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 FIRST BOOK 
 
 LESSONS IN CHEMISTRY, 
 
 ftf ITS 
 
 APPLICATION TO AGRICULTURE* 
 
 FOR THE USE OF 
 
 FARMERS AND TEACHERS. 
 
 BY 
 
 JOHN F. HODGES, M.D. 
 
 '/ 
 
 IIONOKiRY MEMBER OF THE PHARMACEUTIC IRbTITCTE OF NORTH GERMANY 
 
 J'ELLOW OP THE CHEMICAL SOCIETY OF LONDON, PROFESSOR OF 
 
 CHEMISTRY TO THE ROYAL BELFAST INSTITUTION, 
 
 AND TO THE CHEMICO-AtiRICCLTVRAL 
 
 — TT— -.. . SOCIETY OF ULSTER. 
 
 LONDON: 
 SIMMS AND M'INTYRE, 
 
 13, PATERNOSTER ROW, AND 26, DONEGALL STREET, 
 'BELFAST. 
 
 1848. 
 
# 
 
TO THE MEMBERS OP THE CHEMICO-AGRICULTUKAIi 
 SOCIETY OP ULSTER. 
 
 My Lords and Gentlemen, — 
 
 As you have afforded abundant proofs of zeal for the diffusion of 
 agricultural knowledge, and as it is your efforts that have mainly 
 contributed to promote that desire for miore extended information 
 in the scientific principles of their profession, which at present 
 prevails among the farmers in the North of Ireland, I take the 
 hberty of dedicating to you this htUe Work, which I trust may, 
 in 'some degree, prove instrumental in rendering this knowledge 
 more accessible to all classes of our co\xatrymen. 
 
 I have the honour to be, 
 
 My Lords and Gentlemen, 
 
 YoTor moat obedient servant, 
 
 JOHN P. HODGES. 
 Belfast, November 1, 1S48. 
 
 I or^eoe 
 
CONTENTS. 
 
 Introductory Rejiarks on the progress of scientific 
 
 knowledge 1 
 
 Influence exerted by chemical discoveries on the commerce and 
 prosperity of nations — RepugnMice of farmers to "book 
 farming" — Changes which have taken place in the opinions 
 which were formerly entertained respecting the application 
 of science to agriculture — Recent progress of practical 
 agriculture — Introduction of guano and bones — Services 
 which chemistry is capable of rendering to the farmer 
 — Ancient state of agriculture in Ireland — Remarkable pro- 
 ductive powers of the soils of this country — Knowledge and 
 energy required for their proper cultivation — Defects of the 
 education at present acquired by -farmers — Objects of the 
 lessons — Obstacles to the progress of agricultural knowledge 
 — Professional education necessary to the farmer — Methods 
 which he should pursue in studying the scientific principles 
 of his art — Sources from which his crops obtain their food — 
 Distinction between simple and compoimd bodies — elements 
 which contribute to the growth of plants and minerals — List 
 of simple apparatus and specimens to be procured by agri- 
 cultural teachers and pupils. 
 
 .CHAPTER I. 
 
 Account of the materials from which plants are formed 19 
 
 Essential conditions for the growth of plants — Properties of the 
 atmosphere— Meaning of the term mixture as distinguished 
 from chemical combination — Illustrative experiments — 
 Decomposition — Nature of the substances of whioh tlie 
 atmosphere is composed — Properties of oxygen gas, and its 
 influence on animal and vegetable life — Instructions for the 
 preparation of gases — Experiments for illustrating the pro- 
 perties of oxygen, nitrogen — Ammonia, carbonic acid— 
 Definition of terms used in agricultural works — Experiments 
 by which the existence of ammonia in the atmosphere was 
 determined — Proportion in which carbonic acid exists in 
 plants — Its existence in water — Its action on the materials of 
 the soil. 
 
IV CONTENTS. 
 
 CHAPTER 11. PAGE 
 
 Materials which water is capable of supplying to plants 34 
 Its composition — Steam — Properties and preparation of hydro- 
 gen gas — Distillation — Solid matters discovered in the water 
 of springs and rivers — Importance of water to the growth of 
 plants — Climate of Ireland — ^its influence on farm work — 
 Evaporation — Advantages of thorough draining. 
 
 CHAPTER HI. 
 
 Materials existing in the soil which contribute to the 
 growth of plants 42 
 
 Potash — Potassium — Carbonate of Potash — Compounds of Soda 
 — Lime — forms in which it exists in Ireland — Gypsum — 
 Magnesia — Magnesian limestone — Oxides of iron and man- 
 ganese — Properties of Silica — Mode in which it is rendered 
 soluble in water — Chlorine — Properties of sulphuric acid — 
 Phosphoric acid — Phosphate of lime — Importance of the 
 inorganic matters discovered in the ashes of plants — Amount 
 of inorganic and organic matters which cultivated plants 
 contain. 
 
 CHAPTER IV. 
 Substances into which plants convert the simple elements 
 
 on which they live 51 
 
 Nature of the compounds produced by plants — method of obtain- 
 ing these compounds for examination — Woody fibre — 
 Cellular tissue — Manufacture of starch — Composition of starch 
 — its transformation into sugar — ^production of British gum 
 and starch sugar — Varieties of gum — Mucilage — Albixmen of 
 the potato — Gluten, method of preparing it from wheat-flour 
 — its composition — Casein — Diastase — Fatty matters, oils, 
 and acids, which are found in plants — Composition of linseed- 
 cake — Quantity of oil and fatty matter in wheat-flour — 
 Purposes which these compounds are designed to serve — 
 Changes by which plants convert the materials of the soil and 
 air into food for man. 
 
 CHAPTER V. 
 
 Structure of plants, and changes which accompany their 
 growth i 63 
 
 The seed — Changes which take place when barley is converted 
 into malt — Parts of which plants consist — Conditions 
 necessary for the development of the seed — Growth of the 
 plant — Course of the sap — Effects produced by plants on the 
 atmosphere — Arrangements by which the imiformity of its 
 composition is maintained — Experiments of various chemists 
 — Influence of light on plants. 
 
CONTENTS. \' 
 
 PAQIS 
 
 CHAPTER VI. 
 
 The soil, its formation and composition 77 
 
 Varieties in the appearance and depth of soils in various parts 
 of Ireland — The subsoil — Agencies by which the hard rock is 
 converted into the arable soil — Vegetation of coral islands — 
 Origin of the organic matters contained in soils — Properties 
 of alumina— Composition of clay — its influence on the fertility 
 of the soil — Importance to the farmer of the knowledge of the 
 composition of the rocks from which soils are derived — 
 Granite — its distribution in Ireland — composition of the 
 minerals which compose it — Deficient ingredients in granite 
 soils and influence of elevation on their fertility — Mica slate 
 — character of the soils derived from it — Clay slate — Variety 
 of agricultural character presented by the soils of this 
 formation — Sandstone and Greywacke soils — Limestone — 
 Magnesian limestone — Qualities of the soils in the centre of 
 Ireland — Trap rocks — Wliite limestone of Antrim — Organic 
 matter of the soil — Nature of peat — Erroneous opinions 
 respecting the influence of humus on vegetation — Physical 
 qualities of soils. 
 
 CHAPTER VII. 
 
 Effects produced on soils by the growth of plants, and 
 plans adopted for maintaining their fertility 95 
 
 Origin of agriculture— effects of cultivation upon wild plants — 
 knowledge necessary to enable the farmer to improve the 
 quality of the soil — Nature of exhaustion — Kind and quantity 
 of inorganic matters contained in the crops cultivated in this 
 country — means adopted for maintaining the productiveness 
 of soils — Green crops — Circumstances which influence the 
 exhausting effects of plants — Rotation of crops — Practical 
 rules for the farmer — Influence of the soil upon the quality of 
 the crop. 
 
 CHAPTER VIII. 
 
 Means adopted for improving the soil, and maintaining 
 
 its fertility by the application of manures 105 
 
 Animal manuri-s — Principles of manuring — Composition of 
 the liquid and solid excrements of man — their importance as 
 applications to the soil — Effects of diet upon their fertilizing 
 qualities — Methods of applying them adopted in various 
 countries — Poudrettc — Urate — Plans proposed for the ap- 
 plication of sewage to agricultural purposes — Means by 
 which night soil and urine may be rendered inodorous- 
 Composition and agricultural value of the urine of the horse, 
 cow, and pig — Calculation of the loss experienced by the 
 farmer who neglects their preservation — Chemical composi- 
 tion and fertilizing qualities of the solid excrements of the 
 domestic animals — Difference in the value of the dung of 
 
Vi CONTENTS. 
 
 PAGK 
 
 young and full-grown animals explained — Farm yard 
 manure — its composition and value — Form of dxmg-stead and 
 tank recommended — Chemical substances to be applied to 
 prevent the escape of ammonia — State in which manure 
 should be used — Guano — its analysis — method of using it — 
 Bones — their effects on exhausted soils — their composition 
 and mode of action — Super-phosphate of lime — Vitriolized 
 bones — directions. for their preparation— Animal substances 
 occasionally employed as manures — Fish and shell-fish — 
 Flesh — Blood — Skin — Horn — Woollen rags — Hair — Refuse 
 of the glue manufacture. 
 
 CHAPTER IX. 
 
 Means adopted for improving the soil and maintaining 
 ■ its fertility by the apphcation of manures 1 43 
 
 Vegetable and mineral MA^fURES — Green manuring — Sea- 
 weeds — Kelp—Peat — Peat charcoal — its preparation and use 
 — Composition of peat ashes — Rape-dust — The husk of the 
 oat — Malt-dust, and the bran of wheat — Mineral and saline 
 manures — Artificial manures — Table showing the composi- 
 tion of the substances employed in their preparation — Use 
 of lime as a manure — ^Analyses of Irish limestones — Effects 
 of lime on the fertility of the soil — ^upon plants — States in 
 which it is applied to the soil — Rules for its application — 
 Marl — Its use as manure — Explanation of the disappoint- 
 ments which sometimes follow its application — Analyses of 
 Irish specimens — Shell-sand — Composition of specimens 
 from iDonegal — Phosphate of lime — Apatite — Discovery of 
 coprolites in the chalk formation — Their value as manure — 
 Existence of phosphoric acid in the Greensand of the North 
 of Ireland — Sulphate of lime — Its employment as a fertilizer 
 — Reports of French agriculturists on its application — Refuse 
 lime and ammoniacal liquor of the gas-works — Preparation 
 and value of sulphate of ammonia — Composts of lime, salt, 
 and peat-mould — Composition of soot. 
 
 ERRATA. 
 
 Page 37, line 2 from bottom, for per cwt. read grains. 
 „ 109, „ 19 „ top, for and read as. 
 „ 109, „ 20 „ top, for fl* „ and. 
 „ 112, „ 16 „ top, for flf«<i! „ or. 
 
PART I 
 
THE FIRST BOOK 
 
 or 
 
 LESSONS IN CHEMISTRY, 
 
 IM ITS 
 
 APPLICATION TO AGRICULTURE. 
 
 FOR THE USE OF THE 
 FARMERS AND TEACHERS OF IRELAND. 
 
 NTRODUCTION. 
 
 The most striking characteristics of the present time are, the 
 numerous applications which are every day made of the 
 knowledge of the laws of nature, which modern science has 
 so successfully investigated. During thirty years of peace 
 the highest intellects of Europe have been dedicated to the 
 advancement of the useful arts; and the discovery of new 
 and refined instruments of research, by giving accuracy to 
 the investigations of the philosopher, have not only enabled 
 him to advance with confidence beyond the footmarks of his 
 predecessors, but even to enter upon and subjugate regions 
 hitherto considered as destined to remain inaccessible to 
 human inquiry. Among the sciences, Chemistry in particular 
 has, within the last few years, advanced with a celerity whicli 
 even the most sanguine could not have anticipated ; and it 
 must be to us ajnatter of congratulation, that it is our 
 fortune to live in an' age in which- the advantages of its 
 brilUant discoveries are experienced by every individual. If 
 we should estimate the value of any science by its effects 
 upon the commerce and prosperity of nations, — by its 
 inHuence upon the useful arts, and its contributions to the 
 enjoyments of our race, — we must give the first place to 
 Chemistry. If we cast our eyes arouud us, we every- 
 where observe this science originating new manufactures or 
 improving old processes, giving to the physician his most 
 powerful remedies in more manageable forms, and separated 
 from injurious principles; in theoretical medicine substituting 
 
X INTRODUCTION. 
 
 for the vague notions of the ancient physiologist clear and 
 definite ideas of some of the most complicated processes of 
 the human economy; instructing the dyer, the iron master, 
 and the bleacher, and contributing in innumerable ways to 
 advance the commercial greatness of the British empire, and 
 to maintain the superiority of her manufactures. 
 
 The science of Chemistry has been cultivated from the 
 most remote times, yet its history for centuries might be 
 comprised in a few pages. At one time the slave of seekers 
 for gold, and of dreamers after an elixir which might render 
 man proof against the shafts of death, its language was 
 rendered purposely obscure, so as to be unintelligible to the 
 bulk of the people. In later times again we find it but the 
 servant of the physician, useful in compounding the drugs 
 which he employed, and exhibiting in its menial garb little of 
 that important character which it has since assumed, and which 
 leads us now to regard it as the surest interpreter of nature, 
 and one of the most powerful instruments in advancing the 
 civilization of the world. With the advance of scientific 
 knowledge which has distinguished the present time, the 
 means for difi'using it over the world have also everywhere 
 increased. The railway, itself a noble monument of what 
 the science of the present age has accomplished, has become 
 one of the gi'eat instruments of extending the influence of 
 her discoveries, and is destined to accomplish far greater 
 things than the famous highways along which the arts and 
 civilization of ancient Rome were carried, and will yet be 
 the means of giving light and knowledge to the remotest 
 corners of the land. 
 
 All professions have not been equally advanced by the 
 application of scientific knowledge. Whilst some by availing 
 themselves of its assistance have been brought to the greatest 
 perfection, others have for years remained stationary, or 
 have only lately received any impulse towai-ds improvement. 
 Among the occupations of men upon which science until veiy 
 lately cast but a feeble and uncertain light, we must place 
 the cultivation of the soil. It would occupy too much time 
 to investigate all the causes of this strange state of things ; 
 it is, however, well known that the art of agriculture, the 
 most ancient as it is the most important of human occupa- 
 tions, for centuries remained almost stationary and seemingly 
 unaffected by the onward march of society. 
 
INTRODUCTION. XI 
 
 Not many years ago all our knowledge of agriculture 
 consisted of the loose notions handed down by tradition from 
 father to son; mere experience was considered a sufficient 
 guide, and every attempt to apply science to the investigation 
 of the interesting phenomena of vegetation, and to the causes 
 upon which the non-productiveness or fertility of a soil 
 depends was sneered at by the farmer. By the great body 
 of the farmers the remarks of the chemist were regarded as 
 useless theories, and *' book-farming" was considered as 
 unworthy the attention of practical men. Within these 
 tew years, however, a great change has taken place in the 
 disposition with which the application of science to agricul- 
 ture was formerly regarded; and, what other arguments 
 could not accomplish, the necessities of a rapidly increasing 
 population, and the anxious struggle to render the produce 
 of the soils of the country sufficient for their support, have 
 been effectual in producing. In England and Scotland large 
 sums of money were expended in the improvement of 
 the mechanical condition of the soil ; the field, unproductive 
 from excessive moisture, was drained — new implements for 
 breaking up and pulverising the heavy clay soils were 
 invented — the thorough drain, the subsoil plough, and the 
 clod crusher, were introduced and proved most valuable 
 auxiliaries ; places at one time considered hopelessly barren 
 were brought into cultivation, and the hill sides were gradually 
 covered with the nutritious grain. The introduction, first of 
 bones and next of guano, and the advantages which 
 followed their application, did much towards unsettling the 
 traditional notions of the husbandman. But, after the use 
 of bones had been continued for some years, it was found 
 that their application was not unifoimly successful ; that in 
 one field they produced luxuriant crops, but had scarcely 
 any efiect in another place. The effect of the application 
 of guano was also observed to be different in different soils, 
 and in some cases totally to disappoint expectation. In 
 some parts of the country also, where lime, which had been 
 introduced as a fertilizer, was appUed, it was found nearly 
 useless ; while, in other districts again, its beneficial operation 
 was most remarkable. In the uncertainty into which the 
 tarmer was thrown by such puzzling and apparently coutra.- 
 dictory results, which threatened to interrupt the progiess 
 of improvement, he was induced to turn for assistance to 
 
 A 2 
 
Xll INTRODUCTION. 
 
 that science which he had at one time so obstinately rejected. 
 It was fortunate that the extraordinary progress of Chemistry, 
 and especially of Organic Chemistry,* enabled the chemist 
 to investigate these important subjects, and to explain in 
 a satisfactory manner the cause of the discordant results 
 which attended the use of appHcations for the improvement 
 of the soil. In this department of Agi'iculture the most 
 valuable services have been rendered by Chemistry ; and we 
 may confidently anticipate, now that those who are interested 
 in the cultivation of the soil are becoming fully aware of its 
 intimate connexion with their pursuits, that it will lead to 
 important improvements in the practice of Agriculture ; and, 
 by making the farmer acquainted with the nature of the 
 materials upon which he has to operate, enable him to 
 increase the produce of his farm, and introduce greater 
 economy in the use of the manm-es employed in maintaining 
 its productiveness. The investigation of the materials which 
 enter into the composition of the plants cultivated by the 
 fanner, and also of the soils in which they are produced in 
 perfection, and of those which are distinguished by their 
 unproductive character, has for several years been vigorously 
 ju'osecuted by some of the most eminent chemists of Europe, 
 and even already from these labours the most beneficial results 
 have been derived. Amongst those whose researches have 
 been most successful, we must assign the first place to that 
 distinguished German philosopher, Baron Liebig of the 
 I uiiversity of Giessen, whose writings have contributed in so 
 great a degree to direct the attention of the agricultural body 
 both in England and in this country, to the important 
 advantages to be derived from the application of scientific 
 knowledge to their pursuits. 
 
 It is, however, only in England and Scotland that im- 
 proved mechanical means and scientific knowledge have, to 
 any extent, been applied to the improvement of the soil. I 
 am glad to admit that the knowledge of the art of agricultm-e 
 is, in many parts of this kingdom, rapidly progressing ; but 
 it is too true that in very few districts have the dormant 
 energies of the soil been as yet called into proper activity by 
 
 * Organic chemistry is that department of science which investigat&s 
 the composition of the parts of animals and vegetables, and of the 
 various substances produced under the influence of life. 
 
INTRODUCTION. XUl 
 
 the application of those methods which, in the sister coun- 
 tries, have been found so successful in rendering large tracts 
 of country, formerly considered incapable of profitable culti- 
 vation, productive of the richest crops. 
 
 Ireland is pre-eminently at the present time, and is probably 
 long destined to continue, an agricultural country, and in her 
 soil and situation is nobly endowed with all the conditions of 
 fertility. It is, however, only of late years that agriculture 
 appears to have been much regarded. The ancient inhabi- 
 tants were occupied as hunters or shepherds ; and the tillage 
 of the soil seems to have received little attention even in 
 comparatively modern periods, as, except in the rich granges, 
 or farms of the religious houses, the wealth of the country, 
 to a great extent, was in cattle and not in corn. Here and 
 there, indeed, there might be a scanty patch of grain which 
 served the chieftain for bread, but our wooded hills and broad 
 plains exhibited for centuries but few traces of agi'icultural 
 occupation. The productive powers of the soils of this 
 country are most remarkable, and enable it, even with its 
 present imperiect culture, to produce crops which excite the 
 astonishment of the most skilful dinners of England and 
 Scotland. This island also possesses, in its geological stnic- 
 ture and genial climate, such advantages as to render it 
 equal to any country in the world for the growth of plants 
 and animals. May we not, therefore, conclude that it will yet 
 be made to yield an amount of food far more than sufficient 
 for rewarding the industry of any population which it will 
 ever contain. But Providence has so decreed that the gold 
 must be extracted with labour from the mine ; not only bodily 
 but mental exertion must be used to develop the resources of 
 our soils. We must bring to the work the calculating but 
 ardent zeal, and the patient industiy and science-directed 
 skill, which converted the once bleak and unprofitable fens of 
 Lincolnshire and the heaths of the Lothians into rich and 
 productive farms. Oiu* farmers must not be unwilling to be 
 taught, or to abandon practices, though sanctioned and con- 
 firmed by the examples of fathers and grandfathers, if more 
 advantageous plans can be pointed out to them. Our old 
 men must study the principles of their profession — the sons 
 of our farmers must be educated not as if they were intended 
 lor the counting-house, the pulpit, or the bar, but to under- 
 stand the composition of the fields and plants, upon the 
 
XIV INTRODUCTION. 
 
 profitable cultivation of which they must depend for their 
 subsistence and advancement in the world. 
 
 Much useful information, on the various departments of 
 rural economy, has, within these few years, been accumulated 
 in various parts of the world by the labours of men of science, 
 to diffuse which among our farmers and landed proprietors, 
 and to exhibit its application to the pecuhar circumstances of 
 this country, in language divested as much as possible of those 
 scientific terms which appear so repulsive to ordinary readers, 
 will be the object of these First Lessons. To assist in some 
 degree in diff"using such knowledge among our countrymen, 
 so as to promote that desire for improvement, which, after a 
 long space of inactivity, is beginning to influence the public 
 mind, I conceive to be a work worthy of the co-operation of all 
 who take an interest in Ireland. To show that such a desire 
 exists at the present time, it is only necessary to point to 
 the agricultural schools which are springing up in so many 
 localities — to the new spirit which has been awakened in the 
 older educational institutions — to an institution established 
 among the tenants and proprietors of our northern province, 
 for the express purpose of making the farmer acquainted with 
 the principles of his profession — to our valuable native 
 journals, devoted exclusively to agriculture, and commanding 
 a large circulation — all these things are gratifying evidences 
 that, as a nation, we have begun to devote ourselves to 
 the subjects which are best calculated to advance our prospe- 
 rity and to earn for us the respect and esteem of other 
 countries. 
 
 One great obstacle to the improvement of agriculture is 
 the custom which yet too commonly prevails, of regarding it 
 solely as an art, requiring merely a certain amount of 
 practical skill for its successful prosecution; and, whilst the 
 vitriol manufacturer, the bleacher, the sugar-refiner, and the 
 dyer, are conducting their processes in strict accordance with 
 certain scientific principles, and whilst every year new appli- 
 cations of chemical knowledge enable them to work with 
 gi'eater certainty and economy, the manufacture of food, by 
 far the most important to human existence, has been left to 
 the direction of men utterly unacquainted with either the 
 materials upon which it is their business to operate, or the 
 conditions required to render their work successful. Whilst 
 in the factory and the manufactory not only the managers are 
 
INTRODUCTION. XT 
 
 familiar with all the processes of their art, but the workmen 
 are carefully trained in the duties allotted to them, how few 
 of our food manufacturers, from the cottier, whose little gaixlen 
 grows potatoes and cabbages, up to the proprietor whose 
 farm of some hundred acres contains plants of different habits 
 and requiring a variety of food and treatment, are yet in 
 possession of that special knowledge which their occupation 
 requires. 
 
 It has uniformly been found that, in all professions, the 
 men who are most successful are those who have most care- 
 fully studied the principles of their busmess ; and why should 
 it be different with the agriculturist? There was, indeed, a 
 time in the agriculture of this country when the virgin soil 
 gave its fmits without much skill or intelligence being 
 required for its cultivation ; but that time has gone by, and 
 our exhausted fields and increasing population require that 
 the farmer, who desires to support himself by the profits of 
 his produce, should make himself acquainted with the condi- 
 tions upon which the successful cultivation of his various 
 crops depends, so that he may increase the amount of food 
 produced upon his farm at the least possible expense. 
 
 Let us suppose that the farmer is anxious to acquire a 
 knowledge of the scientific principles of his art, his first step 
 should naturally be to make himself acquainted with the na- 
 ture of the materials upon which he operates, and of the 
 plants which it is his object to raise. To acquire this know- 
 ledge he must have recourse to Chemistiy. Obsers^ation 
 shows him that the acorn springs up into the oak — that the seed 
 of wheat is the parent of many stalks of gi*ain — that plants 
 flourish in certain circumstances, but decay in others; and 
 that they are, therefore, dependent upon certain circumstances 
 or conditions for their growth. They cannot, like animals, 
 travel about in search of food — they are fixed to one little 
 spot of ground; from whence, then, does the acorn obtain 
 those materials which are moulded into the stately oak — 
 whence does the tiny grain of wheat j)rocure the substances 
 to build up its tall and flinty straw, and its seeds stored with 
 nutritious food ? These are questions of great interest, and to 
 which, until lately, it was not in the power of science to give 
 satisfactory answers. 
 
 It is evident that there are only three sources from which 
 l»!ants can procure the materials for their support, — either 
 
XVI INTRODUCTION. 
 
 from the air which is everywhere above and around them, 
 from the water which exists in the air as vapour and descends 
 from it producing rain, springs, and rivers, or from the soil 
 in which they are fixed. In the infancy of science, when all 
 our knowledge of these subjects was made up of conjectures, 
 to each of these sources the duty of afibrding the essential 
 food of plants was in turn attributed. We now, however, 
 know that neither the air, the water, or the soil, is by itself 
 sufficient to maintain the growth of the crops that we culti- 
 vate for food, but that they all unite in contributing to supply 
 the simple elements, the raw materials, from which both the 
 parts of vegetables and the nutritive matters which render 
 them valuable to man are produced. 
 
 It must appear astonishing to those who learn it for the 
 first time, that all the varied forms of rock and water, of 
 plant and animal, presented to us in this world in which we 
 live, so different in their appearance and properties, consist 
 of no more than sixty-two different substances; and that of 
 these only about fourteen are extensively employed in nature. 
 These sixty-two substances have as yet resisted all the efforts 
 of the chemist to procure from each of them more than one 
 kind of matter: — thus, from iron, which is one of the number, 
 we can procure nothing but iron. From this circumstance 
 iron, and substances like it, which contain only one kind of 
 matter, have been considered simple or elementary bodies. 
 If, however, we examine a piece of limestone rock, the soil 
 from our fields, or the water which flows in our rivers, we 
 find that they contain several distinct kinds of matter — that 
 they are w^hat are termed compound bodies. The variety of 
 appearance which the elementary bodies present enables us to 
 divide them into classes. Thus some of them, like iron and 
 lead, are solids, while others of them are known as liquids ; 
 and others again, thin and invisible like the gas which 
 illuminates our streets, are termed airs or gases. The elemen- 
 tary bodies are seldom found in a separate state ;* gold and 
 
 * The rnajority of these elementan'- bodies are seldom met with in 
 nature. The folloAving list contains all those wliich it is essential for 
 the agricultural student to remember, or the teacher to illustrate: — 
 Oxygen, Sulphur, Calcium, 
 
 Hydrogen, Phosphorus, Magnesium, 
 
 Nitrogen, Carbon, Alumimmi, 
 
 Chlorine, Silicon, Manganese, 
 
 Bromine, Potassium, Iron; 
 
 Iodine, Sodium, 
 
INTRODUCTION. XVll 
 
 >iWcr arc indeed occasionally discovered in minnte quantities, 
 but the value attached to these substances is a proof that 
 they constitute but a small portion of the forms of matter 
 usually met with around us. 
 
 There is a constant tendency in nature to produce com- 
 pounds. Expose a piece of bright iron to the air, and it is 
 f^radually covered with a reddish brown coating; and if we 
 weigh it we find that it has increased in weight. It has in fact 
 united with another simple body,* which is one of the constitu- 
 ents or elements of the air. It is the disposition which the ele- 
 nientaiy bodies possess of uniting together, that presents us 
 with the apparently endless variety of forms of matter which 
 we everywhere observe. When the farmer spreads upon his 
 field the burned limestone which he has procured from the 
 kiln it, though already a compound substance, becomes still 
 more complicated in its composition. Like the iron, it unites 
 with one of the ingredients of the air,f and at the same time 
 increases in weight and experiences a material alteration in 
 its properties ; before its exposure to the air it was a hard, 
 causticj substance, but after that, it assumes the form of a 
 mild powder, which experience has taught the farmer contri- 
 butes to increase the fertility of his soils. 
 
 In the following chapters, my object will be to make the 
 young farmer acquainted with so much of the characters of 
 the elementaiy and compound bodies which we meet with in 
 nature, as it is important for him to know, and also to point 
 out to him such applications of this knowledge as may be 
 useful to him in the practice of his profession. I trust that 
 he will be induced to accompany me from the beginning, and 
 diligently endeavour to obtain clear ideas of the various sub- 
 jects which may be brought before him. 
 
 • Oxygen. (7.) j Carbonic acid. (20.) 
 
 X Caustic, capable of producing a burn. 
 
XVlll INTRODUCTION. 
 
 LIST OF APPARATUS, ETC. TO BE PROCURED BY TEACHERS FOR 
 THE PURPOSE OF EXHIBITING TO THEIR PUPILS THE EXPERI- 
 MENTS DESCRIBED IN THE LESSONS. 
 
 1 . Two small retorts, or, instead of them, the flasks in which Florence 
 
 oil is usually sold; these flasks may be purchased from the grocer, 
 and, when fitted with good corks and bent glass or tin tubes, form 
 excellent vessels for preparing gases. 
 
 2. A small spirit lamp for heating retorts, &c.; or, when it cannot 
 
 conveniently be procured, a lamp sufficient for the purpose may 
 be constructed by using a small bottle, such as an ink-bottle fitted 
 with a cork, through which a piece of tin or glass tube is passed for 
 holding the wick: cotton wick may be procured from the chandlers. 
 
 3. A stock of glass tubes, each about the thickness of a large quill, for 
 
 bending over the spirit lamp, to form tubes for conducting gases, 
 &c may be purchased at the glass-house. 
 
 4. A holder for supporting retorts, &c. over the flame of the spirit 
 
 lamp, may be formed from a piece of stout iron wire and a 
 wooden stand, as represented in Fig. 1, or purchased, 
 o. Red and blue litmus papers, for testing acids and alkalies, may be 
 purchased from a druggist. 
 
 6. Two slips of platinum foil, or, instead of them, slips of thin window 
 
 glass. 
 
 7. Half-a-dozen glass rods, or, instead of them, narrow slips of window 
 
 glass, will be required for stirring liquids, &c. 
 
 8. An apparatus for burning hydrogen gas may be formed from a 
 
 piece of tobacco pipe passed through a cork, carefully fitted to 
 a four-ounce vial. 
 
 9. Half a dozen test tubes of thin glass, or instead of them ale-glasses, 
 
 for testing liquids. 
 
 10. A glass or porcelain funnel, and some sheets of white filtering paper. 
 
 11. A small porcelain mortar and pestle. 
 
 12. Apothecaries' scales and weights, which cost about 4s. 6d. 
 
 13. Half-a-dozen small vials with glass stoppers, containing 2 oz. sul- 
 
 phuric acid, 2 oz. muriatic acid, 1 oz. phosphorus, ^ oz. caustic 
 potash, ^ oz. tincture of iodine, 4 oz. spirits of Avine. 
 
 14. Half-a-dozen wide-mouth bottles with corks, containing 2 oz. black 
 
 oxide of manganese, for the preparation of oxygen gas; 4 oz. 
 
 chlorate of potash, 2 oz. carbonate of soda, 4 oz. metallic zinc in 
 
 fine cuttings, 4 oz. charcoal in small pieces, 4 oz. carbonate of 
 
 ammonia. 
 The above are all that are absolutely necessary. The list, however, 
 may be extended at the pleasure of the teacher, and include specimens 
 of the salts and artificial manures described in the lessons. The 
 pupil may also be encouraged to collect specimens of the rocks to be 
 foimd in the district in which, the school is situated, which will form 
 a most useful foundation for a school museum. A coloured geological 
 map of the country should also have a place in every agricultural 
 school. 
 

 CHAPTER I. 
 
 ACCOUNT OF THE MATERIALS FROM ^VHICH PLANTS ARE FORMED; 
 MATERIALS EXISTING IN THE AIR. 
 
 1. I HAVE Stated, that for the growth of our cultivated 
 crops, the essential conditions are the air, the soil, and water. 
 I say our cultivated crops, for it is familiar to us that a very 
 large class of plants, the weeds which gi'ow so luxuiiantly in 
 the sea that washes our coasts, and which, in some parts 
 of the world, navigators tell us, cover many miles of the 
 ocean, are wholly immersed in water, and derive no support 
 from the soil. But, though the sea-weed can extract from 
 the water all the materials required for its nourishment, 1 
 need scarcely say that tlie plimts which we cultivate for food 
 require a soil, as well as water and air, for then* develop- 
 ment. Such, therefore, being the sources from which the 
 nutritive materials are derived that enable the seed to throw 
 out its stalk and root, and to produce substances adapted for 
 our use, it must be most interesting, and not without impor- 
 tant practical advantages for the fanner, to understand some- 
 thing of the part which the ah-, the water, and the soil, 
 
 everally perform in the nourishment of his crops. Fortu- 
 nately, the advance of organic chemistry within these few 
 years enables us satisfactorily to investigate many things 
 connected with this subject, which, formerly, it would have 
 been impossible to explain. 
 
 2. It will be evident that, before entering upon this 
 inquiry, it is necessary that you should acquire a knowledge 
 of the simple bodies or elements of which air, water, and the 
 soil are composed, and of their properties; as, without be- 
 coming familiar with the materials upon which you have to 
 act, you cannot expect that you should successfully employ 
 them in regulating the development of vegetation. It will 
 require no great exertion of mind to obtain this knowledge, 
 and its possession will greatly facilitate your comprehension 
 "f those beautiful processes by which the life of plants and 
 animals, and the harmony of creation, are maintained. 
 
 B 
 
20 LESSONS ON CHEMISTRY. 
 
 3. We will commence with the air or atmosphere, as that 
 great ocean of vapour which surrounds the earth is called^ 
 and in which both plants and animals live. This gi'eat mass 
 of gases,* without the presence of which neither plant nor 
 animal could exist, possesses very remarkable physical proper- 
 ties ; but to these it is not necessary at present to direct your 
 attention. We cannot see the air, but we feel it in the 
 breeze which strikes upon us as we walk briskly along, re- 
 sisting our progress; and we hear it sighing in autumn 
 among the falling leaves, and howling in winter in the fierce 
 wind which rushes through our valleys. You can easily 
 convince yourselves that, though invisible, it possesses sub- 
 stance, by trying to press together the sides of an inflated 
 bladder, and, when the bladder is compressed, if you pierce 
 it with a pin, the air will rush out with force.f For our 
 purpose, it will be necessary that we should consider the na- 
 ture of the substances which compose the atmosphere, for it 
 is not an elementary body, as the ancient philosophers taught, 
 and as many uneducated people yet imagine, but formed by 
 the mixture of several airs, which possess, when separate, the 
 most energetic properties. 
 
 4. It may be useful in this place to explain the meaning 
 of the term mixture, which I have just employed as distin- 
 guished from chemical combination, as these tenns frequently 
 occur in works which treat of the chemistry of agriculture. 
 When we stir together a quantity of sand and common soda, 
 such as is used in bleaching, we produce a mixture of these 
 substances which partakes of the characters of both. We 
 can at once perceive that it is a compound of sand and soda. 
 If we place the mixtiu-e in boiling water, the soda will dis- 
 solve, and can be poured off with the water, leaving the sand 
 unchanged. But if, after mixing the sand and soda, we place 
 them in an iron or clay vessel, and expose them to a very 
 strong heat, we produce a compound in which no trace of the 
 
 * Gases are thin, elastic, and invisible substances, of which the gas 
 employed in illuminating towns is an example. Many of them have 
 neither colour, taste, nor smell ; but, though not to be detected by our 
 senses, they possess most energetic and remarkable properties. 
 
 ■f Illustration. — Attempt to fill a wide-mouthed bottle by placing 
 it with its mouth downwards in a basin of water, and you will find that 
 the water will not pass into it : something (the air) resists its entrance ; 
 but if you incline the bottle to one side, the air, being lighter than water, 
 will escape in bubbles, and the water will enter and occupy its place. 
 
MATERIALS WHICH PLANTS DERIVE FROM THE AIR. 2 1 
 
 sand can be observed, and which, according to the quantity 
 of soda employed, either dissolves entirely in boiling water, 
 or forms an insoluble transparent substance like glass.* 
 These experiments afford us an example of the changes 
 which the union of elements or compounds is capable of pro- 
 ducing. In the first case, the new body produced by simply 
 mixing the substances together pai'takes of the properties of 
 its constituents. We can distinctly observe the sand and 
 soda unchanged. But in the second case, when they com- 
 bine^ a body may be formed possessing properties and appear- 
 ance totally unlike those of the substances employed to 
 produce it. In the first case, the substances are said, as 
 with the sand and soda, to be merely mixed; in the second, 
 to be in chemical combination. 
 
 5. There is, also, another mode in which changes are pro- 
 duced in the form and appearance of the bodies around us, 
 and to which I shall have frequent occasion to allude. Its 
 operation is just the reverse of those which I have above de- 
 scribed; for, instead of causmg variety, by bringing bodies 
 together in new forms, it separates or breaks up the com- 
 pounds formed by nature. It acts as the lime-burner who 
 places in his kiln the compound limestone, and, by means of 
 heat, tears asunder its constituents, producing a substance 
 possessing properties very different from those of the lime- 
 stone rock of our hills. This process of change, which is 
 continually going on around us, is termed decompositioii. 
 1 will again return to its consideration. 
 
 6. Let us, however, continue our inquuy into the nature 
 of that great mixture of gases with which we were engaged, 
 (a) If you were to take some buniing wood or coal, and 
 attempt to kindle a fii'c, and at the same time close up the 
 top of the chimney and the mouth of the fireplace, you 
 would find that the fire would not bum. You must ^ give 
 it air," or the lighted fuel would be extinguished, {h) If 
 you were to place a healthy plant, growing in a pot, within 
 a large, carefully closed bottle, and supply it only with dis- 
 
 • A soluble glas8 has been employed on the Continent as an appli- 
 •cation to paper and wood, in theatres and public buildings, to diminish 
 the liability to take tire. It is best made by fusing together a mixture 
 of 70 parts carlx)nate of potash (salt of tartar), 54 parts carbonate of 
 soda, and 152 parts of ground flints or pure white sand. The glass pro- 
 duced- will readily dissolve in water, and may be applied like a varnish. 
 
22 LESSONS ON CHEMISTRY. 
 
 tilled water, that is, water from which the air has been ex- 
 pelled by boiling, like the fire, it would soon die, — we must 
 " give it air," or it will not flomish. (c) If we take a piece 
 of wax taper, and fix it on a cork so as to allow it to float 
 on a basin of water, and then light it and invert over it a 
 large, wide-mouthed bottle, the taper will continue to bum 
 for a short time, but will at last die out; and if we now 
 cautiously introduce a second lighted taper into the bottle, 
 it will be immediately extinguished, (d) If, instead of a 
 lighted candle or a plant, we were to place in a closed bottle 
 a mouse, or any small animal, it would live for only a short 
 time, and the hfe of a second animal, introduced after the 
 death of the first, would, like the light of the candle, be im- 
 mediately extinguished. Air, therefore, undergoes a change 
 by supporting the hfe of plants and animals, or the flame of 
 a candle. It appears to contain something indispensable to- 
 both animal and vegetable life, and deprived of which it is 
 incapable of feeding flame or supporting animal existence. 
 
 7. The air is thus proved to contain a substance remark- 
 able for its influence in supporting life and flame. This sub- 
 stance seems to form but a small portion of its bulk and to 
 be soon consumed. Such indeed we know from chemical 
 investigation is the case, this substance being a gas, one of 
 the simple bodies termed Oxygen, which forms only about a 
 fifth part of the atmosphere. This gas, besides forming a part 
 of the air, is also locked up in immense quantities in combi- 
 nation with rocks and minerals, and by exposing some of 
 these to heat, we can decompose them, in the same manner 
 that the limestone is decomposed in the kiln, and drive off 
 their oxygen so that we can procure it in a separate form,* 
 
 * As it is most desirable that -the teacher should- prepare small 
 quantities of the gases described in the lessons, and illustrate their pro- 
 perties to his pupils, it will be useful to describe the apparatus and ope- 
 rations required for their preparation and collection. When a bottle 
 is filled with water, as already described, it may be raised up in 
 the water, and will remain full, provided its mouth be kept immersed. 
 If we now plimge another bottle, in common language termed empty, 
 but really containing air, into the water in such a manner as to allow 
 the bubbles which escape to rise imder the mouth of the bottle filled 
 with water, the air will gradually drive out the water, and occupy its 
 place. If we bring a bottle full of gas, or a tube from which it is es- 
 caping, under the mouth of a bottle of water as just described, the 
 water will in like manner be driven out, and we will procure a bottlfr 
 of the gas, which we may remove from the basin and preserve foi- 
 
MATERIALS WHICH PL.\NTS DERIVE FROM THE AIU. 
 
 23 
 
 and examine its remarkable properties. In the air its 
 amount is so small that its properties are not so striking. 
 
 exainiiiation, if we close it securely with a cork dexterously inserted, 
 without raising its mouth above the surface of the water in the basin. 
 A common wash-hand basin may be used for collecting gas; but a 
 small trough formed of tin-plate, and provided vnth a shelf pierced with 
 two or three holes, termed a pneumatic trough, is usually employed. 
 Water is poured into this trough until it rises about an inch above the 
 surface of the shelf, and when it is desired to collect the gas, a bottle fidl 
 of water is placed with its mouth directly over one of the small holes, 
 and under the same hole the tube from which the gas escapes is placed. 
 The directions wliich we are about to give for the preparation of 
 oxygen will now be understood without difficulty. Oxygen gas is one 
 of the most extensively diffused bodies in nature, forming about a half 
 of the crust of the earth, and being an essential ingredient of water and 
 of the bodies of plants and animals. It is never met with, except in 
 combination with other bodies, and the usual method of procuring it in 
 a separate state is to apply a strong heat to certain substances which 
 contain it in large quantity. Tlius, by placing in a retort, or Florence 
 flask fitted with a cork, through which a bent tin or glass tube passes, 
 a mixture of two parts of Chlorate of Potash, with one part of black 
 oxide of Manganese (49), both substances being previously rubbed to 
 tine ix)wder in a mortar, and applyuig heat to the vessel by means of a 
 spirit lamp, the tube of the retort, or that attached to the flask, being placed 
 as described under the mouth of a bottle inverted and full of water, the 
 gas will escape tlu-ough the tube, and expel the water from the bottlt. 
 The engraving will show the arrangement of the apparatus required. 
 
 Illustration of the properties 
 of Oxygen. 
 
 a. A tube may be filled 
 with tlie gas, which will be 
 foimd to possess neither co- 
 lour, smell, nor taste. 6. 
 Into another tube filled with 
 gas, and removed from the 
 trough, by placing the thumb 
 under water over its mouth, 
 a bit of taper, with its flame 
 just extinguished, may be 
 introduced; the flame will immediately be rekindled, and burn with in- 
 creased brilliancy, but the gas will not itself take fire. It is a supporter 
 of combustion, but not itself combustible. 
 
 c. A piece of piiosphorus about the size of a small 
 |jea, placed upon the iron spoon, may be ignited by touch- 
 ing it with a piece of lighted wood, and immediately in- 
 troduced into a half-pint lx)ttle of the gas. It ^nll burn 
 with a dazzling white light. When the quantity of oxy- 
 gen in the atmospheric air is diminished 8 per cent, 
 (Liebig), the latter becomes injurious to animal life, and 
 incapable of 8Ui)porting combustion. 
 
 n2 
 
 I^'ig. 1. 
 
 o 
 
 
24 LESSONS ON CHEMISTRY. 
 
 Its presence, however, as we have stated, is indispensable far 
 the support of life and flame (6). Thus, in the diluted state 
 in which it exists in the air of our rooms, it gives our fires 
 and candles the power to burn ; by its influence the coal is 
 slowly consumed, giving a comfortable warmth to our dwell- 
 ings, and the tallow and the wax of our candles gradually 
 burn, affording us a cheerful light. But when a candle or 
 other ignited body is introduced into a vessel of pure undi- 
 luted oxygen, all the energy of its properties is displayed, 
 the candle no longer burns quietly as in common air, and 
 even though extinguished before being introduced, if a par- 
 ticle of its wick continues to glow, it will immediately burst 
 into a vivid flame and be rapidly consumed. Even metallic 
 bodies, which like iron are merely melted when exposed to 
 our most intense fires, if heated in a vessel of this gas, burn 
 with brilliant sparks. 
 
 8. When the oxygen gas which for a time supported the 
 flame of a taper in the bottle of air is consumed (6 c), four- 
 fifths of the latter remain behind, invisible like the air 
 itself, but deprived, as we have stated, of those properties 
 which render it capable of supporting flame and animal 
 life. This substance, which forms the great bulk of the air, 
 consists nearly altogether of a gas termed Nitrogen, which 
 though incapable of supportmg life when separated from 
 oxygen, yet is one of the most essential ingredients of the 
 flesh of animals, and of all those vegetable productions which 
 serve as nutritive food.* Without the presence of some 
 substance containing it, no plant could arrive at maturity, 
 or produce any of those matters in their roots and seeds 
 
 * Nitrogen gas may be prepared by igniting a small piece of 
 Phosphorus placed in a little cup, standing on a soup-plate half filled -with 
 water, and covering it with a confectioner's jar, or wide-mouthed bottle 
 {Fig. 3). The burning Phosphorus unites with the oxygen of the air 
 
 contained in the bottle, and the com- 
 pound formed (a substance termed 
 phosphoric acid) dissolves in the 
 water contained in the plate, leaving 
 (^ r) H the nitrogen gas of the air. lake 
 
 oxygen, nitrogen is devoid of taste, 
 smell, or colour. That it is neither 
 inflammable nor capable of support- 
 ing Jiame, may be shown by intro- 
 
 ducing a lighted candle into the 
 
 Fig, 3. bottle. It is rather lighter than air. 
 
MaTEKIAL> which 1M>ANTS DERIVl-: FROM TUI. All; 
 
 H lilcli render them valuable as food for man and the inierior 
 iiiimals. 
 
 9. The most singular character of nitrogen is the indispo- 
 sition which it exhibits to enter into combination with other 
 bodies. The other simple undecompounded bodies, like oxy- 
 i:;en, &c. have a constant tendency to unite together, but 
 resisting what appears to be a general law, this gas can 
 with diihculty be forced into combination ; so that it is con- 
 sidered that, as existing in the air, it serves merely to modify 
 the energetic properties of oxygen, but takes no part in con- 
 tributing to the formation either of plants or animals. How, 
 then, is this element, which is so unwilling to unite with 
 other bodies, and yet so indispensable to animal and vegetable 
 existence, obtained by plants ? This important question will 
 be answered as we proceed. 
 
 1 0. In addition to oxygen and nitrogen, the preponderating 
 ingredients of the atmosphere, there are invariably diffused 
 through it exceedingly minute portions of two other gaseous 
 bodies designated ammonia and carbonic acid.* These bodies, 
 though existing in the air in quantities which render them 
 almost imperceptible, you will find are of the greatest im- 
 portance, and may be regarded as pre-eminently required for 
 the nourishment of plants. The first of these bodies, am- 
 monia, is, like oxygen and nitrogen, a kind of air. It is, 
 however, not like them simple, but has by the chemist been 
 discovered to consist of two of the simple elements, one of 
 them the unsocial element nitrogen, which we lately noticed, 
 and which, in this compound, has united itself with a gas 
 which we have yet to describe, named hydrogen. In ammo- 
 nia, nitrogen loses all the inertness that distinguished it 
 in its separate state, and takes under various forms a most 
 active part in several important operations which I shall 
 have occasion to notice. 
 
 11. Before proceeding further, it is necessary that you 
 should understand the meaning of some terms which I will 
 have occasion to employ, and which you will frequently meet 
 in reading works on agricultm-e. You have probably observed 
 
 • Dr. Clarke gives tlie following statement, in round numbers, of 
 f. . ..„.,.. wit ion of the atmosphere: — 
 
 Nitrogen 1900 volumes. 
 
 Oxygen 500 do. 
 
 Carbonic acid 1 <'.'j- 
 
26 LESSONS ON CHEAIISTRY. 
 
 that the kind of cabbage used to prepare pickles (red cab- 
 bage), which when growing in the garden is of a violet 
 colour, becomes of a bright red when placed in vinegar. If 
 you were to pour upon the cabbage leaves water mixed with 
 a few drops of vitriol, or spirits of salts, precisely the same 
 change of colour would be produced. Now substances which, 
 like vuiegar, vitriol, and spirits of salts, possess a sour taste, 
 and alter the violet colour of cabbage leaves to a red, are 
 termed acids by chemists; and strips of paper coloured by 
 being dipped in liquids procured by boiling in water the 
 leaves of the red cabbage, the common violet, or a certain 
 blue vegetable colouring matter called litmus, are employed 
 by them in their experiments, for the purpose of testing or 
 ascertaining the presence of these substances. 
 
 12. When common potash, or the soda ash employed in 
 bleaching, is dissolved in water, and tested by means of the 
 prepared papers just described, the colour of the paper is not 
 changed to red. On the contrary, if the paper be reddened 
 by the action of an acid, and afterwards dipped in the solu- 
 tions, its original blue colour will be restored.* To sub- 
 stances which like potash and soda ash possess a peculiar 
 acrid, disagreeable taste, and restore the blue colour to red- 
 dened test-papers, chemists give the name of alkalies. 
 
 1 3. When acids and alkalies are mixed together in proper 
 proportions, they enter into chemical combination^ and form 
 what are termed neutral compounds, in which neither acid 
 nor alkaline characters can be detected. Thus the taste of 
 vitriol, (sulphuric acid) is intensely sour, but if we gradually 
 add to it potash, which is an alkaline substance, we can procure 
 a compound in which neither by the taste nor the test-paper 
 can we detect the characters which distinguished these sub- 
 stances before their union, f Such compounds of acids and 
 alkalies are very numerous, and are designated salts by 
 chemists, and receive a name derived from the ingredients 
 
 * When the blue liquid, obtained by steeping or boiling red cabbage 
 or violets in water, is mixed with an alkaline liquid, as a solution of 
 potash, soda ash, or ammonia, its colour is changed to green. 
 
 f The teacher may impress the nature of the change which is 
 effected by chemical combination, upon the minds of his pupils by 
 illustrating the properties of sulphuric acid and soda (soda ash) in 
 their separate state, and as imited in sulphate of soda (glauber salt), 
 which compound exhibits no trace of the acid and alkaline characters of 
 its constituents. 
 
MATERIALS WHICH PLANTS DERIVE FROM THE AIR. 27 
 
 which exist in them: thus the compound of sulphuric acid 
 with potash is termed sulphate of potash. 
 
 14. Though neither nitrogen nor hydrogen (which, I 
 have saidf unite together to form ammonia), in a sepai-ate 
 state possesses smell or taste, the compound evolves the 
 peculiar pungent odour of smelling salts, and is also distin- 
 guished from its elements by exhibiting the properties which 
 I have described as characteristic of the class of bodies 
 termed alkalies. It has a caustic alkaline taste, restores the 
 blue colour of reddened test papers, and readily enters into 
 chemical combination with acids, forming salts, several of 
 which are employed as manures. 
 
 15. This singular pungent smelling gas has not been 
 found, like oxygen, to enter to any great extent into the 
 composition of rocks and minerals, but it is produced in large 
 (juantities in various natural processes. Thus it is formed in 
 those great chemical operations which accompany volcanic 
 eruptions, and is also evolved wherever animal or vegetable 
 matters are exposed to a high temperature, or are undergoing 
 that more gradual dissolution of their parts which we term 
 decay. You may recognise its characteristic penetrating 
 odour upon burning a piece of bone or a feather, and you 
 may convince yourselves that the vapom- is alkaline by bring- 
 ing near it a slip of reddened test paper. It is given off by 
 the liquid manure of the farm-yard, and you will detect its 
 smell upon opening the door of an ill- ventilated stable, and 
 in the neighbourhood of a carelessly managed manure heap. 
 
 16. Ammonia also differs from its elements by dissolving 
 readily in water, and a strong solution of it is sold by the apo- 
 thecary. From its solubility in water, the rain which falls upon 
 the unprotected manure heap flows away laden with it, and 
 in the sewer water of our towns, enormous quantities of it are 
 swept into the sea which ^urrounds these islands. It has 
 been calculated that in the water of a single sewer in London, 
 upwards of a ton weight of ammonia is every day poured 
 into the Thames! 
 
 17. In the distillation of coal to produce the gas used for 
 lighting our cities, a liquid containing a very large amount 
 of ammonia is formed, which is extensively used in the arts, 
 and has also been employed with great advantage as a 
 manure, under the name of " gas liquor." {See Manures.) 
 
 18. Ammonia is considerably lighter than common air; and 
 
28 LESSONS ON CHEMISTRY. 
 
 therefore, when the farmer perceives its penetrating odour 
 near the manure-heap, or where guano has been stored, he 
 may be certain that it is escaping into the atmosphere, and 
 that, if neglected, these manures will gradually be rendered 
 less capable of benefiting his fields. Chemistry teaches us 
 how by very simple means, as will be hereafter described, 
 this loss of ammonia may be prevented.* 
 
 19. Though Saussure, whose works contributed to direct 
 the attention of philosophers to the substances which serve 
 for the food of plants, suspected the presence of this gas in 
 the atmosphere, it was reserved for that great chemist, whose 
 writings may be said to have originated the modern theory 
 of agriculture, to demonstrate its existence by experiment. 
 Liebig, with his usual sagacity, reasoned that the difficulty 
 of detecting the presence of ammonia must arise from the 
 extremely minute portion of it which existed in the few 
 cubic inches of aii' usually submitted to examination, and 
 that we would more easily convince ourselves of its presence 
 by operating upon some pounds of rain water; by which 
 means we should obtain in solution, carried down with the 
 rain, the whole amount of it diffused through several cubic 
 feet of air. Accordingly, he collected rain water in the 
 neighbourhood of Giessen, where he resides, when the wind 
 was blowing in the dkection of the town, so that the rain 
 could not obtain any ammonia from the smoke, &c. Several 
 hundred pounds of this water were boiled to dryness in a 
 
 * Ammonia is most conveniently prepared by introducing into a 
 flask a mixture of one part of sal-ammoniac and two parts of quick- 
 lime, and applying a gentle heat. The substances must, previously to 
 being mixed, be reduced separately to a fine powder. As ammonia is 
 very soluble in water, it cannot be collected over the water trough, but 
 bottles and tubes may be filled with it by fixing, by means of a cork, 
 to the mouth' of the flask, a tube of glass of sufficient length to 
 pass to the bottom of the vessel used to receive the gas. 
 When inverted over the tube (^Fig. 4) the light gas will 
 entirely expel the atmospheric air from the receiver. If 
 you close the receiver and bring it over a vessel contain- 
 ing water, and withdi-aw the cork, the water will rush 
 up with force, and unite with the gas. This experiment, 
 when a large bottle of gas is used, and the water is 
 mixed with some blue vegetable colour reddened by the 
 addition of a few drops of vinegar, is exceedingly striking. 
 The water rushes into the bottle, and its blue colour is 
 restored by the alkaline gas. Water saturated with this 
 gas is what is sold as liquid ammonia. Fig. 4. 
 
MATERIALS WHICH PLANTS DERIVE FROM THE AIR. 29 
 
 copper Still, with the addition of a small quantity of muriatic 
 acid,* a substance which unites with ammonia, so as to pre- 
 vent the heat driving it away, and a compound of the am- 
 monia and the acid was obtained in the vessel. Liebig 
 estimated that, if a pound of rain water contained one-fourth 
 of a grain of ammonia, a field of 26,910 square feet would 
 receive annually upwards of 80 lbs. of it, or 65 lbs. of 
 nitrogen;! so that a statute acre would each year receive, in 
 the ram which falls upon its surface, about 129 lbs. of am- 
 monia, containing 106 lbs. of nitrogen, j 
 
 20. The other compound which the atmosphere contains 
 is a gas called Carbonic Acid, formed by the union of the 
 black inflammable substance charcoal, or, as chemists term it, 
 carhouy with oxygen. 
 
 21. When wood or peat is burned in a close vessel or in 
 a heap covered over with sods, in such a manner that the 
 air has not free access to it, as is occasionally done by farmers 
 in preparing turf for manure, it does not consume as when 
 Inimed in our fires, but there is left a considerable quantity 
 of a black-coloured porous substance, lighter than the material 
 employed, and which may be exposed to the most intense 
 heat without undergoing any change, provided we exclude 
 the air. This substance is insoluble in water, and consists 
 chiefly of one of the sunple elementary bodies termed carbon, 
 combined with some earthy impurities. In the process of 
 manufacturing gas for illumination, coal, which is a compound 
 of carbon with several gases, is exposed to a strong heat in 
 
 * Muriatic acid is the liquid sold as spirits of salts. It is a solution in 
 water of a pungent suffocating gas of a sour taste, formed by the union 
 of hydrogen and chlorine. The solution is very sour, and, when brought 
 into contact with ammonia, immediately unites with it, forming a white 
 solid substance named chloride of ammonium, or sal-ammoniac. Tlie 
 ammonia coming off from manure-heaps may be detected by bringing 
 near the manure a narrow slip of window glass, or a feather wet 
 >vith spirits of salts, when the white solid compound will be produced 
 on the glass. 
 
 t By weight, 100 lbs. of ammonia consist of 82 i lbs. of nitrogen 
 and I7i ll)s. of hydrogen. 
 
 X A aseful property of charcoal, and one which renders it most inte- 
 resting to the farmer, is its remarkable power of absorbing gases and 
 of giving them out again wlien moistened with water : thus, of ammonia, 
 wood cliarcoal absorbs 90 times, and of oxygen 1) times, its own volume. 
 The coke of the gas manufacturer usually contains from 75 to 95 per 
 cent, of pure carbon- 
 
30 LESSONS ON CHEMISTRY. 
 
 an iron vessel, the volatile gases pass away, and in the vessel 
 remains a black substance, the carbon of the coal. 
 
 22. When a piece of wood, or common charcoal, is burned 
 in a vessel of oxygen gas, or with free exposure to the air, 
 as in an open fire, it almost entirely disappears, and merely 
 a small quantity of ash is left. In both cases, the cai'bon 
 which they contain enters into chemical combination with 
 oxygen, and the result of this union is the gaseous compound 
 carbonic acid, which I have mentioned is one of the ingre- 
 dients of the atmosphere. 
 
 23. If we place in a bottle a few pieces of common 
 limestone, and pour over them some spirits of salts (muri- 
 atic acid) or common vinegar, a bubbhng up of the Hquid 
 will be produced by the escape of a gas from the stone; 
 but if we repeat this experiment with pieces of hmestone 
 from the same quarry after they have been burned in the 
 kiln, neither spirits of salts nor vinegar will produce any 
 escape of gas. If, however, we take a small quantity of the 
 same bunied limestone, after it has remained some weeks 
 exposed to the air, spread over your fields, and treat it in the 
 same manner, it seems to have recovered its original quali- 
 ties, and a copious evolution of gas takes place, which, when 
 examined by the chemist, is found to be identical with the 
 gas which is locked up in combination with lime in the lime- 
 stone rock, and also with the gas produced when charcoal is 
 burned in the air or in oxygen gas.* 
 
 * To procure Carbonic acid we proceed as described above. The gas 
 however, being soluble in water, must not be collected over the trough ; 
 but, as it is considerably heavier than atmospheric air, we can readily 
 fill bottles with it, by a process exactly the reverse of that described 
 for collecting ammonia, thus, instead of directing the tube of the flask 
 vpwards to the bottom of an inverted receiver, we make it pass down- 
 wards to the bottom of a bottle standing in its usual position. The 
 heavy gas settles down to the bottom of the receiver, and displaces the 
 lighter atmospheric air which flows from the mouth of the bottle. We 
 may discover that all common air has been expelled by bringing a 
 lighted splinter of wood near the mouth of the bottle, when it will be 
 extinguished. Carbonic acid consists of 6 parts of carbon and 16 parts 
 of oxygen ; and, though the former of these is an inflammable sub- 
 stance, and the latter a gas remarkable for its power of supporting com- 
 bustion, when chemically combined in the above proportions, they pro- 
 duce a compound which immediately extinguishes flame. The teacher 
 should fill several bottles with the gas, and illustrate its properties. 
 
 a. It possesses acid properties. — When the tube from which the gas 
 is escaping is made to descend into a glass containing some of the blue? 
 
MATERIALS WHICH PLANTS DERIVE FROM THE AIR. 31 
 
 24. Carbonic acid gas constitutes but a small part of the 
 atmosphere, 5,000 gallons of au* containing only about two 
 gallons of it; but it is produced in enormous quantities by 
 various operations in nature : thus, it is formed by the burn- 
 ing of the coal consumed in our fires, the process of burning 
 consisting merely in the union of the combustible matter of 
 the vegetable substance, whether it be the remains of ancient 
 forests as coal, or the wood which is at present gi-owing on 
 the earth, with the oxygen of the atmosphere, and its con- 
 version into this in\dsible gas. In some volcanic countries it 
 is also evolved from the earth. It is considerably heavier 
 than common air, and consequently accumulates in caverns 
 and deep wells; and, being incapable of supporting life, it 
 has frequently occasioned the death of persons incautiously 
 descending into them. Like nitrogen it is incapable of sup- 
 porting flame, and this quality has been the means of warn- 
 ing workmen of its presence in suspected places : thus, if a 
 candle bums brightly in a well or newly opened cave, it is 
 safe to descend ; but if the candle be extinguished, or even 
 bum feebly, we should endeavour to remove the deleterious 
 gas before we enter. The most effectual means of doing this 
 is to pour into the well or cave a few gallons of a mixture of 
 quick lime and water; the carbonic acid unites with the lime 
 in the same manner as when it meets with it in the open 
 field, and the poisonous gas is locked up in the same state in 
 which it exists in the limestone mountain, and is rendered 
 incapable of doing injury. 
 
 25. It has already been shown (23) that carbonic acid 
 exists in limestone. In Ireland it forais a large portion of the 
 rocks of that formation which occupy so much of the centre of 
 the kingdom; and the "hard chalk" cliffs of Antrim, the 
 red limestone of Strangford Lough, and the black of Dublin, 
 contain nearly 44 per cent, of then- weight of this gas. When 
 limestone is heated in the limekiln, the carbonic acid gas is 
 
 liquid, procured by boiling the leaves of the red cabbage in water, the 
 colour of the liquid is changed to a bright red. 
 
 h. It is heavier than air, and extinguishes flame — A bottle filled 
 with it may be inverted over a lighted taper, when the heavy gas will 
 descend and put out the light. 
 
 c. The tube conducting the gas may be allowed to descend into a 
 wine glass containing some lime water, when the water will imme- 
 diately be rendered milky from the formation of a compound of the car- 
 bonic acid and lime (carbonate of lime.) 
 
 C 
 
32 LESSONS IN CHEMISTRY. 
 
 driven off, the rock loses nearly half its weight, and the es- 
 caping gas has frequently proved fatal to persons who have 
 fallen asleep near the place where lime was being burned. 
 
 26. Carbonic acid gas is also given out in enormous quan- 
 tities from the lungs of animals in breathing. The air which, 
 in a single expiration, we expel from our lungs contains from 
 3j to 4 per cent of it, and it has been calculated that the 
 air which, in the course of a day, is expired by a full-gi'own 
 man, actively employed, will yield as much of this gas as 
 would be produced by burning 1 3 oz. of charcoal in an open 
 fire. It is also, like ammonia, evolved wherever animal or 
 vegetable substances are undergoing decomposition (15); so 
 that when farm-yard manure, or vegetable matters of any 
 kind, are mixed with the soil of yom- cultivated fields, a 
 gradual and continued supply of both ammonia and carbonic 
 acid is produced. But though carbonic acid is thus from so 
 many sources continually escaping into the atmosphere, we 
 find as has been stated (24), that it constitutes but a small 
 part of its bulk. I will have occasion, in a subsequent 
 chapter, to explain how the accumulation of this gas, so in- 
 jurious to animal life, is prevented, and its production made 
 to contribute to the support of the crops which you cultivate. 
 
 27. The examination of the materials of which our culti- 
 vated plants are composed shows us that, when deprived of 
 water, nearly 50 per cent, of their weight consists of carbon. 
 But, as it has ah-eady been stated (21) that that substance 
 is insoluble in water, it is evident that it c^inot, in its ordi- 
 nary form, be taken up by vegetables. It is necessary that 
 it should in some way be rendered soluble. This Nature 
 effects by combining it with oxygen to produce the gas 
 which I have just been describing; for carbonic acid dissolves 
 j-eadily in water, the agreeable taste of spring water and 
 several fermented liquors being due to its presence. It is not 
 only soluble in water, but possesses, when in solution, the 
 power of dissolving lime and several other bodies not capable 
 of solution in pure water. We know that it is by the sol- 
 vent action of this gas contained m the streams which trickle 
 over rocks containing lime that that earth is dissolved, and 
 communicates hardness to our springs.* When boiled, the 
 
 * If a current of carbonic acid be allowed to pass for some time 
 through the milky liquid described in note c, page 31, it will gradually- 
 become clear, carbonate of lime being soluble in an excess of this gas. 
 
MATERIALS WHICH PLANTS DERIVE FROM THE AIR. 33 
 
 carbonic acid is expelled, and the water being incapable of 
 retaining the lime in solution, deposits it as a crust on the 
 sides of the vessel, and becomes *' soft." You ^vill find that 
 an acquaintance with the properties of this gas will assist us 
 in explaining many interesting matters connected with the 
 soil. 
 
 28. The atmosphere is the never-failing reservoir from which 
 innumerable tribes of plants receive the carbon necessary for 
 their support. From the same source, also, the countless 
 tons of carbon which the ancient forests required for their 
 growth were derived. These, by a wise provision of nature, 
 now supply us in our beds of coal with valuable deposits of 
 fuel, which, consumed in our fires, unite once more with the 
 oxygen of the air, and thus, after a rest of many thousand 
 years, the carbon again takes its place in the atmosphere, to 
 serve as food for plants, to cover the surface of the earth 
 with shady forests and waving grain, to give strength to 
 the tree and perfume to the flower, and to produce food for 
 the support of man and animals. How well calculated is 
 such information as that which I am now endeavouring to 
 communicate to excite our desire for knowledge — to enlarge 
 our ideas of that wisdom by which such arrangements have 
 been planned! 
 
 29. Besides the gases which I have described as compos- 
 ing the atmosphere, there are also diffused through it minute 
 quantities of various gaseous compounds produced in the in- 
 numerable operations going on everywhere around us; but 
 these form so trifling an amount of its vast volume, and so 
 little affect its general qualities, that it is not necessary for 
 our purpose to notice them. 
 
34 LESSONS IN CHEMISTUY. 
 
 CHAPTER 11. 
 
 MATERIALS EXISTING IN WATER. 
 
 30. We have passed in review the substances which enter 
 into the composition of the atmosphere, and which therefore 
 are accessible to the growing plant: we will now consider 
 what Water is capable of supplying for its nourishment. 
 
 Composition of Water. — This substance, which is met with 
 in nature under three forms — in a hard solid form, as ice ; in 
 a fluid state ; and in a gaseous form, as vapour or steam — 
 was, like the air, imagined by the ancient philosophers to be 
 a simple element. It seems difficult to be believed by those 
 unacquainted with the wonderful things which chemistry is 
 capable of demonstrating by experiment, that the pure, 
 healthful, and refreshing liquid, which in every country in the 
 world is such a necessary of existence, should be composed of 
 an unwholesome gas, one of the most inflammable bodies in 
 nature, united with that remarkable life-and-flame-supportuig 
 element, oxygen, which we described as being so important an 
 ingredient of the air that we breathe. 
 
 31. If we cause water to boil, we produce steam^ the bulk 
 of which is 1,694 times gi-eater than the water from which it 
 is formed. If we pass the steam through an iron tube, such as 
 a gun barrel, placed across a small furnace and kept at a red 
 heat, we find that a peculiar gas issues from the tube, which 
 we can collect over water, while at the same time its inner 
 surface acquii-es a coating of rust. This gas is named 
 Hydrogen, and is the inflammable element which, united 
 with oxygen, forms water. In the experiment, the steam, in 
 passing over the red-hot metal, is decomposed; one of its 
 ingi-edients, as we have stated, issues from the pipe as a gas, 
 while its other element, oxygen, unites with the metal, pro- 
 ducing the covering of rust, which is what is termed an 
 oxide, being a compound of oxygen and iron. Hydrogen gas 
 forms one pound in every nine pounds of water, so that for 
 
MATERIALS EXISTING IN WATER. 35 
 
 every nine parts bj weight of water converted into steam 
 and decomposed, one part of hydi-ogen escapes as gas, while 
 eight parts of oxygen enter into combination with the iron of 
 the tube. 
 
 32. Hydrogen gas, as has already been mentioned (14), 
 unites with nitrogen to form ammonia, and constitutes 
 three pounds in every 17 lbs. of that compound. It is, 
 like oxygen, destitute of colour, taste, or smell. It has not 
 been found in nature except in combination with some other 
 body. It is most inflammable, though, strange to say, not 
 capable of supporting combustion: thus, if we fill a bottle 
 with this gas and introduce into it a lighted candle, the flame 
 will be extinguished, but the gas itself, where it is in contact 
 Avith the air at the mouth of the bottle, will take fire and hum 
 tvith a pale yellow fiame, so that the candle will be relighted as 
 we withdraw it from the bottle.* Oxygen gas, it will be 
 remembered, possesses properties exactly the reverse of those 
 just described; it is, unlike hydrogen, a powerful supporter 
 of combustion but cannot itself be inflamed. 
 
 33. Hydrogen gas is the lightest body in nature, a hun- 
 dred cubic inches of it weighing only about 2\ grains, while 
 the same quantity of air would weigh 30 grams ; therefore 
 
 * Hydrogen gas may be conveniently prepared by placing some cut- 
 tings of the metal zinc, or even a few iron nails in a bottle, furnished with 
 a tube as before described, and pouring upon them some oil of vitriol 
 diluted with three or four times its bulk of water; the water is decom- 
 posed, and hydrogen gas separates from it, escaping through the tube, 
 and may be collected in a vessel over water, or in a bladder provided 
 with a stop-cock. It may even be prepared, when no proper apparatus 
 can be procured, by placing the materials described in a common ale 
 y;lass, and covering the glass with the hand or a piece of moistened card 
 paper to detain the gas. In collecting the gas over the water-trough, 
 so as to prevent its being mixed with the common air which the bottle 
 contains, fill a receiver twice the size of the gas l)ottle, and allow the 
 impure gas to escape before collecting for experiment Ex — Place in a 
 lialf-pint bottle about half an oz. of cuttings of zinc, half till the bottle 
 with water, and pour in vitriol until the gas comes off briskly, then 
 close the bottle with a sound cork through which a gas-jet or a bit of 
 the tulje of a clay pipe has been inserted, and allow the action to go on 
 for a few minutes to ensure the escape of the common air contained in the 
 bottle ; apply a light to the jet, and the gas will inflame and continue to 
 bum with a pale yellow flame. Hold over the flame a saucer, and tlie 
 burning hydrogen given oft* from the decomposed water will seize upon 
 oxygen from the air, water will be ireproduced, and the gaucer will be 
 covered with moisture. 
 
 c2 
 
36 LESSONS IN CHEMISTRY. 
 
 when a balloon is filled with this gas it rises up through the 
 atmosphere in the same way that a bubble of air ascends 
 to the surface of water. Formerly it was generally em- 
 ployed for fillmg balloons, but coal gas, which is cheaper, 
 is at present preferred for that purpose. Coal-gas, which 
 is now so extensively employed for illuminating our cities, is 
 one of those extraordinary products for which we are indebted 
 to science. It is a compound of hydrogen and carbon, and 
 in preparing it by the distillatipn of coal in large iron vessels, 
 a small quantity of nitrogen contained in the coal is also 
 driven off, which combines with a portion of the hydi'ogen 
 to form ammonia. In the manufacture of gas the ammonia 
 is removed by passing the impure gas through water, and 
 this "gas-water," as has already been mentioned, is employed 
 as a manure. 
 
 34. The chemist can by various processes cause hydi'ogen 
 and oxygen to unite so as to form water ; thus, if when hydro- 
 gen gas is escaping from a jet like that used for burning coal- 
 gas, we set fire to it, and hold over the flame a common saucer, 
 soot will not be deposited as when coal-gas is burned, but the 
 saucer will be covered with drops of water. In burning, hy- 
 drogen unites with the oxygen of the atmosphere, and water is 
 produced. Water formed in an experiment in this way is 
 chemically pure, but in this pm-e state it is never met with in 
 nature. It is in fact essential for the purposes which it is designed 
 to serve that it should invariably contain other substances. One 
 of its properties is its power of dissolving gases ; some it ab- 
 sorbs in large, and others in only small proportions. Thus, 
 while the mixture of coal-gas and ammonia of the gas-works 
 is passed through it, the former escapes scarcely diminished, 
 while the latter is retained. This property of water exercises 
 an important influence upon its effects on vegetation. We 
 invariably discover in rain and snow-water the constituents 
 of the air, carbonic acid, oxygen, nitrogen, and ammonia. But 
 spring and river- water, besides containing the above gases, are 
 also contaminated with certain matters derived from the soil. 
 If we place a few drops of spring- water on a slip of glass, and 
 boil to dryness over a lamp or candle, the water is converted 
 into steam, while the solid matters which were dissolved in it 
 remain behind, in the form of a white or brown crust. It is 
 by a similar process that the chemist procures pure water. 
 He boils a quantity of spring-water to dryness in a glass or 
 
MATERIALS EXISTING IN WATER. 37 
 
 iron vessel, aud allows the steam to pass through pipes kept 
 constantly cold, by which means the steam again assumes its 
 fluid form, as we observe when a cold plate is placed opposite 
 the steam issuing from a tea-kettle, the impurities of the 
 water remain behind in the boiler. The same operation of 
 distillation is constantly going on in nature ; at every tempera- 
 ture and in every country, from the ice-bound seas of the 
 north to the tropics, it has been found that water slowly 
 passes to the state of vapour. The water on the surface of 
 the earth, in passing into steam, leaves behind it the matters 
 which it held in solution in its liquid state, and when it 
 descends again to the earth in rain it is almost pure. 
 
 35. The solid matters that we discover in spring- water are 
 the same that are found in the rocks of the country, and when 
 we recollect that it contains carbonic acid, it is easy to under- 
 stand how lime, and other mineral substances not soluble in 
 pure water, may be dissolved by it from the rocks over which 
 it has passed in its course. Both the kind and quantity of 
 mineral matters which are found in the springs and rivers 
 of a country vary very much, and are found to depend upon 
 the composition of the rocks or soils over which their waters 
 flow. The water of rivers, as might be expected, contains 
 less matter in solution than that of springs, which, penetrat- 
 ing slowly through the earth, dissolve and take up the ingre- 
 dients of the beds of rocks or sand through which they pass. 
 In limestone districts we find the springs containing a large 
 amount of lime, while again where they issue from the granite 
 rock they are found to contain a mere trace of that substance, 
 and to be comparatively free from impurities.* Some waters 
 also contain a considerable amount of vegetable matter; thus 
 in the water of the river Lys in Belgium, I have found so much 
 as 2-86 per cent, of organic matters in the gallon. The quan- 
 tity of mineral matters dissolved in any water must evidently 
 
 * Water of a stream near Rostrevor, County Down, an imperial grs. 
 
 gallon contained of solid matter 10 
 
 Water of a stream supplying a flax-pool at Moneyrea, Co. Down 10 
 
 of a well at Shannon Grove, Co. Down 11 
 
 of a pump do. do. do 28 
 
 of a well at Stranmillis, near Belfast »... 60 
 
 do. Irish Street, Downpatrick, Co. Down 140 
 
 do. (St. Dillon's Well) do. 40 
 
 do. Whitehouse, near Belfast 14^ 
 
 do. Belfast 127 
 
38 LESSONS IN CHEMISTRY. 
 
 exercise a considerable influence upon its use in various opera- 
 tions, and especially upon the animals which use it for drink. 
 Boussingault, the celebrated agricultural chemist, has du-ected 
 his attention to this subject, and has calculated that by the salts 
 dissolved or held in solution in the water used as drink by 
 his cattle, 2 cwt. of alkaline salts (13) were added to his 
 dung heap every year. 
 
 36. Water, therefore, by its power of absorbing the gases 
 of the air, and dissolving the mineral matter of the soil, affords 
 a means by which these substances may be introduced into 
 the interior of the plant, and we shall see that it is requisite 
 that all the matters which the soil suppUes should be dis- 
 solved in this useful fluid before they can contribute to 
 promote vegetation. 
 
 37. As in the laboratory of the chemist water can be decom- 
 posed into its elements, so when it penetrates into the interior 
 of the plant, it can undergo decomposition under the influence 
 of those curious agencies which the living vegetable is capa- 
 ble of exercising upon matter, its hydrogen being employed 
 in the production of various compounds. Water is regarded 
 as the chief source of the hydrogen of plants ; and when it is 
 worked up in the vegetable structure, oxygen is separated 'in 
 its gaseous form, and returned to the atmosphere. 
 
 38. The quantity of water which is annually deposited 
 upon the earth in rain differs very much in different coun- 
 tries. Over the whole earth it is estimated at from 32 to 33 
 inches, but from various causes the proportion of moisture 
 which some countries receive greatly exceeds this amount. 
 Thus, in different parts of England (Dr. Prout), it varies 
 from 22 inches, as at London, to 68 inches, at Keswick, 
 whilst at St. Domingo it amounts to so much as 150 inches. 
 The water of the ocean is constantly passing into vapour 
 and forming clouds, which are conveyed by the winds to a 
 considerable distance into the interior of a country. From 
 the pecidiar position of Ireland, with its west coast exposed 
 to the currents which carry with them clouds charged with 
 the moisture exhaled from the immense expanse of the At- 
 lantic, and which from various causes, and especially from 
 coming into contact with the cold mountain ranges that fringe 
 our coasts, have their temperature so much reduced that they 
 are condensed into rain, which is precipitated in frequent 
 showers over the land, the moisture of the climate of this coun- 
 
MATERIALS EXISTING IN WATER. 39 
 
 try has become proverbial, and exercises considerable influence 
 upon its agricultural character. From the observations which 
 have already been made, it appears, as might be expected, that 
 the quantity of rain that annually falls in this country on the 
 west and south-west coast, considerably exceeds that which 
 has been observed at Dublin, Belfast, and several places on 
 the eastern shores. It has been estimated that the total 
 amount of rain which falls over the entire surface of the island 
 would, if collected, cover it to the depth of 36 inches ; and 
 that, of this water, not more than 1 2 inches annually reach 
 the sea. The number of days upon which rain falls in 
 Ireland is greater than in England or on the continent; 
 thus, it is stated that on an average we have only 150 
 days yearly on which no rain falls. The constant evapora- 
 tion of so large an amount of water from the surface of the 
 island must exercise an unfavourable influence upon its tem- 
 perature; for, to convert water into steam, to make it eva-. 
 porate, a certain amount of heat is consumed. When we dip 
 our hands in water on a hot day, and wave them through 
 the air, they are rendered cool by the " loss of the heat 
 required to convert the water into vapour. Upon the same 
 principle, the surgeon directs the patient to cover an inflamed 
 part with pieces of linen dipped in water, or in mixtures 
 which evaporate with greater rapidity. It is in the same 
 way that our undrained fields are rendered cold, and the har- 
 vests in several districts delayed by the excessive moisture 
 of the soil; the rays of the sun which should ripen the crop 
 being expended in converting the surface water into vapour.* 
 The thermometer, or measurer of heat, employed by the 
 chemist shows a diflerence of several degrees between the 
 
 * The difficulty of drying agricultural produce was noticed a good 
 many years ago by the celebrated Arthur Young. Fanners, however, 
 in England have but little idea how much farm-work is influenced by 
 our humid and variable climate. As an instance of this, we find it 
 stated in the Farmer's Gazette, that while on the east coast of Ireland, 
 in the neighbourhood of Dublin, the dew has dried up so that the hay- 
 maker can commence his work in the morning at seven or eight o'clock, 
 and keep the hay opened out without danger of injury from the evenr^ 
 ing's dew till six in the evening ; on the west coast washed by the 
 Atlantic ocean, in Kerry and Cork, he considers himself fortunate 
 if he can commence work in the hay-making season at nine a.m. and is 
 obliged to gather tlie liay at four in the afternoon to protect it from the 
 heavy dews or " sea-fogs." 
 
40 LESSONS IN CHEMISTRY. 
 
 temperature of the soil in a field which has been thorough 
 drained and one which is lying neglected beside it. The 
 undrained soil, therefore, is correctly regarded as cold by the 
 farmer, and an extensive system of drainage is among the 
 most important means to be adopted for improving the pro- 
 ductive powers of our fields, and for enabling them to enjoy 
 some of the advantages which other countries derive from a 
 warmer sun. The undrained bogs and sheets of water 
 which, like Loughs Neagh, Corrib, and Allen, cover so much 
 of the country, must exercise a most injurious influence upon 
 its general temperature ; thus, it is found that the mean tem- 
 perature of the island is about 49^ degrees of the theraio- 
 meter, which is only 4^ degrees above the temperature at 
 which many seeds placed in the ground refuse to vegetate. We 
 need not, therefore, be surprised that, in many undrained dis- 
 tricts, especially in our northern counties, but a small return 
 should be given by the soil, and that the harvest should 
 be delayed far beyond the safe and proper season. An 
 excess of moisture in our soils is, in fact, their chief agricul- 
 tural defect, and fortunately it is in the power of our farmers 
 to correct this evil. The thorough drain will remove the 
 water which consumes the heat of the sun, and allow the air 
 to pass into the interior of the soil, warming it and giving it 
 that temperature which will cause the dormant seed to vege- 
 tate, and at the same time supply to the young plant the 
 gases requu'ed to promote its growth.* Nor will the advan- 
 tages to be derived from the drainage of the country be con- 
 fined to the farmer; all classes will be benefited in the 
 increased salubrity of the climate, and the removal of many 
 causes of disease. 
 
 39. Water, therefore, we have seen, not only, like the air, 
 supplies plants with gases essential to their growth, but also 
 
 * I am informed by Doctor Orr that forty years ago, in a townland 
 about two miles east from the Castlereagh hills in Down, the harvests 
 were twelve or fourteen days on an average earlier than in Castlereagh, 
 where the farms are more elevated and exposed ; but that now, by supe- 
 rior cultivation, draining, manuring, &c. the case is altered, and the 
 crops an-ive at maturity from six to eight days earlier than in the 
 former locality. 
 
 It is stated that in Aberdeenshire, in consequence of extensive 
 drainage during the last twenty years, the crops ripen ten or fourteen 
 days sooner than they formerly did. — Mr, Gray in Prize Essays of 
 the Highland Society. 
 
MATERIALS EXISTING IN WATER. 4 1 
 
 senes as the means by which they procure certain mineral 
 matters no less indispensable to their development. These 
 matters arc not to be discovered in the atmosphere or in rain 
 Avater, but exist in the rocks of which the ground on which 
 wc tread is composed, and which, broken into fragments of 
 various sizes, from the finest dust to the stone that turns the 
 plough aside, and, mixed with the decaying remains of the 
 weeds or crops that have grown upon them, constitute the 
 arable soil of the farmer. It is the carrying out of certain 
 plans to enable plants in the readiest manner to supply them- 
 selves with the materials for their support which are stored 
 in the soil that gives employment to the industrious labourer, 
 and that requires both practice and science on the part of 
 him who has the management of the work. 
 
42 LESSONS IN CHEMISTRY. 
 
 CHAPTER III. 
 
 MATERIALS EXISTING IN THE SOIL. 
 
 40. We have considered the nature of the materials which 
 the living plant obtains from the air and water, the impor- 
 tant gaseous elements with which the Creator has stored the 
 immense expanse of the atmosphere, and which in every part 
 of the world are accessible to the vegetable tribes. I trust 
 that you have received such clear ideas of the properties of 
 these gases that you will be prepared to understand some 
 remarks which I pui-pose making on the part assigned to 
 them in building up the structure of your crops. We will, 
 however, in the first place, direct our attention to the ingre- 
 dients which the earth in which plants ai-e fixed — the soil, 
 as it is termed — supplies for their support. 
 
 41. Suppose a stack of hay or of com in one of your fields 
 should accidentally be consumed by fire, you would find upon 
 examination that the greater portion of the stack had burned 
 away, had- vanished into the air, and that there remained 
 merely a small quantity of ashes which had resisted the fire. 
 If you were to take a ton weight of sea-weed, and, after 
 drying it, set fire to it in the rude furnace or kelp-kiln which 
 is used by the farmers along our coasts, you would find that 
 the great bulk of it would vanish into the air, but that there 
 would remain in the kiln about 100 lbs. of a grey ash in a 
 soHd mass, like the slag of the iron-smelter, which could be 
 fused by heat, but not consumed. 
 
 42. When the ash left upon burning a stack of grain or a 
 heap of sea- weed is examined by the chemist, he finds that 
 it is not a simple substance like iron or charcoal, but is made 
 up of nine or ten different substances, with the names and 
 appearance of most of which you are probably familiar. You 
 may remember that I stated (31) that iron when it unites 
 with oxygen gas becomes coated with rust, which is a com- 
 pound of that metal and oxygen, forming what chemists term 
 " an oxide of iron." In the ashes of plants we discern several 
 
MATERIALS EXISTING IN THE SOIL. 43 
 
 compounds of the same gas with metals and other elemen- 
 tary bodies, some of which possess alkaline and others acid 
 })roperties. These substances arc usually termed the earthy 
 or inorganic constituents of plants. They are named Potash, 
 Soda, Lime, Magnesia, Oxide of Iron, Oxide of Manganese, 
 Silica, Chlorine, Sulphuric Acid, Phosphoric Acid. 
 
 43. Potash forms the greater part of the well-known 
 alkaline substance sold by the grocer as Salt of Tartar, and 
 also of the potashes used by some bleachers in this country. 
 It is a compound of oxygen with a curious inflammable metal, 
 Potassium, which, when thrown upon water, decomposes 
 it, and unites with one of its elements, oxygen, while the 
 other element, hydi'ogen, is separated, and burns with a 
 beautiful flame. The same decomposition and production of 
 flame are witnessed even when the metal is placed on a plate 
 of ice. By simple exposure to the air also, it loses its 
 metallic brilliancy by uniting with oxygen. In all these 
 cases the same compound, oxide of potassium or potash^ is 
 formed. Potash exists in considerable quantities in the 
 ashes of land plants, especially in those of the common 
 bracken,* and of the wormwood. It is obtained by washing 
 the ashes with water; the potash, being soluble, is dissolved 
 out, and when the water is boiled to dryness in an u'on pot, 
 it is obtained united with carbonic acid, forming what is 
 termed carbonate of potash. It is in this way that the potash 
 of commerce is prepared, and that substance, separated from 
 various impurities, is termed pearl ash. Potash is also con- 
 tained in considerable quantity in the ashes of several kinds of 
 sea- weed: thus in the ashes of some sea- weed from the 
 mouth of the Clyde, there was found so much as 22 per 
 cent of that substance.! By dissolving carbonate of potash 
 (potash or pearl ash) in water and boiling it with some quick- 
 lime, you can separate the carbonic acid from it, and obtain 
 a solution, which, when decanted from the sediment that is 
 formed (carbonate of lime) and boiled to dryness in a covered 
 vessel, will yield pure or caustic potash. 
 
 44. Soda is a substance closely resembling potash in its 
 characters. It is met with in the washing soda of the 
 grocer, in the soda ash and barilla of the bleacher, m the 
 
 • The pteris aquilina of the botanist. 
 
 t By Dr. Godechens, of Hamburg, in the laboratory of Professor 
 Will at Giessen. 
 
44 LESSONS ON CHEMISTRY. 
 
 salt cake of the glass manufacturer, and in the well-kno-wn 
 " bakmg soda." It is the chief constituent of the ashes of 
 sea- weeds, is likewise found in the waters of several inland 
 lakes, and it also occurs in some countries covering the sur- 
 face of the land. 
 
 Soda, like potash, is not a simple body, but a compound 
 of oxygen with Sodium, a rare metal, which in its separate 
 state is only to be found in the laboratory of the chemist.* 
 
 45. Lime or quicklime is so well known to the farmer 
 that it is scarcely necessary to describe its characters. Like 
 potash and soda, it is a compound of a metallic body with 
 oxygen, being an oxide of a metal termed Calcium. It is 
 not met with in nature in a caustic state, but, combined with 
 carbonic acid, forming carbonate of lime (25) it is abundantly 
 diffused, and is found in every county in Ireland with the 
 exception of Wicklow, sometimes rising into great mountain 
 masses ; in other cases, as in the great central plain, forming 
 a subsoil of limestone gravel. Carbonate of lime, when pure, 
 as in statuary marble, has the following composition in the 
 hundred parts: — 
 
 Lime . . . . 5fi 
 Carbonic acid . 44 
 
 100 
 When the compound is heated in the kiln, the carbonic 
 acid assumes its original form of gas, and escapes, the stone 
 losing 44 per cent, of its weight, and becoming caustic. A 
 piece of limestone, you are aware, will not dissolve in pure 
 water, but after burning it becomes slightly soluble, and 
 dissolves in about 750 times its weight of water. 
 
 46. Lime is also found in Ireland, and in many parts of 
 the world, combined with sulphuric acid (oil of vitriol) 
 and water. The compound is known as sulphate of lime, 
 gypsum, and plaster of Paris, and is raised for agricultural 
 purposes at Carrickmacross, in Monaghan. It also occurs 
 crystallized along the shore at Killroot, near Carrickfergus, 
 in Antrim. In England it is found in great abundance, in 
 several counties, in a compact state, and presenting various 
 shades of colour. It is so soft that it can be scratched easily 
 with the nail. The crystallized variety found near Carrick- 
 
 * Common potash when exposed to the air attracts moisture and 
 becomes liquid (deliquesces) while the common soda of the shops (car- 
 bonate of soda) crumbles down to a white powder (effloresces). 
 
MATERIALS EXISTING IN THE SOIL. 45 
 
 t'ergus readily splits into thin layers, which are as tran- 
 sparent as glass. Gypsum is slightly soluble in water: 500 
 parts of cold water dissolving one part of it. When burned, 
 it parts with the water combined with it, and can be readily 
 reduced to a fine powder. In this dry state it exhibits a 
 remarkable character, which has rendered it of gi-eat value 
 in the arts, for when mixed with water, to the consistence 
 of a paste, it hardens into a compact mass. Unburned 
 gypsmn usually contains about 2 1 per cent of water. 
 
 47. Magnesia is also a familiar substance. It is the calcined 
 magnesia of the apothecary — and like the bodies just described, 
 is a compound of oxygen with a metal, being an oxide of 
 magnesium. It exists abundantly in the waters of the 
 ocean, and in various parts of the world is found in com- 
 bmation with carbonic acid forming rocks which also contain 
 lime, and are termed magnesian limestones. These rocks 
 occupy a considerable extent in England, but in Ireland 
 appear in only a few situations. They may be observed at 
 Cultra, in the neighbourhood of the pleasant little village of 
 Holywood, county of Down. Carbonate of Magnesia when 
 exposed to heat parts with its acid more readily than car- 
 bonate of lime. The caustic magnesia produced is not so 
 soluble in water as quicklime: one part of it requiring 5,142 
 times its weight of water for its solution. Rain water, how- 
 ever, charged with carbonic acid, is found to dissolve it more 
 readily than lime. 
 
 48. Oxide of Iron — The well-known metal, Iron at once 
 the most abundant and the most important metallic substance 
 found in nature, exists in every part of the world, combmed 
 with oxygen, and is also a constituent of almost all our rocks. 
 It has already been explained that when a piece of iron is ex- 
 posed to the air, it is gradually covered with areddishbro^vnrust, 
 which is a compound of the metal with oxygen (42), taken 
 from the air. This rust is termed by the chemist peroxide of 
 iron, as there is another compound of iron, which contains a 
 smaller proportion of oxygen, and is named protoxide^ or first 
 oxide of iron.* Both of these oxides exist in the soils of 
 this country. The first oxide has a great disposition to 
 
 Iron. 
 
 * The first, or protoxide of irou, consists in the 100 
 
 parts of 77.23 22.77 
 
 The second, or peroxide of irop, of 69..'H 3U.G6 
 
46 LESSONS IN CHEMISTRY. 
 
 unite with more oxygen, and the change which the farmer 
 frequently observes in the colour of the newly turned up 
 mould from dark brown to an ochrey red, is produced by the 
 })rotoxide of iron existmg in the soil being converted, 
 by exposure to the air, into the reddish brown peroxide. 
 Protoxide of iron and its compounds are considered to be 
 injurious to plants. You will, therefore, perceive how the 
 various mechanical processes which tend to expose the particles 
 of the soil to the influence of the oxygen of the atmosphere, 
 may not only improve their textm-e, but produce important 
 chemical changes in the ingredients which they contain. 
 
 49. Oxide of Manganese. Manganese is a metal which, in 
 many respects, resembles ii'on. It unites with oxygen in 
 several proportions, and a small amount of some of its com- 
 pounds is discovered in the ashes of plants. 
 
 50. Silica is the earthy substance which constitutes the 
 bulk of flint. Hence, it is frequently termed " earth of 
 flints." It also forms a large part of sandstone, sand, and 
 of the greater number of rocks with which we are acquainted. 
 Itock crystal — beautiful specimens of which are found in the 
 granite of Mourne — is almost pure Silica, and the white sand 
 produced by the v)ethering of Muckish, and other mountains 
 in Donegal, also contains it nearly free from foreign ingre- 
 dients. Pure Silica is a snow-white tasteless powder. It 
 is insoluble in water, and in all acids, except one named 
 Fluoric Acid. When heated with potash or soda, it forms, 
 according to the quantity employed, an insoluble transparent 
 glass, or a compound that dissolves in water. In combining 
 with these substances silica performs the part of an acid, and 
 the compounds are termed silicates; when the alkali largely 
 predominates the silicates dissolve readily in water, but when 
 only a small amount is present, the compound is not dissolved 
 by water, and is only slowly acted upon by strong acids; 
 thus common window glass is an insoluble silicate, and the 
 greater number of rocks consist chiefly of silica united with 
 variable proportions of iron, lime, and other elements. The 
 carbonic acid, and probably other acids, produced during the 
 decay of vegetable matters slowly decompose the compounds 
 of silica existing in the soil and in the straw of the manure 
 heap, and when thus separated from the elements with which 
 it was combined, silica becomes soluble in water, and capable 
 of being taken up by the roots of plants. 
 
MATERIALS EXISTING IN THE SOIL. 47 
 
 51. Chlorine is a suffocating, unwholesome gas, existing 
 in bleaching liquor, and in common salt, united with the metal 
 vSodium, which is found in soda.* It possesses the property 
 of destroying vegetable colours and the odour of putrefac- 
 tion, and is at present extensively used in bleaching and 
 in the hospitals for fumigation. 
 
 52. Sulphuric Acid is the important sour liquid, oil of 
 vitriol, employed so extensively in various manufacturing 
 processes. It is a compound of the well-known substance 
 sulphur with oxygen. It is rarely to be found in a separate 
 state in nature, but exists in a great many important com- 
 pounds. The compounds formed by its union with alkalies, 
 earths, and metals, are termed sulphates; (7) thus, in Epsom 
 salts, it exists in combination with magnesia, forming sulphate 
 of magnesia; in Glauber salts and salt cake, in combination 
 with soda, forming sulphate of soda; and in gypsum, as already 
 stated, (46) combined with lime, it forms sulphate of lime. 
 The properties of sulphur are familiarly known ; it is found 
 in a separate form in Iceland and Sicily; and, combined with 
 iron, in a mineral called pyrites, in Wicklow, in Ireland. It 
 enters into the composition of several important vegetable 
 compounds, and also forms one-twentieth part of the weight 
 of hair and of the wool of the sheep.f 
 
 53. Phosphoric Acid, or acid of bone earth. The name 
 of this substance is probably not so familiar to you as those 
 we have been considering. You must, however, have heard 
 of phosphoins, the curious waxy-looking substance which 
 gives out light in the dark, and when it is rubbed, takes fire. 
 That substance was formerly but little known to the majority 
 of people, and only to be found in small quantities in the 
 shop of the chemist; but, at present, in lucifer matches and 
 
 ' Common salt contams two-fifths of its weight of the metal sodium, 
 combined with chlorine. The compound in the language of chemists is 
 termed chloride of sodium, Chlorine also combines with potassium, the 
 metal which exists in potash, forming a substance termed chloride of 
 potassium, which resembles common salt in appearance, and is occa- 
 sionally used in the manufacture of alum. It exists in the ashes of 
 seaweeds, and is prepared in large quantities by the manufacturers of 
 iodine. 
 
 f It has been calculated that in the wool grown in Great Britain and 
 Ireland erery year, five million pounds of sulphur are abstracted from 
 the soil, to supply which to the plants upon which the sheep live, jk* 
 less than 13,000 tons of gypsum would be required. 
 
 d2 
 
48 LESSONS IN CHEMISTRY. 
 
 other useful contrivances for producing instantaneous light, it 
 is everywhere to be found ; and, in London alone, it is stated, 
 that so much as 200,000 lbs. of it are annually consumed. 
 When a piece of phosphorus is set on fire it unites with 
 the oxygen of the air, and produces a white, solid, and 
 strongly acid compound, which is phosphoric acid. This 
 acid enters into the composition of all our cultivated plants, 
 and united with lime produces a compound named phosphate 
 of lime, which forms the chief part of bones, and also exists 
 in considerable quantity in the milk of animals.* 
 
 54. Such is a plain account of the substances which the 
 ashes of your crops invariably contain. In the infancy of agri- 
 cultural science it was imagined that these earthy matters 
 exercised no influence upon the plants of which they had 
 formed a part — that they were only accidentally present. 
 But as chemistry advanced and examinations of the ashes of 
 plants became more numerous and accurate, it was ascer- 
 tained, beyond all question, that these substances were most 
 important — nay, indispensable to the existence of the vege- 
 table kingdom, and that without their presence in the plant, 
 even could it grow, it would be without value and incapable 
 of serving us for food. 
 
 55. Within the last few years repeated examinations of 
 both wild and cultivated plants have been made by chemists 
 in this country and on the Continent, and it has been clearly 
 shown, by careful experiment, that for a plant to come to 
 perfection, or to form its seed, the soil in AvLicli it is placed 
 must contain the materials which we have just described, as 
 entering into the composition of the incombustible ash of 
 vegetables. But the discovery that every plant which springs 
 up along the roadside, or is carefully tended in the farm, 
 requires a certain amount of mineral matters for its develop- 
 ment, is not the only useful intelligence which science has 
 derived from this inquiry, or which it can afi'ord to the 
 farmer. It has, in addition, given to us a piece of infonna- 
 tion which is destined to exercise the gi'catest influence upon 
 
 * In the ashes of sea plants two elementary bodies are discovered 
 which do not exist in the crops of the farmer. These are termed iodine 
 and bromine. Iodine is a metallic looking substance, something like 
 black lead in appearance ; it is procured from kelp, and is at present 
 very extensively employed in medicine. Bromine is a reddish brown 
 liquid with a peculiar disagreeable pungent smell, which, when inhaled, 
 excites violent irritation of the nostrils. It bleaches vegetable colours 
 like chlorine. 
 
MATEBIALS EXISTING IN THE SOIL. 
 
 49 
 
 the practice of agriculture in every part of the world. It 
 has demonstrated that, not only does every plant require 
 that the substances above described should be present in 
 the soil for its use, but that the different families into which 
 we are accustomed for convenience to divide our crops, are 
 distinguished by a remarkable difference in the proportions 
 in which these substances are found to exist in their incom- 
 bustible remains, and that different plants, like wheat and 
 clover, though growing upon soils of every variety of compo- 
 sition, invariably select different proportions of particular 
 kinds of matter for their nourishment, some plants being found 
 to contain in their ashes, and, consequently, to take up from 
 the soil chiefly potash and soda, and others again silica or 
 phosphorus, or sulphur. The value of this information will 
 be fully illustrated in a subsequent chapter. 
 
 5(5. The proportions in which the materials that have just 
 been described enter into the constitution of plants are sub- 
 ject to considerable variations. The following tables, however, 
 constructed from the analyses of Boussingault will give you 
 an idea of the composition of the organic portion of your 
 ordinary crops, and also of the amount of matters derived 
 from the soil, which that distinguished chemist found in the 
 plants grown upon his farm in the east of France. 
 
 1 00 lbs. of the following plants in the fresh state usually 
 contain — 
 
 • 
 
 Dry 
 Matter. 
 
 Water. 
 
 Wheat 
 
 85 5 
 
 14-5~ 
 
 Rye 
 
 83-4 
 
 16-6 
 
 Oats 
 
 79-2 
 
 20-8 
 
 Potatoes .... 
 
 24-1 
 
 75-9 
 
 Mangel Wurtzel .... 
 
 12-2 
 
 87-8 
 
 Turnips ..... 
 
 7-5 
 
 92-5 
 
 Jerusalem Artichokes . 
 
 20-8 
 
 79-2 
 
 Peas ..... 
 
 91-4 
 
 8-6 
 
 Wheat Straw .... 
 
 74-0 
 
 26-0 
 
 Rye Straw . . . . 
 
 81-3 
 
 18-7 
 
 Oat Straw 
 
 71-3 
 
 28-7 
 
 Pea Straw .... 
 
 88-2 
 
 11-8 
 
 Clover Hay .... 
 
 790 
 
 210 
 
 Stems of the Jerusalem Artichoke 
 
 87-1 
 
 12.9 
 
oO 
 
 LESSONS IN CHEMISTRY. 
 
 57. When all moisture has been expelled from the above 
 substances, 100 lbs. of the dry matter has the following com- 
 position : — 
 
 
 
 1 
 
 1 
 
 d 
 
 1 
 
 
 ^ 
 
 & 
 
 o 
 43-4 
 
 1 
 
 
 Wheat 
 
 46-1 
 
 5-8 
 
 2-3 
 
 2-4 
 
 Rye . . . 
 
 46-2 
 
 5-6 
 
 42-2 
 
 1-7 
 
 2-3 
 
 Oats .... 
 
 50-7 
 
 6-4 
 
 36-7 
 
 2-2 
 
 4-0 
 
 Potatoes . 
 
 44-0 
 
 5-8 
 
 44-7 
 
 1-5 
 
 4-0 
 
 Mangel Wurtzel . 
 
 42-8 
 
 5-8 
 
 43-4 
 
 1-7 
 
 6-3 
 
 Turnips . 
 
 42-9 
 
 5-5 
 
 42-3 
 
 1-7 
 
 7-6 
 
 Jerusalem Artichokes . 
 
 43-3 
 
 5-8 
 
 43-3 
 
 1-6 
 
 6-0 
 
 Peas 
 
 46-5 
 
 6-2 
 
 40-0 
 
 4-2 
 
 31 
 
 Wheat Straw . 
 
 48-4 
 
 5.3 
 
 38-9 
 
 0-4 
 
 7-0 
 
 Rye Straw 
 
 49-9 
 
 5-6 
 
 40-6 
 
 0-3 
 
 3-6 
 
 Oat Straw . 
 
 50-1 
 
 5-4 
 
 39-0 
 
 0-4 
 
 51 
 
 Pea Straw 
 
 45-8 
 
 5-0 
 
 35-6 
 
 2-3 
 
 11-3 
 
 Clover Hay 
 
 47.4 
 
 5-0 
 
 37-8 
 
 21 
 
 7-7 
 
 Stems of the Jerusalem ") 
 Artichoke . . j 
 
 45-7 
 
 5-4 
 
 45-7 
 
 0-4 
 
 2-8 
 
ol 
 
 CHAPTER IV. 
 
 SUBSTANCES INTO WHICH PLANTS CONVERT THE SIMPLE 
 ELEMENTS UPON WHICH THEY LIVE. 
 
 58. We have for so far strictly confined our attention to 
 the consideration of tlie store of materials which a bountiful 
 Providence has placed in the air, the water, and the earth, 
 for the nourishment of the vegetable tribes. We have seen 
 that four elementary bodies, — Oxygen, Nitrogen, Hydrogen, 
 and Carbon, — constitute the great bulk of every plant, and 
 that the remaining portion is composed of a few mineral com- 
 pounds with most of which you are familiar. The materials 
 employed by nature are few in number, yet how varied are 
 the forms they are made to assume in the plants and flowers 
 that cover the earth! 
 
 59. You will now inquire, what is the nature of those sub- 
 stances into which plants convert the raw materials of their 
 food, and which are discovered in the structure of the vege- 
 table and m the various forms of nutritive matter stored m 
 then- seeds and roots? The question is natural, and leads to 
 one of the most interesting parts of our subject. 
 
 The compounds which plants contam, produced by the 
 union of the simple elements that I have described, are almost 
 innumerable. The greater number of them, however, exist 
 in exceedingly minute quantities: thus, the bitter substance 
 Quinine, which is found in Peruvian Bark, and which at 
 present is so extensively employed in medicine ; the bitter prm- 
 ciple which chemists extract from the bark of the root of the 
 apple-tree ; the curious element Iodine, which is obtained from 
 the ash of sea- weeds, and the various colouring matters which 
 almost all plants contain, form so small a proportion of the 
 entire bulk of vegetables, that for the practical farmer in this 
 country these considerations would be without any real ad- 
 vantage. But in every plant which it is the object of the 
 farmer's care to bring to perfection, we find about half-a-dozen 
 of compound bodies, distinguished by a remarkable similarity 
 if composition, and upon the presence of which their value as 
 iood depends. To the consideration of these forms of matter 
 
52 LESSONS IN CHEMISTRY. 
 
 we will therefore confine our attention, and endeavour to 
 trace, so far as the light of science can clearly point out, the 
 cui'ious processes by which they are produced by the living 
 plant from the gases of the atmosphere and the materials of 
 the soil. Several of the substances to which I refer are 
 procured from plants for food and other purposes, and are 
 well known to every farmer. 
 
 60. If we proceed to examine any of our food-yielding 
 plants, or the uncultivated tribes of the roadside or the 
 mountain, we can, by a little care, make ourselves acquainted 
 with their composition. 
 
 If we place in a Florence oil-flask some shavings of wood, 
 and boil them successively in spirits of wine and water, con- 
 tinuing the boiling with each Hquid so long as it dissolves 
 anything, we will at last procure a white fibrous substance 
 insoluble in water, and which has neither smell nor taste. 
 This substance is termed woody fibre, and fonns the bulk of 
 the greater number of plants. The fibre of the Flax plant, 
 which is so valuable for manufacturing pui'poses, and to pro- 
 cure which of good quality is the great object of the flax- 
 growers of Ulster, consists of woody fibre united with a small 
 portion of matters derived from the soil. It has been found 
 that this woody matter of plants is chiefly composed of a 
 peculiar substance to which the name of cellular fihre is 
 usually given, and which is regarded as the earliest foi-med 
 portion of their structure. In the development of the vegetable 
 kingdom, cellular fibre is the chief building material employed. 
 It can, by chemical means, be procured from all the parts of 
 plants, and as prepared from the fibre of cotton it was found 
 by a celebrated French chemist, who has particularly studied 
 this subject, to possess the following composition : — 
 
 Carbon . . . 44-35 
 Hydrogen . . 6*14 
 
 Oxygen . . .49-51 
 
 100 
 
 It is curious to observe that in cellular fibre, no matter 
 from what plant derived, whether from the spongy rush or 
 the firm oak, the hydrogen and oxygen exist in the same 
 proportions in which these gases unite to form water; that is, 
 one part of hydrogen is combined with eight parts of oxygen. 
 
SUBSTANCES PRODUCED BY PLANTS. 53 
 
 f) 1 . When the wood of a tree is examined by a powerful 
 microscope, it is observed to consist of layers, one of which is 
 composed of the ceUular fibre just described, while the others 
 consist of an incrusting substance which differs from it in 
 containing more cai'bon, and hydrogen in a larger amount, 
 than would combine with the oxygen which it contains, to 
 form water. Many interesting researches have lately been 
 made respecting the composition of these layers, but the 
 inquiry is of peculiar difiiculty and must be regarded as only 
 commenced. 
 
 62. When a piece of wood is placed in vitriol, it is blackened 
 and assumes the appearance of charcoal ; thus, you may have 
 observed that a piece of cork placed in a phial containing vitriol 
 gives a deep black colour to the entire liquid. The strong 
 acid decomposes the woody matter and unites with its hydro- 
 gen and oxygen, the elements of water which it contains, 
 while its carbon is set free. 
 
 63. The greater part of the heart- wood and bark of trees 
 is composed of woody fibre. It constitutes 50 per cent of the 
 weight of barley straw dried in the air, and about 80 per 
 cent of the weight of the dried straw of the flax plant. In 
 the root crops, however, its amount is but small, the white 
 turnip in its fresh state containing only three per cent of it, 
 but as the plants grow old its quantity increases, so as to 
 render them stringy and unfit for the table. 
 
 64. Starch. Next to woody fibre, starch is one of the 
 most common forms into which plants convert the materials 
 derived from the air. It can be readily procured and its 
 properties examined. 
 
 If we grate a potato upon a common grater placed over 
 a basin, and allow a stream of water to fall upon the grater, 
 so long as it flows through milky we perform a mechanical 
 analysis of that root. 7\.t the bottom of the basin a white 
 l)0wder is gradually deposited from the water. This powder 
 is the well-known substance Starch, which is met with in 
 greater or less quantity in every vegetable, and which under 
 different names — as arroiv root when procured from the roots 
 of a West Indian plant, sago when extracted from the pith of 
 a species of palm, and/az-ma when manufactured from pota- 
 toes, — is used for food in almost eveiy country. No matter, 
 however, from what plant or in what climate starch has been 
 produced, the chemist recognises its composition to be the 
 
 '<<^ 
 
54 LESSONS IN CHEMISTRY. 
 
 same, and is able at once to detect its presence by a property 
 which it possesses of producing a beautiful purple colour when 
 brought into contact with a solution of the metallic-looking 
 substance iodine,* which I have described as an ingredient of 
 the sea and of the plants which live in its waters. {See note^ 
 p. 48.) Like cellular tissue, starch contains no nitrogen, but 
 consists solely of carbon, and of hydrogen and oxygen united 
 in the proportions in which they exist in water. Starch, as 
 the mode in which it is procured shows, is insoluble in cold 
 water, but dissolves, as you are aware, in boiling water, pro- 
 ducing a jelly-like liquid. By the influence of several che- 
 mical agents, and also by means of a peculiar substance 
 generated in plants, starch can be made to undergo important 
 changes, which, as they are of great interest in connexion 
 with the gi'owth of plants, it will be necessary briefly to 
 consider. 
 
 66. When a portion of farina or any kind of starch is 
 placed in a flask with water and boiled, a thick jelly is pro- 
 duced, which when dried has the appearance of glue, is, like 
 the starch itself, insoluble in cold water, and is in the same 
 way coloured blue by a solution of iodine. If we make an 
 infusion of barley, and add to it the starch jelly, and keep 
 them some time together, no change is produced; the starch 
 remains undissolved ; but if the grains of barley employed in 
 making the steep have been allowed to vegetate in the field, 
 or have been made to vegetate by art, by " malting" as it is 
 termed, there is a most surprising diflference in the effect 
 produced. The starch is seen to grow gradually more liquid, 
 and in the course of a few minutes its consistence entirely 
 disappears, and it becomes as thin and transparent as water. 
 If we evaporate to dryness the transparent solution, we do 
 not obtain a jelly-like mass such as would result from evapo- 
 rating a simple solution of starch, but a yellow powder which 
 differs from it in being readily soluble in cold water. The 
 solution of this powder is not rendered blue, but of a wine- 
 red colour, by the addition of iodine, showing that the starch 
 originally contained in the liquid has undergone some singular 
 change, and in fact, that the elements which compose it are 
 no longer united in the same form. 
 
 66. This yellow powder possesses the properties of a gum, 
 
 * A solution of iodine in spirits of wine is sold by tlte apotliecarj' as 
 tincture of iodine. 
 
SUBSTANCES PEODUCED BY PLANTS. 55 
 
 and is termed Dextrin, In the vegetating barley, therefore, 
 there must exist some agent which is not to be found in the 
 immalted grain and which is capable of eflfecting this impor- 
 tant transformation. It is a truly brilliant achievement for 
 modern science to have succeeded in investigating this curious 
 subject, and to have ascertained that the agent which pro- 
 duces the change is a peculiar substance named Diastase, ricli 
 in nitrogen, and which you shall presently see performs an 
 important office in the first period of vegetable Hfe. 
 
 But science, though it can trace and regulate the changes 
 produced by this curious agent, is unable to form it from its 
 elements, but can merely employ it as developed by nature 
 in the vegetating grain. A method, however, has been dis- 
 covered, which enables us to a certain extent to imitate its 
 effects ; and as the process is of very great interest and may 
 yet become of practical importance to these countries, I will 
 briefly describe it. 
 
 67. If we place in a porcelain dish over a lamp some 
 water containing a few drops of vitriol, and when the water 
 boils add gradually to it a small quantity of starch previously 
 beaten into a paste with water, the starch, instead of becom- 
 ing a jelly, as when boiled with pure water {^5), is rendered 
 liquid, and after a few minutes' boiling, a drop of the solution, 
 taken out and touched with the solution of iodine, no longer 
 displays the blue colour which is characteristic of starch, 
 but a wine-red tinge, such as that exhibited in the solution 
 of the gum produced by the action of malt. If we continue 
 the boiling a few minutes longer, the iodine will produce no 
 change in the liquid, and if we now take the dish fi*om the 
 lamp, and add to it some powdered chalk until the acid taste 
 of the solution be destroyed, and allow the mixture to settle 
 that the compound which the chalk and the acid forms (46) 
 may subside, the clear liquid will be found perfectly sweet, 
 and crystals of sugar may be procured from it by careful 
 evaporation. 
 
 68. Starch also undergoes transformation fiom the action 
 of other agents: thus, when it is heated to a temperature 
 somewhat higher than that at which water boils, as is prac- 
 tised in the preparation of what is called British gum, it is 
 converted into dextrin ; some sugar is also produced in tlie ope- 
 ration, and even the simple exposure of starch jelly to the air 
 tor a long period has been found to produce the same changes. 
 
 E 
 
56 LESSONS IN CHEMISTRY. 
 
 69. Gum is another substance which exists in several 
 plants in considerable quantities. You are familiar with it 
 as exuded from the stems of the cheiTy, plum, and other 
 trees, and also with a kind of it sold in this country under the 
 name of gum arable, and which is procured from a plant 
 of the acacia family, a native of Africa. There are two 
 vaiieties of gum procured from plants: one, soluble in cold 
 vmter and becoming a jelly or mucilage, like gum arable; and 
 another, represented by the gum of the cherry-tree, soluble in 
 boiling but insoluble in cold tvater. Both kinds of gum, like 
 starch, dextrin, and cellular fibre, contain carbon united with 
 oxygen and hydrogen, the gases existing in the proportions 
 in which they fonn water. 
 
 70. Mucilage. There is another substance, termed muci- 
 lage, resembUng gum in its composition and several of its 
 properties, which is found in the root of the common mallow, 
 in linseed, and other oily seeds. It does not, however, like 
 gum, dissolve in boiling water, but merely swells out in bulk. 
 Like starch, it can be converted into sugar by the action of 
 vitriol. 
 
 7 1 . Sugar, the characters of which are so well known, exists 
 in the juice of several plants in great abundance, so that its 
 extraction is a valuable branch of industry. Among the 
 ])lants familiar to us m this country, the beet-root afibrds the 
 largest amount of sugar, and in France is extensively culti- 
 vated for its manufacture. It exists also in small quantity in 
 the juice of the turnip and parsnip, and in ripe fruits, and its 
 presence may be detected by the taste in the clover and young 
 corn. There are several varieties of sugar, the principal of 
 which are, cane sugar, extracted from the sugar-cane of our 
 colonies, and grape sugar, which is met with in the dried 
 raisin, in the apple and other fruits, and in honey. It is into 
 ,«rape sugar that starch and the other forms of vegetable 
 matter are converted by the action of the chemical means 
 that I have described. 
 
 72. There are also pecuhar varieties of sugar found in 
 manna, in liquorice, and in the juices of several plants, which 
 differ slightly in composition and properties from those I 
 have mentioned; but the two chief kinds, cane and gi-ape 
 sugar, contain oxygen and hydrogen united, and carbon nearly 
 in the same proportion as in starch and gum. 
 
 73. Albtoien. ^y gi'ating a potato as already described, 
 
SUBSTANCES PRODUCED BY PLANTS. 57 
 
 under a stream of water, we eftect a separation of its parts ; 
 the starch contained in it is carried through the sieve and 
 gradually deposited from the water, while in the sieve a 
 tibrous matter is retained. If we boil the clear liquid from 
 which the starch has fallen down, a froth or curdy matter 
 forms on its surface, which, from its resemblance to the coa- 
 gulated white of egg^ scientifically termed albumen, has been 
 named vegetable albumen. Though this substance exists in 
 plants in much smaller quantities than those we have lately 
 been considering, yet we find it invariably present in their 
 juices. It performs an important part in contributing to 
 the nourishment of animals, and is distinguished from starch, 
 gum, and sugar, by containing nitrogen, which is an essential 
 constituent of flesh (8), and also a small amount of sulphur 
 and phosphoinis. In all its leading chemical characters, it 
 agrees with animal albumen.* 
 
 74. Gluten. If you place some wheat-flour in a muslin 
 bag and knead it with your fingers under a stream of water, 
 so long as the water is rendered milky, you will find upon 
 opening the bag that the flour has diminished in bulk, and 
 that there remains a gi-ey, adhesive, elastic matter, which, like 
 birdlime, can be drawn into threads. This substance which 
 does not wash away is called gluten, and is found in con- 
 siderable amount in all vegetables, and especially in those 
 parts of our cultivated plants which we value for food. From 
 the milky fluid which runs through the bag starch will subside, 
 and by pouring off" the clear liquid after the deposit has taken 
 place, and boiling it, white flakes of albumen will separate. 
 The gluten of wheat consists chiefly of a substance termed 
 by Liebig vegetable fibrine, which, like albumen, approaches 
 closely to the fibre of muscle in its composition. It contains 
 about 15 per cent of nitrogen and a small amount of sulphur. 
 
 75. Vegetable Casein. When peas are bruised in a mortar 
 and the pulp then mixed with a considerable proportion of 
 water, and strained through a piece of muslin, a milky liquid, 
 from which starch is gradually deposited, passes through the 
 sieve. If, when the liquid has become clear, it be decanted and 
 boiled, no coagulation takes place as when albumen is present, 
 
 * The characteristic smell of rotten eggs is produced by the sulphur 
 contained in the albumen or white coming off united with hydrogen in 
 the form of a gas named sulphuretted hydrogen. The black stain which 
 stale eggs produce on silver spoons is also occasioned by this gas. 
 
58 LESSONS IN CHEMISTRY. 
 
 but its sui'face becomes covered with a pellicle or skin, resem- 
 bling the scum which forms on the surface of boiling milk; or, 
 if to the liquid we add a few drops of vinegar, a curd falls to 
 the bottom resembling in appearance the curd of milk, and 
 which analysis shows to be almost similar in composition. 
 The substance which exhibits these characters is named vege- 
 table casein, and sometimes legumin, from its being procured 
 from leguminous plants, that is, those which have the seeds 
 enclosed in a pod, and in which it takes the place that in 
 wheat is occupied by gluten. Like gluten and albumen, it is 
 rich in nitrogen, and also contains sulphur as an essential 
 ingredient.* 
 
 76. Diastase. We have seen that when barley sprouts, it 
 acquires certain properties which are not possessed by the 
 unmalted grain. Chemists can procure from the part of the 
 potato which is attached to the young shoot, and also from 
 generating (or sprouting) barley and wheat, a peculiar prin- 
 ciple which they have named diastase, and which cannot be 
 procured from unmalted grain or from that portion of a potato 
 distant from the shoot. This substance has not been com- 
 pletely investigated, but, like gluten, albumen, and vegetable 
 casein, is rich in nitrogen, and is supposed to be produced 
 by the transformation of some of these compounds. Its 
 effects upon starch are most remarkable, the diastase contained 
 in one pound of malted barley being sufficient to convert five 
 pounds of starch into sugar. 
 
 77. Fatty Matters, Oils, and Vegetable Acids. — In plants 
 there are to be found, in addition to the substances already 
 noticed, certain fatty matters and oils, and also a great num- 
 ber of acid principles, which, though forming usually but 
 a minute portion of their substance, frequently exercise an 
 
 * The fallowing is the composition of the bodies above descril^ed : — 
 
 Albumen. Fibrine. Casein 
 
 Vegetable. AnimaL Vegetable. Animal. Vegetable. Animal. 
 
 Carbon . 
 Hydrogen 
 Nitrogen 
 Oxygen . 
 Sulphur &c. 
 
 . 54-74 
 
 . 7-77 
 . 15-85 
 
 • 21-64 
 
 55-461 
 
 7-201 
 
 15-673 
 
 21-665 
 100.000 
 
 54-603 
 
 7.302 
 
 15.810 
 
 22-285 
 
 54-686 
 
 6-835 
 
 15.720 
 
 22-759 
 
 64-138 54.825 
 
 7-156 7 153 
 
 15-672 15-625 
 
 23-034 22-394 
 
 
 100-00 
 
 100-000 
 
 100-000 
 
 100-000 100-000 
 
SUBSTANCES PRODUCED BY PLANTS. 59^ 
 
 important influence on their value for food. Tiie fatty mat- 
 ters in plants are usually accumulated in the seeds, though 
 found in greater or less quantity in all their parts. In the 
 linseed and other, seeds which contain them in large amount, 
 the oil is separated for commercial purposes by the pressure 
 of powerful machinery; — ^the mass or cake which is left is 
 not entirely free from oil, and also contains other valuable 
 substances of the seeds, and is at present in great demand 
 for feeding cattle. Frequently, however, the fatty matters 
 exist in so minute quantities, or are retained with so much 
 force, in the cells of plants, that they cannot be abstracted by 
 simple pressure; but the chemist can remove and ascertain 
 their quantity by boiling the bruised seed in ether, in which 
 they readily dissolve. The solution, when exposed to the air, 
 allows the ether to evaporate while the oil remains behind.* 
 78. When the gluten procured by treating wheat flour as 
 described (74) is boiled in ether, we procure from it a fatty oil, 
 which is not very difierent in composition from the fat which 
 lubricates the machinery of the human body. A hundred 
 pounds of wheat yields about two pounds of this oil. The fatty 
 matters resemble starch and sugar in containing no nitrogen, 
 being formed from carbon, hydrogen, and oxygen only; they 
 
 * Composition of the cake of linseed, and of the cake of the seed of 
 the Camelina sativa, or " Gold of Pleasure," according to the analyses 
 of Professor Johnston — 
 
 English Gold 
 
 English 
 
 American 
 
 of Pleasure. 
 
 Linseed Cake. 
 
 Linseed Cake. 
 
 Water . . . .9-95 
 
 10-05 
 
 10-07 
 
 MucOage . . . 36-08 
 
 39-10 
 
 36-25 
 
 Albumen and Gluten . . 25*50 
 
 22-14 
 
 22-26 
 
 Oil ... . 12-42 
 
 11-93 
 
 12-38 
 
 Husk .... 10-16 
 
 9-53 
 
 12-69 
 
 SaUne matter (Ash; & Sand 6-89 
 
 7-25 
 
 6-35 
 
 100 100 100 
 
 The following is the produce in France, per acre, of oil and cake of 
 the plants most familiar to the Irish farmer — 
 
 Seed produced 
 
 per acre, 
 cwt. qr. lbs. 
 
 Winter Rape . . . 16 2 18 
 
 Gold of Pleasure . . 17 1 16 
 
 Flax . . . . 15 1 25 
 
 Hemp . . . 7 3 21 
 
 Summer Rape. . . 11 3 17 
 
 Total of oil 
 
 
 
 per acre. 
 
 OU 
 
 Cake 
 
 in lbs. avoir. 
 
 per cent. 
 
 per cent 
 
 641-6 
 
 33 
 
 62 
 
 545-8 
 
 27 
 
 72 
 
 385-0 
 
 22 
 
 69 
 
 2290 
 
 25 
 
 70 
 
 412-5 
 
 30 
 
 65 
 
60 LESSONS IN CHEMISTRY. 
 
 are, however, distinguished from those compounds by con- 
 taining a less amount of oxygen.* 
 
 Vegetable Acids. The sour or acid principles contained in 
 plants are numerous; some of them contain merely carbon 
 and oxygen, while others consist of these elements in union 
 with hydrogen in various proportions. In the living plant 
 these acids are united with various ingredients derived from 
 the soil, and when the plant is burned they are decomposed, 
 producing carbonic acid, and the alkaline and earthy substances 
 with which they were combined are discovered in the ash in 
 the form of carbonates. We have examples of vegetable 
 acids in the acid of vinegar (acetic acid), which exists in the 
 juice of several plants ; in the acid of apples (malic acid) in 
 the acid of the cuckoo son:el (oxalic acid), in the acid of 
 grapes (tartaric acid), and in the acid of lemons (citiic acid). 
 These compounds, however, are of so little practical importance 
 to the ordinary farmer, that it would be out of place to 
 describe their properties. 
 
 79. Such then, are the forms into which plants convert the 
 crude materials supplied to them by Nature. The great mass of 
 all vegetables, as well as of the nutritious substances formed 
 within their structure, consists, as we have seen, of carbon, 
 derived from the carbonic acid of the atmosphere. This ele- 
 ment, which the air that surrounds the growing plant is at all 
 times capable of conveying to it in unlimited quantity, simply 
 
 * The quantity of oil and fatty matter contained in our cultivated 
 plants has not, until lately, received much attention from chemists. 
 Professor Johnston, in his lectures, gives the following as the results of 
 some analyses of the flour from seven samples of wheat grown by Mr. 
 Burnett, of Glenarm, County of Antrim, at Gadgirth in Ayrshire. 
 The results obtained show, that the proportion of oil, as of the other 
 substances contained in our crops, is materially influenced by soil and 
 cultivation: — 
 
 Oil per cent. 
 
 1. From the undressed soil 1*4 
 
 2. Dressed with Guano and Wood Ash . . 1*9 
 
 3. Artificial Guano and Wood Ash . 2*2 
 
 4. Sulphated Urine and Wood Ash 2-2 
 
 5. , , Sulphate of Soda 2-0 
 
 6. Common Salt 2-7 
 
 7. Nitrate of Soda 2-3 
 
 But the proportion of oil in the flour is much less than in the entire 
 grain: thus, while a sample of grain gave Professor Johnston, in the 
 first flour, only 1^ pear cent of oil, he obtained from the bran above 3 
 per cent. 
 
SUBSTANCES PRODUCED BY PLANTS. 61 
 
 by uniting with water, or with the gases hydrogen and oxygen 
 which compose it, is capable of producing woody fibre, starch, 
 sugar, and the various oils and acids. The same elements 
 also, by uniting in dilierent proportions with nitrogen, derived 
 from the ammonia of the atmosphere, and with a small pro- 
 portion of sulphur and phosphorus taken up from the mineral 
 matters of the soil, form a class of compounds approaching 
 closely in their composition to the substances of which the 
 bodies of animals are composed. These compounds are de- 
 signed for food — are, in fact, the ready-formed materials of 
 blood and flesh. It is surely well calculated to excite admi- 
 ration when we reflect how, out of half-a-dozen of elements, 
 such a variety of important compounds is produced. If you 
 take a piece of the muscle of an animal — a piece of mutton 
 chop, for example — and examine it, you will find that it con- 
 sists chiefly of a fibrous substance. If you pour water upon 
 it, you can render it quite white — ^you will wash away the blood 
 upon which its red colour depends. Upon examining it you 
 will also find that a portion oifat is mixed up with it. If you 
 dry the flesh and burn it, you will find that, like the plant, 
 it consists of two parts — a part which disappears into the 
 air, and an incombustible ash which remains. This ash, 
 when examined by the chemist, is found to contain the very 
 same substances that we have described as composing the 
 incombustible part of plants. I have already stated that 
 the gluten, the albumen, and casein of the vegetable world 
 are almost identical with the fibre of muscle, and that the 
 fatty matters which exist in the seeds of plants (78) contain 
 the same elements, united in nearly the same proportions, as 
 the fat with which the human body is supplied to facilitate the 
 movements of our joints and muscles. Thus, in the interior 
 of the plant. Nature prepares a store of materials, which, like 
 the ready-formed wheels and screws that the watchmaker 
 has merely to put in their proper places, in constructing or 
 repairing a watch, are capable, when taken into the stomach, 
 of being at once selected and applied to -build up the frame 
 and covering of the body. The soil of the field and the car- 
 bonic acid, the wateiy vapour, and the ammonia of the air, 
 contain the elements of flesh and blood ; but these elements 
 must undergo certain changes before they can serve us for 
 food. The oflice of plants is to efiect these changes. They 
 are the agents incessantly at work extracting from the at- 
 
62 LESSONS IN CHEMISTRY. 
 
 mosphere its gases, and from the earth its minerals, for our 
 use. By the industry of the fanner, as I shall have occasion to 
 show, the amount of the above nutritive compounds may be 
 immensely increased, and, at the same time, the soil made to 
 support a greater number of plants, and consequently to afford 
 a larger amount of food for man. 
 
63 
 
 CHAPTER V. 
 
 STRUCTURE OF PLANTS AND CHANGES WHICH ACCOMPANY 
 THEIR GROWTH. 
 
 80. Having completed our survey of the raw materials with 
 which nature has stored the soil and the air, to be employed 
 by the crops of the farmer and the tribes of plants innume- 
 rable which cover the surface of the earth for the production 
 of the compounds which render them so valuable to man for 
 food and medicine, and which afford him materials for his 
 dress and dwellings, our attention is naturally directed to the 
 arrangements, the machinery by which these compounds are 
 fonned. With every seed that the farmer, depending upon 
 the scriptural promise,* commits to the soil, a new machine, 
 far more curious than the locomotive steam-engine, or the 
 most refined mechanical contrivance of the factory, is set in 
 motion. To produce this seed all the energies of the plant 
 have been exerted, it is the last and finished work of vege- 
 table life, and in its structure admirably adapted for its 
 important office. We will therefore commence with its con- 
 sideration. 
 
 81 . Leaving it to the botanist to describe the different forms 
 in which seeds are presented to us, and the numerous curious 
 contrivances by which nature protects them from injury, and 
 secures their dispersion over the earth, in some cases pro- 
 viding them with silky wings to float through the air, and in 
 others enveloping them in dense flinty coverings or canoe-like 
 cases, which enable them to glide unmjured over the waters 
 of seas and rivers, we will briefly inquu*e into the changes 
 which are observed to accompany the development of the 
 young plant. 
 
 82. You know that when in a favourable season you place 
 the seeds of any of your plants in the soil of the field, in the 
 course of a few days they undergo the same changes that we 
 observe when barley is being converted into the " malt" of 
 the brewer. The seed softens and swells, and there are 
 pushed out two portions of its inner substance, which gra- 
 dually increase in size and extend themselves in opposite 
 
 * " While the earth remaineth, seed-time and harvest, and cold and 
 lieat, aud summer and winter, and day and night, shall not cease." 
 
64 LESSONS IN CHE3IISTRY. 
 
 directions. One of these is to become the root, and the other 
 the stem of the future plant. 
 
 83. This is the beginning of the work and in the fir.^t 
 stage the ingredients of the soil in which it is placed contri- 
 bute nothing to its growth. In the seed itself there is laid 
 up a supply of all the earthy matters which are for some time 
 required. Daily, however, the young plant increases in size, 
 its colour as it approaches the surface becomes of a greener 
 hue, the root pierces deeper into the soil and minute hair-hke 
 fibres branch off from it, leaves covered on their surface with 
 innumerable pores or mouths unfold themselves on the stem, 
 and it now begins to condense within its structure the 
 gases with which the air surrounds it, and to convert them 
 into wood, starch, and the various compounds which we 
 lately described. Next the flower comes, and following it 
 the fruit and seed, and then in the commonly cultivated 
 annual* crops the work which the plant was produced to ac- 
 complish being finished, the wheels cease to go on, and neither 
 sun nor soil can stimulate them to new motions. The mature 
 seeds, if not gathered by the husbandman, are deposited in 
 the earth or dispersed by the winds. The plant withers and 
 dies, and the dead matter undergoes a series of changes by 
 which it restores to the soil and the atmosphere the materials 
 which, for a time, had been abstracted by the living vegetable 
 and confined within its substance, f 
 
 84. As it will be required frequently to refer to the offices 
 performed by the organs of plants, it mil be necessary briefly 
 to describe their structure. 
 
 Every farmer is familiar with the parts of which a tree 
 consists, he knows that a root binds it firmly to the soil, that 
 a stem covered with a hark rises up into the air, and that 
 
 ' Annual plants are those which ripen and die in tlie course of one 
 year. Biennial plants are those which, like the carrot, produce leaves 
 the first year, and in the second ripen their seeds and die. Perennial 
 plants are those which like trees live for a number of years. 
 
 f Seeds may be kept for a considerable time uninjured, but the diiFerent 
 species vary very much in this respect; thus, wheat has germinated 
 after 100 years (Pliny), and rye after 140 years (Home), while the 
 seeds of coffee cannot be kept any time without risk. Every year the 
 ' loss to the farmer from seeds unsound, from bad preservation and other 
 causes, is enormous; and, when we take into account the impositions 
 practised by unprincipled dealers, we may fairly assume, that on the 
 average, more than one half of the seeds sown in this country are lost. 
 
STRUCTURE AND GROWTH OF PLANTS. 65 
 
 j;Teen leaves are hung around it upon numerous branches as 
 if to seize the winds that pass over them. 
 
 85. The stem. — When the trunk of a tree which has been 
 cut across by the carpenter, is examined, it is found to consist 
 of a number of layers or rings embracing each other, and en- 
 closing a central mass termed the pith. The hark foims the 
 (.'xterior portion of the stem, and is capable of being divided 
 into several distinct layers, the outer of these layers which 
 has been compared to the thin membrane (cuticle) that covers 
 the human body, and which rises into a bladder when the skin 
 is blistered, is termed the epidermis. In plants having hollow 
 stems like the gi-asses, the epidermis is a part of great impor- 
 tance, and is found to contain a large amount of silica, (50) 
 forming a glassy network which gives strength to their struc- 
 ture. In some plants there is so much siliceous matter de- 
 posited in the epidermis, that when rubbed together they pro- 
 duce sparks. 
 
 86. Within the layers which form the bark, we observe a 
 series of rings composing the wood, the outer of these layers 
 are soft and spongy, and are the latest formed portions of the 
 stem. When the wood and inner layers of the bark are ex- 
 amined by a microscope they are observed to be composed of 
 hollow tubes or vessels, which extend from the root to the 
 branches, while the central spongy mass, the pith, consists 
 chiefly of cellular fibre, (60) traversed by tubes which are 
 arranged in a horizontal direction. In old forest-trees the 
 pith is found to have entirely disappeared, and to be replaced 
 by firm wood, and in many of our rapidly growing cultivated 
 crops, as in the carrot and parsnip, it is torn up by the gi'owth 
 of the plant, leaving a hollow stem. 
 
 87. Though the stems of the greater number of trees 
 possess the regularity of structure just described, yet many of 
 our most familiar plants, as the grasses, exhibit an entirely 
 difi^erent arrangement of parts. This diflference of structure 
 has led Botanists to divide our cultivated plants and forest- 
 trees into two great classes, which they have designated by 
 terms derived from the Greek language, one of those classes 
 comprehends all those plants in which, as in that lately de- 
 scribed, (85) the exterior layers of the woody matter of the stem 
 are the latest formed,* the plant growing, as it were, by the 
 
 • The plants of this dirision are termed exogenous, from growing at 
 tho outside. 
 
^ LESSONS m CHEMISTRY. 
 
 production of new layers external to those previously formed. 
 In the other division they have arranged all those plants in 
 which the growth takes place by the formation of new wood 
 at the centre.* If you cut a stalk of young grass across you 
 will have an opportunity of examining the structure of a plant 
 of the second of these divisions. When it is viewed with the 
 microscope, it appears to consist of a mass of cellular fibre, 
 like the pith through which a number of tubes extend in a 
 vertical direction. 
 
 88. For the sake of clearness, we will, however, confine 
 our attention to the structure of the plants of the first division, 
 which includes the greater number of forest-trees, and among 
 our crops the potato, the turnip, the carrot, the bean,' and 
 the pea. 
 
 89. The branches are simply prolongations of the stem, and 
 like it, consist of bark, pith, and woody matter. 
 
 90. The leaves exhibit almost every variety of form and 
 beauty, and are of the greatest importance to the growth of 
 plants. They consist internally of a fine network of branching 
 vessels, which may be regarded as extensions of the vertical 
 tubes of which the wood of the stem is composed, while the 
 green exterior part is traversed by minute vessels which spread 
 themselves on the surface of the leaf, and communicate with 
 the vessels which run along the inner layers of the bark. The 
 entire leaf is covered with a delicate membrane, which is an 
 extension of the epidermis, and is perforated with minute 
 holes or pores.f These little openings are especially numerous 
 on the side of the leaf which is turned towards the ground. 
 
 91. The root, like the branches, is considered to be merely 
 a continuation of the stem of the plant, and in its structure 
 there is considerable resemblance; but as it descends into 
 the earth its texture alters very much, it gi'ows soft and 
 spongy, and loses the green colour which is displayed by the 
 parts above the surface. It sends oiF into the soil in all 
 directions minute hairhke branches^ which the microscope 
 
 * Such plants are termed endogenous from growing at the centre, and 
 hare but one lobe in the seed, while in the exogenous plants, as in the 
 common bean, the seed is capable of being divided into two or more 
 lobes; the grasses, among which botanists include wheat, barley, oats, 
 rye, rice, &c., belong to the endogenous plants. 
 
 f Stomates. | Radicles. 
 
STRUCTURE AND GROWTH OF PLANTS. 67 
 
 shows to consist of delicate tubes terminating in a porous 
 sponge-like mass of cellular fibre. The pores discovered in 
 the spongy extremities of the root-branches are so exceed- 
 ingly minute, that it is impossible for solid matters, no matter 
 how finely divided, to pass through them. It is, however, 
 by these pores that the living plant is supplied with some of 
 the materials most essential to its existence, and the power 
 which the spongy extremities of the root possess of sucking 
 in the moisture of the soil and the matters dissolved in it, 
 and of conveying it to every part of its structure, is one of 
 the most remarkable phenomena which the study of plants 
 presents. You will now perceive the immense importance 
 of a proper supply of water to vegetable life; dissolved in that 
 useful liquid, the gases, carbonic acid, oxygen, and ammonia, 
 as well as the earthy and saline matters of the soil, can readily 
 be taken up by the plant and employed in its development. 
 
 92. Growth of Plants. After this survey of the parts 
 which constitute the machinery of the plant, let us consider 
 the nature of the changes by which it can within its structure 
 convert the simple materials which it imbibes into the various 
 interesting compounds lately described. 
 
 Development of the seed. As has already been stated 
 (81), a seed when placed in the ground is observed in the 
 course of a short tune to undergo a remarkable alteration, 
 like what is produced by malting barley. It swells up and 
 acquires a sweet taste, and from its interior two portions 
 extend themselves, which gradually increase in size and 
 become the root and stem of the future plant. 
 
 93. In the first stage of its growth the young plant lives 
 at the expense of the matters stored within the seed ; water 
 alone of the materials existing in the atmosphere and the 
 soil contributmg to its development ; and instead of accumu- 
 lating food from the air which penetrates into the soil, a 
 portion of the carbon of the seed enters into combination with 
 the oxygen of the atmosphere and is given off as carbonic 
 acid. In the seed there is laid up a store of starch and 
 gluten, but it will be recollected, that these compounds are 
 insoluble in water (64, 74) and could not therefore enter 
 into the vessels of the young plant: but under the influence 
 of a certain temperature and moisture the gluten undergoes 
 decomposition, and the curious substance diastase, (76) which 
 in tho hands of the brewer converts the insoluble stai'ch o( 
 
 F 
 
68 LESSONS IN CHEMISTRY. 
 
 the grain into the sugar of the wort, is produced. By means 
 of this substance, which is discovered just at the point where 
 the vessels extend from the seed to the sprout, the starch is 
 dissolved, and, accompanied by the transformed gluten, made 
 to contribute under the form of dextrin and sugar to the 
 production of cellular fibre, of which the earliest formed parts 
 of the young vegetable are composed. 
 
 94. For the healthy germination of the seed, as the first 
 stage of vegetable growth is usually termed, there are certain 
 essential conditions. 
 
 Moisture. Water is necessary in all the curious chemical 
 changes by which the transformations lately described are 
 efiected. It is well known to the farmer that by steeping 
 hard seeds in water for some time previous to sowing he will 
 facilitate their growth. A perfectly dry seed will remain 
 for years without exhibiting any sign of life, but if placed in 
 a damp situation its inactivity disappears and it begins to 
 germinate. An excess of water in the soil is, however, 
 injurious to healthy vegetation, though some seeds sprout 
 and flourish in situations where most of our cultivated grains 
 would rot or produce an inferior crop. 
 
 95. Air. Without a proper supply of air no seed can ger- 
 mmate. When a piece of charcoal is burned in a vessel of 
 oxygen gas, it is found that the bulk of the gas in the vessel 
 is not diminished, but that its properties have been changed, 
 a quantity of carbonic acid gas is formed equal in volume 
 to the oxygen which has disappeared. A precisely similar 
 change is effected by causing seeds to germinate in a receiver 
 containing common air or pure oxygen. In both cases, 
 oxygen gas disappears, and nearly an equal bulk of carbonic 
 acid is produced at the expense of the carbonaceous matters 
 (starch, &c.) of the seed.* Buried too deep in the soil where 
 the oxygen of the atmosphere cannot reach them, seeds 
 remain for centuries unchanged. 
 
 . 96. Heat. A proper temperature is no less necessary for 
 the development of the seed than air and moisture. Below 
 the temperature at which water freezes, germination does not 
 take place. 
 
 In Europe and North America, the corn crops germinate 
 at temperatures from 43° to 48° (Boussingault), and merely 
 
 * Some acetic acid (78) is also produced in germination; thus, ger- 
 minating seeds placed upon blue test paper are found to colour it red. 
 
STRUCTURE AND GROWTH OF PLANTS. 69 
 
 iive through the cold of wmter withont makhig progress, 
 until the wann sim of spring gives a genial lieat to the soil. 
 When seeds are too deeply covered, not only is the free 
 access of ah- prevented, but they are not sufficiently warmed 
 by the sun. In undrained soils the seed immersed in stag- 
 nant water docs not receive a proper supply of air and that 
 increase of temperature which we have seen facilitates the 
 transformation of starch into grape sugar and other com- 
 pounds (68) is prevented, so that the plant which springs 
 up is insufficiently nourished and seldom comes to full per- 
 fection. You will now be enabled to understand how in the 
 thorough-drained field not only earlier but more luxuriant 
 crops may be produced, and that by carefully pulverising the 
 soil so as to allow the air to pass fii'eely through it, we will 
 materially hasten vegetation. 
 
 97. But, though it is injurious to bury seeds too deep in 
 the soil, it will not do to leave them uncovered on its sur- 
 face — not only does a light covering of porous earth protect 
 them from sudden changes of temperature which might destroy 
 them, but it prevents the action of light, which is found to 
 interfere with those chemical changes by which oxygen gas is 
 absorbed and a portion of the carbon of the seed converted 
 into carbonic acid (95). 
 
 98. (h'owth of the plant — Let us suppose that all the con- 
 ditions required for the germination of the seed have been 
 present, and that the machinery of the young plant thus set 
 in motion has produced a root, furnished with its spongelike 
 fibres stretching out into the surrounding soil, that a stem 
 rises up into the air, and that waving leaves, agitated by every 
 breeze, are hung around it with their pores or mouths pre- 
 pared for the reception of food, and that it is capable of deriving 
 the materials for its increase from all the sources described. 
 How are these materials made to contribute to its develop- 
 ment? 
 
 99. No sooner is the first true leaf of the young plant 
 produced, than the mode of its growth undergoes a complete 
 change, and a new circle of chemical operations begins. It 
 no longer requires the matters contained in the seed, but seeks 
 its nourishment in the soil in which it is placed and in the 
 air that surrounds it. At this period the curious principle 
 diastase is found to haye disappeared, its assistance bemg no 
 more wanted. 
 
70 LESSONS IN CHEMISTRY. 
 
 100. The little openings or pores, by which the membrane 
 that covers the leaves is perforated, and the spongy ex- 
 tremities of the rootlets are the channels through which, in 
 the form of carbonic acid, ammonia, and water, the growing 
 plant is supplied with the carbon, nitrogen, hydrogen, and 
 oxygen, which compose the bulk of its structure, and in the 
 water sucked up from the soil it also receives the saline and 
 earthly substances that we discover in its ashes (42). When 
 our cultivated crops, at this stage of their growth, find in the 
 soil an abundant supply of the peculiar matters which they 
 require, they rapidly increase in size, and produce more 
 numerous leaves and rootlets, and are thus enabled to appro- 
 priate more of the food which the air affords, but when these 
 matters are not present in sufficient quantity in the soil, or 
 are locked up in an insoluble form, it is impossible for them to 
 come to perfection. 
 
 101. The gaseous and inorganic matters which, dissolved in 
 water, the roots pump up from the soil, are conveyed by means 
 of the vertical tubes, which compose the wood of the stem 
 (86), to the leaves, and being there diffused through the net- 
 work of branching vessels that cover the surface of the leaf, the 
 solution (the sap) experiences an important chemical change, 
 and also loses a considerable amount of water by evaporation. 
 Thus altered, the sap descends by the vessels which run 
 along the under smface of the leaf to the inner bark, where 
 it contributes to the development of the plant. The quan- 
 tity of water which is separated from the leaves of a plant 
 by evaporation, must powerfully influence its growth, for iii 
 proportion as it escapes into the air, more water will be 
 sucked up by the roots from the soil, and thus new supplies 
 of the dissolved gases and inorganic matters be conveyed to 
 the leaves to be converted into food. When from a continu- 
 ance of dry weather the soil becomes incapable of supplying 
 the water evaporated, the leaves are seen to shrivel up, and 
 the growth of the plant is retarded. Dr. Hales calculated 
 that the water converted into vapour by the leaves of a plant, 
 was seventeen times more than that given off in perspiration 
 from the human body. He found by experiment, that a sun- 
 flower lost one pound four ounces and a cabbage one pound 
 three ounces a day by evaporation. 
 
 102. It is in the leaves that the sap undergoes those 
 changes in its composition by which it becomes capable of 
 
SUBSTANCES PRODUCED BY PLANTS. 71 
 
 forming cellular fibre, and the various compounds that render 
 plants " the sustenance and the banquet of animated nature!" 
 The agent by which these alterations are effected is light. 
 
 103. When some fresh leaves of a healthy plant are placed 
 in a tumbler filled with water, and inverted in a saucer also 
 filled with water, and exposed to the sunshine, in a short 
 time bubbles of air are observed to ascend to the bottom of 
 the tumbler. This air when examined is found to possess 
 the properties which belong to pure oxygen gas (7), and is 
 beheved to be produced by the decomposition of carbonic 
 acid dissolved in the water (27)^ ^or when boiled water is 
 employed in the experiment no oxygen is separated from 
 the leaves of the plant. It is only, however, in the pre- 
 sence of light that the leaves of plants possess the power of 
 decomposing carbonic acid (97). During the night season 
 their roots continue to absorb the moisture from the soil and 
 to evaporate it from then* leaves, but the carbonic acid which 
 they receive escapes without undergoing decomposition ; in- 
 stead of giving off oxygen they condense it in their structure, 
 though numerous experiments prove that the amount of that 
 gas which vegetables liberate during the day considerably 
 exceeds that which they abstract from the air at night. The 
 following beautiful experiment, tried by the illustrious Davy, 
 will show you the effect which plants exercise upon the air 
 that smTounds theuL A piece of turf four inches square, 
 clothed with grass, was placed in a porcelain dish which swam 
 on the surface of a larger basin containing water in which 
 carbonic acid was dissolved; over the dish containing the 
 grass a glass vessel of the capacity of 230 cubic inches was 
 inverted, so as to cut off all communication with the external 
 air. The apparatus was exposed in an open place and so 
 arranged that fresh water containing carbonic acid could be 
 supplied occasionally to the water in the larger dish. After 
 eight days it was found that the air in the glass vessel had 
 increased by at least 30 cubic inches of gas which, when 
 examined, was found to contain four per cent more oxygen 
 than the air of the atmosphere. 
 
 105. It will be recollected that it was stated that the 
 poisonous gas, carbonic acid, is from innumerable sources 
 continually escaping into the atmosphere (26), The air that 
 we exhale from our lungs contains a quantity of that gas, 
 which, if existing in the same proportion in the air that we 
 
 f2 
 
72 LESSONS IN CHEMISTRY. 
 
 inhale, would soon prove fatal to animal life. We know also, 
 that by the combustion of the fuel in our cities, and during 
 the decay of animal and vegetable matters, enormous quan- 
 tities of carbonic acid are produced at the expense of the 
 life-supporting oxygen. Yet the atmosphere maintains its 
 composition unchanged (26), and analysis has proved that the 
 wonderful mixture of gases that we draw into our lungs does 
 not contain less oxygen or more carbonic acid than that 
 which was inhaled by our ancestors many thousand years 
 ago. 
 
 106. The experiments above described will at once suggest 
 to you the means by which nature prevents an undue accu- 
 mulation of carbonic acid in the atmosphere. By a beautiful 
 arrangement the existence of the vegetable tribes has been 
 made to depend upon the decomposition of that gas, noxious 
 to man hut essential to their growth, and every green leaf 
 which plants hang out into the au' is provided with an appa- 
 ratus by which it is decomposed, and an equal bulk (103) 
 of pure oxygen liberated to serve for the respu-atioa of 
 animals. 
 
 107. The diffused light of day is sufficient to enable plants 
 to decompose carbonic acid and appropriate the carbon which 
 it contains, but in the bright sunshine their growth proceeds 
 with greater vigour, and the more plants are exposed to the 
 sun the richer are they found to become in all those com- 
 pounds in which that element abounds. It is only in the 
 presence of the light that the leaf acquires its beautiful green 
 colour, or fonns woody fibre (61). In the deep mine and 
 dark cellar, plants grow, but exhibit a sickly blanched appear- 
 ance, and produce compounds of a different kind from those 
 which we discover in them in their healthy condition.* 
 
 From what has been stated respecting the composition of 
 starch, cellular fibre, and the other compounds of which the 
 bulk of our crops consists, you can readily understand how by 
 the decomposition of the carbonic acid and water which the 
 sap contains, all the materials which their formation requires 
 may be procured by the growmg plant. The changes which 
 the curious principle diastase is capable of effecting in the 
 hands of the chemist, enables us to conceive how in one part 
 
 * Thus, in the blanched shoots of the potato a poisonous principle 
 called eolanin, is discovered which, when the plant becomes green by 
 exposure to the light, disappears. 
 
SUBSTANCES PRODUCED BY PLANTS. 73 
 
 of the plant the same elements may exist in the form of a 
 sweet and soluble sugar, and in another of a tasteless and 
 insoluble starch. The changes by which albumen, casein, 
 and the various compounds containing nitrogen, may be 
 produced from the food which the plant receives, are not so 
 easily understood, and their explanation would require details 
 which, however interesting to the scientific agriculturalist, 
 would be unsuitable in an elementary work. In another 
 place I shall have occasion to allude to the influence which 
 it has been found that an artificial supply of substances, rich 
 in nitrogen, exercises on the production of these valuable 
 compounds by the crops that you cultivate. 
 
PART II 
 
CHAPTER VI. 
 
 THE SOIL ITS FORMATION AND COMPOSITION. 
 
 108. We have for so far been occupied with the con- 
 sideration of the nature of the raw materials which exist in 
 the air and the earth for the development of the vegetable 
 tribes, and of the peculiar forms so important to man which 
 they are made to assume. It will be interesting and useful, 
 now that we have finished this inquiry, to direct our attention 
 to the soil, that great storehouse, from which plants procure 
 the earths, the alkahes, and the metallic compounds which are 
 invariably found to enter into their structure, forming their 
 skeleton and giving them strength and fiimness. 
 
 1 09. By the term soil is understood that layer of earth 
 which the farmer ploughs and cultivates, and which gives 
 support to his crops. Its colour and appearance vary very 
 much. It occurs as the rich black mould of the garden, the 
 turfy soil of the bog, the heavy red clay, or light-coloured 
 calcareous covering. Its depth also varies from a few inches, 
 as where it covers the clay-slate rocks of Down and Mona- 
 ghan, to many feet, as in the deep sandy and alluvial beds 
 of earth which constitute the arable land in many parts of 
 Ireland. 
 
 110. When we examine the soil of a cultivated field 
 minutely, it is found to consist of various proportions of sand, 
 gravel, and dust, mixed with decaying remams derived from 
 the roots and leaves of plants that have grown upon it, and 
 the bodies of worms and insects that have lived in it. When 
 we penetrate below these we find a layer of earthy materials, 
 broken pieces of rock, and hard clay, containing fewer traces 
 of animal or vegetable matter. This is what is termed the siib- 
 soil, and beneath this everywhere at varying depths is to be 
 found a solid floor, composed of that kind of rock which pre- 
 vails in the district. In one place we will find it consisting 
 of a blue or white limestone, in another, of the black basalt, 
 and in other localities, of the red sandstone or grey slate. 
 There was a time when no soil covered the hard rock, and 
 
78 LESSONS IN CHEMISTRY. 
 
 its naked surface exhibited no trace of vegetable life. But 
 every one must have observed how the surface of the rocks 
 of a country gradually crumbles into powder, which, of differ- 
 ent degrees of fineness, accumulates in the sheltered hollows, 
 or is washed down upon the plains.* 
 
 1 1 1 . In nature everything is subject to that change of form 
 j which we designate decay. The period at which this takes 
 / place is different for different forms of matter, but the differ- 
 i ence is merely one of time. The flinty rock, the hardest 
 
 ■ metal, the densest wood, gradually change their forms. The 
 , great agents in producing these changes are the gases which 
 / exist in the atmosphere, and which, dissolved in the water 
 \^ that falls from the clouds penetrate into the earth and rest 
 \ upon the surface of our buildings and the face of the rocks 
 I in our fields. By far the most energetic of these gases is 
 ( carbonic acid, which penetrates into the crevices with the 
 rain, and enables it to dissolve the lime, magnesia, and other 
 substances of which the rocks are composed; these are gra- 
 dually washed out, the cohesion of the undissolved portions 
 *' being destroyed, and are easily carried away by the storm 
 \ and rains and deposited upon the fields. 
 
 112. The inferior orders of plants assist in producing these 
 changes. They are pioneers of vegetation, employed by 
 nature in preparing a store of materials for those plants 
 required as food by man. Thus, no sooner does the rain 
 
 * The rapidity with which a rock crumbles to powder by the influence 
 of the atmosphere depends upon its density and power of absorbing 
 moisture. In relation to this subject, I may here give some interesting 
 examinations of Irish rocks, made by Mr. "Wilkinson, architect to the 
 Poor Law Commission. According to his experiments, 
 
 The chalk of Antrim weighs, per cubic foot, 160 lbs. and absorbs 3 
 
 lbs. of water. 
 Shaly Calp weighs, per cubic foot, 160 lbs. and absorbs from 1 to 
 
 4 lbs. of water. 
 The average weight of Sandstone, per cubic foot, is 145 lbs. and it 
 
 absorbs 1 to 6 J lbs. of water. 
 Some Sandstones absorb scarcely any water. 
 The average weight of Granite, per cubic foot, is 170 lbs. 
 The Granite, of Glenties in Donegall, absorbs 4 lbs. of water, and 
 
 that of Newry and Kingstown, ^ lb. per~cubic foot. 
 The average weight of Basalt, per cubic foot, is 178 lbs. and it 
 
 absorbs less than ^ lb. of water, per cubic foot. 
 The average weight of Clay Roofing Slate, per cubic foot, is 177 lbs. 
 
 it absorbs less than ^ lb. of water. 
 
THE SOIL. — TTS FORMATION AND COMPOSITION. TD 
 
 and its gases destroy the smooth surface of the rock and pro- 
 duce hollows, then the seeds of lichens and mosses which 
 are floating about in the air, adhere to it, grow and in- 
 crease, appropriating its materials and then die, giving it a 
 covering of organic matter.* By then* decay also, carbonic 
 acid is generated, which contributes to accelerate the decom- 
 position of the rock, and thus a soil is gi'adually produced. 
 
 113. In countries like Egypt, in which the air is dry and 
 rain is almost unknown, decay does not proceed with such rapid 
 steps as under our moist and changeable atmosphere. The 
 surfaces of monuments in Egypt remain scarcely touched by 
 the passing wings of time, while with us, all the massive 
 buildings erected by the piety or ambition of our forefathers 
 have been swept over as by a whirlwind. 
 
 1 1 4. The rapidity with which rocks wear and crumble 
 depends in a great degree upon their composition ; while the 
 cinders of lava slowly fall into powder, the decay of granite 
 and clay-slate proceeds more rapidly, and sandstone and basalt 
 are still more quickly reduced to dust.* Darwin, in his in- 
 teresting nan*ative of the voyages of the "Adventm*e and 
 Beagle," gives a sketch of the vegetation of some of the 
 coral islands in the Pacific Ocean, which shows the manner 
 in which these singular- formations receive their covering of 
 plants. " The cocoa-nut tree," he says, " at the first glance, 
 seems to compose the whole wood; there are however six 
 other kinds, one of these grows to a veiy large size, but 
 from the extreme softness of its wood is useless ; another sort 
 affords excellent timber for ship-building. Besides the trees 
 the number of plants is exceedingly limited, and consists 
 of insignificant weeds. In my collection, which includes, I 
 believe, nearly the perfect Flora, there are twenty species 
 without reckoning a moss, lichen, and fungus. To this number 
 two trees must be added, one of which was not in flower, 
 and the other I only heard of. The other is a solitary tree 
 of its kind in the whole group, and grows near the beach 
 where without doubt the one seed was thrown up by the 
 
 • I have closely watched the progress of decay in some of our clay- 
 slate rocks, and the powerful effects in their destruction produced by 
 the inrtuence of plants. One of those which I have most commonly 
 observed is the wild sorrel, Humex acetosella, the roots of which I have 
 found forcing themselves for a great length beween the layers of the 
 rock, and in their progress loosening and finally tearing them asunder. 
 The inferior orders of animals also assist in the work. 
 
 O 
 
80 LESSONS m CHEMISTRY. 
 
 waves. I do not include in the above list the sngar-cane," 
 banana, some other vegetables, fruit-trees, and imported 
 grasses. As these islands consist entirely of coral, and at 
 one time probably existed as a mere water-washed reef, all 
 the productions now living here must have been transported 
 by the waves of the sea. In accordance to this the flora has 
 quite the character of a refuge for the destitute : Professor 
 Henslow informs us, that of twenty species nineteen belong 
 to different genera, and these again to no less than sixteen 
 orders!" 
 
 115. In the character and appearance of the soils and sub- 
 soils of every country there are certain striking differences 
 which immediately attract attention. What we have just 
 stated of the mode in which the layers of earth that compose 
 our fields have been produced will at once account for this 
 dissimilarity. It is evident that when the soil has been formed 
 by the crumbling down of a granite rock, it must differ con- 
 siderably in character from that which has been produced by 
 the decay of slate or limestone. When we take a quantity of 
 the soil of a field and expose it to heat in a spoon or any con- 
 venient vessel, we find that, like a plant, it blackens in colour, 
 that as we continue the heat the black portion disappears, 
 and there is left a quantity of fixed incombustible matter. 
 The weight of this incombustible part differs in different 
 soils, in some amounting to 98 per cent of the whole weight, 
 in others forming a considerably smaller proportion. The 
 part that burns and vanishes, usually termed the organic 
 portion, consists of the four elementary substances — carbon, 
 oxygen, hydrogen, and nitrogen — derived either from the 
 vegetables and animals that have lived and died upon the 
 soil, or that have been added to it in manure by the farmer, 
 while the incombustible matter is composed of the mineral 
 substances of the rocks, by the decay of which it had been 
 produced. This mineral portion, no matter from what kind 
 of rock derived, is invariably found to consist chiefly of three 
 substances, Silica, Lime, and a peculiar earth which we have 
 not yet described, termed Alumina. 
 
 116. Alumina. Like lime and magnesia, alumina is a 
 compound of oxygen with a metal. It is a chief ingredient 
 of alum, and also of slate and pipe-clay, and exists pm'e in the 
 sapphire, ruby, and some other rare minerals. It may be pro- 
 cured by adding to a solution of the common alum of the 
 
SOIL. — ITS FORMATION AND COMPOSITION. 8 1 
 
 shops some carbonate of soda (44); a white insoluble 
 gelatinous looking deposit is produced. When this sub- 
 stance, which is alumina^ is collected on a cloth and dried, 
 it becomes a fine white powder, which when mixed with 
 water, forms a tenacious mass which can be moulded into 
 shapes, and it is upon its presence that porcelain, tiles, 
 and brick clays depend for their useful properties. It is 
 never found in a separate state in the soil. The substance 
 which is termed clay by the farmers is composed of alumina 
 chemically combined with silica (50) and a small amount of 
 oxide of iron ; pure porcelain clay, such as is produced by 
 the disintegration or decay of the granite of Mourne, usually 
 consists of about 42 parts of alumina, and 58 of silica. 
 
 117. Though alumina is an invariable ingredient of soils, 
 yet it is not regarded as directly contributing to the nourish- 
 ment of plants. The incombustible part of the soil is therefore 
 distinguished from the ash of the plant by the presence of 
 this substance. Its presence in the soil communicates to it 
 tenacity and the property of retaining moisture; and Liebig 
 is of opinion that by possessing the power of absorbing 
 ammonia from the atmosphere it contributes to fertility. 
 
 118. It has already been stated that the differences which 
 exist in the qualities of the soils of a country depend in a 
 great degree upon the nature of the rocks from which they 
 are derived. It will, therefore, be useful to make you ac- 
 quainted with the composition of the rocks from which the 
 arable soil of this country is derived. 
 
 By examining a geological map of Ireland, that of Grifiith 
 for example, it will be found that different districts are dis- 
 tinguished by certain marks or colours according to the kind 
 of rock of which they are composed. Looking at the shading 
 (blue) which denotes the limestone formation, it will be per- 
 ceived what an immense extent it occupies, extending east 
 and west, from Dublin to Galway, a distance of 120 miles; 
 and north and south measuring 150 miles, and seldom in its 
 course ribing more than 300 feet above the level of the sea. 
 Next in importance, will be observed the clay-slate formation, 
 which in the north occupies so much of the counties of 
 Down, Louth, Monaghan, Longford, and Armagh, and in the 
 south constitutes the prevaihng rock of Wexford, Waterford, 
 Cork, and Kerry. Marked by shades of a different kind, 
 {i-al) and interposed between the limestone and the coast, 
 
82 LESSONS IN CHEMISTRY. 
 
 will be traced the boundaries of the large portion of the 
 island which the granite covers, rising on the coast in 
 northern Down into the graceful tops of the Moume moun- 
 tains, and composing the chief mountain ranges in Louth 
 and Armagh; still farther north forming the uncultivated 
 uplands of Donegal ; running again more than sixty miles 
 south-west of Dublin, and on the far west coast of the bay 
 of Galway, opposing a rocky barrier to the Atlantic. In 
 the north, particularly in Antrim, we find several rocks 
 basalt, white-chalk limestone, green sand, &c. of a different 
 kind from those which I have just mentioned, and which 
 give that portion of the island its peculiar character. 
 
 1 1 9. When we examine the composition of the various rocks 
 which exist in this and in other countiies, we find that they 
 are composed of the same materials which analysis discovers 
 in the soil. The study of the rocks of the country is there- 
 fore of interest to the farmer, and the character of its soils 
 may in a general way be predicted from an examination of 
 \ a map oa which its prevailing rocks are represented. The 
 ' crumbling of a trap rock we may infer will afford a rich 
 loam, like what is found in many parts of Antrim, while the 
 granite rocks, especially if much elevated or exposed, will 
 ', yield a poor and unproductive soil. Frequently, however, 
 , the soil of a district differs exceedingly in composition from 
 the rock upon which it rests, and consists of materials carried 
 by floods of water or other causes from rocks at a con- 
 . siderable distance. The rich soils which gave the deltas of 
 Egypt their ancient renown, have been derived from the 
 mud earned down by the waters of the Mle, and the fields 
 (polders) of the Dutch fanners, are formed from the earthy 
 materials washed from the plains and mountains of Germany 
 by the waters of the Rhine, and which the industry of that 
 people, by means of dykes have preserved from the action 
 of the sea. The Rhine, we are told, brings with it 400 
 tons of solid matter daily. In many districts in Ireland, the 
 soil is composed of transported materials consisting of clay 
 and rolled limestone, and some of these deposits are of a 
 remarkably productive character. It would be impossible, 
 without entering into such details as would be out of place in 
 this work, to describe intelligibly all the vaiieties of rock 
 which occur in Ireland. It will however serve to extend 
 your knowledge of the composition of soils, to give a short 
 
SOIL. ^ITS FORMATION AND COMPOSITION. 
 
 83 
 
 acconut of tho leading formations. I shall commence witli 
 the consideration of the granitic rocks. 
 
 1 20. .iiE^^jiTE^as we have seen, covers a large space in this 
 country; it composes also nearly the whole of Scotland, north 
 of the Grampians. It contains nearly all the ingredients which 
 plants require, but some of them in exceedingly small quan- 
 tity. It is mnTjTOSP.d of thrpft minerals, quartz. 
 feldspar \ and oq^sioftayj in some of the mountains described 
 as granite, a mineral named ho rnblende, takes the plage of 
 mica, which, as it possesses considerable difference of composi- 1 
 tion, must materially influence the character of the soil 
 derived from this rock. Mica, feldspar, and hornblende pos- 
 sess the following composition in the hundred parts. 
 
 Mica. Feldspar. Hornblende. 
 
 Silica 
 
 . 46-10 
 
 66'd 
 
 45-69 
 
 Alumina 
 
 31-60 
 
 17-8 
 
 12-18 
 
 Potash and Soda . 
 
 . 8-39 
 
 16-3 
 
 trace. 
 
 Lime . . . . 
 
 _: 
 
 trace. 
 
 13-83 
 
 Magnesia 
 
 . 
 
 do. 
 
 18-79 
 
 Oxide of Iron . 
 
 8-65 
 
 do. 
 
 7-32 
 
 Oxide of Manganese 
 
 . 1-40 
 
 do. 
 
 0-22* 
 
 121. From the variety of composition which granite ex- 
 hibits, the character of its soils may be expected to vary. 
 Though in the North of Scotland and in the West of Ireland 
 granite soils being usually elevated, are regarded as most 
 unproductive, yet industry can render them capable of yielding 
 food, for on the lofty summits of the Wicklow mountains, 
 1600 feet above the level of the sea, splendid crops of 
 turnips and flax are produced. The deficient ingredients 
 in granite are phosphoric acid and lime, and accordingly the 
 farmers in Moume and the agricultural improvers in other 
 granite districts find that, by the application of lime, or of 
 bones, which contain both lime and phosphoric acid, they 
 can procure excellent crops of oats and wheat {see manures), 
 
 * These minerals may be distinguished by the following characters: — 
 
 Quartz or Silica occurs usually crystallized in granite. It will scratcli 
 glass; a knife will not scratch it, but produces a streak like that made 
 by a lead pencil. 
 
 Mica is of various colours; it occurs of a yellow colour in the Dublin, 
 and of a black in the Newry granite. It is met with in shining scales, 
 which split into layers when heated in tho flame of a candle, and arc so 
 soft that they can be cut with a knife. 
 
 Feldspar^ the next ingredient of granite, forms a large portion of its 
 
 g2 
 
84 LESSONS IN CHEMISTRY. 
 
 When hornblende is present, the agricultural capabilities of 
 
 the soil will be of a higher character; in addition to the 
 
 potash supplied in abundance by the decomposing feldspar, 
 
 the soil will then contain a large amount of lime and magnesia. 
 
 / 1 22. — MicaSl^e. Resting upon the sides of the granite 
 
 f mountains and covering a considerable surface of the country, 
 
 J especially in Ulster, where it constitutes the greater part of 
 
 / Donegal, Derry, and Tyrone, we find this rock, which derives 
 
 ) its name from mica (120) being its chief ingredient. It is 
 
 ^Iso met with in the north-east of Antrim, in the glens 
 
 between Cushendall and Ballycastle. It is not found in 
 
 Munster, but in Connaught it is the prevailing rock, and in 
 
 the west of Mayo extends from Broadhaven to the sound 
 
 of Achill, and it also spreads over a considerable surface in 
 
 Galway. It is met with in a few spots in Wicklow. This 
 
 rock splits into slaty layers which usually exhibit some 
 
 appearance of the shining particles of mica. Its composition 
 
 varies very much, and the soils which rest upon it exhibit 
 
 considerable variety of character. It decomposes very slowly, 
 
 and in general affords but thin and poor soils, which, being 
 
 bulk. Its usual colour is pale white, but it occasionally occurs of a 
 flesh-red. It consists of silica, potash, and alumina. The silica is 
 united as an acid with potash, forming a silicate of potash, (50) and 
 with alumina, forming a silicate of alumina. The last of these com- 
 pomids is the porcelain clay which in England is of so much value. 
 From its composition, feldspar in granite readily decays. The rain 
 charged with carbonic acid unites with the potash, thus forming soluble 
 carbonate of potasli, which is dissolved, while the insoluble clay, the 
 cohesion of the rock being destroyed, is carried along and deposited in 
 the valleys, leaving behind on the hills merely a sterile sand and gravel. 
 Feldspar can be scratched by quartz. 
 
 Hornblende, as it occasionally occurs in the granite of the County of 
 Down, (syenitic granite), is of a dark green or black coloiir and usually 
 crystallized. It does not, like mica, split into layers when heated. 
 
 A specimen of granite from Annalong, County Down, examined 
 in my laboratory had the following composition : — 
 
 Silica 
 
 . 74-00 
 
 Peroxide of Iron . 
 
 3-00 
 
 Alumina . 
 
 . 12-20 
 
 Lime .... 
 
 0-22 
 
 Magnesia . 
 
 . 0-45 
 
 Potash and Soda . 
 
 9-33 
 
 Fluoric Acid and Water 
 
 . 0-50 
 
 100-00 
 
THE SOIL. — ^ITS FORMATION AND COMPOSITION. 85 
 
 usually eleyated, yield but indifferent crops. In sheltered 
 positions, however, and when it conies into contact with 
 limestone and other formations, it improves in character. 
 In Scotland the mica slate formation is largely developed, but 
 in England it occurs only in South Devon and in Anglesea. 
 Several specimens of clays produced by the decomposition of 
 the mica slate of Donegal!, and deposited at Milford and 
 other places on the northern coast, appear well adapted for 
 the manufacture of draining -tiles.* 
 
 1 23.— ^CU^AYSi^AXE. The rocks which receive this name 
 are found overlying those last mentioned, and occasionally, 
 where the mica slate is absent, rest directly upon the 
 granite. These rocks are of a slaty character and of con- 
 siderable thickness, and the upper layers, which are found to V 
 contain remains of shells and vegetables, are usually termed c 
 upper slate to distinguish them from those in which no "organic ) 
 remains" have been discovered, and which are described as / 
 lower slate. The lower slate covers a great extent of the 
 kingdom, resting upon the flanks of the Mourne range, and 
 forming nearly the whole of Down and Louth, except a small 
 portion north of Dundalk. In the south it fonns parts of 
 Wicklow, Tipperary, and Cork. In the south also, the upper 
 clay slate extensively prevails in Cork and Kerry, but in 
 Ulster and Connaught it is only to be met with in Galway 
 and Mayo, and in small patches in Tyrone and Fennanagh. 
 
 1 24. The predominating ingredient in the clay-slate rocks is a 
 compound of silica and alumina in the state in which they exist 
 in porcelain clay (115). In addition to these they contain silica 
 and oxide of iron with traces of lime, magnesia, and alkalies. 
 They also frequently contain a mineral named chlorite^'\ which 
 
 ' Analysis of a subsoil resting on decomposing mica slate at Ballyma- 
 cool, County Donegal. 100 parts had the following composition: — 
 
 Water 
 
 . 1-60 
 
 Organic Matters 
 
 3-00 
 
 Sand and Earthy Matter 
 
 . 88-50 
 
 Peroxide of Iron 
 
 4-00 
 
 Alumina . 
 
 . 1-60 
 
 Lime .... 
 
 no trace. 
 
 Magnesia . 
 
 . 0-3G 
 
 Phosphoric Acid . 
 
 ? 
 
 Alkalies . 
 
 . 0-24 
 
 99-10 
 ■f This mineral is very abundant in tlie clay-slate rocks of Dovm. 
 Its name is derived from a Greek word, signifying green. 
 
8& ISSSQRS Bl CBXMSStXT. 
 
 fpna tkoBft a gi w i a fc «oiiNDr. In aoae plans tiiej are cl- 
 hatd aad ant tmSty iImjmihwwwwI, Iwt m otiier 
 as waea dose to Ike nici^ lAmy tnMUti doirn nora 
 TIk aoib pfodaced bjr tiheir decaj exhibit coih 
 jaoRMK Tsnetj' of igmritana fiJuufatiBf^ aad tbcsr ftitifilT 
 BCoasideiabtflBflaeaQedbjthepRseMeofotibernM^ aad 
 abo Ivf Ae posbka of tke lajers of ro^ wpim wfadti tbej 
 Oa^besannla of the loaad hms whkh stad tiie 
 of Dowa aad Mfnij^ia^ Amj are in genoal fig^it 
 nqmnag Ingt s^gSm oi mMBm&'^ }m when 
 Ab lad: ipoa iiiidk thrfr mt is bat sBgjhlly iacfiaed, liMff 
 are of gmtor d ep t^ aad a ban liaiisscd, as ia setaral 
 parts of Ae Gdn^ of IXma, I7 Terns of cutwaate of fins, 
 of csoasdenUe fertifi^. Ia aoie of tiie alile dB&fids m 
 Uctci; beaiy dsj'soils arefcaad^ widch, wfaea aadraiiwd are 
 vQiked wiA dMnaitTv bat bj jadSnoaB maagement are 
 eqpaUe of jiettig burge oopB of vbnL la Scodaad tiie 
 lodks of Ml taauliua jidd poor aoiis, aad are ia lanj 
 DiaoBS oo'vafadl vw oott aaol acac^L 
 
 125. Ialboaei^ggedMBod3or^bMiwes»''wbidiaretobe 
 iplbra^gjb OecidtbaladfiddaiaBiaBjof te 
 bal iHndb^ are lapid^ fisi^pearii^ before 
 Ae pickaxe of Ae eataqpnaieg fiDOMr, Ae daj shte aiajbe 
 m Tanoas states of decajv preseaCiag: diffeRBt abades 
 , fitaa Ae dose^ fiaftji aad aaiftered grej reck to tbt 
 red firuMe date^ adncb is gmliiHji ovaibGngdowa 
 i taoetas ia Ae coloar aad textare of 
 tihered^depeadddd^iqMaitbe donees abidi eiraBdaioi&- 
 !■■* jwMiMw ^^ ^^ -ww^ -^^f TfiffHiWiiBB JDn lae aautereii 
 
 of Ae oxfgei of Ae dr, aadOe bi^ber 
 tibe bmaaiah red pwtixide is fined, arbicib as it is 
 
 DCipnsa 
 
 AepaitidBSofAe 
 
 topieees. Tboa^daj date ia its 
 
 aenif al tibe cfcaiiatjn reqmied b j 
 
 of Aen exist ia it ia rerj sauU 
 
 tb>t 
 
 Alt Ae aoas lenaed 6nm 
 Lineisbideed 
 
87 
 
 aaft, tad is npfBtd wkii 
 
 126L ffA w ygpM M — ^ff 
 iMMBlam nu^aSTnie «p m tibe 
 iflid,m LoB^bfd, BotoiMnMB, aw 
 Tippenrj, and liaeridc, we fiad dnt tiKj 
 
 njiifaoae 
 eonidered, and iHndi seems fo be 
 of saad of ijuiou dc^^ees of 
 analnuM 
 jcfloir bj pomade of im; sack is tte 
 
 wfcat kas bea iamed tibt eld red 
 of a greai mamher of beds, aad isjilaeed 
 tihedaf-dateaadAe 
 
 bdow^ttefimSniCcoiiianiaeoHi^enble amamAci 
 127. Hieieare 
 
 pOStHMifiOBl 
 
 stooe. Tbeee^ bowet cf; aie of bat 
 iao^lfafewoflbeBOrtbenieoafia. Tbeaoili 
 
 b^^ jndme&we, bat as wa^ be expected froat Ibe 
 
 DOVB. 
 
 . 15-41 
 1-1« 
 2-36 
 0.49 
 4-*4 
 
88 LESSONS IN CHEMISTRT. 
 
 of composition which the beds present, they differ very much 
 in value. They are in general loose and porous; and ai-e 
 especially adapted for the cultivation of fruit-trees and deep 
 rooted plants ; occasionally when the silica is in minute grains, 
 and clay forms the cementing material, a moderately cohesive 
 soil is produced. In England the open soils on the old 
 sandstone in Hereford and the neighbouring counties are 
 famous for their orchards, and in this country the best fruit- 
 growing districts of Kilkenny and Limerick are situated on 
 this formation. The new red sandstone may be observed in 
 the valley of the Lagan and also at various points along the 
 coast of Antrim, where it occasionally contains beds of 
 Gypsum (46) and rock-salt. 
 
 128. Limestone g^RMATiON. — The limestone formation 
 covers but a small space in England and Scotland, but in Ii-e- 
 land as we have already stated, it is largely developed, 
 occupying fully two thirds of the island, and being found in 
 every county with the exception of Wicklow. By the geolo- 
 gist it has been recognised as consisting in this country of three 
 distinct formations or beds. ThejsfLaienamed from theirj)Osi;;^ 
 ition the_upper, middle, and lower limestones. ~^T^lower lime- 
 stone forms the prevailing rock of the central counties, and af- 
 fords the fine black marbles of Carlow, Galway, and Kilkenny, 
 as well as the red marbles of Armagh. The middle limestone, 
 which has received the name of Calp, occurs in the neighbour- 
 hood of Dublin, and consists of a dark limestone, containing 
 a large amount of clay, and not more than 68 per cent of car- 
 bonate of lime. The upper limestone is not found in the 
 central flat country, but in the north is discovered in Sligo, 
 Fennanagh, and Leitrim, and in the south in Tipperary, 
 Carlow, and Kilkenny. If you look at the distribution of the 
 limestone fomiation, as laid down in the geological map, you 
 will perceive, as has already been stated, that it occupies the 
 great central plain of the island, extending in a straight line 
 from DubUn to the coast of Galway, on the shore of the 
 Atlantic. Its level, however, is frequently disturbed by the 
 protrusion of sandstone rocks, and branches of it may be 
 observed extending a considerable way from the central 
 mass in Donegal and other counties. 
 
 129. In connexion with the limestone formation we may 
 notice a variety of hmestone which is found in a few places in 
 Ireland, and which, from containing a considerable amount of 
 
THE SOIL. — ITS FORMATION AND COMPOSITION. 89 
 
 mapiesia, is termed magnesian limestone. In England these 
 rocks are of great importance, and largely developed, but 
 in this country they possess but little agricultural interest. 
 Magnesian limestone is found at Cultra, near Plolywood, in 
 the County of Down, on the shore of Belfast Lough, and 
 varies in colour from a light yellow to brown. It also 
 occm'S at Howth, near Dublin, and in three or four other 
 places in Ireland. 
 
 1 30. Though, as we have seen, the limestone formation may 
 be regarded as forming the floor upon which the soil in a very 
 large portion of the island rests, yet it is found that in the 
 central plain the soils, even where placed upon a bed of this 
 foimation, possess characters which render it evident that 
 they cannot have been produced by the decay of limestone 
 rocks. Thus, analysis discovers that they are signally defi- 
 cient in lime, and experience shows that their productiveness 
 is materially increased by its application. "In those localities 
 where the clayey diluvial gi-avel is interposed between the 
 surface and the rock, the soil is usually wet and clayey; so 
 much so as to become impervious to water. Hence has arisen 
 the tendency to the growth of bog moss {Sphagnum Palustre) 
 and other aquatic plants, which have gi'adually produced the 
 bogs that occur so abundantly among the Eskers or gravel 
 hills of our central districts. In those parts of the great lime- 
 stone district in which the gravel deposits have not extended, 
 the soil is rich and is capable of producing any kind of agri- 
 cultural crop; but in these fertile plains less exertion has 
 been displayed than in other parts of the country where the 
 soil is of inferior quality ; but where, owing to the industry of 
 the people, the quantity and quality of the crop per acre, is 
 superior to that produced on the rich calcareous loams." — 
 {Gnffiihs.) 
 
 131. Xrap or VOLCANIC ROCKS^ The next group of rocks ^ 
 to which I would direct your attention, as affording soils by ) 
 their decomposition, are those which cover a large portion of ^ 
 the northern part of the kingdom, and are kno wn b z_JJ>»^ 
 
 j[a;a£a^f^a8ajt,_^reensto^ne^ aff d^j^:^i2i; ^Q/ig. These rocks 
 are usually consioered to have been converted into their 
 present state by the action of fire, to be in fact composed of ^ 
 matter ejected from volcanoes ; occasionally we observe them 
 forced up in nan-ow ledges between rocks of an entirely 
 different character. These are usually termed whin dykes. 
 
90 LESSONS m CHEMISTRY. 
 
 The chief development of these rocks is in the Comity of 
 Antrim, where a flood of volcanic matter seems at one time 
 to have been poured over the beds of chalk, converting it 
 into what is, in the north of Ireland, termed " white lime- 
 stone." The volcanic rocks of Antrim border the north-east 
 coast of that county for many miles, forming the picturesque 
 cliffs which give that portion of the country its pecuhar 
 character, assuming, in the Giant's Causeway, the form of 
 angular pillars, and in the magnificent promontory of Fah'head 
 rising in massive columns to a height of 636 feet above the 
 level of the sea. Detached masses of greenstone may be 
 observed protruding in many parts of the kingdom; thus, 
 Croghan Hill, in the IQng's County, Carlingford mountain, 
 in Louth, and Urrisberg, in Gal way, are examples of this 
 rock. The volcanic rocks are of but limited extent in 
 England, but in Scotland they cover a considerable area. 
 They contain a gi-eat variety of ingredients, are readily 
 acted upon by the weather, and the soils which are pro- 
 duced by their decomposition present great variety both in 
 colour and composition. In Ireland they are usually fer- 
 tile, but their character is greatlj' influenced by position. 
 When they are flat they favour the accumulation of water, 
 and are often covered with peat and marsh, and in many 
 cases the soils produced by their decay contain so much 
 iron as to prove injurious to the growth of the farmers' 
 crops. The iron of the decomposing particles of rock is 
 washed down by the rain, and frequently accumulates in 
 the subsoil, forming an ochrey layer or pan^ which is some- 
 times so hard as to be with difficulty broken up. Upon 
 soils in which this accumulation has taken place, the crops 
 thrive well until the roots descend to the pan, when they 
 gradually fail, the excess of iron acting as a poison to the 
 plants. Greenstone is sometimes composed of feldspar and 
 hornblende (see analyses), and in other cases, of the former 
 and augite, a mineral which like hornblende is rich in lime, 
 so that in this mixture we have most valuable ingredients 
 for the nourishment of plants. Below are given analyses of 
 some of these rocks, and also of a soil resting upon them.* 
 
 * The beds of ochre which of various colours are observed along our 
 north-east coast and also in the interior of Antrim have been produced 
 by the decay of volcanic rocks. The following is the composition of 
 Basalt and also of a specimen of red ochre from the cuttings of the 
 
THE SOIL. — ^ITS FORMATION AND COMPOSITION. 91 
 
 1 32. Wm TE Li ^gSTONE. The rocks known to the farmers 
 in the northof Irelandby the name of white limestone^ though 
 of great agricultural value as a source of manui-e, do not to 
 any great extent dkectly contribute to the production of soils. 
 These rocks extend over the greater part of Antrim and over 
 parts of Down and Deny, and are regar^d ljX~Sg^Qgjg^gLM 
 i(jenticalwi^Lihe__beds^ of chgilk which are so extensively 
 develope3m England, and merely altered in hardness by 
 the action of the, vplcanic.j'pcks. Bemg, however, covered 
 over witiTtEelmmense mass of basalt upon which the soils in 
 Antrim chiefly rest, the limestone is only occasionally visible. 
 It may be traced from the neighbourhood of Moira in Down .> 
 to the banks of Lough Foyle, and is obseiTed making its ap- \ 
 pearance beneath the basalt at various points along the north- K 
 east coast. The white limestone belongs to what is termed ^ 
 the chalk formation, which consists of a group of calcareous 
 rocks, and beds of sand, clay, and marl. Some of the beds 
 of the group contain a lai'ge quantity of fossil shells and 
 other "organic remains," and considerable attention has 
 lately been directed, both in this country and in England, to 
 the deposits of green-sand found immediately below the white 
 limestone {chalk), by the discovery that these beds contained 
 
 Ballymena Eailway and of a subsoil in the neighbourhood of Larne 
 examined in ray laboratory. The subsoil was taken from a field 
 belonging to Dr. Kirkpatrick, on which the oat crop had several years 
 failed after exhibiting a most promising appearance. 
 
 Basalt. Ked ochre. 
 
 Silica . . . .53-70 26-00 
 
 Alumina . . . 2541 26-93 
 
 Lime .... 4.55 trace. 
 
 Magnesia ... 1-37 73 
 
 Oxide of Iron . . . 8-95 Peroxide 36-57 
 Sulphuret of Iron . . traces. 
 Water .... 4*30 10-33 in 100 parts. 
 
 Subsoil from near Larne, Co.' Antrim. 
 
 Sand and Siliceous matter . . .58-00 
 
 Peroxide of iron . . . . 12-60 
 
 Alumina 12-00 
 
 Carbonate of lime . . . . 0-40 
 
 Magnesia 0-58 
 
 Sulphuric Acid and traces of Alkalies . 0-20 
 
 Organic matters 10-06 
 
 Water 6-15 
 
 99.98 
 H 
 
92 LESSONS m CHEmSTRY. 
 
 a large amount of phosphate of lime, (53) the componnd 
 from which bones derive their chief fertilizing qualities, and 
 might, therefore, be advantageously employed as manure. 
 
 133. In the variety of composition presented by the rocks 
 upon which the soil rests, we have a striking instance of wise 
 arrangement ; did they consist of merely one kind of matter, it 
 would be impossible that our cultivated plants could grow, for 
 as you have seen, we are not acquainted with any of these plants 
 that does not require more than one kind of matter for its food.* 
 In every country, however, not only have we a great variety 
 of rocks, but few of these are absolutely pure; limestone does 
 not contain merely lime, nor the quartz rocks of Donegal 
 merely silica. In these apparently pure rocks chemistry dis- 
 covers minute quantities of other ingredients. The more 
 complex the composition of any rock, the greater probability 
 of the soils formed from it proving fertile. This is illustrated 
 by the well known productiveness of those districts where 
 several kinds of rock occur. 
 
 1 34. Organic matter of the soil. It has already been stated 
 (115) that when a portion of soil is burned until all black- 
 ness has disappeared, it is found to have decreased in weight, 
 and that the incombustible ash which remains consists of the 
 saline and earthy inorganic matters which are contained in the 
 rocks by the decay of which it was produced, while the part 
 that consumes is composed of the remains of the vegetables 
 that have grown upon it, or have been mixed with it by the 
 farmer. In all cultivated soils in this country, we discover 
 a considerable proportion of this organic matter, and in peaty 
 soils it frequently amounts to 60 or 70 per cent. In tropical 
 countries the decay of the vegetable matter proceeds rapidly, 
 and all the carbon of dead plants is restored to the atmos- 
 phere in the form of carbonic acid, but in Ireland and other 
 cold countries this change is not so perfect, and the remains 
 of vegetables accumulate in the soil, and when moisture is 
 present frequently undergo a peculiar kind of decomposition, 
 by which they are converted into the substance termed peat. 
 
 * The teacher will observe, that I have said that all our cultivated 
 plants require more than one kind of mineral food, but respecting the 
 exact number of substances which are essential to their growth, we are 
 not yet sufficiently informed to decide. The only plants which have yet 
 been discovered to contain no inorganic matter, are the little mould 
 plants, which form on the surface of solutions of sugar and other organic 
 substances. (Mulder.) 
 
tHE son. — ITS FORMATION AND COMPOSITION. ^3 
 
 It was fonnerly erroneously supposed, that upon tlie 
 presence of the decaying vegetable matter which gives the 
 dark colour to the soil of the meadow and garden, and of 
 which peat is chiefly composed, that the power of a soil to 
 grow plants depended. Tliis substance you will find fre- 
 quently mentioned in agricultural works under the names of 
 Humus and " vegetable mould ;" and some chemists suppose 
 that by its decay certain acids, rich in carbon, arc produced in 
 the soil, which in some forms of combination are capable 
 of being taken up by the growing plant, and employed for its 
 nourishment. The researches of Liebig, however, and other 
 eminent authorities, are entirely opposed to this opinion, and 
 have demonstrated that for a soil to be capable of support- 
 ing any plant it is necessary that it should contain the 
 inorganic matters that we discover in the ashes of that plant. 
 From what has already been stated you will readily un- 
 dei-stand the explanation which is given of the beneficial 
 efifects which experience has taught the farmer are derived 
 from decaying vegetable matters in the soil. By the gradual 
 union of the carbon of the dead vegetable with the oxygen 
 of the air, carbonic acid is produced and slowly evolved from 
 every particle of organic matter to which the air has access, 
 and thus a more abundant supply of that source of food to 
 plants is provided. The carbonic acid as it is formed is 
 taken up by the roots of plants, and thus the crop attains a 
 greater development than when dependent upon the ordinary 
 supply of that gas afibrded by the atmosphere. *' If," says 
 Liebig, in his Letters on Chemistry, "we suppose all the con- 
 ditions for the absorption of carbonic acid present, a young 
 })lant will increase in mass, in a limited time only, in pro- 
 portion to its absorbing surface ; but if we create in the soil 
 :i new source of carbonic acid by decaying vegetable sub- 
 stances, and the roots absorb at the same time three times as 
 much carbonic acid from the soil as the leaves derive from 
 the atmosphere, the plant will increase in weight fourfold. 
 This fourfold increase extends to the leaves, buds, stalks, «fec. 
 and in the increased extent of surface the plant acquures an 
 increased power of absorbing nourishment from the air." 
 
 1 35. What is termed the physical qualities of soils, that is, 
 their tenacity, porosity, power of absorbing and retaining 
 water, &c. materially influence both the labour required for 
 then* cultivation and their productiveness. The atmosphere 
 
94 LESSONS IN CHEMISTRY. 
 
 and water, you have seen, supply plants with some of the most 
 essential ingredients of their food, it is therefore important 
 that the soil in which they are fixed, should possess that 
 texture best adapted to allow the air and rain freely to 
 penetrate to their roots. It is not, however, sufficient that a 
 soil be loose and open, it must, at the same time, possess that 
 degree of consistence which will afford plants a firm support. 
 So far as its physical qualities are concerned, "the most 
 productive soil is that which is so constituted as to maintain 
 such a degree of moisture in very diy and in very wet sea- 
 sons, as only to give a healthy supply of it to the plants. 
 Such a soil gives to plants the means of fixing their roots 
 sufficiently deep to support them during the period of their 
 growth, and allows them to ramify in every direction in 
 search of nourishment, where they may easily abstract the 
 elements of vegetable life without being injured by a redundant 
 or a deficient supply of moisture, during any period of their 
 growth." — {Morton.) Though the physical qualities of a 
 soil, and the proportions of sand-clay and vegetable matter 
 which it contains, its elevation above the sea, and its depth, 
 have, as the experienced farmer knows, an important influence 
 upon its fertility, yet " a soil," as the chemist Sprengel, the 
 head of the Prussian agricultural school, says, " is often 
 neither too heavy nor too light, neither too wet nor too dry, 
 neither too cold nor too waim, neither too fine nor too coarse, 
 lies neither too high nor too low, is situated in a propitious 
 climate, is found to consist of a well-proportioned mixture of 
 clayey and sandy particles, contains an average quantity of 
 vegetable matter, and has the benefit of a warm aspect and 
 favouring slope ; and is, notwithstanding all these advantages 
 unproductive, because it does not contain the chemical ingre- 
 dients which plants require for their nourishment,'''* An 
 inspection of the analyses of the rocks from which the soils of 
 this country are derived, will show you that they are capable 
 of supplying these chemical ingredients in very different 
 proportions, and will also convince you that the only certain 
 method of estimating the agricultural capabiHties of any 
 particular soil, is by acquirmg a knowledge of its chemical 
 composition. 
 
95 
 
 CHAPTER VII. 
 
 EFFECTS WHICH THE GROWTH OF PLANTS PRODUCES UPON THE 
 SOIL, AND PLANS ADOPTED FOR MAINTAINING ITS FERTILITY. 
 
 136. Having in the preceding chapters described the 
 conditions which are necessary for the existence of plants, 
 and also the sources from which the materials that we discover 
 in their structure are derived, we may now with greater 
 advantage proceed to the consideration of the effects which 
 the gi'owth of those cultivated by the farmer has been ob- 
 served to produce upon the soil, and also of the various plans 
 which have been adopted for the purpose of maintaining its 
 fertility or of increasing its natural capabilities. 
 
 Observation teaches us that nature, without the aid of man, 
 provides food in sufficient abundance for the growth of the 
 lierbs and trees with which she clothes the surface of the 
 uncultivated soil ; and in the infancy of society the wild roots, 
 herbage, and fraits of the field and forest were sufficient for 
 the support of the wandering tribes that were thinly scattered 
 over the earth. But as population increased, and men asso- 
 ciated together in numbers in cities and villages, the necessity 
 of producing, in the vicinity of their habitations, a larger 
 -upply of vegetable food than the soil spontaneously afforded, 
 laid the foundation of agriculture. For centuries the know- 
 Itidge which in these countries was possessed of the cultivation 
 of plants was extremely limited, generally only a few vegeta- 
 bles occupied the attention of the farmer, and it is known, that 
 many of the plants which are now highly esteemed for food, 
 were at one time useless weeds; thus, the potato in its wild 
 state in South America, travellers tell us, would scarcely in 
 the produce of an acre afford food sufficient to sustain an 
 Irish family for one day (Darwin) : the peach of our gardens 
 is said in its original state among the mountains of Hindostau 
 to bear a bitter and poisonous fruit, and the now valuable 
 turnip, when uncultivated, is found to yield a bulb not much 
 larger than a pig-nut. The highly nutritious grain crops also 
 that we now grow upon our farms, in their natural condition 
 contained bat a triffing amount of nutritious matter, but by 
 h2 
 
96 LESSONS IN CHEMISTRT. 
 
 cultivation they have been made to store up in their seeds 
 that large amount of gluten and other flesh-forming principles 
 for which they are at present so highly valued. 
 
 1 37. The main object of the farmer is to improve and deve- 
 lope the wild plants of the field, or to keep those which in the 
 course of cultivation have been increased in value in proper 
 coadition ; for experience has taught him that if he neglect 
 his duty they gradually deteriorate, and become again worth- 
 less for food. It is evident that he cannot properly understand 
 his business or expect to assist its progress without such 
 knowledge of the materials of his fields, and of the influence 
 which the air, the water, and the soil, exercise upon vege- 
 tables, as I have in the preceding chapters endeavoured to 
 communicate. 
 
 138. At a very early period, farmers were led to perceive, 
 that a close connexion must exist between the soil and the 
 kinds of plants produced upon it, that the wild plants of the 
 upland were different from those of the marsh, and that 
 every district had its peculiar flowers and grasses. It was 
 only, however, when chemistry had come to their assistance, 
 that the true nature of the connexion became intelligible. 
 We now know that certain plants flourish in some situations, 
 and refuse to gi'ow in other localities, because in the former 
 the soil is capable of yielding the materials which are requi- 
 site for their full development, while in the latter it is 
 incapable of supplying them with these materials. 
 
 139. Nature of Exhaustion. — Experience has also taught 
 the farmer that though a field may be fertile, that is, fm-nished 
 with the earths, alkalies, and other materials essential to the 
 development of plants, yet that if the same crops be grown 
 upon it for a gi'eat number of years in succession, it will 
 sooner or later become incapable of yielding remunerating 
 harvests, unless assisted by art. 
 
 Some useful information respecting the effect which the 
 gi'owth of crops is capable of producing upon the soil may be 
 obtained by considering the practice of farmers in other coun- 
 tries. When the Irish emigrant in America bums down the 
 trees of the ancient forest in his new settlement, and commits 
 the seed to the freshly broken-up ground, he is astonished by 
 a produce fai' exceedmg anything to which he had been ac- 
 customed in his former experience, and for years he obtains 
 immense crops of rich gi-ain without the necessity of manurmg 
 
EFFECTS PRODUCED BY PLANTS ON THE SOIL. 97 
 
 or any apparent falling off, and congratulates himself upon 
 the possession of a farm of inexhaustible fertility. Such is the 
 case at present in many of the newly settled states, the soils 
 of which are supposed by their cultivators to possess some 
 peculiar qualities different from those of the old world. But 
 the same thing was observed in the tobacco lands of the early 
 settled southern states, where we are told wheat and tobacco 
 were produced in succession, without manure, for upwards of 
 a hundred yeai's ; but at last a time arrived when these lands 
 would scarcely return the seed, and the same thing must happen 
 in the other states if the same injudicious system be pursued. 
 Formerly in the plantations of our West Indian colonies, sugar 
 could be produced without any necessity for manuring the 
 sugai'-cane plantations, but at present that is impossible, and 
 the planters are obliged to send to this country and to Eng- 
 land for the materials which then- exhausted fields require, 
 or, as is done in some settlements, remove to other districts 
 where the soil has been less injured. Now the so-called vir- 
 gin fields of North America are not different in composition 
 from what the soils of Ireland were, at the time they were first 
 broken up by the plough. Waving forests once covered our 
 hills, and their remains for centuries enriched the soil with 
 mineral ingredients, but as population increased, our husband- 
 men, like the farmers of Virginia, grew upon them crop after 
 crop of scourging gi'ain, and fed upon them flocks of cattle 
 which were exported to other countries without any return 
 being made for the thousands of tons of materials thus taken 
 away. But our farmers did not know that in their crops and 
 cattle they were selling the materials of their fields, nor was 
 the planter in British Guiana until lately aware, when he 
 burned the crushed sugar-canes and threw away the ashes, 
 that they were capable of supplying to his soils nearly all 
 the ingredients which the crop had withdrawn from them. 
 
 1 40. The soil, you have seen, is produced either by the 
 crumbling down of the bed of rock upon which it rests, or by 
 the materials transported by water from other parts of the 
 country. It can contain only the mineral substances of which 
 the rocks are composed, and some of the most important of 
 these, we have seen, exist in exceedingly minute quantities, and 
 being by decomposition rendered soluble in water, may be carried 
 away by the action of rain. At all events, the available stock 
 of materials in even the best soils bemg limited, a time must 
 
98 LESSONS IN CHEMISTRY. 
 
 arrive when the most fertile soil in the country will be deprived 
 of its power of production. I have already, in chapter iii. 
 given an account of the characters of the substances which 
 plants extract from the earth for their nourishment, and also 
 directed attention to the fact that the different crops which 
 the farmer cultivates, take up these substances in unlike pro- 
 portions (55). I shall now return to this important subject, 
 and consider more fully the peculiar action which the crops 
 usually grown in the country exert on the soil. It is to be 
 regretted that so little of the information which I am about 
 to communicate, is based upon analyses of the plants of 
 our own island. This great want, I hope, before many years 
 will be supplied, and we will then be enabled with greater 
 advantage to devise plans for the economical management of 
 our farming operations. I will, in the following table, give 
 the per centage composition of the ashes of the crops most 
 important to the Irish farmer. 
 
 141. This table will be found interesting as showing the 
 relative proportions in which the ingredients of the soil enter 
 into our crops, and it becomes of the greatest practical value, 
 when we calculate from it the amount of these substances, 
 which are every year taken away from a fann in the course of 
 cultivation. In Ireland we are destitute of that information, 
 respecting the acreable produce of the different parts of the 
 kingdom, which would be desirable in inquiries of this kind ; 
 and very few of our farmers have any accurate return of the 
 proportions of grain and straw yielded by their grain crops, 
 or of roots and leaves produced by their turnips and other 
 root crops. 
 
 142. An examination of the annexed table, and also of the 
 tables given in chapter iii. pages 49 and 50, in which the 
 amount of dry matter and of ash contained in the crops 
 usually grown by the farmer is stated (57), will show you, 1st, 
 That the absolute quantity of the ingredients of the soil which 
 plants abstract during their growth, varies with the kind of 
 plant examined, and also with the part of the plant. Thus 
 the proportion of ash which a hundred pounds of dried wheat 
 leave when burned, is only about two pounds; while the 
 same weight of dried clover hay, and of the dried bulb of the 
 turnip, affords more than seven pounds, and the dry leaves 
 of cabbage from eighteen to twenty-six pounds. 
 
99 
 
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 ounqdins 
 
 omeo<o_.„- 
 
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 ooooce<3c^>^oC)oo 
 
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 3PH0IR0 
 
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 O -H 
 
 cj'*o-«ro«oiciO»rac«jroo-*oc^ 
 
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 &H Cu, Oh « t?: iJ O 
 
100 LESSONS IN CHEMISTRY. 
 
 2d. That different plants, as has akeady been stated (55), 
 though requiring all the mineral substances described (42), 
 invariably select different proportions of particular kinds of 
 matter for their nourishment, the root crops, for example, 
 requiring large supplies of the alkalies, and the clover crops 
 of lime, &c. 
 
 3d. That not only do our field crops exhibit a partiality 
 for certain matters of the soil, but that different parts of the 
 same plant select dissimilar quantities of these substances-^ 
 thus the table shows us that while the straw of wheat yields 
 an ash containing so much as Q6 parts in the hundred of 
 silica, the grain contains but a trifling amount of that 
 substance ; and that while the ash of the straw affords only 
 3 per cent of phosphoric acid, the inorganic matter of the 
 grain yields 49 per cent. If you glance at the composition 
 of the potato tuber, you will find that it is distinguished by 
 containing a very large proportion of the alkalme substance 
 potash, and a small amount of lime, while for the development 
 of the tops, a considerable quantity of lime is required. The 
 discovery of the unlike proportions in which the ingredients of 
 the soil enter into the structure of the different parts of plants 
 leads to important conclusions, and is capable of affording to 
 the practical man a rational explanation of many things 
 which appeared unaccountable to him in the growth of his 
 crops. It teaches him, that as the different parts of the 
 plant requu'e the materials of the soil in different proportions, 
 a crop may at one period of its growth thrive vigorously, and 
 at another droop away; that a crop of wheat, or any other 
 grain, may sprmg up with luxuriant growth, and promise a 
 rich return, yet form but a poor and starved-looking seed, 
 and again, how a plump and healthy head may be produced, 
 while the straw thrown up is weak and stunted. It enables 
 him also to understand how one soil, or one district of 
 country, may refuse to yield profitable returns of certain crops, 
 and yet afford ample food for plants of a different race. 
 
 1 43. Modes adopted for improving the soil and maintaining 
 its fertility. There are three methods which have been adopted 
 for this purpose, viz : Fallowing^ the alternation of crops, and 
 the application of manures. The first of these, termed Fal- 
 lowing* consists in ploughing up the land into ridges at 
 
 * The tQxm. fallow is supposed to be derived from a Latin word signify- 
 ing yellow, the land when in fallow presenting a yellow appearance, 
 
EFFECTS PRODUCED BY PLANTS ON THE SOIL. 101 
 
 the beginning of winter, and allowing it to remain in that 
 state, exposed to the action of the weather. By this meana 
 the rocky particles of which the soil is composed, by the in- 
 fluence of the gases of the air and moisture, are gradually 
 made to crumble, and the alkalies contained in them set 
 free in a proper state to be taken up by plants. It is 
 e\'ident that the various mechanical operations of the farmer, 
 such as frequent plonghings, &c. must facilitate this decom- 
 position of the mineral matters of the soil, and serve to im- 
 prove its productiveness. It was formerly supposed that the 
 fallowing of land was indispensable to renew its fertility when 
 exhausted, and that plants grown npon it separated from 
 their roots certain excrements which it was necessary should 
 be decomposed by free exposure to the air, and that by so doing 
 the land was "sweetened" and rendered again fit for bearing 
 crops. Many philosophers, however, consider that it has not 
 been satisfactorily proved that plants give out organic matters 
 from their roots, and are of opinion that the benefits of fallow- 
 ing are to be ascribed to its facilitating the liberation of the 
 inorganic principles of plants (42) which were locked up in the 
 soil. By this system, however, the fanner was obliged to 
 dispense for one year with any return from his field, either as 
 food for man or animals, and at present it is but seldom 
 employed in advanced agricultural districts, except on the most 
 stubborn clays where the thorough drain, and other means of 
 improving the texture of the soil, have not yet been adopted. 
 The introduction of what are termed green crops into the 
 period formerly occupied by the unprofitable fallow, has not 
 only produced a complete revolution in our system of hus- 
 bandry, but greatly increased the produce of this country. 
 
 144. Rotation of crops. A field, if made to produce the 
 same crops for a number of years in succession may, as has 
 been shown, in the grain and cattle sold off" the farm, be 
 impoverished by the loss of all the inorganic matters which it 
 contained in a fit state to serve plants for food, and thus suffer 
 a general exhaustion ; or it may by the growth of a plant 
 requiring chief y the alkalies or lime, supposing the active 
 oil* to contain the usual amount of these ingi*edieuts, be 
 
 The term active soil has appropriately been employed by an English 
 chemist, Dr. Daubeny, to denote that portion of the soil of a field, in 
 which the mineral matters required by plants exist in a condition 
 capable of being taken up by the growing crop. 
 
102 LESSONS IN CHEMISTRY. 
 
 rendered by their loss incapable of supporting crops requiring 
 a large supply of these matters, such as turnips and clover, 
 and yet be capable of affording sufficient nourishment to 
 plants which are found to select chiefly materials of a differ- 
 ent kind. Experience taught that whilst crop after crop 
 of the same plant materially exhausted the soil, the injury 
 produced by changing the crops grown was not so great; 
 and even before chemistry had enabled us to understand the 
 effects produced by the growth of plants, farmers in many 
 advanced districts, were induced to put a limit to the number 
 of crops of the same kind grown in succession. 
 
 145. In considering the effects which the different kinds of 
 plants exert upon the soil, it is necessary to recollect what has 
 been stated, that not only do the different plants of the farm 
 give a preference to particular kinds of food, but that the 
 different parts of the same plant require different proportions 
 . of these materials for their growth. Such being the case, it is 
 obvious that the exhausting effect which the production of any 
 crop exerts upon the soil, will be influenced in a great degree 
 by the purpose for which it is cultivated. Thus, plants like 
 wheat, oats, barley, beans, peas, and flax, cultivated for their 
 seeds, which are collected and used for food or sent to market, 
 require a large supply of mineral materials and especially of 
 phosphoric acid, a substance which you are aware is con- 
 tained in very small amount in even the most fertile soils, 
 and must therefore produce a different effect from the crops, 
 such as potatoes, tm*nips, mangel-wurtzel, and clover, which 
 we grow for the sake of their roots or fohage, or of flax when 
 pulled before the seeds come to maturity. The study of the 
 food of plants, therefore, points out to us the propriety of 
 alternating with the wheat, and other crops which require for 
 the formation of their seeds a large amount of nitrogen and 
 phosphates, others, like the foliage and root crops, which do 
 not contain the same amount of these substances, and are 
 besides capable of condensing from the atmosphere a larger 
 amount of its materials. In many districts in Ireland the 
 farmers yet act with the same kind of thoughtlessness* that 
 distinguished the early settlers in North America ; they 
 scourge the soil with crop after crop of grain until it will 
 
 * Improvements in practice are of slow progress. Even in the County 
 of Antrim, which can boast of so many intelligent farmers, I have been 
 shown fields producing a seventh crop of oats. 
 
EFFECTS PRODUCED BY PLANTS UPON THE SOIL. 1 03 
 
 scarcely return the seed, and then leave it " to rest" in un- 
 profitaljle pasture. The same mode of cropping was common 
 in many parts of England before the introduction of what 
 has been termed the Norfolk system, which led the way to the 
 improved management of the soil which at present distin- 
 ^fuishes the North of England, and which has been followed 
 and improved in Scotland, and is gradually making its way 
 into this country. In this system the laud is every year 
 made to produce food by a skilful application of the prmciples 
 which have been laid down. 
 
 146. The investigations which have been made within the 
 last two or three years have led to some curious observations 
 on the composition of the ashes of plants, which, if corroborated 
 by future researches, will be of gi-eat practical importance. 
 It is known to the chemist, that in the mineral kingdom, 
 certain substances are found to replace one another in the 
 composition of minerals ; thus, soda in some minerals takes 
 the place usually occupied by potash, &c. ; and in plants a 
 similar cmious substitution of one substance for another has 
 been detected. Thus, in the ashes of clover grown upon soils 
 rich in potash and poor in soda, the former of these substances 
 is found in large quantity, while in soils in which soda is 
 abundant and potash deficient, the soda is found to occupy 
 the chief place in the ashes of the plant. The same thing 
 has been discovered in other plants. The ash of the oak, for 
 example, is usually found to contain potash, but on the sea- 
 coast of North America, at Long Island, soda has been found to 
 take its place (Gai-duier). The study of these curious substi- 
 tutions opens an interesting field to the agricultural chemist. 
 
 147. The practical rules to be deduced from the foregomg 
 observations are — 
 
 I. That plants which requu-e chiejly the same kind of 
 materials for their support should not be grown in 
 succession. 
 II. That as the effects which different crops produce upon 
 the fertility of the soil are influenced by the purpose 
 for which they are grown, that plants cultivated fur the 
 sake of their seedsy as wheat, barley, oats, flax, should 
 be made to alternate with those which are cultivated 
 for their roots, foliage^ qv fibre, as turnips, clover, &c., 
 and also hemp and flax when the seeds are not allowed 
 to ripen. 
 
 I 
 
104 LESSONS IN CHEMISTRY. 
 
 III. That the greatest possible interval should be introduced 
 in the rotation between plants of the same kind, by the 
 growth of as great a variety of crops as the climate 
 of the country will allow ; thus, instead of the farmer 
 confining himself to wheat, barley, oats, turnips, pota- 
 toes, and clover, he should cultivate beans, peas, 
 vetches, mangel wurtzel, carrots, parsnips, beet, flax, 
 hemp, &c. 
 148. Influence of soil upon the quality of the crops. — The 
 remarkable difference in the quality of the grain produced 
 upon soils differing in their composition, has long been recog- 
 nised by experienced purchasers. I have been informed by 
 an intelligent starch manufacturer in Belfast, that the wheat 
 grown in the barony of Ards, in the County of Down, 
 and in the neighbourhood of Bangor in the same county, 
 is highly valuable for his purposes, while that grown near 
 Ai-magh yields in general a much smaller amount of starch. 
 Another manufacturer is so fully convinced of the supe- 
 riority of the wheat of the neighbourhood of Bangor, that he 
 wiUingly gives five shillings per ton above the market price 
 for that produced in the parish of Balloo. The general 
 statement on the subject is, that soils rich in organic matter 
 or highly manured with decomposing animal or vegetable 
 substances, afford a grain which is richer in gluten than that 
 produced by lighter and more sparingly manured soils, and 
 those of the slate formation. The above statement respecting 
 the value of the wheat grown in some districts of the North 
 of Ireland, seems to confirm the statement. 
 
105 
 
 CHAPTER VIII. 
 
 MEANS ADOPTED FOR IMPROVING THE SOIL AND MAINTAINING ITS 
 FERTILITY BY THE APPLICATION OF MANURES. 
 
 ANIMAL MANURES. 
 
 149. To maintain the fertile condition of the soil, it is 
 necessary that the materials which are every year removed from 
 it shonld be restored. It contains, in mineral matters, and in 
 the decomposing remains of vegetables, an abundant, but not 
 always available supply of these materials ; so it is required 
 that certam artificial means should be adopted, to bring its 
 dormant powers into activity, to make the clay-slate and 
 granite give up their alkaUes, and to convert the insoluble 
 silica contained in them into a state in which it can become 
 soluble in water, so as to be taken up by the roots of plants. 
 Analysis has taught us, that the different famiUes of plants 
 which we cultivate, exhibit a partiality for certain ingredients 
 of the soil, and that the tendency of cultivation is to convert 
 vegetables which, in their natural state, abstract but a small 
 amount of phosphorus, and other elements, into powerful 
 exhausters of those substances: thus, the wheat and other seed 
 crops must find in the soil an abundant supply of the com- 
 pounds of phosphorus, (53) or they will not come to perfection ; 
 and, as these compounds are contained, in such minute quan- 
 tities, in even our most fertile soils, as to be discovered only 
 by refined investigation, it is evident, that their power of 
 producing full crops of such plants, without assistance, must 
 be extremely limited. In the present state of the fields of 
 this country, neither fallow nor the rotation of crops is sufii- 
 cient to preserve them from exhaustion; and the application 
 of certam matters to the soil, for the purpose of supplying 
 its deficient ingredients, has been found necessaiy. From 
 the earliest period, the use of manures in maintaining and 
 increasmg the productiveness of soils has been known to 
 farmers, in various countries. 
 
 150. In considering the principles of manuring, you must 
 bear in mind the effects which, as has already been explained, 
 plants produce upon the soil You have seen, that our crops 
 appropriate certain matters, which become a part of their 
 
1 06 LESSONS IN CHEMISTRY. 
 
 structure, and the loss of which, by the sale of our farm 
 produce, must as eifectually impoverish our fields, as if we 
 were, by a chemical process, to remove from them these 
 ingredients. Crops of weeds spring up in neglected places, 
 year after year, without any decrease in luxuriance, because 
 they die on the spot where they have been produced, and 
 restore, by their decay, the matters on which they had lived, 
 and thus keep up the fertility of the soil ; but it is not possi- 
 ble, in this manner, to maintain the productiveness of our 
 cultivated fields. Only that part of the plant produced which 
 is unfit for food, can be directly restored. But, although we 
 cannot directly replace in the soil the seeds, the roots, and 
 the fibre employed for food and clothing. Nature has so 
 arranged, that all the materials which during their growth, 
 they have abstracted from it, after they have fulfilled the 
 important purposes for which they are cultivated, may, by 
 the care of the husbandman, be collected and restored, for 
 the production of new crops of vegetables. In the present 
 arrangements of these countries, however, but little attention 
 is devoted to these sources of manm*e ; and farmers are every 
 year obliged to expend large sums of money, in the pm*chase 
 of substances to replace the materials of their soils, washed 
 into the sewers and rivers of the country. 
 
 151. You have seen, that the power of the soil to yield 
 crops, depends upon its containing a full supply of certain 
 mineral matters, which serve for their nourishment. From 
 the most remote periods, farmers have been accustomed to 
 apply to their exhausted fields the excrements of animals and 
 of birds, and have found that these manures were capable of 
 renewing their fertility. It is only of late years, however, 
 that the cause of the valuable properties of these matters has 
 been satisfactorily investigated, nor is the explanation diflacult 
 to understand. The food consumed by man and animals 
 becomes a part of their bodies. — The roots and grasses which 
 the cow eats contain the mmeral matters which gave fertility 
 to the fields in which they were grown, so that these matters 
 become a portion of the bone and flesh of the animal. The 
 seeds, roots, and flesh which afford us food must, in the same 
 manner, enter into our substance ; and when the flesh of an 
 animal is dried and burned, it is found, like the vegetable, to 
 consist of two portions, one of which, sunilar to the organic 
 part of the plant, is combustible and disappears (41), and a 
 
ANIMAL MANURES. 107 
 
 mineral indestructible matter^ which, resembling the ash of 
 plants, consists of the ingredients that compose our fertile soils. 
 The bones of animals, also, when burned, are found to lose a/ 
 considerable portion of their weight, disagreeable smelling gases 
 escape, and a mass of earthy matter remains in the furnace, to 
 the composition of which I will hereafter have occasion to 
 direct your attention, as it contains some of the most valuable 
 materials required for the nourishment of plants. Thus, the 
 bodies of both men and animals are derived from the same 
 materials as the plants that we cultivate — both are from the 
 soil — creatures of the dust: the plant directly deriving the 
 materials of its gi'owth from the minerals of the field and the 
 gases of the air, and the animal indirectly, through the vege- 
 table creation. Chemistry has clearly shown us, that the 
 lime of our limestone mountains, the potash which exists in 
 our granite rocks (120), and the phosphorus of our soils, by 
 the wonderful arrangements of Providence, become food for 
 our crops, and ultimately build up the structure of our bodies. 
 Nor are these materials which Nature provides in the earth 
 squandered ; a wonderful economy is displayed in every part 
 of creation. The matters which we receive in our food, 
 which become blood, and flesh, and solid bone, are not 
 allowed, even during life, to remain inactive. They have no 
 sooner performed the oflice assigned to them, than they are 
 discharged from the body; and, in the liquid and solid excre- 
 ments, both of man and animals, we discover the mineral 
 materials contained in the bread and the beef, the seeds and 
 the roots, which had composed their food. (156), It has been 
 calculated that, in the case of a horse, which consumes 151bs. 
 of hay and 4-1 lbs. of oats per day, 21 ounces of the mineral 
 matters which the hay and oats took from the soil are taken 
 into his system — in a year, about 480 lbs. of these. If the 
 horse, in the course of a year, increase in weight lOOlbs., and 
 if, in this matter added to his substance, we discover only 7ft)s. 
 of the mineral substances received in his food, the remaining 
 473lbs. must have been discharged from the body — (Liebig.) 
 These matters arc actually found in the excrements. The 
 following tables of the composition of the liquid and solid 
 excrements of man will show you, that in them we have the 
 same mineral matters which arc discovered in the ash of our 
 cultivated plants. 
 
 i2 
 
108 LESSOKS m CHEMISTRY. 
 
 152. Composition in 1000 parts of the urine of man:- 
 
 Water 
 
 933-0 
 
 Urea 
 
 30-1 
 
 Uric acid 
 
 1-0 
 
 Free lactic acid,* lactate of ammonia, and 
 
 
 animal matter .... 
 
 17-1 
 
 Mucus of the bladder . . 
 
 0-3 
 
 Sulphate of potash .... 
 
 3-7 
 
 Sulphate of soda .... 
 
 3-2 
 
 Phosphate of soda .... 
 
 2-9 
 
 Phosphate of ammonia 
 
 1-7 
 
 Common salt 
 
 4-5 
 
 Sal ammoniac 
 
 1-6 
 
 Phosphates of lime and magnesia, with 
 
 
 traces of silica .... 
 
 1-0 
 
 1000-0 
 
 153. The solid excrements of a man, according to the 
 analysis of Berzelius, had the following composition : — 
 
 Water 733 
 
 Albumen, and other animal matters . 185 
 
 Saline matters 12 
 
 Undecomposed food . , . . 70 
 
 1000 
 
 154. When dried, the solid excrement contained, in 1000 
 parts, 132 of inorganic matters, which had the following 
 composition : — 
 
 Carbonate of soda .... 8 
 Sulphate of soda, with sulphate of potash, 
 
 and phosphate of soda ... 8 
 Phosphate of lime and magnesia, and traces 
 
 of gypsum . . . . 100 
 
 Silica 16 
 
 132 
 
 The matter, therefore, discharged from the body, like the 
 food, and the bone and muscle which it forms, is a mixture 
 of organic and inorganic substances. The liquid excrements 
 especially, being rich in compounds of Nitrogen, and being 
 characterized by containing urea'\ — a substance which, by 
 the decomposition that mine, when discharged from the 
 
 * The name Lactic acid, or acid of milk, is given to the acid formed 
 in sour milk, in the fermentation of the juice of the Turnip, and in the 
 souring of the grains of the Distillery. 
 
 f Urea contains nearly 47 per cent, of nitrogen. 
 
ANIMAL MANURES. 1 09 
 
 body, undergoes, is changed into a volatile salt (13) termed 
 carbonate of ammonia : while the solid excrement also affords 
 nitrogen, and the compounds of phosphoric acid — ^which are 
 so valuable for the food of plants. In these excrements, Nature 
 supplies 2is with all that our fields require, to produce the 
 richest a'ops. 
 
 155. Value of Urine and Night-Soil. — It may be said, 
 that experience had taught our farmers the value of the excre- 
 ments of man, before chemistry had been directed to the im- 
 provement of agriculture; yet it remained for that science to 
 discover upon what their action depended, and, though it has 
 shown us that they contain the very ingredients upon which 
 plants live, how little have we, in this . country, profited by 
 this knowledge; urine is not merely neglected by the farmer; 
 — in all the large cities of the empire, how much money has 
 been expended to remove it expeditiously beyond our reach ! 
 There was a time when our farmers could afford to cart the 
 accumulated manure of their cattle to the sea-beach, to allow 
 the water to wash it away, and was formerly done by the 
 farmers on the coast of Antrim, — as is even yet practised 
 by the peasants on the banks of the Wolga ; at present, they 
 collect the droppings of their cattle, and the litter of their 
 stables and cow-houses, in their farm-yards, and apply it to 
 their exhausted fields, after it has been exposed for months 
 to the air, and its most valuable parts washed out by the 
 rains. No wonder, then, that they must purchase foreign 
 manures, and expend money in supplying their fields with 
 the matters which they require, when the potash, the soda, 
 and other soluble inorganic matters of their manure heaps, 
 are thus neglected, and whole tons of fertilizing materials 
 drawn from their farms are sold to our cities, where they are 
 cai'elessly wasted, and allowed to pollute the atmosphere, and 
 generate disease I 
 
 156. From what has been already said, (151) it is 
 evident, that the value of excrements for manure will vary 
 with the diet ; thus, the people of a district where much 
 animal food and bread are consumed, will afford a manure 
 richer in fertilizing ingredients than where the inhabitants 
 are poorly fed. On the continent, this is so well known by 
 experienced farmei'S, that they will give a higher price Ibr 
 the house manure of certain districts, where the people use 
 animal food, than for that produced where the diet, for a 
 
1 10 LESSONS IN CHEinSTRY. 
 
 considerable part of the year, is of a less nourishing description. 
 In Flanders, night-soil and urine have long been regarded 
 as the most valuable manures ; and their careful preservation 
 is an important feature in the husbandry of that country. 
 By the Belgian farmer, the value of the liquid and solid 
 excrements of an individual, is estimated at £1 IT*, per 
 annum,* and so carefully is every trace of these manures 
 collected in the towns, that the public authorities are reheved 
 from all the expense and trouble which, in this and other 
 countries, are incurred in the removal of nuisances. In China, 
 also, which has preceded us in so many of our boasted im- 
 provements, strict laws are enacted for the careful preserva- 
 tion of human excrements, and in every house, and along the 
 highways, vessels are placed for receiving them. Travellers 
 inform us, that they mix the night soil with clay so as to 
 form it into cakes which are called taffo^ and are exposed for 
 sale in all the cities of the celestial empire. 
 
 157. Preservation of human excrements^ and methods of 
 applying them to the soil. — On the continent, where attention 
 has long been properly directed to the subject, various plans 
 have been adopted for the preservation of these manures. In 
 Flanders, the farmers not merely carefully collect the excre- 
 ments of their own neighbourhood, but purchase the contents 
 of the cess-pools in the towns, and store them in tanks of suf- 
 ficient capacity to contain aU the manure accumulated during 
 several months. They apply them in the liquid state — usu- 
 ally after the sowing has been completed, by conveying them 
 from the pits, in casks, and distributing them over the fields. 
 
 158. In Paris a difi'erent plan is adopted. The contents 
 of all the cess-pools of the city are taken away by night, to a 
 place in the suburbs, where they are deposited in an immense 
 shallow tank, where they are allowed for some time to remain ; 
 and, when the solid matters have fallen down, the liquid is 
 made to run into a second tank, at a lower elevation, and 
 again from it into a third basin, from which the cleai* liquid 
 
 * K we suppose, according to the calculation of Liebig, that the 
 solid matter contained in the urine of an individual annually amounts 
 to 6 7 lbs of equal fertilizing value to genuine Peruvian guano; then if 
 all the urine of a town like Belfast containing 100,000 inhabitants, was 
 collected and applied to the soil, our fields would receive the enormous 
 quantity of six million seven hundred thousand pounds, or nearly 3,000 
 tons of manure, which, at the ordinary selling price of guano, would 
 be worth thirty thousand pounds. 
 
ANIMAL MANURES. 1 I 1 
 
 is permitted to flow away into the sewers. Tho solid matter 
 thus deposited, when it has acquired sufficient consistence to 
 be shovelled out, is collected and dried, by exposure to the 
 air under sheds. This manure is termed poudrette, and 
 contains, in 100 parts, about 1*8 parts of ammonia. By 
 this method, it is evident much of the valuable matters of the 
 manure is lost, as a considerable proportion of its ingredients 
 are soluble in water, and must be carried away in the liquid. 
 There is also a great loss of ammonia during the drying, and 
 the volatile gases evolved by the decomposition of the 
 organic matters contained in it decrease the amount of its 
 fertilizing ingredients so much, that this method of treating 
 excrement has been justly condemned by the leading agri- 
 culturists of France. In England, within the last foui* or 
 five yeai-s, the contents of the water-closets and cess-pools 
 of London, and some other cities, have, to some extent, been 
 purchased by fanners, and are removed, in their natural 
 state, in waggons, constructed for the purpose; but, as the 
 offensive odour of the manure has interfered with the general 
 adoption of this plan, various methods have been tried, both 
 to remove its nauseous smell, and to convert it into a more 
 portable form; and, at the present time, several companies 
 exist, which prepare manures from night soil and urine, by 
 mixing them i;\ith gypsum, animal charcoal, and other 
 substances. 
 
 159. Among these compounds, one, sold under the name 
 of urate, has been highly recommended as a valuable fertiliser. 
 It is said to be prepared by mixing burnt gypsum with urine, in 
 the proportion of 1 Olbs. of gypsum to seven gallons of urme, 
 and, after the solid matter has settled down, the liquid is 
 drawn off. The manure so prepared contains the phosphoric 
 acid of the urine, in combination with the lime of the gypsum, 
 and also a small portion of organic matter. In addition to 
 gypsum, some manufacturers of m-ate add to the excrements 
 animal charcoal, which must add considerably to the value of 
 the manure. Judging, however, from a sample which was 
 lately examined in my laboratory, I do not consider it worth 
 the price at which it is usually sold to the farmer, as all the 
 valuable ingredients contauaed in it could be purchased, at a 
 cheaper rate, from the manufacturing chemist. 
 
 160. At present, in England, considerable attention is 
 directed to the application to agricultural purposes of the sewage 
 
1 1 2 LESSONS IN CHEMISTRY. 
 
 matter of towns, which, besides night soil and urine, con- 
 tains the sweepings of the streets, and the refuse of sculle- 
 ries. Two plans for this purpose have been introduced. 
 According to the first, it is proposed to collect the sewage in 
 tanks provided with forcing-pumps, to raise the liquid and 
 the matters suspended in it over a "stand-pipe," of peculiar 
 construction, from which, by a series of pipes, it might be 
 conveyed into the country for a considerable distance, and 
 applied to the fields by a hose. Mr. Chadwick, who has 
 zealously advocated this method of applying manure, states, 
 that he has found by experiment, that by means of a 2J 
 inch hose, and a pressure of 80 feet, he could with the labour 
 of two men, one to remove the hose and another to direct 
 the nozzle, distribute 2,000 gallons of liquid sewage in an 
 hour, which from analysis has been found equivalent to 
 3 cwt of guano, and 15 tons of stable dung, and would there- 
 fore be sufficient dressing for an acre of ground, at an expense 
 of 6d. ; while the cost of loading and spreading an equivalent 
 quantity of stable manure on land close to the farm was about 
 lis. He estimates the total expense of the delivery of liquid 
 manure, including the interest on the machinery and capital, 
 at 1*. per acre. The hose can be made of strong canvass 
 saturated with coal tar, which protects it from the rot. This 
 method of applying the liquid of our sewers secures the 
 preservation of all the matters of the manure, and must be 
 regarded as preferable to any other plan, where the proper 
 arrangements for the purpose can be obtained. 
 
 161. Within these few years many interesting trials of the 
 value of sewer water, as manure, have been made in England 
 and Scotland, the results of which have been most encouraging. 
 Thus, on the property of the Duke of Portland, at Clipstone 
 Park, a sterile sand has been converted into luxuriant 
 meadow land by being irrigated with the drainage of a 
 small village ; and fields which were considered dear at five 
 shillings per acre, rendered worth £11 per acre. In the 
 neighbourhood of Edinburgh the most extraordinary effects 
 have also been produced by the application of the drainage 
 water of the city; "so that," as Mr. Smith of Deanston 
 states, "land which let formerly at from 40^. to £6 per 
 Scotch acre, is now let annually at from £30 to £40 ; and 
 that from sandy land on the sea-shore which might be worth 
 2*. 6d. per acre, lets at an annual rent of from £15 to £20. 
 
ANIMAL MANURES. 1 1 3 
 
 That which is nearest the city brings the highest rent, chiefly 
 Ixicause it is near and more accessible to the point where the 
 grass is consumed, but also partly from the better natural 
 quality of the land. I'he average value of the land, irre- 
 spective of the sewer-water application, may be taken at £3 
 per imperial acre, and the average rent of the irrigated land 
 at £30, making a difference of £27 ; but £2 may be de- 
 ducted as the cost of management, leaving £25 per acre of 
 clear annual income due to the sewer-water." 
 
 162. The second plan proposed is to collect the sewage 
 matters in tanks, and, by the addition of slaked lime, made 
 into a cream with water, to throw down their most valuable 
 ingredients, and to collect and dry the deposit.* Though 
 by this method of treating the contents of sewers a solid and 
 portable manure is obtained which must possess considerable 
 fertilizing value, yet only a part of the ingredients of the 
 sewage is obtained, much of the Nitrogen present escapes in the 
 form of Ammonia, and a considerable amount of the soluble 
 inorganic or saline matters remain dissolved in the liquid 
 which is allowed to flow away after the removal of the deposit. 
 
 163. What has just been stated of the valuable fertilizing 
 qualities of human excrements, and the importance which 
 is at present attached to their preservation in other countries, 
 may, I hope, induce you to give greater attention to these 
 manures. Night soil and urine may be readily converted into 
 manures, and their offensive odour removed, by very simple 
 means which should be known to eveiy farmer. Thus, by ad- 
 ding to them coal-ashes or saw-dust, moistened with a solu- 
 tion made by dissolving the substance called "green vitriol," 
 
 * The following is the composition of a specimen of the deposit, pro- 
 cured from sewage, by the addition of cream of lime, Avhich, in the 
 course of some experiments, undertaken at the request of the Corpora- 
 tion of Belfast, I had occasion to analyze. 125 parta of the deposit, 
 dried at 212°, contained as follows: — 
 
 Organic matters, capable of yielding 6.925 parts of ammom'a 81.25 
 
 Phosphate of lime (bone earth) 10.46 
 
 Sulphate of lime (gypsum) 2.00 
 
 Carbonate of lime 19.63 
 
 Lime 8.43 
 
 Magnesia 1.23 
 
 Alkaline chlorides 0.33 
 
 Sand, &c 1.67 
 
 126.00 
 
114 
 
 LESSONS IN CHEMISTIIY. 
 
 {Sulphate of Iron), in water,* the escape of the disagreeable 
 smelling gases will be prevented and the good qualities of the 
 manure preserved. Even without the use of the solution of 
 green vitriol, by mixing the excrements with the charcoal pro- 
 cured by burning peat with a smothered fire, a valuable com- 
 pound capable of being applied with the drill may be prepared. 
 In France the vegetable matter at the bottom of rivers is char- 
 red in close vessels, and advantageously employed for this pur- 
 pose ; spent bark, and burned clay, are also used. Dry peat 
 mould is also a most valuable material for mixing with night 
 soil, and is much employed by the farmers in Normandy and 
 other parts of France ; two parts of the peat mould, one part 
 of gypsum in powder, and one part of night soil, form a 
 mixture which may be at once applied to the soil and has 
 been found to possess the greatest value as manure. 
 
 164. Urine of the cow, horse, pig, and sheep. — The 
 solid excrements of the domestic animals have long been 
 regarded as valuable manures, and have been employed 
 from the earliest times to increase the fertility of the soil. 
 But the value of the urines of animals has not until within 
 these few years been properly understood; and in general 
 but little attention is, in this country, paid to their pre- 
 servation. It is however to be expected, that when in- 
 struction in the principles of agricultural chemistry is made 
 a part of the ordinary education of the young farmer, the rich 
 supply of the matters which plants require for their food, 
 contained in those liquids, will no longer be disregarded. 
 
 The following table will make you acquainted with the 
 amount of organic and inorganic matters which 1,000 parts 
 of the uiine of the cow, horse, pig, and sheep, and also that 
 of man, are capable of conveying to the soil: — 
 
 Water, 
 
 Man. 
 
 Cow. 
 
 Horse. 
 
 Pig. 
 
 Sheep. 
 
 933-00 
 48-56 
 18-44 
 
 921-32 
 41-98 
 36-70 
 
 910-76 
 48-31 
 40-93 
 
 978-80 
 
 6-24 
 
 15-96 
 
 960-00 
 28-00 
 12-00 
 
 Organic matters, 
 Inorganic matters 
 
 1000-00 
 
 1000-00 
 
 1000-00 
 
 1000-00 
 
 1000-00 
 
 * 10 oz. of Sulphate of Iron may be added to each 20 gals, of urine. 
 
ANIMAL MANURES. 1 15 
 
 165. The quantity of the urine discharged by the do- 
 mestic animals, as well as the relative amount of organic 
 and saline matters contained in it, will, however, like 
 that of man, as has already been mentioned (156), vary 
 according to the quantity and quality of the food consumed, 
 and are also materially affected by the age and condition of 
 the animal. You will be surprised to hear that the quantity 
 of urine voided by an animal is not in proportion to the 
 amount of drink which is taken ; thus, it has been found by 
 experiment that the horse, which daily requires several gallons 
 of water for drink, does not annually afford a larger quantity 
 of urine than man, whose daily drink does not exceed a few 
 pints; the cow also does not, as the following table will show, 
 yield an amount of urine in proportion to the water taken 
 into the stomach. Thus : — 
 
 lbs. 
 Man annually aflFords 1,000 lbs. of urine, containing of solid matter 67 
 Horse, „ 1,000 „ „ „ 89 
 
 Cow, „ 13,000 „ ;; „ 1,023 
 
 The small quantity of urine voided by the cow and the 
 horse,* compared with the enormous amount of water which 
 these animals consume, is explained by the large amount of 
 fluid which is constantly escaping from their surface in 
 insensible perspiration, and also in the watery vapour which is 
 given out from their lungs in respiration ; while in man only 
 about a tenth part of the liquid taken into the stomach is 
 separated from the skin. If you refer to the table in page 
 114, you will perceive that the urine of the horse contains 
 a larger amount of solid matter than any of the other liquids, 
 and must therefore be capable of exercising a powerful effect 
 upon plants. 
 
 1 66. The chief difference between the urine voided by the 
 domestic animals and man, is in the composition of the in- 
 organic or saline matters which it contains. In the m-ine of 
 the horse and cow, merely a trace of phosphoric acid is found, 
 the inorganic matter wliich it affords consisting chiefly of 
 alkaline carbonates (43), sulphates (13), and common salt, 
 while the urine of man and of swine is distinguished by a 
 large amount of the compounds of phosphoi-us. The effects 
 
 • Boussingault found by experiment that a horse which in 24 hours 
 drank 36 lbs. of water, gave only three pounds of lu-ine. 
 
 . TH£ vr 
 
IM 
 
 LESSONS m CHEMISTRY. 
 
 which these liquids would produce when applied to the fields 
 must therefore be very different. The urine of man and of 
 the pig is specially adapted to promote the growth of our 
 seed-crops, and that of the horse and cow for the root-crops, 
 which requu*e to be supplied with alkalies.* 
 
 167. To fix upon your minds what I have stated respecting 
 the loss which our farmers experience by neglecting to econo- 
 mise the liquid excrements of the domestic animals, you 
 have merely to calculate, from the information which I have 
 given, the value of the fertilizing materials which are annually 
 wasted, on almost eveiy farm in this country. Thus, a 
 fai-mer who keeps three cows and one horse, and col- 
 lects merely the solid dung, allowing the urine to escape 
 into the drains, loses annually in the cow urme (165) 
 3069 lbs. and in that of the horse, 89 lbs. ; in all, upwards 
 of 28cwt. of dr?/ fertilizing matter, equal in value to the best 
 Peruvian guano, and which at the usual price of that substance 
 would be worth £14, and be capable, without the addition of 
 any other manure, of keeping seven acres of land in the 
 most fertile condition. 
 
 168. Solid excrements of the domestic animals. — The dung 
 of the cow and horse, and of the other domestic animals, is 
 found to differ materially from the urine in composition ; while 
 
 * Mr. M'Lean, in the Transactions of the Highland and Agricultural 
 Society^ gives the following report of the comparative value of urme, 
 moss saturated with urine, and subsoil saturated with urine, in an 
 experiment upon the hay crop of 1842. 
 
 ' Application.; 
 
 S 2 
 
 ll 
 
 ,3 
 s 
 
 I 
 
 > 
 
 
 
 Nothing 
 
 
 15 
 
 15 
 
 s. d, 
 
 52 2 
 33 4 
 
 s. d. 
 
 7 6 
 7 G 
 
 St. lbs. 
 125 10 
 
 300 00 
 
 240 00 
 200 00 
 
 St. lbs. 
 
 174 4 
 114 4 
 
 74 4 
 
 2,500 
 1,600 
 1,G00 
 
 Moss saturated 
 Subsoil do. 
 
ANIMAL MANURES. 117 
 
 Uie liquid is deficient in phosphates, the solid excrement 
 •ontains a large amount of these valuable compounds. Both 
 •(jgether aftbrd us all the elements necessaiy for the develop- 
 ;neut of plants. The fresh dung of the cow and horse ha:^ 
 respectively the following composition in the 100 parts: — 
 
 Cow, Horse. 
 
 Water 79.724 ... 78.3G 
 
 Organic matters 1G.046 ... 19.10 
 
 Saline matters 4.230 ... 2.54 
 
 The composition of the saline matters of each in the 1 00 
 parts is as follows: — 
 
 Cow dung/ Horse dung. 
 
 Phosphate of Lime 10.9 ... 5.00 
 
 Phosphate of Magnesia 10.0 ... 36.25 
 
 Carbonate of Lime ... 18.75 
 
 Phosphate of Iron 8.5 
 
 Carbonate of Potash 1.5 
 
 Sulphate of Lime 3.1 ... 
 
 Silica 68.7 ... 40.00 
 
 Loss 2.3 ... 
 
 100.0 lOO.UO 
 
 169. The dung of the cow, however, usually contains a 
 larger amount of water than stated in the above analysis ; 
 and as the chief portion of the nitrogen contained in its food 
 is separat<jd in the urine, it does not so readily run into 
 fermentation, and is correctly regarded as affording a coUler 
 manure than horse-dung. The quantity of solid matter, 
 you have seen, which is annually voided by the horse in 
 tlie urine, does not amount to one-tenth part of that which 
 is contained in the urine of the cow; and as the food which 
 the former animal receives consists chiefly of the dry and 
 nutritious grains, its solid excrement rapidly decomposes, 
 and gives out much heat when placed in the soil; and 
 hence it is frequently mixed with other manures for the 
 purpose of inducing fermentation. From the rapidity with 
 which it decomposes, much of the valuable qualities of horse- 
 dung are usually lost to the farmer by allowing it to accumu- 
 late in the stable or fai'm-yard. Boussingault found that 
 fresh horse-dung which, deprived of water, contamed in the 
 J 00 lbs. so much as 2^^ft)3. of nitrogen, lost by fermentation 
 
118 LESSONS IN CHEMISTRY. 
 
 9. 10 lbs. of its weight, and aflforded only one pound of that 
 substance which it is so important to economise. 
 
 170. The dung of the pig usually contains about 75 per 
 cent of water, and is generally regarded as affording a colder 
 manure than that of the horse or cow; but as the pig is a 
 general feeder, the manure which it yields will frequently be 
 rich in nitrogen. On the continent it is much employed in the 
 cultivation of hemp, but is supposed to give a disagreeable 
 flavour when appHed to the root-crops. 
 
 171. The dung of the sheep is of great importance as a 
 manure in many districts, both in England and this country. 
 In Wiltshire, the usual method of applying it is by folding 
 the sheep on the bare fallow, and shiftmg the hurdles every 
 night so as to distribute the manure over the field. On the 
 light soils of Norfolk also, it has been found of great advan- 
 tage to allow the sheep to consume the crops in the field, by 
 which means the manure is trodden in, and its rapid fermenta- 
 tion prevented, and the ground at the same time consolidated. 
 In the quantity of nitrogen which it contains, and conse- 
 quently in its tendency to ferment, sheep-dung may be 
 regarded as intermediate between that of the cow and horse. 
 All these manures contain the ingredients which plants 
 remove from our fields, and by their careful restoration to 
 the soil you will supply your crops with the materials which 
 they require, in the form best adapted for their nourishment. 
 Experience has taught farmers how much the value of the 
 manure which is produced by an animal, is influenced by the 
 food with which it is supplied ; and that a cow fed upon highly 
 nutritious substances, such as bean-meal and oil-cake (77), 
 yields a manure containing a larger amount of fertihzing 
 matter than one fed upon straw and turnips. 
 
 172. It has also been found that the quality of the dung 
 of an animal depends upon its age and the purpose for 
 
 / which it is Icept. Thus, the dung of growing animals is not 
 
 ?so rich in fertilizing materials as that of full-grown cattle. 
 
 \ To enable you to understand how this is, it will be useful 
 
 ] briefly to describe the changes which food is made to undergo 
 
 ( when taken into the body. You will recollect that I stated 
 
 to you in a preceding chapter (79), that the great bulk of 
 
 / every plant cultivated for food consisted of certain compounds 
 
 ] produced by the union of the four simple elementary bodies, 
 
 (^oxygen, hydrogen, nitrogen, and carbon; and that while one 
 
ANISIAL MANURES. i 1 1^ 
 
 class of these compounds, gluten, albumen, &c was ilistin- \ 
 guished by containing a large amount of nitrogen, and was / 
 in fact almost identical in composition with the substance of \ 
 the flesh of animals, another class of bodies — starch, sugar, i 
 fat, &c was composed solely of carbon and the elements of j 
 water united in various proportions. You are already aware ( 
 that the gluten, and other nitrogenized matters contained in \ 
 the seeds and herbage which are eaten by animals, sei-ve to/ 
 l)uild up their bodies — are converted into their substance;] 
 but in the greater number of plants used for food, the pro- / 
 portion of compounds containing nitrogen is exceedingly small j 
 as compared with those resembling starch and sugar m{ 
 composition, the former on an average amounting to only) 
 1 1 per cent, while the latter average from 70 to 80 per cent.S 
 *' What," you will inquire, " becomes of the carbon which is v. 
 eaten by animals?" ) 
 
 173. You may recollect that I stated (26) that an enormous 
 amount of carbonic acid is given out in respiration. The air __ 
 that we draw into our lungs in breathing contains only the *> . 
 one two- thousand-five-hundredth part of its bulk of that gas ; 
 yet, when we throw it out again into the atmosphere, its 
 proportion is found to be increased so as to form two gallons* 
 
 in every hundred expired ; a full-grown man, using vigorous 
 exercise, giving out every day from his lungs as much 
 carbonic acid as would be produced by the combustion of 
 about fifteen ounces of charcoal. This separation of carbon 
 in the form of carbonic acid from the lungs of animals, is 
 indispensable to the continuance of life, and is made to serve 
 an important purpose in the animal economy. 
 
 1 74. When a pound of starch or sugar is set on fire it 
 bums and disappears, the carbon contained in it unites with 
 the oxygen of the air, producing carbonic acid gas (22) and 
 ;:iving out heat; and the carbonaceous compounds, starch, 
 ttc. which the animal eats, are believed to undergo, within i 
 the body, by the intiuence of the oxygen of the inspired air, 
 })recisely similar changes as when burned, the carbonic acid 
 i;as being discharged from the mouth and nostrils, while the 
 heat which is generated by their combustion, as it may be 
 t(;rmed, serves to maintain that temperature of the body 
 which health requires. Thus, you perceive that those com- 
 pounds, though incapable of being employed in the formation 
 of bone or muscle, are indispensable to animal life. 
 
 k2 
 
1 20 LESSONS IN CHEJnSTRT. 
 
 175. So much, therefore, of the carbon of the mixed food 
 eaten by animals being thus separated in respiration, it is evi- 
 dent that the part which remains must become relatively richer 
 in nitrogen and the other ingredients ; and consequently, when 
 expelled from the body in the Uquid and solid excrements, be 
 capable of exerting a more powerful effect as manure than 
 the same weight of the unaltered food applied to the soil. It 
 has been ascertained, by careful analysis of the food and 
 excrements of a horse fed on hay and oats, that, while in 
 the food, carbon and nitrogen existed in the proportion of 
 28 parts of the former to 1 part of the latter, in the dung 
 there were but 10^ parts of carbon to 1 part of nitrogen. 
 Thus, the investigations of the chemist beautifully confirm 
 the accuracy of the opinion long entertained by practical 
 farmers. 
 
 176. After the above remarks, you will readily understand 
 the explanation which chemistry affords of the difference in 
 the value of the manure produced by young animals and full- 
 grown cattle. In the droppings of a. full-grown animal, you 
 have seen, the food eaten is discharged improved in its ferti- 
 lizing qualities; but, in the growing animal, much of the 
 gluten and inorganic matter of the food is employed in the 
 development of its bones and muscles ; hence the dung dis- 
 charged from the body is not so rich in nitrogen and saHne 
 matters. In fattening animals, the increase in bulk is pro- 
 duced not at the expense of the gluten and other nitrogenized 
 matters of the food, fat, like starch, containing no nitrogen 
 (78), and being formed from carbon, hydrogen, and oxygen 
 only ; nearly all the nitrogen therefore of the highly nutritious 
 food which the animals receive is discharged in their dung. 
 
 177. Farm-yard Manure. — The refuse of the farm, the 
 straw used for litter, mixed with the liquid and solid excre- 
 ments of the cow-house, stable, and piggery, constitute what 
 is termed "farm-yard manure," which has long been regarded 
 as the most important source of the materials required for 
 the growth of the farmers' crops. It is generally supposed 
 that this manure must contain eveiything which plants 
 require for their nourishment, and to be all-sufficient to restore 
 fertility to any description of soil; but you will readily 
 understand, from what has been stated respectmg the varia- 
 ble composition of the excrements of animals, as well as of 
 the plants produced on the farm, that it must vary exceed- 
 
ANIMAL MANURES. 121 
 
 ingly in value, and in many cases be deficient in some of the 
 most essential ingredients. 
 
 178. A slight consideration of the nature of the substances 
 which compose the manure heap, will show you how much 
 its value may be lessened by the ordinary wasteful practice 
 of the farmers in this country. In the first place, it consists 
 of a mixture of vegetable matters, which have been trodden 
 under the feet of cattle, and saturated with their urine, and 
 therefore in the most favourable condition for undergoing 
 fermentation. In the course of some weeks after the mix- 
 ture has been formed, you find, upon examining the heap, that 
 heat is produced, and that a kind of slow combustion is going 
 on within it. The effect of this fermentation or combustion 
 is to break up the structure of the straw and other vegetable 
 matters present, and, in the escape of the pungent smelling 
 ammonia and other gases which fill the farm-yard with their 
 odours, you perceive that some of the ingredients of the 
 mixture have become volatile, and are escaping into the 
 atmosphere.* 
 
 179. Now, every pound of ammonia which escapes, carries 
 with it the nitrogen which would have been sufiicient for 
 the growth of 60ibs. of com. As the fermentation of the 
 manure proceeds, more and more of the organic matter pre- 
 sent undergoes decomposition, and is converted into volatile 
 gases ; so that, after rotting for several months, its weight 
 is found to have greatly diminished, and it has become a 
 black, friable mass.f Nor is it merely the organic matters 
 of the mixture that are lost. Considerable portions of the 
 excrements of animals readily dissolve in water, and the 
 tissues of the straw, leaves, and other vegetable remains, 
 being broken up by the fermentation, the mineral matters 
 
 * If a piece of moistened red litmus test-paper be brought near a 
 smoking manure heap, it will be rendered hhie^ and a glass rod mois- 
 tened -with spirits of salts (muriatic acid) will be covered with a white 
 crust of sal ammoniac, produced by the union of the acid -vvith the 
 escaping ammonia. 
 
 ■j" Some instructive experiments made on the continent show us how 
 much manure is wasted by allowing it to remain exposed in heaps. Thus, 
 a hundred loads of fresh dung were reduced at the end of 
 
 Loads Loads 
 
 81 days, to 73.3, sustaining a loss of 2().7 
 
 254 „ G4.4 „ 35.6 
 
 884 „ 62.5 „ 37.5 
 
 493 „ 47.2 „ 52.8 
 
1 22 LESSONS IN CHEMISTRY. 
 
 which they contain are rendered soluble. The first shower 
 of rain, therefore, which pours upon the heap more water 
 than it can soak up, flows away, carrying with it some of 
 the phosphoric acid, sulphuric acid, potash, and other valuable 
 ingredients, which had given fertility to yom- fields. These 
 substances, with some of the ammonia, which is exceedmgly 
 soluble in water (16), are swept into the drains.* 
 
 Thus, though the manure heap is formed of materials rich 
 in all the substances which enter into the composition of our 
 crops, as usually managed, it must, when applied to the land, 
 be deficient in much of its original fertilizing power. 
 
 180. Farm-yard manure usually contains about 70 per 
 cent of water, 20 per cent of organic matters, and 10 per 
 cent of earthy and saline matters ; and it is calculated that, 
 on the average, 10 tons of it convey to the soil about 1 cwt. 
 of ammonia and 781bs. of phosphoric acid, and the same 
 amount of potash. From the great variety, however, of 
 materials composing it, every sample of this manure will vary 
 widely in composition, and an account of the analyses of it 
 which have been published, would convey but little infor- 
 mation to the farmer. It will be of greater consequence to 
 consider how the loss of the volatile matters which are set 
 free during fermentation, and also of the inorganic matters 
 which are so liable to be washed out by eur frequent showers, 
 may be most efi'ectually prevented. 
 
 In wet weather, you will observe on every part of the 
 country a black stream oozing from the farm-yards, and 
 
 * The drainings of farm-yard dung have been analyzed, and found 
 to be exceedingly rich m fertilizing matters. The follo-vvuig is the 
 composition of an imperial gallon of the liquid, examined in the Labo- 
 ratory of the Agricultural Chemistry Association of Scotland : — 
 
 Ammonia 21.6 grs. 
 
 Organic matter 77.6 
 
 Inorganic matter, or ash .... 618.4 
 
 617.5 grs. 
 The inorganic matter contained in the liquid consisted of 
 
 Alkaline Salts 420.4 grs. 
 
 Phosphates of Lime and Magnesia 44.5 
 
 Carbonate of Lime 31.1 
 
 Carbonate of Magnesia, and loss 3.4 
 
 Silica, and a little Alumina 19.0 
 
 518.4 grs. 
 
ANIMAL MANURES. 123 
 
 flowing away unheeded into the sewers ; and in the hot days 
 of summer, the pungent odours which are given out from the 
 carelessly heaped together contents of the stables, will show 
 you that the farmer, ignorant of his profession, is uncon- 
 sciously allowing the most active matters of the manure to 
 escape into the air. 
 
 181. ^[anagement of farm-yard manure. To secure all 
 the good qualities of the fertilizing substances collected 
 together in the manure heap, it will not do to leave it to 
 chance. You must not allow the air to run away with one 
 part, and the rain with another part, of its most usefol 
 matters. It is of the utmost importance that you carefully 
 preserve and restore every particle of the materials abstracted 
 from your fields. All the arrangements of the farm-yai-d 
 and offices should be made subservient to this purpose, and 
 the money expended in providing a proper receptacle for the 
 manure will be fully repaid in the increased luxuriance of 
 your crops. 
 
 You should not, as too frequently done, allow the manure, 
 upon its removal from the cow-houses and stables, to be 
 spread over the fann-yard, but' have it immediately carried 
 to a place prepared for its reception, at a convenient distance 
 from the office-houses. This dung-stead should, if possible, 
 be placed in the north side of the farm-yard, and if the 
 ground be porous, it should be puddlel with clay and paved, 
 so as to be rendered completely water-tight. It is not ne- 
 cessary that it be excavated below the surface of the yard, 
 but it should be made to slope, so that the liquid which 
 escapes from the manure may flow into a water-tight reser- 
 voir provided for its reception. In some of the best agri- 
 cultural districts on the continent, the manure-stead is sepa- 
 rated into two divisions by a tank, usually about four feet 
 deep, and of breadth proportionate to the size of the heap; 
 the sides and bottom of this reservoir are well puddled with 
 clay and lined with masonry; and the more ettectually to con- 
 vey into it all the drippings from the manure, the sides of the 
 heap are surrounded with a paved channel. At one extremity 
 of the tank a strong wooden pump is fixed, by which the 
 liquid can, at pleasure, be discharged over the manure, by 
 means of a canvass hose, or wooden spouts, or pumped into 
 casks to be conveyed to the fields. 
 
 All the farm buildings should be spouted, and the water 
 
124 LESSONS IN CHEMISTRY. 
 
 from the spouts, as well as that which falls upon the yard, 
 should be conveyed away, by drains so constructed that 
 it may be allowed to flow over the adjoining fields, or 
 used to dilute the contents of the tank. The liquid from the 
 byres and stables, which has not been absorbed by the litter, 
 and also the drainage from the farm-house, should be con- 
 veyed to the tank by drains, which are readily formed by 
 inverted draining-tiles bedded in clay, and covered over with 
 boards or flags. To prevent any loss of space, the tank, 
 when placed across the manure-stead, may be covered with 
 a close wooden grating, and the dung piled upon it, by which 
 means the evaporation of the liquid will be prevented, and 
 any escaping gases absorbed by the manure. Some farmers 
 consider it necessary to cover the manure with a roof, but 
 when the yard is carefully drained, it may be dispensed with, 
 as the rain which falls upon the heap will tend to prevent 
 too rapid fermentation, and any matters dissolved out will 
 be found in the tank. 
 
 182. The manure should be evenly spread upon the dung- 
 stead, and the sides of the heap preserved perfectly straight, 
 and care should be taken to prevent the temperature rising 
 too high. When it rises above 82 degrees of the thermo- 
 meter, it should be moderated by an application of liquid from 
 the tank. Fermentation should not be allowed to proceed 
 farther than when the straw commences to lose its consis- 
 tence. At this period it is admu-ably adapted to promote the 
 growth of plants, and when it is not convenient to remove to 
 the fields, some sulphuric acid, sulphate of lime, or sulphate 
 of iron, should be added to the liquid before pumping it on 
 the heap. " Farmers," says an able continental writer on 
 this subject, " often hesitate to make the necessary arrange- 
 ments to save their liquid manure, because they imagine they 
 can obtain it in very small quantity. They do not consider 
 that the little stream of liquid manure which trickles from 
 their dunghill runs during nearly the whole yeai', and increases 
 with every rain. With 6 or 8 horses, as many cows and 
 oxen, and 100 sheep, there may be obtained more than 200 
 hectolitres* yearly, when the arrangement to collect it is 
 made in a manner by which none will be lost. With this 
 quantity distributed in the fields, many thousand pounds 
 
 * A hectolitre is about 22 gallons. 
 
ANIMAL MANURES. 1 25 
 
 more of fodder will be harvested than could have been pro- 
 cured without it."* 
 
 Though many of our small farmers cannot be expected to 
 construct tanks and receptacles for manure such as have been 
 above described, yet even the poorest holder of land in this 
 country has it in his power to do something to prevent the 
 present shameful waste of the materials which his crops 
 require, and the neglect of which, you are now prepared to 
 acknowledge, must as certainly tend to the exhaustion of his 
 fields, as if he were every year to throw a portion of their 
 produce into the sea. Remember that if you wish to succeed 
 as a fanner, it is not enough to possess a kindly soil or to 
 caiTy off the first prizes at the ploughmg-match, if you are 
 every year obliged to purchase those matters to feed your 
 crops which are allowed to escape into the air, or to be washed 
 into the sewers fi'om your neglected manure heap. How 
 much money expended in the purchase of guano, and other 
 foreign manures, might be saved by a careful economy of the 
 ingredients abstracted from your fields ! 
 
 183. If you refer to a preceding chapter in which the 
 method of preparing pure ammonia is described {page 28, 
 note)j you will find that that substance, so important to vege- 
 table life, h readily separated from certain compounds in 
 which it exists, by mixing them w ith quicklime ; thus, for 
 example, when the salt termed sal ammoniac (19), in which 
 that gas exists in chemical combination with muriatic acid 
 (page 29), forming a compound free from smell, is mixed with 
 caustic lime, the acid unites with the lime, while the ammo- 
 nia escapes, giving out its characteristic odour. Soda, 
 potash, and magnesia, in the caustic state (43, 47), also 
 possess the property of decomposing the. salts of ammonia; 
 hence when the farmer, as is so frequently practised in some 
 parts of Ireland, adds quicklime to his manure heap, the 
 carbonate of ammonia (154), produced by the decay of the 
 nitrogenised matter contained in it, is decomposed, and the 
 volatile ammonia expelled into the atmosphere. As it is of 
 
 • A simple and perfectly effectual plan of distributing the liquid 
 manure, is to affix a piece of board, about a foot sijuare, opposite to tlie 
 hole in the end of the manure barrel, so that wlien the phig is with- 
 drawn, the liquid, as it gushes out, may strike against it. By this 
 method the manure is spread out with considerable regularity, as the 
 cart on which the barrel is fixed passes slowly along, 
 
1 26 LESSONS IN CHEMISTRY. 
 
 vital importance to the farmer that none of this ingredient of 
 manure, so essential to the full development of his crops, 
 should be allowed to escape, one or other of the chemical 
 substances above described should be employed. When 
 describing the method by which Liebig detected the ammonia 
 existing in the atmosphere (19), I mentioned that he added 
 to the rain water in which it was dissolved a small quantity 
 of muriatic acid, by which the heat used in evaporating the 
 water was prevented driving it away. Several other acids 
 also possess this property ; and when the salts which sulphuric 
 acid forms by combining with iron, green vitriol (163), and 
 with lime, gypsum^ are mixed with decomposing manure or 
 night soil, the acid enters into chemical combination with the 
 ammonia and converts it into a solid compound, which, 
 though soluble in water, and therefore capable of being taken 
 up by plants, is securely ^a:ec? in the manure heap.* 
 
 1 84. It is not necessary that the small farmer should con- 
 struct an expensive tank ; a treacle hogshead, or even a large 
 tub sunk in the ground close to the manure heap, will be found 
 a very good substitute for it. In a small establishment, 
 nearly all the liquid manure of the stable and cow-houses may 
 be completely absorbed by the litter; or, where enough of 
 straw cannot be obtained, by spreading under the cattle dry 
 peat-mould, saw-dust, or even dry soil from the fields, as is 
 done by the careful farmers in many parts of this country. 
 The manure, when removed from the houses, should be 
 placed in a sheltered position upon a bottom of earth well 
 beaten down, so as to be rendered as retentive of moisture as 
 possible, and made to slope towards the tub ; a trench dug 
 round the heap will serve to prevent the entrance of 
 surface water. In districts where peat mould can be con- 
 veniently pi'ocured, its use will be found of great value to the 
 farmer; by adding a layer of it occasionally to the manure 
 
 * The teacher may usefully impress the above remarks on the minds 
 of his pupils, by placing before them some sal ammoniac and quicklime, 
 and allowing them to examine them. Neither of these substances, he can 
 show them, gives out any smell ; but by rubbing together in the mortar 
 one teaspoonful of the former with two of the latter, the pungent odour 
 of ammonia will be immediately evolved. The nature of the escaping 
 gas may be tested (11) by bringing near the mortar a piece of moistened 
 red test-paper, which mil be rendered blue by the alkaline gas. The 
 property which certain substances possess of fixing ammonia may be 
 convincingly shown by pouring into the mortar a teaspoonful of spirits 
 of salts, when the pungent odour of smelling salts will be destroyed* 
 
\ 
 
 ANIMAL MANURES. 12? 
 
 heap, and moistening it with liquid from the tub, the ferti- 
 lizing qualities of the manure will be greatly increased. 
 
 185. It is considered indispensable by many persons 
 when the liquid manure is to be applied directly to the fields, 
 that it should be allowed to remain for some time in the 
 reservoir, that it may undergo fermentation. But this plan 
 •would require tanks of greater capacity than are likely to be 
 provided by the greater number of farmers. When used as 
 a top-dressing, if diluted vnih four or five times its bulk of 
 water, or the washings of the byres and dwellmg-house, it 
 may be applied without apprehension; for manuring the 
 ploughed soil before sowing, it is unnecessary to dilute it. 
 On the continent, the farmers consider the liquid manure to 
 be peculiarly adapted for the cultivation of potatoes and other 
 root-crops; and in Belgium, light sandy soils, which in this 
 country would be regarded as worthless, are made to yield 
 splendid crops of hay by frequent applications of it. 
 
 1 86. From reflecting upon the loss which is experienced 
 in the ordinary method of treating manure, many intel- 
 ligent farmers in this country have adopted the plan of 
 conveying the fresh unfermented dung directly from the stable 
 to the fields, and of allowing it there to undergo the changes 
 required to enable it to assist vegetation. Opposite opinions 
 •especting the propriety of this practice are held by some* of 
 
 !ir most experienced cultivators. But from a careful con- 
 sideration of the subject, and from observing the success with 
 Avhich this method has been followed, both in our own and 
 )ther countries, I would advise you, instead of allowing the 
 
 laniu-e to accumulate in heaps, to convey it as frequently 
 
 IS possible to your fields, and to bury it at once in the soil. 
 ■\'hile the action of rotten dung is soon exhausted, the fresh 
 jiianure affords a steady supply of food to plants by its 
 . radual decomposition, and the heat given out by its decay, 
 
 iie benefit of which is usually lost to the fanner, must also 
 
 )ntribute to promote vegetation. It has been objected that 
 i'»r crops which, like the tm-nip, require to be rapidly pushed 
 J or ward in the first period of their growth, fully fermented 
 jnanure is necessary, but for these crops a small quantity of 
 iU'uano or dissolved bones should be invariably applied with 
 the farm manure. This practice is followed with gi-eat 
 
 uccess on the well-managed farms of the Messrs, Andrews 
 
 iear Comber, Count v Down. 
 
128 LESSONS IN CHEMISTRT. 
 
 187. Guano. — One of the most extraordinary features in 
 the agriculture of the last half century is the importation into 
 this country of enormous quantities of various animal sub- 
 stances, for the purpose of being employed in increasing the 
 produce of our farms. Every part of Europe has been 
 ransacked for bones to manure the fields of England and 
 Scotland, and within the last four or five years thousands of 
 tons of the droppings of sea-birds, deposited on the coast of 
 South America and Africa, have been purchased for the same 
 purpose. It has been stated that between 1841 and 1844, 
 England imported not less than 70,000 tons of this manure, 
 the very name of which was a few years ago scarcely known 
 in this country. Thus, whilst we neglect the fertilizing mate- 
 rails at our doors, we have not hesitated to send 5,000 miles 
 for the mineral matters contained in the excrements of birds. 
 
 188. It is unnecessary to describe the characters of the 
 substance which is termed guano, as that manure is now well 
 known to every farmer. It consists of the excrementitious 
 matter deposited by sea-birds, which in certain parts of the 
 world congregate in immense flocks, covering the islands and 
 promontories which they frequent with their droppings. It 
 appears to have been used from the earliest times by the 
 natives of Peru, who by its assistance and the employment of 
 irrigation, were enabled to produce lich crops of grain from 
 sterile sandy soils. Before the year 1841, though small 
 quantities of it had been brought to this country, it attracted 
 but little attention, and was regarded merely as an agricul- 
 tural curiosity until Lord Stanley, at the meeting of the 
 lloyal Agricultural Society of England, held in that year at 
 Liverpool, gave an account of its extraordinary fertilizing 
 qualities ; and the successful results which followed the trials 
 which were made of it, at once established its character as a 
 most important addition to our animal manures. 
 
 1 89. The fii'st guano brought to this country was from the 
 islands near the coast of Peru, and was sold at from 225. to 
 285. per cwt. ; but as the demand for the manure increased, 
 another deposit of it was discovered on the island of Ichaboe 
 on the coast of Africa, which however was in a short time 
 exhausted. Other deposits, both on the coast of America 
 and Africa, have since been found out, and at present aflford 
 a considerable supply, though of inferior value to the Peru- 
 vian and Ichaboe guanos. 
 
ANIMAL MANURES. 1*29 
 
 190. In guano, we find all the inorganic materials which 
 existed in the food of the birds by which it has been deposited, 
 for, by a peculiarity in the sti'uctui-e of bu'ds, both the liquids 
 secreted by the kidneys and the solid contents of the bowels 
 are discharged from the same apertme, and thus both the 
 soluble salts which had been taken into the circulation, and 
 the undigested matters of the food are contained in these 
 deposits. In countries like Peru, where rain seldom falls, 
 the soluble parts of the excrements djied up by the wai-m 
 sun, remain for centuries, and the substances containing 
 nitrogen (uric acid, &c), are not decomposed into volatile 
 compounds, so that in the best preserved samples of Peruvian 
 guano the smell of ammonia is scarcely to be perceived, while 
 in samples of the manm-e bi'ought from other places not so 
 favoui-ably situated for its pj-esei-vation, the alkalme salts 
 have neaily disappeared, and a strong pungent ammoniacal 
 odour is evolved by the decomposing nitrogenised matters, 
 thus while genuine Pei'uvian and Bolivian guanos yield in 
 general from 10 to 16 per cent of ammonia, the guano brought 
 from Patagonia consists chiefly of the insoluble Phosphates 
 (53), and affords only about 3 or 4 per cent of ammonia. 
 
 191. The composition of guano has been studied by ex- 
 perienced chemists, both on the continent and in this countr}-. 
 The most complete analyses which have been published, are 
 those of Mr. Deuham Smith, communicated to the Chemical 
 Society. The followmg is the composition of a sample of 
 PeiTivian guano, said to be of very superior quality ; 1 00 parts 
 contained — 
 
 Wat€r 21-510 
 
 Organic matter and combined water 12-296 
 
 Potash '. 1-144 
 
 Soda 3-430 
 
 Ammonia 6-434 
 
 Lime 15-356 
 
 Magnesia 0-764 
 
 Muriatic acid 2-414 
 
 Sulphuric acid 2-106 
 
 Oxalic acid 12-850 
 
 Phosphoric acid 16-328 
 
 Uric acid 2*308 
 
 Humus 2-060 
 
 Sand 1-648 
 
 Loss -352 
 
 100-000 
 
130 
 
 LESSONS m CHEMISTRY. 
 
 The above analysis is interesting, as exhibiting the true 
 composition, and very complex nature of this curious deposit ; 
 but it is obvious, that for agricultural purposes, a different 
 kind of analysis is required, in which the amount of the 
 various substances, which give this manure its peculiar value, 
 may be clearly understood by the farmer. Accordingly, in 
 estimating the value of a sample of guano, the method which 
 is followed in the laboratory of the Chemico- Agricultural 
 Society, is to furnish the farmer with a clear statement of 
 the per centage of water, organic matters, with the amount 
 of ammonia which they are capable of yielding by decompo- 
 sition ; phosphates of lime and magnesia, and substances like 
 common salt (chloride of sodium) and gypsum, which, though 
 valuable for the food of plants, can be more economically 
 supplied in other ways. 
 
 192. The following table exhibits the composition of four 
 samples of guano lately sold in Belfast, 100 parts of each 
 sample contained respectively : — 
 
 
 i 
 
 § 
 
 1 
 
 1 
 
 
 1 ■ 
 1 
 
 
 1 
 
 1 
 
 
 Ph 
 
 
 
 Ph 
 
 
 HI 
 
 s 
 
 ^ 
 
 > 
 
 Water 
 
 13-00 
 
 29-20 
 
 20-68 
 
 29-40 
 
 Organic matters Sf 
 
 
 
 
 
 ammoniacal salts 
 
 52-32 
 
 34-00 
 
 39-12 
 
 15-44 
 
 Alkaline sulphates 1 
 & common salt, &c. / 
 
 4-67 
 2-49 
 
 8-10 
 
 12-20 
 
 5-28 
 
 Phosphates of Lime 
 
 
 
 
 
 and Magnesia ... 
 
 25-72 
 
 27-70 
 
 25-52 
 
 41-04 
 
 Gypsum 
 
 
 
 
 1-06 
 
 Carbonate of Lime 
 
 
 
 
 4-34 
 
 Sand and earthy 
 
 
 
 
 
 matter 
 
 1-80 
 
 1-00 
 
 2-48 
 
 3-44 
 
 
 100-00 
 
 100-00 
 
 100-00 
 
 100-00 
 
 The organic matters 
 
 
 
 
 
 and ammoniacal 
 
 
 
 
 
 salts, were capable 
 of yielding of 
 
 
 
 
 
 
 
 
 
 Ammonia 
 
 13-01 
 
 8-05 
 
 10-84 
 
 2-5 
 
ANIMAL MANURES. 1 'i 1 
 
 193. The value of guano, as manure, depends chiefly upon 
 the compounds of nitrogen, and the phosphates which it con- 
 tains ; the alkalies and other ingredients of plants are usually 
 })re3ent in too small quantity to exercise any decided effects 
 upon vegetation; hence the judicious farmer, who is de- 
 sirous of keeping his fields in proper condition, should add 
 to it the ashes of sea- weeds (kelp) or common salt, to supply 
 the materials in which it is deficient. A well-known English 
 agriculturist, the Rev. Mr. Huxtable, states, that he has found 
 that the most profitable way of using guano is, some weeks 
 before sowing, to mix each cwt. of it with 1 cwt. of salt and 
 1 cwt. of gypsum. For the reasons just stated, it has been 
 found better to manm-e with a mixtm-e of yard dung and 
 guano than with guano alone ; and careful experiments made 
 in Scotland have shown that these manures, mixed in the 
 proportion of 10 to 14 tons of dung to 3 to 5 cwt. of guano, 
 will raise a larger crop in the first instance, than from 30 to 
 40 tons of dung alone, and leave the land in as good, if not 
 better condition, for the aftercrops, at about one-half the 
 expense of the dung." The wholesale price of Peruvian 
 guano in Liverpool is at present £9 9*. per ton. It is 
 usually applied at the rate of from 3 to 5 cwt. to the statute 
 acre, and to prevent the seeds being injured, it should, 
 previous to sowing, be mixed with dry soil, peat mould, 
 or with salt and gypsum, as above described. AVhen guano 
 was first introduced into this country, the farmers, who 
 had been accustomed to regard bulk as necessary to a good 
 manure, applied it in such large quantities that the crops 
 were in many cases destroyed. 
 
 With regard to the permanency of guano, considerable 
 apprehensions were at first entertained, but experience has 
 shown that its beneficial eftects upon the crops are not 
 confined to a single season. 
 
 194. Adulteration of Guano. — The character of guano, as 
 manm-e, has sutiered severely from the tricks of an unprin- 
 cipled class of manure manufacturers, by whom it is fre- 
 <iuently so skilfully adulterated as to render detection im- 
 l)ossible without scientific examination. It might be expected 
 that I would give some directions to enable farmers to dis- 
 cover these adulterations, but I do not think that the chemical 
 analyses of soils or manures can properly be performed by 
 the farmer. In every case the purchaser of guano should 
 
 L2 
 
132 LESSOICS m CHEMISTRY. 
 
 insist upon being supplied with an analysis, such as above 
 given, in which the amount of phosphates and ammoniacal 
 compounds, with the quantity of ammonia which they are 
 capable of yielding by decomposition, is clearly stated. 
 These are the substances which it would cost the farmer 
 most to purchase in the manure market, and their amount 
 in a sample of guano, may be taken as representing its 
 actual value. 
 
 195. Bones — At the present time bones are even more 
 extensively employed than guano for manuring. Their 
 reputation has progressed with the extension of the turnip 
 husbandry, and their use has, in no small degree, contributed 
 to improve the agriculture of districts which, from being 
 inaccessible to the more bulky manures, were formerly re- 
 garded as hopelessly barren. 
 
 196. For many years, crushed bones have been regarded 
 by the English farmer as his most valuable fertilizer ; and by 
 their appUcation alone, the fields of Cheshire, and other coun- 
 ties, exhausted by producing substances rich in phosphates, 
 as milk and cheese (54), had their ancient fertility restored. 
 In both England and Scotland, their importance is at present 
 very generally acknowledged. It is stated by a well-informed 
 authority, that one-third of the whole turnip-crop of these 
 countries depends upon them. In Ireland, though within the 
 last two or three years, there has been a considerable exten- 
 sion of their use among the more inteUigent farmers, yet a 
 large bulk of the bones collected in this comitry are purchased 
 by the Scottish farmer; and thus our fields are exhausted, 
 not only by the cattle which are fed upon them for the Eng- 
 lish market, but by the loss of the compounds of phosphorus, 
 which the crushed bones that we export contain. 
 
 1 97. Composition of Bones. — Like the plants upon which 
 the animal feeds, and from which, it is evident, all the mate- 
 rials for its growth must have been derived, bones consist of 
 two parts — a part which disappears into the air when they 
 are exposed to a strong heat, in the open fire, and an in- 
 combustible ash which remains. In the plant, the combusti- 
 ble or organic part, constitutes by far the largest portion of its 
 bulk. The ash left by burning a hundred weight of turnips 
 would weigh only about three-fourths of a pound ; but when 
 bones are burned, the ash weighs more than the combustible 
 matter which disappears. Bones differ in density, and in the 
 
ANIMAL MANURES. 133 
 
 amount of combustible matter which they contain, according 
 to the age of the animal, and other circumstances. A bushel 
 usually weighs from 42 lbs. to 45 lbs. Fresh bones, as ap- 
 plied to the land, contain about twenty per cent of water. 
 The following is then* per-centage composition, when dry: — 
 
 Organic combustible matters, 33^1bs. 
 
 Incombustible matter or ash, consisting of 
 
 Phosphate of lime (bone earth), 55 j^ 
 
 Phosphate of magnesia, 3 
 
 Carbonate of lime, 3f 
 
 Salts of Soda, 3^ 
 
 Fluoride of calcium, 1 
 
 100 lbs. 
 
 198. The organic portion of bones consists of oil, and of 
 a jelly-like matter possessing nearly the same composition as 
 horn, skin, and hair. This matter is capable, by its slow 
 decay in the soil, of producing two gases — carbonic acid and 
 ammonia — by means of which, it is considered, that carbon, 
 which we recognise as the chief constituent of wood, starch, 
 &c. (60-64) and, also, nitrogen, the element so indispensable 
 to the formation of the seed, may be supplied to the rootlets 
 of the growing vegetable, and employed for its development. 
 The organic matter of 100 lbs. of bones is capable of yielding 
 
 ' about 5 J lbs. of nitrogen. The earthy matter consists chiefly 
 of the phosphates which, as I have repeatedly explained, are 
 of such immense importance to our soils. 
 
 199. How do Bones act? — The mode in which bones 
 prove serviceable is yet an unsettled question among scientific 
 agriculturists. Formerly, before chemistry had demonstrated 
 the importance of the inorganic elements of plants, it was 
 generally supposed that all their qualities, as fertilizers, were 
 due to the organic matter which they contained. This opi- 
 nion, however, was considerably shaken by the observations 
 of many farmers, who had employed burnt bones, and the 
 bones which are boiled at Manchester for the manufacture of 
 glue, apparently with equal, and, in some cases, it is reported, 
 with superior eflfects to those produced by crushed bones. 
 At present, many persons are inclined to attribute all the 
 effects produced to the phosphates which they supply to the 
 exhausted soil. Sprengel, who is a supporter of this opinion, 
 instances their failure in places in the north of Germany, 
 where other animal manures, rich in organic matter, had 
 
1 34 LESSONS IN CHEMISTRY. 
 
 with advantage been applied, and maintains, that it depended 
 upon the soil being ah-eady supplied with compounds of 
 phosphorus. Professor Johnston, who is among the most 
 earnest advocates for the fertilizing vhtues of the organic 
 matter of bones, does not accept Spren gel's explanations of 
 the failure of bones in Northern Germany, but argues, that it 
 arises from the undrained state of the land to which they 
 were applied. There can be no doubt that the organic mat- 
 ter of bones, as theory would lead us to suppose, possesses 
 valuable qualities as a manure. The liquid which is ex- 
 tracted by boiling bones, in the dyeing manufactories of 
 Manchester, even after it has been deprived of so much of its 
 size as to be considered unfit for stiffening, is found to pro- 
 mote vegetation, and is eagerly purchased by the farmers of 
 Lancashire and Cheshire. Burnt and boiled bones have been 
 found to commence then* action sooner than those unburned ; 
 but this cannot be regarded as a proof that the organic por- 
 tion is of no value, but merely shows, that the fat and 
 gelatine may retard the progress of decay, and the action of 
 the gases, by which the insoluble phosphates are rendered fit 
 for being taken up by plants. Again, the observations fre- 
 quently made by experienced practical farmers, in England 
 that twenty stones of horse-hair, which are considered to 
 contain organic matter equivalent to that of sixteen bushels 
 of bones, will not produce an equal effect upon the soil, may 
 also be regarded as a proof, that, to the phosphates, bones 
 owe a large share of their useful qualities. We may fairly 
 assume, that the effects which burnt or unburnt bones pro- 
 duce upon a soil will, like the effects of all special manures, 
 be materially affected by chemical composition. When a 
 field contains a sufficient supply of organic matter, and is 
 deficient in phosphates, burnt bones may produce the most 
 immediate and decided effects; while, upon a soil which has 
 become poor in decomposing vegetable matter, the crushed 
 bones will be found the best application. Though there are 
 few soils in Ireland that would not be gxeatly benefited by 
 the use of burnt bones alone, yet I would not advise our 
 farmers to prepare them in that form, or to destroy matters 
 which we know contain ingredients of great value. From 
 what has been stated of the fertilizing qualities of the size 
 liquid, and also of the ash or bone earth, we may, I think, 
 conclude, that both of these substances, as tlieir composition 
 
ANIMAL MANURES. 135 
 
 would lead us to suppose, are capable of contributing to the 
 j^rowth of plants ; and, in the present state of our knowledge, 
 and before we are warranted by experiments made on the 
 soils — not of Germany, England, or Scotland, but of those 
 formed from our Irish rocks, and under the influence of our 
 Irish climate — I would, I repeat, not advise the farmer to 
 follow the opinion of those who would direct him to bum 
 bones before applying them to his fields. It would, I con- 
 ceive, be almost as judicious for him to bm-n Patagonian 
 guano, to procm-e the phosphates which give that substance 
 its chief value. (1 85) 
 
 200. To what crops should bones be applied? — Popular 
 opinion, and th^ practice of the most experienced farmers, 
 have pointed them out as specialhj adapted for the turnip- 
 crop. Like guano (191), bones contain all the ingredients 
 which plants require for their growth; but their analysis 
 (197) shows us that some of the inorganic matters are not 
 present in sufficient quantity to render it safe for the farmer 
 to rely upon them as the only manure for his fields for a 
 number of years. When the soil is deficient in alkalies, if 
 you grow upon it a crop of turnips, 20 tons of which, in the 
 tops and bulbs, carry away so much as 265^ lbs. of potash 
 and soda, its fertility will be seriously impaired, if no other 
 manure than bones be used ; hence it is advisable that the 
 farmer should combine with them farm-yard dung, common 
 salt, kelp, or some other manure capable of supplying these 
 
 iibstances. 
 
 20 1. What is the difference in the action of bones and guano ? 
 — This is a frequent question. Like bones, guano can be se- 
 parated, by burning, into two parts — an organic combustible 
 portion, which is consumed, and a fixed, incombustible ash. 
 This ash usually contains the same ingredients that we dis- 
 cover in bone earth; but, in the different kinds of guano, 
 they are found in very unlike proportions. The proportions 
 of organic matter and ash also differ very much in the dif- 
 ferent varieties of that substance which are brought to this 
 country: thus, in the genuine Peruvian, the organic matters, 
 
 ipable of yielding ammonia, range from 50 to 60 per cent, 
 and the phosphates of lime and magnesia average about 26 
 per cent; while in the Patagonian, and some other varieties, 
 the relative proportion of these substances is very different, 
 and approximates them to bones m their composition. Hut 
 
1 36 LESSONS IN CHEMISTRY. 
 
 equal weights of crushed bones and good Patagonian guano, 
 applied to the same field, do not, it has been found, produce 
 an equal return. 
 
 202. The experience of farmers shows, that, weight for 
 weighty the guano, especially on dry and sandy soils, is capa- 
 ble of yielding larger crops. This superiority of guano is to 
 be explained, first, by the fine state of division in which its 
 constituents are presented to the soil; and, in the second 
 place, by the readiness with which its organic matters yield 
 up their ammonia. Bones cannot, without difficulty, be 
 reduced to a coarse powder, except by the assistance of 
 powerful and expensive machinery. Placed in the soil in a 
 coarse state, they decay but slowly; and many years must 
 elapse before all their ingredients are converted into a form 
 in which they can produce their efiects upon the crops of the 
 farmer. The fanners, in some parts of Scotland, are accus- 
 tomed to apply them broken into half-inch and three-quarter 
 inch pieces ; but in this state their application will not be 
 productive of the immediate results which are observed when 
 they are applied in a more minutely divided state, and 
 which, especially for the tm-nip-crop, it is most important to 
 produce. 
 
 203. In England, various plans have been adopted to 
 secure their more ready decomposition. Some persons place 
 them in a heap, covered over with earth, and allow them to 
 heat and ferment, by which means their decomposition, when 
 placed in the soil, is considerably accelerated; others, again, 
 mix them with farm-yard manure, and leave them to ferment. 
 Both plans are useful ; but to chemistry the practical farmer 
 is indebted for another mode of effecting their division, which 
 far surpasses any method hitherto attempted, and which has, 
 dming the last two or three years, been extensively adopted, 
 with the most signal success, — I allude to the decomposition 
 of bones by the action of sulphuric acid (vitriol), or of 
 muriatic acid (spmts of salts). By means of these cheap 
 and well-known acids, it has been found, that they can be 
 converted into the most effective and economical form in 
 which they can be given to the soil. For this valuable 
 method, the English agriculturist is indebted to that great 
 man, whose writings have done so much to direct public 
 attention, in this country, to the services which science is 
 capable of rendermg to the farmer. In his report on the 
 
ANIMAL MANURES. 1 37 
 
 (.hemistry of agriculture, Baron Liebig says, that "the most 
 easy and practical method of effecting the division of bones, 
 is to pour over them half their weight of sulphuric acid, 
 diluted with three or four parts of water, and after they have 
 been digested for some time, to add about one hundred parts 
 of water, and to sprinkle the mixture before the plough. In 
 a few seconds, the free acids unite with the bases contained 
 in the earth, and a neutral salt is formed, in a state of very 
 fine division. Experiments, instituted on a soil formed from 
 Grauwacke (126), for the purpose of ascertaining the action 
 of the manure thus prepared, have distinctly shown, that 
 neither com nor kitchen plants suffer injurious effects in 
 consequence, but that, on the contrary, they thrive with 
 much vigour." 
 
 204. The difficulty of applying liquid manure, which re- 
 quires water-carts, and arrangements not generally accessible 
 to farmers, suggested other methods of applying " dissolved 
 bones," which are now usually adopted. It has been found, 
 that by drying up the liquid mixture, by the addition of dry 
 peat-mould, by sawdust, or even by vegetable earth, it could 
 be converted into a form in which it might be more conve- 
 niently used by the majority of farmers. 
 
 205. The chemical changes produced upon bones by the 
 action of sulphuric acid, which is the acid now usually em- 
 ployed, are very important. When the diluted acid is 
 poured upon the bones, there is at first a violent frothing 
 up or effervescence, such as we observe when we pour vitriol 
 upon pieces of limestone. This effervescence is produced 
 by the rapid disengagement of carbonic acid, which is a 
 constituent of both limestone and bones; and, in both cases, 
 the same compound, sulphate of lime, or, as it is commonly 
 termed, gijpmm, is produced. But bones, as the analysis 
 shows, in addition to the compound of carbonic acid and 
 lime, which is one of their ingredients, also contain a large 
 amount (5 8 J per cent) of the insoluble phosphates. The 
 sulphuric acid also unites with a portion of the lime, in these 
 compounds; while the excess of the compound of phos- 
 phorus (phosphoric acid) which is separated, unites with the 
 remainder of the lime, to produce a new compound, which, 
 from containing a larger amount of phosphorus than the 
 original phosphates, is termed super-phosphate of lime. This 
 new phosphate is soluble in water, and is, therefore, capable 
 
1 38 LESSONS IN CHEMISTRY. 
 
 of at once ministering to the growth of plants. The organic 
 matters of the bones also undergo decomposition, and are 
 converted into new forms. Thus, by the influence of this 
 acid, the fertilizing qualities of bones can be rendered imme- 
 diately available, and the chief objection to then- use removed. 
 206. There are various names given to this preparation of 
 bones, which occasionally create confusion, as dissolved bones, 
 sulphated hones, super-phosphate of lime, vitriolized hones. 
 * Of these names the last is, probably, to be prefeiTed, as it 
 at once expresses the ingredients of the compound. The 
 extended use of this valuable manure, at the present time, 
 requires that I should make a few remarks on the plan to be 
 followed, in its preparation by the farmer. Various methods 
 are adopted ; but the following can be recommended : — 
 
 I. How the hones shoidd he prepared. — The bones to be 
 used cannot be broken too small; the more extensive the 
 surface presented to the action of the acid, the more rapid 
 and perfect will be the solution. The bones usually employed 
 are in too large pieces ; and a higher price should willingly 
 be given for them when reduced to powder. The price of 
 half- inch bones, as they are termed, is in Belfast 25. 6fZ. per 
 bushel. In every farm-yard, an old sugar hogshead should 
 be kept, into which all the bones, woollen rags, old hats, and 
 broken leather, should be thrown, and preserved, for being 
 reduced to manure in the vitriol vat. 
 
 II. Quantity of vitriol to he used. — The acid should be 
 pm'chased of full strength ; that is, of the specific gravity at 
 which it is sent from the manufactory, viz. 1-845. It should 
 be kept in a close vessel, as, when exposed, it rapidly attracts 
 moisture from the air, and becomes weaker. It must not be 
 forgotten, that it will burn both the skin and clothes, if 
 allowed to come into contact with them. When the strong 
 acid is mixed with water, a considerable amount of heat is 
 produced : twenty-five pounds of oil of vitriol, mixed with ten 
 pounds of water, will raise the temperature to 266 degrees. 
 The proportion of acid to be used in the preparation of 
 vitriolized bones, is one hundred weight of acid for every two 
 hundred weight of bones to be dissolved. A smaller am^ount 
 of acid is frequently applied; but the above proportions 
 will give the most satisfactory results. Vitriol, of full 
 strength, can be purchased fi'om the manufacturer at \d. 
 per pound. 
 
ANIMAL MANURES. 1 39 
 
 TIL Quantity of water ^ and mode of applying it. — When 
 undiluted vitriol is poured upon bones, violent action is pro- 
 duced, but continues for a very short time, as the gypsum, 
 which is the first new compound formed, covers the surface 
 of the pieces of bone with a crust, which prevents the acid 
 from coming into contact with the unaltered portions, and, in 
 consequence, its action is retarded, and a perfect solution is 
 not procured. If you drop some concentrated vitriol upon a^ 
 piece of limestone, there is a bubbling up, or effervescence, 
 from the escape of carbonic acid gas, but it continues only 
 for an instant. A crust of gypsum forms and protects the 
 stone from the acid ; but, if you use vitriol diluted with water, 
 the action and escape of gas continue for a much longer time. 
 The best plan, therefore, is to thoroughly moisten the bones 
 you intend to dissolve, by pouring over them a quantity of 
 water, and allowing them to soak in it for an hour or two 
 before adding the acid. The quantity of water used should 
 be three or four times that of the vitriol to be employed. 
 This mode of applying the water obviates the trouble of 
 mixing together the vitriol and water in a separate vessel, as 
 some recommend, and the heat generated, by adding the 
 strong acid to the moistened bones, greatly facilitates the 
 decomposition, and hastens the preparation of the compound. 
 
 207. Animal substances occasionally employed as Manures. 
 — In addition to bones and guano, there are several animal 
 substances used as manures in England and on the continent, 
 but which are seldom or only casually applied by the Irish 
 farmer. Of these substances, therefore, only a brief account 
 will be necessary. Fish and shell-fish have long been con- 
 sidered most valuable fertilizers. It is, indeed, complained, 
 that unless made into a compost with soil, they prove too 
 strong for the land. On the east coast of Scotland, Stephens, 
 in The Book of the Farm, informs us that, in the fishing 
 villages, where the fish are smoked or salted, the refuse is 
 prnxhased by the farmers, and constitutes an efficient manure 
 lor every kind of crop. " Thirty barrels of fish heads and 
 guts, half of cod and half of haddock, are," he states, 
 " enough of manure for one acre. The barrel contains thirty 
 gallons, and four make a cart-load. The refuse sells at 
 Is. 6d. per barrel. In preparing fish refuse for manure, it is 
 emptied from the barrels on a head-ridge of the field to be 
 manured, and mixed with a quantity of eaith, sufficient to 
 
 M 
 
140 LESSONS ON CHEMISTKY. 
 
 cover the refuse completely. It is driven fresh to the field, 
 whenever a supply can be obtained from the fishers. In two 
 or three months the compost is ready for use, and, as a 
 manure for turnips, is superior to farm-yard dung, and equally 
 beneficial on light and heavy soils. When used for turnips, 
 the compost is spread with shovels, out of the cart, along the 
 drills, at the rate mentioned, over which the drills are split, 
 and the seed sown along the drills by the machine. Of 
 course, it may be applied to bare fallow, for wheat as well as 
 for green crops." On the coasts of Ireland, we possess 
 numerous deposits of muscles, and other varieties of shell- 
 fish, which could be conveniently applied as manure. On 
 the shores of Strangford Lough, there are immense accumu- 
 lations of vegetable matters and mud, full of shells, which 
 might, with very little expense, be carted over the fields, but 
 which, so far as I am aware, have not yet been economized 
 by the farmer. In Donegal also, at Mulroy Bay, and in 
 several other localities, there exist beds of shell-sand, which 
 are, at the present time, extensively used as manure. 
 
 208. The flesh of animals, and blood, which may be re- 
 garded as liquid flesh, are not, to any extent, used as manures 
 in this country. Originally derived from plants, both contain 
 the most valuable ingredients of the soil, and are also rich in 
 nitrogen. In Paris, the blood from the slaughter-houses is 
 carefully collected and dried, and, in that state, sold at Ss. 
 per cwt. Recent flesh and liquid blood possess the following 
 
 composition : Flesh. Blood. 
 
 Water 77 80 
 
 Organic matters 22 19 
 
 Phosphate of lime § ) . 
 
 Other saline matters ^ 3 
 
 100 100 
 
 209. The inorganic matter, or ash, of the blood of the ox, 
 according to Dr. Enderlin, contains the following ingredients 
 of plants : — 
 
 Phosphate of Soda 16-77 
 
 Common Salt 59-34 
 
 Chloride of Potassium 6-12 
 
 Sulphate of Soda (Glauber Salt) 3-85 
 
 Phosphates of Lime and Magnesia 4-19 
 
 Oxide and Phosphate of Iron 8-28 
 
 Gypsum and Loss 1-45 
 
 100 
 
ANIMAL MANURES. 1 4 1 
 
 Rlood decomposes with facility, and is, therefore, a good 
 addition to the compost heap, as it induces the decomposition 
 of other substances. 
 
 210. The parings of the shins of animals, and horn 
 ^'havings, contain a larger amount of nitrogen than blood or 
 liesh; skin leaves, when buraed, only J per cent, and honi 
 about ^ per cent of ash. In the neighbourhood of tan-yard?, 
 where they can be procured, these substances are used with 
 great advantage ; but at present, they are chiefly consumed in 
 the manufacture of glue. Horn shavings decompose slowly in 
 the soil; therefore, where an immediate effect is required, 
 they should be either made into a compost, or dissolved in 
 the vitriol vat with the bone manure. 
 
 211. Woollen rags and hair. — The first of these substances 
 is very extensively used in England, especially in the hop- 
 growing districts; 20,000 tons being, it is said, annually 
 applied to the soil by the farmers in Kent, Sussex, Oxford, 
 and Berkshire. Rags are also occasionally used for wheat 
 and potatoes, and are considered to be most efficacious on 
 the light chalk soils. They are cut into pieces with an 
 instrument like a turnip-cutter, and are spread by hand over 
 the land, at the rate of 12 or 15 c^^1;. per acre. They de- 
 compose slowly on the soil, and should therefore be either 
 ploughed in a considerable time previous to putting in the 
 seed, or made into a compost. They are sold at from £3 1 2s. 
 to £5 per ton. Both rags and hair are poor in inorganic 
 matter, but contain a larger amount of nitrogen than blood 
 or flesh. Like bones, they consist of an organic or combus- 
 tible matter, and an incombustible ash. 
 
 In China, hair is considered one of the best manures ; but 
 in this country it is seldom that it can be procured in sufficient 
 quantities. Occasionally, it can be purchased at the tan- 
 yards at from £4 IO5. to £5 per ton. As met with in 
 Belfast, it is usually mixed with about the fourth of its weight 
 of lime. 
 
 2 1 2. The refuse of the glue manufacture, technically termed 
 ** gumps," is occasionally used as a manure in certain locali- 
 ties. It is a variable mixture of animal matters — hair, 
 bones, lime, bone earth, and sand. This refuse is sold in 
 two states, — as a moist mass, and in dry, brick-shaped lumps 
 of a dirty white colour. The following is the composition of 
 two samples of glue refuse, from the manufactory of Mr. 
 
142 
 
 LESSONS m CHEMISTRY. 
 
 Tucker of Belfast, which were lately analyzed in my Labora- 
 tory. 1 00 parts of each contained as follows : — 
 
 Water, 
 
 Organic matters, hair, &c 
 
 Gypsum and traces of alkalies,... 
 
 Carbonate of Lime, 
 
 Carbonate of Magnesia, 
 
 Phosphate of Lime (bone earth), 
 Sand, 
 
 r».,„ ^r.e,,c^ Refuse as taken 
 Dry refuse, from the boilers. 
 
 100-0 
 
 37-0 
 30-0 
 
 28-4 
 
 1-6 
 3-0 
 
 100-0 
 
 The dry refuse, I found, would be capable of yielding two 
 parts, and the fresh " gumps" seven parts of ammonia. The 
 moist refuse should therefore be preferred by the farmer, 
 and would prove a useful manure ; as, besides the amount of 
 ammonia which it would be capable of affording by its de- 
 composition, a ton weight of it would convey to the soil 
 about 36 lbs. of phosphate of lime (53). It must, however, 
 be expected to vary very much in composition, so that the 
 actual value of any sample can only be determined by analysis. 
 The moist refuse is sold in Belfast at 125. 6d. per ton. 
 
143 
 
 CHAPTER IX. 
 
 MEANS ADOPTED FOR IMPROVING THE SOIL AND MAINTAINING 
 ITS FERTILITY BY TEE APPLICATION OF MANURES. 
 
 VEGETABLE AND MINERAL MANURES. 
 
 213. Vegetable Manures. — The animal manures which 
 have been described in the i)reccding chapter, you have seen 
 derive then: valuable qualities from containmg certain com- 
 pounds which, by their decay, are capable of affording am- 
 monia (154), and also the various inorganic materials which 
 are equally indispensable for the nourishment of our crops. 
 Therefore, by placing these manures in the soil, we restore 
 to it the matters taken away in the course of cultivation. 
 When we apply to our fields the decomposing straw, leaves, 
 and other vegetable remains of the manure heap, we in the 
 same way replace in the soil, the ingredients which the stems 
 and leaves of our crops had appropriated during their growth. 
 
 214. Green manuring But in addition to employing ani- 
 mal excrements, and the decomposing litter and refuse vegetable 
 matters collected in the manure heap, the farmers in various 
 parts of Europe have been accustomed from the earliest 
 times to enrich their poor or exhausted soils, by growing 
 apon them certain crops, which instead of being used for 
 food, are ploughed in to serve as manure. This practice of 
 green manuring^ as it is termed, is regarded as signally 
 beneficial in the countries in which it is practised; thus the 
 farmers in the north of Germany find that the most effectual 
 method of obtaining good crops of rye from sterile sandy soils 
 is to manure them with several crops of spuiTcy or of white 
 lupins, and in the United States, both clover and Indian corn 
 are frequently ploughed in for the purpose of enriching the 
 land. In some parts of England and Scotland, buck-wheat 
 and vetches are grown as manure- crops, and turnips arc also 
 occasionally ploughed in spring as a preparation for wheat. 
 
 215. When green vegetables are buried in the soil, they un- 
 dergo the same changes as when placed in the manure heap ; 
 they are rapidly resolved into their original elements, and yield 
 up the mineral matters and gases which they had accumuLitctl 
 
 M 2 
 
1 44 LESSONS IN CHEMISTRY. 
 
 during their growth, and thus " the destruction of an existing 
 generation becomes the means for the production of a new- 
 one ; death becomes the source of life." 
 
 216. If you recollect that the great bulk of every plant is de- 
 rived from the air, you will readily understand, that by burying 
 in the soil the crops produced upon it, you will not merely 
 restore the matters which they had abstracted during their 
 growth, but increase its natural fertility by adding to it the 
 elements which they had appropriated from the inexhaustible 
 storehouse of the atmosphere. The plants selected for the 
 purpose of being ploughed in are such as draw largely upon 
 the air for their nourishment, and which can be made at little 
 expense, in a short time, to produce a large crop of leaves 
 and stems. It is usual to turn them into the soil just before 
 the period of flowering, as at that time they are found to 
 contain the largest amount of useful matters. But besides 
 increasing the amount of organic matter in poor soils, much of 
 the beneficial effects of green manuring is to be attributed to 
 the mineral matters contained in the decaying plants. Thus, 
 when a crop of grass is ploughed down, the inorganic matters 
 which the deeply penetrating roots had extracted from the 
 subsoil, are transferred to the comparatively exhausted surface, 
 and brought within the reach of the succeeding crop. In 
 Ireland, though crops are rarely cultivated with the design of 
 being used as manure, yet the application of various lands of 
 vegetable matter to the soil, is among the most important 
 means employed to maintain its fertility; thus the sea- weeds 
 or wrack, which are found in so great abundance on our 
 coasts, and the deposits of vegetable matter in our bogs, are 
 used in every part of the country where they can be obtained. 
 
 2 1 7. Sea-weeds. — These plants have long been employed by 
 the farmers on the coasts of France, Scotland, and Ireland ; and 
 as analysis shows that they contain all the ingredients which 
 our crops requh-e, they must be capable of contributing to the 
 fertility of any description of soil. In many districts in 
 Ireland, no other manure than "sea- wrack" is applied, and 
 by its assistance the land is enabled, year after year, to pro- 
 duce the most exhausting crops. Sea-weeds are frequently 
 employed for dressing meadow lands, and are found greatly 
 to improve the quality of the grass; they are also formed 
 into composts with farm-yard maiiure, and, as they contain 
 a considerable amount of nitrogen, they rapidly ferment, and 
 
VEGETABLE MANURES. 145 
 
 as usually allowed to remain for months exposed to the 
 weather, must lose much of their valuable qualities. By 
 adopting the precautious which I described as necessary, in 
 the management of farm-yard dung, much of this loss may be 
 prevented. The fresh weeds are also frequently placed in 
 the drills with the potato sets, and, thus used, produce a 
 most abundant crop, though the potatoes are said to be more 
 waxu than those grown on farm dung. It is necessary to 
 prevent the sets coming into immediate contact with the 
 weeds, as they are said to be injured when placed upon it; 
 applied to cabbages, they are found greatly to improve their 
 flavour. The fresh weeds are usually employed at the rate 
 of 30 tons to the statute acre. 
 
 218. Composition of sea-weeds:. — As taken from the sea or 
 cut from the rocks, sea-weeds contain a very large amount 
 of water; the leaves {frond) of the bladder- wrack, and 
 the stalks and leaves of the tangle, which are highly valued 
 by the farmers on our coasts, contain in the 100 parts 
 respectively as follows: — 
 
 Bladder-wrack, ... 
 
 Leaves of tangle, 
 
 Stalk of do. ... 
 
 Do. do. ... 
 
 A ton therefore of the above weeds, mixed together, would, 
 when fresh, convey to the soil about 123 lbs. of mineral 
 ingredients. 
 
 219. Formerly, enormous quantities of sea- weeds were 
 bunied on the coasts of Ireland and Scotland for the sake of 
 the soda (44), which is one of the chief constituents of their 
 ashes; but at present that alkali is procured from other 
 sources, and only a limited amount of kelp^ as the fused ashes 
 are termed, is prepared for the use of the Iodine manufac- 
 turer (page 48, note). From several analyses of the kelp 
 prepared on the north-east coast of Ireland, I was some time 
 ago induced to recommend it to the attention of farmers, as 
 a valuable and convenient source of the saline matters 
 removed from our fields by cultivation, and especially for 
 supplying the alkalies so essential to the gi'owth of the potato 
 
 Vater 
 
 Organic combustible- 
 
 Ash. 
 
 
 matter. 
 
 68-8 
 
 26-20 
 
 5-0 
 
 8M 
 
 13-10 
 
 5-8 
 
 84-0 
 
 10-40 
 
 5-6 
 
 83-1 
 
 11-06 
 
 5-8 
 
146 LESSONS IN CHEMISTRY. 
 
 and turnip-crops. The following are the ingredients useful 
 to plants, which 1 00 parts of Irish kelp contain* : — 
 
 Potash, 8-22 
 
 Soda, 25-82 
 
 Lime, 5*17 
 
 Magnesia, 8-47 
 
 Sulphuric acid, 20-17 
 
 Phosphoric acid, ...: 5-43 
 
 Chlorine, 11-70 
 
 Silicic acid, 5-71 
 
 220. Kelp, therefore, presents us with a supply of some of 
 the most important and expensive elements of plants, in a 
 convenient and portable form, so that they can readily be 
 carried into the interior of the country, where their action 
 might bo expected to prove more beneficial than near the 
 coast, where sea- weeds are frequently applied to the land, and 
 the rains, carried over the fields by the sea-breeze, deposit a 
 certain amount of saline matters. 
 
 221. When sea- weeds are burned, to be used as manure, 
 the ashes should not be fused into solid masses, as is usual 
 in preparing kelp, as it is a very troublesome operation to 
 reduce them to powder; the vegetable matter should be only 
 half consumed, by which means the ashes will be obtained 
 in a loose form, more convenient for distribution over the 
 fields. Kelp is usually sold on the coasts of Ulster at from 
 30*. to £3 per ton. 
 
 222. Peat — Among the numerous vegetable substances 
 which this country affords, capable of being employed by the 
 skilful farmer in maintaining the fertility of the soil, are the 
 contents of our bogs. 
 
 There are three forms in which bog-stuff" or peat is used 
 as manure by experienced farmers. 1 st, — Made into a com- 
 post with farm-yard manure. 2d, — Converted into a kind of 
 charcoal, by being burned with a smothered fire. And 3d, — 
 As consumed with free exposure to the air, and reduced to 
 ashes. I will describe the methods adopted for its prepara- 
 tion in the above forms, and also their properties. 
 
 223. Peat earth, though from a very early period occa- 
 sionally employed as a manure, was first brought into general 
 
 * The teacher will find some remarks on kelp as a manure, in a report 
 which I addressed to the Chemico- Agricultural Society of Ulster, in 
 May, 1846. 
 
VEGETABLE MANURES. 117 
 
 notice by the late Lord Meaclowbank. It is well known, 
 that in its natural state, it exhibits very little disposition to 
 decompose, and is therefore not much esteemed as an addition 
 to land. Lord ^leadowbank, however, proposed to form it 
 into a compost, by mixing it with hot fermenting farm-yard 
 dung, by which means its indisposition to decay is overcome, 
 and it is in a short time converted into a highly-fertilizing 
 manure. He recommended, that one ton of strong fermenting 
 farm-yard manure should be placed in alternate layers with 
 two and a-half tons of dry peat mould. The value of this 
 compost is now fully appreciated by some of the most expe- 
 rienced farmers in this country and Scotland. 
 
 224. When turf is required for manure, it should be raised 
 from the bog in dry weather, and allowed to remain for a 
 week or two exposed to the air. It may then be used to 
 form the manure heap. The proper fermentation of the mass 
 will be promoted by occasionally watering it with some 
 liquid from the cow-house ; or the dry mould, instead of being 
 formed into a compost, in the manner advised by Lord 
 Meadowbank, may be Advantageously employed as a means 
 of absorbing, or sucking up the various liquid manures, 
 urine, &c. 
 
 225. Dr. Shier, in a note to his edition of "Davy's 
 Agricultural Chemistry," states that he has repeatedly tried 
 the following compost, and has found it to raise a better crop 
 of turnips than an ordinary dose of farm-yard manure: — 
 "Ten tons of half-dried peat that had been several times 
 turned, and well exposed to the air, were mixed with six 
 bushels of sifted bone dust, weighing 5 6 lbs. or 58 lbs. per 
 bushel, and turned. At the next turning, the mass was mixed 
 with 56 lbs of sulphate of ammonia, and as much nitrate of 
 soda. After standing a few days, it was fit for use." The above 
 mixture would yield a most valuable manure ; but in many 
 parts of Ireland, it would be impossible to procure either 
 sulphate of ammonia or nitrate of soda. Farmei^s, however, 
 who reside in the neighbourhood of large towns, may employ 
 with great advantage the ammoniacal liquor of the gas 
 works for moistening the heap, in the preparation of peat 
 composts. 
 
 226. I have already recommended tanks for liquid manure, 
 as essential to the economy of every well-regulated farm 
 establishment. A simple manure tank, of the kind described, 
 
148 LESSONS IN CHEMISTRY. 
 
 could easily be procured by the small farmer; and in districts 
 where peat abounds, would be found most useful, and enable 
 him to prepare a supply of rich manure. A bed of the dry 
 peat mould might be formed, and where a pump is not at 
 hand, a bucketful or two of the contents of the tank could be 
 used for moistening it, and by adding occasionally some 
 fresh mould, a valuable compost would be produced, contain- 
 ing the most essential ingi-edients required for the nourishment 
 of his crops. 
 
 227. Along the coast, where sea-weeds can be procured, 
 they present us with an excellent substance for mixing with 
 peat, to convert it into manure, as the weeds rapidly ferment, 
 and communicate to the mould the tendency to decay. 
 
 228. Peat Charcoal, — When peat is burned with a 
 smothered fire, it is converted into a light and friable char- 
 coal, which has been found to possess a high value, not only 
 as a fertilizer, but for the manufactm-e of gunpowder, and the 
 various industrial purposes for which wood charcoal is 
 usually employed. When it is remembered, that nearly one- 
 seventh of the entire surface of Ireland is covered with bogs, 
 the consideration of the various plans proposed for converting 
 their contents into a more valuable form, becomes of great 
 importance. 
 
 229. Preparation of peat charcoal. — For this purpose the 
 following simple directions have been given by Mr. Rogers, 
 who has devoted much attention to the subject: — If prac- 
 ticable, have the turf of a good, hard kind, and as dry 
 as possible. Let it be piled in a circular, conical shape, 
 something like a hand-cock of hay, about from three to five 
 feet across at the bottom. Place all the first layer of sods 
 standing on their ends, and resting against each other, in the 
 shape of an A; and let the second layer lie against the back 
 of the first, continuing each layer in that manner up to the 
 top, filling in between with sods placed on their ends upright : 
 by this means the air will be admitted freely through the 
 whole, and produce combustion throughout. Set it on fire, 
 by straw underneath, and after a short time the entire heap 
 will become a red mass. When in this state, and not till 
 then, it is to be extinguished perfectly. This may be done by 
 a moderate portion of water, if the charcoal be for manure ; 
 but even in that case it should only be just sufficient to extin- 
 guish it. It may also be smothered, either by means of a 
 
VEGETABLE MANURES. 149 
 
 tarpaulin clipped in water, or by damp sods, or scraws, placed 
 over the whole, so as to perfectly exclude the air. This must 
 be done effectually, or it Avill continue to bum ; and a very 
 certain way to do this is, to throw round it at the base, after 
 the tai-panlin or scraws have been placed over the wliole heap, 
 a lew shovL'Kuls of clay, so as to prevent any air from 
 entering underneath. AVhen charcoal is to be prepared on a 
 large scale for extensive farms, an extinguisher made of sheet 
 iron, sufficiently large to cover the heap and rest close in the 
 ground, will be desirable; and can be made at a trifling cost. 
 Two handles, extending about a yard at each side, in the 
 forai of a T, will enable it to be lifted, and placed over the 
 heap, without inconvenience from the heat, &c When the 
 heap of charcoal has become cold, the lumps may be broken 
 up by mallets or pounders, with very little labom-, and, 
 for general purposes, should be about the same size as coarse 
 sand. 
 
 230. Having described the preparation of peat charcoal, 
 and the valuable fertilizing qualities which it has been found 
 to possess, I will now endeavour to reply to the inquiry 
 which has several times been addressed to me by persons 
 desirous of applying it as a manure: — Is it, hy itself, to he 
 regarded as a sufficient manure for all the crops of the 
 farmer? Trials, made both in this country and on the con- 
 tinent, have shown, that, drilled in with wheat, it has tended 
 greatly to promote the growth of that grain. It has also 
 been used alone, with success, as a manure for the turnip 
 and potato crops; but I do not consider that it could be 
 judicious to advise you to rely upon it as sufficient, in all 
 cases, to ensure a full return. Such advice might lead to 
 disappointment, and induce you to neglect what I regard as 
 a really important addition to our stock of home manure. 
 
 231. It should be regarded by the farmer not as a univer- 
 sal medicine, capable of curing all the diseases of a neglected 
 and worn-out field, but as a useful auxiliary, which, when 
 combined with kelp, dissolved bones, or saturated with the 
 fertilizing liquids, at present permitted to run away from his 
 stables and cow-houses, will give him a cheap and valuable 
 compound, containing everything that his crops require for 
 their full development, and which may be relied on with 
 confidence — mixed, as I lately described, with ordinary farm- 
 yard dung, it will also be found to contribute, in no small 
 
150 LESSONS ON CHEmSTRY. 
 
 degree, to its value (184), by retaining matters which, as 
 that manure is usually managed, are lost to the fai'mer. 
 
 232. Inorganic matters contained in peat. — In an exami- 
 nation, lately made of this manm-e, as it is usually prepared 
 by skilful farmers in Scotland, it was found that every hun- 
 dred pounds of peat charcoal, placed on a field, would convey 
 to it the following ingredients. The proportion of ashes will, 
 of course, vary, according to the extent to which the air is 
 allowed to penetrate to the heap, in burning the peat, 
 and their composition will also be difierent, in various 
 samples. 
 
 Charcoal, 5412 
 
 S ulphates of Potash, Soda, and Magnesia, 6*57 
 
 Alumina, 2-99 
 
 Oxide of Iron, 4-61 
 
 Sulphate of Lime (gypsum), , 10*49 
 
 Carbonate of do 8*54 
 
 Phosphate of do 0-90 
 
 Siliceous matter, 10-88 
 
 99-10 
 
 The above mixture affords the very materials which every 
 plant that is grown must procure, to form its leaves, its 
 stalk, and its seeds. 
 
 233. The amount of phosphate of lime in charred peat is, 
 however, not sufficient to induce the farmer to rely upon it as 
 his only manure, for a number of years; and it will be 
 advisable for him to apply with it some of the fertilizers 
 above described.* 
 
 * I was lately favoured by J. J, Burnett, Esq. Glen arm, with a state- 
 ment of the results of some experiments made by him at Gadgirth, in 
 AjTshire, with mixtures of charcoal, kelp, and other manures, which 
 are exceedingly interesting. 
 
 Experiments with various manures — Crop, Swede turnips. 
 
 Applied per Scotch acre. Weight per Scotch acre. 
 
 No. 1. 20 tons of farm manure 1 cwt. African) gg tons 10 cwt. 
 
 guano, 1 cwt. charcoal (wood), 3 
 
 No. 2. 20 tons farm manure, 2 cwt. Peruvian? „< *q_o 
 
 guano, 1 cwt. wood charcoal, ^ 
 
 No. 3. 20 tons farm manure, 1 cwt. African guano, \ go ^ . ^ ^ , 
 
 8 bushels ground kelp, 2 cwt. salt, S 
 
 No. 4. 20 tons farm manure, 4 cwt. concentrated^ qi . 
 
 ' y o\ tons, 
 
 manure, ) 
 
VEGETABLE MANURES. 1 5 1 
 
 234. JRape-dust — As the most valuable portions of the 
 organic and inorganic matters of vegetables are accnmulated 
 in the seeds, their application to the soil, when then* power of 
 germinating has been destroyed, must prove exceedingly useful. 
 In Italy, the seeds of the white lupin, and in England, the 
 cake (77) which remains when the linseed, rape, and other 
 oily seeds are subjected to pressure for the preparation of 
 the oil, are much employed as manure. The cake contains 
 all the nitrogen and inorganic matters of the seeds, and 
 must therefore possess great activity as manure. It is 
 usually crushed into dust, and applied in that form. In 
 many parts of England rape-dust is regarded as especially 
 beneficial in promoting the growth of grain, and particularly 
 upon thin, poor soils, deficient in organic matter. Its effects 
 are rapidly produced, but are not of long contmuance. 
 Combined with more lasting manures, it has been found of 
 great value in starting the turnip-crop. The most economical 
 and certain method of applying it, according to Mr. Hannam, 
 is by drilling it in with the seed ; and, in using it, care should 
 be taken, as with all rapidly fermenting manures, to mix it 
 with a little earth, so as to prevent its coming into imme- 
 diate contact with the seed (193). In Belgium, the farmers 
 mix both rape and linseed-cake with their liquid manure, to 
 
 The soil was a medium clay, with a hard subsoil, but was thorough - 
 drained and subsroiled. Lot No. 3 was the best in appearance the whole 
 season, although the worst part of the field, as to soil ; and the turnips 
 on this lot were more solid and firm in texture. The crop was sown on 
 the 10th June, 1844, and weighed in February, 1845. 
 
 Tlie concentrated manure, of which the following is an analysis, by 
 Professor Penny of Glasgow, cost 4s. per cwt. 
 
 ANALYSIS OF CONCENTRATED MANURE. 
 
 Organic matter soluble in water 3*93 
 
 Salts of Ammonia 1*50 
 
 Salts of Potash and Soda 1-28 
 
 Organic Salts of Lime and Magnesia 8-40 
 
 Phosphate of Lime and Magnesia 6-30 
 
 Carbonate of Lime and Magnesia 1"30 
 
 Oxide of Iron 0*80 
 
 Animal matter, &c. insoluble in water 34-50 
 
 Silica, &c 2G-23 
 
 Water 15-00 
 
 Loss ..... 1*76 
 
 100-00 
 K 
 
152 LESSONS IN CHEMISTRY. 
 
 improve its qualities, and apply the mixture with great 
 advantage to the flax-crop. In England, rape-dust is applied 
 at the rate of from 8 to 16 bushels per acre, and is usually 
 sold at about £7 per ton. 
 
 235. The husk of the oat^ malt-dust^ and the bran of 
 wheats may all be used with advantage as manures, and 
 should be economized by the farmer. Wheat bran, especially, 
 should be regarded as a valuable fertilizer, being rich in both 
 nitrogen and saline matters. It has been used with remark- 
 able effect in England.* Added to the manure heap, and pro- 
 perly preserved from excessive fermentation, all these vege- 
 table substances will be found useful applications to the soil. 
 
 236. It may be useful for you to recollect, in considering 
 the effects which the various animal and vegetable substances 
 employed as manures, are capable of producing, that the 
 immediate effects which may be expected to follow their 
 application will depend chiefiy upon the amount of matters 
 capable, by their decomposition, of yielding ammonia, which 
 they contain, while the permanence of their action will depend 
 upon the amount of inorganic mattei-s, and especially of the 
 phosphates of lime and magnesia. 
 
 237. Mineral and saline manures. — Formerly it was ima- 
 gined that the only substances capable of supplying food to 
 plants were those derived fi'om animals and vegetables; and 
 though, in various parts of the world, lime, marl, gypsum, 
 saltpetre, and other mineral and saline matters, dug out of 
 the earth, had been used with extraordinary success in in- 
 creasing the fertility of the soil, yet it was considered that 
 these substances were not true manures, but merely in some 
 unknown manner stimulated plants to consume larger quan- 
 tities of the food supplied in the soil, and, in consequence, 
 accelerated its exhaustion, " enriching the fathers while they 
 impoverished the sons." The progress of agricultural che- 
 mistry has, however, given us more correct opinions with 
 
 * Professor Johnston gives the following as the average composition 
 of the bran of wheat : — 
 
 Water 131 
 
 Albumen coagulated 19-3 
 
 Oil 4-7 
 
 Husk, and a little starch 55*6 
 
 Saline matter 7*3 
 
 1000 
 
VEGETABLE MANURES. 153 
 
 respect to the action of these substances, and has sho^vn us 
 that, like the inorganic matters contained in the ashes of sea- 
 weeds and peat, and in the excrements of animals, they increase 
 the produce of the soil, because they supply it with some of 
 the materials indispensable to the growth of plants. 
 
 238. From the information which you have acquh-ed, you 
 will find no difficulty in understanding why the application 
 of one kind of mineral or salme matter should occasionally 
 disappoint the expectations of the farmer; why gypsum should 
 promote the growth of the crops in one district, and produce 
 no effect in another part of the country; or why lime or 
 marl should, after a number of years, cease to insure a fertile 
 return, and seem even to injure the land. You are aware 
 that it is only in proportion as you place in the soil the 
 materials taken away in cultivation that you can expect 
 to maintain its productiveness ; that lime or nitrate of soda, 
 or saltpetre, will be sufficient to enable it to yield crops ow/y 
 when the eight or nine other substances which are discovered 
 in the ashes of your crops are already present in sufficient 
 quantities; and that if, year after year, you carry away in 
 your crops several of these substances, and replace only one 
 or two of them in the manures which you apply, exhaustion 
 must sooner or later be expected to occur. 
 
 239. Artifieial manures. — The striking effects which at- 
 tended the use of guano and bones, which led the most 
 sceptical to admit that bulk was not indispensable to the 
 efficacy of manures; and the information which chemists 
 communicated, that the materials from which these substances 
 derived their fertilizing power were the same that existed in 
 fertile soils, and in the ashes of plants, suggested the possi- 
 bility of compounding mixtures adapted to the special wants 
 of the various crops cultivated by the farmer; and within 
 these few years so great has become the demand for these 
 artificial compounds, that a new and important trade has 
 been created in preparing them. In England and Scotland, 
 at the present time, enormous quantities of mineral sub- 
 stances and chemical compounds are used as manures: of 
 sulphuric acid alone, it is said that last year as much as 
 1 27,750 lbs. were consumed by the farmers in one agricultural 
 district in Yorkshire. 
 
 240. I have already, in Chapter III. described to you the 
 leading characters of the mineral and saline matters which are 
 
154 
 
 LESSONS IN CHEMISTRY. 
 
 discovered in the ashes of plants, and the table given at p. 99, 
 will show you the proportions in which the crops that you 
 cultivate require them for their growth. Though the success 
 of the experiments which have been made with various saline 
 compounds, both in England and Scotland, are most encou- 
 raging, yet in the present circumstances of the agriculture of 
 this country, with rich stores of fertilizing materials acces- 
 sible to every farmer, your attention should be dh-ected 
 rather to the economy of the natural supplies of these matters, 
 which have lately been described, than to the preparations of 
 the chemical manufacturer. The following table, however, 
 will be found useful to those who possess the means, and are 
 desirous of entering upon this new path, which the progress 
 recently made in the study of the composition of the 
 inorganic matter of plants, has opened up to the improving 
 agi'iculturist. 
 
 Composition in 100 parts of the saline and mineral substances 
 employed in the preparation of special manures. 
 
 Carbonate of Potash 
 Carbonate of Soda, 
 
 dry 
 
 CrystaUized 
 
 
 Sulphate of Soda | 
 Glauber Salt, dry j 
 CrystaUized 
 
 Nitrate of Potash \ 
 Saltpetre > 
 
 Nitrate of Soda I 
 Cubic Nitre J "' 
 
 Carbonate of Lime . 
 
 Sulphate of Do. ^ 
 
 Gypsum, Crystal- > 
 lized J 
 
 B urned 
 
 Carbonate of Mag- ) 
 
 nesia ) 
 
 Sulphate of Do. / 
 
 Epsom Salt 
 
 31-43 
 
 15-43 
 
 43-71 
 
 51-69 
 
 63-44 
 
 63-40 
 
 56-18 
 24-85 
 
 46-31 
 
 58-47 
 
 32-40 
 
 68-57 
 
 46-56 
 
 58-58 
 21-81 
 43-82 
 19-38 
 
 36-60 
 
 56-29 
 32-90 
 41 53 
 
 62-76 
 
 55-77 
 
 2079 
 
 31 ; .. 
 
 70 ; 50-90 
 
 * Nitric acid is the " aquafortis " of the apothecary. It is a sour 
 corrosive liquid, which, in combination with potash, forms the salt 
 termed nitrate of potash, and with soda, nitrate of soda. It is itself not 
 an elementary body like chlorine (51), but a compound of nitrogen and 
 oxygen — 14 lbs. of nitrogen and 40 lbs. of oxygen forming 54 lbs. uf 
 
VEGETABLE MANURES. 1 65 
 
 24 1 . Use of lime as manure. — When common limestone 
 {carbonate of linie) is buraed in the kiln, the carbonic acitl, 
 which forms so large a portion of its bulk (45), is expelled 
 into the air, and it becomes a porous mass, and experiences 
 an important alteration in its properties. As it exists in the 
 mountains, it is, as you are aware, both tasteless and insolu- 
 ble; but, by burning, it acquires a caustic taste, and is 
 rendered slightly soluble in water. In the bui-ned state, lime 
 has, from a very early period, been employed as an applica- 
 tion to the soil in every part of Europe, and in many parts of 
 this country is consumed at the present time in enormous 
 quantities. As the effects which lime is capable of producing; 
 upon the soil, are in general very little understood by the 
 greater number of our farmers, it will be necessary for us 
 carefully to consider the nature of its operation, and also 
 the composition of the rocks from which it is procured. 
 
 242. When water is thrown upon burned or quick lime, it 
 rapidly absorbs it, gives out so much heat as to char wood, 
 a ad falls into pieces. When exposed to the air, it also 
 attracts moisture, and crumbles to powder; in this state it is 
 termed slaked^ or slacked lime, and is found to have increased 
 considerably in weight, a ton of quicklime being converted into 
 about 25 cwt. of slaked lime. It also gradually attracts car- 
 bonic acid from the air, and returns to the state of carbonate, 
 though even after a very long period portions of it remain 
 caustic. In this state it is usually termed mild hme, thougii, 
 when allowed to slake in the fields, only about one-half of 
 it is found to have entered into combmatiou with carbonic 
 acid.* 
 
 nitric acid. It is formed in compost heaps during the decay of organic 
 matters containing nitrogen, and produced in tlie atmosphere during 
 thunder-storms. It is believed by many persons that its compounds 
 exercise a powerful effect on the growth of plants, by supplying 
 nitrogen. 
 
 ■ The teacher may allow his pupils to perform the following simple 
 experiments : — 
 
 1. Let 25 grains of common uwbumed lime be weighed, and intro- 
 duced into a glass containing about two teasipoonfuls of muriatic acid 
 {spirits of salts), diluted with an equal quantity of water ; a copious 
 effervescence will be produced, and it will nearly all dissolve : test the 
 gas which escapes, as directed at page 30. When the cftervescence has 
 ceased, pour off the liquid without disturbing the undissolved matt»-r, 
 which may be washed so as to remove all trace of tlie acid, by pouring; 
 water ttpon it and decanting; the sediment collected on a piece of blotting- 
 
 n2 
 
156 
 
 LESSONS IN CHEMISTRY. 
 
 243. The following analyses will show you the composition 
 of several varieties of limestone, employed for agricultural 
 pui-poses in Ireland: — 
 
 
 o 
 
 il 
 s 
 
 1 
 
 13 
 
 t 
 
 1 
 
 r 
 
 o 
 
 3 
 
 1 
 
 1 
 
 
 Magheramorne, 
 Antrim 
 
 98-63 
 
 0-38 
 
 0-10 
 
 0-08 
 
 0-45 
 
 H 
 
 Glendun, do. 
 
 95-03 
 
 0-55 
 
 0-18 
 
 2-00 
 
 1-20 
 
 H 
 
 Lame,* do. 
 
 71-66 
 
 2-67 
 
 ? 
 
 9-42 
 
 14-61 
 
 H 
 
 Moira, Down 
 
 96-80 
 
 0-76 
 
 0-12 
 
 0-40 
 
 0-55 
 
 H 
 
 Castle espie, do. 
 
 94-40 
 
 1-38 
 
 0-05 
 
 0-40 
 
 2-40 
 
 H 
 
 Holywood, do. 
 
 48-33 
 
 44-11 
 
 0-31 
 
 2-25 
 
 5-00 
 
 H 
 
 Brown's Hill, Car- 
 low 
 
 95-00 
 
 — 
 
 — 
 
 
 
 4-50 
 
 Griffith 
 
 Dublin (calp^ .... 
 
 68-00 
 
 
 
 , 
 
 9-0 
 
 18-00 
 
 Knox. 
 
 Clones, Monaghan 
 
 89-08 
 
 1-97 
 
 
 
 0-66 
 
 8-16 
 
 Jones, 
 
 Newton Gore 
 
 65-10 
 
 1-40 
 
 
 
 0-66 
 
 32-85 
 
 do. 
 
 Belturbet, Cavan 
 
 98-00 
 
 1-28 
 
 — 
 
 0-30 
 
 0-42 
 
 do. 
 
 * Blue Lias Lime. 
 
 
 
 
 1 
 
 The above analyses of limestone rocks from various parts 
 of Ireland, will show you that they differ considerably in 
 their composition, and that when burned, they will convey 
 different quantities of lime to the soil. It is only lately that 
 attention has been directed to the amount of phosphate of 
 
 paper, dried before the fire and weighed, will show the amount of earthy 
 impurities which the specimen of limestone contained. 
 
 2. Take 100 grains of quicklime, pour water upon it as long as it 
 drinks it up ; observe the heat given out ; collect and weigh the powder 
 which it forms, and note the increase in weight produced. Drop some 
 of the powder into some diluted muriatic acid ; if the lime has been care- 
 fully burned, there should be no escape of gas. 
 
 3. Introduce the remainder of the powder, with two or three glassfuls 
 of water, into a bottle ; cork the bottle, and shake the mixture ; allow 
 the undissolved part to settle down, and pour off the clear liquid, which 
 is lime-water, and preserve it for experiment in a well corked vial. 
 Test the lime-water, and you will find it alkaline (12). Blow air into 
 it through a glass tube or straw, and it will become muddy from the 
 formation of carbonate of lime, carbonic acid being contained in the air 
 from the limgs (26). 
 
VEGETABLE MANURES. 157 
 
 lime, which, as all the analyses made in my laboratory 
 show, our limestone rocks, like those which have been 
 examined in England, contain. The amount of this valuable 
 ingredient, as well as the other inorganic matters present, 
 must exercise a considerable influence upon the effects which 
 they produce. 
 
 244. Lime, when applied to the soil, produces changes 
 both in its texture and chemical composition, of great im- 
 portance to the farmer. Thus, it renders the stiff clays loose 
 and porous; and the numerous beds of limestone gravel, 
 derived from the crumbling down of limestone rocks, which 
 exist in many parts of Ireland, and are so frequently found 
 beneath the bogs, aflford the farmer the very means required 
 for consolidating and improving the qualities of the surface. 
 There are, indeed, no soils in this country that would not be 
 materially benefited by the judicious application of this 
 valuable substance. 
 
 245. How it adds to the fertility of the soil. — You have seen 
 that there is no plant which you cultivate that does not 
 require a considerable proportion of lime for its food ; it must 
 therefore be an essential ingredient of every productive soil ; 
 and as year after yeai' it is carried away in your crops, it must 
 occasionally be applied. Upon soils formed by the crumbling 
 down of the clay-slate and granite rocks, its frequent ap- 
 plication is necessary, and to the farmers in the west of 
 Scotland, and in Down and Louth, limestone is absolutely 
 indispensable. But in addition to directly affording an 
 essential element to plants, it is also believed to act as a 
 powerful chemical agent in rendering accessible to your crops 
 the stores of fertilizing matters, locked up in an insoluble state, 
 in the rocky particles of the soil, in combination with silica. 
 In granite and many other rocks, silica exists in chemical 
 combination with potash, in a form in which it is but slowly 
 acted upon by the rain; but when these silicates (50) are 
 crushed and mixed with hot lime, and water poured upon 
 them, it is found that after some time chemical changes are 
 produced, by which the silica and the potash are converted 
 into a form in which they can be dissolved in water, and 
 therefore serve for the nourishment of plants. These impor- 
 tant chemical changes must also, to some extent, take place 
 in the soil when it is mixed with lime. In many soils whicli 
 contain an excess of vegetable matter, like our peat bogs. 
 
158 LESSONS IN CHEMISTRY. 
 
 certain vegetable acids are formed, which frequently render 
 the land sour and unfavourable to the growth of useful 
 plants ; much of the beneficial effects of limeing such soils is 
 ascribed to the lime entering into combination with, and 
 neutralizing, these acids. It also promotes the decay of the 
 inert vegetable matters, and thus not only sets free the inor- 
 ganic ingredients which they contain, but disposes theii* 
 elements into forms (carbonic acid, &c.) capable of yielding 
 up food to plants. 
 
 246. A compound of sulphur and iron, sulphuret of iron, 
 is found in small quantities in almost all the rocks from which 
 soils are derived ; you must have observed it sparkling in the 
 sunshine, on the face of the clay- slate and basaltic rocks in 
 many parts of the country, like a sprinkling of brass dust. 
 This compound is insoluble in water, but, by exposure to air 
 and moisture, it unites with oxygen, and is converted into 
 sulphate of iron, "green vitriol" (163), which readily dis- 
 solves, and is found to exercise, when in excess, an injurious 
 effect upon the crops. The addition of carbonate of lime, to 
 soils in which this salt is contained, proves useful by decom- 
 posing it, — gypsum and insoluble peroxide of iron (48) 
 being formed, while the carbonic acid escapes. 
 
 247. Effects of lime upon plants. — The effects of lime in 
 improving the quality of the crops to which it has been 
 applied, have long been remarked; thus, when applied to old 
 grass-lands, it extirpates coarse and unpalatable plants, and 
 favours the growth of the tender and nutritious white and red 
 clovers. It is said to add to the quantity of gluten pro- 
 duced by the corn-crops, and to increase the weight of the 
 grain; mixed with salt, it gives strength to the straw on 
 mossy lands, where the crops are so frequently lodged. It is 
 also found not merely to improve the quality of almost every 
 crop, rendering the pea more easily boiled and the potato less 
 watery, but it shortens the period of its growth, and hastens 
 the ripening of both grain and roots. 
 
 248. Neither experience nor theory can point out exactly^ 
 how much lime should be added to a soil. Professor Johnston 
 states, from the results of his calculations, that in Scotland, at 
 least sufficient should be present to give three per cent to a 
 soil " which contains an ordinary proportion of vegetable 
 matter and the other food of plants," which to one entirely 
 destitute of lime, would, when the soil is twelve inches deep. 
 
VEGETABLE MANURES. 159 
 
 require an addition of 48 tons of quicklime. To undrained 
 soils it must be applied in greater quantities than when the 
 excess of water has been removed, as the moisture present 
 not merely produces a greater proportion of acid compounds, 
 which it is necessary to neutralise, but prevents its full 
 operation. In determining the quantity of lime required by 
 any particular soil, it is therefore evident we must be guided 
 both by a consideration of its physical qualities, and its chemi- 
 cal composition as determined by analysis.* 
 
 249. The state in which lime is applied must materially in- 
 fluence its effects upon the soil. It is, as you are aware, used 
 by farmers: — 
 
 C Shell lime applied directly from 
 1 . In the caustic state. < the kiln. 
 
 ( Slaked by the addition of water. 
 
 TAs slaked by absorption of 
 
 2. In the partially mild ) moisture from the air, and in 
 state. ^ part combined with carbonic 
 
 (^ acid. 
 
 {As chalk, marl, shell-sand, coral- 
 sand, limestone-gravel, and 
 as burned lime rendered mUd 
 by long exposure to the air. 
 250. For full directions as to the best methods of applying 
 lime in the various states in which it is used, I must refer you 
 to the works of writers on the practice of agriculture. The 
 following general rules will, however, serve to direct you in 
 regulating its application : — 
 
 I. That in reclaiming peaty soils, or those composed of 
 intractable clay, or which contain substances in- 
 jurious to plants (246), it should be applied as 
 hot as possible from the kiln. 
 
 • It is only lately that the attention of chemists has been directed to 
 the cliangcs which limestone may undergo by burning; thus, it has been 
 found by analysis (Johnston), that when burned with coal several new 
 compounds are produced, the sulphur which the coal contains uniting 
 with the lime so as to form gypsum, while the silica contained in the 
 earthy matter of the limestone and in the coal, upon the expulsion of 
 the carbonic acid, enters into combination with some of the caustic lime, 
 producing a silicate of lime, thus convertmg the silica into a state in 
 which it may, when placed on the soil, contribute to the support of 
 plants. 
 
1 60 LESSONS IN CHEMISTRY. 
 
 II. That where the soil is poor in vegetable matters, and 
 
 especially when lime has already been applied, it 
 should be laid on the land in the mild state, or 
 made into a compost with the scourbigs of ditches, 
 clay, peat-mould, or other vegetable matters. When 
 applied in this compost form, a smaller dose of lime 
 is found to be sufficient, and the fertility of the soil 
 is most eflfectually maintained. 
 
 III. That as it has a tendency to sink down in the soil, it 
 
 should not be buried too deep. 
 
 IV. That on commencing to improve a farm to which lime 
 
 has not been applied for some time, the most judi- 
 cious method is to add a sufficient amount of it to 
 influence the composition of the soil, and after five 
 or six years to maintain its condition by short doses, 
 at the rate of about 8 bushels yearly per acre. 
 
 V. That quicklime, for the reasons already given, should 
 
 not be mixed with, or applied at the same time as 
 farm-yard dung, guano, or other manures which 
 afibrd ammonia by then- decay (183). 
 
 VI. That where the soil is naturally deep, or where new 
 
 soil has been brought to the surface and the land 
 has not been properly drained, a larger dose of lime 
 will be required than would be sufficient for a light 
 or well-dramed soil. 
 
 251. Marl, shdl-sand, coral-sand. — Besides limestone, 
 there are several other sources of lime accessible to the Irish 
 farmer. The most important of these are the deposits of 
 marl and shell-sand, which are found in so many parts of the 
 kingdom. The term marl is applied by the farmer to a kind 
 of calcareous earth, found at the bottom of bogs, and forming 
 beds in the small lakes which exist in so many counties. 
 Agricultural writers usually confine the term to earths con- 
 taining not less than 20 per cent of lime. In this country, 
 however, the quantity of lime in the substances regarded as 
 marl, varies from 5 to 96 per cent. The marls met with in 
 Ireland differ very much in then- composition ; some of them 
 contain a considerable amount of organic matter, and are 
 dried with difficulty {peaty marls) ; others, again, appear to 
 be almost entirely composed of minute shells, and crumble 
 readily into powder when exposed to the air {shell-marls) ; 
 
VEGETABLE MANURES. 
 
 \i\{ 
 
 and ill some districts, the calcareous matter is mixed with an 
 adhesive clay (day-marls). 
 
 252. The following; is the composition of some specimens 
 of mails, examined in my laboratory. In 100 parts, they 
 contain respectively as follows: — 
 
 Cariwnate of Lime 
 
 (Carbonate of Magnesia .... 
 
 Organic matter 
 
 Oxide of Iron and Alumina, 
 
 Insoluble sand 
 
 Water 
 
 96-50 
 1-03 
 0-60 
 0-30 
 0-40 
 1-16 
 
 99-99* 
 
 o a 
 
 30-72 
 
 0-82 
 
 3-10 
 
 1-80 
 
 38-54 
 
 24-96 
 
 99-94 
 
 W 
 
 54-90 
 
 1-50 
 
 5-00 
 
 1-56 
 
 10-00 
 
 27-20 
 
 100-16 
 
 39-60 43-44 
 0-801 0-55 
 3-90 2-20 
 
 3-70 1-60 
 52-00 50-00 
 
 100-00; 98-39 
 
 liesides therefore conveying to the soil, when applied as 
 manure, a considerable amount of carbonate of lime, these 
 marls, you perceive, would also enrich it by the addition of 
 other ingredients useful to plants. They also usually contain 
 a minute quantity of phosphate of lime, which must contri- 
 bute to their fertilizing power. So far as their chief ingre- 
 dient, lime, is concerned, their chemical effect upon the soil 
 must be the same as that exerted by mild lime. The 
 Extremely minute state of division, however, in which the 
 carbonate of lime exists in marls, will facilitate its action, 
 and the organic matter associated with it, will render its effects 
 less injurious upon soils poor in vegetable matter. Peaty 
 marls usually retain a large amount of water, which renders 
 their removal fi-om the bogs expensive; it has, therefore, 
 been recommended to burn them ;f and Liebig, who attributes 
 their efficacy, as manure, chiefly to the changes produced 
 by the lime contained in them on the clay of the soil, 
 .^rrongly advises that burnt marl should in all cases be 
 
 * This marl consisted chiefly of nunute shells, and had been partially 
 dried by exj)<)sure to the air ; the other specimens were peaty marls. 
 
 t Wet marls may also be dried, by mixing thorn with shell lime, 
 which will become slaked at the expense of the water of the marl. 
 
1 62 LESSONS IN CHEMISTRY. 
 
 preferred. This plan of treating them is, however, only to be 
 adopted when your object is merely to obtain the chemical 
 effects of the lime present. 
 
 253. Abont thirty years ago, enormous quantities of the 
 powdery marl, such as that from the barony of Lecale, of 
 which the analysis is given above, were applied to the fields 
 of Down, and with such beneficial effects, it is said, as in 
 many instances to raise the value of the land fourfold. But 
 after a time the produce decreased, and marl fell into disre- 
 pute as a manure, and has not for some years been much 
 employed in that district. And so it will always happen, 
 until farmers become acquainted with the nature of the sub- 
 stances which they apply to their fields. Precisely the same 
 thing occun-ed in Nottinghamshire, with regard to bones. 
 At their first introduction, then* price being low, it was ima- 
 gined that, as in small quantity they had done good to the 
 soil, a larger supply should be even more useful ; but after 
 some time, to the great disappointment of the farmers, good 
 effects ceased to follow their application, and it was not until 
 the Duke of Portland, by the publication of the results of 
 experiments made on his farm, convinced them that the 
 soil had been overcharged with bone earth, that they directed 
 their attention to other applications. The farmers of Down, 
 in the grain exported from Strangford and Killough, had, for 
 several years, taken away from their faims nine or ten of the 
 materials which rendered them fertile, only two or three of 
 which could be replaced in the marl used to keep up the 
 condition of the soil. 
 
 254. Shell-sand. — Valuable collections of sand, containing 
 a large amount of broken shells, exist on the coasts in many 
 parts of Ireland. As this sand usually contains both carbo- 
 nate of lime and animal matter, derived from the shells, and 
 some of the saline ingredients of the sea- water, it must pos- 
 sess considerable efficacy as manure. It may also, like marl, 
 be expected to convey to the soil a small amount of phosphate 
 of lime. It occurs of various degrees of fineness, and, as 
 might be expected, differs very much in value in different 
 localities. The fresh shell-sand from the sea-shore should 
 always be preferred to that which has been long exposed 
 at a distance from the coast, as it will contain a larger 
 amount of animal matter capable of affording ammonia by its 
 decay. 
 
VEGETABLE MANURtS. 163 
 
 255. Two specimens of shell- sand from the county of 
 Donegal, lately examined, were found to possess the following 
 composition : — 
 
 RathmuUan. Melmore, Mulroy Bay. 
 
 Carlwnate of Lime 74-40 54-36 
 
 ofMaf,mesia .... 0-69 3-78 
 
 Oxide of Iron and Alumina 1 -30 0-36 
 
 Phosphate of Lime 
 
 Organic matter 5*10 5-66 
 
 Sand and Siliceous matter 16-60 35-36 
 
 Water 1*50 056 
 
 I 99-59 99-98 
 
 On the coasts of France, shell-sand is much valued, and is 
 applied to the land at the rate of 10 to 15 tons per acre. In 
 addition to the large amount of carbonate of lime and other 
 useful ingredients which it usually contains, Boussingault 
 calculates that 100 tons of it would convey to the soil as 
 much nitrogen (derived from the animal matter) as 32 J tons 
 of farm-yard manure. 
 
 256. Coral-sand. — This substance, which is procured in 
 large quantities by the fishermen on the south coast of Ire- 
 land, affords the farmer another valuable source of lime. It 
 resembles shell-sand in its fertilizing qualities, but contains a 
 larger amount of animal matter, and being therefore richer in 
 nitrogen, will prove more immediately active. 
 
 257. Phosphate of Lime, — I have already explained to 
 you that bones (199) owe much of their fertilizing qualities 
 to the compounds of phosphoric acid which they contain. By 
 referring to the table, at p. 99, you may observe that that 
 acid is an essential ingredient of all the plants which you 
 cultivate, and is especially required for the production of those 
 parts of your crops valuable for food. It exists in exceedingly 
 minute quantities in even the most fertile soils, and every 
 means of obtaining supplies of it must, therefore, be of great 
 importance to agriculture. Some years ago, great interest 
 was excited by the discovery, in Spain, of a mineral called 
 apatitey which contained so much as 37 per cent of phosphoric 
 acid ; and recently, considerable attention has been directed 
 to the discovery of Professor Henslow, that in certain rocks 
 in Suffolk and Essex, there exist beds of water-worn nodules, 
 which have been termed coprolites* containing so much as 
 
 * Tliese curious nodules are supposed by geologists to be the fossil 
 dung of extinct animals. 
 
 
 
] 64 LESSONS IN CHEMISTRY. 
 
 60 per cent of phosphate of lime. Many hundred tons of 
 these coprolites have lately been used for manure, and they 
 have even been applied dissolved in sulphuric acid, as a sub- 
 stitute for " vitriolized bones," mth the very best results. It 
 has already been mentioned (132), that in the Greensand and 
 other rocks, constitutmg what is termed the chalk formation^ 
 which covers a considerable surface in England, and in Ireland 
 extends, with occasional interruptions, from Moira in Down 
 to Lough Foyle in Deny, a considerable amount of phosphate 
 of lime has also been found to exist. It is chiefly in the 
 Greensand, which appears to have been used several years 
 ago in some parts of Antrim, with good effects, as a manure 
 for both potatoes and oats, that that valuable substance has 
 been discovered.* 
 
 258. Sulphate of Lime. — This substance, which is also 
 known by the names oi plaster ofParis^ aiahastei\ and gypsum^ 
 has already been recommended as an important ad(ition to 
 the manure heap (183); but, besides its use in the preseiTa- 
 tion of other manures, it has, for a very long period, been 
 extensively applied as a fertilizer in various parts of Europe, 
 and is at present one of the most favourite applications of the 
 farmers in many parts of the United States of America. At 
 one time, it was believed that it was capable of increasing 
 the produce of every description of crop; but, from the 
 results of careful experiments made by experienced agricul- 
 turists, both in France and England, more correct opinions 
 of its fertilizing qualities are now entertained. The use of 
 this manm-e was considered of so great importance in France, 
 that a particular inquiry into the circumstances connected 
 with its employment and effects, was considered worthy of 
 the attention of the government, and a report on all the 
 information collected was made to the Eoyal Central Agri- 
 cultural Society of France. " The following series of ques- 
 tions and answers, I believe," says Boussingault, " embrace 
 most of the points of any interest connected with the employ- 
 ment of gypsum. 1 St, Does plaster act favourably on arti- 
 ficial meadows? Of 43 opinions given, 40 are in the 
 affirmative, and 3 in the negative. 2d, Does it act favour- 
 ably on artificial meadows, the soil of which is very damp ? 
 
 * A nodule, discovered in the greensand, near Camckfergus, by Mr. 
 M^Adam, and examined in my laboratory, was found to contain so much 
 as 42 per cent of phosphate of lime. , 
 
VEGETABLE MANURES, 1 V)5 
 
 Ten opinions given ; unanimously, no. 3d, Will it supply the 
 place of organic manure? or, will a barren soil be converted 
 into a fertile soil by the use of it? Seven answers given; 
 unanimously, no. 4 th, Does gypsum sensibly increase the 
 crops of the Cereals ? Of 32 opinions, 30 are negative, and 
 2 affirmative." 
 
 259. Gypsum may be applied either in the burned or 
 unbumed state, the only change produced by burning it being 
 the expulsion of the water which it contains. It is sparingly 
 soluble in water, and is usually applied as a top-dressing in 
 calm, moist weather; and its effects are said to be more 
 apparent when the white powdered gypsum adheres to the 
 leaves and stalks of the young grasses (Mr. C. Johnson). It 
 is said that its presence in the soil causes the seeds of 
 peas and beans to become hard, so that they are not 
 easily boiled. As this mineral manm*e exists in considerable 
 quantity in the north of Ireland, and can be obtained from 
 England at a very cheap rate, it should receive more attention 
 in this countiy. 
 
 260. The refuse lime of the gas-works has lately been em- 
 ployed as a manure, in the neighbourhood of towns where esta- 
 blishments for the manufacture of gas exist. From a half to 
 two-thirds of its weight usually consists of carbonate of lime, 
 and it also contains variable proportions of caustic lime, gypsum, 
 coal-tar, and compounds of sulphur. It may be interesting to 
 mention the purpose for which so much lime is used in the 
 gas-works. When coal is distilled, along with the illuminating 
 gas produced, certain volatile bodies are also evolved, which, 
 as they would interfere with its purity, it is necessaiy to re- 
 move ; thus carbonic acid gas (24) and ammonia, and the disa- 
 greeable smellmg gas, sulphuretted hydrogen, are given off (set 
 page 57). The manufacturer, however, by passing the mixed 
 gases over slaked lime, is enabled to detain the carbonic acid 
 and sulphuretted hydrogen, and, as it wei*e, sifts the illumi- 
 nating gas from these impmities. The compounds of sulphur 
 and lime which are produced, dissolve in water, and exercise 
 an injurious effect upon plants; but, by exposure to the air, 
 these salts are converted into gypsum, and are thus rendered 
 useful aj>plication3 to the soil; so that if gas-lime is to be 
 nsed as manure, this precaution should always be adopted 
 It has been used, with great advantage, in the neigh bourhooc' 
 of Belfast, made into a compost with weeds, the seeds oi 
 
166 LESSONS IN CHEMISTRY. 
 
 which it completely destroys, as an application to grass-land. 
 It is usually applied at the rate of 6 tons to the acre, and is 
 sold in Belfast at Is. 8d. per ton. At present, this substance, 
 which might be usefully employed were its proper treatment 
 generally known, is, I am informed, thrown away at several 
 gas establishments. 
 
 261. Ammoniacal liquor of the gas-works. — The prepara- 
 tion of coal-gas exhibits several beautiful applications of 
 chemical knowledge ; thus, the manufacturer finds in lime a 
 cheap and effectual means of purifying the gas from carbonic 
 acid and sulphuretted hydrogen, the presence of which would 
 materially affect the brilliancy of its flame ; and is also ena- 
 bled, by a peculiar arrangement of his apparatus, to separate 
 from it certain liquid products which possess considerable 
 commercial value. One of these is the watery fluid known 
 as gas, or ammoniacal liquor. This liquor is found to hold in 
 solution variable quantities of the carbonate and other salts of 
 ammonia. It is at present, in many places, used for the pre- 
 paration of a salt called sulphate of ammonia, which is formed 
 by adding sulphuric acid to it, and evaporating to dry- 
 ness. You may recollect that it is this compound which is 
 produced, when sulphuric acid or gypsum is mixed with fer- 
 menting urine. Sulphate of ammonia has been used, with 
 good effects, as an application to both wheat and potatoes;* 
 1 00 lbs. of it usually contain 35 lbs. of ammonia, but it is 
 occasionally adulterated with sulphate of soda (52) and 
 other cheap salts.f Its present wholesale price in London is 
 16.?. per cwt. The gas liquor can be obtained at a very 
 low price, and has been found a useful manure for grass and 
 clover. It should be diluted, before its application, with 3 
 or 4 times its bulk of water, and its effect will be rendered 
 more permanent by neutralizing it (13) with some sulphuric 
 acid, or by mixing some gypsum with it to fix the ammonia. 
 It is appHed at the rate of 100 gallons per acre. 
 
 262. Lime, salt, and peat-mould. — A compost formed of 
 
 * The application of a mixture of sulphate of ammonia and vitriolized 
 bones, has been found exceedingly useful in improving the verdure and 
 destroying the moss which springs up in old worn-out lawns. 1^ cwt. 
 of the sulphate of ammonia, and 5 bushels of bones, will be sufficient for 
 an acre. 
 
 f The teacher may readily test the purity of a sample of sulphate of 
 ammonia, by heating a little of it, on the pomt of a knife, over the spirit- 
 lamp, when, if pure, it will all be converted into vapour. 
 
VEGETABLE MANURES. J 67 
 
 these substances is much vahied in many districts. The good 
 effects of salt have already been mentioned. It has been 
 used for a long period as a manure, though, when applied in 
 too large quantities, it totally destroys vegetation. The 
 refuse salt of the provision stores can be procured at a very 
 low price ; and, as it is mixed with blood and other animal 
 matters, it will be found even more useful than pure salt for 
 manuring. The best method of intimately mixing lime and 
 salt, is to dissolve the salt in water and use it for slaking 
 the lime ; the effects of the mixture are mutual decomposition 
 of the lime and salt (chloride of sodium), chloride of calcium 
 and caustic soda being produced, both of which are readily 
 soluble in water. When peat-mould is added, a compost is 
 formed, of great value as a manure for soils deficient in vege- 
 table matter, and requiring lime and soda. 
 
 263. Soot, which is occasionally employed as a top-dressing 
 to grass and wheat, is a variable mixture of clayey matters, 
 iron, sulphate of ammonia, gypsum, and certain organic 
 compounds. Its fertilizing qualities are to be ascribed chiefly 
 to the sulphate of ammonia which it contains.* The amount 
 of this ingredient, which different samples are capable of 
 affording, is shown by analysis to vary from 10 to 30 per 
 cent. It should be applied in damp weather. 
 
 • The teacher may convince his pupils that ammonia is contained in 
 soot, by moistening a little of it with water, and mixing it with quick- 
 lime, when a pungent ammoniueal odour will be perceived. 
 
INDEX. 
 
 P\GE 
 . 60 
 
 . 60 
 
 . 29 
 
 . 4G 
 
 . 47 
 
 ACID, Acetic — Citric — Malic 
 
 Tartaric 
 
 r Carbonic— Muriatic .... 
 
 Fluoric 
 
 Phosphoric— Sulphuric 
 
 Nitric 1 54 
 
 meaning of the term 26 
 
 Alkalies, properties of 26 
 
 Apparatus necessary for teachers xviii 
 
 Atmosphere, the composition of . . 25 
 
 properties of 20 
 
 materials which 
 
 plants derive from 33 
 
 — discovery of Am- 
 monia in 28 
 
 Ammonia, preparation of 28 
 
 properties of 27 
 
 Ammoniacal liquor 166 
 
 Alumina, properties of . . ., 80 
 
 Ashes, turf— composition of 150 
 
 of Sea-Weeds 146 
 
 Alternation of crops 1 00 
 
 Agriculture, origin of 95 
 
 Agricultural education, value of. . xv 
 
 Animal manures 1 05 
 
 heat, how maintained .... 119 
 
 young, dung of 120 
 
 Albumen 56 
 
 13 ONE S, composition of 1 33 
 
 use of, as manure 135 
 
 effects of, on the soil 1 32 
 
 organic matter of 132 
 
 Nitrogen in — crushed .. 132 
 
 Vitriolized preparation of 138 
 
 how to be applied 137 
 
 Blood, composition of 140 
 
 saline matters in 140 
 
 PAGE 
 
 CHEMISTRY, agricultural, value 
 
 of X 
 
 — progress of ix 
 
 Chemical combination defined. . . . 21 
 
 Carbonic acid gas, properties of . . 31 
 
 Carbon, in plants 32 
 
 consumed in respiration . . Hi* 
 
 Carbonate of Lime 44 
 
 Potash 4:i 
 
 Magnesia 45 
 
 Ammonia 109 
 
 Coal-gas, composition of 165 
 
 Calcium ' 44 
 
 Chlorideof 167 
 
 Chlorine, properties of 47 
 
 Chloride of Sodium 47 
 
 Crops, composition of the ash of. . 99 
 influence of soils on their 
 
 quality 1 04 
 
 Clay-slate formation 85 
 
 analysis of 87 
 
 soils 86 
 
 Caustic Potash 43 
 
 Soda 43 
 
 Lime 155 
 
 DEXTRIN, properties of 55 
 
 Diastase in malt 58 
 
 Distribution of rocks in Ireland . . 83 
 
 Development of plants 67 
 
 Dublin limestone, analysis of ... . 1 56 
 
 ELEMENTS, number of xvi 
 
 defined xvi 
 
 Excrements, aiumal, as manures . . 1 09 
 Evaporation renders soils cold .... 39 
 Effects which plants produce on 
 the soil 95 
 
INDEX. . 
 
 1G9 
 
 i;iTi'ct.« of cultivation on wild 
 plants 'J5 
 
 of lime on plants 158 
 
 Epidermis of plants 65 
 
 Experiments with lime 155 
 
 FATTY matters in plants 58 
 
 Flesh, composition of 140 
 
 Fibrine, analysis of 68 
 
 Fish, use of, as manure 139 
 
 Shell 139 
 
 Fam\-yard manure, composition of 122 
 
 Feldspar, composition of ....... . 83* 
 
 Fallow 100 
 
 \ S, meaning of the term 20 
 
 liquor 166 
 
 Gases, preparation of 22 
 
 Gemniiuition 63 
 
 Geological structure of Ireland .. 81 
 
 Gluten, how prepared 57 
 
 Gold of pleasure, cake of 59 
 
 Green manuring 143 
 
 sand 91 
 
 phosphoric acid in .. 164 
 
 Growth of plants 67 
 
 Granite, composition of 83 
 
 Gum, cherry-tree 56 
 
 British 55 
 
 Gypsum, use of; as manure 164 
 
 action of, on urine 114 
 
 Guano, history of 128 
 
 analyses of 130 
 
 value of 131 
 
 Rev. Mr. Huxtable's method 
 
 ©fusing 131 
 
 adidteration of 131 
 
 PAGE 
 
 KELP, -composition of 146 
 
 proper method of preparing 1*46 
 
 HAIR, as manure 141 
 
 Hydrogen, properties of 34 
 
 preparation of 35 
 
 Sulphuretted 57 
 
 Humus, nature of 93 
 
 Horse, dung of 117 
 
 I lomblende, its composition 83 
 
 Horn shavings as manure 141 
 
 I RELAND, productive powers of xiii 
 
 early agriculture of . . xiii 
 
 climate of 40 
 
 Irish farmer In America 96 
 
 Iron, oxides of 45 
 
 - sulphate of, fixes Ammonia 126 
 
 'line 48 
 
 tincture of 54 
 
 LEGUMIN 58 
 
 Lime, sources and properties of . . 44 
 
 slaking of 155 
 
 how applied as manure 1 59 
 
 injurious effects of, on farm- 
 yard manure 125 
 
 chemical effects of 157 
 
 Lime-water, a test for carbonic 
 
 acid ,. 31 
 
 preparation of 156 
 
 Liquid manures, value of 116 
 
 how distributed , . 125 
 
 Leaves, structure of ; 66 
 
 Light, effects of, on plants 72 
 
 Liquorice, sugar in 56 
 
 List of apparatus for teachers . . xviii 
 
 MANURES, animal 
 
 artificial 
 
 vegetable 
 
 mineral and saline. 
 
 Manure, farm-yard, changes which 
 
 accompany its decay 
 
 neglect of ... . 
 
 —-^ directions for 
 
 105 
 lb3 
 143 
 152 
 
 121 
 121 
 
 its preservation 123 
 
 nomical . 
 
 - heap — ^tank eco- 
 
 ammoma m 
 
 Magnesia, properties of 
 
 sulphate, composition of 
 
 Manganese, oxide of 
 
 Mica slate 
 
 Marls, analyses of . . 
 Mucilage 
 
 126 
 122 
 
 45 
 4(i 
 4() 
 81 
 161 
 56 
 
 NITROGEN, properties of 24 
 
 preparation of • . . . . 24 
 
 Night soil, value of 110 
 
 preservation of lia 
 
 Nitrates, composition of 151 
 
 OXYGEN, properties of i.i 
 
 how prepared 23 
 
 necessary to animals . . 22 
 
 Oils, how obtained 59 
 
 use of, in plants 61 
 
 Organic matter of soils 92 
 
 of bones 133 
 
 of crops, composi- 
 tion of .'jO 
 
170 
 
 INDEX. 
 
 PAGE 
 
 PEAT, fomiation of 92 
 
 charcoal, preparation of . . 148 
 
 ashes, composition of 149 
 
 Plants, materials from which they 
 
 are formed 15) 
 
 inorganic matters in 12 
 
 Potash, preparation of 43 i 
 
 sulphate of 27 j 
 
 carbonate of 43 
 
 Potassium .* ' * 43 
 
 Phosphoric acid 47 
 
 Peruvian Bark,' quinine in 51 
 
 Potato, wild 95 
 
 Peat, composts ofy^ 166 
 
 Poudrette ..\ HI 
 
 QUARTZ 83 
 
 Quicklime i 155 
 
 .. 112 
 
 RAPE dust as manure 
 
 Refuse of the Glue manufacture . 
 
 lime of gas-works 
 
 River water, solid matters in . . . 
 Rotation of crops 
 
 SAP, course of , 
 
 Sandstone formation 
 
 Saijid, coral 
 
 Silica and Silicates 
 
 Seeds , 
 
 as manure , 
 
 Stem, composition of the . , 
 
 Salts defined 
 
 Soils, materials existing in 
 
 formation of 
 
 transported 
 
 Soot, composition of 
 
 151 
 141 
 165 
 37 
 101 
 
 70 
 87 
 
 163 
 46 
 63 
 
 151 
 65 
 26 
 80 
 79 
 82 
 
 167 
 
 Sewage, composition of 
 
 value of, as manure . 
 
 Starch, composition of 54 
 
 sugar 55 
 
 use of 119 
 
 varieties of 53 
 
 Sodium' 44 
 
 Soda, and compounds of 43 
 
 SulpTiuric'acid 47 
 
 action of, on bones 137 
 
 Sulphuret of Iron in soUs 158 
 
 Shell-sand, composition of 162 
 
 Sugar, composition of 56 
 
 TAFFO 110 
 
 Trap, or Volcanic rocks 89 
 
 Testing 26 
 
 Test-papers 26 
 
 URINE, how apphed 127 
 
 of man, composition of . . 108 
 
 animals, composition of 1 1 4 
 
 Urea, Nitrogen in 108 
 
 Urate, how prepared 1 1 1 
 
 VEGETABLE Casein..... 57 
 
 Fibrme 57 
 
 Acids 60 
 
 Albumen 58 
 
 WATER, composition of 34 
 
 materials supplied to 
 
 plants by 40 
 
 Wool of the sheep, sulphur in 47 
 
 Woollen rags as manure 141 
 
 Woody fibre 52 
 
 "Wheat, oil in CO 
 
 THE END. 
 
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