. 111). 2~. Yet the crude mass of wood, as it exists in a full-grown tree, containing various substances in its pores, cannot be represented by carbon and the elements of water alone. It appears always to contain a small excess of hydrogen, which is greater in some trees than in others. Thus in the chesnut and the lime, this excess is greater than in the pines, while in the latter it is greater than in the oak and the ash. [For a series of analyses of different kinds of wood by Peterson and Schodler, see Thomson's Organic Chemistry, p. 849.] 3~. These substances are, in many cases, mutually convertible even in our hands. They are probably, therefore, still more so in nature. It is to be observed, however, that all the transformations we can as yet effect are in one direction only. We can produce the above compounds from each other in the order of lignin or starch, gum, cane sugar, grape sugar-that is, we can convert starch into gum, and gum into sugar, but we cannot reverse the process, so as to form cane from grape sugar, or starch from gum. The only apparent exception to this statement with which we are at present acquainted, occurs in the case of starch. When this substance is dissolved in cold concentrated nitric acid, and then mixed largely with water, a substance [the Xyloidin of Braconnot] falls to the bottom, which is a compound of the nitric acid with woody fibre (C, HS O3.) [Pelouze, see Berzelius Arsberdttelse, 1839, p. 416.] In this instance, if the above observation is correct, there appears to be an actual conversion of starch into woody fibre. But what we are as yet unable to perform may, nevertheless, be easily and constantly effected in the living plant. Not only may what is starch in one part of the tree be transformed and conveyed to another part in the form of sugar,-but that which, in the form of sugar or gum, passes ppwards or downwards with the circulating sap, may, by the instrumentality of the vital processes, be deposited in the stem in the form of wood, or in the ear in that of starch. Indeed we know that such actually does take place, and that we are still, therefore, very far from being able to imitate nature in her power of transforming even this one group of substances only. 4~. Among, or in connection with, the great masses of vegetable matter which consist mainly of the above substances, we have had occasion to notice a few which contain nitrogen as one of their constituents-and which, though forming only a small fraction of the products of vegetable growth, yet appear to exercise a most important influence in the general economy of animal as well as vegetable life. The functions performed by diastase in reference to vegetable growth, and to the transformations of organized vegetable substances, have already been in some measure illustrated,-we shall hereafter have an opportunity of considering more IMPORTANCE OF THE VEGETABLE ACID, 127 fully t.;e influence which gluten and vegetable albumen exercise over the general efficiency of the products of vegetation in the support of animal life, and over the changes which these products must undergo, before they can be converted into the substance of animal bodies. In a former lecture (Lecture IV., p. 66), I have had occasion to draw your attention to the comparatively small proportion in which nitrogen exists in the vegetable kingdom, and to show that it must nevertheless be considered as much a necessary and constituent element in their composition as the carbon itself; the very remarkable properties we have already discovered in the compounds above mentioned strongly confirm this fact, and illustrate in a striking manner the influence of apparently feeble and inadequate causes in producing important natural results. 50. With the exception of acetic acid, which in constitution is closely related to sugar* and gum, all the acid substances to which it has been necessary to advert, contain an excess of oxygen above what is necessary to form water with the hydrogen they contain. Thus VINEGAR = C4 H 3 03 contains no excess of oxygen. TARTAkIC ACID C4 H2 05 3 of oxygen it excess. MALIC ACID I _ H O 2 CITRIC ACID C4 I2 04 * OXALIC ACID C2 0C 3.~ 3 It requires a little consideration to enable us to appreciate the true importance of these and other organic acids, in the vegetable economy. At first sight they appear to form a much smaller part of the general products of vegetation than is really the case. We must endeavour to conceive the quantity actually produced by a single tree loaded with thousands of lemons, oranges, or apples,-or again, how mruchl is formed during the growth of a single comparatively small plant of garden rhubarb in spring, if we would obtain an adequate idea of the extent to which these acids are constantly formed in nature. On the other hand, we must recollect also that the greater portion of the acid of fruits disappears as they ripen, if we would understand the true nature of the interest which really attaches to the study of these substances, of the changes to which they are liable, and of the circumstances under which in nature these changes take place. 6~. I will venture here to draw your attention for a moment to the nature and extent of that remarkable power over matter, which the chemist, as above explained, appears to possess. Such a consideration will be of value not only in illustrating how far we really can now, or may hereafter, expect to be able to influence or control natural operations, [see Lecture Il., p. 32,] but what is probably of more value still, exhibiting the true relation which man bears to the other parts of creation; and, in some measure, the true position he is intended to occupy among them. 1~. We have seen that the chemist can transform certain substances one into the other, in a known order; but that as yet he cannot reverse that order. Thus far his power over matter is at present limited; but this limit he may at some future period be able to overpass, and we' It is identical-in constitution with caramel (p. 114) —the uncrystallizable sugar of syrups. For Vinegar. Caramel. (C4 H3 C3 X 3) = Cl2 H9 09. 128 POWER OF THE CHIEMIST OVER MATTER. know not how far. The discovery of a new agent, or of a new mode of treatment, may enable him to accomplish what he has not as yet the means or the skill to perform. 2~. He has it in his power to form, actually to produce, some of the organic or organized substances which occu. in living plants. He can form gum, and grape sugar, in any quantity. Thus far he can imitate and take the place of the living principle it self. Numerous other cases are known, in,vhich he displays a similar power. By the action of nitric acid upon tarch or sugar, [see Lecture III., p. 47,] he can form oxalic acid, which as has already been shown, occurs very largely in the vegetable kingd )m. By the action of heat upon citric acid, he can decompose it ani produce an acid which is met with in the Wolfsbane (Aconitum napellus), and hence is called aconitic acid.* Also by the action of sulphuric acid he can change salicine and phlorizine-substances extracted respectively from the bark ofthe willow and from that of the root of the apple tree-into a resinous matter and grape sugar. So., of the compounds which are found in the solids and fluids of animal bodies, there are some which he has also succeeded in forming by the aid of his chemical artElated by such achievements, some chemists appear willing to hope that all nature is to be subjected to their dominion, and that they may hereafter be able to rival the living principle in all its operations. It is true that what we now know, and can accomplish, are but the beginnings of what we may fairly expect hereafter to effect. But it is of consequence to bear in mind the true position in which we now stand, and the true direction in which all we at present know seems to indicate that our future advances in knowledge, and in control over nature, are likely to proceed. And this leads me to observe3~. That our dominion is at present limited solely to transforming and decomposing. We can transborm woody fibre into gum or sugarwe cannot form either gum or sugar by the direct union of their elements. We can resolve salicine by the acid of sulphuric acid into resin and grape sugar; but we cannot cause the elements of which they consist to unite together in our hands, so as to form any one of the three. We cannot even cause the resin and the sugar to re-unite and rebuild the salicine from which they were derived. So we can by heat drive off the elements of water from the citric and cause the aconitic acid to. appear; but we cannot persuade the unwilling compounds, when thus separated, to return to their former condition of citric acid; and, if we could, we should still be as far removed from the power of commanding or compelling the direct union of carbon, hydrogen, and oxygen, in such proportions, and in such a way, as to build up either of the two acids in question. Again, we can actually form oxalic acid by the action of nitric acid'These two acids differ from each other only ly the elements of an atom of water. Thus Citric Acid.. = 1 C1 04 Aconitic Acid. C 4 Hi 03 Difference.. = HI 0 or, one ofwater. Tt is easy to see, therefore, how, by the evolution of the elements of an atom of water, the one acml I m^ he change(d into the other. The scientific reader will excuse me (if on the grounds of simplicity alone) for representing, both here and in the text, the citric acid by C H2 Oi0, instead ofby Ci2 H3 0i + 3tfO, which:,iebig and his pupils prefer. TRUE PROSPECTS OF CHEMICAL SCIENCE. 129 upon starch, or wood, or sugar, or any other of a great variety of vegetable substances-but we cannot prepare it by the direct union of its elements. We can only as yet procure it from substances which have already been organized-which have been themselves produced by the agency of the living principle. The same remarks apply with slight alteration to those substances of animal origin to which I have above alluded as being within the power of the chemist to produce at will. There is hardly an exception to the rule, that in producing organic substances, as they are called, the chemist must employ other organic substances which are as yet beyond his art-which, so far as we know, can only be formed under the direction of the living principle. Thus the sum of the chemist's power in imitating organic nature consists, at present, in his ability10. To transform one substance found only in the organic kingdom into some other substances, produced more or less abundantly in the same- kingdom of nature. This power he exercises when he converts starch intosugar, or fibrin into albumen or casein. 2~. To resolve a more complex or compound substance into two or more which are less so, and of which less complex substances some may be known to occur in vegetable or animal bodies. 3~. To decompose organic compounds by means of his chemical agents, and as the result of such decompositions to arrive at one or more compounds, such as are formed under the direction of the living principle. In no one case-can he form the substances of which' animals and plants chiefly consist, out of those on which' animals and plants chiefly live. But this is the common and every-day result of the agency of the living principle. Is there as yet, then, any hope that the chemical laboratory shall supersede the vascular system of animals and plants; or that the skill of the chemist who guides the operations within it, shall ever rival that of the principle of life which presides over the chemical changes that take place in animal and vegetable bodies? The true place, therefore, of human skill-the true prospects of chemical science-are pointed out by these considerations. No science has accumulated so many and such various treasures as chemistry has done during the last 20 years-none is at present so widely extending the bounds of our knowledge at this moment as the branch of organic chemistry-men may therefore be excused for entertaining more sanguine expectations from the progress of a favourite science than sober reasoning would warrant. Yet it is of importance, I think, and especially in a moral point of view, that amid all our ardour, we should entertain clear and just notions of the kind and extent of knowledge to which we are likely to attain, and-as knowledge in chemistry is really power over matter-to what extent this power is likely ever to be carried. At present, if we judge from our actual knowledge, and not from our hopes-there is no prospect of our ever being able to imitate or rival living nature in actually compounding from their elements her numeroqs and varied productions. That we may clearly understand, and be able to explain many of her operations, and even to aid her in effecting them, is no way inconsistent with an inability to imitate her by the resopurces of art. This will, I trust, appear more distinctly in the subsequent lectur.e, LECTURE VII. Chemical changes by which the substances of which plants chiefly consist are formed from those on which they live.-Changes during germination-during the growth of the plantduring the ripening of fruit.-Autumnal changes. HAVING thus considered the nature and chemical constitution of those substances which constitute by far the largest part of the solids and fluids of living vegetables, we are now prepared for the further question -by what chemical changes these substances of which plants consist, are formed out of those on which they live? The growth of a plant from the germination of the seed in spring till the fall of the leaf in autumn, or the return of the succeeding springtime, may in perennial plants be divided into four periods-during which they either live on different food, or expend their main strength in the production of different substances. These periods may be distinguished as follows: 1~. The period of germination-from the sprouting of the seed to the formation of the perfect leaf and root. 2~. From the expansion of the first true leaves to the period of flowering. 3~. From the opening of the flower to the ripening of the fruit and seed. 4~. From the ripening of the seed or fruit, till the fall of the leaf and the subsequent return of spring. On the ripening of the fruit the functions of annual plants are in general discharged, and they die; but perennial plants have still important duties to perform in order to prepare them for the growth of the following spring. The explanation of the chemical changes to which our attention is to be directed will be more clear, and perhaps more simple, if we consider them in relation to these several periods of growth. ~ 1. Chemical changes which take place during germination and during the development of the first leaves and roots. The general nature of the chemical changes which take place during germination is simple and easy to be comprehended. Let us first consider shortly the phenomena which have been observed to accompany germination, and the circumstances which are most favourable to its rapid and healthy progress. 1~. Before a seed will begin to sprout, it must be placed for a time in a sufficiently moist situation. We have already seen how numerous and important are the functions which water performs in reference to vegetable life (Lecture II., p. 36,) in every stage of a plant's growth. In the seed no circulation can take place-no motion among the particles of matter-until water has beer largely imbibed; nor can the food be conveyed through the growing vessels, unless a constant supply of fluid be afforded to the seed and its infant roots. 2~. A certain degree of warmth-a slight elevation of temperature — is also favourable, and in most cases necessary, to germination. EFFECT OF AIR AND LIGHT ON GERMINATION. 131 The degree of warmth which is required in order that seeds may begill to grow, varies with the nature of the seed itself. In Northern Siberia and other icy countries, plants are observed to spring up at a temperature but slightly raised above the freezing point (32~ F.,) but it is familiar to every practical agriculturist, that the seeds he yearly consigns to the soil require to be protected from the inclemency of the weather, and sprout most quickly when they are stimulated by the warmth of approaching spring, or by the heat of a summer's sun. The same fact is familiarly shown in the malting of barley, where large heaps of grain are moistened in a warm atmosphere. When germination commences, the grain heats spontaneously, and the growth increases in rapidity as the heap of corn attains a higher temperature. It thus appears that some portion of that heat which the growth of the germ and radicles requires, is provided by natural processes in the grain itself; in some such way as, in the bodies of animals, a constant supply of heat is kept up by the vital processes-by which supply the cooling effect of the surrounding air is continually counteracted. We have seen in the preceding lecture, that the transformations of which starch and gum are susceptible, take place with greater certainty and rapidity under the influence of an elevated temperature. It will presently appear that such transformations are also affected during germination; there is reason, therefore, to believe that the external warmth which is required in order that germination may begin, as well as the internal heat naturally developed as germination advances, are both employed in effecting these transformations. And, as the young sprout shoots more rapidly under the influence of a tropical sun, it is probable that those natural agencies in general, by which such chemical transformations are most rapidly promoted, are also those by which the progress of vegetation is in the greatest degree hastened and promoted. 3~. It has been observed that seeds refuse to germinate if they are entirely excluded from the air. Hence seeds which are buried beneath such a depth of soil that the atmospheric air cannot reach them, will remain long unchanged, evincing no signs of life-and yet, when turned up or brought near the surface, will speedily begin to sprout. Thus in trenching the land, or in digging deep ditches and drains, the farmer is often surprised to find the earth, thrown up from a depth of many feet, become covered with young plants, of species long extirpated from or but rarely seen in his cultivated fields. 4~. Yet light is, generally speaking, prejudicial to germination. Hence the necessity of covering the seed, when sown in our gardens and corn fields, and yet of not so far burying it that the air shall be excluded. In the usual method of sowing broad-cast, much of the grain, even after harrowing, remains uncovered; and the prejudicial influence of light in preventing the healthful germination of such seeds is no doubt one reason why, by the method of dibbling, fewer seeds are observed to fail, and an equal return of corn is obtained from a much smaller expenditure of seed. The reason why light is prejudicial to germination, as well as why the presence of atmospheric air is necessary, will appear from the following observation:5~. When seeds are made to germinate in a limited portion of atmos 132 SEEDS SPROUT ONLY IN THE PRESENCE OF OXYGEN. pheric air, the bulk of the air undergoes no material alteration, but on examination its oxygen is found to have diminished, and carbonic acid to have taken its place. Therefore, during germination, seeds absorb oxygen gas and give off carbonic acid. Hence it is easy to understand why the presence of air is necessary to germination, and why seeds refuse to sprout in hydrogen, nitrogen, or carbonic acid gases. They cannot sprout unless oxygen be within their reach. We have seen also in a previous lecture that the leaves of plants in the sunshine give off oxygen gas and absorb carbonic acid,-while in the dark the reverse takes place. So it is with seeds which have begun to germinate. When exposed to the light they give off oxygen instead of carbonic acid, and thus the natural process is reversed. But it is necessary to the growth of the young germ, that oxygen should be absorbed, and carbonic acid given of-and as this can take place to the required extent only in the dark, the cause of the prejudicial action of light is sufficiently apparent as well as the propriety of covering the seed with a thin layer of soil. 6~. During germination, vinegar (acetic acid) and diastase are produced. That such is the case in regard to the latter substance, has been proved in the previous lecture, (p. 118.) That acetic acid is formed is shown by causing seeds to germinate in powdered chalk or carbonate of lime, when after a time acetate of lime* may be washed out from the chalk (Braconnot) in which they have been made to grow. The acid contained in this acetate must have been formed in the seed, and after, wards excreted or thrown out into the soil. 7~. When the germ has shot out from the seed and attained to a sensible length, it is found to be possessed of a sweet taste. This taste is owing to the presence of grape sugar in the sap which has already begun to circulate through its vessels. It has not been clearly ascertained whether the vinegar or the diastase is first produced when germination commences, but there seems little doubt that the grape sugar is formed subsequently to the appearance of both. 8~. The young shoot which rises upwards from the seed consists of a mass of vessels, which gradually increase in length, and after a short time expand into the first true leaves. The vessels of this first shoot do not consist of unmixed woody fibre. It is even said that no true wood is formed till the first true leaves are developed.-[Lindley's Theory of Horticulture.] The vessels of the young sprout, therefore, and of the early radicles, probably consist of the cellularfibre of Payen. They are unquestionably formed of a substance which is in a state of transition between starch or sugar and woody fibre, and which has a constitution analogousf to that of both. Having thus glanced at the phenomena which attend upon germination, let us now consider the chemical changes by which these phenomena are accompanied. 1~. The seed absorbs oxygen and gives off carbonic acid. We have Acetate of lime is a compound of acetic acid (vinegar) and lime, and may be prepared by dissolving chalk in vinegar. It is very soluble in water. t By analogous I mean which may be represented by carbon and wa'er. HOW AND WHY VINEGAR IS FORMED. 133 already seen that the starch of the seed (C.12 HIo Oo,) may be represented by carbon and water,-by 12C + 10HO. Now it appears that in contact with the oxygen of the atmosphere, a portion of the starch is actually separated into carbon and water, the carbon at the moment of separation uniting with the oxygen, and forming carbonic acid (CO2). This acid is given off into the soil in the form of gas, and thence partially escapes into the air; but for what immediate purpose it is evolved, or how its formation is connected with the further development of the germ, has not hitherto been explained. 2~. The formation of acetic acid (vinegar) from the starch of the grain is also easy to comprehend. For, as we have already seen, STARCH... C12 H 0 010 3 of VINEGAR.. = C12H9 09 Difference - Hi 0O; or the elements of an atom of water. Therefore, in this early stage of the growth of the germ a portion of the starch is deprived of the elements of an atom of water, and at the same time transformed into vinegar. Why is this vinegar formed? It is almost as difficult to answer this question as to say why carbonic acid is evolved from the seed, though both undoubtedly serve wise and useful ends. It has been explained in the preceding lecture how the action of dilute acids gradually changes starch into cane sugar, and the latter into grape sugar. While it remains in the sap of the sprouting seed, the vinegar may aid the diastase in transforming the insoluble starch into soluble food for the plant, and may be an instrument in securing the conversion of the cane sugar, which is the first formed, into grape sugar,-since cane sugar cannot long exist in the presence of an acid. After the acetic acid is rejected by the plant, it may act as a solvent on the lime and other earthy matters contained in the soil. Liebig supposes the especial function of this acid-the reason why it is formed in the germ and excreted into the soil-to be, to dissolve the lime, &c., which the soil contains, and to return into the pores of the roots, bearing in solution the earthy substances which the plant requires for its healthy growth. This is by no means an unlikely function. It is only conjectural, however, and since the experiments of Braconnot have shown that acetate of lime, even in small quantity, may be injurious to vegetation, it becomes more doubtful how far the formation of this compound in the soil, and the subsequent conveyance of it into the circulation of the plant, can be regarded as the special purpose for which acetic acid is so generally produced during germination. 3~. The early sap of the young shoot is sweet; it contains grape sugar. This sugar is also derived from the starch of the seed. Being rendered soluble by the diastase formed at the base of the germ, the starch is gradually converted into grape sugar as it ascends. The relation between these two compounds has been already pointed out. STARCH..=. C,2 H10 010 GRAPE SUGAR... = H,1 O01 Difference.... H2 O0; or the elements of two atoms of water. The water which is imbibed by the seed 134 HOW THE SUGAR IS FORMED IN THE SPROUT. from the soil, forms an abundant source from which the whole of the starch, rendered soluble by the diastase, can be supplied with the elements of the two atoms of water which are necessary to its subsequent conversion into grape sugar 4~. The diastase is formed when the seed begins to sprout, at the expense of the gluten or vegetable albumen of the seed, but as its true constitution is not yet known, we cannot explain the exact chemical changes by which its production is effected. 5~. When the true. leaf becomes expanded, true wood first appears in sensible quantity. By what action of the sun's rays upon the leaf the sugar already in solution in the sap is converted into woody fibre, we cannot explain. The conversion itself is in appearance simple enough, since GRAPE SUGAR.. =C11 H 012, and WOODY FIBRE.. = C12 118 08 Difference.... H4 04; or the former must part with the elements of four atoms of water only, to be prepared for its change into the latter. But the true nature of the molecular* change by which this transformation is brought about, as well as the causes which lead to it and the immediate instruments by which it is effected, are all still mysterious. ~2. Of the chemical changes which take place from the formation of the true leaf to the expansion of the flower. When the true leaf is formed the plant has entered upon a new stage of its existence. Up to this time it is nourished almost solely by the food contained in the seed,-it henceforth derives its sustenance from the air and from the soil. The apparent mode of growth is-the same, the stem shoots upwards, the roots descend, and they consist essentially of the same chemical substances, but they are no longer formed at the expense of the starch of the seed, and the chemical changes of which they are the result are entirely different. 1~. The leaf absorbs carbonic acid in the sunshine, and gives off oxygen in equal bulk.f It is in the light of the sun that plants increase in size-their growth, therefore, is intimately connected with this absorption of carbonic acid. If carbonic acid be absorbed by the leaf and the whole of its oxygen given off again,. carbon alone is added to the plant by this function of the leaf. But it is added in the presence of the water of the sap, and thus is enabled by uniting with it to form, as it may be directed, or as may be necessary, any one of those numerous compounds which may * All bodies are supposed to consist of particles or molecules of exceeding minuteness, and all chemical changes which take place in the same mass of matter are supposed to be owing to the different ways in which these particles arrange themselves. We may form a remote idea of the way in which different positions of the same particles may produce different substances, by considering how different figures in Mosaic may be produced by different arrangements of the same number of equal and similar frawgments of various colours. t Such is sensibly the result of experiment. How far this result can be considered as universally true, will be examined hereafter t It will be recollected that carbonic acid contains its own bulk of oxygen gas: if, therefere, the leafgive off the same bulk of oxygen as it absorbs of carbonic acid, the result must ba as stated in the text. HOW PLANTS ARE NOURISHED BY CARBONIC ACID? 135 be represented by carbon and water, (p. 111,) and of which, as we have seen, the solid parts of plants are chiefly made up. There are two ways in which we may suppose the oxygen given off by the leaf to be set free, and the starch, sugar, and gum, to be subsequently formed. A. The action of light on the leaf of tie plant may directly decompose the carbonic acid after it has been absorbed, and cause the oxyen to separate from the carbon, and escape into the air;-while at the same instant the carbon thus set free, may unite with the water of the sap in different proportions, so as to produce either sugar, gum, or starch. Suppose 12 atoms of carbonic acid (12 CO2) to be thus decomposed, and their carbon to unite with 10 of water (10 HO), we should have from 12 of CARBONIC ACID. = C12 which united to 10 of W\ATER... HO O10 would give 1 of GuM or of CANE SUGAR C12 H10 010 while 24 of oxygen would be given off; the whole of which would have been derived from the carbonic acid absorbed by the plant. B. Or the action of the sun's rays may be directed, in the leaf, to the decomposition, not of carbonic acid, but of the water of the sap. The oxygen of the water may be separated from the hydrogen, while at the same instant the latter element (hydrogen) may unite with the carbonic acid to produce the sugar or starch. The result here is the same as before, but the mode in which it is brought about is very differently represented, and appears much more complicated. Thus, suppose 24 of water (24 HO) to be decomposed, and to give off their oxygen into the air, 24 of oxygen would be evolved as in the former case, the whole of which would be derived from the decomposition of water, while there would remain 24 of HYDROGEN.. = t;4 Let this act on 12 of CARBONIC ACID = C 024 and we have as the result.... C1 H24 024; Starch, &c. Water. or C12 H,1 Oio0 + 14 HO. According to this mode of representing the chemical changes, water is first decomposed and its oxygen evolved, then its hydrogen again combines with the carbon and oxygen of the carbonic acid, and forming two products-water and sugar or starch. This view is not only more complicated, but it supposes the same action of light to be-continually, at the same time, and in the same circumstances-both decomposing water and re-forming it from its elements. While, therefore, there can be no doubt, for other reasons not necessary to be stated in this place, that the light of the sun really does decompose water in the leaves of plants, and more in some than in others-yet it appears probable that the oxygen evolved by the leaf is derived in a great measure from the carbonic acid which is absorbed; and that the principal part of the solid substance of living vegetables, in so far at least as it is derived from the air, is produced by the union of the'carbon of this acid with the elements of the water in the sap.* I ought not to pass unnoticed the opin.on of Persoz (Chemie Moleculaire), that the starch, gum, &c., of plants are formed by the union of carbonic oxide (CO) with he neces 136 IS CARBONIC ACID ABSORBED FROM THE SOIL? We have seen reason to conclude (p. 63) that, while plants derive much of their sustenance from the air, they are also fed more or less abundantly by the soil in which they grow. From this soil they obtain through their roots the carbonic acid which is continually given off by the decaying vegetable matter it contains. This carbonic acid will ascend to the leaf, and will there undergo decomposition along with that which is absorbed by the leaf itself. At least we know of no function of the root or stem by which the carbonic acid derived from the soil can be decomposed and deprived of its oxygen before it reaches the leaf. It is distinctly stated, indeed, by Sprengel, [see above, p. 92,] that when the roots of a plant are in the presence of carbonic acid, the oxygen given off by the leaf is greater in bulk than the carbonic acid absorbed. But there is one observation in connection with this point which it seems to me of importance to make. The leaves supply carbon to the plant only in the form of carbonic acid, and they give off a bulk of oxygen gas not exceeding that of the acid taken in, [see note, below.] But if the carbon derived from the soil be also absorbed in the form of carbonic acid, and if the oxygen contained in this portion of acid is also given off by the leaf-either the quantity drawn from the soil must be small, compared with that inhaled from the air, or the oxygen given off by the leaf must, in the ordinary course of vegetation, be sensibly greater than the bulk of the carbonic acid which it absorbs. We are too little familiar with the chemical functions of the several parts of plants to be able to pronounce a decided opinion on this point; but it appears evident that one or other of the three following conditions must obtain:(a). Either in the general vegetation of the globe the bulk of the oxygen gas given off by the leaf during the day must always be considerably greater than that of the carbonic acid absorbed by it; or (b). The root or stem must have the power of decomposing carbonic acid and of separating and setting free its oxygen; or (c). The plant can derive no considerable portion of its carbon from the soil, in the form of carbonic acid. If the experiments hitherto made by the vegetable physiologists be considered of so decisive a character as to warrant us in rejecting the two former conditions, the third becomes also untenable. sary proportions of oxygen and hydrogen derived from the water of the sap. This opinion implies that, in the leaf, carbonic acid (CO2 ) is decomposed into carbonic oxide and oxygen (CO + 0), and that water likewise is decomposed,-the oxygen produced by both decompositions being given off either into the air by the leaves, or into the soil by the roots. The production of grape sugar, therefore, according to.this hypothesis, would be thus repre sented:- There are retained, and given.off. From 12 of CARBONIC ACID = 2CO2 - - C12 012 O12 From 12 of WATER- - 12HO. -. H12 012 Ct2 H12 O12 04 grape sugar Of the 24 of oxygen thus given off, the opinion of Persoz is, that only one-half is evolved by the leaf,-and the principal fact on which his opinion rests is that observed by De Saussure, that plants of Vinca minor gave off by their leaves, in his experiments, only two-thirds of the oxygen contained in the carbonic acid they absorbed. This result has led Berzelius also to conjecture that the leaves of plants do not retain merely the carbon of the carbonic acid, but some compound of carbon with oxygen, containing much less of this element than the carbonic acid does (Traite de Chemie, V., p. 69). The principal objection to this view, however, is the quantity of oxygen it supposes to be rejected by the root. The experiments on which it is founded require confirmation and extension. HOW SUGAR IS TRANSFORMED INTO STARCH. 137 3~. Without dwelling at present on this point, the above considerations may be regarded as giving additional strength or probability to the conclusions we formerly arrived at (p. 63) from other premises-that the roots, besides carbonic acid, absorb certain other soluble organic compounds, which are always present in the soil in greater or less quantity, and that the plant appropriates and converts these into its own substance. Some of these organic compounds may readily, and by apparently simple changes, be transformed into the starch and woody fibre of the living vegetable. The illustration of this fact will be reserved until, in the second part of these lectures, I come to treat of the vegetable portion of soils, and of the chemical nature and constitution of the organic compounds of which it consists, or to which it is capable of giving rise. 4~. The chemical changes above explained (a), show how, from carbonic acid and the elements of water, substances possessed of the elementary constitution of sugar and gum may, by the natural processes of vegetable life, obtain the elements of which they consist, and in the requisite proportions. They throw no light, however, upon the mechanism by which these elements-are constrained, as it were, to assume first the form of gum or sugar, or soluble starch, and afterwards, in another part of the plant, of insoluble starch and woody fibre. It is known that the sap deposits starch and woody fibre in the stem, only in its descent from the leaf,-and it is, therefore, inferred that the action of light upon the sap, as it passes through the green parts, is necessary to dispose the elements to arrange themselves in the form of vascular fibre or lignin. And as, by the agency of nitric acid, starch appears to be convertible into woody fibre (p. 126), it is not unlikely that the soluble substances, containing nitrogen, which are present in the sap may-as diastase does upon starch-exercise an agency in transforming the soluble sugar, gum, &c., of the sap into the insoluble starch and woody fibre of the seed and the stem. We are here, however, upon uncertain ground, and I refrain from advancing any further conjectures. Two great steps we have now made. We have seen how the germ lives and grows at the expense of the food stored up in the seed-and how, when it has obtained roots and leaves, the plant is enabled to extract from the air and from the soil such materials as, in kind and quantity, are fitted to build up its several parts during its future growth. That considerable obscurity still rests on the details of what takes place in the interior of the plant, does not detract from the value of what we have already been able to ascertain. ~ 3. On the production of oxalic acid in the leaves and stems of plants. In the preceding section we have studied the origin of those substances only which form the chief bulk of the products of vegetation, and which are characterized by a chemical constitution of such a kind as enables them to be represented by carbon and water. But during the stage of vegetable growth we are now considering, other compounds totally diffbrent in their nature are also produced, and in some plants in sufficient quantity to be deserving of a separate consideration. Such is the case with oxalic acid. The circumstances under which this acid occurs in nature have al 138 PRODUCTION i F OXALIC ACID IN PLANTS. ready been detailed. It is found in small quantities in many plants. The potash in forest trees is supposed to be in combination with oxalic acid, while in the lichens oxalate of lime serves a purpose similar to that performed by the woody fibre of the more perfect plant; it forms the skeleton by which the vegetable structure is supported, and through which its vascular system is diffused. The production of this acid in the living plant is readily understood when its chemical constitution (C2 03) is compared with that of carbonic acid (CO2). For 2 of CARBONIC ACID = C2 04 1 of OXALIC ACID = C2 03 Difference.. O That is to say, 2 of carbonic acid are transformed into 1 of oxalic acid by.the loss of 1 equivalent of oxygen-or generally, carbonic acid by the loss of one-fourth of its oxygen may be converted into oxalic acid. But the leaf absorbs carbonic acid and gives off oxygen. In the lichens, therefore, which contain so much oxalic acid, a large portion of the carbonic acid absorbed is, by the action of light, deprived of only one-fourth of its oxygen, and is thus changed into oxalic acid. The same is true to a smaller extent of the sorrel leaves and stems, which owe their sourness to the presence of oxalic acid-of the leaves and stems of rhubarb also-in a still smaller degree of the beech and other large trees, in which much potash, and probably also of marine plants, in which much soda is found to exist. It must be owing to the peculiar structure of the leaves of each genus or natural order of plants, that the same action of the same light decomposes the carbonic acid in different degrees -evolving in some a less proportion of its oxygen, and causing in such plants the formation of a larger quantity of oxalic acid. The fact of the production of this oxalic acid, to a very considerable amount in many plants, is a further proof of the uncertainty of those experiments from which physiologists have concluded that the leaves of plants emit a bulk of oxygen sensibly equal to that of the carbonic acid absorbed.* I have referred the production of more or less oxalic acid in different plants to the special structure of each, and this must be true, where, in the same circumstances, different results of this kind are observed to take place-as where sorrels and sweet clovers grow side by side. Yet the influence of light of different degrees of intensity on the same plant, is beautifully shown by the leaves of the Sempervivum arboreum, of the Portulacaria afra, and other plants which are sour in the morning, tasteless * Were we permitted, in the absence of decisive experiments, to state as true what theo. retical considerations plainly indicate, we should say1~. That plants containing much oxalic or other similar acids, and not deriving much car. bonic acid fron the soil, must give off from their leaves a bulk of oxygen less than that of the carbonic acid absorbed. 2~. That plants containing no sensible quantity of such acids, nor fed by carbonic acid from the soil, may evolve oxygen sensibly equal in bulk to the carbonic acid absorbed. 3~. That if little of these acids be present, and much carbonic acid be absorbed from the soil, the volume of oxygen given off by the green parts of the plant must be sensibly greater thban that of the carbonic acid they absorb. 40. That the leaves of the pines and other trees containing much turpentine-in which hydrogen is in excess-must at all times give off oxygen in greater bulk than the carbonic acid they absorb. They must decompose water as well as carbonic acid, anl evolve the oxygen of both. ACTION OF THE FLOWER LEAVES ON THE AIR. 139 in the middle of the day, and bitter in the evening.-[Sprenge, Chemie, II., p. 321.] During the night the oxygen has accumulated in these plants and formed acids containing oxygen in excess (p. 127.) As the day advances this oxygen is given off; under the influence of light the acids are decomposed, and the sourness disappears. In the juices of plants before the period of flowering, other acids are met with besides the oxalic acid, though in much smaller quantity. As the most important of these, however, occur more abundantly in fruits, we shall consider the theory of their formation in the following section. ~ 4. Of the chemical changes which take place between the opening of the flower and the ripening of thefruit or seed. The opening of the flower is the first and most striking step taken by the plant towards the production of the seed by which its species is to be perpetuated. That at this period a new series of chemical changes commences in the plant is obvious from the following facts:10. That the flower leaves absorb oxygen and emit carbonic acid both by day* and by night (p. 95.) 2~. That they also occasionally emit pure nitrogen gas. 3~. That the juice of the maple ceases to be sweet when the flowers are matured (Liebig,) and that, in the sugar cane and beet root, the sugar becomes less abundant when the plant has begun to blossom. These facts sufficiently indicate the conmencement of new changes in the interior of plants at this period of their growth. That such changes go on until the ripening of the seed is also evident from these further observations:1~. That the husk of the future seed, as in the corn-bearing grasses (wheat, oats, &c.,) is filled at first with a milky liquid, which becomes gradually sweeter and more dense, and finally consolidates into a mixture of starch and gluten, such as is presented by the flour of different species of corn. 2~. That the fruit in which the seeds of many plants is enveloped is at first tasteless, afterwards more or less sour, and finally sweet. In a few fruits only, as in the lime, the lemon, and the tamarind, does a sufficient quantity of acid remain to be sensible to the taste, when the seed has become perfectly ripe. The acid and cellular fibre both diminish while the sugar increases. 30~. That fruits, while green, act upon the air like the green leaves and twigs-but that, as they approach maturity, they also absorb or retain oxygen gas (De Saussure.) The same absorption of oxygen takes place when unripe fruits are plucked and left to ripen in the air (Berard.) After a time the latter also emit carbonic acid. I.-FORMATION OF THE SEED. In the case of wheat, barley, or other plants, which yield farinaceous seeds, we have seen that previous to flowering the chief energy of the living plant is expended in the production of the woody fibre of which its stem and growing branches mainly consist; and we have also been able to understand,'in some degree, how this woody fibre is produced from tihe ordinary food of the plant. When the flower expands, how-' By day the absorption is the greater, but the bulk of the oxygen taken in is always greater than that of the carbonic acid given off. 140 FORMATION OF THE SEED, AND RIPENING OF THE FRUIT. ever, the plant has in general, and especially if an annual plant, reached nearly to maturity, and woody fibre is little required. The most important of its remaining functions is the production of the starch and gluten of the seed, and of the substances which form the husk by which the seed is enveloped. In the first stages of the plant's growth, the starch of the seed is transformed into gum and sugar, and subsequently, when the leaves are expanded, into woody fibre. In the last stages of its existence, when it is producing the seed, the sugar of the sweet and milky sap is gradually transformed into starch-that is to say, a process exactly the converse of the former takes place. We are able, in some measure, to explain the mode and agency by which the former transformation is effected-the latter, however, is still inexplicable. We can ourselves, by the agency of diastase, transform starch into sugar; and, therefore, can readily believe such transformations to be effected in the young plant;-but we as yet know no method of re-converting sugar into starch; and, therefore, we can only hazard conjectures as to the way in which this change is brought about in the interior of the plant during the formation of the seed. It is said that nitrogen is given off by the flower leaf. We know that this element is present in the colouring matter of the petal, and that it is a necessary constituent of the albumen and gluten, which are always associated with the starch of the seed. It is plain, then, that the nitrogeneous substances [substances containing nitrogen,] contained in the sap at all periods of the plant's growth, are carried up in great quantity to the flower and seed vessel. These substances are supposed to be concerned as immediate agents in effecting the transformations which there take place. More than this, however, we cannot as yet venture even to conjecture. Il. —RIPENING OF THE FRUIT. In these plants, again, which invest their seed with a pulpy fruit-in the grape, the lemon, the apple, the plum, &c.-other changes take place, at this period, of a more intelligible kind, and other substances are, formed, on the production of which less obscurity rests. At one stage of their growth, these fruits, as has been already stated, are tasteless-in the next, they are sour-in the third, they are more or less entirely sweet. I. In the tasteless state they consist of little more than the substance of the leaf-of vascular, or woody fibre, filled with a tasteless sap, and tinged with the colouring matter of the green parts of the plant. For a time, this young fruit appears to perform in reference to the atmosphere the usual functions of the leaf-it absorbs carbonic acid and gives off oxygen, and thus extracts from the air a portion of the food by which its growth is promoted, and its size gra(iually increased. II. But after a time tlits fruit becomes sour to the taste, and its acidity gradually increases-while at the same time it is observed to give off a less comparative bulk of oxygen than before. Let us consider shortly the theory of the production of the more abundant vegetable acids contained in fruits. 1~..The tartaric acid which occurs in the grape is represented by C4 H2 O5 (p. 124). There are two ways in which we may suppose this acid to be formed FORMATION OF TARTARIC, DIALIC, AND CITRIC ACIDS. 141 in the fruit-either directly from the elements of carbonic acid and water with the evolution of oxygen gas-or from the gum and sugar already present in the sap aided by the absorption of oxygen from the atmosphere. Thus A. 4 of CARBONIC ACID = C4 0o 2 of WATER o. =- H2 02 - Tartaric Acid. Sum.. =C4 H2 10 or C4 H2 5 + 50. That is, one equivalent of tartaric acid may be formed from 4 of carbonic acid absorbed by the leaf or fruit, and 2 of the water of the sap, while 5 of oxygen are at the same time given off by the leaf. Or, B. If Grape Sugar be C12 H12 O12 of GRAPE SUGAR = C4 H3 03 3 of OXYGEN.. 03 Tartaric Acid. Water. Sum.. =C4 H13 06 or C4 H 05 + HO0 Thet is, by the absorption from the air of a quantity of oxygen equal to that which it already contains, grape sugar may be converted into tartaric acid and water. In the sorrels and other sour-leaved plants, which contain tartaric acid in their general sap, the acid may be formed by either of the processes above explained. In the sunshine their green parts absorb carbonic acid and evolve oxygen. If any of these green parts give off only - of the oxygen contained in the carbonic acid they drink in, tartaric acid may be produced (A.) In the dark they absorb oxygen and give off carbonic acid. If the bulk of this latter gas which escapes be less than that of the oxygen which enters, a portion of the sugar or gum of tie sap may, as above explained (B.), be converted into tartaric acid. We have as yet no experiments which enable us to say by which of these modes the tartaric acid is really produced in such plants-or whether it may not occasionally be compounded by both methods. In green fruits also, in the sour grape for example, it may, in like manner, be produced by either method. The only experiments we yet possess, those of De Saussure, though not sufficient to decide the point, are in favour of the former explanation (A.) In the estimation of this philosopher, the proportion of the oxygen of the carbonic acid which is retained by the fruit, is sufficient to account for the acidity it gradually acquires. 20. Malic and citric acids.-These acids are represented (p. 127) by the common formula C4 H2 04. They may be produced from water and carbonic acid, if three-fourths only of the oxygen of the latter be given off. Thus 4 of CaRBONIC ACID = C4 08 2 of WATER.. = Ha 02 Malit Acid. Sum.. = C4 H2 O0 = C4 H2 04 + 60. That such a retention of one-fourth of the oxygen of the carbonic acid occasionally takes place in the green fruit, is consistent with the observations of De Saussure. The lime and the lemon are fruits on which the most satisfactory experiments might be made with the view of fiDally determining this point. _y detert-nini — --- 1 —`~ 142 CONVERSION OF ACIDS INTO SUGAR. III. This formation of acid proceeds for a certain time, the fruit becoming sourer and sourer; the acidity then begins to diminish, sugar is forned, and the fruit ripens. The acid rarely disappears entirely, even from the sweetest fruits, until they begin to decay; a considerable portion of it, however, must be converted into grape sugar, as the fruit approaches to maturity. This conversion may take place in either of two ways. 1~. By the direct evolution of the excess of oxygen. Thus 3 ofTARTARIC ACID = C12 H6 O5 6 of WATER... = H6 O0 -- ----- Grape Sugar. Sum. = C 1 H, 0, == C12 H12 012 + 90. Or grape sugar may be formed from 3 of tartaric acid and 6 of the water of the sap, by the evolution, at the same time, of 9 of oxygen. Citric and malic acids, in the same proportion, would form grape sugar by the evolution of 6 of oxygen only. Do fruits, when they have reached their sourest state, begin thus to give off an excess of oxygen? I know of no experiments which as yet decide the point. 2~. By the absorption of oxygen and the evolution of carbonic acid. Thus in the case of tartaric acid, I of TARTARIC ACID = C4 H2 05 I of OXYGEN.. _ =,1 -th of Grape Carbonic Sugar. Acid. Sum.. = C4 H. 06 = C2 H2 0 +- 2 C02 Where one of oxygen is absorbed and two of carbonic acid given off, Or in'the case of the malic and citric acids, 1 of MALIC ACID C= 4 H2 04 2 of OXYGEN.. = 0 - ---- Pith of Grape Carbonic Sugar. Acid. Sum..= C4 H, 0 =2 Co H2 02 - 2 CO0 Where 2 of oxygen are absorbed and 2 of carbonic acid given off. We know from the experiments of Berard that, when unripe fruits are plucked, they do not ripen if excluded from the access of oxygen gas-but that in the air they rifen, absorbing oxygen at the same time, and giving off carbonic acid. This second method (2~) therefore exhibits the more probable theory of the ripening of fruits after they are plucked; and if-as they become coloured-fruits imitate the petals of the flower in absorbing oxygen from the air and giving off carbonic acid, it will also represent the changes which take place when they are permitted to ripen on the tree. During the ripening of the fruit, it has been stated that the woody or cellular fibre it contains gradually diminishes, and is converted into sugar. This is familiarly noticed in some species of hard or winter pears. In sour fruit, the cellular fibre seldom exceeds 21 per cent. of their whole weight;-iin ripe fruits, however, it is still less, and as the constitution of this substance is so analogous to that of grape sugar, there is no difficulty in understanding that. it may be readily converted into the latter, though the immediate agency by which the transformation is effected is as yet unknown to us. CHANGES AFTER THE FRUIT HAS RIPENED. 143 ~ 5. Of the chemical changes which take place after the ripening of the fruit and seed. When the seed is fully ripe, the functions of annual plants are discharged. They no longer require to absorb and decompose carbonic acid, for their growth is at an end. Their leaves begin, therefore, to take in oxygen only, become yellow, and prepare along with the entire plant, for being finally resolved again into those more elementary substances from which they were originally compounded. On trees and perennial plants, however, a further labour is imposed. In the ripened seed they have deposited a supply of food sufficient to sustain the germ that may spring from it, until it is able to-seek food for itself; but the young buds already formed,-and which are to shoot out from the stem and branches in the ensuing spring,-are in reality so many young plants for which a store of food has yet to be laid up in the inner bark, and in the wood of the tree or shrub itself. In the autumn; the sap of trees and permanent shrubs continues to flow rapidly till the leaf withers and falls, and the food of the plant is converted partly into woody fibre, as was the case during the earlier period of the year, and partly into starch. The former is deposited beneath the inner bark to form the new layer of wood by which the tree is annually enlarged; the latter-partly in the same locality, as in the birch and pine-partly throughout the substance of the wood itself, as in the willow-while in the palm trees and cycadee, it is intermingled with the central pith. The chemical changes by which thefood is capable of being converted into these substances have already been considered. They proceed during the entire autumn, do not cease so long as the sap continues to move, and even in the depth of winter slowly and silently operate in storing up farinaceous matter-in readiness, like the starch in the seed, to minister to the nourishment of the young bud, when the warmth of the coming spring shall awaken it from its long sleep. ~ 6. Of the rapidity with which these changes take place, and the circumstances by which they are promoted. But remarkable as those chemical changes are, the rapidity with which they sometimes take place is no less surprising. From carbonic acid and water we have seen that the plant, by very intelligible processes, can extract the elements of which its most bulky parts consist-and can build them up in many varied ways, most of which are probably beyond the reach of imitation. But who can understand or explain the extraordinary activity which pervades the entire vascular system of the plant, when circumstances are favourable to its growth? A stalk of wheat has been observed to shoot up three inches in as many days, of barley six inches in the same time, and a vine twig almost two feet, or eight inches a day (Du HameI). Cucumbers have been known to acquire a length of twenty-four inches in six days, and in the Botanic Garden at Brussels I was shown a bamboo five inches in diameter, which had increased in height nine feet in twenty-seven days, sometimes making a progress of six to eight inches in a day. In our climate we meet with few illustrations of the rapidity with which plants are capable of springing up in the most favourable circumstances, and the above examples probably give us only an imperfect idea of the ve 144 INFLUENCE OF SALINE SUBSTANCES AND MANURES. locity with which the bamboo, the palm, the tree fern, and other vascular plants, may grow in their native soil and climate. And with what numerous and complicated chemical changes is the production of every grain of the substance of these plants attended-how rapidly must the food be selected and absorbed from the air and from the soil-how quickly transformed and assimilated! The long period of time during which, year after year, these changes may proceed in the same living vessels, or in the same tree, is no less wonderful. Oaks have lived to an age of 1500 or 2000 years-yew trees to 3000 years-and other species are mentioned as having flourished from 4500 to 6000 years; while even a living rose tree (rosa canina) is quoted by Sprengel as being already upwards of 1000 years old.-[Sprengel, Lehre vom Diinger, p. 76.] The rapidity of the growth of a plant, and the length of its life, are equally affected by circumstances. On a knowledge of these circumstances, and of the means of controlling or of producing them, the enlightened practice of agriculture is almost entirely dependent. Over the natural conditions on which vegetation in general depends, we can exercise little control. By hedge-rows and plantations we can shelter exposed lands, but, except in our conservatories and hot-houses, the plants we can expect to cultivate with profit will always be determined by the general climate in which we live. So the distribution of rain and sunshine are beyond our control, and though it is ascertained that a thundery condition of the atmosphere is remarkably favourable to vegetable growth, [Sprengel, Lehre vom Diinger, p. 73], we cannot hope that such a state of the air will ever be induced at. the pleasure or by the agency of man. But under the same natural conditions of climate, there are many artificial methods by the use of which it is within our power to accelerate the growth, and to increase the produce, of the most valuable objects of ordinary culture. Thus the germination of.seeds in general is hastened by watering with a solution of chlorine (Davy), or of iodine or bromine (Blengini), and Davy found that radish seed which germinated in two days when waered with solutions of chlorine or sulphate of iron, required three when watered with very dilute nitric acid, and five with a weak solution of sulphuric acid. It is familiarly known also in ordinary husbandry, that the application of manures hastens in a similar degree the development of all the parts of plants during every period of their growth-and largely increases the return of seed obtained fiom the cultivated grains. Ammonia and its compounds likewise, and nitric acid and its compounds, with many other saline substances existing in the mineral kingdom and occurringin soils, or which- are produced largely in our manufactories, have been found to produce similar effects. It would be out of place here to enter upon the irmportant and interesting field opened up to us by a consideration of the influence exercised by these and other substances, in modifying both in kind and in degree the chemical changes which take place in living vegetables. The true mode of action of such substances-their precise effects-the circumstances under which these effects are most certainly produced-and the theoretical views on which they can be best accounted for-will form a subject of special and detailed examination in the third part of the present lectures. LECTURE VIII. How the supply of food for plants is kept up in the general vegetation of the globe.-Propor. tion of their food drawn by plants from the air. -Supply of carbonic acid.-Supply of ammonia and nitric acid.-Production of both in nature.-Theory of their action on living vegetables.-Concluding observations. HAVING shown in the preceding Lecture in what way, and by what chemical changes, the substances of which plants chiefly consist may be produced from those on which they live,-there remains only one further subject of inquiry in connection with the organic constituents of plants. Plants, as we have already seen, derive much of their sustenance from the carbonic acid of the atmosphere; yet of this gas the air contains only a very small fraction, and in so far as experiments have yet gone, this fractional quantity does not appear to diminish-how, then, is the supply of carbonic acid kept up? Again, plants most probably obtain much of their nitrogen either from ammonia or from nitric acid; and yet, neither in the soil nor in the air do these compounds permanently exist in any notable quantity,-whence then is the supply of these substances brought within the reach of plants? The importance of these two questions will appear more distinctly, if we endeavour to estimate how much of their carbon plants really draw from the atmosphere-and how much of the nitrogen they contain must be derived front sources not hitherto pointed out. ~ 1. Of the proportion of their carbon which plants derive from the atmosphere. On this subject it is perhaps impossible to obtain perfectly accurate results. Several series of experiments, however, have been published, which enable us to arrive at very useful approximations in regard to the proportion of their carbon which plants, growing in a soil of ordinary fertility, and in such a climate as that of Great Britain, actually extract from the air by which they are surrounded. 1~. In an experiment made in 1824, upon common borage (Borago officinalis), Lampadius found that after a growth of five months (from the 3rd of April to the 6th of September) this plant produced ten times as much vegetable matter as the soil in which it grew had lost during the same period.* In other words, it had drawn nine-tenths of its carbon from the air. 2~. The experiments of Boussingault were made, if not with more care, at least upon a greater number of plants, and were protracted through a much longer period. It is necessary that we should understand the principle on which they were conducted, in order that we may be prepared to place confidence in the determinations at which he arrived. * The above experiment may have been correctly made, but the result appears at first sight too startling to be readily received as indicative of the proportion of their sustenance drawn by plants from the air in the general vegetation of the globe. 146 PROPORTION OF CARBON DRAWN FROM THE AIR. If we were to examine the soil of a field on which we are about to raise a crop of corn-and should find it to contain a certain per-centage, say 10 per cent. of vegetable matter (or 5 per cent. of carbon);-and after the crop is raised and reaped should, on a second examination, find it to contain exactly the same quantity of carbon as before, we could not resist the conviction, that, with the exception of what was originally in the seed, the plant during its growth had drawn from the air all the carbon it contained. The soil having lost none, the air must have yielded the whole supply. Or if after examining the soil of our field we mix with it a supply of farm-yard manure, containing a known weight, say one ton of carbon, and when the crop is reaped find as before that the per-centage of vegetable matter in the soil has suffered no diminution,* we are justified in concluding that the crop cannot, at the utmost, have derived from the soil any greater weight of its carbon than the ton contained in the manure which had been added to it. Such was the principle on which Boussingault's experiments were conducted. He determined the per-centage of carbon in the soil before the experiment was begun-the weight added in the form of manurethe quantity contained in the series of crops raised during an entire rotation or course of cropping, until in the mode of culture adopted it was usual to add manure again-and lastly, the proportion of carbon remaining in the soil. By this method he obtained the following results in pounds per English acre, in three different courses of cropping, and on the same land: Carbon Carbon Difference, or in the in Carbon derived REMARKS. manure. the crops. from the air. r The first was a 5 years' course-of potatoes or First Course 2513 7544 5031 red beet with manure, wheat, clover, wheat, -Second do. - 6839 oats; the second and Second do. -- - - 6839 most productive rotation was abandoned on Third do. - - 3921 account of the climate; the third was a 3 years' course. The result of the first course indicates that-the land remaining in equal condition at the end of the four years as it was at the beginningthe crops collected during these years contained three times the quantity of carbon present in the manure, and therefore the plants, during thei? growth, must on the whole have derived two-thirds of their carbon from the air. It will be shown in a subsequent section that even when the soil is lying naked the animal and vegetable matter it contains is continually undergoing diminution, owing to decomposition and the escape of volatile substances into the air. It is fair, therefore, to assume that a conI need scarcely remark that, in the hands of a good farmer, who keeps his land in good heart-the quantity of organic matter in the soil at the end of his course of cropping should be as great, at least, as it was at the beginning of his rotation, before the addition of the manure. WEIGHT OF CARBON'JN THE ATMOSPHERE. 147 siderable portion of the carbon of the manure and of the soil would naturally disappear during the four years' cropping above-mentioned, and that, therefore, the proportion of carbon derived from the air in Boussingault's experiments, must have been really considerably greater than is indicated by the numerical results. Let two-thirds of the entire quantity of carbon contained in a series of crops be taken as the average proportion, [Lecture II., p. 31,] which, on cultivated land in our climate, must be derived from the air in the form of carbonic acid-and let the average weight of the dry crop reaped be estimated at a ton and a half per acre. Then, if the crop contain half its weight of carbon,* the plants grown on each acre must annually extract from the air 10 cwt. or 1120 lbs. of carbon in the form of carbonic acid. ~ 2. Of the relation which the quantity of carbon extracted by plantsfrom the air, bears to the whole quantity contained in the atmosphere. But the question will here at once suggest itself to you-does not the quantity thus extracted from the air really form a very large proportion of the whole weight of carbon which is contained in the atmosphere? A simple calculation will give us clear ideas in regard to this interesting point. We have already seen that, by the results of De Saussure, the average quantity of carbonic acid in the atmosphere of our globe may be estimated at 50- part of its entire bulk. This is equal very nearly to 3o- of its weight.t Or taking the whole weight of the atmosphere at 15 lbs. on the square inch-that of the carbonic acid will be 0-009 lbs. or 63 grs. per square inch. But as carbonic acid contains only 27- per cent. of its weight of carbon, the weight of this element which presses on each square inch of the earth's surface isonly 17- (17'39) grs. Upon an acre this amounts to 7 tons.t But if the crop on each acre of cultivated land annually extracts from the air half a ton of carbon, the whole of the carbonic acid in the atmosphere would sustain such a vegetation over the entire globe for 14 years only. And if we even suppose such a vegetation to extend over one hundredth part of the earth's surface only, it still appears sufficient to exhaust the carbonic acid of the air in 1400 years. Boussingault states, that of all the plants usually cultivated for food-so far as his expert. ments have gone-the Jerusalem artichoke draws the largest portion of its sustenance fron the air-or yields the greatest weight of food from the smallest uweight of mcnure. It is true generally indeed that all those plants, which, like the Jerusalem artichoke and the white carrot, grow freely on sandy soils containing little vegetable matter and with the addition of little manure, extract the greatest proportion of their sustenance from the air. Su:ch plants, therefore, are likely to prove the most profitable articles of culture where such soils and a scarcity of manure simultaneously prevail. t The mean of 225 experiments made by De Saussure between t827 and 1829 gave as above stated about 4-10000 or 1-2500th part for the mean bulk of the carbonic acid in the air, which is nearly 6-l000ths of its whole weight. Among these observations the maximum was 5-8 ten-thousandths, the minimum 3-15. If we take the maximum bulk at 6-10000ths of the air-the maximulm 2eigid. of the carbonic acid is nearly 9-L0000ths of that of the atmosphere. In elementary works it is generally stated in round numbers at 1-1000th of the weight of the air, but if the best experimental results we possess are to be any guide to us, this is at least one-third too high. It is also of consequence to remark, that this estimate of the whole weight of the carbonic acid in the air is founded on the supposition that, in the highest regions of the atmosphere the carbonic acid is present in a proportion nearly equal to that in which it is found imme diately above the earth's surface-which is by no means established. 15-583 lbs.-an acre being 4840 square yards, containing each 1296 square inchess 148 HOW THE SUPPLY OF CARBONIC ACID IS RENEWED, A very short period, compared even with the limits of authentic history, has yet elapsed since experiments began to be made on the true constitution of the atmosphere; we have no very trustworthy data, therefore, on which to found a confident opinion in regard to the permanence of the proportion of carbonic acid which it now contains. The later observations of De Saussure do give a considerably lower estimate of the quantity of this acid in the air than that which was deduced from the results of the earlier experimenters; but the imperfection of the modes of analysis formerly adopted was too great, to justify us in reasoning rigorously from the inferences to which they led. We cannot safely conclude from them that the proportion of carbon in the atmosphere has really diminished to any sensible extent during this limited period; while the recorded identity of all the phenomena of vegetation renders it probable that the proportion has not sensibly diminished even within historic times. From what sources, then, is the supply of carbonic acid in the atmosphere kept up?-and if the proportion be permanent, by what compensating processes is the quantity which is restored to the atmosphere produced and regulated? ~ 3. How the supply of carbonic acid in the atmosphere is renewed and regulated. On comparing, in a previous lecture, the quantity of rain which falls with that of the watery vapour actually present in the air, we saw reason to believe that even in a single year the same portion of water may fall in rain or dew and ascend again in watery vapour several successive times. Is it so also with the carbon in the air? Does that which feeds the growing plant to-day, again mount up in the form of carbonic acid at some future time, ready to minister to the sustenance of new races, and to run again the same round of ever-varying change? Such is, indeed, the general history of the agency of the carbonic acid of the atmosphere; but when once it has been fixed in the plant it must pass through many successive changes before it is again set free. The conditions, also, under which it is restored to the atmosphere are so diversified, and the agencies by which, in each case, it is liberated, are so very distinct, as to require that the several modes by which the carbon of plants is reconverted into carbonic acid and returned to the air, should be made topics of separate consideration. I. —ON THE PRODUCTION OF CARBONIC ACID BY RESPIRATION. The air we breathe when it is drawn into the lungs, contains vo-5th of its bulk of carbonic acid; when it returns again from the lungs, the bulk of this gas amounts, on an average,* to ~-th of the whole; or it. quantity is increased one hundred times. The actual bulk of the carbonic acid emitted from the lungs of a single individual in 24 hours varies exceedingly; it has been estimatedhowever, on an average, to contain upwards of five ounces of carbon.t * It varies in different individuals from 2 to 8 per cent. of the expired air. In animals it varies also with the species. The air from the lungs of a cat contains from 5; to 7 per cent, of a doa from 4- to 6tt, of a rabbit from 4 to 6, and of a pigeon from 3 to 4 per cent. of the whole bulk. —Dulong, Annal. de (Chim. et de Phys., third Series, I., p. 455. t Davy, and Allen, and Pepys, estimated the weight of carbon evolved in a day at upwards of 11 ounces, a quantity which all writers have concurred in receiving with suspicion. THE COMBUSTION OF ORGANIC MATT'ER. 149 A full grown man, therefore, gives off from his lungs, in the course of a year, upwards of 100 lbs. of carbon in the form of carbonic acid. If the quantity of carbon thus evolved from the lungs be in proporti6n to the weight of the animal, a cow or a horse ought to give off six times as much as a man.* From indirect experiments, however, Boussingault estimated the quantity of carbon actually lost in this way by a cow at 2200 grammes in 24 hours, and by ahorse at 2400 grammes.-[Ann. de Chim. et de Phys., lxxi., pp. 127 and 136.] These quantities are equal to 6 or 7 times the amount of carbon given off from the lungs of a man. If we suppose each inhabitant of Great Britain, young and old, to expire only 80 lbs. of carbon in a year, the twenty millions would emit seven hundred thousand tons; and, allowing the cattle, sheep, and all other animals, to give off twice as much more, the whole weight of carbon returned to the air by respiration in this island would be about two millions of tons, or the quantity abstracted from the atmosphere by four millions of acres of cultivated land. Whence is all this carbon derived? It is a portion of that which has been conveyed into the stomach in the form of food. Suppose the carbon contained in the daily food of a full grown man to amount to one pound-which is a large allowance-then it appears that, by the ordinary processes of respiration, at least one-third of the carbon of his food is daily returned into the air. JIn other animals the proportion returned may be different from what it is in man, yet the life ofall depends on the emission to a certain extent of the same gas.t And since all are sustained by the produce of the soil, it is obvious that the process of animal respiration is one of those methods by which it has been provided that a large portion of the vegetable productions of the globe should be almost immediately resolved into the simpler forms of matter from which it was originally compounded, and again sent up into the air to minister to the wants of new races. II.-ON THE PRODUCTION OF CARBONIC ACID BY COMBUSTION. Another important source of carbonic acid is familiar to us in the re sults of artificial combustion. In the previous lecture I have shown how, by the action of the sun's rays upon the leaf, the carbonic acid absorbed from the atmosphere is deprived of its oxygen, and its carbon afterwards united to the elements of water for the production of woody fibre. During the process of combustion, this labour of the living leaf is undone-the carbon is made to combine anew with the oxygen of the atmosphere, and the vegetable matter is resolved again into carbonic acid and water. Thus, when wood (woody fibre) is burned in the air, oxygen disappears, and carbonic acid and watery vapour are alone produced. The theory of this change is simple.' Estimating the ordinary weight of a man at 150, and of a cow at 800 to 900 lbs.-See Sprengel, Lehre vore Dinger, p. 208. That the proportion must be less in the larger animals is certain, since the daily food of a cow may be stated generally as equivalent to 25 lbs. of hay, containing upwards of 10 Ibs. of carbon. If one-third of this were given off from the lungs, the quantity of carbon (31 lbs..) evolved would be ten times greater than was indicated by the experiments of Boussingault, and nearly double of what the weight of a cow, compared with tnat of a man, requires. 7* 150 PRODUCES CARBONIC.ACID AND WATER. It will be recollected (p. 135) that in forming an equivalent of woody fibre or of sugar, 24 of oxygen were given off, chiefly by the leaf-so in agaif resolving these substances into carbonic acid and water, 24 of oxy gen are absorbed. Thus1 of WOODY FIBRE = C,2 H8 08 24 of OXYGEN. = 024 -------- 12 of 8 of Carbonic Acid. Water. Sum... =C12 H 032 = 12C02 + 8HO. Or, 1 of CANE SUGAR = C12 Hio Olo 24 of OXYGEN.. - 24 ___- -__ 12 of 10 of Carbonic Acid. Water. Sum... -C2 Hlo 034 = 12CO2 10 HO. The same law holds in regard to all other vegetable substances. They are resolved into carbonic acid and water, in proportions which necessarily vary with the chemical constitution of each. It applies also to all bodies of vegetable origin, among which nearly all combustible minerals may be reckoned. The peat and coal we burn in our houses and manufactories, when supplied with a sufficiency of atmospheric air, are resolved during combustion into carbonic acid and watery vapour. Some vegetable substances contain a small quantity of nitrogen. When these are burned, this nitrogen escapes into the atmosphere,generally in an uncombined state,-and mingles with the air. So in animal substances, nearly all of which contain nitrogen as an essential constituent. During perfect combustion the whole of the carbon is dissipated in the form of carbonic acid, while the nitrogen rises along with it in an elementary state. The result of this uniform subjection of all combustible matter to the operation of this one law, is the constant production on the surface of the globe of a vast quantity of carbonic acid;-the re-conversion of large masses of organic matter into the more elementary compounds from which it was originally formed. How interesting it is to contemplate the relations, at once wise and beautiful, by which through the operation of such laws, dead organic matter, intelligent man, and living plants, are all bound together! The dead tree and the fossile coal lie almost useless things in reference to animal and vegetable life,-man employs them in a thousand ways as ministers to his wants, his comforts, or his dominion over nature-and in so doing, himself directly though unconsciously ministers to the wants of those vegetable races, which seem but to live and grow for his use and sustenance. It is impossible to say what proportion of the carbon absorbed during the general vegetation of the globe, is thus annually restored to the atmosphere by the burning of vegetable matter. That it must be very great, will appear from the single fact, that by far the greater part of the globe is dependent for its supply of fuel on the annual produce of its forests;-while even in those more favoured countries where mineral coal abounds, the quantity of wood consumed by burning falls but little short of the entire yearly growth of the land. LAW OF THE DECAY OF VEGETABLE MATTER. 151 In connection with this subject, I must draw your attention to one interesting, as well as important, fact. I have spoken of coal as a substance of vegetable origin, and there is no doubt that all the carbon it contains once floated in the air in the form of carbonic acid. Biut the period when it was so mixed with the atmosphere is remote almost beyond conception. When, therefore, we raise coal from its ancient bed and burn it on the earth's surface, we add to the carbon of the air a portion which has not previously existed in the atmosphere of our time. The coal consumed in Great Britain alone is estimated at 20 millions of tons, containing on an average at least 70 per cent., or 14 millions of tons of carbon. But if the annual produce of an acre of cultivated land contain half a ton (p. 147)-of carbon derived from the air, the coal consumed in this country would supply carbonic acid to the crops grown upon 28 millions of acres. Or, since in Great Britain about 34 millions of acres are in cultivation (p. 12), the coal we annually consume produces a quantity of carbonic acid which is alone suficient to supply food to the crops that grow upon seven-eighths of the arable land of this country. ~H. —PODUCTION OF CARBONIC ACID BY THE NATURAL DECAY OF VEGETABLE MATTER; LAW OF THIS DECAY. Over large tracts of country in every part of the globe, the vegetable productions of the soil are never cropped or gathered, but either accumulate-as occasionally in our peat bogs; or decay and gradually disappear -as in the jungles of India or in the tropical forests of Africa and Southern America. The final results of this decay are the same as those which attend upon ordinary combustion,' but the conditions under which it takes place being different, the immediate results are to a certain extent different also. When a vegetable substance is burned in the air, the oxygen of the atmosphere is the only material agent in effecting the decomposition. The carbon of the burning body unites directly with this oxygen and forms carbonic acid. In the natural process of decay, however, at the ordinary temperature of the atmosphere, vegetable matter is exposed to the action of both air and water;;these both co-operate in inducing and carrying on the decomposition, and hence carbonic acid is not, as in the case of combustion, the chief or immediate result. A detail of all the steps through which vegetable matter is known to pass before it is finally resolved into carbonic acid and water, would be difficult for you to understand, and is here unnecessary. A general view of the way in which by the united agency of air and water, the decay of organic substances is effected and promoted, may be made very intelligible, and will sufficiently illustrate the subject for our present purpose. In combustion, as we have seen, the whole of the vegetable substance is resolved directly into carbonic acid and water, at the expense of the oxygen of the atmosphere. In natural decay a small and variable portion only is so changed, but to the extent to which this change does take place carbonic acid is directly formed and sent up into the air. Suppose putch a change —a slow corn ustion it reality-to take place to a certain 152 BY NATURAL DECAY IT IS FINALLY RESOLVED extent, and let us consider what becomes of the remainder of the vegeta ble matter. 1~. If we add 6 of CARBONIC Ac.. =_ C6 012 to 6 of LIGHT CARBURETTED _ HYDROGEN (CH2) - C6 H2 we have the sum.. C12 H12O12; or, one of grape sugar;-that is, one of grape sugar may be formed out of the elemnents of 6 of carbonic acid, and 6 of light carburetted hydrogen. Or, conversely, grape sugar being already produced, it may be resolved or decomposed into these two compounds in the same proportions, without the aid of the oxygen of the atmosphere. 2~. So if to I of WOODY F1BRE = Ci2 HY O8 we add 4 of WATER.. = H4 04 -. —-- Carbonic Light CarbuAcid. retted Hydrogen. w-e have, as before, C 2 H,,2 01l= 6 C02 6 CH2; Or by the aid of the elements of 4 atoms of water, woody fibre may be resolved into 6 of carbonic acid and as many of light carburetted hydrogen. 3~. Again, in the case of a vegetable acid, if to 1 of TARrARIC ACID = C4 Hs 05 we add l of OxYGEN. 01= Carbonic Light Carbu. Acid. retted Hydrogenm we have C4 H O = -3 CO +- CHs; That is, by the aid of one of oxygen from the air, one of tartaric acid may be resolved into 3 of carbonic acid, and 1 of light carburetted hydrogen. It is easy to see how any other of the more common vegetable productions may-either at the expense of its own elements, as in grape sugar-or by the aid of those of water, as in woody fibre-or of the oxygen of the atmosphere, as in tartaric acid-be resolved into carbonic acid and light carburetted hydrogen, in certain proportions. Now, such a resolution does really take place to a considerable extent in nature, during the decay of organic substances in moist situations. Hence the evolution of light carburetted hydrogen from dead vegetable matter in marshy places and stagnant pools-hence the production of' the same gas in compost heaps, and especially in rich and heated farmyard manure-and hence also its occurrence in such vast quantities in many of our coal mines. You will now be able to appreciate one of the reasons why this light carburetted hydrogen has been supposed by some physiologists (p. 50}, to contribute as food to the ordinary nourishment of plants. It is produced in nature in many and varied situations, and it has been fiound by experiment to exercise a visible influence upon the growth of plants;, -being so produced where young plants grow, is it never imbibed by them?-being possessed of this influence, is it entrusted with no control over the general vegetation of the globe? However this may be, by far the greatest portion of both these gases escapes into the air; —tlte carbonic acid to fulfil those purposes which INTO CARBONIC ACID AND WATER. 153 have already been considered,-the light carburetted hydrogen to undergo a further change, by which.it also is resolved into carbonic acid and water. Thus; if to 1 of LIGHT CARBURETTED HYDROGEN = CH2 we add 4 of OXYGEN........ 04 --- Carbonic Acid. Water. We have CH2 04 or CO + 2 HO Or one of this gas with 4 of oxygen may be changed into 1 of carbonic acid and 2 of water. Now, when this gas escapes into the air it becomes diffused through a large excess of oxygen, and is thus ready, at any instant, to be decomposed. Through the atmosphere streams of electricity are continually flowing, and every wandering spark that passes athwart a portion of this mixture decomposes so much of the light gas, and produces in its stead the equivalent proportions of carbonic acid and watery vapour. Thus it happens that of the vast quantity of this and other combustible gases which are continually escaping into the air, so few traces are discernible even by the aid of the most refined processes of art. By a wise provision of nature such substances as are void of use to either animals or plants, if not speedily removed from the air altogether, are there converted into such new forms of matter as are fitted to minister to the necessities of living beings. Though therefore in the natural decay of vegetable matter in the presence of air and moisture, a certain portion of its carbon escapes into the air in the form of light carburetted hydrogen, this compound is but a step towards the final change into carbonic acid and water. In the soil the vegetable matter is continually undergoing decay, various substances are produced in greater or less quantity, some solid, some liquid, and some gaseous like the light gas-ofwhich we have been speaking,but all of them, like this gas, are only hastening-some by one road, so to speak, and some by another-towards that final destination which sooner or later they are all fated to reach; when in the form of carbonic acid and water they shall be in a condition to minister again to the nourishment of all plants. While in the soil some part of this vegetable matter assumes forms which are capable of entering again into the roots of living plants, and, without further resolution in the air, of being converted by the living plant into portions of its own substance. The nature and composition of these forms of matter, so far as they are known, will be considered in a subsequent lecture. —[See Part II., Lectures XI.-XIII., " On the constitution of soils."] It is upon the final result of this natural decay to which all vegetable matter is subject, that the carbonic acid of the atmosphere depends for its largest supplies. The rapidity with which organized bodies perish, and become resolved into gaseous compounds, depends partly upon the climate and partly on the nature of the substances themselves,-but all hurry forward to the same end, and it is with difficulty that we are able for a time toi arrest or even to retard their steps. It is by this perpetual and active obedience of all dead matter to one fixed law that the existing condition of things is maintained;-and thus it happens that either by the respiration of the animals which live upon it, by the process of 154 EVOLUTION OF CARBONIC ACID N VOLCANIC COUNTRIES. combustion, or by that of spontaneous decay, the entire crop of vegetable produce is apparently, year by year-taking the average of a series of years-resolved into the forms of matter from which it was originally built up;-and the substances on which plants feed at length restored to the air in the precise.proportion in which they have been taken from it. VI.-NATURAL EVOLUTION OF CARBONIC ACID IN VOLCANIC COUNTRIES. The above apparent conclusion would be absolutely true, were there no causes in operation by which the restoration to the air of a portion of the carbon of animal and vegetable substances is prevented-and no other sources, independent of existing organic matter, from which carbonic acid may be supplied to the air. If the whole of the carbon be not returned to the air, the carbonic acid of the atmosphere may be undergoing diminution; while-if a large supply be.constantly: poured into the air from sources independent of vegetable matter, the proportion of carbonic acid may be continually on the increase. We have seen that the combustion of fossil coal adds to the air a large quantity of carbonic acid which has never before existed in the atmosphere of our time. In many volcanic districts also, carbonic acid is observed to issue in large quantity from cracks and fissures in the earth; -accompanied sometimes by water, forming mineral springs, from which the copious emisson of gas is readily perceived;- more frequently, perhaps, rising up alone, and thus escaping general observation. It must obviously be exceedingly difficult to estimate the quantity of gas which rises into the air in such circumstances over an extensive tract of country, fractured and broken up by volcanic agency-where the outlets are numerous, and the rate at which the gas escapes very variable. That in many localities it must be very great, however, there can be no question. In the ancient volcanic district of the Eifel, comprising an area of many square miles around the Laacher See, on the left bank of the Rhine, the annual evolution of carbonic acid from springs and fissures has been estimated by Bischof at not less than 100,000 tons, containing 27,000 tons of carbon. In many other districts, especially where active volcanoes exist, the volume of gas given off may be quite as great, though no attempts have hitherto been made to estimate its real amount. Yet though absolutely large, ti: e quantity of carbonic acid disengaged in this way from the earth, is really small when compared either with the entire quantity supposed to be present in the atmosphere, or with that which is required for the growth of the yearly vegetation of the globe. Suppose that from a thousand spots on the earth's surface a quantity of carbonic acid equal to the above estimate of Bischof escapes constantly into the air, the weight of carbon (27 millions.of tons) thus diffused through the atmosphere would be only equal to that which is yearly drawn from the air by 54 millions of acres of land under cultivation (p. 147), and only twice as much'as that contained in the coal which is annually consumed in Great Britain alone. Still if the whole of the carbon contained in the produce of the general vegetation of the globe be ultimately restored to the air,-either by the respiration of animals, by the natural and slow decay o vegetable mat 155 CARBON PEt4IANENTLY WITHDRAWN FROM THE AIR. ter, or by the more rapid process of combustion,-the constant addition of carbonic acid derived from volcanoes, and from the combustion of fossil coal, should gradually, though slowly, augment the proportion of this gas in the air we breathe;-unless it be perpetually undergoing a permanent diminution, to at least an equal extent, from the operation of other causes. In reference to this point there are three circumstances which are proper to be considered:1~. It has been observed that, as we recede from the land and approach the centre of great lakes, or sail into the open sea, the quantity of carbonic acid in the air gradually diminishes. It is therefore inferred that the sea is constantly, and to a sensible extent, absorbing carbonic acid from the atmosphere, without afterwards restoring it, so far as is yet known, by any compensating process. 2~. The waters which flow into the sea or great lakes constantly bear down with them portions of animal and vegetable matter. These fall-along with the mud which the waters hold in suspension, and are permanently imbedded in the deposits of clay, silt, and sand, which are continually in the course of formation. 3~. In many parts of the world, especially in the latitudes north and south of 45~, vegetable matter accumulates in the form of peat, becomes buried beneath clay and sand, and thus is prevented from undergoing the ordinary process of natural decay. It is impossible to say how much carbon is permanently withdrawn from the atmosphere by these several agencies. There is reason to believe that it is quite as great as the quantity added to the air by the combustion of coal, and by the evolution of carbonic acid in volcanic districts. Indeed, the supply from these two sources appears to return only a small portion of that carbonic acid which is abstracted from the air by the agencies just stated, and which- have been in operation during every geological epoch. Conclusions.-The general conclusions, therefore, which we seem justified in drawing in regard to the supply of carbonic acid to the atmosphere are as follow: 1~. That a large portion of the carbonic acid absorbed by plants is immediately and directly restored to the air by the respiration of the animals which feed upon vegetable productions. 2~, That a still larger portion is more slowly returned by the gradual re-conversion of vegetable substances into carbonic acid and water during the process of natural decay. 3~. That nearly all the remainder is given back in the results of ordinary combustion. 4~. That a further portion, which has not previously existed in the atmosphere of our time, is conveyed to it by the burning of fossil fuel, and by the emission of carbonic acid from cracks and fissures in the surface of the earth; yet that the -quantity thus added cannot be supposed to exceed that which is constantly and permanently separated from the atmosphere by other causes. The balance of all the evidence we possess is probably in favour of the opinion that the carbonic acid in the atmosphere is slowly diminish 156 AMMONIA IN THE AIR-HOW DECOMPOSED. ing; we have, however, no satisfactory evidence either from theory or experiment that it has undergone any sensible diminution in our time.* ~ 4. Of the supply of ammonia to plants. In a previous lecture it has been shown that in our cultivated fields plants derive a portion of their nitrogen from the manure which is added to the soil. But the quantity of this element present in the manure, supposing it all taken up and appropriated by the plant, is seldom equal to that contained in the series of crops which this manure assists in raising. Thus, in the experiments of Boussingault already described (p. 144), the manure added previous to the first, or four years' course, contained 157 parts of nitrogen, while the crops contained 251 parts,-or nearly two-thirds more than could be derived from the artificial manure. Whence is this excess of nitrogen derived, and in what form does it enter into the plant? Liebig replies to these questions, that the whole of the nitrogen absorbed by plants enters in the state of ammonia, and that the excess above what is present in the manure is drawn either from the soil or from the air. This opinion, advanced by so high an authority, demands our attentive consideration. Ammonia has been detected in many clays, and traces of it may be discovered in most soils, but it is not known to be a natural or essential constituent of any of the solid rocks of which the crust of the globe is composed. These clays and soils, therefore, may be supposed to have derived their ammonia from the atmosphere; and Liebig ascribes the fertilizing action of the air upon stiff clays when fallowed, of burned clay when applied as a top-dressing, and of gypsum on grass lands [see note to page 53], to the larger quantity of ammonia which the surface of the soil is by these means caused to absorb and retain. There is no question that ammonia is present in the atmosphere in small and variable quantity (p. 37). Whence is this ammonia derived, and is its quantify sufficient to supply the demands of the entire vegetation of the globe? When animal substances undergo decay, nearly all the nitrogen they contain is ultimately separated from the other constituents in the form of ammonia. During the decay of plants also, a portion of their nitrogen escapes in the state of ammonia. Of the ammonia thus formed, much ascends into the air, chiefly in combination with carbonic acid as carbonate of ammonia (smelling salts), and much remains in the soil. Were the whole of the nitrogen contained in plants and animals to assume the form of ammonia when they decay, and to remain in the soil or in the air, it would always be within the reach either of the roots or leaves of the living races; and thus the same ammonia [or ammonia containing the same nitrogen-supposing the hydrogen to have been changed] might again and again return into the circulation of new vegelable tribes, and be always alone sufficient to supply all the demands of the existing vegetation of the globe. But of the ammonia thus formed, a portion is daily washed from the sc.l- by the rains and carried to the sea, and much more probably is * In another work (Chenmical Geology) now preparing for publication, I have discussed this question in connection with purely Geological considerations and without reference to our titme; but it would be out of place to introduce here any train of reasoning which is not calculated to throw light on the phenomena of the existing vegetation of the globe. AMMONIA EVOLVED FROM VOLCANOES. 157 washed from tne air by the waters of the sea itself, or by the rains which fall directly into the wide oceans; and we know of no compensating process by which this ammonia can be restored to the air, and again made useful to vegetation. Besides, of that which still remains in the air much must undergo decomposition by natural processes. In treating in a preceding section of the evolution of light carburetted hydrogen during the slow decay of vegetable matter (p. 153), I have shown how, in consequence of its admixture with the oxygen of the atmosphere, this gas is finely decomposed, while carbonic acid and water are produced. Ammonia in like manner will burn in oxygen gas, and when mixed with atmospheric air may be decomposed by the electric spark-water at the same time being formed and nitiogen set free. Thus, if with 1 of AMMONIA = NH3 we mix 3 of OXYGEN = 03. —-3 — -~ 3 of water. 1 of nitrogen. we have the sum NH3 03 = 3HO + N or, when diffused through the air, 1 of ammonia, with the aid of 3 of oxygen, wilf yield 3 of watery vapour, while the nitrogen may* mingle with the air in an elementary form. Can we doubt that ammonia is thus decomposed in the air? Not to speak of other forms assumed by the electricity of the atmosphere, can the thunder-storms of the tropical regions pass unheeded the ammoniacal vapours they must meet with in their course? I conclude, then, that of the ammonia which is formed from the nitrogen actually existing in animal and vegetable substances during theit decay, only a comparatively small portion ever returns again to ministel to the wants of new races.t But if plants obtain all their nitrogen from ammonia,b how is this waste repaired-whence are new supplies constantly derived? We have seen that, in certain volcanic countries, carbonic acid is evolved in vast quantities from rents and fissures in the earth. In some of these districts-and this has been observed more especially in Italy and Sicily, and it is said also to some extent in China-ammonia is likewise given of, in combination generally with some acid, and most fiequently with the muriatic acid in the form of sal-ammoniac (muriate of ammonia). " Tis ammonia," Liebig is correct in saying, "has not been produced by the animal organism;" but he assumes a very doubtful position when he adds, "it existed before the creation of human be.ings; it is a part, a primary constituent'of the globe itself."-[Organic Chemistry applied to Agriculture, p. 112.] Where, we might ask, has this ammonia existed during all past time -from what deep caverns of the earth does it now escape? I say may, because it may at the same time combine withoxygen and form nitric acid. — See the following section, p. 239. t I might add, that of the ammonia which does return, and is again absorbed, a portion is subsequently decomposed- in the interior of living plants, as is shown by the evolution of nitrogen from the common leaves of some and the flower leaves of others.." Wild plants obtain more nitrogenfrom7 the amo.sphere, in theformn of ammonia, than they requirefbr their growth, FOR the water whi-ch evaporates through their leaves and blossoms emits, after a time, a. putrid smell-a peculiarity possessed only by such bodies as contain nitrogen."-[Liebig, Organic CIheinisry appliod to Agriculture, p. 85,] Does the fact hero stated, justify the conclusion whiicl appears to be ldrawn from it 158 INDIRECT PRODUCTION OF AMMONIA. This opinion of Liebig, as well as the paramount influence he ascribes to ammonia over the vegetation of the globe, are based chiefly on the fact that we know of no means by which ammonia can be formed by the direct union of the hydrogen and nitrogen of which it consists. But the production of ammonia, by the indirect union of these elements, is daily going on in nature, and can even be effected by different processes of art. Thus1~. When organic substances, which contain no nitrogen, are oxidized in the air, ammonia is not unfrequently formed (Berzelius). Hence it must be produced in unknown quantity during the annual decay of all vegetable substances. 2~. When organic substances are oxidized in the presence of air and water-as when moist iron filings are exposed to the air (Chevallier), or when certain oxidized substances are decomposed in the air by means of potassium (Faraday), or when metals, such as tin filings, are rapidly oxidized by means of nitric acid, ammonia is also produced in variable'quantity. Hence the absorption of oxygen, even by the inorganic substances of the soil, may give rise to the formation of ammonia. But, 3~. The fact which most clearly illustrates the production of ammonia in nature, both on the surface of the earth, in the soil, and far in the interior near the seat of volcanic fires, is this, that if a currant of moist air be made to pass over red-hot charcoal, carbonic acid and ammonia are simultaneously formed.* This is in reality only a repetition in another form of what takes place, as above stated, when vegetable matter decays, or iron filings rust in moist air. The carbon and the iron decompose the watery vapour in the air, and combine with its oxygen, while, at the instantf of its liberation, the hydrogen of the-water combines with the nitrogen of the air, and forms ammonia. The source of the ammonia evolved in volcanic districts, therefore, is no longer obscure. The existence of combustible matter in such districts, and at great depths beneath the surface, can in few cases be doubted, and the passage of a mixed atmosphere of common air and steam over such combustible matter, at a high temperature, appears to be alone necessary to the production of ammonia. It is unnecessary, then, to have recourse to doubtful speculations in order to account for the natural reproduction of ammonia, to a certain extent, in the place' This experiment is easily performed by drawing a current of mixed atmospheric air and steam through a red-hot gun-barrel filled with well-burned charcoal, and causing the current, on leaving the barrel, to pass through water acidulated with muriatic acid. After a time, the water, on evaporation, will be found to contain traces of sal-ammoniac. What thus takes place in a small experiment of this kind must more readily and more largely take place in the interior of the earth, where combustible substances at a high temperature happen to be exposed to a current of atmospheric air, mixed with watery vapour. t A beautiful illustration of the tendency which elementary substances have to unite with each other at the instant of their liberation in what chemists call their nascent state, is mentioned by Runge.-Einlcitung in die technische Cheenie, p. 373. If 1 part of hydrate of potash and 20 of iron filings be heated together, hydrogen only is given off. If 1 of nitrate of potash and 20 of iron filings be heated together, nitrogen only is given off.' But if 40 of iron filings be mixed with 1 of hydrate and-l of nitrate of potash, and then heated, ammonia becomes perceptible. The nitrogen and hydrogen being given off together, at the same instant, some portions of each find themselves in a condition to unite, and thus ammonia is produced. The same result must follow in many natural operations, when hydrogen and nitrogen are set free from a previous state of combination, at the same time, and in the presence of one another. NITRIC ACID EXISTS L/iRGELY IN NATURE. 159 of that which is constantly undergoing decomposition by the agency of causes such as those above described. But is the indefinite quantity of ammonia reproduced by these indi rect methods sufficient to replace all that is lost? Can it be supposed to impart to plants all the nitrogen. they require? These questions will be considered in the following section. ~ 5. Of the supply of nitric acid to plants. In regard to the action of nitric acid upon vegetation it is known1~. That when, in the form of nitrates of soda, potash, &c., it is spread upon the soil, it greatly promotes the growth and luxuriance of the crop and increases its produce; and 2~. That, when other circumstancs are favourable to vegetation-as in certain districts in India-the presence of an appreciable quantity of these nitrates adds largely to the fertility of the soil.* The same effects are unquestionably produced by the addition of ammonia or by its natural presence in the soil. The beneficial influence of both compounds, then, being recognized, the relative extent to whicL each operates upon the general vegetation of the globe will be main ly determined by the circumstances and the quantity in which they res pectively exist or are reproduced. In regard to the "existence of nitric acid, it is not known to form a necessary constituent of any of the solid rocks of which the crust of the globe is composed, but is diffused almost universally through the soil which overspreads the surface. In the hotter regions of the earth, in India, in Africa, and in South America (p. 56), it in many places accu. mulates in sufficient quantity to form-incrustations of considerable thick. ness over very large areas, and in many more it can be separated by washing the soil. Even in the climates of Northern Europe, it is rarely absent from the water of artificial wells, into which the rains, afte filtering through the surface, are permitted to make their way.' On the whole, nitric acid and its compounds appear to exist, ready formed in nature, in larger quantity than either ammonia or any of its compounds. For the following, and other interesting notices, regarding Indian agriculture, I am indebted to Mr. Fleming, of Barochan, in Renfrewshire, whose long residence in the districts to which he alludes, as well as the interest he takes in practical agriculture, renders his testimony very valuable: "The districts of Chaprah, Tirhoot, and Shahabad, near Patna, where a large proportion of the saltpetre sent from Bengal is produced, are considered the most fertile in Bengal, producing 2 and sometimes 3 crops yearly. The natives of these districts, particularly a caste called Quirees (hereditary gardeners), %ho cultivate the best land, and produce the best crops, are in the habit of irrigating their fields with water from wells so strongly impregnated with saltpetre and other salts as to be quite brackish, and they consider onions, turnips, and peas, most benefitted by this irrigation. Grain crops also grow most luxuriantly on lands yielding saltpetre, where there is enough of rain within a week or two after the seed is sown, but if a drought follows the sowing, and continues for 3 weeks or a month, the leaf becomes yellow, and thle-crop fails. "The Hindoos do not generally manure their lands, as the dung of the cattle is used for fuel, but the Quirees collect the ashes of cow dung and ofburned wood, and use it as a manure in some cases, chiefly for the poppy plant. "The Hindoos have for ages been well acquainted with the rotation of crops, and the advantages offallowing land, although a great proportion of the land is almost constantly in rice, Indian corn, or millet, during the rainy season, and in wheat or peas during the dry season." t It occurs in the wells of the neighbourhood of Berlin (Mitscherlich), in the form of ni. trates of potash, lime, and magnesia, in the wells around Stockholm, and may be expected in all wells that are dug (Berzelius).-TraitM de Chemie, iv., p. 71. 160 FORMATION'OF NITRIC ACID. Of these nitrates, as they do of ammonia, the rivers must be continually bearing a portion to the sea, but-there are in nature unceasing- processes of reproduction, by which not only this waste of the nitrates is repaired, but that further waste, also, which is caused by their absorption into the roots and subsequent decomposition in the interior of plants. Let us shortly consider these processes of reproduction. 1~. When a succession of electric sparks is passed through common air, nitric acid (NO5) is slowly but sensibly formed. The currents of electricity which in nature traverse the atmosphere must produce the same effect, and the passage of each flash of lightning through the air must be attended by the formation of some portion of this acid. After a thunder-storm plants appear wonderfully refreshed; in thundery weather they grow most luxuriantly, and other things being equal, those seasons in which there is much thunder are observed to be the most fruitful. Some have ascribed these results to the immediate agency of electricity on the growth of plants.-[Sprengel, Chemie, I., p. 99.] It is not equally possible that they may be connected with this necessary production of nitric acid'? In the rain which fell during 17 thunder-storms, Liebig found nitric acid always present and generally in combination with lime and ammonia. In the rain which fell on 60 other occasions, he could detect it only twice. In minute quantity nitric acid is difficult to detect. How much then must be formed in a thunder-storm, even in our climate, to make the presence of this acid always appreciable in the rain that falls -how vast a quantity in those warmer climates where such storms are so frequent and so appalling! 2~. When a mixture of ammonia with oxygen gas is exploded by passing an electric spark through it, a quantity of nitric acid is formed, even when the oxygen is not sufficient to oxidize the whole of the ammonia* (Bischof). Hence, if in the air, as we have seen reason to believe, the ammonia given off from decaying animal matters, and from other sources, be decomposed by the atmospheric electricity,-there will necessarily be formed at the same instant a portion of nitric acid, at the expense of the nitrogen of the ammonia itself. This nitric acid will, as necessarily, cotbine with some of the ammonia which still remains in the air. Hence the existence and production of nitrate of ammonia in the atmosphere, and the consequent presence of this acid along with ammonia in rain water. Thus the very cause which in the preceding section was shown to operate in constantly diminishing the amount of ammonia in the air, and the operation of which certainly renders improbable the existence of this compound in the atmosphere in the large quantity supposed by some [see especially Liebig's Organic Chemistry applied to Agriculture, p. 74], this same cause is at the same moment constantly reproducing nitric acid. And, though much of what is thus produced must necessarily, as in the case of ammonia, be carried down to the sea by the rains, or be directly absorbed by the waters of the ocean themselves, yet * It was shown above (p. 157), that I of ammonia ( NH3 ) requires 3 of oxygen to decompose it, forming 3 of water, and setting the nitrogen free. But, ir reality, as Bischof has shown, the nitrogen is not wholly set free, but a portion both of its hydrogen and nitrogen combine with oxygen (are oxidized) at the same instant, forming simultaneously both water (HO), and nitric acid ( N05). ARTIFICIAL NITRE BEDS. 161 it is obvious that in whatever proportion we may suppose the ammonia of the air to reach the leaves and roots of plants, in no less proportion must the nitric acid, with which it is associated, be enabled to enter into the circulating system of the various tribes of living vegetables, that flourish on every quarter of the globe. 3~. Again, we have seen that, during the decay of vegetable substances in moist air, ammonia is formed at the expense of the hydrogen of the water and of the nitrogen of the air. In consequence of, or in connection with, such decay, nitric acid is also largely produced in nature. The most familiar, as well as the most instructive examples of this formation of nitric acid is in the artificial nitre beds of France and the north of Europe. These are formed by mixing earth of different kinds with stable manure or other animal and vegetable matters, and exposing the mixture to the air in long ridges or conical heaps, which are occasionally watered with liquid manure, and turned over, to expose fresh portions to the air. After a time, perhaps once a year, the whole is washed, when the water which comes off is found to contain a variable quantity of the nitrates of potash, soda, lime, and magnesia, which are employed for the manufacture of saltpetre. In these nitre beds it has been observed that the production of nitric acid either does not take plaec at all, or only with extreme slowness, unless animal and vegetable matter be present in considerable proportion. And yet the quantity of nitric acid which is formed is much greater than could be produced by the oxidation of the whole of the nitrogen contained in the organic matters present in the mixture.* It is also observed that the nitre beds are more productive when a portion from one outer face of the heap is lixiviated from time to time, and the washed earth added to the other side, than when the whole is lixiviated at once, and again formed into a heap and exposed to the air. It appears, therefore, that organic matters are in our climate necessary to cause the formation of nitric acid to commence, but that after it has begun it will proceed in the same heap for an indefinite period, and at the expense apparently of the nitrogen of the air only. Compost heaps are in general only artificial nitre beds, often unskilfully prepared and badly managed, producing, however, a certain quantity of nitrates, to the presence of which their effect on vegetation may not unfrequently be ascribed.' To this fact we shall hereafter recur. The soils in the plains of India, and in other similar spots in the tropical regions, may be regarded as natural nitre beds, in which, the decay of organic matter being vastly.more rapid than in our temperate regions, the production of nitric acid is rapid in proportion.t 4~, But in many localities in which the presence of organic matter is - Dumas, Traitg de Chemie, II., p. 725. He adds, that 100 lbs. of nitre contain the nitrogen of 75 lbs. of ordinary animal matter, supposed in a dry state, or of 300 or 400 b1s. in its ordinary state of moisture,-a much greater relative proportion of animal matter than is ever added to the heap. t We are as yet too little acquainted with the natural history of the district of Arica in South America, in which, as already stated (p. 56), the nitrate of soda has been accumulated in such large quantity, to be able to say to what special cause the accumulation is due. But as, fiom the description of Mr. Darwin, the locality appears to have been the site of an ancient lake, it is.not unlikely that the nitrate may have been derived from the successive washings of a soil similar to that of India, by rains or periodical floods, which for a long period emptied themselves into or fed the lake. 1lt2 NITRE CAVES.-NITRIC ACID FORMED IN THE SOIL. not to be recognized in sensible quantity, the production of this acid is observed to proceed with a constant and steady pace. Thus, from the walls of certain caves in Ceylon a layer is yearly pared off; which yields an abundant crop of saltpetre (Dr. John Davy). The celebrated Mammoth cave in Kentucky, situated in a limestone ridge, yields an inexhaustible supply of nitrate of lime. During the war with Great Britain, fifty men were constantly employed in lixiviating the earth of this cave, and in about three years the washed earth is said to become as strongly impregnated as at first. Through the cave a strong current of air is continually rushing —inwards in winter, and outwards during the summer months. On the plaster of old walls, especially in damp situations, an efflorescence of this and other nitrates is frequently observed over every part of Europe. In China, according to Davis, the old plaster of the houses is so much esteemed as a manure, that parties will often purchase it at the expense of a coating of new plaster. Old clay walls, and especially the walls of clay-built huts, are said to be very fertilizing to the land, when applied as a top-dressing, and in some parts of England, where the land is poor, the people are said to pile up the soil in the form of walls, in order to improve its quality.. These latter facts seem to indicate that both in China and England nitric acid is produced in similar circumstances, and that to its production the fertilizing action of the old plaster, and of the weathered clay, is alike to be attributed. In the cultivated soil also, this acid is formed in ordinary circumstances. Braconnot found nitrate of potash in the botanic garden at Nancy, in a portion of soil in which poppies (apaaver somniferum) had grown luxuriantly for ten years in succession-in larger quantity in the soil surrounding the interlaced roots of an esclepias incarnata, growing in an ordinary flower-pot, with a hole in the bottom-as well as in moss earth, in which a plant of euphorbia breoni had been grown in a pot.[Ann. de Chim. et de Phys., lxxii., p. 33 to 35.] There is little reason to doubt, indeed, that nitrates are to be found, in greater or less quantity, in all cultivated soils. I shall not enter into a detailed inquiry how this nitric acid is formed. It is probable that as in the atmosphere ammonia may be decomposed and give rise to the formation of nitric acid, so in the soil this acid may result from a similar decomposition, proceeding more slowly, but according to the same natural laws. In warm climates, indeed, it appears certain that the ammonia which is evolved or formed during the decay of animal and vegetable substances, does speedily, and to a great extent, undergo oxidation,* and thus give rise to the greater abundance of nitric acid with which the tropical soils abound. Thus, in the economy of nature, much ammonia is decomposed in the soil also, and hence another cause for the constant diminution of the quantity of this compound in addition to those already detailed in the preceding section. But, besides the portion of this nitric acid, which owes its existence to For the perfect oxidation cf 1 of ammonia, no less than 8 of oxygen are required. Thus 1 of 1 of 3 of Ammonia. Nitric Acid. Water. NH +80 NO05 + 3HO. QUANTITY IN WHICH IT IS REPRODUCEr. 163 the decomposition of ammonia, much, by far the greatest proportion in all probability, derives its origin from the union of the elements of t*he atmosphere itself. This direct union is effected in the air, as has been already shown, by the. agency of atmospheric electricity; but it also takes place in the soil during the oxidation of the other elements contained in the organic matters which are there undergoing decay. The combination of the elements of ammonia in such circumstances proceeds on the principle that bodies, themselves undergoing oxidation, dispose other substances in contact with them (in this instance the nitrogen of the air) to unite with oxygen also. The presence of lime, potash, &c. in the soil, further induces to this oxidation by the tendency of these substances to combine with the acid which is formed by this union of the elements of which nitric acid consists.-It is impossible precisely to estimate the quantity of nitric acid produced in these various ways, through these various agents, and in these varied circumstances, or to balance it accurately against the amount of ammonia continually reproduced, as we have seen, in nature, wherever the necessary conditions present themselves. But, as I formerly concluded, that the amount of nitric acid actually existing in the superficial deposits of our globe is greater than that of ammonia, so I think that, in regard to the reproduction also of these two compounds, the balance is in favour of the former. Since, then, nitric acid is fitted, by the solubility of its compounds, to enter into the circulation of plants in any quantity-since, when applied to them, it does undoubtedly promote, in a remarkable degree, the growth of plants-and since, in nature, it is continually reproduced in every country, and under such varied circumstances-I cannot withhold myself from the conclusion, that, over the general vegetation of the globe, it holds with ammonia at least an equal sway, and is appointed to exercise at least an equal influence over the growth of plants, both in their natural and in their cultivated state. Still the influence of each is not unvaried by locality or by climate. The extent of dominion exercised by the nitrates probably diminishes as we recede from the equator, while that of ammonia increases,-it may be in an equal proportion. The reason of this probable variation will appear in the following section. ~ 6. Theory of the action qf nitric acid and ammonaa. These two compounds act so far in common as to yield a supply of nitrogen to the plants into which they enter. They do so, however, under conditions which may be considerably different, and may be attended by unlike chemical changes. I.-THEORY OF THE ACTION OF NITRIC ACID. 10. The nitric acid of the nitrates entering into the circulation of the roots will ascend to the leaf, and will there be decomposed in the same way as the carbonic and other similar acids are, by the action of the sun's rays. It is only in the light of day that carbonic acid is decomposed in the green parts of plants-so must it be, generally, with the nitric acid which ascends to the leaf. Its oxygen will be given off, while its nitrogen may be retained in the circulating system of the plant. The extent to which this decomposition will take place at each passage 164 THEORY OF THE ACTION OF NITRIC ACID AND OF AMMONIA. of the sap through the leaf will depend, in some degree, on the nature of the base (whether potash, soda, or lime,) with which the acid is in combination, but much more on the intensity of the light to which the green parts of the plant are exposed, and on the temperature of the air in which the plant happens to grow. 2~. It is still uncertain whether this acid is capable of being decomposed in the roots or stems of plants where it is excluded from the light, though it is very probable that it may be so, especially in cases where the juices naturally contain substances in which hydrogen is present in excess, or where such compounds make their way into the circulation of plaonts from the manure that may be applied to their roots. Thus in the pines, in which turpentine (C40 H3s) naturally abounds, such a decomposition may the more readily occur, inasmuch as it would not necessarily imply the production and evolution of any gaseous substance. Thus 1 of OIL OF TURPENTINE, = C40 H32 with the oxygen of 1 Of NITRIC ACID (NO5) = 05 gives 1 of RESIN,...... = C40 H32 O By uniting with the oxygen of the nitric acid, therefore, oil ot turpentine, in such trees, might be changed into resin during its passage through the stem, while the nitrogen, being set free, might, at the moment of its liberation, unite with other elements to form those parts or productions of the tree into which this element enters as a necessary constituent. The above must be considered merely as an illustration of the kind of changes which may possibly take place in the interior of certain plants, and in the absence of light, when the nitrates happen to be present. Were I to affirm that such changes actually do occur in the presence of nitric acid, the theoretical chemist would have a right to expect that several collateral questions should be discussed, the consideration of which would here be out of place. 3~. The nitrates may also act in another way, which does not involve the necessity of the total decomposition of the acid they contain. We know that in nature many substances are capable of inducing chemical changes in other compound bodies, without themselves undergoing decomposition. Some beautiful illustrations of this have already been given in a previous lecture, when treating of the action of sulphuric acid upon starch and woody fibre, [Lecture VI.. pp. 113, 114.] But the fact which most immediately bears on the influence of the nitric acid in the living plant, is that mentioned in I.. 126,-that by solution in this acid in the cold, starch is converted into a substance having the composition of Woody fibre. In the interior of the plant changes of this kind may be produced by simple contact only, with the nitric acid, so that, without being decomposed, it may be materially serviceable in promoting those molecular changes which are necessary to the healthy and rapid growth of the plant. II.-THEORY OF THE ACTION OF AMMONIA. 1~. Ammonia is capable of contributing to the growth of the plant, by means of the hydrogen, as well as of the nitrogen it contains. We iS AMMONIA DECOM6POSED IN THE DARK? 165' have seen [notes to pages 136 and 138,] that, according to the results of the best experiments, the whole of the oxygen of the carbonic acid absorbed, is not given off by the leaves of all plants even in the sunshine,-while in the dark this gas is largely and directly imbibed from the air. If in the sap of a plant there be present at the same time a quantity of ammonia, the hydrogen of this ammonia may unite directly with the oxygen of the carbonic acid, forming water and a proportionate quantity of one or other of the several compounds (p. 112), which may be represented by carbon and water. Thus 3 of CARBONIC ACID, = C3 O0 and the hydrogen of 2 of AMMONIA (NH3) = H6 ------- 3~ of Grape 3 of Sugar. Water. give.... C3 H6 06 = C3 H3 03 + 3HO so that where ammonia is present, and circumstances are favourable, sugar or starch may be formed in variable quantity, without the necessary evolution of oxygen gas. This change will take place in the interior of the leaf. And, if the direct decomposition of carbonic acid, and the evolution of its oxygen by the agency of the sun, take place at the same time-with a rapidity proportioned to the intensity of the light,this simultaneous production of sugar,,&c., from. the presence of ammonia, must aid the increase and growth of the plant; and may be one main cause of the fertilizing action of this compound, which has been so long and so generally recognized. When the hydrogen of the ammonia is thus worked up, the quantity of oxygen which escapes from the leaf must be less in proportion; and hence another cause (p. 138) for those discrepancies which have been observed in regard to the bulk of oxygen given off, compared with that of the carbonic acid taken in, by the leaves of different plants. But at the same time the nitrogen is set free. This nitrogen will either be again compounded in the plant with other elements, or, if not required for its healthy growth-that is, if more largely present than is required by the plant-it will be directly emitted by the leaves, or sent downwards and permitted to escape by the root. Hence the reason why pure nitrogen is evolved from the leaves of some plants (p. 95), and why ammonia exercises a beneficial action upon vegetation, in cases where all the nitrogen it contains is neither retained nor required by.the plant. Does this decomposition necessarily require the agency of light? May it not take place in the absence of the sun? I will mention one or two facts which seem to throw light upon this point. 1~. Plants grow in the dark. Though feeble and blanched, they increase largely in bulk; they must, therefore, have the power of assimilating their food to a certain extent, independent of the sun's rays. 2~. Several species of Poa, Plantago, Trifolium arvense, Cheiranthus, &c., become green in the perpetual darkness of mines (Humboldt). 3~. When a little hydrogen is mixed with the air, plants become greenish, even in the dark (Sennebier); and when exposed to the sun, the green becomes unusually intense in such a mixture (Ingenhouss). 8 166 MODIFYING EFFECT OF CLIMATE. The immediate and visible effect of an application of ammonia, or of soot, or of any top-dressing containing ammonia, is to render the green colour much more intense, and in the darkest weather. It is therefore probable, I think, that the hydrogen of the ammonia contributes to this immediate effect, and that the ammonia itself may be decomposed and its elements appropriated to the nourishment of the living vegetable, either by the unaided vital powers of the plant, or in the presence of a feeble light only. Like water, ammonia is peculiarly liable to decomposition, not always of that perfect kind which, for the sake of simplicity, I have endeavoured to explain in the present lecture, yet such as to render the elements of which it consists available to the general nourishment of the plant. ~ 7. Comparative influence of nitric acid and of ammonia in dfferent climates. It follows, from what is above stated, that the beneficial influence of ammonia upon vegetation will be readily perceived in all climates in which plants are found to flourish. Its effects will be greater and more rapid where the heat and light are more intense,-only because by these agents the functions of all life are stimulated. Not so with the nitric acid in the nitrates. In the presence of organic compounds, that is, in the sap of the plant, it is less easily decomposed than ammonia. It requires the interference of more powerful agentsof a higher temperature, or of more brilliant light,-and thus its efficacy upon vegetation will be more dependent upon season and climate. Now, we have seen that in tropical countries the nitrates are produced in the greatest abundance, and there the high temperature and the brilliant sun should render them most useful to vegetation. Such is well known to be the case, and it may be regarded as one of those bountiful adaptations with which all nature is full-that in these warmer regions, the ammonia produced in the soil is first converted into nitric acid, that it may remain fixed, and that this acid again is decomposed by the same agents (light and heat), when it enters the living plant, and is required to minister to its growth. On the other hand, it may no less be regarded as a wise provision, that in colder and more uncertain climates, where warm and brilliant summers are less to be depended upon, that compound of nitrogen (ammonia) should more abound, which is most easily decomposed in the living plant, which is fitted in comparative darkness to yield up its nitrogen, and by the hydrogen it contains, to compensate in some slight degree for the partial absence of the sun's rays. From these views, therefore, we should draw this further practical conclusion-that in our climate, ammonia is sure to promote vegetation, and in every season, while the nitrates will produce their taximumn effect, other things being equal, in such only as have abundant warmth and sunshine. Is this conclusion consistent with observation? Will it serve to explain any of the apparent failures which have occasionally been experienced in the employment of the nitrates? ~ 8. Stimulating influence of these conmpounds. There remains one other point in regard to the effect of these two compounds upon vegetation, to which I would request your attention. STIMULATING INFLUENCE OF NITRIC ACID.AND OF AMMONIA. 167 We have seen that the quantity of nitrogen contained in a crop raised by the aid of farm-yard manure, is very much greater than that which exists in the manure itself, and the views just exposed serve to indicate the sources from which the excess is derived. But suppose that upon two patches of ground, of equal quality, the one of which is manured and the other not, equal quantities of the same seed be sown, it is consistent with experience-that the crop reaped from the manured portion will not only contain more nitrogen than that reaped from the unmanured portion, but so much more as shall considerably exceed that contained in the manure itself. Thus suppose the crop raised from the unmanured land to contain 100 lbs. of nitrogen, and that the manure laid on the other portion contained 100 lbs. also, the crop which is reaped from this latter portion, in favourable seasons, will exceed, and probably very far exceed, 200 lbs. Hence the effect of the ammonia, &c., in the farm-yard manure, is not merely to yield its own nitrogen to the plant, but to enable it, in some way hitherto unexplained, to draw from other sources a larger portion of the same element than it would otherwise do. So also with the nitrates. If two equal portions of the same grass or corn-field, in early spring, be, measured off, and one of them be topdressed with nitrate of soda or with saltpetre, the weight of nitrogen contained in the crop of hay or corn reaped from the latter, will generally be found to exceed that contained in the crop from the former, by a quantity much greater than that which was present in the nitrate with which the land was dressed.* In addition, therefore, to the nitrogen diThe following calculations illustrate the statement in the text:-Mr. Gray, of Dilston, [see Journal of Royal English Agricultural Society,] applied nitrate of soda to grass land in the proportion of 112 Ibs. to the acre. The produce without nitrate amounted to 2 tons 81 stones with 112 lbs. of nitrate to 3 tons 146 stones Increase, 1 ton 65 stones, or 3150 lbs. And 3150- 112 288 lbs. the increase of hay from each pound of nitrate of soda. l But allowing this hay to contain only one per cent. of nitrogen, 28 lbs. will contain 42 ounces of ni. trogen, which is nearly double the quantity actually present in the nitrate employed. Again, in the case of a crop of grain-Mr. Hyett applied nitrate of soda to a field of wheat and compared the produce with that from an equal p'rtion to which no top-dressing was applied. CORN. STRAW. Bush. pks. pts. Cwt. qrs. lbs. Nitrated.... 43 2 11 31 2 3 Without nitrate.. 33 2 6 23 1 21 Excess, 10 0 5 8 0 10 Calculating the bushel of corn at 60 lbs., the excess of corn amounted to 600 lbs., containing 24% per cent. or 147 Ibs. of gluten and albumen. The nitrogen in these substances, when properly dried, is from 15 to 17 per cent. If we suppose the gluten not to have been quite dry, and allow only 14 per cent,. of nitrogen, 147 lbs. would contain 20% Ibs. of this element. But the nitrated corn contained 5 per cent. more gluten and albumen than the un-nitrated, which in 33 bushels (2000 Ibs.) gives 100 Ibs. of gluten in excess, containing 14 Ibs. of nitrogen. And 8 cwt. of straw (900 lbs.) contained one-third of a per cent. of nitrogen, [Boussingault,] or in all 3 lbs. Therefore the quantity of nitrogen present in the nitrated crop above that in the un-nitrated was as follows: 10. In 600 Ibs of wheat at 24,1 per cent. of gluten....... 20% Ibs. Nitrogen. 2~. In 20)0 lbs. of wheat at5 percent. of gluten contained in excess, 14 lbs. do. 3~. In 900 lbs. of straw at one.third per cent........ 3 lbs. do. Total nitrogen... =37% lbs. But the nitrogen in 1 cwt. of dry nitrate of soda, as already stated, is only 19 lbs. or little t[ Dry nitrate of soda contains about 162 per cent. of nitrogen, being 19 lbs. to the cwt., or two and three-fifth ounces to the pound; but as it is usually applied, it contains from 5 to 10 per cent. of water. The nitrogen, therefore, may be estimated at 2% ounces in the pound.] 168 HOW THIS INFLUENCE IS MANIFESTED. rectly conveyed to the plant by these nitrates, they also exercise some other influence, by which they enable the living vegetable to draw from natural sources a much larger supply than they would otherwise be capable of doing. What is this influence, and how is it explained? This I suppose to be that kind of influence to which writers on agriculture are in the habit of alluding, when they speak of certain substances stimulating plants, or acting as stimulants to their growth, though the term itself conveys to the mind no distinct idea of the mode of operation intended to be indicated-of the way in which the effect is produced. In the present case, this special action of ammonia and the nitrates, and perhaps also of immediate applications of manure in general, appears to arise from their affording to the plant, in its early youth, a copious supply of nitrogenous food, bywhich it is enabled at once to shoot out in a more healthy and vigorous manner. It thrusts forth roots in greater numbers, and to greater distances, and is thus enabled to extract nourishment from a greater extent and depth of soil than is ever reached by the sickly plant-it expands larger and more numerous leaves, and thus can extract from the air more of ekery thing it contains which is fitted to supply the wants of the living vegetable; as the stout and healthy savage can hunt and fish to support many lives, while the feeble or sickly can scarcely secure sustenance for himself alone. Feed a wild animal well the first few months of its life, and you may set it loose to prey for itself; starve it in its infancy, and its growth and strength will be stunted, and it may lead a wretched and hungry life. Even in soils, then, and situations, which are capable of yielding to the plant every thing it may require for its ordinary growth, it is an important object of the art of husbandry to discover what substances are especially necessary or grateful to particular crops, and to apply these directly, and in abundance, to the new-born plant,-in order that it may acquire sufficient strength to be able to avail itself in the greatest degree of the stores of food which lie within its reach. Concluding observations regarding the organic constituents of plants. We have now considered the most important of those questions connected with the organic elements of plants, which are directly interesting to the practical agriculturist. We have seen1~. That all vegetable productions consist of two parts-one the organic part, which is capable of being burned away in the air-the other, the inorganic part, which remains behind in the form of ash. 2~. That this organic part consists of carbon, hydrogen, oxygen, and nitrogen only. 3~. That plants derive the greater part of their carbon from carbonic acid, of their hydrogen and oxygen from water, and of their nitrogen from ammonia and nitric acid. 4~. That by far the largest portion of those substances which form *the principal mass of plants, such as starch and woody fibre, consists of carbon united to oxygen and hydrogen in the proportions in which they more than half the quantity, which in consequence of the presence and action of the nitrate the wheat was enabled to obtain and appropriate above the quantity appropriated by the wheat in the un-nitrated part of the field. It requires no further proof, therefore, to show that the nitrate of soda and the nitrates must act in some other way in reference to vegetation, than by simply supplying aportion of nitrogen. CONCLUDING OBSERVATIONS. 169 cxist in water,-or, in other words, may be represented by carbon and water in various proportions. 5~. That the food on which they live enters by the roots and leaves of plants,-that the leaves, under the influence of the sun, decompose the carbonic acid, give off its oxygen, and retain its carbon,-and that this carbon, uniting with the elements of water in the sap, forms those several compounds of which plants chiefly consist. 6~. That the supply of carbonic acid in the atmosphere is kept up partly by the respiration of animals, partly by the natural decay of dead vegetable matter, and partly by combustion. That ammonia is supplied to plants chiefly by the natural decay of animal and vegetable substances-and nitric acid partly by the natural oxidation of dead organic matter, and partly by the direct union of oxygen and nitrogen, through the agency of the atmospheric electricity. 7~. That while both of these compounds yield nitrogen to plants, they each exhibit.a special action on vegetable life, in virtue of the hydrogen and oxygen they respectively contain-and exercise also a so-called stimulating power, by which plants are induced or enabled to appropriate to themselves, from other natural sources, a larger portion of all iheir constituent elements than they could otherwise obtain or assimilate. In illustrating these several points, it has been necessary to enter occasionally into details which, to those who have heard or may read only the later lectures, may not be altogether intelligible. I am not aware, however, of having introduced any thing of which the full sense will not appear on a reference to the statement by which it is preceded. We are now to consider the inorganic constituents of plants,-their nature,-the source (the soil) from which they are derived,-their uses in the vegetable and animal economy,-how the supply of these substances is kept up in nature,-and how, in practical husbandry, the want of them may be at once efficaciously and economically supplied by art. This division of our subject, though requiring a previous knowledge of the principles discussed in the foregoing lectures, will be more essentially of a practical nature, and will lead us to consider and illustrate the great leading principle by which the practical agriculturist ought to be guided in the cultivation and improvement of his land. We shall here also find much light thrown upon our path by the results of geological inquiry; and it is in the considerations I am.now about to bring before you, that I shall have to direct your attention most especially to the principal applications of Geology to Agriculture. LECTURES ON THE APPLICATIONS OF CHEMISTRY AND GEOLOGY TO AGRI CULTUR E ON THE INORGANIC ELEMENTS OF PLANTS. LECTURE IX. Inorganic constituents of vegetable substances.-Relative proportions of organic and inorganic matter in plants.-Unlike proportions in unlike species.-Kind of inorganic matter which exists in different species.-Nature and properties of the several inorganic elemen tary bodies found in plants. THE consideration of the inorganic constituents of plants is no less important to the art of culture than the study of their organic elements, which has engaged our sole attention in the preceding part of these lectures. It has already been shown that when vegetable substances are heated to redness in the air, the whole of the so-called organic elements-car bon, hydrogen, oxygen, and nitrogen-are burned away and disappear; while there remains behind a fixed portion, commonly called the ash, which does not burn, and which in most cases undergoes no diminution when exposed to a red heat. This ash constitutes the inorganic portion of plants. The organic or combustible part of plants constitutes, in general, from 88 to 99 per cent. of their whole weight, even after they are dried. Hence the quantity of ash left by vegetable substances in the green state is often exceedingly small. It therefore long appeared to many, that the inorganic matter could be of no essential or vital consequence to the-plant-that being, without doubt, derived from the soil, it was only accidentally present,-and that it might or might not be contained in the juices and solid parts of the living vegetable, without materially affecting either its growth or its luxuriance. Were this the case, however, the quantity and quality of the ash left by the same plant should vary with the soil in which it grew. If one soil contained much lime, another much magnesia, and a third much potash, whatever plant was grown upon these several soils should also contain in greatest abundance the lime, the magnesia, or the potash, which abounded in each locality-and the nature, at least, of the ash, if not its proportion, should be nearly the same in every kind of plant which is grown upon the same soil. Careful and repeated experiments, however, have shown1~. That on whatever soil a plant is grown, if it shoots up in a healthy manner and fairly ripens its seed, the quantity and quality of the ash is nearly the same; and 2~. That though grown on the same soil, the quantity and quality of the ash left by no two species of plants is the same-and that the ash differs the more widely in these respects, the more remote the natural affinities of the several plants from which it may have been derived. Hence there is no longer any doubt that the inorganic constituents contained in the ash are really essential parts of the substance of plants, -that they cannot live a healthy life or perfect all their parts without them,-and that it is as much the duty of the husbandman to supply these inorganic substances when they are wanting in the soil, as it has always been considered his peculiar care to place within the reach of 13-4 178 WEIGHTS OF ASH LEFT BY DIFFERENT SPECIES. the growing plant those decaying vegetable matters which are most likely to supply it with organic food. For the full establishment of this fact, we are indebted to Sprengel. Others, as De Saussure, have published many important and very useful analyses of the inorganic matters left by plants, but for the illustration of.the important practical bearing of this knowledge of their inorganic constituents on the ordinary processes of agriculture, we are, I believe, in a great measure indebted to the writings and numerous analytical researches of Sprengel. It is difficult to conceive the extent to which the admission of the essential nature and constant quality of the inorganic matter contained in plants, must necessarily modify our notions and regulate our practice in every branch of agriculture. It establishes a clear relation between the kind and quality of the crop, and the nature and chemical composition of the soil in which it grows-it demonstrates what soils ought to contain, and, therefore, how they are to be improved-it explains the effect of some manures in permanently fertilizing, and of some crops in permanently impoverishing the soil-it illustrates the action of mineral substances upon the plant, and shows how it may be, and really is, in a certain measure, fed by the dead earth:-over nearly all the operations of agriculture, indeed, it throws a new and unexpected light. Of this, I am confident, you will be fully satisfied when I shall have discussed the various topics I am to bring before you in the present part of my lectures. ~ 1. Of the relative proportions of inorganic matter in different vegetable substances. As above stated, the inorganic matter contained in different vegetable productions varies from 1 to 12 per cent, of their whole weight. The following table exhibits the weight of ash left by 100 lbs. of the more commonly cultivated plants-according to the analyses of Sprengel [Chemie, vol. ii., passim]:Undried. Dried in air.' Grainof Perct. Potato..... 083 lbs. - 265 lbs. Wheat. 1-18 lbs. Turnip..... 063 7-05 Rye... 104 Do. white.. 0 8 J. Barley. 2-35 Carrot..... 0-66 5'09 Do. dried at 212, 2-52 J. Parsnip..... 082 4-34 Oats... 2-58 Leaf of Potato. 4-79 Field Beans. 2-14 -- Turnip... 1' 8 2'91 Peas. 2-46 -- do. white. 21-8 J. — Carrot... 198 10-42 - Parsnip... 3-00 15-76 Dry straw of Perct. - Cabbage.. 53 75.5 Wheat.. 351 lbs. Oats... 5.74 Green. In hay. Barley... 5-24 Lucerne... 2-58 lbs. 9-55 lbs Rye... 2-79 Red Clover... 157 7-48 Beans... 3'12 White Clover.. 174 9-13 Peas... 4-97 Rye Grass.... 1-69 5-3 Of the substances in this column the potato lost by drying in the air 69 per ct. of water, the turnip 9t, the carrot 87, the turnip leaf 86, the carrot leaf, the parsnip, and the parsnip leaf, each 81, and the cabbage leaf 93 per cent. IT VARIES WITH THE SPECIES OF PLANTS. 179 In the parts of trees dried in the air there are found of inorganic matterWood. Leaves. Wood. Leaves. In the Elm.. 188 11-8 In the Oak.. 0-21 4-5 Willow. 0:45 8-23 Birch.. 034 5.0 Poplar. 1-97 9-22 Pitch pine 0-25 3-15 Beech. o 036 6-69 Comm. furze 0-82 3'1 J. In looking at the preceding tables, you cannot fail to be struck with one or two points, which they place in a very clear light. 1~. That the quantity of inorganic matter contained in the same weight of the different crops we raise, or of the different kinds of vegetable food we eat, or with which our cattle are fed, is very unlike. Thus 100 lbs. of barley, or oats, or peas, contain twice as much inorganic (earthy and saline matter, that is,) as an equal weight of wheat or ryeand the same is the case with lucerne and white clover hays, compared with the hay of rye grass. 2~. The quantity contained in different parts of the same plant is equally unlike. Thus 100 lbs. of the grain of wheat leave only ] lbs. of ash, while 100 lbs. of wheat straw leave 3- lbs. So the dry bulb of the turnip gives only 7 per cent., while the dry leaf leaves 13 per cent. of ash when it is burned. The dry leaves of the parsnip also contain nearly 16 per cent., though in its root, when sliced and dried in the air, there are only 4 per cent. of inorganic matter. In trees the same fact is observed. The wood of the elm contains less than 2 per cent., while its leaves contain nearly 12 per cent.;-the wood of the oak leaves only ~th of a per cent., while from its leaves 4j per cent. or 22 times as much are obtained. The leaves of the willow and of the beech also contain about. twenty times as much as the wood of these trees does, when it has been dried under the same conditions. These differences cannot be the result of accident. They are constant on every soil, and in every climate; they must, therefore, have their origin in some natural law. Plants of different species must draw from the soil that proportion of inorganic matter which is adapted to the constitution, and is fitted to supply the wants of each;-while of that which has been admitted by the roots into the general circulation of the plant, so much niust proceed to and be appropriated by each part as is suited to the functions it is destined to discharge. And as from the same soil different plants select different quantities of saline and earthy matter, so from the same common sap do the bark, the leaf, the wood, and the seed, select and retain that proportion which the healthy growth and developement of each requires. It is with the inorganic, as with the organic food of plants. Some draw more from the soil, some less, and of that which circulates in the sap, only a small portion is expended in the production of the flower, though much is employed in forming the stem and the leaves. On the subject of the present section, I shall add two other observations. 1~. From the constant presence of this inorganic matter in plants, and from its being always found in nearly the same proportion in the same species of plants,-a doubt can hardly remain that it is an essential part of their substance, and that they cannot live and thrive without it. But that it really is so, is placed beyond a doubt, by the further experimen 180 QUALITY OF THE ASH FROM DIFFERENT PLANTS. tal fact, that if a healthy young plant be placed in circumstances where it cannot obtain this inorganic matter, it droops, pines, and dies. 2~. But if it be really essential to their growth, this inorganic matter must be considered as part of the food of plants; and we may as correctly speak of feeding or supplying fbod to plants, when we add earthy and mineral substances to the soil, as when we mix with it a supply of rich compost, or of well fermented farm-yard manure. I introduce this observation for the purpose of correcting an erroneous impression entertained by many practical men in regard to the way in which mineral substances act when applied to the soil. By the term manure they generally designate such substances as they believe to be capable of feeding tle plant, and hence reject mineral substances, such as gypsum, nitrate of soda, and generally lime, from the list of manures properly so called. And as the influence of these substances on vegetation is undisputed, they are not unfrequently considered as stimulants only. Yet if, as I believe, the use of a wrong term is often connected with the prevalence of a wrong opinion, and may lead to grave errors in practice,-I may be permitted to press upon your consideration the fact above stated-I may almost say demonstrated-that plants do feed upon dead unorganized mineral matter, and that you are, therefore, really manuring your soil, and permanently improving it, when you add to it such substances qf a proper kind. ~ 2. Of the kind of inorganic matter found in plants. I have said above, of a proper kind-for it is not a matter of indifference to a plant, what kind of earthy or saline matter it takes in by its roots. Each species of plant, we have seen, withdraws from the soil a quantity of inorganic matter, which is peculiar to itself, and which, as a whole, is nearly constant. So also each species, in selecting for itself a nearly constant weight of inorganic matter, while it chooses generally the same.kind of saline and earthy ingredients as other plants do, to make up this weight, yet picks them out in proportions peculiar to itself. Thus for example, lime is present in the ash of nearly all plants, but while 100 lbs. of the ash of wheat contain 8 pounds of lime, the same weight of the ash of barley contains only 44 lbs. So also potash is contained in the ash of most plants grown for food, but in the ash of the turnip, there are 371 per cent. of potash, while in that of wheat there are only 19 per cent. Again, in different parts of the same plant, a like difference prevails. The ash of the turnip bulb contains 16~ per cent. of soda, —that of the leaf, little more than 12 per cent. On the other hand, the lime in that from the bulb constitutes less than 12 per cent. of its weight, while in that of the leaf it amounts to upwards of 34 per cent. These relative proportions among the different kinds of inorganic matter contained in the ash of plants-like the whole weight itself of the ash-is nearly constant in the same species, and in the same part of a plant, when it is grown in a propitious soil. It is not, therefore, as I have already said, a matter of indifference to the living vegetable, whether it meets with this or with that kind of inorganic matter in the land on which it grows-whether its roots are supplied with lime, or with potash, or with soda. The soil mnust contain all these substances, and in such THE SOIL MUST CONTAIN WHAT THE PLANT REQUIRtES. 181 quantity as easily to yield to the crop so much of each as the kind of plant specially requires. And if one of these necessary inorganic forms of matter be rare or wholly absent, the crop will as certainly prove sickly or entirely fail, as if the organic food supplied by the vegetable matter of the soil were wholly withdrawn. It is, therefore, as much the end of an enlightened agricultural practice to provide for the various requirements of each crop in regard to inorganic food, as it is to endeavour to enrich the land with purely vegetable substances. Since, also, as above shown, not only the relative quantity of inorganic matter, but its kind or quality, likewise, is different in different plants,-it may be, that a soil on which one crop cannot attain to maturity may yet surely and completely ripen another-a fact which is proved by every-day experience. The soil, which is unable to supply with sufficient speed all the lime or the potash required for one crop, may yet easily meet the demands of another, and afford an ample return to the husbandman when the time of harvest comes.* *On the other hand, this consoling, at once, and stimulating reflection must arise in the mind of the practical agriculturist from the consideration of the above facts-that if the soil contain all the inorganic substances required by plants, and in sufficient quantity, it will grow, if rightly tilled, any crop which is suited to the climate,-or conversely to make it capable of growing any crop, he has only-along with his usual supplies of animal or vegetable matter-to add in proper quantity these inorganic substances also. Here a crowd of questions cannot fail to start up in your minds. You will ask, for example, 1~. What are the several inorganic substances usually present in cultivated plants, and what their respective proportions? 2~. Which of them are most generally present in the soil? 3~. In what form can those which are less abundant be added most easily, most advantageously, and most economically? We shall consider in succession these, and along with them other On the same principle, also, some of the interesting facts connected with the grafting of trees are susceptible of a satisfactory explanation. The root of a tree selects from the soil the kind and quality of inorganic matter which are required for the healthy maturity of its own parts, Any other tree may be grafted on it, which in its natural state requires the same kind of inorganic matters in nearly the same proportion. This is the case generally with varieties of the same species-more rarely with trees or plants of different species-and least frequently with such as belong to different genera. The lemon may be grafted on the orange, because the sap of thelatter contains all the earthy and saline substances which the former requires, and can supply them in sufficient quantity to the engrafted twig. But the fig or the grape would not flourish or ripen fruit on the same stock-because these fruits require other substances than the root of the orange cares to extract from the soil, or in greater quantity than the sap of the orange can supply them. It is not for want of organic food, for of this the sap of nearly all plants is full-and we have seen in our previous lectures, how the sugar of the fig, the tartaric acid of the grape, and the citric acid of the lemon, may all be produced by natural processes from the same common organic food. When we plant a tree or sow a crop on a soil which does not contain all that the tree or crop requires, the tree must slowly perish,-the crop cannot yield a profitable return. So it is in grafting. The sap of the stock must contain all that the engrafted bud or shoot requires in every stage of its growth. Or to recur to our former illustrationif the potash or lime required by the grape be not taken up and in sufficient quantity by the root of the orange, it will be in vain to graft the former upon the latter with the hope of its coming to maturity or yielding perfect fruit. This principle may also serve to explain many other curious and hitherto obscure cir. Cumstances connected with the practice of the gardener. 182 ELEMENTARY SUBSTANCES FORMED IN THE ASH. subsidiary questions, which will hereafter present themselves to. our notice. ~ 3. Of the several elementary bodies usually met with in the ash of plants What is understood by the term element or elementary body among chemists has already been explained (Lect. I., p. 22), as well as the number and names of those elements with, which we are at present acquainted. Of these elementary bodies we have seen that the organic part of plants contains rarely more than four, namely, carbon, hydrogen, oxygen, and nitrogen, in various proportions. In the inorganic part there occur nine or ten others, generally in combination, either with oxygen.or with one another. The names of these inorganic elements are as follow: Name. In combination with Forming CHLORINE. Metals CHLORIDES.. IODINE.. do. IODIDES. SULPHUR. do. SULPHURETS. Hydrogen SULPHURETTED HYDROGEN.* Oxygen SULPHURIC ACID. PHOSPHORUS do. PHOSPHORIC ACID. POTASSIUM. do. POTASH. Chlorine CHLORIDE OF POTASSIUM. SODIUM.. Oxygen SODA. Chlorine CHLORIDE OF SODIUM OR F COMMON SALT. CALCIUM. do. CHLORIDE OF CALCIUM. Oxygen LIME. MAGNESIUM do. MAGNESIA. ALUMINIUM do. ALUMINA. SILICON. do. SILICA. IRON and do. OXIDES. MANGANESE 5 Sulphur SULPHURETS. Other elementary bodies, chiefly metallic, occur in some plants-occasionally, and in very small quantity,-but, so far as is yet known, they do not appear to be either necessary to their growth, or to exercise any material influence on the general vegetation of the globe. Of all the above elementary bodies it may be said, generally, 1~. That with the exception of sulphur,t they are not known to exist or to be evolved, in any quantity, anywhere on the surface of the globe, in. their simple, elementary, or uncombined state; and that, therefore, in this state they in no way affect the progress of vegetable growth, or require to occupy the attention of the practical agriculturist. 2~. They all, however, exist in nature more'or less abundantly in a state of combination with other substances, and chiefly with oxygen, [for an explanation of the meaning and of the laws of chemical combination, see Lecture II., p. 32]-but in no state of combination are they known to be generally diffused through the atmosphere of the globe, so as to be Called also Hydro-sulphuric Acid. t Given off in vapour from active volcanoes, and from rents and fissures in ancient volcanic countries. CHLORINE AND MURIATIC ACID. 183 capable of entering plants by their leaves or other superior parts. They must all, therefore, enter by the roots of plants,-must consequently exist in the land,-and must all be necessary constituents of that soil in which the plants that contain them grow. It will not be necessary, therefore, to consider so much the relative proportions in which these elementary bodies themselves exist in plants, as that of the several chemical compounds which they form with oxygen, or with one another-in which states of combination they exist in the soil, and are found in the circulation and substance of the plant. As a preliminary to this inquiry, however, it will be proper to lay before you a brief outline of the nature and properties of these compound bodies themselves-and of the direct influence they have been found to exercise upon vegetable life. ~ 4. Of those compounds of the inorganic elements which enter directly into the circulation, or exist in the substance and ash of plants. I —CHLORINE AND MURIATIC ACID. Chlorine.-If a mixture of common salt and black oxide of manganese [sold by this name in the shops] be.put into a flask or bottle of colourless glass, and sulphuric acid (oil of vitriol) be poured upon-it, a gas of a greenish-yellow colour will be given off, and will gradually fill the bottle. This gas is distinguished by the name of chlorine. It is readily distinguished from all other substances by its greenishyellow colour, and its pungent disagreeable smell. It extinguishes a lighted taper, but phosphorus, gold leaf, metallic potassium and sodium, and many other metals, take fire in it and burn of their own accord. It is nearly 4~ times heavier than common air, and therefore may be readily poured from one vessel to another. WTater absorbs twice its own bulk of the gas, acquiring its colour, smell, and disagreeable astringent taste. Animals cannot breathe it without suffocation-and, when unmixed with air, it speedily kills all living vegetables. The solution of chlorine in water was found by Davy to promote tile germination of seeds. It does not exist, and is rarely evolved, [see Lecture V., p. 94,] in nature in a free or uncombined state, and therefore is not known to exercise any direct action upon the general vegetation of the globe. It exists largely, however, in common salt (chloride of sodiuln), every 100 lbs. of this substance containing upwards of 60 lbs. of chlorine. Indirectly, therefore, it may be supposed to influence, in some degree, the growth of plants, where common salt exists naturally in the soil, or is artificially applied in any form to the land. Muriaiic acid, the spirit of salt of the shops, consists of chlorine in combination with hydrogen. It is a gas at the ordinary temperature of the atmosphere, but water absorbs between 400 and 500 times its bulk of it, and the acid of the shops is such a solution in water, of greater or less strength. Muriatic acid has an exceedingly sour taste, corrodes the skin, and in its undiluted state is poisonous both to animals and plants. It dissolves common pearl ash, soda, magnesia, and limestone, with effervescence; and readily dissolves also, and combines with, many earthy substances which are contained in the soil. 184 IODINE, SULPHUR, AND SULPHUROUS ACID. When applied to living vegetables in the state of an exceedingly di lute solution in water, it has been supposed upon some. soils, and in some circumstances, to be favourable to vegetation. Long experience, however, on the banks of the Tyne, and elsewhere, in the neighbourhood of the so-called alkali* works, has proved that in the state of vapour its repeated application, even when diluted with much air, is in many cases fatal to vegetable life. Poured in a liquid state upon fallow land, or land preparing for a crop, it may assist the growth of the future grain, by previously forming, with the ingredients of the soil, some of those compounds which have been occasionally applied as manures, and which we shall consider hereafter. Chlorine is represented by Cl, and muriatic acid by HCI. I. —IODINE. Iodine is a solid substance of a lead grey colour, which, when heated, is converted into a beautiful violet vapour. It exists in combination chiefly with sodium, as Iodide of Sodium, in sea water and in marine plants; but it has not hitherto been detected in any of the crops usually raised for food. Like chlorine, it is poisonous both to animals and plants.; and was found by Davy to assist and hasten germination. It may possibly exert some hitherto unobserved influence upon vegetation, when it is applied to the soil in districts where sea-ware is largely collected and employed as a manure. Iodine is slightly soluble in water, and this solution has been mentioned in a previous lecture (VI., p. 107), as affording a ready means of detecting starch by the beautiful blue colour it gives with this substance. III.-SULPHUR, SULPHUROUS AND SULPHURIC ACIDS, AND SULPHURETTED HYDROGEN. 1~. Sulphur is a substance too well known to require any detailed description. In an uncombined state itoccurs chiefly in volcanic countries,'but it may sometimes be observed in the form of a thin pellicle on the surface of stagnant waters-or of mineral springs, which are naturally charged with sulphurous vapours. In this state it is not known materially to influence the natural vegetation in any part of the globe. It has, however, been employed with some advantage in Germany as a top-dressing for clover and other crops to which gypsum in that country is generally applied. The mode in which it may be supposed toact will be considered hereafter.* 2~. Sulphurous acid.-When sulphur is burned in the air it gives off a gaseous substance in the form of white fumes of a well known intensely suffocating odour. These fumes consist of a combination of the sulphur In these works carbonate of soda (the common soda of the shops) and suilphate of soda 26 0.9 2-3 Oxide of Manganese.trace. 03) Phosphoric Acid.. 02 35 4-8 1-8 9'9 Sulphuric Acid.. 14 22 10 61 13 3 Chlorine... 01 13 09 0-6 11-4 Carbonic Acid.. - - 11 0 100 100 100 100 100 The most striking differences in the above table are the comparatively large quantity of potash in the oat straw-of lime in that of barleyof phosphoric acid in that of wheat-of sulphuric acid in that of ryeand of all the saline substances in rape straw. These differences are not to be considered as constant, nor will the numbers in any of the above columns represent correctly the composition of the ash of any variety of straw we may happen to burn (see p. 183), but they may be safely depended upon as showing the general composition of such ashes, as well as the general differences which may be expected to prevail among them. That such ashes should prove useful to vegetation might be inferred not only from their containing many saline substances which are known to act beneficially when applied to the land, but from the fact that they have actually been obtained from vegetable substances. If inorganic matter be necessary to the growth of wheat, then surely the mixture of such matters contained in the ash of wheat straw is more likely than any other we can apply to promote the growth of the young wheat plant. A question might even be raised, whether or not in some soils, rich in vegetable matter, the ash alone would not produce as visible an effect upon the coming crop, as the direct application of the straw, either in the dry state or in the form of rotted farm-yard manure. And this question would seem to be answered in the affirmative, by the result of many trials of straw ashes which have been made in Lincolnshire. In this county the ash of five tons of straw has been found superior in efficacy to ten tons farm-yard manure, (Survey of Lincolnshire, p. 304, quoted in British Husbandry, II., p. 334.) This is perfectly consistent with theory, yet as vegetable matter appears really essential to a fertile soil, and as the quantity of this vegetable matter is lessened in some degree by every corn crop we raise, it cannot be good husbandry to manure for a succession of rotations with saline substances only. The richest soil by this procedure must ultimately be exhausted. On the other hand, where much vegetable matter exists, and especially what is usually called inert vegetable matter, it may be an evidence of 358 COMPARATIVE EFFECTS OF STRAW AND STRAW ASH. great skill in the practical farmer to apply for a time the ashes only of his straw-or some other saline mixture to his land. The practice of burning the stubble on a windy day has been found in the East Riding of Yorkshire to produce better clover, and to cause a larger return of wheat, (British Husbandry, ii., p. 333)-for this purpose, however, the stubble must be left of considerable length. In Germany, rape straw-which the above table shows to be rich in saline and earthy matter, and, therefore, exhausting to the land-is spread over the field and burned in a similar manner. The destruction of weeds and insects which attends this practice, is mentioned as one of its collateral advantages, (Sprengel, Lehre vom Diinger, p. 355.) In the United States, where, according to Captain Barclay, the straw is burned merely in order that it may be got rid of, (Agricultural Tour in the United States, pp. 42 and 54,) it would cost little labour to apply the ash to the soil from which the straw was reaped, while it would certainly enlarge the future produce-and in Little Russia, where from the absence of wood the straw is universally burned for fuel, and the ashes afterwards consigned to the nearest river, the same practice might be beneficially adopted. However fertile, and apparently inexhaustible, the soils in this country may appear, the time must come when the present mode of treatment will have more or less exhausted their productive powers. It is not advisable, as I have already said, wholly to substitute the ash for the straw in ordinary soils, or in any soils for a length of time, yet that it may be partially so substituted with good effect-or that straw ashes will alone give a large increase of the corn crop, and therefore should never be wasted-is shown by the following comparative experiments, conducted as such experiments should be, during an entire rotation of four years. The quantity of manure applied, and the produce per imperial acre, were as follows: 15 cwt. barley 3 tons stable dung 2 tons of rotten No manure. straw burned in the straw dung eight on the ground. state. months old. 10. Turnips, 22 lbs. 81 cwt. 183 cwt. 16% cwt. 2~. Barley, 141 bush. 304 bush. 301 bush. 30` bush. 3~. Clover, 8 cwt. 18 cwt. 20 cwt. 21 cwt. 4~. Oats, 32 bush. 18 bush. 38 bush. 40 bush. The kind of soil on which this experiment was made is not stated, (British Husbandry, ii., p. 248,) but it appears to show, as we should expect, that the effects of straw ash are particularly exerted in promoting the growth of the corn plants and grasses which contain much siliceous matter in their stems-in short, of plants similar to those from which the ash has been derived. Theory of the action of straw ash.-That it should especially promote the growth of such plants appears most natural, if we consider only the source from which it has been obtained, but it is fully explained by a further chemical examination of the ash itself. The soluble matter of wood ash in general contains but a small quantity of silica-while that part of the straw ash which is taken up by water contains very much. Thus a wheat ash analyzed by Berthier contained of COMPOSITION AND USE OF DUTCH ASHES. 359 Soluble salts.. 19 per cent. Insoluble matter... 81 " 100 and that which was dissolved by water consisted of Silica... 35 per cent. Chlorine.. 13 " Potash and soda.. 50 " Sulphuric acid... 2 " 100 so that it was a mixture of soluble silicates and chlorides with a little sulphate of potash and soda. These soluble silicates will find an easy admission into the roots of plants, and will readily supply to the young stems of the corn plants and grasses the silica which is indispensable to their healthy growth. f. Turf or peat ashes, obtained by the burning of peat of various qualities, are also applied with advantage to the land in many districts. They consist of a mixture in which gypsum is usually the predominating useful ingredient-the alkaline salts being present in very small proportion. Of ashes of this kind those made in Holland, and generally distinguished by the name of Dutch ashes, are best known, and have been most frequently analyzed. The following table exhibits the composition of some varieties of ashes from the peat of Holland and from the heath of Luneburg, examined by Sprengel:Dutch Ashes (grey). Luneburg Ashes (reddish)...~__.~. _ —' - _ - -- Best Inferior Worst Good Producing quality, quality. quality. quality. little effect. Silica....... 47-1 55-9 70'4 31-7 43-3 Alumina....... 45 3-5 4'1 5'1 9-7 Oxide of Iron..... 6-6 5-4 4-1 17-7 193 Do. of Manganese... 10 4'3 0-2 0-5 3-5 Lime...... 13-6 8-6 6.1 31-9 71 Magnesia...... 4-9 1'6 3-9 1'0 4-6 Potash....... 02 0-2 01 01 - Soda....... 1'0 -39 0-4 0-1 Gypsum Sulphuric Acid..... 72 6-4 3-4 6-2 0-2 Phosph. of Lime Phosphoric Acid.... 2-0 0-8 1 3 12 0'2 Common Salt Chlorine..... 12 30 0-5 0'1 0'1 Carbonic Acid..... 41 6.4 5-5 4-4 12'0 Charred Turf.... 6-6 - - - 100'0 100'0 100'0 100'0 100.0* In the most useful varieties of these ashes it appears, from the above analyses, that lime abounds-partly in combination with sulphuric and phosphoric acids, forming gypsum and phosphate of lime-and partly with carbonic acid, forming carbonate. These compounds of lime, therefore, may be regarded as-the active ingredients of peat ashes. Sprengel Lehre vom Dunger, p. 363 et eqg. 360 COMPOSITION AND USE OF COAL ASHES.' et the small quantity of saline matter they contain is not to be considered as wholly without effect. For the Dutch ashes are often applied to the land to the extent of two tons an acre-a quantity which, even when the proportion of alkali does not exceed one per cent., will. contain 45 lbs. of potash or soda, equal to twice that weight of sulphates or of common salt. To the minute quantity of saline matters present in them, therefore, peat ashes may owe a portion of their beneficial influence, and to the almost total absence of such compounds from the less valuable sorts, their inferior estimation may have in part arisen. In Holland, when. applied to the corn crops, they are either ploughed in, drilled in with the seed, or applied as a top dressing to the young shoots in autumn or spring. Lucerne, clover, and meadow grass are dressed with it in spring at the rate,of 15 to 18 cwt. per acre, and the latter a second time with an equal quantity after,the first cutting. In Belgium the Dutch ashes are applied to clover, rape, potatoes, flax, and peas-but never to barley. In Luneburg the turf ash which abounds in oxide of iron is applied at the rate of 3 or 4 tons per acre, and by this. mleans the.physical character of the clay soils, as well as their chemical constitution, is altered and improved. In England peat is in many places'burned fbr the sake of the ashes it yields. Among the most celebrated for their fertilizing qualities are the reddish turf ashes of Newbury, in Berkshire. The soil from beneath which the turf is taken abounds in lime, and the ashes are said to contain from one-fourth to one-third of their weight of gypsum, [British Husbandry, ii., p. 334.] They are used largely both in Berkshire and Hampshire, and are chiefly applied to green crops, and especially to clover.* g. Coal ashes are a mixture of which the composition is very variable. They consist, however, in general, of lime often in the state of gypsum, of silica, and of alumina mixed with a quantity of bulky and porous cinders or half burnt coal. The ash of a coal from St. Etienne, in France, after all the carbonaceous matter had been burned away, was found by Berthier to consist of Alumina, insolublein acids... 62 per cent. Alumina, soluble. 5 " Lime...... 6 " Magnesia..8 " Oxide of Manganese... 3 Oxide and Sulphuret of Iron. 16 " 100 Such a mixture as this would no doubt benefit many soils by the alumina as well as by the lime and magnesia it contains; but in the English and Scotch coal ashes a small quantity of alkaline matter, chiefly soda,f is generally present. The constitution of the ash of our best coals, therefore, may be considered as very nearly resembling that of peat ash, and as susceptible of similar applications. When well 50 bushels per acre (at 3d. a bushel, or 12s. 6d. an acre) increase the clover crop fully one fifth.-Morton ( On Soils," p. 170. t From the common salt with which our coal is so often impregnated. CANE ASHES.-CRUSHED AND DECAYED TRAPS AND LAVAS. 361 burned, it can in many cases be applied with good effects as a top-dressing to grass lands which are overgrown with moss; while the admixture of cinders in the ash of the less perfectly burned coal produces a favourable physical change upon strong clay soils. h. Cane Ashes.-I may allude here to the advantage which in sugargrowing countries may be obtained from the restoration of the cane ash to the fields in which the canes have grown. After the canes have been crushed in the mill they are usually employed as fuel in boiling down the syrup; and the ash, which is not unfrequently more or less melted, is, I believe, almost uniformly neglected-at all events, is seldom applied again to the land. According to the principles I have so often illustrated in the present Lectures, such procedure must sooner or later exhaust the soil of those saline substances which are most essential to the growth of the cane plant. If the ash were applied as a top-dressing to the young canes, or put into the cane holes near the roots-having been previously mixed with a quantity of wood-ash, and crushed if it happen to have been melted-this exhaustion would necessarily take place much more slowly. i. Crushed Grarite.-We have already seen that the felspar existing in granite contains much silicate of potash and alumina. It is, in fact, a natural mixture, which in many instances may be beneficially applied, especially to soils which abound in lime. It is many years since Fuchs proposed to manufacture potash from felspar and mica by mixing them with quicklime, calcining in a furnace, and then washing with water. By this means he said felspar might be made to yield one-fifth of its weight of potash. (Journal of the Royal Institution, I., p. 184.) Mr. Prideaux has lately proposed to mix up crushed granite and quicklime, to slake them together, anat to allow the mixture to stand in covered heaps for some months, when it may be applied as a top-dressing, and will readily give out potash to the soil. Fragments of granite are easily crushed when they have been previously heated to redness, and there can be little doubt, I think, that such a mixture as that recommended by Mr. Prideaux would unite many of the good effects of wood ashes and of lime. k. Crushed Trap.-I need not again remind you of the natural fertility ofdecayedtrap soils (Lec. XII., ~4,) and of the improvementwhich in many districts may be effected by applying them to the land. When granite decays, the potash of the felspar is washed out by the rains, and an unproductive soil remains-when trap decays, on the other hand, the lime by which it is characterised is not soon dissolved out, so that the soil which is produced is not only fertile in itself, but is capable of being employed as a fertilizing mixture for other soils. Thus when itis much decayed it is dug out from pits both in Cornwall and in Scotland, and is applied like marl to the land. 1. Crushed Lavas.-Of the fertile and fertilizing nature of the crushed or decayed lavas I have also already spoken to you (Lee. XII., ~ 4). In St. Michael's, one of the Azores, the natives pound the volcanic matter and spread it on the ground, where it speedily becomes a rich mould capable of bearing luxuriant crops. At the foot of Mount Etna, whenever a crevice appears in the old lavas, a branch or joint of an Opuntia 362 EXPERIMENTS WITH MIXED MANURES. (Cactus Opuntia,-European Indian-Fig) is stuck in, when the rootsinsinuate themselves into every fissure, expand, and finally break up the lava into fragments. These plants are thus not only the means of producing a soil, but they yield also much fruit, which is sold as a refreshing food throughout all the towns of Sicily. (Decandolle, quoted in the Quart. Journ. of Agr., IV. p. 737.) These are all so many natural mineral mixtures of which we may either directly avail ourselves, or which we may imitate by art. Experiments with mixed manures. NOTE.-As a valuable appendix to the preceding observations on mixed manures, I am permitted to insert the following very interesting results obtained during the present season, 1842, from experiments made on the estate of Mr. Burnet, of Gadgirth, near Ayr. The crop to which the several manures were applied was wheat of the eclipse variety, sown on the 29th of October, 1841, and reaped on the 15th of August last. The soil is a loam with subsoil of clay, tile drained and trenched ploughed. It had been in beans the previous year, and gave six quarters per acre, which were sold at 46s. a quarter. No manure had been applied with the bean crop, and except a good dose of lime before sowing the wheat, nothing but the saline mixtures mentioned below was applied with this latter crop. PRODUCE. 100 Ibs. grain Application per imperial acre. r — --- Weight per produced of Straw. Grain. bushel. fine four. cwt. iush. Ibs. lbs. Ibs. Sulphate of Ammonia, 2 cwt.* 35 39 54 60 635 Wood-ashes, 4 cwt.... Sulphate of Ammonia, 2 cwt. Sulphate of Soda, 2 cwt.. 444 49 6 60 63h Wood-ashes, 4 cwt... Sulphate of Ammonia, 2 cwt. Common Salt, 2 cwt.. 45 49 0 60 652 Wood-ashes, 4 cwt... Sulphate of Ammonia, 2 cwt. Nitrate of Soda. I cwt. 44~ 48 20 59 54* Wood-ashes, 4 cwt.. No Application....293 31 38 61+ 76* The reader will observe here that though the first mixture produced a large increase both of straw and grain, a stilllarger additional increase was caused by mixing with the substances of which it consisted either common salt or sulphate of soda or nitrate of soda. Each of these three substances produced nearly the same effect. The soda, therefore, more than the acid with which it was combined, must in these cases have acted beneficially. The comparatively small proportion of fine flour yielded by the nitrated wheat, and the comparatively large proportion ob* The sulphate of ammonia was prepared from urine, and, therefore, contained other admixtures (page 349). The straw was strongest, coarsest, and longest in ripening, where this sulphate was applied. The two guanos produced little luxuriance, but the lots to which they were applied were soonest ripe. XMPORTANCE OF SUCH EXPERIMENTS. 363 tained from that to which no application was made, are also highly deserving of notice. Mr. Burnet has transmitted to me samples of the flour from these several growths of wheat, with the view of determining the relative proportions of gluten they contain. The result of this examination, which cannot fail to be interesting, will be given in a succeeding Leeture —before which, however, I hope the whole of Mr. Burnet's experiments will be laid before the public. It will be observed that Mr. Burnet has exercised a sound discretion in making and trying mixtures not hitherto specifically recommendedIt is by the result of such varied experimental trials, made by intelligent practical men, on different soils and crops, and with mixtures of which the constitution is exactly known, that we shall be able hereafter to correct our theoretical principles-as well as to simplify and render more sure our general practice.'Since writing the above, I am informed that the silicate ofpotash, referred to at p. 349, is manufactured by BMessrs. Dymond, of London, and may be obtained from the London dealers at 56s. a cwt. I expect also, that a silicate ofsoda will soon be brought into the market by the Miessrs. Cooksons, of the Jarrow Alkali Works, at a much lower price. The probable efficacy of these substances, as manures, has, no doubt, been extolled too highly by some-their real efficacy, however, is well deserving of investigation. I insert in the Appendix No. VII, therefore, some suggestions for experiments with these substances, in the hope that during the spring of 1843, some experiments on the subject may be made. LECTURE XV1I. Use of lime as a manure.-Value of lime in improving the soil. —Of the composition of common and magnesian lime-stones.-Burning and slaking of lime.-Changes which slaked lime undergoes by exposure to the air.-Various natural states in which carbonate of lime is applied to the land.-Marl-shell and coral sand,-lime-stone sand and gravel, -crushed lime-stone.-.-Chemical composition of various marls, and shell and lime-stone sands. —Their effects on the soil. —Use of chalk. —Is lime necessary to the soil 7-Exhausting effect of lime.-Analogy between this action of lime and thar of wood-ashes. Quantity of lime to be applied.-Effects of an overdose. —Form in which it may be most prudently used. —When it'ought to be applied in reference to the season-to tle rotation — and to the application of manure.-Its general and special effects on different soils and crops.-Circumstances which influence its action.-Length of lime during which its effects are perceptible. —Theory of the action of time.-Necessity and nature of tlie exhaustion which it sometimes produces.-Sinking of lime into the soil.-Why the application of lime must be repeated.-Action of lime on living animals and vegetables. Suggestions of theory.-Use of silicate of lime. HAVING explained to you the action of the most important saline and mixed mineral substances which are or may be beneficially applied to the soil, I have now to draw your attention to the use of lime -the most valuable and the most extensively used of all the mineral substances that have ever been made available in practical agriculture. It has, and with much reason, been called " the basis of all good husbandry' —it well deserves, therefore, your most serious attention as practical men, and on my part the application of every chemical light by which its usefulness may be explained and your practice guided. This consideration also will justify me in dwelling upon it with some detail, and in illustrating separately the various points, both of theory and practice, which present themselves to us, when we study the history of its almost universal application to the soil. ~ 1. Of the composition of common and magnesian lime-stones. 10. Common lime-stones.-Lime is never met with in nature except in a state of chemical combination (Lee. I., ~ 5,) with some other substance. That which is usually employed in agriculture is met with in the state of carbonate. Carbonate of lime, or common lime-stone, consists of lime and carbonic acid, and when perfectly pure and dry, in the following proportions:per cent. Carbonic acid..... 437 Lime............ 56-3 or one ton of pure dry carbonate of lime contains 11H cwts. of lime. 100 J Limestones, however, are seldom pure. They always contain a sensible quantity of other earthy matter, chieflysilica, alumina, and oxide of iron. with a trace of phosphate of lire, sometimes of potash and soda, and often of animal and other organic matter. In lime-stones of the best quality the foreign earthy matter or impurity does not exceed 5 per cent. of the whole-white it is often very much less. The chalks and COMMON AND MAGNESIAN LIME-STONES. 365 mountain lime-stones are generally of this kind. In those of inferior quality it may amount to 12 or 20 per cent., while many calcareous beds are met with in which the proportion of lime is so small that they will not burn into agricultural or ordinary building lime-refusing to slake or to fall to powder when moistened with water. Of this kind is the Irish calp and the lime-stone nodules which are burned for the manufacture of hydraulic limes or cements.* It is easy to ascertain the quantity of earthy matter contained in lime-stone, by simply introducing a known weight of it into cold diluted muriatic acid, and observing or weighing the part which, after 12 hours, refuses to dissolve or to exhibit any effervescence. It is to the presence of these insoluble impurities that lime-stones in general owe their color, pure carbonate of lime being perfectly white. 2~. Alagnesian lime-stone.-Though often nearly white, the magnesian lime-stones of our island are generally of a yellow color. They cannot by the eye be distinguished from common lime-stones of a similar color, but they are characterised by containing a greater or less proportion of carbonate of magnesia, which is more or less easily detected by analysis. Pure carbonate of magnesia consists of per cent. Carbonic acid..517 Magnesia......48-3 or one ton of pure dry carbonate of magnesia - contains 95 cwts. of magnesia. 100 It contains, therefore, a considerably larger proportion of carbonic acid than is present in carbonate of lime. Magnesian lime-stone is very abundant, is indeed the prevailing rock in many parts of England (Lec. XI., sec. 4,) but the proportion of carbonate of magnesia it contains is very various in different localities. Even in the same quarry different beds contain very unlike proportions of magnesia, and are therefore more or less fitted for agricultural purposes. Thus several varieties of this lime-stone, examined'by myself, from different parts of the county of Durham, contained the two carbonates in the following proportions: ~ V tU.-', Garmondsway......97-5 2-5 trace trace Hard compact grey. Stony-gate........ 980 1 61 0-27 0-12 Crystallinefine grained yellow Fulwell...........95-0 2-1 0-3 26 Honey-combed crystalline Seaham (A)....... 96-5 2-3 0-2 1.0 Hard fine-grained compact. " (B).......95-0 1-3 0-2 3-5 Hard porous brown. Hartlepool.........54.5 44-93 0-33 0-24 Oolitic yellow. HumbledonHill (A) 57-9 41-8. 0-28 Perfect encrinal columns. " " (B) 60-41 38-78 1 0'81 Consistinginpartencrinalcol. Ferry Hill......... 541 44-72 1-58 4-6 Yellowish compact. Some of these varieties, as we see, contain very little carbonate of * Thus that of Aberthaw contains about 86 of carbonate of lime and 11 of clay, &c.; that of Yorkshire 62 of carbonate of lime and 34 of clay; of Sheppy 66 of carbonate of lime and 32 of clay. These lime-stones are burned, and then crushed to an impalpable powder, which sets almost immediately when mixed up with water. 366 OF THE BURNING AND SLAKING OF LIME. magnesia, and therefore, are found to produce excellent lime for agricultual purposes-while in others this substance forms nearly onehalf of the whole weight of the rock. Similar differences are found to prevail in almost every locality. This admixture of magnesia in greater or less quantity is not confined to the lime-stones of the magnesian lime-stone formation properly so called. It is found in sensible quantity in certain beds of lime-stone in nearly every geological formation, and there are few natural lime-stones of any kind in which traces of it may not be discovered by a carefully, conducted chemical examination. The simplest method of detecting magnesia in a lime-stone is to dissolve it in diluted muriatic acid, and then to pour clear lime water into the filtered solution. If a light white powder fall, it is magnesia. The relative proportions in two lime-stones may be estimated pretty nearly by dissolving an equal weight of each, pouring the filtered solutions into bottles which can be corked, and then filling up both with lime water. On subsiding, the relative bulks of the precipitates will indicate the respective richness of the two varieties in magnesia. ~ 2. Of the burning and slaking of lime. Burning. —When carbonate of lime or carbonate of magnesia is heated to a high temperature in the open air the carbonic acid they severally contain is driven ofi; and the lime or magnesia remains in the caustic state. When thus heated the carbonate of magnesia parts with its carbonic acid more speedily and at a lower temperature than carbonate of lime. On the large scale this burning is conducted in lime kilns, one ton good lime-stone yielding about 11 cwts. of burned, shell, quick, or caustic lime. Slaking. —When this shell or quick-lime, as it is taken from the kiln, is plunged into water for a short time and then withdrawn, or when a quantity of water is poured upon it, heat is developed, the lime swells, cracks, gives off much watery vapor, and finally falls to a fine, bulky, more or less white powder. These appearances are more or less rapid and striking according to the quality of the lime, and the time that has been allowed to elapse after the burning, before the water was applied. All lime becomes difficult to slake when it has been for some time exposed to the air. When the slacking is rapid as in the rich limes, the heat produced is sufficient to kindle gunpowder strewed upon it, and the increase of bulk is from 2 to 31 times that of the original lime shells. If the water be thrown on so rapidly or in such quantity as to chill the lime or any part of it, the powder will be gritty, will contain many little lumps which refuse to slake, will also be less bulky and less minutely divided, and therefore will be less fitted either for agricultural or for building purposes. When quick-lime is left in the open air, or is covered over with sods in a shallow pit, it gradually absorbs water from the air and from the soil, and falls, though much more slowly, and with little sensible development of heat, into a similar fine powder. In the rich limes the increase of bulk may be 3 or 3N times; in the poorer, or such as contain much earthy matter; it may be less than twice. FURTHER CHANGES UNDERGONE BY SLAKED LIME. -367 HIydrate of lime. —When quick-lime is thus slaked it combines with the water which is added to it, and becomes converted into a milder or less caustic compound, which among chemists is known by the name of hydrate of lime. This hydrate consists of Lime. 76 per cent.? or one ton of pure burned lime becomes Water.. 24 "" 6 nearly 25 cwt. of slaked lime. 100 It is rare, however, that lime is so pure or so skilfully and perfectly slaked as to take up the whole of this proportion of water, or to increase quite so much as one-fourth part in weight. Hydrate of Magnesia.-When calcined or caustic magnesia is slaked, it also combines with water, but without becoming so sensibly hot as quick-lime does, and forms a hydrate, which consists of Magnesia. 69*7 per cent. ) or one ton of pure burned magnesia beWater.. 30-0 " comes 283 cwt. of hydrate. 100 When magnesian lime is slaked, the fine powder which is obtained consists of a mixture of these two hydrates, in proportions which depend of course upon the composition of the original lime-stone. An important difference between these two hydrates is, that the hydrate of magnesia will harden under water or in a wet soil in about 8 days-forming a hydraulic cement.'Hydrate of lime will not so harden, but a mixture of the two in the proportions in which they exist in the Hartlepool, Hlumbledon, and Ferryhill lime-stones (page 365), will harden under water, and form a solid mass. In the minute state of division in which lime is applied to the soil, the particles, if it be a magnesian lime, will, in wet soils, or in the event of rainy weather ensuing immediately after its application, become granular and gritty, and cohere occasionally into lumps, on which the air will have little effect. This property is of considerable importance in connection with the further chemical changes which slaked limes undergo when exposed to the air or buried in the soil. ~ 3. Changes which the hydrates of lime and magnesia undergo by prolonged exposure to the air. When the hydrates of lime or magnesia obtained by slaking are exposed to the open air, they gradually absorb carbonic acid from the atmosphere, and tend to return to the state of carbonate in which they existed previous to burning. By mere exposure to the air, however, they do not attain to this state within any assignable time. In some walls 600 years old, the lime has been found to have absorbed only one-fourth of the carbonic acid necessary to convert the whole into carbonate; in others, built by the Romans 1800 years ago, the proportion absorbed has not exceeded three-fourths of the quantity contained in natural limestones. In damp situations the absorption of carbonic acid proceeds most slowly. 1~. Change undergone by pure lime during spontaneous slaking. — In consequence, however, of the strong tendency of caustic lime to absorb carbonic acid, a considerable quantity of the hydrate of lime first 368 OF CALCINED AND SLAKED MAGNESIA. formed, during spontaneous slaking, becomes changed into carbonate during the slaking of the rest. But, when it has all completely fallen, the rapidity of the absorption ceases, and the fine slaked lime consists of Carbonate of lime..... 57'4 Hydrate of lime later. 302. }2 42-6 water 10'2 100 or, a ton of lime, left in the open air till it has completely fallen to powder, contains about 8j cwt. in the state of hydrate. If left to slake in large heaps, the lime in the interior of those heaps will not absorb so much carbonic acid till after the lapse of a very considerable time. More caustic lime (hydrate) also will be present if it be left to slake, as is often done for agricultural purposes, in shallow pits covered with sods, to defend it from the air and the rains. After the lime has attained the state above described, and which is a chemical compound* of carbonate with hydrate of lime, the further absorption of carbonate acid from the air proceeds very slowly, and is only completely effected after a very long period. 2~. When slaked in the ordinary way lime falls to powder, without having absorbed any notable quantity of carbonic acid. Numerous small lumps also remain, which, though covered with a coating of hydrate, have not themselves absorbed any water. The absorption of carbonic acid by this slaked lime is at first very rapid,-so that where the full effect of caustic lime upon the soil is required, it ought to be ploughed in as early as possible,-but it gradually becomes more slow, a variable proportion of the compound of carbonate and hydrate above described is formed, and even when thinly scattered over a grass-field, an entire year may pass over without effecting the complete conversion of the whole into carbonate. 3~. Calcined or burned magnesia, whether in the pure state or mixed with quick-lime, as in the magnesian limes, absorbs carbonic acid more slowly-and by mere exposure to the air will probably never return to its original condition of carbonate. When allowed to slake spontaneously, three-fourths of it become ultimately changed into carbonate, and form a compound of hydrate and carbonate which is identified with the common uncalcined magnesia of the shops. This compoundf consists of Carbonate of magnesia....... 69'37 Hydrate of magnesia....... 16.03 Water.......14,60 100 and it undergoes no further change by continued exposure to the air. But if slaked by the direct application of water, magnesia, like lime, This compound consists of one atom of carbonate of lime (Ca O + C02) combined with one of hydrate (Ca 0 + HO,) and is represented shortly by Ca C + -Ca H-in which Ca denotes calcium (Lec. IX., ~ 4,) Ca O or Ca oxide of calcium or lime, CO2 or C carbonic acid (Lee. II., ~ 1,) and H O or H water (Lec. II. ~ 6.) t It is represented by the formula 3 (Mg C + H) + Mg H. STATES IN WHICH LIME IS APPLIED. 369 forms a hydrate only, without absorbing any sensible quantity of carbonic acid. The hydrate thus produced is met with in the form of mineral deposits on various parts of the earth's surface, and this mineral is not known to undergo any change or to absorb carbonic acid though exposed for a great length of time to the air. When magnesian limes are slaked by water, therefore, the magnesia they contain may remain in whole or in part in the caustic state (of hydrate), which will change but slowly even when exposed to the air. When it is left to spontaneous slaking, one-fourth of it at least will always remain in the caustic state, however long it may be exposed to the air. Should a lime be naturally of such a kind, or be so mixed with the ingredients of the soil as to form a hydraulic cement or an ordinary mortar, which will solidify when rains come upon it, or when the natural moisture of the soil reaches it-the absorption of carbonic acid will in a great -measure cease as it becomes solid, and a large proportion of the lime will remain caustic for an indefinite period. ~ 4. States of chemical combination in which lime may be applied to the land. There are, therefore, four distinct states of chemical combination, in which pure lime may be artificially applied to the land. 1 Q. Quick-lime or lime-shells, in which the lime as it comes from the kiln is uncombined either with water or with carbonic acid. 2~. Slaked lime or hydrate of lime, in which by the direct application of water it has been made to combine with about one-fourth of its weight of water. In both these states the lime is caustic, and may be properly spoken of as caustic lime. 3~. Spontaneously slaked lime, in which one-half of the lime is combined witl water and the other half with carbonic acid. In this state it is only half caustic. 4~. Carbonate of lime-the state in which it occurs in nature, and tot which burned lime, after long exposure to the air, more or less perfectly arrives. In this state lime possesses no caustic or alkaline (p. 48, ~ 5, note) properties, but is properly called mild lime. 5~. BI-carbonate of lime may be adverted to as a fifth state of combination, in which, as I have previously explained to you (pp. 45-6, ~ 1), nature usually applies lime to the land. In this state it is combined with a double proportion of carbonic acid, and is to a certain extent readily soluble in water. Hence, springs are often impregnated with it, and the waters that gush from fissures in the lime-stone rocks spread it.through the soil in their neighbourhood, and sweeten the land. 1 shall hereafter speak of these several states under the names of quick-line, hydrate of lime, spontaneously slaked lime, carbonate of lime, and Bi-carbonate of lime. By adhering to these strictly correct names, we shall avoid some of that confusion into which those who have hitherto treated of the use of lime as a manure have unavoidably fallen. The term m.ild, you will understand, applies only to that which is entirely in the state of carbonate. Magnesia, in the magnesian limes, may in like manner be either in the state of calcined magnesia, of hydrate of magnesia., of spontaneously 370 VARIOUS NATURAL FORMS OF CARBONATE OF LIME. slaked-meaning by this the compound of hydrate with carbonate-of carbonate, or of Bi-carbonate of magnesia, the latter of which is soluble in water to a very considerable extent. (It dissolves in 48 times its weight of water-or a gallon of water will dissolve 5 ounces of the Bi-carbonate containing 1s ounces of magnesia.) ~ 5. Of the various natural forms in which carbonate of lime is applied to the land. In the unburned or natural state, lime is met with on the earth's surface in numerous forms-in many of which it can be applied largely. easily, and with economy to the land. 1~. Marl.-Of these forms that of marl occurs most abundantly, and is most extensively used in almost every country of Europe. By the term marl, is understood, as I explained to you, when treating of soils (Lec. XI., ~ 3,) an earthy mixture, which contains carbonate of lime, and effervesces more or less sensibly when an acid (vinegar or diluted muriatic acid-spirit of salt) is poured upon it. Generally, also, the tenacious marls, when introduced into water, lose their coherence, and gradually fall to powder. This test is often employed to distinguish between marly and other clays, yet the falling asunder, though it afford a presumption, is not an infallible proof that the substance tried is really a marl. Marls are of various colors, white, grey, yellow, blue, and of various degrees of coherence, some occurring in the form of a more or less fine, loose, sandy powder, others being tenacious. and clayey, and others, again, hard and stony. These differences arise in part from the kind and proportion of the earthy matters-they contain, and in part, also, from the nature of the locality, moist or dry, in which they are found. The hard and stony varieties are usually laid upon the land, and exposed to the pulverising influence of a winter's frost before they are either spread over the pasture or ploughed into the arable land. Some rich inarls consist in part or in whole of broken and comminuted shells, which clearly indicate the source of the calcarebus matter they contain. COMPOSITION OF MARLS FROM Luneburg. Osnabruck. Magdeburg. Brunswick. Wesermarsh. Brunswihk. powdery. stony, clayey. loamy, powdery. stony. Quartz-Sand & Silica.. 5-6 2330 584 73-4 78'9 711 Alumina............ 0-4 10-0 8-4 1-9 31] 4-0 Oxides of Iron........ 42 1-9 6-7 32 3'8 6-5 Do. of Magnesia...... trace trace 0'3 0-3 0-3 1'1 Carbonate of Lime.... 85-5 35-0 18"2 18'1 8-2 13-3 Do. of Maonesia.... 1-25 0'9 3'8 1-5 3-0 2'6 Sulphuret of Iron..... 7-3 - - Potash & Soda, com- 005 trace 1-6 0-8 09 02 bined with Silica.. t Common Salt......... 0-03 trace trace trace 01 trace Gypsum............ 0-06 0,9 2 1 0-1 0-5 trace Phosphate of Lime 12 p(onleearth) 0-5 0 -3 -5 07 1-2 1 Nitrate of Lime....... 0-01 - - carbon Organic Matter....... 0 -6 20 - - - - 100 100 100 100 100 100 UNLIKE EFFECTS OF DIFFERENT MARLS. 371 The characteristic property of true marls of every variety is, I have said, the presence of a considerable per centage of carbonate of lime in the state of a fine powder, and, in general, diffused uniformly through the entire mass. To this calcareous matter the chief efficacy of these marls is no doubt to be ascribed, yet as they always contain other chemical compounds to which the special efficacy of certain varieties has sometimes been ascribed, it may not be improper to direct your attention to the preceding table, in which the constitution of several marls, from different localities, is represented, after the analyses ot Sprengel. Several reflections will occur to you on looking at these tables-such as, First-that marls differ very much in composition, and therefore must differ very much also in the effects which they are capable of producing when applied in the same quantity to the same kinds of land. Second-that, among other differences, the proportion of carbonate of lime is very unlike-in some varieties amounting to 85 lbs. out of every hundred, while in others as little as 5-lbs. are present in the same weight. You will understand, therefore, how very different the quantity applied to the land must be, if these several varieties are to produce an equal liming or to add equal quantities of lime to the soil. You will see that each of three persons may be adopting the best practice with his own marl-though the one add only 12 to 20 tons per acre, while the second adds 50 to 60, and the third 100 to 120 tons. third-that the proportion of phosphate of lime (bone-earth) is in some marls considerably greater than in others. Thus with every ton of the first of the above marls you would lay on the soil 52 lbs. of bone earth-about as much as is contained in a cwt. of bone dust-while with the second you would only add 11 lbs. _In so far as their effects upon the land depend, or are influenced by the presence of this substance, therefore, they must also be very different. And, Fourth-that the mechanical effects of these marls upon the soil to which they are added must be very unlike, since some contain 70 or 80 lbs. of sand in every hundred-while others contain a considerable quantity of clay. The opening effects of the one marl, and the stiffening effects of the other, when they are laid on in large quantities) cannot fail to produce very different alterations in the physical characters of the soil. 2~. Shell Sand.-The sands that skirt the shores of the sea are found in many localities to be composed, in large proportion, of the fragments of broken and comminuted shells. These form a calcareous sand, mixed occasionally with portions of animal matter, and, when taken fresh from the sea-shore, with some saline matter derived from the sea. Such is the case in many places on the coast of Cornwall. From these spots the sand is transported to a distance of many miles into the interior f6r the purpose of being laid upon the land. It has been estimated (De la Beche's Geological Report on Cornwall, -c., p. 480) that seven millions of cubic feet are at present employed every year in that county for this purpose. On the western coast of Scotland also, and on the shores of the island of Arran and of the Western Isles, this shell sand abounds, and is 16* -372 COMPOSITION OF SHELL AND CORAL LANDS. applied extensively, and with remarkably beneficial effects, both to the pasture lands and to the peaty soils that cover so large an area in this remote part of Scotland. It is chiefly along the coasts that it has hitherto been extensively employed, and it is transported by sea to a distance of 80 or 100 miles. " In the island of Barray alone, there are four square miles of shells and shell sand of the finest quality and of an indefinite depth" (Macdonald's Agricultural Survey of the Hebrides, p. 401.) When covered with a dressing of this shell sand the peaty surface becomes covered with a sward of delicate grass-and the border of green herbage that skirts the shores of these islands in so many places is to be ascribed either to the artificial applications of such dressing or to the natural action of the sea winds in strewing the fine sand over them, when seasons of storm occur. The coast of Ireland is no less rich in such sand in many parts both of its northern and southern coasts. A century and a half ago, it is known to have been used for agricultur.tl purposes in the north of Ireland-and nearly as long ago to have.een brought over to the opposite (Galloway) coast of Scotland w n a view of being applied to the land (Macdonald.) In the south, a cording to Mrs. Hall, (Mrs. Hall's.Ireland,) the coral sand raised in Bantry Bay alone produces ~4000 or ~5000 a-year to the boatmen who procure it and to the peasants who convey it up the country. On the coast of France, and especially in Brittany, opposite to Cornwall, on the other side of the English channel, it is obtained in large quantity, and is in great demand (Payen and Boussingault, Annales de Chim. et de Phys., third series, iii., p. 92.) It is applied to the clay soils and to marshy grass lands with much advantage, and is carried far inland for this purpose. It is there called trez, and is laid on the land at the rate of 10 to 15 tons per acre. On the southern coasts of France, where shell sand is met with, it is known by the name of tanque or tangue. The shell sand of Cornwall contains from 40 to 70 per cent. of carbonate of lime, with an equally variable small admixture of animal matter and of sea salt. The rest is chiefly siliceous sand. Other varieties have a similar composition. Two specimens of tangue from the south of France. analysed by Vitalis, and one of shell sand from the island of Isla, partially examined by myself, consisted of Tanene from the Shell Sand So, h of France. from Isla. Sand, chiefly siliceous..........20-3 40 7 Alumina and Oxide of Iron..... 4-6 46 7 to 6 Carbonate of Lime.............660 47.5 28 to 34 Phosphate of Lime.............?? 0-3 Water, and loss................ 91 79 - 100 100 100 30. Coral sand is similar in its nature to the shell sand with which it is often intermixed on the sea-shore. It is collected in considerable quantities, however, by the aid of the drag-being torn up by the fishermen in a living state-on the coasts of Ireland (Bantry Bay and elsewhere,) and on the shores of Brittany, especially near the mouths of the rivers. In this fresh state it is preferred by the farmer, probably be USE OF LIME-STONE SAND AND GRAVEL. 373 cause it contains both more saline and more animal matter. This animal matter enables it to unite in some measure the beneficial effects which follow from the application of marl and of a small dressing of farm-yard or other valuable mixed manure. Payen and Boussingault ascribe the principal efficacy of the shell and coral sands to the small quantity of animal matter which is present in them. These chemists estimate the relative manuring powers of difflrent substances applied to the land by the quantities of nitrogen which they severally contain, and thus, compared with farm-yard manure, attribute to the shell and coral sands the following relative values:Contain of Relative Nitrogen. value. 100 lbs. of Farm-yard Manure.. 0-40 lbs. 100 do. of Coral Sand (Merl)... 0-512 Ibs. 128 do. of Shell Sand (Trez)... 013 lbs. 321* That is to say, that, in so far as the action of these substances is dependent upon the nitrogen they contain, fresh coral sand is nearly onethird more valuable than farm-yard manure, while fresh shell sand is only equal in virtue to one-third of its weight of the same substance. Though, as I have already had frequent occasion to observe to you, much weight is not to be attached to such methods of estimating the relative values of manuring substances by the proportions of any one of the ingredients they happen to contain-yet the fact, that so much animal matter is occasionally present in the living corals, accounts in a satisfactory manner for the immediate effects of this form of calcareous application. This animal matter acts directly and during the first year; the carbonate of lime begins to show its beneficial influence most distinctly when two or three years have passed. 4~. Lime-stone Sand and Gravel.-In countries which abound in lime-stones, there are found scattered here and there, in the hollows and on the hill-sides, banks and heaps of sand and gravel, in which rounded particles of lime-stone abound. These are distinguished by the names of lime-stone sand and gravel, and are derived from the decay or wearing down of the lime-stone and other rocks by the action of water, Such accumulations are frequent in Ireland. They are indeed extensively diffused over the surface of that island, as we might expect in a country abounding so much in rocks of mountain lime-stone. In the neighbourbood of peat bogs these sands and gravels are a real blessing. They are a ready, most useful, and largely employed means of improvement, producing, upon arable land, the ordinary effects of liming, and, when spread upon boggy soils, alone enabling it to grow sweet herbage and to afford a nourishing pasture. The proportion of carbonate of lime these sands and gravels contain is very variable. I have examined two varieties from Kilfinane, in the county of Cork (?). The one, a yellow sand, contained 26 per cent, of carbonate of lime-the residue, being a fine red sand, chiefly siliceous; the other, a fine gravel of a grey colour, contained 40 per cent. of carbonate of lime in the form chiefly of rounded fragments of blue lime-stone, the residue con, Pisting of frag nents of sand-stone, of quartz, and of granite, Annales de Chim. et de Phys., third series, iii., p. 103. 374 CRUSHED LIME-STONES.-EFFECTS OF MARLS. The application of such mixtures must not only improve the physical characters of the soil, but the presence of the fragments of granite, containing undecomposed felspar and mica (Lee, XII., ~ 1), must contribute materially to aid the fertilizing action of the lime-stone with which they are mixed. 5~. CriLshed Lime-stone.-The good effects of calcareous marls and of lime-stone gravels naturally suggest the crushing of lime-stones as a means of obtaining carbonate of lime in so minute a state of division that it may be usefully applied to the soil. Lord Kames was, I believe, the first who in this country endeavoured to bring this suggestion into practical operation. He is said to have caused machinery to be erected for the purpose in one of the remotest districts of Scotland, but from some cause the plan seems never to have obtained a proper trial. One of the results which, as we have already seen., follows from the burning of rich lime is this, that it naturally falls to a very fine powder as it slakes. Where coal or other combustible is cheap, therefore, it may possibly be reduced to a fine powder by burning, at a less cost than it could be crushed. Yet there are two cases or conditions in which crushing might be resorted to with equal advantage and economy: First, where coal is dear or remote, while lime-stones and water power are abundant. There are many inland districts in each of the three kingdoms where these conditions exist, and in which, therefore, the erection of cheap machinery might afford the means of greatly fertilizing the land; and, Second, there are in many localities rocks rich in- calcareous matter, which are nevertheless so impure, or contain so much other earthy matter, that they cannot be burned into lime. Yet, if crushed, these same masses of rock would form a valuable dressing for the, land. Many lime-stones of this impure character, which are really useless for. building purposes-which do not fall to powder when burned, and which have, therefore, been hitherto neglected as useless-might, by crushing, be made extensively available for agricultural purposes. The siliceous lime-stones (corn-stones) of the old red sand-stone, the earthy beds of the mountain lime-stone, and many of the calcareous strata of the Silurian system might thus be made to improve more extensively the localities in which they are severally met with. The richer limes now brought from a great distance, and at much expense-as on the Scottish borders-might be in a great measure superseded by the native produce of the district. ~ 6. Effects of marl and of the coral, shell, and lime-stone sands, upon the soil. The effects which result from the application of the above natural forms of carbonate of lime are of two kinds. 1~. Their physical effect in altering the natural texture of the soils to which they are added. This effect will necessarily vary with the nature of the earthy matter associated with the lime. Thus the clay marls will inmprove, by stiffening, such soils as are light and sandythe shell sands and liree-stone gravels, by opening and rendering more OBSERVED EFFECTS OF MARLS. 375 free and easier worked such soils as are stiff, intractable, and more or less impervious —while either will impart solidity and substance to such as are of a peaty nature or over-bound with other forms of vegetable matter. 2~. Their chemical effect in actually rendering the soil productive of larger crops. This effect is altogether independent of any alteration in the physical properties of the soil, and is nearly the same in kind, whatever be the variety of marl, &c., we apply. It differs in degree, chiefly according to the proportion of calcareous matter which each variety contains. This action of the pure carbonate of lime- they contain is supposed to be modified in some cases by the proportion of phosphate of lime, &c. (p. 370,) with which it maybe mixed-it is certainly modified by the animal and saline matters which are present in the recent corals and shell sands. The several effects of marls and calcareous sands being dependent upon circumstances so different, it is not surprising that the opinions of practical men should, in former times, have been divided in regard to the action of this or that marl upon their respective soils. In no two localities was the substance applied to the land exactly alike, and hence unlike results must necessarily have followed, and disappointment been occasionally experienced from their use. And yet the importance of rightly understanding the kind and degree of effect which these manuring substances ought to produce may be estimated from the fact, that a larger surface of the cropped land in Europe is improved by the assistance of calcareous marls and sands-than by the aid of burned lime and farm-yard manure put together. It is not easy in any case to estimate with precision what portion of the effect caused by a given marl is due to its chemical and what to its physical action. Even the pure limes, when applied in large doses, produce a change in the texture of the soil, which on stiff lands is beneficial, and on light or sandy fields often injurious. In all cases, therefore, the action of lime applied in any form may be considered as partly physical and partly chemical-the extent of the chemical action in general increasing with the proportion of lime which the kind of calcareous matter employed is known to contain. The observed effects of marls and shell sands, in so far as they are chemical, are very analogous to those produced by lime as it is gener. ally applied in the quick or slaked state in so many parts of our islands. They alter the nature and quality of the grasses when applied to pasture-they cover even the undrained bog with a short rich grassthey extirpate heath, and bent, and useless moss-they exterminate the weeds which infest the unlimed corn fields-they increase the quantity and enable the land to grow a better quality of corn-they manifest a continued action for many years after they have been appliedlike the purer limes they act more energetically if aided by the Qccasional addition of other manure-and like them they finally exhausta soil from which the successive crops are reaped, without the requisite return of decaying animal or vegetable matter. * Of shell marl the same quantity exhausts sooner than clay marl (Kames). This is owing chiefly to the larger proportion of lime contained in the former. 376 OF THE USE OF CHALK AS A MANURE. But to these and other effects I shall have occasion to draw your attention more particularly in a subsequent part of the present lecture. ~ 7. Of the use of chalk as a manure. Chalk is another form of carbonate of lime which occurs very abundantly in nature, and which, from its softness, has in many parts of England been extensively applied to the land in an unburned state. The practice of chalking prevails more or less extensively in all that part of England (Lec. XI., ~ 8,) over which the chalk formation extends. It is usually dug up from pits towards the close of the autumn or beginning of winter, when full of water, and laid upon the land in heaps. During the winter's frost the lumps of chalk fall to pieces, and are readily spread over the fields in spring. The quantity laid on varies with the quality of the soil and of the chalk itself, and with the more or less perfect crumbling it undergoes during the season of winter, and with the purpose it is intended to serve. It gives tenacity and closeness to gravelly soils,* opens and imparts freeness to stiff clays, and adds firmness to such as are of a sandy nature. If a physical improvement of this kind be required, it is laid on at the rate of from 400 to 1000 bushels an acre. But some chalks contain much more clay than others, and are employed, therefore, in smaller proportions. For the improvement of coarse, sour, marshy pasture, it is applied at the rate of 150 to 250 bushels an acre, and speedily brings up a sweet and delicate herbage. It is also said to root out sorrel from lands that are infested with this plant. These effects are precisely such as usually follow from the application of marl, and, like marl, the repetition of chalk exhausts the land, if manure be not afterwards added to it in sufficient quantity. But the chalking of the Southern Downs and of the Wolds of Lincolnshire and Yorkshire would appear to differ in some respects from ordinary marling. On the thin soils immediately resting upon the chalk, experience has shown that repeated dressings of chalk recently dug up, may be applied with much benefit. To a stranger, also, it appears singular that an admixture of that chalk which lies immediately beneath the soil is not productive of the same advantage. Even the chalk of an entire district is, in some cases, rejected by the farmer, and he will rather bring another variety from a considerable distance, than incur the less expense of laying on his land that which is met with on his own or on his neighbors' farms. Thus the Suffolk farmers prefer the chalk of Kent to lay on their lands, and are at the cost of bringing it across the estuary of the Thames, though chalk rocks. lie alnost everywhere around and beneath them. The cause of the diversities which thus present themselves in the practice of experienced agriculturists, partly at least, is to be sought for in the qualities of the different varieties of chalk employed. Careful analyses have not yet shown in what respects these chalks differ in chemical constitution, and until this is ascertained we must remain in * Mr. Gawler, North Hampshire, states that a gravel thus stiffened, instead of 12 to 16 bushels of wheat, yielded afterwards 24 to 30 bushels.-British Husbandry, i., p. 280. EFFECTS OF CHALK ON THE WOLDS. 377 some measure in the dark, both as to the way in which a dressing of chalk acts in improving a soil already rich in chalk, and why chalk from one locality should act so much more beneficially than another. Writh one thing, however, we are familiar, that the upper beds of chalk abound in flint, and where they form the surface support a thin and scanty herbage-while the under chalks are more tenacious and apparently more rich in clay, and support generally a soil which yields valuable crops of corn. An admixture of the lower, therefore, ought to implrove the soils of the upper; and as the chalks of Kent consist of these lower beds, we can understand why the practical farmer in Suftblk should prefer them to the upper chalks of his own neighbourhood. Still we cannot, as yet, give the scientific reasons why the one chalk should be better than the other. A rigorous chemical analysis can alone determine with certainty why the one should produce a different effect from the other. Chalks may differ in the proportion of clay.or of organic matter with which they are associated-in the quantity of silica (the substance of flints) or of silicates they contain,-in the amount of magnesia or of phosphate of lime which can be detected in them-or of saline matter which a careful examination will discover,-and they may even differ physically in the fineness of the ultimate particles of which the substance of the chalk is composed.* All such differences may modify the action of the several varieties in such a way as, when accurately investigated, to enable us to account for the remarkable preference manifested by practical men for the one over the other. Until such an investigation has been carefully made, it is unfair hastily to class among local prejudices what may prove to be the results of long practical experience. On the chalk Wolds of Lincolnshire and Yorkshire the practice of chalking even the thin soils is now comparatively old in date. The lowest chalks are there also much preferred,-they are laid on at the rate of 60 to 80 cubic yards per acre, and they cause a great improverment, especially upon the deep lands, as they are called, where th( soil is deepest. Corn does not yield so well, nor ripen so early, or these deep soils, as where a thinner covering rests upon the chalk. - I1 is naturally also unfit for barley or turnips, the latter plant being espe. cially infested with the disease called fingers and toes [British Husbandry, iii., p. 124] (Strickland). But a heavy chalking removes al the above defects of these deep soils, and for a long period of time The corn ripens sooner, is larger in quantity, and better in quality and the turnips grow perfectly free from disease. These, however, are to be regarded as only the usual effects of a large addition of lime to a soil in which previously little existed. It is fact which will naturally strike you as remarkable, that soils which res upon chalk, as well as upon other lime-stone rocks, even at the deptl of a few inches only, are often, and especially when in a state of nature, so destitute of lime that not a particle can be detected in them. Thai lime in any form should benefit such soils is consistent with uniform " Ehrenberg has discovered that chalk is in a great measure composed of the skeletons, shells, or other exuvial (spoils) of marine microscopic animals. 378 LIME ALWAYS PRESENT IN FERTILE SOILS. experience. I shall presently have an opportunity of directing your attention to the two concurring causes by the joint operation of which lime is sooner or later wholly removed from the soil, even where, asin the Wolds, it rests immediately upon the chalk. ~ 8. Is lime indispensable to the fertility of the soil? It is the result of universal experience wherever agriculture has been advanced to the state of an art, that the presence of lime is useful to the soil. Not only is this fact deduced from the result of innumerable applications of this substance to lands of every quality, but it is established also by a consideration of the known chemical constitution of soils which are naturally possessed of unlike degrees of fertility. Thus sandy or siliceous soils are more or less barren if lime be absent-while the addition of this substance in the form of marl or otherwise renders them susceptible of cultivation. So clay soils, in which no lime can be detected, are often at once changed in character by a sufficient liming. Felspar soils contain no lime, and they are barrenand the same is true of such as are derived immediately from the degradation of the serpentine rocks. Trap soils, on the other hand-such as are derived from decayed basalts or green-stones-are poor in proportion as felspar abounds in them. Where augites and zeolites are present in large proportion in the trap from which they are formed, the soils are rich, and may even he used as marl. The only difference in this latter case is, that lime is rot deficient (Lee. XII., ~ 4),-and to this difference the greater fertility may fairly be ascribed. But let it be conceded that lime is useful to or benefits the soil in which it exists, you may still ask-is lime indispensable to the soil?is it impossible for even an average fertility to be manifested where lime is entirely absent? There are two different considerations, from each of which we may deduce a more or less satisfactory answer to this question. 1~. The result of all the analyses hitherto made of soils naturally fertile show that lime is universally present. The per-centage of lime in a soil may be very small, yet it can always be detected when valuable and healthy crops will grow upon it. Thus the fertile soil of the Marsh lands in Holstein contains 0'2 per cent. of carbonate of lime. Salt marsh in East Friesland 0-6 6" t4 Rich pasture near Durham 1-31 t" t But though the per centage of lime in these cases appears small, the absolute quantity of lime present in the landis still large. Thus suppose the first of these soils, which contains the least, to be only six inches in depth, and each cubic foot to weigh only 80 lbs.-it would contain about 3500 lbs. of carbonate of lime, upwards of a ton and a half, in every acre. And this lime would be intimately mixed with the whole soil, in which state it is always most effective in its operation. It may also be inferred with safety, that if the upper six inches contained this proportion of lime, the under soil would probably be richer still, since litte tends not so much to diffuse itself through, as to sink downwards into the soil. STATE IN WHICH LIME EXISTS IN THE SOIL. 379 2~. The results of all the chemical examinations hitherto made in regard to the nature of the inorganic matter contained in the sap and substance of plants indicate,-if not the absolute necessity of lime to the growth of plants,-at least that in nature all cultivated plants do absorb it by their roots from the soil, and make use of it in some way in aid of their growth. In so far as our practice is concerned, this is very much the same as if we could prove lime to be absolutely indispensable. The ash of the leaf and bulb of the turnip or potatoe, of the grain and straw of our corn-bearing plants, and of the stems and seeds of our grasses, all contain lime whenever and wherever they are grown. And most of them attain high health and luxuriance only where lime is easily attained. Grant, then, that lime appears to be, perhaps virtually is, a necessary food of plants, without which their natural health cannot be maintained, nor functions discharged,-still the quantity which must be present in the soil to sapply this food is not necessarily large. Even in favorable circumstances we have seen (Lec. X., ~ 3,) that the average crops during an entire rotation of four years may not carry off more than 250 lbs. of lime from the acre of land, a quantity which even the marsh soils of Holstein would be able to supply for half a century, could the roots readily make their way into every part of the soil. Still we may safely hold, I think, that this quantity of lime at least is indispensable-if cultivated plants are to flourish and ripen. So much, at least, must in practice be every year added to cultivated land in one form or another, where the crops are in whole or in part carried off the land. Where it is not added either artificially or by some natural process, infertility must gradually ensue. We shall presently see that lime has other functions to perform in the soil, and that there are natural causes in constant operation in our climate which render a larger addition than this desirable at least, if not indispensable to continued fertility. ~ 9. State of combination in which lime exists in the soil. This litne, which we have concluded to be an indispensable constituent of fertile soils, may be present in several distinct states of combination. 1~. In that of chloride ofcalcium.-This compound, as we have already seen (Lec. IX., ~ 4,) is very soluble in water, and is not unfrequently to be detected in the sap, especially of the roots of plants. Its solubility, however, exposes it to be readily washed out of the soil by the rains, and perhaps for this reason it is not one of those forms of combination in which lime is recognised as a uniform or necessary constituent of the soil. Its presence may be detected by boiling half a pound of the soil in distilled water, filtering and evaporating the solution to dryness. If the dry mass become moist on exposure to the air, and if, after being dissolved in water, it give a white precipitate with oxalate of ammonia, and after being rendered sour by a few drops of nitric acid, a white precipitate again with nitrate of silver, it may be inferred to contain chloride of calcium. 2~. In that of sulphate of lime or gypisum.-In this state also it is not a constant, and in a few cases only an abundant, constituent of the soil. 380 HUMATE OF LI51E IN THE SOIL. Its presence may be detected by the deposition of minute crystals on the sides of the vessel during the evaporation of the solution obtained by boiling the soil in distilled water. Or, its presence may be inferred if; after observing that oxalate of ammonia causes a precipitate in one small portion of the solution, it be found that nitrate of baryta also throws down a white precipitate from another small portion. 3~. In the state of phosphate.-This compound is probably present, though always in small proportion, in every soil which is capable of raising a nutritious vegetation. It may be readily detected by treating 500 grains of the dry soil for 12 hours with dilute muriatic acid, and occasionally stirring. If to the filtered solution caustic ammonia be added, a brownish precipitate will usually fall. If this precipitate be separated, and treated with acetic acid (vinegar), it will all dissolve if no phosphoric acid be present. If this experiment be carefully performed, and a residue remain undissolved, the presence of phosphoric acid in the solution, and of phosphate of lime in the soil, may be safely inferred. 4~. In the state of silicate, lime rarely exists in the soil in any considerable quantity. It is chiefly in such as are derived from the decay of the trap rocks or of some varieties of granite (sienite), that silicate of lime is to be expected to occur. If, after being treated with dilute sulphuric acid, as above described, the soil be digested for some hours at a gentle heat with concentrated muriatic acid-a solution will be obtained from which ammonia will again throw down a brown precipitate. If oxalate of ammonia now cause a white precipitate of oxalate of lime, and if, on evaporating to dryness, the solution leave a portion of silica insoluble in acids, we may infer that the soil most probably contains some lime in the state of silicate. 5~. In the state of carbonate, lime is generally supposed most usually to exist, and most abundantly in all soils. If on pouring dilute muriatic acid upon a soil, a visible effervescence or escape of minute bubbles of gas manifest itself, or if, when the experiment is made in a tube closed at one end, and inverted over water or mercury, bubbles of gas collect in the upper end of the tube-the soil contains some carbonate. If after ammonia has been added to the solution, oxalate of ammonia throws down a white precipitate of oxalate of lime-the soil contains carbonate of lime. 6~. In the state of humate.-In combination with humic acid (Lee. XIII., ~ 1,) lime exists most frequently in soils which abound in vegetable matter-in peaty soils, for example, to which quick-lime or marl of any kind has been added for the purpose of agricultural improvement. The presence of lime in the state of humate is only to be detected by carefully determining the relative weights of the carbonic acid given off'during the action of dilute muriatic acid upon the soil, and of the lime contained in the solution thus obtained, (see Appendix.) If for every 100 grains of carbonic acid there be more than 77'24 grains of lime, the remainder or excess has existed in the soil in combination with humic or some analogous organic acid.* * To such analogous acids belong the crenic and apocrenic acids (Lec. XIII., ~ 1.) The existence of these acids in the soil is by no means problematical. According to-Professor HIermann, of Moscow, they exist in the rich black soil (Tchornoi Zem.) of Little Russia, to the amount of 4 per cent. QUANTITY OF LIME TO BE APPLIED TO THE SOIL. 381 Few investigations have as yet been made in regard to the proportion of lime which exists in the soil in the state of humate. It has generally been taken for granted-either that a soil was destitute of lime if it exhibited no sensible effervescence with dilute muriatic acid,-or when further research was made, and the quantity of lime taken up by this acid rigorously determined, that the whole of this lime must have existed in the soil in the state of carbonate. That this is not necessarily the case, however, appears to be proved by some recent examinations of certain soils in Normandy, which contain as much as 14 to 15 per cent. of lime, and yet exhibit no effervescence, and contain no carbonate. The whole of the lime is said to be in the state of humate. M. Dubuc, who has published the analyses of these soils, attributes much of their fertility to the presence of the humate of lime. Thus he says that the soils of Containing per cent. Of Carbonate. Of Humate. Yields of Wheat. Lieuvin, Neubourg, and Sistot, 0 18 to 20 12 to 15 fold. Pavilli....... 0 5 8 to 10' Bieville...... 24 0 8 to 10 Clay ofOuche.. 0 1 4 to 5 The first two yielding a wheat crop every second year, the third only at longer intervals. Whatever degree of influence on the fertility of the soil it may appear proper to attribute to the existence of lime in the soil in the state of humate, it is manifestly of some importance that its presence in this state of combination should be more frequently and more carefully sought after. The only one of the above compounds which is usually added to the land, for the purpose of producing the ordinary effects of lime, is the carbonate. Gypsum is applied only in small quantity for certain special purposes, and does not always produce a sensible effect. It is incapable, therefore, of performing those purposes in the soil which are served either by quick-lime or by the carbonate. The humate of lime is probably formed in our lime cozmposts, especially when much vegetable matter is contained in them, and may thus be not unfrequently applied directly to the land. ~ 10. Of the quantity of lime which ought to be added to the soil. The quantity of lime which ought to be added to the soil is dependent upon so many circumstances, that it is impossible to state any general rule by which, in all cases, the practical man can safely regulate his procedure. 10. To soils which contain no lime, or to which it is added for the first time, a larger dose must be given. We have seen that a certain minimum portion of lime is indispensable to a productive soil. If we suppose this smallest quantity to be no greater than in the surface of the marsh lands of Holstein (p. 378)then with a soil six inches in depth, which contains no lime, we ought to mix a ton and a half, say 40 bushels of slaked lime, and by successive yearly additions to supply the annual waste. But to mix this feeble dose of lime intimately with the soil to a depth of six inches would obviously require an expenditure of labor which' 382 MORE OUGHT TO BE LAID ON CLAY, WET, AND MARSHY SOILS, the practical farmer could rarely afford. It would be greater economy, therefore, in most cases to add a dose several times larger, and this not only because the same amount of labor would diffuse it more generally through the whole soil, but because this larger liming would render less necessary the immediate addition of new supplies to repair the unavoidable waste. But there is reason to believe that the proportion of lime which the soil ought to contain, if it is to be successfully subjected to arable culture, ought to be much larger than is above assumed as the smallest or minimum quantity. If we suppose one per cent. to be necessary, then eight, tons of lime-shells, or upwards of 300 bushels of slaked lime, must be mixed with a soil six inches in depth, to impart to it this proportion-or half the quantity, if it be kept within three inches of the surface. Even a very large dose of lime, therefore, does not, if it be well mixed, materially alter the constitution of the soil. 2~. But experience has proved that the quantity of lime which a skilfui farmer will add to his land will vary with many other circumstances besides the depth of his soil, and the proportion of lime it already contains. Thusa. On clay lands more lime is necessary than on light and. sandy soils. This may be partly ascribed to the physical effect of the lime in opening and loosening the stiff clay-but independent of this action the particles of lime are liable to be coated over and enveloped by the fine clay, and thus shut out from the access of the air. These particles, therefore, must be more numerous in such a soil, if as many of them are to be exposed to the air as in lighter land, through which the atmospheric air continually permeates. b. On wet and marshy soils, a larger application still may be made with safety, and partly for the same reason. The moisture surrounding the lime shuts out the air, without the ready access of which lime cannot perform its importantfunctions. The same moisture tends to carry down the lime and lodge it more speedily in the subsoil. The continued evaporation also keeps such soils too cold (Lec. II., ~ 7), to allow the chemical changes, which lime in favorable circumstances produces, to prbceed with the requisite degree of rapidity. The soluble compounds which are formed as the consequence of these changes are, in wet and marshy soils, dissolved by the moisture, and so diluted as to enter in smaller quantity into the roots of plants. And lastly, in certain cases, new compounds of the lime with the earthy and stony matters of the soil are formed, which may either harden into visible lumps of mortar and cement, or into smaller particles of indurated matter, in which the lime is no longer in such a state as to be able to act in an equal degree as an improver of the soil. In cold and wet clays, in which all these evil conditions occasionally meet, it is not surprising, therefore, that large doses of lime should sometimes have been added without producing any sensible benefit whatever. (" An instance is mentioned in the Nottingham Report of 720 bushels having been laid on an acre of clod clay land without any benefit whatever."-British Husbandry, i., p. 296.) c. Again, when the soil is also rich in vegetable matter, lime may 3e still more abundantly applied. Thus, when a field is at once wet AND SUCH AS ARE RICH IN VEGETABLE MATTER. 383 or marshy, and full of vegetable matter, as our peat bogs are, lime may be laid on more unsparingly than under any other circumstances. For in this case, besides the action of the access of water, as above explained, the vegetable matter combines with and masks the ordinary action of a considerable quantity of the lime. By this combination, no part of the ultimate influence of the whole lime upon the soil is necessarily lost; in most cases the immediate effect only is lessened, which the same quantity applied to other soils would have been seen to produce. In favorable circumstances its action is retarded and prolonged, the compounds it forms with vegetable matter decomposing slowly, and, therefore, remaining long in the soil. To the exact chemical constitution of the compounds thus formed, as soon as lime is mixed up with a soil rich in vegetable matter, and to the chemical changes which these compounds gradually undergo, it will be necessary to direct our attention when we come to study the theory of the action of lime, as an improver of the soil. d. Not only the natural depth of the soil, as already stated, but also the depth to which it is usually ploughed, and to which it is customary to bury the lime, will materially affect the quantity which can be safely applied. A dose of lime which would materally injure a soil into which the plough rarely descends beyond two or three inches, might be too small an application where six or eight inches are usually turned over by the plough. When new soil, also, is to be brought up, which may be supposed to contain no lime, or in which noxious substances are present, a heavier dose of lime must necessarily be laid upon the land. 3~. Such are the circumstances in which large applications of lime may be usefully applied to the land. In soils of an opposite character, not only will smaller quantities of lime produce an equally beneficial effect, but serious injury would often be inflicted by spreading it too lavishly upon your fields. The more dry and shallow the soil,' the more light and sandy, the less abundant in vegetable matter, the more naturally mild its locality, and the drier and warmer the climate in which it is situated-the less the quantity of lime which the prudent farmer will venture to mix with it. It is to the neglect of these natural indications that the exhaustion and barrenness that have occasionally followed the application of lime are to be ascribed. It is only in rare cases, such as the presence of much noxious mineral matter in the soil, that these indications can be safely neglected. ~ 11. Ought lime to be applied in large doses at distant intervals, or in smaller quantities more frequently repeated? The quantity of lime which ought to be applied to the land must, as we have seen, vary with its quality, and with the conditions in which it is placed. Hence the practice in this respect necessarily varies in every county and in almost every district. But a difbfrence of opinion also prevails among practical.men, as to whether that quantity of lime which land of a given kind may require ought to be applied in large doses at long intervals, or in smallquantities frequently repeated. The indications of theory in reference to this point are clear and simple. 384 OUGHT LIME TO BE APPLIED IN LARGE OR SMALL DOSES. A certain proportion of lime is indispensable in our climate to the production of the greatest possible fertility. Let us suppose a soil to be wholly destitute of lime-the first step of the improver would be to add to this indispensable proportion. This would necessarily be a large quantity, and, therefore, to land limedfor thefirst time theory indicates the propriety of adding a large dose. Every year, however, a certain variable proportion of the lime is removed from the soil by natural causes. The effect of this removal in a few years becomes sensibly apparent in the diminished productiveness of the landl.' After the lapse of five or six years, during which it has been gradually mixing with the soil, the beneficial effects of the lime is generally the most striking-after this they gradually lessen, till at the end of a longer or shorter period, the land reverts to its original condition. To keep land in its best possible state, therefore, the natural waste ought frozm time to time to be supplied by the addition of smaller doses of lime at shorter intervals. Such is obviously the most natural course of procedure, and he who farms his own estate, and has therefore no strong inducement to do otherwise, will, on the first breaking up of new land, give it a heavy liming, and whether he afterwards retain it in arable culture or lay it down to grass, will at intervals of 4 to 6 years give it a new dose of onefourth to one-eighth of the original quantity. But local circumstances and customs interfere in many well-farmed districts with this most natural treatment of the soil. In the county of Roxburgh, for example, on entering upon his farm, which holds on a lease of 19 or 21 years, the tenant begins by liming that portion of his land which is in fallow, or in preparation for turnips, at the rate of 240 to 300 bushels of quick-lime per acre. A similar liming is given to the other portions as they come into fallow, so that at the end of his first rotation (4or 5 years) the whole of his land has been limed at the same rate. He now continues cropping for three or four rotations (14 to 16 years), when if he is sure of remainiug on his farm he begins to lime again with the same quantity as before. If he is to quit, however, he takes the best crops he can get, but incurs no further outlay in the addition of lime. His successor follows the same course-begins by expending perhaps X1000 in lime, and before he leaves at the end of his lease, has, by continued cropping, brought back his land nearly to the same state in which he found it. In the district of Kyle and other parts of Ayrshire, again, lime is laid on-often when preparing for the wheat crop, either by ploughing in the second furrow, or by harrowing in with the seed-at the rate of 40 bushels of shells an acre, and this dose is of course repeated every 4 or 6 years, according to the length of the rotation. If we consider the probable difference in the soil and climate, the proportion of lime added in the two districts does not materiallydiffer. In Ayrshire from 8 to 10 bushels, and in Roxburgh from 10 to 12 bushels, are added for each year.* In both counties, however, many farms may be met with in which the treatment of the land in this respect differs from that which is generally followed. * According to General Beatson (New System of Cultivation, 1820), upwards 100 bushels an acre, at a cost of ~7. 16s., used to be applied to the clay lands of Sussex-on the fallow, before wheat-every foul years. This was 25 bushels per acre for each year. In such lands as these the saving in the article of lime alone, which would follow a judicious drain. age, would be very great. COMPARATIVE ECONOMY OF THE TWO METHODS. 385 In Flanders a similar-difference in the practice prevails in different districts. In some the land is limed only'once in 12 years, in others every third, fourth, or sixth year, according to the length of the rotation. In the former case from 40 to 50 bushels are applied per acre, in the latter from 10 to 12 bushels every third year. In both modes of procedu:., the quantity of lime applied by the year is nearly the same-between 3^ and 4 bushels per acre. These quantities are very much less than those employed in our island, but the soils are also greatly lighter, and the climate, as well as the general treatment of the land, very different. We may consider it, therefore, as a principle recognized or involved in the agricultural practice both of our own and of foreign countries, that nearly the same annual addition of lime ought to be made to the land, whether it be applied at long intervals or at the recurrence of each rotation. There is, therefore, on the whole, no saving in the cost of lime, whichever method you adopt. A slight consideration of the subject, however, may satisfy us that there is a real difference in the comparative economy or profit of the two methods. Let us suppose two acres of the same clay land to be limed respectively with 200 bushels each, and that the one is cropped for twenty years afterwards without further liming, while the other at the end of every five years is dressed with an additional dose of 40 to 50 bushels. In both cases the land would have attained the most productive condition in five orsix years. Let us suppose that in this condition it produced annually a crop of (or equivalent in.nutritive value to) 30 bushels of wheat, and that on neither acre did a sensible diminution appear before the end of ten years. Then during the second ten the crops would gradually lessen in the one acre, while, in consequence of the readdition of the lime as it disappears, the amount of produce would remain sensibly the same in the other acre. Suppose the produce of the former gradually to diminish from 30 to 20 bushels during these ten years,-or that while the one has continued to yield 30 bushels during the whole period, the other has, on an average, yielded only 25 bushels during the latter ten years. If now the second large dose of 200 bushels be added to this latter acre, the cost of liming both will have become sensibly the same, but the amount of produce or of profit from the two acres during the second ten years will stand thus10 crops, of 30 bushels each, amount to 300 bushels. 10 crops, of 25 bushels each, amount to 250 bushels. Difference in favour of frequent liming, 50 bushels per acre, or nearly two whole crops every lease of twenty years. Thus it appears 1~. That, according to the practice of different countries, the quantity of lime which ought to be added, and consequently the cost of adding it, is very nearly the same, whether it be applied in larger doses at longer intervals, or in smaller doses more frequently repeated. 2~. That, after the first heavy liming, the frequent application of small doses is the more natural method-and 30. That it is also the most economical or profitable method, It is possible that other considerations, such as the tenure by which your land is held, may appear sufficient to induce you to depart from 386 MANURE MUST BE ADDED WHERE LIME ABOUNDS. this method; but there seems every reason to believe that it will best reward those who feel themselves at liberty to follow the indications at once of sound theory and of enlightened practice. One thing, however, must be borne in mind by those who, in adopting the best system of liming, do not wish both to injure their land and to meet with ultimate disappointment. Organic matter-in the form of farm-yard manure, of bone or rape dust, of green crops ploughed in, or of peat, and other composts —must be abundantly and systematically added, if at the end of 20 or 40 years the land in which the full supply of lime is kept up is to retain its original fertility. High farming is the most profitable-for the soil is ever grateful for skilful treatment-but he who farms high il the sense of keeping up the supply of lime, must also farm high in the sense of keeping up the supply of organic arid other manures in the soil-otherwise present fertility and gain will be followed by future barrenness and loss. If this is not to be done, it were better to add lime at long intervals, since as the quantity of lime diminishes, the land begins to enjoy a little respite, and has had time in some measure to recover itself-the cropping in both instances being the same-before the new dose is laid upon its surface.* ~ 12. Form and state of combination in which lime ought to be applied to the land. The form and state of combination in which lime ought to be applied to the land depend upon the nature of the soil, on the kind of cropping to which it is subjected, and on the special purpose which the lime is intended to effect. The soil may be heavy or light, in arable culture, or laid down to grass, and each of these conditions indicates a different mode of procedure in the application of lime. So the lime itself may be intended either to act more immediately or to be more permanent in its action-or it may be applied for the purpose of destroying unwholesome herbage, of quickening inert vegetable matter, of generally sweetening the soil, or simply of adding to the land a substance which is indispensable to its fertility. The skilful agriculturist will modify the form and mode of application according as it is intended to serve one or other of these purposes. From the considerations already presented to you (~ 3) in regard to the changes which quick-lime undergoes in the air, it appears to be expedient, 1~. To slake lime quickly, and to apply it immediately upon clay, boggy, marshy, or peaty lands-upon such also as contain much inert or generally which abound in other forms of vegetable matter. 2~. To bents and heaths which it is desirable to extirpate, it should be applied in the same caustic state, or to unwholesome subsoils which contain much iron (sulphate of iron), as soon as they are turned up by the plough. In both these cases the unslaked lime-dust from the kilns might be laid on with advantage. * "In the neighbourhood of Taunton, in Somersetshire, and over all the soil of the new red sand-stone, the farmers lime their land every time it comes in course of fallow for turnips. and this produces excellentcrops, even without dung."-Morton on Soils, third edition, p. 181. The practical reader must not consider this custom of the Somersetshire farmers as at all at variance with what is stated in the text: he must conclude, rather,-if the sentence here quoted is meant to apply that they lime their arable land so repeatedly, and ye add no organic manure-that they will, sooner or later, cease to boast of its fertility COMPARATIVE ECONOMY OF LIME AND MARL. 387 3~. Where it is to be spread over grass lands without destroying the herbage, it is in most cases safer to allow the lime to slake spontaneously, and in the open air rather than in a covered pit. It is thus obtained in. an exceedingly fine powder, which can be easily spread, and, while it is sufficiently mild to leave the tender grasses unharmed, it contains a sufficient quantity of caustic lime (p. 368) to produce those chemical changes in the soil on which the efficacy of quick-lime depends. 4~. Where lime is applied to the fallow, is ploughed in, well harrowed or otherwise mixed with the soil, it is generally of little consequence in which of the above states it is laid on. The chief condition is, that it be in the state of a fine powder, and that it be well spread and intimately mixed with the soil. Before these operations are concluded the lime will be very nearly in the state of combination in which it exists in spontaneously slaked lime —whatever may have been the state of causticity in which it has been applied. You will understand that the above remarks apply only to localities where burned lime is usually or alone used for agricultural purposes. There may be localities where marl also exists, or shell or lime-stone sand, in greater or less abundance, and' in such places it may be a question of some importance to determine which it would be better or more economical to apply. In such a case you may safely proceed upon the principle that the lime in the marls, &c., will ultimately produce precisely the same effects upon your land as the lime from the kiln, provided you lay on an equal quantity, and in an equally ninute state of division. The effect will only be a little more slow, and the full fertility of the land a year or two longer in being brought out. You would therefore consider, 10. How much of the marl or sand must I add to be equal to a ton of lime-shells? This will depend on the per-centage of lime which the marl contains. Suppose it to contain 20 per cent.,or one-fifth of its weight of lime, (not carbonate of lime, but of lime in the state in which it comes from the kiln, 100 lbs. of carbonate containing 56 lbs. quick lime, p. 364,) then five tons of the marl will be equal-to one ton of lime shells. But as the lime in the marls and sands is never in so minute a state of division as in the slaked lime, the same quantity of lime in the former cannot be so equally diffbsed through the soil as in the latter state. An allowance must therefore be made on this account, and an additional quantity equal to one-fourth or one-fifth of the whole added, for the purpose of equalizing the effect. 2~. Which of the two, the quick-lime or its equivalent of marl, can I obtain and apply at the less cost? This will not be difficult to calculate, the proportion of lime contained in the marl being once ascertained. 3~. This question of economy being decided, it is necessary to consider the kind and quantity of the earthy matter with which the lime in the marl is mixed. If it be a lime-sand or sandy marl, it may be unfit to apply to light -and sandy soils; if it be a stiff unctuous clay marl, it may only render stiffer and more difficult to work the clay lands on which you may propose to spread it. In such cases as these, however economical the use of marls or lime-stone sands may be, the intelligent farmer will prefer the addition of quick-lime wherever it is readily accessible. 17 388 USE AND ADVANTAGE OF THE COMPOST FORM. Sussex is one of those districts in which the ancient use of marl has given place to the employmnent of burned lime, (Beatson,)-chiefly, I believe, from the nature of the local marl being less adapted to the stiff clay lands of that county. ~ 13. Of the use ana advantage of the compostform. As there are many cases in which lime ought to be applied unmixed and In the caustic state, so there are others in which it is best and most benefcially laid upon the land in a mild state and in the form of compost. 1~. When lime is required only in small quantities, it can be more evenly spread when previously well mixed with from 3 to 8 times its buill of soil. 2~. On light, sandy, and gravelly soils, when of a dry character, unmixed lime will bring up much cow-wheat (melaanpyrlum) and red poppy. If they are moist soils, or if rainy weather ensue, the lime is apt to( run into mortar, and thus to form either an impervious subsoil, or lumps of a hard conglomerate, which are brought up by the plough, but do not readily yield their lime to the soil. These bad consequences are all avoided by adding the lime in the form of compost. 30. Applied to grass lands-unless the soil be stiff clay-or much coarse grass is to be extirpated,-it is generally better and safer to apply it in the compost form. The action of the lime on the tender herbage is by this means moderated, and its exhausting effect lessened upor soils which contain little vegetable matter. 4~. In the compost form the same quantity of lirne acts more immediately. While lying in a state of mixture, those chemical changes which lime either induces or promotes have already to a certain extent taken place, and thus the sensible effect of the lime becomes apparent in a shorter time after it has been laid upon the land. 5~. This is still more distinctly the case when, besides earthy matter, decayed vegetable substances, ditch scourings, and other refuse, are mixed with the lime. The experience of every practical man has long proved how very much more enriching suchl composts are, and more obvious in their effects upon the soil, than the simple application of lime alone. 6~. It is stated as the result of extended trial in Flanders and in parts of France, that a much smaller quantity of lime laid on in this form will produce an equal effect. For this, one cause may be, that the rains are prevented from acting upon the mass of compost as they would do upon the open soil-in washing out either the lime itself or the saline substances which are produced during its contact with the earthy and vegetable matter with. which it is mixed. 7~. The older the compost the more fertilizing is its action. This fct is of the same kind with that generally admitted in respect to the action of marls and unmixed lime-that it is more sensible in the second year, or in the second rotation, than in the first. In conclusion, it may be stated that this form of application is especially adapted to the lightest and driest soils, and to such as are poorest in, vegetable matter. In this form, lime has imparted an unexpected fertility even to the white and barren sands of the Landles (Puvis,) and upon the dry hills of Derbyshire it has produced an almost equal benefits PERIOD FOR THE APPLICATION OF LIME. 389 ~ 14. When ought lime to be applied? This question may refer either to the period in the lease, in the rotation, or of the year in which lime may most beneficially be laid upon the land. We have already considered this point in so far as it refers to the lease, while discussing the propriety of applying lime in large or small doses. In regard to the period of the year and of the rotation, there are three principles by which the procedure of the practical man ought chiefly to be directed. 1~. That lime takes some time to produce its known effects upon the soil. —It ought, therefore, to be applied as long as possible before the crop is sown. That is, in the early autumn, where either winter or spring corn is about to be sown,-on the naked fallow where the land is allowed to be at rest for a year,-or on the grass fields before breaking up, where the pasture is to be immediately succeeded by corn. 2~. That quick-lime expels ammoniafrom decomposed andfermenting manure. When such manure, therefore, is applied to the land, as it is in all our well-farmed districts, quick-lime should not be so laid upon the land as to come into immediate contact with it. If both must be applied in the same year, they should be laid on at periods as distant from each other as may be convenient, or if this necessity does not exist, the lime should be spread either a year before or a year after the period in the rotation at which the manure is usually applied. It is for this reason, as well as for the other already stated, (1~.) that lime is applied to the naked fallow, to the grass before breaking up, or along with the winter wheat after a green crop which has been aided by fermented manure. WVhen ploughed into the fallow, or spread upon the grass, it has had time to be almost completely converted into the mild state (that of carbonate,) before the manure is laid on. In this mild state it has no sensible. effect in expelling the ammonia of decomposing manure. Again, when it is applied in autumn along with, or immediately before the seed, the volatile or ammoniacal part of the manure has already been expended in nourishing the green crop, so that loss can rarely accrue from the admixture of the two at this period ot the rotation. The excellent elementary work of Professor Lowe, (Elements oi Practical Agriculture, third edition, p. 63,) contains the following remark:-' It is not opposed to theory that lime should be applied to the soil at the same time with dung and other animal and vegetable substances, as is frequent in the practice of farmers." This is strictly correct only in regard to marls, lime-sand, &c., or to perfectly milc lime, any of which may be mixed, without loss, with manure in any state. Of quick or caustic lime it is correct only when the animal or vegetable matter has not yet begun to ferment. With recent animal or vegetable matter, quick-lime may be mixed up along with earth into a compost, not only without the risk of much loss, but with the prospect of manifest advantage: 3~. That quick-lime hastens or revives the decomposition of inert organic matter.-This fact also indicates the propriety of allowing the 390 LIME HASTENS ORGANIC DECOMPOSITION. lime as much time as possible to operate before a crop is taken from land in which organic matter already abounds. Or where fermenting manure is added, it advises the farmer to wait till spontaneous decomposition becomes languid, when the addition of lime will bring it again into action and thus maintain a more equable fertility. In a work upon soils, which I have frequently commended to your notice, (Morton "On Soils," third edition, p. 181,) you will find the following observations: —" Writers on agriculture have stated that lime hastens the decay of vegetable matter, whereas the fact is, that it retards the process of the decomposition of vegetable matter. If straw or long dung be mixed with slaked lime, it will be preserved; while if mixed with an equal portion of earth, the earth will hasten its decay." The two facts stated in this last sentence are, I believe, correct, yet it is nevertheless consistent both with theory and universal observation, that lime in the soil promotes the decomposition of organic matters, both animal and vegetable. This will appear more clearly when we come to study the precise nature of the action of lime upon organic substances in general. The above remarks, in regard to the best time for applying lime, refer chiefly to quick-lime, the state in which, in England, it is so extensively used. Marls and shell-sands can cause no loss when mixed with the manure, and therefore may with safety be laid on at any period of the rotation. The same remark applies with greater force to the lime composts. These may be used precisely in the same way as, and even instead of, the richer manures —may be laid, without risk, upon grass lands of any quality, and at any period-or as a top dressing on the young corn in spring, when the grass and clover seeds are sown by which the corn crop is to be succeeded. And as the compost acts more speedily than lime in any other form, it is especially adapted for immediate application to the crop it is intended to benefit. To wet lands also, it is well suited, and to such as are subject to much rain, by which, while the surface is naked, the soluble matters produced in the soil are likely to be very much washed away. ~ 15. Of the effects produced by lime. The effects of pure lime upon the land, and upon vegetation, are ultimately the same, whether it be laid on in a state of hydrate or of carbonate. If different varieties produce unlike effects, the quantity of lime applied being the same, it is because in nature lime is always rnere or less mixed with other substances which are capable of modifying the effects which pure lime would alone produce. The special effects of marls, &c., when they differ from those of burned lime, are to be ascribed to the presence of such admixtures. In general, however, the chemical action of the marls and calcareous sands is precisely the same in kind as that of lime in the burned and slaked state, and sc far the effects which we have already seen to be produced by marls, (p. 374,) represent also the general effects of lime in any form. These general effects may be considered in reference to the land on which it is laid, and to the crops which are, or may be, made to grow upon it. EFFECTS OF LIME UPON THE LAND AND CROPS. 391 I.-EFFECTS OF LIME UPON THE LAND. Pure lime, like the marls, produces both a mechanical and a chemical effect upon the soil. The former is constant with all varieties of tolerably pure lime, and is easily understood. It opens and renders Ireer such soils as are stiff and clayey, while it increases the porosity of such as are already light and sandy. To the former its mechanical action is almost always favourable, to the latter not unfrequently the reverse. From its chemical action the benefits which follow the use of lime are chiefly derived. These benefits are principally the following:1~. It increases the fertility of all soils in which lime does not already abound, and especially adds to the productiveness of such as are moist or contain much inert vegetable matter. 2~. It enables the same soils to produce crops of a superior quality also. Land which, unlitned, will produce only a scanty crop, (3 or 4 fold,) of rye, by the addition of lime alone, will yield a 6 or 7 fold re turn of wheat. From some clays, also, apparently unfit to grow corn it brings up luxuriant crops. 3~. It increases the elffct of a given application of manure; calls into action that which, having been previously added, appears to lie dormant; and though, as we have already seen, (p. 386,) manure must be plentifully laid upon the land, after it has been well-limed, yet the same degree of productiveness can still be maintained at a less cost of manure than where no lime has been applied. 4~. As a necessary result of these important changes, the money value and annual return of the land is increased, so that tracts of country which had let with difficulty for 5s. an acre, have in many localities been rendered worth 30s. or 40s. by the application of lime alone, (Sir J. Sinclair.) II. —-- FFECTS OF LIME ON THE PRODUCTIONS OF THE SOIL. 1~. It alters the naturalproduce of the land, by killing some kinds of plants and favouring the growth of others, the seeds of which had before lain dormant. Thus it destroys the plants which are natural to siliceous soils and to moist and marshy places. From the corn-field it extirpates the corn-marigold, (chrysanthemum segetum, [Bonninghausen]) while, if added in excess, it encourages the red poppy, the yellow cow-wheat, (melampyrum pratense,) and the yellow rattle, (rhinanthus crista galli,) and when it has sunk, favours the growth of the troublesome and deep-rooted coltsfoot. Similar effects are produced upon the natural grasses. It kills heath, moss, and sour and benty* (agrostis) grasses, and brings up a sweet and tender herbage, mixed with white and red clovers, more greedily eaten and more nourishing to the cattle. Indeed, all fodder, whether natural or artificial, is said to be sounder and more nourishing when grown upon land to which lime has been abundantly applied. On benty grass the richest animal manure often produces little improvement until a dressing of lime has been laid on. In Liddisdale, on the Scottish border, is a large tract of land in what is there called fring bent, not worth more than 3s. an acre. If surface-drained and limed at a ccst o0 ~2 to ~3 an acre, this becomes worth 12s. an acre for sheep pasture. An intelligent and experienced border farmer assures me that such land would never forget 40 to 60 bushels of lime per acre. 392 LIME IMPROVES THE QUALITY OF THE CROP. It is partly in consequence of the change which it thus produces in the nature of the herbage, that the application of quick-lime to old grasslands, some time before breaking up, is found to be so useful a practice. The coarse grasses being destroyed, tough grass land is opened and softened, and is afterwards more easily worked, while, when turned over by the plough, the sod sooner decays and enriches the soil. It is another advantage of this practice, however, that the lime has time* to diffuse itself through the soil, and to induce some of those chemical changes by which the succeeding crops of corn are so greatly benefitted. 2~. It improves the quality of almost every cultivated crop. Thus, upon limed land, a. The grain of the corn crops has a thinner skin, is heavier, and yields more flour, while this flour is said also to be richer in gluten. On the other hand, these crops, after lime, run less to straw, and are more seldom laid. In wet seasons, (in Ayrshire,) wheat preserves its healthy appearance, while on unlimed land, of equal quality, it is yellow and sickly. A more marked improvement is said also to be produced both in the quantity and in the quality of the spring-sown than of the winter-sown crops, (Puvis.) b. Potatoes grown upon all soils are more agreeable to the taste and more mealy after liame has been applied, and this is especially the case on heavy and wet lands, which lie still undrained. c. Turnips are often improved both in quantity and in quality when it is laid on in preparing the ground for the seed. It is most efficient, and causes the greatest saving of farm-yard manure where it is applied in the compost form, and where the land is already rich in organic matter of various kinds. d. Peas are grown more pleasant to the taste, and are said to be more easily boiled soft. Both beans and peas also yield more grain. e. Rape, after a half-liming and manuring, gives extraordinary crops, and the same is the case with the colsa, the seed of which is largely raised in France for the oil which it yields. f. On flax alone it is said to be injurious, diminishing the strength of the fibre of the stem. Hence, in Belgium, flax is not grown on limed land till seven years after the lime has been applied. 3~. It hastens the maturity of the crop.-It is true of nearly all our cultivated crops, but especially of those of corn, that their full growth is attained more speedily when the land is limed, and that they are ready for the harvest from 10 to 14 days earlier. This is the case even with buck-wheat; which becomes sooner ripe, though it yields no larger a return, when lime is applied to the land on which it is grown. 4~. The liming of the land is the harbinger of health as well as of abundance. It salubrifies no less than it enriches the well cultivated district. I have already drawn your attention (p. 310) to this as one of the incidental results which follow the skilful introduction of the drain over large tracts of country. Where the use of lime and of the drain go together, it is difficult to say how much of the increased healthiness of the district is due to the one improvement, and how much *A comparatively long period is sometimes permitted to elapse before the grass land is broken up after liming. Thus at Netherby, " lime or compost is always applied to the third year's pasture, which is renovated by it, and in two or three years breaks up admirably for oats." LIME SHOULD BE KEPT NEAR THE SURFACE. 393 to the other. The lime arrests the noxious effluvia which tend to rise more or less from every soil at certain seasons of the year, and decompcses them or causes their elements to assume new forms of chemical combination, in which they no longer exert the same injurious influence upon animal life. How beautiful a consequence of skilfil agriculture, that the health of the community should be promoted by the same methods which most largely increase the produce of the land! Can you doubt that the All-benevolent places this consequence so plainly before you, as a stimulus to further and more general improvement-to the application of other knowledge still to the amelioration of the soil? ~ 16. Circumstances by which the effects of lime are modified. These effects of lime are modified by various circumstances. WVe have already seen that the quantity which must be applied to produce a given effect, and the form in which it will prove most advantageous, are, in a great measure, dependent upon the dryness of the soil, upon,the quantity of vegetable matter it contains, and on its stiff'or open texture. There are several olher circumstances, however, to which it is proper still to advert. Thus, 1~. Its eflects are greatest when well mixed with the soil, and kept near the surface within easy reach of the atmosphere. The reason of this will hereafter apl)eear. 2~. On arable soils of the same kind and quality, the effects are greatest upon such as are newly ploughed out, or upon subsoils just brought to day. In the case of subsoils, this is owing partly lo their containting naturally very little lime, and partly to the presence of noxious ingredients, which lime has the power of neutralizing. In the case of surface soils newly ploughed out, the greater effect, in addition to these two causes, is due also to the large amount of vegetable altn other organic matter which has gradually accumulated within them. It is tone presence-of this organic matter which has led to the establishment of the excellent practical rule-" that lime ought always to precede putrescent manures when old leys are broken up for cultivation." 3~. Its effects are greater on certain geological formations than on others. Thus it produces much effect on drifted (diluvial) sands and clays-on tile soils of the plastic and wealden clays (Lee. XI.,. 8)on those of the new and old red sand-stones, of the granites, and of many slate-rocks-anid, generally, on the soils formed from all rocks which contain little lime, or from which the lime may have been washed out during their gradual degradation. On the other hand, it is often applied in vain to the soils of the oolites (Lee. XI., ~ 8), and other calcareous formations, because of the abundance of lime already present in them.. The advantage derived from chalking thin clay soils resting immediately upon the chalk rock (Lee. XI., ~ 8, and.page 376), is explained by the almost entire absence ot lime from these soils. The clay covering of the chalk wolds has pro bably been formed, not from the ruins of the chalk rock itself, but from the deposit of muddy waters, which rested upon it for some time before those localities became dry land. 4~. Lime produces a greater proportionxal improvement upon poor soils 394 LAND MAY BE SATURATED WITH LIME. than on such as are richer (Dr. Anderson.) This is also easily understood, It is of poor soils in their natural state of which DIr. Anderson speaks.* In this state they contain a greater or less quantity of organic matter, but are nearly destitute of lime, and hence are in the most favourable condition for being benefitted by a copious liming. Experience has proved that by this one operation such land may be raised in money value eight times, or from 5s. to 40s. per acre; but no practical man would expect that arable land already worth (c2 per acre, could, by liming or any other single operation, become worth -16 per acre of annual rent. The greater proportional improvement produced upon poor lands by lime is only an illustration, therefore, of the general truththat on poor soils the efforts of the skilfll improver are always crowned with the earliest and most apparent success. 5~. In certain cases, the addition of lime, even to land in good cultivation, and according to the ordinary and approved practice of the district,. produces no effect whatever. This is sometimes observed where the custom prevails, as in some parts of Ayrshire and elsewhere, to apply lime along with every wheat crop (p. 384,) and on such farms especially where the land is of a lighter quality. Where from 40 to 60 bushels of lime are added at the end of each rotation of 4 or 5 years, the land may soon become so saturated with lime that a fresh addition will produce no sensible effect. Thus Mr. Campbell, of Craigie, informs me of a trial made by an intelligent farmer in his neighbourhood, where alternate ridges only were limed without any sensible difference being observed. No result could show more clearly than this-that for one rotation at least the expense of lime might be saved, while at the same time the land would run the less risk of exhaustion. Another fact mentioned by Mr. Campbell proves the soundness of this conclusion. The lime never fails to produce obvious, benefit where the land is allower( to be 4 or 5 years in grass-where it is applied, that is, only once in 8 or 9 years. The fair inference is, therefore, that in this district as well as in others where similar effects are observed, too much lime is habitually added to the land, whereby not only is a needless expense incurred, but a speedier exhaustion of the soil is insured. Good husbandry, therefore, indicates either the application of a smaller dose at the recurrence of the wheat crop-or the occasional omission of lime altogether for an entire rotation. The practical farmer cannot have a better mode of ascertaining when his land is thus fiully supplied with lime-than by making the trial upon alternate ridges, and marking the effect. 6c. On poor arable lands, which are not naturally so, but which are worn out or exhausted by repeated liming and cropping, lime produces no good whateverf (Anderson, Brown, Morton.) Such soils, if they do not already abound in lime, are, at least, equally destitute of numerous >ther kinds of food, organic and inorganic, by which healthy plants are nourished, —and they are only to be restored to a fertile condition by a * "I never met," he says, " with a poor soil in its natural state, which was not benefitted in a very great degree by calcareous matter when administered in proper quantities. But I have met with several rich soils, which are fully impregnated with dung, on which lime applied in any quantity produced not the smallest sensible effect." t' " It is scarcely practicable to restore fertility to land, even of the best natural quality, which has been thus abused; and thin moorish soils, after being exhausted by lime, are Rot to be restored." (Brown.) LIME DOES NOT BENEFIT EXHAUSTED LANDS. 395 judicious admixture of all This truth is confirmed by the practical observation, that on soils so exhausted farm yard manure along with the lime does not produce the same good results as in other cases. All that the soil requires is not supplied in sufficient abundance by these two substances laid on alone. 7~. On lands of this kind, and on all in which vegetable matter is wanting, lime may even do harm to the immediate crop. It is apt to singe or burn the corn sown upon them (Brown)-an effect which is probably chemical, but which may in part be owing to its rendering more open and friable soils already, by long arable culture,' too open. (Morton.) 8~. A consideration of the circumstances above adverted to explains why, in some districts, and even in some whole provinces, the use of lime in any form should be condemned and even entirely given up. The soil has been impoverished through its unskilful application-or, by large admixtures of lime or marl for a series of years, the soil has been so changed as to yield no adequate return for new additions. Thus for a generation or two the practices of liming and marling are abandoned, to be slowly and reluctantly resumed again, when natural causes have removed the lime from the soil, and produced an accumulation of those other substances which, when associated with it, contribute to the productiveness of the land. ~ 17. Effects of an overdose of lime. There are several effects which are-familiar to the practical man as mare or less observable when lime in any form is laid too lavishly upon the land. Thus 1~. It is rendered so loose by an overdose as to be capable of holding no water (Kames). Upon stiff clays a very large quantity indeed will be required to produce this effect. 2~. By an overdose of quick-lime the land is hardened to such a degree as to be impervious to water or to the roots of plants. Several parts of the Carse of Gowrie are thus rendered so hard as to be unfit for vegetation-(Lord Kames' Gentleman Farmer, edit. 1802). This effect will be observed only in soils which are naturally wet and undrained, or where much rain has fallen and lingered on the land after the lime has been applied (p. 388). 3~. But the most injurious effect of an over-liming, whether it be laid on at one or at successive periods, isthe exhaustion by which it is succeeded. "A An overdose of shell-marl," says Lord Kames, "laid perhaps an inch thick, produces for a time large crops, but at last renders the soil capable of bearing neither corn nor grass, of which there are many examples in Scotland." The same is true of lime in any form. The increased fertility continues as long as there remains an adequate supply of organic (animal and vegetable) matter in the soil, but as that disappears the crops every year diminish both in quantity and in quality. An interesting illustration of this exhausting power of lime is afforded by the observed effects of long-continued marling upon certain poor soils in the province of Isere, in France. The marl there employed is a sandy marl, containing from 30 to 60 per cent. of carbonate of lime — 17* 396 LENGTH OF TIME DURING WHICH LIME ACTS. very much like the lime-sand of Ireland or the shell-sand ofthe Western Islands already described (p. 371). A layer of this marl one-third of an inch thick, applied at intervals to a soil producing in its natural state only a three-fold return of rye every other year, causes it to yield for the first 10 or 12 years an eight-fold return of wheat. But after 40 years' marling, the farmers now complain that the land will give only a four-fold return of wheat. But the cause of this reduction is to be found in the constant cropping with corn, in the growing of no green crops, and in the addition of no manure..Yet even with this treatment the lind is still more productive than before the marling was commenced. It produces four returns instead of three, and it grows wheat where before only rye would thrive and ripen. From the possession of this exhausting property has arisen the almost universally diffused proverb, that lime enriches thefathers but inpove'rishes the sons. The fault, however, is not in the lime, but in the improvident fathers, who in this case, as in so many others, exhaust and inconsiderately squander the inheritance of their sons. If care be taken to keep up the supply of organic matter in the soil-by copious additions of manure or otherwise (p. 380)-lime may be added freely and a system of high farming kept up, by which both the present holder of the land and his successors will be equally benefitted. The opinion expressed by some of the highest authorities among practical men, that too much lime cannot be added, provided the soil abound sufficiently in vegetable matter, may perhaps be rather overstated; but it undoubtedly embodies the result of long-continued general observation-that the exhausting effect of lime may be postponed indefinitely by a liberal management of the land.* ~ 18. Length of time during which lime acts. It is the fate of nearly all the superficial improvements of the soil, that they are only temporary in their duration. The action of lime ceases after a time, and the land returns to its original condition. The length of time which must elapse before this takes place will depend, among other circumstances, upon the quantity of lime added to, or originally contained in, the soil-upon the kind of cropping to which it is subjected-on the nature of the soil itself-on the slope and exposure and natural moisture of the land, and on the climate in which it is situated. We have seen that on the arable lands of the south of Scotland 20 years is the longest period during which the doses there applied act beneficially upon the crops-while in other parts of the country renewed applications are considered necessary at much shorter intervals. Mr. Dawson, of Frogden, who introduced the practice of liming into the Border counties of Scotland, observed that, when harrowed in with the grass seeds, its effect in improving the subsequent pasture was sensible for 30 years after. A heavy marling or chalking* in the southern and In Germany the necessary union of manure and marl is in the mouth of every peasant- ---- Ohne lmist Ist das Geld fiir mergein verquist. t Applied at a cost of 30s. oIn 0s. per acre, according to the locality — Mr. Pusey, Royah Agricultural Journal, iii., p. 185. LIME NATURALLY SINKS INTO THE SOIL. 397 Midland counties of England is said also to last for 30 years, and the same period is assigned to the sensible effect of the ordinary doses of lime-sand in Ireland, and of shell-sands and marls in several parts of France. The effect of the lime lessens gradually, and though at the end of an assignable number of years it becomes almost insensible, yet it does not altogether cease till a much ater period. This period is in some cases so protracted that intelligent practical men are in many districts to be met with who believe-that certain grass lands would never forget a good dose of lime (p. 391, note). ~ 19. Of the sinking of lime into the soil. One of the causes of this gradual diminution of the action of lime is to be found in the singular property it possesses of slowly sinking into the land, until it almost entirely disappears from the surface soil. It has been long familiar to practical men, that when grass lands, which have been limed on the sward, are after a time broken up, a white layer or band of lime is seen at a greater or less depth beneath the surface, but lodging, generally, where it has attained its greatest depth between the upper, loose and fertile, and the lower, more or less impervious and unproductive soil. In arable lands the action of the plough counteracts this tendency in some measure, bringing up the lime again from beneath, and keeping it mixed with the surface mould. Yet, through ploughed land it sinks at length, especially where the ploughing is shallow, and even the industry of the gardener can scarcely prevent it from descending beyond the reach of his spade. The chief cause of this sinking is to be found in the extreme minuteness of the particles into which slaked lime naturally falls. If a portion of slaked lime be mixed with water it forms a milky mixture, in which some lime is dissolved, but much more is held in suspension in an extremely divided state. When this milk is allowed to stand undisturbed, the fine particles subside very slowly, and are easily again disturbed, but if thrown upon a filter they are arrested immediately, and the lime-water passes through clear. Suppose these fine particles to be mixed with the soil, and the rain to fall upon them, it will carry them downwards through the pores of the soil till the close subsoil acts the part of a filter, and arrests them. This tendency to be washed down is common not only to lime, but to all minutely divided earthy matter ofa sfficiently incoherent nature. Hence the formation of that more or less impervious layer of finely divided matter which so often forms the subsoil beneath free and open surface soils. And that lime shlould appear alone or chiefly to sink on any cultivated field, may arise from this circumstance-that the continued action of the rains had long before carried downwards the finer incoherent particles of other kinds whi-ich existed naturally in the soil, and therefore could find little else but the lime on which this action could be exercised. This explanation is satisfactory enough in the case of light and open soils. which are full of pores, but it appears less so in regard to stifl clays and to loamy soils. which are not only close and apparently void of pores, but seem then:selves to consist of particles in a sufficiently Pimute state of divisitn to admit of their being carried down by th. 398 EFFECTS OF SINKING, AND REMEDIES FOR'IT. rains in an equal degree with lime itself. This difficulty induced Lord Dundonald to suspect the agency of some chemical principle in producing the above effect.* As the lime, however, is unchanged after it has descended, is still in a powdery state, and exhibits no appearance of having been dissolved, it is difficult to imagine any chemical action by which such a sinking could have been brought about. It is possible that in grass lands the earth-worms, which contribute so much to the gradual production of a fine mould, may, b) bringing up tie other earthy matters only, contribute to the apparent sinking of the lime, as well as of certain other top-dressings.t The effects of this sinking are to remove the lime from the surface soil, and to form a layer of calcareous matter which in wet or impervious bottoms will harden and form a more or less solid bed or pan, throurgh which the rains and roots refuse to penetrate, and which the subsoil plough in some districts can tear up with difficulty. On our stiffer soils it encourages the growth of the troublesome coltsfoot, and in the open ditches of the wholesome water-cress. The practical remedies for this sinking are of two kinds: 1~. The ploughing of a deeper furrow, and hence one of the benefits which in many localities follow the use of the trench plough (p. 322). 20. The sowing of deep-rooted and lime-loving crops, such as lucerne and sainfoin, which in such soils not only thrive, but bring up in their stems, and restore to the surface, a portion of the lime which had previously descended, and thus make it available to the after-crops. ~ 20. Why liming must be repeated. Lime which sinks, as above described, does not wholly escape from the soil, but may by judicious management be again brought to the surface. Such a sinking therefore, does not necessarily call for the addition of a fresh dose of lime, nor does it explain the reason why in practice the application of lime to the land must at certain intervals be every where repeated. We have already seen that the influence of the lime we have laid upon our fields after a time gradually diminishes-the grass becomes sensibly less rich year by year, the crops of corn less abundant, the kind of grain it will ripen less valuable. Does the lime, you might ask, actually disappear from the soil, or does it merely cease to act? This question has been most distinctly answered by an experiment of Lampadius. He mingled lime with the soil of a piece of ground till it was in the proportion of 1-19 per cent. of the whole and he determined subsequently, by analysis, the quantity of lime it contained in each of the three succeeding years. The first year it contained. 1-19 per cent. carbonate of lime. The second year.. 089 " The third year.... 0-52 " The fourth year..... 024 " t * "In claye.y and loamy soils, which are (.) equally diffusible with lime, and nearly of the sime specific gravity. I;e tendency which lime has to sink cannot be accounted for simply on mecthaical prin,-ipies "-Lord Dundonald's Agricultural Chemistry, p. 45. f See in a subser'.'fr.t lecture the remarks on laying olown to grass; also the Author's EJlemenrs of Agricultural Clheistry, p. 212. Schibler, Agricut'iurl C,/cemie. ii., p.!4\. WHY LIMING MUST BE REPEATED. 399 There can be no question, therefore, that the lime gradually disappears or is removed from the soil. The agencies by which this removal is effected are of several kinds. 1~. In some cases it sinks, as we have already seen, and escapes into the subsoil beyond the reach of the plough or of the roots of our culti-.vated crops. 2~. A considerable quantity of lime is annually removed from the soil by the crops which are reaped from it. We have already seen (Lec. X., ~ 4,) that in a four years' rotation of alternate green and corn crops the quantity of lime contained in the average produce of good land amounts to 248 lbs. This is equal to 60 lbs. of quick-lime or 107 lbs. of carbonate of lime every year. The whole of this, however, is not usually lost to the land. Part at least is restored to it in the manure into which a large proportion of the produce is usually converted. Yet a considerable quantity is always lost-escaping chiefly in the liquid manure and in the drainings of the dung-heaps-and this loss must be repaired by the renewed addition of lime to the land. 3~. But the rains and natural springs of water percolating through the soil remove, in general, a still greater proportion. While in the quick or caustic state, lime is soluble in pure water. Seven hundred and fifty pounds of water will dissolve about one pound of lime. The rains that fall, therefore, cannot fail, as they sink through the soil, to dissolve and carry away a portion of the lime so long as it remains in the caustic state. Again, quick-lime, when mixed with the soil, speedily attracts carbonic acid, and becomes, after a time, converted into carbonate, which is nearly insoluble in pure water. But this carbonate, as we have already seen (Lec. III., ~ 1), is soluble in water impregnated with carbonic acid-and as the drops of rain in falling absorb this acid from the air, they become capable, when they reach the soil, of dissolving an appreciable quantity of the finely divided carbonate which they meet with upon our cultivated lands. Hence the water that flows from the drains upon such lands is always impregnated with lime, and sometimes to so great a degree as to form calcareous deposits in the interior of the drains themselves, where the fall is so gentle as to allow the water to linger a sufficient length of time in the soil. It is impossible to estimate the quantity of lime which this dissolving action of the rains must gradually remove. It will vary with the amount of rain which falls in each locality, and with the slope or inclination of the land; but the cause is at once universal and constantly operating, and would alone, therefore, render necessary, after the lapse of years, the application of new doses of lime both to our pastures and to our arable fields. 4~. During the decay of vegetable matter, and the decomposition of mineral compounds, which take place in the soil where lime is present, new combinations are formed in variable quantities which are more soluble than the carbonate, and which therefore hasten and facilitate this washing out of the lime by the action of the rains. Thus chloride of calcclm, nitrate of lime, and gypsum, are all produced-of which the two former are eminently soluble in water-while organic acids also regsoIt irom the decay of the organic matter, with some of which the lime ibras readily soluble compounds (salts) easily removed by water. 400 ACTION OF LIME UPON THE SOIL) AND AS TIE FOOD OF PLANTS. The ultimate resolution of all vegetable matter in the soil into carbonic acid and water (Lec. VIII., ~ 3,) likewise aids the removal of the lime. For if the soil be everywhere impregnated with carbonic acid, the rain and spring waters that flow through it will also become charged with this gas, and thus be enabled to dissolve a larger portion of the carbonate of lime than they could otherwise do. Thus theory indicates, what I believe experience confirms, that a given quantity of lime will disappear the sooner from a field, the more abundant the animal and vegetable matter it contains. ~21. Theory of the action of lime. Lime acts in two ways upon the soil. It produces a mechanical alteration which is simple and easily understood, and is the cause of a series of chemical changes, which are really obscure, and are as yet susceptible of only partial explanation. In the finely divided state of quick-lime, of slaked lime, or of soft and crumbling chalk, it stiffens very loose soils, and opens the stiffer clays,-while in the form of limestone gravel or of shell-sand, it may be employed either for opening a clay soil or for giving body and firmness to boggy land. These effects, and their explanation, are so obvious to you, that it is unnecessary to dwell upon them. The purposes served by lime as a chemical constituent of the soil are at least of four distinct kinds. 1~. It supplies a kind of inorganic food which appears to be necessary to the healthy growth of all our cultivated plants. 2~.. It neutralizes acid substances which are naturally formed in the soil, and decomposes or renders harmless other noxious compounds which are not unfrequently within reach of the roots of plants. 3~. It changes the inert vegetable matter in the soil, so as gradually to render it useful to vegetation. 4~. It causes, facilitates, or enables other useful compounds, both organic and inorganic, to be produced in the soil,-or so promotes the decomposition of existing compounds as to prepare them more speedily for entering into the circulation of plants. These several modes of action it will be necessary to illustrate in some detail. ~ 22. Of lime as the food of plants. In considering the chemical nature of the ash of plants (Lece X., ~ 3 and 4), we have seen that'lime in all cases forms a considerable proportion of its whole weight. Hence the reason why lime is regarded as a necessary food of plants, and hence also one cause of its beneficial influence in general agricultural practice. The quantity of pure lime contained in the crops produced upon one acre during a four years' rotation amounts, on an average, to 242 lbs. which are equal to about 430 lbs. (say 4 cwt. ) of carbonate of lime, m the state of marl, shell-sand, or lime-stone gravel. (See Lec. X., ~ 3.) It is obvious, therefore, that one of the most intelligible purposes served by lime, as a chemical constituent of the soil, is to supply this compuratively large quantity of lime, which in some form or other must enter into the roots of plants. ACTS CHIEFLY UPON THE ORGANIC MATTER OF THE SOIL. 401 But the different crops which we grow contain lime in unlike proportons. Thus the average produce of an acre of land under the followmg crops contains of limeGrain or roots. Straw or tops. Total. Wheat, 25 bushels,... 15 7-2 8-7 lbs. Barley, 38 bushels,.. 21 129 15-0 lbs. Oats, 50 bushels,. 25 5-7 8-2 lbs. Turnips, 25 tons,. 45-8 93-0 138-8 lbs. Potatoes, 9 tons,.. 6-6 259-4 266-0 lbs. Red clover, 2 tons,... 126-0 126-0 lbs. Rye grass, 2 tons,... 330 33-0 lbs. These quantities are not constant, and wheat especially contains much more lime than is above stated, when it is grown upon land to which lime has been copiously applied. But the very different quantities contained in the several crops, as above exhibited, shew that one reason why lime favours the growth of some crops more than others is, that some actually take up a larger quantity of lime as food. These crops, therefore) require the presence of lime in greater proportion in the soil, in order that they may be able to obtain it so readily that no delay may occur in the performance ofthose functions or in the growth of those parts to which lime is indispensable. ~ 23. The chemical action of lime is exerted CHIEFLY upon the organic matter of the soil. There are four circumstances of great practical importance in regard to the action of lime, which cannot be too carefully considered in reference also to the theory of its operation. These are1~. That lime has little or no effect upon soils in which organic matter is deficient. 2~. That its apparent effect'is inconsiderable during the first year after its application, compared with that which it produces in the second and third years. 3~. That its effect is most sensible when it is kept near the surface of the soil, and gradually becomes less as it sinks towards the subsoil. And, 4~. That under the influence of lime the organic matter of the soil disappears more rapidly than it otherwise would do, and that after it has thus disappeared fresh additions of lime produce no further good effect. It is obvious.from these facts, that in general the main beneficial purpose served by lime is to be sought for in the nature of its chemical action upon the organic matter of the soil-an action which takes place slowly, which is hastened by the access of air, and which causes the organic matter itself ultimately to disappear. ~ 24. Of theforms.in which organic matter usually exists in the soil, and circumstances under which its decomposition may take place. I.-The organic matter which lime thus causes to disappear is presented to it in one or other of five different forms: 1~. In that of recent, often gre? moist, and undecomposed roots, leaves, and stems of plants. 402 UPON THE DECOMPOSITION OF ORGANIC MATTER. 2~. In that of dry, and still undecomposed, vegetable matter, such as straw. 3~. In a more or less decayed or decaying state, generally black or brown in colour-and often in some degree soluble in water. 4~. in what is called the inert state, when spontaneous decay ceases to be sensibly observed. And 5~. In the state of chemical combination with the earthy substances -with the alumina for example, and with the lime or magnesia-already existing in the soil. Upon these several varieties of organic matter lime acts with different degrees of rapidity. II.-The final result of the decomposition of these several forms of organic matter, when they contain no nitrogen, is their conversion into carbonic acid and water only (Lee. VIII., ~ 3). They pass, however, through several intermediate stages before they reach this point-the number and rapidity of which, and the kind of changes they undergo at each stage, depend upon the circumstances under which the decomposition is effected. Thus the substance may decompose1~. Alone, in which case the changes that occur proceed slowly, and arise solely from a new arrangement of its own particles. This kind of decomposition rarely occurs to any extent in the soil. 2~. In the presence of water only.-This also seldom takes place in the soil. Trees long buried in moist clays impervious to air exhibit the kind of slow alteration which results from the presence of water alone. In the bottoms of lakes, ditches, and boggy places also, from which inflammable gases arise, water is the principal cause of the more rapid decomposition. 3~. In the presence of air only.-In nature organic matter is never placed in this condition, the air of our atmosphere being always largely mixed with moisture. In dry air decomposition is exceedingly slow, and the changes which dry organic substances undergo in it are often scarcely perceptible. 4~. In the presence of both water and air.-This is the almost universal condition of the organic matter in our fields and farm-yards. The joint action of air and water, and the tendency ofthe elements of the organic matter to enter into new combinations, cause new chemical changes to succeed each other with much rapidity. It will of course be understood that moderate warmth is necessary to the production of these effects.* 5~. In the presence of lime, or of some other alkaline substance (pottsh, soda, or magnesia).-Organic matter is often found in the soil in -uch a state that the conjoined action of both air and water are unable to hasten on its decomposition. A new chemicalagency must then be' At amiliar illustration of the conjoined efficacy of air and water in producing oxidation is -xhihited in their action upon iron. If a piece of polished iron be kept in perfectly dry air;t will not rust. Or if it be completely covered over with pure water in a well-stoppered,)ottle, from which air is excluded, it will remain bright and untarhished. But if a polished rod of ir)on be put into an open vessel half full of water, so that one part of its lenagh only is under water-then the rod will begin very soon to rust at the surface of the water, and a nrown ochrey ring of oxide will form around it, exactly where the air and water meet. From this point the rust will -radually spread upwards and downwards. So it is with the organic matter of the soil. Wherever the air and water meet, their decomposing action Upon it,in ordinary temperatures, soon beconmes perceptible., INFLUENCE OF ALKALINE SUBSTANCES. 403 introduced, by which the elements of the organic matter may again be set in motion. Lime is the agent which for this purpose is most largely employed in practical agriculture. ~ 25. General action of alkaline substances upon organic matter. It is this action of alkaline matters upon the organic substances of the soil in the presence of air and water that we are principally to investigate. When organic matter undergoes decay in the presence of air and water only, it first rots, as it is called, and blackens, giving off water or its elements chiefly, and forming humus-a mixture ofhumic, ulmic, and some other acids, (Lec. XIII., ~ 1,) with decaying vegetable fibre. It then commences, at the expense of the oxygen of the air and of water, to form other more soluble acids (malic, acetic, lactic, crenic, mudesic, &c.,) among which is a portion of carbonic-and, by the aid of the hydrogen of the water which it decomposes, one or more of the many compounds of carbon and hydrogen, which often rise up, as the marsh-gas does, and escape into the air, (Lec. VIII., ~ 3.) Thus there is a tendency towards the accumulation of acid substances of vegetable origin in the soil, and this is more especially the case when the soil is moist, and where much vegetable matter abounds. The effect of this super-abundance of acid matter is, on the one hand, to arrest the further natural decay of the organic matter, and, on the other, to render the soil unfavorable to the healthy growth of young or tender plants. The general effect of the presence of alkaline substances in the soil is to counteract these two evils. They combine with and thus remove the sourness of the acid bodies as they are formed. In consequence of this the soil becomes sweeter or more propitious to vegetation, while the natural tendency of the vegetable matter to decay is no longer arrested. It is thus clear that an immediate good effect upon the land must.follow either from the artificial application or from the natural presence of alkaline matter in the soil-while at the same time it will cause the vegetable matter to disappear more rapidly than would otherwise be th:e case. But the effect of such substances does not end here. They a-,tually dispose or provoke-pre-dispose, chemists call it-the vegetablea matter to continue forming acid substances, in order that they may co lbine with them, and thus cause the organic matters to disappear more rapidly than they otherwise would do-in other words, they ha-iten for ward the exhaustion of the vegetable matter of the soil. Such is the general action of all alkaline substances. This action they exhibit even in close vessels. Thus a solution of- grape sugar, mixed with potash, and left in a warm place, slowly forms melassic acid-while in cold lime-water the same sugar is gradually converted into another acid called the glucic. But in the air other acids are formed in the same mixtures, and the changes proceed more rapidly. Such is the case also in the soil, where the elements of thp. air and of water are generally at hand to favor the decomposition. But the nature of the alkaline matter which is present determines also the rapidity with which such changes are produced. The most powerful alkaline substances-potash and soda —produce all the above effects most quickly; lime and magnesia are next in order; and the alumina of the clay soils, though much inferior to all of these, is far from being without an important influence. 404 ACTION OF CAUSTIC LIME UPON ORGANIC MATTER Hence one of the benefits which result from the use of wood-ashes containing carbonate of potash, when employed in small quantities, and along with vegetable and animal manures, as they are in this country; but hence also the evil effects which are found to follow from the application of them in too large doses. Thus in countries where wood abounds, and where it is usual, as in Sweden and Northern Russia, to burn the forests and to lay on their ashes as manure, the tillage can be continued for a few years only. After one or two crops the land is exhausted, and must ag'in be left to its natural produce. ~ 26. Special effects of CAUSTI( lime upon the several varieties of organic matter in the soil. The effects of lime upon organic matter are precisely the same in kind as those of the alkalies in general. They are only less in degree, or take place more slowly, than when soda or potash is employed. Hence, the greater adaptation of lime to the purposes of practical agriculture. 1~. Action of caustic lime alone upon vegetable matter.-If the fiesh leaves and twigs of plants, or blades and roots of grass, be introduced into a bottle, surrounded with slaked lime, and corked, they will slowly undergo a certain change of color, but they may be preserved, it is said, for years, without exhibiting any striking change of texture (Mr. Garden.) If dry straw be so mixed with slaked lime, will exhibit still less alteration. In either case also the changes wil. be even less perceptible, if, instead of hydrate of lime, the carbonate (or mild lime,) in any of its forms, be mixed with these varieties of vegetable matter. On some other varieties of vegetable matter,-such, for example, as are undergoing rapid decay, or have already reached an advanced stage of decomposition,-an admixture of slaked lime produces certain perceptible changes immediately, and mild lime more slowly, but these changes being completed, the tendency of lime alone is to arrest rather than to promote further rapid alterations. Hence, the following opinions of experienced practical observers must be admitted to be theoretically correct-in so far as they refer to the action of lime alone. " If straw of long dung be mixed with slaked lime, it will be preserved." (Morton, On Soils. 3d edition, p. 181.) " Lime mixed in a mass of earth containing the live roots and seeds of plants, will not destroy them.' (Morton.) " Sir H. Davy's theory, that lime dissolves vegetable matter, is given up; in fact, it hardens vegetable matter. (Mr. Pusey, Royal Agricultural Journal, iii., p. 212. These opinions, I have said, are probab.y correct in so far as regards the unaided action of lime. They even express, with an approach to accuracy, what will take place in the interior of compost heaps of a certain kind, or in some dry soils; but that they cannot apply to the ordinary action of lime upon the soil is proved by the other result of universal observation, that lime, so far from preserving the organic matter of the land to which it is applied, in reality wastes it-causes, that is, or disposes it to disappear. 2~. Action of caustic lime on organic matter in the presence of air and water.-In the presence of air and water, when assisted by a IN THE PRESENCE OF AIR AND WATER. 405 favoring temperature, vegetable matter, as we have already seen, undergoes spontaneous decomposition. In the same circumstances lime promotes and sensibly hastens this decomposition,-altering the forms or stages through which the organic matter must pass-but bringing about more speedily the final conversion into carbonic acid and water. During its natural decay in a moist and open soil, organic matter gives off a portion of carbonic acid gas, which escapes, and forms certain other acids which remain in the dark mould of the soil itself. When quick or slaked lime is added to the land, its first effect is to combine with these acids-to form carbonate, humate, &c., of lime-till the whole of the acid matter existing at the time is taken up. That portion of the lime which remains uncombined, either slowly absorbs carbonic acid from the air or unites with the carbonate already formed, to produce the known compound of hydrate with carbonate of lime,-(that compound, namely, which is produced when quick-lime slakes spontaneously in the air-see p. 368,)-waiting in this state in the soil till some fresh portions of acid matter are formed with which it may combine. But it does not inactively wait; it persuades and influences the organic matter to combine with the oxygen of the air and water with which it is surrounded, for the production of such acid substances-till finally the whole of the lime becomes combined either with carbonic or with some other acid of organic origin. Nor at this stage are the action and influence of lime observed to cease. On the contrary, this result will, in most soils, be arrived at in the course of one or two years, while the beneficial action of the lime itself may be perceptible for 20 or 30 years. Hence there is much apparent ground for the opinion of Lord Kames,' that lime is as efficacious in its (so called) effete as in its caustic state." Even the more strongly expressed opinion of the same acute observer, " that lime produces little effect upon vegetables till it becomes effete"-derives much support from experience-since lime is known to have comparatively little effect upon the productiveness of the land till one or two years after its application; and this period, as I have said, is in most localities sufficient to deprive even slaked lime of all its caustic properties. Of the saline compounds, (saline compounds or salts are always formed when lime, magnesia, potash, soda, &c., combine with acids,) which caustic lime thus forms, either immediately or ultimately, some, like the carbonate and humate, being very sparingly soluble in water, remain more or less permanently in the soil; others, like the acetate of lime, being readily soluble, are either washed out by the rains or are sucked up by the roots of the growing plants. In the former case fhey cause the removal of both organic matter and of lime from the land; in the latter they supply the plant with a portion of organic food, and at the same time with lime —without which, as we have frequently before remarked, plants cannot be maintained in their most healthy condition. 27. Action of mild (or carbonate of) lime upon the vegetable matter of the soil. The main utility of lime, therefore, depends upon its prolonged after-action upon the vegetable matter of the soil. What is this action, and in what consis-;..e benefits to which;f gives rise?" 406 ACTION OF CARBONATE OF LIME UPON VEGETABLE MATTER. In answering this question, it is of importance to observe that all the effects produced by alkaline matter in general-whether by lime or by potash-in the caustic state, are produced in kind also by the same substances in the state of carbonate. The carbonic acid with which they are united is retained by a comparatively feeble affinity, and is displaced with greater or less ease by almost every other acid compound which is produced in the soil. With this displacement is connected an interesting series of beautiful reactions, which it is of consequence to understand. You will recollect that the great end which nature, so to speak, has in view, in all the changes to which she subjects organic matter in the soil, is to convert it-with the exception of its nitrogen-into carbonic acid and water. For this purpose it combines at one time, with the oxygen of the air, while at another it decomposes water and unites with the oxygen or the hydrogen which are liberated) or with both, to form new chemical combinations. Each of these new combinations is either immediately preliminary to or is attended by the conversion of a portion to the elements of the organic matter into one or other of those simpler forms of matter on which plants live. Now during these preliminary or preparatory steps, acid substances, as I have already explained, are among others constantly produced. With these acids, the carbonate of lime, when present in the soil, is ever ready to combine. But in so combining, it gives off the carbonic acid with which it is already united, and thus a continual, slow evolution of carbonic acid is kept up as long as any undecomposed carbonate remains in the soil. I do not attempt to specify by name the various acid substances which are thus formed during the oxidation of the organic matter, and which successively unite with the lime, because the entire series of interesting and highly important changes, which organic substances undergo in the soil, has as yet been too little investigated, to permit us to do more than speak in general terms of the nature of the chemical compounds which are most abundantly produced. Of two facts, however, in regard to them, we are certain-that they are simpler in their constitution than the original organic matter itself; from which they are derived-and that they have a tendency to assume still simpler forms, if they continue to be exposed to the same united action of air, water, and alkaline substances. Hence the compounds which lime has formed with the acid substances of the soil, themselves hasten forward to new decompositions, -unite with more oxygen, liberate slowly portion after portion of their carbon in the form of carbonic acid, and of their hydrogen in the form of water, till at length the lime itself is left again in the state of carbonate, or in union with carbonic acid only. This residual carbonate begins again the same round of changes through which it had previously passed. It gives up its carbonic acid at the bidding of some more powerful organic acid produced in its neighborhood, while this acid, by exposure to the due influences, undergoes new alterations till it also is finally resolved into carbonic acid and water. Two circumstances are deserving to be borne in mind in reference to these successive decompositions-first, that in the course of them more soluble compounds of lime are now and then formed, some of SUMMARY OF THE CHANGES PRODUCED.Bo Y L4iM'i., 407 which are washed out by the rains, and escape from_ ti.-e soil, while others minister to the growth of plants;-and seco nd, tL,.it -ery much carbonic acid is produced as their final result —of';vh.icl al (so part is taken up by the roots of plants, and part escapes into th; Wair. Thus at every successive stage a portion of organic matter i-s!ost to the soil. If this quantity be greater than that which is yeal.y -:iined in the form of roots or decayed leaves and stems of pants or f manure artificially added, the soil will be gradually exhauster ---— if i',sn it will every year become more rich in vegetable matter. It is also to be borne in.mind, that although, for th,:,'p oise of illustration, I have supposea the carbonate of lime firsti: fored! in the soil to be subsequently combined with other acids, wsvic. L at..:iaally decompose and leave it again in the state of carbon;i, -yet it will rarely happen that the whole of the carbonate of lime in the soil will be in any of these new states of combination. In general, a part of it only is thus at any one time employed in working up the acid substances produced. But it is necessary that it should be universally diffused through the soil in order that it may be everywhere at hand to perform the important part of its functions above explained. It is only where little lime is present, or where decaying vegetable matter is in exceeding abundance, that the whole of the carbonate can at one and the same time disappear (p. 380.) The changes, therefore, which lime and organic matter, supposed to be free from nitrogen, respectively undergo, and their mutual ac-. tion in the soil, may be summed up as follows:1~. The organic matter, under the influence of air and moisture, spontaneously decomposes, and besides carbonic acid which escapes, forms also other acid substances which linger in the soil. 2~. With. these acids the quick-lime combines, and, either by its union with them or with carbonic acid from the air, soon (compararatively) loses its caustic state. 3'. The production of acid substances by the oxidation of the organic matter-goes on more rapidly under the disposing influence of the lime, whether caustic or carbonated. These acids combine with the lime, liberating from it, when in the state of carbonate, a slow but constant current of carbonic acid, upon which plants at least partly live. 4~. The organic acid matter which thus unites with the lime continues itself to be acted upon by the air and water, aided by heat. and light-itself passes through a succession of stages of decomposition, at each of which it gives off water or carbonic acid, retaining still its hold of the lime, till at last being wholly decomposed it leaves the lime again in the state of carbonate, ready to begin anew the same round of change. During this series of progressive decompositions, certain more soluble compounds of lime are formed, by which plants are in part at least supplied with this earth, and which with the aid of the rains carry off both lime and organic matter from the soil. And, again, the more rapid the production of the acid substances 408 COMPARATIVE UTILITY OF BURNED AND UNBURNED LIME. which result from the union of the organic matter with oxygen, the more abundant ii general also the production of those gaseous and volatile compounds which they form by uniting with hydrogen, so that, in promoting the formation of the one class of bodies, lime also favors the evolution of the other in greater abundance, and thus in a double measure contributes to the exhaustion of the soil. The disposing action of lime to this twin form of decomposition, few varieties of organic:matter can resist,-and hence arises the well known efficacy of lime in resolving and rendering useful the apparently inert.,vegetable substances that not unfrequently exist in the soil. ~ 28. Of the comparative utility of burned and unburned lime. Is there no advantage, then, you may ask, in using caustic or burned rather than carbonated or unburned lime? If the ultimate effects of both upon the land be the same, why be at the expense of burning? Among other benefits may be enumerated the following:1~. By burning and slaking, the lime is reduced to the state of an impalpable powder, finer than could be obtained by any available method 3f crushing. It can in consequence be diffused more uniformly through.he soil, and hence a smaller quantity will produce an equal effect. This minute state of division also promotes in a wonderful degree the chemical action of the lime. In all cases chemical action takes place between exceedingly minute particles of matter, and among solid substances the more rapidly, the finer the powder to which they can be reduced. Thus a mass of iron or lead slowlyrusts or tarnishes in the air, but if the mass of either metal be reduced to the state of an impalpable powder-which can be done by certain chemical means-it will take fire when simply exposed to the air at the ordinary temperature, and will burn till it is entirely converted into oxide. By mere mechanical division the apparent action of the oxygen of the air upon metals is augmented and hastened in this extraordinary degree-and a similar result follows when lime in an impalpable state is brought into contact with the vegetable matter upon which it is intended to act. 2.'. The effect of burned lime is more powerful and more immediate than that of unburned lime in the form of chalk, marl, or shell sand. Hence it sooner neutralizes the acids which.exist in the soil, and sooner causes the decomposition of vegetable matter of every kind to commence, upon which its efficacy, in a greater degree, depends. Hence, when it can easily be procured, it is better fitted for sour grass or:arable lands, for such as contain an excess of vegetable matter, and especially for such as abounds in that dead or inert form of organic matter which requires a stronger stimulus-the presence of more powerful chemical affinities, that is-to bring it into active decomposition. In such cases, the lime has already done much good before it has been brought into the mild state-and remaining afterwards in this state in the soil, it still serves, in a great measure, the same slower after-purposes.as the original addition of carbonate would have done. "3~. Besides, if any portion of it, after the lapse of two or three years, still linger in the caustic state, (p. 368,) it will continue to provoke more rapid changes among the organic substances in the sol., than mild lime alone could have done. ORGANIC MATTER OF THE SOIL CONTAINS i 4~. Further, quick-lime is soluble in water, and hence ev' that falls and sinks into the soil carries with it a portion of long as any of it remains in the caustic state. It thus reac matters that lie beneath the surface, and alters and ameliorated the subsoil itself.' 5~. It is not a small additional recommendation of quick-lime, tha> by burning it loses about 44 per cent. of its weight, thus enabling nearly twice the quantity to be conveyed from place to place at the same cost of transport. This not only causes a direct saving of money,-as when the burned chalk of Antrim is carried by sea to the Ayrshire coasts-but an additional saving of labor also upon the farm,-where the number of hands and horses is often barely sufficient for the necessary work. ~ 29: Action of lime on organic substances which contain nitrogen. I have hitherto, for the sake of simplicity, directed your attention solely to the action, whether immediate or remote, which is exercised by lime upon organic matter supposed to contain no nitrogen. Its action upon compounds in which nitrogen exists is no less beautiful and simple, perhaps even more intelligible and more obviously useful to vegetation. There are several well known facts which it is here of importance for us to consider1~. That the black vegetable matter of the soil always contains nitrogen. Even that which is most inert retains a sensible proportion of it. It exists in dry peat to the amount of about 2 per cent. of its weight, and still clings to the other elements of the organic matter, even after it has undergone those prolonged changes by which it is finally converted into coal. Since nitrogen, therefore, is so important an element in all vegetable food, and so necessary in some form or other to the healthy growth and maturity of plants, it must be of consequence to awaken this element of decaying vegetable matter, when it is lying dormant, and to cause it to assume a form in which it can enter into and become useful to our cultivated plants. 2~. That if vegetable matter of any kind be heated with slaked lime, the whole of the nitrogen it may contain, in whatever state of combination it may previously exist, will be given off in the form of ammonia. The same takes place still more easily if a quantity of hydrate of potash or of hydrate of soda be mixed with the hydrate of lime. Though it has not as yet been proved by direct experiment-yet I consider it to be exceedingly probable, that what takes place quickly in our laboratories, at a comparatively high temperature, may take place more slowly also in the soil, and at the ordinary temperature of the atmosphere. 3~. That when animal and vegetable substances a:r mixed with earth, lime, and other alkaline matters, in the so-called nitre beds, (Lee. VIII., ~ 5,) ammonia and nitric acid are both produced, the quantity of nitrogen contained in the weight of these compounds extracted being much greater than was originally present in the animal and veg:table matter employed (Dumas.) Under the influence of alkaline substances, therefore, even when not in a caustic state, the decay of animal anl vegetable matter in the presence of air and moisture causes some of the nitrogen. of the atmosphere to become fixed in the soil in the form of MPOSITION OF ALL ORGANIC SUBSTANCES..1ic acid. What takes place on the confined area of a j take place to some extent also in the wider area of a.nd well-manured field..ction of alkalies in the nitre bed, disposing to the productlitric acid, we observe the same kind of agency, which we already attributed to lime, in regard to the more abundant elemnts which exist in the vegetable matter of the soil. It gently per-,uades all the elements-nitrogen and carbon alike-to unite with the oxygen of air and water, and thus ultimately to form acid compounds with which it may itself combine. The action of lime upon such organic matters containing nitrogen as usually exist in the soil, may, therefore, be briefly stated as follows:1~. These substances, like all other organic matter, undergo in moist air-and, therefore, in the soil-a spontaneous decomposition, the general result of which is the production of ammonia, and of. an acid substance with which the ammonia may combine. This change is precisely analogous to that which takes place in such substances as starch and woody fibre, which contains no nitrogen. In each case, one portion of the elements unites with oxygen to produce an acid, the other with hydrogen to form a compound possessed of alkaline or indifferent properties. Thus,With oxygen,-vegetable matter produces carbonic, ulmic, and other acids. animal matter produces carbonic, nitric, ulmic, and other acids. With hydrogen,-vegetable matter produces marsh.gas or other carburetted hydrogens. " animal matter produces ammonia. If the ammonia happen to be produced in larger relative quantity than the acids with which it is to combine, or if the carbonic be the only acid with which it unites, a portion of it may escape into the air. This rarely happens, however, in the soil, the absorbent properties of the earthy matters of which it consists being in most cases sufficient to retain the ammonia, till it can be made available to the purposes of vegetable life. When caustic (hydrate of) lime is added to a soil in which ammonia exists in this state of combination with acid matter, it seizes upon the acid and sets the ammonia free. This it does with comparative slowness, however-for it does not at once come in contact with it alland by degrees, so as to store it up in the pores of the soil till the roots of plants can reach it, or till it can itself undergo a further change by which its nitrogen may be rendered more fixed (p. 411.) Carbonate of lime, on the other hand, still more slowly persuades the ammonia to leave the acid substances (ulmic, nitric? &c.,) with which it is combined, and yielding to it in return its own carbonic acid, enables it in the state of soluble carbonate of ammonia to become more immediately useful to vegetation. 2~. But in undergoing this spontaneous decay, even substances containing nitrogen reach at length a point at which decomposition appears to stop-an inert condition in which, though nitrogen be present as in peat, they cease sensibly to give it off in such a form or quantity as to AMMONIA AND NITRIC ACID FORMED. -. be capable of ministering to vegetable growth. Here caustic 1. in more quickly, and mild lime by slower degrees, to promote ther decay. It induces the carbonaceous matter to take oxyge, the air and from water and to form acids; and the nitrogen to unitethe hydrogen of the water for the production of ammonia-thus helping forward the organic matter in its natural course of decay, and enabling it to-fulfil its destined purposes.in reference to vegetable life. 3~. But the ammonia which is thus disengaged in the soil by decaying organic matter, though not immediately worked up, so to speak, by living plants, is not permitted to escape in any large quantity into the air. The soil, as I have already stated, is usually absorbent enough to retain it in its pores for an indefinite period of time. And as in nature and upon the earth's surface the elements of matter are rarely permitted to remain in a state of repose, the ammonia, though retained apparently inactive-in the soil, is yet slowly uniting with a portion of the surrounding oxygen and forming nitric acid (Lee. VIII., ~ 5, note.) When no other base is present, this nitric acid, as it is produced, unites with some of the ammonia itself which still remains, forming nitrate of ammonia -but if potash or lime be present within its reach, it unites with them in preference, and forms the nitrate of potash or of lime. But lime, if present, is not an inactive spectator, so to speak, of this slow oxiclation of ammonia. On the contrary, it promotes this final change, and by being ready to unite with the nitric acid as it forms, increases and accelerates its production, at the expense of the ammonia which it had previously been instrumental in evolving. 4~. One other important action of lime, by which the same compounds of nitrogen are produced in the soil, may in this place be most properly noticed. It is a chemical law of apparently extensive application. that when one elementary substance is undergoing a direct chemical union with a second in the presence of a third, a tendency is imparted to the third to unite also with one or with both of the other two, although in the same circumstances it would not unite with either, if present alone. Thus, when the carbonaceous matter of the soil is undergoing oxidation in the air-that is, combining with the oxygen of the atmosphere-it imparts a tendency to the nitrogen also to unite with oxygen, which when mixed with that gas alone, (the atmosphere consisting, as you will recollect, of nitrogen and oxygen-Lec. II., ~ 4,)it has no known disposition to do. The result ofthis is the production of a small, and always a variable, proportion of nitric acid during the decomposition in the soil, of organic matter even, which itself contains no nitrogen. Again, it is an equally remarkable chemical law, that elementary bodies which refuse to combine, however long we may keep them together in a state of mixture, will yet unite readily when presented to each other in what is called by chemists the nascent state-that is, at the moment when one or other of them is produced or is separated from a previous state of combination. Thus when the organic matter of the soil decomposes water in the presence of atmospheric air, its carbon unites with the greater part of the oxygen and hydrogen which are set at liberty, and at the same time with more or less of the oxygen of the atmosphere-but at the _S CHEMICAL CHANGES BENEFIT VEGETATION. it the nitrogen of the atmosphere, which is everywhere seizes a portion of the hydrogen and forms ammonia. Thus Jle, and in any one limited spot; a minute, but over the entire of the globe, a large quantity of ammonia is produced during oxidation even of the purely carbonaceous portion of the organic matter of the soil. Now in proportion as the presence of lime-promotes this decay of vegetable and other organic matter in the soil-in the same proportion does it promote the production of ammonia and nitric acid, at the expense of the free nitrogen of the atmosphere, and this may be regarded as one of the valuable and constant purposes served by the presence of calcareous matter in the soil. ~ 30. How these chemical changes directly benefit vegtation. You will scarcely, I think, inquire how all these interesting chemical changes which attend upon the presence of lime in the soil are directly useful to vegetation, and yet it may be useful shortly to answer the question. 1~. Lime combines with the acid substances already existing in the soil, and thus promotes the decomposition of vegetable matter which those acid substances arrest. The further decompositions which ensue are attended at every step by the production either of gaseous compounds-such as carbonic acid and light carburetted hydrogenwhich are more or less abundantly absorbed by the roots and leaves of plants, and thus help to feed them-or of acid and other compounds, soluble in water, which, entering by the roots, bear into the circulation of the plant not only organic food, but that supply of lime also which healthy plants require. 2~. The changes it induces upon substances in which nitrogen is present are still more obviously useful to vegetation. It eliminates am - monia from the compounds in which it exists already formed, and promotes its slow conversion into nitric acid, by which the nitrogen is rendered more fixed in the soil. It disposes the nitrogen of more or less inert organic matter to assume the form of ammonia and nitric acid, in which state experience has long shown that this element is directly favorable to the growth of plants. 30. It influences in an unknown degree, the nitrogen of the atmosphere to become fixed in larger proportion in the soil, in the form of nitric acid and ammonia; than would otherwise be the case, and this it does both by the greater amount of decay or oxidation which it brings about in a given time, and by the kind of compounds which, under its influence, the organic matter is pCosuaded to form. The amount of nitrogenoum food placed within reach of plants by this agency of lime will vary with the climate, with the nature of the soil, with its condition as to drainage, and with the more or less liberal and skilful manner in which it is farmed. ~ 31. Why lime must be kept near the surface. Nor will you fail to see the important reasons why lime ought to be kept near the surface of the soil-since 1~. The action of lime upon organic matter is almost nothing In ACTION OF LIME UPON SALINE SUBS,'1 the absence of air and moisture. If the lime sink, there(i. the constant reach of fresh air, its efficacy is in a great degreb 2~. But the agency of the light and heat of the sun, though I'h not hitherto insisted upon their action-are scarcely less necessary tothe full experience of the benefits which lime is capable of conferring. The light of the sun accelerates nearly all the chemical decoiipositions that take place in the soil-while some it appears especially to promote. The warmth of the sun's rays may penetrate to some depth, but their light can only act upon the immediate surface of the soil. Hence the skilful agriculturist will endeavor, if possible, to keep some of his lime at least upon the very surface of his arable land. Perhaps this influence of light might even be adduced as an argument in favor of the frequent application of lime in small doses, as a means of keeping a portion of it always within reach of the sun's rays; and this more especially on grass lands, to which no mechanical means can be applied for the purpose of bringing again to the surface the lime that has sunk. There are, at the same time, as you will recollect, good reason also why a portion of the lime should be diffused through the body of the soil, both for the purpose of combining with organic acids, already existing there, and with the view of acting upon certain inorganic or mineral substances, which are either decidedly injurious, or by the action of lime may be rendered more wholesome to vegetation. In order that this diffusion may be effected, and especially that lime may not be unnecessarily wasted where pains are-taken by mechanical means to keep it near the surface, an efficient system of.under-drainage should be carefully kept up. Where the rains that fall are allowed to flow off the surface of the land, they wash more lime away the more carefully it is kept among the upper soil-but where a free outlet is afforded to the waters beneath, they carry the lime with them as they sink towards the subsoil, and have been robbed again of the greater part of it before they escape into the drains. Thus on drained land the rains that fall aid lime in producing its beneficial effects, while in undrained land they in a greater or less degree counteract it. ~ 32. Action of lime upon the inorganic or mineral matter of the soil. Though the main general agency of lime is exerted, as we have seen, upon the organic matter it meets with, yet it often also produces direct chemical changes upon the mineral compounds existing in the soil, which are of great importance to vegetation. Thus 1~. Lime, either in the mild or in the caustic state, possesses the property of decomposing the sulphate of iron, whicY especially abounds in peaty soils, and in many localities so saturates the subsoil as to make it destructive to the roots of plants. Sprengel mentions a case where the first year's clover always grew well, while in the second year it always died away. This, upon examination, was found to be owing to the ferruginous nature of the subsoil, which-caused the death of the plant as soon as the roots began to penetrate it. When salts of iron exist in the soil, a dressing with lime will bring the land into a wholesome state without other aid. The lime will combine with the acid, and form gypsum, if it is the sulphate of iron that is present, while the first oxide of iron which is set free will, by .POSES SULPHATES AND WSLICATES, SETS FREE / the air, be converted into the second or red oxide, in state this metal is no longer hurtful to vegetation. W hen these salts are to be decomposed and removed from the subsoil, lime must be aided by the subsoil plough and the drain. Unless an outlet beneath be provided for the surface water, by which the rains may be enabled to wash away slowly the noxious substances from the subsoil, even the addition of a copious dose of lime will only produce a temporary improvement. 2~. Lime decomposes also the sulphates of magnesia and of alumina, both of which are occasionally found in the soil, and, being very soluble salts, are liable to be taken up by the roots in such quantity as to be hurtful to the growing plants. When soils which contain any of the three salts I have mentioned have once been limed or marled, it is in vain to add gypsum in the hope of favoring the clover crop, since the lime, in decomposing the sulphates, has already formed an abundant supply of this compound for all the purposes of vegetation. 3~. Among the earthy constituents of the soil, we have already seen that there often exist fragments of felspar and of other minerals derived from the granitic and trap rocks, which contain potash or soda in the state of silicates. These silicates we know to be slowly decomposer by the agency of the carbonic acid of the air, (Lee. X., ~ 1,) ana their alkali set free in a soluble state. This decomposition is said to be prompted by the presence of lime (p. 361.) Again, the stalks of the grasses and the straw of the corn-bearing plants contain much silica in combination with potash and soda. In farm-yard manure, therefore, much of these silicates is present, and when mixed with the soil, there appears little reason to doubt that they are of much-benefit to the growing crops. On these silicates, in the presence of carbonic acid and moisture, the lime acts as it does upon the mineral silicates. It aids in the liberation of the potash and soda, and thus promotes the performance of those important functions which these alkalies are destined to exercise in reference to vegetable growth (p. 328.) While the alkali is set free the lime itself combines with the silica, and hence one source of the silicate of lime which, as I have already mentioned to you, (p. 380,) usually exists in sensible quantity in our cultivated soils. It has been stated by Sprengel (Lehre vom Diinger, p. 310,) as one reason why the addition of lime must be repeated so frequently upon some soils in which silica abounds, that an insoluble silicate of lime is found, which is of no use to vegetation. But the silicates of lime are slowly decomposed by the agency of the carbonic acid of the air and of decaying vegetation, and to this cause in a previous lecture (Lee. XII., ~ 4,) I have ascribed much of the fertile character of the trap and syenitic soils, and of their beneficial action when laid on as a manure. 4~. Potash and soda exist to some extent in clay soils in combination with their alumina. The presence of lime has a similar influence in setting the alkalies free from this state of combination also. 5~. Alumina has the property of combining readily with many vegetable acids, and in the clay soils exercises a constant influence, similar in kind to that of lime and other alkaline substances, in persuading the ALKALINE SUBSTANCES, AND DECOMPOSES CO organic matter to those forms of decay in which acid cofi. more abundantly produced. Hence, clay soils almost alwa'ys coi. portion of alumina in combination with organic matter. This orgas,. matter is readily given up to lime, and by the more energetic action of this substance is sooner. made available to the wants of new races of plants. 6~. I shall bring under your notice only one other, but a highly important, decomposing action, which lime exercises in soils that abound in vegetable matter. In the presence of decaying organic substances the carbonate of lime is capable of slowly decomposing common salt. producing carbonate of soda and chloride of calcium. It exercises also,a similar decomposing effect, even upon the sulphate of soda, and, according to Berthollet, (Dumas Traite de Chemie, ii, p. 334.) incrustations of carbonate of soda (of Trona or Natron, which is a sesquti carbonate of soda,) are observed on the surface of the soil, wherever carbonate of lime and common salt are in contact with each other. If we consider that along all our coasts common salt may be said to abound in the soil, being yearly sprinkled over it by the salt sea winds-that generally, along the same coasts, the application of sulphates produces little sensible effect upon the crops, and that, therefore, in all probability they abound in the soil, derived, it may be, from the same sea spray-we may safely conclude, I think, that the decomposition now explained must take place extensively in all those parts of our island which are so situated, if lime in any of its forms either exists naturally or has been artificially added to the land. The same must be the case also in those districts where salt springs occur, and generally over the new red sand-stone formation, in which sea salt more especially occurs. And if we further consider the important purposes which the carbonate of soda thus produced may serve in reference to vegetation-that it may dissolve vegetable matter and carry it into the roots-that it may form soluble silicates, and thus supply the necessary siliceous matter to the stems of the grasses and other plants-and that rising, as it naturally does, to the surface of the soil, it there, in the presence of vegetable matter, provokes to the formation of nitrates, so wholesome to vegetable life-we may regard the decomposing action of lime by which this carbonate is produced as among the most valuable of its properties to the practical farmer, wherever circumstances are favorable for its exercise. ~ 33. Action of lime on animal and vegetable life. It is only necessary to allude, in conclusion, to one or two other useful purposes which lime is said to serve in reference to animal and vegetable life. Thus 1~. It is said to prove fatal, especially in the caustic state, to worms, to slugs,* and to many insects injurious to the farmer, and to destroy their eggs and larvue. In Scotland it has been found in some instances to check the ravages of the fly. On the other hand, in the state of carbonate, it is propitious to the growth of the land snail and similar creaWhen the wheat crop is attacked by slugs above ground, nothing will do so much goof as slaked lime, sown over the crop before sunrise.-Iillyard, Royal Agricultural Journa iii, p. 302, LIME KILLS INSECTS AND SEEDS..,il bear shells. In highly limed land the former may be seen e. d at the roots of the hedges, from which they make frequent inarsions/upon the young crops, and are, I believe, especially hurtful to the turnips. 2~. It is found to prevent smut in wheat. For this purpose the seed is steeped in lime, and afterwards dried with slaked lime, or lime water is poured upga the heap of corn, which is turned over, and left for 24 hours (Hillyard.) 30 It is also said to prevent the rot and foot-rot in sheep fed upon pastures on which, before liming, the stock was liable to be affected by these diseases (Prideaux.) 4~. In regard to its action upon living plants, it is certain that it ex~ tirpates certain of the coarser grasses from sour pastures and brings up a tenderer herbage; but practical men appear to differ in regard to its effects upon the roots and seeds of the more troublesome weeds. According to some, the addition of lime to a compost, or to the soil, will kill the roots of weeds and render unproductive such noxious seeds as may happen to be present. According to others (p. 405,) this is a mistake. I believe the truth to be, that lime will lead to their destruction and decay, if the circumstances are favorable or if proper pains be taken to effect it. But air and moisture are necessary to insure this, as they are to effect the rapid decay of dead organic matter. If the ingredients of the compost be duly proportioned, or if the dose of lime added to the land be sufficiently large, and if in each case the mixture be frequently turned, the final destruction of roots and seeds may in general be safely calculated upon. 34. Use of silicate of lime. There is one compound of lime which, though occurring occasionally m all soils, has not hitherto been applied to the improvement of the land even in localities where it most abounds. This compound is the silicate of lime. I have already directed your attention to the presence of this compound in the trap rocks, and to the fertile character which it imparts to the soils which are formed by the natural degradation of these rocks. In those districts where the smelting of iron is carried on, the first slag that is obtained consists in great part of silicate of lime. This slag accumulates in large quantities, and is employed in some districts for mending the roads. It is not unworthy the attention of the practical farmer-as an improver of his fields-especially where caustic lime is distant and expensive, or where boggy and peaty soils are met with in which vegetable matter abounds. On such land it may be laid in large quantity. It will decompose slowly, and while it imparts to the soil solidity and firmness, will supply both lime and silica to the growing crops, for a long period of time. I have thus drawn your attention to the most important topics connected with the use of lime, so efficacious an iiis;rument in the hands of the skilful and improving farmer for ameliorating the condition and increasing the productiveness of his land. If I have appeared to dwell long upon this subject, it is because of the value which I know to be attached by practical rmen to a correct exposition of the virtues of lime and of the theory by which its effects are to be explained. I believe that in the theoretical part I have been able to point out to you the leading chemical principles upon which its influence depends-if any thing is still dark, it is because our knowledge is not yet complete. A few years more, and we may hope to have the mists which hang over this, as over many other branches of agricultural chemistry, in a great measure cleared away. LLECTURE XVII. Of organic manures.-Vegetable and animal manures.-Green manuring; ploughing in of spurry, the white lupin, the vetch, buck-wheat, rape, rye, borage.-Natural green manuring.-Improvement of the soil by laying down to grass and by planting.-Use of seaweed.-Dry vegetable manures: dry straw, chaff, rape-dust, malt-dust, saw-dust, cotton seeds, dry leaves.-Decayed vegetable matter: use of peat, tanriers' bark, and composts of vegetable matter.-Charcoal powder, soot.-Relative value, theoretical, and practical, of different vegetable manures. By organic manures are understood all those substances either of vegetable or of animal origin, which are applied to the land for the purpose of increasing its fertility. It will be convenient to consider these two classes of organic substances separately. The parts of vegetables may be applied to the soil in three different forms-in the green, in the dry, and in the more or less naturally decayed, fermented, or artificially decomposed state. ~ 1. Of green manuring, or the application of vegetable matter in the green state. By green manuring is meant the ploughing in of green crops in their living state-or of green vegetables left or spread upon the land for the purpose. 1~. Ve have seen in the preceding lecture how important air and water are to the decomposition of organic matter. Now green vegetable substances contain within themselves much water, undergo decomposition more readily, therefore, than such as have been dried, and are more immediately serviceable when mixed with the soil. 2~. In the sap of plants also there generally exist certain compounds containing nitrogen, which not only decompose very readily themselves, but have the property of persuading. or inducing the elements of the other organic matters, with which they are in contact, to assume new forms or to enter into new chemical combinations. Hence, the sap of plants almost invariably undergoes more or less rapid decomposition even when preserved from the contact of both air and water. When this decomposition has once commenced in the sap it is gradually propagated to the woody fibre and to-the other substances of which the mass of the stems and roots of plants is composed. Hence, recent vegetable matter will undergo a comparatively rapid decomposition, even when buried to some depth beneath the soil-and the elements of which it consists will form new compounds'more or less useful to living plants, in circumstances where dry and where many forms even of partially decomposed vegetable matter would undergo no change whatever. 3~. Further-when green vegetable matter is allowed to decay in the open air, it is gradually resolved more or less completely into carbonic acid, which escapes into the air and is so far lost. But when buried beneath the surface, this formation of carbonic acid proceeds less rapidly, and other compounds-preparatory to the final resolution into carbonic acid and water-are produced in greater quantity and ,ALES READILY DECAY, AND ENRICH THE SOIL. Joi. Thus byburying vegetable substances in his land,een state, the practical man actually saves a portion of the,-c food of plants, which would otherwise so far run to waste.,-~. Firnal.y: Green vegetable substances, by exposure to the air, gradually give up a portion of the saline matter they contain to the showers of rain that fall. This more or less escapes and is lost. But if buried beneath the soil this saline matter is restored to the land, and where the green matter thus buried is in the state of a growing crop, both the organic and inorganic substances it contains are more equally diffused through the soil than they could be by any other known process. On one or other of these principles depend nearly all the special advantages which are known to follow from green manuring and from the employment of green vegetable matter in the preparation of composts. ~ 2. Important practical results obtained by green manuring. But this explanation of the principles on which the efficacy of green manuring depends, does not fully illustrate the important practical results by which, in many localities, it is uniformly followed. Let us glance at these results. 1~. The ploughing in of green vegetables on the spot where they have grown may be followed as a method of manuring and enriching all land, where other manures are less abundant. Growinlg plants bring up from beneath, as far as their roots extend, those substances which are useful to vegetation-and retain them in their leaves and stems. By ploughing in the whole plant we restore to the surface what had previously sunk to a greater or less depth, and thus make it more fertile than before the green crop was sown. 2~. This manuring is performed with the least loss by the use of vegetables in the green state. By allowing them to decay in the open air, there is, as above stated, a loss both of organic and of inorganic matter-if theybe converted into fermented (farm-yard) manure, there is also a large loss, as we shall hereafter see; and the same is the case, if they are employed in feeding stock, with a view to their conversion into manure. In no other form can the same crop convey to the soil an equal amoun71t of enriching matter as in that of green leaves and stems. Where the first object, therefore, in the farmer's practice, is so to use his crops as to enrich his land-he will soonest effect it by ploughing them in in the green state. 3~. Another important result is, that the beneficial action is almost immediate. Green vegetables decompose rapidly, and thus the first crop which follows a green manuring is benefitted and increased by it. But partly for this reason also the green manuring-of corn cropped land-if aided by no other manure, must generally be repeated every second year. 4~. It is said that grain crops which succeed a green manuring are never laid-and that the produce in grain is greater in proportion to the straw, than when manured with fermented dung. 5~. But it is deserving of separate consideration, that green manuring is especially adapted for improving and enriching soils which are poor in vegetable matter. The principles on which living plants draw a part-sometimes a large part-of their sustenance from the air, GREEN MANURE MOST USEFUL TO POOR ANn have already been discussed, and I may presume that yotl —: understand the principles and admit the fact. Living plantrts, contain in their substance not only all they have drawn ujfrom~. soil, but also a great part of. what they have drawn fromn..the air. Plough in these living plants, and you necessarily add to the soil more than was taken from it-in other words, you make it richer in organic matter. Repeat the process with a second crop and it becomes richer still-and it would be difficult to define the limit beyond which the process could no further be carried. Is there any soil then, in the ordinary climates of Europe, which is beyond the reach of this improving process? Those only are so on which plants refuse to grow at all, or on which they grow so languidly as to extract from the air no more than is restored to it again by the natural decay of the organic matter which the soils already contain. But for those plants which grow naturally upon the soil, agricultural skill may substitute others, which will increase more rapidly, and proluce a larger quantity ofgreen leaves and stems for the purpose of being buried in the soil. Hence, the selection of particular crops for the purpose of giving manuring-those being obviously the fittest which in the given soil and climate grow most rapidly, or which produce the largest quantity of vegetable matter in the shortest time and at the smallest cost. ~ 3. Of the plants which in different soils and climates are employed for green manuring. On this principle is founded the selection of different plants in different soils and climates for the purpose of green manuring. That which in Italy will yield the largest produce of leaves and sterns, at the least cost, and in the shortest time, may not do so in the North of England or of Germany-and that which will enrich a poor clay or an exhausted loam may refuse even to grow, in a healthy manner, upon a drifting sand. 1~. Spurry (Spergula Arvensis.)-It is to poor dry sandy soils that green manuring has been found most signally beneficial, and for such soils no plant has been more lauded than spurry. It may either be sown in autumn on the corn stubble or after early potatoes, and ploughed in in spring preparatory to the annual crop, or it may be used to replace the naked fallow, which is often hurtful to lands of so light a character. In the latter case, the first sowing may take place in March, the second in May, and the third in July-each crop being ploughed in to the depth of three or four inches, and the new seed then sown and harrowed. When the third crop is ploughed in, the land is ready for a crop of winter corn. Von Voght (Vortheile der griinen Bedungung) states that by such treatment the worst shifting sands may be made to yield remunerative crops of rye-that the most worthless sands are more improved by it than those of a better natural quality-that the green manuring every other year not only nourishes sufficiently the alternate crops of rye, but gradually enriches the soil-and that it increases the effect of any other manure that may subsequently be put on. He adds, also, that spurry produces often as much improvement if eaten off by cattle as if ploughed in, and that when fed upon this plant, either green or in the state )f hay, cows not only give more milk, but of a richer quality. 18* OF THE VETCH, BUCKWHEATS ETC. ve/Lupins.-In Italy, and in the south of France, the white J extehsively cultivated as a green manure. In Germany, also,.as been found to be one of those plants by which unfruitful sandy soils may'be most speedily brought into a productive state. The superiority of this plant for the purpose of enriching the soil depends upon its deep roots, which descend more than two feet beneath the surface -upon its being little injured by drought, and little liable to be attacked by insects-on its rapid growth-and upon its large produce in leaves and stems. Even in the North of Germany it is said to yield, in three and a half to four months, 10 to 12 tons of green herbage. It grows in all soils except such as are marly and calcareous, is especially partial to such as have a fecruginous subsoil, and besides enriching, also opens stiff clays by its strong stems and roots. 3~. The Vetch is inferior in many of its qualities to the white lupin-yet in Southern Germany it is often sown on the stubble, and ploughed in after it has been touched with the frost, and has begun to decay. In England also the winter tare ploughed in early in spring has been found highly advantageous (British Husbandry, I., p. 407.) It is a more precarious, however, and a more expensive crop than either of the former, and requires a better soil for its successful growth. 40. Buck- Wheat is also too uncertain a crop, and the high price of its seed renders it inferior in value to spurry on sandy soils. It is superior to this latter plant, however, on poor heaths. In Southern Germany it is sown on the stubble, and ploughed in when it is 18 or 20 inches high. 5~. Rape can only be sown upon a soil which is already in some measure rich, but it has the advantage of continuing to grow very late in the autumn, and of beginning again very early in spring. It sends down deep roots also, and loosens clayey soils by its thick stems. In the light soils of Alsace it is sown after early peas and potatoes, and manures the land for the succeeding crop of wheat or rye. 5~. Rye is pronounced by Von Voght to be the best of all green manures for sandy soils, but it is also the most expensive. It is a very sure crop and begins to grow very early in the spring, but it is not deep rooted. It has been used with advantage in Northern Italy and in Germany. 6~. Turnips have been sown in Sussex with good effect as a stubble crop for ploughing in in spring, and in Norfolk and elsewhere the portions of the turnip bulbs which are left when they are eaten off by sheep contribute, when ploughed in, to enrich the land for the barley that is to follow. Turnip tops are in many places ploughed in with much benefit to the land.* Potatoe tops also might be dug or ploughed in with equal advantage. 7'. Bora,'e has been strongly recommended in Germany, and especially by Lampadius. It is stated by this experimenter that borage draws from the air ten times as much of the elements of its organic matter as it does from the soil, and that therefore it is admirably fitted for enriching the land on which it grows. 8~. Red Clover is often ploughed in as a manure. On the Rhine it * "I find no better way of mannring for wheat after turnips, than ploughing in the tops while still green, as soon as the turnips are taken off the land."-.-Mr. Campbell, of (raigie. GREEN MANURING SUITABLE FOR AFTrER-QiO is sown for this purpose, being ploughed in before it beg,. In French Flanders two crops of clover are cut. and the third'., in, and in some parts of the United States of North Americh the'ci. which alternates with the wheat crop is ploughed in as theonly ma. nure (Barclay's "Agricultural Tour in the United States."): White Clover is not so valuable for this purpose, for neither is it so deep rooted nor does it yield so large a crop of stems and leaves. 9~. Old Grass.-Perhaps the most common form of green manuring practised in this country is that of ploughing up grass lands.of various ages. The green matter of the sods serves to manure the after-crop, and renders the soil capable of yielding a richer return at a smaller expense of manure artificially added. In regard to all these forms of green manuring.it is to be observed that they enrich the soil generally, and are therefore well fitted to prepare it for after-crops of corn; they will not fit it, however, for a special crop, such as turnips, which requires to be unnaturally forced or pushed forward at a particular period of its'growth. ~ 4. Will green manuring alone prevent land from becoming exhausted? If by green manuring is meant the growing of vegetable matter upon one field, and ploughing it in green into another, as is sometimes done, it may be safely said that, when judiciously practised, land may by this single process be secured for an indefinite period against exhaustiori. But if we plough in only what the land itself produces, and carry off occasional crops of corn, the time will ultimately come when any soil thus treated will cease to yield remunerating crops. A brief consideration of the subject will satisfy you of this. Suppose a loose sand to be improved by repeatedly sowing and ploughing in crops of spurry or white lupins, the green leaves and stems fix the floating elements of the atmosphere, and enrich the soil with organic matter, while the roots, more or less deep, bring up saline matters to the surface, and thus-supply to the plant what is no less necessary to its healthy growth. But the rains yearly wash away from the surface, and the corn crops remove, a portion of this saline matter. This portion the crops grown for the purpose of green manuring yearly renew by fresh supplies from beneath. But no subsoil contains an inexhaustible store of those saline substances which plants require. Hence, though by slkilful green manuring waste land may be brought to a remunerative state of fertility, it will finally relapse again into a state of nature, if no other methods are subsequently adopted for maintaining its productiveness. The process maybe a slow one, and practical men may be unwilling to believe in the possibility of a result which does not exhibit itself within the currency of a single lease, or during a single life-timeyet few things are more certain than that in general the soil must sooner or later receive supplies of saline manure in.one form or another, or else must. ultimately become unproductive. It may be considered as a proof of this fact that, in all densely peopled countries in which agriculture has been skilfully prosecuted, the manufacturing of such manures has become an important branch of business, giving employment to many hands, and affording an investment to much capital. The following table, in addition to other particulars, exhibits the PRACTICE OF GREEN MANURING..scilons of dry organic and saline matter, capable of be-,-o/the surface soil by a few of those plants which are em-,.a ~ S bD e t' -b. D, on bta b b b p e a u a s C d o ~. tOO -Co z Po Se Return.......... 1fold. 14 fold. 2fold. 12 fold. 12fold. l0fold. 91fold. 7fold. 5 fold. 3fold. Water................ 3 42 42 43 4-2 4-3 4-3 4-2 4-2 4-2 Gluten..............342 339 32-9 32-9 35-1 13-7 12-2 12-0 9-6 9-2 Albumen.......... 1'0 1'3 3 1 3 1-4 1-1 0-9 1-0 0-8 0-7 Starch................413 41-4 428 42-4 39-9 61-6 63-2 62-3 65-9 66-6 Sugar............... 1-9 1 6 1 5 1-5 1'4 1 6 1-9 1-9 1-9 1-9 Gum................. 1'8 1-6 1-5 1-5 1-6 1 -6 1'9 1'9 1-6 1-8 Fatty Oil. 0' 9'1.. 1 0 0'9 1 0 1-0 0'9 10 1-0 1-0 SolublePhosphates,&c. 0 5 0-6 0'7 0-7 0-9 0-6 0-5 0'5 0-5 0-3 Husk and bran.....13-9 14-0 13 8 14-2 142 14-0 14-0 14-9 14-0 14-0 99'8 99-7 99-7 99-7 99-7 99-6 99-8 99-7 99-8 99-7 The large per-centage of gluten obtained by the use of the first five In these flours the aluten was not determined by washing out the starch, but by a more refined method of ultimate analysis, as it is called, by which the per-centage of nitrogen is determined, and the proportion of gluten, &c., calculated from this. When the per-centago. of nitrogen is small, as in wheaten flour, this method is open to many sources of error. See a paper by Mr. John Hannam, Quarterly Journal of Agriculture, lviii., p. 173. 504 EFFECTS OF GERMINATION AND BAKING manures is very striking, if the determinations are really to be depended upon. They are certainly interesting in a theoretical point of view, and are deserving.of careful repetition. In reference to their, bearing upon practical farming, however, it must not be forgotten, that the results of small experiments are never fully borne out when they are repeated on the large scale-that the relative value of different animal manures is materially affected by the kind of food on which the animal has livedthat independent of manires, there are circumstances not yet made out which materially affect the produce of single patches*-and that it will rarely be in the power of thepractical farmer to apply at pleasure to his fields the relative proportions of the several manures used by Hermbstadt. Thus, if instead of 20 tons of farm-yard manure he wished to try blood or urine alone, he miust apply 24 tons of the former, and 70 tons of the latter-quantities which it might be both difficult to procure and inconvenient to apply. The most practically useful results yet published in regard to the action of the different manures upon the weight of the crop, the proportion of flour yielded by it, and of gluten in the flour, are those of Mr. Burnet, to which I have already had occasion to draw your attention.t These results were as follow:Produce Fine Flour Gluten KIND OF MANURE. per acre. from the grain, in the flour. Nothing... 31 bshls. 76- lbs. 9-4 per cent. Sulphated urine and wood ashes. 40 " 66 < " 10-5 " Do. and sulphate of soda. 49 " 631 " 9-7 " Do. and common salt.. 49 " 652 ( 9-6 " Do. and nitrate of soda.. 48 "C 542 " 100 " We perceive here a slight increase in the per-centage of gluten when the manures were applied, but nothing which at all resembles the great differences given by Hermbsatdt, or which renders it probable that by skilful management, as some have supposed, we may hereafter be able to raise in our fields whole crops of corn which shall yield a flour containing 20 or 30 per cent. of gluten. ~ 11. Of the effects of germination, and of baking, upon theflour of wheat. The effects of germination and of baking upon the flour of wheat are very analogous to each other. [n both cases, a portion of the starch is changed into gum and sugar. 1~. Germination.-I have already described to you (p. 118), the very beautiful change which takes place during the sprouting of the seeds of plants-how a portion of their gluten is changed into diastase, and how, by the agency of this diastase, the starch of the seed is changed into gum and sugar. In an experiment made by De Saussure, 100 parts of the farina of wheat had by germination lost 6 parts of starch, and in their stead had acquired 31 of gum and 2k of sugar. The effect of this change-which proceeds as the plant continues to grow-is to make the starch soluble, and thus capable of entering into the circulation of the young plant. 2~. Baking.-It is the larger proportion of gluten usually contained in the flour of wheat that renders it so much better fitted for the bakinpg of See Appendix, pp. 59 and 79. T See p. 362 and Anppndix pp. 49 and 71. UPON THE FLOUR OF WHEAT* 505 bread than the flour of any other grain. If the gluten be washed out of the' flour, and put alone into the oven, it will swell up, become full of pores, and assume a large size. The comparative baking qualities of different samples of flour may be judged of by the height to which, in similar vessels, the gluten of equal weights of flour is thus observed to rise. We have already seen that by heating in an oven, dry starch is gradually changed into gum (British gum, p. 113), and into a species of sugar-becoming completely soluble in water. Such a change is produced upon a portion of the starch of wheaten flour when it is baked in the oven. Thus in 100 parts of the flour, and of the bread of the same wheat, Vogel found respectivelyStarch. Sugar. Gum. Flour... 68 5 Bread... 53 31 18 So that a very considerable portion of gum had been produced at the expense of the starch. The yeast which is added to the dough in baking, acts in the same way as when it is added to the sweet wort of the brewer. It induces a fermentation by which the sugar of the flour is changed into carbonic acid and alcohol. The carbonic acid is liberated in the form of minute bubbles of gas throughout the whole substance of the dough and causes it to rise, the alcohol is distilled off in the oven. If too much water have been added to the dough-or if it have not been sufficiently kneaded-or if the flour be too finely ground-or if the paste be not sufficiently tenacious in its nature, these minute bubbles will run into each other, will form large air holes in the heart of the bread, and will give it thatopen irregularly porous appearance so much disliked by the skilful baker. Good bread should be full of small pores and uniformly light. Such bread is produced by a strong flour; that is, one which will rise well, will retain its bulk, and will bear the largest quantity of water. The quantity of water which wheaten flour retains when baked into bread depends in some degree upon the quality of the flour. In the Acts of Parliament relating to the assize of bread, it is assumed that a sack of flour (280 lbs.) will produce 80 quartern loaves, or 320 lbs. of bread. According to this calculation the flour should take up and retain when baked one-seventh of its weight of water. But the quantity of water retained by the flour now in use is very much greater, and the profit to the baker, therefore, very much more than this calculation supposes. This is shown by the quantity of water which is lost by wheaten bread, whether of first or second quality, when it is dried by prolonging heating, at' a temperature not exceeding 220~ F. The home-made bread (white and brown) baked in my own house, and in two other private houses in Durham, lost of water by drying in this wayHow long baked. Water per vent. 1~. White... 24 hours. 43-3 Brown*.. 24 do. 44-0 2~. Brown... 42 do. 44-1 White.. 36 do. 42-9 3~. White.. 9 do. 44-1 The brown bread is made from the whole grain of the wheat as it comes from the millstones-nothing being separated by sifting. 506 WATER TAKEN UP BY FLOUR IN BAKING. So that wheaten bread one day old contains about 44, and two days old, about 43 per cent. of water. Something, however, will depend upon the size of the loaves. This proportion is almost exactly the same as that contained in the white bread of Paris. According to Dumas, the water in the common white bread of Paris amounts toHours baked. Water per cent. 2....... 45.7 4....... 45-3 10....... 43-0 24... 43-5 We may assume, therefore, 44 per cent. as very nearly the average quantity of water contained in good white bread both in England and in France. Bread baked for public establishments contains more water,not being generally so well fired, or being baked in the form of many loaves stuck together, instead of in separate tins, as is done with homemade bread. Such is the case with the soldiers' bread of our own country, and the barrack bread of Paris (pain de munition) which contains about 51 per cent. of water. We have already seen (p. 499) that English wheaten flour contains, on an average, about 16 per cent. of water. If, therefore, the bread baked from it, as it comes from the mill, contain 44 per cent., every hundred pounds consist ofDry flour. 56 6 Water in the flour (naturally). 10 2 Water added by the baker.. 33j 100 Or, the flour, in baking, takes up half its weight of water. A hundred pounds of flour, therefore, as it comes from the mill, will give very nearly 150 pounds of bread. ThusFlour contains Bread contains Dry flour.... 84 84 Natural water... 16 16 -- Water added. 50 100 - Weight of bread 150 A sack of flour, therefore, or 280 lbs., ought to give about 420 lbs. of well baked bread. Something must be deducted from this for the-loss by fermentation, and for the dryness of the crusts. Allowing 5 per cent. for these, a sack of flour should give 400 lbs. of bread of the best quality,* or 100 quartern loaves. The cost of fine white bread, therefore, compared with that of corn and flour, ought to be very nearly as follows:Cost of Flour, Cost of Bread, Market price of per sack- per stone. per quartern loaf. Grain per qr.t 35s. Is. 9d. 41d. 47s. 40s. 2s. Od. 44d. 52s. Unmixed with potatoes, which are employed by many bakers in considerable quantity Mixed witn the yeast they are said to make the bread lighter. t This column has been calculated for me, from the price of the flour, by my friend Mr. John Robson, miller, in Durham. The practical rule is, that 6 bushels of corn should give one sack of flour, and that the miller should have the offal for his trouble. RELATIVE COST OF CORN, FLOUR, AND BREAD. 507 Cost of Flour, Cost of Bread, Market price of per sack. per stone. per quartern loaf. Grain per qr. 45s. 2s. 3d. 52d. 60s. 50s. 2s. 6d. 6d. 67s. 55s. 2s. 9d. 63d. 72s. 60s. 3s. Od. 7~d. 80s. The economy of baking at home, therefore, at the usual prices of bread, seems to be very considerable. ~ 12. Of the supposed relation between the per-centage of gluten in flour, and the weight of bread obtainedfrom it. It has been assumed by recent chemical writers that the quantity of water absorbed by flour, and consequently the weight of bread obtained from it, depends, in whole or in great part, upon the proportion of gluten which the flour contains. The following facts, however, do not accord with this supposition. 1~. Household bread, made respectively from the flour of a French wheat and of a wheat from Taganrog, retained nearly the same percentage of water, though the one sample contained upwards of twice as much gluten as the other. ThusGluten per cent. Water per cent. in the Flour. in the Bread. Flour of Brie... 107 47.4 Flour of Taganrog.. 227 47-0 This one fact might be supposed to settle the question, but I shall mention others. 2~. The flour from Odessa wheat contains about {th more gluten than French flour in general, and yet it absorbs very little more water (Dumas). This Dumas accounts for by the fact that the starch of the Odessa wheat forms hard transparent horny particles, which take less water to moisten them than the impalpable powder yielded by the softer French wheats-so that the gluten does not appear to produce its full effect. I do not know how far this explanation is consistent with the fact that the hard flinty wheats give the best biscuit flour-what the baker calls the strongest, which rises best, and absorbs the most water.* 3~. Rice is said to contain very little gluten-not estimated by any to amount to more than 6 or 7 per cent.-and yet it is stated as the result of numerous trials, that an admixture of a seventh part of rice flour causes wheaten flour to absorb more water.t 4~. If the hard wheats be ground too fine they lose a part of their apparent strength, the flour becomes dead, as it is sometimes called, and refuses to rise as it would do if sentto the baker in a more gritty and less impalpable state. 5~. Lastly, the admixture of very minute quantities of foreign matter, by way of adulteration, is said to have a remarkable influence upon the quantity of water which the flour will absorb. In some parts of Belgium it appears to have been the practice to adulterate the bread with a small quantity of sulphate of copper.: This salt is dissolved in water, and * That such is the case also in foreign countries, see a letter from the British Consul at Lisbon, in Davy's Agricultural Chemistry, Lecture III. t Dumas' Traite de Chimie, vi., p. 396. $ Blue vitriol-a violent poison. 508 COMPOSITION OF BARLEY. the solution added to the water with which the dough is to be made, in the proportion of about one grain to two pounds of flour. It gives the bread a fairer colour, and thus permits the use of inferior flour, and it causes the bread to retain about six per cent. more water without appearing moister. Even in the small proportion of one grain of the sulphate to 6, or 7 lbs. of flour, it produces a very sensible effect (Kuhlman). Other adulterations also exercise a similar influence. Alum improves the colour of the bread, raises it well, and causes it to keep water, but it requires to'be added in larger quantity than the more poisonous sulphate of copper. Common salt likewise makes the paste stronger, and causes it to retain more water, so that the addition of salt is a real gain to the baker. From all these facts, therefore, we may infer that, independent of the relative proportions of gluten, very slight differences in compositionsuch as have not yet been sought for or appreciated-may materially affect the relative weights of bread obtained by the baker from different samples of wheaten flour. ~ 13. Of the cormposztion of barley, and the influence of different manures upon the relative proportions of its several constituents. The grain of barley consists of nearly the same substances as that of wheat, but in proportions somewhat different. These proportions, however, are affected both by the kind of manure with which the land is dressed, and by the nature of the soil on which the seed is sown. 1~. Manure.-The effect of manure appears from the following table, containing the results of Hermbstadt, obtained in the same way as those with wheat already described (p. 503):KIND OF 5S | MAoNURE g | Q. e - OxBlood....... 10-4 13-6 5-7 0-4 59-9 4-6 4-4 04 0-4 16 Night-soil...... 10-2 13-6 5-8 0-5 59-6 4-5 4-3 0-5 0-6 13 Sheep's dnng... 10-3 13-5 5-7 0-4 59-9 4-6 4-4 0-4 0-3 16 Goat'sdung... 10-4 13-5 5-7 0-4 59:9 4-6 4-5 0-4 0-3 15 Human urine... 10-3 13-6 5-9 0-5 59-6 4-4 4-4 0-4 0-7 13l Horse dung.... 10-4 13-5 5-7 0'4 59-7 4-6 4-5 0-4 0-4 13 Pigeon's dung. 10-4 13-5 5-6 04 59-8 4'6 4-5 0-4 0-4 10 Cow'sdung..... 10-8 13-6 3-3 0-2 61-9 4'8 4-6 0-3 0-3 11 Veget manure.. 10-8 13-6 2'9 0-2 62-2 4'9 4'8 0-2 0-1 7 No manure... 108 13-6 2-9 0-1 62-5 5-0 4`7 0-1 0-1 4 In so far as reliance is to be placed upon the numbers in the above table, as indicative of the general effect of the several manures mentioned, it would appear that the relative proportions of gluten, albumen, and starch do not vary very much until we come to cow-dung, when the former two substances sensibly diminish. Further experiments, however, are required upon this subject (see page 514). 2~. Soil.-The effect of soil upon the barley crop is known to all practical farmers-so that the terms barley-land and wheat-land are the usual designations for light and heavy soils adapted especially to the growth of these several crops. On clay lands the produce of barley is greater, but it is of a coarser quality, and does not malt so well-on loams it is plump and full of meal-and on light chalk soils the crop is light, but the grain is thin in the skin, of a rich colour, and well adapted EFFECT OF MALTING- UPON BARLEY. 509 for malting.* The barley of the light lands in Norfolk is celebrated in the North of England for its malting properties-and the brewers refuse the barley of the county of Durham, even at a lower price, when Norfolk barley is in the market. When-unfit for malting, barley affords a fattening food for pigs and for some other kinds of stock. ~ 14. Effect of malting upon barley. During the germination good barley increases in bulk one-half. In order that it may do so, it must be uniformly ripe-a quality of great value to the maltster. This maximum bulk is generally acquired in 24 hours after it has been moistened and laid in heaps. In drying, however, the barley again diminishes in bulk, so that the dried malt rarely exceeds by more than 1th or Ilth the bulk of the grain as it came from the -market. The well-dried malt, however, is lighter by'th tnan the barley from which it is made-100 lbs. of barley yielding about 80 lbs. of malt. This is not all loss of substance, since by a similar drying the barley itself before malting would lose about 12 per cent of water. The loss of substance, therefore, is only about 8 per cent. This diminution of solid matter arises in part from the loss of the little roots which form the malt-dust (cummins), of' which I have already spoken (p. 436) as being a valuable manure, and of which 4 or 5 bushels are obtained from 100 bushels of barley. The colour of the malt varies with the temperature at which it is dried. If the heat does not exceed 100~ F. a very pale malt is obtained, which gives a very white beer. A heat not rising above 180~ gives an amber coloured malt —while for brown malt the temperature may rise as high as 260~ F. By mixing these varieties beer of any colour may be made. But in the porter breweries it is usual to prepare a quantity of malt of a brownish black colour (burned malt), by adding a portion of which any required shade of colour is imparted to the liquor. During germination a variable quantity of the gluten is converted into diastase (p. 119), and about two-fifths (40 per cent.) of its starch into sugar or gum (dextrine). The quantity of diastase produced depends upon the extent to which the germination has proceeded. It is greatest at the moment when the gemmule is about to burst from the seed, and to form the young shoot. I have already explained the beautiful purpose served by this diastase in converting the insoluble starch of the grain into soluble sugar and gum. When the beer is to be made wholly from malt, it is unnecessary to continue the germination till the largest quantity of diastase is produced. It is sufficient if the gemmule, on holding up a grain of the barley, be seen within the skin to have attained one-half or two-thirds of the length of the seed. The diastase then produced is more than enough to convert the whole of the starch of the grain into sugar (p. 120). But if raw grain, as in some of our distilleries, is to be added to the malt, then the malting should be prolonged till the bud is about to burst through the husk, so that the largest possible supply of diastase may be contained in it. In this way also malt -is prepared when it is to be employed " The barlev on the compact clays (in Hants) is of a coarser quality, but produce greateron the light chalk soils it is well calculated for malting-the skin is thin, and colour rich but light-in fullness of meal and plumpness of appearance it never equals the barleys grown in Staffordshire, and upon loamy lands." —Mr. Gawler in British Husbandry, iii. p. 12, 22 510 COMPOSITION OF OATS AND RYE. in the manufacture of syrup (glucose) from potatoe flour-a branch of industry which has become of some.mportance in certain parts of France. ~15. Composition ofoats, and effect ofmanures in modifying that composition. The relative proportions of husk and meal in the several varieties of the oat differ in a greater degree, probably, than in any other grain. Thus, the potatoe-oat is known to be richer in meal, the rartary-oat in husk. The round grain of the former is chiefly grown in Scotland, for grinding into meal, the latter in England, for feeding horses. But even the round potatoe-oat varies much in the produce of meal which it gives. Many samples yield only half their weight of oatmeal, others 9 stones out of 16, while some give as much as 12 stones from the same quantity, or three-fourths of their weight. In one variety of oat Vogel found 66 per cent. of meal and 34 of husk, which is equal to 10^ stones of meal from 16 of grain. He also extracted from the meal 2 per cent. of oil, and 59 of starch, and observed it to lose by drying upwards of 20 per cent. of water. Soil, season, climate, variety of seed sown, and the kind and quantity of manure applied-all affect the amount of produce and the chemical composition of the oats that are reaped. According to Hermbstadt, the effect of different manures in modifying the composition of the produce of the same seed are represented by the numbers in the following table: KIND 0OF 1 5 - MANURE. ^ b iS? CdOxBlood....... 12 0 19-3 5-0 0-4 53-1 3-8 5-5 0-3 0-4 121 Night-soil...... 12-1 19-2 4 6 0-4 53-3 3-8 5-4 0-3 0'5 141 Sheep's dung.,, 12-6 13-3 4-0 0-5 54 0 5-2 5-5 0 3 0-4 14 Goat'sdung.... 12-9 17-0 4-3 0-4 53-2 5-4 5-7 0-3 0-4 15 Human urine... 13-0 17-0 4-4 0-5 53-1 5'0 5-7 0-4 0-6 13 Horse dun..... 13-1 16-0 4-0 0-5 54 5 5-2 5-6 0-3 0-5 14 Pigenn's dung.. 123 18-3 3-2 0-3 53-2 5-0 6-8 0-3 0-3 12 Cowdung...... 11-6 15-0 3-1 0-3 55-0 6 8 7 3 0-3 0.3 16 Veget. manure.. 10 8 13-0 2-0 0-2 59-9 6-4 7-0 0-2 0-2 13 Unmanured..... 10 8 12-0 1-9 0-2 60-0 6-4 7-0 0-3 0-1 5 The differences in this table are very striking [see p. 515]. ~ 16. Composition ofrye, and effect ofdifferent manures upon its composition. The grain of rye approaches nearest to that of wheat in the quantity of gluten it contains, and in the consequent fitness of its flour for baking into bread. It sometimes also contains much sugar-recent rye-bread having almost invariably a sweet taste-but the proportion of sugar appears to be by no means constant. Thus Einhof and Greif exhibit the composition of a sample of r)e-flour, examined by each of them, respectively as follows:Einhof, per cent. Grief, per cent. Husk... 6-4 Gluten (not dried). 9-5 12-8 Albumen... 33 3.0 Starch... 611 58'8 Sugar... 33 10.4 Gum...111 7-2 Loss... 53 7-8 100 100 COMPOSITION OF RICE. 511 Perhaps no great degree of faith is to be placed in these analyses. If they are to be depended upon, they show that very remarkable differences indeed may exist in the relative proportions of some of the constituents of rye flour. The flour of rye is said to be more absorbent of moisture from the air than that of any other grain.* Rye delights in a sandy soil, and is cultivated in general in such as are poor in vegetable matter, and to which manure is not very abundantly added. The experiments of Hermbstadt, whose results are exhibited in the following table, do not show any very striking difference to have been produced upon the composition of the grain by the use of the different animal manures: KIND OF "A. o2 e 2 0 MANURE. F = o 5 ( OxBlood....... 101 04 12-0 3-6 52-2 3-6 6-2 1-0 0-8 14 Night-soil...... 100 107 11-9 3-2 52-4 3-5 6-3 0 9 0 9 131 Sheep's dung... 100 10-8 11-9 3-4 52-3 3 6 6-1 1-1 0'6 13 Goat'sdung..... 10-0 10-8 119 3 4 52-2 3-5 6-0 1-0 0-9 124 Human urine... 10-1 10-8 12-0 3-5 50 2 3-3 4-6 1-1 4-2 13 Horse dung.... 10-0 10-7 11-9 2-8 51-2 4-0 4-6 1-0 3 6 11 Pigeon's dung.. 10-1 10-5 11-6 37 52-2 3 7 4-7 0-9 2-3 9 Cowdung..... 10-0 10-4 10-8 2-0 54-3 3-9 5-7 0-9 1-8 9 Veget. manure.. 10-0 10-7 8-8 2-6 55-1 4'8 5-2 0'9 1-7 6 Unmanured..... 10 0 10-1 8-6 2 6 56-3 4-7 5-4 0-9 1-3 4 The above table exhibits a larger increase in the return or produce from some of the animal manures than from others, but we do not see any of those remarkable differences in the composition of the flour, which are observable in the results obtained by the application of different manures to the wheat crop. The substance extracted from rye, and called gluten by Hermbstadt, is different from the gluten of wheat, and is more like the glutine extracted from the latter grain. When dough made of rye flour is washed in water, it nearly all diffuses itself through the liquid, leaving little more than the husk or bran behind. The starch deposits itself from the milky liquid, or may be separated by the filter. When the liquid is evaporated to dryness, and the dry mass boiled in alcohol, the so-called gluten is dissolved out, and may be separated front the alcohol by distillation. It must then be washed with water to free it from sugar. Like the gluten of wheat, it is now insoluble in water, and is less cohesive than gluten. Both of these forms of gluten are supposed to have the same composition as vegetable fibrin and albumen, and as the curd of milk. ~ 17. Composition of rice, maize (Indian corn), and buck-wheat. 1~. Rice is usually supposed to differ from other kinds of grain by the larger proportion of starch which it contains. The large quantities of rice consumed by the native inhabitants of India, and of other warm countries, has often appeared surprizing to foreigners. Chemists have explained this alleged fact by supposing the small per-centage of gluten contained in rice, as shown by the following analyses, to be insufficient for the sustenance of the body-when no other food is used-unless this grain be eaten in exceedingly large quanA sample of rye meal, dried in my laboratory, lost only 142 per cent. of water, and of rye bread leavened 44, and yeasted 46 per cent. This rye meal may possibly have been mixed. 512 OF MAIZE OR INDIAN CORN. tities. It is probable, however, that the nitrogenous constituents of rice -are stated too low in the analyses of Braconrot, and that it contains albumen or casein, or some analogous substance, which has been passed over by this chemist. A series of carefully repeated analyses of different varieties of rice, if it did not modify, would at least fix our present opinions in regard to its theoretical value as food for man.* Two samples of rice examined by Braconnot, were found by him to be composed ofCarolina. Piedmont. Water... 5'0 7-0 Husk.. 48 4-8 Gluten.... 3-6 3-6 Starch.. 85-07 83-8 Sugar.... 03 0'05 Gum.. 07 01 Oil..... 013 0-25 Phosphates.. 04 04 100 100 20. Maize or Indian corn is celebrated for the large return of food which it yields from a given extent of land, and for its remarkably fattening qualities when given to poultry, pigs, and cattle. Buckwheat is also a very nourishing grain. They consist respectively ofDry maize (Payen). Buckwheat (Zenneck). Husk.... 50 26-9 Gluten, &c.... 1-2 10-7 Starch... 71 52-3 Sugar- and gum.. 0-5 8'3 Fatty matter... 8. 9 0-4 Colouring matter.. 505 Salts..... 8? 24-53f 98-6 The above analysis of maize must be incorrect, as it supposes the fatty matter to amount to nearly 36' per cent. of the weight of the corn. Dumas has lately stated it at 8-9 per cent.-instead of 8-9 in 24-55 parts, as found by Payen —and Liebig denies that Indian corn contains more than 5 per cent. of fatty matter. New analyses, therefore, are required of this grain also. Indeed it may be said in general of all the substances used, especially in feeding animals, that we have not yet the requisite knowledge to enable us to reason accurately in regard to the special operation of each in sustaining the body or in promoting the growth of fat.$ Five varieties of rice, as it is sold in the shops, examined in my laboratory, lost of water and gave of-ash per cent. respectivelyWater. Ash. Water. Ash. Madras rice.. 13 5 0-58 Carolina rice... 130 033 Bengal rice.... 1 0-45 Do. flour.. 14-6 0-35 Patna rice.... 13-1 0-36 The water in these samples is very much greater than in those examined by Braconnot. By exposure to the air the rice in a few days re-absorbed nearly all it had lost by drying. The ash of rice contains more alkaline matter than that of wheat, and is very difficult to barn white. t Dumas, Traitl de Chimie, vi., p. 394. t A sample of Indian corn examined in my laboratory, lost of water 13-6 per cent., and left of white earthy ash 1'3 per cent. GENERAL EFFECT OF MANURES. 513 ~ 18. On the alleged general:effect of different manures in modifying the amount of gluten and albumen in wheat, barley, oats, and rye. Among the general deductions in regard to the special influence of manures upon the quality of the grain we reap, that which has been received with the greatest confidence is this-that the richer in nitrogen the manure we apply, the richer in gluten the grain we reap. The only experiments, having any pretensions to accuracy, by which this opinion has hitherto been supported, are those of Hermbstadt. The results of these experiments are contained in the four tables to which I have directed your attention under the heads of wheat, barley, oats, and rye. As the opinion founded upon them is one which, if correct, is of great practical value,-it will be proper to examine the experiments themselves a little more narrowly. Are they really deserving of implicit credit.? Do they justify the conclusion that has been drawn from them? Turn first to the experiments upon wheat, of which the results are embodied in the following table, repeated from page 503:s0 rd a) C: b bf t 61Z fca o 5/ a po a a Return........... 14fold. 14 fold. 1 fold. 12 fold 12 fold. 1 0 fold. 9 fold. 7fold. 5 fold. 3 fold. Water............. 4-3 4- 42 43 2 4' 3 42 4 3 42 - 4-2 42 2 Gluten............... 34-2 33-9 32-9 32-9 35-1 13-7 12-2 12-0 9-6 9-2 Albumen.............. 10 13 1-3 1-3 1-4 1-1 0-9 1-0 0-8 0-7 Starch.............. 41-3 41-4 42-8 42-4 39 9 61-6 63-2 62-3 65 9 66-6 Sugar................ 1'9 1-6 1-5 1'5 1'4 1-6 1-9 1'9 1'9 1-9 Gum......... 18 1-6 1 5 1-5 1-6 1 6 1-9 1'9 ] 6 1-8 Fatty Oil............ 09 11 110 0,9 1'0 1-0 0'9 1 0 1-0 - la SolublePhosphates,&c. 0-5 0-6 0-7 0'7 0'9 0-6 0'5 05 0'5 0 3 Husk and bran........13-9 14-0 138 14-2 14-2 14-0 14-0 14 9 14-0 14-0 99-8 99'7 99-7 99'7 99-7 99-6 99-8 99-7 99' 8 99-7 1~. Water present. —The water in each of these 10 specimens of grain was nearly the same, about 4 per cent. I have already stated the quantity of water in English flour to amount to about 16 per cent. on an average. Many samples of wheat also have been dried in my laboratory. From the results I extract the following, showing the water lost by corn grown in four different parts of the world:English, Lammas red...... 15'1 per cent. Seminoff wheat..... 13-2 " St. Petersburg..... * 16-1 " Burletta wheat..... 13'1 " This weight of water is lost when the grain, as it is sold in the market, is crushed and then heated to a temperature not exceeding 220~ as long as it loses weight. The above quantities of water are very much greater than those found in the wheats of Hermbstadt. I cannot offer these results, however, as a proof of inaccuracy on the part of this experimenter, as I have not had access to his original memoir. It is only fair towards him, therefore, to conclude that, before they were subjected to analysis, his wheats had been artificially dried in a very considerable degree. 2~. Oil in the different samples.-Again, it appears remarkable that the quantity of oil in all the samples of wheat in the above table is nearly identical, and is also very small. I have examined the fine flour yielded by several samples of the same wheat, grown by Mr. Burnet, of Gad 514 OIL IN DIFFERENT SAMPLES OF WHEAT. girth, upon the same field, but dressed with different manures, [Appendix, pp. 55 and 71,] and the proportions of oil which they yielded in the state in which they came from the mill, were as follows:Per cent. 1~. From the undressed soil..... 1 4. 2~. Dressed with guano and wood-ash...... 19 3~. With artificial guano and wood-ash.. 2'2 4~. Sulphated urine and wood-ash...22 5~. Do. do. and sulphate of soda.... 20 6~. Do. do. and common salt..... 2-7 7~. Do. do. and nitrate of soda... 23 The two facts-that the quantity of oil in nearly all the above samples is so much greater than was found by Hermbstadt in any of his specimens, and that the proportion varied with the kind of manure with which the wheat had been dressed-these two facts, I think, show that the analyses of Hermbstadt have not been made with such a degree of accuracy as to justify us in relying with confidence upon the general deductions to which they seem to lead. 3~. Relative effects of these manures upon diferent crops.-If we compare together the relative proportions of gluten and albumen contained in the several samples of wheat, barley, oats, and rye, examined by Hermbstadt, and exhibited in his tables, we shall find that the effects of his manures were by no means unifom upon the several crops. Thus, when manured withThe gluten and albumen per cent. taken together were in the Kind of Manure. Wheat. Barley. Oats. Rye. Ox blood.. 35-2 6-1 5-4 15-6 Night soil... 352 6'3 5-0 15-1 Sheep's dung... 342 6-1 45 15-3 Human urine... 36 5 6-4 4'9 15-5 Horse dung... 148 61 4 5 14-7 Pigeon's dung... 131 60- 3-5 15-3 Cow dung... 13-0 3-5 3-4 12-8 Nothing.. 99 30 2-1 11-2 Upon the numbers in this table I offer you the following remarks:a. Upon the wheat, the effect of the horse and pigeon's dung, in increasing the amount of gluten and albumen, was little more than onefifth of that produced by the sheep's dung. Thus the wheat contained of gluten and albumen,Per cent. Increase of gluten. Undressed.... 99 With sheep's dung... 34-1 24'2 per cent. With horse dung.... 14'7 4'8 With pigeon's dung... 13.1 3-2 But we hae seen (p. 470) that in so far as the nitrogen is concerned, dry horse and sheep's dung ought to produce equal effects, while pigeon's dung should have three times the effect of either.* Whatever be the cause of the increased proportion of gluten in the experimental wheats of Hermbstadt, it cannot, therefore, have been owing solely to the proportion of nitrogen in the manures he applied. 22 of dry pigeon's dung are equal to 65 of sheep's, or 64 of horse's dung. DIFFERENT PROPORTIONS OF GLUTEN. 515 b. Again, upon the barley, oats, and rye, the sheep's cung produced little more effect than the horse's dung. It might be said that this was because these two manures contain nearly the same proportions of nitrogen. But if so, why did they not produce like effects also upon the wheat?-and why did pigeon's dung impart less gluten than either, to all these varieties of grain? c. The unsatisfactory nature of these experiments is still more clearly seen when we compare the relative proportions of nitrogen, contained in the several manures applied, with the proportions of the same element contained in the several crops to which these manures had been added. This comparison is made in the following table-the quantity of nitrogen in sheep's dung and in the crops manured with it being called 100:Proportions of Proportions of nitrogen added to the Manure applied. nitrogen, in crop by eac,h manure.' the manure. r —-------- Wheat. Barley. Oats. Rye. Sheep's dung.. 100 100 100 100 100 Horse dung... 102 16 75 100 66 Pigeon's dung.. 300 9 48 43 55 Cow dung... 97 6 1 66 22 The relation which exists among the numbers in the first of the above columns, is totally unlike that which exists among those in any of the others. In none of the crops does the quantity of nitrogen in the manure bear a perceptible relation to that contained in the grain that was reaped. The theory, therefore, that the quantity of gluten in the crop is always determined by that in the manure, and that the amount of gluten in the grain we reap may at pleasure be increased by the use of maanres which are rich in nitrogen-this theory derives in reality no solid support from the experiments of Hermbstadt. The theory may indeed be correct, but it is not sustained by any rigorous experiments hitherto made-and the prudent man will place little reliance upon it, until its correctness shall have been proved by future and more rigorously conducted investigations. ~ 19. Composition of peas, beans, and vetches. The seeds of leguminous plants in general contaiti a large quantity of a substance-very analogous to the gluten of wheat-to which the name of legu. in has been given. To extract this legumin, bruised beans, peas, or vetches, are steeped in tepid, water for some hours, then rubbed to a pulp in a mortar with their own weight of warm water, and, after an hour, strained through linen. The strained liquid deposits, at first, a quantity of starch,,but is obtained nearly clear by filtration. To the filtered solution diluted acetic acid (vinegar) or sulphuric acid is added in small quantity, when the legumin coagulates and falls in the form of nearly insoluble flocks, These columns are calculated by mnltiplying together the increase of crop and the increase in the per centage of gluten and albumen. Thus in the case of wheatIncrease of crop. Increase of gluten. Pioduet. Proportions. Sheep's dung.. 9 fold X 24-3 per cent. = 218-7 = 100 Horse dung.. 7 fold X 4-9 per cent. = 343 = 16 Pigeon's dung... 6 fold X 3 2 per cent. = 19-2 = 9 Cow dung.. 4 fold X 3-1 per cent. 12-4 6 516 COMPOSITION OF PEAS, BEANS AND LENTILS. which are easily collected on a filter. The addition of an excess of acid will re-dissolve the coagulated legumin, which is again thrown down by a few drops of a solution of carbonate of soda or of ammonia; a slight excess of either of the latter, however, will cause the precipitate a second time to disappear. The legumin of the pea and bean, therefore, differs from the gluten of wheat, in being soluble in water (Dumas), and in very dilute acid or alcaline solutions. The solution of legumin in water is coagulated when heated nearly to boiling, in which respect it resembles albumen (white of egg), and it is also coagulated by rennet, in which, and in its relations to acids and alcalies, it resembles casein, the curd of milk. Legumin. has, indeed, by Liebig, been called vegetable casein, from an impression that it is identical in composition and properties with the pure curd of milk. The semi-transparent solution of legumin in water, obtained directly from beans-or peas, gradually becomes opaque, and slowly deposits the legumin in an insoluble state. This is owing to the production of a small quantity of acid by the decomposition of the sugar or other substances present in the liquid. This acid slowly coagulates the legumin in the same way as when dilute acids are artificially added to the solution. It is proper to mention that other chemists consider legumin, like casein, [see the following lecture,] to be nearly insoluble in water, and that in the solutions from the bean and the pea it is rendered soluble by the presence of a little potash, soda, or lime —the liquid becoming turbid as soon as a quantity of acid is formed to combine with these alcaline substances. According to Dumas, pure legumin dried in vacuo at 2840 F. consists ofFibrin Albumen Glutine Casein Legunin. of of of of Wihei Wheat. Wheat. Wheat. Carbon.... 504 53-23 53-74 53-05 -5346 Hydrogen.. 6-9 7 01 7'11 7-17 7-13 Nitrogen.... 18-2 1641 15-65 15-94 16-04 Oxygen, sulphur; & phosph.... 24-5 23-35 23-50 23-84 23-37 100 100 100 100 100.For the purpose of comparison, I have inserted the composition, according to the same chemist, of the several nitrogenous compounds existing. in wheat. If these analyses be correct, legumin contains more nitrogen than the fibrin, the albumen, the glutine, or the casein of wheat, and is almost identical with the gelatine of bones. The important consequence deduced - from this fact, by Dumas, in reference to the feeding of'animals, we shall consider in a subsequent lecture. Above, I have given the composition of legumin, the- nitrogenous principles contained in peas and beans, as found by Dumas, from which it would appear to contain morenitrogen than any of the other vegetable principles hitherto found in cultivated grains. The legumin analysed by Dumas was extracted from sweet almonds. Since the preceding sheet was prepared for press, a further analysis of legumin, extracted from beans, has been published by Rochleder,* which Annale der Chem. et Pharmccie, xlvi., p. 155. ANALYSIS OF LEGUMIN. 517 does not agree with that of Dumas, but represents this leguiin as identical with casein, the curd of milk (see the following lecture), and as differing in properties as well as in composition from that of the almond. The legumin of beans and peas is soluble in cold water, and the solution, upon evaporation, forms a skin on the surface which is renewed as often as it is removed. It is not coagulated by boiling, but is immediately thrown down in fine flocks by acetic acid, which, when added in excess, does not redissolve it (Liebig). The legumin from sweet almonds is also soluble in cold water, but, like albumen, falls in flocks when the solution is heated nearly to boiling. It is precipitated also by diluted acetic acid, and is again dissolved when an excess of this acid is added (Dumas). The two substances, therefore, are different in their properties. Their constitution is represented respectively byLEGUMIN FROM Beans Sweet almonds (Rochleder). (Dumas). Carbon.... 54-5 50-4 Hydrogen... 7-4 6-9 Nitrogen.... 14-8 18'2 Oxygen... 23-3 24-5 100 100' When we come to consider the feeding of animals, we shall find that this difference in the composition of the two varieties will materially affect the view we must take in regard to the action of each in contributing to the support-of the various parts of the animal body. The approximate composition of the entire peas and beans is thus stated by Einhof. [Zierl Encyclopcedie, ii., p. 52]. Composition of the grain. Composition of the meal. Water. Husk. Meal. Sfarch. Legumin. Gum,&c. Peas... 14-0 105 75-5 65'0 23 12 Field Beans.. 155 16-2 68-3 690 19 12 A series of rigorous analyses of the seeds of leguminous plants is at present much to be desired. According to those of Braconnot and Einhof, certain species examined by them consisted ofKidney Field beans, Lentils, Peas. beans. (Einhof.) dried* (Einhof.) Water..... 125 230 15-6 Husk...... 8 3 70 10'0 18i7 Legumin, albumen, &c.. 26 4 23'6 11 7 38-5 Starch..... 43-6 43-0 50-1 32-8 Sugur 20 02 2 3'1 Gum,&c...... 4-0 15 6-0 Oil and fat... 12 07'- 1 Salts and loss... 20 1-0 4'4 0'9 1000, 100'0 100'0 100-0t These analyses agree in showing that the seeds of leguminous plants By drying, the lentils lost 14 per cent. of water. t Dumas Trait e Chimie, vi. p. 307, comparad with Thomson's Vegetable Chemistry, p. 884, Schiibler's Agricultur Chemie, ii., p. 194, and Sprengel's Chemie fir Landwirthe, ii., P' hb'eCievp. 358. 618 EFFECT OF SOILS AND,, MANURES UPON PEAS. are especially rich in substances containing nitrogen (legumin and albumen), and are therefore fitted to contribute much to the nourishment of those animals which, in- consequence of the state of their growth and health, or the purposes for which they are reared and maintained, require a large supply of this important element. ~ 20. EJfect of soils and manures upon the quality of peas and beans. The quality of the seeds of leguminous plants is also affected by the mode of culture to which they are subjected, and by the kind of soil in which they are raised. 1~. Effect of animal manures.-The dung "of sheep or horses has been found to impart a better flavour to the pea, and to render the husk thinner than when that of hogs or oxen has been used." [British Husbandry, ii., p. 217.] 2~. Effect of mineral manures.-The effect of gypsum and of other sulphates upon leguminous plants is universally known (p. 482.) The beneficial influence of a mixture of gypsum and common salt upon sickly crops of beans and peas is very strikingly displayed in the interesting ex periments of Mr. Alexander, of Southbar, to the details of which I have already had occasion to draw your attention. [See Appendix, p. 217.] 3~. Effect of lime.-Dr. Anderson says, " that the pea cannot be reared to perfection in any field which has not been either naturally or artificially impregnated with some calcareous matter," but that " a soil which could hardly have brought a single pea to perfection, although richly manured with dung, if once limed, will be capable of producing abundant crops of peas ever (?) afterwards, if duly prepared in other respects." [Essays, ii., p. 302.] 4~. Boiling or melting quality of peas.-But the most singular circumstance in connection with this class of seeds, to which the airicultural chemist has hitherto been. directed, is the property possessed by peas and beans of boiling soft or mouldering into a pulp more or less easily, according to the kind of land in which they are raised or to the species of manure with which they are dressed. The observations, however, which I have found upon record in reference to this point are of a contradictory character. Thusa. Sprengel says "that peas which are raised after liming or marling boil soft more easily, and are more agreeable to the taste than when raised after manure." [Die Lehre vom Dunger, p. 297.] b. A French authority, on the other hand, quoted by London, [Encyclopmdia of Agriculture, p. 837,] says, that "stiff land or sandy land that has been limed or marled, or to which gypsum has been applied, produces peas that will not melt in boiling, no matter what the variety may be. The same effect is produced on the seeds and pods of beans and of all leguminous plants. To counteract this fault in the boiling, it is only necessary to throw into the water a small quantity of the common soda of the shops." c. The author of the British lHusbandry, [ii., p. 217,] says, "that shell marl or lime is found to forward this crop more than any other mineral manure, though it is said to.communicate a degree of hardness to the grain whicn renders it unfit for boiling." SOME PEAS REFUSE TO BOIL SOFT. 519 Independently of all applications to the soil, I believe it is generally observed that good boilers are produced upon light,,sandy, and gravelly soils; while heavy, wet, undrained (and newly broken up?) land usually produces bad boilitig peas and beans. Thus melting peas (sidder peas, as they are locally called) for the Birmingham market are grown on the slopes of the gravelly hill of Hopwas, two miles from Tamworth, on -he Lichfield road-the red clay lands of the vale of the Tame producing in general pig; peas or beans only. It is on similar soils that melting barley and mealy potatoes are produced, and the effect upon the three crops may probably be due to a common cause. At all events it is probablea. That the boiling quality of the pea crop is not Owing to the quality of the seed-since peas of both varieties have been raised from the same seed.t b. That it is not generally owing to the seasons, since some land produces hard peas every year. If the wetness of the soil indeed have any influence, a rainy season may cause the production of bad boilers upon land from which soft peas are usually reaped. 40. Chemical difference between the two varieties of pea.-Why does one of these varieties of pea melt more readily than the other? For the same reason very nearly that one potatoe boils mealy, and another waxy, and that one sample of barley melts better in the mash-tub than another. - Melting peas and barley and mealy potatoes contain a larger proportion of starch than samples which are possessed of an opposite quality. The pea, as we have seen, consists essentially of legumin and starch. The former coagulates and contracts, or runs together into a mass by boiling,-the latter, on the contiary, expands, becomes more bulky, tends to burst the husk, and to separate into single grains. -Ifthe tendency to contract and cohere be greater than the disposition to expand and separate-in other words, if the legumin predominate-the pea does not melt, while if the starch be abundant the pea. boils well. It is possible that the addition of a little soda may'cause hard peas to melt, since legumin is soluble in a solution of soda, but in watersimpregnated with lime all peas are said to boil soft much less readily than in such as are free from that ingredient. [Dumas, Trait6 de Chimie, vi.] It is only when peas and beans are raised for the food of man that the possession of the melting property becomes a matter of importance; It is rather because they are more agreeable to the palate than because they are ascertained to be-more nutritive, that they are preferred'in this state. When we come to consider the feeding of stock, we shall see that, according to the present state of our knowledge, the opinion may reasonably be entertained that insoluble peas are really better adapted for the feeding and fattening pigs and other stock-the purpose for which they are employed-than those which are possessed of the melting quality. It is a difference in the chemical composition of the seeds of leguminous plants that makes them melt more or less easily-but by what iMuch used for the feeding of pigs. t Some however suppose it to depend upon the age of the-seed, or the time of sowing. -Brit'sh Ilusbandry, ii., p. 217, 520 COMIPOSITION OF POTATOES. quality in the soil ormanure is this difference in composition produced? In regard to lime the evidence is contradictory. Gypsum may render them harder since legnumin contains sulphur, and a portion of the effect of gypsum upon leguminous crops is supposed to arise from its yielding sulphur to the growing plants, and thus promoting the production of legumin. Wet and clay lands also favour the production of legumin more than that of starch-but in what way, we are not yet in possession of experimental results of sufficient accuracy to enable us to say. ~ 21. Of the composition of potatoes, and the effect of circumstances in modifying their composition. 1~. Composition of pctatoes.-Potatoes, in addition to much water, consist of starch, gum, woody fibre, and albumen. The proportions of these several constituents are very variable. Thus, according to Einhof and Lampadius, the following kinds of potatoe consisted in 100 parts of20. Influence of the state of ripeness.-According to Korte the quantity of dry solid matter contained in the potatoe depends very much upon the state of ripeness to which it has attained. The ripest leave 30 to 32 per cent. of dry matter, the least ripe only 24 pet cent. The per centage of starch varies from 8 to 16 per cent. The mean result of his examination of 55 varieties of potatoe gave him for the solid matter 24-9, and for the starch 11.85 per cent. [Schiibler, Agricultur Chemie, ii., p. 213.] 3~. Influence of variety.-Much appears also to depend upon the variety of potatoe. Thus the following varieties of potatoe grown at Barrochan in Renfrewshire, in 1842, yielded respectivelyConnaught cups.... 21 per cent. of starch. Irish blacks..... 16 White dons..... 13 Red dons..... 10 4 " -while, according to a starch manufacturer in the neighbourhood, 11per cent. has been the average quantity obtained from the conmmon rough red of good quality during the last four years. The difference in the quantity of starch yielded by the above-named varieties is the more striking when taken in connection with the weight of each per acre, raised from the same land, treated in the same way. These weights were as follows:Containing of Manure. Produce per acre. starch. Cups, with 4 cwt. of guano 132 tons 2-9 tons. Red Dons, with 4 cwt. of guano 141 " 1'5 " White Dons, with 3 cwt. of guano 18' " 2-4' So that, of these three crops, that of cups; which weighed the least, gave the largest produce of starch. It yielded nearly twice as much as the red dons, which were half a ton heavier, and one-fifth more than even the white dons, the crop of which was greater by five tons an acre. Such differences as these, in the relative quantities of starch, which may be obtained from an acre of the same land by the growth of different varieties of potatoe are deserving of the attentive consideration of the practical man. See Aj, endix, p. 61. THE PROPORTION OF STARCH VARIES VERY MUCH. 521 Larger quantities of starch than any of those above stated have been obtained from potatoes by some experimenters. Thus from the Per cent. of'starch. Kidney potatoe, Dr. Pearson obtained... 28 to 32 Apple do. Sir H. Davy..... to 20 Shaw do. Vauquelin.. 18-8 L'Orpheline do........ 244 The first and last of these proportions are probably very riare in our climate. 40. Effect of keeping.-Those potatoes are said to keep best in which the starch is most abundant, but in general keeping has an effecta. -On the proportion of starch.-By keeping till the spring, potatoes lose from 4 to 7 per cent. of their weight, and the quantity of starch they are capable of yielding suffers a considerable diminution. Thus, according to Payen, the same variety of potatoe yielded of starch in October, 17*2 per cent. January, 155'per cent. November, 16-8 " February, 15-2 December, 15-6 " March, 15-0 " April, 14'5 " This diminution is probably owing to the conversion of a portion of the starch into sugar and gum. When potatoes are rendered unfit for food by being frozen and suddenly thawed, the quantity of starch which they are capable of yielding is said to have undergone no diminution. 6. On the proportion of gluten.-The proportion of gluten also appears to become less when potatoes are kept. Thus, in new potatoes Boussingault found the gluten amount to 21 per cent., but in old potatoes to only 1 per cent. of their weight. To this natural diminution of the, proportion of starch and gluten, is probably to be ascribed the smaller value in the feeding of stock, which experience has shown very old potatoes to possess. 5~. Effect of soils and manures.-The potatoe thrives best on a light loamy soil-neither-too dry, nor too moist. The most agreeably'-flavoured table potatoes are almost always produced from newly broken up pasture ground, not manured, or from any new soil. [London's Encyclopaedia of Agriculture, p. 847.] When the soil is suitable, they delight in much rain, and hence the large crops of potatoes obtained in Ireland, in Lancashire, and in the west of Scotland. No skill will enable the farmer to produce crops of equal weight on the east coast where rains are less abundant. It has not been shown, however, that the weigh, of starch produced in the less rainy districts is defective inan equal degree. Warm climates and, dry seasons, as well as dry soils, appear to increase the per-centage of starch. Potatoes are considered by the farmer to be an exhausting crop, and they require a plentiful supply of manure. By abundantly manuring, however, the land in the neighbourhood of some of our large towns, where this crop is valuable, have been made to produce potatoes and corn every other year, for a very long period. 6~. Influence of saline manures. —I have already drawn your attention to the remarkable influence of certain saline substances in promoting the growth of the potatoe crop in some localities. The most striking effects of this kind hitherto observed in our island have been produced by mix. 522 OCCASIONAL FAILURE OF SEED POTATOES. tures of the nitrate of soda with the sulphate of soda or with the sulphate of magnesia.* The effect of such mixtures affords a beautiful illustration of the principle I have frequently before had occasion to press upon your attention-that plants require for their healthy growth a constant supply of a considerable number of different organic and inorganic substances. Thus upon a field of potatoes, the whole of which was manured alike with 40 cart loads of dung, the addition ofa. Nitrate of soda alone gave an increase of 3- tons.'Sulphate of soda alone gave... 0 " While one half of each gave... 5} " b. Sulphate of ammonia alone gave.. 1 Sulphate of soda....... But one half of each gave.... 61 " c. Nitrate of soda alone gave... 3- " Sulphate of magnesia alone gave.. 2 And one half of each gave.... 9 These results are very interesting, and when confirmed by future repetitions of such experiments-and followed up by an examination of the quality and composition of the several samples of potatoes producedcannot fail to lead to very important practical conclusions. 7~. Occasional failure of seed potatoes.-The seeds of all cultivated plants are. known at times to fail, and the necessity of an occasional. change of seed is recognised in almost every district. In the Lowlands of Scotland potatoes brought from the Highlands are generally preferred for seed, and on the banks of the Tyne Scottish potatoes bring a higher price for seed than those of native growth. This superior quality is supposed by some to arise from the less perfect ripening of the up. land potatoes, and in conformity with this view the- extensive failures which have taken place during the present summer (1843) have been ascribeo to the unusual degree of ripeness attained by the potatoes during the warm dry autumn of the past year. This may in part be a true explanation of the fact, if-as is said-the ripest potatoes always contain the largest proportion of starch-since some very interesting observations of Mr. Stirrat, of Paisley, would seem to indicate that whatever increases the per-centage of starch, increases also the risk of failure in potatoes that are to be used for seed.t This subject is highly deserving of further investigation. For the particulars of these experiments see the Appendix. t I insert Mr. Stirrat's letter upon this subject, not only because his observations are interesting in themselves, but because they are really deserving of the careful attention of practical men:" SIR, —The follewing experiment with potatoes was tried with the view of discovering the cause of so many failures in the crops of late years, from the seed not vegetating, and rotting in the ground. I had an id'ea that the vegetative principle of the plant might become weak in consequence of being grown on land that had been a long time subjected to cropping, and not allowed any length of time to lie at rest. I, therefore, raised a few bolls on land that had lain lea for 70 years (being part of my bleach green), and found that these on being planted again the following year were remarkably strong andhealthy, and not a plant gave way, and I have continued the same method for the last six years, and the result has, in every instance, been equally favourable. Four years ago, one boll of my seed potatoes was planted along with some others in a field of about an acre, the other seed was grown on the farm, and.the seed all gave way excepting that got from me.' They were all planted at the same time and EFFECT OF SALINE SUBSTANCES 523 8~. Effect of saline top-dressings on the quality of the seed.-It may be doubted, however, whether the relative:proportions of starch are to be considered as the cause of the relative values of different samples of seed potatoes. This proportion may prove a valuable test of the probable success of two samples when planted, without being itself the reason of the greater or less amount of failures. With the increase of the starch it is probable that both the albumen and the saline matter of the potatoe will in some degree diminish, and both of these are necessary to its fruit fulness when used for seed. The value of the saline matter is beautifully illustrated by the observation of Mr. Fleming, that the potatoes top-dressed. with sulphate and nitrate of soda in 1841, and used for seed in 1842, "presented a remarkable contrast to the same var.ety of potatoe, planted alongside of them, but which had not been so top-dressed in the previous season. These last came away weak, and of a yellowish colour, and under the same treatment in every respect did not produce so good a crop by fifteen bolls (3V tons) an acre." This observation, made in 1842, is confirmed by the appearance of the crops now growing (July, 1843) upon Mr. Fleming's experimental fields. The prosecution of the enquiry opened up by his experiments promises to lead to the most valuable practical results.* They may teach us how to secure at all times a fruitful seed, and thus to dispense with supplies of imported produce. ~ 22.'The composition of the turnip, the carrot, the beet, and the parsnip. 1~. Composition.-The potatoe is characterised by containing a large proportion of starch in connection with a small quantity of albumen-the turnip and carrot by containing, in place of the starch, a variable prowith the same manure. From these circumstances, I am of opinion, that if farmers were careful in raising their own seed potatoes from land that has lain long in a state of rest(a)-or where that cannot be had, the same object can be obtained by bringing new soil to the surface by trenching as much as is necessary, or by the use of the subsoil-plough-failures of the potatoe crop from the seed not being good, would become much less frequent I am somewhat confirmed in this opinion by the fact, that it has been found for the last dozen of years that generally the best seed potatoes have been got from farms in the moors or high lands of the country. The reason of this may be that these high lands have been but of late brought under crops of any kind, and many of them but newly brought from a state of nature, and the superiority of seed potatoes from these high lands may not at all arise (as is generally supposed) from a change of soil or climate. " Potatoes raised on new soil, or on ground that has been long lying lea, are not so good for the table as the others, being mostly very soft, and, by the following experiment, it would appear that they contain a much less quantity of farina than those which are raised from land that has been some time under crop, and, perhaps, this is the reason why they arc belter for seed. From one peck of potatoes, grown on land near Paisley, which has been almost constantly under crop for the last 30 years, I obtained neariy 7 Ibs. of flour or starch; and from the other peck, grown on my bleach green, the quantity obtained was under 4 lbs., from which it would seem that as the vegetative principle of the plant is strengthened, the farinaceous principle is weakened, and vice versa. JAS. STIRRAT." Paisley, 22d November, 1842. (a) Mr. Finnie, of Swanstone, informs me that the growing of potatoes intended for seed upon new land, has long been practised by good farmers. Mr. Little, of Carlesgill, near Langholm, writes me that in Dumfriesshire, they obtain the best change of potatoe seed from mossy land-of oats and barley from the warmer and drier climate of Roxburghshire. The grains, he adds, degenerate by once s.ng, still looking plump when dry, but having a thicker husk, and weighing two or three poc(ids less per bushel. The deterioration of seeds, in general, is a chemico.physiological subbjet of great interest and importance, and will doubtless soon be taken up and investigated. In the Appendsix, p, 47, the experiments are recorded, and in p. 66 I have more fully ad. verted to the interesting results likel.y to be derived from the continuance of such experiments. 524 COMPOSITION OF THE TURNIP, CARROT, AND BEET. portion of sugar, and of a gelatinous gummy-like substance, to which the name of pectin has been given. In the Swedish turnip and-in beetroot the sugar predominates, in the white turnip and in the carrot the pectin is usually present in the larger quantity. The composition of the turnip, the carrot, and the beet varies very much, and is influenced by a great variety of circumstances. We are not in possession of any recent detailed analyses of these roots. The following table exhibits the component parts of several varieties, as they have been given chiefly by Hermbstadt, [Schiibler, Ag. Chem., ii., p. 207]: Variety of Turnips. Sugar ------—, Common, beet Parsnip White. Swedish. Cabbage. Carrot. (Payen). (Crome). Water... 79-0 80-0 78-0 80'0 85-0 79-4 Starch and fibre. 72 53 6-0 9-0 3-0 6-9 Gum (pectin?). 25 3-0 3'5 1-75 2-0 6-1 Sugar.... 8-0 9'0 9'0 7-8 10'0 5-5 Albumen... 2-5 20 2.5 1.1 1 21 Salts..... 0-5 0-5 0-5 ---? Loss..... 0-3 09 05 oil 035 100 100 100 100 100 100 These analyses are very defective, and apply with any degree of correctness only to the specimens actually operated upon. Any reasonings, therefore, which are founded upon them can only lead to probable or approximate conclusions. 2~. The proportion of sugar contained in the sap of these roots is greatest when they are young, and diminishes as they ripen. In the beet, it has been observed that the nitrates of potash and ammonia are present in considerable quantity, and that in the old beet these nitrates become more abundant as the sugar diminishes. In the beet, also, when raised by the aid of rich manure, the production of nitrates is increased more than that of sugar.* The same may possibly be the case with the common cultivated turnips. It would not be without interest, both theoretically and practically, to ascertain by experiment, the relative composition of the same variety-of turnip, grown on the same soil, by the aid of rich farm-yard manure, and by the aid of bones or of rape-dust. The one may produce more sugar, the other more albumen or nitrates. Such differences may materially affect the value of the crop, either in the feeding of stock or in the production of an enriching manure. It is in suggesting and carrying on enquiries of this kind that the joint labours of the practical farmer and of the theoretical chemist are likely, among other ways, to promote the advancement of a rational and scientific agriculture. 3~. Effect of soils, and manures.-These roots delight in a rich, open, and loamy soil-and the weight of produce varies much with the kind of manure that may have been applied to them. [See, for, many instructive illustrations of this fact, the experiments upon turnips, detailed in the Appendix, pp. 43 et seq.] No experiments, however, have yet been made to determine the relative proportions of water and of their other constituents which the same turnips contain, when raised by the According to Payen, the beet, wten raised with street manure, contains 20 times as much saltpetre as when raised in the ordinary manner. WATER IN DIFFERENT VARIETIES OF TURNIP. 525 aid of different manures, nor, consequently, the true effect of these manures upon the relative values of the several crops. 4~. Quantity of water in different varieties of turnip.-The same remark may be made in regard to the several varieties of turnip. All those examined by Hermlstadt, as appears from the above tables, contained 20 to 22 per cent. of solid matter (78 to 80 of water), while other experimenters have found as little as from 8 to 15 of solid matter in turnips, and generally less in the white and large globe turnip than in the yellow and more solid Swede. Thus, four varieties of the above roots contain of water and solid matter, according to three different experimenters:WATER PER CENT. DRY MATTER PER CENT. of, rHerrb'- ~ — _ Einhof. Playfair. HH - Enho Pfar. E —hof. sadl. ayfatirdHeriubdt. White turnip 92 89 79 8 11, 21 Swedish do. 87- 85 80 121 15 20 Cabbage do. 86 - 78 14 - 22 white. Carrot.. 86 87 80 14 13 20 The above differences are very -reat, especially when we look to the relative proportions of dry matter in which the nutritive power resides. They are of much importance, therefore, to the feeding of stock, and the circumstances under which they occur, are deserving of a careful investigation. 5~. Relative nutritive properties df the potatoe and the turnip.-The potatoe is usually considered more nutritive than the turnip, weight for weight, and no doubt it generally is so. But if we compare together the quantities of solid matter which the two roots may contain, we shall see' how very far wrong our estimate may be in any special case. ThusThe turnip contains of solid matter from 8 to 22 per cent. The potatoe do. do. 24 to 32 " -so that, while the driest turnips may contain four times as much solid matter as the most watery potatoes, very dry potatoes may contain nearly as much as very juicy turnips. It is impossible, therefore, without an actual examination of the samples, to pronounce upon the relative amount of food which is likely to be contained in any equal weights of turnips and potatoes. The very discordant estimates which different feeders of stock have formed in regard to the relative value of these crops in the production of beef or mutton is partly owing to this cause. [Other causes for these- discordant estimates will be stated in Lecture XXI.] Until the effects of equal weights of the different kinds of food, estimated in the drystate, are carefully'ascertained, it will be impossible to obtain results of a general kind, or upon which any real confidence can be placed. ~ 23. Of the composition of the green stems of peas, vetches, clover, spurry, and buck-wheat. The -stems and leaves of plants which are given as green food to animals diffr much in, composition, according to the age they have attained, to the- rapidity of their growth, to the nature of the soil, the season, and the mode of culture. They are generally supposed to be richest in nutritive matter when the plant has just come into flower: 526 COMPOSITION OF THE GREEN STEMS OF PEAS, ETC. The following table exhibits the approximate'composition of the green stems of some clovers and vetches, as they have been given by Einhof and Crome: a.>, 5)0 ~o,,, < C <,s -~ 0 A, S L. _ g,;o L, ~ a ~4 Water...800 760 80-0 75-0 77-0 82-5 77-5 79-5 86-0 Starch... 340 1-4 1-0 2-2 2-3 4-7 296 3-8 1-3 Woody fibre.. 1031 13-9 115 14-3 120 10-0 10-4 11-5 7-0 Sugar... 455 21 1'5 0-8 - - Albumen. 090 2-0 15 1-9 2-3 0-2 1-9 0-7 1-8 Extractive matter and gum... 065 3-5 3-4 4-4 5-5 2-6 76 3-6 29 Phosphate of lime. 0-19 1-0 0'8 08 -S - - - Wax and Resin. - 0 02 0-6'?? 09 1'0 100 100 99-9 100 99-6 100 100 100 100 ~ 24. Of the composition of the grasses when made into hay. 1~. An-elaborate examination of the, grasses of this country, in the dry state, with the view of determining their relative nutritive properties, was made-by the late Mr. Sinclair, gardener to the Duke of Bedford. His method was to boil in water equal weights of each species of hay till every thing soluble was taken up, and to evaporate the solution to dryness. The weights of the dry matter thus obtained he considered to represent the nutritive values of the grasses from which the several samples of hay were made. The results of Mr. Sinclair, however, have lost much of their value, since it has been satisfactorily ascertaineda. That the proportion of soluble matter yielded by any species of grass, when made into hay, varies not only with the age of the grass, when cut, but with the soil, the climate, the season, the rapidity of. growth, the variety of seed sown, and with.many other circumstances which are susceptible of constant variation. b. That animals have the power of digesting a greater or less proportion of that part of their food which is insoluble in water. Even the woody fibre of the hay is not entirely useless as an article of nourishment-experiment having shown that the manure often contains less of this insoluble matter than was present in the food consumed.* (Sprengel.) c. That some of the substances which are of the greatest importance in the nutrition of animals-such as vegetable fibrin, albumen, casein, annd legumin-are either wholly insoluble in water or are more or less perfectly coagulated and rendered insoluble by boiling with water. Mr. Sinclair, therefore, must have left behind, among the insoluble parts of This will not appear surprising when it is recollected that., by prolonged digestion in diluted sulphuric acid, insoluble woody fibre may be slowly changed into soluble gum or sirgar (see p. 112). The proportion of the woody fibre which will be thus worked up in the stotmachof an animal will depend, among other circumstances, upon the constitution of the animal itself, upon the abundance of food supplied to it, and upon the more or less perfect mastication to which the food is subjected. WOODY FIBRE AND GLUTEN IN THE GRASSES. 527 nis hay, the greater proportion of these important substances. Hence, the nature and weight of the dry extracts he obtained could not fairly represent either the kind or quantity of the nutritive matters which the. hay was likely to yield when introduced into the stomach of an animal. For these reasons I do not think it necessary to dwell upon the results of his experiments.* 2~. Woodyfibre in the grasses.-In the stems of the grasses (in hay and straw), woody fibre is the predominating ingredient. They are not destitute of starch, gum, and sugar, but they are distinguished from all the other usual forms of animal food, by the large quantity of woody) fibre, and of saline or earthy matter which they contain. The; proportion of woody fibre in the more common grasses, in their usual state of dryness when made into hay and straw, is thus given by Sprengel (see p. 106):Per cent. Per cent. Wheat straw, ripe.... 52 Pea straw, ripe.. 30 Barley straw, do....50 Bean straw, do..... 51 Oat straw, do..... 40 Vetch hay, do..... 42 Rye straw, do...... 48 Ied clover, do..... 28 Indian corn, do.. 24 Rye grass, do;.... 35 The proportions of woody fibre here given, however, can be considered only as approximations. The riper the straw or grass, the less soluble matter does it contain, and every farmer knows how much soil, season, and manure, affect the quality of his artificial grasses. One field will grow a hard wiry rye-grass, while another will produce a soft and flexible plant, and a highly nutritious hay. 30. Gluten in the grasses.-Boussingault, who considers the relative nutritive value of the vegetable substances employed for fodder to be indicated by the proportions of nitrogen they severally contain, has arranged grass and clover hays and the straws of the corn plants, in their usual state of dryness, in the following order:Or gluten, Equal effects Nitrogen &c., should be per cent. per cent. produced by Hay from mixed grasses 1 1 100 lbs. Do. aftermath... 154 9-3 75 " Do. from clover in flower 1'5 9-3 75 Pea straw... 195 12' 3 64 " Lentil straw.. 1.01 6-4 114 Indian corn straw. 0-54 3 4 240 Wheat straw.. - - 520 Barley straw... - 520 Oat straw... - - 550" We shall have occasion to compare the above theoretical, values (equivalents) assigned to the several kinds of fodder, with the results of They will be found at length in the Appendix to Davy's Agricultural Chemistry, or in a tabulated form in Schiibler's Agricultur Chemie, ii., p. 208. t It is usually supposed that the aftermath is not so valuaDle as the first produce. Schwertz, however, considers it more nourishing by one-tenth part.:t " The value of all gtraw for fodder must depend on the mode in which it is harvested. In Scotland, the order in which the farmer places his straw for fodder is —st, pea; 2nd, bean; 3d, oat; 4th, wheat; 5th, barley. While in England, where the bean is quite withered before it is cut, it stands last in the scale."-Mr. Hyett, Royal Agricultural Journal, iv.,p. 148. 528 COMPOSITION OF HEMP AND LINT SEEDS. practical experience, when we come to direct our attention more particularly to the feeding of stock. 4~. Fatty matter in the grasses.-Besides woody fibre, starch, gum, and gluten, dry hay and straw contain also a variable proportion of fatty matter. According to Liebig, it does not exceed 1.56 per cent. in hay, while, according to Dumas and Boussingault, as much as 3, 4, or even 5 per cent. of fat can be extracted from it. To this fact we shall also re turn when considering the methods of fattening stock. 5~. Inorganic matter in the grasses.-The proportion of saline and earthy matter contained in the grasses is an important feature in their composition. This, as I have already said, is much larger than in any of the other kinds of food usually given to animals, being seldom less than 5, and occasionally amounting to as much as 10 per cent. of their weight when in the state of hay or straw. A large'proportion of the ask left by the stems of the corn plants, and by many grasses, consists of silica. The straw of the bean, pea, and vetch, and the different kinds of clover hay, contain little silica, its place in these plants being supplied by a large quantity of lime and magnesia. ~ 25. Of hemp, line, rape, and other oil-bearing seeds. The oily seeds are important to the agriculturist from their long acknowledged value in the feeding and fattening of cattle. Lintseed is extensively used for the latter purpose, both in its entire state and in the form of cake-when the greater part of the oil has already been expressed from it. All these seeds, however, are not equally palatable to cattle. Some varieties they even refuse to eat. Among these is the rape-seed, from which so much oil is expressed, and the cake left by which is now so extensively employed as a manure. These seeds are distinguished from those of the corn plants, by containing, instead of starch or sugar, a predominating proportion of oil; and instead of their gluten a substance soluble in water, which possesses many of the properties of the curd of cheese (casein). We are in possession of a somewhat imperfect analysis of hemp seed and of the seed of the common lint, according to which the varieties examined consisted in 100 parts ofHemp seed Lime seed (Bucholz). (Leo Meier). Oil........ 19.1 11-3 Husk, &c.... 383 444 Woody fibre and starch. 5'0 15 Sugar, &c.... 16 10'8 Gum....... 90 7-1 Soluble albumen (Casein?). 24-7 15-1 Insoluble do.... 3-7 Wax and resin.... 1'6 3-1 Loss..... 07. 3-0 100 100 These analyses show that, besides the oil, these seeds contain considerable proportions of gum and sugar and a large quantity of a substance here called soluble albumen, of which nitrogen is a constituent part, but PROPORTION OF OIL IN DIFFERENT SEEDS. 529 which differs in its properties from the gluten and albumen of the seeds of-the corn-bearing plants, and has much resemblance to the curd of, milk.' Besides their fattening properties, therefore-which these seeds probably owe in a great measure to the oil they contain-this peculiar albuminous matter ought to render them very nourishing also; —capable of promoting the growth of the growing, and of sustaining the strength of the matured, animal. The quantity of oil contained in different seeds of this class, and even in the same species of seed when raised in different circumstances, is very variable. These facts will appear from the following table, which represents the proportions of oil that have been found in 100 lbs. of some of the more common seeds:Oil per cent. Oil per cent. Line seed.. 11 to 22 Sun-flower seed... 15 Hemp seed..... 14 to 25 Walnut kernels.. 40 to 70 Rape seed..... 40 to 70 Hazel-nut do.... 60 Poppy seed. 36 to 53 Beech-nut do.... 15 to 17 White mustard do. 36 to 38 Plum stone do...33 Black do. do... 15 Sweet almond do... 40 to 54 Swedish turnip do.. 34 Bitter do. do... 28 to 46 It seems tobe a provision of nature, that the seeds of nearly all plants should contain a greater or less proportion of oil, which is lodged for the most part in, or immediately beneath, the husk, and, among other purposes, may be intended to aid in preserving the seed. We shall hereafter see that this oily constituent is of much importance also to the practical agriculturist. ~ 26. General differences in composition among the different kinds of vegetable food, It may be, useful shortly to recapitulate the leading differences in chemical constitution which exist among the different kinds of vegetable food to which I have directed your attention in the present lecture. We have seen that each of the varieties of food contains a greater or less proportion of three different classes of chemical substances-an organic substance containing nitrogen, an organic substance containing no nitrogen, and an in-organic substance. But it is interesting to mark how in each class of those vegetable products which we gather from the earth for our sustenance. the organic substances vary either in composition or in chemical characters, while the inorganic matter alters also either in kind or quantity. Thus10. -In the seeds of the corn plants-wheat, oats, &c.-the predominating ingredient is' starch, in connection with a considerable proportion of gluten, and a small quantity of saline matter consisting chiefly of the phosphates of potash and of magnesia, and in the case of barley of a considerable proportion of lime. 2~. In the- seeds of leguminous plants-the pea, the bean, the vetch, &c.-starch is still the predominating ingredient,.but it is connected with a large quantity of legumin, and with a greater proportion of inorganic matter-in which phosphate of lime also is more abundant. 30~. In the oil-bearing seeds-those of hemp, lint, &c.-oil is often the 530 SPECIAL DIFFERENCES AMONG SEEDS AND ROOTS. predominating ingredient, and it is connected with a large proportion of a nitrogenous substance, resembling the curd of milk (casein), and with a quantity of ash about equal to that in the pea, hut in which the phosphate of lime is said to be still more abundant. 40. In, the potatoe-starch is the greatly predominating ingredient, but it is united with albumen nearly in the same proportion as it is with gluten in wheat. The inorganic matter is nearly in the same proportion to the dry organic matter, as in the pea and the bean, but is much more rich in potash and soda. Still it is more rich in the earthy phosphates than the ash left by wheat and oats, and is inferior in this respect only to that of barley. 5~. In the turnip-sugar and pectin take the place of the starch, and these are associated with albumen, and with a proportion of inorganic matter about equal to that of the potatoe, abounding like it in potash and soda, but more rich in the phosphates of lime and of magnesia. 6~. In the stems of the grasses and clovers —woody fibre becomes the predominating ingredient, associated apparently with albumen, and with a larger proportion of inorganic matter than in any of the other crops. In the straws and in some of the grasses which are cut for hay, silica forms a large portion of this inorganic matter. In the clovers, lime and magnesia take its place. The natural differences above described not only exercise an important influence upon the mode of culture by which the different crops may be most successfully and most abundantly raised, but also upon the way in which they can be most skilfully and economically employed in the feeding of stock. To this latter point we shall return hereafter. ~ 27. Average composition and produce of nutritive matter per acre, by each of the usually cultivated crops. 1~. Average composition.-The relative proportions of the several most important constituents contained in our cultivated crops vary, as we have seen, with a great number of circumstances.' The following table exhibits the average composition of 100 parts of the more common grains, roots, and grasses, as nearly as the present state of our knowledge upon the subject enables us to represent it. (See table at top of next page.) In drawing up this table, I have adopted the proportions of gluten, for the most part, from Boussingault. Some of them, however, appear to be very doubtful. The proportions of fatty matter are also very uncertain. With a few exceptions, those above given have been taken from Sprengel, and they are, in general, stated considerably too low. It is an interesting fact, that the proportion of fatty matter in and immediately under the husk of the grains of corn, is generally much greater than in the substance of the corn itself. Thus I have found the pollard of wheat to yield more than twice as much oil as the fine flour obtained from the same sample of grain;* and Dumas states that the husk of oats sometimes yields as much as 5 or 6 per cent. of oil. We shall perceive the practical value of this fact when we come to consider the use of bran and pollard in the fattening of pigs and other kinds of stock. * Thus the four portions separated by the miller from a superior sample of wheat grown in the neighbourhood of Durham, gave of oil respectively:-fine flour, 15 per cent.; -pollard, 2-4; boxings, 3-6; and bran, 3-3 per cent. AVERAGE COMPOSITION OF THE DIFFERENT CROPS. 531 Husk or Starch, Gluten, al- Fatty Saline Water. woody gum, and burnen, le matter. matte fibre. sugar. gumin,&c. Wheat-... 16 15 55 10to15 2 to 4 J 2'0 Barley... 15 15 60 12 2 2-5 J 2'0 Oats... 16 20 50 145 1 5-6 J 3-5 Rye... 12 10 60 14-5 30 1'0 Indian corn.. 14 15? 50 12-0 5 to 9 D. 1-5 Buckwheat.. 16? 25 1 50 14-5 0-4. 1-5 Beans.... 16 10 40 28'0 2+ 3-0 Peas... 13 8 50 24-0 2'-8 2-8 Potatoes.. 751 5 12'2-25 03 0-8 to 1 Turnips... 85 3 10 1-2 0'8 to 1 Carrots... 85 3 10 2-0 0-4 1-0 Meadow hay. 14 30 40 7-1 2 to 5D, 5 to 10 Clover hay.. 14 25 40 9-3 3-0 9 Pea straw.. 10to15 25 45 12-3 15 5 Oat do... 12 45 35 1-3 0' 8 6 Wheat do... 12to15 50 30 1-3 0-5 5 Barley do... do. 50 30 1-3 0' 8 5 Rye do... do. 45 38 1 3 05 3 Indian corn do.. 12 25 52 3-0 17 4 2~. Gross produce per acre.-The gross produce, per acre, of the different crops varies as we have already seen (p. 487) in different districts of the country. The weight of each crop in pounds, however, will, in general, approach to one or other of the quantities represented by the numbers in the following table:Produce Weight Total weight per acre. per bushel. in pounds. Wheat.... 25 bush. 60 lbs. 1500 -.... 30 - 1800 Barley.... 35 " 53 Ibs. 1855.....40" - 2120 Oats..... 40 42 lbs. 1680 -.... 50 " 2100 Rye...... 25" 54 lbs. 1350:. 30- -1620 Indian corn.... 30' 60 lbs. 1800 Buckwheat.. 30 " 46 lbs. 1380 Beans.... 25" 64 lbs. 1600 -..... 30 -1920 Peas.... 25 " 66 lbs. 1650 Weight of produce. Weight of produce. Potatoes... 6 tons. Carrots.. 25 tons. — ~- 12 tons. Meadow hay.. 1 tons. Turnips...20 tons. Clover hay.. 2 tons. -~- ~ 30 tons. 532 PRODUCE PER ACRE. Weight of produce. Weight of produce. Wheat straw. 3000 lbs. Rye straw. 4000 lbs. -- 3600' - 4800 " Barley straw..2100" Bean straw.. 2700 "? -- 2500. 3200 " Oat straw...2700 Pea straw.. 2700 " 3500" 3~. Average produce of nutritive matter per acre.-In the gross produce above given, there are contained, according to the first table, the following average proportions of nutritive matter of various kid-s:AVERAGE PRODUCE OF NUTRITIVE MATTER OF DIFFERENT KINDS FROM AN ACRE OF THE USUALLY CULTIVATED CROPS. uskor Starch, Gluten, Oil or fat. Saline Gross produce. woody sur c. Oilo matter. fibre.. m attr. bush. lbs. lbs. lbs. lbs. lbs, lbs. Wheat.. 25 1,500 225 825 150 to220 30 to 60 30. 30 1,800 270 990 180to260 36 to 72 36 Barley.. 35 1,800 270 1080 216 45 + 36 40 2,100 315 1260 252 52 -' 42 Oats.. 40 1,700 340 850 230? 95 60 50 2,100 420 1050 290? 118 75 Rye... 25 1,300 130 780 190 40 13.. 30 1,600 160 960 230 48 16 Indian corn 30 1,800 270 900 216 90 to 170 27 Buck wheat 30 1,300 320? 650 180 5 + 21 Beans.. 25 1,600 160 640 450 32 + 48 -.. 30 1,900 -190 760 530 36 + 57 Peas..25 1,600 130 800 380 45 45 tons. Potatoes. 6 13,500 675 1620 300 45 120 12 27,000 1350 3240 600 90 240 Turnips. 20 45,000 1350 4500 540?? 400 30 67,000 2010 6700 800?? 600 Carrots. 25 56,000 1680 5600 1120 200 560 Meadow hay 1- 3,400 1020 1360 240 70 to 170 220 Clover hay 2 4,500 1120 1800 420 135 to 225 400 Pea straw. - 2,700 675 1200 330 40 135 Wheat straw - 3,000 1500 900 40 15 150 -. -- 3,600 1800 1080 48 18 180 Oat straw. - 2,700 1210 950 36 20 135 - 3,500 1570 1200 48 28 175 Barley straw - 2,100 1050 630 28 16 105 - 2,500 1250 750 33 20 125 Rye straw. - 4,000 1800 1500 53 20 120 -. 4,800 2200 1800 64 24 144 The most uncertain column in this table is that which represents the quantity of oil or fat contained in the several kinds of produce. The importance ot the whole table to the practical man will appear more clearly when we come to treat of th}: feeding of stock. LECTURE XX. Of milk and its products.-Properties and composition of the milk of different animals.Circumstances which affectithe quality and quantity of milk-species, size, variety, age, health, and constitution of the, animal, time of milking, kind of food, &c.-Mode of separating and estimating the several constituents of milk.-Sugar of milk, and acid of milk. (Lactic acid), their compositidn and properties.-Souring of milk, cause of.-Creamcomposition anddvariable proportions of-mode of estimating its quantity-the gulacfometer.-Churning of milk and cream.-r-Comiposition of'butter.- Buot.er-milk.-The solid and liquid fats contained in butter-margarin and butter oil —their separation and properties.Rancidity and preservation of butter.- Composition and properties of the curd (casein).Curdling of milk, natural and artificial-by acids and by animal membranes.-Making and action of rennet-how explained.'-Manufacture of cheese.-Varieties of cheese.-Aver. age-produce of butter and cheese.-Colouring of butter and cheese.-The whey.-Saline matter in the whey.-Nature of the saline constituents of milk.-rFermentation of milk.Intoxicating liquor from milk.-Milk vinegar.-Purposes served by milk in the economy of nature. OF the indirect products of agriculture, milk, and the butter and cheese manufactured from it, are among the most important. In our large towns these substances may almost be considered as necessaries of life, and many extensive agricultural districts are entirely devoted to the production of them. The branch of dairy husbandry also presentsmany curious and interesting questions to the scientific enquirer, and upon These questions modern chemistry has thrown much, light. To the consideration of this subject, therefore, it is my intention to devote the present lecture. ~ 1. Of the properties and composition of milk. 1o. Properties of milk,-The milkl of most animals is a white opaque liquid,. having a slight but peculiar odour-which becomes more distinct when the milk is warmed-and an agreeable' sweetish taste. It. is heavier than water-usually in the proportion of about 103 to 100.* When newly taken from the animal, cow's milk is almost always slightly alcaline. It speedily loses this character, however, when exposed to the air, and hence even new milk often exhibits a slight degree of acidity.t When left at rest for a number of hours, it separates into two portions, throwing up the lighter part to the surface in the fbr "of cream. If the whole milk, or the cream alone, be agitated in a proper -vessel (a churn), the temperature of the liquid undergoes a slight increase, it becomes distinctly sour, and the fatty matter separates in the form of'butter. If.a little acid, such as vinegar or diluted muriatic acid, be added to milk-warmed to about 100~ F., it irmmediately coagulates and separates into a solid and a liquid part-the curd and the whey. The same effect is produced -by the addition of rennet or of sour milk —and ittakes place naturally when milk.is left to itself until it becomes sour. At a very low temperature, or when kept in a cool place, milk remains'sweet for a considerable time. At the temperature of 60~-F. it soon Or it-has q specific gravity of 1020 in woman's milk, to 1041 in sheep's milk; water being 1000. tlit is said that if the animal remain long unmilked, the milk will begin to sour in the Udder, and that hence it is sometimes slightly aclidwhen fresh drawn from the cow. 23 534 PROPERTIES AND COMPOSITION OF MILK. turns or acquires a sour taste, and at 70~ or 80~ it sours with still greater rapidity. If sour milk be gently warmed it undergoes fermentation, and may be made to yield an intoxicating liquor. By longer exposure to the air it gradually begins to putrify, becomes disagreeable.to the taste, emits an unpleasant odour, and ceases to be a wholesome article of food. The milk of each species of animal is distinguished by some characters peculiar to itself. Ewe's milk does not differ in appearance from that of the cow, but it is generally more dense and thicker, and gives a pale yellow butter, which is soft, and soon becomes rancid. The curd is separated from this milk with greater difficulty than from that of the cow. Goat's mills generally possesses a characteristic unpleasant odour and taste, which is said to be less marked in animals of a white colour or that are destitute of horns. The butter is always white and hard, and keeps long fresh. The milk is considered to be very wholesome, and is often recommended to invalids. Ass's milk has much resemblance to that of the woman. It yields little cream, and the buutter is white and light, and soon becomes rancid. It contains much sugar, and hence soon passes to the state of fermentation. 2~. Composition of milk.-Milk, like the numerous vegetable products we have had occasion to consider, consists, besides water, of organic substances destitute of nitrogen-sugar and butter; of an organic substance containing nitrogen in considerable quantity-the. curd or casein; and of inorganic or saline matter, partly soluble and partly insoluble in pure water. The proportions of these several constituents vary in different animals. This appears in the following table, which exhibits the composition of the milk of several animals in its ordinary state, as found by Henry and Chevallier:Woman. Cow. Ass. Goat. Ewe. Casein (cheese).. 152 4-48 1.82 4'08 4-50 Butter... 3-55 3-13 0-11 3-32 4 20 Milk sugar... 6-50 4-77 6-08 5-28 5.00 Saline matter... 045 0-60 0-34 0'58 0-68 Water... 87-98 87-02 91-65 86-80 88-62 100 100 100 100 100 From the numbers in the above table, it appears that the milk of the cow, the goat, and the ewe, contains much more cheesy matter than that of the woman orthe ass. It is probably this similarity of asses' nilk to that of the human species, together with its deficiency in butter, which, from the most remote times, has reconmmended it to invalids, as a light and easily digested drink. ~ 2. Of the circumstances by which the composition or quality of the milk is modified. But the composition or quality of milk varies with a great variety of circumstances. Let me direct your attention to a few of these. 1~. Distancefrom the time of calving.-The most remarkable depar INFLUENCE OF THE HEALTH OF THE ANIMAL. 535 ture from the ordinary composition of milk is observed in the beistings, colostrum or first milk, yielded by the animal after the birth of its young. This milk is thicker and yellower than ordinary milk, coagulates by heating, and contains an unusually large quantity of casein or cheesy matter. Thus the first milk of the cow, the ass,- and the goat, consisted, in some specimens examined by Henry and Chevallier, ofCow. Ass. Goat. Casein.. 151 11i6 24-5 Butter.. 2-6 0-6 5-2 Milk sugar. - 4-3 3-2 Mucus.. 2'0 0-7 3-0 Water.. 803 82.8 64-1 100 100 100 The increase in the proportion of cheese is peculiarly great in the first tnilk of the ass and the goat. This state of the milk, however, does not long continue. It gradually assumes its ordinary qualities. After ten or twelve days from the time of calving, its peculiarities disappear, though in the celebrated dairy districts of Italy it is considered that the milk does not reach perfection until about eight months after calving. [Cataneo, 11 latte e i suoi prodotti, p. 27.] 2~. Age of the animal.-It is observed that milk of the best quality is given only by cows which have been already three or four times in calf. Such animals continue to give excellent nilk till they are ten or twelve years of age, and have had seven or eight calves, when they are generally fattened for the butcher. 3~. Climate and season of the year.-Moist and temperate, climates are favourable-to the production of milk in large quantity. In hot countries, and in dry seasons, the quantity is less, but the average quality is richer. Cool weather favours the production of cheese and sugar in the milk, while hot weather increases the yield of butter, [Sprengel, Chemie ffir Landwirthe, ii., p. 620.] In spring the milk is more abundant and of finer flavour. In autumn and winter, other things being equal, it yields less cheese, but a larger return of butter.* Where cattle are fed upon pasture grass only, this observed difference may be derived from a natural difference in the quality of the herbage upon which the cow is fed. 4~. Health and general state of the animal.-It is obvious that the quality of the milk must'be affected by almost every change in the health of the animal. It is sensibly less rich in cream also, as soon as the cow becomes pregnant, and the same is observed to be the case when it shows a tendency to fatten. The poorer the apparent condition of the cow, good food being given, the richer in general is the milk. 5~. Time andfrequency of milking. —f the cow be milked only once a day, the milk will yield a seventh part more butter than an equal quantity of. that which is obtained by two millings in the day. When the milk is drawn three times a day, it is more abundant but still less British Hlusbandry, ii., p. 404. This opinion seems to contradict that of Sprengel in the preceding paragraph. Does this difference arise from the locality and other unlike circum stances in which the observationsiof the two writers were severally made-or are there no accurate experiments upon the subject from which a correct result can be drawn 3 536 INFLUENCE OF THE BREED ON THE QUALITY OF MILK. rich. It is also universally remarked, that the morning's milk is of better quality than that obtained in the'evening. 6~. Period at which it is taken, during the milking. —The milk in the udder of the cow is not uniform in quality. That which is first drawn off is thin and poor, and gives little cream. That which is last drawnthe stroakings, strippings, or afterings —is rich in quality, and yields much cream. Compared with the first milk, the same measure of the last will give at least eight and often sixteen times as much cream (Anderson). The quality of the cream also, and of the milk when skimmed, is much better in the later than in the earlier drawn portions of the milk. 7~. Treatment and moral state of the animal.-A state of comparative repose is favourable to the performance of all the important functions in a healthy animal. Any thing which frets, disturbs, torments, or renders it uneasy, affects these functions, and, among other results, lessens the quantity or changes the quality of the milk. Such is observed to be the case when the cow has been newly deprived of her calf-when she is taken from her companions in the pasture field-when her usual place in the cow-house is changed-when she is kept long in the house after thespring has arrived-when she is hunted in the field or tormented by insects-or when any other circumstance occurs by which irritation or restlessness is caused, either of a'temporary or of a permanent kind. I do not enquire at present into the physiological nature of the changes which ensue-to the dairy farmer it is of importance chiefly to be familiar with the facts. 8~. The race or breed and size of the animal.-The quality of the milk depends much upon the race and size of the cow. As a general rule, small races, or small individuals of the larger races, give the richest milk from the samne kind of food. Thus the small Highland cow gives a richer milk than the Ayrshire. The small Alderneys give a richer cream than any other breed in common use in this country." The small Kerry cow is said to equal the Alderney in this respect, while the small Shetlander has been found in the north of Scotland to give from the same food a more profitable return of rich milk than any of the larger races. A14 these breeds are hardy, and will pick up a subsistence from pastures on which other breeds would starve. The old Yorkshire stock, a cross between the short-horn and the Holderness, is preferred by the London cow-keepers as giving the largest quantity of milk, though poor in quality. The long-horns are preferred in Cheshire and Lancashire because of their producing a greater quantity of cheese. The Ayrshire kyloe, on ordinary pasture, is said to be unrivalled for abundant produce (Ayton) -though the milk is not so rich as that of the small breeds. Various crosses have been tried in different parts of the island-and in almost every district it has been found that the produce of some particular stock is best adapted to the climate, the soil, the natural grasses, the prevailing husbandry, or to the kind of dairy produce which it is the interest of the farmer to raise in his own peculiar neighbourhood. " A very striking illustration of the difference in the quality of the milk of two breeds, in the same circumstances, is given by Mr. Malcolm, in his Compendium of Modern Husbandry. He kept an Alderney and a Suffolk cow, the latter the best he ever saw. During seven years, the milk and butter being kept separate, it was found, year after year, that the value of the Alderney exceeded that of the Suffolk, though the latter gave more than' double the quantity of milk at'a meal.-British Husbandry,.ii., p. 397. EXPERIMENTS WITH DIFFERENT KINDS OP FOOD. 537 In the South of Europe, the Swiss breeds are considered the best for dairy purposes, and of these that of the Canton of Schweitz, which, in size, is internediate between the large cattle of Fribourg and Berne, and the small breed of Hasti. They have enornious udders and give much milk, but like that of the Sufiolk cows it is less rich in butter and cheese. The influence of breed alone upon the quality of the milk is well illustrated by the result of a series of trials made at Bradley Hall, in Derbyshire. During the height of the season, and when fed upon the same pasture, cows of four different breeds gave per dayOr I lb. of butter was Breed, Milk. Butter. yielded by Holderness.. 29 quarts, and 38~ oz. 12 quarts of milk. Alderney.... 19 " 25 " 12 " Devon... 17 " 28 94 Ayrshire... 20 " 34 " 92 The Ayrshire cows gave the richest milk and a larger quantity of both milk and butter than the Alderneys or Devons, but the Holderness breed surpassed them all. It gave i lb. more butter than the Ayrshire, and nearly one-half more milk. It would appear, therefore, to be admirably adapted to the purposes of the town dairyman, whose profit arises from milk and cream only. It does not appear what is the relative value of this breed in the production of cheese.. 9~. The kind of food. —But the kind of food has probably more influence upon the quality of the milk than any other circumstance. It is familiar to every dairy farmer that the taste and colour of his milk and cream are affected by the plants on which his cows feed, and by the food he gives them in the stall. The taste of the wild onion and of the turnip, when eaten by the cow, are often perceptible both in the niilk and in the butter. If madder be given to cows the milk is red, if they eat saffron it becomes yellow. It has also been observed from the most remote times, that when fed upon one pasture a cow will yield more cheese, upon another more butter. From this has arisen the practice more or less observed in all dairy districts of varying the food of the cattle-of giving some artificial food in addition to that obtained in the natural pastures-of leaving the animal at liberty to roam over wide pastures and thus to seek out for itself, as the sheep does on extensive sheep-walks, those different kinds of herbage which are necessary to the production of a rich and valuable milk-or in more inclosed districts, and where different soils exist on the same farm, of turning them during the former part of the day into one field, anddduring the latter part into another. Various sets of experiments have been made with the view of determining the relative quantities of butter and cheese produced by the same animals, when fed upon different kinds of food. Much, however, remains yet to be done both by the practical dairy farmer and by the analytical chemist, before this subject can be fully cleared up. According to theory, as I shall more fully explain in my next lecture, the leguminous plants-clover, tares, &c., and the cultivated seeds of such plants — peas and beans, ought to promote the production of cheese; while oilcake, oats, and other kinds of food which contain much oily matter, ought to favour the yield of butter. The most recent experiments we possess, however, do not lend any decided confirmation to these theoreti 538 EXPERIMENTS WITH DIFFERENT KINDS OF FOOD. cal views. The most extensive series of trials lately published is that of Boussingault, [Annales de Chim. et de Phys., lxxi., p. 79,1 from which I select the following:FIRST SERIES MADE ON A FRENCH COW. Days after Kind of food. Quarts Composition of the milk per cent. Daysafr Kind of food. of,-_ —calving, milk. Casein. Butter. Sugar. Salts. Water. 200 Hay... 5 3-0 4-5 4-7 0-1 87-7 207 Turnips... 5 30 4-2 5-0 0-2 87-6 215 Beet. 5 3-4 4-0 5-3 02 87-1 229 Potatoes... 4 4 3-4 40 -59 0-2 86-5 302 Hay and oil-cake 2t 3-4 3-6 6-0 0'2 86-8 SECOND SERIES MADE ON A SWISS COW. 176 Potatoes and hay 8- 3-3 4-8 5-1 0-3 86-5 182 Hay and clover 77 4-0 4-5 4-0 0-3 87-2 193 Clover... 88 40 2-2 4-7 0-3 88-8 204' Do. in flower. 6 3-7 3-5 52 0-2 874 In the first series of experiments the proportion of cheesy matter and of sugar was greatest when beets, potatoes, and oil-cake were given, while the largest proportion of butter was obtained from the use of hay and the least from oil-cake. In the second series the proportion both of cheese and of butter-decreased by the use of clover, while the quantity of milk was not permanently increased. These two series of experiments may appear to be deserving of less reliance because they were not made on successive days, but at varying intervals of time. But some recent experiments, made in Lancashire by Dr. Playfair, are little more satisfactory.- These were made upon.a short-horned cow, which was fed one day in the field on after-grass, and during the four succeeding days in the stall, upon weighed quantities of different kinds of food. [Memoirs of the Chemical Society, i., p. 174.] Composition of the milk. Day's Food. Qts. - Casein. Butter. Sugar. Salts. Water.. 10. After-gra-ss \. 5. Evening's milk.. 4 5-4 3-7 38- 06 86-5.Morning's do.. 4 39 5 6 3-0 0-5 870 2~. 28 Ibs. Hay........ Evening's do.. 3 49 5-1 3-8 05 85-7 2 lbs. Oatmeal..... Morning's do.. 4 54 3 9 4-8 05 854 30. 28 lbs. Hay........Eve o^i'bl-^tmeal-'- Evening do~ 4 - 2 lbs., Oatmeal.... ing's do 4 SbsBean Flour. Morning's da 3-9 4-6 45 0-7 86-3 40. 241bs. Potatoes... Evening's do.. 5 39 6 7 4-6 0'6 84-2 1 lbs Bn Four. Morning's do. 4 2-7 4-9 5-0 0-5 86'9 8 lbs. Bean Flour.; 50. 14 lbs. Hay....... Eveing's do..:5 3-9 4-6 3'9 0-5 87-1 30 lbs. Potatoes... Morning's do.. 44 3'5 4-9 3'8: 0-5 87-3 In these experiments there appears an increase in the proportion of butter and sugar, and in the quantity of milk on the fourth day, when the potatoes, hay, and bean flour were given together. On the fifth, when potatoes and hay only were given, the quantity of milk went on increasing, but it was poorer in quality. Could we infer any thing, then, from a single day's trial, it would be that the bean meal had aided in the production of butter and sugar —istead of cheese, as theory would indicate -while the steamed potatoes had added to the quantity of the milk. But no sensible results can justly be expected in regard to the influence INFLUENCE OF THE STATE OF PREGNANCY. 539 of this or that food, except by a much more prolonged series of careful observations. If we compare the quantity of albumen and casein contained in the food, with that yielded in the milk during the four days' experiments of Dr. Playfair, we shall find no perceptible relation between the two quantities. Thus, the cow on theAlbumen Of Casein 2d day eat 2- lbs., and yielded 0'93 lbs. 3d " 5 " " 1'0 " 4th " 4 " " 0 75 " 5th " 1-7 "'; 0-94 " So that, whether, as on the third day double the quantity was eaten, or, as on the fifth, little more than half as much as was consumed on the second day, the produce of cheesy matter in the milk was sensibly the same, on each of the three days. \We must not, however, from these, experiments, infer that the kind of food really has no influence upon the quality of the milk-for this conclusion is contradicted by general experience. We must wait rather for renewed and more extended practical researches, by which both our theory and practice may probably be amended, and by which the conclusions may be reconciled to which they respectively lead us. [See the following Lecture " On the feeding of stock."] 10~. State of pregnancy. — have already stated (p. 535), that the richness in cream diminishes as soon as thp cow becomes pregnant. The same is no doubt true also of the amount of cheese which the same volume of milk will be capable of yielding. It must become poorer in every respect, or else considerably less in quantity (p. 541), as soon as the cow is with calf, since a portion of the food which might otherwise have been employed in the production of milk, must now be directed to the nourishment of the young animal in the womb of the mother. In the experiments to which I have just directed your attention in regard to the effect of the kind of food upon the quality of the mill, the state of pregnancy of the animal was not taken into consideration, though, as I have already said, this must necessarily exercise an important influence upon the quality of the itilk, whatever be the kind of food upon which the animal may have been fed.. To this the want of, accordance between theory and experiment is probably in part to be ascribed. 11~.'Individual form and constitution of the animal.-But it is well known that animals of the same breed, fed on the same food, will yield milk not only in different quantities, but also of very different quality. In regard to the form, Mr. Youatt states that the " Milch cow should have a long thin head, with a brisk but placid eye,-should be thin and hollow in the neck, narrow in the breast and point of the shoulder, and altogether light in the forequarter-but wide in the loins, with little dewlap, and neither too full fleshed along the chine, nor shewing in any part an inclination to pit on much- fat. The udder should especially be large, round, and full, with the milk veins protruding, yet thin skinned, but not hangring loose or tending far behind. The teats should also stand square, all pointing out at equal distances and of the same size, and alBoth of the cows experimented upon'by Boussingault were with calf, Dr Piayfair does not mention whether his was so or not. 540 EFFECT OF INDIVIDUAL FORM AND CONSTITUTION. though neither very large nor thick towards the udder, yet long and tapering towards a point. A cow with a large head, a high backbone, a small udder and teats, and drawn up in the belly, will, beyond all doubt, be found a bad milker." [Youatt's Cattle, p. 244, quoted in British Husbandry, ii., p. 397.], Thus, while much depends upon the breed, the form of the individual also has much influence upon its value as a milker. But independent of form, the quality of the milk is greatly affected by the individual constitution of every cow we feed. Thus in a report of the produce of butter yielded by each cow of a drove of 22, chiefly of the Ayrshire breed-all of which we may presume to have been selected for dairy purposes with equal regard to their forms-and which were all fed upon the same pastures in Lanarkshire, the yield of milk and butter by four of the cows in the same week is given as follows:Milk. Butter.. A yielded.. 84 quarts, which gave... 31 lbs. F and R each..86 " " ".... 5 lbs. G yielded... 88' " ".....7 lbs.* Showing that, though the breed, the food, and the yield of milk was nearly the same, the cow G produced twice as much butter as the cow A-or its milk was twice as rich. This result would have been still more interesting had we known the relative quantities of grass consumed by these two cows respectively. I will not insist upon other causes by which the quality of the milk is more or less materially affected. It is said that when stall fed the same cow will yield more butter than when pastured in the field-that the age of the pasture. also influences the yield of butter-ani that salt mingled with the food improves both the quantity and the quality of the milk There are, probably, few circumstances which are capable in any way of affecting the comfort of the animal which will not also modify tile quality of the milk it yields. ~ 3. Of the circumstances which affect the quantity of the milk. The epithet good-m-ilUer applied to a cow has very different significations in different districts and countries. Thus the experiments of Boussingault upon the effect of different kinds of f6od on the quality of the milk (p. 538) were made upon a French cow which was considered a good milker, and yet when in best condition never gave more than 7.1 quarts a day. Two, or even two and a half, times that quantity is not considered extraordinary in the height of the season in many parts of our island. There are three circumstances which principally affect the quantity of milk-namely, the breed, the kind of food or pasture, and the distance from the time of calving. 1~. The breed.-The smaller breeds of cattle yield, as is to be expected, a smaller daily produce of milk-though from the same weight of food they occasionally give even a greater volume of milk than the larger breeds. Good ordinary cows in this country yield, on an average, from 8 to 12 Prize Essays of the Highland Society, New Series, ii., p. 258. CIRCUMSTANCES AFFECT THE QUANTITY OF MILK. 541 quarts a day. The county surveys state the average daily produce 3f dairy cows to be, inDevonshire... 12 qts. Lancashire... 8 to 9 qts. Cheshire.... 8 " A.yrshire... 8 " But the best Ayrshire kyloes will yield an average of 12- quarts daily, during 10 months of the year (Ayton). The yearly produce of the best Ayrshire kyloes is stated by Mr. Ayton at......... 4000 qts Of average Ayrshire stock...... 2400 " Good short-horns, grazed in summer, and fed on hay and turnips in winter (Dickson)..... 4000' Mixed breeds in Lancashire (Dicson).... 3500 Large dairy of mixed long and short-horns, at Workington Hall, taking an average of 4 years (Mr. Curwen).. 3700" Crossed breeds in many localities are found more productive in milk than pure stock of any of the native races of cattle. 2~. Food and pasture. —In the same animal the quantity of milk is known to be greatly influenced by the kind of food. This is best understood in the neighbourhood of large towns where the profit of the dairyman is dependent upon the quantity* rather than upon the quality of his milk. Hence the value of highly succulent fbods-of the grass of irrigated meadows-of mashed and steamed food-of brewers' grains —of turnips, potatoes and beets-and of other similar vegetableproductions which contain much water intimately mixed with nutritive matter, and thus tend both to aid in the production of milk and to increase its quantity. 3~. Distance from the time of calving.-It is a well-known fact that cows in general after the first two months from the time of calving, though fed upon the sane food in equal quantity, begin gradually to give less milk, till at the end of about 10 months they become altogether, or nearly, dry. In the best Ayrshire kyloes, the rate of this decrease is thus represented by Mr. Ayton: First fifty days, 24 qts. per day,-or in all, 1200 qts. Second do. 20.' " " 1000" Third do. 14 " 700 Fourth do. 8 L" "' 400" Fifth do. 8 " " " 400 Sixth do. 6 " " " 300" Some cows indeed do not run dry throughout the whole year, but these may be considered as exceptions-to the general rule. By feeding them upon brewer's grains, mashes, and succulent grass, the milk-sellers near our large towns occasionally keep the same cow in profitable milking condition for three years and upwards.t Such cows are generally fattened after they have become dry-indeed as they cease to give milk, they generally lay on fat in its stead-and, as soon as they are considered ripe, are sold off to the butcher. It is quoted, even by foreign writers, as a fair joke against the dairy establishments of our large towns, that among the advantages possessed by one which was advertised for sale, much stress was laid upon a never-failing pump.-See I latte e i suoi prodotti; p. 67. t Even on shipboard I have heard of a cow being kept in milk during the whole of a three years' cruise-the food being principally a kind of pease soup. After the first year, how. ever, the milk is said to become thinner and more watery. 23" 542 MODE OF SEPARATING THE CONSTITUENTS OF MILE. ~ 4. Of the mode of separating-and estimating the several constituents of milk. 1~. If a weighed quantity of milk be allowed to stand for-a sufficient length of time, the cream will rise to the top, and may be easily skimmed off. If this cream be'gently heated the butter in an oily fo6rm will collect upon the surface, and when cold may be separated from the water beneath, and its weight determined. 2~. If the skimmed milk be gently -warmed, and a little vinegar or rennet then added to it, the curd will separate, and may be collected in a cloth, pressed, dried, and weighed. 30. If a second equal portion of tlke milk be weighed and then evaporated to dryness by a gentle heat and again weighed, the loss will be the quantity of water which the milk contained. 4~. If now the dried milk be burned in the air till all the combustible matter disappears, and the residue be weighed, the-quantity of inorganic saline matter will be determined. 5~. Supposing those processes to be performed with tolerable accuracy, the difference between thes sum of the weight of the water, butter, curd, and ash, and the weight of the milk employed, will nearly represent that of the sugar contained in the given quantity of milk. For many purposes a rude examination of milk after this manner may be sufficient, but where any thing like an accurate analysis is required, more refined methods must be adopted. In such cases, the following appears to be the best which has hitherto been recommended. [Haidlen, Annal. der Chem. & Phar., xlv., p. 263.]. a., The butter. —The weighed quantity of milk is mixed with onesixth of its weight of common unburnt gypsum previously reduced to a very fine powder. The whole is then evaporated to dryness with frequent stirring at the heat of boiling water (21o2 F.) A brittle mass is obtained, which is reduced to fine powder. By digesting this powder in ether, the whole of the butter is dissolved out, and' by evaporating the ether, may be obtained in a pure state and weighed. Or'the powder itself, after being, treated with ether, may be dried and weighed. The butter is then estimated by the loss. 6. The sugar.-Afterthe removal of the butter, alcohol is poured upon the powder and digested, with it. This takes up the sugar with a little saline matter soluble in alcohol. By evaporating this solution and weighing the dry residue, the quantity of sugar is determined. Or, as before, the powder itself may be dried and weighed and the sugar estimated by the loss. If we wish to estimate the small quantity of inorganic saline matter which- has been taken up along with the sugar, it maybe done by burning the latter in the air, and weighing the residue. c. The saline matter.-A second weighed portion of milk is now evaporated'carefully to dryness and again weighed. The loss is the water. The dried milk is then burned in the air. The weight of the incombustible ash indicates the proportion of inorganic saline matter contained in the milk. d. The casein.-The weight of the butter, sugar, saline matter and water being thus known and added together, the deficiency is the weight of the casein. PROPERTIES OF THE SUGAR OF MILK. 543 ~ 5. Of the sugar of miilk, and of the acid of-milk or lactic acid. Before I can hope to make you understand the nature of the changes which take place during the souring, the churning, and the curdling of milk, it will be necessary to make you acquainted with the sugar of milk, and with lactic acid or the acid of milk. 1~. Sugar of milk.-When the curd is separated from milk, the raw whey afterwards boiled-with or without the addition of new and butter milk-and the floating churd slimmed off or separated by straining throuh aa cloth,,the whey is obtained nearly free from butter and cheese. By mixing it while hot with well beat white of egg,' the remainder of the curd is coagulated, and may be removed by again straining through cloth. If the clear whey, thus obtained, be boiled down in a pan to one fourth of its bulk, then poured into an earthen dish, and set aside for a few days in a cool place, minute hard white crystals gradually deposit themselves upon the sides and bottom of the vessel. These crystals are sugar of milk. A second portion may be obtained by evaporating the remaining whey still further, and again setting aside. If the whey be at once evaporated to dryness a white mass of impure sugar is-prepared, which in many places is used as an article of food. Of the purer variety large quantities are extracted from milk by the Swiss shepherds, and in their country it forms an important article of commerce. The sugar of milk is less sweet than that of the grape, or of the sugar cane. - It is harder also, and much less soluble in water, and is gritty between the teeth. This sugar. undergoes no change when exposed to the air, either in the dry state or when dissolved in water. But'if a little of the curd of milk (casein) be introduced into the solution it gradually becomes sour, lactic acid is formed, and the liquid begins to ferment. Carbonic acid is given off-as is the case during, the fermentation of other'liquids-and alcohol is produced. In-milk the two substances are naturally intermixed, and it is the presence of the cheesy matter, as we shall hereafter see, which at favourable temperatures always causes milk of every kind first-to become sour and then to ferment. The gluten of wheat and animal membranes of various kinds produce a,similar effect upon solutions of sugar of milk. A piece of bladder, or of the gut or stomach of an animal, immersed into a solution of the sugar, changes it by degrees into lactic acid, and upon this influence depends the effect of the calf's stomach, in the form of rennet, in the curdling of milk. The effect of such membranes is more speedy after they have been some time taken from the body of the animal, a fact which also accords with the long experience of the dairy districts in the preparation of rennet. When a little sulphuric or muriatic acid is added to a solution of milk sugar, it is slowly converted into grape sugar. This change is hastened very much by boiling it with the acid. It is supposed that previous to the fermentation of milk the sugar it contains undergoes a similar change into the sugar of grapes. Milk sugar has not hitherto been formed by art. It exists in the milk of all mammiferous animals, and from this source alone have we hitherto been able to obtain it. 2~. The acid of milk —lactic acid.-When milk is exposed to the air for a length of time it acquires a sour taste, which gradually increasesin 54L4 THEI ACID OF MILK, OR LACTIC ACID. intensity till at length the whole begins to ferment. This sour taste is owing to the production of a peculiar acid, to which the name of acid of milk or lactic acid has been given. The same acid is formed during the fermentation of the juices of the beet, and of the turnip, in sour cabbage (sauer criaut), and sour malt, in brewers' grains which have become sour, in the sour vegetable mixtures with Twhich cattle are often fed, in the waste liquor of the tanners, in the fermented extract of rice, and in large quantity during the fermentation of the gluten in the manufa6ture of starch from wheaten flour, or of a mixture of oat-meal or beanmeal with water, which is allowed to stand and beconle sour. The acid, therefore, differs from the sugar of milk in so far that it can readily be formed, and in any quantity, by artificial means. As it is not'emrployed for any economical purposes, I shall not trouble you with the methods, by which this acid is obtained in a state of purity. It is rarely found in milk when first dirawn from the cow, but it very soon begins to be formed in it. It is produced fiom the sugar, through the influence of the cheesy matter of the milk. The pure acid may be mixed with cold milk without causing it to curdle, but if the mixture be heated, the curd forms and speedily separates. It is for the same reason that milk may be distinctly sour to the taste, and yet may not coagulate, But if such milk be heated it will curdle immuediately.. So cream when sour may not appear so, till it is poured into hot tea, when it will break and leave its cheesy matter floating on the surface. ~ 6. Of the mutual relations which exist between lactic acid and the cane,. grape, and milk sugars. It is important, and I think it will prove interesting to you, to understand the beautifully simple relation which exists between the sugar of milk and this lactic acid, which plays so important a part in nearly all your daily operations. Cane sugar, grape sugar, milk sugar, and lactic acid, as they exist in solution in water or in milk, may all be represented as compounds of carbon with water-or of carbon with hydrogen and oxygen in the proportions in which they exist in water. Thus they consist respectively of12-Carbon +-12 Water Cane sugar... 12C + 12H - 120 or 12C +- 121-HO 12 Carbon + 14 Water Grape sugar. 12C -- 14H -F 140 or 12C + 14HO 24 Carbon + 24 Water Milk sugar... 24C +- 24H + 240 or 24C + 24HO 6 Carbon + 6 Water Lactic acid... 6C + 6H + 60 or 6C + 6HO 4 Carbon + 3 Water Acetic acid (vinegar) 4C + 3H +- 30 or 4C + 3HO I have added acetic acid to this list, to show you that the lactic acid bears a similar relation to the sugars as this acid does, You will recollect that starch, gum, and woody fibre, have also a similar relation to the sugars-and that by certain apparently simple transformations these C, H, and 0, as in our former lectures, representing respectively carbon, hydrosen, and gJygea, and HO vater-a compound of hydrogen with oxygen, CHANGE OF MILl SUGAR INTO LACTIC ACID. 545 several substances are capable of being converted into grape sugar. In like manner all these sugars by a similar simple transformation are readily converted into one or other of the two acids above named. Starch, gum, and woody fibre in favourable circumstances are transformed intc sugar, (see Lecture VI., p. Ill)-the sugars, in favourable circumstances, are further transformed into the lactic or the acetic acids. We have seen that animal membranes or the curd of milk have the property of cha nging these sugars into lactic acid. This they do, though excluded from the action of the air,, and without the escape of any gas. The above formula show with what apparent simplicity this may be accomplished. In fact, cane sugar, milk sugar, and lactic acid, as above represented, consist of the same elements united together in the same proportions. It is easy to conceive therefore in what way the one may be transformed into the other. 1~. Two of lactic acid are represented by 12C - 12H +- 120, which is the formula for cane sugar. The transforming action of the, animal membrane, or of the casein in its state of incipient decay, is therefore simply to cause the elements of the sugar to assume a new arrangement -in which instead of cane sugar they form a substance having the very different properties of lactic acid. 2~. Again, milk sugar is represented by 24C + 24H + 240, and 4 of lactic acid are also equal to 24C + 24H 1 + 240; the change which takes place when milk becomes sour, therefore, is easily understood Under the influence of the casein the elements of a portion of the milk sugar are made to assume a new arrangement, and the sour lactic acid is the result. There is no loss of matter, no new elements are called into play, nothing is absorbed from the air or given off into it-but a simple transposition of the elements of the sugar takes place, andthe new acid compound is produced. These changes appear very simple, and yet how difficult it is to conceive by what mysterious influence the mere contact of this decaying membrane or of the casein of the milk, can cause the elements of the sugar to break up their old connexion, and to arrange themselves anew in another prescribed order, so as to form a compound endowed with properties' so very different as those of lactic acid. It is beautiful to see the simple means by which in nature so many important ends are accomplished-to observe how they are all veiled to the uni.nstructed-and how every slight accession to our knowledge opens up new wonders to us even in those ordinary operations with which during our whole lives we have been most familiar. From these intellectual, in addition to other rewards, which constantly follow the study of nature, you will with me draw the conclusion — which is ever pressing itself upon our attention-that it is the will and intention of the Deity, that all his works shall be thoroughly studied and investigated. But you will, I think, agree with me in drawing this conclusion, because of the further and higher moral effect also which such investigations tend to produce upon the mind. Every fresh discovery, as it opens up new fields of knowledge, forces upon us more distinctly the sense of our own ignorance. In the case before us we are delighted by,the apparent simplicity which the several transformations of starch intc 546 SOURING AND PRESERVING OF MILK. sugar, and of the latter into lactic acid, may be brought about, and seem almost to understand how it is done, since it can be effected by a simple transposition of their elements. But the after-thought occurs-by what kind of power is this change effected? The materials are certainly present, but how are they made to shift their relative positions, and move into their new places? We have conquered one intellectual difficulty only to encounter another apparently still harder to overcome. It was said first, I believe by Priestley, [Experiments and Observations, ii., p. ix., edition 1781,] "that the greater the circle of light, the greater is the boundary of darkness by which it is confined." Thus they who know the most are the'most strongly impressed with the sense of their own want of knowledge. What a fine result this is of large acquirements! And how touchingly it was expressed by Sir Isaac Newton, when.he likened his great discoveries; to the gathering of a few pebbles along the sea-shore-the vast ocean of natural knowledge lying-still unexplored before him! ~ 7. Of the souring and preserving of milk. The natural souring of milk requires now little explanation. It arises from the gradual conversion of the sugar into the acid of milk by the action of the caseih. There are, however, one or two circumstances connected with it to which it may be proper to advert. 10. If milk be kept at a low temperature, it may be preserved for several days without becoming sensibly sour. This is effected in Switzerland by immersing the milk vessels in a shallow trough of cool water, which, by means of a running stream, can at any time be renewed. In such circumstances the action of the cheesy matter in converting the sugar into lactic acid is very slow. 2~. But if the milk be kept at the temperature of 65~ or 70~ F. it becomes sour with great rapidity, and if afterwards raised to the boiling point curdles immediately. An easy way of preserving milk or cream sweet for a longer time, or of- removing the sourness when it has already come on, is to add to it a small quantity of the common soda, pearl ash, or magnesia of the shops. Enough is added, when a little of the milk poured into boiling water no longer throws up any curd. As the small quantity of soda or magnesia thus added is not unwholesome, cream may in this way-be kept sweet for a considerable time, or may have its sweetness restored when it has already become sour. 3~. I have already observed to you that animal membrane, the curd of milk, or any of those substances which possess the power of changing sugar into lactic acid, loose that power if the solution in which they are present be raised to the boiling temperature. Hence if milk be introduced into bottles, be then well corked, put into a panwith cold water, and gradually raised to the boiling point, and after being allowed to cool be taken out and set away in a cool place, the milk may be preserved perfectly sweet for upwards of half a-year. 1 mentioned also that if the solution containing the sugar and cheesy matter be again exposed to the air after boiling, it will gradually resume the property of transforming the sugar into lactic acid. Hence, if milk be boiled, it is preserved sweet for a longer-period of tim.e, but the casein gradually resumes its transforming property, and at the end of a SEPARATION OF CREAM FROM THE MILK. 547 few days turns it sour. If, however, the milk be -boiled every'morning or every second.morning, the souring property of the casein is at every boiling destroyed again, and the milk may thus be kept fresh for two months or more. 4~. Another mode of preserving milk is to evaporate it to dryness by a gentle heat, and under constant stirring. By this ineans a dry mass is obtained which may be preserved for a length of time, and which when dissolved in water is said to possess all the properties of the most excellent milk.. It is known in Italy by the name of latteina. [I1 latte e i suoi prodotti, p. 19.] ~-8. Of the separation and measurement of cream, the galactometer, the composition of cream, and the preparation of cream-cheese. 1~. Separation of cream.-The fatty part of the milk which exists in the cream, and which forms the butter, is merely mixed with and held in suspension by the water of which the milk chiefly consists. In the udder of the cow it is in some measure separated from, and floats on, lhe surface of the milk, the later drawn portioni being always the richest in cream. During the mnilking, the rich and poor portions are usually mixed intimately together again, and thus the after-separation is rendered slower, more difficult, and less complete. That this is really so, is proved by two facts-first, that if milk be well shaken or stirred, so as to mix its parts intimately together before it is set aside, the cream will be considerably longer in rising to the surface-and second, that more cream is obtained by keeping the milk in separate portions as it is drawn, and setting these aside to throw up their cream in separate vessels, than when the whole milking is mixed together. When the collection of cream, therefore, is the principal object, economy suggests that the first, second, third, and last drawn portions of the milk should be kept apart from each other. Even in large dairies this could easily be effected by having three or four pails, in'one of which the first, in another the second milk, and so on, might be collected. Cream does not readily rise through any considerable depth of milk; it is usual, therefore, to set it aside in broad shallow vessels in which the milk stands at a depth of not more than two or three inches. By this means the cream can be more effectually separated within a given time. But the temperature of the surrounding air materially affects the quantity of cream which milk will yield, or the rapidity with which it rises to the surface and can be separated. Thus it is said that from the same milk an equal quantity of cream may be extracted in a much shorter time during, warm than during cold weather —that, for example, milk may be perfectly creamed in36 hours, when the temperature of the air is 500 F. 24 " " " 55~- F. 18 to 20 hours "4 " 68~ F. 10 to 12 4 4 " 77~ F. -while, at a temperature of 34~0 to 370 F., milk may be kept for three weeks, without throwing up any notable quantity of cream (Sprengel). The reason of this is that the fatty matter of the milk becomes partially solidified in cold weather, and is thus unable to rise to the surface of the milk so readily as it does when in a warm and pemectly fluid state. 548 COMPOSITION OF CREAM. The above remarks apply to milk of ordinary quality and consistency. In very thin tr poor milk, in which little cheesy matter is contained, the cream will rise more quickly. 2~. Measurement of cream —the galactometer.-The richness of milk is very generally estimated by the bulk of cream which rises to its surface in a given time. For the purpose of testing this richness, a simple instrument, dignified.by the learned name of a galactometer (milk-gauge), has been recommended and may often be useful. It consists of a narrow cylindrical vessel or long tube of glass, divided or graduated into 100 equal parts. This vessel is filled up to 100 with tihe milk to be tested, and at the end of 24 or 36 hours, the quantity ofacream which has risen is estimated by the number of degrees of space which it occupies at the top of the milk. If it cover 3 degrees the milk yields 3 per cent., if 7 degrees 7 per cent. of cream. This instrument, however, will give a result which will be generally -less than the truth, because the cream will always rise slowly through 5 or 6 inches of milkthe smallest length which the instrument can conveniently be-and most slowly in the; richest and thickest milk. Unless considerable care be taken, therefore, this milk-gauge may easily lead to erroneous conclusions in regard to the relative degrees of richness of different samples of milk. 3~. Composition of cream.-Cream does not consist wholly of fatty matter (butter), but the globules of fat'as they rise bring up with them a variable proportion of the casein or curd of the milk, and also some of the milk sugar. It is owing to the presence of sugar that cream is capable of becoming sour, while the casein gives it the property of curdling when mixed with acid liquids or with acid fruits. The proportion of cheesy matter present in cream depends upon the richness of the milk and upon the temperature at which the milk is kept during the rising of the cream. In cool weather the fatty matter will bring up with it a larger quantity of -the curd, and form a thicker cream, containing a greater propotaion of cheesy matter. The composition of cream, therefore, is very variable-much more so than that of milkand depends very much -upon the mode in which it is collected. A specimen of cream, examined by Berzelius, which had a density (specific gravity) of 1-0244, consisted of — Butter, separated by agitation....... 4-5 per cent. Cheesy matter, separated by coagulating the buttermilk............ 3-5 " Whey....... 92-0 " 100 Some of the butter remained, as is usually.the case, in the buttermilk, and added a little to the weight of the' curd which was afterwards separated, but the result of this analysis is sufficient to show that cream in general contains a very considerable proportion of cheesy mattersometimes almost as much cheese as butter.*'The clouted cream of Devonshire and other Western counties, as well as the butter prepared from it, probably contains an unusually large quantity of cheese. Itis prepared by straining the warm milk into large shallow pans into which a little water has previously been put, allowing these to stand from 6 to 12 hours, and then carefully heatin, them over a slow fire, or on a hot plate, till the milk approac hes the boiling point. The nIilk, however, must CREAM-'CHEESE AND MASCARPONI. 549 I would remark, however, that this cream examined by Berzelius must have been of an exceedingly poor quality-little richer, indeed, than common milk, since 100 lbs. of it would only have yielded 4~ lbs. of. butter. Cream of good quality in this country, when skilfully churned, will yield about one-fourth of its weight of butter, or one wine gallon of cream, weighing 8 Ilbs., will give nearly 2 lbs of butter.* 4~. Cream-cheese.-You will now readily understand the nature of what is called creaml-cheese-how it differs from ordinary cheese and from butter, and why it so soon becomes first sour, and then rancid. In preparing this cheese the cream in this country is generally, I believe, either tied up in a cloth or put into a shallow cheese vat, and allowed to curdle and drain without any addition. The cheesy matter and butter remain thus intimately intermixed, and it is more or less rich, according as the proportion of butter to the cheesy matter in the cream is greater or less. This cheese becomes soon rancid and unpleasant to the taste, because the moist curd, after a certain length of exposure to the air, not only decomposes and becomes unpleasant of itself, but acquires the property of changing the butter also and of imparting to it a disagreeable taste and smell. In Italy, cream-cheeses, called mascarponi, are made by heating the cream nearly to boiling, and adding a little sour whey as the oily matter begins to separate. The whole then coagulates, and the curd is taken out and set to drain in shapes. As the sour whey is apt to give this cheese an unpleasant flavour or a yellow colour, it is said to be better to take 20 grains of Tartaric acid for each quart of cream, to dissolve it in a little water, and to add this, instead of the sour whey, to the hot cream. The acid runs off in the whey of the cream, and the cheese is colourless and free from foreign flavour. The masca?rponi, like the English cream-cheeses, are covered with leaves or straw, are littled pressed or handled, and must be eaten fresh. ~ 9. Of the separation of butter by churning or otherwise. Milk is a kind of natural emulsion in which the fatty matter exists in the state of very minute globules, suspended in a solution of casein and sugar. Cream is a similar emulsion, differing from milk chiefly in containing a greater number of oily globules and a much smaller proportion of water. In milk and cream' these globules appear to be surrounded wvith a thin white shell or covering, probably of casein, by which they are prevented fronm running into one another, and collecting into larger oily drops. But when cream is heated for a length oftime, these globules, by their lightness, rise to the surface, press nearer to each other, break through not actually boil, nor must the skin of the cream be br'oken. The dishes are now removed into the dairy, and allowed to cool. In summer the cream should be churned on the-ifollowing day-in winter it may stand over two days. The quantity of cream obtained is said to be one-fourth greater by this melhod, and the milk which is left is proportionably poor. When milk on which no cream floats is heated nearly to boiling in the air, apellicle of cheesy matterforms on its surface. Such a pellicle may form in a less degree in the scaldding process of Devonshire, and may thus increase the bulk of the cream. The Corstorphine cream of Mid-Lothian resembles the clouted cream very much, and is made in a very similar way. A series of analyses of cream, collected under different circumstances, might throw some useful light upon the manufacture and preservatior'f butter. 550 OF THE SEPARATION OF BUTTER. their coverings, and unite into a film of melted fat. In like manner, when milk and cream are strongly agitated by any mlechanical means, the temperature is found to rise, the coverings of the globules are broken or separated, and the fatty matter unites into small grains, and finally into lumps, which form our ordinary butter. This union of the globules appears to be greatly promoted by the presence of a small quantity of acid-since in the practice of churning it never takes place until the milk or cream has become somewhat sour. These two facts afford an explanation of the various methods which are in different places adopted for the preparation of butter. 1~. By heating the cream. —When rich cream is heated nearly to boiling, and is kept for some time at that temperature, the butter gradually rises and collects on the surface in the form of a fluid oil. On cooling, this oil becomes solid, and may be readily removed from the water and curd beneath. The fatty matter of the milk is thus obtained in a purer form than when, butter is prepared in the usual way. It may, therefore, be kept for a longer period without salt and without becoming rancid, but it has neither the agreeable flavour nor the consistence of churned butter, and is, therefore, scarcely known in. our climate as an article of food.* The same oily kind of butter may also be obtained by melting the churned butter and pouring off the transparent liquid part which floats upon the top. This is the only form in which sweet butter is known in many parts of Russia. In warm weather it has the consistence of a thick oil, is used instead of oil for many culinary purposes, and is denoted, indeed, by the same Russian word. It may be kept for a considerable time without-salt. 2~. By churning the cream-a. Sour cream.-Cream for the purpose of churning is usually allowed to become sour.. It ought to be at least one day old, but may with advantage be kept several days in cool weather-if it be previously well freed from milk and- be fiequently stirred to keep it from curdling. This sour cream is -put into the churn and worked in the usual way till the butter separates. This is collected into lumps, well beat and squeezed free from the milk, and in some dairies is washed with pure cold. water as long as the water -is rendered milky. -In other localities the butter is not washed, but, after being well beat, is carefully freed from- the remaining milk by repeated squeezings and dryings with a clean cloth. Both methods, no doubt, have their advantages. In the same circumstances the washed butter may'be more easily preserved in the fresh state, while the unwashed butter will probably possess a higher flavour. b. Sweet- cream.-If sweet cream be put into the churn the butter may be obtained, but in most cases it requires more labour and longer time, without, in the opinion of good judges, affbrding in general a finer quality of butter. In all cases the cream becomes sour during the agitation and before the butter begins distinctly to form (see p. 554.) c. Clouted cream.-The churning of the clouted cream of this and other countries forms an exception to the general rule just stated, that more time is required in the churning of sweet creams. Clouted cream It is said, that when melted butter is poured into very cold water, it acquires the consis' tency and appearance of common butter. CHURNING THE WHOLE MILK. 551 may be churned in: the morning after it is made, that is, within 24 hours of the tinme when the milk was taken from the cow-and from such cream it is well known that the butter separates with very great ease. But in this case the heating of the cream has already disposed the oily matter to cohere, an incipient running together of the globules has probably taken place before the cream is removed from the milk, and hence the comparative ease with which the churning is effected. I suppose thereis something peculiar in butter prepared in this way, as it is known in other counties by the name of Bohemian butter. It is said to be very agreeable in flavour, but it must contain more cheesy matter than the butter from ordinary cream. 3~. Churning the whole milk.-Butter m very many districts is prepared from the whole milk. This is a much more laborious methodfrom the difficulty of keeping in motion such large quantities of fluid. It has the advantage, however, it is said, of giving a larger quantity of butter; and in the neighbourhood of the towns in Scotland and Ireland the ready sale obtained for the butter-milk is another inducement for the continuance of the practice. At Rennes, in Brittany, the milk of the previous evening is poured into the churn along with the warm morning's milk, and the mixture is allowed to stand for some hours, when the whole is churned. In this way it is said that a larger quantity of butter is obtained, and of a more delicate flavour. [II latte e i suoi prodotti, p. 112.] In the neighbourhood of Glasgow, according to Mr. Ayton,* the milk -is allowed to stand 6, 12, or 24 hours in the dairy till the whole has cooled, and the cream has risen to the surface. Two or three milkings, still sweet, are then poured, together with their cream, into a large vessel, and are left undisturbed till the whole has become distinctly sour, and is completely coagulated. The proper sourness is indicated by the formation of a stiff' brat upon the surface which has become uneven (Ballantyne). Great care must be taken, however, to keep the brat and curd unbroken until the milk is about to be churned, for if any of the whey be separated the air gains admission to it and to the curd, and fermentation is induced. By this fermentation the quality of the butter may or may not be affected, but that of the butter-milk is almost sure to be injured. In Holland the practice is a little different. The cream is not allow ed to rise to the surface at all, but the milk is stirred two or three times a day, till it gets sour, and so thick that a wooden spoon will stand in it. It is then put into the churn, and the working or the separation of the butter is assisted by the addition of a quantity of cold water. By churning the sour milk in one or other of these ways, the butter is said to be " rich, sound, and well-flavoured." If it be greater in quantity-which appears to be the opinion of those who practise it in this country, in Germany, and in Holland-it' is, according to Sprengel, because the fatty matter carries with it from the milk a larger quantity of casein than it does in most cases from the cream alone (?). ~ 10. Of the composition of butter. Butter prepared by any of the usual methods contains more or less of * In his Daily Husbandry, a work much praised,, and which I regret that I have never seem 552 COMPOSITION OF BUTTER. all the ingredients which exist in milk. It consists, however, essentially of the fat of milk intimately mixed with a more or less considerable proportion of casein and water, and with a small quantity of, sugar of milk. Fresh butter is said to contain about one-sixth of its weight (16 per cent.) of these latter substances, and five-sixths of pure fat (Chevreul). How much of the 16 per cent. usually consists of cheesy matter has not yet been determined.* It is probable, however, that the proportion of cheesy matter contained in butter varies very much. The thickness and richness of the milk — the mode of preparing the butter, whether from the whole milk or from the cream —the way in which the cream is separated from the milk, whether by clouting or otherwise-and the nature of the food and pasture, must all affect in a very considerable degree the relative proportions of the fatty and cheesy matters of which our domestic butter consists. Besides the casein and sugar, butter also usually contains some colouring substance derived from: the plants on which the cow has fed, and some aromatic or other similar ingredients to which its peculiar flavour is owing, and which are also derived from the food on which the animal lives. The fat of butter may be readily separated from all these substances, and obtained in a nearly, pure state. Fresh newly-churned butter is melted in a cylindrical jar at a temperature of 140~ to 180~ F., the fluid oil poured off into water heated to the same temperature, and repeatedly shaken with fresh portions. as long as any thing soluble is taken up. When left at-rest in a warm place, the melted fat rises to the surface in the form of a nearly colourless transparent oil, which, on cooling, hardens into a colourless mass. This pure fat may be preserved for a much longer time without becoming rancid (Thenard). It is the various substances with which its fatty matter is mixed that give to common butter its tendency to become so speedily rancid and to acquire an unpleasant taste. To the numerous precautions which have been adopted with the view of counteracting this tendency, and of preserving the sweet taste of butter, I shall presently direct your attention. ~ 11. Of the average quantity of butter yielded by milk and cream, and of the yearly produce of a cow. 1 have already made you acquainted with some of those numerous circumstances by which the quality of milk is affected. These same circumstances will necessarily more or less affect the quantity of butter also, which a given weight or measure of milk can be made to yield. Thus in the King William's town dairy (County Kerry), the average quantity of milk and butter yielded by the Kerry and Ayrshire breeds respectively was, in a whole yearAyrshire cow, 1328 quarts, of which 9~ to 9j- quarts gave 1 lb. of butter. *Since the above was written, two samples of fresh butter, from cream, examined in my laboratory, have yielded only 0-6 and 0'7 per cent. respectively of cheesy matter. Thisis certainly a much smaller quantity than I had expected. Does butter from the whole milk contain more I A series of such examinations would prove not uninteresting. QUANTITY OF BUTTER YIELDED BY MILK. 553 Kerry-cow, 1264 quarts, of which from 8 quarts to 8- gave 1 11). of butter. Showing, as I have before stated, (p. 536), that the small Kerry cow, upon the same pasture, will give a richer milk even than the Ayrshire. In Holstein and Lunenburg again, it is considered, on an average, that 15 quarts of milk will yield 1'lb. of butter. -The milk in that country, therefore, must be very much poorer in butter. [Journal of the Royal Agricultural Society, I. p. 386.] The result of numerous trials, however, made upon the milk and cream of cows considered as good butter-givers, in this country, has established the following average relation between milk, cream, and butter:Milk. Cream. Butter. 18 to 21 lbs. ( 4 lbs. 9 to 11 qts. 2or 1 lb. The cow, therefore, that yields 3000 quarts of milk should produce, -where butter is the principal object of the farmer, about 300 lbs. of butter, or 1 lb. a day for 300 days in the year. This is not a large daily produce, since some cows have been known to give for a limited time as much as two or even three pounds of butter in a single day. It is a large quantity however, taken as the average of a lengthened period of time, and hence such cases as that of Mr. Cramp's cow, which for four years continuously yielded nearly a pound and a half of buttert every day, are naturally quoted as extraordinary. In most districts the average of the whole year is much less than a pound a day, even for ten months only. In Devon, for the first twenty weeks after calving, a good cow will yield 12 quarts of milk a-day, from which, by the method of scalding, a pound and a quarter of butter can be extracted. In South Holland, [Loudon's Encyclopmedia,] a good cow will produce during the summer months about 76 Ibs. of butter. In the high pastures of Scaria in Switzerland, a cow will yield during the ninety days of summer about 40 lbs. of butter, or less than half a pound a day. In Holstein and Lunenburg it is considered a fair return if a cow yields 100 lbs. of butter, and even in England, [British Husbandry, 1I., p. 404,] 160 to 180 lbs. is reckoned a fair annual produce for a cow, or from 8 to 9 ounces a day for ten months in the year. ~ 12. Of the circuimstances which affect the quality of butter. It is known that the butter produced in one- district of the country, differs often in quality from that produced in another, even though the same method of manufacture be adopted. In different seasons also the same farm will produce different qualities of butter-thus it is said that cows which are pastured yield the most pleasant butter in May, when the first green fodder comes in-that the finest flavoured is given by cows fed upon spurrey (Sprengel)-that it is generally the hardest when the animal lives upon dry food-and that autumn butter is best for long keeping.' The quarts spoken of in this lecture are old wine quarts, of which 5 make'an irperial gallon. A wine gallon of milk or cream weighs about 8 lbs. 4 oz., an imperial gallon about 10 lbs. 5 oz. About two imperial gallons, therefore, should yield a pound of butter. It gave in four years 2132 Ibs. of butter from 23,559 quarts of milk, or 16 quarts a day, of which 11 quarts gave a pound of butter. 554 FIRST. AND SECOND MILK AND CREAM. These differences may all be ascribed to varieties or natural differences in the pasture or fodder upon which the cow is fed.* The constitution of the animal also is known to- affect the quality of the butter-since there are some animals which with the best food will never give first-rate butter. In all such cases as these, however, the quality of the butter is almost entirely dependent upon that of the milk fron which it is made, so that whatever affects the quality of the milk must influence also that of the butter prepared from it. But as I have already considered the circumstances by which the quality of the milk is principally modified' (p. 534), I shall not further advert to this. subject at present. But from the same milk, and even from the same cream, by different modes of procedure, very different qualities of butter may be obtained. The mode of making or extracting butter, therefore, is highly worthy of your attention. Let us consider a few of the more important circtumstances under which different qualities of blutter may be extracted from the same. quality of milk or cream. 1~. First and second drawn milk.-If the milk be collected in two or three successive portions, as it comes from the cow, we have already seen (p. 536), that the last drawn portion will be much richer than-that which has been taken first.' The cream yielded by it will also be richer, and of a finer and higher flavour. Whether, therefore, the butter be extracted directly from the whole milk, or from the cream, the butter obtained from the three successive portions will differ in quality almost as much as the several portions of milk themselves. A practical application of this fact is made in some of the Highland counties of Scotland, and in other districts, where the calves are allowed to-suck,: or are fed with, the first half of the milk as it comes from the cow-the latter and richest half only being reserved for dairy purposes..This second milk is found to afford an exquisite butter. 2~. First and second cream.-In like manner the first cream that rises upon any milk is always the richest, and gives the finest flavoured butter. The after-creamings are not only poorer in butter, but yield it of a whiter colour and of inferior quality. This fact again is well understood, and has been long practically applied in the neighbourhood of Epping, which is celebrated for the excellence of its butter. The cream of the first. 24 hours is set aside and churned by itself. The second and third creams produce a pale; less pleasant butter, which always- sells for an inferior price. Any admixture of the after-creamings causes a corresponding diminution in the value of the butter produced. To produce the most exquisite butter the cream of the first eight hours only ought to be taken. 3~. Mode of creaming.-The rapidity with which cream rises to the surface, either naturally or when influenced by art, affects the quality of the cream, and consequently that of the butter made from it. In warm weather it rises more quickly than in cold, and more quickly still when the milk is heated, as in the preparation of clouted cream. The butter * The influence of the food given in the stall and of the plants eaten in the pasture, upon the colour and flavour of the butler, is familiar to all practical men. The turnipy taste of the butter in winter-the garlic taste in summer. where the wild onion grows in the pastures -and the alleged effect of raw potatoes-in winter, in giving a rich colour to the butter, are common examples of this kind. TOO RAPID OR CVER-CHURNING. 555 (Bohemian butter) obtained from such cream-from cream thus rapidly brought to the surface-may be expected to differ both in flavour, in consistency, and in composition, frolm that yielded by the cream of the same milk when allowed to rise in the usual manner. 4~. Sourness of the cream.-For the production of the best butter it is necessary that the cream should be sufficiently sour before it is put into the churn. Butter made from sweet cream (.not clouted), is neither good in quality nor large in quantity, and longer time is required in churning. It is an unprofitable method (Ballantyne). 5~. Quickness in churning. —The more quickly milk or cream is churned, the paler, the softer, and the less rich the butter. Cream, according to Mr. Ayton, may be safely churned in an hour and a half, while milk ought to obtain from two to three hours. The churning ought also to be regular, slower in warm weather that the butter may not be soft and white, and quicker in winter that the proper temperature may be kept up. Mir. Blacker has lately introduced into this country a barrel-churn invented by a Mr. Valcourt, which, being placed in a trough of water of the proper temperature, readily imparts the degree of heat required by the milk or cream without the necessity of adding warm water to the milk, and churns the whole in ten or twelve minutes. It is said also to give a larger weight of butter from the same quantity of milk. If the quality be really as good by this quick churning, the alleged inferiority in the quality of butter churned quickly in the colmmon churn can not be due to the mere rapidity of churning alone. 6~. Over-churning.-When the process of churning is continued after the full separation of the butter, it loses its fine yellowish, waxy appearance, and becomes soft and light coloured. The weight of the butter, however, is said to be considerably increased; and hence that in Lancashire over-churning is frequently practised in the manufacture of firsh butter for immediate sale (Dr. Traill.) 7~. Temperature of the milk or cream.-Much also depends upon the temperature of the milk or cream when the churning is commenced. Cream when put into the churn should never be warmer than 53~ to 55~ F. It rises during the churning from 4~ to 10~ F. above its original temperature. When the whole milk is churned, tne temperature should be raised to 65~ F., which is best done by pouring in hot water into the churn while the milk is kept in vmotion.* The importance of attending to the temperature and to the quickness of churning, when the best quality of butter is required, is shown by the two following series of results obtained in the churning of cream at different temperatures and with different degrees of rapidity. The first series was obtained in the August ar;d September of 1823, by Dr. Barclay and Mr. Allan. The quantity of cream churned in each experiment was 15 wine gallons, weighing frorrm 8 lbs. to 8{ lbs. per gallon. Ballantyne, Transactiorisof the Highland Society, New Series, I., p. 24. Some object to thismethod of adding hot water,saying that it renders the butter pale and less valuable in the market. This is by no means universally the case, and the keeping the milk in motion, while the water is added, may possibly, in some cases, make the difference. In other cases. may be owing to natural differences in the quality of the milks operated upon. 556 TEMPERATURE OF THE MILK OR CREAM. Temperature. Quantity of Time in Butter No. Begin- End Churning. per gallon. Quality of the Butter. nimig. Hours. lb. oz. 1 50~ 60~ 4 1 15T Very best, rich, firm, well tasted. 2 55~ 65~ 3N 1 151 Not sensibly superior to the former. 3 58~ 67~ 3 1 14 Good, but softer. 4. 60~ 68~ 3 1 121 Soft and spongy. 5 -66~ 750 21 1 10l Inferior in every respect. The results of these experiments prescribe the temperature of 50 to 55~ F. for.the cream when put into the churn, and from 32 to 4 hours as the most eligible for producing butter, both in the largest quantity and of the finest quality. Something, however, appears to depend upon the quality of the cream; since the indications of the next series of experiments differ considerably from the above, in so far at least as regards the length of time expended in churning. The following experiments were made in Edinburgh, by Mr. Ballan. tyne, between June and August, 1825. The quantity of cream he used at each churning was 8 wine gallons-weighing 8'lbs. to the gallon, extcept hat of the fourth experiment, which weighed 4 ounces less. Temperature. Time in Quantity of., C —-------- Churn- Butter No. Of the When but- ing. per gallon. Quality of the butter. cream. ter came. Hours. lbs. oz. 1 56~F. 60~F. 11 2 1 Inferior; white and softer than No. 2. 2 52~ 560 - 2 0? The flavour and quality of these two 3 52~ 56 2 2 0 butters could not be surpassed. 4 65~ 67~ 1 15 Soft, white,\and milky. 5 50~ 531O 3 1 151 Good-evidently injured by long churning. 6 531~ 5710 1 2 03 Most excellent. High in flavour and colour, and solid as wax. To obtain butter from cream, therefore, both finest in quality and largest in quantity, these two series of experiments prescribe the following temperatures of the cream, and times in the churningTemperature. Time. First.. 50 to 55~ 31 to 4 hours Second.. 53~ 1 to 1a " In the temperature both agree. It is probable that the nature of the cream obtained at different seasons or in different localities may render a longer time necessary in the churning on some occasions or in some places than in others. It is certain that the sourer the cream, the sooner generally will the butter come.* 8~. Churning the entire milk.-It is in connection with the temperature at which milk and cream. may respectively be best and most economically churned, that the chances of obtaining a butter of good quality at every season of the year appear to be greater when the whole milk is used' than when the cream only is put into the churn. Cream, when the churning commences, should not be warmer than 55,F.-.-milkoughtto be raised to 65~ F. In winter, either of these temperatures-may be easily attained. In cold weather it is often necessary In sweet cream, when the butter is long in coming, the addition of a little vinegar, brandy, or whiskey, will hasten the churning. ADVANTAGE OF CHURNING THE ~WHOLE MILK. 557 to add hot water to the cream to raise it even to 550. But in summer, and especially in hot weather, it is difficult, even in cool and well ordered dairies, to keep the cream down to this comparatively low temperature. Hence if the cream be then churned, a second rate butter, at best, is all that can be obtained. Milk, on the other hand, requires a temperature of 650-ten degrees higher than cream-and therefore neither summer nor winter weather materially affects the ease of churning it. In winter, its temperature is raised by hot water, as that of cream is, and even in summer there can be few days in our climate-where the milk is kept in a well contrived dairy-in which it will not be necessary to add more or less hot water in order to raise the milk to 65~ F. Thus, where the entire milk is churned, the same regular method or- system of churning can be carried on throughout the whole year. No difficulty is to be apprehended from the state of the weather, nor, so long as the quality of the milk remains the same, is there reason to apprehend any change in the quality of the butter. The winter butter and the summer butter may be alike firm, finely fla voured, and rich in colour. The alleged advantages of churning the entire milk rather than the cream may be thus stated:a. The proper temperature can be readily obtained, both ill winter and in sum tmer. b. A hundred gallons of entire milk will give in summer five per cent. morq butter than the cream from the same quantity of milk will give (Ballantyne). c. Butter of the best quality can be obtained without difficulty bpth in winter and in summer. d. No special attention to circumstances or change of method is at any time required. The churning in winter and summer is alike simple and easy. e.. The butter is not only of the best quality while fresh, but is also best for long keeping, when properly cured or salted (Ballantyne). To these advantages it is set off, that except in the neighbourhood of large towns, the butter-milk is of little value-while from the skimmedmilk, a marketable cheese can always be manufactured. But this ought to be no objection, where churning the whole milk would otherwise be preferred, since it is little more difficult to m ake cheese from the sour butter-milk than from the sweet skimmed-milk. To this point I shall direct your attention hereafter. 9~. Cleanliness.-It seems almost unnecessary for me to allude to cleanliness as peculiarly necessary to the manufacture of good butter. But I do so to bring under your notice the fact, that cream is remarkable for the rapidity with which it absorbs and becomes tainted by any unpleasant odours. It is very necessary that the air of the dairy should be sweet, that it should be often renewed, and that it should be open in no direction from which bad odours can come. ~ 13. Of the fatty substances of which butter consists, and of the acid of butter (butyric acid,) and the capric and caproic acids. 1~. Butter-fat.-I have already mentioned to you that if the butter as it is taken from the churn be melted in water of a temperature not ex24 558 THE FATTY SUBSTANCES IN BUTTER. ceeding 180~ F., and be then washed with repeated portions of warm water, a nearly colourless fluid oil is obtained, which, if not transparent, becomes so when filtered through paper, and when cool congeals into a more or less pure white solid fat. If this-fat be put into a linen cloth and be submitted to a strong pressure in a hydraulic or other press at the temperature of 60~ F., a slightly yellow, transparent oil will flow out, and a solid white fat will remain behind in the linen cloth. The solid fat is-known to chemists by the name of margarine. The liquid oil is peculiar to butter, at least it has not hitherto been found in any other substance; it is therefore called the oleine of butter, or simply butter-oil. The pure fat of butter consists almost entirely of these two substances, there being generally present in it only a small quantity of certain fatty acids, which I shall presently introduce to your notice. Thus a specimen of butter made in the month of May gave a fat which was found by Bromeis to consist of about — Margarine.... 68 per cent. Butter oil.... 30 " Butyric, caproic, and capric acids. 2... 2 " 100* But the proportion of the solid and fluid fats in butter varies very much. It is familiar in every dairy that the butter is harder and firmer at one time and with one mode of churning than with another,-and this greater firmness depends mainly upon the presence of the solid fat (margarine) in larger proportion. According to Braconnot, summer butter contains much more of.the butter-oil tlian winter butter does; and he states their relative proportions in these two seasons, in the butter of the Vosges, which he examined, to be as follows:Summer. Winter. Margarine... 40 65 Butter oil... 60 35 100 100 Of course these proportions ire not to be considered as constant. Indeed, the proportion of oil here given for summer butter is much greater than in the butter examined by Bromeis. It is probable, therefore, that the relative proportions of the two fats are affected by climate, by season, by the race, the food, and the constitution of the animal; by the way in which the butter is made, by the manner in which it is kept, and by other circumstances not hitherto investigated. 2~. Margarine.-This solid fat, which exists so largely in butter, is also'the solid ingredient in olive oil, and in goose and human fat. Butter, therefore, appears to be a most natural food forthe hurnan race, since it contains so large a proportion of one of those substances which enter directly into the constitution of the human frame. Margarine is white, hard, and brittle, and melts at 118~ F. In the pure state it may be kept for a length of time without undergoing any sensible change, but in the state of mixture in which it exists in milk and butter it is apt to absorb oxygen from the atmosphere, and to be partially' Annal. der Chem. und Phar., xlii., p. 70. PROPERTIES OF THE SUGAR OF MILK. 559 changed into butter oil, and into one or other of those fatty acids which are present in butter in smaller quantity. 3~. MVargaric acid. —When this fat (Margarine) is introduced into a hot solution of caustic potash, it readily dissolves and forms a soap. If the solution of this soap in water be decomposed by the addition of diluted sulphuric acid a white fatty substance separates, which, after being collected, dried, and dissolved in hot alcohol, crystallizes as the solution cools, in the form of pearly scales. This substance is known by the name of the margaric (or pearly) acid. Margarine consists of this acid in combination with a sweet substance known by the name of glycerine, or oil sugar.* Margaric acid is represented by the formula 34 C + 34 H + 4 0, or C34 H34 04. To this formula it will be necessary in a few minutes to revert. Butter oil.-The liquid fat expressed from butter has the appearance of an oil, sometimes colourless, but often tinged of a yellow colour. It has the taste and smell of butter —mixes readily with alcohol, and becomes solid when cooled down to 32~ F.-the freezing point of water. It dissolves without difficulty in a solution of caustic potash, and forms a soap. Acid of butter-oil —oleic acid of butter.-When the solution of the oil in caustic potash is diluted with much water, and decomposed by the addition of diluted sulphuric acid, an oily substance is separated, which is different from the original oil of butter, possesses acid properties, and is known by the name of the oleic acid of butter. This fatty acid has never hitherto been obtained from any other substance than the oil of butter, and the oil consists of the acid in combination with oil-sugar. You will recollect that margarine consists of margaric acid in combination with the same sugar (p.. 558.) *Such is the apparent composition of the two fatty substances, margarine and butter-oil, inasmuch as when they are dissolved in a solution of caustic potash, and their solutions afterwards decomposed by an acid, they are resolved respectivelyMargarine-into margaric acid and oil-sugar; Butter-oil-into butter oleic acid and oil-sugar. But, for the benefit of my chemical readers (my other readers will please to pass over this note), it is necessary to state1~. That a compound is supposed to exist, consisting of 3 atoms of carbon united to 2 o hydrogen-C3 HI2, to which the name of lipyle is given. 2~. That this radical C3 H2 unites with an atom of oxygen, forming C3 HI2 0, or oxide of lipyle. 3~. That in neutral fatty bodies, such as margarine, this oxide exists in combination with a fatty acid. Thus, for example, thatS l of margarice acid.. = C34 H34 04 Margarine consists of of oxide of lipyle... C3 H2 Forming, together, 1 of margarine............ C37 H36 05 And b tteroil of oleic acid of butter.= C34 1131 05 of of oxide of lipyle. C3 H 0 Forming, together, I of butter-oil............. = C37 1133 06 40. And that when this oxide of lipyle is separated from its combination with the fatty acids it unites with a quantity of water, and forms glycerine or oil-sugar. Thus2 of oxide oflipyle.........=. C6 H4 02 united to 3 of water............ H3 03 give 1 of glycerine (oil-sugar).-. = C H7 05 5~. The above is the view,f Berzelius, but Redtenbacher has recently suggested, [Anna/, der Chem. und Phar., XLVII., p. 141,] that a known substance called acrolein exists in the 650o CHANGE OF MARGARLNE INTO OLEIC ACID. When pure, this oily acid is colourless and transparent, and is remarkable for the rapidi'y with which it absorbs oxygen from the atmosphere, and becomes converted into new chemical compounds. It is represented by the formula 34C + 31H 4- 50, or C34 H31 05. Let us compare this formula with that of the margaric acid: Margaric acid = C34 H34 04 Butter oleic acid... C3 H31 05 Difference...... H3 -O1 or, if 3 of hydrogen be taken from the margaric acid and 1 of oxygen added to it, it will be converted into the oleic acid. Now this may be efftcted by simply supposing one atom of margaric acid to absorb four atoms of oxygen from the atmosphere. Thus1 of margaric acid C34 H34 04 4 of oxygen.. = O 1 of oleicaacid + 3 of water. C34 H34 08, or C34 H31 -05 + 3HO. So that either in the body of the animal, in the milk while it remains in the udder,, or when it is exposed to the air after being drawn from the cow, or even in the churn itself, it may happen that a portion of the margaric acid may absorb oxygen and become changed into the oleic acid. It may also be that this.change, this absorption of oxygen, is promoted by warm and retarded by cold weather, and that thus the butter is rendered generally softer in the summer and harder in the winter season. But these are as yet only conjectures; for, after all, the relative proportions of the soft and hard fat in butter at different times of the year may depend upon natural differences in the herbage at the several seasons, or upon some other causes which have not as yet been in vestigated. 5~. Butyric, capric, and caproic acids.-These substances, as I have already-stated to you, exist in butter only in small quantity-,to the amount of 2 or 3 per cent. To these acids, and especially to the capric and caproic, butter owes its disagreeable smell when it becomes rancid. They do not exist, naturally, to any unpleasant extent in perfectly fresh butter-they are gradually formed in it, however, when fresh butter is exposed to the air. I do not enter into any detail of their properties, or of the mode of extracting them from butter, because these points fats in combination with the fatty acid. This acrolein is represented by C6 H4 02, which is exactly the constitution of 2 of lipyle. So that according to this view the solid fat of butter would consist of2 of margaric acid.... = 68 H68 08 1 of acrolein...... C6 H4 02 2 of margaric acid.. C74 H72 O 0 and, by a like substitution of acrolein for oxide of lipyle, may the constitution of butter-oil be represented. The principal known fact in favour of this view of Redtenbacher is, that when glycerine is distilled with anhydrous phosphoric acid, acrolein is produced. He supposes that the acid takes-the elements of3 atoms of water from glycerine, forming acrolein: since if from1 of glycerine...... CG H7 05 we take 3 of water......... - 3 03 Acrolein remains....= CG H4 02 The conversion of acrolein into glycerine, when it is separated from the fatty acids, is supposed to proceed, as in the case of lipyle, from its combination with the water at the, moment of extrication. Further researches are yet required to clear up this subject. PROPERTIES OF THE CURD OF MILE. 561 are of less interest or importance to you. It is necessary only, to a clear understanding of the kind of changes which take place when butter becomes rancid, that I should exhibit to you the formula by which thesb acid bodies are severally represented:Butyric acid = Cs I1s 04 Caproic acid - Ci2 H9 03 Capric acid C= Cis H14 03 We shall see how these substances are produced from the solid and fluid fats of butter, when we come to treat of the preservation of butter. ~ 14. Of casein or the curd of milk and its properties. The casein or cheesy matter of milk may be obtained nearly pure by the following process:-Heat a quantity of milk which has stood for 5 or 6 hours, as if you intended to prepare clouted cream (p. 548), let it cool,'and separate the cream completely. Add now to the milk a little vinegar and heat it gently. The whole will coagulate, and the curd will separate. Pour off the whey, and wash the curd well by kneading it with repeated portions of water.'When pressed and dried, this will be casein sufficiently pure for ordinary purposes. It may be made still more pure by dissolving it in a weak solution of carbonate of soda, allowing the solution to stand for 12 hours in a shallow vessel, separating any cream that may rise to the surtace, again throwing down the curd by vinegar, washing it frequently, and occasionally boiling it with pure water. By repeating this process-two or three timies, it may be obtained almost entirely free from the fatty and saline matters of the milk. Casein thus prepared reddens vegetable blues, and is therefore a slightly acid substance. It is very sparingly soluble in water-400 lbs. of cold water dissolving only 1 lb. of pure casein (Rochleder). It dissolves readily, however, and in large quantity, in a weak solution of the carbonate of potash or of soda, and to some extent even in lime-water. These solutions are coagulated by the addition of an acid-of sulphuric acid, of vinegar, or of lactic acid-and the curd readily separateson the application of a gentle heat. If a large quantity of acid be added, a portion of the casein is re-dissolved. This property of dissolving in weak alcaline (potash or soda) solutions, satisfactorily explains what takes place during the curdling of milk, as we shall hereafter see (p. 567). The casein of milk is identical in chemical constitution with the fibrin of wheat, the legumin of the pea and bean,* and the albumen of the egg or of vegetable substances. Hence the opinion has naturally arisen among chemists, that the cheesy matter contained in an animal's milk is derived directly, and without change, from the food on which it lives. The probability of this opinion will come naturally under our consideration in the following lecture. (See next lecture, " On the feeding of' stock."') Casein possesses still one property more remarkable than any of its * In page 394 it is stated, on the authority of Dumas, that the legumin of the pea and bean differs in composition from fibrin and album-en. Since that sheet was published, it appears, from the experiments of Rochleder (Annal. der Chem. und Pharm., xlvi., p. 162), that the legumin which Dumas extracted from the almond, analysed, and supposed to be identical with the legumin of the bean and pea, is not so, but is in reality a different substance; an4 that'the legumin of peas does agree in composition with the casein of milk. 562 ACTION OF CASEIN UPON SUGAR. others, and exceedingly interesting to the practical agriculturist. Let me explain this property a little more in detail. ~ 15. Of the relations of casein to the sugars and the fats. 1~. Relation to the sugars. —a. Production, of lactic acid.-I have already adverted (p. 543) to the remarkable property which casein possesses of gradually converting milk or other sugars into lactic acid. If a small quantity cC this substance, either in'the state of fresh curd or in the purer form jus, described, be introduced into a solution of cane-sugar, or of sugar of milk, lactic acid begins very soon to be formed. Thus the casein it contains is the cause of the souring of milk. In like manner it is the casein contained in bean or pea-meal which makes it so soon become sour when mixed with water. b. Production of butyric acid.-But the transforming action of casein doos not end when this change is produced. After a longer time a further alteration is effected by its means. A fermentation commences, during which carbonic acid and pure hydrogen gases are given ofif and butyric acid is produced (Pelouze and Gelis). Let us consider the nature of this new change. Butyric acid is represented by Cs Hs 04; and lactic acid, as we have seen, by C6 H6 06; therefore4 of lactic acid..... C24 H24 024 and 3 of butyric acid... -C G24 H24 012 Difference..... 012 That is to say, that 4 of lactic acid, in order to be converted into 3 of butyric acid, must give off 12 of oxygen. But during the fermentation which accompanies the change no oxygen is given off. The gases which escape are carbonic acid and hydrogen. The oxygen given off by one portion of the lactic acid, therefore, must combine with the elements of another portion, and conv;ert it into these gases. Thus to1I of lactic acid.. C9 H9 09 Add 12 of oxygen.. = 029 of carbo-. 6 of hy- 3 of nic acid drogen water. And we have... C9 H O21 =9 C 02 + 6H + 3 O; or, while 4 atoms of lactic acid are converted into 3 of butyric acid, 12 of lactic acid are at the same time converted into 9 of carbonic acid gas, 6 of hydrogen gas, and 3 of water. The gases escape and cause the fermentation, while the water remains in the solution.* Ihave taken in the text the smallest numbers by which the general change could be represented in the simplest way. According to Pelotuze and Gelis, however, the hydrogen given off is sensibly one-third of the bulk of the carbonic acid when the butyric fermentation is in its vigour. To satisfy this condition, therefore, much higher numbers must be taken; such as the following:20-of lactic acid.. = Co' Hiso0 Ot0 are converted into 15 of butyric acid.... Cl0o Hit0 O60 Giving off....... And these 60 of oxygen decompose 6 of lactic acid, as above described. Thus to6 of lactic..... C H3 6 3636 Add 60 of oxygen.. 060 -.. -6 of carbonic acid + 12 hydrogen + 249 water. And we have.. C36 H36 096 = 36CO2 + 132I + 24HO, where the carbonic acid gas i exactly three times the bulk of the Hydrogen gas produced. OF THE RANCIDITY OF BUTTER. 563 The outyric acid thus- produced is a colourless transparent volatile liquid, which emits a mingled odour of vinegar and of rancid butter. To the production and presence of this acid, therefore, in the milk or cream or in the manufactured butter, the rancidity of this important dairy product is partly to be ascribed. 2~. Relation to the f/atty! bodies.-It is probable that in certain circumstances the.casein of milk is capable of inducing chemical changes in the fatty bodies as well as in the sugars, but this conjecture has not, as yet, been verified by rigorous experimental investigation. 3~. Relation to fats and sugars mixed.-It is known, however, to act upon fatty bodies when.mixed with sugar. Thus, if a small quantity of casein be added to a solution of sugar, lactic acid is produced for a certain length of time, but it ceases to be sensibly formed before the whole of the' sugar is transformed into this acid. If now a quantity of oily matter be added to the mixture, the production of lactic acid will recommence. and may continue till all the sugar is changed. If more sugar be added by degrees, the formation of acid will go on again, and, after a while, will cease. The introduction of a little more oil will again give rise to the production of acid, and, at length, the acid will cease to be formed, while'both sugar and oil are present. The casein originally added has now produced its full effect (Lehmann). It appears, therefore, that in the presence orf sugar, casein is capable of changing or decomposing the fatty bodies also, and of giving birth to oily acids of various kinds. Now, in milk, in cream, and in butter, the casein is mixed' with the sugar of the milk and the fats of the butter, and thus is in a condition for changing at one and the same time both the sugar into lactic or butyric acid, and the butter into other acids of a fatty kind. Among those latter into which the butter-oil is convertible may probably, be reckoned the capric and caproic acids, which are still more unpleasant to the smell and taste than the butyric acid, and which are known. to be present in rancid butter~ 16. Of the rancidity and preservation of butter. rWe are now prepared, in some measure, to understand the changes that take place when butter becomes rancid-and the way in which those substances act which are usually employed for preserving it in a sweet and natural state. 10. When butter becorres rancid, there are two substances which change —the fatty matters and the milk sugar with which they are mixed. There are also two agencies by which these changes are induced-the casein present in butter, and the oxygen of the atmosphere. The quantity of casein or cheesy matter which butter usually contains is very small, but, as we have seen, it is the singular property of this substance to induce chemical changes of a very remarkable kind, upon other compound bodies, even when mixed with them in very minute quantity. 2~. As it cones from the ecow, this substance, casein, produces no change on the sugar or on the fatty matters of the milk. But after a Every chemist is aware, however, that in decompositions of this kind, it is seldom that one single product is obtained alone. Though the above formula, therefore, represents truly how butyric acid may be produced from lactic acid under the circumstances, yet other substances are not unfrequently formed during the actual experiment, by which the result is more or less complicated. 564 INFLUENCE OF THE CHEESY MATTER. short exposure to the air it alters in some degree, and acquires the power of transforming milk sugar into lactic acid. Hence, as we have seen, the milk begins speedily to be6ome sour.- Further changes follow, and, among other substances, butyric acid is formed. In butter the same changes take place. The casein alters the sugal and the fatty matters, producing the butyric and other acids, to which its rancid taste and smell are to be ascribed. In the manufacture of butter, therefore, it is of consequence to free it as completely as possible from the curd and sugar of milk.. This is done in some dairies by kneading and pressing only; in others, by washing with cold water as long as the latter comes off'milky. The washing must be the most effective method, and is very generally recommended for butter that is to be eaten fresh. In some dairies, however, it is carefully abstained from, in the case of butter which is to be salted for long keeping. There are two circumstances which, in the case of butter that is to be kept for a length of time, may render it inexpedient to adopt the method of washing. The water may not be of the purest kind, and thus may be fitted to promote the future decomposition of the butter. Sprengel says that the water ought to contain as little lim-e as possible, because the butter retains the lime and acquires a-bad taste from it. BBut the water mav also contain organic substances in solution-vegetable or animal matters not visible perhaps, yet usually present even in spring water. These the butter is sure to extract, and they mtay materially contribute to its after-decay, and to the difficulty of preserving it from rancidity. Again, the washing with water exposes the particles of the butter to the action of the oxygen of the atmosphere much more than when the butter is merely well squeezed. The effect of this oxygen, in altering either the fatty matters themselves or the small quantity of casein which remains mixed with them, may, no doubt, contribute to render some butters more susceptible of decay. 3~. But the casein, after it, has been a still longer time or more fully exposed to the air, undergoes a second alteration, by which its tendency to transform the substances with which it may be in contact, is considerably increased. It acquires the property also of inducing chemical changes of another kind, and it is not improbable that the more unpleasant smelling capric and caproic acids may be produced during this period of its action. In the preservation of butter, therefore, for a length of time, it is of indispensable necessity that the air should be excluded from it as completely as possible. In butter that is to be salted also, it is obvious that the sooner the salt is applied and the whole packed close, the better and sweeter the butter is likely to remain. 4~. The action of this cheesy matter, and its tendency to decay, are arrested or greatly retarded'by the presence of saturated solutions of certain saline and other substances. Of this kind is common salt, which is most usually employed for the purpose of preserving butter. Saltpetre, also, possesses this property in a less degree, and is said to impart to the butter an agreeable flavour. A syrup or strong solution of sugar will likewise prevent both meat and butter from becoming rancid. Ilike salt HOW TO PURIFY SALT FOR BUTTER. 565 petre, however, it is seldom used alone, but it is not uncommon to employ a mixture of common salt, saltpetre, and sugar, for the preservation of butter. Where the butter has been washed, this admixture of canesugar may supply the place of the milk-sugar which the butter, originally contained, and may impart to it a sweeter taste. The salt should be as pure as possible, as free, at least, from lime and magnesia as it can be obtained, since these substances are apt to give it a bitter or other disagreeable taste..It is easy, however, to purify the common salt of the shops from these impurities by pouring a couple of quarts of boiling water upon a stone or two of salt, stirring the whole well about, now and then, for a couple of hours, and afterwards straining it through a clean cloth. The water which runs through is a saturated solution of salt, and contains all the impurities, but may be used for common culinary purposes or may be mixed with the food of the cattle. The salt which remains on the cloth is free from the soluble salts of lime and magnesia, and may be hung up in the cloth till it is dry enough to be used for mixing with the butter or with cheese. The quantity of salt usually employed is from 2-th to 218th part of the weight of the butter —with which it ought to be well and thoroughly incorporated. The first sensible effect of the salt is to make the butter shrink and diminish in bulk. It becomes more solid and squeezes out a portion of the water-with which part of the salt also flows away. It is not known that the casein actually combines with the salt, nor, if it did, considering the very small quantity of this substance which is present in butter, could much salt be required for this purpose. But the points to attend to in the salting of butter are to take care that all the water which remains in the butter shall be fully saturated with salt-that is to say, shall have dissolved as much as it can possibly take up-and that in no part of the butter shall there be a particle of cheesy matter which is not also'in contact with salt. If you exclude the air, the presence of a saturated solution of salt will not only preserve this cheesy matter from itself undergoing decay, but will render it unable also to induce decay in the sugar and fat which are in contact with it." It is really extraordinary that such rigid precautions should be necessary to prevent the evil influence of half a pound of cheesy matter, or less, in a hundred pounds of butter (p. 551). 5~. Though the curd or casein appears to be the enemy against whose secret machinations the dairy farmer has chiefly to guard, yet the oxygen of the atmosphere is a second agent by which the fatty matters of butter are liable to be brought into a state of decomposition, and the presence of which, therefore, should be excluded as carefully as possible. We have seen that by the action of oxygen the solid margaric acid of butter may be changed into the oleic or liquid acid of butter (p. 560.) Mr. Ballantyne thus describes the method of salting butter practised at his dairy farm of 30 cows, near Edinburgh:-" The butter is drawn warm from the churn, and it is an invariable rule never to wash it or dip it into oate, uwhen intended to be salted. The dairymaid puts it into a clean tub, which is previously well rinsed with cold water, and then works it with cool hands till all the milk is thoroughly squeezed out; Half the allowed quantity of salt is then added, and well mixed up with the buter, and in this state it is allowed to stand till next morning, when it is again wrought ulp, any brine squeezed out, and the remainder of the salt added. It is then packed inlo kits, which, when full, should be well covered up, and placed in-a cool dry store-a small quantity of salt is usually sprinkled on the surface. The proportion of salt used at this dairy is half-a-pound to fourteen pounds of butter."Joursnal of Agriculture, Nezo Series, vol. 1., p. 26. 24* 566 EVIL EFFECT OF THE AIR UPON BUTTER. This is the first stage in the decomposition, which, when once begun, generally spreads or extends with increasing rapidity.* Again, I have also stated that this fluid (oleic) acid of butter absorbs oxygen with great rabidity from the air (p. 560), and changes rapidly into other compounds. This is the second stage, and is succeeded by others, which itis unnecessary to enumerate. To this action of the air is partly to be ascribed that peculiar kind of rancidity, which, without penetrating into the interior of well packed butter, is yet perceptible on its external surface, wherever the air has come in contact with it. A knowledge of this action of the atmosphere, therefore, urges strongly the necessity of closely incorporating and kneading together the butter in the cask or firkin-that no air holes or openings for air be left-that the cask itself be not only water-tight but air-tightand that it should never be finally closed till the butter has shrunk in as far as it is likely to do, and until the vacancies, which may have arisen between the butter and the cask, have been carefully filled up again. ~ 17. Of the-natural and artificial curdling of milk. When milk is left to itself for a certain length of time it becomes sour and curdles. The curd and whey, however, do not readily separate unless a gentle heat be applied, when the curd contracts in bulk, and either squeezes out and floats upon the whey, or, when cut into pieces or placed in a perforated cheese-vat, allows the whey freely to flow from it. If the mixed curd and whey fromt the entire milk be allowed to simmer for a length of time at a slow fire, the buttery part will separate from the cheese, and will float on the top in the form of a fluid oil. 1~. Natural curdling.-The natural curdling of milk is produced by the lactic acid, which, as we have seen (p. 544), is always formed from the milk-sugar when milk-is allowed to stand for any length of time in the air. It does not curdle immediately upon becoming sour, for a reason which I shall presently explain. 2~. Artificial curdling.-But it is not usual in the manufacture of cheese to allow the milk to sour and curdle of its own accord. The process is generally hastened by the artificial addition of acid, or of some substance, such as rennet, by which the natural production of acid is ace celerated. Almost any acid substance will have ihe effect of curdling milk. Muriatic acid (spirit of salt),, diluted with water, is said to be extensively, though not universally, employed in Holland for this purpose. In other countries vinegar, tartaric acid, lemon juice, cream of' I do not know whether a converse change is ever observed in butter by long keeping in contact with brine-whether it ever becomes very sensibly harder.- Tallow, as is well known to candle-makers, and especially to the manufacturers of stearin candles, becomes harder by keeping, indeed sometimes is unfit for use until it is a year old-candles in a damp place become harder by keeping-and in tallow that has lain long in a wet mine the oily part has been found entirely changed into the solid fat of tallow (Beetz)..A similar change, therefore, is not impossible nor inexplicable in butter also-only if it ever do take place, we should expect the changed butter to be less solid and dense thanrbefore. t " To coagulate a cotyla of milk we add a cyathus of sweet vinegar" (Dioscorides). Milk is also curdled by ardent spirits, by, the juice.of the fig, and by a decoction of theeflowers of the artichoke, of the white and yellow bed-straw (galium), and of the crowfoot (ranunculus Jga.ramula and lingula). The Tuscan ewe-cheese is curdled with the juice of the fresh, or *with a decoction of the dried flowers of the wild thistle, or with the flowers of the artichoke, which gives a cheese of finer colour and less pungent taste. NATURAL AND ARTIFICIAL CURDLING OF MILK. -567 tartar, and salt cf sorrel have been occasionally used, and in Switzerland -especially in the manufacture of the schabzieger cheese-it is customary to add merely a little sour milk for the purpose of producing the curd. 3~. Chemical action of the acid.-But how does the acid act in causing the. milk to curdle, and why is it necessary to allow a little time to elapse and to apply also a gentle heat before the curd will completely separate? In regard to casein or the cheesy matter of milk, we have seen (p. 561)a. That though nearly insoluble in pure water, it dissolves readily in water containing in solution a small quantity of potash or soda, either in the caustic or carbonated state. In other words the casein, which is an acid substance, unites chemically with the potash or the soda, and forms a compound which is soluble in water. b. That when an acid is added to this solution, it takes the potash or soda from the casein and combines with it, leaving the curd again in its original insoluble state, and causing it, therefore, to separate from the water. Now in milk, as it comes from the cow, the casein is in chemical combination with a small quantity of soda, by which it is rendered soluble in the water of which the milk chiefly consists. When the milk stands for a time in the air, the sugar of milk, as we have seen, is transformed' into lactic acid-this acid takes the soda from the casein, and forms lactate of soda, and the cheesy matter, in consequence, being itself insoluble in water, separates in the form of curd. The application of a gentle heat acts in two ways. It aids the acid in more completely taking the soda from the casein, and causes the latter at the same time to shrink in, to' become less bulky, and thus to separate readily from the whey. If we add an acid artificially to milk, the effect is exactly the same. Either muriatic acid, or tartaric acid, or vinegar, or sour milk, will, in the same way, take the soda from the casein, and render it insoluble. And that this is the true action is readily proved by adding a little soda to curdled milk, when the curd will be re-dissolved, and the milk will become sweet. Add acid to it now, or let it sour naturally a second time, and the curd will'again be separated. The action of rennet is in some degreedifferent, though no less simple and beautiful. Let us first, however, consider what rennet is, and how. it is prepared. ~ 18. Of the preparation of rennet. Rerinet is prepared from the salted stomach or intestines of the suckling calf, the unweaned lamb, the young kid, or the. young pig.* In general, however, the stomach of the calf is preferred, and there are various ways of curing and preserving it. 1~. Preparing the stomach.-The stomach of the newly killed animal' contains a quantity of curd derived from the milk on which it has been fd. In most districts (Switzerland, Gloucester, Cheshire) it is usual to Dried pig's bladder is often employed instead of the dried kid's stomach for curdling the goat's nr.ilk on Mont Dor. 568 METHODS OF MAKING THE RENNET. remove by a gentle washing the curd and slimy matters which are present in the stomach, as they are supposed to impart a strong taste to the cheese. In Cheshire the curd is frequently salted separately for immediate use. In Ayrshire and Limburg, on the other hand, the curd is always left in the stomach and salted along with it. Some even give the calf a copious draught of milk shortly before it is killed, in order that the stomach may contain a larger quantity of the valuable curd. 2~. Salting the stomnach.-In the mode of salting the stomach similar differences prevail. Some merely put a few handfuls of salt into and around it, then roll it together, and hang it near the chimney to dry Others salt it in a pickle for a few days, and then hang it up to dry (Gloucester), while others again (Cheshire) pack several of them in layers with much salt both within and without, and preserve them in a cool place till the cheese-making season of the following year. I They are then taken out, drained from the brine, spread upon a table, sprinkled with salt which is rolled inl with a wooden roller, and then hung up to dry. In some foreign countries, again, the recent stomach is minced very fine, mixed with some spoonfuls of salt and bread-crumb into a paste, put into a bladder, and then dried. In Lombardy the stomach, after being salted and dried, is minced and mixed up with salt, pepper, and a little whey or water into a paste, which is preserved for use. [Cattaneo, I1 latte e i suoi prodotti, p. 204.] In whatever way the stomach or intestine of the calf is prepared and preserved, the almost universal opinion seems to be, that it should be kept for 10 or 12 months before it is capable of yielding the best and strongest rennet. If newer than 12 months, the rennet is thought in Gloucestershire " to make the cheeses heave or swell, and become full of eyes or holes." [British Husbandry, ii., p. 420.] 3~. Making the rennet.-In'making the rennet different customs also prevail. In some districts, as in Cheshire, a bit of the dried stomach is put into half a pint of lukewarm water with as much salt as will lie upon a shilling, is allowed to stand over night,. and in the morning the infusion is poured into the milk. For a cheese of 60lbs. weight, a piece of the size of half-a-crown will often be sufficient, though of some skins as much as 10 square inches are required to produce the same effect [Dr. Holland.] It is perhaps more common, however, to take the entire stomach (dried-maws, veils, reeds, or yirning5 they are often called), and to pour upon them from one to three quarts of water for each stomach, and to allow them to infuse for several days. If only one has been infused, and the rennet is intended for immediate use, the infusion requires only to be skimmed and strained. But if several maw-skins be infused-or, as is the custom in Cheshire, as many as have been provided for the whole season-about two quarts of water are taken for each, and, after standing not more than two days, the infusion is poured off, and is completely saturated with salt. During the summer it is constantly skimmed, and fresh salt added from time to time. Or a strong brine may at once In Northumberland the dried stomach is sometimes called the keslap, which is evidently the German kldse-lab, cheese-rennet. Loppert and aispert, applied in Northumberland and the West of Scotland respectively to sour, curdled milk is derived from the same German tb, rennet, orlaber, to coagulate, THEORY OF THE ACTION OF RENNET. 569 be poured upon the skins, and the infusion, when the skins are taken out, may be kept for a length of time. Some even recommend that the liquid rennet should not be used until it is at least two months, old. When thus kept, however, it is indispensable that the water should be fully saturated with salt. In Ayrshire, and in some other counties, it is customary to cut the dried stomach into small pieces, and to put it, with a handful or two of salt and one or two quarts of water, into a jar, to allow it to stand for two or three days, afterwards to pour upon it another pint for a couple of days, to mix the two decoctions, and, when strained, to bottle the whole for future use. In this state it may be kept for many. months.* In all the methods above described, the exhausted skins are thrown away. Where they are cut into pieces, as in Cheshire and Ayrshire, they cannot of course be put to any second use, but where they are steeped whole, there is every reason to believe that they might be used with almost equal advantage a second or even a third time. Accordingly, it has long been the custom in the north of England to re-salt the stomach after it has been once steeped, and when long dried, as before, to use it a second and even a third time for the preparation of rennet. When we explain the mode in which rennet acts, you will see that the same skin may, with good reason, be expected to yield a good rennet, after being salted again and again for an indefinite number of times. In making rennet, sorme use pure water only, others prefer clear whey, others a decoction of leaves-such as those of the sweetbriar, the dogrose, and the bramble-or of aromatic herbs and flowers, while others, again, put in lemons, cloves, mace, or brandy. These various practices are adopted for the purpose of making the rennet keep better, of lessening its unpleasant smell, of preventing any unpleasant taste it might give to'the curd, or finally of directly improving the flavour of the cheese. The acidity of the lemon will, no doubt, increase also the coagulating power of any rennet to which it may be added. 4~. How the rennet is used.-The rennet thus prepared is poured into the milk previously raised to the temperature of 90~ or 95~ F., and is intimately mixed with it. The quantity which it is necessary to add varies with the quality of the rennet-from a table-spoonful to half a pint for 30 or 40 gallons of milk. The time necessary for the complete fixing of the curd varies also from 15 minutes to an hour or even an hour and -a half. The chief causes of this variation are the temperature of the milk, and the quality and quantity of the rennet employed. But how does the rennet act in causing this coagulation? Before we can answer this question it is necessary to enquire what rennet really is. ~ 19. Theory of the action of rennet. It has been stated, and hitherto almost generally received, that the only effective substance contained in'rennet is the gastric juice derived from the stomach of the calf. -To this persuasion is, no doubt, to be ascribed A table-spoonful of this rennet, according to Mr. Aiton, will coagulate 30 gallons of milk, and will curdle it in five or ten minutes, whereas the English rennet requires from one to three hours. This superiority he ascribes to the custom of leaving the curdled milk in the stomach, He denies also that this milk gives any harsh taste to the cheese. 570 THE SUBSTANCE OF THE STOMACH CHANGES the custom both of preserving the natural contents of the stomach-and of generally throwing away the bag after being once salted, dried, and extracted. The gastric juice which exudes from the interior surface of the stomachs of all animals is known to curdle milk readily, and, therefore, it was natural to ascribe the action of rennet to the presence of this substance, and to infer that, )eing once extracted, it was in vain to expect much advantage from salting and infusing the membrane a second time. But the three factsa. That in most places it is customary to wash the interior of the stomach before salting it, and thus to remove the greater part of the gastric juice it may contain; b. That besides, in many places, the hags are laid up in brine for weeks and months, and are then drained out of this brine before they are dried-by which any gastric juice remaining must be almost entirely removed,-and c. That after being dried and steeped once for the preparation of rennet, experience has proved that they may again be salted and used over again; -these three facts, I think, shew that the efficacy of rennet does not depend upon any thing originally contained in the stomach' but upon something derived from the substance of the stomach itself. Now when considering the properties of milk-sugar and of lactic acid, I have stated that if a piece of the fresh membrane of the stotnach or intestine, or even of the bladder of an animal, be exposed to the air for a few days, and be then immersed into a solution of milk-sugar, it will gradually transform the sugar into lactic acid. In milk this membrane would produce a similar effect, aiding and hastening the natural souring and curdling effect of the casein. By exposure to the air, the surface of the membrane has undergone such a degree of change or decomposition, as enables it to induce the elements of the sugar to alter their mutual arrangement, and to unite.together in such a way as to form lactic acid. If the'moist membrane be exposed for a longer time to the air this change of its surface will penetrate deeper, and it will become more effective in inducing the transformation of the sugar into lactic acid. But, at the same time, a portion of its surface may run into a state of putrefaction, and besides acquiring a disagreeable odour may become capable also of bringing on fermentation and putrefactive decay in the solutions upon which it may be made to act. It is not expedient, therefore, to attempt to heighten the transforming effect of animal membranes by exposing them for a greater length of time to the air in a moist and fresh state. But if the membrane be salted, and thus preserved from the rapid -action of the air, it will be protected from putrefaction in a great degree, while, at the same time, it will undergo that gradual change upon its surface to which its power of transforming solutions of sugar is ascribed. And this change will be materially hastened and increased and made to penetrate deeper, if the salted membrane be subsequently dried slowly in the air by a gentle heat, and be afterwards kept for a length of time where the air has more or less ready access to it. Such is the mode of treatment to which the calf's stomach is subjected for the preparation of rennet, and it is an important practical observation that the membrane WHEN EXPOSED A SHORT TIME TO THE AIR. 571 should be kept at least 12 months, if it is to acquire very powerful coagulating properties. It is necessary further to remind you that when malt is steeped in water for a few minutes, a substance, named diastase, is extracted from it, which possesses the remarkable property of changing starch into sugar in a very short time, and, in large quantity (p. 119). Now if this diastase be exposed to the air for a length of time, it undergoes a change similar to that experienced by the surface of animal membranes, and acquires the property of transforming sugar into lactic acid. After undergoing this Change it still dissolves readily in water, and if a solution of it be poured into one of sugar, the transformation of the latter into lactic acid gradually proceeds. There exist~ therefore, substances soluble in water, which possess the same power as slightly decayed but insoluble animal membrane, of converting sugar into lactic acid. During the protracted drying and decay of the salted stomach, the change undergone at length by the surface of the membrane is such as to produce a quantity of matter capable of dissolving, in water, and which also possesses the property of quickly converting the sugar into the acid of milk. This matter, water extracts from the dried skin, and it forms the active ingredient in rennet. I need not further explain to you upon what this activity dependssince as you already know any thing which will rapidly change sugar into lactic acid, will also, if gently warmed, rapidly curdle milk (p. 567). Thus the action of rennet resolves itself simply into a curdling of milk by the action of its own acid. It is the same thing as when sour milk in Switzerland is at once mixed with that from which the cheese is to be made; or it is only a more speedy way of bringing about the curdling that takes place when milk sours naturally and is then gently warmed till the curd separates. But how, it may be asked, is the coagulation effected so much more rapidly by the action of rennet than when the milk is left to sour of its own accord? It is because the whole of the animal matter in the rennet is already in the state in which it easily transforms the sugar into acid, and being intimately mixed with the whole milli in a warm state, it produces acid near every particle of the cheesy matter. From this cheesy matter the acid formed takes away the soda that holds it in solution, and thus renders it insoluble or curdles the milk. In milk, on the other hand, which is left to sour and curdle of itself, the casein must first be changed by the action of the air before it can transform the sugar and produce acid. This change takes place more or less slowly, and chiefly at the surface of the milk where it is in contact with the air. The souring, therefore, must also proceed slowly, and the curdling of which it is the cause. It is no objection to this explanation of the action of rennet, that neither the milk nor the whey become sensibly sour during the separation of the curd. The acid, as it is produced, combines directly with the soda previously united to the curd, and renders the latter insoluble-while, if any excess of acid do happen to be formed, it is -in great part taken up and retained mechanically by the curd, and thus is not afterwards sensibly perceived in the whey. 572 USE OF THE CURD FOUND IN THE CALF'S STOMACH. Using the same skin a second time.-If this then be a true explanation of the action of rennet-if the coagulating ingredient in it be merely a portion of the changed membraneof the stomach itself-it is obvious that thebag, after being once used, may be again salted and dried with advantage. The slow decay may, after a second salting, become still slower, and thus it may require to be longer kept after the second, than after the first salting, before it will give a rennet as powerful as that which was first extracted from it. But unless it be merely the inner membrane of the stomach and intestines which is capable of undergoing that kind of change upon which the coagulating power depends, there is no apparent reason, as I have already stated to you, why the same maw skin may not be salted, dried, and steeped many times over. Use of whey.-Again, in the making of rennet there seems some propriety in the use of whey rather than of water. The whey may contain a portion of the rennet which had been added to the milk from which it was extracted, and may thus be able of itself to curdle milk. It is sure also to contain some milk-sugar, which, being changed into acid when the whey is poured upon the dried stomach, will add to the coagulating power of the rennet obtained. Use of the curdled milk contained in the stomach.-Does the view we have taken'of the action of rennet throw any light upon the use of the curdled milk found in the stomach? Is it of any service, or ought it to be rejected? We are certain that it must be of service in coagulating milk, since in Cheshire, according to Dr. Holland, it is frequently taken out and salted by itself for immediate use. But a slight consideration of the properties of casein, as I have already stated them to you (p. 562), will explain why this curdy matter should be serviceable for such a purpose. You will recollect that casein, after being exposed to the air for a short time, acquires, like animal membranes, the property of converting sugar into lactic acid (p. 562), and of curdling mnilk. Now. the curdy matter taken from the stomach of the calf, after being exposed to the air, acquires this property as completely as a more pure curd will do. If salted and kept, it will be changed still further, and will acquire this property in a greater degree. In short, keeping will affect the curd precisely in the same way as it does the membrane of the stomach itself, and will render it alike fit to be employed in the preparation of rennet. Nor is it unlikely that fresh well-squeezed curd, if mixed with much. salt and kept in slightly covered jars for 10 or 12 months, might yield a rennet possessed of good coagulating properties. It thus appears that, so far as economy is concerned, the curdy matter contained in the calf's stomach ought to be preserved and salted for use., If in any district this curd be suspected to impart an unpleasant flavour to the cheese, this bad effect may probably be remedied by taking it out of the stomach, washing it well with water-as is done in some dairy districts-mixing it with salt, and then returning it into the stomach again. Another practical conclusion may also be drawn from this explanation of the action of the stomach. Since it is the membrane alone that acts, there can no loss accrue by carefully washing the stomach as well as the curd it contains. On the contrary, by so doing we may remove CHEESE OF DIFFERENT QUALITIES-HOWV OBTAINED. 573 from its inner surface some substances which, if allowed to remain, might afterwards act injuriously upon the flavour or upon the other qualities of the cheese. ~ 20. Of the circumstances by which the quality of cheese is affected. All cheese consists essentially of the curd mixed with.a certain portion of the fatty matter and of the sugar of milk. But differences in the quality of the milk, in the proportions in which the several constituents of milk are mixed together, or in the general mode of dairy management, give rise to varieties of cheese almost without number. Nearly every dairy district produces one or more qualities of cheese peculiar to itself. It will not be without interest to attend briefly to some of these causes of diversity. 1~. Natural differences in the milk.-It is obvious that whatever gives rise to natural differences in the quality of the milk must affect also that of the cheese prepared from it. If the milk be poor in butter, so must the cheese be. If the pasture be such as to give a milk rich in cream, the cheese will partake of the same quality. If the herbage or other food affect the taste of the milk or cream, it will also modify the flavour of the cheese. 2~. Milk of different animals.-So the milk of different animals will give cheese of unlike qualities. The ewe-milk cheeses of Tuscany, Naples, and Languedoc, and those of goat's milk made on Mont Dor and elsewhere, are celebrated for qualities which are not possessed by cheeses prepared from cow's milk in a similar way. Buffalo milk also gives a cheese of peculiar qualities, which is manufactured in some parts of the Neapolitan territory. Other kinds of cheese again are made from mixtures of the milk of different animals. Thus the strong tasted cheese of Lecca and the celebrated Roquefort cheese are prepared from mixtures of goat with ewemilk, and the cheese of Mont Cenis* from both of these mixed with the milk of the cow.t 3~. Creamed or uncreamed milk.-Still further differences are produced according to the proportion of cream which is left in or is added to the milk. Thus if cream only be emlployed, we have the rich creamcheese which must be eaten in a comparatively recent state. Or, if the cream of the previous iight's milking be added to the new milk of the morning, we may have such cheese as the Stilton of England, or the small. soft, and rich Brie cheeses, so much esteemed in France. If the entire milk only be used, we have. such cheeses as the Cheshire, the Double Gloucester, the Cheddar, the Wliltshire, and the Dunlop cheeses of Britain, the Kinnegad cheese, I believe, of Ireland, and the Gouda and Edam cheeses of Holland.'Even here, however, it makes a difference whether the warm milk from the cow is curdled alone, as at Gouda and Edam, or whether it is mixed with the milk of the evening before, as is generally done in. Cheshire and Ayrshire. Many persons are of opinion that cream, which has once been separated, can never be so well'Lecca iv- a province in the Eastern pact of the Neapolitan territory; Roquefort, a town in the pastoral department of Aveiron, in the South of France, famed for its sheep; and Mont Cenis, a mountain in Savoy. t The milk of 2 goats-is mixed with that of 20 sheep and 5 cows. 574 BUTTER-MILK, WHEY, AND VEGETABLE CHEESES. mixed again with the milk, that a portion of the fatty matter shall not flow out with the whey and render the cheese less rich. If, again, the cream of the evening's milk be removed, and the skimmed milk added to the new milk of the next morning, such cheeses as the Single Gloucester are obtained. If the cream be taken once from all the-milk, the better kinds of skimmed-milk cheese, such as the Dutch cheese of Leyden, are prepared-while if the milk be twice skimmed, we have the poorer cheeses of Friesland and Groningen. If skimmed for three or four days in succession, we get the -hard and horny cheeses of Essex and Sussex, which often require the axe to break them up. 4~. Butter-milk cheese.-But poor or butterless cheese will also differ in quality according to the state of the milk from which it is extracted. If the new milk be allowed to stand to throw up its cream, and this be then removed in the usual way, the ordinary, skimmed-milk cheese will be obtained by adding rennet to the milk. But if, instead of skimming, we allow the milk to stand till it begins to sour, and then remove the butter by churning the whole, we obtain the milk in a sour state (buttermilk). From this milk the curd separates naturally by gentle heating. But being thus prepared from sour milk and without the use of rennet, butter-milk cheese differs more or less in quality from that which is made from sweet skimmed milk. The acid in the butter-milk, especially after it has stood a day or two, is capable of coagulating new milk also, and thus, by mixing more or less sweet milk with the butter-milk before it is warmed, several other qualities of mixed butter and sweet milk cheese may readily be manufactured. If, as is stated by Mr. Ballantyne, the churning of the whole milk gives butter in larger quantity, of better quality, and more uniformly throughout the whole year (p. 558), the-manufacture of these butter-milk cheeses is deserving of the attention of dairy farmers, especially in those districts where butter is considered as the most important produce. 5~. Whey-cheese.-The whey which separates from the curd, and especially the white whey, which, is pressed out towards the last, contains a portion of curd, and not unfrequently a considerable quantity of butter also. When the whey is heated, the curd and butter rise to the surface, and are readily skimmed off. This curd alone will often yield a cheese of excellent quality, and so rich in butter, that a very good imitation of Stilton cheeee may sometimes be made with alternate layers of new milk-curd and this curd of whey. 6~. Mixtures of vegetable substances with the milk.-New varieties of cheese are formed by mixing vegetable substances with the curd. A green decoction of two parts of sage-leaves, one of marigold, and a little parsley, gites its colour to the green cheese of Wiltshire; some even mix up the entire leaves with the curd. The celebrated Schabzieger cheese of Switzerland is made by crushing the skim-milk cheese after it is severalfmonths old to fine powder in a mill, mixing it then with one-tenth of its weight of fine salt and one-twentieth of the powdered leaves of the mellilot trefoil (trifolium melilotus cerulea), and afterwards with oil or butter-working the whole- into a paste, which is pressed and carefully dried. Potato cheeses, as they ara calleoi, are made in various ways. One TEMPERATURE -AND HEATING OF THE MILK. 575 pound of sour milk is mixed with five pounds of boiled potatoes and a little salt, and the whole.is beat into a pulp, which, after standing five or six days, is worked up again, and then dried in the usual way. Others mix three parts of dried boiled potatoes with two of fresh curd, or equal weights, or more curd than potato according to the quality required. Such cheeses are made in Thuringia, i in Saxony, and in other parts of Germany. In Savoy, an excellent cheese is made by mixing-one of the pulp of potatoes with three of ewe milk curd, and in Westphalia a potato cheese is made with skimmed milk. This Westphalian cheese, while in the pasty state, is allowed toundergo a certain extent of fermentation before it is finally worked up with butter and salt, made into shapes and dried. The extent to which this fermentation is permitted to go determines the flavour of the cheese. ~ 21. Circumstances under which cheese of different qualities may be obtained fron the same milk. But from the same milk, in the same state, different kinds or qualities of cheese may be prepared according to the way in which the milk or the curd is treated. Let us consider also a few of the circumstances by which this result may be brought about. 10. Temperature to which the milk is heated.-The temperature of new or entire milk, when the rennet is added, should be raised to about 95~ F. -that of skimmed milk need not be quite so high. If the milk be warmer the curd is hard and tough, if colder, it issoft and difficult to obtain free from the whey. When the former happens to be the case, a portion of the first whey that separates may be taken out into another vessel, allowed to cool, and then poured in again. If it prove to have been too cold, hot milk or water may be added to it-or a vessel containing hot water may be put into it before the curdling commences-or the first portion of- whey that separates may be heated and poured again upon the curd. The quality of the cheese, however, will always be more or less affected when it happens to be necessary to adopt any of these remedies. To make the best cheese, the true temperature should always be attained as nearly as possible, before the rennet is added. 2~. Mode in which the milk is warmed.-If, as is the case in some dairies, the milk be warmed in an iron pot upon the naked fire, great care must be taken that it is not singed or fire-fanged. A very slight inattention may cause this to.he the case, and the taste of the cheese is sure to be more or less affected by it. In Cheshire the milk is put into a large tin pail, which is plunged into a boiler of hot water, and frequently stirred till it is raised to the proper temperature. In large dairy establishments, however, the safest method is to have a pot wilh a double bottom, consisting of one pot within another-after the manner of a glue-pot-the space between the two being filled with water. The fire applied beneath thus acts only upon the water, and can never, by any ordinary neglect, do injury to the milk. It is desirable in this heating, not to raise the temperature higher than is necessary, as a great heat is apt to give an oiliness to the fatty matter of the milk. 3~. The time during which the curd stands is also of importance. It sho uld be broken up as soon as the milkis fully coagulated. The longer it stands after this the harder and tougher it wi: become. 576 QUALITY AND QUANTITY OF THE RENNET. 4~. The quality of the rennet is of much importance not only in regard to the certainty of the coagulation, but also to the flavour of the cheese. In some parts of Cheshire, as we have seen, it is usual to take a piece of:the dried membrane and steep it overnight with a little salt for the ensuing morning's milk. It is thus sure to be fresh and sweet if the dried maw be in good preservation. But where it is customary to steep several skins at a time, and to bottle the rennet for after-use, it is very necessary to saturate the solution completely with salt and to season it with spices, in order that it may be preserved in a sweet and wholesome state. In some parts of Scotland the rennet is said to be frequently kept in bottles till it is almost putrid, and in this state is still put into the milk. Such rennet may not only impart a bad taste to the cheese, but is likely also to render it more difficult to cure and to bring on putrefaction afterwards and a premature decay. 5~. The quantity of rennet added ought to be regulated as carefully as the temperature of the milk. Too much renders the curd tough; too little causes the loss of much time, and may permit a larger portion of the butter to separate itself from the curd. It is to be expected also that when rennet is used in great excess, a portion of it will remain in the curd, and will naturally affect the kind and rapidity of the changes it afterwards undergoes. Thus it is said to cause the cheese to heave or swell out from fermentation. It is probable also that it will affect the flavour which the cheese acquires by keeping. Thus it may be that the agreeable or unpleasant taste of the cheeses of certain districts or dairies may be less due to the quality of the pastures or of the milk itself, than to the quantity of rennet with which it has there been customary to coagulate the milk. 6~. The way in which the rennet is made, nb less than its state of preservation and the quantity employed, may also influence the flavour or other qualities of the cheese. For instance, in the manufacture of a celebrated French cheese-that of Epoisse-the rennet is prepared as follows:-Four fresh calf-skins, with the curd they contain, are well washed in water, chopped into small pieces, and digested in a mixture of 5 quarts of brandy with 15 of water, adding at the same time 2~ lbs. of salt, half an ounce of black pepper, and a quarter of an ounce each of cloves and fennel seeds. At the end of six weeks the liquor is filtered and preserved in well corked bottles, while the membrane is put into saltwater to form a new portion of rennet. For making rich cheeses, the rennet ahould always be filtered clear. [I1 latte e i suoi prodotti, p. 274.] Again, on Mont Dor, the rennet'is made with white wine'and vinegar. An ounce of common salt is dissolved in a mixture of half a pint of vinegar with 21 pints of white'wine, and in this solution a prepared goat's stomach or a piece of dried pig's bladder is steeped for a length of time. A single spoonful of this rennet is said to be sufficient for 45 or 50 quarts of milk. No doubt the acid of the vinegar and of the wine aid the coagulating power derived from the membrane. Rennets prepared in the above ways must affect the flavour of the cheese differently from such as are obtained by the several more or less careful methods usually adopted in this country. 7~. When acids are used alone-as vinegar, tartaric acid, and muriatic acid sometimes are-for zoagulating the milk, the flavour of the HOW THE WHEY IS SEPARATED. 577 cheese can scarcely fail to be in some measure different from that which is prepared with ordinary rennet. 8~. The way in which the curd is treated. —It is usual in our best cheese districts carefully and slowly to separate the curd from the wheynot to hasten the separation, lest a larger portion of the fatty matter should be squeezed out of the curd and the cheese should thus be rendered poorer than usual. But in some places the practice prevails of washing the curd with hot water after the whey has been partially separated from it. Thus at Gouda in Holland, after the greater part of the whey has been gradually removed, a quantity of hot water is added, and allowed to remain upon it for at least a quarter of an hour. The heat makes the cheese more solid and causes it to keep' better. In Italy, again, the so-called pear-shaped caccio-cavallo cheeses and the round palloni cheeses of Gravina, in the Neapolitan territory, are made from curd, which, after being scalded with boiling whey, is cut into slices, kneaded in boiling water, worked with the hand till it is perfectly tenacious and elastic, and then made into shapes. The water in which the curd is washed, after standing 24 hours, throws up much oily matter, which is skimmed off and made into butter. The varieties of cheese prepared by these methods no doubt derive the peculiar characters upon which their reputation depends from the treatment to which the curd is subjected-but it is obvious that none of them can be so rich as a cheese from the same milk would be, if manufactured in a Cheshire, a Wiltshire, or an Ayrshire dairy. 9~. The separation of the whey is a part of the process upon which the quality of the cheese in a considerable degree depends. In Cheshire more time and attention is devoted to the perfect extraction of the whey than in almost any other district. Indeed, when it is considered that the whey contains sugar and lactic acid, which may undergo decomposition, and a quantity of rennet which may bring on fermentation-by both of which processes the flavour of the cheeses must be considerably affected -it will appear of great importance that the whey should be as completely removed from the curd as it can possibly be. To aid in effecting this a curd-mill, for chopping it fine after the whey is strained off, is in use in many of the large English dairies, and a very ingenious, and I believe effectual, pneumatic cheese-press for sucking out the whey was invented by the late Sir John Robinson, of Edinburgh. [Transactions and Prize Essays of the Highland Society, vol. x., p. 204.] But the way in which the -whey is separated is not a matter of indifference, and has much influence upon the quality of the cheese. Thus in Norfolk, according to Marshall, when the curd is fairly set, the dairymaid bares her arm, plunges it into the curd, and with the help of her wooden ladle breaks up minutely and intimately mixes the curd with the whey. Thissshe does for 10 or 15 minutes, after which the curd is allowed to subside, and the whey is drawn off. By this agitation the whey must carry off more of the butter and the cheese must be poorer. In Cheshire and Ayrshire, again, the curd is cut with a knife, but is gently used and slowly pressed till it is dry enough to be chopped fine, and thus more of the oily matter is retained. On the same principle, in making the Stilton cheese, the curd is not cut or broken at all, but is pressed 878 KIND OF SALT, AND HOW IT IS APPLIED. gently and with care till the whey gradually drains out. Thus the butter and the curd remain intermixed, and the rich cheese of Stilton is the result. Thus you will see that while it is of importance that all the whey should be extracted from the curd, yet that the quickest way may not be the best. More time and care must be bestowed in order to effect this object, the richer the cheese we wish to obtain. You will see, also, how the quality of the milk or of the pastures may often be blamed for deficiencies in the richness or other qualities of our cheese, which are in reality due to slight but material differences in our mode of manufacturing it. 10. 7'he kind qf salt used is considered by many to have some effect upon the taste of the cheese. Thus the cheese of Gerom6, in the Vosges, is supposed to derive a peculiar taste from the Lorena salt with which it is cured. In Holland, also, the efficacy of one kind of salt over another for the curing of cheese is generally acknowledged, [British Husbandry, ii., p. 424.] It is indeed not unlikely that the more or less impure salts of different localities may affect the flavour of the cheese, but wherever the salt may be manufactured, it is easy to obtain it in a uniform and tolerably pure state, by the simple process of purification, which I have already described to you (p. 565.) 110. The mode in which the salt is applied.-In making the large Cheshire cheeses the dried curd, for a single cheese of 60 lbs., is broken down fine and divided into three equal portions. One of these is mingled with double the quantity of salt added to the others, and this is so put into the cheese-vat as to form the central part of the cheese. By this precaution the after-salting on the surface is sure to penetrate deep enough to cure effectually the less salted parts. In the counties of Gloucester and Somerset the curd is pressed without salt, and the cheese, when formed, is made to absorb the whole of the salt afterwards through its surface. This is found to answer well with the small and thin cheeses made in these counties, but were it adopted for the large cheeses of'Cheshire and Dunlop, or even for the pine-apple cheeses of Wiltshire, there can be no doubt that their quality would frequently be injured. It may not be impossible to cause salt to penetrate into the very heart of a large cheese, but it cannot be easy in this way to salt the whole cheese equally, while the care and attention required must be greatly increased. 12~. Addition of cream or butter to the curd.-Another mode of improving the quality of cheese is by the addition of cream or butter to the dried and crumbled curd. Much diligence, however, is required fully to incorporate these, so that the cheese may be uniform throughout. Still this practice gives a peculiar character to the cheeses of certain districts. In Italy they make a cheese after the manner of the English, [II latte e i suoi prodotti, p. 277], into which a considerable quantitv of butter is worked; and the Reckem cheese of Belgium,is made by ad6 ing half an ounce of butter and the yoke of an egg to every pound of pressed curd.,13~. The colouring matter added to the cheese is thought by many to affect its quality. In foreign countries saffron is very generally used to give a colour to the milk before it is coagulated. In Holland and in Cheshire annatto is most commonly employed, while in other districts the marigold or the carrot, boiled in milk, are the usual colouring matters. MODE OF CURING THE CHEESE. 579 The quantity of annatto employed is comparatively small-less than nalf an ounce to a cheese of 60 lbs.-but even this quantity is considered by many to be an injurious admixture. Hence a hative of Cheshire prefers the uncoloured cheese, the annatto being added to such only as are intended for the London or other distant markets. 14~. Size of the cheese.-From the same milk'it is obvious that cheeses of different sizes, if treated in the same way, will at the end of a given number of months possess qualities in a considerable degree different. Hence, without supposing any inferiority, either in the milk or in the general mode of treatment, the size usually adopted for the cheeses of a particular district or dairy, may be the cause of a recognized inferiority in some quality which it is desirable that they should possess in a high degree. 15~. The method.of curing has very much influence upon the afterqualities of the cheese. The care with which they are salted-the warmth of the place in which they are kept during the first two.or three weeks-the temperature and closeness of the cheese-room in which they are afterwards preserved-the frequency of turning, of cleaning froili mould, and of rubbing with butter-all these circumstances exercise a remarkable influence upon the after-qualities of the cheese. Indeed, in very many instances the high' reputation of a particular dairy district or dairy farm is derived from some special attention to one or other or to all of the apparently minor points to which I have just adverted. In Tuscany, the cheeses, after being hung up for some time at a proper distance from the fire, are put to ripen in an underground cool and damp cellar; and the celebrated French cheeses of Roquefort are supposed to owe much of the peculiar estimation in which they are held, to the cool and uniform temperature of the subterranean caverns in which the inhabitants of the village have long been accustomed to preserve them. In Rosshire it is said to be the c'ustom with some proprietors to bury their cheeses under the sea sand at low water, and that the action of the sea-water in this situation renders them more juicy and of an exquisite flavour. 16~. Arnmoniacal cheese.-The influence of the mode of curing upon the quality is shown very strikingly in the small ammoniacal chheses of Brie, which are very much esteemed in Paris. They are soft:unpressed cheeses, which are allowed to ripen in a room the temperatuli6i of which is kept between 60~ and 70~ F. till they-begin to- undergo the putrefactive fermentation and emit an ammoniacal odour. They are generally unctuous, and sometimes so small as not to weigh more than an ounce. A little'consideration, indeed, will satisfy you, that by varying the mode of curing, and especially the temperature at which they are kept, you may produce an almost endless diversity in the quality of the cheeses you bring into the market. 17~. Inoculating cheese.-It is said that a cheese, possessed of no very striking taste of its own, may be inoculated with any flavour we approve of, by putting into it with a scoop a small portion of the cheese which we are desirous that it should be made-to resemble. Of' course this can apply ouly to cheeses otherwise of equal richness, for we could scarcely expect to give a single Gloucester the flavour of a Stilton, 580 AVERAGE QUANTITY OF CHEESE YIELDED. by merely putting into it a small portion of a rich and esteemed Stilton cheese. ~ 22. Of the average quantity of cheese yielded by different varieties of milk, and of the produce of a single cow. There appear to be very great differences in the proportions of cheese yielded by milk at different seasons and in different localities. In milk, of an average quality, there are contained from 4 to 5 per cent. of casein or dry cheesy matter (p. 534),which, if all extracted,would give — 6 lbs. to 7 lbs. of skimmed milk cheese, or? fiom 100 lbs. of 9 lbs. to 10 lbs. of entire milk cheese, milk. This is very nearly the proportion actually obtained in some of the best dairy districts in the summer season. ThusIn Ayrshire-10 lbs. of milk, or? gave 1 lb. of whole milk 1 imperial gallon, cheese; or 136 wine quarts gave 127hlbs. of cheese three months old.* In Gloucester-7 lbs. of milk, or? gave 1 lb. of double 31 wine quarts, Gloucester this is a much larger proportion, and is probably much above the average of the county. In Holstein, it is said that 100 Ibs. of milk will give aboutNew skimnied milk cheese.... 6 lbs. Butter........ 3- " Butter-milk........ 14 " Whley..... e 763 100 lbs. But this statement is so far indefinite that it affords us no means of judging how much curd is left in the butter-milk, nor how much water was present in the new cheese. Indeed, most of the statements on record are deficient in this respect, that the dryness of the cheese is not accurately expressed. In Cheshire, the average produce of a cow is reckoned at-360 lbs. of whole milk cheese, or about 1 lb. per day for the whole year. Taking 8 wine quarts of mn-ilk as the average daily yield of a cow in that county, we have as the average produce of the milk the whole year through1 lb. of cheese from 8 wine quarts, or 16 lbs. of milk. It is indeed undoubted, that the proportion of cheese varies very much with the season of the year and with the dryness of the weather. Though, therefore, in summer 7 or 8 lbs. of milk may sometimes yield a pound of cheese, it is possible that as much as 20 lbs. of milk may at other seasons be required to give the same quantity. Thus inSoutht I Holland, the summer produce of a cow is reckoned at about 200 lbs. of skiimmed milk cheese, and 80 lbs. of butter; or in a week 10 lbs. of ski;:A, ed milk cheese, and 4 to 7 lbs. of butter. Of whole milk cheese-some expect as much as 3 or 4 lbs. a day.'Mr. Alexander, of Southbar, informs me that the result of his experience with a dairy of 40 cows in the higher part of Ayrshire, near Muirkirk, is, that90 imperial quarts of sweet milk give an Ayrshire stone of 24 Ibs. of full milk cheese, while the, same quantity of skim milk gives only 16 lbs. of skimmed milk cheese. That is very nearly — 9 lbs. of new milk give 1 lb. of full milk cheese. 14 Ibs. of skim-milk give 1 lb. of skim-milk cheese (see p. 585). MILK SPIRIT ANID MILK VINEGAR. 581 In Switzerland, generally, a cow, giving 12 quarts of milk a day will, during the summer, yield a daily produce of 12 lbs. of whole or full milk cheese-or 10 - quarts of milk, about 21 lbs., will give a pound of cheese. In the high pastures of Scaria, again, in the same country, one cow will give for the 90 days of summer about 60 lbs. of skimmed-milk cheese and 40 lbs. of butter-or 11 ounces of cheese per day. It appears, therefore, as we should otherwise expect, that the average produce of cheese is affected by many circumstances-but that in this country 8 to 10 lbs. of good milk, in the summer season, will yield one pound of whole milk cheese. ~ 23. Of the fermented liquor from milk, and of milk vinegar. Milk is capable of undergoing what is called the vinous fermentation, and of yielding an intoxicating liquor. The Tartars prepare such a liquor from mare's milk, to which the name of kounmaiss is given. When made from cow's milk it is called airen, and is less esteemed because generally of a weaker quality. The Arabians and Turks prepare a similar liquor, which the former call leban, and the latter yaourt. In the Orkney Islands, and in some parts of the north of Scotland and Ireland, butter-milk is sometimes kept till it undergoes the vinous fermentation, and acquires intoxicating qualities. It is the sugar contained in milk which, by the fermentation, is changed into alcohol. As mare's milk, like that of the ass, contains more sugar (p. 534) than that of the cow, it gives a stronger liquor, and is therefore naturally preferred by the Tartars. By distillation ardent spirits are obtained from koumiss, and when carefully made in close vessels, a pint of the liquor will yield half an ounce of spirit. The koumiss is prepared in the following manner: To the new milk, diluted with a sixth of its bulk of water, a quantity of rennet, or what is better, of sour koumiss, is added, and the whole is covered up in a warm place for 24 hours. It is then stirred or churned together till the curd and whey are intimately mixed, and is again left at rest for 24 hours. At the end of this time it is put into a tall vessel, and agitated till it becomes perfectly homogeneous. It has now an agreeable sourish taste, and in a cool place may be preserved for several months in close vessels. It is always shaken up before it is drunk. This liquor, from the cheese and butter it contains, is a nourishing.as well as an exhilarating drink, and is not fbllowed by the usual bad effects of intoxicating liquors. It is even recommended as a wholesome article of diet in cases of dyspepsia or of general debility. Milk vinegar.-If the koumiss be kept in a warm place the spirit disappears and vinegar is formed. In some parts of Italy a milk vinegar of pleasant quality is prepared by adding honey, sugar, spirit, and a little yeast to the boiled whey, and setting the mixture aside to ferment in a warm place. [I1 latte e i suoi prodotti, pp. 415 and 450.] ~ 24. Of the composition of the saline constituents of milk When milk is boiled down to dryness, and the dry residue burned, a small quantity of ash remains behind. The proportion which the weight of this ash bears to that of the whole milk is variable-as the qualities of the milk itself are-so that 1000 lbs. will leave sometimes 25 582 USE OF MILK IN THE ANIMAL ECONOMY. only 2 lbs., at others as much as 7 lbs. of ash. This ash consists of a mixture of common salt and chloride of potassium (p. 188), with the phosphates of lime, magnesia, and iron. The relative proportions of these several substances yielded by 1000 lbs. of the milk of two different cows, were as follows [Haidlen, Annal. der Chem. und Phar., xiv., p. 273]: I. II. Phosphate of lime..... 2-31 lbs. 3-44 lbs. Phosphate of magnesia... 0 42 " 064 Phosphate of peroxide of iron. 0-07' 0-07 " Chloride of potassium... 144 " 1-83 " Chloride of sodium.... 024 " 0-34' Free soda....... 0-42 " 0-45 " 4-90 " 6-77 " It is probable that the phosphates and chlorides existed as such in the milk as it came from the cow, the free soda is believed to have been in combination with the casein, and to have held it in solution in the milk. You will recollect that the explanation I have given of the curdling of milk is, that the acid produced in, or added to, the milk, takes this soda from the casein, and renders it insoluble in water, and that in consequence it separates in the form of. curd (see p. 566). ~ 25. Purposes served by milk in the animal economy. Milk is the food provided for the young animal, at a period when it is unable to seek food for itself. It consists, as we have seen, of1~. The casein or curd.-This being almost identical in constitution with the lean part or fibrin of the muscles serves to promote the growth of the flesh of the animal. 2~. T'he fat or butter, which is mainly expended in supplying fat to those parts of the body in which fat is usually deposited. 3~. The sugar, which is probably consumed by the lungs during respiration. 4~. The saline matter, from which come the salts contained in the blood, and the earthy part of the bones of young and growing animals fed upon milk. These several purposes served by milk will come again under our consideration in the following lecture. lNOTES. 1~. On the churning of butter in the French churn. Mr. Burnett, of Gadgirth, has favoured me with the following information regarding the merits of the French churn mentioned in page 555:"I see you make mention, in page 555 of your Lectures, of a churn lately introduced by Mr. Blacker from' France. I got one of these from Mr. Blacker about two years ago, and have proved its merits to be very great. I use none else, and have been the means of distributing it over CHURNING IN THE FRENCH CHURN. 683 different parts of England and Scotland. It is made of tin, of a barrel shape, and is placed in a trough of water, heated or otherwise, to convey the proper temperature to the cream. I have tried many experiments to ascertain the proper temperature for churning cream in this churn, and have found that 58~ F. produces the best quality of butter in the shortest time-the time occupied being from ten to twenty minutes. At 60~ it was often done in five to seven minutes, and although a little soft at first, produced butter of a good colour and quality-on no occasion was it ever white. I also tried 56~ F. It took generally one hour, was harder, but no better in quality than that of 58~. "With regard to the quantity of butter from a given quantity of cream, I found that in July, when the cows were on good pasture, and occasionally house-fed on clover16 quarts of cream produced. 12 lbs. 8 oz. 24 do. do. do.. 16 ibs. 12 oz. 30 do. do. do.. 20 lbs. 8 oz. Or, 70 quarts produced..... 49 lbs. 12 oz. When fed on cabbage50 quarts of cream produced.. 32 lbs. Again50 quarts of cream produced.. 32 lbs. 4 oz. 60 do. do. do... 40lbs. Or the whole six quarts of cream.in July gave 4 Ibs. qf butter. "On churning, the wlhole milk in this churn, 100 quarts of milk at 60~ produced 8 lbs. of butter of excellent quality in one hour and a half-8 quarts of hot water were put into the churn according to the old system. "'100 quarts of milk from the same cows at 64~ produced only 7 lbs. of butter of a soft and inferior quality, and took two hours to churn, 16 quarts of hot water being put into the churn- on this occasion.'' The whole milk was sometimes churned in less than one hour, but from that to one hour and a half was the general time occupied, whereas three to four hours is the time occupied in churning in the common churn. 4' To ascertain whether the whole milk or the cream produced the greatest quantity of butter in this churn, I took the milk of five cows (Ayrshire breed) for one week in July'.last, amounting to 508 quartsthe yield of butter was 36 lbs. 11 oz. I then took the same quantity of milk from the same cows for the same period of time, and let it stand for cream-the butter produced was 37 lbs. 4 oz. The food and other circumstances were quite the same. "To test the quality of my butter, I sent it last summer to a show at Ayr, and obtained the second premium both for fresh and salt; the heat at which it was churned was 58~, and the time not exceeding half an hour." On these observations of Mr. Burnett, I must in fairness remark, that several other persons who have used this churn, have not reported by any means so favourably of its merits. Perhaps they have not known how to manage it so skilfully. 2~. Quantity of milk and butter yielded by Ayrshire cows. Mr. Alexander, of Southbar, has furnished me with the following pro 584 COMPARATIVE PROFIT OF portions of cream and butter yielded by his dairy of 38 cows, at Wellwood, in the higher part of Ayrshire, near Muirkirk, during six several days in November and December, 1843:Cream Butter Date. in imp. galls, in pounds. November 1..... 16 432," 7..... 19t 47~ "' 14.... 184- 43'" 21...... 21X 47 " 29..... 18 39 December 7..... 19 431 In all.... 112,galls. gave 2632 or, seven quarts of cream in November gave four pounds of butter. The cream appears from the table to have become gradually less rich, though the whole quantity did not diminish. Mr. Alexander remarks, that " the proportion of cream varies in his dairy from n th to Tth of the bulk of the milk, and that the Guernsey or Highland, or any black or black-marked cow, gives more cream from the same quantity of milk." That is, they give a richer milk. This is a curious physiological fact, and is probably related to an observation made in the fattening of these races, that the same quantity of food goes further in fattening a black or black-marked,.than a dun or white beast. I do not suppose that any thing of this kind has been observed in the Durham breed-as white animals, of pure blood, are often great favourites with the breeders of Tees-Water stock. 3~. Profit of making butter and cheese compared with that of selling the milk. For the following particulars I am also indebted to Mr. Alexander. The produce of cheese and butter is the average of his experience at Wellwood, in Ayrshire. There are three ways in which the milk is usually disposed of. It is sold in the state of new milk, or it is made into full milk cheese, and the whey given to pigs-or it is made into butter, and the skim-milk sold, or made into cheese, or given to pigs. The profit of each of these three methods, at the Ayrshire prices, is as follows approximately:s. d. a.-90 quarts of new milk, at 2d. a quart, are sold for. 15 0 b.-90 quarts of new milk give 24 lbs. of full milk cheese, which, at 4 d., per lb. are sold for.... 9 0 The whey is worth, at least......0 6 9 6 c.-90 quarts of milk, churned altogether, give 9 lbs. of butter, at 9d......... 6 9 90 quarts of butter-milk, at Id. per quart...3 9 10 6 In the country, where the butter-milk cannot be sold, it is given to the pigs, and does not yield so large a return. MAKING BUTTER AND CHEESE. 585 s. d. d. 90 quarts of new milk give 18 quarts of cream, yielding 9 lbs. of butter at 9d., as before..6 9 18 quarts of butter-milk, at ld. 0. 9 70 quarts of skim-milk,at d...... 2 11 10 5 When the skim-milk cannot be sold, it may be given to the pigs. or it may be made into skim-mnilk cheese. In the latter case the profit is as follows:s. d. e. —Butter and butter-milk, as before.... 6 70 quarts of skim-milk give 16 lbs. of cheese, which, at 3d. per lb....... 4 0 11 6 Thus we have 90 quarts of milks. d. a-sold as new milk, worth.... 15 0 b-made into full-milk cheese.. 9 6 c-made into butter and butter-milk, where the latter can be sold..... 10 6 d-made into butter and skim-milk, where the latter can be sold.. 10 5 e-m-ade into butter and skim-milk cheese.. 11 6 In the country, therefore, according to these calculations, the most profitable way is to make butter and skim-milk cheese- The farmer is thus in a great measure independent of an adjoining population. The small quantity of butter-milk he thus obtains he will easily be able to dispose of, or otherwise to employ to advantage. According to Mr. Ayton, it is still more profitable to feed calves with the milk, but I find many people differ from him on this point. At all events, a good and ready market is required for the veal. LECTURE XXI. Of the feeding of animals, and the.purposes served by their food.-Substances of which the parts of animal bodies consist.-Whence do the animals derive these substances-are they all present in the food — Use of the starch, gum., and sugar contained in vegetable food.-Functions of a full-grown animal.-Of the respiration of animals.-General origin and purposes served by the fat in carnivorous ani herbivorous animals.-Of the digestive process in animals.-Purposes served by food and digestion.-The food sustains the fullgrown animal.-Necessity of a mixed food.-It sustains and increases the fattening aninial.-Relative fattening powers of different kinds of food.-How circumstances affect this fattening property.-Purposes servedlby food in the pregnant-in the young and growing animals, such as the calf-and in the milk cow.-Effect of different kinds of food on the quality of the milk.-Fattening of the cow as the milk lessens in quantity-Experimental, economical, and theoretical value of different kinds of food for these several purposes.Circumstances-which affect these values.-Soil, manure, form in which the food is givenventilation, light, warmth, exercise, activity, salt and other condiments. HAVING in the preceding lectures considered the composition of the direct products of the soil-grains, roots, and grasses-and of the most important indirect products-milk, butter, and cheese-the only part of our subject which now remains to be discussed is the relative values of these several products in the feeding-of animals. Under this head it will be necessary to enquire how far these values are affected by the ae, thethe growth, the constitution, and race of the animal-by the purposes for which it is fed-and by the circumstances under which it is placed while the food is administered to it. ~ 1. Of the substance of which the parts of animals consist. The bodies of animals consist of solid and fluid parts. 1~. The solid parts are chiefly made up of the muscles, the fat, and the bones. a. The muscles, in their natural state, as I have already had occasion to mention (p. 444), consist in 100 parts of aboutDry matter... 23 Water.. 77 100 so that, to add 100 lbs. to the weight of an animal in the form of muscle, only 23 lbs. of solid matter require to be incorporated with its system. When the muscular or lean part of beef, mutton, &c., is washed in a current of water for a length of time-the blood, to which the red colour is owing, and all the soluble substances, gradually disappear, and the muscle becomes perfectly white. In this state, with the exception of some fatty and other matters which still remain intermixed with it, the white mass forms what is known to chemists by the name of fibrin. This name is given to it because it forms the fibres which run along the muscles and constitute the greater portion of their substance. The following table exhibits the relative proportions of muscular fibre and other substances contained in the flesh of several different animals in its natural state, [Schlossherger, Annalen der Pharmacie, December, 1842, p. 344]: COMPOSITION OF RECENT MUSCLE. 587 Calf. * o o10. o. g s'2 0Muscular fibre,vessels.nerves and cellular substance. 17'5 15-0 16-2 16-8 18-0 17-0 165 120 11-1 Soluble albumen and colouring matter of blood (l/ematosin)..... 2-2 3-2'26 2-4 2-3 4-5 3-0 52 4-4 Alcoholic extractcontainingt 1 4 1 1.0 1 saline matter..24 Watery extract, containing t1. 1-0 16 0-8 ) 15 1.7 saline matter..... Phosphate of lime, with a little albumen*..... trace 01 trace trace 0-4 - 06 - 22 Water and loss... 77-5 79-7 78-2 783 76-9.76-0 77-3 80-1 80-5 1100100 100 0 100'100 100 10 00 The proportions in the above table are not to be regarded as constant; they seem, however, to shew what we should otherwise expect,'tlatthe muscular part of fishes contains a less proportion of fibrin than that of land animals in general. When dried beef is burned it leaves about 4- per cent. of incombustible ash-or 100 Ibs. of the muscle of a living animal- in its natural state contain about one pound of saline or inorganic matter. Of this inorganic matter, it is of importance to know that about twothirds consist of phosphate of lime. Thus to add 100 lbs. to the muscular part of a fullgrown animal, there must be incorporated with its substance about — Water 77 lbs. Fibrin, with a little fat.. 22 " Phosphate of lime... " Other saline matters.. 100 b. The fat of animals consists, like the fat of butter, of a solid and fluid portion. The fluid fat is in great part squeezed out when the whole is submitted to powerful pressure. The fluid portion of the fat, called by chemists oleine, so far as it has yet been examined, appears to be-identical in all animals. It is also the same thing exactly as the fluid part of olive oil,. of the oil of almonds. and of the oils of many other fruits. It exists in larger quantity in the fat of the pig than in that of. the sheep, and hence pork fat is softer than beef or mutton suet. From lard it is now expressed on a great scale in the United States of America, for burning in lamps and for other uses. The manufacturers of stearine candles express it from beef and mutton fat, but chiefly for the purpose of obtaining the solid part in a harder state, that it may make a more beautiful and less fusible candle. The -fluid oil of animal fats, however, is known to difler from the liquid part of butter (butter-oil) described -in the preceding Lecture (p. 559), and from the fluid part of linseed and other similar oils which dry, and form' This phosphate of lime is over and above that which exists naturally in, and is inseparable from, the muscular fibre itself aid from the albumen. 588 OF FAT, AND OF WHAT BONES CONSIST. a kind of varnish when exposed to the air. These latter facts are not without their importance, as we shall hereafter see. The solid part of the fat of animals is known to'vary to a certain extent among different races. Thus the solid fat of man is the same with that of the goose, and with that which exists in olive oil and in butter. To this the name of margarine is given. But the solid fat of the cow, the sheep, the horse, and the pig, differs from that of man, and is known by the name of stearine. The solid and fluid parts are mixed together in different proportions in the fat, not only of different animals, but of the suame-anirnal at different periods, and in different parts of its body. Hence the greater hardness observed in the suet than in other portions of the fat of beef and mutton, and hence also the different quality and appearance of the fat of an ox according to the kind of food upon which it has been fed or fattened. c. Tlhe bones, like the muscles, consist of a combustible and an incombustible portion, but in the bones the'inorganic or incombustible part is by much the greater. To the organic matter of bones the name of g'elatine or glue is given, and it can be partly extracted from -them by boiling. The proportion of gelatine which exists in hones varies'with the kind of animal-with ihe part of the body from which the bone is taken -and very often with the age and state of health of the animal, and with the way in which it has beenaccustomed to be fed. It is greater in spongy bones, in the bones of young animals, and probably also in the bones of such as are in high' condition. In perfectly dry bone it rarely exceeds from 35 to 40 per cent. of the whole weight. The incombustible portion consists for the most part of phosphate and carbonate of lime. The relative proportions of these two earthy compounds also vary with the kind of animal, with its age, its condition, its food, and its state of health. To form 100 Ibs. of bone the animnal will usually require to incorporate with its own substance about35 pounds of gelatine, 55 pounds of phosphate of lime, 4 pounds of carbonate of lime, 3 pounds of phosphate of magnesia, 3 pounds of soda, potash, and common salt. 100 d. Hair, horn, and wool, are distinguished from the muscular parts of the animal body by the large proportion-about five per cent.-of sulphur which they contain. They consist of a substance which in other respects closely resembles gluten and gelatine in its chemical composition. (page 445). When burned, they leave from one to two per cent. of ash, which in the case of a variety of human hair, which left 1.1 percent. of ash, was found by Van Laer to consist ofPer cent. Soluble chlorides and sulphates.... 0-51 Oxide of iron.......... 039 Phosphate and sulphate of lime, phosphate of magnesia and silica. 0-20 1-10 The inorganic matter contained in Lair is therefore, generally speak OF HAIR, HORN, AND WOOL, AND OF BLOOD. 589 ing, the same in kind as that which exists in the muscular fibre and in the bone. It contains the same phosphate of lime -and magnesia-the same sulphates and the same chlorides, among which latter common salt is the most abundant. The absolute quantity of ash or inorganic matter varies, as well as the relative proportions in which the several substances are mixed together in the different solid parts of the body, but the substances themselves of which the inorganic matter is composed are nearly the same, whether they be obtained from the bones, from the muscles, or frommthe hair. 20. Of the fluid parts of the body, the blood is' the most important, and by far the most abundant. The body of a full grown man, of moderate dimensions, contains about 12 lbs. of blood, [Lehmann, Physiologische Chemie, I., pp. 113 and 338,] that of a full grown ox, six times as heavy, cannot contain less than 70 or 80 lbs. Blood consists of aboutPer cent. Water........ 80 Organic matter...... 19 Saline matter..... 1 100 The organic matter consists chiefly of fibrin, which, when the blood coagulates, forms the greater part of the clot-and of albumen, which remains dissolved in the serum or fluid part of clotted blood, but which, like the white of egg, runs together into insoluble clots when the serum is heated. The saline matter remains dissolved in the serum after the albumen has been separated by heating, and consists chiefly of phosphates, sulphates, and chlorides-nearly the same compounds as exist in the soluble part of the ash left by the solid parts of the body. Besides this soluble saline matter which remains in the serum, a portion of phosphate of lime and a small quantity of phosphate of magnesia exist also in the fibrin and in the albumen of the blood. Thus in the dry state these substances contain respectively of the mixed phosphatesAlbumen of ox blood.... 1'8 per cent. I Berls \ Fibrin of human blood... 0-7 per cent. \ erzelus Thus the same saline and earthy compounds, which form so large a portion of the bones, are distributed every where in sensible proportions throughout all the more important'solids and fluids of the body ~ 2. Whence does the body obtain these substances? Are they contained in the food? Whence does the body derive allthe substances of whichits several parts consist? The answer to this question appears at first sight to be easy. They must be obtained from the food. But when the enquiry is further con-'sidered, a reply to it is not so readily given. It is true, indeed, that the organic part of the food contains carbon, hydrogen, oxygen, and nitrogen-the elements of which the organic parts of the body are composed. The in-organic matter also which exists in 25* 590 WHENCE THE FAT AND BONES OF ANIMALS. the food contains the lime, the magnesia, the potash, the soda, the sulphur, the phosphorus, and the iron, which exist in the inorganic parts of the animal body-so that the question seems already resolved. The body obtains from the food all the elements of which it consists, and if these be not present in the food, the body of the animal cannot be properly built up and supported. But to the chemist and physiologist the more important part of the question still remains. In what state do these elements enter into the body? Are the substances of which the food consists decomposed after they are talken into the stomach? Are their parts first torn asunder, and then re-united in. a different way, so -as to form the chemical compounds of which the muscles, bones, and blood consist? Are the vital powers bound to labour, as it were, for the existence and support of the body? Do they compound or build up out-of their ultimate elements the various substances of which the body is composed-or do they obtain these substances ready prepared from the vegetable food on which animals, il general, are fed? The answer which recent chemical researches give to this second question forms one of the most'beautiful contributions which have been made to animal physiology in our time. 10. We have seen that the flour of wheat and of our other cultivated grains consists in part of gluten, of albumen, or of casein. These substances all contain nitrogen, and are identical in constitution with each other, and with the fibrin of which' the muscles of animals chiefly consist.* The substance of the muscles exists ready formed, therefore, in the food which the animal eats. The labour of the stomach is in consequence restricted to- that of merely selecting these'substances from the food and dispatching them to the several parts of the body, where they are required. The plant compounds and prepares the materials of the muscles-the stomach only picks out the bricks, as it were, from the othler building materials, and sends them forward to be placed where they happen to be wanted. -2. Again, we have seen that in all our crops, so far as they have been examined, there exists a sensible proportion of fatty or oily niau.er more or less analogous to the several kinds of fat which exist in the bo]lies of animals. In regard to'this portion, therefore, of the body, the vegetable performs also the larger part of the labour. It builds up fatty substances out of their elements-carbon, hydrogen, and nitrogen. These substances the stomach extracts from the food, and the body appropriates them, after they have been more or less slightly changed, in order to adapt'them to their several purposes. There may possibly be other sources of fat, as we shall hereafter see, but the simplest, the most natural —and probably, where a sufficient supply exists, the only one had recourse to by the healthy animal-is the fat which is found, ready formed, in the vegetable food it eats. 3~. Further, the bones, the muscles, and the blood, contain phosphate The chemical reader, who is aware of the exact state of our knowledge upon this subject, will perceive that I speak here of the identity of these' substances only in so far as the proportions-of carbon, hydrogen, oxygen, and nitrogen are concerned. IIt is unnecessary to allude in this place to the different proportions of sulphur and phosphorus they are kn;wn to contain —as the more popular nature of this work will not permit me to discuss the refined, though singularly beau.ifil, physiological questions with which these differences are connected. THE FUNCTION OF RESPIRATION. 591 of lime, phosphate of magnesia, common salt, and other saline compounds. These same compounds exist, ready formed, in the vegetable food, associated generally with the gluten, the albumen, or the casein, it contains. The materials of the harder parts of the body, theretbre(the phosphates) as well as the inorganic saline substances which are found in the blood, and in the other fluids of the body-are all formed in or by the plant, or are by it extracted firm the soil and incorporated with the food on. which the animal is to live. Not only, therefore, do the mere elements of which the parts of the bodies of animals are formed, exist in the food-but they occur in it, put — together and combined, nearly in the state in which they are wanted, in order to form the several solids and fluids of the body. The plant, in short, is the com pounder of the raw materials of living bodies. The animal uses up these raw materials-cutting them into shape when necessary, and fitting them to the several places into which they are intended to be built. This is a very simple, and yet a very beautiful view of one of the many forms of chemical connection which exist between the processes and purposes of animal and vegetable life. Nature seems to divide the burden of building up living bodies between the vegetable and the animal kingdoms-the lower appearing to exist and to labour only for the good of the higher race of beings. ~ 3. Of the respiration of animals, and of the purposes served by the starch, gumai, and sugar, contained in vegetable food. But, besides the gluten of plants and seeds, which supplies the materials from which the muscular parts of animals are formed, the oilwhich is converted into the fat of animals, and the saline and earthy matters of plants which supply the salts of the blood and the earth of thebonesvegetable food in general contains a large proportion of starch, sugar, gum, and other substances which consist of carbon and the elements of water only (p. 111). What purpose is served by this part of the food? Is it merely taken into the stomach and again rejected, or is it decomposed and mtade to serve some vital purpose in the economy of the living animal? From the fact that so large a part of all vegetable food consists of these substances, we might infer that they were destined to serve some important purpose in the animal economy. To the herbivorous animal' they are, in fact, almost necessary for the support of a healthy life. In order to understand this fact, it will be necessary briefly to advert to the respiration of animals-the chemical changes produced by it, and the purposes it is supposed to serve in the animal economy. 1o. Of Ihe function ofrespiration.-All animals possessed of lungs alternately inhale and exhale the atmospheric air. They breathe, that is, or respire. The air they. draw into their lungs, supposing it to be dry, consists by volume (pp. 32 anl 148) very nearly ofNitrogen...... 79-16 Oxygen..... 20-80 Carbonic aci.'..... 0-04 100 592 FAT SUPPORTS, RESPIRATION IN SOME, -rthe proportion of carbonic acid being very small. But as it is breathed out again it consists of aboutNitrogen...... 7916 Oxygen-..... 16-84 to 12 Carbonic acid...... 4'00 to 8 100 -the proportion of oxygen being considerably less, that of carbonic acid very much greater, than before.- On an average the natural proportion of carbonic acid in the -air is fo-und to,be increased 100 times after it is expelled by breathing from the lungs. Now carbonic acid consists, as we have previously seen, of carbon and oxygen. In breathing, therefore, the animal throws off into the air a quantity of carbon-in the formi of carbonic acid-which varies at different times, in ditferent species-of animals, and in different individuals of the same species. By a healthy man the quantity of carbon thus thrown off varies from 5 to 13 ounces, and by a cow or a horse from 3 to 5 pounds, in 24 hours. All this carbon must be derived from the food.!The animal eats, therefore, not merely to support or to add weight to its body, but to supply the carbon also which is wasted by respiration. 2~. How the respiration-is fed.-What part of'the fbod supplies the waste caused by respiration? How is the respiration fed? In animals which live upon flesh-carnivorous animals-it is the fat of their food from which the carbon given off' by their lungs-is derived. It is only when the fat fails-in quantity that the lean or muscular part of the flesh they eat is decomposed for the purpose of supplying carbon to their lungs. In an animal to which no food is given for a time, the lungs are fed, so to speak, from fat also. But in this case it is the living fat of the animal's own body. When digestion is fully performed and hunger is keenly experienced, the body begins to feed upon itself-the lungs still play, respiration continues for many days after food has ceased to be administered, but the carbon given off'is cdrived from the substance of the body itself. The fat first disappears-escapes with the breath-and afterwards-the'muscular part is attacked. Hence the emaciation which follows a prolonged abstinence from food. In animals which live upon vegetable food again-herbivorous animals-it is the starch, gum, and sugar, of the food which supply the carbon for respiration. It is only when the food does not contain a suf ficient supply of these compounds that the oil first, and then the gluten, are decomposed, and made to yield their carbon to the lungs. In man, who lives on both: kinds of food, and- in the domestic dog, and the pig,which also eat indifferently both animal and vegetable food, the carbon of respiration may- be derived in part, from the fat, and in part from the starch and sugar which they eat-according, as they are chiefly supported by the one or by the other kind of food. It may be asked how we know that such are the parts of the food, to which the duty of supplying the demands of the lungs is especially committed. There are several considerations which lend force to this opinion. Of these I-will draw your attention to one or two. a. Why is the fa' rather than the lean part of the food of carnivorous STARCH AND SUGAR IN OTHER RACES. 593 animals devoted to the service of the lungs, and why do starving animals lose their fat first? Because the chemical decomposition by which carbon can be derived from the fat is simpler and more easily effected than that by which it can be obnai ed from muscular fibre. By combination with oxygen, fat can be converted into carbonic acid and water only, of which the former will pass off by the lungs and the latter in the urine. The muscular fibre, on the other hand, contains much nitrogen (p. 444), and, if deprived of its carbon for the uses of respiration, must undergo very complicated decompositions, and form a series of compounds, the use of which, in the animal economy, it is not easy to perceive. Besides, in producing the carbonic acid of the lungs from the fat of the animal food or of the living body, there is less waste of material. Fat consists wholly of the three elements, carbon, hydrogen, and oxygen. These all disappear entirely in the form of carbonic acid and water-both of which are used up. Muscle, on the other hand, besides nitrogen, contains a constant proportion of sulphur and phosphorus. If the muscle, then, be decomposed for the purpose of supplying carbon to the lungs, not only the large quantity of nitrogen, but the sulphate and phosphorus also, would go to waste, and would pass off in the urine. In nature,:however, such waste is rarely seen to take place; and, therefore, as a general rule, the respiration will be supported by the muscular fibre only when other kinds of food are deficient. b. But in the stomachs of herbivorous animals, why are the starch and sugar especially appropriated to the use of the lungs? The food of animals which live upon vegetable substances contains fat as well as starch — why then is the starch in this case dissipated by the process of respiration, while the fat is applied as it is supposed to another use? The answer to this question is both beautiful and satisfactory. Starch, gum, and sugar, consist of carbon and water only, and we can conceive them in their passage through the body to be'actually separated into these two substances-in which case the carbon has only to combine with oxygen and form carbonic acid, to be ready to pass off by the lungs. Here, therefore, only one chemical combination is required-the union of carbon with oxygen. It is the simplest way in which we can conceive carbon to be supplied for the use, or for the purposes of the lungs.* B t it is otherwise with fat. Though nearly all kinds of fat consist entirely of'carbon, hydrogen, and oxygen-yet they cannot be supposed to consist only of carbon and water. They contain much more hydrogen than is necessary to form water with the oxygen which is present in them. If, then, the carbon of these fats be separated, this excess of hydrogen will also be set free, and if the former be made to combine with oxygen to form carbonic acid, the latter must also combine- with hydrogen to form water. Thus two chemical changes must go on simultaneously, for which more oxygen will'be required, and which involve more labour in the system than when the carbon alone is to be combined with oxygen. It is natural, therefore, that where both starch and oil are present together, the former should be first converted to the uses of the lungs, the latter only when the supply of starch or sugar has been exhausted. The chemical reader will understand that I am here only giving a popular view of the final result of the several changes through which the carbon no doubt passes before it escapes in the form of carbonic acid. 594 PURPOSES SERVED BY RESPIRATION. There appears, therefore, to be a beautiful adaptation to the wants and convenience of animals in.the large proportion of starch, gum, and sugar, which the more abundant varieties of vegetable food contains. In obtaining carbon from these, the least possible labour, so to speak, is imposed upon the digestive organs of the herbivorous races. The starch and sugar abound because much carbon is required, while fatty matter or oil is present in smaller quantity, because comparatively little of this is necessary to the performance of the usual healthy functions of the animal body. And it is another adaptation of the living body to the circumstances in which it may be placed, that when starch or sugar cannot be obtained, the oil of the food is consumed for the supply of carbon to the lungs —and failing this also, the gluten and albumen of the vegetable food or the muscular fibre of the animal food, or even of the living animal itself. 3~. Purposes served by respiration. —But for what purpose essential to life do animals respire? If the starch and sugar be so necessary to feed the respiration-the breathing itself must be of vital importance to the living animal. Some doubts still exist upon this point. It is generally believed, however, that carbon is consumed or given off from the lungs for the purpose of sustaining the heat of the living body. When starch, or sugar, or gum, are burned in the open air, they are changed into carbonic acid and water, and at the same- time produce much heat. It is supposed that in the body the same change-the conversion of starch and sugar into carbonic acid and water-taking place, heat must in like manner be produced. A slow combustion, in short; is supposed to be going on in the interior of the animal-the heat of the body being greater, in proportion to the quantity of.carbonic acid given off from the lungs. In favour of this view many strong reasons have been advanced, but there are also objections against it of considerable weight, which cannot as yet be satisfactorily removed. Were we to adopt this opinion in regard to the main purpose served by respiration as the true one, it would afford a very distinct reason for the large amount of starch existing in all our cultivated crops. Respiration, according to this view, is necessary to supply heat to the animal, and this respiration is most simply and easily fed by the starch contained in the vegetable food. The life and labours of the plant again minister to the life and labours of the animal. ~ 4. Of the origin. and the purposes served by the fat of animals. 10. The immediate origin or source of the fat of animals depends upon the kind of food with which the animal is fed. Carnivorous animals obtain or extract it ready formed from the flesh they eat-herbivorous animals from the vegetable food on which they live. It has only been lately shown that the corn, hay, roots, and herbage, on which cattle are fed, contain a sufficient quantity of oily matter ready formed to supply all the fat which accumulates in their bodies-or which, by the milk cow, is yielded in the form of butter. Before the different kinds of food had been analyzed, with the view of determining the quantity of oil and fat they severally contain, it was supposed that the fat of animals was derived almost solely from the starch and sugar or gum, of ORIGIN OF THE FAT OF ANIMALS. 595 which so large a proportion of vegetable food consists. This opinion, however, has given way before the advance of analytical -research. Animals fatten quickest upon Indian corn, or oil cake, or oil mixed with chopped straw, or upon oily seeds and nuts-or, as in the case of poultry, on a mixture of meal or suet-because these kinds of food contain a large proportion of fatty matter ready formed which the animal can easily extract, and after a slight chemical change can convert into a portion of its own substance. The conversion of starch or sugar into fat in the animal body implies a chemical change-of a less simple nature —one which seems to impose upon the vital principle a greater amount of labour than is implied in the simple appropriation of the fat which exists ready forme-d in the food. If, then, there be in the food as much fat as is necessary to supply all that the animal appropriates to itself, and if it is observed to lay on or appropriate more when the food is- richer in fatty oils, we are led to believe that the natural-purpose.served by the oil in the vegetable food is to supply the fat othefa he animal body. In other words, the-vegetable ministers to the animal and lessens-its labour by preparing beforehand the materials out of which the animal is to build up the-fatty parts of'its body. But though this is the general-source. of the.fat of animals, circum-. stances may occur in' which the only vegetable food which the animal can procure does not contain a sufficient proportion of fat' to supply all the wants of its body-or to enable-it to perfborm the several natural functions it is destined to fulfil. Thus wax is a kind of fat, and it has been shown (Milne Edwards) that, when fed upon pure sugar, the bee is capable of forming wax froni its food. When fed upon such sugar, it not-only lays up a store of honey, but it continues to build its cells of wax. Now the starch of the food is readily changed into sugar. It may be so changed in the stomach of man and of other animals. That power which the bee possesses they also may in cases of emergency be able to exercise. Where a sufficient supply of oil for the necessary uses of the-animal is not-contained in the food it eats, it may form an additional portion from the starch or sugar in which its food abounds. According to the present state of our knowledge, therefore, the most probable opinion in regard to the origin of the fat of animals seems to be expressed in these two proposition. a. That the fat of animals is contained ready formed, and is usually derived from the vegetable or other food on which they live-and that when the food abounds largely in fat, the animal lays it more quickly and abundantly upon its own body. b. That when the food does not contain a sufficient proportion of fat to enable the animal comfortably to perform the various functions of its body, it has the power to form-an additional quantity from the starch or sugar it eats —but that it will not readily fatten or lay on large additions of fat upon its body when fed upon farinaceous, saccharine, or other food in which oil is not naturally contained." * For the sake of the chemical reader I may be permitted here to show by what kind ol chemical changes-10, the fat of animals in general may be derived from the starch or sugar of their food; and 2~, how the peculiar kinds of fat contained' in the body of any given animal may be formed from the peculiar kinds of fat contained in its food. 1.' How fat may beformed from starch or sugar.-These two substances, as we have already seen, may be represented by carbon and water only CHANGES OF OX FAT INTO HUMAN FAT. 596 2~. The purposes served by the fat.-In all healthy animals which take a sufficient quantity of exercise to maintain them in a healthy conCarbon. Water. Starch,......consisting of 12 + 10, represented by Ci2 HLO O0o Cane sugar, consisting of 12 + 11, represented by Cl2 HIl OLt Fat, again, margarine for example, the solid fat of the human body, is represented (p. 559, note,) by C37 IHs 05. Compare this with 4 of starch, and we have4 of starch....... C48 H40 040 1 of margarine...... C37 H36 05. Difference....... =' CLH4 035 This difference is equal to, or may be represented by, 11 of carbonic acid + 4 of water.+ 9 of oxygen 11 CO2 4110 H + 90 So that by the separation of carbonic acid, which may be given off from the lungs-of water, which may or may not remain in the system, —and of a portion of oxygen, which may be used up in various ways in the blood, the starch or sugar of the food may be-converted into fat. That in some such way these substances may be changed into the fat of animals was first insisted upon and explained by Liebig; and it is probable, as I have said in the text, that in cases of emergency fa'-is really formed in the animal body from such kinds of food. But when Liebig put forth his views on this subject, it was not known that vegetable substances naturally contained so large a proportion of fat as has since been found in them. The necessity for the constant production or formation of fat in the body itself, therefore, is not now so apparent, andt the soundest. opinion, according to our present knowledge, seems to be that, while the vegetable food usually supplies all the fat ready formed which the animal requires, yet that a conversion of a certain part of the starch, gum, sugar, and even of the cellular fibre of the food, into fat, may take place, when all the wants of the body are not supplied by the fat which the food naturally contains. Of course this opinion applies only to animals in perfect health. In certain diseased states of the body a larger and more constant production of fat from the food may take place as appears to be the case in animals which no diminution of food seems to prevent from laying on fat.' 2~. How the peculiar kinds offat in the body may be derivedfrom the peculiar kinds of fat in the food. a. We have already seen (p. 558) that the solid part of butter, of olive oil, and of the goose, is identical with the solid fat of the human body. When eaten by man, therefore, these several kinds of fat may be at once conveyed, without change, from the stomach to the several parts of the body where they are required. From' this circumstance these kinds of fat seem remarkably fitted for the fool of man. b. The solid fat of the ox and the sheep is called stearine. Upon this man lives much and converts it into the solid fat (margarine) of his own body. This may take place after the following mamner: 2 of margarine....... — C74 H72 0io 1 of stearine........ C4 Ho9 07 Difference..H.... = C3 H3 O0 If we double this difference, we have CG H0 O6; which is the formula for lactic acid. Recent researches, however, have failed in detecting this acid in the blood-if it be formed at all, therefore, it must exist only in a transition state, and must be speedily converted into other compounds. The final, result may possibly be the evolution of the 3 of carbon (C3 by the lungs in the form of carbonic acid. c. That the body or its parts possess the power of easily transforming these different kinds of fat one into the other, we know, also, from other facts. Thus the ealf lives upon milk, and from the two kinds of fat contained in the cream of the milk, it forms-the solid and liquid fats of its own body. The stearine of the animal in this case may be formed from the margarine of the butter, being exactly the converse oftheprevious case, while the butter oil may be changed into the liquid fat of the tallow. This latter is more difficult to explain, since the composition of elaine-the liquid fat of the ox, calf, and sheep —compared with that of butter oil, presents a considerable difference. Thus — Elaine........ C47 H42 O6 Butter oil... - C37 -H33 06 Diffarence...'= Cio H9 What becomes of this difference, Co Hs9, we are unable as yet precisely to explain. By the intervention of a little oxygen it might readily give rise to a little more fat. d. The cow and calf together, however, illustrate very clearly the existence of this transforming power of the animal body. We are unacquainted, as yet. with the composition of the several kinds of fat which occur in vegetables-but we krnow that out of these the cow can form the two kinds of fat —the stearine and the elaine —whith exist in its own tallow, and at the same time the two kinrds'of fat-margarine and butter-oil —which are found in its milk. The calf, again, can change these two latter fats into those which its own body, as PURPOSES SERVED BY THE FAT. 597 dition, the principal purposes served by the fat are simple and the same. It lubricates the joints-covers and protects the internal viscera-keeps the muscles separate, and enables them to play freely among each other -males the hair and skin soft and flexible,-and, by filling up hollows, contributes to the roundness and plumpness of the parts, and defends the extremities of the bones from external injury. When exercise is taken, a portion of the fat of the body appears to be more or less changed and removed, and is afterwards found in the perspiration, or in the dung. It is to make up for this natural waste that all'animals, even when the fat of their body undergoes no increase, require a certain supply to be daily' given to them, in their food. The accumulation of fat in animals seems to be an effort of nature to lay in a store of food in time of plenty, which may be made available in the performance of-the usual functions of the animal when a time of scarcity comes. If the food contain too little oil to lubricate'the joints and to supply the natural waste of this kind of matter, then the store of fat which has been accumulated in time of plenty is drawn upon, a portion of it is worked up, so to speak, and the fat of the.body diminishes in quantity. We have seen also that the respiration of carnivorous animals is supported at the expense of the fat which they eat-and that the leanness which attends upon starvation is owing to the fat of the living body beingconsumed in supplyingthecarbongiven off from the lungs. Another purpose, therefore, for which animals seem to be invested with the power of laying on fat, is, that a store of food for the purposes of respiration may be carried about in the body itself, to meet any unusual demand which the food may not be able wholly to supply. ~ 5. Of the natural waste of the parts of the body in a full grown animal. WTe have seen that, if the food of the animal he unable to supply' the carbon given off'from the lungs, and the fat which the movements of the limbs require, the parts of the body themselves are laid under contribu tion in order to supply these substances. Thus, when the.food is stinted, the body necessarily undergoes a waste from this cause. But this is not a constant waste. It is prevented by the use of a larger quantity of food. The parts of the body, however, do undergo a constant and natural waste, to make up for which is one of the main purposes served by the food. It has been ascertained by physiologists, that all the parts of the body undergo a slow and insensible process of renewal. The hair and the nails we can see to be constantly renewed. They grow, or are thrust outwards. But the muscles and even the bones are by little cnd little rewell as that of its mother, requires. And, lastly, man by eating the fat of the calf can re convert it into margarine and those other fatty substances which are found in the various parts-of his body. Substances which can thus so frequently and so readily be changed, the one into the other, must be very closely connected, and the mode in which their mutual transformations are effected will, no doubt, prove to be simple when these are rightly understood. The chemical reader will understand that it is for the sake of simplicity only that I have in this note compared together the entire- fats stearine, margarine, &c., instead of the fatty acids only which they are known to contain. The reader will consult with piuch advantage and satisfaction upon this subject, a work upon Chemical Physiology, by Professor Mulder, of UtrechL (Procve eener Algemeene Physiolo gische Scheikunde, p. 260, el seq.) of which I am happy to say that a translation from the Dutch is now in progress by my assistant, Mr. Fromberg, and will speedily be published by the Messrs. Blackwood. 598 FOOD REQUISITE FOR THE NATURAL WASTE. moved inwardly and rejected in the excretions-the place of that which is removed being supplied by new portions of matter derived from the food. This removal, though unfelt by us, goes on so rapidly that in a space of time, which varies from one to five years, the whole body of the animal is renewed. There does not rem!ain, it is said, in any of our bodies, a single particle of the same matter which formed their substance three or five years ago. It is just as if we were to take a single old brick every day out of the corner of a house, and put in a new one-the form and dimensions of the house would remain unaltered, and yet in the course of a few years its walls would be entirely renewed. In full grown animals, some parts of the body are renewed more rapidly than others-the muscles, for example, more frequently and rapidly than the bones and the brain. In young animals, again, the whole body is oftener renewed than in such as- are advanced in years, but all the parts of all animals are believed to be more or less quickly removed and replaced. Tmhe new materials which are conveyed to the different parts of the body are deriveddirectly from the food. The fibrin of the muscles is' replaced from the gluten which the food contains-the fat from its oiland the earthy matter of the bones and the salts of the blood, from the phosphates and saline substances which are naturally present in it. On the other hand, those parts which are extracted from the muscles and bones, and carried off in the excretions, are decomposed during their removal. New chemical compounds are produced from them, which are found in the urine and dung of the animal, and which give to these excretions their richness and value in the manuring of the soil. ~ 6. Of the kind and quantity offood necessary to make up for the natural waste in the body of a full -rown animal. The substances which constantly disappear from the body in consequence of the natural waste above described, are of three kinds-the fibrin and other analogous organic compounds, which form the muscles and the cartilage of the bones-the earthy phosphates (of lime and magnesia), which form so large a proportion of the bones, and exist in small quantity in the muscles also-and the soluble saline substances, which abound in the blood and in the other fluids of the living animal. In the solid and liquid excretions, a larger quantity of each of these three classes of compounds is carried out of the body. How much of each must be contained in the daily food of a full-grown animal in order that it may be kept in its actual condition? 1~. Quantity of fibrin or other analogous compounds (albumen or casein) which the daily food must contain.-The most accurate experiments that have yet been nmade upon this subject (Lecanu) appear to show that a full grown man rejects in his urine alone about half an ounce of nitrogen (230 grs.) every 24 hours. This quantity of nitrogen is contained in about three ounces of dry muscular fibre, which must, therefore, every day be decomposed or removed in order to yield it. But if the body is kept in condition, this quantity of fibrin must be daily restored again by the food. Now, to supply three ounces of dry fibrin, there must be eaten about — IN THE BODY OF A FULL-GROWN ANIMAL. 599 30 ounces of wheaten flour; or 45' of wheaten bread; or 14'- of fresh beef or mutton; or 12 " of pease or bean meal; or' 4 " of cheese;* Or, if we live wholly upon potatoes or milk, we must eat no less than six cr seven pounds of the former daily, or drink three or four imperial pints of the latter-if we would restore to the body as much of the substance of its muscles and cartilage as, is daily removed from it by the urine. But the urine is not the only channel through which nitrogen is given off from the animal body.'A considerable, though, of course, a variable proportion is found in the solid excretions or dung, which has also been derived from the substance of the body itself. A small quantity of.nitrogen is believed to be-given off from the lungs also in breathing, and from the skin in the perspiration, which'nitrogen must have been either directly or'indirectly derived from the food. And, lastly, of the fibrin or other food containing nitrogen which may be introduced into the stomach, a portion must pass the mouths of the absorbent vessels as it descends through the intestines and thus escape with the dung, without having performed its part in the ordinary nourishment of the body. It is impossible to male any correct estimate of the amount of nitrogen which escapes from the animal in the several ways just noticed-in the solid excretions from the lungs and from the skin-or of the quantity of food which is necessary to supply its place. If we suppose the lossthrough all these sources taken together to be equal to one-half or twothirds of that which is f6und in the urine, then the whole quantity of dry fibrin which the food ought to contain would amount to four and a half or five ounces in the day. To supply this, we must eat of bread, beef cheese, potatoes, or milk, one half more than the quantities already specified. No experiments-have hitherto oeen published from which we can determine the average quantity of nitrogen rejected in the excretions of the horse, the cow, or the sheep, and, consequently, the amount of waste which takes place in ordinary circumstances in the muscles and cartilage of these animals. If we suppose that in the horse or cow it is in direct proportion to their weights, compared with that of a full grown man-or five times greater than in a man-then the loss of dry fibrin would amount to 20 or 25 ounces in the 24 hours. To supply this, the animal must eat the following quantities of one or other of the kinds of food here mentioned 120 lbs. of turnips. 17 lbs. of clover hay. 115 " of wheat straw. 12 " of pea straw. 75 " of carrots. 12 t of barley. 67 " of potatoes. 10 " of oats. 20 " of meadow hay. 5 " of beans.f Or instead of the whole quantity of any one of these, a half or quarter or any other proportion of each may be taken, and the animal will proSupposing the wheaten flour to contain 10 per cent. of gluten, and the cheese one half its weight of dry curd (see also pp. 506 and 631.) t These numbers are calculated from the table giver, in p. 531. 600 A MIXED FOOD NECESSARY TO ANIMALS. bably be found to thrive better on the mixture than if fed upon any one of these kinds of food alone. 2~. Quantity of fixed saline matter and of earthy phosphates which the food ought to contain.-A full grown animal rejects in its dung, its urine, and its perspiration, as much saline and earthy matter as its food contains. If its body is merely maintained in its existing condition, only that which is removed from it by the' daily waste is restored to it by the daily food. Thus whatever quantity of saline and earthy matter is present in the food, an equal quantity is found in the excretions of the living animal. But how much of that which is found in the excretions has actually formed part of the living body, and been removed from it in consequence of the natural waste? This we have no means as yet of determining. It must be considerable, but it varies with many circumstances, and the experiments which have hitherto been made and published do not enable us to say how much the average waste really is, and how much of the several more common kinds of food ought to be consumed by a full grown animal, in order to supply it with the necessary daily proportion of saline and earthy substances. The benefits so often derived from the use of salt in the feeding of stock show how a judicious admixture of saline matter with the food may render its other constituents more available than they would otherwise be, to the support and increase of the animal body. ~ 7. The health of the animal can be sustained only by a mixed food. From what I'have already stated, you see that the vegetable food eaten by a full grown animal for the purpose of keeping up its condition should contain1~. Starch or sugar, to supply the carbon given off in respiration. 2~. Fat or fatty oil, to supply the fatty matter which exists more or less abundantly in the bodies of all animals. 3~. Gluten or fibrin, to make up for the natural waste of the muscles and cartilage. 4~. Earthy phosphates, to supply what is removed from the bones of the full grown animal by the daily waste; and- 5~. Saline substances-sulphates and chlorides-to replace what is daily rejected in the excretions. Hence the food upon which any animal can be fed with the hope of maintaining it in a healthy state must be a mixed food. Starch, or sugar alone, or pure fibrin or gelatine alone, will not sustain the animal body, because these substances do not contain what is necessary to build up all its parts, or to supply what is daily given off during respiration and in the excretions. The skilful feeder, therefore, will not attempt to maintain his stock on any kind of food which does not contain a sufficient supply of every one of the kinds of matter which the body requires. Two other points he will also attend to. First, he will occasionally change the kind of food, or will vary the proportions in which he gives the different kinds of fodder to his feeding stock. This practice is founded on the fact that, although every crop he raises contains a certain proportion of all the substances which the animal requires, yet some contain one of these in larger quantity than others do, and by an occasional ADDITIONAL FOOD REQUIRED FOR FATTENING. 601 change or variation he may hope more fully to supply to the animal the necessary quantity of each. Second, he will adapt the kind and quantity of food to the age of the animal, and to the other purposes for which it is fed. This rule depends partly upon the same fact, that different vegetables contain the several kinds of necessary food in different proportions, but in a great degree also upon the further fact, that the animal requires these substances in different proportions, according to its age and to the special purpose for which it is fed. Let me direct your attention to this latter fact a littler more at length. ~ 8. Of the kind and quantity of additional food required by the fattening animal. In the animal which is increasing in size or in weight, the food has a double function to perform. It must sustain and it must increase the body. To increase the body, an additional quantity of food must be consumed, but the kind or nature of this additional food will depend upon the kind of increase which the animal is making or is intended to make. One of the important objects of the stock farmer is to make his full grown animals lay on fat, so that they may as quickly as possible, and at the least cost, be made ready for the butcher. To effect this object, he adjusts the kind and quantity of the food he gives, to the practical object he wishes to attain. We have already seen reason to believe, that the natural and immediate source of the fat of animals is in the oily matter, which the food contains. If we wish only, or chiefly, to lay on fat, therefore, we ought to give some kind of food which contains a larger proportion of fatty matter than that upon which the animal has been accustcmed to live. This is what the practical man has actually learned to do. To his sheep and oxen he gives oil-cake or linseed oil mixed with chopped straw, to his dogs cracklings,* to his geese and turkeys Indian corn, which contains much oil, and to his poultr; beef or mutton suet. Many experiments are yet wanting to determine with accuracy the proportion of fat contained in all the different kinds of food usually consumed by animals. Nearly all we yet know upon this subject is exhibited in the tabular view of their composition to which I have already directed your attention (p. 531.) One thing, however, of considerable practical. value has been recently ascertained-that the oily matter of seeds exists chiefly near their outer surface,-in or immediately under the skin or husk. This fact is shown in the case of wheat, by the following results of the examination of two varieties of this grain, one grown near Durham, the other in France. The result as to the French grain is given by Dumas: PER OENTAio OF PATTY 01L. English. French. Fine flour... 5 1-4 Pollard... 2-4 4-8 Boxings.. 3'6 - Bran..... 3-3 5-2 Cracklings are the skinny parts of the suet from which the tallow has been for the most' part squeezed out by the tallow chandlers. Might cattle not be fattened upon cracklings crushed and mixed with their other food? Miight not some cheap varieties of oil also be mixed with their food for the purpose of fattening. 602 FATTY MATTER IN THE HUSKS OF SEEDS. This fact of the existence of more fat in the husk than in the inner part of the grain, explains what often seems inexplicable to the practical man-why bran, namely, which appears to contain little or no nourishing substance, should yet fatten pigs and other full grown animals, when given to them in sufficient quantity along with their other food; It also explains why rice dust should be found to fatten stock,* though the cleaned and prepared rice contains but little oil, and is believed, therefore, to be unfitted for laying on fat upon animals with any degree of rapidity. No doubt the dust from pearl-barley and from oats, as well as the husk of these grains, might be economically employed by the stock feeder where they can readily be obtained. ~ 9. Kind and quantity of additional food required by a growing animal. The young and growing animal requires also that its food should be adjusted to its peculiar wants. In infancy the muscles and, bones increase rapidly in size when the food is of a proper' kind. This food, therefore, should contain a large supply of the phosphates, from which bone is formed, and of gluten or fibrin, by which the muscles are enlarged. Some kinds of fodder contain a larger proportion of these phosphates. Such are corn seeds in general, and the red clover among grasses. Somen. again contain more of the materials of muscles. Such are beans and peas among our usually cultivated seeds,'and tares and other leguminous plants among our green crops. Hence the skilful feeder or rearer of stock can often select with judgment that kind of food which will specially supply-that which the animal, on account of its age or rapid,growth, specially requires-or which, with a view to some special object, he wishes his animal specially to lay on. Does he admire the fine bone of the Ayrshire breed? —he will try to.stint it while' youing of that kind of food in which the phosphates abound. Does he wish to strengthen his stockl, and to enlarge their bones?-he will supply the phosphates liberally while the animal is rapidly growing. An interesting application of these principles is seen in the mode of feeding calves adopted in different districts. Where they are tobe reared for fattening stock, to be sold to the butcher at two or three years old, they are well fed with good and abundant food from the first, that they may grow rapidly, attain a great size, and carry much flesh. If starved and stunted while young, they often fatten rapidly when put at last upon a generous diet, but they never attain to their full natural size and weight. When they are reared for breeding stock or for milkers, similar care is taken of them in the best dairy countries from the first, though in some the allowance of milk is stinted, and substitutes for milk are early given to the young animals. But it is in rearing calves for the butcher that the greatest skill in feeding is displayed, where long practice has made the farmers expert in this branch of husbandry. - To the man who has a calf and a milk cow, the principal question is, how can I, in the locality in which I am placed, make the most money of my calf and my milk? Had I better give my calf a Iittle'of the milk, and sell the remainder in the form of new * Rice dust is very good food for fattening pigs, makes excellent pork, and is very profitt able when given along with whey. FEEDING OF YOUNG CALVES. 603 milk-or bad I better make butter and gi:;e the skimmed milk to my calves-or will the veal, if I give iy calf all the milk, pay me a better price in the end? The result of many trials has shown, that in some districts the lkigh price-obtained for well fed veal gives a greater profit than can be derived from the milk in any other way. While the calf is very young-during the first two or three weeksits bones and muscles chiefly grow. It requires the materials of these, therefore, more than fat, and hence half the milk it gets, at first, may be skimmed, and a little bean meal may be mixed with it to add more of the casein or curd out of which the muscles are to be formed. The costive effect of the bean meal must be guarded against by occasional medicine, if required. In the next stage, more fat is necessary, and in the third week at latest, full milk, with all its cream, should be given, and more milk than the mother supplies if the calf requires it. Or, instead of the cream, a less costly kind of fat may be used. Oil-cake, finely crushed, or linseed meal, may supply at a cheap rate the fat which, in the form-of' cream, sells for much money. And, instead of the additional milk, bean meal in larger quantity may be tried, and if cautiously and skilfully used, the best effects on the size of the calf and the firmness of the veal may be anticipated. In the third or fattening stage, the custom is, with the same quantity of milk, to give double its natural quantity of cream-that is, to supply in this way the fat which the animal is wished chiefly to lay on. This cream may either be mixed directly with the mother's milk, or, what is better, the. afterings of several cows may be given to the calf along with its food. For the expensive cream there might no doubt be substituted many cheaper kinds of fat which the young animal might be expected to appropriate as readily as it does the fat of the milk.:Linseed meal is given with economy. Might not vegetable oils and even animal fats be made up into emulsions which the calf would readily swallow, and which would increase his weight at an equally low cost? A fat pease-soup has been found to keep a cow long in milk; might it not be made profitable also to a fattening calf? The selection of articles of food which will specially increase the size of the bones in the growing animal, by supplying a large quantity of the phosphates, is at present limited in a considerable degree. The grain of wheat, barley, and oats-is the source from which these phosphates are most certainly and most abundantly supplied to the animals that feed upon them. But in many cases corn is too expensive a food, and those kinds of corn which contain the largest proportion of the phosphates supply only a comparatively small quantity in a given time to the growing animal. Why should not bone-dust or bone-meal be introduced as an article of general food for growing animals' There is no reason to believe that animals would dislike it-none that they would be unable to digest it. With this kind of food at our command, we might hope to minister directly to the weak limbs of our growing stock, and at pleasure to provide the spare-boned animal with the materials out of which a limb of.great strength might be built up. Chemical analysis comes further to our aid in pointing out the kind of food we ought to give for the purpose of increasing this or that part (i04 FOOD REQUIRED DURING PREGNANCY. of tne animal body. Thus in regard to the same growth of bone, it appears that, while linseed and other oil cakes are mainly used with the view of adding to the fat, some varieties are more fitted at the same time to minister to the growth of bone than others are. Thus, four varieties of oil-cake examined in my laboratory, contained respectively of earthy phosphates and of other inorganic matter in 100 lbs. the following quantities: PER CENTAGE OF Earthy ph4osphates. Other inorganic matter. British linseed cake.. 2-86 2-86 Dutch do... 270 2-54 Poppy cake.... 5-22 1'24 Dodder cake... 667 3-37 The numbers in the first column, opposite to poppy and dodder cake, show that these varieties of oil-cake contained a much larger proportion of the phosphates than the others did, and consequently that an equal weight of them would yield to growing stock more of those substances which are specially required to build up their increasing bones. ~ 10. Kind and quantity of additional food required by a pregnant animal. The food of the pregnant animal must sustain-thefull-grown mother, and must add at the same time to the substance of her unborn young. The quantity of food which is necessary to sustain the mother-if herself flll-grown, which is often far from being thecase-varies with many circumstances. It is said that in the stall an ox or a cow will eat one-fifth of its weight of turnips in a day. or one-fiftieth of dry food, such as hay and straw. With this allowance of food the animal would probably increase in weight in some degree,-but'according to Riedesel one-sixtieth of its weight of dry hay is necessary merely to sustain it. From what we have already seen of the composition of the different grasses, it is obvious that the quantity required will be much affected by the kind of hay with which the animal is fed. To nourish the young calf in the womb of its mother, an additional quantity of food must be given, and this quantity must be increased as the state of pregnancy advances. And though the kind of additional food which is given must readily supply the materials of the growing bones and muscles of the foetus, yet it must contain also a larger quantity of starch or sugar also than the mother in her ordinary state would require. This is owing to the circumstance that the mother must now breathe for two animals, fbr herself and her young. The quantity of blood is increased, more oxygen is taken in by the lungs, and more carbon is given off' in the form of carbonic acid. To supply this carbon, more of farinaccous or saccharine food must be eaten from the time when pregnancy takes place, and it must increase as the young animal enlarges in size. Except in the way of feeding the mother, in all respects well, I am not aware that any experiments have been made with the view of specially affecting the condition of the future calf by the kind of food given to the mother. A certain proportion of bone and muscle no doubt must FOOD REQUIRED BY A COW IN MILK. 605 be supplied to the young animal by the food given to the mother, or the bones and muscles of the mother herself will be laid under contribution to supply it-but it does not appear impossible to affect the size of the bone by the quantity of phosphates which are given in the food, or the growth and development of the muscles by that of the gluten, fibrin, or casein with which the mother is fed. Might not an addition of bone-meal to the food of the pregnant cow give a calf of larger bone? Would not beanmeal or skim-milk add to the size of its muscles? ~ 11. Kind and quantity of additional food required by a milking animal. After the young animal is born, the mother has still to feed it with her milk. And as the calf grows rapidly, the food it requires increases daily with its bulk, land the demands upon the mother therefore every day become greater. At this period, therefore, the cow must obtain larger supplies of food to sustain herself and to produce a sufficient quantity of milk for her calf than at any other period. If these adequate supplies are not given, a portion is daily taken from her own substance-her body becomes leaner, and her limbs more feeble, while her young also-is stinted and puny in its growth. By-and-bye, however, the calf begins to pick up food for itself. It begins to live partly upon vegetables. The mother is in consequence relieved of a part of her burden-her udders are less drawn upon-the quantity of inilk secreted becomes less-she begins again to lay muscle and fat upon herself-her udders at length become dry, and she slowly recovers, her original plump condition. She has, indeed, at this period a tendency to fatten if the same supply of food is continued to her, and in many districts it is customary to feed her off at this time for the butcher. What I have already said of the artifices by which the food given to the cow may possibly be made to affect the bodily character of the future calf, applies equally to the means of more or less effectually promoting the growth of the young animul while it isfed solely upon milk. The kind of food given to the mother may make the milk richer in curd, which will promote the growth of muscle-or richer in phosphates, by which the enlargement of the bones of the calf will be assisted. Scarcely any two samples of milk, indeed, are found, upon analysis, to contain the same proportion of phosphates and of other saline substances, and there is little reason to doubt that if an unusual quantity of these be given in the food of the mother, an unusual quantity will be found also in the milk she produces. For the production of milk the mother requires an adequate additional supply of all the substances which we have seen to be necessary to the support of the unborn fcetus-of the starch as well as of the gluten and saline substances of the food. But it is interesting to mark the very different purposes to which the additional supply of starch in her food is now applied. The pregnant mother requires this starch to supply the carbon given off more abundantly during her increased respiration. She breathes, as I have already said, for her young and for herself, and therefore gives off more carbon from her lungs. 26 606 USES OF MILK IN THE ECONOMY OF NATURE. But when the young animal is born it breathes for itself. It must, therefore, be supplied with that kind of food which seems specially in, tended to meet the wants of respiration. The additional starch eaten by the mother, therefore, instead of being breathed away in her own lungs, is conveyed in the form of sugar into the food of the young animal. It is changed into the sugar of the milk, and the natural function of this sugar is-to supply the carbon which the young animal gives off when it begins to breathe for itself. It is not difficult to understand the kind of process by which the starch of the mother's food is converted into the sugar of her milk. If to 2 of starch = 24C + 20H + 200, we add 4 of water= 4H + 40, we have 24C + 24H + -240, which is -the formula for milk sugar. In passing through the digestive organs of the cow, thereibre, the elements of the 2 of starch require only to be combined with4 those of 4 of water to be converted into-the sugar of milk. But though it is not difficult to understand in what way this change may be effected, yet it is exceedingly interesting to find that such a chemical change as this should be made to commence at a certain special epoch with-a view to a certain special end. Milk is a perfect food for a growing animal, containing the curd which is to form the muscles, the butter which is to supply the fat, the phosphates which are to build up the bones, and the sugar which is to feed the respiration. Nothing is wanting in it. The mother selects all the ingredients of this perfect food from among the useless substances which are mingled in her own stomach with the food she eats-she changes these ingredients chemically in such a degree as to present them to the young animal in a state in which it can most easily and with least laboui employ them for sustaining its body-and all this she begins to do at a given and appointed moment of time. -How beautiful, how wonderful, how kindly provident is all this! But apart from its natural use in the economy of nature, milk may be regarded as an article of manufacture-an important article of agricultural husbandry. As a mere producer of milk for other purposes than the feeding of calves, the cow will be differently fed according to the purpose for which her milk is intended to be employed, or the form in which it is to be carried to market. a. The town dairyman, who sells his new milk to daily customers, requires quantity rather than quality. He gives his cattle, therefore, succulent food in which water abounds-green grass-forced rapidly forward by irrigation or otherwise-green clover, young rye, brewers' grains, or hay tea.* In this way, without the actual addition of water, he can make his milk thin, and increase its bulk. b. Those, again, who desire much rich cream, or who grow milk for A mixed hay tea and pease soup, which is excellent for making cows give milk, is prpared by putting hay into a pot in alternate layers, sprinkling between each a handful of pease-meal, adding water and bringing to a boil, TO PRODUCE MILK FOR CHEESE OR BUTTER. C07 the manufacture of butter, pay less attention to the bulk of the milk itself than to that of the cream they can collect-from its surface. The proportion of butter is increased by the use of food which contains much fatty matter-of any of those kinds of food,'indeed, by which an ox can be made rapidly to lay on fat. Oil-cake has by some been objected to as likely to give a taste to the milk, but it may be safely used in small quantity, and gives an abundant and good flavoured cream. c. In cheese countries, again, it is the curd that is chiefly in request. No doubt the value of a cheese depends much upon the proportion of butter it contains diffused throughout its substance, but the weight of cheese produced upon a farm depends mainly upon the quantity of curd which the milk of the dairy yields. Where skim-milk cheese is made, the weight of produce obtained depends almost solely upon the richness of the milk in curdy matter. Clovers, vetches, and pea straw abound in casein or vegetable curd, and thus give a rich and productive milk to the cheese maker, while bean-meal and pease-meal, in so far as they can be given to the cow with safety, may with advantage be employed to produce the same effect. As every thing which tends tolay on fat on the animal is likely also to increase the proportion of butter in its milk, so every thing which promotes the growth of muscle will also add to the richness of the milk in curd or cheese. g 12.- Influence of size, condition, warmth, exercise, and light, on the quantity of food necessary to make up for the natural waste. But the quantity of food of any kind which an animal'will require is affected by many circumstances. T'hus10. The size and condition of the animal will regulate very much the quantity of food which is necessary to sustain it. The larger the muscles and bones the greater will be the daily waste, and the greater the quantity, therefore, of the food necessary to replace it. If an animal require a 50th or a 60th of its weight of dry food daily, of course his size and weight will regulate almost entirely the quantity of food he ought to eat. A knowledge of this circumstance is occasionally of economical value to the stock feeder or dairy farmer, and will modify very much the line of conduct he may be inclined to adopt as the most profitable. A large animal requires more food to keep it in its actual conditionto make up, that is, for the natural waste. If you wish to convert much produce into much rich dung, therefore, keep large animals. They will convert a large quantity of vegetable matter into manure without adding any thing to their own substance. If one-fiftieth of its weight of dry food be necessary to sustain it, then an animal of 100 stones weight will convert two stones of hay daily into dung. Whatever it eats beyond the two stones, will go to the increase of its weight. But a small animal, of 50 stones, requires only one stone a day to sustain its body, or converts one stone wholly into dung. Whatever it eats beyond this quantity, therefore, will go to the production of increased beef and bone. Hence, if I have a given quantity of vegetable produce, [ ought to be able to manufacture more beef from it by the use of small cattle than of large, provided my large and small stock are equally pure in breed, are equally quiet, and are as kindly feeders. 608 INFLUENCE OF EXERCISE AND WARMTH. The same reasoning applies to dairy cows of different breeds. If I give two stones of hay to a small Shetland cow, she may not convert more than one of them into dung, the other she may consume for the production of milk. But if I give the same quantity to a cow of double the size, nearly the whole two stones may be converted into dung-may be employed in sustaining the animal-and if she yield any milk at all, it will be poor and thin. This reasoning accounts for the fact which has been long observed, that small breeds of cattle give the richest milk, and that such as the small Orkney breed yield the largest produce of butter and cheese from the same quantity of food. They waste less of their food in sustaining theirown bodies. Lean, spare cows also require less to sustain them; and hence the skin-and-bone appearance of the best milkers among the.Ayrshire and Alderney breeds. 2~. The quantity of exercise which an animal takes, or of fatigue it is made to undergo, requires a proportionate adjustment in the quantity of food. The more it is exercised the more frequently it breathes,- the more carbon it throws off from its lungs, the more starch or sugar consequently its food must contain. If more is not given to it, the fat or other parts of the body will be drawn upon, and the animal will become leaner. Again, the natural waste of the muscles and bones is said to be caused by, or at least to be in proportion to, the degree of motion to which the several parts of the body are subjected. Take more exercise, therefore, move one or more limbs oftener than usual, and a larger part of the substance of these limbs will be decomposed, removed, and rejected in the excretions. Hence the reason why hard work requires good food, and, why the strength of all.animals is diminished, if they be subjected to great fatigue and are not in an equal degree supplied with nourishing food, by which the wasting parts of the body may be again built up. 3~. The degree of warmth in which the animal is kept, or. the temperature of the atmosphere in which it lives, affects also the quantity of food which the animal requires to eat. The heat of the animal is inseparably connected with its respiration. The more frequently it breathes, the warmer it becomes, and the more carbon it throws off from its lungs. It is believed, indeed, by many, that the main purpose of respiration is to keep up the heat of the body, and that this heat is produced very much in the same way as in a common fire, by a slow combustion of that carbon- which escapes in the form of carbonic acid from the lungs. Place a man in a cold situation, and he will either starve or he will adopt some means of warming himnsel:. He will probably take exercise, and by this means cause himself to breathe quicker. But to do this for a length of time, he must be supplied with more food. For not only does he give off more carbon from his lungs, but the exercise he takes causes a greater natural waste also of the substance of his body. So it is with all aninials. The greater the difference between the temperature of the bodv and that of the atmosphere in which they live, the more food they require to "feed the lamp of life"-to keep them warm, that is, and to supply the natural waste. Hence the importance of plantations as a shelter from cold winds to grazing stock-of open sheds to protect fattening stock from the nightly dews and colds-and even of EFFECT OF ABSENCE OF LIGHT. 609 closer covering to quiet, and gentle breeds of cattle or sheep, which feed without restlessness and quickly fatten. A proper attention to the warmth of his cattle or sheep, therefore, is of great practical consequence to'the feeder of stock. By keeping them warm he diminishes the quantity of food which is necessary to sustain them, and leaves a larger proportion for the production of beef or mutton. Various experiments have been lately published, which confirm the opinions above deduced from theoretical considerations. Of these I shall only mention one by MSr. Childers, in which 20 sheep were folded in — the open field, and 20 of nearly equal weight were placed under a shed in a yard. Both lots were fed for three months-January, February, and March-upon turnips, as many as they chose to eat, half a pound of linseed cake, and half -a pint of barley each sheep per day, with a little hay-and salt. The sheep in the field consumed the same quantity of food, all the barley and oil-cake, and about 19 lbs. of turnips per day, from first to last, and increased on the whole 36 stones 8 lbs. Those under the shed consumed at first as much food as the others, but after the third week they eat 2 lbs, of. turnips each less in the day, and in the ninth week, again 2 lbs. less, or only 15 lbs. a day. Of the linseed-cake they also eat about one-third less than the other lot, and yet they increased in weight 56 stones 6 lbs., or 20 stones more than the others. Thus the cold and exercise in the field caused the one lot to convert more of their food into dung, the other more of it into mutton.: But why did the sheltered sheep also consume less food? Why did they not eat the rest of the food offered them, and convert it also into mutton? Because.the stomach of an animal will not do more than a certain limited amount of work in the way of digesting, after the wants of the body are fully supplied.'When circumstances cause the sustaining quantity of food to increase, the digestive powers are stimulated into unusual activity, and though plenty'of food be placed before the animal it may be unable to consume and digest more than is barely sufficient to keep it in condition. If tie sustaining portion be lessened, by placing the.animal in new circumstances, more food may be digested than is absolutely necessary to supply the daily waste-that is to say, the animal may increase in weight. But the unusual stimulus being removed, it may not now be inclined, perhaps not be able, to digest so large a quantity as it did before when that large quantity was necessary to sustain its body —that is to say, that while it increases-in weight it will also consume less food. 4-. The absence of light has also-a material influence upon the effects of food in increasing the size of animals. Whatever excites attention.in an animal, awakens, disturbs, or makes it restless, appears to increase the natural waste, and to diminish the effect of food in rapidly enlarging the.body. The rapidity with which fowls are fattened in the dark is well known to rear'ers of poultry.* In India, the habit prevails of sewing up the eyelids of the wild hog-deer, the spotted deer, and other wild It is astonishing with what rapidity fowls (dorkings) increase when well fed, kept in con. fined cribs, and in a darkened room. Fed on a mixture of 4 lbs. of oatmeal, 1 lb. of suet, and I lb. of sugar, with milk for drink five or six'imes a day in summer, a dorking will add to its weight 2 lbs. in a week, sometimes 11 lbs. in four days. A young turkey will lay on 3.DS. a week, under the same treatment. 610 VENTILATION AND CLEANLINESS. animals when netted in the jungles, with the view of taming and speedily fattening them. The absence of light indeed, however produced, seems to soothe and quiet all animals, to dispose them to rest, to make less food necessary, and to induce them to store up more of what they eat in the form of fat and muscle. An experiment made by Mr. Morton, on the feeding of sheep, shows the effect at once of shelter, of quiet, and of the absence of light upon the quantity of food eaten and of mutton produced from it. Five sheep, of nearly equal weights, were fed each with a pound of oats a-day and as much turnips as they chose to eat. One was fed in the open air, two in an open shed-one of them being confined in a cribtwo more were fed in a close shed in the dark-and one of these also was confined in a crib, so as to lessen as much as possible the quantity of exercise it should take. The increase of live weight in each of the five, and the quantity of turnips they respectively consumed, appear in the following table: Increase LIVE WEIGHT. for each I —— ncrease. Turnips 100 lbs. of Nov. 18. March 9. eaten. turnips.'Ibs. lbs. Ibs. lbs. lbs. Unsheltered.... 108 131 7 23'7 1912 1-2 In open sheds.... 102- 1298 27-8 1394 2' 0 Do., but confined in cribs 108 130-2 22-2 1238 1-8 In a close shed in the dark 104 132-4 28-4 886 3-1 Do., but confined in cribs 111 13tL3 20 3 886 2-4 From this table it'appears, as we should have expecteda. That much less-one-third less-turnips was eaten by the animal which was sheltered by the open shed, than by that which was without shelter; while in live weight it gained four pounds more. b. That in the dark the quantity of turnips eaten was one-half less, and the increase of weight a little greater still. c. But that when confined'in cribs-though the food eaten might be a little less-the increase in weight was not so great. The animal, in fact, was fretful and restless in confinement, and whatever produces this effect upon an animal prevents or retards its fattening. d. That the most profitable return of mutton from the food consumed, is when the animal is kept under shelter and in the dark. Such a mode of keeping animals, however, must not be entered upon hastily or without due consideration.. The habits of the breed must be taken into account, the effect of the confinement upon their health must be frequently attended to, an'd, above all, the ready admission of fresh air and a good ventilation must not be forgotten. By a neglect of the proper precautions, unfortunate'results have frequently been obtained and a sound'practice brought into disrepute. 5~. Ventilation and cleanliness indeed are important helps to economy in the feeding of all animals. Shelter and warmth will do harm, if free and pure air is not admitted to the fattening stock. The same is true of cleanliness, so favourable, to the health of all animals. The cleaner their houses and skins are kept,'the more they thrive under any given form of treatment in other respects. EFFECT OF THE SOURING OF FOOD. 611 ~ 13. Influence of the form or state in which the food is given on the quantity required by an animal. The state in which the food is given to his stock has often an important influence upon the profits of the feeder. Thus1~. The souring of the food, in some cases, makes its use more economical.- Arthur Young details several series of experiments on the fattening of pigs, in which bean meal was given mixed with water in the sweet state, and after it had been allowed to stand several days to sour. In every case in which it was given sour, the pork obtained gave a profit upon the price of the meal, while in every case in which the same meal was given sweet and in equal quantity, the price obtained for the pork was less than that which was paid for the meal. Upon sour food, indeed, pigs are universally observed to fatten best. In Holstein, it is customary to collect waste green herbage of every kind, and to let it sour in water. It then fattens pigs which would scarcely thrive on it before. During this souring of vegetable matter in water, it is lactic acid-the acid of milk —which is chiefly produced. This acid, therefore, would appear' to favour the increase of size'in the pig, and to this cause may-be owing the profitable use of sour whey in feeding this kind of stock in cheese-making districts. I have been told by some cow-feeders who use brewers' grains, that the dry cows, when fattening off, relish the grains most when slightly sour, and fatten most quickly upon them. From others, however, I have obtained a contrary opinion, and have been assured that fattening stock of all kinds like the grains best, and thrive best upon them, when perfectly sweet and fresh. It is a matter of doubt, therefore, whether or not the souring of food generally, of all kinds and for all kinds of stock, can be safely tried or recommended. 2~. The boiling or steaming of dry food, and even of potatoes and turnips, is recommended by many as an economical practice. I believe that the general result of tle numerous -experiments which have been made upon this subject in various parts of the country is in favour of this opinion in so far as regards fattening and growing stock. It seems a more doubtful practice in the case-of horses which are intended for heavy and especially for fast work-though even for these animals the use of steamed food is beginning to be adopted by some of the most extensive coach contractors. [Stephens' Book of the Farm.] 3~. It is a curious fact not less worthy of the attention of the chemist than it is of the practical man, that the age of the food singularly affects its value in the nourishment of animals. Thus new oats are not considered fit for, hunters before the months.of February or March. They affect the-heels and limbs with something like grease, and make the horse unfit for fast work, Nor is it merely water which the grain loses by the five or six months' keeping-for if it be dried in the kiln it is still unfit for use, from its stimulating in an extraordinary degree the action of the kidneys. Some chemical change takes place in the interior of the oat which has not yet been investigated. The potato, on the other hand. by keeping, loses much of its nutritive value, even before it has begun to sprout-and every feeder knows that turnips which have shot into flower, add much less than before to the weight of his fattening stock. 612 INFLUENCE OF SOIL AND CULTURE ON THE 14. Influence of soil and culture on the nutritive value of agricultural produce. I have on several former occasions, (pages 500 to 528), directed your attention to the remarkable influence which soil, culture, and climate have upon the chemical composition of the different corn and green crops usually raised:for food. Every such change of composition alters also the nutritive value of any given crop. If the wheat or barley be richer in gluten, it will build up more muscle-if it abound more in starch, a smaller weight of it will supply the carbon of respiration-if it be richer in fatty matter, it will round off the edges of the bones, and fill up the inequalities in an animal's body more quickly with fat. Such differences as these I have already shown you do really exist among samples of the same kind of grain grown upon soils either of different quality, or of the same quality when differently cultivated or manured. But this different culture or manuring afelcts the relative proportions of the several kinds of inorganic matter also-the phosphates and other saline substances —which are known to exist necessarily in all vegetable productions. In illustration -of this, I wouldldirect your attention to the following analyses-made in my laboratory by Mr. Frombergw-of the ash of two samples of the same kind of turnip (red topped yellow) raised by Lord Blantyre, on the same field, the one.with guano alone, the other with farm-yard dung alone.- The quantity of ash left by the two varieties of turnip was 0-68 and.0-7 per cent. respectively, and this ash was composed as follows:Composition of the ash of turnips raised with guano, and witl farm-yard dung. GUANO. DUNG. Interior. Exterior. Interior. Exterior. Chloride of Potassium. 556 503 5-40 10-71 Sulphate of Potash.. 30'85 37 04 31-20 35-47 Carbonate of Potash.. 11 38 9'03 36-74 17-63 Phosphate of Potash.. 20-93 10-17 5-51 3-65 - --- - Lime. 4-55 4'49 1-58 2-02 --- --- Magnesia. 0-34 1-62 2-63 3-13 Alumina. 4-87 9.94 0-92 2-76 Carbonate of Lime 9. 952 9-72 11-56 14-82 Alumina..... 5-09 2-79 0'94 0-46 Oxide of Manganese.. 321 5-90 2-60 5.33 Silica...... 165 3-43 - 304 97-95 99'16 99-08.99-02 The most striking difference between the two varieties of ash is in the proportion of phosphates they respectively contain. The ash of the guano turnips contained from 25 to 30 per cent. of phosphates, that of the dung turnips only from 9 to 11 per cent.' This could not fail to make an important difference in their relative values for the feeding of stock whose bones are growing, and which require, therefore, a larger supply of phosphates in their food.. The phosphates of lime and magnesia form, as we know, one of the valuable constituents of guano, but we could scarcely have inferred that this manure would have caused so much larger a proportion of these phosphates to enter into the constituents of the turnips raised with them. NUTRITIVE VALUE OF AGRICULTURAL PRODUCE. 613 It is not unlikely that turnips, raised from bones, will also abound more largely in phosphates than turnips raised from dung or rape dust, and may therefore be better fitted for growing stock. ~ 15. Can we correctly estimate the relative feeding properties of different kinds of produce under all circumstances. Since the several nutritive effects of different'kinds of food are dependent upon so many circumstances-upon the state of the animal itself-the purpose for which it is fed-the mode in which it is housed and protected-the form and period at which it is given-can it be possible to classify them in an order which will indicate their relative feeding values in all cases and for all purposes? This is obviously impossible. We may easily arrange them in the order of their relative values in reference to some one of the several purposes for which food is given. We: may shew in as many different tables the order of their relative values in laying on fat-in increasing the muscles-or in promoting the growth of bone; but we cannot arrange theoretically, nor can experiment ever practically classify, all our common vegetable productions in one invariable order which shall truly represent their relative values in reference to each of these three different points:1~. Experimental values.-This, however, practical writers have often attempted to do. Making their experiments in different circumstances, with different varieties of the samre produce, upon different kinds of stock, or upon animals fed for different purposes, they have obtained results of the most diversified kind, and have classified the several kinds of fodder in the most unlike order. I select a few of these results for the sakeof illustration. Taking 10 lbs. of meadow hay as a standard,-then, to produce an equal nutritive effect, the different quantities of each of the other kinds of fodder represented by the numbers in the following table ought to be used-according to the several. authors whose names are given. Experimental quantities of fodder which must be used to produce an equal nutritive effect, according toSchwertz. Block. Petri. Thaer. Pabst. Meyer. Middleton. Meadow hay. -10 10 10 10 10 10 10 Aftermath hay 11 - 10 - - Clover hay. 10 10 9 9 10 - Green clover in flower and lucerne. - 43 - 45 42 - - Lucerne hay 9 - 9 9 10 - Wheat straw. - 20 36 45 30 15 Barley straw.. 40 19 18 40 20 15 Oat straw.. 40 20 20 40 20 15 Pea straw. - -16 20 13 15 15 Potatoes.. 20 22 20 20 20 15 Old potatoes. 40 - - Carrots.... 27 37 25 30 25 23 34 Turnips... 45 53 60 52 45 29 80 Wheat.. 4 3 6 6 - - Barley.. - 3 6 - 5 5 Oats.... —. 4 7 - 6 - F'rom an inspection of this table, we should naturally conclude eitner 26 614 THEORETICAL NUTRITIVE VALUES. that the different kinds of fodder vary very much in quality, or that those who determined their relative values by experiment must have tried their effects upon very different kinds of stock, fed probably also for different purposes. Both of these conclusions are no doubt true. We know that the same kind of produce does vary very much in chemical constitution, but it is not likely that different samples of the same kind of turnip are so unlike each other that 29 lbs. of the one will go as far in feeding the same animal as 80 lbs. of another. These great differences in the table, therefore, seem to show that different kinds or varieties of fodder have been used, or under different circumstances, or results so discordant could scarcely have been obtained. A certain value, it is true, attaches to the numbers in the table when those given by the different authors nearly agree. Thus, about 20 of potatoes and 30 of carrots appear to be equal in -nutritive value to 10 of hay. It must be confessed, however, that this subject of the experimental value of different kinds of farm produce in feeding stock of the same kind for'the same purposes is still almost wholly uninvestigated. Will none of: the skilful stock feeders, of whom so many are now springing up, turn their attention to this interesting field-of experimental inquiry? 2~. Theoretical values.-But the theoretical values of different kinds of food in reference to a particular object, can be determined by analytical: investigations made in the laboratory. This has been done in a very able'manner by Boussingault, in-reference to the value of different kinds of fodder in the production of muscle. These values, according tc his analyses, are as follow, 10 of hay being again taken as a standard:Theoretical quantities of different kinds of vegetable produce which will produce equal effects in the growth of muscle (Boussingault):Hay....... 10 Potatoes... 28 Clover hay, cut in flower. 8'Old potatoes... 41 Lucerne do...... 8 Carrots....... 35 Aftermath do..... 8 Turnips.... 61 Green clover, in flower.. 34 White cabbage.. 37 Green lucerne.....35 Vetches...... 2 Wheat straw.... 52 Peas.... 3 Rye straw.... 61 Indian corn.... 6 Barley s.w... W 52 Wheat..... 5. 5 Oat straw...... 55 Rye....... 5 Pea straw....... 6 Barley.... 6 Vetch straw...... 7 Oats..... 5 Potato leaves..... 36 Bran.'.. 9 Carrot leaves.... 13 Oil-cake.... 2 Oak leaves...... 13 This table possesses muchvalue. It cannot, however, be'relied upon as a safe guide in all cases by the feeder, because of the differences in the composition of our crops, which arise from the mode of culture and the kind'Jf manure employed. It possesses, however, a higher value from this circumstance-that as muscle'in most animals forms the larger portion of their bulk, the order in which different kinds of vegetable food promote the growth of this part of the body, may in most cases be adopted as the order also of their relative values in sustaining animals and keeping them in ordinary condition. The same remark, however, will not EFFECT OF MODE OF FEEDING ON THE MANURE. 615 apply to animal food, since we may have a kind of animal food, such as gelatine, which would greatly promote the growth of muscle, but which. from its composition, is capable of ministering so little to the wants of the other parts of the body that it will not even support life for'any length of time. ~ 16. Effect of different modes of feeding on the manure and on the soil. There remains still one practical point in connection- with the feeding of stock, to which I think you will feel some interest in attending. The production of manure is an object with the European farmer of almost equal importance with the production of milk or the fattening of stock. What influence has the mode of feeding or the purpose for which the animal is fed, upon the quantity and quality of the manure obtained? 1~. The quantity of the manure depends upon the quantity of food which is necessary to-sustain the animal. With the exception of the carbon, which escapes from the lungs in the form of carbonic acid, and a comparatively small quantity of matter which forms the perspiration, the whole of the food which -sustains the body is rejected again in the form of dung. Now the sustaining food increases with the size of the animal, with the coldness of the temperature in which it is kept, and with the quantity of exercise it is compelled to take. Large, hardly worked, much driven, and coldly housed animals, therefore, if ample food is given them, will produce the largest Quantity of manure. It might be possible, indeed, tc keep large animals for no other purpose but to manufacture manure-by giving them an unlimited supply of food, using means to persuade them to eat it, and causing them at-the same time to take so much exercise as to prevent them from ever increasing in weight. 2~. Quality of the manure. —The quality of the manure depends almost entirely upon the kind of food given to an animal, and upon the purpose for which it is fed. a. The full-grown animal, which does not increase in weight, returns in its excretions all that it eats. The manure that it forms is richer in saline matter and in nitrogen than the food, because, as I have already explained to you in detail (p. 472), a portion of the carbon of the latter is sifted out as it were by the lungs, and diffused through the air during respiration. In other respects, whatever be the nature of the food-the quantity of saline matter or of gluten it contains-the dung will contain nearly the same quantities of both or of their elements. b. The-case of the fattening animal again is different. Besides the sustaining food, there is given to the animal some other fodder which will supply an additional quantity of fat. If this additional food be only oil, then the dung will be little affected by it. It will be little richer than the dung of the full-grown animal to which the same sustaining food is given. But if the additional food contain other substances besides fat —saline substances, namely, and gluten-then these will all pass into the dung and make it richer in precise proportion to the quantity of this additional food which is given. Thus if oil-cake be given for the purpose of laying on fat-the usual sustaining food at the same time being supplied-the 616 WHY OLD PASTURES CONTINUE RICH. dung will be enriched by all those other fertilizing constituents present in the oil-cake which are. not required or worked up by the fattening animal. Hence it is that the dung of fattening stock is usually richer than that of stock of other kinds. Oil-cake would be a rich manure were it put into the soil at once; it is not surprising, therefore, that after it has parted with a portion of its oil it should still add much to the richness of common dung. A knowledge of the kind of material, so to speak, which the animal requires to fatten it, explains in a considerable degree another practical fact of some consequence through which it is not easy at first sight to see. one's way. There are in various parts of the island certain old pastures which, fromn time immemorial, have been celebrated for their fattening qualities. Full-grown stock are turned upon them year after year in the lean state, and after a few months are driven off again fat and plump and fit for the butcher. This, I have been told when on the spot, has gone on time out of mind, and yet the land, though no manure is artificially added, never becomes less valuable or the pasture less rich. Hence the practical man concludes that the addition of manure to the soil is unnecessary, if the produce be eaten off by stock-that the droppings of the animals which are fed upon the land are alone sufficient to maintain its fertility. But the reason of this continued richness of such old pastures is chiefly this-that the cattle, when put upon them, are usually full-grown -they have already obtained their full supply of bone and nearly as much muscle as they require. While on the fields they chiefly select fat from the grasses they eat, returning to the soil the phosphates, saline substances,- and most of the nitrogen which- the grasses contain. Their bodies are no doubt constantly fed or renewed by new portions of these substances extracted from the food they eat, but they return to the soil an equal quantity from the daily waste of their own bodies-and thus are indebted to, and carry off the land, little more than the fat in which they are observed daily to increase. But as the materials of the fat may be, and no doubt originally are, derived wholly-perhaps indirectly,: yet wholly-from the atmosphere, the land is robbed of nothing in order to supply it, and thus may continue for many generations to exhibit an equal degree of fertility. I give this only as a general explanation, by which the difficulty may be solved, where no other more likely explanation can be found in the local circumstances of the spot, or of the district in which such rich old pastures exist. c. The growing animal, again, does not return to the soil all it receives. It not only discharges carbon from its lungs, but it also extracts phosphates from its food to increase the size of its bones, gluten to swell out its muscles, and saline substances to mingle with the growing bulk of its blood. The dung of the growing animal, therefore, will not be so rich as that of the full-grown animal fed upon the same kind and quantity of food. Hence from the fold-yard, where young stock are reared,, the manure will not be so fertilizing, \weight for weight, as from a yard in which full-grown or fattening animals only are fed. d. The milk cozs exhausts still further the food it eats. In the lean THE GROWING ANIMAL AND THE MILK COW. 617 milk cow, which has little muscle or fat-to waste away, and, therefore, little to repair, the sustaining food is reduced to the smallest possible quantity. -This small portion of food is all that is returned to the husbandman in her dung. The phosphates, salts and gluten, and even the starch, of the remainder of the food she eats, are transformed in her system,. and appear again in the form of milk. The dung of the milk cow must be very much poorer, and less valuable, compared with the food she eats, than that of any other kind of stock. It is true that the bulk of her dung may not be very much less than that of a full-grown animal which'is yielding no milk, but this bulk is made up chiefly of the indigestible'woody fibre and other comparatively useless substances which her bulky food contains. The ingredients of the milk have been separated from these other substances as the food passed through her body, and hence, though bulky, the dung of the milk cow is colder and less to be esteemed than that of the dry cow or of the full-grown ox. Nothing can more strikingly illustrate the difference between.the effect of the digestive organs of the fattening ox and those of the milk cow upon the'food they consume, than the well-known and remarkable difference in quality which exists between distillery dung, obtained from fattening cattle fed upon the refuse of the distilleries, and cow-feeders' dung, voided by milk cows fed upon nearly the same kind of foodnamely, the refuse of the breweries. ~ 17. Summary of the views illustrated in the present Lecture. The topics discussed in this Lecture are of so interesting a kind, and so beautifully connected together, that you will permit me, I am sure, briefly to draw your attention again to the most important and leading points. 10~. It appears that all vegetables contain ready formed-that is, form during their growth from the food on which they live-those substances of which the parts of animals are composed. 2~. That from the vegetable food it eats, the animal draws directly and ready-formed the materials of its own body-phosphates to form the bones-gluten, &c., to build up its muscles-and oil to lay on'in the form of fat. 3~. That during the process of respiration a full grown man throws off from his- lungs about 8 oz.-a cow or horse five times as much-of carbon every 24 hours; and that the main office of the starch, gum, and sugar of vegetable food is to'supply this carbon. -In carnivorous animals it is supplied by the fat of their food-in starving animals, by the fat of their own bodies-and in young animals, which, live upon milk, by the milk sugar it contains. 4~0 That muscles, bone, skin, and hair undergo a certain necessary daily waste of substance-a portion of each being removed every day and carried out of the body in the excretions. The main function of the gluten, the phosphates, and the saline substances in the food of the full' grown animal, is to replace the-portions of the body which are thus removed, and to-sustain its original condition. Exercise increases this natural waste and accelerates the breathing also, so as to render necessary 618 SUMMARY OF THE VIEWS LLUSTRATED. a larger sustaining supply of food-a larger daily quantity to keep the animal in condition. 5~. That the fat of the body is generally derived from the fat of the vegetable food-which fat undergoes during digestion a change or transformation by which it is converted into the peculiar kinds of fat which are specially fitted to the body of the animal that eats it. In carnivorous animals, the fat is also derived directly from the fat of their foodwhich is, in like manner, changed in order to adapt it to the constitution of their own bodies. In cases of emergency, it is probable that fat may be formed in the animal from the starch or sugar of the food. 6~. In the growing animal, the food has a double function to perform, it must sustain and it must increase the' body. Hence, if the animal be merely increasing in fat, the food, besides what is necessary to make up for the daily waste of various kinds, must also supply an additional proportion of oil or fat. To the growing animal, on the-other hand, it must supply also an additional quantity of gluten for the muscles, and of phosphates for the bones. If to each of a number of animals, equal quantities of the same kind of food be given, then those which. require the smallest quantity of food to sustain them will have the largest proportion to con vert into parts of their'own substance. Hence, whatever tends to increase the sustaining quantity-and cold, exercise, and uneasiness do so -will tend, in an equal degree, to lessen the value of a given weight of food, in adding to the weight of the animal's body. To the pregnant and to the milk cow the same remarks apply. The food is partly expended in the production of milk, and the smaller and leaner the cow is, less food being required to sustain the body, the more will remain for the production of milk. 7~. Lastly, that the quantity.and quality of the dung-while they depend in part upon the kind of food with which the animal is fed-yet even when the same kind of food is given, are materially affected by the purpose for which the animal is fed. If it be full-grown and merely kept in condition, the dung contains all that was presentin the food, except the carbon that has escaped'from the lungs. If it be a growing animal, then a portion of the phosphates and gluten of the food are retained to add to its bones and muscles, and hence the dung is something less in quantity and considerably inferior in quality to that of the fullgrown animal. So it is in the case of the milk cow, which consumes comparatively little in sustaining her own body, but exhausts all the food that passes through her digestive organs; for the production of the milk which is to feed her young. -The reverse takes place with the fattening ox. He takes little else from the rich additional food he eats but the oil with which it is intended that he should invest his own body. Its other constituents are for the most part rejected in his excretions, and hence the richness and high price of his dung. Such are the main -points I have endeavoured to illustrate to you in this Lecture-they involve so many interesting considerations, both of a CONCLUDING S.ECT10N. 619 theoretical and of a practical kind, that had my limits permitted I could have wished to dwell upon them at still greater length. ~ 18. Concluding Section. I have now brought the subject of these Lectures to a close. I have gone over the whole ground which in the outset I proposed to tread. It is the first time, I believe, that much of it has been trodden by scientific men, and I have endeavoured in every part of our journey to lay before you, as clearly as I could, everything we knew of the country we passed over, in so far as it had a practical bearing or was likely to be susceptible hereafter of a practical application. In the first Part, I directed your attention to the organic portion of plants-showed you of what substances it consisted-on what kind of organic food plants live-and by what chemical changes the peculiar organic compounds of which they consist are formed out of the organic food on which they live. In the second Part,- I explained in a similar way the nature, composition, and origin of the inorganic portion of plants. I dwelt, also, upon the nature, origin, and natural differences which exist among the soils on which our crops are grown, and'from which the inorganic constituents of plants are altogether derived. This led me toexplain the connection which exists between Agriculture and Geology, and the kind of light which this interesting science is fitted to throw upon the means of practically improving the soil. In the third Part, I dwelt upon the various means which may be adopted for increasing the general productiveness of the land-whether these means be of a mechanical or chemical nature. The whole doctrine of manures was here discussed and many suggestions offered to your notice, which have already led tointeresting practical results. In the fourth Part, I have explained the chemical composition of the several kinds of vegetable produce which are usually raised for foodshowed upon what constituents their nutritive values depend-and how soil, climate, and manure affect their composition and their value as food. The nature and composition of milk and of its products-butter and cheese-the theory of their manufacture, and the circunstances upon which their respective quantities and qualities depend-and, lastly, the way in which -food acts upon and supports the animal body, and how the value of the. manures they make is dependent upon the purpose for which the animal is fed-these subjects have also been considered and discussed in this fourth Part. In discussing new topics I have had occasion to bring before you many new views. This, however, I have not done lightly or without consideration, and I feel it to have been one of the greatest advantages which have attended the periodical form in which these Lectures have been brought before the public, that it has allowed me leisure to think, to inquire, and to make experiments in regard to points upon which it was difficult at first to throw any satisfactory light. It is gratifying to me to know that the general diffusion which these Lectures have obtained, has already done some service to the agriculture of the'country. FINIS; h-1Wvv~vAvnC*. ^ APPENDIX: CONTAINING ISUGGESTIONS FOR EXPERIMENTS IN PRACTICAL AGRI. CULTURE, WITH RESULTS OF EXPERIMENTS MADE IN 1841, 1842, AND 1843, APPENDIX. No. I. SUGGESTIONS FORE EXPERIMENTS IN PRACTICAL AGRICULTURE DURING THE ENSUING SPRING AND SUMMER. ONE of the most important objects which chemistry is at present desirous of attaining for the improvement of practical agriculture, is the discovery and application of specific or special manures. We know that certain substances, such as fold-yard manure, are capable of fertilizing to a considerable extent almost any land, and of causing it to yield a better return of almost any crop. But we know also that manures or fertilizers of nearly every kind are more efficacious on one soil than on another, and that some answer better also for one species of crop than for another. The case of gypsum will serve to illustrate both these positions. The effects of'gypsum in the United States, in Prussia, and other parts of Germany, and in some districts of England, are said to be absolutely astonishing; iwhile in many other parts of our Island, of Germany, and even of the United States, the benefit derived from it has not repaid the trouble and expense incurred in applying it. Gypsum, therefore, is especially adapted for use in certain soils only. Again, the remarkable effects of gypsum have been observed most distinctly on clover* and certain kinds of grass. The same benefits have not followed, to any thing like an equal extent, from its use on barley, oats, wheat, or other kind of grain. Therefore, while specially adapted to certain soils, it is also specially adapted to certain crops. It is a kind of specific manure for clover and some of the grasses. Now, neither of these subjects which it is so important to investigate,neither that of the manures which are especially fitted for'each soil, nor of those which are specially fitted for each crop,- can be determined either from theory or from experiments devised and executed in the laboratory of a chemist. The aid of the practical farmer, of many practical farmers, must be called in. Numerous experiments, or trials, must be made in various localities, and by different individuals,-all, however, according to the same rigorous and accurate method,-in order that, from the comparison of many results, something like a, general principle may be deduced. It is partly with a view to determine the mode of action of certain fertilizers, and partly in the hope of obtaining some additional light on the subject of manures specifically adapted to particular crops, that I venture to suggest to you the propriety of making one or more of the following sets of experiments, during the spring and summer of the present year. I could have much enlarged In regard to its use in Germany, Lampadius says,-" It may with certainty, be stated, that by the use of gypsum the produce of clover and'the consequent amount of live stock have been increased at least one-third."-DIE LEHRE VON DEN MINERLALISOHEN DUNGMITTBLN, p. 34. 2 OF GRASS AND CLOVER. [Appendix, the list of suggestions, but I neither wish to fatigue your attention, nor to place before you more work of the kind than can be readily accomplished, with little expense of time, labour, or money. Another season will, I hope, afford us an opportunity of interrogating nature by further, and perhaps more refined, modes of'experimenting. 1. OF GRASS AND CLOVER. 1~. It is beyond dispute, that on certain soils, gypsum causes a largely increased growth of grass and clover, but experiment alone appears capable of determining on what soils it is likely to be thus beneficial. Such experiments, therefore, ought to be made on every farm, on a small scale at first, and at little cost,* but made with care and accuracy, and with a minute attention to weights and measures. 2~. The action of gypsum appears to be entirely chemical, but the only explanation of this action yet attempted is far from being satisfactory. It-is desirable therefore, that experiments with other substances should be made, which are likely to throw light on the theory. - Important practical results may at the same time be obtained-they are' sure, indeed, to follow from a right understanding of the theory. In the neighbourhood of Lyons, it has been found that very dilute sulphuriC acidt (oil of vitrol) exhibits the same beneficial effect upon clover, that has elsewhere attended the use of gypsum. It is desirable, therefore, that a comparative experiment should be made with this acid-on a portion of the same field to which the gypsum is applied. Where the one fails the other may act. 3~. It was observed by Dr. Home, of Edinburgh, so early as the year 1756, that sulphate of soda; had a remarkable effect in promoting the growth of plants -its action being nearly equal to that of saltpetre or nitrate of soda. This fact, though mentioned by Lord Dundonald, has been lost sight of by practical men, the sulphateof soda being generally represented as too high in price to be available as a fertilizer.~ The use of saltpetre, however, and of nitrate of soda, both of which are more than double the price.of sulphate of soda, show that the cost of this latter article should not' stand in the way of an accurate trial of its value as a fertilizer on various crops. Dry stlphate- of soda can be readily obtained from any of the alkali works on the Tyne,l'and being an article of domestic manufacture, it is proper that its merits should be ascertained, and, if it can be available, that its use should be encouraged. From the circumstance of its containing sulphuric acid,'therefore, I would recommend that it should be tried on clover and grass, in comparison with gypsum and sulphuric acid, and on a portion of'the same field. It may succeed where the others.fail. 4~. Nitrate of soda also, as a top-dressing on grass land, has been often used with great benefit. I have seen grass land in Dumfiiesshire,_which, after being long let for' pasture at 30s. an acre, had been sprinkled with an annual topdressing of nitrate of soda at the rate of 20s. an acre, and had since readily let at.~4 an acre, yielding thus an annual profit of 30s. an acre to the landlord. In other districts, again, it has been found to, answer better for corn. Thus after a discussion on this subject inrthe Gloucester Farmers' Club, it was agreed, that nitrate' of soda "was a very valuable manure for white straw crops, but The price of gypsum in London is about 2s. 6d. per cwt. in Newcastle, 3s. t Gypsum consists of sulphuric acid and lime. I Glauber salts-consisting of sulphuric acid and soda. ~ Lord Dundonald says-" From experiments it has been proved to promote vegetation in a very high degree. The high price at present of this article precludes the use of it, but could it be made and sold atla cheap rate,' i would prove a most valuable acquisition to agriculture." Since the'time of Lord Dundonald some trials made in Germany have shown it to have a beneficial action on rye, potatoes, and fruit trees. I Messrs. Allan & Co., of the Heworth Alkali Works, deliver it in Newcastle and the neigh bouring towns, at 9. or lOs. per-cwt. No. I.] OP GRASS AND CLOVER. 3 when applied to green crops the benefit was not sufficiently great to counter-balance the expense."' In Northumberland, where it has been tried in a skilful manner by Mr. Gray, of bilston, it was found to yield a most profitable return on both hay and barley. These results show the necessity of further trials, not only forthe purpose of illustrating the cause of the beneficial action of this saline substance, but also with the view of arriving at some general rule by which the practical man may be guided, in determining on what fields, and for what crops on those fields, the nitrate of soda may be beneficially applied This experiment, like the others above-mentioned, will be much more valuable, if made in such a way that the result can be compared with that obtained by the use of other chemical agents. I would, therefore, propdse that in the same field of grass or clover, a portion should be measured off, to be topdressed with nitrate of soda, that thus not only the absolute, but also the comr pa'ative, weight of the produce may at the same time be ascertained. 5~. There are other trials also, from which this general subject is capable of receiving illustration. The fertilizing power of gypsum has been explained by its supposed action on the ammonia which is presumed to exist in the atmosphere. If this be the true explanation, a substance containing ammoniashould act at-least as energetically. At all events, the action of fold-yard manure and of putrid urine is supposed to depend chiefly on the ammonia they contain or give off. Now, among the substances containing ammonia in large quantity, which in most towns are allowed to run to waste, the ammoniacal liquor of the gas works is one which can easily be obtained, and can be applied in a-liquid state at very little cost. It must be previously diluted with water till its taste and smell become'scarcely perceptible. I would propose, therefore, as a further experiment, that along with one or more of the substances above-mentioned, the ammoniacal liquor of the gas works should be also tried-, on a measured portion of ground, and, if possible, in the same field. 6~. Soot, as a manure, is -supposed to act partly, -if not chiefly, in consequence of the ammonia it contains. In Gloucestershire it is applied to potatoes and to wheat, chiefly to the latter, and with great success. In the Wolds of Yorkshire it is:also applied largely to the wheat crop, at the rate of about 24 bushels to the acre.* - In this county it is frequently used on-grass land, to the, amount of 20 bushels an acre, and though I am not aware that it is extensively employed upon clover, I am inclined to anticipate that the sulphur it containst in addition to the ammonia, would render it useful to this plant. At all events, comparative experiments in'the same field with the gypsum and th6 ammoniacal liquor, are likely to lead to interesting results. ~. Common salt, highly recommended as a manure by some, has been as much depreciated by others, and hence, when directly applied, is considered as a doubtful fertilizerby almost all. The obscurity-in regard to its use. however, rests chiefly on the'quantity which ought to be employed. The result'of comparative experiments made in Germany, showed -that a very few pounds per acre were sufficieht to produce a largely increased:return of grass-while in England it has been beneficially, applied within the wide limits of from five to twenty Bushels per acre, and, when used for cleaning the land for autumn, of,thirty bushels an acre. Among the comparative experiments upon grass,and clover here suggested, the effect of salt might also be tried with the prospect of practical benefit. It would give an additional interest to the experiments and supply,an additional term of comparison.' The price is from 6d. to Is. a bushel. In this county the soot is said -to be often of an inferior quality, and brings therefore a less price. t The gypsum, I might also say, for much of our soot contains gypsum, the lime being derived chiefly from the sides of the flue. 4 OF GRASS AND CLOVER. [Appendix, The ertire series of experiments, therefore, which I would recommend, would occupy eight patches on a clover or grass field, one of which would be left undressed for the purpose of comparison. Thus, each plot being half an acre Gypsum. Sulphate of Ammoniacal Gypsum. Soda. Liquor. Sulphuric Nitrate of Common Soot. Acid. Soda. Salt. The ammoniacal liquor and the soot are placed as far as possible from the gypsum and sulphuric acid, that they may not interfere with each other's action. In a large field they might be placed still farther apart, and other trials might be made in one or two of the vacant places. The appearance of each patch should be entered, with the date, in an experiment book, at weekly intervals, and the final produce both of hay and of aftermath. carefully noted, both as to weight and qtuality. Nor will the experiment be completed when the crop for the year is gathered in; but, where it is possible, two further points should be ascertained,1~. The relative feeding or nourishing properties of the produce. To those who rear and fatten cattle, this is a matter of great importance, and it is one. which they could easily determine, at least very approximately. 2~. What has been the permanent effect of the several substances on the soil, as indicated by the comparative quantity and quality of the crop obtained from each half acre, on the sutcceeding or during the two following years. The result of these further observations may materially modify the-conclusion we should draw from the comparative weight-and quality of the'produce of the first year. I shall only observe, in conclusion, on this head, that the result of.a simultaneous trial of all these substances in the same field would not only throw much light on the specific action of each on the grass or clover in general, but would be of permanent utility to that farm or locality in which the experiments were made. It would indicate the kind of fertilizer which was best adapted to the farm or neighbourhood, in the existing condition-of its general culture. It would form a local record, useful not only to the tenant who made the experiment (if well made) and by whom the farm at the time was tenanted,'but more useful by far, and more permanently so, to the owner of the land,, whose interest in it is supposed to be not only greater, but much more lasting. In regard to the quantities of the several substances above-mentioned, which are to be applied to each acre, they may probably be varied according to cir-'cumstances, but the following may be recommended in the comparative experiments:.10. Gypsum 2 to 3, cwt. per acre. 2~. Sulphate of Soda 1 cwt. per acre.'30. Nitrate of Soda 1 cwt. per acre. 40. Soot 20-bushels per acre-this in different districts may be varied according to the known quality Of the soot. 5~. Of Sulphuric Acid from 30 to 40 lbs. per acre, applied at three or four several intervals-and diluted with at least 200 times its weight of water. Or so much water may be added as to make it perfectly. tasteless, or so weak as not sensibly to injure the texture of a plant left inmit during the previous night.* 6~. Of Ammoniacal Liquor 100 to 200 gallons per acre, according to its strength, for this is constantly varying. It must also be diluted with so large a quantity of water as will render it perfectly tasteless, and is likely to prove most beneficial if laid on at several successive periods.'The quantity above.mentioned amounts to about two gallons of the acid of the shops, and ti dlouAld be diluted with three or four hundred gallons of water. zNO. I.] OF WHEAT, BARLEY, AND OATS. 5 7~. Of common salt it will be safer to apply not more than four to sixbushels an acre; though, where time and circumstances permit, comparative trials might also be made on the efficacy of salt when applied in different proportions, to the same land on which the other experiments are made. As to the time when these several dressings.ought to be applied, some variation may be made according to the state of the young crop. They need not, in general, be used before the 10th of April, and they should, rarely be later than the middle of May. It will be desirable that in the detail of every set of experiments, the kind and quality of the soil (and subsoil) should be stated-with its drainage and exposure-and the kind of grass. or clover which had been sown upon it. II. OF WHEAT, BARLEY, AND OATS. It is known that saltpetre and nitrate of soda produce highly beneficial effects on all these varieties of grain. There remains much to be done, however, before the principle of their operation, or the circumstances on which their most useful application depends, can be clearly understood. Their relative effects on the same kind of grain must be made the subject of more frequent, more precise, and more carefully conducted experiments-and these effects must be compared with those of other fertilizing substances, in oider that we may arrive ultimatejy at some comparative estimate of the practical value of each, in increasing the growth and produce-of those crops which are the staples of animal food. A.-Of Wheat. It is confidently stated by some, as a general rule, that saltpetre is more advantageous than nitrate of soda, when applied to wheat. On the other hand, it is beyond question that the application of nitrate of soda to Wheat has been found productive of remarkable benefit. Is saltpetre especially adapted for wheat of all varieties, on all soils, and under every variety of managert/ent, and is nitrate of soda, in like manner, especially fitted for barley and oats l These are questions to which.the experiments hitherto made do not enable us to give a reply. New data must be obtained before we can have the means of reasoning usefully in regard to any of them. I would propose, therefore,1~. That where two varieties of wheat are sown on the same field, or on different fields of precisely the same kind of land and in the same condition, that two half acres of each variety should be measured off, and that one half acre of each should'be dressed with saltpetre, and the other with nitrate of soda, at the rate of.1 cwt. per acre; If three varieties could be so treated, the experiment would be the more valuable. It would thus be determined how far the effect of each of these nitrates was dependent upon the variety of wheat sown-and what was the relative action of each nitrate upon any of the varieties. 2~. That when the same varieties of wheat are sown upon two or more different soils-in different parts of a farm-that one portion of the wheat on every different soil should.be dressed with nitrate of soda, and another with nitrate of potash (saltpetre). By this experiment, it would be shown how far the effect of these substances is dependent on the nature of the soil, and how far the action of the one, compared with that of the other, is modified by diversity of soil._ In these different experiments, the management is presumed to be the same. If the experiments be repeated by several persons in different parts of the country,the effects of difference of management will, in a great measure, be shown in the diversity of the results. 3~. With the view of ascertaining the comparative effect of the sulphate of soda on this crop, I would suggest that in each case above specified, an equal area should be set aside to be dressed with this salt, in the proportion of 1 cwt. per acre. Of each variety of whea, therefore, and on each variety of soil, four patches 6 OF WHEAT, BARLEY, AND OATS. [AppendiX, of equal area, say half an acre, should be measured off-one of which should-be undressed for the purpose of comparison: thus-. —_- As before, the nature of the soil and the kind of Nitrate of a grain must be recorded-the appearance of each patch Soda. a P'. noted-week by week-with the time of ripening and ______ __ _ reaping-and the respective qualities and weights of the grain and straw collected from each half acre. Sulphate of The quantity of gluten contained in the wheat Soda. should also be determined, or a sample of the flour transmitted for the purpose to the writer of these suggestions, accompanied by a detail of the experiments they are intended to illustrate. B.-Of Barley and Oats. To barley and oats the above remarks all apply, with this difference, that to these crops saltpetre' is said to be less beneficial than the nitrate of soda. In connection with these crops, however, I would make the following additional observation. According to any theory of the action of the nitrates of potash and soda which readily presents itself, their effect on any crop which they are equally capable of benefitting ought to be nearly equal, weight'for weight. The nitrate of soda ought to have a decidedly more powerful action, were it not that the state of moisture in which it is generally sold, increases its weight so much as in a great measure to deprive it, in equal weights, of this superiority. But while 1 cwt. of saltpetre (nitrate of potash) is recommended as a sufficient dressing for.an acre, 14 to 1 cwt. of nitrate of soda is recommended for an equal area It would, therefore, be desirable where nitrate of soda is applied to any large extent of land, either with oats or barley, to make a comparative trial on three equal portions of the same field, with 1, 14, and 1 cwt. per acre, respectively. In addition, therefore, to the experiments suggested in regard to wheat, with the view of determining1~. The absolute and relative efficacy of saltpetre and nitrate of soda on different varieties of the grain; 2~. The same on different varieties of soil; 3~. And under diversities of management,-as in the previous treatment of the land, &c.; There may be added, in regard to oats and barley, another series of trial to determine4~. The relative effects of the different proportions of the nitrate of soda, which is at present svpposed to be specially beneficial to these kinds of grain. If any one be desirous of uniting this latter series with the former, it'may be done thus-.., --.'- -f 1 The vacant half-acre' being as before left Sulphate -of Nitrate of for the purpose of comparison. Such an - Soda. Serate saaltprete. entire series might be made at the same _____-. _ ____ time on a field of Tartary and of potatoe Nit f Nitrat — ofoats, and on two or more varieties of barNitrate of Nitrate of ley. Soda, Soda, 1 cwlt., 1'cwt. These top-dressings may all be sown -- -. —-__.__'wt._ - broad-cast —on the wheat most conveniently when the seeds are sown in April or May, and on the barley and oats when the fields have become distinctly green. I may be permitted to add, as inducements to practical men, to try one or more of these experiments in the accurate manner above described: 1~. That the result will be directly available and of immediate practical value on his own farm, to the person by whom they are carefully made. That they No..] OF TURNIPS. 7 will be-permanently useful to his landlord (if, carefully recorded), ought to be an inducement to the latter to give every facility and encouragement to his tenant in making them. 2~. That, instead of involving expense and outlay, which in many instances may ill be spared, they a.e sore in almost every case to do more than repay the cost of making them, by the increased quantity or value of the produce obtained. Any of the series of experiments, on'the scale suggested, may be made for five pounds, so that were the outlay all to be lost, the accurate knowledge obtained in reference to the general tillage,of his land, would be worth more money to the holder of a farm of a hundred acres. 3~. I need scarcely add, as a further inducement, the additional interest which such experiments give to the practice of farming-and the means they afford of calling forth the intelligence of the agricultural population. The moment a man begins to make experiments under the guidance of an understood.principle, from that moment he begins to think. To obtain materials for thought he will have recourse to books-and thus every new experiment he makes, will further stimulate and awaken his intellect, and lead him to the acquisition of further knowledge. Does it require anything more than this general awakening of the minds of the agricultural class, to advance the science of agriculture as surely and as rapidly as any of the other sciences, the-practical application of which have, led to those extraordinary developments of natural resources which are the characteristic and the pride of our time e III. OF TURNIPS. The raising of turnips is of such vast importance in the prevailing system of husbandry, that any improvement in the mode of culture must be of extensive and immediate benefit. Experiments so numerous and so varied have been made with this view, that it may almost seem superfluous in me now to make any further suggestions on- the subject. But when experiments have been made with a view to one subject only, it often happens in all departments of natural.science, that as newviews are advanced or more precise methods pointed out, it becomes necessary to repeat all our former experiments,-either for the purpose of testing the results they gave us, or of observing new phenomena to which our attention had not previously been directed. I. Numerous experiments, for example, have been made upon the use of bones in the raising of turnips, but they have been chiefly directed to economical ends and so far with the most satisfactory results. But among fifty intelligent and thinking practical men, and who all agree in regard to the profit to be derived from the use'f bones with the turnip crop, how many will agree in regard to the mode in which they act-how'few will be able to give-a satisfactory reason for the opinion they entertain! The sameiis true of theoretical chemists, some attributing their effect more especially to the earthy matter, others to the gelatine they contain. Dry bones contain about two-thirds of their weight of earthy matter, the other third consisting chiefly of animal matter resembling glue. Of the earthy matter five-sixths consist of phosphate of lime and magnesia, and the rest chiefly of carbonateof lime. Thus a ton of bone dust will containAnimal matter.... 746 bs. Phospate of lime, &c.. 1245 Carbonate of lime, &c.... 249 2240 On which of these constituents does the efficacy of bones chiefly depend X Does it depend upon the animal matter? This opinion is in accordance with the following facts:1~. That in the Doncaster report it is said to be most effectual on calcareous soils,-for in the presence of lime all organic matter more rapidly decomposes 27 8 OF TURNIPS. [Appendix. -2. That horn shavings are a more powerful manure than bones,-since horn contains only one or two per cent. of earthy matter.* 3~. That before the introduction of crushed bones, the ashes of burned bones had been long employed to a small extent in agriculture, but have since fallen almost entirely-into disuse. 4~. That old sheep skins cut up and laid in the drills, have been found to yield as good a crop of turnips and after-crop of corn, as the remainder of the field which was manured with bones. 5~. That "40 lbs. of bone dust are sufficient to supply three crops of wheat, clover, potatoes, turnips, &c., with phosphates,"t while one to two-thirds of a ton of bones, containing from 400 to 800 lbs. of phosphates, is the quantity usually applied to the land. On the other hand, the quantity of animal matter present in a ton of bones (746 lbs.) is so small, and its decomposition so rapid during the growth of the turnips-while at the same time the effects of-the bones are s,o lasting and so beneficial to the after-crop of'corn-that many persons hesitate in considering the great excess of phosphates applied to the land, as really without any share of influence, in the production of the crops. Thus Sprengel, an authority of the very highest character, both in theoretical and practical agriculture, is persuaded that the phosphates are the sole fertilizin ingredients in bones, and he explains the want'of success from the use of crushed bones in. Mechlenburg and North Germany, on the supposition that the soils in those countries already contain a sufficient supply of phosphates, while in England generally they are deficient in these compounds. Further, if the animal matter be the fertilizing agent in bones, why are not they of equal efficacy on grass land as upon turnips? With the view, therefore, of leading to some rational explanation of the relative effects of the several constituents of bones, it would be desirable to institute comparative experiments of the following kind1~. With half a ton of bones per acre. 2~. With three orfour cwt. of horn shavings or glue per acre. 3~. With two cwt. of burned bones per acre. 4~. With six or seven cwt. of burned bones per acre. The quantity of burned bones in No. 4 is that which is yielded by a ton of fresh bones; that in No. 3 is upwards of five times what should be taken up by the crops-as great part of what is added must be supposed to remain in the soil, while some must be dissolved and cair'ied off by the rains. The result of such experiments as these, if made accurately on different soils will lead us sooner to the truth than whole volumes of theoretical discussion. II. Nitrate of soda has also been applied with great benefit in the culture of turnips. Some experiments, exceedingly favourable in an economical point of view, have been made by Mr. Barclay, of Eastwick Park, Surrey,t who found that one cwt. per acre, drilled in with the seed, gave as great a return of Swedes as 15 bushels of bones,with 15 of wood ashes per acre, and when the nitrate of soda was sown broadcast, from 20 to 25 per cent. more. In every part of the country, therefore, this substance ought to be tried. And as this nitrate is very soluble in water, and may therefore be readily carried'off by the rain, and as that only which is within reach of the plant is of any avail, I would suggest that not more than one-fourth of the whole should be drilled in with the seed, for the purpose of bringing away the plant; and that after the thinning by the hoe, the rest should be strewed along the rows by the hand or by the drill. In This, I believe, is rather a matter of opinion than the result of a sufficient number of actual. trials. Some trials made by Mr. Hawden (British Husbandry, I. p. 895) gave results very unfavourable to horn shavings. t Liebig, p. 84. The acre here spoken of is the Hessian, about three-fifths of the English acre.- The English, therefore, will require 66 lbs. t journal of the English Agricultural Society, I.p. 428. No. I.] OF TURNIPS. 9 this way the whole energy of the salt being expended where it is required, the greatest possible effect will be produced. III. I have already stated the reasons which lead me to anticipate highly beneficial effects to vegetation from the use of sulphate of soda; I would suggest,: therefore, a trial of this salt on the turnips also, at the same- rate of I cwt.' per acre, and applied in the way above recommended for the nitrate of soda. Of course the intelligent farmerwill vary the proportions and mode of application of these substances, as his leisure or convenience permit, or as his better judgment may suggest to him. The entire series of experiments on turnips, above suggested, may be represented as follows, adding two plots for different proportions of the nitrate and sulphate of soda:- Burned Bones, NitrateofSoda, Bone Dust, or 2 cwt. per acre. 1U cwt. per acre. Crtushed Bnes, 1ton per acre. Burned Bones, Sulphate of Horn Shavings, 6 or 7 cwt. per Soda, or Glue, 7 or 8 acre. 1 cwt. per acre. cwt.peracre. Sulphate of Nitrate of Unmarnured. Soda. Soda, 1k cwt. per acre.I cwt. per acre. Some of these experiments most of you may easily try. Those with the burned bones and horn shavings, which in this part of the country are less easy to be obtained, it is not to be expected that many of you will think of undertaking. I hope, however that they will not be-lost sight of by those who possess facilities for obtaining them in sufficient quantity to make a satisfactory experiment. In many parts of the United States, gypsum is the universal fertilizer for every crop, and among the rest it is said'to benefit-turnips. The same opinion is entertained in- Germany. I am not aware how far, in what way, or with what results, it has been applied to the turnip crop in this country. A simple mode of testing its efficacy, however, would be to strew it over the plants when in the rough leaf, on- part of a field, the whole of which had - been already - manured in the ordinary way with fold-yard manure. The difference of produce would thus show its efficacy, in the given circumstances; and the experiment could be made effectually at the cost of a single cwt. of gypsum. I have not included rape dust, among the trials above suggested, though it is undoubtedly, under certain modes of management, a beneficial manure both to corn aid turnip crops. There is also a diversity of opinion as to the cause of its fertilizing action, as well as a manifest difference in the effect of different samples of the dust on the same soil. Though, therefore, certain experiments which- Imay on a future occasion suggest, would undoubtedly throw light on the cause of the good qualities of this manure, yet as its action (taking different samples)-is not ionstant on the same soil, results obtained with it cannot possess the same importance, either theoretical or practical, as those which are observed to follow from the ue of bones and of n salinesubstances, the composition of which is nearly invariable. Many farmers, however, are in the habit of constantly using rape dust.'If any of these could conveniently make experiments on the effect of different samples of the cake, from different kinds of seed, and from different oil mills, and would accurately note the results, they would perform an important service in preparing the way for that clear explanation of the cause of its fertilizing action, which is at present wanted,* and which experiment alone can discover to us. * Its good effects are-generally attributed to the oil which is left in the seed, and its vary. ing action to the different quantities of oil left in it by different crushers. I doubt, however, if the oil ought to be considered as more than a secondary cause of its baeeficial action. 10 OF POTATOES. [Appends, IV. OF POTATOES. 1~. Nitrate of soda has been applied with great benefit to potatoes also. After the potatoes have been harrowed down and (hand) hoed, and the plants are four to six inches above the ground, it.is applied by the hand round the stem of the plants, and the earth then set up by the plough. Mr. Turnbull, in Dumbartonshire; last year used it in this way at the rate of l to 2 cwt. per Scotch acre, (14 English acres,) and the produce exceeded that of the land to which no nitrate was applied, by 20 Scotch bolls to the Scotch acre. 2~. Applied in the same way there is every reason to believe that the sulphate of soda would have a highly beneficial effect also. I repeat my recommendation that this substance should be fairly tried with every crop, because it is a product of our own manufactories, which can be supplied in unlimited quantity, and without the chance of any material increase of cost: while the nitrate of soda is already in the hands of speculators, and within a short period has risen in the market to the extent of nearly one-third of its former price. In plastering their potatoes, the Americans generally put in a spoonful of gypsum with every cutting-a similar method, if preferred, might be adopted with the nitrate and sulphate of soda, though the chance of loss by percolation through the soil, would, by this, method, be in some degree.increased. In Flanders, wood ashes and rape dust are frequently thrown in by the hand, when each cutting is introduced. 3~. I- shall have occasion hereafter to recommend to the attention of-the practical farmer, many waste materials of various kinds, thrown outfrom our manufactories, the application of which to useful purposes would be a great national benefit. In reference to the culture of potatoes, I will here bring under your notice the chloride of calcium, which is said to have been beneficially applied to various crops, but to potatoes especially, with surprising effect. Under the influence of-this substance the sunflower'and maize have grown to the height of 14 to' 18 feet, and potatoes have-attained the weight of 2 to 3 lbs.* In Germany, Sprengel also found it useful to potatoes-(Cthenziejfiir Landzoirthe, I. p. 635.) Thousands of tons of chloride of calcium may every year be prepared from the waste materials which floWy into the river Tyne, from the alkali works upon its banks. Thousands of gallons of the solution of this substance yearly run off from the works cf Messrs. Allan & Co. at Heworth, and might be procured for little more than the expense of-collecting. It is also contained largely, though mixed with other substances, in the motherliquor of the salt pans; and from the numerous salt works on the coast, might readily be obtained for trial. When prepared in the dry state, this substance rapidly deliquesces and runs into a liquid. The most' convenient way of applyin it, therefore, would be in the state' of solution-so. largely diluted as to have only a slight taste-and by means of a watering cart so contrived as to allow it to flow on the tops of the ridges and young plants, by which unnecessary waste would be prevented. Without knowing the strength of the- solution likely to be obtained from the works, it is impossible to give any idea of the quantity of the chloride of calcium which ought to be employed; but 500 gallons per acre may safely be used, it the solution be so far diluted as to have only a decided taste of the substance.. The experiments here suggested, therefore, require four patches, as follows:----- These experiments are supposed to be made in ground Nitrate of- Sulphate of already prepared for the potatoe crop, by the usual quanSoda. lto l Soda, lto 1X tity of manure. I think it not unlikely, however, that cwt. pr acre. cwt. pr acre. by planting the potatoe in the midst of nitrate or sulChloride of phate'(sprinkled over with dry soil) at the rate of X cwt. Calcium, 500 Manure per acre, and afterwards applying 1 cwt. per acre, when gals. pracre. -only. the plants are hoed, a crop might be obtained without' the use of manure. Of course, such an ecxperiment as * The Rohan, a French variety of potatoe lately introduced into the United States-by the ordinary mode of culture-yields tubers, very mazy of which weigh 3 lbs. and many attain to No. I.] OP MIXED MANURES. 11 this, though important to be made, should be tried cautiously, and on such a scale as to secure the experimenter fiom any serious loss. In the above suggestions I have introduced nothing in regard to mixed manures-though where plants require for the supply of all their wants nine or ten different ingredients, of which the soil they grow in can perhaps yield in sufficient quantity only three or four, it is obvious that the very best consequences may follow fiom the employment of mixed manures. To this class belong common night-soil urine, animalised carbon, poudrette (night-soil mixed with lime and gypsum), the poudre vegetatif (a mixture of soot and saltpetre), the uratte (now manufactured in London), and many.others. The mode of preparing, and the special uses of these and other mixed ma nures, will be explained in the third part of these lectures, which will be devoted to the consideration of the nature and uses, and-to the theory of the action of natural and artificial fertilizers. In the mean time it is desirable, in the first place, to obtain results from which the special action of each, when used alone, can be fairly deduced. \ That these experiments may have their full value, it is indispensable that a measured portion of each field should be left without manure or dressing of any kind, in order that a true idea may be formed of the exact effect of each substance employed. Experiments are valuable to the practical man if they merely-show the superiority of one species of manure over another, but they are insufficient to show how much each of them tends to increase the produce-or to enable us to arrive at a satisfactory explanation of the mode in whichthey severally act in promoting vegetation. - Among other important experiments lately published, to which the above observation is applicable, may be mentioned those of Mr. T. Waite of Doncaster. The effects of nitrate of soda on his land were very striking, showing a remarkable increase of produce over bone dust, rape-dust, or rotten fold-yard manure-but he does not seem.to have determined the produce of the same land during the same season and wlvi'ho'lt Lmnure. We have, therefore, no term of comparison, by means of which we can ascertain the absolute or even'the exact-comparative effect of the different substances employed. It has been well observed by Sir Elumphry Davy, "that nothing is more wanting in agriculture than experiments in which all-the circirinstances are minutely and scientifically detailed, and that this art will advance in proportion as ithbecomes exact in its methods."* The above suggestions are submitted to practical men in the hope that they may assist in introducing such exact methods into our agricultural operations, and at the samre time promote the theoretical advancement of the most important art of life. Exact methods lead to theoretical discoveries, while these are no less certainly followed by important practical improvements. No. II. (gee Lecture II, p. 37.) IN illustration of the effect of sudden alternations of temperature on vegetable substances, explained in a note subjoined to page 37, I quote with pleasure the the weight of5Ibs. When perfectly ripe, it is said to be an excellent table potatoe, and to be best in the spring;-Albany Cultivator, for March, 184t. Agricultural Chemistry, Lecture L 12 ON SUDDEN ALTERNATIONS OF TEMPERATURE. [Appendix, following instructive letter from an ably conducted monthly journal published at Albany, in the State of New-York, under the title of the Cultivator. It is extracted from the Number for March last:"In regard to Irish potatoes, a still thinner covering of earth than the one just mentioned suffices with us to preserve thenm from rotting. Indeed, it would seem as if they could freeze and thaw several times, during winter, without being destroyed, provided they are covered with earth all the time; for we often find them near the surface and perfectly sound, in the spring, when spading up the ground in which the crop had grown during the previous season. There they must have undergone freezing and thawing whenever the earth was in either state, as it often is to a much greater depth than the potatoe roots ever extend. Why should those roots always be destroyed when they freeze above ground, and not suffer equally when frozen under gr'ound? "The reason why potatoes, apples, &c. become soft, and rot when frozen and then thawed suddenly, uncovered and in open air, is the sudden thawing. You may put a heap of apples on the floor o(fa room, or other dry place, where they will freeze perfectly hard, and if covered close with any thing that will exclude the air, when the weather becomes warm enough to thaw. the apples will remain sound and uninjured; after they'are thus closely thawed. The cover may be of the coarse tow of flax, or any article that will cover them close and exclude the air. So apples may be packed in a tight barrel, if full and headed up so as to exclude the air. They may be suffered to remain so in a garret, or any dry place where it freezes hard, and they will be found sound and free from injury, if the barrel remains tight till they are thorou6ghly thawed. It is the siudden thawing that causes the apples or other vegetables to become soft and rot. "So if the fingers on your hand be frozen, and youexpose them to sudden heat by warming them at the fire and they suddenly thaw, the flesh will.mortify and slough of. But, if you freeze your fingers or other limbs, and put them in snow, and rub gently till they thaw,-or if put into a pail of water just drawn from the well, which will be less cold than your frozen fingers,-they will thaw slowly, and suffer but little injury. "So during the early autumnal frosts in September, if the morning after the frost is cloudy, thefrost will be slowly drawn from the frozen vegetables, and they will be uninjured; but if they receive the rays of the early and clear sun, they thaw so suddenly, that they will hang their heads and perish. If wet with water from the well, long enough to extract the frost before the sun shines on them, they do not suffer.'" Onions are a difficult root to keep in winter. If they are put in a cellar warm enough to save them from frost, they will vegetate and be deteriorated. I put them in the warehouse, where they freeze as hard as if out of doors. If in a heap, I cover them close with some old clothes, or any thing that covers close to exclude the air. The same if in boxes or casks. They freeze hard, but it does not appear to injure them for present use,if thawed by putting them into a pail of fresh-drawn water, to draw out the frost just before cooking them. Onions. thus kept, will be in good condition in the spring, after thawing under cover from the air. "I put parsneps, carrots, beets, &c., in boxes or casks, and then cover them with potatoes, which preserves them from drying." In further illustration of this subject I need only recall to the recollection of the gardener the well known fact, that, when the winter frosts begin to set in, and his finest flowers to be nipped, those continue to blow the longest, on which the sun's rays fall latest in the day. Dahlias protected in this way, will bloom occasionally for weeks, after those vhich regard the eastern sky are completely withered. Professor Lindley has published a series of valuable observations on the effects;of extreme cold upon plants. The general results of these observations are stated in his "Theory of Horticulture," p. 88. But the conclusions at which Non. II.] ON SUDDEN ALTERNATIONS OF TEMPERATURE. 13 he has arrived are deduced from the appearance presented by the plant after it was thawed. He found the tissue more or less lacerated, the contents of the air and sap vessels intermingled, and the colouring matter and other secretions decomposed. He attributes the laceration to the freezing and consequent expansion of the juices, but this cannot be the necessary consequence of that freezing, since it does not appear, if the whole tuber or leaf be slowly thawed. I would explain the phenomena as follows:1~.- When the leaf, fruit, or tuber freezes, the fluid portions slightly expand in becoming solid, but the air in the air vessels contracts in atleast an equal degree, and thus allows a lateral expansion of the sap vessels sufficient to prevent lesion. When the temperature is slightly raised, the air expands but slightly, and ice is melted long before the gaseous substances reaclftheir original bulk. 2~ But if the rays of the sun strike suddenly upon the leaf or fruit, the surface may at once be raised in temperature 30~ or 400 F. The air will consequently expand suddenly, and before the sap is thawed may have distended and torn the vessels, and caused sap and air to be mutually intermingled. 3~. But the moment the sun's rays strike upon the green leaf, its chemical functions commence. It begins to absorb and decompose carbonic acid: and as in the frozen part of the leaf the circulation is not, and in consequence.of the lesion cannot be, established, the chemical action of the sun's rays must be expended upon the stagnant sap; andhence those changes not only in the sap itself, but even in the solid parts, which are seen to take place in the withered leaf. 4~. Though not in a state of growth, the tuber of the potatoe contains the living principle, and there must be such a circulation going on in its interior as to maintain an approximate equilibrium of temperature throughout its substance. A sudden thawing of the exterior, will, as in the leaf, expand the air before the circulation can be established throughout the frozen mass. The solid, fluid, and aeriform substances whlich nature has separated and set apart from each other, will thus all be intermingled, and fiom their mutual action, those chemical changes of which we know the starch of the potatoe to. be susceptible, will speedily ensue;-in other words, the potatoe will rot. The practical applications of these views are' numerous. If a sudden frost come on,-protect your delicate flowers in the early morning fiom the rays of the approaching sun, and cover with straw or earth the potatoes which have been left overnight in the field. No. III. RESULTS OF EXPERIMENTS ON PRACTICAL AGRICULTURE DURING THE SPRING AND SUMMER OF 1841. (See Appendix, No. 1., and LectureS VIII. and IX.) IN a previous article inserted in this Appendix, and which was published early in the present spring (April, 1841,) I ventured to offer to the practical agrictilturist some suggestions in regard to the expcri7mental use of certain unmixed manures. From the results of these experiments, which I was quite sure some of the many zealous agriculturists of the day would be induced to undertake after the manner, and with the precautions, I had pointed out, I anticipated 14 RESULTS OF EXPERIMENTS ON PRACTICAL AGRICULTURE. [,AppZex, a two-fold advantage. In the first place, that important practical benefits to the agriculture of certain districts would be derived from them, and secondly, llat interesting and important light would be thrown by them on many parts of agricultural theory. It is by experiment that all the remarkable resultstheoretical as well. as practical-of modern chemistry have been arrived at; but by experiments cautiously made,-frequently repeated, and logically reasoned from. The proceedings of the practical farmer are a continued course of experimental trials, and to convert him into an experimental philosopher, and"to lead him to philosophical results, it is necessary only that his experiments should be made zoith a constant reference to weight and measure, and should be repeated under varied and carefully noted. conditions-and that he should be taught to draw from them no conclusions more general than they really justify. The following results of experiments made during the past summer confirm all my anticipations. Though necessarily somewhat limited, and local in their nature, they, nevertheless, present on the whole a beautiful illustration of what we have yet to expect from a continuation of such experimental researches, conducted in so skilful a manner. I need- not especially commend the experiments of Mr. Fleming: for I can scarcely, 1 think, render a betterservice to practicalagriculture than by placing all of them in the hands of practical men, and earnestly commending them to their careful consideration and imitation. I. Experiments made near Aske Hall, on the property of the'Earl of Zetland, on lots of half an acre each....OQCT O 1. Soot —put on Mail 24-10 buzshels cost 6s. Gd. 6. Weight of grass when mown. 3 tons 16 cwt. Weight when made into hay; 1 15 "- ^ O I _________________:___________ S 2. Salt-put on May 24 — bushels cost 6s. 6d. l I O ~ t C tz Weight of grass when mown, 3 tons 19 cwt. b (Weight when made into hay, 1 "16 3. No Manure. Weight of grass when mown, 3 tons 12 cwt. *g _ - 9~ 3 Weight when made into hay, 1 " 6 ". cu c G 4. Nitrate of Soda —put on May 24-4 stones. ~ - |, r- t' e Cost 11s. 1 - Weight of grass when mown, 4 tons 10 cwt;:. m; n b Weight when made into hay, 1 " c12 ". V C v 5. Sulphate of Soda (in crystals)-put on May - i - i. 24-4 stones cost 10s. 0...O C cQ C Weight of grass when mown, 3 tons 3 cwt. J._. m, t Weight when made into hay, 1 "' " 6. Silphuric Acid- - put on May 26, put on W * 9,, June 7, 3 put on June 1 t1-:5bs. cost 5s. ~ ) -_ Weight of grass when mown, 3 tons 4 cwt. o C s:;j. Weight when made into hay, 1 " 6 "." N. B. The cost of the manure does not include the expense of laying.it on. No. III.] RESULTS OP EXPERIMENTS ON PRACTICAL AGRICULTURE. 15 Mr. Turner, his lordship's agent, thus writes:"The plan I followed in putting on the different manures, and the quantities used, accorded as nearly as I could manage it, with the directions given in your published lectures. "The field on which the experiments were tried is situate in. a high, bleak climate, and consists of a thin light soil, upon a bad subsoil of barren clay resting upon limestone. It had been completely exhausted by a succession of white crops, and was full of weeds and quickens.. I had it well ploughed, and took a crop of drilled turnips fairly, but not extravagantly, manured. The crop was a poor one. I ploughed the land as soon as the turnips could be got off. Drained it; and in the spring-worked it very fine. The following August I sowed it away with grass seeds without a crop. The-seeds came up beautifully, and were tie admiration- of all who saw them, keeping a deep green through the winter, and beginning to grow early in the spring; and it was on this crop that the experiment was-tried early in the succeeding summer. " I need scarcely remark, that the crop of grass for such land was enormous, and has'fully repaid the money expended upon it, with the exception of draining, and in two or three years I have no doubt but it will repay this also." REMARKS. — On comparing the effect of these several top-dressings- as indicated by the results above stated, the reader will be struck with the extraordinary increase caused by the addition of common salt. I have in the text (Lecture IX., p. 190,) indicated a principle which may serve to explain in sorze measure both the localities in which the use of common salt may be expected to be beneficial, and the reason why in many parts of our island the employment of this substance has not been attended by any large measure of success. The position of the land experimented upon by Mr. Turner, is such as to lead us to expect- it to be improved by common salt, according to the views there stated. The nitrate of soda produced less effect than either the common salt or the soot, but it gave an increase which was double of that yielded by the sulphate of soda: The latter salt, however, was applied in the state of crystals, which.contain 55 per cent. of water, so that less than one half of that weight of dry salt was used, which was recommended in the suggestions I offered for the employment of this substance in practical agriculture. At the same time, the price paid by Mr. Turner for this salt was /bur times as great as it ought to have been. Any quantity of the dry sulphate of soda may be procured at 10s. a cwt., at which price it is forwarded in casks to all parts of the country by Messrs. Allan & Co., Heworth Alkali Wcrks, Newcastle. The most valuable practical suggestion to be derived from these experiments is certainly this-that a liberal use of common salt is likely to increase in a great degree the produce of grass in the locality where they Were made, and on the same kind of soil. This valuable discovery will far more than repay the expense and trouble of the entire series of experiments. No application can be so cheap as this, so long c as it succeeds. At the same time a mixture'of the other substances-the ni4,ate and the sulphate, which were partially successful- might possibly prove still more efficacious on the grass, and might be expected even to ameliorate the condition of the land for the furtlier production of white crops. In a future part of this Appendix I intend to offer some suggestions in regard to the kind and quantity of the ingredients which may, with probable advantage, enter into the c.onstitution of these mixed maiurecs. I have calculated and introduced into Mr. Turner's table an additional column, exhibiting the weight of hay yielded by 100 lbs. of grass, with the view of showing the relative succulence of the several crops when cut. As a general rule, the weight of dry hay does not exceed one-fourth of the weight of the grass when cut. In the experiments of Mr. Turner, however, the weight of hay in every case was much beyond this quantity-the most succulent crop, -that to which no dressing was applied, yielding 36 per cent. of hay. This gen27* 16 RESULTS OP EXPERIIENTS ON PRACTICAL AGRICULTURE. [Appendix. eral result may have been partly due to the state of ripeness in which all the grasses were cut, while the greater produce of hay from the dressed portions may indicate the-relative ripeness, and therefore dryness, of each when cut down. It is evident, therefore. that the relative values'of crops of grass or clover are not to be judged of by the several weights when green, but by the weights of the dry hay. This is- further confirmed' by the results of an experiment with nitrate of soda, communicated to me by Mr. Carruthers, of Warmonbie, near Annan, in which the relative weights of hay obtained were nuLtcA more infacvouL of'the use.of the nitrate.than the several weights of grass yielded by the dressed and undressed portions of the field. On the contrary, from a field on Oliver Farm, near Richmond, Mr. Sivers informs me, that the weight of hay was muc/c less in favour* of the use of the nitrate of soda than the relative weights of grass.' In all cases, therefore; the weight-of the dry crops obtained by different'methods should be compared with each other, as the safest testof the relative merits of the several modes of procedure by which they have respectively been raised. -II. Experiments made at Erskine, on the property of Lord Blantyre. I insert the clear and well-digested statement of his Lordship's agent without alteration:"Freelanql, Erskinse, by Old Kilpatrick, Glasgow, 29/h July, 1841. " Sir-Agreeably to Lord Blantyre's instructions I send you a copy of the results of some experiments with manures on young grass for hay, undertaken on two separate pieces of land-the one a very good light soil (subsoil gravel); the other stiff clay soil with a clay subsoil. The manures, were applied on 1st May, the hay cut on the 1st and weighed on the 19th July current; the extent of each'plot one-twentieth of an imperial acre. From the small extent of each plot it will'be evident that the results cannot be exactly-depended on, farther than as a general result; because in so small a portion of land the least variation in the soil or crop naturally will affect the results very materially; still, on the whole, I am of opinion that the experiment gives the comparative view of the value of the;different manures used pretty nearly. "'One thing has astonished us with regard to soda (nitrate). On all the fields i have observed it sown on, the part dressed has a much greater vigour of aftermath than where no nitrate of soda was given: showing that this manure is not so evanescent as was generally supposed. " I am, Sir, your most obedient servant, " JAS. WILSON." Experiments with Maniur7es as a top-dressing for Iay, at Erskine, 1841. REMARKS.-It will be observed in these experiments, that the saltpetre and nitrate of soda produced nearly an equal increase on both kinds of soil, the nitrate of soda having the greater effect on the light, the nitrate of potash on the -heavy soil. Next to these on the light soil are the conmmon salt and sulphate of soda, though on the heavy soil the common salt had the better effect of the two. It is to be observed, however, that in this case the sulphate was used in crystals and therefore only in half the quantity recommended. Had twice the quantity been;employed upon the light soil the produce might have equalled thatfrom the nitrates. It is a-singular illustration, however, of the necessity of applying different substances to different soils-that so far as this experiment is to be depended upon, the sulphate of soda almost entirely failed on the heavy land. The most valuable practical deduction from these experiments also, is, that ton both the soils in question, the grass land, in its present conditio'l, may be salted to advantage. At the same time, it appears probable that on the light soil the increased produce would amply repay the cost of applying either nitrate or sulIn Mr. Sivers' experiments, 100 square.yards, nitrated, gave 68 stones of hay, unnitrated 52 stones, but when dry they were reduced to-12 stones each. How very much more succulent these grasses were than those of Mr. Turner! NO. III.] c(N MANURE AS A TOP-DRESSING FOR HAY. 17 phate of soda at the rate of 120 lbs. per acre-the latter being in its dry or uncrystallized state. The effect, generally, of all the dressings is strikingly greater dn the light soil-a fact which speaks strongly in favour of the adoption of any of those methods by which the openness and friability of the land has been found to be permanently promoted. On the stiff soil, even the ammonia, by some deemed so vitally necessary to vegetation, appears to have produced no sensible alteration. Manures used, and quantities applied, to - s n m Total produce Total additional each plot of 1-20th of an acre. X - per weight per. Imperial Acre. Imperial Acre. Exp. 1. Good light soil, subsoil gravel. ts. cwt. qrs. lbs. ts. cwt. qrs. lbs. 1 1 lb. sulphuric acid, diluted in 47 271 8 1 -16 - 7 3 1 Illb. sulpgalls, uwaterr;~~Ci~.'.71 44 2 8 1 16 - 7 3_ 12 galls. water 2 6lbs. saltpetre (nitrateof potash) 322 95 2 17 2 0 - 16 3 24 3 6 bs. nitrate-ofsoda... 339 112 3 0 2 4 1 0 0 0 4 6 lbs. sulphate of soda (in crystals) 2-92 65 2 12 0 16 - 11 2 12 5'171bs. gypsum... 254 27 2 5 1 12 -4 3 8 6 1 bush. wood charcoal (pounded) 277 50 2 9 1 24 - 8 3 20 7 4 bush. common salt, 25 galls. water 294 67 2 12 2 0 - 11 3 24 8 gal. ammoniacal liquor, 47 gls.water 277 50 2 9 1 24 - 8 3 20 9 No application.... 227 - 2 0 2 4 Exp. II. Clay soil, subsoil clay. 1 lb. sulphuric acid, diluted in 47 256 6 2 5 24 - 4 2 16 galls. water 2 6 lbs. saltpetre (nitrate of potash) 286 56 2 11 0 8 - 10 0 0 3 6lbs. nitrate of soda... 22 52 1 10 1 12 - 9 1 4 4 6lbs. sulphate of soda (in crystals) 232 2 1 1 120 - 0 1 12 5 17lbs. gypsum.... 240 10 2 2 3 12 1 3 4 6 1 bush. wood'charcoal (pounded) 257 27 2 5 3 16 - 4 3 8 7 bush. common salt, 25 galls. water 2693 39 2 8 0 4 - 6 3 24 8 1 gal. ammoniacalliquor, 47gls.water 201 - 15 1 6 - - - - 9 No application. -.. 23. 20 2 1 0 8 - - The Dressings were applied 1st May, the Grass cut 1st July, and the Hay weighed 19th July. IIT. Experiments made under the immediate superintendence of W. Fleming, Esq., of Barochan, near Paisley, and on his own property. The statement is drawn up by Mr. Fleming himself. 1.-Experiments on Hay with Nitrate and Sudphate of Soda and withiGypsum, Description of I Rate per Weight per Weight No.- Field. Dressing, limp. o RooRood, green. when stack'd 1 Covenlea. Nothing. -' 3361 lbs. 1120 lbs. 2 Do. Nitrate of Soda. 40 lbs. 4907 " 1636" 3 Do. Sulphate of Soda. 40 lbs. 3966 -1322" 4 Do. Gypsum. 10 lbs. 3831 1277" 1 Crook's High Nothing. 4436 1478 2 Do. Nitrate of Soda. 40 lbs. 4999 1666 1 Crook's Low. Nothing. 2185 728 2 Do. Nitrate of Soda. 40 Ibs. 3764 1254 " 3 Do. Gypsum. 80 lbs. 3110 1036 "......._..,1 18 EXPERIMENTS ON:INTER RYE. [Appendss, Character of the Soil-Nos. 1 2, 3, and 4 were good sharp soil, on, rotten rock, (decayed trap,) all as near as possible the same description of land, drained, and lying together. Nos. 1 and 2, Crook's High, stiff clay, drained; the hay was after wheat. Nos. 1, 2, and 3, Crook's Low, light clay-loam, drained; the hay was after barley. On Covenlea the dressings were applied on the 22nd-of April, and the hay cut on the 2nd of July; on the other fields the nitrate and gypsum were applied on the 12th of April, and the hay cut on the 9th of July. N. B. The above is the average of trials in three parts of the Covenlea field; a small portion of moss was also sown with nitrate of soda, in the low part of tile same field, but no benefit was observable, beyond the usual dark green colour which appeared about ten days after the application. The sulphate of soda, although evidently beneficial, does not produce the dark green colour. In the Crook's fields the effect of nitrate of soda in producing the dark green colour was as remarkable as in the Covenlea field. The gypsum on both fields seems to have had a good effect, particularly on the aftermath clover. REIARKiS.-In these experiments also the sulphate of soda was used in only half the quantity recommended. By referring to the prices paid by 1M. Fleming, it will appear that the'use, of sulphate of soda gave an increase of 200 lbs. of hay for. Is. 9d. (or 500 lbs. for 4s. 5d.), while the nitrate of soda gave an increase of 516 lbs. for 7s. 10d.; so that, though the actual increase of hay per rood was considerably less by the use of the sulphate, yet that increase was obtained at little more than-half the cost of the same weight of increase derived from the nitrate. A similar remar'k applies to the gypsum, so that these experiments give ample encouragement for the application of both these substances ini somewhat large quantity to succeeding crops, on the same land. i. —Experiments on7 TWinter Rye, dressed with Nitrate of Soda, Liame with Potash, Sulphate of Soda, and Muriate of Ammonia (Sal Ammoniac.) XRate per Weight of Bushels No. Field. Description of rood Grain.. Straw per Dressing. imperial. per rood. per rood. rood. 1 Garden Plot. Nothing. 160 lbs. 1024 lbs. 32 Do. Nitrate of Soda. 40 lbs. 336 " 1664 " 6,1 3 Do. Lime and Potash. 40 " 272" 1344 " 5 4 Do. Sulphate of Soda. 40" 224" 1152 " 44 5 Do. Mur. ofAmmonia, 5'" 232" 1216 " 4| Character of-the Soil.-Tilly clay, which had been trenched, and in potatoes the year before. The Rye was sown on their being lifted in October, 1840. The applications were made on the 14th of April, the grain was cut on the 9th of August, and thrashed on the 25th. N. B. As early as the end of April the effects of the nitrate of soda were very apparent'from the dark green colour produced, and broad leaves, and after it was ripe the heads were longer than any of the others; but it was so strong that it was laid a month before it was cut; none of the others were laid. Every application seems to have done good, by increasing the produce. The potash and lime was made by slaking quick-lime and sand with a solution of potash, and allowing them to lie together for a month. As much was used as contained 1 lb. of carbonate of potash to the pole. REMARKS.-F-t-.Fm these experiments, it appears that, besides the proportionate increase of straw, that of grain was From nitrate of soda, 12 bushels for 31s. Od;, or 2s. 9d. per bush.; lime and potash, 7 - { for 33s. 6d., or 4s. 9d. sulphate of soda, 3' for 7s. Od., or 2s. 4d. ",' sal-ammoniac, 5 " for 1s. 9d., or 2s. 2d. 6: No. III.] EXPERIMENTS ON WHEAT FIELD. 19 Although, therefore, the total increase by the employment of sulphate of soda and rmuriateof ammonia, in the proportions actually put on, was not so great as by the use of the other two dressings, yet this increase was obtained-at a considerably less cost per bushel. The lime and potash, though producing an important effect, will probably not yield a remunerating return with this crop on this soil, while the results.hold out a fair inducement for the trial of the last two dressings in larger and varied proportions. The five samples weighed respectively,-4.5 3-5, 51 3-4, 51 4-5, 52 3-5, and 48 4-5 lbs. per bushel, so that, while on all the dressed plots the grain was heavier than on the undressed, that which was dressed with sulphate of soda was considerably the heaviest. 3.-Expeirnients on Whteat field, Crook's (crop, 1841.) - e scrWeight of Weight Weight of toDescription Rate peri produce of of tal produce, No. of Top-dressing. Scotch acre. Grain of Grain when cut, of th, acre. pr. bshl. ith an acre.. 1 Nitrate of Soda. 160 lbs. 209 lbs. 63 lbs. 9,500 lbs. 2 Potash 160 lbs. 10 " 62 " 8,930 " and Lime. 40 bush. 3 Common Salt. 160 lbs. 249 " 62 " 12,540 4 Mur. Ammonia. 20 lbs. 208 " 2 " 8,360 " 5 Nitrate of Soda 80 lbs. 214 62" 8,620" and Gypsum. 160 bush. 6 Nitrate of Soda 80 lbs. 40 " 624" 11 40 " 62, 11,970-" and Rape-dust. 5 cwt. 7 Mur. Ammonia 20 lbs. 2 63 " 9,50 30 6' 9,500 GI and Lime. 40 bush. " 8 Common Salt 28 lbs. 20 " 63" 8,740 and Lime. 80 bush. 9 Nothing. -- 190 " 61 " 8,050 " Character of the Soil.-The land was a heavy loam, and of as nearly as possible the same quality. It had been in potatoes, and the wheat was sown when they were lifted in October, 1840. The applications were all made on the 13th of April, and the crop was reaped on the 2d of September. The produce of -th of a Scotch acre, thrashed and weighed and well cleaned, gave an average of from 32 to 33 bushels of 61 lbs. each per Scotch acre of grain. REMARKS.-This table presents us with two remarkable results,-that obtained by the use of common salt, and that from a mixture of soda and rapedust. Thus, exclusive of the straw,Nitrate of soda alone gave 152 lbs. of wheat for 31s., or 12s. 2d. per bushel; Nitrate with rape-dust gave 400 lbs. of wheat for 43s. 6d., or 6s. 9d. per bushel; Common salt gave 472 lbs. of wheat for 3s. 6d., or 6d. per bushel., The increased produce, by the use of common salt, is by far the most valuable result to Mr. Fleming in an economical point of view, and plainly indicates the kind of application he can most profitably make-to his wheat crops at leaston land similar to the above, and in the district where he resides, Neither the nitrate of soda nor the mixture of this salt with rape-dust, gave such an increase as to repay their own cost, unless when corn is very high. It is interesting, however, to observe that the mixture with rape-dust gave so large an increase, though the value of this particular experiment is lessened by the absence of any trial with rape-dust alone, by which the effect of each of the ingredients ought to be judged of. I have reckoned the rape-dust at ~7 a ton, so that 5 cwt.'would cost 28s., and we know that a top-dressing of this substance alone, i n a somewhat larger quantity, gives a remunerating return in many of our wheat lands. 2:0 EXPERIMENTS ON EARLY POTATOES. [Appendix, Mr. Outhwaite, of Banesse, in the North Riding of Yorkshire, a skilful and enterprising practical farmer, who has for some years been using rape-dust over a great breadth of his wheat crop, has favoured me with the result of one of his more accurate trials on spring wheat, made during the past season. The wheat was sown after turnips taken off in April, and part of the field was dressed with rape-dust at the rate of 51 cwt. (or at ~7 a ton, of 40s.) per acre. The produce of the dusted portion was 39 bushels, and of the undusted 29 bushels per acre, and the increase of straw was one-fifth of the whole. Both samples were of equal weight, and sold at the same price,-8s. 3d. per bushel. In this experiment the increased 10 bushels cost 40s., or 4s. per bushel, giving, on a large breadth of land, a handsome remuneration. These results will, I trust, encourage others to make trials similar to those of Mr. Fleming and Mr. Outhwaite-; while these gentlemen will, doubtless, be induced each to try that application Which has succeeded so well in the other's hands. It might be useful as well as interesting to compare the produce of four plots arranged and dressed as follows:Common Salt Common Salt. Rape-dust. andmRape-dust. Nothing. 4.-Experiments on Early Potatoes, 1841. All were dunged in the usual manner with farm-yard manure, at the rate of about 30 cubic yards per acre. The potatoes were all planted on the 25th of March, on the same heavy black soil. The several dressings were applied on the 20th of May, and the potatoes were all lifted on the 28th of September. Description Rate Produce Weight of I. of per imp. per imp. Produce of Z Top-dressing, acre. acre. 18 yards drill. -__ -- _ —-- - -_ _- -: _ __ Note. —-The 1 Nothing. - 66 bolls. 77 lbs. peck is 35 Ibs. 2 Nitrate of Soda. 160 lbs. 80 " 93 " weiht,and16 3 Sulphate of Soda. 1)0 " 73 " 86 " make a boll,4Do. & Nitr.of Soda'200 107." 124" or 5 cwt. This break of ground consists of a piece of poor clay mixed.with moss, about 9 inches deep; subsoil a very stiff blue till. The dung was old from the farm-yard, about the ordinary quantity (30 cubic yards per acre) spread upon the land, and dug in. The potatoes were drilled in with the hoe; as the ground was wet the plants came up but weak, The nitrate of soda was sown before the other topdressings, and had remarkably quick effect, as it showed the thiid night after being sown. The sulphate of soda does not occasion the dark green colour which is seen upon the potatoes after the dressing of the nitrate, but there is not the smallest doubt of its beneficial effects, although not in so great a degree as the-nitrate. The mixture, which is composed of ]ds of sulphate of soda and Id of nitrate, has a wonderful effect in strengthening the growth (which it keeps longer than with nitrate alone), and the mixture has the same effect in producing the dark green colour as the nitrate alone. RFMARKS.-That a mi.xturte of substances is likely to be more efficacious as a dressing, than the applicatiofi of one substance alone, except in peculiar circumstances, is consistent not only with long practical experience —for how many substances are mixed together in.farm-yard manure?-but also with the theoretical principles laid down in the text. [See Lectures IX. and X.] These experiments upon potatoes show that this crop upon Mr. Fleming's land was benefitted by both nitrate and sulphate of soda, but in a vastly greater degree by a mixture of the two. And I might consider my suggestion in regard to the employment of sulphate of soda as a manure, to have been of no mean use in practical agriculture, had it led to nothing else than to this happy mixture of Mr. Fleming. I have received also from Mr. Fleming's gardener (Mr. Alexander Gardiner) No. III.] EXPERIMENTS ON EARLY POTATEES. 21 a very well digested and well drawn up paper, detailing numerous experiments made by himself during the past summer. Among these is one upon the use of this same mixture upon thepotatoe crop, which I shall quote in his own words: "April 26th.-Planted potatoes of the redDon variety, soil a mellow loam, two feet deep, subsoil yellow till. Farm-yard dung was trenched in some days before planting, at the rate of 40 cubic yards per acre; sets drilled in with the hoe. Plants came up very regular, and were top-dressed with a mixture of 2 sulphate and f-nitrate of soda on June 2nd, at the rate of 2 cwt. per acre. They grew very strong after this application. Stems six or seven feet in length, dark green, and the produce, when lifted in October, was 16 Renfrewshire pecks of 35 lbs. each per Scotch fall of potatoes fit for market." This produce is equal, I believe, to about 26 tons per Scotch, or 21 tons- per imperial acre, about equal to that of Mr. Fleming with the same mixture. And what an amazing luxuriance of vegetation, to yield at once stems seven feet in length and upwards of 20 tons of tubers per acre! Those who are the most sceptical in regard to the benefits to be derived from agricultural experiments, when well conducted, will scarcely question the importance of this result-the most backward in making experiments will be anxious to repeat this upon his own potatoes. The cost of the mixture to be applied in the quantity used by Mr. Fleming is'as follows: — s. d. Sulphate of Soda 150 lbs. in cryat ls pe cwt. or 6 9 1501 bs. in crystals at 5s.~ Nitrate of Soda..75 lbs. at 22s.... 4 9 21 6 The return for this 21s. 6d. was in each of the above cases upwards of 8 tons'of potatoes. I may here mention also two other interesting experiments of Mr. Gardiner, in which he tried the effect of sal-ammoniac upon his potatoe crop,10. In the one he mixed sal-ammoniac, previously dissolved in water, in the proportion of 1 lb. to each'cubic yard of a compost formed fiom the refuse of the garden, and planted early potatoes with it at the rate of 35 cubic yards per acre. The produce was one-sixth more than when no ammonia was used. The variety of potatoe was Taylor's forty-fold, the soil moss and clay. The cost of this application was 19s. per acre. 20. Sal-ammoniac, dissolved in water, was sprinkled on moss or peat earth, at the rate of 20 lbs. to a ton of earth, and, after strewing a little lime at the bottom of the drills, this mixture was put in at the rate of 2 tons per acre. The potatoes were 14 days later in coming through the ground than the same variety planted with farm-yard manure. They were strong in the stem, of a dark green colour, and equal, in point of produce, to the otheis. The variety of potatoe was the Irish apple, the soil a very light brown loam, of that description locally named deaf. I may observe on this latter experiment, that the application is not so simple as it appears. The lime would decompose the sal-ammoniac, and form c7doride of calcizim, while ammonia would be liberated. The effect, therefore, may be partially due to both. It will be recollected that in a previous part of this Appendix I suggested the trial of this chloride of calcium as a top-dressing for various crops. 5.-Experiments on Moss Oats, sown about 1st May, 1841, top-dressed 25th Jsune. " These top-dressings were applied on the 5th of June, and by the 24th there was a striking improvement, especially on No. 2,and No. 7. It was quite visible in greater strength and eveni'ss of crop. One or two of the others also showed improvement, but not so visibly as to merit particular notice. I examined them from time to time, and at different dates- the appearances much the same as noticed upon June 24th, I again examined them a few days before 22 EXPERIMENTS ON OATS. [Appendiax, they were cut, when I was much satisfied with No. 2; the straw appeared to me as stiff and shining and the ear as well filled, as if it had been grown upon stiff loam, and I consider the same dressing, applied to grain crops upon moss, will insure a good crop of well-filled oats. No. 7 was nearly as good, but the want of the bones being dissolved was a drawback. However, I consider the two merit the expense. of another trial." No. Top-dressing per pole (imperial). 1 Nothing. 2 Bones dissolved in sulphuric acid and nitrate of soda i lb. 3 Sulphate of soda - lb., bone dust - peck. 4 Potash 1 lb., lime and'bone dust peck. 5 Chloride of calcium 1 lb., bones - peck. 6 Lime, potash, and chloride of calcium, 1 lb. each. 7- Po'tash and lime, nitrate, and bones, ~ lb. each. Chcaracter of the Soil.-Moss 4 feet to clay, No, 2 the best crop and heaviest grain (not thrashed). Nos. 3, 4, and 5 not so good as No. 2, but all much better than Nos. 1 or G. No. 6 the worst-not better-than No. 1. No. 7 very good-next to No. 2. -REMARKS.-These experiments of Mr. Fleming on moss oats may be considered as affording another illustration of the benefits which are yet to accrue to practical agriculture fiom the suggestions of natural science. It is well known to those who have directed their attention to the reclaiming of peat lands, that the crops of oats raised on such land yield abundance of straw, but that the ear is small and badly filled. It is also well known that claying such lands is an almost unfailing remedy for this defect in the ear, as well as for the less important one which is also observed in the straw. My friend, Mr. Alexander, of South Bar, a neighbour of Mr. Fleming, and, like him, extensively engaged in the improvement of peat lands, finding, as most other persons have, that in some localities the claying of his land was very- expensive,* conceived the idea that some chemical application might be made to this soil, which would supply what the defective oat plants required, and thus supersede the necessity of claying. He was pleased to communicate this opinion to me-stating the defeet in the crop, and asking a chemical remedy. Looking chiefly to what was evidently required by the ear, I suggested a trial of various mixtures, in all of which,-from an idea that phosphates, among other substances, might be necessary to compllete the ear,-bone-'dust formed a necessary part. The result of these suggestions is seen in the above experiments of Mr. Fleming. - They have been varied and improved upon, as Mr. Fleming's united chemical knowledge and practical skill enabled him to do, and as first results on a-new field of research, Nos. 2 and 7 may be considered as highly encouraging, if not, indeed, eminently successful. Too much confidence; however, must not be placed on the effects observed in one or two instances; yet I hope those above stated are such as will.induce others to repeat the experiments with equal care, in order that another year, affording us more numerous results, may enable us to base our- conclusions upon a larger experience. 6.-Ex;periments nupon Oats top-dressed.witlh Sulphate and Nitirate of Soda (lower end of Barn Parlk.) "The first was sown on the 11th May, viz., 3 ridges with sulphate of soda, at the rate of 1: cwt.per acre. This was examined from time to time, but there * Mr. Garden, of Glenae House, near Dumfries, a gentleman to whom, though personally unknown, I am indebted for many valuable comnainications, informs me that, in improving his porous peat lands, he has found it necessary to lay on a coating of clay six inches thick, at an expense of ~15 an acre. A coating of two or three inches on their peat, he says, sinks down, and in a few years descends beyond the reach of the plough, and hence it is more economical to lay on at once an entire soil of six inches. No. III.] EFFECTS OF SULPHATE AND NITRATE OF SODA. 23 appeared to be little, if any, difference from the general crop (it has not yet been thrashed.)- Next, 3 ridges were sown with nitrate of soda, at the rate of 80 lbs. per acre. This made a little alteration both in colour and strength. but it was too little to make a very decided difference. Also, alongside of the last-mentioned, a piece was dressed with a mixture of suiphate and nitrate of soda, in the proportion of rdls of the former to ird of the latter. This immediately took the lead of the others both in colour and'strength, so much so, that by May 27th it could be seen from a distance. Many examinations were made of them all during the season, and this always appeared the best. A few days before it was cut, it showed the largest and best filled ear. There-was a piece of yellow-coloured earth at the bottom of the field, showing the presence of iron, upon which was sown potash and lime. The plant was yellow and sickly-looking, but immediately after the application it acquired a dark green colour, and became vigorous, and yielded a crop at least equal to any in the field. There were some other dressings put on other ridges of this field, but it was dry weather directly after they were sown, and the crop was too far forward before they began to take effect to say any. thing decided about thlem. By mistake there were two varieties of oats sown upon the field, which prevented the experiments being so decided, as the dressings were put on indiscriminately upon-the land beforeit was known." REMARKS. —The only remark I need make upon these experiments is, to suggest to my readers that, by repeating the above trials upon oats with Mr. Fleming's mnixtlures, they may not only benefit their own crops, but may also aid materially in the advancement of practical agricultural knowledge. 7. —0n the effect of Sulphate of Soda applied as a top-dressing to Beans and Peas. "The first dressing was applied the 4th of MAay, -on some. beans on a border in the garden; the drills that were dressed quickly took the lead. of the others. There was no alteration of colour, but greater strength, and it tillered wonderftlly. -There were five or six stems from every seed sown, and the pods were larger and more numerous, and the beans in the pods a great deal larger than the same variety undressed. It was also put upon some of the ridges of the beans in the field, and with the same effect, and gave a very large crop (not yet thrashed.)-. " Upon peas in the garden it appeared to add little, if any thing, to the strength of straw, but those that were dressed had a fatr greater number of pods, and those better filled, and the peas of a better flavour,. and it seems a valuable dressing for all legimninouss crops. When sown in the drills along with the peas, it nearly killed every one of them, while the same quantity, put on as a top-dressing to some drills next to them (where the peas were two inches high,) did no injury. REMARXS.-The testimony of Mr. Fleming to the value of sulphate of soda as a dressing for leguminous crops, is very valuable and satisfactory. We may hope that next year will furnish us with experiments, all the results of which shall have been so carefully ascertained, as to enable us to decide upon the economical value of this sulphate as a manure, by a comparison of the amount of increase in the crop, with the cost of the application. 8.-On, Nitrate of Soda as a top-dressing to Gooseberry and Crrant bushes. " It was applied April 14th, at about the rate of, cwt. per acre, or j lb. per bush. It had the effect; in the course of a week, of producing on the bushes a dark green colour and broader leaves, and the fiuit setbetter and more plentifully, especially on some red currants that had borne little for two years. These set their fruit well, and yielded double their former produce. The dressedbushes kept the lead in strength and vigour all the season, and now, when the undressed bushes have lost their leaves, the others are quite green." 9.-" Many experiments were tried in the garden on turnips, by top-dressing with nitrate of soda, but with no perceptible effect. However, the Swedish, and 24 ON EXPERIMENTS WITH GUANO. [Appendix red-top yellow, in a field of rather stiff soil, were benefitted, the former yielding I more produce in weight, and the latter 3 more weight. WM. FLEMING. " Barochan, 26th October, 1841." Note.-The prices paid by Mr. Fleming were as follow:-Bone dust (fine) Is. 9d. per bushel; sulphate of ammonia (in crystals) 28s. per cwt.; potash (very impure) 24s. per cwt.; sulphate of soda (in crystals) 5s. per cwt.; nitrate of soda 22s.; and sal-ammoniac 60s. per cwt. No. IV. SUGGESTIONS FOR COMPARATIVE EXPERIMENTS WITH GUANO AND OTHER MANURES. Guano is the name given in South America to the dung of the sea fowl which hover in countless flocks along the shores of the Pacific, and which, from time immemorial, have deposited their droppings on the rocks and the islands which are met with along the coast o, Peru. Besides the fresh white guano which is deposited year by year in these localities, there exist, in some spots, large accumulations more or less buried beneath a covering of drifted sand, which have been thus buried and partially preserved from an unknown antiquity. This ancient guano is of a brown colour, more or less dark, and forms layers or heaps of limited extent, but which are said sometimes to exceed even 60 feet in thickness. In the time of the Incas this substance was known and highly valued as a manure, -the country along the coast for a length of 200 leagues was entirely manured by it, —the islands on which it was formed were carefully watched and preserved,-and it was declared to be a capital offence to kill any of the sea fowl by which it was deposited. Ever since that time it has been more or less employed for the same purpose, and much of the culture now practised on this thinly-peopled coast is entirely dependent for its success, if not for its existence, on the stores of manure which the sea fowl thus place within reach of those parts of the country which are susceptible of cultivation. In modern times, however, the access of foreign shipping, and the want of careful protection, have driven away many of the sea fowl, and lessened to a very great degree the production of the recent guano. Thus the country is more dependent than in former times on the more ancient deposits, which are now assiduously sought for, and when discovered beneath the sand, are carefully excavated and transported to the sea-ports for sale. The dung of birds of all kinds, when exposed to the air, gradually undergoes decomposition, gives off ammonia, and acquires a brown colour. As this ammonia is one of the most fertilizing substances it contains, it will be readily understood that the old brown guano is much less valuable as a manure than that which is recent and white; hence the care of the ancient Peruvians in collecting the fresh, and their comparative neglect of the ancient guano. When the brown guano is put into water, a large quantity of it-sometimes 70 per cent. of the whole-is dissolved. Hence, it is, because the climate of Peru is so dry and arid that in the plains rain scarcely ever falls, that the guano can accumulate as it is found to do. North and south of this line of coast, where rains are less unfrequent, such accumulations are not met with, though the birds appear equally plentiful, and it may be safely stated that, had the climate of Peru been like that of England, the rains would have washed the guano from the rocks almost as rapidly as it was deposited. Of the brown guano several cargoes have lately been brought to England by No. IV.] ON EXPERIMENTS WITH GUANO. 25 an enterprising merchant in Liverpool, and it has been deservedly recommended to the attention of British agriculturists. It has already been tried upon various crops, both of hay and corn, upon turnips also, and upon hops, and there can be no doubt whatever that in our climate, as well as in that of Peru, it is fitted to promote vegetation to a very remarkable degree. This brown guano varies much in quality, according probably to the degree of exposure to the air to which it has been subjected, or to its position in the deposit from which it has been dug. Two; different portions, taken at random from the same box, gave me the following very different results:1~.-Water, salts of ammonia, and organic matter, expelled by a red heat,....23', per et. Sulphate of soda,. 1'8 Common salt, with a little phosphate of soda,.. 303 " Phosphate of lime, with a little phosphate of magnesia and carbonate of lime,..... 44'4 " 100* 2~.-Ammonia,... = 70 Uric acid,.... 0-8 Water, carbonic and oxalic acids, &c., expelled 5 per. by a red heat,... = 515 J Common salt, with a little sulphate & phosphate of soda, 11'4" Phosphate of lime, &c..... 293 100 According to M. Winterfeldt, this brown guano is sold at the ports near which it is obtained at about 3s. a cwt. It might, therefore, if this be correct,,e imported into the country, and sold at less than 10s. per cwt. The price at present asked, however, is 25s. per cwt., a cost at which it is doubtful if the English agriculturist can afford to use it. In any case it seems improbable that the guano can continue to be imported into this country for any length of time. It is absolutely necessary to the cultivation of the land in Peru,-and it is also diminishing in quantity, —the first settled government, therefore, which is formed in that country, must prohibit the further exportation of a substance so important to-the national interests.. It is a matter not unworthy of the attention of chemists, therefore, to consider whether a mixture similar to the guano, and of equal efficacy, cannot be formed by art —not only at a cost so reasonable as at once to make the British. farmer independent of the importer,-but also in such abundance as at the same time to place so valuable a manure within the reach of all. The following mixture contains the several ingredients found in guano in nearly the average proportions; and I believe it is likely to be at least as efficacious as the natural guano, for all the crops to which the latter has hitherto been applied in this country:-. s. d. 315 lbs. [7 bushels] of bone dust at 2s. 9d. per bushel. 0 19 0 100 lbs. of sulphate of ammoniat containing 35 lbs. of ammonia at 20s. a cwt.... 018 0 5 lbs. of pearl-ash...... 0 1 0 100 lbs. of common salt..... 0 2 0 11 lbs. of dry sulphate of soda.... 0 1 0 531 lbs. of artificial guano cost.... 2 1 0 * The first contained also 8 per cent. and the second 1t per cent. of sand, which has been left out of the true composition of the guano considered as free from sand. t Sulphate of ammonia is now manufactured largely at Glasgow, and may be had for less than 20s. a cwt. 26 ON EXPERIMENTS WITH GUANO. [Appendix, The quantity liere indicated may be intimately mixed with 100 lbs. of chalk, and will be fully equal in efficacy, I believe, to 4 cwt. of guano, now selling at ~5. At the same time if is desirable that the relative efficacy both of this mixture (artificial guano), and of the American guano, should be tried by actual experiment in comparison with other substances of known value, and which are supposed to act in a way somewhat similar. The substances with which I would suggest that such comparative experiments should, in the first place, be made, are farm-yard manure, bone dust, and rape dust, and the following scheme -exhibits the proportions in which they may be added to the different plots of land on which the experiments are intended to be made:20 tons of 20 bushels of 6 cwt. of guano, 6 cwt. of bones mixed with farm-yard manure. with ashes. h artificial guano. withashes. chalk or gypsum. rtificial an 10 tons do. 20. f 10 tons of farm- 10 tons offarm-yard with 10 bushels of 2e vt. o yard manure with manure with 3 cwt. bone dust. rape wi 3 cwt. of guano. of artificial guano.. 10 tons do. 10 cwt. of 10 tons do. with 2 wtth 10 cwt. of rape with 3 cwt. 10 tot.s do. wit cwt. of artificial rape dust. ofgno. guano. The practical farmer need not be deterred by the formidable array of experiments above suggested. He may try any two or three of them, and his results will be valuable in proportion to the accuracy with which his land is measured and his manures and crops weighed. I have taken 20 tons of farm-yard manure as a standard, though in many highly farmed parts of the country no more than 15 tons'are usually applied. Twenty bushels of bones are recommended by the Doncaster report, and I have lately found that in the Lothians 1 cwt. of rape dust is considered to replace 1 ton of farm-yard manure. This proportion of course will vary with the quality of the latter manure; but whatever quantity of this latter we take as the standard of comparison, it is easy to adjust the proportions of the other substances accordingly. I have not recommended any trial to be made with more than 6 cwt. of guano, because, where farm-yard manure is valued only at 6s. or 7s. per ton, 5 cwt. of the former would cost as much as 20 tons of'the latter.* The above experiments are intended to be made with the green crop, and to be continued during an entire rotation:t any pair of them, however, may be tried on single crops, whether of corn or of turnips and potatoes. In this way -guano ought also to be tried against nitrate of soda and against bones, upon seeds and upon old grass-lands. The mode in which such experiments may be made will speedily suggest themselves to the intelligent farmer. In all cases the r'esults should be accusately r-ecorded, and, if possible, published.' When this paragraph was written, the price of guano was 25s. a cwt.; it is now (May, 1842) reduced to 15s. t By this I mean that the effect of these several manures, applied oncefor all to the green crop at the commencement of the rotation, should be traced on each successive crop through the entire course of cropping. %.wyCRIM"-' ------ No. V.] OF THE PHYSI(AL PROPERTIES OF THE SOIL. 27 No. V. OF THE EXA3IINATION AND ANALYSIS OF SOILS. 10. Selection of speiimens of soils.-In the same field different varieties of soil often occur, and some recommend that in collecting a specimen for analysis, portions should be taken from different parts of the field and mixed together, by which an average quality of soil would be obtained. But this is bad advice, when the soils in different parts of the field are really unlike. Suppose one part of a field to be clay, and another sandy, as is often the case in this county, and that an average mixture of them is submitted to analysis, the result you get will apply neither to the one part of the field nor to the other-that is, it will be of little or no value. In- selecting a specimen of soil, therefore, one or two pounds should be taken from each of four or five parts of the field where the soil appears nearly alike, these should be well-mixed together and dried in the open air or before the fire. Two separate pounds should then be taken from the whole for the purpose of analysis, or if it is to be sent to a distance should be tied up in clean strong paper, or what is much better, should be enclosed in clean well-corked bottles. I.-OF THE PHYSICAL PROPERTIES OF THE SOIL. 2~. Determination of the density of the soil.-In order to determine the density of the soil, a portion of it must be dried at the temperature of boiling water (212~),'till it ceases to lose weight, or upon a piece of white paper in an oven at a heat not great enough to render the paper brown. A common phial or other small bottle perfectly clean and dry may then be taken and filled up to a mark made with a file on the neck, with distilled or pure rain water, and then carefully weighed. Part of the water may then be poured out of the bottle, and 1000) grains of the dry soil introduced in its stead, the bottle must then be well shaken to allow the air to escape from the pores of the soil, filled up again with water to the mark on the neck, and again weighed. The weight of the soil, divided by the difference between the weight of the bottle with soil and water and the sum of the weights of the soil and the bottle of water together, gives the specific gravity. Thus, let the bottle with water weigh 2000 grains, and with water and soil 2600, thenGrains. The weight of the bottle with water alone =....... 2000 The weight of the dry soil......... 1000 Sum, being the weight which the bottle with the soil and water would have had could the soil have been introduced without 3000 displacing any of the water......... But the weight of the bottle with soil and water was... 2600 Difference, being the weight of water taken out to admit 1000 400 grains of dry soil..... Therefore, 1000 grains of soil- have the same bulk as 400 grains of water, or the soil is 32 times heavier than water, since 1000 400 = 25 its specific gravity. 30. Determination-of the absolute weight. —The absolute weight of a cubic foot of solid rock is obtained in pounds by multiplying its specific gravity by 633-the weight in pounds of a cubic foot of water. But soils are porous, and contain more or less air in their interstices according as their particles are more or less fine, or as they contain more or less sand or vegetable matter. Fine sands are heaviest, clays next in order, and peaty soils the lightest. The simplest mode of determining their absolute weight, therefore, is to weigh an exact imperial half pint of the sgil in any state of dryness, when this weight 28 or THE PHYSICAL PROPERTIES OF THE SOIL. [Append&'r multiplied by 150, will give very nearly the weight of a cubic foot of the soil in that state. 4~. Determtinatian of the relative proportions of gravel, sand, and clay.-Five hundred grains of the dry soil may be boiled in a flask half full of water till the particles are thoroughly separated from each other. Being allowed to, stand for a couple of minutes, the water with the fine matter floating in it may be poured off into another vessel. This may be repeated several times till it appears that nothing but sand or gravel remains.. This sand and gravel is then to be washed completely out of the flask, dried, and weighed. Suppose the. weight to be 300 grains, then 60 per cent.* of the soil is sand and gravel. The sand and gravel are now'to be sifted through a gauze sieve more or less fine, when the gravel and coarse sand are separated, and may beweighed and'their proportions estimated. These separate portions of gravel and sand should now be moistened with water and examined carefully with the aid of a microscope; with the view of ascertaining if they are'-wholly silicious, or if they contain also fragments of different kinds of rock-sand-stones, slates, granites, traps, lime-stones, or ironstones. A few drops of strong muriatic acid (spirit of salt) should also be added-when the presence of lime-stone is showh more distinctly by an effervescence, which can be readily perceived by the aid of the glass,-of per-oxide of iron by the brown colour which the acid speedily assumes,-and of black oxide of manganese by a distinct smell of chlorine which is easily recognised. In the subsequent description of.the soil, these points.should be carefully noted. Suppose the- sand and gravel ~to contain half its weight of fine sand,, then our soil would consist of coarse -sand and small stones 30 per cent., fine sand 30 per cent., clay and other lighter matters 40 per cent. 50. Absorbing power of the soil.-A thousand grains of the perfectly dry soil, crushed to powder, should be spread over a sheet of paper and exposed to the air'.for twelve or twenty-four hours. and then weighed. The increase of weight shows its. power of absorbing moisture from the air. - f it amount to 15 or 20 grains, it is so far an indication of great agricultural capabilities, 60. Its power of holding szater.-This same. portion of soil may now be put into a funnel upon a doublet filter and cold water poured upon it, drop by drop, till the whole is vet and the water begins to trickle down the neck of the filter. It may now be covered with a piece of glass and allowed to stand for a few hours, occasionally adding a few drops of water, until there remains no doubt of the whole soil being perfectly soaked. The two filters and the soil are then to be removed from the funnel, the filters opened and spread for a few minutes upon a linen cloth to remove the drops of water which adhere to the paper. The wet soil and inner filter being now put into one scale, and the outer filter in the other, and the whole carefully balanced, the true weight of the -wet soil is obtained.: Suppose the' original. thousand -grains now to weigh 1400, then the soil is capable of holding 40 per cent. of water. 7~. Rapidity with which the soil dries.-The wet soil with its filter may now be spread out'upon a plate and exposed to, the air, in what may be considered ordinary circumstances of temperature and moisture, for 4, 12, or 24 hours, and the loss of weight then ascertained. This will indicate the comparative rapidity with which sucl- a soil would dry, and the consequent urgent demand for draining, or the contrary. As great a proportion of the water is said to evaporate from a given weight of sand saturated with water, in 4 hours, as friom an equal weight of pure clay in 11, and of peat in 17 hours-when placed in the same circumstances. 8~. Power of absorbing heat fronm the sun. —In the preceding experiment a portion of pure quartz sand- or of pipe clay may be employed for the purpose of *As 500: 300:: 100 to 60 per cent. t;That is, one filter within another. t 1000: 400, the increase of weight as 100: 40. NO. V.] OF THE PHYSICAL PROPERTIES OF THE SOIL. 29 obtaining a comparative result as to the rapidity of drying. The same method may be adopted in regard to the power of the soil to become warm under the influence of the sun's rays. Two small wooden. boxes, containing each a layer of one of the kinds of soil, two inches in depth, may be exposed to the same sunshine for the same length of time, and the heat they severally acquire determined by a thermometer, buried about a quarter of an inch beneath the surface. Soils are-not found to differ so much in the actual temperature they are capable of attaining.under such circumstances-most soils becoming 20~ or 30~ warmer than the surrounding air in the time of summer-as in the relative degree of rapidity with which they acquire this maximum temperatureand this, as stated in the text, appears to depend chiefly upon the darkness of their colour. The determination of this quality, therefore, except as a matter of curiosity, may, at the option of the experimenter, be dispensed with. II.-OF THE ORGANIC MATTER PRESENT IN THE SOIL. 90. Determination of, tile pc? —celtageof organic nmatter.-The soil must be thoroughly dried in an oven or otherwise, at a temperature not higher than between'250~ to 3000 F. Humic and ulmic acids will bear this latter temperature without change. An accurately weighed portion( 100 to 200 grains) must then be burned in the open air, till all the blackness disappears. This is best done in a small platinum capsule over an argand spirit or gas lamp. The loss indicates the total weight of organic matter present. It-is scarcelyever possible, however, to render soils absolutely dry without raising them to a temperature so high as to char the organic matter present, and hence its weight, as above determined, will always somewhat exceed the truth, the remaining water being driven off along with the organic matter when the soil is heated to redness. This excess, also, will in general be greater in proportion to the quantity of clay in the soil, since this is the ingredient of most soils from which the water is expelled with the greatest difficulty. 10~. Determin.ation of the h/cmic acdiid.-This acid, whether merely mixed with the soil, or combined with some of the lime and alumina it contains, is extracted by boiling with a solution of the common soda of the shops. Into about two ounces by measure of a saturated solution of this salt, contained in a flask, 200 or 300 grains of soil, previously reduced to coarse powder, are introduced, an equal bulk of water added, and the whole boiled or digested on the sand bath with occasional shaking for an hour. The flask is then removed from the fire, filled up with water, well shaken, and the particles-of soil afterwards allowed to subside., The clear liquid is then poured off. If it has a brown colour it has taken up some humic acid. In this case, the process must be repeated once or twice with fiesh portions of the soda solution, till the whole of the soluble organic matter appears by the pale colour of the solution to be taken up. These coloured solutions are then to be mixed and filtered.'The filtering generally occupies considerable time, the humic and ulmic acids clogging up the pores of the filter in a remarkable manner, and permitting the liquid to pass through sometimes with'extreme slowness. When filtered, muriatic acid is to be slowly added to. the coloured liquid — which should be kept in motion by a glass rod —till effervescence ceases, and the whole has become dictinctly sour. On being set aside the humic acid falls in brown flocks. A filter is now to be dried and carefully weighed,* the liquid filtered through it, and the humic acid thus collected. It must be washed in the filter with pure water-rendered slightly sour by muriatic acidt-till all the soda is ~ This is best effected by putting the filter into a covered porcelain crucible of known weight, and heating it fir ten minutes over a lamp or otherwise, at a temperature which just does not discolour the paper, allowing then the crucible to cool under cover, and when cold weighing it. The increase above the known weight of the crucible is that of the filter which, besides being recorded in the- experiment book, should also be marked in several places on the edge of the filter with a black lead pencil. t This is to prevent in some measure the humic acid from passing through the filter, which it is very apt to do, when the saline matter is nearly washed out of it. 30 OF THE ORGANIC MATTER PRESENT IN THE SOIL. [Appendix, separated from it,* when it is to be dried at 250Q F., till it ceases to lose weight. The final weight, minus that of the filter, gives the quantity of humic acid contained in the portion of soil submitted to examination. As it is rarely possible to wash the humic acid perfectly upon the filter, rigorous accuracy requires that the filter and acid should be burned after being weighed; and the weight of ash left, minus the known weight of ash left by the filter,t deducted from that of the acid as previously determined. It is to be observed here that by this, which is really the only available method we possess of estimating the humic acid, a certain amount of loss arises from its not being wholly insoluble, the acid liquid which passes through the filter being always more or less of a brown colour.t 11~. Determination of the insoluble h cnds.-Many soils after this treatment with carbonate of soda are still more or less of a brown colour, evidently due to the presence of other organic matter. To separate this, Sprengel recommends to boil the soil, which has been treated with carbonate of soda, and which we suppose still to remain in the flask, with a solution of caustic potash, repeated, if necessary, as in the case of the soda solution. By this boiling, the vegetable matter, which'was insoluble in the carbonate of soda, is changedin constitution and dissolves in the caustic potash, giving a, brown solution, from which it may be- separated in brown flocks by the addition of muriatic acid, and then collected and weighed as above described. In some soils, also, distinct portions of vegetable fibre, such as portions of roots, &c., are present, and may be separated, mechanically dried, and weighed. 12~. Of otiler or-nan, i, sbtstances present in tIle soil.-The sum of the weights of the-above substances deducted fiom the whole weight of organic matter, as determined by burnin, gives that — of ol/lr organic substances present in the soil. The quantity of these is in general comparatively small, and, unless they are soluble in water, there is no easy method of separating them, and determining their weight. The foilowi n two methods, however, may be resorted to:1~., Half a pound or more of the moist soil may be boiled with two separate pints of distilled water, the liquid filterad and evaporated to a small bulk. From clay soils, wlien thus boiled with water, the fine particles do not readily subside. Sometimes, after standing for several days, the water is still muddy, and passes muddy through the filter, but, after being evaporated, as above recommended, to a small bulk, most of the fine clayey matter remains on the paper when it is again filtered. As soon as it has thus passed through clear, the liquid may be evaporated to perfect dryness at 250' F., and weighed. Being now treated with water-a portion will be dissolved-this must be poured off, and the insoluble remainder again perfectly dried and weighed. If this remainder be now heated to redness in the air, any organic matter it contains will be burned off, and its weight ascertained by the loss-on again weighing. This loss may be considered as hurnic acid rendered'insoluble by drying.~ It does not require to be added to the weight of humic acid already determined (10~), because in that experiment a portion of soil was employed which had not been boiled in water, and from which therefore the carbonate of soda would at once extract all the humic acid. The present experiment need only be made when it-is de* This is ascertained by collecting a few drops of what is passing through upon a piece of clean glass or platinum, and drytin them over the lamp, when, ifa perceptible stain or spot is left, the-substance is not sufficiently washed. t The ash left by the paper employed for filters should always be known. This is ascertained, once for all, by drying a quantity of it in the way described in the previous note, weighing it in this dry state, burning it, and again weighing the ash that is left. In good filtering paper, the ash ought not to exceed one per cent. t The portion which thus remains in the solution may be precipitated by adding a small,quantity of a solution of alum, and afterwards pouring in ammonia in excess. The alumina falls coloured by the organic matter, and after being collected on a filter, washed, and dried, the weight of organic matter in the precipitate may be determined approximately as described under 12~ (2~). ~ See Lecture xiii., ~ 1. .No. V.] OF THE ORGANIC MATTER PRESENT IN THE SOIL. 31 sirable to ascertain how much humic acid a soil contains in a state in which it is soluble in water. Where ammonia, potash, or soda is present in the soil, some chemists consider this quantity to be very considerable, and to exercise an important'influence upon vegetation., That which was taken up by water from the dried residuum is again to be evaporated to dryness, dried at 150~, weighed, and burned at a low red heat. The loss is organic matter, and may have been crenic or apocrenic, or some other of the organic acids formed in soils, the compounds of which, with lime, alumina, and prot-oxide of iron, are soluble in water. If any little sparkling or burning like match-paper be observed during this heating to redness, it may be considered as an indication of the presence of nitric acid-in the form of nitrate of potash, soda, or lime. In this case the loss by burning will slightly exceed the true amount of organic matter present, owing to the decomposition and escape of the nitric acid also. The mode of estimating the quantity of this acid, when it is present in any sensible proportion, will be hereafter described. 20. The caustic potash employed to dissolve the insoluble humus (110) takes up also any alumina which may have been in combination with the humic acid or may still remain united to the mudesous* or other organic acids. When the solution is filtered and the humic acid separated by the addition of muriatic acid till the liquid has a distinctly sour taste, this alumina, and the acids with which it is in combination. still remain in solution. After the brown flocks of humic acid, however, are collected on the filter, the alumina may be thrown down from the filtered solution by adding caustic ammonia to the sour liquid, until it has a distinctly ammoniacal smell. The light precipitate which falls must be collected on a filter and washed with hot water till the potash is as completely separated as possible. It is then to be dried at 300~ F., weighed and heated for some time in a close crucible over the lamp, at a temperature which begins to discolour it, and again weighed. Being now burned in the air till it is quite white, and weighed, the last loss may be considered as mudesous or some similar acid. The reason why this second method of drying over the lamp is here recommended, is, that alumina and nearly all its compounds part with their water with great difficulty, and even with the precautions above indicated, it is notunlikely that a larger per-centage of organic matter may thus be indicated, than in reality exists in the soil. The check which the accurate experimenter has upon all these determinations is this, that the sum of the several weights of the humic acid, the insoluble humus, the vegetable fibre, and of the crenic and mudesous acids, if present, should be somewhat less than that of the whole combustible organic matter, as determined by burning the dry soil in the open air (90). This quantity we have seen to be in most cases greater than the truth, because any remaining water or any nitric acid the soil may contain, are at the same time driven off. I may further remark upon this subject that the quantity of alumina thus dissolved by the caustic potash is in most soils very small, and the quantity of organic matter by which it is accompanied in many cases so minute, that the determination of it may be considered as a matter of curiosity, rather than one of practical importance. III.-OF THE SOLUBLE SALINE MATTER IN THE SOIL. 130. With a view to determine the nature of the soluble saline matter in the soil, a preliminary experiment must be made. An unweighed portion must be introduced into five or six ounces of boiling distilled water in a flask, and kept at a boiling temperature, with occasional shaking for a quarter of an hour. It may then be allowed to subside, after which the liquid is to be filtered till it passes through clear. It is then to be tested in the following manner. Small * Except where gypsum is present in the insoluble portion, which is not unfrequently the case, when the loss will be partly water-since gypsum, after being dried at 250~, loses still about 20-8 per cent, of water when heated to redness. 28 32 OF THE SOLUBLE SALINE MATTER IN THE SOIL. [Appendsx, separate portions are to be put into so many clean wine glasses, and the effect produced upon these by different chemical substances carefully noted. If with a few drops ofa. Nitrate of Baryta, it gives a white powdery precipitate, which does not disappear on the addition of nitric or muriatic acid, thle solhtiio7 contains sldlp/uric acid, If the precipitate does appear, it contains carbonic acid. In this latter case, the liquid will also effervesce on the addition of either of the acids above mentioned. b. If with oxalate of anmo.onia, it gives, either immediately or after a time, a white cloud, it contains lime,* and the greater the milkiness, the larger the quantity of lime may be presumed to be. c. If with nitrate of silver,it gives a white curdy precipitate, insoluble in pure nitric acid, and speedily becoming purple in the sun, it may be presumed to contain chlorine. d. If with caustic anmmonia, it gives a pure white gelatinous precipitate, it contains either alutminna, or mag'nesia, or bot/i. In this case, muriatic acid must be added till the-precipitate disappears, and the solution is distinctly acid If on the addition of ammonia in- excess, the precipitate reappears undiminished in quantity, it contains alumiana only. If it be distinctly l-ss in quantity, we may infer the presence of both magnesia and alumina; and if no precipitate now appears, that it contains mdgnlesia on?/l. Ifa large quantity of magnesia be present, it may be necessary to re-dissolve and acidify the solution a second ti4ne beeore, on the re-addition of ammonia, the precipitate would entirely disappear. If the precipitate, by ammonia, have more or less of a browi colour, the presence of iron, and perhaps maCnbganese, may be inferred. If, on the second addition of ammonia, the colour of the precipitate has disappeared, it ha3 been due to the manganese only-if it still continue brown, it is owing chiefly or altogether to the presence of oxide of iron. If'the colour of the precipitate, by ammonia, be very dark, it consists almost entirely of oxide of iron, and may contain little or no alumina,-when it is only more or less brown, the presence of both alumina and oxide of iron may with certainty be inferred. e. If, after the first addition of ammonia, the solution be filtered to separate the alumina, the oxides of iron and manganese, and the magnesia that may be thrown down-if oxalate of ammonia be then added till all the lime falls, and the liquid be again filtered, evaporated to dryness, and then heated to incipient redness in the air, till the excess of oxalate of ammonia is destroyed and driven off-and if a soluble residue then remain, it is probable that potasl or soda, or both, are present. If, on dissolving this residue in a little water, the addition of a few drops of a solution of tartaric acid to it produce a deposite of small colourless crystals- (of cream of tartar), or if a drop of a solution of bi-chloride of platinum produce in a short time a yellow powdery precipitate, it contains potasl. If no precipitate is produced by either of these-re-agerts as they are called-the presence of soda may be inferred. If the yellow precipitate, containing potash and platinum, be separated by the filter, and the solution, after being treated with sulphuretted hydrogen and filtered to separate the excess of bi-chloride of platinum, be evaporated to dryness-if, then, a soluble saline residue still remain, the solution contains soda as well as potash. It is to be observed that some magnesia, if present, may accompany the potash and soda through these several processes. After the separation of the potash, a little caustic ammonia will detect the presence of magnesia, but it will rarely be found so far to interfere with this prelim7inary examination as to prevent the experimenter from arriving at correct results (see p. 35, f). * The learned reader will understand why, for the sake of simplicity, I take no notice of substances not likely to be present in the soil-as, for example, baryta, which would here be thrown down along with the lime, or ofox-lic acid, which, equally with the' sulphuric or carbonic (a), would give awhite precipitate with nitrate of baryta. t Not precipitated from its solution by ammonia, for if precipitated it is partly at least chloride of magnesium. NO. V.] OF THE SOLUBLE SALINE MATTER IN THE SOIL. 33 f. If the addition of bi-chloride of platinum to the solution directly filtered from the soil give a yellow precipitate, it contains either potash or ammonia. It, when collected on the filter, dried, and heated to bright redness in the air, white fumes are given off by this yellow precipitate, and only a spongy mass of metallic platinum remains behind, the solution contains amlmonin a only. If, with the platinum, be mixed a portion of a soluble substance having a taste like that of common salt, and giving again a yellow precipitate with bi-chloride of platinum, it contains polash-and if the spongy platinum contained in the burned mass, after prolonged heating, amount to more than 57 per cent. of its weight, or if it be to the soluble matter in a higher proportion than that of 4 to 3, the solution contains both polCas/ and ammonia. The presence of L7anonia in the saline substance, or in the concentrated solution, is more readily detected by adding a few drops of a solution of caustic potash, when the smell of ammonia becomes perceptible, or if in.too small quantity to be detected by the smell, it will, if present, restore the blue colour to reddened litmus paper.: Tiis experiment is best made in a small tube. g. If, when the solution, obtained directly from the soil, is evaporated to dryness, and the residue heated to redness in the air, a deflagration or burning like match-paper be observed, nitric acid is present. Or, if the dry mass, when put into a test tube with a little muriatic acid, evolves distinct red fumes on being heated, or enables the muriatic acid to dissolve gold-dust, and form a yellow solution; or, if to a colourless solution, of green vitriol (sulphate of iron), introduced into the tube along with the muriatic acid, it imparts more or less of a brown colour-in any of these cases the presence of nitric acid may with certainty be inferred. It will be only on rare occasions, however, that salts, so soluble as the nitrates, will be found in sensible quantity in the small portion of a soil likely to be employed in these preliminary experiments. A. If ammonia throw down nothing (see under d) from the solution, and if no precipitate appear when chloride of calcium or magnesium is afterwards added, the solution contains no phosphoric acid. But if ammonia cause a precipitate, and after this is separated by the filter, nothing further falls on adding either of the above chlorides, the phosphoric acid, if any is present, will be contained in the precipitate which is upon the filter. Let this, after being well washed with distilled water, be dissolved off with a little pure nitric acid diluted with water, and then neutralized as exactly as possible with ammonia. If a solution of acetate (sugar) of lead now throw down a white precipitate, phosph6ric acid is present. The phosphate of lead-the white precipitate which falls-melts readily before the blow-pipe, and, on cooling, crystallizes into a bead with beautiful crystalline facets. Or-if the precipitate thrown down by ammonia be wholly or in part insoluble in pure acetic acid (vinegar), that which is undissolved contains phosphoric acid. If acetic acid dissolve the whole, it may be inferred that no phosphoric acidispresent in the soil. But if no precipitate be thrown down by ammonia, instead of the chloride of calcium above recommended, a few-drops of a dilute solution of alum may be mixed with the solution, after adding the ammonia, and the whole well shaken. If the white precipitate, which-now falls, dissolve wholly in acetic acid, no phosphoric acid is present, and vice versa. These preliminary trials being made, notes should be kept of all the appear. ances presented, as the method to be adopted for separating and determining the weight of each substance will depend upon the number and nature of those which are actually found to be present. 14~. Determination of the quantities of the several constituents of the soluble saline matter.-The quantity of soluble saline matter extracted from a moderate quantity of any of our soils is rarely so great as- to admit of a rigorous analysis, and the preceding determination of the kind of substances it contains will be in most cases sufficient. Cases may occur, however, in which much 34 OF THE SOLUBLE SALINE MATTER IN THE SOIL. [Appendix, saline matter may be obtained;* it will be proper, therefore, briefly to state the methods by which the respective quantities of each constituent may be accurately determined. a. Estimation of the Sldph1uric Acid.-The solution being gently warmed, a few drops of nitric acid are to be added until -the solution is slightly acid, and any carbonic acid that may be present is expelled, after which nitrate of baryta is to be added to the solution as long as any thing falls. The white precipitate (sulphate of baryta) is then to be collected on a weighed filter, well washed with distilled water, dried over boiling water as long as it loses weight, and then weighed. The weight of the filter being deducted,t every 100 grains of the dry powder are equal to 34-37 grains of sulphuric acid. b. Estimation of the C/lorine.-The solution of nitrate of silver must be added as long as any-precipitate falls, the precipitate then washed, dried at 2120 F., and weighed as before. Every 100 grs. of chloride of silver indicate 24-67 grs. of chlorine, or 40'88 grs. of common salt. c. Estimation of the Lime.-A little diluted muriatic acid being added to throw down the excess of silver, and a little sulphuric acid to separate the excess of baryta, added in the former operations, and the precipitates separated by filtration-caustic ammonia is to, be poured in, till the solution is distinctly alcaline. * This is the case with the rich soils of India and Egypt, and of other warm climates. This will appear from the following analyses of some Indian soils, made on the spot by Mr. Fleming, of Barochan, during the hours of leisure left him by his more important duties:Analysis af soils in North and South tBehar, Bengal Presidency —(200 grains of eacht being analysed.) - ab o of w3a pe acre ~so~Q~sa Sl fro S thwe a darict lo soapyw l l 1 to the touch when moist, hard and cracks when dry; I I / 5(1 2~. Soil fromt the same distrit.Also soapy whpen I a/than No. 1. 3. From he same district.-Heavy red clay soil f 10. Near Gya, South Behar.-Ofa dark colour, soapy to the touch h hing wheat s, cotton, or poppy in the dry 20 6 4l 720 20 110 3 yields a crop of rice and one of wheat the wet sear. Nevar lies fallow, but is covered with water during part of not inundated in the rainy season, and is producti from 30 to 50manure I itbushes of wheat per and cow re. 4~. Soil from Nthe same district.-Also soapy wen 20 14 10 81314 5 1 yieldin tand crops when dry- not inundated producing 19 9 9 1 216 130 7 7producin wheat, b are, an cotton, or poppy in the dry 20 6 42020 110 3 season, ad Indian corn and millet in the wet usuallyson not inundated in the rains, and sometimes manured ith ashes ofoodl andht cow producing nearly 40. Soil from North Behar, Tirhoot. —A deep loam, 7 1 14 6 thyielding twosame crops yearly; not inundated, produciveas No. 4ducin 19 9 91 2 16 130 7 7 wheat, barley, Indian corn, indigo, poppy, &c. From 25 to 35 bushels of wheat per acre; is not usually masnured. F 50. Tirhoot.-Soil light coloured; producing nearly 1.3 7 8 2 1 12 140 6 6 the same crops, but not so productive as No. 4. Saline efflorescence in patches. ( 6~. Tirhoot.-Not so productive as No. 5, and some 12 3 4 - 1 6 152 14 91 patches nearly sterile from the saline efflorescence, except in the rainy season, when it produces good crops of Indian corn. Soil light coloured. I have already alluded (Lecture VIII., p. 159) to the influence which this large proportion of saline matter exercises upon the luxuriance of the vegetation.' Or the whole may be heated to redness in the air, and the filter burned away. In this case the weight of ash left by the paper must be ascertained by previous trials, and the duo proportion deducted from the weight of the sulphate. No. V.] OF THE SOLUBLE SALINE MATTER IN THE SOIL. 35 If no precipitate fall, oxalate of ammonia is to be added as long as any white powder appears to be produced. The solution must then be left to stand over night-that the whole of the lime may separate,- the white powder afterwards collected on a filter, washed, dried, and burned with the filter, at a low red heat. The grey powder obtained is carbonate of lime, every 100 grs. of which contain 43-71 grs. of lime. d. Es.timation of the:0.i le of Iron cnI, of thle Alumina.-But if a precipitate fall on the addition of amlmonia, as above prescribed-the solution may contain magnesia, alumina, and the oxides of iron, and manganese. In this case the precipitate is to be re-dissolved by the addition of muriatic acid till it is distinctly acid, and ammonia again added in slight excess. If any precipitate now fall, it will consist only of alumina and oxide of iron, unless magnesia and oxide of manganese be present in large proportion, when a minute quantity of each may fall at the same time. Theprecipitate is to be collected on the filter as quickly as possible;-the funnel being at the same time covered with a plate of glass to prevent as much as possible the access of the air,-washed with distilled water, and then re-dissolved in muriatic acid. This is best effected by spreading out the filter in a small porcelain dish, adding dilute acid till all is dissolved, and then washing the paper well with distilled water. A few drops of nitric acid are then to be added, and the solution heated, to peroxidizethe iron. A solution of caustic potash added in ex;cess will at first throw down both the oxide of iron and alumina, but will afterwards re-dissolve the alumina, and leave only the oxide of iron. This is to be collected on a filter, washed, dried, heated to redness, and weighed. Every 100 grains of this peroxide of iron are equal to 89-78 grains of protoxide, in which state it had most probably existed in the original solution. To the potash solution muriatic acid is added till the alkali is saturated, or till the solution reddens litm?/s pape.r*k when the addition of ammonia precipitates the alumina. As it is difficult to wash this precipitate perfectlyfree from potash, it is better to dissolve it again in imuriatic acid, and to re-precipitate it by caustic ammonia. When well washed, dried, and weighed, this precipitate gives the true quantity of alumina present in the portion of salt submitted to analysis. e. Estimation of the ZlaMcztaneCse.-To the ammoniacal solutions from which the oxalate of lime has been precipitated (c), a solution of hydro-sulphuret of ammonia is to be added. The manganese will fall in the form of a flesh red sulphuret. When this precipitate has fully subsided, it niust be collected on the filter and washed with water containing a very little hydro-sulphuret of ammonia. The filter is then put into a glass or porcelain basin, the precipitate dis. solved off by dilute muriatic acid, and the solution filtered, if necessary. A solution of carboiate of potash then throws down carbonate of manganese, which is collected, dried, and heated to redness in the air. Of the brown powder obtained 100 grains indicate the presence of 93-84 grains of protoxide of manganese in the salt or solution under examination. f. Estinmation of the Maoseesia.-If no potash or soda be present in the residual solution, the determination of the magnesia is easy. A few drops of muriatic acid are added, and the whole gently heated, and afterwards filtered, to separate the sulphur of the excess of hydro-sulphuret of ammonia previously added. The solution is then evaporated to dryness, and the dry mass heated to redness -to drive off all the ammoniacal salts previously added. A few drops of diluted sulphuric acid are added to what remains, to change the whole of the magnesia into sulphate, the mass again heated to redness and weighed. One hundred grains of this sulphate indicate the presence of 34-01 grs. of pure magnesia. But if potash or soda be present-the weight of which it is desirable to determine-the simplest method is to take a fresh portion, 15 to 20 grains, of the Litmus paper is paper stained by dipping it into a solution of litmus, a vegetable blue co lour, prepared and sold for tie purpose of detecting the presence of free acids, by which it is reddened. 36. OF THE SOLUBLE SALINE MATTER IN THE SOIL. [AppendtX, saline matter under examination. If any sulphuric acid be present in it add nitrate of baryta drop by drop to the solution till the whole of the acid is exactly thrown down-if possible, no excess of baryta being left in the solution-then precipitate the alumina' and oxides of iron and manganese, and the lime, if any of these be present, and, finally evaporate to dryness, and heat to redness as before. The dry mass is now to be dissolved in water, adding, if necessary to complete the soltction, a few drops of muria;ic acid. A quantity of red oxide of mercury is then tq be added to the concentrated solution, and the whole boiled down to dryness. Water now dissolves out the potash and soda only, and leaves the magnesia mixed with oxide of mercury. This is to be collected on a filter, washed-not with too much water-and heated to redness, when the magnesia remains pure, and may be weighed. g. Esimnation of the Potashl and'Soda.-The solution containing the potash and soda, is to be evaporated to dryness, and heated to redness to drive off any mercury, it may contain. The weight of the mass which consists of a mixture of chloride of potassium with chloride of sodium (common salt) is accurately determined, it is then dissolved in a small quantity of water, and a solution of bi-chloride of platinum added to it in sufficient quantity. Being evaporated by a very g ntle heat nearly to dryness; weak alcohol is added, which dissolves the chloride of sodium and any excess of salt of platinum which may be present. The yellow powder is collected on a weighed filter, washed well with spirits, dried by a gentle heat and weighed on the filter. Every 100 grains indicate the presence of 19'33 grains of potash, or 30'56 grains of chloride of potassium. The quantity of chloride of sodium is estimated from the loss. The weight of the chloride of potassium above found, is deducted from that of the mixed ~chlorides previously ascertained, the remainder is the weight of the chloride of sodiun. Every 100 grains of chloride of sodium (common salt)' are equivalent to 53-29 of soda.'h. Estimation of the Ammon.ia.-If ammonia be present in the solution along with potash and other substances, the method by which it can be most easily estimated is to introduce the solution into a large tubulated retort, to add water until the solution amounts to nearly an English pint-then to introduce a quantity of caustic potash or caustic baryta, and to distil by a gentle heat into a close receiver, containing a little dilute muriatic acid, until- fully one half has passed over. Bi-chloride of platinum is then to be added to the solution, which has come over, previously rendered slightly acid by muriatic acid, and the whole is evaporated nearly to dryness by a very gentle heat. Dilute alcohol is then added to wash out the excess of the salt of platinum, and the yellow powder is collected on a filter, washed with spirit, dried by a very gentle heat, and weighed. One hundred grains indicate the presence of 7'69 grains of ammonia. Or the yellow powder, without being so carefully dried, may be heated to redness, when only metallic platinum will remain. One hundred grains of this metallic platinum indicate the presence of 17-39 grains of ammonia. i. Estimation of the Phosphoric Acid.-If phosphoric acid be present in the solution, it will be contained in the precipitate thrown down by ammonia (d). As it will never be found but in very small quantity, the rigorous determination of its amount is a matter of considerable difficulty. The following method already described (13~, A,) may be adopted. The precipitated alumina, oxide of iron, &c., thrown down by ammonia, after being dried, are to be mixed with three times their weight of pure dry carbonate of soda, and fused together in a platinum crucible. The fused mass is then to be treated with cold distilled water till every thing soluble is taken up. The filtered solution is next to be gently heated and exactly neutralized with nitric acid, when a solution of nitrate of silver will throw down a white precipitate of phosphate of silver, which is to be collected, dried, and weighed. Every hundred grains of it are equal to 23-51 of phosphoric acid, or 48-50 of bore earth. No. F'. OF THE SOLUBLE SALINE MATTER IN THE SOIL. 37 Or the filtered solution may be treated with muriatic acid, ammonia added in excess, and then a solution of chloride of calcium. Bone earlt/ will fall, which is to be collected, washed, heated to redness, and weighed. One hundred grains of it contain 48'45 of phosphoric acid. The former method is probably the better, but neither of them will give more than an approximation to the truth. That portion of the fused mass which cold water has refused to take up is to be dissolved in muriatic acid, and again precipitated by ammonia. The clear solution which passes through is to be added to the first ammoniacal solution (c), from which the lime is not yet thrown down, as when little alumina and oxide of iron are present, a small portion of lime and magnesia, if contained in the salt under examination, may have fallen along with them in combination with phosphoric acid. The.alumina and oxide of iron which rest on the filter are to be separated and estimated as already described (l). /. Estimation of t/le Ci)rbonic A i-d. The lime and magnesia dissolved by cold diluted muriatic acid are partly in combination with carbonic acid and partly with the humiic, ulmic, andi other vegetable acids. To determine the carbonic acid, 100 grains of the soil dried at 1!2-, [ile to be introduced into a small weighed flask, and then just covered by a weighed quantity of cold diluted muriatic acid. After 12 hours, when the action has ceased, a small tube is to be introduced into the flask and air sucked through it till the whole of the carbonic acid is drawn out of the flask. The loss of weight will indicate the amount of carbonic acid very nearly. It would be more rigorously ascertained by fitting into the mouth of the flask a tube containing chloride of calcium, and then heating the solution to expel the carbonic-acid. Every hundred grains of carbonic acid indicate the presence of 77'24 grains of lime in the state of carbonate. The weighlt of lime in this state, deducted from the whole weight obtained as above (c), gives the quantity which is it combination with other orlan.ic acids. IV. —OF THE INSOLUBLE EARTHY MATTER- OF THE SOIL. 15~. When the soil has been washed with distilled water as above directedit is to be treated in the cold with diluted muriatic acid-and allowed to stand with occasional stirring for 12 houlrs. By this means the carbonates of lime, magnesia, and iron, and the phosphates of lime, and alumina, are dissolvedwith any lime, magnesia, oxide of iron, or alumina, which may have, been in combination with organic acids. The iron, alumina, and phosphoric acid are to be precipitated by ammonia, the lime by oxalate of ammonia, and such other steps taken as may be necessary, according to the methods already described. 16'. The undissolved portion miay now be'treated with hot concentrated muriatic, kept warm and occasionally stirred for two or three hours, and. the solution afterwards evaporated to Iclyness.'The dry matter is then to be moistened with a few drops of muriatic acid, and subsequently treated with water. What remains undissolved- is silica, which must be collected, on a filter, dried, heated to redness, and weigled. The solution may contain oxide of iron, alumina, lime, magnesia, potash, and soda. -A ny of the four last substances, which may be detected in it, have most probably existed in the soil, in combination with silica-in the state of silicates. 17~.'But the soil may still contain alumina, not soluble in hot muriatic acid. To ascertain if this be the case, and to separate and determine this portion of the alumina, if present, elthelrof two methods may le adopted. a. The residual soil may be drenched with concentrated sulphuric acid and heated for a considerable time till the sulphuric acid is nearly all driven offi On treating with water, and adding ammonia to the filtered solution, alumina, and oxide of iron, if any have been present, will be thrown down. If any alumina be thus separated. tks treatment with sulphuric acid must be repeat 00 The following scheme exhibits the successive steps which are to be taken in order to separate the several inorganic substances from the solution in muriatic acid bythe methods described. Digest the soil in distilled water, dry at 2500, weigh, digest with dilute muriatic acid for 12 hours, and filter the solution. This solution should be decidedly sour, and may contain lime, magnesia, alumina, oxide of iron, oxide of manganese, potash, soda, and ~ phosphoric acid. 1. Add caustic ammonia in excess. 9. To the clear solution add oxalate of ammonia, and cover it from the air. 2. Oxide of iron. alumina, and phosphoric acid are precipitated. O ___ —_____ —— ~- __Di —---- act —-caci Digest in acetic acid. r 11. Add hydrosulphuret of ammonia. 10. Oxalate of lime r- ----— d — __.N__ ~ falls, wash, heat 6. Solution contains alumina 3. Phosphates of alumina and M 13. Render sour by muriatic a- 12. If manganese is present it to redness to con- and oxide of iron; add am- iron remain undissolved. 13. Render sour by fandloxi ad sphet; ofisrsoen cid, boil, filter, evaporate to -falls as sulphlret; dissolve vert it into carbo- monia, and digest the preci- Fuse with carbonate of soda, drvness, and heat to incipienit in muriatic acid, precipitate nate, and weigh. pitate in a solution of caustic and wash with distilled water redness to drive off all the by carbonate of soda, wash, potash (p. 33.) (p. 34.) Z ammoniacal salts. Redissolve heat to redness in the air, and r —-- -- A —— e —.. in a little water, mix with a weigh, p. 33. 8. Add muriatic 7. Oxide of 5. Phosphoric acid 4. Alumina.little pure red oxide of mer- acid till the so- iron re- is dissolved. Neu- and oxcury, evaporate again to dry- lution is sour; mains; tralize by nitric ide of ness, heat to redness, and then ammonia wash & acid, &eddnitrate iron retreat with water. in excess. Al- weigh. of silver, when main...____,___ _., umina falls; phosphate of sil- dissolve 15. The solution contains the 14. Caustic magnesia remains; washandweigh. ver will fall; or in murichlorides of potassium and wash, heat to redness, and by muriatic acid, atic acid sodium, if present. Evaporate weigh. and add chloride and add to dryness, weigh, re-dissolve of calcium and totheso- in water, and add bi-chloride caustic ammonia, lution (6) ~ of platinum to separate the when bone earth potash, p. 34. will fall, (p. 34.) 17. The chloride of sodium re- 16. Wash the precipitate with mains in solution, and its weak alcohol, dry by a gentle weight is found by deducting heat, and weigh from the weight of the mixed chlorides (15) that of the chloc ride of potassium (16). Fz No. F.j OF T'HE SOLUBLE SALINE MATTER IN THE SOIL. 39 ed, till on treating with water and ammonia, as before, no more alumina appears. b. Or that portion of the soil on which hotr mruriatic acid refuses to act may be mixed with twice its weight of carbonate of soda, and heated in a platinum crucible till the whole is completely fused. The mass'is then to be treated with diluted muriatic acid till every thing soluble is taken up, the filtered solution evaporated to dryness, the dry mass moistened with muriatic acid, and again treated with water. If any thing is left undissolved it will be silica, and if any alumina be contained in the solution, it will be precipitated by ammonia, and may be collected, washed, dried, and weighed, as already described. The solution may also be tested for magnesia, and if any be present it may be separated by the process already explained. The former of these two methods is to be preferred as the simpler, though it will also require considerable care and attention. That which the sulphuric acid leaves behind must be washed, dried, heated to redness, and weighed. It will be found to consist chiefly of quartz sand, and finely divided siliceous matter. The'accuracy and care with which the whole of these processes, have been conducted is tested by adding together the weights of the several substances that have been separately obtained. If this sum does not differ more than one per cent. from the weight of the soil employed, the results may be considered as deserving of confidence. One of the points in which a beginner is most likely to err, is in the washing of the several precipitates he collects upon his filters. As this is a tedious operation, he is very likely to wash them, at first, only imperfectly, and thus to have an excess of weight when his quantities are added together-whereas a;small loss is almost unavoidable. The precipitates should'always be washed with distilled water, and the washing continued until a drop of what passes through leaves no stain when dried upon a bit of glass. No. VI. ACTION OF GYPSUM.-(Seepages 333-34.) In the text I have stated what appear to me the most probable effects: which gypsum is fitted to produce upon the soil. Some of the numerous opinionsthat have been entertained upon this point are thus summed up by Hlubeck: — "According to Kollnler, the action of gypsum depends upon the power possessed by lime to form with the oxygen and-carbon of the atmosphere compounds which are favourable to vegetation; according to Ratckert, it acts like any other food; according to Mayer and Browin, it merely improves the physical properties of the soil; while, according to Roil, it is an essential constituent of the plant. Hedlwig called gypsum the saliva and gastric juice of plants; Humboldt, Girtaer, and Albert Treere considered it as a stimulant by which the circulation of plants is promoted; and C/Laptal ascribed its action to a supposed power of supplying water and carbonic acid to plants. Davy regarded it as an essential constituent of plants, because it acts only where gypsum is wanting in the soil, while other English agriculturists have supposed it to promote fermentation in the soil. According to Laubender, it acts as an exciting power without mixing itself with the sap of the. plant; according to Liebig, it fixes the'ammonia of the atmosphere; and, according to Braconnot, and Sprengel, it supplies sulphur for the formation of the legumin of the leguminous plants (the most probable view)."-Ernidhr7ung der Pjlanzcn, p. 70, note. To the above extract I may add, that Mr. Cuthbert Johnson, so long known for his many valuable writings upon agriculture, in following out the above idea of Reil and Davy in a recent paper on the use of gypsum (Jour. of the Royal 280 40 ACTION OF GYPSUM. [Appendx, Agr. Society, ii., p. 108,) has stated that a crop of clover or sainfoin contains 1J to 2 cwt. of gypsum per acre, exactly the quantity which the farmers of Kent and Hampshire find it useful to apply to their grass lands every year. This stateoent affords a very simple explanation of the use of gypsum, and one which at first sight leaves nothing, to be desired. But it'proves too much,. for it supposes the whole of the gypsum which is laid upon the grass or clover field to be removed year by year in the crop, and makes no allowance either for the quantity which must necessarily be carried off by the rains, or for that which must be sometimes at least laid on in the form of farm-yard or other similar manure. Nor does the result Ef analysis confirm the above statement as to the quantity of gypsum contained in the crop of clover or sainfoin. By referring to page g220, it will be seen that 1000 lbs. of dry hay do not contain, on on average, more than 4 lbs. of sulphuric acid-equal, supposing it all to be in combination'with lime, to 84 lbs. of gypsum. Or a crop of 14 tons of hay, contains the elements of about 30 lbs. of gypsum-only about a sixth part of what is usually added' as a top-dressing to the land. No. VII. SUGGESTIONS FOR EXPERIMENTS WITH THE SOLUBLE SILICATES OF POTASH AND SODA. In the text (pp. 207 and 349,) I have had frequent occasions to refer to thepre-, sence in the soil of the silicates of potash and soda, and to their supposed action in supplying silica to the stems of the grasses and of the corn-bearing plants. It would be interesting in a theoretical point of view, to ascertain, by experiment, more fully than has hitherto been done, how far the application of these substances to the growing crops would, as a general rule, improve or otherwise affect their growth. But as those experiments which have already been made (page 349), afford a strong presumption in favour of their economical value, it becomes a matter of practical interest also to investigate their apparent effects upon each of our cultivated crops. These experiments are placed within the reach of the practical farmer during the ensuing season, by the introduction of the above compounds into the market at a reasonable rate (page 363). I therefore subjoin a few suggestions forexperiments with these silicates, in the hope that some of the many zealous and intelligent practical men, who are now directing their attention to the applications of chemical science to agriculture, may be induced to enter upon this field of inquiry during the ensuing spring. 1~. In order to convey silica into the plant, it appears to be chemically indifferent whether the silicate of potash or that of soda be placed within reach of its roots. But as the silicate of soda can be manufactured very much cheaper than that of potash, it is desirable above all to try the effects of this compound -upon the grasses and corn-bearing plants especially. 2~. But as in the ashes of most plants potash is found in larger quantity than soda, it is possible that the effect of the silicate of potash upon some soils may be so much greater than that of the salt of soda as to counterbalance the difference of expense. Hence the propriety of extended trials with this compound also.3c. But as in the ashes of all our cultivated plants both potash and soda are found, it may be that a mnixture of the two silicates may act better than either alone. It will be proper, therefore, to apply such a mixture in different proportions, and to compare it effects with those of each of the silicates laid on singly. No. VIII.] OF THE SOLUBLE SILICATES OF POTASH-AND SODA. 41 The first series of comparative experiments, therefore, would be as follo'rs: SIlicate The aplAication may be from 1 cwt. to 1I Sa Silicate of- cwt. per acre, laid on as a top-dressing in Silicate of Pa, moothing. moist weather early in the spring. (r it Soda. tSilicate o w, nete Soda. may be mixed with a large quantity of wa--- -- -- -—' --- -;ter, and applied with a water-cart. In either licate of Poilcateof, case it ought to be ini the state of a fine powder. Potash. X Silicateof But although the.bove applications produce a-beneSoda. ficial- effect upon the crops, it will not necessarily follow ____________ __ ~that the silica, which the silicates contain, has had any share in bringing about the good result. By mere exposure to the air for a length of time the potash or soda of those silicates will absorb carbonic acid fiomn the atmosphere, and be converted into carbonates. The same will take place more rapidly still in the soil, where carbonic acid abounds This conversion of the alkali into carbonate will set free a large part of the silica-in a state it is true in which it is in some degree soluble in water (page 206,) -but in whicn, nevertheless, it will find its way into the plant with much moredifficulty than if it had remained in the state of a soluble silicate. Now as the carbonates of potash and soda are known to promote vegetation (page 328),-though even with these, sufficient trials have not yet been made. -it is possible as I have remarked above, that a good effect may follow the application of the silicates, and yet it may be altogether due to the action of the carbonates which are formed by their decomposition. It is of consequence to ascertain if this really be the case, because the -quantity of carbonates which would be formed by the decomposition of the silicates could be laid on directly at one half of the price at which the silicates can as yet be sold. The second series of comparative- experiments, therefore, which it would be interesting to try, wouldbe such as the following - The quantities here indicated are by the acre-that Silicate of Crude of carbonate of soda is given so great, because this salt Potash, Potash or contains upwards of three-fifths its weight of water (see I cwt. Pearla h,, p. 2l5.) 75 lbs. __._____ __ j._ Another consideration ought not here to be omitted. Sie Crystallize Nature, as has been frequently illustrated in the text Silicate of bnate feeds her plants with a mixture of many different suboc%,1 [t. of Soda, stances, and by the aid of such mixtures they always 150ibs. thrive the best. The full benefit of the silicates, when applied alone, will be experienced only when every other ingredient which the plant requires is already present in the soil, and in sufficient abundance. But this can-rarely be the case. Its success will be more sure, therefore, if it be applied in a state of mixture with other saline substances which are known to be more or less useful to vegetation, and which will not, upon admixture, decompose these silicates. Such are common salt and the sulphate and nitrate of soda. A third series of comparative experiments, therefore, might be made, in which friom 1 to 1i cwt. per acre of the following mixtures might be applied: —~. Equal weights of common salt, of dry sulphate of soda, of nitrate of soda, and of silicate of potash; 20. Equal weights of the same substances, omitting the silicate of potash; 3~. Equal weights of common salt, of dry sulphate of soda, of nitrate of potash, arid of silicate of soda; and 4~. Equal weights of the same substances, omitting the silicate of soda, or substituting carbonate of soda in its stead. The sulphate of magnesia (Epsom salts) or of lime (gypsum) can not be safely used along with the silicates, as the magnesia or lime they contain may decompose the silicates-forming sulphate of potash or soda and silicate of magnesia or lime, in which the silica is insoluble, and could not, therefore, until. further chemical change took place, find its way into the roots of the plant. 42 SEXPERIMENTS ON TURNIPS. [AAptndez, No. VIII. RESULTS OF EXPERIMENTS IN PRACTICAL AGRICULTURE, MADE IN 1842. I have much-gratification in laying before my readers the results of a second year's series of experiments undertaken in consequence of suggestions thrown out in previous parts of this Appendix, or of opinions expressed in the body of the work. It is one of the numerous good results which have followed from the issue of these Lectures in a periodical form that I have the pleasure of incorporating in the same volume the results of experiments made during two successive years. No one, who studies with care the experinrents which follow, and the few remarks I have appended to themi-, will hesitate in pronouncing them to be as a whole the most valuable contributions to accurate experimental agriculture ever hitherto published. The results are not all equally important, nor all equally instructive, but they are the first fruits of a new line of research, which will lead,us hereafter- to the discovery of important general truths. They show that practical men are now on the right road, and-spreading as scientific knowledge now is among the agricultural body-I trust there is no fear of their hereafter being prevented from pursuing it. A.-EXPERIMENTS ON TURNIPS. I. The first series of experiments was made with the view of obtaining answers to these two questions: 1~. What are the relative effects of different saline substances upon the turnip crop -_nder the same circzrlzstances? and 9~. How far may these substances be employedalone to su)ersede farm-yard manure in the culture of turnips Turnips grown in Salter's Bog.-Field furrow-drained and subsoil ploughefd. Manures ap. plied partly in drills before sowing on 1st June, and partly as top-dressing on 28th July, 1842. The salt and nitrate of soda last applied were dissolved in-water; the others applied dry. The quantity of land in each plot was one-thirteenth of an acre. I Manure applied. Produce REMARKS. No. Description of ---- ---- weight The rest of the field, Dressing. lstJune. 28thJuly Tota}. of bulbs. grown with farm-yard....- -- ----- — ____- --- _ -_ -- - manure, was a fair avelbs. Ibs. Ibs. sts. lbs. rage crop. Those expe. 1 Nothing.... - - - 43 11 rimented upon were a 2 Common Salt....... 2 6 8 23 0 complete failure, owing Common Salt....... - 4 4 partly, no doubt, to the Rape-dust.......... 67 - 67 severe drought of the sea4 Nitrate of Soda. 2 6 8 36 6 son, but chiefly to the Nitrate of Soda..... 46 a e i d Nitrate of Soda... 4 4 8 want of farm-yard dung. R Rape-dust.-,...... 667 - 67 The seeds brairded badNitrate of Soda..... 4 1 ly, and the drills were Sulphate of Soda.. 4 blanky throughout. Few 7 Sulphate of Soda.. 2 6 8 29 7 of the plants reached any 8 Sulphate of Soda.. 4 4 39 12 size, and the best of themi Rape-dust.... 67 - 67 were inferiorto the plants 9 Rape-dust.......... 67 67 134 46 3 immediately adjoifing10 Guano............ 8 9 17' 61 6 sown at the sane time, & buh. bush. bush.'similarly treated, except 11 Soot............... 1 1 21 9 9 as respectsthe manuring. The foregoing experiments were made at the suggestion of Lord Blantyre on the'home farm, at Lennox Love, near Haddington, and have been reported to me, at his Lordship's request, by Mr. William Goodlet, under whose immedidiate superintendence the whole were conducted. The reader will not suppose, because they proved what are commonly called No. VIII. EXPERIMENTS ON TURNIPS. 43 failures, that therefore they are of no value. On the contrary, they so far satisfactorily answer the questions they were intended to solve. They show 1~. That saline manures in that locality cannot economically take the place of farm-yard manure, even for a single season. 20. That saline manures are even hurtful in the'present condition of the land, when employed alone-producing a smaller crop than if no manure had been applied at all, and some of them in a remarkable degree. This appears to be especially the case with common salt, which at the rate of 1 cwt. an acre reduced the crop of bulbs nearly to one-half of what was yielded by the unmanured portion of the field. It is still more striking that nitrate of soda applied at the same rate should diminish the crop though in a less degree than common salt-arid that soot should almost kill it entirely, and that 15 cwt. of rape-dust per acre should produce scarcely any effect. In regard to guano, it was applied in too small quantity to do all the good of which it was.capable had it been laid on more largely. If 6 or 8 cwt. instead of 1 cwt. per acre had been used, the crop would probably have equalled that obtained by the use of farm-yard manure. There is no doubt that.to the extreme drought of the season, as Mr. Goodlet observes, must be ascribedcthe injury or actual lessening of the crop, in this case, by the use of saline manures. The drought brings up the saline matters to the surface, and thus enables it to encrust, and weaken, or entirely kill, the growing plants. The want of rain in 1842 was much more felt-in the Eastern part of Scotland than in the West, where the greater part of the succeeding experiments were made, and where occasional showers refreshed the land. One other observation I may make. Had-the saline matters been mixed with a fair proportion of farm-yard manure, it is probable that even on this field the effects would have been very different. One reason for this expectation is, that the plants being kept in a rapidly growing state-partly use up, and even eagerly appropriate, a large portion of the saline matter as it rises to the surface -and by their strength are enabled to resist the injurious action of any excess, which in ordinary circumstances is likely to remain. The reader, however. will not ask why the experiments were not so made-for he has already seen that their object was to ascertain the effect of saline manures applied alone. From their results, -however, he will draw for himself the important practical rule, that in ordinary circumstances it is unsafe to trust his turnip crop tos saline -manures alone-that they may assist the action of farm-yard or other similar mixed manures, but cannot supply their place. But upon this point the succeeding series of experiments throw much further light. II. The special object of the following four series of experiments was to as certain1~. Tlhe relative effects chiefly of various mixed manures upon several varieties of turnips; and 2~. Whether any of these mixtures could alone be economically used to supersede farm-yard manure. They were made at the home-farm at Barochan, near Paisley, under the direction and superintendence of Mr. Fleming, whose excellent experiments, made in 1841, are recorded in a previous part of this Appendix (pp. 17 to 24). Mr. Fleming describes himself as much indebted to his overseer, MIr. Gardiner, without the aid of whose zeal, intelligence, and careful superintendence, so numerous a body of experiments could neither have been made,- nor the results accurately ascertained. 10. Comparative Experiments with various substances used as manures, for growing Swedish Turnips: seed sown 6th June, bulbs lifted 25th Nov., 1842. REMARKS.-The land is alight loam, loose in texture, and of alight brown colour. Sub, soil hard, and full of small stones: it is of as nearly as possible the same quality. The tur. nip seed was all sown upon the same day. Rain came on the night after sowing, and in Consequence the crops brairded well, and came away strong. Those which show the great. est weight in the Table kept the lead of the others all the season. The numbers of the plotS in the Table are placed in the order in which they followed each other on the ground. The crop would probably have been larger had there been more rain, 44 EXPERIMENTS ON TURNIPS. [Appendixc, Quantity Produce Produceof CostofManure ORCHARD FIELD. applied of Bulbs, Bulbs, topped per imperial No. I per topped & aind tailed, per Acre,including Description of Manures used. imperial' tailed, per imperial carriage and Acre. imp Acre. acre. putting on. Ibs. tons. cwt. qrs. X. s. d. 1 Peat and Night-soil, mixed.... 20 tons. 4800 17 2 3 6 12 0 2 Gypsum,............. 5 cwt. 40S0 14 11 2 0 12 6 Carbonate of Lime....... 20 bush. 4640 16 11 2 0 3 0 Sulphate of Amminonia......... cwt. 3 Quick-lime........ 20 bush. 4320 15 8 2 1 12 0.Soot 20 bush. 4 Sulphur...................6. lbs. 3980 14 13 1 0 2 0 5 Imitation of Daniel's mixture.. 50 bush. 4400 15 14 1 0 15 0 6 Wood Charcoal Powder....... 50 bush. 4240 15 2 3 2 10 0 7 Fresh Animal Charcoal....... 10 cwt. 5920 21 2 3 2 10 0.8 Exhausted Animal Charcoal... 10 cwt. 5560 4 19 17 1 2 0 0 9 Turnbull's Humus............ 50 bush. 4800 -7 2 3 2 10 0 10 Bones-diss. in Muriatic Acid... 10 cwt. 5200 18 11 3 3 0 0 11 Barochan Artificial Guano.... 3cwt. 4960 17 14 L 1 10 0 12 Turnbull's do. do..... 3 cwt. 4080 14 11 2 1 4' 0 13 Natu-ral Guano............... 3 cwt. 6560 123 8 2 3 15 0 14 Saltd, ck 50 bush. 4240 15 2 3 0 15 9 3 months old...... 15 Soot.........50 bush. 4480 16 0 0 1 0 0 167 qP otash and Lime mixed,14, 50-bush. 4400 15 14 1 1 17 6 months old............. 17 Quick-lime.............. 50 bush. 3200 11 8 2 0 9 9/ 18 Wood-ashes............... 50 bush. 3600 12 17 1 1 5 0 19 Bone dust........... 40 bush. 4160 14 17 1 5 10 10 20 Rape-dust..................... ton. 4000 14 5 3 8 10 0 21 Woollen Rags.............. ton 3920 14 0 9 9 0 22 Farm-yarid dung............. 20 tons. 5200 18 11 2 10 10 0 23 Noting........ 3440. 12 5 3 2~. Results of Experiments with various Substances used as manures for growing Early Liverpool Yellow Turn ips, sown 9th June, and lifted 2d December, 1842. The quantity of land in each plot nwas one-eighth of an imperial acre. BERRIE K(NOWES FIELD, uQtantlit of Cost per Acre, Prodtce of inu re. ap. including: Bulbs. topped No. ipionof sused. -plied per im- carriage and and tailed, per N~- Description of Manur.es used. A cre'__ pertal Acre. putting on. imperial Acre. a. d. tons. cwt. qrs. 1 [ Natural Guano at:25s... 5 cwt. 6 5 0 32 2 2'[ Wood-ashes 20................... 20 bush. 0 10 0 Barochan Artificial Guano......... 5 ew. 2 10 0 21 2 3 2 Wood-ashes........................ 20bush. 0 10 0 1 3 Rape-dust............... 15 cwt. 6 10 0 24 11 2 4 i Turnbull's Artificial Guano.......... 5. cw 21 6 5 3 Wood ashes................... 20bush. 0 10 0 5 Soil simple.......................... 11 8 2 16 Turnbull's Humus....... 50 bush. 2 1i 6 13 14 1 7 Bone-dust..................... 30 hbush. 4 3 6 17 2 3 8 Potash & Lime mixed, 14 mos. old... 50 bush. 1 17 6 14 5 3 9 Salt & Lime mixed, 3 mos. old....... 50 bush. 1 ) 0 0 18 17 1 10 Sulphate of Magnesia........... cwt. 0 8 0 14 17 1 11 Sulphate of Ammonia.............. 1 cwt. 1 1 0 24 11 2 12 Nitrate of Soda..................... 1 cwt. 1 5 0 27 2 3 13 Sulphate of Ammonia........ 56. 0 11 20 17 2 14Nitrate of Soda............... 56 Ibs. 0 12 6 14 Sulphate of Magnesia......... 28 Ilbs. 02 6 11 11 2 Wood-ashes................. 40 bush. 0 0 Sulphate of Ammonia...............84 lbs. 0 16 0? 15 J Sulphate'of Magnesia............ 40.... Ibs, 0 3 4 16 14 1 Lime and Potash. 20............... bsh 0 8 0 16 Turnbull's Artificial Guano.......... 5 cwt. 2 - 1 6 21 4 1 17 Barochan Artificial Guano.......... 5 wt. 2 10 0 24 2 1 18 ISoil simple.............../... 12 17 1 No. VIII.] EXPERIMENTS ON TURNIPS. 45 REMARKS.-The soil is a light hazel loam incumbent upon sand-stone rock. It was trenched with the spade, in the spring of 1842, out of pasture grass, to the depth of 16 inches, and the rock quarried out when it came nearer the surface than that depth, it was again pointed over before sowing, after which the drills were made upon the fiat surface with the hoe, at the distance-of 27 inches between them, the manzure sozmn in by the hand, and covered up, the seed sown and rolled in. The weather was very dry at the time they were sown, and continued so till about the 20th June, accompanied with east winds and bright sunshine. They brairded moderately well, and most of them came away strong and healthy. In examining them, and in the working them, which was done by the hand-lhoe, many of them showed a remarkable difference troit the others; particularly No. 1 was preeminent above the othersfor size of bulbs and strength of foliage. Many of the bulbs were 11 Ibs. in weight; those with the saline and alkaline manures, such as Nos. 8, 9, 10, and 12, were much smaller in bulbs a- l-l leaves than No. 1, but were remarkable for firmness and solidity of bulbs. No. 11 was larger in size both of bulbs and leaves, but soft and light in weight. No. 7 had very firm solid bulbs, as had also Nos. 2 and 4. The numbers of the plots given in the Table indicate the order in which they were grown in the field. The Barochan Artificial Guano consisted of Bones dissolvedin Muriatic Acid......2 cwt.. Nitrate of Soda.................. 28 lbs. Charcoal powder................ 2 cwt. Sulphate of Soda and,.' Sulphate of Ammonia...............1 cwt. Sulphate of agnesia eac Common Salt and Gypsum, each...1. cwt. - Wood-ashes............ 5 cw...12 cwt. 1 qr. 20'lbs. See note to page 47. 3~. Experiments with various Manures on nine Acres of Turnips on the Farm at Crooks, 1842. Quantity Produce' d Value Date of of Laud Manures, and quantities applied to in Tons lnof of maSowing. per Scotch the land sown, per Scotchi are. per Scotch.np. nures; z; acre. acre. Turnip.acre. applied. A. R.. s. 1 May 28. 1 1 Rape-dust 5 cwt.', I-umus 25 bushels, Bone-dust, 12 bushels, Peat ashes 5 carts.................... 22- Swedes. 4 15 2 May 30. 1 0 Iape-dust 5 cwt., Bones 10 bushels,, iuimus 25 bush., Ashes 5 carts.... 20 Do. 4 10 3 June 6. 1 2 Johnstone town-dung 30 tons at 6s., Bones'14 bush. at 2s. 6d......... 24 Yellow. 10 15 4 June 11. 0 3 Farm-yard dung 25 tons at 7s., Bones 10 bush. at':s. 6d............... 19 Do. 10 0 5 June 15. 1 0 Artificial Guano (No. 1., p. 50) 2 cwt., Humus 40-bush., Peat ashes 5 carts. 20 Do. 3 5 6 June 17. 1 1 Natural Guano 1 cwt, Humus 40 bushiels...................Do. 2 15 7 June28. 1 1 Humus 57 bush., Bones 10 bush..... 14 Do. 4 2 8'July 4. 1 1 Artificial Guano mix., (No. II., p. 50.) 121 White. 5 12 REMARKS.-No. 1. Soil a stiff loam, moist, and in good order; when the seed was sown it brairded well, and came away at once. No. 2. Soil rather lighter than the former; seed brairided well, and came away at once. No. 3. Soil-the same as above; brairded quickly in consequence of a shower of rain. No. 4. Soil lighter than No. 3; a bad braird, and turnips long of springing for want of rain No. 5. Soil as above; long of brairding in consequence of want of rain. No. 6. Soil as above; and like No. 5, still very dry for want of rain; a late braird. No. 7. Soil lighter, mixed with peat; no rain-bad braird. No. 8. Soil heavy clay loam; no rain, and a bad braird. The two latter,-from drought and late sowing, did not grow much till the end of September; and when checked by frost in the beginning of November, were still growing vigorously. N. B.-The land was of different qualities, the seed also sown at different times, and in very different states of the atmosphere, with respect to' moisture, yet the average produce was good; and although it is not easy to say which of the artificial manures, under such circumstances, was actually the best, the general result shows that any of these used will produce on my land a good average crop of turnips, and at a less expense than farm-yard manure, and tends to confirm- the correctness of various experiments tried by me on a smaller scale. The measurements having been made by the Scotch chain, I have not altered them; No. 8 would probably have been the best turnips, had they been sewn earlier, and been'assisted by a fall of rain. 4b EXPERIMENTS ON TURNIPS. [Appendix, 4~. Results of Experiments with different mixed manures, in growing White Globe Tzur nips, on new trenched land, Bucklather Field. Sown 13th July, and lifted 16th December, 1842. Quantity Price of Weigit in Weight int Description of Manure used. per Mare imperial Tons, &c. imperial per pounds pr. per impez Acre. Acre. X th Acre. rial Acre.;~. s. d. lbs. tons. cwt. 1ITrnbull' Humus.....T........... 60 bush. 3 0 0 5950 21 5 2 Turbull's improved Bones........ 5 cwt. 1 10 0 4900 17 10 3 Barochan artificial'Guano............. 5cwt. 2' 10 0 6300 22 10 4Natural Guano................... 5 cwt. 6'5 0 9170 39 15 The Natural Guano was purchased December, 1841, when the f rice was ~25 per ton. It can now be had for X~12. REMARKS.-The land was trenched 18 inches deep, and completely drained at the distance of 18 feet, with tile drains laid 30 inches deep, in Feb. 1842. Previous to this it was in a wet, sour state. It was again pointed over with the spade, ard the drills made for the manures with the hoe upon the level surface. The manures were then sown'in the bottom of the drills with ihe hand, and a little earth being put over them, the seed was sown, covered, and rolled. The weather had been dry for some time before sowing, but rain came on that day, they brairded quickly, and continued to grow till lifted-the field being well sheltered. The tops of Nos. 2, 3, and 4 were of a dark green colour, and remarkably luxuriant, many of the bulbs weighing from 5 to Slbs. No. 1 was of a lighter green, but strong and healthy, and many of the bulbs of this lot were 5 and 6 lbs. The bulbs of all of them were finely shaped. III. The object of the two following series of experiments was the same as in those of Mr. Fleming. 1~. Results of comparative experiments upon Swedes and other T7riips made on the home farm of Mr. Alexander, of Southbar, near Paisley, in 1842. The soil of the field was a deep loam, with a slight admixture of peat-the subsoil was partly a light clay and partly a sandy gravel. It was thoroughly tile-drained and-subsoiled to the depth of fourteen inches. Quantity Cost per Produce per-..bubs No. Kind of Manures. per imperial imperial cre per imp. Acre. Acre. _ _ )"~~~~~~, j~~. ~ s. _ _ SWEDES, sown 8th Mlay. 1 Bonedust...........................32 bush. 4 8 24 tons. 2 Bones...16 bus 5 8 28 tons. Bones u............................ bush. ) c tn. Ash-dung......................... 12 tons. 3 Farm-yard dung............... to. 1 4 3 tons. Mixture of Yellow 4 White, sown 20th July. 4 Guano..................... 3 cwt. 310 20 tons. Guano....................16 24 ons Farm-yaid manure......... 8 tons. -Mr. Alexander adds, I must here notice particularly the result'of the last two experiments. The seed sown was a mixture of yellow and white, and the period of sowing as late as the 10th July. The weather at the time being favourable, they brairded quickly, grew with great vigour, and when all the other turnips in the field became affected with mildew they stood as, green as ever. This (viz., the non-mildewing) I attribute greatly to the guano, as well-as to the late sowing, never before having seen such a weight-of turnips produced, sown so late in the season. I applied other artificial manures on both of these fields with a due proportion of dung, varying the quantities and modes of application, as appeared to me best to test their qualities, but as the comparative effect is so difficult to decide upon, I can only here observe, with any certainty,'that though the turnips brairded quicker when the dung was assisted with these manures, particularly where Turnbulls humus was applied, the crops afterwards did not appear to me to be materially aided. 2~. Result of experiments upon Yellow Turnips made by Mr. Alexander, of Southbar, atWellwood Farm, Muirkirk, Ayrshire, 1842. The nature of the. soil on which the experiments were made was reclaimed moss (then about 2 feet deep), having a clayey subsoil, but which had been thoroughly drained with tiles at fifteen feet apart. The field had- produced white and hay No. VIII.] EXPERIMEsNTS ON TURNIPS. 47 crops,.but, as far as known, had never been previously green-cropped. The whole of it received the same labour, preparatory to sowing, and the weather during the operation (which lasted four days) was the same, thus giving to each-experiment an equal chance. The period of sowing was fiom the 15th to 19th of May;.the turnip seed used was Skirving's improved purple-topped yellow; the dung used was the produce of the farm, and, with the exception of the foreign guano, all the other manures applied were those manufactured and sold by Mr. Turnbull, of Glasgow. -The extent of ground for each experiment was one acre, Scotch measure. - f. Quantity Cost of Produce Cost fo per, Manuthnr ia Bulbs - No. Kind of Manure..per hn { i ub M anure imperial per impe- per iumpe-po a - Acre. rial Acre. r ial Acre. perton ~. s. d. s. d. 1 Farm-yard Dung.... 12 tons. 4 4 0 o. 3 31 1 Humus.2.... 2cl. 4 4 0 <-8 tons wt. a Farm-yard Dung. 12 tons. 4 4 0 2 Humus'............ cwt. 0 7 0, 24 " 4 1 Artificial Guano... 1 " 0 6 06 3 F arm-yard Dung lrs. 12 tons. 4 4 0 " 4 111 " Prepared Bones'.... 21 cwt. 0 15 0 ( arm-yard Dung... 12 tons. 4 4 0] Humus.......... 90 lbs. 0 3 9 4 mproved Bones..... 90 " 0 4 10 16 " 6 7 Artificial Guano.... 90 " 0 5 6 Ammoniacal Salts..- 45 " 0 8 0) 5 Artificial Guano.. 3- cwt. 1 3 0. 94" 2 5 _6Guan......... 3 3 5 0 28 " 2 4 IV. Effect of Gypsum on the Tuirnip Crop. In 1841, Mr. Burnet of Gadgirth, near Ayr, applied a top-dressing of gypsum to part of a field of turnips, and found that it nearly doubled the crop. In 1842, Mr. Campbell, of Craigie, in the same neighbourhood, "dressed a six acre field, with the exception of a few rows, with two cwt. of unburned gypsum per acre. The crop over the whole was excellent, but there was no perceptible difference between, the dressed and the undressed part." How are these discordant results to be reconciled 1 The following questions suggest-themselves as worthy of investigation1~. Is gypsumB really propitious to the tlurn'ip crop,-atd to every variety alike? 2~. Are the unlike results above obtained to be ascribed to the abundant presence, in the one case, of gypsum in the soil, or in the manure ploughed in, and its absence in the other-or to the variety of turnip cultivated 1-or 3~. Can the sea-spray supply gypsum to Mr. Campbell's estate, which is within two miles of the coast, while it is less bountiful to that of Mr. Burnet, which is six miles inland 1. B-EXPERIMENTS ON POTATOES. I. Results obtained by Mr. Campbell, of Craigie. Four equal drills of potatoes were treated as follows: — o~. Guano, 3 cwt. per acre....p.. produce 5 pecKs. 20. Farm-yard dung, 40 cubic yards per acre... produce 6 do. 3~. Do., top-dressed afterwards with 60 lbs. of nitrate of soda, produce 6 do. 4~. Do., top-dressed with 160 lbs. sulphate-and nitrate, mixed, produce 6 do.* Turnbull's Hliumus is formed from urine and night-soil mixed with gypsum and charcoal and then dried. Turnbull's prepared Bones are bones and flesh dissolved in muriatic acid, and mixed with about an equal quantity of charcoal in powder. Turnbult's Artificial Guano is, I believe, prepared bones, with a little salt and sulphate of ammonia prepared from urine, and dried with a stove-heat. ,. ~.....- Comparative Experiments with various substances used as manures for growing Potatoes, planted 18th a'.8. "' May,'and lifted 12th October, 1842..8' I^ J a, 17 ^'~ w j,.The qouantity of hind in each plot was one-sixteenth of an imperial acre. asaesi a'i'*es "^ (u- Produce in Produce in Cost of Mag o EtS No. and }IQuantity of Ma- bolls (of 5 cwt. Tons, &c, nure pracre, I:: c~:~.^, ~ S1*^"'"^ o ~ No. Description of Manures used, nure applied per ea.), Renfrew-[ per imperial including ^ g~.):~ +* S ~ y o.2 o' 0j3 * and kinds of Potatoes. imperial Acre. shire measure Acre. carriage and'S^ A JS-10 ~,'^ E:~~~' ~. _ _ ________ ____ per imp. acre. putting on. ^5 a'g IA. — TWhite Don Potato. bolls. pks. lbs. tns. cwt. qrs. ~. s. d. cow.^ i.S , Xs "~ O' 15 Rape-dust.................... 1 ton........ 40 0 0 10.0 0 812 0 ^^or^, a'- )- ~.116 Rape-dust'and Wood-ashes......'2... S. 1 i' 25hhis.asheo 56 0 0'14 0 0 9 46'J?~- z, o-"' - 0 ^^ 17 Potash & Lime (1 lb. potash to I bush. lime) 60 bushels...... 39 0 0 9 15 0 2 2 0.^ -oa~,, V; 2. ^ ^^^,t FS 18 Gypsum........................ 5 cwt.. 39 0 0 9 15 0 0 12 6 ac a a ( i a 10 Salt & quicklime (4 cwt. salt to 1 tns lime) 60 bushels.. 34 0 0 8 10 0 1 0 0 3.ca =o O'Yn,s-.. "'sS) 20 Humus and Wood-ashes........40" 25bhls.ashes 36 0 0 9 0 0 2 14 0 a 3..-21 Bone- dust............................ 45 bushels...... 39 0 0 9 15 0 6 14 0 k 0 80s ~acc a 5 a 0g eo hC.-Connaught Cups Potato. g~.~ ~! S -5-S~~ ^o..-[22 Soil, simple.................. 23 0 0 5 15- 0 5 -o c'8:S 0 g --. ~:., 23 Bone-dust............................45 bushels.. 39 0 0 9 15 0 6 14 0 Ca 0 s 24 -ENatural.Guao4 ct.| 54 14 2 13 14 1 5 1 6 Cc. br o 24..-..Natural Guano...................... 4 cwt..........,Ea.S d 2 m,: 125 Rape-dust............................. ton.... 52 0 0 13 0 0.~_ a ~' 8 -~' a"' 0. ~ -26 Turnbull's Humus..................... 50bushels...... 43'.0 0 10 15 0 2 12 0 8: m a 0,'-. o(t The above manures were put in with the potato cuttin, —no top-dreasing being afterwards applied. dr,'R 4 No. VIII.] EXPERIMENTS ON POTATOES. 49 2~. The object of the two following series of experiments was to ascertain1~-: The relative effect of different saline substances applied adong with farm-yard manaire; and-2~. Whether the effects were greater when mixed with the manurse at the time of planting, or when subsequently applied, as a top-dressing, to the growing plants. 1~. Result of Experiments with saline substances in top-dressing Early American Potatoes. Planted 18th April, top-dressed 1st June, and lifted 28th September, 1842. Low Field, Barochan. Thbe ~quantity of land in each plot was one-eighth of an imperial acre..I.. e Pdc dCost of Quantity IProduce Produ Produce in Prodce in dressings pr. Description of of dressing in pecks bolls of 5 tons, &c., imp. acre, No. Top-dressing. applied of 35 cwt. each per imperial including per pounds per imperial acre. carriage and imp. acre. each. acre. putting on. cwt. pecks. bolls. tns. cwt. qrs.. s..d. 1 Nitrate of Soda....... 1 128 64 16 - - 1 1 0 2'Sulphatc —of Ammonia. 1 116 58 14 10 - 1 1 0 3 Sulphate of Magnesia.. 106 53 13 5 - 0 12 6 4 Nitrate of Potash.... 1 148 74 18 10 -, 2 3 0 5 iNothing but Dung...40 cubicyds. 98 49 12 15. - 0 0 0 6 Sulphate of Soda...... 1 144 Nitrate of Soda... 18 - - 1 7 Sulphate of Soda;..... 2 90' 49 12 15 - 0 15 0 8Sulphate of Sida. 1 81 Sulphate ofAmmnonia: 1W I 151 75'18 17 2 1 4 9 r Sulphate of Mdagnesia..-. I..180 90 10- 190 _~ ^'^Sog:: J I ISO 90 22 10 - 1 9 0 Nitrate of Soda..... 1 REMARKS.-The soil is a light loam of good quality, subsoil hard, stoney till, and retentive of water. The potatoes were planted with the spade at the distance of 26 inches between drills. The manure, farm-yard dung at'the rate of 40 cubic yards per acre, spread in the bottom of the drills-cut sets laid on this and covered up. (The cut tubers planted were the produce of those top-dressed last season (see Appendix, page 20). Camre away strong and healthy, of a dark green colour, and were very remarkable from the contrast which they presented to the same variety of Potato —planted alongside this experimental ground -that had not been dressed last season. These last came away weak, and of a yellowish green colour, and, under the same treatment in every respect, did not produce so good a crop by 15 bolls per acre). Nos. 1, 2, 4, 6, 8, and 9, had all the same effect in altering the colour of the stems and leaves to a darker green. Nos. 3 and 7 had not that effect, but No. 3 added greatly to the produce. No. 7 made no visible alteration, but burned the tops se. verely at the time of dressing, as did most of the others this dry season; this burning was in most cases only temporary. 20. Results of Experiments with different saline sub.sances; mixed with farmyard dung at the'time of planting, in growing Early American Potatoes. Planted 29th April, and lifted 31st August, 1842. The quantity of land in each plot was one-eighth of an imperial acre. Cost of Salts Quantity Produce Produce Produce used, per Description applied per in pecks in bolls, of in tons, acre, incluNo. of Manure and Salts, imperial of 35 lbs. 5 cwt. &c., per ding pntting acre. each. each, per acre. on,exclusive acre. of Dung.' Pecks. Bolls. Ins. cwt. qrs.. s. d. 1 Farm-yard Dung alone.. 35 cubic yds. 71 35k 8 17 2 2 Com Salt,addedtoDung 2 cwt. 70 3b 8 15 0 0 4 0 3 Nitrate of Soda, do. 1( " 99 49- 12 7 2 1 12 0 4 Slliph.' of Magnesia, do. 2 a 9i 45 [11 7 2 0 17 0 5 Sulph. of Ammonia, do. 11" 107 53T 13 7 2 1 12 0 6 Sulph. of Soda, do. 2 d 64 32 8- 0 0 17 0 7 Silicate of Potasht do. 1 c 120 60 15 0 0 ___' Dung 5s. 6d. per cubic yard, exclusive of cartage and spreading. t The silicate of potash or soluble glass was directly prepared from caustic potash and sand or silex fused together, 50 EXPERIMENTS ON POTATOES. [Appendix, REMARKS.-The soil upon which the above were grown was a subsoil, the upper soil having been taken off at different times. It was trenched two feet deep in the Spring of 1841, and which had to be done with the mattock, it being too hard for the spade alone, it was cropped that season with potatoes, manured with 40 cubic yards'of compost of weeds, cut grass, and half-rotten leaves. It was again trenched to the same depth after the crop of potatoes was lifted; and was again planted in the Spring of 1842 with potatoes, manured with 35 cubic yards of farm-yard dung, mixed in the proportions stated with the above salts. The potatoes were planted with the spade, at the distance of two feet between the drills, the manure being put in the bottom of. the drills, the salts sown by the hand above it, and then all mixed together with a dungfork. The cut sets were laid upon the mixture, and covered up. As was remarked in 1841, the potatoes with No. 3 were eight to ten days brairded before the others; also Nos. 5 and 7 were earlier than the others, those three being allfairly up in drills;before the others made their appearance through the ground. Nos. 2, 4, and 6 were latest, and very irregular in coming up, and upon. examining the drills a few of the sets appeared to have been burned..There was a marked dissimilarity in the stems and leaves of thesepotatoes through the summer. Nos. 3, 5, and 7, were all of a darker green colour and stronger than the others. No. 7- was remarkable for intenseness of colour and length of stems, so much so that it appeared to be a different variety of potato. No. 4 was fully better in appearance than Nos. 2-and 6, which were of a yellowish green colour and had a stunted appearance all the season.-When this ground was first broken up, a pound of it was boiled in pure rain water and filtered, which was then evaporated, the residue weighed 42 grains, mostly soluble salts, but hardly a trace of common salt. 30. The following experiments were made with the view of determining how far economical mixtures might be made to supersede farm-yard manure in the growth of potatoes:10. Account of an Experiment- in growing Potatoes (rish Pink Eyes) with the following mixture of substances, instead of farm-yard dung, planted 20th April, 1842. Quantity in- Cost of' No. Ingredients. tended to ma- Substances nure four for acres. four acres. cwts. qrs. lbs. ~. s. d. 1 Rape-dust............. 510 0 2 Bones dissolved in Muriatic Acid. 2 0 0 0 -12 0 3 Sulphate of Magnesia............ 0 2 24 0 6 0 4 Carbonate of Lime.............. 2 0 0 1 6 5 Nitrate of Soda.............. 0 2 0 0 10 0 6 Com on Salt................ 1 2 0 2 3 7 Sulphate of Soda............. 1 2 0 - 9 0 8. Sulphate of Armmonia....... 0 2 0 0 10 0 9 Sulphur..'......... 0 0 2 0 1 0 10 Dry Moss-Earth..............'6 2 0 0 20 0 26 4 1 9 REMARKS.-The'above mixture was sown in the drills at the rate of about 5 cwts. per imperial acre, at a cost.of little more than ~1; sterling, and produced a fair crop of potatoes of a remarkably fine quality, 43 bolls per acre of imperial Renfrewshire measure, weighing 5 cwt. each, upon a poor and light, although new soil, but not worth more than 25s. per acre. Great caution is required in using this mixture, as it is very apt to burn the cut sets if laid directly upon them. A little earth should be put between the cut potato and the manure. 2~. The following mixture was made, and lay together for five weeks, when it was sown in the bottoms of potato drills upon a poor'tilly soil, and White Don Potatoes planted with it 30th April, 1842. No. Ingredients. Quantity mixed Cost of Sub- to manure one stances for acre. one acre. cwts. qrs. bush. ~. s. d. 1 Saw-dust, mostly from Alder.... 40 2 Potash & Lime mixed, 14 mos. old 100 7 6 3 Common Salt...... 1 2 0 2 3 4 Sulphate of Ammonia....... 0 1 0 5 Sulphate of Soda................ 0 2 0 3 6 6 Sulphate of Magnesia........... 0 2 0 4 0 7 Coal Tar, 20 gallons, say-....;....0 10 0 __ ___________________ 3 2- 50 2 7 3 No. VIII.| EXPERIMENTS ON POTATOES. 51 REMARKS.-The potatoes planted with the above mixture came quickly through the ground, and were very luxuriant in foliage. They were lifted 15th October, after being cut down by frost whilst still unripe and growing. On being taken up, they were found to yield a produce ot 56 bolls of Renfrewshire measure weighing 5 cwts. each, per acre, of very fine potatoes, many of which weighed from 24 to 30 oz. each. N. B-This mixture, after being put together, fermented, and was frequently turned, but kept dry. The several series of experiments made upon potatoes by Mr. Fleming are deserving of careful consideration, and many of them of judicious repetition. They are all well contrived or devised, and each series skilfully arranged. In agricultural experiments it is of the greatest possible consequence that the practical man should- have a clear and definite object distinctly in view. If so, his experiments' may be signally successful in his own estimation, while, economically considered, they may be total failures. This, as we have seen, was, to a certain extent, the case with-the first series of experiments made upon Lord Blantyr&'s farm, as above detailed (p. 42). The applications in some instances lessened the crop, but the result, nevertheless, threw considerable light upon the questions which the trials were intended to solve. In making an experiment, the practical farmer asks a question of nature;-in arranging the form and details of his experiment, he is putting together the words by which his question is to be expressed.- If his question be clearly put, nature will give him, sooner or later, a clear and distinct answer-if, he have skill enough in nature's language to understand what she has said to him. I say, sooner or later, for it may be sometimes ]necessary to repeat the question, either because something has intervened to. prevent nature, so to speak, from hearing his question;-because it has not been'accurately expressed-or because something in the seasons, or otherwise, has prevented her answer from being clearly understood-perhaps from being heard or read at all. Circumstances may even prevent the answer from being given until a second summer come round, when, if We are not on the alert, it may never be received at all. The above experiments, as well as those which follow, form an excellent study for the practical farmer in reference to this matter. Every series is planned with a view to a given end, the circumstances are carefully noted before, during, and at the close'of each' of the several trials, and the answers are recorded with a very praiseworthy degree of accuracy. I shall place together, in one view, the most important of the deductions' to which the experiments of 1842 appear to have led, when I shall have laid before the reader the, whole of the tables which-have as yet been placed in my hands. C.-EXPERIMENTS UPON BARLEY. The object of the following experiments, also made by Mr. Fleming, was to ascertain the relative effect of different saline substances, when applied, as topdressings, to a crop'of white barley. The results, as shown in the last column, are suffidiently interesting. Results of Experiments with various substances used as top-dressings upon Barley (common white). The Barley sown.14th April, top-dressed 6th May, and cut down 25th August, thrashed, cleaned,-measured, and weighed 5th October, 1842. The quantity- of land in each plot was one-eighth of an imperial acre. REMARKs.- -The soil of this field is a light loam, as nearly as possible uniform in quality, and had lain about ten years in pasture previous to the spring of 1842, when it was all trenched with the spade twelve:inches deep. It had been thorough-drained with tiles some years before breaking up. After being trenched, it was dressed over, except where the experiments were, with two chaldrons of lime per acre, slaked with water, in which common salt had been dissolved, and before sowing the barley, with the exception of the. experiment ground, it was top-dressed over with two and a half cwts. of Tirnbull's artificial guano per acre, harrowed in, as was also the top-dressing No. 3 in the table of experiments. The bar. ley was sown broadcast, 2I bushels per acre. Owing to the extraordinary drought at time of sowing, it did not braird well till rain came; after which it made rapid progress. Advantage was taken of heavy rains to put on the top-dressings, all of' which were sown at the time above stated, viz., 6th May, except No. 4, wlhich was not sown till the 17th, at which 52 EXPERIMENTS UPON BARLEY. [Appendix ~~ "~Iii2 52- i^' ^ -iir ___ R ODEN HILL FIELD. b o ~ s -b,a'.No. Description. - d | a g of Top-Dressings. s d; -: ~ a.c'. - E [. =0 bL.S f.. -C S = i 5 i.- m,b lbs lbs. lbs.'Ibs.' bs.. d bush. l.bs. Nitrate of Soda.. 10,. 182.36 01 0 5 20 5 20 CommonSalt...............14 0 n Sulphate of.Soda. 21 6 po8 7 4 e c7 e, 6 2 Sulphate of Magnesia....... 7 0 5 3 Natural Guano, at25sa.... 42 2192 432 589 54 9 7 64:0 4 Nirate of Potash. 14 [1665 255 590 54 3' 6 37 42 5 Common Salt.....4....... 2.1735 378 495 57 0 6 53 3 6 Nothing...................- 1620 325 425 55 -- 47 15 7 Turnbull's Artificial Guano.. 42 11925 334 480 54 3 0 49 26 time thee was little rain, and, in consequence, it bwrned the plant, of hich they did not recover all the season, and the ground got full of weeds. No. 5 burned the plants also, but they recovered quickly, and gave a good return. As was roe.warkd before, inherever common salt was put on as: a top-dressing on grain crops, either of rheat, barley, or oats, and on whatever description of soil upon this estate, the grain was invariably heavier per bushel, and had fewer seaks or tails in proportion to-the quantity of grain per acre, than asny of the other dressings applied here. From the frequent mentionof spade culture in these experiments, many may consider that they were upon a very small scale. which is not the case, the greater proportion of them being- very extensive., Mr. Fleming, to give-employment to the destitute labourers, having-dug and trenched about thirty acres of land instead of ploughing it, which abcounts for thie frequent mention of' spade culture, which; when it can be got executed at aimoderate rate (particularly trenching at.4. per acre), is very advantageous, and seems superior to trench ploughing. A. F. GADINE0R.D.-EXPERIMENTS UPON OATS. The first of the following series of experiments was made at Lenn ox-Love, at the request of Lord Blantyre, the, second at Barochan, under the direction of Mr. Fleming. The general object of both was the same-to ascertain the relative effect of different saline substances applied as top-dressings upon young oats; but those of Mr. Fleming have, besides, the special object of cascertainiu g the efIct of certain mixtures upon oats W/len grown upon mossy land. 1~. Oats, second crop, after old lea. Soil sharp loam; subsoil clay resting on sand-stone'rock. Oats sown 14th March; lop-dressings applied 13th May; crop cut 27th Aug,;. and thrashed 9th Sept., 1842. The quantity of land in each plot was one-eighth of an impoerial acre. MAN-URE S.- -t' Weight taken from -.~' - --- 3 2/Thrashing Mill of -,.5 ~ 6 4'QUARRY PARIK, s 5.g c [,'-,, ['.e-Lv..ox;LovE..... -I I.' LENNOx-LOVE.., No... r.. ~' - ^ o ^ ~ Description of Z f,. I'." " Dressing. C5 - - U ma d''.'' Ilbs. as. d. lbs. lbs. lbs. lbs. Ibs'. lbs. bushs. bush. bush. i Common Salt..7..... 7 9 Q 4 * *l Rae-dust Sa.. 11... 12 4 5 4 6 - 4 Nitrate of Soda.. 14 31 588 205 2'. 276 86 394 5-19 - 1-56 Nitrate. ofSoda..... ~ 5NratefSoa 87616 231 17 296 72 40, 5-56 - 1-19' Nitrate-of Soda..-. 20 504 187 128 1 266 38 39 4-81 194 Sulphate of Soda... 7., 1,.. 7. Sulphate of Soda.... 14 10 504: 188 11 249 56 391 4-82 - 1-93 8SuRap edufso.. 75 672 263 20 355 34 40 6'56 S- d 19 9, Rape-dust,.....-.' 224 14 0 616 224 26 324 42 40- 5-62 - 1-13 1 Guano.............. 28 50 938 351.30 496 61 404 875 2-00 - 11, Soot....... 4bush..40 532 193 11 269 59 37 5-12 - 63 S diWaste water from gas 12 work diluted with 4 6galIs. - 700 273 15 390 22 39 7-00 -25 - times itsbulk of water - No. VIII.] EXPERIMENTS UPON OATS. 53 2~. Results of Experiments with various substances used as top-dressings upon Oats (Sandy Oats), sown 16th April, upon drainedpeat moss Nos. 2, 3, and 5 top-dressed on the same day; No. 1 dressed 6th May, cut down 14th September, and thrashed, cleaned, and weighed 6th Oct. 1842. The quantity ofland in eahplot was one-eigh(h of an imperial. acre. SHAW PARK FIELD, BAROOHAN. 0 S;0' a s No. rn., Description of Dressing.' |.a ) _' 2 -. a. - W er2bO gl ls Ibs. Ibs. bs. Ibs. s. d. bush.lbs Sulphateof Ammonia........ 121 lbs. Nitrateof Soda...... 9. lbs. 1220 305 450 40 1 8 61 0 3 Bones dissolved in Muriatic-. 2 0 Acidt............. 2 bs. 1340 32 40 40 2 3 6 60 40 4 Nothing...... 960 210 320 39 43 3 Sulphate of Ammonia......... 7 lbs. ) 1 4 (Silicate of Potash............. 14 bs. 2 5 Sulphate o( Soda........... 14 lIbs. 1600 350 620 43 1 2 65 5 Bones dissolved in Muriatic | Acid.................. 14 Ibs. J 1. 2 0 parts than others, incumbent upon gravel of a stiff retentive quality. It had been partly drainedi some years ago, but owing to the nature of the soil the drails did not act well. In the spring of 1842, it was again drained with tiles, and trenched over with the spade to the depth of 16 inches, and sorme of the gravel subsoil brought rip among the moss. The ground being divided into lots for the purpose, the top-dressings Nos. 2,-3, and 5 were sown on the 16th April, and slightly harrowed in; the oats were then sown ard harrowed in No. I was made from 1e0 lbs. sulphate of ammonia dissolved ii 100 galls. of water (proportions for an imperial acre), and sprinkled upon the oats during the time of rain on 6th May. No. 5 was sown upon a lot where the moss was fully the deepest. They all brairded well; Nos. 2 and 5 coming rather earlier than the others, and of a darker colour, parlicularly No. 2. No. 1, after being watered with the solution, became also of a darker green, but neither Nos. I nor 2 were so strong in the straw as Nos. 3 and 5, both of which were remarkable for strength and luxuriance, especially No. 5, which kept the lead of the others all the season. E.-EXPERIMENTS UPON WHEAT. The following three Experiments upon wheat exhibit Very interesting results: 10. The first series was made on the home farm of Lord Blanttyre at Lennox Love, and was intended to ascertain the relative effects in that locality of different, chiefly saine, manures applied as top-dressings to spring wheat. MANURES Weighttaken from'3'...L____ Thrashing Mill of.i a LENNOX-LCVEr. O- ^ Description of l s. * Dressing..*.-I____ _...._ __ __ _ ___ 6 ___ Ibs. s. d. Ibs. lbs. lbs. Ibs Ibs. lbs. bushs. bush. bush. 1 Nothing........ - - 1036 365 10 5071154 616 5-96 - - 2 Common Salt....... 14 0 4 1003 l 349 20 547 92 611 5-750 - -206 Coimnmro Salt...... 73 rap St......1 112 ( 7 o 1148 386 171 610 1341 612 6 250) 29 - 4 Nitrate of Soda...... 14 3 1 1120 36351 201 598 1381 60S 5-970 -014 - a 5 p ie-dusto.... 112 ( 8 7 1176 394 174 648 1161 61' 6 375 419 - Nitrate of Soda... 7 6sI6 pithate of Soda.! 77 2 0 1078 364 12 595 107 60 6 000.044 - Sulphate of Soda.. 7 4 7 Sulphate of Soda.... 14 1 0 896 2S61 11 4831151 60 4750 - 1206 Sulphate of Soda 112 75 980 339 101- 514 116 61 5562 - 394 R ftape-dust_......... 112 I 6~ 6. / ~ /'394 9 Rape-dust........ 224 14 0 1106 -399 14 575 116 621 6381 -425 110 Guano..... 2 8 5 0 1092 367' 14 566 145 611 6 010 044 11 Soot...... 4 bush. 4 0 1036 361 14 564 97 60, 5 939 - -017 _ 4 -.. _~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 54 EXPERIMENTS UPON WHEAT. [Appendzx REMARKS.-Spring Wheat after Turnips, South-Lawn. Soil loamy clay; subsoil clay Drained every furrow before breaking up from old grass in the autumn of 1839; ploughed deep and subsoiled in spring of 1841. Wheat sown-5th February, 1842; manures applied 13th May; crop cut 24th August; and thrashed 10th September, 1842. The quantity of land in each plot was one-eighth of an imperial acre. 2~. The object of the second series, made at Barochan, was to ascertain the relative efect of certain mixed, chiefly saline, maznures applied as top-dressings to winter wheat. Results of Experiments with various substances used as top-dressings, upon Winter Wheat. -Dressed 9th May, and cut 7th September, 1842. The quantity of land in each plot was onesixteenth of an imperial acre. a a- n.a a5- at CROOK'S FARM, m d. 3 F P C I a a *. I BAROCHAN. -.. l.E l S? S No. O -'_ - Description of:.- -.- Top Dressings. 5 =E g C I/ o a _ a~ _ A-_ _ _______ jL l 0!c _ ED_3 lbs. lbs. bs. lbs. lbs. s. d. bush. lbs. Ibs. Nothing.......... 400 95 160 61 0 0 24 56 2560 Natural Guano...... 2 540 115 230 60 4 41 30 40 3680 2 Turnbull's Artificial Guano........... 21 420 95 175 611 1 8 24 56 2800 3 Common Salt...... 21 360 80 1.50 622 0 4 21 27 2400 4 ulhate of Soda.... 480 101 190 61 26 30 3040 Nitrate of S'_oda..... 8 Il 5 m onr Salt. 21 460 90 170 63 07 22 54 2720 Dissolved Bones...?' 46 9 1770 3 Rape-dust........ 351. 7 S, ulphate ofMagnesia.1 5101 110 200 62 2 7 28 24 3200 REMARKS.-The soil is a heavy loam, incumbent upon a deep clay. The wheat was sown at the end of Novemlber, 1841, after a crop of yellow turnips. The turnips were manured with 20 tons of town dung per acre. Owing to the-severity of the winter of 1841 and spring of 1842, the plants were very thin upon the ground. In April,- 1842, it was sown down with grass seeds, harrowed and rolled, alter which it tillered and gradually recovered. At the time the dressings were put on there was rain, but in general it was dry weather after,-and in consequence the top-dressings did not produce such great results as they did in 1841. The field was examined from time to time, and the appearance -of each experiment as noted down is fully borne out by the results given in the table, viz.:-No. I was taller in the straw, longer in the ear, and of a darker green colour than any of the others; No. 6 was next, and No. 4 was third. In point of appearance there was in the others no perceptible difference from the general crop, except No. 3, which appeared to have checked the growth of the plants, and from this check;they scarcely recovered all the season. It is however remarkable that wherever common salt was applied the grain was heavier per bushel. It will be observed, with reference to the e.xperiment upon wheat grown on this land last year, that the application of comnwn salt had a very great effect, and would probably have also benefitted tho general crop this year, had it not beenifor the extraordinary drought of the season (see Appendix, p. 17.) 3~. The object of the third series, made by Mr. Burnet, of Gadgirth, neaAyr, was the same as those of Mr. Fleming. The mixtures employed, however, were different, and the tabulated results are at least equally interesting and satisfactory. Results of Experiments with mixed Manures used as top-dressings upon Winter Whea (Eclipse variety), sown 29th October, 1841, and reaped 15th August, 1842. The quantity of land in each plot was one-fourth of an tmperial acre. The soil a loam, with subsoil of clay; tile-drained and trench-ploughed. Had been in beans the year previous, and had no manure with that crop nor with the wheat, except the above applications, harrowed in in spring. No. 6 at a cost of ~2. 4s., has produced an in' crease over No. 1 of~6. 19s. 3J. being again of i4. 15s. 3d. No. VIIl.] EXPERIMENTS UPON WHEAT. 55 S' d *~ S S ~ ^ - GADGIRTH, C-3 M- 3 - c _m NEAR AYR. > c c a 3 - Manures applied- | - U, 0 t C 16th April. f. D...,, D-. -.5 0....... *.0 0b & =0 0. ODi z ____ __ _:. - __. l _ cwtqrs lbs wtqr lbs wvt qrs l bs. lbs bald. I bsL. sbl. L. s. s. s d. L. Ibs. 1 No application.. 7 1184 4 3 231 4 0 16 614 9 31 38111. - I - 9y2 Guano a cwt. & Wood-ashes.... 72 18 5 0 24 4 1 9 614 10 32 20 11 6 0 5 - 2 0 88 3 Arlificial Guano I cwt. & Woodashes cwt.... 6 3 25 5 017 4 1 10 594 9 322411 60 5 - 112 88 4 Sulph. ofAmmo- nia a cwt.,Woodashes cwt...... 8 3 21 6 2 7 5110 60 17 395414 0219 6 3 2 0 85 5 Sulph. of Ammo- nia- l cwt., Sulph. of Soda 4 cwt.,. & Wood-ashes 1 cwt..... 11 0 18 7 0 9. 6 2 81 60 13 49 6 17 46 3 16 9 2 16 81 6 Sulph. of Ammonia ~ cwt., Cormon~Salt- cwt,- do Wood-ashes 1 cwt.. 11 1 4 7 1 24 6 2 60 9 49 0 17 36 2 17 3 2 4 84 7 Sulph. of Ammonia- cwt., Nitrate. of Soda l cwt., & Wood-ashes 1 cvt............ 11 0 5 7 0 23 6 1 25 59 11 48-20 1618 5 17116 1413 4 70 8 Turnbull's GLano 1 cwt., Sulph: of Lime 1 cWt,, & Wood-ashes I I-.... 80 6 52- 8 42 2 60 23 334411160 152 3 1 16 81 F.-EXPERIMENTS UPON PASTURE- AND OTHER GRASSES. I. Experiments made by Mr. Alexander, at Wellwood, in 1842. A. On crops of meadow and -ye glrass hay. 10. One Scots acre of well-drained mossy meadow, and full of timothy grass, was top-dressed during the last week of April, with 1 cwt. improved bones, i cwt. glauber salts, cwt. of charcoal, all well mixed with ashes., RESULT.Crop much improved, and came to 180 Ayrsliire stones (of 24 lbs.) per ncre. I may mention that this meadow suffered generally much from the severe drought; the above kept its growth best. 2~. One Scots acre of well-drained mossy meadow, full of timothy grass, was top-dressed during the last week of'April, with I cwt. of.artificial guanoi 12 bushels of humus, well mixed with a quantity of ashes. RESULT.-Not so good; more affected by drought; crop 160 stones per acre; the rest of- the undressed meadow land, on an average, 140 stones per acre. 3~. Three acres of rye grass hay, upon a very lighit sharp soil, was top-dressed during the last week of April,-with 3 cwt. of artificial guaho, 21 cwt. of improved bones, 1 cwt. of charcoal, all mixed with a quantity of ashes. RESULT. —-I cannot pronounce that the hay on the three acres was increased in bulk; the crop. was alight one on the whole field, owing to-.the severe drought, and the very dry nature of the soil this season, therefore, gave this experiment no fair trial, I would say, however, that I have rarely seen such an appearance of white clover since the hay was cut, and particularly on the dressed land. f9 ^...: ~ EXPERIMENTS UPON PASTURE. GRASS, [Append&zr, B. On pasture grass. Three years'?old lea. The extent 2 acres 3 roods Scots measure, divided into three equal parts, and the manures applied duringa the last week of April -No, 1. Dressed with 1 cwt. of anmmoniacal salts, I cwt. of sulphate of soda (glauber salts). No. 2. Dressed with a cwt of ammoniacal salts, 3 cwt. of glauber salts, 3 cwt. of common salt. No. 3. Dressed with I cwt. of ammoniacal salts, ~ cwt. of glauber salts, - cwt. of nitrate of soda. RESULrTS.-1-NOS. 1, 2, and 3 were much alike; in all the three cases the vegetation was quickened and improved; but, as is always the case with experiments on pasture, unless the:cattle were kept off for the whole season, and the produce:cut, it is not easy to say. how far the above application went to imnprove the grass; but certainly the small field did wonders —-for it pastured fifteen early calves nearly all the season. II. The following carefully conducted series of experiments were made by Mr. Fleming, of Barochan, with the view of determining the r:elative efet of saline subslances upon the weight of the hay crop, on the field where the experimental wheat of 1841 was grown:Result of Experimenls tried upon sown Grass, cut for Hay ot 30th June, 1842, Crook's Farm, where the Wheat grew in 1841. (See preceding part of this Appendix, p. 19.) The quantity of land in each plot was one sixteenth of an imzperial acre. 1 I c1 - I 4i~Cd'_ __ __ __ _ _ _ _. -- c su - * "a o'~ a Za lbs. lbs. Is. lbs. lbs lbs.. tns.cw.t.qrs, Nothing...............s....710 11,360 - 195 275 5 1 2 I Sulphate of Soda........ 21 484 7,740 - 1163. 337 3 9 0 2 Common Salt........... 21- 67210960 - 176 262 4 17 3 3 Nitrae of Soda........... 1. 1125 18,100 6640 351 312 8 0 3 Sulphate ol Sod 7....... 4 Nitrate of Soda, mxed.. 515 8,20 186 362 3 3 132 Nitrate of Soda, mixed.. 3 — 5 Natural Guano......... 101 932 14,920 3560:2561 275 6 13 6 S liateof Pofash 2*. I 75712210 760 198 262 5 8 1 Gypsu n...........2...1... - 2 015 7 Siphitate of Aminonia..... 7. 820 13.120 1760!225 275 5 17 0 8 Trnbul's Guano....... 14 595 9,520 6 312 4 50 d9 S"mrnon alt ***;. 1 bushel 3 795 12,720 1360 228 287 5 13 2.10 Hay of Barley LadUSt, 18 940 15,840 3680b305 1 324- 6 14 1 nured withlt i ertdust, 1841. REMARKS.-Nos. j, 2, 3, 4, 5, and 8, were all dressed on the.9th of April, the weather being very dry at the time; and their effects were hardly perceptible; but in thte last week of April Nos. 3 and 4sahowed an -improvement over the others. We had heavy rains the first week of May, and by the 7th lof May the nitrate of sodi (No. 3) could be seen at a distance by the alteration of the colour to dark oreen, and its-height above the others; unpn.that da;.y Nos. 1 and 2 showed no visible alteration from the ut. ressed. No. 3- was the best of any.: taller, and of a dark green colnor, and thicker swardetd. No. 4 shoted little or rio alteration in colour, but tasfully longer than the gener al crop, anid presented the remark able appearance, as did No. 1, in heing nea7rly all Festuca Rubra, krith hardly. any rye grass, although of'this grass, viz. (Festuca Rubra), none Zoas sown; the field'having been sown with'ye grass; timothy, and red clover. No. 5 darker than No. 4 in the colour, and good; but No, 8 hardly inrproved. Nos. 6, 7, 9, and 10, were dresse.d upon the 7th of May. The men in plouhing up the stubble of 1841 found that the ridges which were top dressed that season with nitrate of soda, were more difficult to plough, from the strength and depth of the grass roots, than the ridges undressed, each alternate ridge only having been dressed. Prices ofManures. —Sulphate of soda, 7s. per cwt.; Nitrate of soda, ~1. per cwt.; Natural Guano,,25s. per cwt.; Artificial Guano; 8s. per cwt.; Silicate ofPotash or Sollble Glass, 15s. per cwt. Sulphate of Ammonia, ~1. per cwt. No. VIII.]. EXPERIMENTS UPON MIXED CROPS. 5 G-EXPERIMENTS UPON MIXED CROPS. The following interesting experiment was made by Mr. Alexander, for the purpose of ascertaining the effect qf-a miXtzLre of gypsumr and common salt upon a mixed crop of oats, beans, and peas:Result of an experiment upon the effect of gypsum and common salt, applied as a top-dressing at Wellwood, Muirkirk, 184'2. Four Scotch acres of strong soil, bordering on clay, broken up from two-yearold pasture, were sown with oats, beans, and peas (which is called in; Scotland masl/leat, and is a first-rate fodder for dairy stock).'They all came well, up, but worming and other causes injured the crop so much that I had serious intention of ploughing it up, and sowing turnips. Instead of doing so, I top-dressed the whole four acres with the following substances, well-pounded and mixed together, and this being done immediately before copious rains, the mixture was washed into the soil:-12 cwt. gypsum-(from Turnbull), which, with carriage, cost 8s.; 4 cwt. common salt, which, with carriage, cost 8s. -— this and the gypsum, 16s. Cost of top-dressing, 4s. per acre..'he effect was like magic; the plants immediately assumed a deeper green colour, and grew wonderfully,'and this field took the lead of all'my other oats, and when reaped the field generally was the best I had. Oats, beans, and peas were all particularly well-filled. I may state further, that after the dressing it stood the severe drought better than any of my other crops. Wellwood is 23 miles from the sea, and 550 feet above-it. From other experiments which I had before made, but which I shall not further enter on here, I am convinced that common salt is a great auxiliary in that locality (if not to most others distant from the sea), and it ought to be far more extensively used. H.-EXPERIMENTS UPON BEANS. The following experiments were made by Mr. Alexander, of Southbar, at his farm of Wellwood, in Ayrshire, with the view of ascertaining the relative apparent effects of different saline top-dressings upon beans at different periods of theirb growth:Experiments made at Wellwood upon a crop of beans (1842). The ground was maiured, previous to sowing, with 15 tons of farm-yard dung per Scotch acre, and the other manures applied when the beans were about two inchies high (they were so ini broad-cast). The extent of ground was 21 acres Scots measure, divided into four equal proportions. No. 1'. Dressed with cwt. of sulphate of soda, ~ cwt. of nitrate of soda. R'EsULT.-The effect of the dressing was seen soon after application, by deepening the colour of the plants. The beans were deficient in stiaw, but remarkably well podded and filled. No. 3. Dressed with 4 cwt. of sulphate of soda, 1 cwt. of gypsum. RESULT. -More straw than the foregoing, and rather better crop. No. 3. Dressed with 1 cwt. improved bones, cwt. artificial guano, 3 bushels'Turnbull's humus. RESULT.-About the same as No. 1. No. 4. At first not dressed; but, in consequence of being weakly, was afterwards top-dressed with 3 cwt. of gypsum, and 1 cwt. of common salt, done in consequence of the highly beneficial effect produced on the four acres of mashlam crop above alluded to. - RESULT. — T/togh done so late that the beans were already coming into. flower, it helped them rmauh, and they'ended as well as any of the above. It may here be remarked, that all the beans were, particularly for that high district, heavy, being on trial soon after mowing 65 to 66 lbs. per bushel. I. Observations upon the effect of the top-dressings applied in 1841 upon the crop of 1842. The following remarks are quite as interesting- as any thing contained in the numerous experiments made this year at Barochan by Mr. Fleming's skilful 58 EXPERIMENTS UPON MIXED CROPS. [Appendix, overseer. They are, I believe, the'first systematic series- of observations of the Kind yet published. They are valuable, therefore, as the first steps in the line of prolonged observations upon the same land made during successive seasons, by which prolonged observations only can we'hope to eliminate the effect of ourv'ariable seasons, and to arrive at true deductions in regard to the kind and amount of effect which this or that manure is fitted'to produce. I do hopethat Mr. Gardiner, who is capable of observing so'well, and of experimenting so accurately, will not lose the opportunity which the preseait year will afford him of continuing these important observations:- 1~. Top-dressings upon hay, Covenlea field (see Appendix, p. 17). On lo6king over this field at different times, and particularly early last spring, the square on which nitrate of soda and bones mixed had been sown was earlier, and of a darker green colour, than any of the rest of the field, and when stocked with cattle, the portion top-dressed was. more relished, and consequently always eaten quite bare. 2~. Upon part of the pleasure.ground-soil a very stiff blue clay-nitrate'of soda was'sown at the rate- of 160 lbs. per acre. After this application white clover came up: very thick and strong, and it was cut three different times with the-scythe, and each time it came up stronger and thicker than the surrounding grass, whilst, before dressing, it was the weakest, and this-season, 1842, it is better, and the portion.dressed still easily distinguished. 30. The field' at Crook's farm (see Appendix, p. 17), which had been' top. dressed with nitrate of soda applied on each alternate ridge, on beingploughed up fiom hay stubble was found tougher upon the dressed ridges, the grass roots being stronger and deeper in the soil of those ridges which had been dressed. 4~. At p. 21 of this Appendix an experiment upon moss-oats is recorded. This was sown down with a mixture of grass and clover seeds, and cut for hay this season, 1842. In examining the hay crop some of the dressings on the oats of last year seemed to have had a good effect on the hay crop.of this year. Nos. - and 2 were the worst of any; No. 3 very little better, rather more clover; No. 4 excellent, very thick of red -and'white clovers and rye-grass, and the hay Was of a good quality; No. 5 a little better than No. 3, but far from being equal to No. 4-; No. 6 the best of any, full of red and white clovers and rye-grass, and had three-fourths more hay. upon it than all the others, except No.4;'No. 7 not better than the undressed'; Nos. 6 and 4 presented a most remarkable appearance compared' with the'others, and any person seeing them, and not knowing the circumstances of the case, would have said that these two portions only had been cultivated, whilst the rest had been leftin a state of nature. After being cut for hay,'the aftermath of these two portions still presented the same difference of appearance in the sward, and they-continue of a better colour. A. F. GARDINER. GENERAL REMARKS ON THE ABOVE EXPERIMENTTS OF 1842. However valuable the above experiments may be, and however interesting the results to which some of them may appear to lead, it is of importance to bear in mind1~. That they are the results only of a ^rngle season, and that a remarkably dry one. 2~. That they show the effect of the substances employed in certain localities only-the localities differing in the nature of their soil-in their distance from, and height above, the sea-and in the average fall of rain to which they are subject. 3~. That the results are obtained by trials upon certain varieties of each crop only, and may not be obtained even on the same spots with other varieties-of turnips for example, of potatoes, oats, wheat, or barley. 4~. And that other causes, not yet noted, may have existed of sufficient ini No. VIII.] EXPERIMENTS UPON TURNIPS. 69 fluence to prevent the exact results from being obtained upon a repetition of the experiment. 5~. Above all, it must be borne in miind that we are yet in the first infancy of accurate experimental qgriculture-that it will take many careful repetitions of our experiments before we can eliminate the effects of the seasons-of the alti-.tude of our farms, their distance from the sea, the falls of rain to which they are subject, and, the kind of soil of which they consist. In the mean time our most careful deductions must be considered as partial only, and as open to doubt -as facts by the combination and comparison of which we are hereafter to arrive at more general truths. W:ith these preliniinary observations, I turn to the experiments themselvesA. —TThe ex periments upon turnips. The first series, those of Lord Blantyre-except the general answer that saline substances cannot replace farm-yard manure-afford no very satisfactory results. They exhibit, indeed, some striking circumstance s-such as 1~. That 100 lbs. of salt per acre may, in a dry season, reduce the natural or unaided produce of turnips one-half-and that the same weight of nitrate of soda may reduce it one-fourth. 2~. That'in such a season as much as 16 cwt.'of rape-dust per acre may be applied, one-half drilled in, and one-half as atop-dressing, withoutprzoducing any sensible benefit. 3~. That the same may be the case, if eight cwt. of rape-dust be drilled in, and half a cwt. of nitrate of soda be afterwards applied as a top-dressingwhile if the same weight of common salt be used as a top-dressing instead, the crop will be increased one-half. These results are too anomalous to be considered for the present as more thae accidental. They may possibly be explained either by the different degrees 0i moisture of the several parts of the field in- which:the mixtures were applied-. or on the. supposition, which is very probable, that in the concentrated state some of these saline substances are mzore,' hutful to the growing plant than others. It is to be regretted that the season was so unpropitious to this series of experiments, for though the following experiments of Mr. Fleming afford some valuable information, further knowledge still is wanted in regard to the relative effects oj different saline substances qtpon the g-rowth of turnips, where no fermentible manure is applied. 4~. In these experiments, a striking contrast is presented between the effects of rape-dust and those of guano. 16 cwt. per acre of the former gave only 3{ tons of turnip bulbs,'while 2 cwt. per acre of the latter gave 5 tons. It appears, therefore, that rape-dust requires moist weather or occasional rain, vwhile guano, even in very dry seasons, will produce a considerable effect. This is consistent with what we know of the employment of the latter substance as a manure on the arid plains of Peru. II. The next four series of experiments, those of Mr. Fleming, are rich in results and suggestions. 10. Limits of error.-The first observation which a careful examination of them-will lead the reader to make-and it appears to me to be a very important one in reference to all future experiments of this kind-is suggested by the second series-those upon early yellow turnips, p. 44. In this series there are included two. plots (Nos. 5 and 18), upon which no manure was used. Upon one of these the produce amounted to 12 tons 17 cwt., upon'the other to 11 tons 8 cwt. only-being a difference of 12 tons, or oneeighth of the whole. This difference between two equal portions of the same field, apparently similar in'soil, could scarcely, I think, have been anticipated, and it shews that —where the produce obtained by the application of two unlike manures, to this turnip crop, does not disfer more than lj tons per acre, the effects 60 EXPERIMENTS UPON TURNIPS. [Appendix, of the two manures-smay be considered as practicallylequal —since this amount of difference may have arisen from the unlike qualities of the two plots of land, to which the manures were respectively applied. ~This is an important practical rule for enabling us to judge accurately in regard to the true effect of the several manures employed in the series of experiments (p. 44) referred to, but the factitself suggests also an important modification in the mode of conducting all similar comparative experiments in future. In my previously published Suggestions, I have recommended the setting apart of one undressed portion only of the field on which the trials were madeconsidering that the produce of this portion would represent the average fertility of the whole undressed.part of the field. But these experiments of Mr. Fleming seem to shew that this opinion cannot safely be entertained. It appears to be necessary, therefore, in all future experiments from which accurate deductions are intended to be drawn-that two undressed plots, at least, should, in eachi case, be measucred out, andl their relative produce ascertained, in order to afford a trust-worthy average of the unaided fertility of the land. Suggestion I.-For the clearing up of this point, however, it would be very desirable to institute a series of weighings of the produce of equal portions of land, in. several different parts of the same field, the whole of which has been tilled and manured in the same way. This would throw some certain and satisfactoty light'upon the amount of variation which, from natural causes, may take place in the same crop, grown upon different parts of the same field, and under the same circumstances. We should thus be enabled to allow for the influence of natural causes upon the results of such experiments as are made, -with-the view of determining the true action of the different manures we apply. Suggestion II.-But if some slight difference in the soil, which the eye cannot detect, be capable of materially affecting the natural produce of'the unmanured parts of a field, it may also be sufficient to modify-that is, to increase or to lessen-the effects produced by the saline and other manures we apply to the different parts obf the same field. It suggests itself, therefore, as the more prudent and wary course of experiment to dress two plots at least with each of the manures whose relative virtues we are desirous of testing, and these in different parts-of the piece of land upon which our trials are made. The mean produce of the two or more plots-we thus dress, compared with the mean produce of thoseto which no'dressing has been given, will indicate more nearly the average effect of the manure we have been trying, upon the given soil and crop. The reader will perceive in'the new precautions thus indicated, one of thosepractical results which year by year will necessarily flow from the continuation of the train of inductive experimental research, now, I hope, fairly entered upon by the practical agriculture of our'country. 20. GLuano.-Among the other experiments upon turnips here stated, those upon guano are the most practically successful. Thus, per acre, without any farm-yard manure 3 cwt. of guano alone gave 23 tons 8 cwt. of Swedes.. (p. 44). 25 cwt.hofgu ano with 32 tons 2 cwt. of-Early Yellow (p. 44). 20 bushels of wood-ashes 5 cwt. of guano alone'32 tons 15 cwt. of White Globes. (p. 46). 31 cwt. do..20 tons 0' cwt. of Yellow 4' White mixed (p. 46).'3 cwt. do. 28 tons 0. cwt. of Purple-topped Yellow (p 47). These results are very gratifying, since they.seem to shew that for the turnip crop this light and portable manure may be substituted with safety for farmyard dung.'But they are more gratifying in connection with the large reduction which has lately taken place in the price of this substance. In none of the cases above'mentioned did the quantity applied exceed 5 tons per acre. This quantity may now be purchased for three guineas, though when these experiments were undertaken it'cost, 6 5s. It is no small matter of congratulation, tha; his important reduction has been No VII.] EXPERIMENTS UPON TURNIPS. 61 mainly brought about by the expression of scientific opinion, and by the readi.. ness with-which various persons, manure-manufacturers and others, have put in practice the suggestions contained in the preceding part of this Appendix (p. 26), for the formation of an artificial mixture in imitation of the natural guano. The fear of competition produced its natural effect upon the market, and led the importers of this substance to content themselves with a smaller profit. It is to be hoped that the more extended sale which has followed the reduction, ill leave the spirited merchants who first brought it into the country no reason to regret the diminution in price. The benefits which the practical agriculturist derives from one such reduction as this are not all at first sight perceptible. The demand for guano has so greatly lessened the call for rape-dust, that it has also fallen in price from ~8 to ~5 10s. per ton. Thus ramified and extended are the results of a single chemical, investigation-or the publication of a single well-founded scientific opinion. 3~ Artificial Guano. —In connection with this subject it is important to ascertain to what extent the attempts to manufacture a substitute for the natural guano have been attended with success-in so far as the turnip crop is concerned. The only comparative results which the above experiments present, are the followin,-those upon Swedes being obtained by the use of 3 cwt. of each mixture, those upon the yellow and white turnips by the use of 5 cwt. of each: — Swedes. Early Yellow. White Globe. 1~. Nothing-.. 12 tons 5 cwt. 12 tons 17 cwt. - tons-cwt 2~. Natural guano. 23 8 " 3 " 2 "'32' < 15 ":33. Barochan artificial guano 17 " 14 " 24 2' 2' 22', 10 " 4~. Turnbull's artificial guano 14 " 11 " 21 " 4 " - - These results show that, when equal quantities are employed- equal results are not obtained from the natural guano and from the aitificial mixtures. It also appears that Mr. Fleming's mixture is muchl.more efficacious than tha, of Mr. Turnbull. They are e madeupwithi some modifications, after-the recip given in the preceding part of this Appendix (p. 25), but are, no doubt, suscep tible of improvement. It is, indeed, one of the indirect - benefits which will resuit fiom the introduction of this foreign manure, that it will stimulate to experiments, by which we shall, no doubt, at last successfully imitate it-and wit, -lead, at the same time, to a more general and thorough understanding of the principles upon which mixed manures ought to be compounded, and of the mode of preparing them with the greatest possible economy. Maniy crude mixtures- may be made at first, by dealers in manure and others, and many instane ces of wsVant of success may occur, but now that we have adopted / he system of recordint resltls, iwh.etler ap)parenqtly sicc(ess.ful or the contrcoary'thete is little fear %f otlur arrivinso at satisfactory and economicric tuttlhs at last. Sugaetestionl. I.-In experiments made for.the purpoe of aiding the real advance of scientific agriculture, I would suggest /tCht no omix.ture should be used of w/ic;/t t he compositiion is not exactliy /not —-W which, therefore, has not been either made by the experimenter himself or by some dealer upon whose honor perfect reliance is to be placed. The use of the random mixtures now. sold under so nmany different names,: however successful they may be in this or that case, can never lead to the discovery of useful agricultural principles, and, therefore, are unworthy of the attention of the cultivator of inductive-expe7rimentval' agriclttlre. 4~. SSulpht.ate of 7amoti7lai.-These remarks lead me to notice the effect ascribed in Mir. Fleming's second table (p. 44), to sulphate of ammonia-one cwt, of which nearly doiubled the crop. Thus — Thle unmanured soil gave.. 12 tons 17 cwt.'With 1 cwt. of sulphate of ammonia 24 11 " This is exactly.equal to the effect produced by 15 cwt. of rape-dust at a cost of s6 10s... But the sulphate of ammonia here employed was that prepared by thie Messrs. Turnbull,.of Glasgow-w-hich is not merely sulphate of ammonia, but a variagle and.undelteramizned mixl.re. It is prepared from urine, and I be 62 EXPERIMENTS UPON TURNIPS. [Appendzi lieve is contaminated also with a considerable proportion of saline-substances artificially added to it. That it contains many substances useful to plants there can be no doubt, and that it may prove a valuable manure.is exceedingly probable, but nader ils preset name it canr only lead to false deductions in experimnental agriculture-and the use of it, therefore, in comparative trialssuch as these we are now discussing, ought to be avoided. It is only, as I have already said., from the use of pure substances mixed in known proportions, that valuable, because undoubted, conclusions can be drawn. It isin vain to attempt to eliminate the effects of diversity of soil'and climate, if new causes of diversity are introduced by the very substances with which our experiments are made. 5~. Bones dissolved in lutria.tic acid.-The action of bones is not in general exhausted in a. single season. If they are in the state of fine dust, they decompose more quickly and cease to act in a shorter space of time. By dividing them still more minutely, or by vsolution in an acid, it has been thought that their apparent efficacy might be increased. Mr. Fleming, in 1841, made some experiments which. seemed to justify this conclusion. In the present tables other results are exhibited, which favour-the same opinion. I place together here the results upon potatoes, as well as upon turnips, for the purpose of comparison:Bone-dust. Bones in mariatic acid. 16 CWT. 18 CWT. 3 WT.. 10 CWT. tons. cwt. tons. cwt. tons. cwt. tons. cwt. Swede Turnips... 7 - 1- - - 18 11 White Don Potatoes. - 9 15 12 15 - - These results, the only ones contained in our tables which can be compared together, are both greatly in favour of the dissolved bones, in so far as- the action itpon the first crop is concerned. It will require longer observation to determine in which form the same weight of bones will produce the more lasting effects-and will be the more economical on the whole. 6~. Nitrate of soda.-The effect of 1 cwt. of this salt per acre upon the early yellow turnip is very remarkable (p. 44), having given upwards of 27 tons of bulbs, at a cost of 25s. It is to be regretted that no similar experiment is recorded upon the other varieties of turnip, either by Mr. Fleming or by Mr. Alexander. In the text (Lecture XV., p., 335 to p. 342) an abstract of all the published results hitherto obtained by the use of nitrate of soda will be found in a tabulated form. 7~. Lime. — An interesting result in Mr.'Fleming's first table may hereafter lead to some satisfactory ezperimenltal determinations of the points considered still doubtful in regard to the form in which, and the time when, lime may be most efficaciously applied, in,reference to the culture of particular crops. He caused carbonate of lime and caustic (newly slaked ) lime to be sown in the drills without manure, and the effect upon the crop of Swedes was as follows: Soil ufnmanured. -.. 12 tons 5 cwt. Carbonate of lime, 20 bushels 16 " 1 Caustic lime, 50 bush els. 11 " 8 The immediate effects of lime applied in these two forms was very differentthe-.caustic lime lessened the turnip croropwhile the carbonate increased it by 4- tons. This effect most probably arose from the lime, in its caustic state taking from the soil -the carbonic and other organic acids from which the roots in the early infancy of the plant would have derived a portion of their nourishm-ent, and thus retarding and stunting their growth. At all events the experiment seems to indicate that lime ought to be in the state of carbonate the mildt state-more or less entirely, if it is intended to benefit the crop to which it is ilmmediately applied.- When mixed with manure, however, where vegetable matter abounds in the soil, or where the lime is merely harrowed into the surface'-in all which cases it will readily become' in a great measure, saturated with carbonic/acid-the skilful farmer will understand that the.-deduction drawn from the preceding experiment will not apply. No. VII1.] EXPERIMENTS UPON TURNIPS. 63 8~. Rape-dust. —The results exhibited in this year's experiments, generally, are not so favourable to the employment of this substance as was to be expected. The reason, however, is, probably, that which has already been suggested in discussing the results obtained at Lennox Love-that rape-dust requires a moist soil'or occasiornal showers. But this itself is an impoitant probable deduction. The reader will find a comparative view of the whole of the results with this substance in the text (see Lecture XVII.) 9~. Awnital Charcoal.-The effect of animal charcoal upon Swedes in Mr. Fleming's experiments is only inferior to that of guano. It is certainly deserving of further trials, and especially in comparison with what is called e.zhausted animal charcoal-that which has already been used in the refining of sugar. In France, the latter is said to be preferred to the former, and to be sold by the sugar refiners at a higher price than they pay for it in the recently prepared state. 10~. Other mixed mnanures. — In regard to other mixed manures, the reader will find much practical information by the study especially of No. 3 of Mr. Fleming's tables, p. 45; and of Nos. 1 and 2 of those -of Mr. Alexander; p. 46. These are the more worthy of the attention of the-practical man, since Mr. Fleming considers himself justified in remarking as the general result of the experiments in p. 45, that any of the mixtures, used will in his land produce an average crop of turnips at a less expense than far m-y:ard manuLre. This is the kind of result which it ought to be the ambition of every practical man to work out for himself upon his own land. 11~. Size and weight of bulbs. —There remains only one other topic in connection with these experiments to which space will permit me at present to advert. In the remarks upon the table inserted in p. 44, it is stated that the turnips on the plots dressed withGuano and wood-ashes —were pre-eminent fo? size of budbs. Sulphate of ammnonia —larg e in bulb, but soft, and light in weight. Potash and lime, salt and lime, sulphate of magnesia, nitrate of soda-small im bulb, but firm and solid. Bone-dust and the artificial guanos-both containing bones-the bulbs firm and solid, but not remnarkable in size. Now upon the, solidity of the bulb-other things being equal-it may be presumed that the relative nourishing properties of different species, of turnip will materially depend. The quantity of water which different specimens of the same variety of turnip contain varies from 79 to 91 per cent.-that is, somee turnips of the sanze species contain onlil/f or-fifths, while others contain epwards of nine-tentlbs of their wei:ight of water?. In other words, the same variety of turnip may contain such unlike quantities of water, that 2 tons grown on one spot may not -contain more than 1 ton grown in another. The weight of bulbs, therefore, is no safe criterion of the quantity of food raised on different parts of the same field-where the general treatment, or the substances applied to aid the growth, have been different. Now in the above experiments the guano gave 32 tons of very large, the sulphate of ammonia 24 of soft, and the nitrate of soda 27 of small and solid bulbs. t is probable, therefore, that the actual quantity of food raised by the aid of the nitrate of soda was much greater than even by the natural guano. It may also have been that the 141 tons of solid bulbs given by the sulphate of magnesia, or the 124 raised from the land without manure at all, may have contained as much nutriment as the 24 tons of soft bulbs raised by the sulphate of ammonia. Sutggestion IV.-The bare possibility of such a circumstance as the last, shows how little absolute confidence we can place in the numerical results as yet obtained, consi/dered a.s evidencesof. the greater or less lamount of food, which the use of this or that kind of manure will enable us to raise from a given extent of land. It suggests, also, the necessity of a further determination of the ~relative.quantity of water contained in our experimental turnip crops. This will; without difficulty, be effected by selecting three or four turnips'of different 299 64 EXPERIMENTS UPON POTATOES. [Appendiz, sizes from each sample-cutting a slice from either side, and one from the middle of each turnip-weighing the whole-drying them then, first in the air, afterwards before a gentle fire, and lastly in an oven so hot as-not to brown white paper or dry flour, and then weighing. The loss being the weight of the water in the turnips, will enable the experimenter to determine the relative quantities of food raised upon his different plots, and therefore the relative value of his different applications or methods of culture. In this suggestion the reader will perceive another of those precautions which the prosecution of our experimental inquiries renders necessary-future years will suggest others —but the increase of trouble will not.deter the zealous la — bourer in this important field-for the more precautions and difficulties multiply, the greater the honour will be to those who by perseverance shall successfully overcome them. B.- The Experiments upon Potatoes. Nearly all the experiments in the first table of results (p. 48) were made with mixed manures. 1~ Guano and rape-dutst.-Among these tle effect of guano is again striking, and upon two of the varieties greatly exceeds -that of rape-dust. Thus, the produce of the three varieties tried wasWhite Don. Red Don. Connaught Cups. Unaided soil... tons 1 cwt. 6 tons 15 cwt. 5 tons 15 cwt. With 3 cwt. guano.. 18 " 9 " _- " ", With 4'cwt. guano. " - " 14 " 6' 13 14" With 1 ton of rape-dust. 12 " 6 " 10': 0 " 13 " 0 " WVe are not enabled, by the experiments before us, to compare its effect with that of farm-yard manure. A curious question suggestsitself upon the inspection of the above numbers -one which could scarcely have arisen in our minds, had not differences such as- the above presented themselves among the results of our experiments. Nothing is more common than to ask which of several varieties of potato is the more prolific-and a practical man who has made the trial has no difficulty in giving an immediate answer to the question. But-the experiments of Mr. Fleming seem to say that the relative weight of crop yielded by each of two or wore varieties of potato, depends upon the way in which you treat or maanure them.' With one treatment a variety (A), With another a variety (B), will give the heaviest crop. Thus, our three varieties gave withWhite Don. Red Don. Connaught Cups. Natural guano. 18 tons 9 cwt. 14 tons 6 cwt. 13 tons 14 cwt. Rape-dust.. 1 " 6 " 10' Q " 13 " 0 " Both substances agree in saying that the white is considerably more prolific than the red Don. But while the -guano adds that both Dons are more prolific than the Cups, the rape-dust pronounces the latter variety to be superior to either of the former. - Now it may have happened that in the last case of the three, the rape-dust, from some circumstance not noticed, may have acted better than in the other two cases, and that in this way the discordance may have arisen. Unfortunately, however, there are- upon record no other experiments made upon any two of the varieties of potato- with other substances used in like proportion -by which this question might have been in some measure solved. But the interesting, and as it may hereafter prove, important inquiry suggests itselfwhat is the order of relative prodLuecliveness of the several varieties of the same cletivated plant, when they are severally dressed or manured with..this or with that substance? This question will, no doubt. hereafter lead to extended series of very refined experimental inquiries, from which not only much knowledge but much practical benefit may be derived. Suggestion V.-It may be, for instance, that a given variety of potato, turnip, oat, barley, &c., is more valuable as'food, more agreeale to the taste,:or brings No., VIII.] EXPERIMENTS UPON POTATOES., 6S a better price in the market —but by the ordinary modes of culture is the least productive of those generally cultivated. It would then be not only an interesting, but an important economical question to ask-could this variety be rendered more productive by a different mode of treatment-one especially adapted to its own nature 7 Would the practical man not rejoice to think that such a result could be brought about by the aid and suggestions of science? Yet this is the result to which the refined series of experiments suggested by the question above proposed may possibly lead..May I venture to hope that some of my more zealous readers will be induced, during the present or succeeding- summer, to make trials of the relative effects of the same saline or other known substances and mixtures, upon different varieties of the same crop —of potatoes, turnips, wheat, &c., in circumstances otherwise equal, in some such form as the following: Variety A. Variety B. Variety C. Variety D. Variety E. Substances. Substances. Substances. Substances. Substances. A I.. A|. B. | C. A, B. | C, A. B.. | C A. B. | C. The results if carefully ascertained are sure.to lead to good, if they should not be successful at once in solving the problem above proposed. 3~. Solidity and size of the potatoes. —Nothing is said in the observation of Mr. Fleming; or his overseer- in regard to the size or solidity of the different varieties of potato, or of the different samples of the same variety on which the experiments were made. Yet in connection with the remarks I have already offered upon these qualities of the turnip, it is proper to add that the potato is subject to similar variations in the proportion of water it contains-and, therefore, in the relative amount of nourishment capable of being afforded by equal weigh ts of its different varieties. Some potatoes contain less than 70, others upwards of 80 per cent. of water, so that while 100 tons of one sample will give only 20 tons of nourishment, the same weight of another will give -30 tons, or one half more. In general, such as grow on heavy or clay soils, or such as are less ripe, contain the most, while those which have been planted upon sandy spots, or are fully ripe, contain the least water. But the effect produced by different soils we begin now to see may be produced by different methods of dressing or nmedicating our crops also: Suggestion VI.-I-t would be interesting to determine, therefore, by actual experiment, the relative proportions of water contained in the produce of the several experimental patches of potato ground upon the same field, when equally ripe, or when dug up on thle same day. This would afford us the means of approximating still more closely to the true economical action of our different manures upon the potato crop. It may turn out that in certain cases the increase of produce, as indicated by a greater weight, is only apparent, while the increased amount of food raised may in other cases be considerable, though the balance indicates no increase of weight. Did we know the relative proportions of water in the several' samples of-the three varieties of potato raised by Mr. Fleming by the aid of guano, and of rape-dust, already compared together, our conclusion in regard to their relative productiveness, when treated by either substance, might be materially-altered. I hope, therefore, that this point also will hereafter arrest the attention of some of our experimentalists. 4~. Permanent effects of saline manur'es on the future productiveness of the seed.-Recommending to my practical readers a careful consideration of the effects of an admixture of wood-ashes with the several dressings applied to the turnip and potato crop, I pass on to the two following series of experiments with saline manures upon the potato crop,'as given on p. 49. These. two series are well conceived, and the' results very instructive. Of the3e results the one which seems to me most deserving - Fthe attention of the practical man is cons &6 EXPERIMENTS UPON POTATOES. [Appendi.', tained in a few words, thrust in as it were, among the remarks appended to the table (1, p. 49.) In the later printed copies I have caused them to be put in italics, with the view of bringing them into notice. If thereader will turn to p. 20 of this Appendix, he will find a remarkable experiment recorded, in which, by top-dressing well-manured potatoes,' with a mixture of 3 of nitrate and of sulphate of soda, the enormous crop of 30 tons an acre was obtained from the small plot experimented upon.' Some of these potatoes were kept for seed, and planted alongside of others of the same variety, which had not been so dressed, and the resullt is stated-in the few words above referred to-" These last, under the same treatment in every respect, did not produce so good a crop by 15 bolls (3I tons) per acre." In so far, therefore, as this experiment is to be relied upon-for we must not be hasty in drawing general conclusions-it appears that the benefit to be derived from a skilful treatment of the potato plant does not terminate with the greater immediate crop we reap, but extends also into future years, improving the seed and renderinr its after-culture more productive.'Suggestion VII.-This idea is worth pursuing, were it only for the purpose of making out the possible existence of so impartant a physiological law-how much more when it appears so pregnant with important practical results. But' thus it is in all cases, that the prosecution of experimental research, with inrmediate reference either to purely scientific or to purely practical results, ends in improving and benefitting both abstract science and economical practice. I am unwilling to follow out or,to reason upon this possible law, as if it were really established; but the possibility of its truth appears to throw light upon such questions as this-why the seed must occasionally be changed if large crops are to be continually reaped. One soil may be adapted to give the plant a large supply of this or that substance in. which the other soil is comparatively deficient; and it may be possible to medicate our seed-corn, while growing, so as to give it the qualities Which at present it can acquire only by a change of soil. All this, however, can be only determined by experiment, and the intelligent reader will nct fail to be struck with the remarkable richness of these first trials, in suggestions for future carefully conducted experimental researches. 5~. Hows should saline zmanures be applied to the potato crop?-Ought they to be mixed with the manure, or to be applied as a" top-dressing? Mr. Fleming's experiments do not fully solve this question; because the soil on his two fields was'very unlike in quality. Thuis with manure alone the one field produced 12 tons 15 cwt., the other only 8 tons 17 c'wt per acre. A perfectly satisfactory solution of the question can be obtained, only by experiments with the same sub-.stances, upon the same soil, and with the same variety of potato. Yet the experiments now before us add considerably to our knowledge upon this point, and such of them as, are capable of being compared together are much in Jfavour of mixing the saline subslances'with the manure. Thus applied in nearly equal proportions by both methods, nitrate of soda, sulphate of magnesia, and sulphate of ammonia, gave the following results:FIRST FIELD. SECOND FIELD. Top-dressed. Mixed with manure. tons. cwt. tons. cwt Manure alone....... 12 15 8 17 Nitrate of soda.... 16 0 12 7 Sulphate of magnesia.. 13 5 11 7 Sulphate of ammonia...- 14 10 13 7 The proporlionate increase, therefore, in these three cases, is greatly in favour of mixing with the manure, but something may depend upon the soil and season; and, therefore, other experiments are necessary before we can draw a general conclusion. It may prove that some act better when applied in the one way, and some in the other. 6~0 Sdphdkate of soda.-Withi this substance applied in either way, the iingu No. VIII.] EXPERIMENTS UPON POTATOES, BARLEY AND OATS. lar and consistent result was obtained.that 2 cwt. per acre caused no alteration whatever in the weight of the produce upon either of the two on which the trials were made. Of the respective qualities of the crops nothing is stated. 7~. Sulphate with nitrate of soda. —The above result with sulphate of soda alone, is the more remarkable from the known effect produced by this and other sulphates when mixed with nitrate of soda. This year, also, the mixture of nitrate with sulphate of soda added one-half (6 tons per acre) to the crop, a greater proportionate increase even than in the experiment of 1841, which gave an increase of 8 tons out) of a total produce of 30 tons per acre. But this season Mr. Fleming has tried, with still greater success, a mixture of 1 cwt. each of sulphate of magnesia and nitrate of soda, the produce rising by the use of this top-dressing to 22- tons. The relative effects of the two sulphates would have been more clearly proved, had the proportions of nitrate of soda applied per acre in the two mixtures been the same. 8~. Nitrates, of soda and potash.-Another interesting fact to add to those alrerdy registered upon the relative efficiency of these two saline substances, is presented in page 49. One hundred weight and ahalf ofNitrate of soda gave..... 16 tons. Nitrate of potash gave...... 184 tons. This difference may have been due to accidental causes-or the 18J tons of the one result may have contained no more food than the 16 tons of the other; but the multiplication of accurate experiments will eventually lead us to the truth. Apparent failures and discordant results must not discourage the practical man. By recording all trust-worthy results, the light will almost spontaneously spring up at last. 90. Silicate of potash.-The results obtained by the use of this substance, and the remarks appended to them (p. 50), are deserving of much attention. In reference to this compound, and to the silicate of soda, I beg the reader to turn to the suggestions contained in this Appendix, p. 40. 100. Mixed manures.-The mixtures in page 50 will no doubt be imitated, and by those who can obtain them of known composition, comparative experiments may be. tried with advantage both to theory and to practice, C.-The Experiments upon Barley. The true practical value of the experiments upon barley will be shown by placing them in the following form:Increase. ~ s. d. Cost per bush. Nitrate of soda with common salt, gave 5 bush. for 0 17 6 - 3s. 8d. Sulphate of soda with sulphate of mlagnesia, 71 bush, for 0 15 6 - 2s. Id. Guano (at 25s.),.. 17 bush. for 3 18 0 - 4s. 7d. Common salt,...6 bush. for 0 4 6 - Os. 9d. Turnbull's artificial guano,.. 2 bush. for 1 4 0 - 12s. Od. The cheapest application, without doubt, upon this soil, is common salt. At half the above price guano would produce the barley at 2s. 3d. per bushel, and the larger quantity reaped, together with the value of the straw in the preparation of manure, may satisfy many that either guano or the mixture of sulphates may be used with profit. It is a further recommendation of the common salt, however, that it produced the heaviest, while guano produced tte lightest grain. From the experiment with nitrate of potash no result can faiily;be drawn, in consequence of the great drought of-the season (see Mr. Gardiner's remarks). D.-The Experiments vpon Oats. 1~. Negative effect of saline mcanures.-The first of the two series of experiments above recorded being made at Lennox Love-like those made at the same place upon turnips-derive their principal interest from the illustration they afford of the negative effect of-saline manures upon the oat crop, under thein 68 EXPERIMENTS UPON OATS AND WHEAT.. [Appendix, fluence of great heat and drought. I select the more simple and striking cases of diminution. The undressed part of the field produced 54 bushels per acre Common salt diminished this produce by 6 bushels. Nitrate of soda...... 12 " Sulphate of soda........ 15s " Rape-dust.........'9g Soot....... 12 while 2 cwt. of guano raised the produt Vto 70 bushels, being an increase of 16 bushels. These results not only confirm the deductions which we have already drawn from the preceding experiments upon potatoes and turnips-that guano will act even in our'driest seasons, while rape-dust requires at least occasional rain-but they go further in showing that, like the saline substances, rape-dust, and even soot, will.materially diminish the oat crop, if the season be disting-uished by remarkable drought. 2~. -Moss oats. —The experiments upon moss oats (p. 53) are a continuation and extension of those of 1841 with greater attention to accuracy in the determination of the produce. The last column in the table speaks for itself. The general produce of the field being 43 bushels per acre. Increase. Cost per-bush. Sulphate of ammonia gave... 9 bushels 2s. 3d. Sulphate of soda with nitrate of soda gave 18 bushels Is. 7d. Bones in muriatic acid gave.. 18 bushels Is. 6d. Silicate of potash, mixed with the above, gave 22 bushels 2s. Od. In the last two cases the straw, which is usually imperfect in oats grown upon moss land, was strong and healthy. It is obvious, therefore, that all these experiments deserve repetition, though, as here set forth, the increase of grain by Nos. 2 and 3 was obtained at the least cost, and, therefore, to the economist will appear most important. E.-The Experiments uQpon WhMeat. I. Efect of drou&ghts-The first series, those made at Lennox Love, afford in. teresting illustrations of the effect of great.drought in modifying the action ofsaline manures and of rape dust, upon the wheat crop. The more prominent results are distinctly brought out when thrown into the following form. The produce of the undressed part of the field being 47. bushels an acre, this produce was affected by the several substances employed in the following manner — Decrease per acre.- Increase per acre. Common salt, 1 cwt.... 1 bush. - Sulphate of soda, 1 cwt.... 94 bush. - Soot, 32 bush.-..... slight. Nitrate of soda, 1 cwt.. slight. Rape-dust, 16 cwt.... 31 bush. Guano, 2 cwt..... - bush. Thus, the nitrate of soda and the soot did no harm, though the drought did not permit them to do any good. Common salt slightly, and sulphate of soda largely diminished the crop of grain-while of these four substances the sulphate was the only one which diminished the yield of straw. Nitrate of soda and soot largely increased it. On the other hand, guano slightly increased the yield of grain, and rape-dust added 34 bushels to the naturalproduce, both also augmenting the weight of the straw by about one-tenth of the whole. In this case, then, the rape-dust surpassed in beneficial effect the natural guano, though, as we have already seen, it proved greatly inferior to the latter when applied in similar proportions to oats, potatoes, and turnips. 2~. Suggestion VIII.-Tdtisfact suggests an interesting inqui'ry. It isknown that Jne of the most lucrative modes in which rape-dust has been hitherto Nof. VIII.] EXPERIMENTS UPON OATS AND WHEAT. 69 employed as a manure has been in top-dressing the wheat crop (see the preceding part of this Appendix, p. 19). Has it,therefore, some special adaptation to the wheat crop-which will account at once for its comparative failure upon oats, turnips, and potatoes, and for its superior efficacyto guano upon the wheat crop -in the proportions stated, and even in a very dry summer The comparative efficacy of the two substances applied in various proportions is certainly deserving of further investigation. It will be a gain not only to practical but to theoretical agriculture, should it be established thatrape-dust can be profitably applied to the wheat crop, in circumstances when it would be thrown away upon oats or turnips. By turning to the next series, that of Mr. Fleming (p. 54), it will be seen that the last result there stated is also favourable to the- action of rape-dust upon the wheat crop.* 3~. Mttually counteracting i1fluence of different msanures.-But another curious observation presents itself in the table of Lord Blantyre's results. It is in the apparent struggle between the good and evil influences of the rape-dust on the one hand, and of the saline substances on the other, when they were applied together to the same plot of wheat (see Appendix, p. 19). Thus, when applied in the proportions above stated- Increase. Decrease. Common salt gave... - 1 bush. Rape-dust gave..... 3bush. One-half of each gave.. bush. Or the natural effect of thle rape-dust was lessened one-third when mixed with the given weight of commono salt. So, alsoIncrease. Decrease. Sulphate of soda gave... 91 bush. Rape-dust gave.... 3 bush. One-half of.each gave.... -3 bush. Or the influence of 1 cwt. of sqlphate of soda for evil was one-third greater than that-of 16 cwt. of rape-dust for good-in the given circumstances of soil, climate, and crop. This result, which at present seems only curious, may hereafter'lead to the establishment of interesting truths capable of practical application. Suppose, for instance, that upon two fields rape-dust were applied to the wheat crop at the rate of 16 cwt. per acre, and that the one field contained naturally in its surface soil the proportion of sulphate- of soda employed in Lord Blantyre's experiment, while the other contained none-then in the one case the rape-dust would not only expend all its influence in overcoming the tendency of the sulphate to lessen the crop,-but would even -seem to do harm if the produce were compared with that of another field, of apparently similar soil, near the surface of.which this abundance of sulphate did not exist; while, in the other case, the rape-dust, having no counteracting influence to overcome, would spend itself entirely in increasing the'growth of the plant and.the final yield of grain. Or suppose an artificial guano or other mixed manure artificially prepared, to contain two or more substances which, in -the soil they are applied to, have a. tendency to produce opposite effects-the one to increase, the other to diminish, the amount of produce-the effect of this conflicting action of its component substances would be such-as to render the mixture of less efficacy, perhaps of no efficacy at all-it might be even injurious to the crops,-although it contained substances which, if applied alone, would have exhibited a powerful fertilizing action. These two illustrations are sufficient to show the kind of light which observations, such as the one above adverted to, may hereafter throw upon practical agriculture. II. The substance of Mr. Fleming's table (p. 54), may be thus presented, See also the subsequent observations on the experiments upon beans. 70 EXPERIMENTS UPON WHEAT. [Appendix, The unaided produce of the soil was 25 bushels an acre, and the effect of the dressings as follows:Increase. Decrease. Guano, 3 cwt..6 bush. Rape-dust, 5 cwt., sulphate of magnesia, 4 cwt. 31 bush. Sulphate of soda, 1 cwt., nitrate of soda, - cwt. 1- bush. Common salt, 3 cwt..... 3h bush. Common salt, 3 cwt., dissolved bones, 1 cwt.. - 2 bush. Turnbull's artificial guano produced no sensible effect. Under the circumstances, besides being favourable to guano, the above result is also in favour of the mixed sulphate and nitrate of soda, which we have seen to operate beneficially upon so many othe: cultivated plants. The entire crop appears to have been injured, not only by the summer's drought, but by the severity of the preceding winter. In regard to common salt, it is worthy of remark, that the grain dressed by it, whether oats, barley, or wheat, in Mr. Fleming's experiments of this year, has been always heavier per bushel than any of the other samples tried. This accords with the previous results of some other experimenters; but it does not agree with Mr. Fleming's observations upon the wheat of 1841, nor with those of Mr. Burnet for 1842, and therefore cannot yet be considered as a universal consequence of the application of this substance as a top-dressing. II1. The experiments of Mr. Burnet, of Gadgirth, have already been partially detailed in the text (Lect2re XVI., p. 362), and their value explained. The) are important, chiefly, as showing — 1~. Economical mixtures.-That mixtures can be prepared which, upon somB soils, surpass guano in efficacy and in economical value, at its former price. The price being now reduced, other experiments are required, yet still the less effect of guano upon the wheat crop is in accordance with the results of Lord Blantyre. A wet season, however, may alter the numerical relation which these results exhibit. It will be observed that here also-Turnbull's guano produced no sensible effect. 2~. Effect of soda.-The efficacy of the salts of soda, whether the sulphate, the nitrate, or common salt, upon Mr. Burnet's land, are also very strikinghalf a hundred weight per acre of either producing an additional increase of about 10 bushels of grain. 3~. Yield of'fiour.-Into his tabulated results, Mr. Burnet has introduced a new element, and, as it seems to me, an important one in an economical point of view, namely, the qmanLtity of fine foiuEr yielded by equal weights of the several samples of graiib. The differences presented in this column are very striking. Thus 100 lbs. of the grain reaped from the plot which wasUndressed, gave...... 761 lbs. of fine flour. Dressed with guano 681 lbs. " With sulphate of ammonia... 661 lbs. ". With sulphate of ammonia and nitrate of soda... 54 lbs. " It would be interesting to learn from an experienced miller to what extent such differences affect the money value of the grain to the manufacturer of flour. 40. Amount of gluten.-Through the anxiety of Mr. Burnet to draw as much information as possible from his excellent experiments, I am able to present another feature in regard to the action of these saline and other substances upon the quality of the prodtce. It is known that the quantity of gluten contained in different samples of flour is very unlike, and that the nutritive property of the flour depends, to a certain extent -upon this quantity of gluten. It has also been stated, as the result of experiment, that the grain which is raised by means of manure containing the largest quantity of nitrogen, is also the richest in gluten. With a view to these questions, Mr. Burnet transmitted to me a pound of each of the samples No. VIII.] EXPERIMNTS UPON WHEAT. 71 of flour (see Appendix,-p. 5), and upon examination I found them to contain the following proportions of gluten:Water per cent. Gluten per cent. No. 1. No application..... 16-3 9-4 2. Guano and wood-ashes... 1615 9'3 3. Artificial guano and do..... 16'8 9'6 4. Sulphate of ammonia and do... 16'4 10-5 5. Do., do., and sulphate of soda.... 157 97 6. Do., do., and common salt..... 15'7 9'6 7. Do., do., and nitrate of soda..... 16-4 10'0 8. Turnbull's guano, gypsum, and wood-ashes. 15'2 9'1 These results are not without their interest, for though they do not show any striking difference in the per-centage of gluten, yet upon the whole the result is in favour of those samples to which the sulphate of ammonia* had been applied. One of these. No. 4, exceeded the undressed grain by about one per cent., or one-ninth of the whole gluten it contained. Were the amount of this gluten alone therefore to determine the feeding quality of the grain, this sample might be considered as considerably the most nutritious. But besides the relative proportions of fine flour which they severally yielded, there are other important considerations which bear upon this question, and must influence our judgment. ~These considerations it.wouldbe out of place to present among the present observations. They will be found stated in the text of the Lectures, (XIX., p. 498 et'seq.) where we treat of the composition of wheat and other varieties of grain-and of their respective values in the feeding of man and.other animals. F. — Te Experimentss upon Grass. I. The experiments of Mr. Alexander are not very remarkable or conclusive. The meadow, which was drained moss full of timothy -grass, gave naturally 1 ton 4 cwt. of hay, whereas the one dressing raised the produce to 1 ton 8 cwt., the other to 1 ton 11 cwt., per imperial acre. The cost is not stated. II. But those of Mr. Fleming are very interesting. By referring to page 17 of this Appendix, it. will be seen that in 1841 Mr. Fleming obtained a greatly increased produce of hay'by the use of nitrate of soda. -He informs me that in making the present experiments he was desirous of again testing the efficacy of this salt upon grass, on the same kint of laad, and of. comparing it with that produced by other saline substances. He selected also a portion of the same' field, on another part of which the trials upon wheat had been made in 1841 (see Appendix, p. 19), with the view of ascertaining if any analogy could be traced or-difference detected, between their action in 1841 upon sw/leat, and th/eir effect in 1842 on sown gracsses —rye-grass, timothy, and red clover. Both objects have been in some measure attained. I shall first present a summary of the results. OF HAY. INCREASE. DECREASE. tons cwt. tons'cwt. tons cwt. The undressed soil produced.. 1 8 0 5 Sulphate of soda, 3 cwt. 1 3 - Nitrate of soda, 11 cwt.... 2 10. 1 2 Sulphate of soda, 1 cwt.. Nitrate of soda,, cwt... Common salt, 3 cwt..... 1 6 - 0 2 Common salt, 2 cwt.. 12 0 4 Soot, 16 bushels. Sulphate of ammonia, 1 cwt...1 13 0 5 Guano, 1 cwt........ 1 18 0 10 It will be borne in mind that this is Turnbull's sulphate of ammonia, already adverted to in page 61 of this Appeudix. 72 EXPERIMENTS UPON GRASS. [Append=, A mixture of silicate of potash with gypsum produced no sensible effect, reither did Turnbull's artificial guano. 10. In this repetition of his experiment, therefore, the nitrate of soda on similar land again increased greatly the produce of hay-giving, at the first cutting, an excess of upwards of 1 ton, at a cost of 30s. 2~. But on comparing this action of the nitrate upon grass with its action in the same field the previous year upon wheat-we find that though it considerably increased the crop of wheat, yet every additional bushel raisedcost 12s. 6d. as the price of the nitrate added to the land (Appendix, p. 19).. It appears, therefore, that upon soils where the nitate will not pay when applied to wheat, it may yet pay well when applied to grass. 30. Again, we find above that 3 cwt. of common salt lessened in a slight degree the crop of hay, while, in 1841, 1- cwt. increased considerably the produce of wheatin the same field-the additional grain reaped from the salted portion costing only.6d. a bushel (p. 19). It would appear, therefore, that on soils vwhere. comnmon salt. can be profitably used upon wheat it may do injury'upon hay. The only circumstance that renders this deduction less safe is that 3 cwt. of salt per acre were applied to the grass, which may have been too much considering the dryness of the season. 4~. The latter remark applies also to the sulphate of soda which was laid on at the rate of 3 cwt. per acre. A less addition might possibly have aided the crop. Yet the negative influence of this salt seems great, since 1- cwt. of nitrate -itself tending to increase the crop-was unable entirely to overcome the diminishing influence of 1 cwt. of sulphate. But the reason of this apparent inefficiency of the nitrate, when mixed with the sulphate, is in some measure explained by the remarkable fact, that on both of the patches to qwhich/ the sulphate of soda was applied, the grass that came up consisted alumost.entirely of redfescue (Festuca Rubra), though rye grass, timothy, and red clover were the only grasses sown. The sulphate, therefore, must first have checked or entirely destroyed the grasses which had already sprung up, and then have incited the dormant seeds offescue to germinate, before the fertilizing agency of the nitrate could come into play. This effect of the sulphate, should it be confirmed by later experiments, will establish the important theoretical principle, that those substances which, when present in the soil, will destroy some of our cultivated grasses, will encourage the growth of others; and the no less important practical truth, that saline substances exercise such a special action on the several crops we grow that we may hope to discover the means of aiding t.rowth of theone or the other at pleasure, and it may be at little cost. Suggestion IX.-It is to be-recollected that in the case of Mr. Fleming's field it may have accidentally happened that the seeds of the fescue particularly abounded in those plots to which the sulphate was applied. With every disposition, therefore, to advance as rapidly as we possibly can, I think it better to suspend our judgment upon this point-until the following two series of experiments shall have been made in two or three different localities:a. By top-dressing any of the ordinary grasses sown-excluding the fescues -on four or more plots, with 2 cwt., 1 cwt., 2 cwt., and 3 cwt. of sulphate of soda respectively, and marking the kind of grasses that most abundantly spring. b. By sowing half an acre of one or more of the fescues, and especially the Rubra, and noting the effect of the sulphate' applied in similar proportions upon as many patches as before. These experiments, it is obvious, would be rendered more interesting were nitrate of soda, alone and mixe, with the sulphate, tried on other plots, and on both varieties of grass. I trust Mr. Fleming, whose educated eye enabled him to detect the interesting fact in question, may be induced himself to prosecute the subject by further experiments. 5~. Suggestion.K.-We have already seen i-. the above joint action of the NO. VIII.] EXPERIMENTS UPON GRASS AND MIXED CROPS. 73 nitrate and sulphate, another illustration ofthekind of struggle we may suppose to go on between substances tending respectively, the one to increase, the other to diminish, the produce. - In the joint action of the common salt and the soot, when applied together, we have a further instance of the same kind-an increase of 4 cwt. only being caused by the application of 16 bushels of soot, when counteracted by an admixture of 3 cwt. of common salt. Applied alone,- the increase of produce would probably have been greater. Will any one undertake experiments with the view of further bringing out this interesting mutually-counteracting influence of different applications 1 6~. I can only call attention to the large yield of hay n urally obtained from that part of the field on which barley dressed with bone-dust in 1841 had previouslygrown.: Mr. Fleming informs me that no sensible difference in the produce of-hay was ooserved between the undressed part of the field and that upon which the 2dressed wheat had grown in 1841, though the crop. was not set apart or weighed, as we might wish it:to have been. 111-. Since the preceding experiments went to press I have received the' following short notice of trials upon hay made by Mr. Campbell, of Islay:" It is very difficult to get.the tenants in our wild part of the world to expend money in the purchase of foreign substances, however beneficial; and for this reason I have been induced to try the substances mentioned below, because, with the exception of sulphuric acid, the others are to be got in abundance in the island-the pigeons' dung may be got in large quantities in the caves, sea-ware on the shore, and lime is abundant and excellent in quality. The experiment was made thusWEIGHT IN POUNDS. Fresh cut. Dry. 1. Nothing............. 40 199 2. Pigeon Dung.......318 275 3. Sea-ware, Lime, and Sulphuric Acid.. 306 269 4. Lime and Sulphuric Acid...... 3 256 1. A field of about ten'acres, lately improved from heather, was chosen; the field was well drained and deep ploughed, so as to raise the subsoil (red loam) with the moss. On its surface the grass was sown down with oats-8 cwt. of each substance was used to the acre. Eight yards square carefully measured from the centre of each variety, and weighed the day they were cut, and again on the day they were put into stack. The hay was fully ripe when cut. 2. The pigeon dung, which looks like peat-dust, was laid on exactly as it was taken from the cave. 3. One ton of lime-shells was mixed with 12 tons fresh sea-ware; after being twice turned, thewhole of the sea-ware was consumed, leaving only small black particles mixed with the lime: the bulk was reduced to five large carts (not weighed); 4 galls. sulphuric acid, mixed with 400 galls. of water, were added to the powder-a violent fermentation took place, and the bulk was further reduced about an eighth. 4. A ton of lime-shells was prepared according to your recommendation slaking the lime with the dilute acid. N. B. One measure of this lime in shells gives three and a half in powder." G.-The Experiments upon Mixed Crops. Mr. Alexander's experiment upon a field of mixed oats, beans, and peas, is very deserving of notice, and- will, I have no doubt, be repeated. Not only did the mixture of gypsum and common salt inicrease the ultimate produce-but, as Mr.: Alexander says, it acted like magic-imparting life and vigour to an apparently dying and worthless crop. H.-The Experiments upon Beans. I. The principal fact of importance in the experiments of Mr. Alexander is the effect he found his mixture of gypsum and common salt to produce upon the 74 EXPERIMENTS UPON BEANS. [Appendix, beans even when already in flower. This is another of those new and practically valuable observations which, year by year, are sure to present themselves to our observing experimenters as their inductive researches are continued. II. I am happy in being able to introduce here, though it reached me too late for insertion among the other tables, the following digest of results upon beans, obtained upon Lord Blantyre's farm at Lennox Love. The object of them was to ascertain the relative effect of certain saline manures, and of rape-dust, and guano, upon beans, after a crop of oats. Experiments upon Beans, after a crop of Oats. The quantity of land in each plot was one-eighth ojfan imperial acre. Seeds sown 25th February; manures applied 13th May; crop cut 8th August; stacked 1st September, 1842; and thrashed 6th February, 1843. MANURES.' Weight taken fromm ~1 [ —_ ]Thrashing Mill of c Increase De FORDHILL; ] O of crease o FIELD, oV E. produce produce oLENNOX LOVE.. c u grai. in grain. No. N a " b..oc lb. Description of o a *Dressing.o cd C 1 ~ i: I (d Q0 1d I d ~ _____ P - I V p s 2 Q..s n'. nc,'.X Ibs. s. d. Ibs. Ibsls. Ib bs. ibs.'bs. lbs. bus.. bsh. lbs. Ibsh. lbs. 1 Common Salt. 14 04 588 231.54 285 225 78 651 35-38 - - 182 31 Rape'dust..'2 ] 3..Rape-dust... 112 ( 70 630 265 53 318 230 82 I66 4'000 *282 - - 32 Nitrate of Soda 71 81 3 Nitrate of Soda 14 3 672 276 63 33 254 79 663 4134 414 - - 22 4 aedustrat2 87 1 644 280 59 339 253 52 661 4210 490 - - 26 Rape-dust.... 2 _ 1 15 Nitrate ofS od2a 7 20 686 282'60 342 258 86. 661 4256 536 - - 25 6 Sulph. of Soda 14 10 700 282 73 355 261 84 661 4,240 52) - - 12 7R Sulph. of Soda 7 5 700 289 65 354 261 85 67 4313 593 - - 20 8 Rape-dust... 224 14 0 700 292 61 353 260 87 661 4-374 -654 - - 24 9 Guano........ 28 5 0 728 280 68 348 263117 661 4-210 -490 - - 17 110 Nothin......- 672 248 85. 333 265 74 661 3720 1t1 Soot.....4 hsh.. 4 - 0 5(6.2341 87 321 21;84 66 3-545 - 2 -175 —'REMARKS.-The soil of Fordhill, on which they grew, is light and of inferior quality-the subsoil is of indurated clay, interspersed with boulders and small stones, and occasionally beds of gravel. The field was drained every furrow previous to its being broken up from old lea- in the winter of 1840-ploughed deep and subsoiled in the autumn of 1841, and manured with farm-yard dung in the drill before sowing the beans in the spring of 1842. Owing to the dryness of the season, the beans were rather short in the straw; the specific manures were applied after the plants had attained some inches in height. The sulphate of soda (dry, not in crystals) blackened and destroyed' the undter leaves, wherever it came in contact with them, but fresh shoots soon appeared, and it did not seemo permanently to injure or retard the growth of the plants. They did not, after the application, shew any marked change of colour; and at no period did they seem to differ much from the rest of the field. A few peas were sown among the beans; and in dressing the grain, an attempt, partially successful, was made to separate them-each experiment underwent the same process in the dressing. Grain column 1st represents the produce in beans-grain column 2nd represents that in peas. The separation, however, not being completely effected, there were left peas among the beans, and some of the smaller and inferior beans among the peas. I thought a distinction of this, kind worth making in the Tables, as I observed that some of the lots contained much more peas than others, and conceived that the relative value of the manure, as applied to either, might thereby in soile measure be shown, as well as their effects on the beans alone more truly exhibited. The gross weights were taken, as those of the other experiments, at the town of Haddington's weighing-machine, before thrashing-the detailed weights and measurements by myself. WM. GOODLET. The produce of the undressed part amounted in the above experiment to 29, bushels, and it is remarkable10. That the soot alone caused a sensible diminution of the gross produce, and alone did not lessen the proportion of peas. 2~. Although the season was so dry the sulphate of soda gave a larger increase than was obtained by the addition of twice its own weight of guano. 3~. That an admixture of half its weight f nitrate with the sulphate of soda No. VIII.] EXPERIMENTS UPON BEANS. 75 did'not increase the produce beyond that of an equal weight of sulphate alone. This is different from the action of the latter salt in the case of the other grain crops and of potatoes. 4~. That 1 cwt. of sulphate of soda produce as great aneffect as 16 cwt. of rapedust-the quantity of grain reaped from both applications being very nearly the same. Suggestion XI.-These striking effects of the sulphate ultimately took place, although when first applied to the young plants it burned and blackened their leaves. I trust that these results will also be tested by repetitions in other years -less droughty, it is to be hoped-and in other parts of the country. For the sulphate of soda, Mr. Alexanders experiment seems to say that gypsum, which is still cheaper, may be economically substituted. 5~. It will be seen that guano upon this crop, as upon the wheat already noticed (p. 68), was less successful than some of the other substances employed. Conclusion.-Upon the observations of Mr. Gardiner in regard to the effect of the dressings of 1841 upon the crop of 1842, I have nothing to add to the remarks I have already made (p. 57) upon their importance, and upon the good that must follow from continuing them. But in concluding these observations, the reader will please to recollect that I have adverted to those points only, in the above tables of results, which appeared to myself most important.. There are many other points to which by a careful study of the tables his attention will naturally be drawn. He will consider the observations themselves also, as only so many gropings after truth. The present state of our experimental inquiries can scarcely be supposed as yet to give us more than a) glimpse here and there of the true light. Like a man who finds himself in a dark dungeon, we are peering through the comparative, gloom of our prison-house, in the hope of finding some mode of escape into the upper day. Like him we may be long in discovering the true outlet, and the passage upwards may be narrow and intricate;-but the same conviction which will give him safety, will ultimately lead us also to the light-that he who persists in trying-marking and recollecting every turning he has explored —may at length escape; but that he who sits still, in indifference, or gives up his quest in despair, is sureto die in darkness. No. IX. ADDITIONAL EXPERIMENTS IN PRACTICAL AGRICULTURE, MADE IN 1842. The following'experiments were made'at Erskine, in Renfrewshire, upon the Home Farm'of Lord Blantyre:Experiment I.-Potato Oats, after old Grass. The soil was variable, chiefly good loam, resting on a subsoil partly gravel and partly sand. The field, having been long in pasture, in many places very wet, was drained in November and December, 1841; ploughed soon after, and sown with oats on the 8th of April. The manures were applied on the 15th of April, and harrowed in with a single stroke of the harrows. One-fourth of an imperial acre being previously measured offor each plot. According to notes taken of the appearance of the crop from time to timeMay 23.-The nitrate of soda (No. 1) looking darker in colour than any of the other plots; next to it, in point of colouri the foreign guano (No. 5) seems best; then the soot (No. 9); then the sulphate of ammonia (No. 2); cannot, however, discern any very decided difference in the appearance of the others. 76 EXPERIMENTS UPON OATS AND GRASS. [Appendix, May 30.-There appears a slight difference in favour of all: the applications in; the order above stated, the sulphate of soda (No. 3) pale in colour. June 28.-Appearance same as on' 30th May. The crop was cut 19th and 20th of August, and-thrashed from the stock on the, 7th of September; the results carefully ascertained, the grain by weight and measure; the straw by weight, as it came from the thrashing-machine; no account taken of the chaff. RESULTS OF' EXPERIMENT. I. —OATS.' -,''.PRODU.CE, ot Good grai. Lihtlrain. I Increase:+ No. Applications. ve - ir "_ s i Decrease -..' - t c W ^ S. a, Grain. Straw. s. d. bsh. lbs. lbs. Ibs. lbs lb, Ibs. Ibs. -1- Nitrate of Soda, 28 Ibs......... 6 3 1 21 42 8 29c 908 - +26k! +191 2 Sulphate of Ammonia, 28 Ibs... 5 0 12 22 40 10 - 770 + 53 3 Sulphate of Soda, 56 lbs........ 30 12 - 40 141 - 762 -18 +45 4 Nothing................ 12 10 41 717 5 Foreign'GnCano..28 lbs....... 6 3 12 41 411 61 - 768 + 6 +51 6 Turnbull's BritishGuano.56 lbs.. 0 12 171 411 101 - 788 +14 + 71 ]7 Turnbull'slmpr'd Bones,56 bs. l3 0 11 2 41 10/ - 675 -49 - 42' 8 Turnbull's Humus, 10 bush.... 10 0 11 8P1, 41 11 - 644 +41 -73 9 Soot, 10 buls.l............. 2 13 30- 41 9[ - 880 -60 + 163 Experiment II:.-0?O Old Pasture Grass to be cut for Hay. The soil was of medium quality, on stony clay subsoil. The part of thei field experimented on was originally very wet, producing scarcely any better herbage than. rushes and other semi-aquatic plants, was drained in 1835, has been three years pastured after a crop of hay from young grass in.. 1838; the, soil is of a blackishi friable texture, the subsoil very retentive. The specific manures were applied on 15th April, with the exception of the soot, which was sown on the plot in the experiment at the same time that the other parts of the field -were dressed with soot, being about the middle of March, and by the: 15th of April were shewinga greener shade-thanthe portion, left forexperiment. -April,25.-Observed the ridge or plot No. 5'(sulphate of ammonia) looking dark in the shade, and that the salt has burned the leaves of daisies and other broad-leaved plants; the moss or fog seems also to he burned, it looks blaclk and unhealthy. May 7.-The ridges or plots Nos. 2, 5, and 7, look decidedly better than the rest; No. 3 also seems farther advanced than where no applications were made. May'23.-No. 2 getting on'ery fast,. and now looks as well as No. 1, which has always had the advantage,(.o appearance) of the other plots. The grass on No. 3 pale in colour, but taller than where no manure was applied. The hay was cut on the 3d of July, and the grass weighed soon, i. e.,' in a few hours after being cut down, but being very sunny weather it was somewhat faded when weighed. The made hay weighed and put into stack on -- Each plot consisted of one-fourtlh of an imperial acre. RESULTS OF EXPERIMENT II.-HAY.; Cost of PRODUCE. No. Applications. applica. Increase tion.. Grass. Hay. in;Hay. s. d. lbs. lbs. Ibs. 1 Soot, 10O'bshels.............. 2 11 2331 970 188 2 Nitrate of Soda, 40 lbs......... 8 2536' 10261 244k 3 Sulphate of Soda, 80 bs.......4. 3 1936 841 59k 4 Nothing'..........- 1760 726 -- 65 Sulphate of Ammonia, 40 lbs.... 7 1 2516k 935 153 6 Nothing....................... 2374 838 7 Foreign Goano, 40 b............ 8 3024 1190 408 Turnbull's.Brtish Guano, 80 lbs. 5 81 2841 1014 262 No.: IX.] EXPERIMENTS UPON WHEAT AND POTATOES. 77.N. B.-I take the average of the two plots which had no manure, as the sum to deduct for finding the increased produce. The second column from the right is made hay, the third is green grass, weighed soon after being cut. Experiment III.-Upon TWheat. Soil, a good strong loam, resting on a heavy subsoil composed of clay and small stones, called till. The wheat was sown in November, 1841, after a crop of potatoes. The field had been long in grass previous to 1840-when it was drained, and ploughed for oats in the spring of 1840-was well dunged with' good farm-yard manure, and was also limed for the potato crop of 1841, so that the field was in very good condition for wheat. The manures were applied 14th April, 1842, and harrowed in with a stroke of the harrows. May 10.-The portion No. 1 seems darker in shade than No. 9 and No. 8. June 28.-A calm day, with gentle rain-many of the lots much bent down, as follows:-No. 1 much bent down. No. 2partly swirled and bent at the end next a planting. No.- swayed at east ead next the planting, not so bad as No. 2. No. 4 less bent down than No. 3. No. 5 much bent down and swirled. Nos. 6 And 7 all standing. No. 8 partly laid down. No. 9 very much swirled and laid. All the laid wheat came up again in a few days after the rain. The wheat was reaped with the sickle, and in due course stacked, in good condition. It was thrashed on the 8th February, 1843. RESULTS OF EXPERIMENT III.-WHEAT. STRAW. -GRAIN. Applications. Total Increase + Total Weight Applictions qu. a or o t per Increase. tity. Decrease -. quant. bushel. No. lbs. Ibs. bush. lbs. Ibs. bush. Ibs. 1 Soot, 10 bushels............... 1213 + 205 13 33 58 2 32 2 ITiirnbull's lumus, 10 bushels... 1055 + 47 12 48 60 1 47 3 iImproved Bones............... 973 - 35 11 58 62 0 57 4,Trirnhull's British Guano........ 1193 + 185 14 43 61 3 42* 5 jForeign Guano'................ 1049 +- 4'1 11 341 611, 0 33: 6 Nothing..................... 1008 -- 1 62 - 7 Sulphate of Soda.............. 1073 65 13 7 62 2 6 Experiment IV.-On Potatoes. Soil, a medium loam, resting on gravel and sand. The field was ploughed from old grass, and sown with oats in 1841; was drained' (where wet) and deep ploughed in the autumn of 1841; prepared for potatoes in the spring of 1842, and well dunged at the rate of about 45 tons of very good dung from Glasgow, per acre. The manures were applied in addition to the dung, by being sprinkcled above ti/e d nng in the drills before placing the sets, then covered by-reversing the drills, on the 21st and 22d of April, 1842. During the season could discover little or no difference in the appearance of the portions dressed with the specific manures, from where no applications were made; the crop was a very equal good one over all the field. One-fourth of an imperial acre in each plot. I can ill reconcile the great produce from No. 4 with the appearances when growing, and have been suspicious. that notwithstanding every precaution being taken to avoid mix. ing, some sheaves of No. 5 plot, have been taken to No. 4, while the crop was in stook, as it was sometimes necessary (during the time the stooks were in the field) to have them repaired, they being blown down once or twice. The cost of the applications, as also -he quantities applied, of the different materials, were the same as in Experiment No. I., on Oats. The light grain is not here taken into account, as it was-too trifling in quantity and quality to-be of any importance, and nearly the same in every case. '~~78 ~ EXPERIMENTS UPON POTATOES. [Appendx, RESULTS OF EXPERIMENT IV.-ON POTATOES. Manures. Cost. PRODUCE ncrease o Decrease -.;No. s. d. tons. cwt. qrs. lbs. cwt. qrs. Ibs., Nitrate of Soda..........14bs. 7 1 17 Sulphate of Soda.......28 lbs. 4 1 4 + SSulphate of Soda.......28 bs. 0 2 19 0 24 0 0 17 Sulphate of Ammonia.....14 Ibs. 4 3 Foreign Guano..............28 bs. 6 3 3 0 0 0 + 0 3 21 4 Turnbull's British Guano....56 Ibs. 4 0 2 19 2 21 + 0 2 14 5 Soot, 74 bushels................. 2 15 3 21 -3 0 14 6 Improved Bones, Turnbull's, 56 Ibs. 3 0 2 19 2 21 + 0 2 14 7 Gypsum, 1 bushel................. 2 18 1 21 -0 2 14 8 Nothing................. 2 19 0 7 The gypsum used turned out to be genuine on analysis.* REMARKS UPON THE PRECEDING EXPERIMENTS. 1~. Effect of the drovlght.-It is to be observed, in the first place, that the great drought of the season exercised an unfavourable influence upon the results of these experiments also. It is necessary, therefore, to suspend our judgment in some measure regarding them-until future experiments in other seasons shall confirm or modify them. 2~. Inferences to-be drawvn fromth the colour of the crop.-A new feature introduced by Mr. Wilson in the account of these experiments, is the appearance presented by the several crops at different specified periods after the dressings were applied. It is a common thing for practical men to estimate the relative produce of different fields or parts of the same field by their appearance, and especially by the colour of the growing crops. Yet that this is not to be depended upon in a corn crop, is proved by the observation that up to the end of June appearances in the oat field -were most in favour of the nitrate of soda, the guano being sezond, and the soot third in order. Yet, when reaped, theNitrate gave an increase of only 21 bushels per acre. Guano........ 24 lbs. per acre. Soot......... 6 bushels per acre. The nitrate did give a little more straw than either of the other two, but that the colour is not an unfailing criterion even' as to the produce of straw or of nay is shewn by the experiments upon oats and upon hay. In both of these List of prices paid for the manures used in the foregoing experiments:1. Foreign Guano............... 25s. per cwt. 2. Turnbull's Guano......... 8s. 3. Turnbull's Improved Bones 6s. 6. " 4. Turnbull's Humus............... Is. per bushel. 5. Nitrate of Soda....... 25s. per cwt. 6. Sulphate of Soda (dry)........ 6s. 7. Sulphate of Ammonia.............. 20s. " 8. Soot......... 31d. perbushel. Nos. 2, 3, 4, and 7, were manufactured and furnished by Turnbull and Company, Chem. ists, Glasgow. The British (Guano No. 2) is said to be made up as follows:2 cwt. of Sulphate of Soda. 2 cwt. of Sulphate of Ammonia. 1 cwt. of Common Carbonate of Soda. 15 cwt. of Improved Bones, manufactured by Turnbull & Co. 20 cwt., or 1 ton. The Improved Bones are said to be hali dissolved bones and half wood-charcoal. I believe the bones include animal matter, as l am informed the carcases of old horses, &c., are all used in the manufacture. JAMES WILSON. Freeland, Erskine, 20th February, 1843 No. IX.j REMARKS UPON PRECEDING EXPERIMENTS. 79 crops the portions dressed with sulphate of soda are described as pale zn coloum, and yet the excess of produce over the undressed parts was as follows:In the oats.. 1 cwt. straw. Where the sulphate was applied. In the hay. 2 cwt. per acre. ) The increase in neither case would be deserving of much attention except as showing satisfactorily that wrong conclusions may be drawn in regard to the efficacy of manures and top-dressings by those who judge only by the eye -and that safe reliance can be placed on those comparative results only which have been tested by weight and measure. I know, indeed. that practical farmers who have applied nitrate of soda to grass land, and havebeen delighted by the beautiful green colour which followed, have occasionally been disappointed by finding that after all this promise the weight of hay obtained was no greater than upon the undressed parts of their fields. As to the feeding qualities of the two kinds of hay no experiments have yet been made, though it is known that cattle prefer that which has been dressed. Suggestion XI.-I put down, therefore, as a distinct suggestion for the purpose of drawing attention to the subject, that this plan of specially noting the appearance of the crops at stated, say monthly periods, should be adopted in all future experiments. This will serve, not merely to show us more clearly what kind of appearances are to be trusted, and how far, as indications of an increase of crop-but may hereafter prove of further importance when experiments shall begin to be instituted upon the feeding properties of crops reaped under different circumstances, and raised under different kinds of management. 3~. Importance of having two or more experimental plots similarly t-reated.The experiments upon hay above-mentioned exhibit another illustration of the fact adverted to in page 59 of this Appendix under the head of limits of error. I there drew the attention of experimenters to the difference in the produce obtained on two equal patches of the same field of turnips, to neither of which any dressing had been applied. At Erskine two equal plots of grass in the same field gave a similar difference of produce. I present both results here for the sake of clearness. The produce per imperial acre wasHay at Erskine. Turnips at Barochan. tons. cwt tons. cwt ist plot........ 4 5 12 17 2d plot.;.... 3 3 8 Difference........ 1 2 1 9 In my remarks upon the difference between the two plots of turnips (Appendix, p. 59), I expressed an opinion that differences equally great, depending not at all upon the substance applied, might be expected on equal portions of those fields upon which our different saline manures may have been applied;-and that very erroneous conclusions might thence be drawn in regard to the absolute and comparative effects of the substances with which our experiments -are made upon the crops to which they are applied. I have since met with a confirmation of this view in a record of two pairs of experiments made with equal quantities of rape cake upon equal plots of red wheat, in the same season, and upon adjoining parts of the same field, [British Husbandry, I., p. 112.) The results of two experiments with different quantities of rape dust were as follows:Produce of Light Rape dust applied. marketcor. Weight per bushel. corn. stones. bush. lbs. oz. Ibs. Ist plot... 59... 26.. 52 10... 46 2ndplot. 59. ~. 2... 50 8... 67 lstplot... 86... 28... 53 4... 35 2nd plot... 86... 22. 51 2.. 91 The differences both in the quantity and in the weight of the grain reaped, is 30 80 REMARKS UPON PRECEDING EXPERIMENTS. [AppeSndix, each of these pairs of experiments,are so great that had they been obtained from plots of ground dressed with different manures we should readily have ascribed them to the unlike action of the substances we had applied. Doubts may naturally arise, therefore, when we look at the several tables of results contained in this Appendix, how far the differences presented in them are really due to the unlike action of the manures employed, and how far to natural causes not hitherto investigated. Can all the experiments made during these last two years with so much care really be vitiated by this source of error 3 The point must be elucidated by further experiment. Should it prove that we have here a general source of error, it is satisfactory atleast that we have discovered it at the threshold as it were of our accurate experimental inquiries, and that we can devise means of avoiding it in future. I therefore repeat the SUGGEsTroNs I. and II., which I ventured to offer in page 60 (Appendix), that some of my readers, of whom I believe many are interested in this subject, would in the ensuing season ascertain accurately the produce of equal measured quantities of the same field, under whatever crop it may be, and publish or transmit the result to me-and that in all future experiments made with the view of ascertaining the effect of different manures upon any crop, two plots at least, and,not adjoining to each other, should be treated alike in each field, and the mean of the several results obtained with each substance taken as the average produce from which their comparative effects are to be estimated. These points appear to me to be of primary importance, and to lie at the foundation of the structure 1 hope we are now beginning to rear with the results of inductive experimental agriculture. 4. Action of soot. -In these experiments a top-dressing of soot increased considerably the produce of oats and wheat, while it diminished the produce of potatoes wAhen mixed with the manure. Thus the produce per acre on the dressed and undressed parts wasOats. Wheat. Potatoes. Undressed.. 49 bush... 44 bush... 11 tons 16 cwt. Dressed... 55 bush... 54 bush... 11 tons 3 cwt. The unfavourable effect upon the potato crop may probably be due to the mode in which it was applied, as in other districts it is very useful to potatoes, and gave, as we have seen, when applied alone to turnips, an increase of 4 tons r acre. (See Mr. Fleming's Experiments, Appendix, p. 43; also, Lecture VII. p. 438). 5. Comnparative action of soot and of nitrate of soda.-The immediate effect of both these substances is to darken the colour and to increase the growth of hay and straw. In this respect the advantage is rather on the side of the nitrate, while the soot in some cases gives a little more grain. Thus the increase of produce per imperial acre of the three crops of hay, wheat, and oats, dressed with each of the three, was nearly as follows:Hay. Wheat. Oats. Grain. Straw. Soot.... 7 cwt.. 10 bush.. 6 bush. 6 cwt. Nitrate of soda. 9 cwt.... 0bush... 61 bush. 7 cwt. In both cases, however, the sooted grass was lighter per bushel. Thus their comparative weights wereWheat. Oats. Sooted.. 58 lbs... 41 lbs. Nitrated... 62 bs... 42, lbs. Nevertheless, the advantage to the practical man is decidedly on the side of the soot, since the cost of 40 bushels of soot per acre was only 12s., while that of 1 cwt. of nitrate of soda was 25s. It is only to be regretted that soot is so variable in its constitution that firm reliance cannot be placed upon the uniformity of its effects. 6~. Action of guano.-In the text, p. 460, I have stated the apparent conclusion to which the Erskine experiments, taken in connection with all the others I have No. IX.] REMABKS UPON PRECEDING EXPERIMENTS. yet met with, seem to point-that it is more tniformly successful when applied to root than to grain crops. The increase of oats in the present experiment did not exceed half a bushel per acre-though that of hay amounted to 14* cwt. 7~. Action of sulphate of soda.-I have already noticed the effect which this salt has in paling the colour of the crop, even when the produce of grass or straw is increased. In regard to the grain, we see in the experiment upon oats that it reduced the crop, 14 bushels per acre-while the wheat crop was increased 10 bushels by a similar application. Is this difference in its effects due to the nature of the soil, or to the special action of the sulphate upon the two crops 1 We have seen in the experiments made in 1842 at Lennox Love (p. 52), that the sulphate of soda diminished the oat crop 15* bushels per acre-an effect, however, which may be mainly ascribed to the great drought in that locality, since even nitrate of soda caused a diminution of 12- bushels. But it also diminished the wheat crop at the same place to the extent of 9l bushels per acre, but upon this crop also the drought appeared to interfere with the natural action of the several top-dressings which were applied, so that no trust-worthy conclusion can be drawn from the apparent results of their action. Suggestion XII.-I have already suggested (p. 72) an interesting experiment with sulphate of soda, in order to test the very curious observation of Mr. Fleming, that when applied to land sown with artificial grasses, it brought up a crop consisting almost entirely of fescue grasses, though none of these had been sown. I would here suggest further that the marked difference observed at Erskine between the action of this sulphate upon wheat and oats should be further investigated-with the view of obtaining a satisfactory answer to this question-Does sulphate of soda act less favourable upon wheat than upon oats in the same soil. Or does an unlike action manifest itself only when the soils are different? I fear the suggestion comes too late for the present year, unless, as I hope, there are experiments already in progress which will throw light upon the question. But the suggestion will not, I believe, be overlooked when another year comes round. It is further worthy of remark, in regard to the action of the sulphate of soda upon the wheat crop, that the straw was stronger and less laid than where any of the other dressings were applied. 8~. Action of sulphate of ammonia. -The substance employed under the name of sulphate of ammonia, as I stated in a previous part of this Appendix (p. 61,) is not what its name implies. The makers, the Messrs. Turnbull, of Glasgow, inform me that it is prepared by adding sulphuric acid to fermenting urine, and evaporating to dryness*. Though such a substance must vary in composition with the urine from which it is prepared, and must contain more or less ammonia according to the degree of fermentation which the urine has undergone, yet good effects may fairly be expected from it. I here exhibit the effect of 1 to 1 cwt. per acre applied to different cropsUndressed. Dressed. Made at Wheat.....44 bush. 54- bush. Erskine. Do.... 31, bush. 40 bush. Gadgirth. Oats..... 49 bush. 50 bush. Erskine. Turnips..... 12l tons. 24* tons. Barochan. Potatoes. 12 ton s. 1 4 tons. do. Do...... 8* tons. 13* tons. do. These results not only recommend this substance to the practical farmer, but they also enforce the remarks I have made in the text upon the value of urine in general, upon the large waste of manure annually incurred by the neglect of it, and upon the virtual money-loss which is suffered by those who allow it to escape from their farm-yards. [See Lecture XVIII., p. 463.] 9~. Action of lTlrnbull's humus.-This humus.- s it is called, is night-soil " In the text I have described it under the name of sulphated urine.-See p. 461. 82 REMARKS UPON PRECEDING EXPERIMENTS. [Appendix, and urine mixed with charcoal and gypsum, and dried by a gentle heat. Its effects upon the wheat crop are, in the present experiments, more favourable than any of those I have'yet placed upon record. TIhe following experimental results exhibit the nature of its action in two localities, both in the same neighbourhood:Undressed. Dressed. Experiments made at Wheat...44 bush. 51 bush. Erskine. Oats... 49 bush. 45 bush. do. Turnips... 124 tons. 134 tons. Barochan. Do... 12 tons. 17 tons, do. Potatoes... 5 tons. 104 tons. do. These results, especially those upcn the corn crops, are not so beneficial as might well be expected fiom a prepared night-soil, and they afford room for the suspicion that the mode of manufacture has been such as to dissipate some of the more valuable constituents. 10~. Experiments upon potatoes.-In the experiments upon potatoes the whole crop averaged 12 tons per acre, and the parts of the field to which the artificial manures were added exhibited no marked increase above this general average. Even the mixture of nitrate with sulphate of soda, which in so many other cases has proved beneficial to the potato crop, in this instance produced only 1 cwt. of increase. It may be that the manure which was added at the rate of 45 tons per acre contained a sufficient supply of all those kinds of food which were added afterwards in the saline and other substances. If so, a larger crop could only have been obtained by the addition of some other substance not tried, for a loam of moderate quality ought to be able to produce more than 12 tons of potatoes per acre. Or it may be that these same artificial manures would have produced a larger increase had they been put on as a top-dressing after the crop had come up, instead of being spread upon the manure before the potatoes were planted upon it. In the experiments of Mr. Fleming made with especial reference to this point, [Appendix, pp. 49 and 66,] it was found that a larger proportionate inccease was obtained from the same saline substances applied in equal quantities to the potato crop when they were spread upon the mcnure, than qvhen they were applied as a top-dressing after the crop had come up. Still the experiments in his case being made in different fields, I stated that the point was not to be considered as established, but was deserving of further investigation. This opinion is strengthened by the results of these experiments of Lord Blantyre: I would therefore beg to offer asSuggestion XIII.-That the application of saline manures to the potato crop-either when the trial is made for the purpose of obtaining practical information, which may, hereafter, be valuable as a guide to the operations of the farmer, on the land where his experiments are made, or for that of arriving at results which may be theoretically useful-that the same proportions should be applied to two or more plots buried with the manure, and to two or more dusted on as a top-dressing. From an accumulation of results obtained in both ways, we shall be able to extract something like a principle by which practical men may be easily guided in that direction which is likely in the greatest number of cases to lead to the greatest amount of profit. 11~. Water itn the potatoes.-I will here add one other observation upon the potato experiments. There was, as we have already remarked, no notable difference in the weight of crop raised upon the several patches. But the quality of the crop-the weight of dry food raised upon the several patches-might really be different notwithstanding. In my remarks, [Appendix, p. 65], upon the Barochan experiments upon potatoes, made in 1842, I have drawn attention to the fact that potatoes sometimes contain as much as 30 per cent. of dry food, and at other times as little as 20 per cent., and therefore that a ton of potatoes of one kind.ay contain 6 cwt., while the same weight of another contains only 4 No. IX.] REMARKS UPON PRECEDING EXPERIMENTS. 83 cwt. of dry nourishment. It may be, therefore, that as by growing in unlike soils or with unequal degrees of rapidity our potatoes may contain different proportions of water, so by different kinds of dressings which act in the same way as natural differences of soil, and cause the plants to develope themselves with greater or less rapidity, the same effects may be produced. One kind of saline substance, such as nitrate of soda, by hastening the growth, may give us a crop of potatoes containing much water, while another, such as sulphate of soda, by retarding the growth, may give a crop containing less water-and thus, though tnere may be no difference in the weight of the two crops, they may be very unlike in the relative proportions of food they contain. If such be the case it is of great practical importance to determine the quantity of water which our several experimental potato crops contain, since without this we may draw very incorrect conclusions as to the value of our experimental manures-placing the highest value upon that which gives the greatest weight of raw material, and esteeming least, perhaps, that which produces the greatest weight of dry food. 1 would again, therefore, draw the attention of my readers to the subject oi Suggestions IV. and VI., [Appendix, pp. 63 and 65,] in reference to the determination of the quantity of water in their experimental root crops. The method of doing this is very simple, and has already been described, [Appendix, p. 64.] Each new series of experimental results we are called upon to examine and analyse, will, I hope, more and more satisfy my readers, as they do myself, that this is the true line of procedure, and that though there may be much in our results at first which may appear contradictory and discouraging, yet that out of these crude results, when combined, compared, and frequently repeated, the real substance of a rational agriculture will, slowly it may be and with difficulty, yet surely at last, be extracted. No. X. RESULTS OF EXPERIMENTS IN PRACTICAL AGRICULTURE, MADE AT BAROCHAN IN 1843. Experiment I.- Upon Potatoes. Comparative effects of guano, farm-yard manure, gypsum, &c., by themselves and in mixture, upon Potatoes of different varieties, planted 25th, 26th, and 27th April; lifted, measured, and weighed from 12th to 14th October, 1843. On one-eighth of an imperial acre. The portion of the field upon which these potatoes were grown contains about five acres; soil-loam of medium texture, super-incumbent upon trap rock. It was trenched with the spade out of seven years old lea in the winter of 1842 and 1843 to the depth of 16 inches, the sward being turn-spaded into the bottom of the trench, and the subsoil a stiff yellow till brought up to the top, which mouldered down to a fine mould during the winter. The drills were formed for the potato cuts with the double-moulded plough, and by the 7th June the plants were all brairded in the rows, and were worked in the usual manner with the plough, drill, grubber, and hand-hoes. After the drills were formed, where the guano was used, it was sown in the drjlls by the hand, on the bottom and sides of the drills, the farm-yard manure being then put in and 30* Wk4 ~ EXPERIMENTS UPON POTATOES. [Appendix, No. Manures., c - aS k ~ Cd w 5 b 3. 3 < S l ___,____ _-_ i.Ql. _ lJc.yds.qs.lbs. ~. s. d. tns. cwt. ~. s. Guano...... 114 0 3 9 0 Perths. ^ Farm yard manure..... 21 0 12 6 5 Reds. 1 Guano0.................. 4 3 1 14 0 3 4 0R ough ~; ~IFarm-yard manur-e..... 2k 0 12 6 P. 17 0 3 0 Reds.'3 Farm-yard manure..... 5 1 6 0 118 14 15 29 10 Do. Guano................. 1 14 0 3 9 C~Gulano ~.., 14 0 3'~9~ c 5 Farm-yard manure..... 2 0 12 6 144 18 36 0 Do. Gypsum............... 14 0 0 2 Farm-yard manure..... 15 10 6 Gypsum, powdered on 122 15 5 30 10 Do. ( sets..0............... 0025 7 Farm-yard manure..... 1 5 1 1 5 0 112 14 0 28 0 Do. Farm-yard manure..... 5 1 5 0) with Gu21 0 1 10) wit G uano. 14 0 3 9 130 16 5 32 10 Buffs. Farm-yard manure.. 22 0 12 6 s10 Get.................. 2 1 0 12015 0 30 0 Do. Guano 1 14 0 39 Berwks. 11 Farm-yard manure... 21 0 12 6 1 6 13 5 26 10 Blues. 12 Farm-yard manure..... 5 0 18 12 0 24 0 Do. Guano 150 14 14 3 4 Farm-yard manure.....[2 0 1 5 03 13 Guano.................. 21 14 0 63 86 10 5 2110 Do. spread upon the top of it. d an cured up with 1 about three inches of soil. P attetion should be paid ano is Do. Guano................; 14 0 2 9 Fammor yard manuread and worked into the soil the crop is the heavier and the betterm-yard maured. When it has been used in a body immediately under the and leaves, and, in general, to ripen the plant prematurely, and both the potatoes 13' GGu ano............... 214 0 6 3 8610 15 10 Do. pand turnips were in con seence deficient in tubers and bulbs. From these circumstances it may be inferred-what is indeed known to be the case- that the guano does not contain all the ingredients which are required by the plants, and that the large proportion of ammoniacal salts it contains-when it is laid in a mass in immediate contact with the roots of the plants-pushes on the growth too quickly with small stems and delicate leaves. Numerous small bulbs are the consequence, and the cultivator being disappointed is led to pronournce ithe eguano worthless, whils t hcrop may be in a gre at measure owing to bad management. Whatever may be the reason, however, it has obeen f d in ue it his s red that wohen sown bthoadast the crop s tof ev ier scripton have better maturefitted, while, on the otheren usedlaid in a body immediately under the plant. it has always been found to induce a strong vigorous growth of stems the roots the reversel, to ripen the ase. plant prematurely, and bothtin the potato for seed, gypsum in powdernips was strewed upin consequence sets whficien newly cut,bers and it will be srom these circumsNo. 6 of the table, it may be inferred-what is in addingown to duce, as whe casre the cuts were ano owdered, as ntino. 6, their superiority over No. 7 (which are required by the plants, and that the large proportion of ammoniacal salts it contains-when it is laid done so) in point of strengtact with thed vigour roots most remar plants-d when lifted the rowtdu too qui cwt. per acre more s an No. 7. It may also inum erous small measulbs are e a means of pquene,ting and the cultivator being disappointere is led to failure nounce the guano worthless, whilst his inferior crop may be in a great measure owing to bad management. Whatever maybe, the reason, however, it has been found in using it here that when sown broad-cast the crops of every description have been benefitted, while, on the other hand, w/ten laid in a body near the roots field where he gypsum was so used on the ae. In cut while the potato for seed, gypsum potatoer s strefailed upon anther field which w as planted t will be stime, butfrom No. 6 of the table, With good effects in adding to the produce, as where the cuts were so powdered, as in No. 6, their superiority over No. 7 (which was not done so) in point of strength and viaour was most remarkable, and when lifted the produce was 1 ton 5 cwt. per acre more than No. 7. It may also in a certain measure be a means of preventing failure in the potato, as there was no failure in this field where the gypsum was so used on the cuts, while the same seed potatoes failed upon another field which was planted at the same time, but No. X.] EXPERIMENTS UPON POTATOES AND HAY. 85 where no gypsum was powdered on the sets. At all events, it is worthy of a more extensive trial as a preventative, and it will in all soils, where it is deficient, add to the produce. It has, at the same time, the merit of being a cheap application. There was no great alteration in point of strength or forwardness till the 1st of July, when all those patches upon which the guano had been used began to take the lead of those planted with farm-yard manure alone. The guano produced a dark green colour and very strong stems and leaves, so much so, that it was found when too late that they had been too near planted, i. e., 32 inches between the drills, and 12 inches between plant and plant. There would have been a far heavier crop if there had been more space, as the strong growing varieties, such as the cups and blues, were nearly choked for want of air. It will be seen from the tables that a mixture of guano and farm-yard manure gave a greater crop than where either of them was used alone. The portion, No. 8, was top-dressed with guano when the potatoes were set up for the last time. It was sown broad-cast between the drills, after which the drill harrow was put through them and the plough followed, it acted immediately by altering the colour to a dark green, the plants putting out, at the same time, new stems and leaves, but owing to its being applied so late in the season, there was a larger proportion of small potatoes than at the others when lifted. After many trials it has been found that the best and most economical way of ulsing c uano for the potato crop is by addisng 2 or 3 cwt. per acre to hlalf the ucsual quantity of farm2yard dung, which will be found to give, at least, as good a crop as double the quantity of d'Lng alone, whilst it is much cheaper in the first cost, and saves much cartage, which is of the greatest moment to the farmer in spring. From its effects upon the oat crop of this season, where it was used as a manure for the turnip crop of 1842, at the rate of 3 cwt. per acre, it seems permanent-as the oats will bear a comparison with those which grew where the land was manured with 40 cubic yards of farm-yard dung, and the hay crop, at this time, looks as strong and forward as any in the. same field. Potatoes manured with guano, or dressed with sulphate and nitrate of soda, appear also lo be imnproved inl, hiealth, and the tubers so grown are less apt to fail when cut and planted the following season. Experiment II.-One Hay. Effect of top-dressings of various substances upon three years old Grass, mostly Timothy, cut for hay in 1843; top-dressed on the 3d of June; cut on the 5th of August; weighed when cut, and again weighed when stacked on the 28th ot August. Quantity of ground under each dressing — Oe-eighth of ab imperial acre. ON ONE-EIGHTH OF AN IMPERIAL ACRE. PER. IMP. ACRE.! 0. a ~h ad 0? a I ~ s o; rs. b sd. scf. s g,. bsNo. Dressings. ^. * o 0 3) ~>dust and coal tar. ~["S 5 s.?u( and coal ta3r. qrs. Tbs.us. d. Ibs. Ibs. st. Ibs. st. Ibs. st. ~. s. d. IbI. 1 Nothing.......... - 1344 -- 52 1I —- 416 6 18 8 350 2 Guano.............. 1 14 3 10 4610 331691 738 10 752 12 10 8 275 4 Muriate of ammonia. 0 20 30 3700235670 017 3 560 9 6 8 2fi5 5 Sulphate of urine, 0 -20 3 380 243684 032 0 672 11 4 0 312 6 Nitrate of soda..... 0 20 0 9 28401496 53 0 1 0 424 7 1 4 265 7 Muriate of ammonia. 0 15 2 8 0 375 Common salt..... 0 15 2 35 Nitrate of soda0. 0 12 0 gNkit~rate ~of soda.. O j30 15211687 Q35 0 69611 12 0 35 Common salt....... I 0 0 4 8 3 _ 86 EXPERIMENTS UPON HAY AND OATS. [Appendix, The part of the field where the above dressings were put is a stiff clay loam lying quite level upon a sandstone rock, and has a south exposure. The dressings were late of being put on, and it was intended for green cutting for soiling, but owing to the abundance of other feeding, the parts dressed were saved for hay. All the dressings except No. 3 had the effect of altering, the colour to a dark green in the course of a week, and they all came away very strong and vigorous. No. 3 (the compost, see note 1~, p. 88,) had the effect of altering the colour in about three weeks after being applied, and came away so rapidly that it soon gained upon the others in point of strength and luxuriance of stems and leaves. It will be seen from the tables that Nos. 4 and 6 gave less hay from 1000 lbs. green cut, when used alone, than any of the others; but with the addition of common salt 1000 lbs. gave more than any of the other dressed portions. Sulphated urine may be considered a salt of ammonia, all of which salts have been found to give greater bulk than almost any other application of salts applied to green produce, but they have invariably been found here to give less dry hay when used by themselves. The extra produce from the sulphated urine is probably owing to its compound nature. It appears from the above, therefore, that the most profitable way of using these salts is by mixing them with oth/ers, and that the more compoLnd the nmixture is the better will be the crop.* Experiment III.-On Oats. Effects of guano upon Oats (potato), sown on the 17th of April; cut and weighed on the 15th of September. Thrashed, cleaned, and weighed on the 24th of October. No. Dressing. a i Or | 05. U.o...u.0':00 55 a 3 C? - 00 5.Cad G" C —d i, 0 3' 5 qrs. s. d. lbs. lbs. lbs. lbs. bush. lbs. bush. lbs. 1 Guano.......... 3 7 6 3300 653 1015 40 16 13 3 20 2 Nothing........- - 2120 539 f 749 42 12 35 - NOTE.-The above quantities were applied to and reaped from one-fousrth of an imperial acre. The portion of the field upon which the above oats were grown is a deep stiff yellow clay, super-incumbent upon sandstone rock. It has been thoroughly drained for a number of years. It had been sown with wheat on the 20th of January, 1843, top-dressed with guano at the same time, which was harrowed in, but owing to the dampness and constant change fiom frost and thaw, the greatest part of the wheat failed, and was ploughed up on the 15th of April, and potato oats sown upon it on the 17th of that month. The oats brairded all alike, showing no difference'in point of earliness; but by the 9th of June a most remarkable alteration had taken place, the portion which had been dressed with guano for the wheat taking the lead of the undressed portion, and being of a dark green colour with broad leaves, and covering the ground well; whilst that which had no dressing was brown and stinted in comparison, and the ground not half covered. The two portions continued throughout the season to present the same difference in their appearance, and at the time of cutting there was more than a foot in length of straw in favour of the dressed portion. It will be seen from the table, however, that although the guano had the effect of giving more bushels per acre, the bushels were lighter in weight by 2 lbs. than the grain from the undressed. It may be remarked, however, that had common See on this subject of mixtures tkse Author's Elements of Agricultural Chemistry and Geology, p. 149. No. X.] EXPERIMENTS UPON OATS AND TURNIPS. 87 salt been mixed with the guano, there is reason to believe, from other trials, that the grain would not have been deficient in weight per bushel. Ammoniacal salts should at no time be dressed upon grain crops, without, at the same time, adding, according to the composition of the soil upon which such crops are grown, such other inorganic ingredients as may be required. Few soils, at least in this part of the country, appear able to supply these in sufficiency to the plants-particularly the phosphates, which seem always deficient. At least the addition of bone-dust or animal charcoal seems always to improve the crops to which they are applied. Experiment IV.-Ons Thrnips. Comparative effects of guano, farmi-yard manure, bone-dust, and, animal charcoal, by themselves and in mixtures,' on Turnips of different varieties; lifted, topped, tailed, and weighed, in Nov., 1843. ON AN EIGHTH OF AN IMPERIAL ACRE. ON AN IMP.ACRE. Cost of Value of No. Variety o01 turnips anId Time of Quantity of manures, Pro- produce kind of manures. Sowing. manure exclusive of Produce. duce. at 15s. applied. cartage. per ton. SWEDISH. June ~ a. d. ts. cts. qrs, ts. cts. 6. s. d, Farm-yard tanure.-.. 5 to 7 24 cub. yds. 0 12 6 1 Guano.. - 42 lbs. 0 3 9 5 6- 0i42 931 7 0 Animal charcoal..... 70 lbs. 0 2 6 Farm-yard manure... - 2 cub. yds. 0 12 6 2 Guano................ - 42 bs. 3 122919 3 Half-inch bones.. - 2. bushels. 0 2 6 3 Farm-yard manure.... - 5 cub. yds. 1 5 0 4 4 2133 1725 7 11 4 Gutanuo.............../ - 70lbs. 06 63 4 1 032 24 6 5 Half-inch bones.... - 5 bushels. 0 10 0 3 4 125 14 - PURPLE-TOP YELLOW. - 1I Guano....... 56 bs. 0 5 0 3 10 228 54 2 6 2 Dung. - 4 cb.yds. 1 26 3 7 0 26 1613 8 0 3 Bools'.4 4 busels. 0 9 0 3 0 0 24 012 0 0 Farm-yard sanure. -, 17 21 cub. yds. 0 12 6 4 10 0 36 018 0 0 4 Guano........... 2 lbs. 0 26 Farm-yard manure.... - 24 cub. yds. 0 12 6 3 3 251012150 Bone-dust........ bushels.... 0 3 0 5 Farm-yard manure, 4 24 yds. 012 6 Guano.......... - 28 bs. 0 2 6 4 1 33) 101915 0 6 Animal charcoal...... 42 lbs. 0 1 6 JONEs' YELLOW TOP. Farm-yard manure.... 21 34 yds. 0 18 8 0 32 016 0 0 1 Animal charcoal.. - 700 0bs. 00206 -Farm-yard manure... 3 yd.s. 0 18 93 2 Bone-dust...... mur. 14 bushels. 0 3 0 Farm-yard manure... 3yds. 0 A 9 310 028 014 0 top-dressing........ 3 _ _ 26w 013 n n' 4 Farm-yard manure... - 3 yds. 3 5 026 300 5 Guano. - 7 lbs. 0 63 2 5 0 18 0900 Farm-yard manure 2 yds. 0 12 6 2 3434 217 1 02 6^ Guanot.............. \ ~ 42 lb s. 0 3,9S,,, 7{ tAnimal charcoal.. 29 14 cwt.' 0 50 2 13 421' 710 136 8S Compost of coal-tar; 3 bushels. 0 3 10 3 12 329 21411 0 and saw-du stb..... 0 3 4. 2111 The field upon which the above turnips ere grown is a light gravelly loam, super-incumbent upon a deep gravelly till. The gloater part of the field was trenched with the spade, and all drained with tiles and soles 30 inches deep and 20 feet apart, in the winter of 1841 and 1842, and in the preparation for the turThe animal charcoal here used is the refuse of the sugar refiners, and contains about jib. of its weight of bone-earth. t This part of the field was trenched. 9S EXPERIMENTS UPON TURNIPS. [Appe.ndz, nip crop in 1842 and 1843, what had not been trenched was subsoiled. The turnip crop was sown at different times, as noticed in the tables. All the parts brairded well and healthy, and continued to grow without intermission through the season. The field contains about 11 acres imperial, and the crop was most luxuriant, so much so, that the lightest turnips in any part of the field would have been reckoned good. The field was drilled for the crop with the double mould plough at 30 inches apart, for swedes and p2urple top-yellow, and 26 and 28 inches for Jones' yellow, which variety is remarkable for very small tops, and, in consequence, may be drilled nearer. The difference in the appearance of the turnips, where the various manures and mixtures had been applied, was very marked. Wherever guano had been applied, the tops were larger than any of the others, except No. 3 of the table (JonLes' yellow), upon which sulphate of soda was top-dressed, after the plants were thinned. The crop upon this portion was remarkable for luxuriance of tops and large bulbs, and gave a very good crop.* No. 6 of the table (Jones' yellow), was upon'spade-trenched land, and is the only lot where a comparison can be made between trenching and subsoiling. Where bone dust was used the tops were not so large, and where the animal charcoal had been added the tops were least of call and the bulbs largest. Upon all the varieties of soils in this farm, the application of animal charcoal or bone dust has been of great benefit to all crops-to wheat, barley, oats, hay, and grass -the crops being bulkier and of superior quality, especially upon soils superincumbent on trap rock, giving an evidence that all such soils upon this estate are in want of phosphates. This has also been proved by the analysis of severalnone of them giving more than a trace of phosphates, and some of them none at all. Upon all these soils animal charcoal or bones seem to be indispensable, because the grain crops cannot be matured without phosphates of lime and magnesia. It appears fronr the many experiments that have been made' here, that guano does not contain a sufficiency of the phosphates to supply the crops to which it is usually applied, and which, from the greater luxuriance of growth its application at all times induces, would be required in greater quantity according to the bulk of crop. A portion of the animal charcoal of the sugar.refiners being mixed with it at the time of sowing, will supply the deficiency, and at all places inland from the sea, common salt will be found a valuable addition. The cultivator who is obliged from deficiency offarm-yard manure to use guano will find that by taking one-half of his usual quantity of farm-yard manure per acre, and making up for the other half by the addition of 2 to 4 cwts. of guano, his crops will be, at least, as bulky, and his after-crops as good, as if he had used 40 cubic yards of good dung. Guano, however, should not be used by itself upon soils that do not contain a certain amount of vegetable matter (i. e. on poor sharp soils), but it will in all cases be found an invaluable manure for thoroughdrained moss soils. NOTES.-1~. The compost of coal-tar and saw-dust used in the preceding experiments is composed of saw-dust or moss 40 bushels, coal-tar 20 gallons, bone-dust 7 bushels, sulphate of soda 1 cwt., sulphate of magnesia 1l cwt., and common salt 11 cwt., put together in a heap, with 20 bushels of quicklime, and allowed to ferment and heat for three weeks, when it is turned, and again allowed to ferment, and is then fit for use. 2~. In using the nitrate of soda for.the last four years in the garden, it has been found that top-dressing the leeks. in' the month of August or September enabled them to resist the effects of winter, whilst' those that were not so dressed have invariably failed, and gone to decay early in the season; at the same time, it increases their bulk in a remarkable manner. Knowing this effect upon leeks,-a crop that if grown to a large size has a great tendency to rot and fail in winter,-might it not have the same effect upon autumn sown wheats if dressed with it after they are brairded? This hint is merely thrown out as worthy of trial, as the salt appears to have the power of toughening the fibre or otherwise enabling the plants to withstand the rigours of winter, and in this way might, perhaps, prevent the wheat crop from failing in winter, which is often the case, to the great loss and disappoint. ment of the farmer WM. FLEMING. Barochan, Feb., 1844. Sulphuric acid and the sulphates appear to exercise a marked action on the turnip crop.-J. No. X., REMARKS UPON PRECEDING EXPERIMENTS. 89 REMARKS. I submit these experiments to the reader without any lengthened comment. The experiments with guano are very seasonable, and will be of much service to the thousands of practical men who are now likely to try this valuable manure. There are three interesting general observations of Mr. Fleming, to which alone I would direct especial attention1~. That the potato sets did not fail when powdered with gypsum, and that the more extensive trials of this substance which he recommends ought certainly fo be encouraged. 20. That potatoes dressed with guano, or with nitrate and sulphate of soda, appear to be improved in health, and are less apt to fail when cut and planted the following year. 3~. That his trap soils are supposed to be especially deficient in phosphates, and that the use of bones, in any form, always improved his crops upon these soils. These three observations are very interesting, and a careful study of the tables of results will lead the reader to make other interesting observations and deductions for himself. It is very satisfactory to me to have been able in this Appendix to incorporate the results of experiments performed ion three successive years by one so skilful and zealous as Mr. Fleming,-conducted every year also with more care, and more likely therefore to lead to important conclusions. The subject of agricultural experiments has now been taken up so warmly and so successfully in almost every part of the country, that we may look forward with confidence to the gradual accumulation of a body of facts, out of which correct and practically useful principles may gradually be elicited. The large body of experimental results, which the prize offered last year by the Highland Society has brought before the public, shows how eagerly the enlightened practical farmers of the present day will follow the guidance of such as are willing to show them how the art by which they live may be really and permanently improved, CATALOGUE OF BOOKS FOR PRACTICAL MEN, PUBLISHED BY C. M. 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The author has been one of the most able contributors to the agricultural pres or the last ten years; aside from this he is a practical farmer and stock-breeder ans consequently knows from his own experience what he is writing about. Commercial Advertiser. This book is by a gentleman of known experience; the work is exceedingly leap, and the farmer will find it a valuable book of reference. —N. Y. Express. It is in fact a brief encyclopedia on the subjects treated, and the farmer will ffirA appropriate information on almost any subject coming within his reach.New York Observer. Here is a book for the million, precisely what its title indicates. Compassed within its pages, the reader will find the subject of soils, manures, crops, and animals, treated in a style easily comprehended.-Spirit of the Times. This work is what might be expected from one so well qualified for the undertaking.-Boston Cultivator. We are glad to meet a publication which can interest, as well as improve the condition of the human race. We commend the work to every American farmer. -Christian Intelligencer. Why shall not every good farmer economize his muscles by storing his mind? We hope this book will find its way into many family and school-libraries.-Netz York Tribune. It (,'ight to be found in every farmer's library.-Jerseyman. It is really a great satisfaction to get hold of an American treatise on Agricultu-e, that has a plain, practical, common sense character of its own. The author of this work is already known to the agricultural public as a thorough practical farmer and stock-breeder. That he well knows what he is about on a farm, these pages abundanty show. No mnere book-maker could have written such a book; and we may add, also, that no mere practical farmer could have written it. A' good practical work" can only be written by a man who has both thought and acted well. What distinguishes this volume, is its conciseness, its clearness, and its perspicuous treatment of the subject in hand. We think, therefore, that Mr Alien's volume, the basis of which is go(d practical farming, as practised by th best cultivators in the United States, with an intelligent reference to those princl pies of science which lie at the root of all successful practice, is likely to be of as much or more real service to us, than any work on agriculture vet issued from the press, and we gladly coinmiedal it to tle perusal of every one. of our readrrs ntgage - in the culltva:ion of iind -- A. J. Downing's Horfiru!tH.isl THE AMERICAN POULTRY YARD; COMPRISING THE DRIGIN, HISTORY, AND DESCRIPTION OF THE DIFFERENT BREEDS OF Ol csfit t i oulttr; WITH Complete Directions for'he;r Breeding, Crossing, Rearing, Fattening, and Preparation for Market; Including Specific Directions for Caponising Fowls, and for the Treatment of the Principal Diseases tb which they are subject. DRAWN FROM AUTHENTIC SOURCES AND PERSONAL OBSERVATION Illustrated by Numerous Engravings BY D. J. BROWNE. With an Appendix, embracing the Comparative Merits of Different Breed of Fowls. BY SAMUEL ALLEN. Price $1, in cloth-75 cts. with paper covers. Published by C. RIf. SAXTON9 123 FiFlton Street, N. Y OPINIONS OF THE PRESS. Mr. Browne was bred and brought up a practical farmer. From his intimate know ledge of the history and habits of our domestic animals, having devoted, probably, more attention to the subject, as a whole, by reading and observation, than any other individual in the country, the task of preparing this work was assigned to him.Salem Register. The style of the engravings and the mechanical execution of the work are excellent -MJaine Farmer. An extensive work on poultry, embracing every information desired.-N. H. Tele fraph. We commend the book and the subject to the thoughts of farmers.-Vt. Watchlma? Every one who may purchase a copy, upon a perusal of the same, will be fully sati eted that their money was well spent.-Bristol PhaF7m.. It is one of the best treatises on the Domestic Fowl ever published.-Jew-Hav. Palladium. The details into which this book enters, on all the subjects connected with the pro fitable raising of fowls, are precisely of that minute and practical character which if needed.-JV. Y. Evangelist. VWe are glad to see that the evident demand for information on the subject of rearing Domestic Fowls has called out so valuable a work as the one before us. —J.'. Daily Tribeue. It contains matter to interest and instruct upon almost everything that concerns the poultry yard, and bears the impress in its pages that its editor'was well qualified to fulfill the task he undertook.-Jlmerican Farnmer. It is the most complete book of its class everpublished, and quite indispensable k all who are interested in raising poultry. — Charleston, S. C., Weekly Gazette. No farmer among us would remain a day longer without the work, did he bult kno its value.-Rahulay Regrister. It is unquestionably the cheapest and best work of the kind extant, and should ha a place in every farmer's library.-fGermantotwn, Ohio, Gazettc. The volume is enriched by an Appendix from the the pen of Mr. Samuel Allen, an experienced breeder of fowls, who has taken m.ch pains to improx c the stock in this couintrly.-N. i.;VAl7i 1ribulne. THE AMERICAN ARCHITECT, Jomplete in 24 Nos., at 25 cents each, or $5 for 24 Nos, $6, bound in 2 vols. PUBLISHED BY C. M. SAXTON, NEW-YORK. THE object of this publication is to introduce ORIGINAL DESIGNS of Country Seats adapted to the varied taste and circumstances of an American population: from the elegant VILLA to the simple COTTAGE and plain FARM-HousE; from PLANTERS' MANSIONS to VILLAGE DOMICILS. In a word, every variety of RURAL RESIDENCES will be embraced, in order to meet the views of every person desiring a COUNTRY HOUSE. In respect to style, cost, arrangement, finish, &c., utility will never be sacrificed: economy in the outlay, with an appropriate style, wil always be kept in view. The requisite details, specifications, plans, and direc tions, with a careful and reliable estimate of the cost, will accompany each design These are essential features of a Practical Work, and no labor will be spared in their preparation. Of the diversity of human dwellings, whether marked by elegance, convenience, or utility, or by the want of them, none can compare in national importance and philosophical interest with the Farm-House-the Holnestead of our species. A triple value attaches to that class of men which feeds all others. With primeval farmers, man's social faculties were first unfolded. With them society began: and among whatever people its shaft has become polished and its cap.tal enriched, it still rests on the cultivators of the soil. So, of their profession, agricu:ture is the great parent of the arts, while its prepared products will forever oe the most essential of all manufactures. Then it was in their dwellings that Architecture itself had its birth; it was they who first abandoned the tent with pastoral life, and began to devise and construct fixed and permanent abodes. The estimates we give are based on New York prices; including the best materials, workmanship, and finish. There is no doubt that in many parts of the country, they may be materially diminished in every one of these respects-ever to the extent of one-half. The selection of designs by those about to build Country Residences is cona nonly attended with embarrassment and always with expense When furnisheo;?y professional men, from general ideas communicated by proprietors, they are seldom satisfactory. The American Architect, by furnishing a collection of designs adapted to all tastes and means, will remove every difficulty in the choice, and save money expended on Plans of no use. It will furnish twelve Elevations, Plans, and Specifications in each year, at a price not exceeding one-seventh of the usual charge for one. Every handsome residence adds value to the grounds attached to it; hence the importance of having such, by those who invest capital in this species of property. With regard to utility-the proper distribution of the apartments and the.i adaptation to the purposes intended is the most important point to be attended to, and they are governed by the Plans. From among the great number of notices, we select the following:" The price is only 25 cents for each number, and it is surely next to Impossible but that such a periodical will obtain a wide circulation."-New York Tribune. " This work promises to supply a want which has long existed, and to be ot essential value."-Salem Register. "This work cannot fail to be useful and popular." —boston Bee. " This is a good and beautiful work, and well adapted to effect a much desired reform in American Architecture."-Boston Traveller. Thi Cost of building from the Plans given, will be from $600 to $5,000, wlts comp vte Specifications from a first-rate Mason and Carpenter, and the prnce given'an be depended upon. AN ESSAY ON MANURES, SUBMITTED TO THE TRUSTEES OF THE MASSACHUSETTS SOCIETY. FOR PRO!MOTIN@ AGRICULTURE, FOCR THEIR PREMIUM. BY SAMUEL L. DANA......... _. -- From the New York Observer: ESSAY ON MANURES. By SAMUEL L. DANA This Essay contains -much useful information for the practical farmer, in a small compass, in reference to the nature and management of manures immediately under his control; the knowledge and practice of which will amply oompensate for the expense of ascertaining its value. NEW YORK: C. M. SAXTON, 123 FULTON STREET. ALSO, STRINGER l& TOWNSEND, H. LONG & BROTHER, W. F. BURGESS, DEWITT & DAVENPORT, WILSON & CO., DEXTER & BROTHER. BOSTON: REDDING & CO. PHILADELPHIA: W. B. ZIEBER, LINDSAY & BLAKISTON. 1850. A PRACTICAL TREATISE ON THE CULTIVATION OF THE GRAPE VINE ON OPEN WALLS. WITH A DESCRIPTIVE ACCOUNT OF AN IMPROVED METHOD OF PLANTING AND MANAGING THE ROOTS OF GRAPE VINES, BY CLEMENT HOARE. TO WHICH IS ADDED, AN APPENDIX, CONTAINING REMARKS ON THE CULTURE OF THE GRAPE VINE IN THE UNITED STATES. NEW YORK: C. M. SAXTON, 123 FULTON STREET. 1851. THE FAMILY KITCHEN GARDENER; CONTAINING PLAIN. AND ACCURATE DESCRIPTIONS OF ALL THE DIFFERENT SPECIES AND VARIETIES OF — "a~sw~s's oz C19WM I AV M W A j M 0: BY ROBERT BUIST, &UTHOR OF THIE AMEIRICAN FLOWER-GARDEN DIRECTORY, ROSE MANUAL, ETC. NEW YORK: C. M. SAXTON, 12o FULTON STREET, ASO, STRINGER & TOWNSEND, H. LONG & BROTHER, W. F. BURGESS, DEWITT & DAVENPORT, WILSON & CO., DEXTER s BROTHER. BOSTON: REDDING & CO. PHILADELPHIA: W. B. ZIEBER, LINDSAY, BLAKISTON. 1&50 THIE AMERICAN BIRD FANCIER; CONSIDERED WITH REFERENCE TO THE BREEDING, REAR.NG, FEEDING, MANAGEMENT, AND PECULIARIT I E OF CAGE AND HOUSE BIRDS. Illustrated with Engravings BY D. J. BROWNE, AUTHOR OF THE SYLVA AMERICANA, THE AMERICAN POULTRY YARD, ETO. NEW YORK: C. M. SAXTON, 123 FULTON STREET. ALSO, STRINGER & TOWNSEND, H. LONG & BROTHER, W. F. BURGETSS DEWITT & DAVENPORT) VWILSON &- CO., DEXTER & BROTHER, PHILADELPHIA: W. B. ZIEBER, LINDSAY & BLAKISTON. BOSTON: REDDING & CO. 1850. LECTURES ON THE GENERAL RELATIONS WHICH SCIENCE BEARS TO PRACTICAL AGRICULTURE, DELIVERED BEFORE THE NEW-YORK STATE AGRICULTURAL SOCIETY. BY JAMES F. W. JOHNSTON, F.R.SS. L.&E. WITH NOTES AND ADDITIONS NEW YORK: C. M. SAXTON, AGRIULTURAL BOOKSELLER, 123 FULTON STREET.