/M, &^cu^-- "ft / Digitized by the Internet Archive in 2017 with funding from University of Illinois Urbana-Champaign Alternates https://archive.org/details/howcropsfeedtrea00john_0 » HOW CROPS FEED A TREATISE ON THE ATMOSPHERE AND THE SOIL AS RELATED TO THE Nutrition of Agricultural Plants. WITH ILLUSTRATTONS. BY SAMUEL W. JOHNSON, M.A., f PROFESSOR OF ANALYTICAL AND AGRICULTURAL CHEMISTRY IN THE SHEFFIELD SCIENTIFIC SCHOOL OF YALE COLLEGE ; CHEMIST TO THE CONNEC- TICUT STATE AGRICULTURAL SOCIETY; MEMBER OF THE NATIONAL ACADEMY OF SCIENCES. NEW YORK: ORANGE JUDD COMPANY 1893 . Entered according to Act of Congress, in the year 1870, by ORANGE JUDD & CO., In the Clerk’s Office of the District Court of the United States for the Southern District oi New York PREFACE. The work entitled “How Crops Grow” has been re- ceived with favor beyond its merits, not only in America, but in Europe. It has been republished in England under the joint Editorship of Professors Church and Dyer, of the Royal Agricultural College, at Cirencester, and a translation into German is soon to appear, at the instiga- tion of Professor von Liebig. The Autlior, therefore, puts forth this volume — the com- panion and complement to the former — with tlie hope that j it also will be welcomed by those who appreciate the sci- ^tific aspects of Agriculture, and are persuaded that a • y true Theory is the surest guide to a successful Practice. ^ The writer does not flatter himself that he has produced , a popular book. He has not sought to excite the imagi- , nation with high-wrought pictures of overflowing fertility - as the immediate result of scientiflc discussion or experi- ^""^ent, nor has he attempted to make a show of revolution- izing his subject by bold or striking speculations. His ^ office has been to dis^est the cumbrous mass of evidence, m which the truths of Vegetable Nutrition lie buried out 5 VI PREFACE. of the reach of the ordinary inquirer, and to set them forth in proper order and in plain dress for their legiti- mate and sober uses. It has cost the Investigator severe study and labor to discover the lav^s and many of the facts which are laid down in the following pages. It has cost the Author no little work to collect and arrange the facts, and develop their mutual bearings, and the Reader must pay a similar price if he would apprehend them in their true signifi- cance. In this, as in the preceding volume, the Author’s method has been to bring forth all accessible facts, to present their evidence on the topics under discussion, and dispassion- ately to record their verdict. If this procedure be some- times tedious, it is always safe, and there is no other mode of treating a subject which can satisfy the earnest inquirer. It is, then, to the Students of Agriculture, whether on the Farm or in the School, that the Author commends his book, in confidence of receiving full sympathy for its spirit, whatever may be the defects in its execution. CONTENTS, Introducttion. .^17 DIVISION L THE ATMOSPHERE AS RELATED TO VEGETATION, CHAPTER I, Atmospheric Air as the Food of Plants. § 1. Chemical Composition of the Atmosphere .21 § 2, Relation of Oxygen Gas to Vegetable Nutrition...^..,., 22 § 3. “ “ Nitrogen Gas to “ “ 26 § 4, ** “ Atmospheric Water to Vegetable Nutrition 34 § 5, « Carbonic Acid Gas “ ** .....38 § 6. * « Atmospheric Ammonia to ** .......49 § 7. Ozone ...63 § 8. Compounds of Nitrogen and Oxygen in the Atmosphere 70 § 9. Other Ingredients of the Atmosphere 91 § 10. Recapitulation of the Atmospheric Supplies of Food to Crops 94 § 11. Assimilation of Atmospheric Pood 97 § 12. Tabular View of the Relations of the Atmospheric Ingredients to the Life of Plants 98 CHAPTER II. The Atmosphere as Physically Related to Vegetation. § 1. Manner of Absorption of Gaseous Pood by Plants DIVISION n. THE SOIL AS RELATED TO VEGETABLE PRODUCTION. CHAPTER 1. Introductory. 104 Tin BOW CROPS PEED. CHAPTER II. Origin anif Formation op Soils 106 I 1. Chemical Elements of Rocks lOT I 2. Mineralogical Elements of Rocks 108 0 § 3. Kocks^ their Kinds and Characters 117 I 4. Conversion of Rocks into Sk>il 122 i 5. Incorporation of Organic Matter with the Soil, and its Effects 135 CHAPTER III. Kinos of Soils, their Definition and Classification. I 1. Distinctions of Soils based upon the Mode of their Formation or Deposi- tion 142 I 2. Distinctions of Soils based upon Obvious or External Characters 14^ CHAPTER IV. Physical Characters of the Soil, 157 § 1. Weight of Soils 158 § 2. State of Division 159 ^ § 3. Absorption of Vapor of Water,. . . 161 I 4. Condensation of Gases 165 § 5. Power of Removing Solid Matters from Solution 171 §6. Perroeability to Liquid Water. Imbibition. Capillary Power 176 § 7. Changes of Bulk by Drying and Frost 183 § 8. Adhesiveness 184 § 9. Relations to Heat 186 CHAPTER V. The Soil as a Source of Food to Crops : Ingredients whose Elements ARE OF Atmospheric Origin. § 1 . § 2 . § 3. § 4. §5. § 6 . § T. § 8 . §9. The Free Water of the Soil in its Relations to Vegetable Nutrition The Air of the Soil ! Non-nitrogenous Organic Matters. Humus The Ammonia of the Soil Nitric Acid (Nitrates) of the Soil Nitrogenous Organic Matters of the Soil. Available Nitrogen Decay of Organic Matters. Nitrogenous Principles of Urine Comparative Nutritive Value of Animoni^-SaUs and Nitrates 199 ,217 I ,222 238 251 274 289 293 300 COJ^TENTS, IX CHAPTER VI. The Soil as a Source op Food to Crops : Ingredients whose Elements ARE Derived from Rocks. § 1. General View of the Constitution of the Soil as Related to Vegetable Nutrition ; 305 § 2. Aqueous Solution of the Soil 309 § .3. Solution of the Soil in Strong Acids 329 § 4. Portion of Soil Insoluble in Acids . . 330 § 5. Reactions by which the Solubility of the Elements of the Soil Is al- tered. Solvent Effects of Various Substances. Absorptive and Fixing Power of Soils 331 § 6. Review and Conclusion - 361 INDEX Absorption and displacement, law of 336 Absorptive power of soils 333 “ “ “ cause c)f.343, 354 “ “ “ significance of 374 Acids in soil 223 “ absorbed by soils 355 Adhesion 165 Adhesiveness of soils 184 Air, atmospheric, composition of.. 21 “ within the plant, composition of 45 Alkali-salts, solvent eflfect of 130 Allotropism 66 Alluvium 145 Aluminum, alumina 107 Amides 276 Amide-like bodies 277, 300 Ammonia 40, 54 “ absorbed by clay 243, 267 “ “ “ peat 360 “ “ “ plants 56, 98 “ condensed in soils 240 “ conversion of into nitric acid 85 “ evolved from flesh decay- ing under charcoal 169 “ fixed by gypsum 244 “ in atmosphere 54 “ “ “ how formed.77, 85 “ of rain, etc 60 “ of the soil, formation of. 239 “ “ “ chemically combined. 243 “ “ “ physically condensed. 240 “ “ “ quantity of. .248 “ “ “ solubility of. 246 “ “ “ volatility of.. 244 Ammonia-salts and nitrates, nutri- tive value of 300 Amphibole 112 Analysis of soils, chemical indica- tions of. 368 mechanical 147 Apatite 116 Apocrenates 231 Apocrenic acid 227, 229 Argillite 119 Ash-ingredients, quantity needful for crops 363 Atmosphere, chemical composi- tion.. 21, 22 “ physical constitution. . 99 Atmospheric food, absorb.ed 99 “ “ assimilated — 97 Barley crop, ash ingredients of. .364 Basalt 120 Bases, absorbed by soils. 335, 359 Bisulphide of iron 115 Burning of clay 185 Calcite 115 Capillarity 175, 199, 201 Carbohydrates in soil 222 Carbon, fixed by plants 43, 48 “ in decay 291 “ supply of 95 Carbonate of lime 115, 102 “ “ magnesia 115, 102 Carbonic acid 38 “ “ absorbed by soil 221 “ “ “ plants.41, 45, 98 “ “ exhaled by plants.. 43, 99 “ “ in the soil 218 “ “ “ water of soil. .220 “ “ quantity in the air.40, 47, 94 “ “ solubility in water. 40, 130 11 XII HOW CROPS FEED. Carbonic acid, solvent action of 128 Carbonic oxide 92 Cliabasite 115 “ action on saline com- pounds 845 “ formed in Roman mason- ry 351 Chalk soils 192 Charcoal, absorbs gases 165 ‘‘ defecating action of. 174 Chili saltpeter 253 Chlorite 113 Chrysolite 114 Clay 132, 134, 154 “ absorptive power, 174 “ effect of, on urine 293 Clay-slate 119 Coffee, condenses gases 168 Color of soil -..190 Conglomerates. . 121 Crenates 231 Crenic acid 227, 229 Decay 289 Deliquescence 163 Deserts 197 Dew 189, 195 Diffusion of gases 100 Diorite 120 Dolerite 120 Dolomite 115, 121 Draining 185 Drain water, composition of 312 Drift 144 Dye stuffs, fixing of 174 Earth-closet 171 Eremacausis 289 Evaporation, produces cold 188 “ amount of, from soil. 197 Exhalation 202, 206 Exposure of soil — 195 Feldspar 108 “ growth of barley in 160 Fermentation 290 Fixtation of bases in the soil 839 Frost, effects of, on rocks 124 “ “ “ on soils 184, 185 Fumic acid 258 Gases, absorbed by the plant 103 “ “ “ porous bodies., 167 “ ■ “ “ soils 165, 166 “ diffusion of 100 “ osmose of 102 Glaciers 124 Glycine 206 Glycocoll 296 Gneiss 119 Granite 118, 120 Gravel 152 “ warmth of 195 Guanin • 296 Gypsum 115 “ does not directly absorb water 162 “ fixes ammonia 244 Hard pan 156 Heat, absorptioivand radiation of,. 188, 193 “ developed in flowering 24 “ of soil 187 Hippuric acid 295, 277 Hornblende 112 Hydration of minerals 127 Hydraulic cement 122 Hydrochloric acid gas 93 Hydrogen, supply of, to plants 95 “ in decay 291 Hydrous silicates, formation of 352 Hygroscopic quality 164 Huniates 230 Humic acid 226, 229 Humin 236, 229 Humus 136, 224, 276 “ absorbent power for water. . 162 “ absorbs salts from solutions. 172 “ action on minerals 138 “ chemical nature of 138 “ does it feed the plant? 232 “ not essential to crops 2:18 “ value of 182 Iodine in sea-water. . . 322 Isomorphism Ill Kreatin 196 Kaolinite 113, 132 Latent heat 188 Lawes’ and Gilbert’s wheat experi- ments 372 Leucite 113 Lime, effects of 184, 185 Limestone... 121, 122 Loam 154 Lysimetcr 314 Magnesite 115 Marble 121 Marl 155 Marsh gas 91, 99 Mica 109 INDEX, XIII Mica slate ... .J 119 Minerals 106, 108 ‘‘ hydration of. 127 “ solution of 127 “ variable composition of 110 Moisture, effect of, on temperature of soil 195 Mold 156 Moor-bed pan . ... 157 Muck 155 Nitrate of ammonia 71, 73 “ in atmosphere. 89 Nitrates 252 “ as food for plants •. . . 271 “ formed in soil 171, 179 “ in water 270 “ loss of. 270 “ reduction of. 73, 82, 85 “ “ “ in soil 268 “ tests for 75 Nitric acid .. 70 “ “ as plant-food 90, 98 “ “ deportment towards the soil :157 “ “ in atmosphere £0 “ “ “ rain-water 86 “ “ “ soil 251,254 “ “ “ “ sources of 256 Nitric oxide 72 Nitric peroxide 72 Nitrification 252, 286 “ conditions of 265, 292 Nitrogen, atmospheric supply to plants 95 “ combined, in decay. 291, 292 “ “ of the soil. , .275 “ combined, of the soil, available 283 “ combined, of the soil, inert 278 “ combined, of the soil, quantity needed for crops.2S8 “ free, absorbed by soil. . .167 “ “ assimilated by the soil 259 “ “■ in soil 218 “ “ not absorbed by vegetation 26, 99 ** “ not emitted by liv- ing plants 23 Nitrogen-compounds, formation of, in atmosphere. 75, 77, 83 Nitrogenous fertilizers, effect on cereals ... 83 Nitrogenous organic matters of soil. 274 Nitrous acid 72 Nitrous oxide 71, 93 Ocher 156 Oxidation, aided by porous bodies. 169, 170 Oxide of iron, a carrier of oxygen. .257 “ ‘‘ hydrated, in the soil. 350 Oxygen, absorbed by plants 98 “ essential to growth 23 “ exhaled by foliage 25, 99 “ function of, in growth 24 “ in soil 218 “ supply 94 “ weathering action of 131 Ozone ... 63 “ concerned in oxidation of ni- trogen 82 “ formed by chemical action. 60, 67 “ produced by vegetation. 67, 84, 99 “ relations of, to vegetable nu- trition...*. 70 Pan, composition of 852 Parasitic plants, nourishment of. . .235 Peat 155, 224 “ nitrogen of 274 Phosphate of lime 116 Phosphoric acid fixed by the soil . . .357 “ presence in soil water 315 Phosphorite 116 Plant-food, concentration of. 320 maintenance of supply. 371 Platinized charcoal 170 Platinum sponge, condenses oxygenl70 Porphyry .120 Potash, quantity in barley crop 863 Provence, drouths of 198 Pyrites 115 Pyroxene 112 Pumice 120 Putrefaction. 290 Quartz 108, 122 Rain-water, ammonia in 60, 88 ‘‘ nitric acid in 86 “ phosphoric acid in 94 Ree Ree bottom, soil of 160 Respiration of the plant 43 Rocks 106, 117 “ attacked by plants. 140 XIV HOW CROPS PEED. Rocks, conversion into soils 122 Roots, direct action on soil 32(i Saline incrustations 179 Saltpeter 252 Salts decomposed or absorbed by the soil 336 Sand 153, 162 Sand filter ^ 172 Sandstone 121 Serpentine 114, 121 Schist, micaceous 119 “ talcose ..121 chlorite 121 Shales 122 Sherry wine region 192 Shrinking of soils 183 Silica 108 “ function in the soil 353 “ of soil, liberated by strong acids 330 Silicates . . .109 “ zeolitic, presence in soils. .349 Silicic acid, fixed in the soil 358 Silk, hygroscopic 165 Soapstone 121 Sod, temperature of 199 Soil 104 “ absorptive power of 333 “ aid to oxidation 17Q “ aqueous solution of 309, 323, 328 “ condenses gases 165, 166 “ capacity for heat 194 “ chemical action in 331 “ composition of. .362, 369 “ exhaustion of. 373 “ inert basis 305 “ natural strength of..., 372 “ origin and formation. .106, 122, 135 “ physical characters 157 “ porosity of. 176 “ portion insoluble in acids 330 “ relative value of ingredients 367 “ reversion to rock 332 “ solubility in acids 329 “ “ water 309 “ source of food to crops .305 “ state of division 159 Soils, sedentary 143 transported 143 “ weight of 158 Solubility, standards of 308 Solution of soil in acids .370 “ “ water 310 Steatite 121 Swamp muck 155 Sulphates, agents of oxidation 258 Sulphate of lime 115 Sulphur, in decay ..293 Sulphurous acid 94 Sulphydric acid 94 Syenite 120 Talc 113 Temperature of soil 186, 187, 194 Transpiration 202, 208 Trap rock 120 U1 mates 230 Ulmic acid. 224, 226. 229 Ulmin 224, 226, 229 Urea 294, 277 Uric acid 295, 277 Urine 293 preserved fresh by clay 293 its nitrogenous principles as- similated by plants 296 Vegetation, antiquity of 138 decay of. 137 action on soil 140 Volcanic rocks, conversion to soil.. 135 Wall fruits 199 Water absorbed by roots 202, 210 functions of, in nutrition of plant 216 imbibed by soil 180 movements in soil 177 proportion of in plant, influ- enced by soil 213 of soil..., ..315, 317 “ bottom water 200 capillary ... 200 hydrostatic 199 hygroscopic 201 quantity favorable to crops. .214 Water-currents 124 Water-vapor, absorbed by soil. 161, 164 “ exhaled by plants 99 “ not absorbed by plants 35, 99 “ of the atmosphere 34 Weathering 131-134 Wilting 203 Woc:-l, hygroscopic 164 Zeolitea 114, 349 HOAV CROPS FEED. HOW CROPS PEED INTRODUCTIOJf* In his treatise entitled How Crops Grow,” the author has described in detail the Chemical Composition of Agrb cultural Plants, and has stated what substances are indis- pensable to their growth. In the same book is given an account of the apparatus and processes by which the plant takes up its food. The sources of the food of crops are, however, noticed there in but the briefest manner. The present work is exclusively occupied with the important and extended subject of Vegetable Nutrition, and is thua the complement of the first-mentioned treatise. Whatever information may be needed as preliminary to an under standing of this book, the reader may find in ‘‘ How Cropa Grow.” * That crops grow by gathering and assimilating food is a conception with which all are familiar, but it is only by following the subject into its details that we can gain hints that shall apply usefully in Agricultural Practice. * It has been at least the author’s aim to make the first of this series of bookie prepare the way for the second, as both the first and the second are written tu make possible an intellij^ible account of the mode of action of Tillage and of Fertilizers, which will be the subject of a third work. 17 18 HOW CROPS FEED, When a seed germinates in a medium that is totally destitute of one or all the essential elements of the plant, the embryo attains a certain development from the mate- rials of the seed itself (cotyledons or endosperm,) but shortly after these are consumed, the plantlet cetises to in- crease in dry weight,^ and dies, or only grows at its ow n expense. A similar seed deposited in orened as in the free air, and oxygen gas was found to be consumed in considerable quan- Fig. 1. tity. When, however, the twigs were confined in an atmosphere of nitrogen or hydrogen, they decayed, with- out giving any signs of vegetation. {Becherches sur la Vegetation^ p. 115.) The same acute investigator found that oxygen is ab- sorbed by the roots of plants. Fig. 2 shows the arrange- ment by which he examined the effect of different gases on these organs. A young horse-chestnut plant, carefully lifted from the soil so as not to injure its roots, had the latter passed through the neck of a bell-glass, and the stem was then cemented air-tight into the opening. The bell 24 HOW CKOPS FEEH. was placed in a basin of mercury, C, D, to shut off its con- tents from the external air. So much water was intro- duced as to reach the ends of the principal roots, and the space above was occupied by com- mon or some other kind of air. In one experiment carbonic acid, in a second nitrogen, in a third hydi o- gen, and in three others common air, was employed. In the first the roots died in seven or eight days, in the second and third they perish- ed in thirteen or fourteen days, while in the three others they re- mained healthy to the end of three weeks, when the experiments weie concluded. {Hecherc/ieSy p. 104.) Flowers require oxygen for their development. Aquatic plants send their flower-buds above the water to blossom. De Saussure found that flowers consume, in 24 hours, several or many times their bulk of oxygen gas. Tins absorption proceeds most energetically in the pistils and stamens. Flowers of very rapid growth experience in this process, a considerable rise of temperature. Garreau, observing the spadix of Arum italicum^ which absorbed 28|- times its bulk of oxygen in one hour, found it 15° F. warmer than the surrounding air. In the lipeuing of fruits, oxygen is also absorbed in small quantity. The Function of Free Oxyg^en. — All those processes of growth to which free oxygen gas is a requisite appear to depend upon the ti*ansfer to the growing organ of mat- ters previously organized in some other part of the plant, and probably are not cases in which external inorganic bodies are built up into ingredients of the vegetable struc- ture. Young seedlings, buds, flowers, and ripening fruits, ATMOSPHERIC AIR AS THE FuOD OF PLANTS. 25 have no power to increase in mass at the expense of the atmosphere and soil; they liave no provision for the ab- sorption of the nutritive elements that surround them ex- ternally, but grow at the expense of other parts of the plant (or seed) to which they ^belong. / The function of free gaseous oxygen in vegetable nutrition, so far as can be judged from our existing knowledge, consists in elFecting or aiding to effect the conversion of the mateiials which the leaves organize or which the roots absorb, into the proper tissues of the growing parts. Free oxygen is thus probably an agent of assimiLaJdan. Certain it is that the free oxygen which is absorbed by the plant, or, at least, a corresponding quantity, is evolved again, either in the un- combined state or in union with carbon as carbonic acid. Exhalation of Oxygen from Foliage. — The relation of the leases and green parts of plants to oxygen gas has thus far been purposely left unnoticed. These organs like- wise absorb oxygen, and require its presence in the atmos- phere, or, if aquatic, in the water which surrounds them ; but they also, during their exposure to lights exhale oxygen. This interesting fact is illustrated by a simple experiment. Fill a glass funnel with any kind of fresh leaves, and place it, inverted, in a wide glass containing water, fig. 3, so that it shall be completely immersed, and displace all air from its interior by agitation. Close the neck of the funnel air-tight by a cork, and pour off a portion ’ of the water from the outer vessel. Expose now the leaves to strong sunlight. Observe that very soon minute bubbles of air will gather on the leaves. These will gradually increase in size and detach themselves, and after an hour or two, enough gas will accumulate in the neck of the funnel to enable the experimenter to 2 26 HOW CROPS FEED. prove that it consists of oxys^en. For this purpose bring the water outside the neck to a level with that inside; have ready a splinter of pine, the end of which is glow- ing hot, but not in flame, remove the cork, and insert the ignited stick into the gas. It will inflame and burn much more brightly than in the external air. (See H. C. G., p. 35, Exp. 5.) To this phenomenon, one of the most im* portant connected with our subject, we shall recur under the head of carbonic acid, the compound which is the chief source of this exhaled oxygen. § 3 . RELATIONS OF NITROGEN GAS TO VEGETABLE NUTRITION. Nitrogen Gas not a Food to the Plant. — Mtrog n in the free state appears to be indifferent to vegetation. Priestley, to whom we are much indebted for our knowl- edge of the atmosphere, was led to believe in 1779 that free nitrogen is absorbed by and feeds the plant. But this philosopher had no adequate means of investigating the subject. De Saussure, twenty years later, having command of better m thods of analyzing gaseous mix- tures, concluded from his experiments tiiat free nitrogen does not at all participate in vegetable nutrition. BouSSingaulFs Experiments. — The question rested un- til 1887, wlien Boussingault made some trials, which, how- ever, were not decisive. In 1851-1855 this ingenious chemist resumed the study of the subject and conducted a large number of experiments with the greatest care, all of which lead to the conclusion that no appreciable amount of free nitrogen is assimilated by plants. His plan of experiment was simply to cause plants to grow in circumstances where, every other condition of de- velopment being supplied, the only source of nitrogen at ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 27 tlieir command, besides that contained in the seed itself, should be the free nitrogen of the atmosphere. For this purpose he prepared a soil consisting of pumice-stone and the ashes of stable-manure, which was perfectly freed from all compounds of nitrogen by treatment with acids and in- tense heat. In nine of his earlier experiments the soil thus prepared was placed at the bottom of a large glass globe, fig. 4, of 15 to 20 gallons’ capacity. Seeds of cress, dwarf beans, or lupins, were deposited in the soil, and a proper supply of water, purified for the purpose, was add- ed. After germination of the seeds, a glass globe, of about one-tenth the capacity of the larger vessel, was filled with carbonic acid (to supply carbon), and was secured air- tight to the mouth of the latter, com- munication being had between them by the open neck at (7. The apparatus was then disposed in a suitably lighted place in a garden, and left to itself for a period which va- lued in the diiferent experiments from to 5 months. At the conclusion of the trial the plants were lifted out, and, to- gether with the soil from which their roots could not be entirely separated, were subjected to chemical analysis, to determine the amount of nitrogen which they had assimilated during growth. The details of these trials are contained in the subjoined 28 HOW CROPS FEED. Table. The weights are expressed in the gram and its fractions. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 14 Kind of Plant, Duration of Eoeperiment. Number of Seeds. , Weight of Seeds. Weight of Crop. Niti'ogen in Seeds. Nitrogen in Croj) and Soil. Dwarf bean 2 months 1 0.780 1.87 0.0349 o.o:no —0.0009 Oat Bean 2 3 “ 10 1 0.377 0.530 0.54 0.89 0.0078 0.0067 0.0210 0.0189 -0.0011 —0.0021 3 “ 1 0.618 1.13 0.0245 0.0226 —0.0019 Oat D/2 2 ‘‘ 4 0.139 0.44 0.0031 0.0030 —0.0001 Lupin 2 0.825 1.82 0.0480 0.048:1 0.1282 0.1246 +0.0003 — 0.00:i6 6 2 202 6.73 7 weeks 6 “ 2 1 0.600 0.343 1.95 1 05 0.0349 0.0:i39 0.0200 0.0204 —0.0010 +0.0004 —0.0002 c; 6 2 0 (>8() 1.53 0.0399 0.0397 Dwarf bean 2 months 2^2 3^2 “ as manure 1 1 o’. 792 0 665 2.35 2.80 0.0354 0.0360 0. 0298 1 0.0277 +0.0006 —0.0021 j Cress 3 10 0.008 1 0.026 ^ |- 0.65 0.0013 0.0013 0.0000 j Lnpin 5 months 2 0 . 627 i j- 5.76 1 0.1827 0.1697 —0.0130 { " as manure 8 2.512 1 1 Sum ....ill. 720 30.11 0.6135 0.5868 —0.0247 While it must be admitted that the unavoidable errors of experiment are relatively large in working with such small quantities of material as Boussiiigaidt here employed, we cannot deny that the aggregnte result of these trials is de- cisive against the assimilation of free nitrogen, since there was a loss of nitrogen in the 14 exjieriments, amounting to 4 per cent of the total contained in the seeds ; while a gain was indicated in but 3 trials, and was but 0.13 per cent of the nitrogen concerned in them. — (Boussingault’s Agronomie^ Cliimie' Agricole^ et Physlologie^ Tome I, pp. 1-64.) The Opposite Conclusions of Ville. — In the years 1849, ^50, ’51, and ’52, Georges Ville, at Grenelle, near Paris, experimented upon the question of the assimilability of free nitrogen. His method was similar to that first employed by Boussingault. The plants subjected to his trials were cress, lupins, colza, wheat, rye, maize, sun-flowers, and to- bacco. They were situated in a large octagonal cage made of iron sashes, set with glass-plates. The air was ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 29 constantly renewed, and carbonic acid was introduced in proper quantity. The experiments were conducted on a larger scale than those of Boussingault, and their result was uniformly tlie reverse. Ville indeed thought to have established that vegetation feeds on the free nitrogen of the air. To the conclusions to which Boussingault drew from the trials made in the manner already described, Ville objected that the limited amount of air contained in the glass globes was insufficient for the needs of vegetation ; that plants, in fact, could not attain a normal development under the conditions of Boussingault’s experiments. — (Ville, S^echerches surla Vegetation^ jip. 29-58, and 53-98.) Boussingault’s Later Experiments. — The latter there- upon instituted a new series of trials in 1854, in which he proved that tlie plants he had previously experimented upon attain their full development in a confined atmosphere under the circumstances of his first experiments, provided they are supplied with some assimi’able compound of ni- trogen, He also conducted seven new experiments in an apparatus which allowed the air to be constantly renewed, and in every instance confirmed his former results. — {Agronomie^ Chimie Agricole et Physiologie^ Tome I, pp. 65-114.) The details of these experiments are given in the folio w^ ing Table. The weights are expressed in grams. Kind of Plant. Duration of Experiment. ±11 1 Lupin 2 Bean . SlBean . 4 Bean . 5 Bean . 6, Lupin Tj Cress. 10 weeks 10 ‘‘ 12 “ 14 “ 13 “ 9 as manure 10 weeks, as manure 1 0.337 1 0.720 1 0.748 1 0.755 2 1.510 1 0.310 I 1 0.300 f 12 [ 0.100 I Sum .4.780 1 2.140 0.0196 0.0187 -0.0009 2 . 000 1 0 . 0322 0 . 0325 -f 0 . 0003 2.84710.03:15 0.0341 i-t-0. 0006 2 . 240 ; 0 . 0339 0 . 0329 —0 . 001 0 5.150 0.0676 0.0666 —0.0010 1 . 730 0 . 0355 0 . 0334 '—0 0021 I I 0 . 533 0 . 0046 0 . 0052 -f 0 . 0006 I 1^. I 16 . Wlo . 2269, 0 . 2240 1-0 . 00:35 30 HOW CROPS FEED. Inaccuracy of Ville’s Results# — In comparing the in- vestigations of Boussingault and Ville as detailed in their own words, the critical reader cannot fail to be struck with the greater simplicity of the apparatus used by the former, and Ids more exhaustive study of the possible sources of error incidental to the investigation — factspvhich are greatly in favor of the conclusions of this skillful and experienced philosopher. Furtheimore Cloez, who was employed by a Commission of the French Academy to oversee the repetition of Ville’s experiments, found that a considerable quantity of ammonia was either generated within or introduced into the apparatus of Ville during the period of the trials, which of course vitiated all his results. Any further doubts with regard to this important sub- ject have been effectually disposed of by another most elaborate investigation. Researcli of Lawes, Gilbert^ aud Pugh.— In 1857 and ’58, the late Dr. Pugh, afterward President of the Penn- sylvania Agricultural College, associated himself with Messrs. Lawes and Gilbert, of Rothamstead, England, for the purpose of investigating all those points con- nected with the subject, which the spiiuted discussion of the researches of Boussingault and Ville had suggested as possibly accounting for the diversity of their results. Lawes, Gilbert, and Pugh, conducted 27 experiments on graminaceous and leguminous plants, and on buckwheat. The plants vegetated within large glass bells. They were cut off from the external air by the bells dipping into mercury. They were supplied with renewed p')rtions of purified air mixed with carbonic acid, which, being forced into the bells instead of being drawn through them, ef- fectually jmevented any ordinary air from getting access to the plants. To give ail idea of the mode in which these delicate investigations are condueted, we give here a ligure and concise description of the appara- ^ rget. ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 31 32 HOW CROPS FEED. tus employed by Lawes, Gilbert, and Pugh, in their experiments made in the year 1858. A, fig. 5, represents a stone-ware bottle 18 inches in diameter and 24 inches high. i?, (7, and are glass 3-necked bottles of about 1 quart capacity. F is a large glass sliacle 9 inches in diameter and 40 inches high. a represents the cross-section of a leaden pipe, which, passing over all the vessels A of the series of 16, supplied them with water, from a reser» voir not shown, through the tube with stop-cock a b. c d eis a leaden exit-tube for air. At c it widens, until it enters the vessel A, and another bent tube, q r s, passes tlirough it and reaches to the bottom of A, as indicated by the dotted lines. The latter opens at g, and serves as a safety tube to prevent water ptissing into d e. The bottles B (7 are partly filled with strong sulphuric acid. The tube B \ inch wide and 3 feet long, is tilled with fragments of pumice-stone saturated with sulphuric acid. At// indentations are made to prevent the acid from draining against the corks with which the tube is stopped. The bottle E contains a saturated solution of pure carbonate of soda. g h is a bent and caoutchouc-jointed glass tube connecting the/nterior of the bottle ^with that of the glass shade F. i /<;, better indicated in 2, is the exit-tube for air, connecting the interior of the shade F with an eight-bulbed apparatus, J/, containing sulphuric acid. w w is a vessel of glazed stone-ware, containing mercury in a circular groove, into which the lower edge of the shade F is dipped. These glass tubes, g ?i, u v, and i k, 2, })ass under the edge of the shade and communicate with its interior, the mercury cutting off all access of ex- terior air, except through the tubes. Another tube, n o, passes air-tight through the bottom of the stone-ware vessel, and thus communicates with its interior. The tubes u v and i k are seen best in 2, which is taken at right angles to 1. The plants were sprouted and grew in pots, within the shades. The tube u V was to supply them with water. The water which exhaled from the foliage and gathered on the inside of the shade ran ofi' through n o into the bottle 0. This water was re- turned to the pots through u v. The renewed supply of pure air was kept up through the bottles and tube A, /?, C\ J), E. On opening the cock a 5, A, water enters A, and its pressure forces air through the bottles and tube into the shade F^ whence it finds its exit through the tube i k, and the bulb-apparatus 3f. In its passage through the strong sulphuric acid of B^ (7, and i), the air is completely freed from ammonia, while the carbonate of soda of A' re- moves any traces of nitric acid. The sulphuric acid of the bulb M puri- fies the small amount of air that might sometimes enter the shade through the tube i /^, owing to cooling of the air in F^ when the current ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 33 was not passing. The outer ends of tlie tubes t and u were closed with caoutchouc tubes and glass plugs. Ill these experiuieiits it was considered advisable to furnish to the plants more carbonic acid than the air. contains. This was accomplished by pouring h^^drochloi ic acid from time to time into the bottle T, whicli contained fragment.s of mai ble. The carbonic acid gas thus liberated joined, and was swept on by the current of air in C. Experiments taught how much hydrochloric acid to add and how often. The proportion ol this gas was kept within the limits which previous experimenters had found permissible, ami was not allowed to exceed 4.0 per cent, nor to f dl below 0.2 per cent. In these experiments the seeds were deposited in a soil purified from nitrogen-compounds, by calcination in a current of air and subsequent washing with pure watei*. To this soil was added about 0.5 per cent of the ash of the plant which was to grow in it. The water used for wa- tering the i)lants was specially purified from ammonia and nitric acid. The experiments of Lawes, Gilbert, and Pugh, fully confirmed those of Boussingault. For the numerous de- tails and the full discussion of collater.d points bearing on the study of this question, we must refer to their elaborate memoir, On the Sources of the Nitrogen of Vegetation.” — {Philosophicjl Transactions^ 1831, II, pp. 431-579.) Nitrog-eii Gfjss i?>» saot Umiftedl — It was long supposed hy vegetable physiologists that when the foliage of plants is exposed to the sun, free nitrogen is evolved by them in small quantit}". In fact, when plants are placed in the circumstances which admit of collecting the gases that exhale fi'om them under the action of light, it is found that besides oxygen a quantity of gas appears, which, unless special precautions are observed, consists chiefiy of nitrogen, which was a ])art of the air that fills the intercellular spaces of the plant, or was dissolved in the water, in which, for the purposes of experiment, the plant is immersed. If, as Boussinirault has recently (1863) done, this air be removed from the plant and water, or rather if its quantity be accurately determined and deducted from that obtained in the experiment, the result is that no nitrogen gas remains. A small quantity of gas besides oxygen was indeed usually evolved from the plant when submerged in water. The gas on examination proved to be marsh gas. Cloez was unable to find marsh gas in the air exhaled from either aquatic or land plants submerged in water, and in his most recent researches (1865) Boussingault found none in the gases given ofi* from the foliage of a living tree examined without submergence. The ancient conclusion of Saussure, Daubeuy, Draper, and others, that nitrogen is emitted from the substance of the plant, is thus shown to have been based on an inaccurate method of investigation. 2 * 34 now CROPS FEED. § RELATIONS OF ATMOSPHERIC WATER TO VEGETABLE NUTRITION. Occurrence of Water in the Atmosphere.— If water be exposed to the air in a shallow, oj)en vessel for some time, it is seen to decrease in quantity, and finally disappears en- tirely; it evaporates, vaporizes, or volatilizes. It is con- verted into vapor. It assumes the form of air, and becomes a part of the atmosphere. The rapidity of evaporation is greater the more ele\ a- ted the temperature of the water, and the drier the atmos- phere that is over it. Even snow and ice slowly suffer loss of weight in a dry day though it be frosty. In this manner evaporation is almost constantly going on from the surface of the ocean and all other bodies of water, so that the air always carries a portion of aqueous vapor. On tlie other hand, a body or mixture whose tempera- ture is far lower than that of the atmosphere, condenses vapor from the air and makes it manifest in the form of water. ^Thus a glass of ice-Avater in a warm summer’s day becomes externally bedewed with moisture. In a similar manner, dew deposits in clear and calm summer nights upon the surface of the ground, upon grass, and upon all exposed objects, whose temperature rapidly falls when they cease to be Avarmed by the sun. Again, when the invisible A-apor which fills a hot tea-kettle or steam-boiler issues into cold air, a visible cloud is immediately fornu'd, which consists of minute droplets of water. In like man- ner, fogs and the clouds of the sky are produced by the cooling of air charged with A^apor. When the cooling is sufficiently great anrl sudden, the droplets acquire such size as to fall directly to the ground ; the water assumes the form of rain. ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 35 Water then exists in the atmosphere during the periods of vegetable activity ns gas or vapor,* and as liquid. In the former state it is almost perpetually rising into the air, Avhile in the latter form it frequently falls again to the ground. It is thus in a continual transition, back and forth, from tlie earth to the sky, and from the sky to the earth. We have given the average quantity of water- vapor in the air at one per c ent ; but the amount is very variable, and is almost constantly fluctuating. It may range from less than one-half to two and a half or three per cent, ac- cording to tem})erature and other circumstances. When the air is damp, it is saturated with moisture, so that water is readily deposited upon cool objects. On the other hand, when dry, it is cajaable of taking up additional moisture, and thus facilitates evaporation. Is Atmospheric Water Absorbed by Plants ? — It has long been supposed that grow ing vegetation has the power to absorb vapor of water from the atmosphere by its foliage, as well as to imbibe the liquid water w hich in the form of rain and dew may come in contact with its leaves. Experiments which have been instituted for the jpurpose of ascertaining the exact state of this question have, how- ever, demonstrated that agricultural pi ants ga ther Uttle. or ngjw ater f rom these s ources . The wilting of a plant results from the fact that the leaves suffer water to evaporate from them more rapidly than the roots can take it up. The speedy reviving of a wilted plant on the falling of a sudden i*ain or on the depo- sition of dew depends, not so much on the absorption by the foliage, of the water that gathers on it, as it does * While there is properly no essential difference between a "as and a vapor, the former term is commonly applied more especially to asriform bodies which are not readily brought to the liquid state, and the latter to those which are easily condensed to liquids or solids. 36 now CROPS FEED. on the suppression of evaporation, which is a consequence of the saturation of the surrounding air with water. Unger, and more recently Duchartre, have found, 1st, that plants l ose w eiirli t (from loss of water) in air that is as nearly as possible saturated with vapor, when their roots are not in contact with soil or liquid water. Du- chartre has shown. 2d. that plants do not g^, but some- times lose weigla when their foliage only is exposed to dew or even to rain continued through eighteen hours, al- though they increase in weight strikingly (from absorption of water through their roots,) when the rain is allowed to fall upon the soil in which they are planted. Knop has shown, on the other hand, that leaves, either separate or attached to twigs, gain weight by continued immersion in water, and not only recover what they may have lost by exposure, but absorb more than they orig- inally contained. {Yersuchs-Stationen^ VI, 252.) The water of dews and rains, it must be remembered, however, does not often thoroughly wet the absorbent sur- face of the leaves of most plants; its contact being pre- vented, to a greet degree, by the hairs or wax of the epidermis. Finally, Sachs has found that even the rpots of plants appear i ncapable of taking up watery vapor. To convey an idea of the method employed in such investigations, we may quote Sachs’ account of one of his experiments. ( V, II, 7.) A young camellia, having several fresh leaves, was taken from the loose soil of the pot in which it hax!ieil by the leaves , and, un- der th confluen ce of sunlight, is decomposed within the plant , its carbon being retained, and in an unknown man- ner becoming a part of the {)!ant itself, while the oxygen \ is exhaled into the atmo^^phere in the free state. Relative volumes of absorbed Carbonic Acid and ex- haled Oxygen. — From the numerous experiments of De Saussure, and from similar ones made recently with greatly improved means of research by Unger and Knop, it is es- tablished that in sunlight the y olume of oiQ;^en exhaled nearly equa l to the volum e of carbooiojicid ab sorbed . Since free oxygen occupies the same bulk as the carbonic acid produced by uniting it with carbon, it is evident that carbon mainly and not oxygen to much extent, is retained by the plant from this source. Respiration and Fixation of Carbon by Plants. — In 1851 Gari-eau, and in 1858 Corenwinder, reviewed ex[)eri- mentally the w'hole subject of the relations of plants to carbonic acid. Their researches fully confirm the conclu- sions derived from older investigations, and furnish some additional facts. We have already seen (p. 22) that the plant requires free oxygen, and that this gas is absorbed by those parts of vegetation which are in the act of growth. As a con- sequence of this entrance of oxygen into the plant, a cor- responding amount of carbonic acid is produced within and exhales from it. There go on accordingly, in the ex- f pan ding plant, two opposite processes, viz., the absorption of oxygen and exhalation of ca^’bonic acid, and the ab- sorption of carbonic acid and evolution of oxygen. The first process is chemically analogous with the breathing of animals, and may hence be designated as respiration. We may speak of the other process as the fixation of carbon. 44 now CROPS FEET). These opposite changes obviously cannot take j)lace at the same points, but must proceed in dilFerent organs or cells, or in different |)arts of the same cells. They further- more tend to counterbalance each otlier in their effects on the atmospliere surrounding the plant. The processes to which the absorption of oxygen and evolution of carbonic acid are necessary, a|)pear to go on at all hours of tlie day and night, and to be independent of the solar light. The ])roduction of carbonic acid is then continually occurring ; but, under tlie influence of the sun’s direct rays, the oppo- site absorption of carbonic acid and evolution of oxygen proceed so much more rapidly, that Avhen we exp'criment with the entire plant the first result is completely masked. In our experiments we can, in fact, only measure the pre^ ponderance of the latter process over the former. In sun- light it may easily happen that the carbonic acid which exhales from one cell is instantly absorbed by anothei*, and likewise the oxygen, which escapes from the latter, may be in part imbibed by the former. In total darknes ; it is be.ieved that carbonic acid is not absorbed and decomposed by the plant, but only produced in, and exhaled from it. In no case has any evolution of oxygen been observed in the absence of light. When, instead of being exposed to the direct rays of the sun, only the diffused light of cloudy days or the soft- ened light of a dense forest acts upon th(‘m, plants may, ac- cording to circumstances, exhale either oxygen or carbonic acid in preponderating quantity. In his earlier investiga- tions, Corenwinder observed an exhalation of carbonic acid in diffused light in the cases of tobac;co, sunflower, lupine, cabbage, and nettle. On the contrary, he found that let- tuce, the pea, violet, fuchsia, periwinkle, and others, evolv- ed oxygen under similar conditions. In one instance a bean exhaled neither gas. These differences are not pe- culiar to the plants just specified, but depend upon the in- tensity of the light and the stage of development in which ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 45 the plant exists. Corenwinder noticed that the evolution of carbonic acid in diffused light was best exhibited by very young plants, and mostly ceased as they grew older. Corenwinder has confirmed and extended these observa- tions in more recent investigations. (Ann, d, SA, JVat,, 1864, I, 297.) He finds that buds and young leaves exhale carbonic acid (and absorb oxygen) by day, even in bright sunshine. He also finds that all leaves exhale carbonic acid not alone at night, but likewise by day, when placed in the diffused light of a room, illuminated from only one side. A plant, which in full light yields no carbonic acid to a slow stream of air passing its foliage, immediately gives off the gas Avhen carried into such an apartment, vice versa. Amount of Carbonic Acid absorbed. — The quantity of carbonic acid absorbed by day in direct light is vastly o^reater than that exhaled diirinsr the nig^ht. According: C' O O o CO Coren winder’s experiments, 15 to 20 minutes of direct sunlight enable colza, the pea, the raspberry, the bean, and sunflower, to absorb as much carbonic acid as they exhale during a whole night. As to the amount of carbonic acid whose carbon is re- tained, Corenwinder found that a single colza plant took up in one day of strong sunshine more than two quarts of the gas. Boussingault (Comptes JRend.^ Oct. 23d, 1865) found as the average of a number of experiments, that a square me- ter of oleander leaves decomposed in sunlight 1.108 liters of carbonic acid per hour. In the dark, the same surface of leaf exhaled but 0.07 liter of this g is. Composition of the Air within the Plant. — Full com tirmation of the statements above made is furnished by tracing tlie changes wliieh take place wdthin the vegeta- ble tissues. Lawes, Gilbert, and Pugh, (Phil. Trans..^ 1861, H, p. 486,) have examined the composition of the 46 HOW CROPS FEED. air contained in plants, as well when the latter are remov- ed from, as when they are subjected to, the action of light. To collect the gas fro:n the plants, the latter were placed in a glass vessel filled with water, from which all air had been expelled by long boiling anaraf ion. — It may be obtained in a state of purity by heat- ing a mixture of cliloride of ammonium (sal ammoniMe) and quieklime. Equal quantities of the two substances just named (50 grams of each) arc separately pulverized, introduced into a flask, and well mixed by shaking. A straight tube 8 inches long is now secui-ed in the neck of the flask, by means of a perforated cork, and heat applied. The ammonia gas which soon escapes in abundance is collected in dry bottles, which are inverted over the tube. The gas, rapidly entering the bottle, in a few moments displaces the twice heavier atmospheric air. As soon as a 3 _ ■ ■ ■ ’ /A- 50 IIOAV CROPS FEED. feather wet with vinegar or dilute clilorliydric acid becomes surrounded with a dense smoke when approached to the mouth of the bottle, tin; latter may be removed, corked, and another put in its place. Three or four pint bottles of gas thus collected will seiwe to illustrate its proper- ties, as shortly to be noticed. Solubility in Water* — This character of ammonia is ex- hibited by removing, under cold water, the stopper of a bottle filled with the gas. The water rushes with great violence into the bottle as into a vacuum, and entirely fills it, provided all atmospheric air had been displaced. The aqua ammonia^ or spirits of hartshorn of the drug- gist, is a strong solution of ammonia, prepared by passing a stream of ammonia gas into cold water. At the freez- ing point, water absorbs 1,150 times its bulk of ammonia. When such a solution is warmed, the gas escapes abund- antly, sc that, at ordinary summer temperatures, only one- half the ammonia is retained. If the solution be heated to lx)iling, all the ammonia is expelled before the water has nearly boiled away. The gas escapes even from very di- lute solutions when they are exposed to the air, as is at once recognized by the senile of smell. Composition. — When ammonia gas is heated to redness by being made to pass through an ignited tube, it is de- composed, loses its characteristic odor and other proper- ties, and is resolved into a mixture of nitrogen and hydro- gen gases. These elements exist in ammonia in the pro- portion of one part by bulk of nitrogen, to three parts of hydrogen, or by weight fourteen parts or one atom of nitrogen and three parts, or three atoms of hydrogen. The subjoined scheme exhibits the composition of ammo* nia, ns expressed in symbols, atoms, and percentages. Symbol. At. wH. Ter cent. N = 14 82.39 Ha = 3 17.61 NHa = 17 100.00 Formation of Ammonia. — 1. When hydrogen and ni- trogen gases are mingled together in the proportions to ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 51 foriD ammonia, they do not combine either spontaneously or by aid of any means yet devised, but remain for an indef- inite period as a mere mixture. The oft repeated assertion that nascent hydrogen, i. e., hydrogen at the moment of liberation from some combination, may unite with free nitrogen to form ammonia, has been completely refuted by the experiments of Will, (Ann, Ch, n, Ph.^ XLV, 110.) The ammonia observed by older experimenters existed, ready formed, in the materials they operated with. 2. It appears from recent researches (of Boettger, Schonbein, and Zabelin) that ammonia is formed in minute quantity from atmospheric nitrogen in many cases of com- bustion, and is also generated when vapor of water and the air act upon each other in contact with certain organic matters, at a temperature of 120° to 163° F. To this sub- ject we shall again recur, p. 77. 3. Ammonia may result from the reduction of nitrous and nitric acids, and from the action of alkalies and lime upon tlie albuminoids, gelatine, and other similar organic matters. To these inodes of its formation we shall recur on subsequent pages. 4. Ammonia is most readily and abundantly formed from organic nitrogenous bodies ; e. g., the albuminoids and similar substances, by decay or by dry distillation. It is supposed to have been called ammonia because one of its most common compounds (sal ammoniac) was first prepared by burning camels’ dung near tlie tem[)le of Jupiter Ammon in Libya, Asia Minor. The name hartshorn, or spirits of liartshorn, by which it is more commonly known, was ado.pted from the circumstance of its preparation by dis- tilling the horns of the stag or hart. The ammonia and ammoniacal salts of commerce (car- bonate of ammonia, sal ammoniac, and sulphate of ammo- nia) are exclusively obtained from these sources. When urine is allowed to become stale, it shortly smells OF iu: 52 now CROPS FEED. of ammonia, which copiously escapes in the form of car- bonate, and may be separated by distillation. When bones are heated in close vessels, as in the manu- facture of bone-black or bone-char for sugar refining, the liquid product of the distillation is strongly charged with carbonate of ammonia. ( Commercial ammonia is mostly derived, at present, from Hhe distillation of bituminous coal, and is a bye-product of the manufacture of illuminating gas. The gases and va- pors that issue from the gas-i-etort in which the coal is heat- ed to redness, are washed by passing through water. This wash water is always found to contain a small quantity of Dammonhi, which may be cheaply utilized The exhalations of volcanoes and fumerolcs likewise contain ammonia, which is probably formed in a similar manner. In the processes of combustion and decay the elements of the orgnnic matters are thrown into new groupings, which are mostly simpler in composition than the original substances. A portion of nitrogen and a corresponding portion of hydrogen then associate tliemselves to form am- monin. Ammonia is a Strong Alkaline Base.— Those bases which h‘ive in general the strongest affinity for acids, are potash, soda, and ammonia. These bodies are very similar in many of their most obvious characters, and are collec- tively denominated the alkalies. They are alike freely soluble in water, have a bitter, burning taste, alike corrode the skin and blister the tongue ; and, united with acids, form the most permanent saline compounds, or salts. Carbonate of Ammonia. — If a bottle be filled with car- bonic acid, (by holding it inverted over a candle until the latter becomes extinguished Avhen passed a little way into the bottle,) and its mouth be applied to that of a vessel containing ammonia gas, the two invisible airs at once ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 53 combine to a solid salt, the carbonate of ammonia, which appears as a white cloud where its ingredients come in contact. Carbonate of ammonia occurs in commerce under the name ‘‘salts of hartshorn,” and with the addition of some perfume forms the contents of tlie so-called smelling-bot- tles. It rapidly vaporizes, exhaling the odor of ammonia very strongly, and is hence sometimes termed sal volatile. Like camphor, this salt passes from the solid state into that of invisible vapor, at ordinary temperatures, without assuming intermediately the liquid form. In the atmosphere the quantity of carbonic acid greatly preponderates over that of the ammonia; lienee it is im^ possible that the latter should exist in the free state, and we must asmme that it occurs there chiefly in combination with carbonic acid. The carbonate of am nonia, whetlier solid or gaseous, is readily soluble in water, and like free ammonia it evaporates from its solution with the first ])ortions of aqueous vapor, leaving the residual water rel- atively free from it. In the guano-beds of Peru and Bolivia, carbonate of ammonia is sometimes found in the form of large trans- jmrent crystals, which, like the artificially-prepared salt, rapidly exhale away in vapor, if exposed to the air. This salt, commonly called bicarbonate of ammonia, con- tains in addition to carbonic acid and ammonia, a portion of water, which is indispensable to position is as follows : ks existence. Its com- Symbol. At. w't. Per cent. NHg 17 21.5 H2O 18 22.8 CO 2 44 55.7 NH3. H2O. CO 2 . 79 100.0 Xests for AinmoiBisi.— If salts of ammonia are rubbed to- ^^ether with daked lime, best with the addition of a few di-ops of water, the ammonia is liberated in tlie gaseous state, and betrays itself (1) by its characteristic odor ; (2) by its reaction on moistened test-i)apers ; and 54 IIOAV CROPS FEED. (3) by givinj^ rise to the formation of white fames^ when any object (e. g.^ a glass rod) moistened with hydrochloric acid, is brought in contact with it. These fumes arise I'rom the foi-mation of solid amrnoniacal salts pro- duced b}^ the contact ot the gases. h. Misder's Test. — For the detection of exceedingly minute tiaces of ammonia, a reaction first pointed out by Nessler may be employed. Di- gest at a gentle heat 2 grammes of iodide of potassium, and 3 grammes of iodide of mercury, in 5 cub. cent, of water; add 20 cub. cent, of wa- ter, let the mixture stand for some time, then filter; add to the filtrate 30 cub. cent, of pure concentrated solution of potassa (1 : 4); and, should a precipitate form, filter again. If to this solution is added, in small quantity, a liquid containing ammonia or an ammonia-salt, ^reddish brown precipitate., or with exceedingly small quantities’ of ammoniu, a yellow coloration is produced from the formation of dimercurammonic iodide, NHg2 I.OH 2 . c. Bohlig's Test. — According to Bolilig, chloi ide of mercury (corrosive sublimate) is the most sensitive reagent for ammonia, when in the free state or as carbonate. It gives a white precipitate., or in very dilute so- lutions (even when containing but 200,000 ammonia) a white turbidity., due to the separation of inercurammonie chloride, NH 2 Hg.Cl. In solu- tions of the salts of ammonia with other acids than c.irbonic, a clear solution of mixed carbonate of potassa and chloride of mercury must be employed, which is prepared by adding 10 drops of a solution of the l^iirest carbonate of potassa, (1 of salt to 50 of water,) and 5 drops of a solution of chloride of mercury to 80 c. c. of water exempt from am- monia (such is the water of many springs, but oi’dinary distilled water rarely). This reagent may be kept in closed vessels for a time without change. If much moi e concentrated, oxide of mercuiy separates from it. By its use the ammonia salt is first eonvei’ted into carbonate by double decomposition with the carbonate of potassa, and the further reaction proceeds as before mentioned. Occurrence of Ammonia in the Atmosphere. — The ex- istence of ammonia in the atmosphere was first noticed by De Sauss ire, and has been proved repeatedly by direct experiment. That the quantity is exceedingly minute has been equally well established. Owing partly to the variable extent to which ammonia occurs in the atmosphere, but chiefly to the difficulty of collecting and estimating such small amounts, the state- ments of those who have experimente 1 upon this subject are devoid of agreement. We present here a tabulated view of the most trust- worthy results hitherto published : ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 55 1,000,000,000 parts of atmospheric air contain of ammonia, according to Graeirer, at Muhlbausen, Germany, average. 333 parts. Fresenius, , “ Wiesbaden, a u 133 “ Pierre, “ Caen, France, 1851-52, “ 3500 u H (( u 1852-53, 500 Bineau, “ Lyons, “ 1852-53, 250 (( n “ Caluire, ‘‘ “ winter, 40 u (( a u u “ summer, 80 (( Ville, “ Paris, “ 1819-50, average. 21 ll a Grenelle, 1851, 21 n Graliam lias shown by experiment (Ville, Recherches sur la Vegetation^ Paris, 1853, p. 5,) that a quantity of ammonia like that found by Fresenius is sufficient to be readily detected by its effect on a red litmus paper, which is not altered in the air. This demonstrates that the at- mosphere where Graham ex^ierimented (London) contained less than '^^|io,ooo,ooo^^^ ammonia in the state of bicar- bonate. The experiments of Fresenius and of Grager were made with comparatively small volumes of air, and those of the latter, as well as those of Pierre, and some of Bineau’s, were mode in the vicinity of dwellings, or even in cities, where the results might easily be influenced by local emanations. Bineau’s results were obtained by a method scarcely admitting of much accuracy. The investigations of Ville {Recherches^ Paris, 1853,) are, perhaps, the most trustworthy, having been made on a large scale, and apparently with every precaution. We may accordingly assume that the average quantity of am- monia in the air is one part in fifty millions, although the amount is subject to considerable fluctuation. From the circumstance that ammonia and its carbonate are so readily soluble in water, we should expect that in rainy weather the atmosphere would be washed of its am- monia; while after ])rolonged dry weather it would con- tain more than usua’, since ammonia escapes from its solutions with the first portions of aqueous vapor. The Absorption of Ammonia by Vegetation. — The gen- eral fact that ammonia in its compounds is appropriated 56 HOW CROPS FEED by plants as food is most abundantly establislmd. The salts of ammonia applied as manures in actual farm prac- tice have produced the most striking effects in thousands of instances. By watering potted p];mts with very dilute solutions of ammonia, their luxuriance is made to surpass by far that of similar plants, which grow in precisely the same condi- tions, save that they are supplied with simple water. Viile has stated, 1851-2, that vegetation in conserv..- tories may be remarkably promoted by impregn:iting the air with gaseous carbonate of ammonia. For this purpose lumps of the solid salt are so disposed on the heating ap- paratus of the green-house as to graduady vaporize, or vessels containing a mixture of quicklime and sal ammo- niac may be employed. Care must be taken that the air does not contain at any time more than four ten-thousandths of its weight of the salt ; otherwise the foliage of tender plants is injured. Like results were obtained by Petzholdt and Chlebodarow in 1852-3. Absorption of Ammonia by Foli- age. — Although such facts indicate that ammonia is directly absorbed by foliage, they fail to prove that the soil is not the medium through which the absorption really takes place. We remember that according to Unger and Duchartre water enters the higher plants almost exclusively by the roots, after it h.as been absorbed by the soil. To Peters and Sachs [Chem, Ackersmemn^ 6, 158) we owe an experiment which appears to de- monstrate that ammonia, like carbonic acid, is imbibed by the leaves of plants. The figure represents the a|)- paratus employed. It consisted of a glass bell, resting below, Fi-. 6. atmospheric air as the food of plants. 57 air-tight, upon a glas^s plate, .and having two glass tubes cemented into its neck above, as in fig. 6. Through an aperture in the centre of the glass ])late the stein of the plant experimented on was introduced, so that its fo- liage should occupy the bel^, while the roots were situated in a pot of eai’th beneath. Two young bean-plants, grow- ing in river sand, were arranged, each in a separate appa- ratus, as in the figure, on June 19th, 1859, their steins be- ing cemented tightly into the opening below, and through the tubes the foliage of each plant received daily the same quantities of moi;^jt atmospheric air mixed with 4-5 per cent of carbonic acid. One plant was supplied in addition with a quantity of carbonate of ammonia, which w^as in- troduced by causing the air that was forced into the bell to stri^am through a dilute solution of this salt. Both plants grew well, until the experiment was terminated, on the 11th of August, when it was found that the plant w^hose foliage was not supplied with carbonate of ammo- nia weighed, dry, 4.14 gm., wliile the other, which supplied with the vapor of this salt, w^eighed, dry, 6.74 gins. The first plant had 20 full-sized leaves and 2 side shoots; the second had 40 leaves and 7 shoots, besides a much larger mass of roots. The first contained 0.106 gm. of niti'ogen ; the second, double that amount, 0.208 gm. Other trials on various plants failed - from the diffi- culty of making them grow in the needful circumstances. The absorption of ammonia by foliage does not appear, like that of carbonic acid, to depend upon the action of sunlight ; but, as Mulder has remarked,* may go on at all times, especially since the juices of plants are very fre- quently more or less charged with acids which directly unite chemically with ammonia. When absorbed, ammonia is chiefly applied by agricul* ♦ Chemie der Ackerkrume, Vol. 2, p. 211. 3* 58 now CROPS FEED. / tural plants to the production of the albuminoid^ .* We C measure the nutritive effect of ammonia salts applied as fertilizers by the amount of nitrogen which vegetation as* similates from them. Effects of Ammonia on Vci^etation. — The remarkable effect of carbonate of ammonia upon vegetation is well described by Ville. We know that most plants at a cer- tain period of growth under ordinary circumstances cease to produce new branches and foliage, or to expand those already formed, and begin a new phase of development in providing for the perpetuation of the species by producing flowers and friutf^ If, however, such plants are exjiosed [ to as much carbonate of ammonia gas as they are capable of enduring, at the time when flowers are beginning to form, these are often totally checki'd, and the activity of growth is transferred to stems and leaves, which assume a new vigor and multiply with extraordinary luxuriance. If flowers are formed, they are sterile, and yield no seed. r Another noticeable effect of ammonia — one, however, ' which it shares with other substances — is its power of deep- ening the color of the foliage of plants. This is an indi- , cation of increased vegetative activity and health, as a \ pale or yellow tint btdongs to a sickly or ill-fed growth. A third result is that not only the mass of v-egetation is increased, but the relative proportion of nitrogen in it is heightened. This result was obtained in the exjieriment of Peters and Sachs just described. To adduce a single other instance, Ville found that grains of wheat, grown in pure air, contained 2.09 per cent of nitrogen, while those which were produced under the influence of ammonia contained 3.40 per cent. * In tobacco, to th3 production of nicotine ; in coffee, of caffeine ; and in many other plants to analogous substances. Plants appear oftentimes to contain small quantities ammonia salts and nitrates, as well as of asparagin, (C4 H3 Ns 03,)a substance first found in asparagus, and which is formed in many plants when they vegetate in exclusion of light. ATMOSPHERIC AIR AS THE FOOD OP PLANTS. 59 Do Healthy Plants Exhale Ammonia ] — The idea having been advanced that in the act of vegetation a loss of ni- trogen may occur, possibly in the form of ammonia, Knop made an exj^eriment with a water-plant, the Typha lati- folla^ a species of Cat-tail, to determine this point. Tlie plant, growing undisturbed in a pond, was enclosed in a glass tube one and a half inches in diameter, and six feet long. The tube was tied to a stake driven for the purpose ; its lower end reached a short distance below the surface of the water, while the uppcT end was covered air-tight with a cap of India rubber. This cap was penetrated by a narrow glass tube, which communicated with a vessel filled with splinters of glass, moistened with pure hydro? chloric acid. As the large tube was placed over the planl a narrow U-shaped tube was immersed in the water t(r half its length, so that one of its arms came within, and the other without, the former. To the outer extremity of the U-tube was attached an apparatus, for the perfect absorption of ammonia. By aspirating at the upper end of the long tube, a current of ammonia-free air was thus made to enter the bottom of the apparatus, stream upward along the plant, and pass through the tube of glass-splint- ers wet with hydrochloric acid. Were any ammonia evolved within the long tube, it would be collected by the acid last named. To guard against any ammonia that possibly might arise from decaying matters in the water, a thin stratum of oil was made to float on the water with- in the tube. Through this arrangement a slow stream of air was passed for fifty hours. At the expiration of that time the hydrochloric acid was examined for ammonia; but none was discovered. Our tests for ammonia are so delicate, that we may well assume that this gas is not ex- haled by the Typha latlfoUa, The statements to be found in early authors (Sprengel, Schubler, Johnston), to the effect that ammonia is exhaled by some plants, deserve further examination. 60 HOW CROPS FEED. The Chenopodlum vulvar la exhales from its foliage a body chemically related to ammonia, and that has been mistaken for it. This substance*, known to the chemist as trimethylamine, is also contained in the flowers of Cra- taegus oxycantha^ and is the cause of the detestable odor of tliese plants, which is that of putrid salt fish.* (Wicke, Liebig'^ s Ann,^ 124, p. 338.) Certain fungi (toad-stools) emit trimethylamine, or some analogous compound. (Lehmann, Sachs' Experiment d Physlologie dec Pjianzen^ p. 273, note.) It is not impossible that ammonia, also, may be exhaled from these plants, but we have as yet no proof that such is the case. Ammonia of the Atmospheric Waters. — The ammonia ])roper to the atmosphere has little (dfect ujion plants through their foliage when they are sheltered from dew and rain. Such, at least, is the result of certain experi- mentb. Boussingault {Agronomle, Chimie Agricole^ et Physv ologie^ T. I, p. 141) made ten distinct trials on lupins, beans, oats, wheat, and cress. The seeds were sown in a soil, and the plants were w.itered with water both exempt from nitrogen. Tlie plants were shielded by glazed cases from rain and dew, but had full access of air. The result of the ten experiments taken together was as follows: W’eiglit of seeds 4.965 grin’s. “ dry harvest 18.730 ^ ‘‘ Nitrogen in harvest and soil. . .2499 “ “ “seeds..; 2307 “ Gain of nitrogen 0192 grin’s = 7.6 per cent of the total quantity. When rains fall, or dews deposit upon the surface of the * Trimethylamine CsHgN = N (Cnj )3 may be viewed as ammonia Nil 3 , in wliicli the three atoms of liydrogen are replaced by three atoms of methyl 011 3 . It is a gas like ammonia, and has its pungency, but accompanied with the odor of stale fish. It is prepared from herring pickle, and used in medicine un- der the name propylamine. ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 61 soil, or upon the foliage of a cultivated field, they bring down to the reach of vegetation in a given time a quantity of ammonia, far greater than what is ditfiised throughout the limited volume of air which contributes to the nour- ishment of plants. The solubility of carbonate of ammo- nia in water has already been mentioned. In a rain-fall we have the atmosphere actually washed to a great de- gree of its ammonia, so that nearly the entire quantity of this substance which exists between the clouds and the earth, or in that mass of atmosphere^ feough w hich the rain passes, is gathered by accumulated within a small space. Proportion of Ammonia in Rain-water, etc.— The pro- portion of ammonia* which the atmospheric waters thus i /* bring down upon the surface of the soil, or upon the foliage of plant has been the subject of inves- / ^ 3 iirations by Boussingault, Bineau, Way, Knop, Bobiere, and Bretschneider. Tlie general result of their accordant I investigations is as follows: In rain-water the quantity of ammonia in the entire fall is very variable, ranging in the country from 1 to 33 ]>ai'ts in 10 million. In cities the \ amount is larger, tenfold the above quantities having been observed. Tlie first portions of rain that fill usually contain much more ammonia than the latter portions, for tlie reason that a certain amount of Avater suffices to wash the air, and what rain subsequently falls only dilutes the solution at first formed. In a long-continued rain, the water that finally falls is almost devoid of ammonia. In rains of short duration, as well as in dews and fogs, which occasion- ally are so heavy as to admit of collecting to a sufficient extent for analysis, the proportion of ammonia is greatest, and is the greater the longer the time that has elapsed since a previous precipitation of water. * In all quantitative statcraents regarding ammonia, NH3 is to be understood, andnotNH4 0. 62 HOW CROPS FEED. Boussingault found in the first tenth of a slow-falling rain (24th Sept., 1853) 66 parts of ammonia, in the last three-tenths but 13 parts, to 10 million of water. In dew he found 40 to 62; in fog, 25 to 72; and in one extraordi- nary instance 497 parts in ten million. Boussingault found that the average proportion of am- monia in the atmospheric waters (dew and fogs included) which he was able to collect at Liebfranenbcrg (near Stras- burg, France) from the 26th of May to the 8th of Nov. 1853, was 6 parts in 10 million {Agronomic^ etc., T. II, 238). Knop found in the rains, snow, and hail, that fell at Moeckern, near Leipzig, from April 18th to Jan. 15th, 1860, an average of 14 parts in 10 million. {Versicchs- Statlonen^ Vol. 3, p. 120.) Pincus and Rollig obtained from the atmospheric wa- ters collected at Insterburg, North Prussia, during the 12 months ending with March, 1865, in 26 analyses, an average of 7 parts of ammonia in 10 million of water. The average for the next fodowing 12 months was 9 parts in 10 million. Bretschneider found in the atmospheric waters collected by him at Ida-Marienhiltte, in Silesia, from April, 1865, to April, 1866, as the average of 9 estimations, 30 ])arts of ammonia in 10 million of water. In the next year the quantity was 23 parts in 10 million. In 10 million parts of rain-water, etc., collected at the following places in Prussia, were contained of ammonia — at Regenwaldo, in 1865, 24; in 1867,28; at Dahme, in 1865,17; at Kuschen, in 1865,5^; and in 1866, 7^ [)arts. {Preus. Ann. d. Laiidwirthschaft^ 1867.) The monthly averages fluctuated without regularity, but mostly witliin narrow limits. Occasionally they fell to 2 or 3 parts, once to nothing, and rose to 35 or 40, and once to 144 parts in 10 million. Quantity of Ammonia per Acre Brought Down by Rain, etc, — In 1855 and ’56, Messrs. Lawes & Gilbert, at Roth- amstead, England, collected on a large rain-gauge having ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 63 a surface of -, -o'oo of an acre, the entire rain-fall (dews, etc., included) for those years. Prof. Way, at that time chem- .i^t to the Royal Ag. Soc*. of England, analyzed the waters, f and found that tlie total amount of ammonia contained in V them was equal to 7 lbs. in 1855, and lbs. in 1856, for J an acre of surface. These amounts were yielded by 663,000 and 616,000 gallons of rain-water respectively. In the waters gathered at Insterburg during the twelve- month ending ])ilarch, 1865, Pincus and Rollig obtained 6.38 lbs. of ammonia per acre. Bretschneider found in the waters collected at Ida-Ma- rienh’itte from April, 1865, to April, 1866, 12 lbs. of am- monia per acre of surface. The significance of these quantities may be most appro- priately discussed after we have noticed the nitric acid of the atmosphere, a substance whose functions towards vege- tation are closely related to those of ammonia. § OZONE. When lightning strikes the earth or an object near its surface, a person in the vicinity at once perceives a peculiar, c 3-called “ sulphureous ” odor, which must belong to something developed in the atmosphere by electricity. The same smell may be noticed in a room in whicli an electrical machine has been for some time in vigorous action. The substance which is thus produced is termed ozone ^ from a Greek word signifying to smell. It is a colorless gas, possessing most remarkable properties, and is of the highest importance in agricultural science, although our knowledge of it is still exceedingly imperfect. Ozone is not known in a pure state free from other bodies ; but hitherto has ordy been obtained mixed with 64 now CROPS FEED. ^several times its weight of air or oxygen.* It is entirely insoluble in water. It has, when breathed, an irritating action on the lutigs, and excites coughing like chlorine gas. Small animals are shortly destroyed in an atmosphere charged with it. It is itself instantly destroyed by a heat considerably below that of redness. The special character of ozone that is of interest in connection with questions of agriculture is its oxjjUziug ^ower. Silver is a metal which totally refuses to combine with oxygen under ordlnaiy circumstances, as shown by its maintaining its brilliancy without symptom of rust or tarnish when exposed to pure air at common or at greatly elevated temperatures. When a slip of moistened silver is placed in a vessel the air of which is charged with ozone, the metal after no long time becomes coated with a black crust, and at the same time the ozone disa;)pears. By the application of a gentle heat to the blackened silver, ordinary oxygen gas^ having the properties already mentioned as belonging to this element, escapes, and the slip recovers its original silvery color. The black crust is in fact an oxide of silver (AgO,) which readily suffers de- composition by heat. In a similar manner iron, copper, lead, and other metals, are rapidly oxidized. A variety of vei^etable pigments, such as indigo, litmus, etc., are speedily bleached by ozone.' This action, also, is simply one of oxidation. Gorup-Besanez {Ann. Ch. u. Ph.. 110, 86; also, rhyfiiologUche Chemie') has examined the deportment of a number of organic bodies towards ozone. He finds that egg-albumin and casein of milk are rapidly altered by it, while flesh fibrin is unatfected. Starch, the sugars, the organic acids, and flits, are, when pure, unaf- fected by ozone. In })resence of (dissolved in) alkalies^ however, they are oxidized with more or less rapidity. It is remarkable that oxidation by ozone takes place only in the presence of water. Dry substances are unaflTected by it. The peculiar deportment towards ozone of certain volatile oils whll be presently noticed. * Babo and Claus {Ann. Ch. u. Ph., 2d Sup., p. 304) prepared a mixture of oxy gen and ozone containing nearly G per cent of the latter. ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 65 Tests for Ozone. — Certain phenomena of oxidation that are attended with changes of color serve for the recognition of ozone. We have already seen (H. C. G.,p. 64) that starch, when brought in contact with iodine, at once assumes a deep blue or purple color. When the compound of iodine with potassium, known as iodide of potas- sium, is acted on by ozone, its potassium is at once oxidized (to pot- ash,) and the iodine is set free. If now ijaper be impregnated with a mixture of starch-paste and solution of iodide of potasr^ium,* we have a test of the presence of ozone, at once most characteristic and delicate. Such ])apcr, moistened and placed in ozonousf air, is spetdi^j turned blue by the action of the liberated iodine upon the starch. By the use of this test the presence and abundance of ozou^ in tii^ atmosphere has been measured. Ozone is Active Oxygen. — That ozone is nothing more or less than oxygen in a peculiar, active condition, is shown by the following experiment. When perfectly pure nnd dry oxygen is enclosed in a glass tube containing moist metallic silver in a state of fine division, it is possible by long-continued transmission of electrical discharges to cause the gaseous ox^^gen entirely to disappear. On heat- ing tlie silver, which has become blackened (oxidized) by the process, the original quantity of oxygen is recovered in its ordinary state. The oxygen is thus converted under the influence of electricity into ozone, which unites with the silver and disappears in the solid combination. The independent experiments of Andrews, Babo, and Soret, demonstrate that ozone has a greater density than oxygen, since the latter diminishes in volume when elec- trized. Ozone is therefore condensed oxygen^ i. e., its molecule contains more atoms than the molecule of ordi- nary oxygen gas. * Mix 10 parts of starch with 200 parts of cold water and 1 part of receiitiy fused iodide of potassium, by rubbing them together in a mortar; then heat to boiling, and strain through linen. Smear pure filter paper with this paste, and dry The paper should be perfectly white, and must be preserved in a well-stoppered bottle. t I. e., charged with ozone. X Recent observations by Babo and Claus, and by Soret, show that the density •f ozone is me and a half times greater than that of oxygen. 66 HOW CHOPS FEED. Allotropism* — This occurrence of an element in two or even more forms is not without other illustrations, and is termed Allotropism. Phosphorus occurs in two conditions, viz., red phosphorus, which crys- tallizes in rhombohedrons, and like ordintiry oxygen is comparatively inactive in its affinities; and colorless phosphorus, whicli crystallizes in octahedrons, and, like ozone, has vigorous tendencies to unite with other bodies. Carbon is also found in three allotropic forms, viz., diamond, plumbago, and charcoal, which differ exceedingly in their chemical and ])hy8ical characters. Ozone Formed byCItcmkal Action. — Not only is ozone produced by electrical disturbance, but it has likewise been shown to originate from chemical action; and, in fact, from the very kind of action which it itself so vig- orously manifests, viz., oxidation. When a clean stick of colorless phosphorus is placed at the bottom of a large glass vessel, and is half covered with tepid water, there immediately appear white vapors, which shortly fill the apparatus. In a little time the pe- culiar odor of ozone is evident, and the air of the vessel gives, with iodide-of-potassium-starch paper, the blue color which indicates ozone. In this experiment ordinary oxy- gen, in the act of uniting with phosphorus, is partially converted into its active raodifieation ; and although the larger share of the ozone formed is probably destroyed by uniting with phosphorus, a ])ortion escapes combination and is recognizable in the surrounding air. The ozone thus developed is mingled with other bodies, (phosphorous acid, etc.,) which cause the white cloud. The quantity of ozone that appears in this experiment, though very small, — under the most favorable circum- stances hut ' of the weight of the air, — ^is still sufficient to exhibit all the reactions that have been described. Schoiibein has shown that various organic bodies which are susceptible of oxidation, viz., citric and tartaric acids, when dissolved in water and agitated with air in the sun- light for half an hour, acquire tlie reactions of ozone. Ether and alcohol, kept in partially filled bottles, also be- come capable of producing oxidizing efiects. Many ot th.e ATMOSPHERIC AIR AS THE FOOD O^F PLANTS. 67 vegetable oils, as oil of turpentine, oil of lemon, oil of cinnamon, linseed oil, etc., possess the property of ozoniz- ing oxygen, or at least acquire oxidizing properties when exposed to the air. Hence the bleaching and corrosion of tile cork of a partially filled turpentine bottle. ^ It is a highly probable hypothesis that ozone may be formed in many or even all cases of slow oxidation, and that although the chief part of the ozone thus developed must unite at once with the oxidable substance, a portion of it may diffuse into the atmosphere and escape immediate combination. Ozone is likewise produced in a variety of chemical re- actions, whereby oxygen is liberated from combination at ordinary temperatures. When water is evolved by g.il- vanic electricity into free oxygen and free hydrogen, the former is accompanied with a small proportion of ozone. The same is true in the electrolysis of carbonic acid. So, too, when permanganate of potash, binoxide of barium, or chromic acid, is mixed with strong sulphuric acid, ox- is disengaged which contains an admixture of ozone.* Is Ozone Produced by Vegetation I — It is an interesting question whether the oxygen so freely exhaled from the foliage of plants under the influence of sunlight is accom- panied by ozone. Various experimenters have occupied * It appears probable that ozone is developed in all cases of rapid oxidation at hijjh temperatures. This has been long suspected, and Meissner obtained strong indirect evidence of the fact. Since the above was written, Pincus has announ- ced that ozone is produced when hydrogen burns in the air, or in pure oxygen gas. The quantity of ozone thus developed is sufficient to be recognized by the odor. To observe this fact, a jet of hydrogen should issue from a fine orifice and burn with a small flame, not exceeding %-incli in length. A clean, dry, and cold beaker glass is held over the flame fora few seconds, when its contents will smell as decidedly of ozone as the interior of a Leyden jar that has just been discharg- ed.^ (F5. IX, p. 473.) Pincus has also noticed the ozone odor in similar ex- periments with alcohol and oil (Argand) lamps, and with stearine candles. Doubtless, therefore, we are justified in making the generalization that in all cases of oxidation ozone is formed, and in many instances a portion of it diffuses into the atmosphere and escapes immediate combination. 68 now CROPS FEED. themselves with this subject. The most recent investiga- tions of Daubeny, {Journal Chein. JSoc.^ 1867, pp. 1-28,) lead to the conclusion that ozone is exhaled by plants, a conclusion previously adopted by Scoutetten, Poey, De Luca, and Kosmann, from less satisfactory data. Dau- beny found that air deprived of ozone by streaming through a solution of iodide of potassium, then made to pa>^s the foliage of a plant confined in a glass bell and ex- pose- 1 to sunliglit, acquired the power of blueing iodide- of-potassium-starcii-paper, even when the latter was shield- ed from the light. Cloez, hovv^ever, obtained the contrary results in a series of experiments made by him in 1855, (Ann. de Chimie et de Phys.^ L, 326,) in which the oxy- gen, exhaled both from aquatic and land plants, contained in a large glass vessel, came into contact with iodide-of- potassium-starch-paper, situated in a nari ow and blackened glass tube. Lawes, Gilbert, and Pugh, in their researches on the sources of the nitrogen of vegetation, (Phil. Trails.^ 1861) examined the oxygen evolved from vegetable matter under the influence of strong light, without finding evidence of ozone. It is not impossible that ozone was really pro- duced in the circumstances of Cloez’s experiments, but spent itself in some oxidizing action before it reached the test-paper. In Daubeny’s experiments, however, the more rapid stream of air might have carried along over the test- paper enough ozone to give evidence of its presence. Al- though the question can hardly be considered settled, the evidence leads to the belief that vegetation itself i'^ a source of ozone, and that this substance is exhaled, to- gether with ordinary oxygen, from the foliage, when act(*d on by sunlight. Ozone in the Atmosphere. — Atmospheric^jls^^ slow oxidation, and combustion, are obvious means of im- pregnating the atmosphere more or less with ozone. I^, * Li;,Uit alone blues this paper after a time in absence of ozone. ATMOSPHERIC AIR AS TUB FOOD OF PLANTS. 69 /the oxygen exhaled by plants contains ozone, this sub- ( stance must be perpetually formed in the atmospheie over ' a large share of the earth’s surface. The quantity present in the atmosphere at any one time must be very small, since, from its strong tendency to unite with and oxidize other substances, it shortly disappears, aad under most circumstances cannot manifest its peculiar properties, except as it is continually reproduced. The ozone present in any part of the atmosphere at any given . moment is then, not what has been formed, but what re- / mains after oxidable matters have been oxidized. We find, accordingly, that atmospheric ozone is most abundant in winter ; *since then there not only occurs the greatest \ amount of electrical excitement * in the atmosphere, which \ produces ozone, but the earth is covered with snow, and thus the oxidalile matters of its surface are prevented from consuming the active oxygen. In the atmosphere of crowded cities, in tlie vicinity of manure heaps, and wherever considerable quantities ot or- ganic matters pervade the air, as revealed by their odor, there we find little or no ozone. There, however, it may actually be produced in the largest quantity, though from the excess of matters which at once combine with it, it cannot become manifest. That the atmosphere ordinarily cannot contain more [ than the minutest quantities of ozone, is evident, if we accept the statement (of Schonbein ?) that it communicates ^(^.r^its odor distinctly to a million times its weight of air. Tiie attempts to estimate the ozone of the atmosphere give varying results, but indicate a proportion far less than ' snificient to be recognized by the odor, viz., not more than 1 part of ozone in 13 to 65 million of air. (Zwengei, ; Pless, and Pierre.) These figures convey no just idea of the quantities of 1 The amount of electrical disturbance is not measured by the number and ' violence of thunder-storms : these only indicate its intensity. 70 HOW CROPS FEED. ozone actually produced in the atmosphere and consumed in it, or at the surface of the soil. We have as yet indeed no satisfactory means of information on this point, but may safely conclude from the foregoing considerations that ozone performs an important part in the economy of nature. Relations of Ozone to Vegetable Nutrition. — Of the direct influence of atmospheric ozone on plants, nothing is certainly known. Theoretically it should be coiisumed by them in various processes of oxidation, and would have ultimately the same efiects that are produced by ordinary oxygen. Indirectly, ozone is of great significance in our theory of vegetable nutrition, inasmuch as it is the cause of chem- ical changes which are of the highest importance in main- taining the life of plants. This fact will appear in the section on Nitric Acid, which follows. § 8 . COMPOUNDS OF NITROGEN AND OXYGEN IN THE ATMOS- PHERE.. Nitric Acid, NOgH. — Under the more common name Aqua fortis (stJ’ong water) this highly important sub- stance is to be found in every apothecary shop. It is, when pure, a colorless, usually a yellow liquid, whose most obvious properties are its sou r, burning taste, and power of dissolving, or acting upon, many metals and other bodies. When pure, it is a half heavier than its own bulk of water, and emits pungent, suffocating vapors or fumes ; in this state it is rarely seen, being in general mixed or di- luted with more or less Avater ; when very dilute, it evolves no fumes, and is even pleasant to the taste. It has the properties of an acid in the most eminent de- gree; vegetable blue colors arc reddened by it, and it ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 71 unites with great avidity to all basic bodies, forming a long list of nitrates. It is volatile, and evaporates on exposure to air, though not so rapidly as water. Nitric acid has a strong affinity for water; hence its vapors, when they escape into moist air, condense the moisture, making therewith a visible cloud or fume. For the same reason the commercial acid is always more or less dilute, it being difficult or costly to remove the water en- tirely. Nitric acid, ns it occurs in commerce, is made by heat- ing together sulphuric acid and nitrate of soda, when nitric acid distils off, and sulphate of soda l emains behind. Nitrate of Sulphuric Bisulphate of Nitric soda. acid. soda. acid. NO 3 Na + H,S O, = HNa SO^ -I- NO 3 H Nitrate of soda is formed in nature, and exists in im- mense accumulations in the southern part of Peru, (see p. 252.) AnlftydrouiS Aiti’ie Acid, N.2O5, is what is commonly under- stood as existing in combination with bases in the nitrates. It is a crystallized body, but is not an acid until it unites with the elements of water. Nitrate of Ammonia, NH3 NO3H, or NH^ NO3, may be easily prepared by adding to nitric acid, ammonia in slight excess, and evaporating the solution. The salt read- ily crystallizes in long, flexible needles, or as a fibrous mass. It gathers moisture from the air, and dissolves in about half its weight of water. If nitrate of ammonia be mixed with potash, soda, or lime, or with the carbonates of these bases, an exchange of acids and bases takes place, the result of which is ni- trate of potash, soda, or lime, on the one hand, and free ammonia or carbonate of ammonia on the other. Aitroiis Oxide, N2O. — When nitrate of ammonia is heated, it 72 now CROPS FEED. melts^ and ually decomposes into water and nitrous oxide, “ laughing gas,” as represented by the equation : — NH4 NO3 = 2 H2O + N2O Nitric acid and the nitrates act as powerful oxidizing agents, i. e., they readily yield up a portion or nil their oxygen to substances having strong affinities for this ele- ment. If, for example, charcoal be warmed with strong nitric acid, it is rapidly acted upon and converted into carbonic acid. If thrown into melted nitrate of soda or saltpeter, it takes fire, and is violently burned to carbonic acid. Similarly, sulphur, phosphorus, and most of the metals, may be oxidized by this acid. When nitric acid oxidizes other substances, it itself lose?* oxygen and suffers reduction to compounds of nitrogen, containing less oxygen. Some of these compounds require notice. Nitric OxidC^ NO. — When nitric acid somewhat diluted with water acts upon metallic copper, a gas is evolved, which, after washing with water, is colorless and permanent. It is nitric oxide. By exposure to air it unites with oxy- gen, and forms red, suffocating fumes of nitric peroxide, or, if the oxygen be not in excess, nitrous acid is formed. Nitric Peroxide^ (hyponitric acid,) NO^, appears as a dark yellowish-red gas when strong nitric acid is poured upon copper or tin exposed to the air. It is procured in a state of purity by strongly heating nitrate of lead : by a cold approaching zero of Fahrenheit’s thermometer, it may be condensed to a yellow liquid or even solid. Nitrous Acid) (anhydrous,) N^Og, is produced when nitric peroxide is mixed with water at a low temperature, niu ic acid being formed at the same time. Nitric peroxide. Water, Nitric acid, 4 NO, + H,0 = 2 NHO 3 + N, O 3 It may be procured as a blue liquid, which boils at the freezing point of water. ATMOSPHERIC AIR AS THE FOOD OP PLANTS. 73 When nitric peroxide is put in contact with solutions of an alkali, there results a mixture of nitrate and nitrite of the alkali. Nitria Hydrate of Nitrate of Nitrite of peroxide, potash. potash. potash. 2 NO, + 2 HKO = NKO 3 -h NKO, + H, O Nitrite of Ammonia^ NH^ NO, is known to tlie chem- ist as a white crystalline solid, very soluble in water. When its concentrated aqueous solution is gently heated, the salt is gradually resolved into water and nitrogen ga^. This decomposition is represented by the following equa- tion : NH, NO, - 2H,0 + 2 N This decomposition is, however, not complete. A por- tion of ammonia escapes in the vapors, and nitrous acid accumulates in the residual liquid. (Pettenkofer.) Addi- tion of a strong acid facilitates decomposition ; an alkali retards it. When a dilute solution, 1 : 500, is boiled, but a small portion of the salt is decomposed, and a part of it is found in the distillate. Very dilute solutions, 1 : 100 , 000 ^ may be boiled without suffering any alteration whatever. (Schoyen.) Schonbein and others have (erroneously ?) supposed that nitrite of ammonia is generated by the direct union of nitrogen and water. Nitrite of ammonia may exist in the atmosphere in minute quantity. Nitrites of potash and soda may be procured by strongly heating the corresponding nitrates, whereby oxygen gas is expelled. The Mutual Convertibility of Nitrates and Nitrites is illustrated by various statements already made. There are, in fact, numerous substances which reduce nitrates to mitrites. According to Schonbein, {Jour. PraJct. Ch..^ 84, 207,) this reducing effect is exercised by the albuminoids, by starch, glucose, and milk-sugar, but not by cane-sugar. V 4 74 HOW CHOPS PEED. It is also manifested by many motals, as zinc, iron, and lead, and by any mixture evolving hydrogen, as, for ex- ample, putrefying organic matter. On the other hand, v^zone instantly oxidizes nitrites to nitrates. Reduction of Nitrates and Nitrites to Ammonia. — Some of the substances which convert nitrates into nitrites may also by their prolonged action transform the latter into ammonia. When small fragments of zinc and iron mixed together are drenched with warm solution of caustic potash, hydrogen is copiously disengaged. If a nitrate bo added to the mixture, it is at once reduced, and ammonia escapes. If to a mixture of zinc or iron and dilute chlor- hydric acid, such as is employed in preparing hydrogen gas, nit l ie acid, or any nitrate or nitrite be added, the evolution of hydrogen ceases, or is checked, and ammonia is formed in the solution, whence it can be expelled by lime or potash. Nitric acid. Hydrogen, Ammonia, W^ater, NO3H 4- 8 H = NII3 + 3 II3O The appearance of nitrous acid in this process is an in- termediate step of tliG reduction. Further Reduction of Nitric and Nitrous Acids. — Un- der certain conditions nitric acid and nitrous acid are still further deoxii- Nitric a.nd Nitrous Acids. — The fact that tlK'Sc substances often occur in extremely minute quantities renders it needful to emplo}^ very delicate tests for their recognition. Price's Test. — Free nitrous acid decomposes iodide of potassium in the sameT^miinner as ozone, and hence gives a blue color, with a mixture of this salt and starcli-paste. Any nitrite produces the same effect if to the mixture dilute sulphuric acid be added to liberate the nitrous acid. Pure nitric acid, if moderately dilute, and dilute solutions of nitrates mixed Avifh dilute sulphuric acid, are without immediate effect upon iodide-of-potassium-starch-paste. If the solution of a nitrate be min- gled with dilute sulphuric acid, and agitated for some time with zinc tilings, reduction to nitrite occurs, and then addition of the starch-paste, e tc., gives the blue coloration. According to Schonbein, this test, first proposed by Price, will detect nitrous acid when mixed with one-hund- red-thou>and times its weight of water. It is of course only applicable in the absence of other oxidizing agents. Green Vitriol Test. — A very characteristic test for nitric and nitrous acids, and a delicate one, though less sensitive than that just describ- ed, is furnished by common green vitriol, or protosnlphate of iron. Nitric oxide, the red gas wdiich is evolved from nitric acid or nitrates by mixing them with excess of strong sulphuric acid, and from nitrous acid or nitrites by addition of dilute sulphuric acid, gives with green vitriol a ]>eculiar blackish-brown coloration. To test for minute quantities of nitrous acid, mix tlie solution with dilute sulphuric acid and cautiously pour this liquid upon an equal bulk of cold saturated solution of green vitriol, so that the former liquid floats upon the latter without mingling much w’ith it. On standing, the coloration will be perceived where the two liquids are in contact. Nitric acid is tested as follow's: Mix the solution of nitrate with an equal volume of concentrated sulphuric acid; let the mixture cool, and pour upon it the solution of green vitriol. The coloration will appear betw’een the two liquids. Formation of IVitrogen Compounds in the Atmosphere, — a. From free nitrogen, by electrical ozone. Schonbein and Meissner have demonstrated that a discharge of elec- tricity through air in its ordinary state of dryness causes oxygen and nitrogen to unite, with the formation of nitric peroxide, NO^. Meissner has proved that not the elec- re HOW CROPS FEED. tricity directly, but the ozone developed by it, accom- plishes this oxidation. It has long been known that nitric peroxide decomposes with water, yielding nitric and ni- trous acids thus : 2 NO, + H,0 - NO 3 H 4- NO,H. It is further known that nitrous acid, both in the free state and in combination, is instantly oxidized to nitric acid by contact with ozone. Thus is explained the ancient observation, first made by Cavendish in 1784, that when electrical sparks are trans- mitted through moist air, confined over solution of potash, nitrate of potash is formed. (For information regarding this salt, see p. 252.) Until recently, it has been supposed that nitric acid is present in only those rains which accompany thuiider- s tor ins. It appears, however, from the analyses of both Way and Boussiiigault, that visible or audible electric discharges do not perceptibly influence the proportion of nitric acid in the air ; the rains accompanying thunder-storms not being always nor usually richer in this substance than others. Von Babo and Meissner liave demonstrated that slleyit electrical discharges develop more ozone than flashes of lightning. Meissner has shown that the electric spark causes the copious formation of nitric peroxide in its im- mediate path by virtue of the heat it excites, which in- creases the energy of the ozone simultaneously produced, and causes it to expend itself at once in the oxidation of nitrogen. Boussiiigault informs us that in some of the tropical regions of South America audible electrical dis- charges are continually taking place throughout the whole year. In our latitudes electrical disturbance is perpetu- ally occurring, but equalizes itself mostly by silent dis- charge. The ozone thus noiselessly developed, though operating at a lower temperature, and therefore more ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 77 slowly than that which is produced by lightning, must really oxidize much more nitrogen to nitric acid than the latter, b^ause its^tio^ never ceases. Formatio^of Nitrogen Compounds in ^^^Tn^sphere. — b. From free nitrogen (by ozone ?) in the processes of combustion and slow oxidation. At high temperatures, — Saussure first observed {^AnUo de (Jhimie,^ Ixxi, 282), that in the burning of a mixture of oxygen and hydrogen gases in the air, the resulting water contains nmmonia. He had previously noticed that nitric acid and nitrous acid are formed in the same process. Kolbe {^Ann, Chem, u, Pharm.^ cxix, 176) found that when a jet of burning hydrogen was passed into the neck of an open bottle containing oxygen, reddish-yellow va- pors of nitrous acid or nitric ])eroxide were copiously pro- duced on atmospheric air becoming mingled with the burning gases. Bence Jones [Phil, Trans, 1851, ii, 399) discovered ni- tric (nitrous?) acid in the water resulting from the burn- ing of alcohol, hydrogen, coal, wax, and purified coal-gas. By the use of the iodide-of-potassium-starch test (Price’s test), Boettger [Jour, far Pralct, Chem,,, Ixxxv, 396) and Schonbein (ibid., Ixxxiv, 215) have more recently confi lin- ed the result of Jones, but because they could detect neither free acid nor free. alkali by the ordinary test-pa- pers, they concluded that nitrous acid and ammonia are simultaneously formed, that, in fact, nitrite of ammonia is generated in all cases of rapid combustion. Meissner ( TJntersuchungen uher den Sauer stoff,, 1863, p. 283) was unable to satisfy himself that either nitrous acid or ammonia is generated in combustion. Finally, Zabelin (Ann, Chem, u, Ph„, cxxx, 54) in a series of careful experiments, found that when alcohol, il- luminating gas, and hydrogen, burn in the air, nitrous acid and ammonia are very frequently, but not always, formed. 78 HOW CROPS FEED. When the combustion is so perfect that the resulting Wfv ter is colorless and pure, only nitrous acid is formed ; when, on tlie other hand, a trace oi' organic matters es- capes oxidation, less or no nitrous acid, but in its place ammonia, appears in the water, and tins under circum- stances that preclude its absorption from the atmosphere, Zabelin gives no proof that the combustibles he ern« ployed were absolutely free from compounds of nitrogen, but otherwise, Ids experiments are not open to criticism. Meissner’s observations were indeed made under some- what different conditions ; but his negative results were not improbably arrived at sinqdy because lie employed a much less delicate test for nitrous acid than was used by Sctionbein, Boettger, Jones, and Zabelin.* [ We must conclude, then, that nitrous acid and ammonia are usually formed from atmospheric nitrogen during rap- id combustion of hydrogen and coinpoun Is of hydrogen and carbon. The quantity of these bodies thus generated is, however, in general so extremely small as to require the most sensitive reagents for their detection. Af low temperatures , — Schonbein was the first to observe that nitric acid may be formed at moderately elevated or even ordinary temperatures. He obtained several grams of nitrate of potash by adding carbonate of potash to the liquid resulting from the slow oxidation of phosphorus in the preparation of ozone. More recently he believed to have discovered that ni- trogen compounds are formed by the simple evaporation of water. He heated a vessel (which was indifferently of * Meissner rejected Price’s test in the belief that it cannot serve to distin^ruish nitrous acid from i)cr()xidc of liydro^^en, II 2 O 2 . He therefore made the liquid to be examined alkaline with a slight excess of potash, concentrated to small bulk and tested with dilute sulphuric acid and protosulphate of iron. {Untet's. u. d, Sauersloff, p. 233). Schonbein had found that iodide of potassium is decom- posed after a little time by concentrated solutions of peroxide of hydrogen, but is unaffected by this body when dilute, {Jour, far jrrakt. Chem.^ Ixxxvi, p. 00). Zabelin agrees with Schiinbein that Price’s test is decisive between peroxide of hydrogen and nitrous acid. {Ann. Chem. u. Pli.., exxx, p. 58.) ATMOSPHERIC AIR AS THE FOOii OF PLA^ITS. 79 glass, porcelain, silver, etc.,) so that water would evapo- rate rapidly from its surface. The purest water was then dropped into the warm dish in small quantities at a time, each portion being allowed to evaporate away before the next was added. Over the vapor thus generated was lield the mouth of a cold bottle until a portion of the vapor was condensed in the latter. The water thus collected gave the reac^tions for nitrous acid and ammonia, sometimes quite intensely, again faint* ly, and sometimes not at all. By simply exposing a piece of filter-paper fv)r a suffi- cient time to the vapors arising from pure water heated to boiling, and pouring a few drops of acidified iodide-of- potassium-starch-paste upon it, the reaction of nitrous acid was obtained. V/hen paper which had been impregnated with dilute solution of pure potash was hung in the va- pors that arose fi’om water heated in an open dish to F., it shortly acquired so much nitrite of potash as to re- acA with the above named test. Lastly, nitrous acid and a nmonia appeared when a sheet of filter-paper, or a piece of linen cloth, which had been moistened with the purest water, was allowed to dry at ordinary temperatures, in the open air or in a closed vessel. {Jour, fur Praht. Chem.^ Ixvi, 131.) These ex- periments of Schonbein are open to criticism, and do not furnish perfectly satisfactory evidence that nitrous acid and ammonia are generated under the circumstances men- tioned. Bohlig has objected that these bodies might be gathered from the atmosphere, where they certainly existj though in extremely minute quantity. Zabelin, in the paper before referred to {Ann. Ch. Ph.. cxxx, p. 76), communicates some experimental results which, in the writer’s ojunion, serve to clear up the mat- ter satisfactorily. Zabelin ascertained in the first place that the atmos- pheric air contained too little ammonia to influence Ness- 80 HOW CROPS FEED. ler’s test/^ which is of extreme delicacy, and wbicli he con* stantly employed in his investigations. Zabelin operated in closed vessels. T’ne apparatus he used consisted of two glass flasks, a larger and a smaller one, which were closed by corks and fitted with gl iss tabes, so that a stream of air entering the larger vessel should bubble through water covering its bottom, and thence passing into the smaller flask should stream through Nessler’s test. Next, he found that no ammonia and (by Price’s test) but doubtful traces of nitrous acid could be detected in the purest water when distilled alone in this apparatus. Zabelin likewise showed tliat cellulose (clippings of filter- p iper or shreds of linen) yielded no ammonia to Nessler’s test when heated in a current of air at temperatures of 120^^ to 160^ F. Lastly, he found that when cellulose and pure water to- gether were exposed to a current of air at the tempera- tures just named, ammonia was at once indicated by Nessler’s test. Nitrous acid, however, could be detected, if at all, in the minutest traces only. 'Views of Schonbein , — The reader should observe that Boettger and Schonbein, finding in the first instance by the exceedingly sensitive test with iodide of potassium and starch-paste, that nitrous acid was formed, when hy- drogen burned in the air, while the water thus generated was neutral in its reaction with the vastly less smsitive litmus test-paper, concluded that the nitrous acid was united with some base in the form of a neutral salt. Af- terward, the detection of ammonia appeared to demon** strate the formation of nitrite of ammonia. We have already seen that nitrite of ammonia, by ex- posure to a moderate heat, is resolved into nitrogen and water. Schonbein assumed that under the conditions of * See p. 54 ATMOSPHERIC AIR AS THE FOOD OP PLAXTS. 81 Ills experiments nitrop^en and water combine to form ni- trite of ammonia. 2]Sr 4- 2H,0 - This theory, supported by tlie authority of so distin- giihhed a philosopher, has becil almost universally credit- ed.'*" It has, iiowever, little to warrant it, even in the way of probability. If traces of nitrite of ammonia can be produced by the immediate combination of these excep- tionally abundant and universally diffused bodies at com- mon temperatures, or at the boiling point of water, or lastly in close proximity to the flames of burning gases, then ht is simply inconceivable that a good share of the atmosphere should not speedily dissolve in the ocean, for the conditions of Schonbein’s experiments preyail at all times and at all places, so far as these substances are con-* cerned. The discovery of Zabelin that ammonia and nitrous acid do not always appear in equivalent quantities or even simultaneously, while diflicult to reconcile with Schbn- bein’s theory, in no wise conflicts with any of his facts. A quantity of free nitrous acid that admits of recognition by help of Price’s test would not necessarily have any effect on litmus or other test for free acids. There re- mains, then, no necessity of assuming the generation of ni- trite of ammonia, and the fact of the separate appearance of the elements of this salt demands another explanation. The Author’s Opinion , — The writer is not able, perhaps, to offer a fully satisfactory explanation of the ficts above adduced. He submits, however, some speculations which appear to him entirely warranted by the present aspects of the case, in the hope that some one with the time at * Zabelin was inclined to believe that his failure to detect nitrous acid in some of his experiments where organic matters intervened, was due to a power pos- sessed by these organic matters to mask or impair the delicacy of Price’s test, as first noticed by Pettenkofer and since demonstrated by Schonbeiu in case of urine. 4 * 82 HOW CROPS FEED. command for experimental study, will estaolisli or disprove them by suitable investigations. lie believes^ from the existing evidence, that free nitro- gen can, in no case, unite directly with water, but in the conditions of all the foregoing experiments, it enters com- lunation by the action of ozone^ as Schonbein formerly maintained and was the first to suggest. We have already recounted the evidence that goes to show the formation of ozone in all cases of oxidation, both at high and low temperatures, p. 67. In Zabelin’s experiments we may suppose that ozone was formed by the oxidation of the cellulose (linen and paper) he employed. In Schonbein’s experiments, wheie paper or linen was not employed, the dust of the air may have supplied the organic matters. The first i-esult of the oxidation of nitrogen is nitrous acid alone (at least Schonbein and Bohlig detected no ni- tric acid), when the combustion is complete, as in case of hydrogen, or when organic matters are excluded from the experiment. Nitric acid is a product of the subsequent oxidation of nitrous acid. When organic matters exist in the product of combustion, as when alcohol burns in a heated apparatus yielding water having a yellowish color, it is probable that nitrous acid is formed, but is afterward reduced to ammonia, as has been already explained, p. 74. Zabelin, in the article before cited, refers to Schonbein as authority for the fact that various organic bodies, viz., all the vegetable and animal albuminoids, gelatine, and most of the carbohydrates, especially starch, glucose, and milk-sugar, reduce nitrites to ammonia^ and ultimately to nitrogen ; and although we have not been able to find such a statement in those of Schonbein’s papers to Avhich we have had access, it is entirely credible and in accordance with numerous analogies. If, as thus appears extremely probable, ozone is devel- oped in all cases of oxidation, both rapid and slow, then AT^fOSPITERIC AIR AS THE FOOD OF PLAXTS. 8D every flame and fire, every decaying plant and animal, the organic matters that exhale from th bubble through solutions of potash, or to stream over fragments of brick or pumice whicli have been soaked in potash or carbonate of potash, these absorbents gradually acquire a small amount of nitric acid. In the experiments of Cloez and De Luca, the air was first washed of its ammonia by con- tact with sulphuric acid. Their results prove, therefore, that the nitric acid was formed independently of ammonia, though it doubtless exists in the air in combination with this base. Proportion of Nitric Acid in Rain-water, etc, — In at- mospheric waters, nitric acid is found much more abund- antly than ill the air itself, for the reason that a small bulk of rain, etc., washes an immense volume of air. Many observers, among the first, Liebig, have found ni- trates in rain-water, especially in the ram of thunder- storms. The investigations of Boussinganlt, made in 1856-8, have amply confirmed Barral’s observation tlia:^ nitric acid (in combination) is almost invariably present in rain, dew, fog, hail, anliou«$ ol* Oas to Tegetalioii.— Whether t ids gas is absorbed and assimilated by plants is a point on which we have at present no information. It might serve as a source both of car- bon and hydrogen ; but as these bodies are amply furnished by carbonic acid and water, and as it is by no means improbable that marsh gas it- self is actually converted into these substances by ozone, tlie question of its assimilation is one of little importance, and remains to be inves- tigated. Schultz (Johnston’s Lectures on Ag. Chem., 2d Ed., 147) found on sev- eral occasions that the gas evolved from plants when exposed to the sun- light, instead of being pure oxygen, contained a combustible admixture, so that it exploded violently on contact with a lighted taper. This observation shows either that the healthy plants evolved a laige amount ot marsh gas, which forms with oxygen an explosive mixture (the fire-damp of coal-mines), or, as is most probable, that the vegetable matter entered into decomposition from too long coLtinuanee of the experiment. Boussincrault has, however, recently found a minute proportion of marsh gas in the air exhaled from the leaves of ))lants that are exposed to sunlight when submerged in water. It does not appear when the leaves are surrounded by air. as the latest experiments of Boussingault, Cloez, and Coren winder, agree in demonstrating. Carl>oiiir, Oxide, CO, is a gas destitute of color and odor. It burns in contact with air, with a flame that has a fine blue color. The result of its combu-tion is carbonic acid, CO + O = CO 2 . This gas is extremely ]misonous to animals. Air containing a few per cent of it is unfit for respiration, and produces headache, insensi- bility, and death. Carbonic oxide may be obtained artificially by a variet}" of processes. If carbonic acid gas be made to stream slowly through a tube containing ignited charcoal, it is converted into carbonic oxide, CO 2 + C = 2 CO. Carbonic oxide is largely produced in all ordinary fires. The air which draws through a grate heaped with well-ignited coals, as it enters the bottom of the mass of fuel, loses a large i)ortion of its oxygen, which there unites with carbon, foi-ming carbonic acid. This gas is carried up into the heated coal, and there, where carbon is in excess, it takes up an- other pj-oportion of thi.^ element, being converted into carbonic oxide. At the summit of the fire, where oxygen is abundant, the carbonic oxide burns again with its peculiar blue color, to carbonic acid, provided the heat be intense enough to inflame the gas, as is the case when the mass ATMOSPHERIC AIR AS THE FOOD OP PLANTS. 93 of fuel is thorouiihly ignited. Wlien, on the other hand, the fire is cov- ered w ith cold fuel, carbonic oxide escapes copiously into the atmos- phere. When ciystallized oxalic acid is heated with oil of vitriol, it yields water to the latter, and falls into a mixture of carbonic acid and carbonic oxide. C 2 H 2 O 4 , 2 H 2 O = CO 2 + CO -f 3 H 2 O. Carbonic oxide may, perhaps, be formed in small quantity in the de- cay of organic matters; though Coren winder {Compt. Rend. 102) failed to detect it in the rotting of manure. ISelatioiis of ^o Vcgotation. — Ac- corJing to Saussurc, while pea-plants languish and die when immersed in carbonic oxide, certain marsh plants {Epilobiam Idrsatnni^ Lytlirum sallcaria., and Pohjijonum perdcnria) flourish as w^ell in this gas as in com- mon air. Saussui-e’s experiments Avith these plants lasted six Aveeks. There occurred an absorption of the gas and an evolution of oxygen. It is thus to be inferred that carbonic oxide may be a source of carlion to aquatic plants. Boussingault {Compt. Rend.., LXI, 493) Avas unable to detect any action of the foliage of land plants ii]>on carbonic oxide, either when the gas was pure or mixed with air. The carbonic oxide Avhieh Boussingault found in 1863 in air exhaled from submerged leaves, proves to have been produced iu the analyses, (from pyrogallate of potash,) and Avas not emitted by the leaves them- selves, as at first supposed, as both Cloez and Boussingault have shown. ]\'itroiis Oxid.e, N 2 O. — This sub-tanee, the so-called langhinq gas., is prepared from nitrate of ammonia by exposing that salt to a heat somewhat higher than is necessary to fuse it. The salt decomposes into nitrous oxide and water. NH4, NO3 = N2O -h 2 II2O. The gas is readily soluble in water, and has a sweetish odor and taste. When breathed, it at first produces a peculiar exhilarating effect, Avhicli is folloAved by stupor and insensibilitA\ This gas has never been demonstrated to exist in the atmosphere. In fact, our methods of analysis are incompetent to detect it, Avhen it is present in very minute quantity in a gaseous mixture. Knop is of the opinion that nitrous oxide may occur in the atmosphere, and has pub- lished an account of expei’iments {Journal filr Prakt. Chern.^ Vol. 50, p. 114) which, according to him, prove that it is absorbed by vegetation. Until nitrous oxide is shown to be accessible to plants, any fuiTher no- tice of it is unnecessary in a treatise of this kind. Iffycl rocliloric Acid HCl, Avhose properties have been described in How Crops Grow, p. 118, is found in minute quantity in the air over salt marshes. It doubtless proceeds from the decomposition of the chloride of magnesium of sea-water. Spreugel has surmised its ex- 94 now CROPS FEED. halation by sea-shore plants. It is found in the air near soda works, be* ing a product of the manufacture, and is destructive to vegetation. S 111 plifli rolls Aciil, SO 2 , and ^ailpliydiric Acid, IIS, (see H. C. G., p. 115,) may exist in the atmosphere as local emanations. In large quantities, as when escaping from smelting works, roasting heaps, or manufactoi ies, they often prove destructive to vegetation. In contact with air tliey quickly suffer oxidation to sulphuric acid, whicli, dissolv- ing in the water of rains, etc., becomes incorporated with the soil. Org’siiiic of whatever sort that escape as vapor into the atmosphere and are ihere recognized by their odor, are rapidly oxidized and have no direct iulluence upon vegetation, so far as is now known. Siispeaidccl !^Oiid I^latters i3i tlie Atmosplicre. — The solid matters which are raised into the air by winds in the form of dust, and are often transported to gi-eat heights and distances, do not propeily belong to the atmosphere, but to the soil. Their presence in the air explains the growth of certain plants {air-phmts) when entirely disconnected from the soil, or of such as ai'c found in pure sand or on the surface of rocks, inca.pahle of performing the functions of the soil, except as dust accumulates upon them. Barral announced in 186:3 {Jour. JAq. proXique., j). 150) the discovery of phosphoric acid in rain-water. Robinet and Luca obtained the same result with water gathered near the surface of the earth. The latter found, however, that rain, collected at a height of 60 or more feet above the ground, was free from it. V ' RECAPITULATION OF THE ATMOSPHERIC SUPPLIES OF FOOD TO CROPS. Oxyj^en^ whether required in the free state to effect chemical changes in the processes of organization, or in combination (in carbonic acid) to become an ingredient of the plant, is superabundantly supplied by the atigoR-,^ pli^re* Carbon. — The carbonic acid of tlie at mosphere is a source of this element sufficient for the most rapid growth, as is abundantly demonstrated by the experiments in wa- ter cult’ire, made by Nobbe and Sh^gert, and by Wolff, (H. C. G., p. 170), in which oat and buckwheat plants were brought to more than the best agricultural develop- ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 95 merit, with no other than the atmospheric supply of carbon. Hydrogen is adequately supplied to crops by w0er, which equally belongs to the Atmosphere and the Soil, although it enters the plant chiefly from the latter. Nitrogen exists in immense quantities in the atmosphere, and we may regard the latter as the primal source of this element to the organic world. In the atinoqihere, how- ever, nitrogen exists for the most part in the free state, and is, as such, so we must believe from existing evidence, un- assimilable by crops. Its assimilable compounds, ammo- nia and nitrii acid^ occur in the atmosphere, but in pro- portions so minute, as to have no influence on vegetable growth directly appreciable by the methods of investiga- tion hitherto employed, unless they are collected and con- centrated by rain and dew. The subjoined Table gives a summary of the amount of nitrogen annually brought down in rain, snow, etc., upon an acre of surfice, a'^cording to the determinations hitherto made in England and Prussia. Amount of Assimilable Nitrogen annually brought down by THE Atmospheric Waters. Locality. Year. Nitrogen per Acre. Water per Acrre. Rothamstcad Soiitliern EnHand 1855* 1850* 1864-5t 18G5-0t 18G4-5t 18()5-6t i8(n-5t 1805^t 1865* 1864-5t 1865* 6.63 lbs. 8.31 ‘• 1.86 ‘‘ 2.50 “ 5.49 “ : 6.81 “ 15.00 10.38 “ 11.83 “ 20.91 6.66 6,633,220 lbs. 6,160.510 “ 2,680.086 “ 4,008,491 6,222,461 “ 5.383,478 5.313.562 “ 4,.358.053 4,877.545 “ 4,031,782 ‘‘ 3.868,646 “ Kuschen, Province Posen, Prussia Insterburg, near Koni^sberg, “ Regen walde, near Stettin, “ — Ida-Marienhiitte, near Breslau, Silesia, Proskau, Silesia, Daliine, Province Brandenburg, “ Averaqe 8.76 lbs. 4.867.075 lbs! From Jan. to Jan. t From Apr. to Apr. t From May to May. Direct Atmospheric Supply of Nitrogen Insufficient for Crops. — To estimate the adequacy of these atmos- pheric supplies of assimilable nitrogen, we may compare their amount with the quantity of nitrogen required in the 96 now CROPS FEED. composition of standard crops, and with tlie quantity con- taine.l in appropriate applications of nitrogenous fertil- izers. The average atmospheric supply of nutritive nitrogen in rain, etc., for 12 months, as above given, is much le than is necessary for ordinary crops. According to D.*. Anderson, the nitrogen in a crop of 28 bushels of wheat and 1 (long) ton 3 cwt. of straw, is 45^ lbs.; that in 2^ tons of meadow hay is 56 lbs. The nitrogen in a crop of clover hay of 2| (long) tons is no less than 108 lbs. Ob- viously, therefore, the atmospheric waters alone are in- capable of furnishing crops with the quantity of nitrogen they require. On the other hand, the atmospheric supply of nitrogen by rain, etc., is not inconsiderable, compared with the amount of nitrogen, which often forms an clfective manur- ing. Peruvian guano and nitrate of soda (Chili saltpeter) each contain about 15 percent of nitrogen. The nitrogen of rain, estimated by the average above given, viz., 8j lbs., corresponds to 58 lbs. of these fertilizers. 200 lbs. of gua- no is for most field purposes a sufficient application, and 400 lbs. is a large manuring. In Great Britain, where ni- trate of soda is largely employed as a fertilizer, 112 lbs. of this substance is a:i ordinary dressing, which has been known to double the grass crop. We notice, however, that the amount of nitrogen sup- plied in the atmospheric wmters is quite variable, as well for dilferent localities as for different years, and for differ- ent periods of the year. At Kiischen, but 2-2^ lbs. \ver>5 brought down against 21 lbs. at Proskau. At Regen waldo the quantity was 15 lbs. in 18G4-5, but the next year it Avas nearly 30 per cent less. In 1855, at Rotham stead, the great(‘st rain supply of nitrogen was in July, amount- ing to 1^ lbs., and in October nearly as much more was brought down; the least fell in January. In 1856 the largest amount, 2 ^ lbs., fell in May; tlic next, 1 lb., in ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 97 April; and the least in March. At Ida-Marienhiitte, Kuschen, and Kegenwalde, in 1865-6, nearly half the year’s atmospheric nitrogen came down in summer ; but at Insterburg only 30 per cent fell in summer, while 40 per cent came down in winter. The nitrogen that is brought down in winter, or in spring and autumn, when the fields are fallow, can be counted upon as of use to summer crops only so far as it remains in the soil in an assimilable form. It is well known that, in general, much more water evaporates from cultivated fields during the summer than falls upon them in the same period ; while in winter, the water that falls is in excess of that which evaporates. But how much of tlie winter’s fall comes to supply the summer’s evaporation, is an element of the calculation likely to bo very variable, and not as yet determined in any instance. We conclude, then, that the direct atmospheric supply of assimilable nitrogen, though not unimportant, is insuf- ficient for crops. We must, therefore, look to the soil to supply a large share of this element, as v ell as to be the medium through which the assimilable atmospheric nitrogen chiefly enters the plant. The Other Ingredients of the Atmosphere, so far as we now know, are of no direct significance in the nutri- tion of agricultural plants. Indirectly, atmospheric ozone has an influence on the supplies of nitric acid, a point we shall recur to in a full discussion of the question of the Supplies of Nitrogen to Vegetation, in a subsequent chapter. § 11 - ASSIMILATION OF ATMOSPHERIC FOOD. Boussingault has suggested the very probable view that the first process of assimilation in the chlorophyll cells of the leaf, — where, under the solar influence, carbonic acid 5 98 HOW CHOPS PEED, is absorbed and decomposed, and a nearly equal volume of oxygen is set free, — consists in the simultaneous deox- idation of carbonic acid and of water, whereby the former is reduced to carbonic oxide with loss of half its oxygen, and the latter to hydrogen with loss of all its oxygen, viz.: Carbonic 4 . w ^ Carbonic Hydro- Oxy- acid ^ oxide gen, gen, CO, + H,0 - CO + H, -f O, In this reaction the oxygen set free is identical in bulk with the carbonic acid involved, and the residue retained in the plant, COH„ multiplied by 12 , would give 12 molecules of carbonic oxide and 24 atoms of hydrogen, which, chemically united, might constitute either glucos. or levulose, C^, O^,, from which by elimination of PI,0 would result cane sugar and Arabic acid, while sepa- ration of 2H,0 w^)uld give cellulose and the other mem- bers of its group. Whether the real chemical process be this or a different and more complicated one is at present a matter of vague probability. It is, notwithstanding, evident that this re- action expresses one of the principal results of the assim- ilation of Carbon and Hydrogen in the foliage of plants. § 12 * The following Tabular View may usefully serve the reader as a recapitulation of the chapter now hnishecl. TABULAR VIEW OF THE RELATIONS OF THE ATMOSPHERIC INGREDIENTS TO THE LIFE OF PLANTS. Absorbed by Plants. Oxygen, by roots, flowers, ripening fruit, and by all growing parts. Carbonic Acid, by foliage and green parts, but only in the light. Ammonia, as carbonate^ by foliage, probably at all times. Water, as liquid, through the roots. Nitrous Acid \ united to ammonia, and dissolved in wa- Nitric Acid ) ter through the roots. iuncertaiu. Marsh Gas ) THE ATMOSPHERE AS RELATED TO VEGETATION. 99 Not absorbed ( Nitrogen. by Plants. ( Water in state of vapor. Exhaled by Plants. ' Oxygen, ) by foliage and green parts, but only in the Ozone? ) light. Marsh Gas in ti-aces by aquatic plants ? Water, as vapor, from surface of plant at all times. Carbonic Acid, from the growing parts at all times. CHAPTER II. THE ATMOSPHERE AS PHYSICALLY RELATED TO VEGETATION. § MANNER OF ABSORPTION OF GASEOUS FOOD BY THE PLANT. Closing here our study of the atmosphere considered as a source of the food of plants, we stiil need to remark somewhat upon the physical properties of gases in rela- tion to vegetable life; so far, at least, as may give some idea of the means by which they gain access into the plant. Physical Constitution of the Atmosphere. — That the atmosphere is a mixture and not a chemical combination of its elements is a fact so evident as scarcely to require discussion. As we have seen, the proportions which sub- sist among its ingredients are not uniform, although they are ordinarily maintained within very narrow limits of va- riation. This is a sufficient proof that it is a mixture. The remarkable fact that very nearly the same relative quantities of Oxygen, Nitrogen, and Carbonic Acid, steadily exist in the atmosphere is due to the even balance which obtains between growth and decay, between life and death. The equally remarkable fact that the gases 100 now CROPS FEED. which compose the atmosphere are uniformly mixed to- gether without regard to their specific gravity, is but one result of a law of nature which we shall immediately notice. Diffusion of Gases. — Whenever two or more gases are brought into contact in a confined space, they instantly begin to intermingle, and continue so to do until, in a longer or shorter time, they are both equally diffused throughout the room they occupy. If two bottles, one fided with carbonic acid, the other with hydrogen, be con- nected by a tube no wider than a straw, and be placed so tliat the heavy carbonic acid is below the fifteen times lighter hydrogen, we sliad find, after the lapse of a ftw hours, that the two gases have mingled somewhat, and in a few days they wnll be in a state of uniform mixture. On closer study of this phenomenon it has been discovered that gases diffuse with a rapidity proportioned to their lightness, the relative diffusibility being nearly in the in- verse ratio of the square roots of their specific gravities. Ily interposing a porous diaphragm between two gases of different densities, we may visibly exhibit the fact of their ready and unequal diffusion. For this purpose the dia- phragm must offer a partial resistance to the movement of the gases. Since the lighter gas passes more rapidly into the denser than the reverse, the space on one side of the membrane will be overfilled, while that on the other side will be partially emptied of gas. In the accompanying figure is represented a long glass tube, 5, widened above into a funnel, and having cemented u[)on this an inverted cylindrical cup of unglazed porce- lain, a. The funnel rests in a round aperture made in the horizontal arm of the support, while the tube below dips beneath the surface of some water contained in the wine- glass. The porous cup, funnel, and tube, being occupie 1 with common air, a glass bell, c, is filled with hydrogen gas and placed over the cap, as shown in the figure. In* THE ATMOSPHERE AS RELATED TO VEGETATION. 101 stantly, biibbh s begin to escape rapidly from the bottom of the tube through the water of the wine-glass, thus demonstrating that hydrogen passes into the cup faster than air can escape outwards through its pores. If the bell be removed, the cup is at once bathed again externally in common air, the light hydrogen floating instantly upwards, and now the water begins to rise in the tube in consequetice of the return to the outer atmosphere of the hydrogen which before had difiused into the cup. It is the perpetual action of tliis diffusive tendency which maintains the atmosphere in a state of such uniform mixture that accurate ana- lyses of it give for oxygen and nitrogen almost identical figures, at all t ines of the day, at all seasons, all altitudes, and all situations, ex- cept near the central surface of large bodies of still water. Here, the fact that oxygen is more largely absorbed by Avater than nitrogen, diminishes by a minute amount the usual proportion of the former gas. If in a limited volume of a mixture of several gases a solid or liquid body be placed, Avhich is capable of chemic- ally uniting with, or otherwise destroying the aeriform condition of one of the gases, it will at once absorb those particles of this gas whicli lie in its immediate vicinity, and thus disturb the uniformity of the remaining mixture. Uniformity at once tends to be restored by diffusion of a portion of the unabsorbed gas into the space that has been deprived of it, and thus the absorption and the diflfusion 102 HOW CROPS FEED. keep pace with oacli otl^er until all the absorbable air is removed from the gaseous mixture, and condensed or fixed in the absorbent. In this manner, a portion of the atmosphere enclosed in a large glass vessel may be perfectly freed from watery vapor and carbonic acid by a small fragment of caustic potash. By standing over sulphuric acid, ammonia is taken fiom it ; a |)iece of phosphorus will in a few hours absorb all its oxygen, and an ignited mass of the rare metal titanium will remove its nitrogen. Osmose of Gases. — By this expression is understood the passage of gaseous bodies through membranes whose pores are too small to be discoverable by optical means^ sucli as the imperforate wall of the vegetable cell, the green cuticle of the plant where not interrupted by stomata^ vegetable parchment, India rubber, and animal membranes, like bladder and similar visceral integuments. If a bottle filled with air have a thin sheet of India rubber, or a piece of moist bladder tied over its mouth and then be placed within a bell of hydrogen, evidence is at once had that gases penetrate the membrane, for it swells outwards, and may even burst by the pressure of the hydrogen that rapidly accumulates in the bottle. Gaseous Osmose is Diffusion Modified by the Infiiience of the Membrane. — The rapidity of osmose * is of course influenced by the thickness of the membrane, and the character of its pores. An adhesion between the mem- brane and the gases would necessarily increase their rate of penetration. In case the membrane should attract or ha\ e adhesion for one gas and not for another, complete separation of the two might be accomplished, and in pro- portion to the difference existing between two gases as re- gards adhesion for a given membrane, would be the de- gree to which such gases would bo separated from each * The osmose of liquids is discussed in detail in “How Crops Grow,” p. 354. THE ATMOSPHERE AS RELATED TO VEGETATION. 103 Other in penetrating it. In case a memi)rane is moistened with water or other liquid, or by a solution of solid mat- ters, this would still further modify the result. Absorption of Gases by the Plant, — A few words will now suffice to npply these facts to the absorption of the nutritive gases by vegetation. The foliage of jDlants is freely permeable to gases, as has been set forth in “ How Crops Grow,” p. 289. The cells, or some portions of their contents, absorb or condense carbonic acid and ammonia in a similar way, or at least with the same effect, as potash absorbs carbonic acid. As rapidly as these bodies are removed from the almosphere surrounding or occupying the cells, they are re-supplied by diffusion from without ; so that although the quantities of gaseous plant-food con- tained in the air are, relatively considered, very small, they are by this grand natural law made to flow in con- tinuous streams toward every growing vegetable cell, 10 -^ n ^ DIVISION II THE SOIL AS RELATED TO VEGETABLE PRODUCTION. CHAPTER I. INTRODUCTORY. For the Husbandman the Soil has this paramount im- portance. that it is the home of the roots of his crops and the exclusive theater of his labors in promoting their growth. Through it alone can he influence the amount of vegetable pi’oduction, for the atmosphere, and the light and heat of the sun, are altogether beyond his control. Agriculture is the culture of the field. The value of the field lies in the quality of its soil. No study can have a grander material significance than the one which gives us a knowledge of the causes of fertility and barrenness, a knowledge of the means of economizing the one and over- coming the other, a knowledge of those natural laws which enable the farmer so to modify and manage his soil that all the deficiencies of the atmosphere or the vicissi- tudes of climate cannot deprive him of a suitable reward for his exertions. The atmosphere and all extra-terrestrial influences that affect the growth of plants are indeed in themselves beyond our control. We cannot modify them in kind or amount ; but we can influence their subserviency to our purposes through the medium of the soil by a proper un- derstanding of the characters of the latter 104 INTRODUCTORY. 105 The General Functions of the Soil are of three kinds : 1. The ashes of the plant whose nature and variations have been the subject of study in a former volume (H. C. G., pp. 111-201,) are exclusively derived from the soil. The latter is then concerned in the most direct manner with the nutrition of the plant. The substances which the plant acquires from the soil, so far as they are nutri- tive, may be collectively termed soil-food, 2. The soil is a mechanical support to vegetation. The roots of the plant penetrate the pores of the soil in all directions sidewise and downward from the point of their junction with the stem, and thus the latter is firmly braced to its upright position if that be natural to it, and in all cases is fixed to the source of its supplies of ash-in- gredients. 3. By virtue of certain special (physical) qualities to be hereafter enumerated, the soil otherwise contributes to the well-being of the plant, tempering and storing the heat of the sun which is essential to the vital processes ; regulating the supplies of food, which, coming from itself or fi-om external sources, form at any one time but a mi- nute fraction of its mass, and in vaiious modes ensuring the co-operation of the conditions which must unite to produce the perfect plant. Variety of Soils* — In nature we observe a vast variety of soils, which difier as much in their agricultural value as they do in their external appearance. We find large tracts of country covered with barren, drifting sands, on whose arid bosom only a few stunted pines or sliriveled grasses find nourishment. Again there occur in the high- lands of Scotland and Bavaria, as well as in Prussia, and other temperate countries, enormous stretches of moor- land, bearing a nearly useless growth of heath or moss. In Southern Russia occurs a vast tract, two hundred mil- lions of acres in extent, of the tschornosem^ or black earth, 5* 103 now CROPS PEED. which is remarkable for its extraordinary and persistent fertility. The prairies of our own West, the bottom lands of the Scioto aod other rivers of Ohio, are other examples of peculiar soils; while on every farm, almost, may be found numerous gradations from clay to sand, from vege- table mould to gravel — gradations in color, consistence, composition, and productiveness. CHAPTER II. ORIGIN AND FORMATION OF SOILS. Some consideration of the origin of soils is adapted to assist in understanding the reasons of their fertility. Geological studies give us reasons to believe that what is now soil was once, in chief part, solid rock. We find in nearly all soils fragments of rock, recognizable as such by the eye, and" by help of the microscope it is often easy to perceive that those portions of the soil which are impal- oable to the feel are only minuter grains of the same rock. Rocks are aggregates or mixtures of certain minerals. Minerals, again, are chemical compounds of Various ele- ments. We have therefore to consider: I. The Chemical Elements of Rocks. II. The Mineralogical Elements of Rocks. III. The Rocks themselves — their Kinds and Special Characters. lY. The Conversion of Rocks into Soils ; to which we may add : V. The Incorporation of Organic Matter Avith Soils. ORIGIN AND FORMATION OF SOILS. 107 § 1 * THE CHEMICAL ELEMENTS OF ROCKS. The chemical elements of rocks, i. e., the constituents of the minerals which go to form rocks, include all the simple bodies known to science. Those, which, from their universal distribution and uses in agriculture, concern us immediately, are with one exception the same that liave been noticed in a former volume as composing the ash of agricultural plants, viz.. Chlorine, Sulphur, Carbon, Silicon, Potassium, Sodium, Calcium, Magnesium, Iron, and Man- ganese. The description given of these elements and of their most important compounds in “ How Crops Grow ” will suffice. It is only needful to notice further a single element. Aluminillll) Symbol Al., At. wt. 27.4, is a bluish silver- Avliite metal, characterized by its remarkable lightness, having about the specific gravity of glass. It is now manufactured on a somewhat large scale in Paris and New- castle, and is employed in jeweliy and ornamental work. It 5s prepared by a costly and complex process invented by Prof. Deville, of Paris, in 1854, which consists essen- tially in decomposing chloride of aluminum by metallic sodium, at a high heat, chloride of sodium (common salt) and metallic aluminum being produced, as shown by the equation, Al^ Clg -f- 6 Na = GNaCl + 2 Al. By combining with oxygen, this metal yields but one oxide, which, like the highest oxide of iron, is a sesqui- oxide, viz.: Alumina^ Al^ O^, Eq. 102 . 8 . — When alum (double sul- phate of alumina and potash) is dissolved in water and ammonia added to the solution, a white gelatinous body separates, which is alumina combined with water, Al^ O 3 , 3 H^O. By drying and strongly heating this hydrated alumina, a white powder remains, which is pure alumina. 108 HOW CROPS FEED. In nature alumina is found in the form of emery. The sapphire and ruby are finely colored crystallized varieties of alumin:i, highly prized as gems. Hydrated alumina dissolves in acids, yielding a numer- ous class of salts, of which the sulphate and acetate are largely employed in dyeing and calico-printing. The sul- phate of alumina and potash is familiarly known under the name of alum, with which all are acquainted. Other compounds of alumina will be noticed presently. 2. MINERALOGICAL ELEMENTS OF PvOCKS. The miner.ilogic.il elements or minerals* which compose rocks are very numerous. But little conception can be gained of the appearance of :i mineral from a description alone. Actual inspection of the different varieties is necessary to enable one to rec- ognize them. The teacher should be provided with a collection to illustrate this subject. The true idea of their composition and use in forming rocks and soils may be gathered quite well, however, from the written page. For minute information concerning them, see Dana’s Manual of Mineralogy. We shall notice the most important. Quartz. — Chemically speaking, this mineral is anhy- drous silica — silicic acid — a compound of silicon and ox- ygen, Si O^. It is one of the most abundant substances met with on the earth’s surface. It is found in nature in six-sided crystals, and in irregular masses. It is usu.ally colorless, or white, irregular in fracture, glassy in luster. It is very hard, readily scratching glass. (See H. C. G., p. 120.) Feldspar (field-spar) is, next to quartz, the most abund- * The word mineral, or mineral “species,” here implit's a definite chemical compound of natural occurrence. ORIGIJiT AND FORMATION OF SOILS. 109 ant mineral. It is a compound of silica with alumina^ and with one or more of the alkalies^ and sometimes vnth lime. Mineralogists distinguish several species of feld- spar according to their composition and crystallization. Feldspar is found in crystals or crystalline masses usually of a white, yellow, on- flesh color, with a somewhat pearly luster on the smooth and level surfaces which it presents on fracture. It is scratched by, and does not scratch quartz. In the subjdned Table are given the mineralogical names and analyses of the principal varieties of feldspar. Ac- companying each analysis is its locality and the name of the analyst. Orthoclase. Albite. Oligoclase. Labradorite. Common, or potash Soda feldspar. Soda-lime feldspar. Lime-soda feldspar. New Rochelle, N. Y. Unionville. Pa. feldspar. Iladdam, Conn. Drummond, C. W. S. W. Johnson. M. C. Weld. G. J. Brush. T. S. Hunt. Silica, 64.23 66.86 64.26 54.70 Alumina, 20.42 21.80 21.00 29.80 Potash, 12. 4T — 0.50 0.33 Soda, 2.62 8.78 9 90 2.44 Lime, trace 1.70 2.15 11.42 Ma;;nesia, 0.48 — — Oxide of iron, trace — — 0.36 Water, 0.24 0.48 0.29 0.40 • Mica is, perhaps, next to feldspar, the most abundant mineral. There are three principal varieties, viz.: Musco- vite, Phlogopite, and Biotite. They are silicates of alumi- na with potash, magnesia, lime, iron, and manganese. Mica bears the common name ‘‘isinglass.” It readily splits into thin, elastic plates or leaves, has a brilliant luster, and a great variety of colors, — white, yellow, brown, green, and black. Muscovite,, or muscovy glass, is some- times found in transparent sheets of great size, and is used in stove-doors and lamp-chimneys. It contains much alumina, and potash, or soda, and the black varieties oxide of iron. Phlogopite and Biotite contain a large percentage of magnesia, and often of oxide of iron. th t 110 now CROPS FEED. The following analyses represent these varieties. Muscovite. Phlogopite. Biotite. Litchfield, Mt.Leinster, Edwards, N. Burgess, Putnam Co., Conn. Ireland. N. Y. Canada. N. Y. Siberia Smith & Brush. Haughton. W.J.Craw. T.S.Hunt. Smith & Brush. H. Rose. Silica, 44. GO 44.64 40.36 40.97 39.62 40.00 Alumina, 3G.23 30.18 16.45 18.56 17.35 12.67 Oxide of iron, 1..34 6.35 trace — 5.40 19.03 Oxide of 0.63 manganese Magnesia, 0.37 0.72 29.55 25.80 23.85 15.70 Lime, 0.50 — — — — Potash, 6.20 12.40 7.23 8.26 8.95 5.61 Soda, 4.10 , 4.94 1.08 1.01 — Water, 5.20 5.32 0.95 1.00 1.41 — Variable Composition of Minerals.- — We notice in the micas that two analyses of the same species differ very considerably in the proportion, and to some extent in the kind, of their ingredients. Of the two muscovites the first contains more of alumina than the second, while the second contains more of oxide of iron than the first. Again, the second contains 12.4® 1^, of potash, but no soda and no lime, while the first reveals on analysis 4®| of soda and 0.5® of lime, and contains correspondingly less potash. Similar differences are remarked in the other anal- yses, especially in those of Biotite. In fact, of the analyse s of more than 50 micas which are given in mineral ogical treatises, scarcely any two per- fectly agree. The same is true of many other minerals, especially of the amphiboles and pyroxenes presently to be noticed. In accordance with this variation in composition we notice extraordinary diversities in the color and ap- pearance of different specimens of the same mineral. This fact may appear to stand in contradiction to the statement above made that these minerals are definite ^ combinations. In the infancy of mineralogy great per- plexity arose from the numerous varieties of minerals that were found — varieties that agreed together in certain char- acteristics, but widely differed in others. OPwIGIN AND FORMATION OF SOILS. Ill Isomorphism* — In 1830, Mitscherlich, a Prussian phi- losopher, discovered tliat a number of the elementary bodies are capable of replacing each other in combination^ from the fact of their natural crystalline form being identic- al ; they being, as he termed it, ieomorphous^ or of like shape. Thus, magnesia, lime, protoxide of iron, protoxide of manganese, which are all protoxide-bases^ form one group, each of wliose members may take the place of the other. Alumina (Ab O 3 ) and oxide of iron (Fe^ O 3 ) be- long to another group of sesquioxide-hases., one of which may replace the other; while in certain combinations silica and alumina replace each other as acids. These replacements, which may take place indefinitely within certain limits, thus may greatly afifect the composi- tion without altering the constitution of a mineral. Of the mineral amphihole., for example, there are known a great number of varieties; some pure white in color, con- taining, in addition to silica, magnesia and lime; others pale green, a small portion of magnesia being replaced by^ protoxide of iron ; others black, containing alumina in place of a portion of silica, and with oxides of iron and mmiganese in large proportion. All these varieties of amphibole, however, admit of one expression of their constitution, for the amount of oxygen in the bases, no matter what they are, or what their proportions, bears a constant relation to the oxygen of the silica (and alumina) they contain, the ratio being 1 : 2 . If the protoxides be grouped together under the gen- eral symbol MO (metallic i)rotoxide,) the composition of the amphiboles may be expressed by the formula MO SiO^. In pyroxene the same replacements of protoxide-bases on the one hand, and of silica and alumina on the other, occur in extreme range. (See analyses, p. 112 .) The gen- eral formula which includes all the varieties of pyroxene is the same as that of amphibole. The distinction of am- phibole from pyroxene is one of crystallization. 112 now CROPS FEED. We might give in the same style formulae for all the minerals noticed in these pages, but for our purposes this is unnecessary. AmphibolC is an abundant mineral often met Avith in distinct crystals or crystalline and fibrous masses, varying in color from pure white or gray (tremolite^ asbestus)^ light green (actl7iolite)^ grayish or brownish green [mithophyl- Ute))^ to dark green and black (hornblende)^ according as it contains more or less oxides of iron and manganese. It is a silicate of magnesia and lime, or of magnesia and protoxide of iron, with more or less alkalies. Wiite. Gray. Ash-gray. Black. Leek green Gouveriieur, Lanark, Cummington , Brevig, Waldheim N. Y. ■ Canada. Mass. Norway. Saxony. Raramelsberg. T. S. Hunt. Smith & Brush. Plantamour. Knop. Silica, 57.40 55.30 50.74 46.57 58.71 Magnesia, 24.69 22.50 10.31 5.88 10.01 Lime, Protoxide of 13.89 13.36 trace 5.91 11.53 iron. 1.36 6.30 as. 14 24.38 5.65 Protoxide of trace 1.77 2.07 manganese. Alumina, 1.38 0.40 0.89 3.41 1.52 Soda, — 0.80 0.54 7.79 12.38 Potash, — 0.25 trace 2.96 — Water, 0.40 0.30 3.04 — 0.50 Pyroxene is of very common occurrence, and consider- ably resembles hornblende in colors and in composition. White. Gray- White. Green. Black. Black. Ottawa, Bathurst, Lake Orange Co., Wetterau, Canada. Canada. Champlain. N. Y. T. S. Hunt. T. S. Hunt. Seybert. Smith & Brush. Gmelin. Silica, 54.50 51.50 50.38 39.30 56.80 Magnesia, 18.14 17.69 6.83 GO 5.05 Lime, 25.87 23.80 19. 10.39 4.85 Protoxide 1.98 20.40 30.40 12.06 of iron. r Sesquioxide 0.35 of iron. Protoxide of trace 0.67 8.72 manganese. Alumina, 6.15 1.83 9.78 15.32 Soda, — — — 1.66 3.14 Potash, — — — 2.48 0.34 Water, 0.40 1.10 — ] 95 — ORIGIN AND FORMATION OF SOILS. 113 Chlorite is a common mineral occurring in small scales or plates whicli nre brittle. It is soft, usually exists in masses, rarely crystallized, and is very variable in color and composition, thongli in general it has a grayish or brownish-green color, and contains magnesia, alumina, and iron, united with silica. See analysis below. Lcucite is an anhydrous silicate of alumina found chiefly in volcanic rocks. It exists in white, hard, 24-sid- ed crystals. It is interesting as being formed at a high heat in melted lava, and as being the first mineral in which potash was discovered (by Klaproth, in 1797). See anal- ysis below. Kaolinite is a hydrous silicate of alumina, which is 23rodaced by the slow decomposition of feldspar under the action of air and water at the usual temperature. Form- ed in this way, in a more or less impure state, it consti- tutes the mass of white porcelain clay or kaolin, which is largely used in making the finer kinds of pottery. It ap- ])ears in white or yellowish crystalline scales of a pearly luster, or as an amorphous translucent powder of extreme fineness. Ordinary clay is a still more impure kaolinite. Chlorite. Leucite, Kaolinite. Steele Mine, N Geiitli. Silica, ^.90 Alumina, 21.77 Sesquioxide of iron, 4.00 Protoxide of iron, 24.21 Protoxide of man<^anese, 1.15 Magnesia, 12.78 Lime, Soda, Potash, Water, 10.59 Talc is often found in pale-green, flexible, inelastic scales or leaves, but much more commonly in compact gray masses, and is then known as soapstone. It is very soft, C. Vesuvius, Summit Hill, Chaudiere Eruption of 1^57. Pa, Falls. Canada. Rammelsberg. S. W. Johnson. T. S. Hunt. 57.24 45.93 46.05 22.96 39.81 38.37 0.63 0.91 0.61 0.93 18. 6i 14.02 14.00 114 now CROPS FEED. has a greasy feel, and in composition is a hydrous silicate of magnesia. See analysis. Serpentine is a tough but soft massive mineral, in color usually of some shade of green. It forms immense beds in New England, New York, Pennsylvania, etc. It is also a hydrous silicate of magnesia. See analysis. Chrysolite is a silicate of magnesia and iron, which is found abundantly in lavas and basaltic rocks. It is a hard, glassy mineral, usually of an olive or brown-green color. See a nalysis below. . Tai.c. Serpentine. Chrysolite. Bristol, Conn. New Haven, Conn. Bolton. Mass. Dr. Lnmmis. G. J. Brush. G. J. Brn'sh. (i4.oa 44.06 40.94 — — 0.27 xidc of iron, , 4.T5 2.53 4 37 .agnesia. 2T.4T S9.24 50.84 Lime, — — 1.20 Water, 4.30 13.49 3.28 Zeolites# — Under this general name mineralogists are in the habit of including a number of minerals which have recently acquired considerable agricultural interest, since they represent certain compounds which we have strong reasons to believe are formed in and greatly influence the properties of soils. They are hydrous silicates of alum- ina or lime, and alkali, and are remarkable for the ease with which they undergo decomposition under the influ- ence of weak acids. We give here the names and compo- sition of the most common zeolites. Their special signif- icance will come under notice hereafter. We may add that while they all occur in white or red crystallizations, often of great beauty, they likewise exist in a state of division so minute that the eye cannot recognize them, and thus form a large share of certain rocks, which, by their disintegration, give origin to very fertile soils ORIGIN AND FORMATION OF SOILS. 115 k Analcime. Chabasite. Natrobite. Scolecite. Thomsonite. Lake Superior. Nova Scotia. Bergen Hill, Ghaut’s Tun Magnet N. J. nel, India. Cove, Ark. C. T. Jackson. Rammelsherg. Brush. P. Collier. Smith & Bmsh Silica, 53.40 52.14 47.31 45.80 36.85 Alumina, , 22.40 19.14 26.77 25 . 55 29.42 Potash, — 0.98 0.35 0.30 — Soda, 8.52 0.71 15.44 0.17 3.91 Lime, 3.00 7.84 0.41 13.97 13.95 Magnesia, — — — — Sesquioxide of iron. — — — 1.55 Water, i).70 19.19 9.84 14.28 13.80 Stilbite. Apophyllite. Pectolite. Laumontite Leonhardite Nova Scotia. Lake Superior. S. W. Johnson. J. L. Smith. J. Bergen Hill. Phippsburgh, Me. Lake Sup’r , D. Whitney. Dufrenoy. Barnes. Silica, 57.63 52.08 55.66 51.98 55.01 Alumina, 16.17 — 1.45 21.12 22.34 Potash, — 4.93 — — — Soda, 1.55 — 8.89 — — Lime, 8.08 25.30 32.86 11.71 10 64 16.07 15.92 2.96 15.05 11.93 Calcite, or Carbonate of Lime^ CaO CO^, exists in na- ture in immense quantities as a mineral and rock. Mar- ble, chalk, coral, limestone in numberless varieties, consist of this substance in a greater or less state of purity. Magnesite^ or Carbonate of Magnesia^ MgO CO^, oc- curs to a limited extent as a white massive or crystallized mineral, resembling carbonate of lime. Dolomite^ CaO CO^ + MgO CO„, is a compound of car-, bonate of lime with carbonate of magnesia in variable proportions. It is found as a crystallized mineral, and is a very common rock, many so-called marbles and lime- stones consisting of or containing this mineral. O O Gypsum, orHydrous Sulphate of Lime^ CaO SO3 + H^O. is a mineral that is widely distributed and quite abundant in nature. When “boiled” to expel the water it is Plaster of Paris. Pyrites, or Bisulphide of Iron^ Fe S^, a yellow shining mineral often found in cubic or octahedral crystals, and frequently mistaken for gold (hence called fool’s gold), 116 now ( ROI'S FEED. is of almost universal occurrence in small quantities. Some forms of it easily oxidize when exposed to air, and furnish the green-vitriol (sulphate of protoxide of iron) of com- merce. Apatite and Phosphorite. — These names are applied to the native phosphate of lim(‘, which is usually combined with some chlorine and fluorine, and may besides contain other ingredients. Apatite exists in considerable quantity at Hammond and Gouverneur, in St. Lawrence Co., N. Y., in beautiful, transparent, green crystals ; at South Burgess, Canada, in green crystals and crystalline masses ; at Hnrdstown, N. J., in yellow crystalline masses ; at Krageroe, Norway, in opaque flesh-colored crystals. In minute quantity apatite is of nearly universal distribution. The following analyses exhibit the composition of the principal varieties. Krageroe, Hnrdstown, Norway. New Jersey. Voelcker. J. D. Whitney. Lime, 53.84 53.37 Phosphoric acid. 41.25 42.23 Chlorine, 4.10 1.02 Fluorine,* 1.23? ? Oxide of iron. 0.29 trace Alumina, 0.38 Potash and soda, 0.17 W ater, 0.42 Phos[)horite is the usual designation of the non-crystal- line varieties. Apatite may be regarded as a mixture in indefinite proportions of two isoinorphous compounds, chlorapatite flicorapatite^ neither of which has yet been found pure in nature, though they have been produced artificially. * Fluorine was not determined in these analyses. The fli^ures given for this element are calculated (by Rammelsberg), and are probably not far from the truth. ORIGIN AND FORMATION OF SOILS. 117 These suhstariccs are again conjpounds of phosphate of lime, 3 CaO with chloride of calcium, Ca Cl^, or fluoride of calcium, Ca Fl^, respectively. § 3 . EOCKS-THEIR KINDS AND CHARACTERS. The Rocks which form tlie solid (unbroken) mass of the earth are sometimes formc^d from a single mineral, but usually contain several minerals in a state of more or less intimate mixture. We shall briefly notice those rocks which liave the greatest agricultural importance, on account of their com- mon and wide-spread occurrence, and shall regard tliem principally from the point of view of their chemical corm position^ since this is chiefly the clue to their agricultural significance. Some consideration of the origin of rocks, as well as of their structure^ will also be of service. Igneous Rocks. — A share of the rocks accessible to our observation are plainly of igneous origin^ i. e., tReir existing form is the one they assumed on cooling down from a state of fusion by heat. Such are the lavas that flow from v;)^canic craters. Sedimentary Rocks. — xVnother share of the rocks are of aqueous origin^ i. e., their materials have been deposit- ed from water in the form of mud, sand, or gravel, the loose sediment having been afterwards cemented and con- solidated to rock. The rocks of aqueous origin are also termed sedimentary rocks, Mctamorphic Rocks. — Still another share of the rocks have resulted from the alteration of aqueous sediments or sedimentary rocks by the effect of heat. Without suffer- ing fusion, the original ma:erials have been more or less converted into new combinations or new forms. Thus limestone has been converted into statuary marble, and 118 HOW CROPS FEED. clay i:i.o granite. These rocks, which are the result of the united action of heat and water, are termed meta- morphic (i. e., metamorphosed) rocks. One of the most obvious division of rocks is into Crys- talline and Fragmental, Crystalline Rocks are those whose constituents crystal- lized at the time the rock was formed. Here belong both the igneous and metamorphic rocks. Tiiese are often plainly crystalline to the eye, i. e., are composed of readily perceptible crystals or crystalline grains, like statuaiy marble or granite ; but they are also frequently made up of crystals so minute, that the latter are only to be recog- nized by tracing tliem into their coarser varieties (basalt and trap.) Fragiaeillal Rocks are the sedimentary rocks, formed by the cementing of the fragments of other older rocks existing as mud, sand, etc. The Crystalline Rocks may be divided into two great classes, viz., the silicious and calcareous / the first class containing silica, the latter, lime, as the predomina ting ingredient. The silicious rocks fall into three parallel series, which have close relations to each other. 1. The Granitic series ; 2. The Syenitic series ; 3. The Talcose or Magnesian series. In all the silicious rocks quartz or feldspar is a prominent ingredient, and in most cases these two minerals are associated together. To the above are added, in the granitic series, mica ; in the syenitic series, amphibole or pyroxene / and in the talcose series, talc.^ chlorite.^ or se^^ pentine. The proportions of these minerals vary indef- initely. The Granitic Series consisting principally of Quartz^ Feldspar.^ and Mica. Granite. — A hard, massive'*' rock, either finely or * Rocks are massive when they have no tendency to split into slabs or plate# ORIGIN AND FORMATION OF SOILS. 119 coarsely crystalline, of various shades of color, depending on the color and proportion of the constituent minerals, usually gray, grayish white, or flesh-red. In common granite the feldspar is orthoclase (potash-feldspar). A variety contains alhite (soda-feldspar). Other kinds (less common) contain oUgoclase and labradorite. Gneiss differs from granite in containing more mica, and in having a handed appearance and schistose * structure, due to the distribution of the mica in more or less parallel layers. It is cleavable along the planes of mica into coarse slabs. Mica-slate or Mica-schist contains a still larger pro- portion of mica than gneiss ; it is perfectly schistose in structure, splitting easily into thin slabs, has a glistening appearance, and, in general, a grayish color. The coarse whetstones used for sharpening scythes, which are quar- ried in Connecticut and Rhode Island, consist of this min- eral. Argillite^ flay-slate, is a rock of flnc texture, often not visibly crystalline', of dull or but slightly glistening surface, and having a great variety of colors, in general black, but not rarely red, green, o^* light gray. Argillite has usually a slaty cleavage^ i. e., it splits into thin and smooth plates. It is extensively quarried in various local- ities for roofing, and writing-slates. Some of the finest varieties are used for whetstones or hones. Other Granitic Rocks. — Sometimes mica is absent ; in other cases the rock consists nearly or entirely oi feldspar alone, or of quartz alone, or of mica and quartz. The rocks of this series offen insensibly gradate into each oth- er, and by admixture of other minerals run into number- less varieties. * Schists or schistose rocks are those which have a tendency to break into slabs or plates from the arrangement of some of the mineral ingredients in layers. 120 now CROPS FEED. The Syenitic Series consisting chiefly of Quartz^ Feldspar^ and Amphibole, Syenite is granite, save that amphibole takes the place of mica. In appearance it is like granite ; its color is usu- ally dark gray. Syenite is a very tough and durable rock, often most valuable for building purposes. The famous Quincy granite of Massachusetts is a syenite. Syenitic Gneiss and Hornblende Schist correspond to common Gneiss and Mica Schist, hornblende taking the place of mica. The Volcanic Series consist' ng of Feldspar^ Amphibole or Pyroxene^ and ZeoUtes. Biorite is a compact, tough, and heavy rock, common- ly greenish-black, brownish-black, or grayish-black in color. It contains amphibole, but no pyroxene, and is an ancient lava. Bolerite or Trap in the fine-grained varieties is scarcely to be distinguished from Diorite by the appearance, and is well exhibited in the Palisades of the Hudson and the East and West Rocks of ISTew Haven. It contains })yrox- ene in place of amphibole. Basalt is like dolerite, but contains grains of chrysolite. The recent lavas of volcanic regions are commonly basaltic in composition, though very light and porous in texture. Porphyry. — Associated with basalt occur some feld- spathic lavas, of which porphyry is common. It consists of a compact base of feldspar, with disseminated crystals of feldspar usually lighter in color than the mass of the rock. Pumice is a vesicular rock, having nearly the composi- tion of feldspar. The Magnesian Series consisting of Quartz^ Feldsp>ar and Talc^ or Chlorite. Talcose Granite differs from common granite in the substitution pf talc for mica. Is a fragile and more easily ORIGIN AND FORMATION OF SOILS. 121 decomposable rock than granite. It passes through talcose gneiss into Talcose Schist^ which resembles mica-schist in colors and in facility of splitting into slabs, but has a less glis- tening luster and a soapy feel. Chloritic Schist resembles talcose schist, but has a less unctuous feel, and is generally of a dark green color. Related to the above are Steatite^ or soapstone^ — nearly pure, granular talc; and Serpentine rock, consisting chiefly of serpentine. The above are the more common and wide-spread si- licious rocks. By the blending together of the different members of each series, and the related members of the different series, and by the introduction of other minernls into their composition, an almost endless variedy of si- licious rocks has been produced. Turning now to the Crystallixe Calcareous Rocks, we liave Granular Limestone, consisting of a nearly pure car- bonate of lime, in more or less coarse grains or crystals, commonly white or gray in color, and having a glistening luster on a freshly broken surface. The finer kinds are employed as monumental marble. Dolomite has all the appearance of granular limestone, but contains a laige (variable) amount of carbonate of magnesia. The Fragmental or Sedimentary Rocks are as fol- lows : Conglomerates have resulted from the consolidation of rather coarse fragments of any kind of rock. According to the nature of the materials composing them, they may be granitic.^ sgenltic.^ calcareous., basaltic., etc., etc. They pass into Sandstones, which consist of small fragments (sand), are generally sillcious in character, and often are nearly 6 122 Jtiuvr CROPS FEED. pure quartz. The freestone of the Connecticut Valley is a granitic sandstone, cont:dning fragments of felds})ar and spangles of mica. Other varieties are calcareous^ argillaceous (clayey)^ basaltic^ etc., etc. Shales are soft, slaty rocks of various colors, gray, green, red, blue, and black. They consist of compacted clay. When crystallized by metamorphic action, they constitute argillite. Limestones of the sedimentary kind are soft, compact, nearly lusterless rocks of various colors, usually gray, blue, or black. They are sometimes nearly pure carbon- ate of lime, but usually contain other substances, and are often highly impure. When containing much carbonate of magnesia they are termed magnesian limestones. They ] ass into sandstones througli intermediate calciferous sand rocks^ and into shales through argillaceous lime- stones. These impure limestones furnish the hydraidic cements of commerce. CONVERSION OF ROCKS INTO SOILS. Soils arc broken and decomposed rocks. We find in nearly ail soils fragments of rock, recognizable as such by the eye, an 1 by help of the microscope it is often easy to perceive that those portions of the soil which are impnlpa- ble to the feel chiefly consist of minuter grains of the same rock. Geology makes probable that the globe was once in a melted condition, and came to its present state through a process of cooling. By loss of heat its exterior surface solidified to a crust of solid rock, totally incapable of sup- porting the life of agricultural plants, being impenetrable to their roots, and destitute of all the other external char- acteristics of a soil. OrjGI^^ AND FOUaIATION of soils. 123 The first step towards tlie formation of a soil must have heeii the pulverization of the* rock. This has leen accom- plished by a variety of agencies acting through long pe- riods of time. The causes which could produce such re- sults are indeed stupendous when contrasted with tlie narrow experience of a single human life, hut are i-eally trifling compared with the magnitude of the earth itself, for the soil forms upon the surface of our globe, whose di- ameter is nearly 8,000 miles, a thin coating of dust, meas- ured in its gr(‘atcst accumulations not by miles, nor scarcely by I'ods, but by feet. The conversion of rocks to soils has been performed, 1st, by Changes of Temperature ; 2(1, by Moving Water or Ice ; 3d, by the Chemical Action of Water and Air ; 4th, by the Influence of Vegetable and Animal Life. 1. — Changes of Tempeeature. The continued cooling of the globe after it had become enveloped in a solid rock-ciust must have been accom- panied by a contraction of its volume. One effect of this shrinkage would have been a subsidence of portions of the crust, and a wrinkling of other portions, thus produc- ing on the one hand sea-basins and valleys, and on the other mountain ranges. Another effect would have been the cracking of the crust itself .‘is the result of its own contraction. The pressure caused by contraction or by mere weight of superincumbent matter doubtless led to the production of the lamin.ated structure of slaty rocks, which may bo readily imitated in wax and clay by aid of an hydraulic press. Basaltic and trap rocks in cooling from fusion often acquire a tendency to separate into vertical columns, ^ somewhat as moist starch splits into five or six-sided frag- ments, when dried. These columns are again transversely jointed. The Giant’s Causeway of Ireland is an illustra- tion. These fractures and joints are, perhaps, the first oc- casion of the breaking down of the rocks. The fact that 124 HOW CROPS FEED. many rocks consist of crystalline grains of distinct min- erals more or less intimately blended, is a point of weak- ness in their structure. The grains of quartz, feldspar, and mica, of a gi*anite, when exposed to changes of tem- perature, must tend to separate from each other; because the extent to which they expand and contract by alterna- tions of heat and cold are not absolutely equal, and be- cause, as Senarmont has proved, the same crystal expands or contracts unequally in its different diameters. Action of Freezing Water, — It is, however, when wa- ter insinuates itself into the slight or even imperceptible rifts thus opened, and then freezes, that the process of dis- integration becomes more rapid and more vigorous. Wa- ter in the act of conversion into ice expands tV of its bulk, and the force thus exerted is sufficient to burst vessels of the strongest materials. In cold latitudes or altitudes this agency working through many years accomplishes stupen- dous results. The adventurous explorer in tlie higher Swiss Alps fre- quently sees or hears the fall of fragments of rock thus loosened from the peaks. Along the base of the vertical trap cliffs of N'ew Haven and the Hudson River, lie immense masses of broken rock reaching to more than half the height of the bluffs them- selves, rent off by this means. The same cause operates in a less conspicuous but not less important way on the surface of the stone, loosening the minute grains, as in the above instances it rends off enormous blocks. A smooth, clean pebble of the very compact Jura limestone, of such kind, for example, as abound in the rivers of South Bavaria, if moistened with water and exposed over night to sharp frost, on thawing, is muddy with the de- tached particles. 2. — Moving Water or Ice. Changes of temperature not only have created differ- ences of level in the earth’s surface, but they cause a con- ORIGi:: AND FORMATION OF SOILS. 125 tinuul transfer of water from lower to higher levels. The elevated hinds are cooler than the valleys. In their re- gion occurs a continual condensation of vapor from the atmosphere, which is as continually supplied from the heated valleys. In the mountains, thus begin, as rills, the streams of water, which, gathering volume in their descent, unite below to vast rivers that flow unceasingly into the ocean. These streams score their channels into tiie firmest rocks. Each grain of loosened material, as carried downward by the current, cuts the rock along which it is dragged so long as it is in motion. The sides of the channel being undermined and loosen- ed by exposure to the frosts, fall into the stream. In time of floods, and always, when the path of the river has a rapid descent, the mere momentum of the water acts pow- erfully upon any inequalities of surface that oppose its course, tearing away the rocky walls of its channel. The blocks and grains of stone, thus set in motion, grind each other to smaller fragments, and when the turbid waters clear themselves in a lake or estuary, there results a bed of gravel, sand, or soil. Two hundred and sixty years ago, the bed of the Sicilian river Simeto was obstructed by the flow across it of a stream of lava from Etna. Since that time the river, with but slight descent, has cut a chan- nel through this hard basalt from fifty to several hundred feet wide, and in some parts forty to fifty deep. But the action of water in pulverizing rock is not com- pleted when it reaches the sea. The oceans are in perpet- ual agitation from tides, wind-waves, and currents like the Gulf-stream, and work continual changes on their shores. Glaciers. — What happens from the rajDid flow of water down the sides of mountain slopes below the frost-line is also true of the streams of ice which more slowly descend from the frozen summits. The glaciers appear like motion- 126 IIOV/ CROPS FEED. less ice-iields, but tliey are frozen rivers, rising in perpet> ual snows and melting into water, after having reached half a mile or a mile below the limits of frost. The snow that accumulates on the frozen peaks of high mountains, which are bathed by moist winds, descends the slopes by its own weight. The rate of descent is slow, — a few inches, or, at the most, a few feet, daily. The motion it- self is not continuous, but intermittent by a succession of pushes. In the gorges, where many smaller glaciers unite, the mass has often a depth of a mile or more. Under the pressure of accumulation the snow is compacted to ice. Mingled with the snows are masses of rock broken off the higher pinnacles by the weight of adhering ice, or loosened by alternate freezing and thawing, below the line of perpetual frost. The rocks thus falling on the edge of a glacier become a part of the latter, and partake its mo- tion. When the movino: mass bends over a convex sur- face, it cracks vertically to a great depth. Into the cre- vasses thus formed blocks of stone fall to the bottom, and water melted from the surface in hot days flows down rmd finds a channel beneath the ice. The middle of the glacis r moves most rapidly, the sides and bottom being retarded by fi-iction. The ice is thus rubbed an 1 rolled upon itself, and the stones imbedded in it crush and grind each other to smaller fragments and to dust. The rocky bed of the glacier is broken, and ploughed by the stones frozen into its sides and bottom. The glacier thus moves until it descends so low that ice cannot exist, and gradually dis- solves into a torrent whose waters are always thick with mud, and whose course is strewn with worn blocks of stone (boulders) for many miles. The Rhone, which is chiefly fed from the glaciers of the Alps, transports such a volume of rock-dust that its muddy waters may be traced for six or seven miles after they have poured themselves into the Mediterranean. 3. — Chemical Action of Water and Air. ORIGIN AND FORMATION OF SOILS. 127 Water acts chemically upon rocks, or rather upon their constituent minerals, in two ways, viz., hy Combination and Solution, Hydration# — By chemically uniting itself to the mineral or to some ingredient of the mineral, there is formed i i many instances a new componnd, which, by being softer and more bulky than the original substance, is the first step towards further change. Mien, feldsp.nr, amphibole, and pyroxene, are minerals whicli have been artificially produced in the slags or linings of smelting furnacc^s, and thus formed they l.ave been found totally destitute of wa- ter, as might be expected from the high temperature i t which they originated. Tet these minerals as occurring in nature, even when broken out of blocks of apparently unaltered rock, and especially when they have been di- rectly exposed to the weather, often, if not always, con- tain a small amount of water, in chemical combinatio.i (water of hydration). Solution. — As a solvent, water exercises the most im- portant influence in disintegrating minerals. Apatite, when containing much chlorine, is gradually decomposed by treatment with water, chloride of calcium, which is very soluble, being separated from the nearly insoluble pliosphate of lime. The minerals which compose silicious rocks are all acted on perceptibly by pure water. This is readily observed when the minerals a-.-e employed in the state of fine powder. If i)ulverized feldspar, amphibole, etc., are simply moistened with pure water, the latter at ■ once dissolves a trace of alkali, as shown by its turning red litmus-paper blue. This solvent action is so slight upon a smooth mass of the mineral as hardly to be per- ceptible, because the action is limited by the extent of surface. Pulverization, wliich increases the surfiice enor- mously, increases the solvent effect in a similar proportion. A glass vessel may have water boiled in it for hours with- out its luster being dimmed or its surface materially acted 128 HOW CROPS FEED. upon, whereas the same glass fint4y pulverized is attack- ed by water so readily as to give at once a solution alka- line to the taste. Messrs. W. B. and R. E. Rogers (Mm. Jour, ySci., V, 404, 1848) found that by continued digestion of pure water for a week, with powdered feldspar, horn- blende, chlorite, serpentine, and natrolite,f these minerals yielded to the solvent from 0.4 to 1 per cent of their weight. In nature we never deal with pure water, but with wa- ter holding in solution various matters, either derived from the air or from the soil. These substances modify, and in most cases enhance, the solvent power of water. Action of Carbonic Acid. — This gaseous substance is absorbt‘d by or dissolved in all natural waters to a greater /or less extent. At com mon ^t ^iaperatures and pressure f water is capable of taking up its own bulk of the gas. At lower temperatures, and under increased pressure, the ^ quantity dissolved is much greater. Carbonated watei\ as we may designate this solution, has a high solvent power on the carbonates of lime, magnesia, protoxide of iron, and protoxide of manganese. The salts just named are as good as insoluble in pure water, but they exist in considerable quantities in most natural waters. The spring and well waters of limestone regions are hard on account of their content of carbonate of lime./^ C halvb- cate waters, are those which hold carbonate of iron in solution. When carbonated water comes in contact with silicious minerals, these are decomposed much more rapidly than by pure water. The lime, magnesia, and iron they contain, are partially removed in the form of carbonates. Struve exposed powdered phonolite (a rock composed of feldspar and zeolites) to water saturated with carbonic * Glass is a silicate of potash or soda, t Mcsotype. ORIGIN AND FORMATION OF SOILS. 120 acid under a pressure of 3 atmospheres, and obtained a solution of which a pound * contained : Carbonate of soda. 22.0 grains. Chloride of sodium, 2.0 a Sulphate of potash, 1.7 (C “ soda. 4.8 u Carbonate of lime. 4.5 u ‘‘ “ magnesia. 1.1 (C Silica, 0.5 cc Phosohoric acid and manganese. traces Total, 37.1 grains. In various natural springs, water comes to the surface so charged with carbonic acid that the latter escapes copiously in bubbles. Such waters dissolve large quantities of mineral matters from the rocks through which they emerge. Examples are seen in the springs at Saratoga, I^. Y. According to Prof. Chandler, the “ Saratoga Spring,” whose waters issue directly from the rock, con- tains in one gallon of 231 cubic inches : Chloride of Sodium (common salt) 398.361 grains. “ “ Potassium, 9.698 a Bromide of Sodium, 0.571 4i Iodide of Sodium, 0.126 (( Sulphate of Potash, 5.400 u Carbonate of Lime, 86.483 (( “ “ Magnesia, 41.050 il “ “ Soda, 8.948 (1 “ “ Protoxide of iron. .879 a Silica, ’ 1.283 Phosphate of lime, trace a Solid matters, 552.799 Carbonic acid gas, (407.647 cubic inches at 52° Fah.) Water, 58,317.110 “ The waters of ordinary springs and rivers, as well as those that fall upon the earth’s surface as rain, are, indeed. * The Saxon pound contains 7,680 Saxon grains. 6 * 130 now CROPS FEED. by no means fully charged with carbonic acid, and tlieir solvent elfect is much less than that exerted by water sat- urated with this gas. The quantity (by volume) of carbonic acid in 10,000 parts of rain-water has been observed as follows: Accord- ing to Lampadiiis, Mulder, Von Baumbauer, Peli^ot, Locality. 8 Country near Freiberg, Saxony. 20 City of Utrecht, Holland. . 40 to 90 “ “ 5 ? The quantities found are variable, as might be expected, and we notice that the largest proportion above cited does not even amount to one per cent. In river and spring water the quontities are somewhat larger, but the cai bonic acid exists chiefly in chemical com- bination as bicarbonates of lime, magnesia, etc. In the capillary water of soils contaii^ing ranch organic matters, more carbonic acid is dissolved. According to a single observation of De Saussnre’s, such water contains 2®| Q of the gas. In a subsequent paragraph, p. 221, is given the reason of the small content of carbonic acid in these v/aters. The weaker action of these dilute solutions, when con- tinued through long periods of time and extending over an immense surface, nevertheless accomplishes results of vast significance. Solutions of Alkali-Salts. — Rain-water, as we liave already seen, contains a minute quantity of salts of am- monia (nitrate and bicarbonate). The water of springs and rivers acquires from the rocks and soil, salts of soda and potash, of lime and magnesia. These solutions, dilute though they are, greatly surpass j)ure water, or even car- bonated water, in their solvent and disintegrating action. Phos])hate of lime, the eartli of bones, is dissolved by pure water to an extent that is hardly appreciable; in ORIGIN AND F0R:^IATI0N OF SOILS. 131 salts of ammonia and of soda, however, it is taken np in considerable quantity. Solution of nitrate of amm onia dissolves lime and magnesia and their carbonates with ^^reat ease.YTS^^g^neral, up to a certain limit, a saline so- / lution acquires increased solvent power by increase in the I amount and number of dissolved matters. This import- ant fact is one to which we shall recui Action of Oxygen. — This element. chemical changes, which is present so largely in the at- mosphere, has a strong tendency to imite with certain bodies whicli are almost universally distributed in tlie rocks. On turning to the analyses of minerals, p. 110, we notice in nearly every instance a quantity of protoxide of iron, or protoxide of manganese. The green, dark gray, or black minerals, as the micas, amphibole, pyroxene, chlorite, talc, and serpentine, invariably contain these prot- oxides in notable proportion. In the fe dspars they exist, indeed, in very minute quantity, but are almost never en- tirely vranting. Sulphide of iron (iron pyrites), in many of its forms, is also disposed to oxidize its sulphur to sul- phuric acid, its iron to sesquioxide, and this mineral is widely distributed as an admixture in many rocks. In trap O ’ basaltic rocks, as at Bergen Hill, metallic iron is said to occur in minute proportion,* and in a state of fine division. The oxidation of these substances materially hastens the disintegration of the rocks containing them, since the higher oxides of iron and of manganese occupy ino! e space than the metals or lower oxides. This fact is well illustrated by the sulphate of protoxirle of iron (cop- ])eras, or green-vitriol), which, on long keeping, exposed to the air, is converted from transparent, glassy, green crys- tals to a bulky, brown, opaque powder of sulphate of sesquioxide of iron. Weathering. — The conjoined influence of water, car;: * This statement rests oil the authority of Professor Henry Wurtz, of New York. 132 HOW CROPS FEED. b piiic ac id, oxygen, and the sal ts held in solution by the atmospheric waters, is expressed by the word ueathering. This term may likewise include the action of fbo&t. When rocks weather, they are decmaposed or dj s^solved^ and new compounds, or new forms of tlie original mat- ter, result. The soil is a mixture of broken or pulverized rocks, with the products of their alteration by weathering. a. Weathering* of Quartz Rock* — Quartz (silicic acid), as occurring nearly pure in quartzite, and in many sand- stones, or as a chief ingredient of all the granitic, horn- blendic, and many other rocks, is so exceedingly hard and insoluble, that the lifetime of a man is not sufficient for the direct observation of any change in it, when it is ex- ]K)sed to ordinary weathering. It is, in fact, the least destructible of the mineral elements of the globe. Never- theless, quartz, even when pure, is not ab^liitely insoluble, particularly in water containing alkali carbonates or sili- cates. In its less pure v arieties, and especially when as- sociated with readily decomposable minerals, it is acted on mo re rapidly . The quartz of granitic rocks is usually roughened on the surface when it has long been exposed to the weather. b. The Feldspars weather much more easily than quartz, thougii there are great differences among them. The soda jmd ffim^ feldspars deconipose ^most readily, while the potash feldspars are often exceedingly durable. The decomposition results in completely breaking up the liard, glassy mineral. In its place there remains a wffiite cr yellowish mass, which is so soft as to admit of crush- ing betAV cen the fingers, and which, though usually, to the naked eye, opaque, and non-crystalline, is often seen, under a pow'crful magnifier, to contain numerous transparent crys- talline plates. The mass consists principally of the crys- talline mineral, haglmite^ aJhy drated-silieftte-of til uirii na, (the analysis of which has been given already, p. 113,) mixed OmGIN AXD FORMATION OF SOILS. 133 with liydrated silicM,a])d often with grains of undecompos- ed mineral. If we compare the composition of pure pot- ash feldspar with that of kaolinite, assuming, Avhat is probably true, that all the alumina of the former remains in the latter, we find Avhat portions of the feldspar have bi^en removed and Avaslied aAvay by the water, which, to- gether Avith carbonic acid, is the agent of this change. Feldspar. Kaolinite. Liberated. Added. Alurnlna 18 3 18 3 0 Silica 64.8 23.0 41.8 Potash 16.9 16.9 Water 6.4 . 6 4 100 47.7 58.7 6.4 It thus appears that, in the complete conversion of 100 parts of potash feldsj)ar into kaolinite, there result 47.7 parts of the latter, Avhile 58.7“ of the feldspar, viz : 41.8“ of silica and 16.9“ of potash, are dissolved out. The potash, and, in case of other feldspars, soda, lime, and magnesia, are dissolved as carbonates. If much Avater has access during the decomposition, all the liberated silica is carried away.^ It usually happens, hoAvever, tliat a por- tion of the silica is retained in the kaolin (perhaps in a manner similar to that in AA'hich bone charcoal retains the coloring matters of crude sugar). The same is true of a portion of the alkali, lime, and oxide of iron, which may have existed in the original feldspar. The formation of kaolin may be often observed in na- ture. In mines, excavated in feldspathic i*ocks, the fis- sures and cavities through which surface Avater finds its Avay downwards are often coated or filled Avith this sub- stance. c. Other Silicious Minerals, as Leucite, ( Topaz. Scapo- 11 te,) etc., yield kaolin by decomposition. It is probable that the micas, which decompose with difficulty, (phlogo- * We have seen (H 0. G., p. 121) that silica, when newly set free from combi- natioDvis, at first, freely soluble in water. £5>vV 134 HOW CROPS FEED, pite, perhaps, excepted,) and the amphiboles and pyrox ! ^es , which are often easily disintegrated, also yield kaolin ; but in tlie case of these latter minerals, the result- ing kaolin ite is largely mixed with oxides and silicates of iron and manganese, so that its properties are modified, and identification is difficult. Other hydrated silicates of alumina, closely allied to kaolinite, appear to be formed in the decomposition of compound silicates. Ordinary Clays, as pipe-clay, blue-clay, brick-clay, etc., are mixtures of Jk^bnite, or of a similar hydrated silicate of alumina, with a variety of other substances, as free silica, oxides, and silicates of iron and manganese, carbon- ate of lime, and fi-agments or fine powder of undecom- posed minerals. Fresenius deduces from his analyses of several Nassau clays the existence in them of a compound having the symbol Al^ 3 SiO^-hH^O, and the follow- ing composition per cent. Silica, 57.14 Alumina, 31.72 Water, 11.14 100.00 Other chemists have assumed the existence of hydrated silicates of alumina of still different composition in clays, but kaolinite is the only one which occurs in a pure state, as indicated by its crystallization, and the existence of the others is not perfectly established. (S. W. Johnson and J. M. Blake on Kaolinite^ etc.^ Am. Jour. May.^ 1867, pp. 351-362.) d. The Zeolites readily suffer change by weathering ; little is known, however, as to the details of their disinte- gration. Instead of yielding kaolinite, they appear to be transformed into other zeolites, or retain something of their original chemical constitution, although mechanic-ally dis- integrated or dissolved. We shall see hereafter that there ORIGIN AND FORMATION OF SOILS. 135 is strong reason to assume the existence of compounds analogous to zeolites in every soil. e. Serpentine and Sla^nesian Silicates are generally slow of decomposition, and yield a meager soil. f. The Limestones^ when pure and com|)act, are very durable : as they become broken, or when impuie, they often yield rapidly to the weather, and impregnate tlie streams which flow over them with carbonate of lime. g. Argillite and Argillaceous Limestones, which have resulted from the solidification of clays, readily yield clay again, either by simple pulverization or by pulverization and weathering, according as they have suftefed more or less change by metamorphism. tNCORPORATION OF ORGANIC MATTER WITH THE SOIL AND ITS EFFECTS. Antiquity of Vegetation. — Geological observations lead to the conclusion that but small portions of the earth’s surface-rocks were formed previous to the existence of vegetation. The enormous tracts of coal found in every quarter of the globe are but the residues of preadamite forests, while in the oldest stratified rocks the remains of plants (marine) are either most distinctly traced, or the abundance of animal forms warrants us in assuming the existence of vegetation previous to their deposition. The Development of Vegetation on a purely Mineral Soil. — The mode in which the original inorganic soil be- came more or less impregnated with organic matter may be illustrated by what has happened in recent years upon the streams of lava that have issued from volcanoes. The lava flows from the crater as red-hot molten rock, often in masses of such depth and extent as to require months to cool down to the ordinary temperature. For many years 136 HOW CROPS FEED. the lava is incapable of bearing any vegetation save some almost microscopic forms. During these years the surface of the rock suffers gradual disintegration by the agencies of air and water, and so in time acquires the power to support some lichens that appear at first as mere stains upon its surface. These, by their decay, increase the film of soil fro:u which they sprung. The growth of new generations of these plants is more and more vigor- ous, and other superior kinds take root among them. 'After another period of years, there has accumulated a tangible soil, supporting herbaceous plants and dwarf shrubs. Henceforward the increase proceeds, more rapid- ly ; shrubs gradually give place to trees, and in a century, more or less, the once hard, barren rock has weathered to a soil fit for vineyards and gardens. Those lowest orders of plants, the lichens and mosses, which pi epare the way for 'forests and for agricultural vegetation, are able to extract nourishment from the most various and the nmst insoluble rocks. They occur abund- antly on all our granitic and schistose rock^. Even on quartz they do not refuse to grow. The white quartz hills of Berkshire, Massachusetts, are covered on their moister northern slopes with large patches of a leathery lichen, which adheres so fii-mly to the rock that, on being forced off, particles of the stone itself are detached. Many of the old marbles of Greece are incrusted with oxalate of lime left by the decay of lichens which have grown upon their surface. Humus* — By the decay of successive generations of plants the soil gradually acquires a certain content of dead organic matter. The falling leaves, seeds and stems of vegetation do not in general waste from the surface as rapidly as they are renewed. In forests, pastures, prai- ries, and marshes, there accumulates on the surface a brown or black mass, termed humus^ of which leaf mold, swamp- muck, and peat are varieties, differing in appearance as in ORIGIN AND FORMATION OF SOILS. 137 the circumstances of their origin. In the depths of the soil similar matters are formed by the decay of roots and other subterranean parts of plants, or by the inversion of sod and stubble, as well as by manuring. Decay of Vegetation, — When a plant or any part of a plant dies, and remains exposed to air and moisture at the common tempei atures, it undergoes a series of chemical and physical changes, which are largely due to an oxida- tion of portions of ite carbon and hydrogen, and the formation of new organic compounds. Vegetable matter is considerably variable in composition, but in all casej chiefly consists of cellulose and starch, or bodies of simi- lar character, mixed with a small [moportion of albuminous and mineral substances. By decay, the white or light- colored and tough tissues of plants become converted into brown or black friable substances, in which less or none of the organized structure of the fr(‘sh plant can be traced. The bulk and weight of the decaying matter constantly decreases as the process continues. WTth full access of air and at suitable temperatures, the decay, which, from the first, is characterized by the production and escape of carbonic aeid and water, proceeds without interruption, though more and more slowly, until nearly all the carbon and hydrogen of the vegetable matters are oxidized to the above-named products, and little more than the ashes of the plant remains. With limited access of air the process rapidly runs through a first stage of oxidation, when it becomes checked by the formation of substances which are themselves able, to a good degree, to resist further oxidation, especially under the circum- stances of their formation, and hence they accumulate in considerable quantities. This happens in the lower layers of fallen leaves in a dense forest, in compost and manure heaps, in the sod of a meadow or pasture, and especially in swamps and peat-bogs. The more delicate, porous and watery the vegetable 138 HOW CROPS FEED. matter, and the more soluble substances and albuminoids it contains, the more rapidly does it decay or humify. It has been shown by a chemical examination of wliat escapes in the form of gas, as well as of what remains as humus, that the carbon of wood oxidizes more slowly than its hydrogen, so that humus is relatively richer in carbon than the vegetable matters from which it origin- ates. With imperfect access of air, carbon and hydrogen are to some extent disengaged in union with each other, as marsh gas (CHJ. Carbonic oxide gas (CO) is proba- bly also produced in minute quantity. The nitrogen of the vegetable matter is to a considerable extent liberated in the free gaseous state ; a portion of it unites to hydro- gen, forming ammonia (NHg), which remains in the de- caying mass ; still another portion remains in the humus in combination, not as ammonia, but as an ingredient of the ill-defined acid bodies which constitute the bulk of humus ; finally, some of the nitrogen may be oxidized to nitric acid. ^ Chemical Nature of Humus. — In a subsequent chapter, (p. 224,) the composition of humus will be explained at length. Here we may simply mention that, under tlie in- fluence of alkalie s and a mmonia , it yields one or more bodies having acid characters, called humic and ulmic. (also geic) acids. Further, by ox idation it gives rise to c renic a nd ap ocrenic acids. The former are faintly acid in their properties ; the latter are more distinctly char- acterized acids. Influence of Humus on the Minerals of the Soil.— > a. Disintegration of the mineral matters of soils is aided by the presence of organic substances in a decaying state, in so far as the latter, from their hygroscopic quality, main- tain the surface of the soil in a constant state of moisture, 1). Organic matters furnish copious supplies of carbonic acid,, the action of which has already been considered ORIGIN AND FORMATION OF SOILS. 139 (p. 128). Boussingault and Lewy [Memoires de Chlmie Agrlcole^ etc.^p. 369,) have analyzed the air contained in the pores of the soil, and, as was to be anticipated, found it vastly richer in carbonic acid than the ordinary atmos- phere. The following table exhibits the composition of the air in the soil compared with that of the air above the soil, as observed in their investigations. Carbonic acid in 10.000 parts of air (by weight). Ordinary atmosphere 6 Air from sandy subsoil of forest 38 “ “ loamy “ “ “ 124 “ “ surface-soil “ 130 “ “ vineyard 146 “ “ “ “ old asparagus bed 122 ‘‘ “ “ “ “ “ newly manured. 233 “ “ “ “ pasture 270 “ “ “ rich in humus 543 “ “ “ newly manured sandy field, during dry weather 333 “ “ ‘‘ newly manured sandy field, during wet weather 1413 That this carbonic acid originates in large part by oxi- dation of organic matters is strikingly demonstrated by the increase in its quantity, resulting from the application of manure, and the supervention of warm, wet weather. It is obvious that the carbonic acid contained in the air of the soil, being from twenty to one hundred or more times more abundant, relatively, than in the common at- mosphere, must act in a correspondingly more rapid and energetic manner in accomplishing the solution and disin- tegration of mineral matters. c. The organic acids of the humns group probably aid in the disintegration of soil by direct action, though our knowledge is too imperfect to warrant a positive conclu- sion. The ulmic and humic acids themselves, indeed, do not, according to Mulder, exist in the free state in the soil, but their soluble salts of ammonia, potash or soda, ha\ e acid characters, in so far that they unite energetical- 140 now CROPS FEED. ly with other bases, as lime, oxide of iron, etc. These alkali-salts, then, should attack the minerals of the soil in a maimer similar to carbonic acid. The same is probably true of crenic and apocrenic acids. d. It scarcely requires mention that the ammonia salts and nitrates yielded by the decay of plants, as well as the organic acids, oxalic, tartaric, etc., or acid-salts, and the chlorides, sulphates, and phosphates they contain, act upon the surface soil where tliey accumulate in the manner al- ready described, and that vegetable (and animal) remains thus indirectly hasten the solution of mineral matters. Action of Living Plants on the Minerals of the Soil.— 1. Moisture and Carbonic Acid. — The living vegetation of a forest or prairie is the means of perpetually bringing the most vigorous disintegrating agencies to bear upon the soil that sustains it. The shelter of the growing plants, not less than the hygroscopic humus left by their decay, maintains the surface in a state of saturation by moisture. The carbonic acid produced in living roots, and to some extent, at least, it is certain, excreted from them, adds its effect to that derived from other sources. 2. Organic Acids within the Plant. — According to Zoller, ( Vs. St. V. 45) the young roots of living plants (what plants, is not mentioned) contain an acid or acid- salt which so impregnates the tissues as to manifest a strong acid reaction with (give a red color to) blue litmus- paper, which is permanent, and therefore not due to car- bonic acid. This acidity, Zoller informs us, is most in- tense in the finest fibrils, and is exhibited when the roots are simjdy wrapped in the litmus-paper, without being at all (?) crushed or broken. The acid, whatever it may be, thus existing within the roots is absorbed by porous paper placed externally to them. Previous to these observations of Zoller, Salm Horst- mar [Jour. far. Prakt. Ohem. XL. 304,) having found in the ashes of ground pine {.Lycopodium complanatum)^ 38® of ORIGIN AND FORMATION OF SOILS. 141 alumina, while in the ashes of juniper, growing beside the Lycopodium, this substance was absent, examine 1 the rootlets of botli plants, and found that the former had an acid reaction, while the latter did not affect litmus- paper. Salm Horstmar supposed that the alumina of the soil finds its way into the Lycopodium by means of this acid. Ritthansen has shov/n that the Lycopodium contains malic acid, and since all the alumina of the plant may be extracted by water, it is probable that the acid reaction of the rootlets is due, in part at least, to the presence of acid malate of alumina. {Jour. far. Prakt. Ghem. LIII. 420.) At Liebig’s suggestion, Zoller made the following ex- periments. A number of glass tubes were filled with water made slightly acid by some drops of hydrochloric acid, vinegar, citric acid, bitartrate of potash, etc. ; the open end of each tube was then closed by a piece of moistened bladder tied tightly over, and various salts, in- soluble in water, as phosphate of lime, phosphate of am- monia and magnesia, etc., were strewn on the bladder. After a short time it was found that the ingredients of these salts were contained in the liquid in contact with the under surface of the bladder, having been dissolved by the dilute acid present in the pores of the membrane, and absorbed through it. Tliis is an ingenious illustra- tion of the mode in which the or< 2 ::anic acids existing in the root-cells of plants may act directly upon the rock or soil external to them. By such action is doubtless to be explained the fact mejitioned by Liebig in the following words : “We frequently find in meadows smooth limestones with their surfaces covered with a network of small fur- rows. When these stones are newly taken out of the ground, we find that each furrow corresponds to a rootlet, which appears as if it had eaten its way into the stone.” {Modern Ag. p. 43 .) 142 HOW CROPS FEED. Tliis direct action of the living plant is probably ex- erted by the lichens, which, as has been already stated, grow upon the smooth surface of the rock itself. Many of the lichens are known to contain oxalate of lime to the extent of half their weight (Braconnot). According to Goeppert, the hard, fine-grained rock of the Zobtenberg, a mountain of Silesia, is in all cases softened at its surface where covered with lichens {Acarospora smar- agdula^ Imbricaria olivacea^ etc,)^ while the bare rock, closely adjacent, is so hard as to resist tlie knife. On the Schwalbenstein, near Glatz, in Silesia, at a height of 4,500 feet, the granite is disintegrated under a covering of li- cliens, the feldspar being converted into kaolin or washed away, only the grains of quartz and mica remaining unal- tered.*^ CHAPTER in. KINDS OF SOILS— THEIR DEFINITION AND CLASSIFI- CATION. § 1 - DISTINCTION OF SOILS BASED UPON THE MODE OF THEIR FORMATION OR DEPOSITION. The foregoing considerations of the origin of soils intro- duce us appropriately to the study of soils themselves. In the next place vfe may profitably recount those defini- tions and distinctions that serve to give a certain degree of precision to language, and enable us to discriminate in some measure the different kinds of soils, which ( ffer great diversity in origin, composition, external charactei s, ♦ See, also, p. 136. KINDS OF SOILS. 143 and fertility. Unfortunately, while there are almost num- berless varieties of soil having numberless grades of pro- duct ive power, we are very deficient in terms by which to express concisely even the fact of their differences, not to mention our inability to define these differences with ac- curacy, or our ignorance of the precise nature of their peculiarities. As regards mode of formation or deposition, soils are distinguished into Sedentary and Transported, The lat- ter are subdivided into Drift,, Alluvial,, and Colluvial soils. Sedentary Soils^ or Soils in place,, are those which have not been transported by geological agencies, but which remain where they were formed, covering or contiguous to the rock fi*om whose disintegration they originated. Sedentary soils have usually little depth. An inspection of the rock underlying such soils often furnishes most valuable information regarding their composition and probable agricultural value; because the still un weathered rock reveals to the practised eye the nature of the min- erals, and thus of the eleme nts, composing it, while in the soil these may be indistinguishable. In New England and the region lying north of the Ohio and east of the Missouri rivers, soils in place are not abundant as compared with the entire area. Nevertheless they do occur in many small patches. Thus the red-sand- stone of the Connecticut Valley often crops out in that part of New England, and, being, in many localities, of a friable nature, has crumbled to soil, which now lies undis- turbed in its original position. So, too, at the base of trap- bluffs may be found trap-soils, still full of sharp-angled fragments of the rock. Transported Soils^ (subdivided into drift, alluvial, and colluvial), are those which have been removed to a dis- tance from the rock-beds whence they originated, by the 144 now CROPS FEED. action of moving ice (glaciers) or water (rivers), and de- posited as sediment in their present positions. Drift Soils (sometimes called diluvial) are characterized by the following particulars. They consist of fragments whose edges at least have been rounded by friction, if the Iragments. themselves are not altogether destitute of angles. They are usually deposited without any stratifi- cation or separation of parts. The materials consist of soil proper, mingled with stones of all sizes, from sand- grains up to immense rock-masses of many tons in weight. This kind of soil is usually distinguished from all others by the rounded rocks or boulders (‘‘hard heads”) it con- tains, which are promiscuously scattered through it. The “Drift” hns undoubtedly been formed by moving ice in that ]:)eriod (;f the earth’s history known to geolo- gists as the Glacial Epoch, a period when the present sur- face of the country was covered to a great depth by fields of ice. In regions like Gi eenland and the Swiss Alps, which reach above the line of perpetual snow, drift is now ac- cumulating, perfectly similar in character to that of New England, or has been obviously produced by the melting of glaciers, which, in former geological ages and under a colder climate, were continuations on an immense scale of those now in existence. A large share of the northern portion of the country from the Arctic regions southward as far as j atitudc 39^, or nearly to the southern boundaries of Pennsylvania and to the Ohio River, including Canada, New England, Long Island, and the States west as far as Iowa, is more or less covered with drift. Comparison of the boulders with the undisturbed rocks of the regions about show that the materials of the drift have been moved soutli wards or southeast wards to a distance generally of twenty to forty miles, but sometimes also of sixty or one hundred miles, from where they were detached from their original beds. KINDS OF SOILS. 145 The surface of the country when covered with drift is often or usually irregular and hilly, the hills themselves being conical heaps or long i-idges of mingled sand, gravel, aud boulders, the transported mass having often a great depth. Tlieso hills or ridges are parts of the vast trains cf material left by the melting of preadaraite glaciers or icebergs, and have their precise counterpart in the moraines of the Swiss Alps. Drift is accordingly not confined to the valleys, but the northern slopes of mountains or hills, whose basis is unbroken rock, are strewn to the summit with it, and immense blocks of transported stone are seen upon the very tops of the Catskills and of the White and Green Mountains. I Drift soils are for these reasons often made up of the most diverse materials, including all the kinds of rock and rock-dust that arc to be found, or have existed for one or several scores of miles to the nortli ward. Of these often only the harder granitic or silicious rocks remain in con- siderable fragments, the softer rocks having been com- pletely ground to powder. Towards the southern limit of the Drift Region the drift itself consists of fine materials which were carried on by the Avaters from the melting glaciers, while the heavier boulders were left further north. Here, too, may often be observed a partial stratification of the transported materials as the result of their deposition from moving Avater. The great belts of yellow and red sand tliat stretch across New Jersey on its southeastern face, and the sands of Long Island, are these finer portions of the drift. Farther to the north, many large areas of sand may, perhaps, prove on careful examination to mark the southern limit of some ancient local glacier. Alluvial Soils consist of worn and rounded materials which have been transported by the agency of running water (rivers and tides). Since small and light particles are more readily sustained in a current of water than 7 146 HOW CROPS FEED. heavy masses, ailuvium is always more or less strat'fied or arranged in distinct layers: stones or gravel ;it the bottom ar.d nearest the source of movement, finer stones or finer gravel above and further down in the path of flow, sand and impalpable matters at the surface and at t])e point where the stream, before turbid from suspended rock-dust, finally clears itself by a broad level course and slow progress. Alluvial deposits have been formed in all periods of the earth’s history. Water trickling gently down a granite slope carries forward the kaolinite arising from decompo- sition of feldspar, and the first hollow gradually fills up with a bed of clay. In valleys are thus deposited the gravel, sr.nd, and r;)ck-dust detached from the slopes of neighboring mountains. Lakes and gulfs become filled with silt biought into them by streams. Alluvium is found below as wed as above the drift, and recent alluvium in the drift region is very often composed of drift mate- rials rearranged by water-currents. Alluvium often con- tains rounded fragments or disks of soft rocks, as lime- stones and slates, which are more rarely found in drift. CollUTial SoilS) lastly, are those which, while consisting in part of drift or alluvium, also contain sharp, angular fragments of the rock from which they mainly originated, thus demonstrating that they have not been transported to any great distance, or are made up of soils in place, more or less mingled with drift or alluvium. DISTINCTIONS OF SOILS BASED UPON OBVIOUS OR EXTER- NAL CHARACTERS. The classification and nomenclature of soils customarily employed by agriculturists have chiefly arisen from con- sideration of the relative proportions of the principal KINDS OF SOILS. 147 mechanical ingredients, or from other liighly obvious qualities. The distinctions, thus established, tiiough very vague scientifically considered, are extremely useful for practical purposes, and the grounds upon which they rest deserve to be carefully reviewed for the purpose of appreciating their deficiencies and giving greater precision to the terms employed to define them. The farmer, speaking of soils, defines them as gravelly^ sandy^ clayey^ loamy ^ calcareous^ peaty ^ ochreous^ etc. Mechanical Analysis of the Soil. — Before noticing these various distinctions in detail, we may appropriately study the methods which are employed for separating the mechanical ingredients of a soil. It is evident that the epithet sandy ^ for example, should not be applied to a soil unless sand be the predominating ingredient ; and in or- der to apply the term with strict correctness, as well as to know how a soil is constituted as regards its mechanical elements, it is nece ssary to isolate its parts and determine their relative quantity. Boulders, stones, and pebbles, are of little present or immediate value in the soil by way of feeding the plant. This function is performed by the finer and especially by the finest particles. Mechanical analysis serves therefore to compare together difierent soils, and to give useful in- dications of fertility. Simple inspection aided by the feel enables one to judge, perhaps, with sufllcient accuracy for all ordinary practical purposes ; but in any serious attempt to define a soil precisely, for the purposes of science, its mechanical analysis must be made with care. Mechanical separation is effected by sifting and wash- ing. Sifting serves only to remove the stones and coarse sand. By placing the soil in a glass cylinder, adding wa- ter, and vigorously agitating for a few moments, then letting the whole come to rest, there remains susjjended in the water a greater or less quantity of matter in a state now CPwOPS FEED. 14 3 of extreme division. This fine matter is in many cases clay (kaolinite), or at least consists of substances resulting from the weathering of the rocks, and is not, or not chiefly, rock-dust. Between this impalpably fine matter and the grains of sand retained by a sieve, there exist numberless gradations of fineness in the particles. By conducting a slow stream of water through a tube to the bottom of a vessel, the fine particles of soil are carried off and may be received in a pan placed beneath. Increasing the rapidity of the current enables it to remove larger particles, and thus it is easy to separate the soil in- to a number of portions, each of Avhich contains soil of a different fineness. Various attempts have been made to devise piecise means of separating the materials of soils meclianically into a definite number of grades of fineness. This may be accomplished in good measure by washing, but constant and accurate results are of course only at- tained when the circumstances of the washing are uniform throughout. The method adopted by the Society of Agricultural Chemists of Germany is essentially the fob lowing ( Yersuchs Stationen^ VI, 144) : The air-dry soil is gently rubbed on a tin-plate sie\ e with round holes three millimeters in diameter; what ]>asses is weighed as fine-eaTth, What remains on the sieve is. washed with water, dried, weighed, and designated as gravel, pebbles, stones, as the case may be, the size of the stones, etc., being indicated by comparison with the fist, with an egg, a walnut, a hazelnut, a pea, etc. Of the^;^AC- earth a portion (30 grams) is now boiled for an hour or mor-* , in water, so as to completely break down any lumps and separate adhering particles, and is then left at rest for some minutes, when it is transferred into the vessel 1 of the apparatus, fig. 8., after having poured off the turbid water with which it was boiled, into 2. This washing ap- paratus (invented by Nobel) consists of a reservoir, A, KINDS OF SOILS. 149 made of sheet metal, capable of holding something more than 9 liters of water, and furnished at h with a stop-cock. By means of a tube of rubber it is joined to the series of Fig. 8. vessels, 2, 3, and 4, which are connected to each ether, as shown in the figure, the recurved neck of 2 fitting water-tight into the nozzle of 1 at a, etc. These vessels are made of glass, and together hold 4 Ill:ers of water; their relative volume is nearly 1 : 8 : 27 : 64, or = : 2^ : 3^ : 41 5 is a glass vessel of somewhat more than 5 liters, capacity. The distance between h and c is 2 feet. The cock, 5, is opened, so that in 20 miTiutes exactly 9 liters of water 150 HOW CROPS FEED. pass it. The apparatus being joined together, and the cock opened, the soil in 1 is agitated by tiie stre am of wa- ter flowing through, and tlie finer portions are carried over into 2^ 3) 4^ an 1 5. As a given amount of water requires eight times longer to pass through 2 than its velocity of motion and buoyant power in the neck of 3 are corre- spondingly less. After the requisite amount of water has run from A, the cock is closed, the who’e left to rest sev- eral hours, when the contents of the vessels are separately rinsed out into porcelain dishes, dried and weighed.* The contents of the several vessels are designated as follows :f 1. Gravi'l, fragments of rock. 2. Coarse sand. 3. Fine sand. 4. Finest or dust sand. 5 Chi^'cy substance or impalpable matter. In most inferior soils the gravely the coarse sand^ and the fine sand^ are angular fragments of quartz, feldspar, amphibole, pyroxene, and mica, or of rocks consisting of titese mimu’als. It is only these harder and less easily decotn posable minerals that can resist the pul\*’erizing agencies through which a large share of our soils have passed. In the more fertile soils, formed from sedimen- tary limestones and slates, the fragments of these strati- fied rocks occur as fiat pebbles and rounded grains. The finest or dust-sand^ when viewed under the micro- scope, is found to be the same rocks in a higher state of pulverization. * See, also, Wolff’s Anieitung zut Untersitehung landwirthscliaftlich-wichtigei- Stoffe,'" 1867, p. 5. t These names, applied by Wolff to the results of washing Ihe sedentary soils of WUrtemberg, do not always well apply to other soils. Thus Grouven, {Zter Salz- munder Bericht, p. 32), operating on the alluvial soils of North Germany, desig- nated the contents of the 4th funnel as “clay and loam,” and those of the 5th vessel as “ light clay and humus.” Again, Schone found {Bulletin^ etc.^ de Moscou^ p. 402) by treatment of a certain soil in Nobel’s apparatus, 45 per cent of “ coarse sand” remainin'! in the 2d fnnnol. The particles of this were for the most part smaller than 1 10th millimeter (l-250lh incli), which certainly is not coarse sand I KINDS OP SOILS. 151 What is designated as clayey substance^ or impalpable matter^ is oftentimes largely made up of rock-dust, so fine that it is suipported by water, when the* latter is in the gentlest motion. In what are properly termed clay-soils, the finest parts consist, however, chiefly of the hydrous silicate of alumina, already described, p. 113, under the mineralogical name of haolinite^ or of analogous com- pounds, mixed with gelatinous silica, oxides of iron, and i arbonate of lime, as well as with finely divided quartz and other gianitic minernls. So gradual is the transition from true kaolinite clay through its impurer sorts to mere impalpable rock-dust, in all that relates to sensible char- acters, as color, feel, adhesiveness, and plasticity, that the term clay is employed rather loosely in agriculture, being not infrequently given to soils that contain very little kaolinite or true clay, and thus implies tlie general physi- cal qualities that are usually typified by clay rather than the presence of any definite chemical compound, like kaolinite, in the soil. Many soils contain much carbonate of lime in an im- palpable form, this substance having been derived from lime rocks, as marble and chalk, from the shells of mollusks, or from coral ; or from clays that have originated by the chemical decomposition of feldspathic rocks containing much lime. Organic matter^ especially the debris of former vegeta- tion, is almost never absent fi*om the impalpable portion of the soil, existing there in some of the various forms as- sumed by humus. As Schone has shown, {Bulletin de la Societe des Natura- Ustes de Moscou^ 1867, p. 363), the results obtaiiu'd by Nobel’s apparatus are far from answering the purposes of science. The separation is not carried far enough, and no simple relations subsist between the separated portions, as regards the dimensions of their particles. If the soil were C( mposed of spherical particles of one kind of matter, or 152 HOW CROPS FEED. having all the same specific gravity, it would be possible by the use of a properly constructed washing apparatus to separate a sample into fifty or one hundred parts, and to define the dimensions of the particles of each of these parts. Since, however, the soil is very heterogeneous, and since its particles are unlike in shape, consisting partly of nearly spherical grains and partly of plates or scales upon which moving water exerts an unequal floating effect, it is difficult, if not impossible, to realize so perfect a mechanic- al analysis. It is, however, easy to make a separation of a soil into a lar.ge number of parts, each of which shall ad- mit of precise definition in terms of the rapidity of flow of a current of water capable of sustaining the particles which compose it. Instruments for mechanical analysis, which ])rovide for producing and maintaining at will any desired rate of flow in a stream of water, have been very recently devised, independently of each other, by E. Schone (loc. cit.^ pp. 331-405) and A. Muller ( Vs. St., X, 25-51). The employment of such apparatus promises valuable re- sults, although as yet no extended with its help have been published. \ Gravelly Soils are so named from the abundance of small stones or pebbles in them. This name alone gives but little idea of the real’y important characters of the soil. Simple gravel is ne:irly valueless for agricultural ])urposes; many highly gravelly soils are, however, very fertile. The fine portion of the soil gives them their crop- feeding power. The coarse parts ensure drainage and store the solar heat. The mineralogical chai acters of the pebbles in a soil, as determined by a practised eye, may often give useful indications of its composition, since it is generally true that the finer parts of the soil agree in this respect with the coarser, or, if different, are not in- ferior. Thus if the gravel of a soil contains many pebbles of feldspar, the soil itself may be concluded to be well supplied with alkalies ; if the gravel consists of limestone, KINDS OF SOILS. 153 we may infer that lime is abundant in the soil. On the other hand, if a soil contains a large proportion of quartz pebbles, the legitimate inference is that it is of compara- tively poor quality. The term gravelly admits of various qualification. We may have a very gravelly or a mod- c‘rately gravelly soil, and the coai se material may be char- acterized as a fine or coarse gravel, a slaty gravel, a granitic gravel, or a diorite gravel, according to its state of division or the character of the rock from which it was formed. But the closest description that can thus be given of a gravelly soil cannot convey a very pi-ecise notion of even its external qualities, much less of those properties upon which its fertility de|)ends. Sandy Soils are those which visibly consist to a large degree, 9vT|^ or more, of sand^ e., of small granular fragments of rock, no matter of what kind. Sand usually signifies grains of quartz\ tliis mineral, from its hardness, withstanding the action of disintegrating agencies beyond any other. Considerable tracts of nearly pure and white quartz sand are not uncommon, and are characterized by obdurate barrenness. But in general, sandy soils are by no means free from other silicious minerals, especially feldspar and mica. When the sand is yellow or red in color, this fxct is due to admixture of oxide or silicates of iron, and points with certahity to the presence of ferruginous minerals or their dccom])osition-products, which often give considera- ble fertility to the soil. Other varieties of sand are not uncommon. In New Jersey occur extensive deposits of so-called green sand^ containing grains of a mineral, glauconite^ to be hereafter noticed as a fertilizer. Lime sand^ consisting of grains of carbonate of lime, is of frequent occurrence on the shores of coral islands or reefs. The term sandy-soil is obviously very indefinite, including nearly the extremes 154 HOW CROPS PEED. of fertility and barrenness, and covering a wide range of variety as regards composition. It is therefore qualified by various epithets, as coarse, fine, etc. Coarse, sandy soils are usually unprofitable, while fine, sandy soils are often valuable. Clayey Soil^ are those in wliich clay or impalpable mat- ters predominate. They are cornmoidy characterized by extreme fineness of texture, and by great retentive power for water; this liquid finding passage through their pores with extreme slowness. When dried, they become crack- ed and rifted in every direction from the shrinking that takes place in this process. It should be distinctly understood that a soil may be clayey without being clay, i. e., it may have the external, physical properties of adhesiveness and imperin (‘ability to water which usually characterize clay, without containing those compounds (kaolinite and the like) which constitute clay in the true chemical sense. On the other hand it were possible to have a soil consist- ing chemically of clay, which should have the physical properties of sand ; for kaolinite has been found in crys- tals jo'oo of an inch in breadth, and destitute of all cohesive- ness or plasticity. Kaolinite in such a coarse form is, how- ever, extremely rare, and not likely to exist in the soil. Loamy Soils are those intermediate in character between sandy and clayey, and consist of mixtures of sand with clay, or of coarse with impalj)able matters. They are free from the excessive tenacity of clay, as well as, from the t( a great porosity of sand. The gradations between sandy and clayey soils are roughly expressed by such terms and distinctions as the following : KINDS OF SOILS. 155 Clay or impalpadfle matters. Sand. Heavy clay contains 75— 90o|o 10- 250 1, Clay loam “ 60—75 25- 40 Loam “ 40-60 40- 60 Sandy loam “ 25—40 60— 75 Light sandy loam contains 10—25 75— 90 Sand 0—10 90—100 The percentage composition above given applies to the dry soil^ and must be received with great allowance, since the transition from fine sand to impalpable matter not physically distinguishable from clay, is an impercep- tible one, and therefore not well admitting of nice discrim- ination. It is furthermore not to be doubted that the difference between a clayey soil and a loamy soil depends more on the form and intimacy of admixture of the ingredients, than upon their relative proportions, so that a loam may exist which contains less sand than some clayey soils. Calcareous or Lime Soils are tliose in which carbonate of lime is a predominating or characteristic ingr ‘dient. They are recognizable by effervescing vigorously when drenched wLh an aci 1. Strong vinegar answers for test- ing them. They are not uncommon in Europe, but in this country are comparatively rare. In the Northern and Middle States, calcareous soils scarcely occur to an extent worthy of mention. While li’.ne soils exist containing 75“ and more of car- bonate of lime, this ingredient is in general subordinate to sand and clay, and we have therefn*e ealcccreous sands^ calcareous clays ^ or calcareous loams. Marls are mixtures of clay or clayey matters, with finely divided carbonate of lime, in something like equal propor- 4 tions.* Peat or Swamp Muck is humus resulting from decayed * In New Jersey, green sand marl, or marl simply, is the name applied to the STrof"! sand ctnployed as a fertilizer. SAell marl is a name desi.i,mating nearly pare earhonate of lime found in swamps. 156 now CROPS FEED. vegetable matter in bogs and marshes. A soil is peaty or mucky when containing vegetable remains that have suf- fered partial decay under water. Vegetable Mold is a soil containing much organic mat- ter that has decayed without submergence in water, either resulting from the leaves, etc., of forest trees, from the roots of grasses, or from the frequent application of large doses of strawy manures. Ochery or Ferruginous Soils are those containing much oxide or silicates of iron; they have a yellow, re perature, as Knop has recently shown, and is unafiected by the relative abundance of vapor: i. e., at a given tem- perature a dry soil will absorb the same amount of moist- ure from the air, no matter whether the latter be slightly or heavily impregnated with vapor, but u ill do this the more speedily the more moist the surrounding atmosphere liappens to be. In virtue of this hygroscopic character, the soil which becomes dry superficially during a hot day gathers water from the atmosphere in the cooler night time, even when no rain or dew is deposited upon it. In illustration of the influence of temperature on the quantity of water absorbed, as vapor, by the soil, we give Knop’s observations on a sandy soil from Moeckern, Sax- ony : l,0()v0 parts of this soil absorbed At 55° F. 13 parts of hygroscopic water. ‘‘ 66° 11.9 U ggo g Knop calculates on the basis of his numerous observa- tions that hair and wool, which are more hygroscopic than most vegetable and mineral substances, if allowed to ah . sorb what moisture they are capable of taking up, contain the following quantities of water, per cent^ at the temper- atures named : At %T Fah., 7.7 per cent. ‘‘ 55° “ 15 5 “ ‘‘ “ 32° ‘‘ 19.3 “ “ PHYSICAL CHARACTERS OP THE SOIL. 165 Silk is sold in Europe by weight with suitable allowance for hygroscopic moisture, its variable content of which is carefully determined by experiment in each important transaction. It is plain that the circumstances of sale may affect the weight of wool to 10 or more per cent. § 4 . CONDENSATION OF GASES BY THE SOIL. Adhesion. — In the fact that soils and porous bodies gen- erally have a physical absorbing power for the vapor of water, we have an illustration of a principle of very wide application, viz.. The surfaces of liquid and solid matter attract the particles of other hinds of matter. This force of adhesion.^ as it is termed, when it acts up- on gaseous bodies, overcomes to a greater or less degree their expansive tendency, and coerces them into a smaller space — condenses them. Absorbent Power of Charcoal^ etc. — Charcoal serves to illustrate this fact, and some of its most curious as well as useful properties depend upon this kind of physical peculiarity. Charcoal is prepared from wood, itself ex- tremely porous,^ by expelling the volatile constituents, whereby the porosity is increased to an enormous extent. When charcoal is kept in a damp cellar, it condenses so much vapor of water in its pores that it becomes difficult to set on fire. It may even take up one-fourth its own weight. When exposed to various gases and volatile matters, it absorbs them in the same manner, though to very unequal extent. De Saussure w^as the first to measure the absorbing power of charcoal for gases. In his experiments, boxwood charcoal was heated to redness and plunged under mer- * Mltscherlich has calculated that the cells of a cubic inch of boxwood have no less than 73 square feet of surface. 166 HOW CROPS FEED. cury to cool. Then introduced into the various gases named below, it absorbed as many times its bulk of them, as are designated by the subjoined figures : Ammonia Hydrochloric acid.... ...85 Sulphurous acid Hydrosulphuric acid.. Protoxide of nitrogen.. ..40 Carbonic acid ...35 - Oxygen •• Carbonic oxide. ... 9X Hydrogen .. 1% Nitrogen ... 7K According to De Saussure, tlie absorption was complete in 24 hours, except in case of oxygen, where it continued for a long time, though with decreasing energy. The oxygen thus condensed in the charcoal combined with the carbon of the latter, forming carbonic acid. Stenhouse more lately has experimented in the same di- rection. From these researches we learn that the power in question is exerted towards different gases with very unequal effect, and that different kinds of charcoal exert very different condensing power. Stenhouse found that one gramme of dry charcoal ab- sorbed of several gases the number of cubic centimeters given below. Name of Gas. Kind of Charcoal. Wood. Peat. Animal. Ammonia 98.5 96.0 43.5 Hydrochloric acid 45.0 60.0 Hydrosulphuric acid 30.0 28.5 9 0 Sulphurous acid 32.5 27.5 17.5 Carbonic acid 14.0 10.0 5.0 Oxygen 0.8 0.6 0.5 The absorption or solution of gases in water, alcohol, and other liquids, is analogous to this condensation, a?id those gases which are most condensed by charcoal are in general, though not invariably, those which dissolve most copiously in liquids, (ammonia, hydrochloric acid). Condensation of Cases by the Soil. — Reichardt and Blumtritt have recently made a minute study of the kind and amount of gases that are condensed in the pores of various solid substances, including soils and some of their PHYSICAL CHARACl'EUS OF THE SOIL, 167 ingredients. {Jour, far praM, Chem,^ Bd, 98, p. 476.) Their results relate chiefly to these substances as ordinarily occurring exposed to the atmosphere, and therefore moi-e or less moist. The following Table includes the more im- portant data obtained by subjecting the substances to a temperature of 284° F., and measuring and analyzing the gas thus expelled. 100 Gram9 10 Vols. 100 Vols. of Gas contained: Substance : in mis. Nitro- Oxy- Carbon- Car- a a gas. gen. gen. ic acid. bonic oxide. Charcoal, air- dry. 164 — 100 0 0 0 “ moistened and dried a^in, 140 50 86 2 9 3 Peat, 162 — 41 5 51 0 Garden soil, moist, 14 20 64 3 21 9 “ air-dry. 33 54 65 2 33 0 Hydrated oxide of iron, air-dry. 375 309 26 4 70 0 Oxide of iron, ignited. 39 52 S3 13 4 0 Hydrated alumina, air-dry. 69 82 41 0 50 — Alumina, dried at 212^, 11 14 83 17 0 — Clay, 33 — 65 21 11 — “ long exposed to air. 26 39 70 5 25 — “ moistened. 29 35 60 6 34 — Hiver silt, air-dry, 40 48 68 0 13 14 “ “ moistened. 24 29 67 0 31 2 “ “ again dried, 26 30 67 9 13 7 Carbonate of lime (whiting,) 1864, 43 52 100 0 0 — “ “ 1865, 39 48 74 18 10 — “ *4 n precipitated, 1864, 65 — 81 19 0 — “ “ “ “ 1865, 51 52 77 15 8 — Carbonate of magnesia. 729 125 64 7 29 — Gypsum, pulverized. 17 — 81 19 0 — From these figures we gather: 1. The gaseous mixture which is contained in the pores of solid substances rarely has the composition of the at- mosphere. In but two instances, viz., with gypsum and precipitated carbonate of lime,^ were only oxygen and ni- trogen absorbed in proportions closely approaching those of the atmosphere. 2. Nitrogen appears to be nearly always absorbed in greater proportion than oxygen, and is greatly condensed in some cases, as by peat, hyJrated oxide of iron, and car- bonate of magnesia. 168 HOW CROPS FEED. 3. Oxygen is often nearly or quite ^\ anting, as in char- coal, oxide of iron, alumina, river silt, and whiting. 4. Carbonic acid, though sometimes wanting entirely, is usually abundant in the absorbed gases. 5. In the pores of charcoal and of soils containing de- caying organic matters, carbonic acid is often partially re- placed by carbonic oxide. The experiments, however, do not furnish proof that this substance is not formed under the influence of the high temperature employed (284° F.) in expelling the gases, rather than by incomplete oxidation of organic matters at ordinary temperatures. 6. A substance, when moist, absorbs less gas than when dry. In accordanco with this observation, De Saussure no- ticed that dry charcoal saturated with various gases evolv- ed a good share of them when moistened with water. Ground (and burnt ?) cofiee, as Babinet has lately stated, evolves so much gas when drenched with water as to burst a bottle in which it is confined. The extremely variable figures obtained by Blumtritt when operating with the same substance (the figures given in the table are averages of two or three usually discordant results), result from the general fact that the proportion in which a number of gases are present in a mixture, in- fluences the proportion of the individual gases absorbed. Thus while charcoal or soil will absorb a large amount of ammonia from the pure gas, it will take up but traces of this substance from the atmosphere of which ammonia is but an infinitesimal ingredient. So, too, charcoal or soil saturated wdth ammonia by cx- ])osure to the unmixed gas, loses nearly all of it by stand- ing in the air for some time. This is due to the fact that gases attract each other ^ and the composition of the gas condensed in a porous body varies perpetually with the variations of composition in the surrounding atmosphere. It is especially the water-gas (vapor of water) which is a fluctuating ingredient of the atmosphere, and one which PHYSICAL CHARACTERS OF THE SOIL. 169 is absorbed by porous bodies in the largest quantity. This not only displaces other gases from their adhesion to solid surfaces, but by its own attractions modifies these adhesions. Reichardt and Blumtritt take no account of water-gas, except in the few experiments where the substances were purposely moistened. In all their trials, however, moist- ure was present, and had its quantity been estimated, doubtless its influence on the extent and kind of absorp- tion would have been strikingly evident throughout. Ammonia and carbonate of ammonia in the gaseous form are absorbed from the air by the dry soil, to a less degree than by a soil that is moist, as will be noticed fully hereafter. Chemical Action mduced by Adhesion. — This physical property often leads to remarkable chemical effects ; in other words, adhesion exalts or brings into play the force of affinity. When charcoal absorbs those emanations from putrefying animal matters wliich we scarcely know, save by their intolerable odor and poisonous influence, it causes at the same time their rapid and complete oxida- tion ; and hence a j)iece of tainted meat is sweetened by covering it with a thin layer of powdered charcoal. As Stenhouse has shown, the carcass of a small animal mny be kept in a living-room during the hottest weather with- out giving off any putrid odor, provided it be surrounded on all sides by a layer of powdered charcoal an inch oi more thick. Thus circumstanced, it simply smells of am^ monia^ and its destructible parts are resolved directly in- to water, carbonic acid, free nitrogen, and ammonia, pre- cisely as if they were burned in a furnace, and without the appearance of any of the effluvium that ordinarily arises from decaying flesh. The metal platinum exhibits a remarkable condensing power, which is manifest even with the polished surface of foil or wire; but is most striking when the metal is 8 170 now CROPS FEED. brought to the condition of sponge, a form it assumes when certain of its compounds (e. g. ammonia-chloride of platinum) are decomposed by lieat, or to the more finely divided state of platinum black. The latter is capable of condensing from 100 to 250 times its volume of oxygen, according to its mode of preparation (its porosity ?) ; and for this reason it possesses intense oxidizing power, so that, for example, when it is brought into a mixture of oxygen and hydrogen, it causes them to unite explosively. A jet of hydrogen gas, allowed to play on platinum sponge, is almost instantly ignited — a fact taken advantage of in Dobereiner’s hydrogen lamp. The oxidizing powers of platinum are much more vig- orous than those of charcoal. Stenhouse has proposed the use of platinized charcoal (charcoal ignited after moist- ening with solution of chloride of platinum) as an es(*ha- rotic and disinfectant for foul ulcers, and has shown that the foul air of sewers and vaults is rendered innocuous when filtered or breathed through a layer of this material.* Chemical Action a Result of the Porosity of the Soil. — From these significant facts it has been inferred that the soil by virtue of the extreme porosity of some of its ingrc'- dients is the theater of chemical changes of the utmost importance, which could not transpire to any sensible ex- tent but for this high division of its particles and the vast surface they present. The soil absorbs putrid and other disagreeable efiiuvia, and undoubtedly oxidizes them like charcoal, though, per- haps, with less energy than the last named substance, as would be anticipated from its inferior porosity. Garments which have been rendered disgusting by the fetid secre- tions of the skunk, may be ‘‘ sweetened,” i. c. deprived of * Platinum does not condense hydrogen gas ; but the metal PcUlaclium^ which occurs associated with platinum, has a most astonishing absorptive power for hydrogen, being able to take up or “occlude” 900 times its volume of the gas. (Graham, Proceedings Boy. 8oc.^ 1868, p. 422.) ABSORBENT POWER OF SOILS. 171 odor, by burying them for a few days in the earth. Tlie Indians of this country are said to sweeten the carcass of the skunk by the same process, when needful, to fit it for their food. Dogs and foxes bury bones and meat in the ground, and afterward exhume them in a state of com» parative freedom from offensive odor. When human excrements are covered with fine dry earth, as in the “Earth Closet” system, all odor is at once suppressed and never reappears. At the most, besides an “ earthy ” smell, an odor of ammonia appears, resulting from decomposition, which appears to ])roceed at once to its ultimate results without admitting of the formation of any intermediate offensive compounds. Dr. Angus Smith, having frequently observed the pres- ence of nitrates in the water of shallow town wells, sus- pected that the nitric acid was derived from animal mat- ters, and to test this view, made experiments on the action of filters of sand, and other porous bodies, upon solutions of diflferent animal and vegetable matters. He found that in such circumstances oxidation took place most rap- idly — the nitrogen of organic matters being converted in- to nitric acid, the carbon and hydrogen combining with oxygen at the same time. Thus a solution of yeast, which contained no nitric acid, after being passed through a filter of sand, gave abundant evidence of salts of this acid. Colored solutions were in this way more or less decolor- ized. Water, rendered brown by peaty matter, was found to be purified by filtration through sand.^ §• 5 . POWER OF SOILS TO REMOVE DISSOLVED SOLIDS FROM THEIR SOLUTIONS. Action of Sand upon Saline Solutions. — It has long been known that simple sand is capable of partially re- ♦ This account of Dr. Smith’s experiments is quoted from Prof, Way’s paper “ On the Power of Soils to Absorb Manure.” {flour. Boy. Ag. 8oc. of England^ XI, p. 317.) 172 HOW CROPS FEED. moving saline matters from their solutions in water. Lord Bacon, in lus “ Sylva Sylvarum,” spenks of a method of obtaining fresh water, which was practised on the coast of Barbary. Bigge a hole on the sea-shore somewhat above high-vvater mark and as deep as low-water maik, which, when the tide cometh, will be filled with water fresh and potable.” He also remarks “ to have re.id that trial hath been made of salt-water passed through eai*th through ten vessels, one witliin another, and yet it hath not lost its saltness as to become potable ; ” but when ‘‘drayned through twenty vessels, hath become fresh.” Dr. Steplien Plales, in a paper read before the Royal Society in 1739, on Some attempts to make sea-water wholesome,” mentions on the authority of Mr. Boyle God- frey that “sea-water, being filtered through stone cisterns, the first pint that runs through will be pure water having no taste of the salt, but the next pint will be salt as usual.” Berzelius found upon filtering solutions of common salt through sand, that the portions which first passed were quite free from saline impregnation. Matteucci extended this observation to other salts, and found that the solu- tions when filtered through sand were diminished in den- sity, showing a detention by tiie sand of certain quantities of the salt operated upon.* Action of Humus on Saline Solutions. — Heiden [IToff- maniTbS Jahreshericht^ 1866, p. 29) found that peat and various preparations of the humic acids, wlien brought in- to solutions of chloride of potassium and chloride of am- monium, remove a portion of these salts from the liquid, leaving the solutions perc;eptibly weaker. The removed salts were for the most part readily dissolved by a small quantity of water. W. Schumacher {Hoff, Jahres,,, 1867, p. 18) observed that humu^, artificially prepared by the * These statements of Bacon, Hales, Berzelius, and Matteucci, are derivet' from Prof. Way’s paper Oii the Power of Soils, etc.” {Jour, Boy, Ag. Soc. oj Eng,, XI, 316.) ABSORBENT POAVER OF SOILS. 173 action of oil of vitriol on sugar, when placed in ten times its quantity of solutions of various salts (containing about ^ per C(‘nt of solid matter) absorbed of sulphates of soda and ammonia, and chlorides of calcium and ammonium, about 2 per cent ; of sulphate of potash 4 per cent ; and of phosphate of soda 10 per cent. Schumacher also noticed that sulphate of potash is able to expel sulphate of ammO“ Ilia from humic acid which has been saturated with the latter salt, but that the latter cannot displace the former. In Schumacher’s experiments, pure water freely dissolved the salts absorbed by the humic acid. Explanation. — Let us consider what occurs in the acj of solution and in this separation of soluble matters from a liquid. The difference between the solid and the liquid state, so far as we can define it, lies in the unequal cohe- sion of the particles. Cohesion prevails in solids, and op- poses freedom of motion among the particles. In liquids, cohesion is not altogether overcome but is greatly weak- ened, and the particles move easily upon each other. When a lump of salt is put into water, the cohesion that otherwise maintains its particles in the solid state is over- come by the attraction of adhesion, which is mutually ex- erted between them and the particles of water, and the salt dissolves. If now into the solution of salt any in- soluble solid be placed which the liquid can Avet (adhere to) its particles Avill exert adhesive attraction for the par- ticles of salt, and the tendency of the latter Avill be to concentrate someAvhat upon the surface of the solid. If the solid, thus introduced into a solution, be exceed- ingly porous, or otherwise present a great amount of sur- face, as in case of sand or humus, this tendency is propor- tionately heightened, and a separation of the dissolved substance may become plainly evident on proper examina- tion. When, on the other hand, the solid surface is rela- tively small, no weakening of the solution may be percep- tible by ordinary means. Doubtless the glass of a bottle 174 HOW CROPS FEED. containing brine concentrates the latter where the two are in contact, though th^fFect may be difficult to dem- onstrate. X Defecating Action of Charcoal on Solutions. — Char- coal manifests a strong surface attraction for various solid substances, and exhibits this power by overcoming the adhesion th(‘y have to the particles of water when dis- solved in that fluid. If ink, solution of indigo, red wine, or bitter ale, be agitated some time with charcoal, the color, and in the case of ale, the bitter principle, will be taken up by the charcoal, leaving the liquid colorless and comparatively tasteless. Water, which is impure from putrefying organic matters, is sweetened, and brown sugars are whitened by the use of charcoal or bone-black. In case of bone-black, the finely divided bonc‘-earth (phos- phate of lime) assists the action of the charcoal. Fixing of Dye-Stuffs • — The familiar process of dyeing depends upon the adhesion of coloring matters to the fiber of textile fabrics. Wool steeped in solution of indigo at- taches the pigment permanently to its fibers. Silk in the same way fastens the particles of rosaniline, which consti- tutes the magenta dye. Many colors, e. g. madder and logwood, which will not adhere themselves directly to cloth, are made to dye by the use of mordants — substances Uke alumina, oxide of tin, etc. — which have adhesion both to the fabric and the pigment. Absorptive Power of Clay. — These effects of charcoal and of the fibers of cotton, etc., are in great part identical with those previously noticed in case of sand and humus. Their action is, however, more intense, and the effects are more decided. Charcoal, for example, that has ab- sorbed a pigment or a bitter principle from a liquid, will usually yield it up again to the same or a stronger solvent. In some instancies, however, as in dyeing with simple col- ors, matters are fixed in a state of great permanence by ABSORBENT POWER OF SOILS. 175 the absorbent ; and in others, as where mordants are used, chemical combinations supervene, which possess extraordi- nary stability. Many facts are known which show that soils, or certain of their ingredients, have a fixing power like that of char- coal and textile fibers. It is a matter of common expe- rience that a few feet or yards of soil intervening between a cess-pool or dung-pit, and a well, preserves the latter against contamination for a longer or shorter period. J. P. Bronner, of Baden, in a treatise on ‘‘ Grape Cul- ture in South Germany,” published in 1836, fii st mentions that dung liquor is deodorized, decolorized, and rendered nearly tasteless by filtration through garden earth. Mr. Huxtable, of England, made the same observation in 1848, and Prof. Way and others have published extended in- vestigations on this extremely important subject. Prof. Way informs us that he filled a long tube to the depth of 18 inches with Mr. Huxtable’s light soil, mixed with its own bulk of white sand. “ Upon this filter-bed a quantity of highly offensive stinking tank water was ])Oured. The liquid did not pass for several hours, but ultimately more than 1 ounce of it passed quite clear ^ free from smell or taste^ except a peculiar earthy smell and taste derived from the soil.” Similar results were obtain- ed by acting upon putrid human urine, upon the stinking* water in which flax had been steeped, and upon the water of a London sewer. Prof. Way found that these effects were not strikingly manifested by pure sand, but appeared when clay was used. He found that solutions of coloring matters, such as logwood, sandal-wood, cochineal, litmus, etc., when fib tered through or sliaken up with a portion of clay, are entirely deprived of color. {Jour. Hoy. Ag. Soc, of Hng.^ XI, p. 364.) These effects of clay or clayey matters, like the fixing power of cotton and woolen stuffs upon pigments, must 176 now CROPS FEED. be regarded for the most part as purely physical. There are other results of the action of the soil on saline solu- tions, which, though perhaps influenced by simple physical action, are preponderatingly chemical in their aspect. These eflects, which manifest themselves by chemical de- compositions and substitutions, will be fully discussed in a subsequent chapter, p. 333. § 6- PERMEABILIir OF SOILS TO LIQUID WATER. IMBIBITION. CAPILLARY POWER. The fertility of the soil -is greatly influenced by its de- portment toward water in the liqui I state. A soil permeable to water when it allows th it liquid to soak into or run through it. To be permeable is of course to be porous. On the size of the pores depends its degree of i^ermeabllity. Coarse sand>, and soils Avhich iiave few but lar(fe pores or interspaces, allow water to run through them readily — percolates them. When, instead of running through, the water is largely absorbed and held by the soil, the latter is said to possess great capillary power ^ such a soil has many and minute pores. Tile cause of capillarity is the same surface attraction which has been already under notice. * When a narrow vial is partly fllled with water, it will be seen that the liquid adheres to its sides, and if it be not more than one-half inch in diameter, the surface of the liquid will be curved or concave. In a very narrow tube the liquid will rise to a considerable height. In these cases the surface attraction of the glass for the water neu- tralizes or overcomes the weight of (earth’s attraction for) the latter. The pores of a sponge raise and hold water in them, in the same way that these narrow (capillary *) tubes sup- * From capUlus, the Latin word for hair, because as fine as hair; (but a hair is no tube, ti.i io often supposed.) PERMEABILITY OF SOILS TO LIQUID WATER. 177 port it. When a body has pores so fine (surfaces so near each other) that their surface attraction is greater than the gravitating tendency of water, then the body will im- bibe and hold water — will exhibit capillarity ; a lump of salt or sugar, a lamp-wick, are familiar examples. When the pores of a body are so large (the surfaces so distant) that they cannot fill themselves or keep themselves full, the body allows the water to run through or to percolate. Sand is most easily permeable to water, and to a higher degree the coarser its particles. Clay, on the other hand, is the least penetrable, and the less so the purer and more plastic it is. When a soil is too coarsely porous, it is said to be leqchy or huxigry. The rains that fall upon it quickly soak through, and it shortly becomes dry. On such a soil, the manures that may be applied in the spring are to some de- gree washed down below the reach of vegetation, and in the droughts of summer, plants suffer or perish from want of moisture. When the texture of a soil is too fine, — its pores too small, — as happens in a heavy clay, the rains penetrate it too slowly; they flow oflT the surface, if the latter be in- clined, or remain as pools for days and even weeks in the hollows. In a soil of proper texture the rains neither soak off into the under-earth nor stagnate on the surface, but the soil always (except in excessive wet or drought) maintains the moistness which is salutary to most of our cultivated plants. Movements of Water in the Soil# — If a wick be put into a lamp containing oil, the oil, by capillary action, gradually permeates its whole length, that which is above as well as that below the surface of the liquid. When the lamp is set burning, the oil at the flame is consumed, and as each particle disappears its place is supplied by a new one, until the lamp is empty or the flame extinguished. 8 * 178 HOW CROPS FEED. Something quite analogous occurs in the soil, by Avliich the plant (cori’esponding to the flame in our illustration) is fed. The soil is at once lamp and wick, and the %oater of the soil represents the oil. Let evapoi-ation of water from the surface of the soil or of the plant take the place of the combustion of oil from a wick, and the matter stands thus : Let us suppose dew or rain to have saturated the ground with moisture for some depth. On recurrence of a dry atmosphere with sunshine and wind, the surface of the soil rapidly dries ; but as each particle of water es- capes (by evaporation) into the atmosphere, its place is supplied (by capillarity) from the stores below. The as- cending water brings along with it the soluble mattei's of the soil, and thus the roots of plants are situated in a stream of their appropriate food. The movement proceeds in this way so long as the surface is drier than the deeper soil. AYhen, by rain or otherwise, the surface is saturated, it is like letting a thin stream of oil run upon the apex of the lamp-wick — no more evaporation into the air can oc- cur, and consequently there is no longer any ascent of watei* ; on the contrary, the water, by its own weight, penetrates the soil, and if the underlying ground be not saturated with moisture, as can happen where the subter- ranean fountains yield a meagre supply, then capillarity will aid gravity in its downward distribution. It is certain that a portion of the mineral matters, and, perhaps, also some organic bodies which feed the plant, are more or less freely dissolved in the water of the soil. So long as evaporation goes on from the surface, so long there is a constant upward flow of these matters. Those portions winch do not enter vegetation accumulate on or near the surface of the ground; when a rain falls, they are washed down again to a certain depth, and thus are kept constantly changing their place with the water, which is the vehicle of their distribution. In regions where rain falls periodically or not at all, this upward flow of the soil- PERMEABILITY OF SOILS TO LIQUID WATER. 179 water often causes an accumulation of salts on the surface of the ground. Thus in Bengal many soils which in the wet season produce the most luxuriant crops, during the rainless portion of the year become covered with white crusts of saltpeter. The beds of nitrate of soda that are found in Peru, and the carbonate of soda and other salts which incrust the deserts of Utah, and often fill the air with alkaline dust, hav^ accumulated in the same manner. So in our western caves the earth sheltered from rains is saturated with salts — epsom-salts, Glauber’s-salts, and salt- peter, or mixtures of these. Often the rich soil of gardens is slightly incrusted in this manner in our summer weather ; but the saline matters are carried into the soil with the next rain. It is easy to see how, in a good soil, capillarity thus acts in keeping the roots of phmts constantly immersed in a stream of water or moisture that is now ascending, now descending, but never at rest, and how the food of the plant is thus made to circulate around the oi*gans fitted for absorbing it. The same causes that maintain this perpetual supply of water and food to the plant are also efficacious in con- stantly preparing new supplies of food. As before ex- plained, the materials of the soil are always undergoing decomposition, whereby the silica, lime, phosphoric acid, potash, etc., of the insoluble fragments of rock, become soluble in water and accessible to the plant. Water charged with carbonic acid and oxygen is the chief agent in these chemical changes. The more extensive and rapid the circulation of water in the soil, the more matters will be rendered soluble in a given time, and, other things be- ing equal, the less will the soil be dependent on manures to keep up its fertility. Capacity of Imbibition. Capillary Power. — No mat- ter how favorable the structure of the soil may be to the 180 HOW CROPS FEED. circulation of water in it, no continuous upward movement can take place without evaporation. The ease and rapid- ity of evaporation, while mainly depending on the condi- tion of the atmosphere and on the sun’s heat, are to a cer- tain degree influenced by the soil itself. We have already seen that the soil possesses a power of absorbing watery vapor from the atmosphere, a power which is related both to the kind of material that forms jhe soil and to its state of division. This absorptive power opposes evaporation. Again, difierent soils manifest widely diflerent capacities for imhihing liquid water — capacities mainly connected with their porosity. Obviously, too, the quantity of liquid in a given volume of soil affects not only the rapidity, but also the duration of evaporation. The following tables by Schiibler illustrate the peculi- arities of diflerent soils in these respects. The first col- umn gives the percentages of liqnid water absorbed by the completely dry soil. In these experiments the soils were thoroughly wet with water, the excess allowed to drip off, and the increase of weight determined. In the second column are given the percentages of vrater that evaporated during the space of four hours from the satu- rated soil spread over a given surface : Quartz sand 25 88.4 Gypsum 27 71.7 Lime sand 29 75.9 Slaty marl 34 68.0 Clay soil, (sixty per cent clav,) 40 52.0 Loam “ 51 45.7 Plough land 52 3:3.0 Heavy clay, (eiiihty per cent day,) 61 34.9 Pure gray clay 70 31 9 Fine carbonate of lime 85 28.0 Garden mould 89 24.3 Humus 181 25.5 Fine carbonate of magnesia ...* 256 10.8 It is obvious that these two columns express nearly the some thing in different ways. The amount of water re- PERMEABir.lTY OF SOILS TO LIQUID WATER. 181 tained increases from quartz sand to magnesia. The rap- idity of drying in the air diminishes in the same direction. Some observations of Zenger ( Wilda^s Centralhlatt^ 1858, 1, 430) indicate the influence of the state of division of a soil on its power of imbibing water. In the subjoin- ed table are given in the first column the per cent of wa- ter imbibed by various soils which had been brought to nearly the same degree of moderate fineness by sifting off both the coarse and the fine matter ; and the second col- umn gives the amounts imbibed by the same soils, reduced to a high state of division by i)ulverization. Coarse. Fine. Quartz sand. 30.0 53 5 Marl (used as fertilizer,) 30.3 54.5 Marl, underlyino^ peat, 39.0 48 5 Brick clay, 00.3 57.5 Moor soil. 101.5 101.0 Aim (lime-sinter,) 10S.3 70.4 Aim i'Oil, ITS. 3 10,3.5 Peat dust. 377.0 308.5 ^ The effects of pulverization on soils whose particles are compact is to increase the surface, and increase to a cor- rc^sponding degree the imbibing power. On soils consist- ing of porous particles, li e lime-sinter and peat, pulver- ization destroys the porosity to some extent and diminishes the amount of absorption. The first class of soils are probably increased in bulk, the latter reduced, by grinding. Wilhelm, ( WildcCs Centralblatty 1863, 1, 118), in a series of experiments on various soils, confirms the above results of Zenger. He found, c. g., that a garden mould imbibed 114 per cent, but when pulverized absorbed but 62 per cent. To illustrate the different properties of various soils for which the farmer has but one name, the fact may be ad- duced that while Schiibler, Zenger, and Wilhelm found the imbibing power of ‘‘ clay ” to range between 40 and 70 per cent, Stoeckhardt examined a “ clay ” from Saxony 182 now CROPS FEED that held 150 per cent of water. So the humus of Seh ab- ler imbibed 181 per cent ; the peat of Zenger, 377 per cent ; while Wilhelm examined a very porous peat that took up 519 per cent. These differences are dependent mainly on the mechanical texture or porosity of the material. The want of capillary retentive power for water in the case of coarse sand is undeniably one of the chief reasons of its unfruitfulness. The best soils possess a medium re- tentive power. In them, therefore, are best united the conditions for the regular distribution of the soil- water under all circumstances. In them this process is not hin- dered too much either by we t or diy weather. The re- taining power of humus is seen to be more than double that of clay. This result might appear at first sight to be in contradiction to ordinary observations, for we are accustomed to see water standing on the surface of clay but not on humus. It must be borne in mind that clay, from its imperviousness, holds water like a vessel, the wa- ter remaining apparent; bat humus retains it invisibly, its action being nearly like that of a sponge. One chief cause of the value of a layer of humus on the surface of the soil doubtless consists in tliis great re- taining power for water, and the success that has attended the })ractice of green manuring, as a means of renovating almost wortldess shifting sands, is in a great degree to he attributed to this cause. The advantages of mulching are explained i:i the same way. Soils which are over-rich in humus, especially those of reclaimed peat-bogs, have some detrimental peculiarities deserving notice. Stoeckhardt ( WiJdas Centralblatt^ 1858, 2, 2:2) examined the soil of a cultivated moor in Saxony, which, when moist, had an imbibing power of 00-69“ After being thoroughly dried, however, it lost its adhesiveness, and the imbibing power fell to 26-30“ |^. It is observed in accordance with these data that such soils retain water late in spring; and when they become CHANGES OP TUB BULK OP THE SOIL. 183 very dry in summer they arc slow to take up water again, so that rain-water stands on the surface for a considerable time without penetrating, and when, after some days, it is soaked up, it remains injuriously long. Light rains after drought do little immediate good to such soils, while heavy rains always render them too wet and cold, unless they are suitably ameliorated. The same is true to a less degree of heavy, compact clays. § CHANGES OF THE BULK OF THE SOIL BY DRYING AND FROST. The Shrinking of Soils on Drying is a matter of no little practical importance. Tiiis shrinking is of course offset by an increase of bulk when the* soil becomes wet. In variable weather we have thercTore constant changes of volume occurring. Soils rich in humus experience these changes to the greatest degree. The surfaces of moors often rise and fall with tlie wet or dry season, through a space of sev- eral inches. In ordinary light soils, containing but little humus, no change of bulk is evident. Otherwise, it is in clay soils that shrinking is most perceptible ; since these soils only dry superficially, they do not appear to settle much, but become fu-l of cracks and rifts. Heavy clays may lose one-tenth or more of their volume on drying, and since at the same time they harden about the rootlets which arc imbedded in them, it is plain that these indis- pensable organs of tlic plant must thereby be ruptured during the protracted dry weather. Sand, on the other hand, does not change its bulk by wetting or drying, and when present to a considerable extent in the soil, its par- ticles, being interposed betweem those of the clay, prevent the adhesion of the latter, so that, although a sandy loam shrinks not inconsiderably on drying, yet the lines of sepa- 184 now CROPS FKED. ration are vastly more numerous and less wide than in purer clays. Such a soil does not cake,” hut remains friable and powdery. Marly soils (containing carbonate of lime) are especially ]): one to fall to a fine powder during drying, since the carbonate of lime, which, like sand, shrinks very little, is itself in a state of extreme division, and therefore more effectually separates the clayey particles. The unequal shrinking of these two intimately mixed ingredients ac- complishes a perfect pulverization of such soils. On the cold, heavy soils of Upper Lusatia, in Germany, the appli- cation of lime has been attended witli excellent results, and the 1 irger share ( f the benefit is to be accounted for by the improvement in the texture of those soils which follows liming. The carbonate of lime is considerably soluble in water charged with carbonic acid, as is the wa- ter of a soil containing vegetable matter, and this agency of distribution, in connection with the mechanical opera- tions of tillage, must in a short time effect an intimate mixture of the lime with the whole soil. A tenacious clay is thus by a heavy liming made to approach the condition of a friable marl. Heaving by Frost# — Soils which imbibe much water, es|)eeially clay and peat soils, have likewise the disagree- able ])roperty of being heaved by frost. The expansion, by freezing, of the liquid water they contain, separates the particles of soil from each other, raises, in fact, the surface for a considerable height, and thus ruptures the roots of grass and especially of fall-sowed grain. The lifting of fence posts is due to the same cause. ADHESIVENESS OF THE SOIL. In the language of the farm a soil is said to be heavy or light, not as it weighs more or less, but as it is easy or r" 185 ADHESIVENESS OE THE difficult to work. The state of, dryness lias great influence 0!i this quality. Sand, lime, and humus have very little adhesion when dry, but considerable when wet. Soils in which they predominate are usually easy to work. But clay or impalpable matter has entirely diflferent characters, upon which the tenacity of a soil almost exclusively de- pends. Dry ‘‘clay,” when powdered, has hardly more consistence than sand, but when thoroughly moistened its particles adhere together to a soft and plastic, but tena- cious mass ; and in drying away, at a certain point it be- comes very hard, and requires a good deal of force to peneti’ate it. In this condition it offers gi*eat resistance to the instruments used in tillage, and when thrown up by the plow it forms lumps which require repeated harrow- ings to break them down. Since the adhesiveness of the soil depends so greatly upon tlie quantity of water con- tained in it, it follows that thorough draining, combined with deep tillage', whereby sooner or later tin* stiflfest clays become read ly permeable to water, must have the best effects in making such soils easy to vrork. The English practice of burning clays speeddy accoiU' plishes the same purpose. When clay i^ burned and tlu n crushed, the particles no longer adhere tenaciously to- gether on moistening, and the mass does not acquire again the unctuous plasticity peculiar to unburned clay. Mixing sand with clay, or incorporating vegetable mat- ter with it, or liming, serves to sepa’*ate the particles from e ach other, and thus remedies too great adhesiveness. Tlie considerable expansion of water in the act of solid- ifying (one-fifteenth of its volume) has already been no- ticed as an agency in reducing rocks to powder. In the same way the alternate freezing and thawing of the water which impregnates the soil during the colder part of the year plays an important part in overcoming its adhesion. The effect is apparent in the spring, immediately after “ the frost leaves the ground,” and is very considerable, 186 HOW CROPS FEED. fuliy one-third of the resistance of a clay or loam to the plow thus disappearing, according to Schiibler’s experi- ments. Tillage, when carried on with the soil in a wet condi- tion, to some extent neutralizes the effects of frost, espe» cially in tenacious soils. Fall-plowing of stiff soils has been recommended, ii j order y) expose them to the disintegrating effects of fro^. § 9 . RELATIONS OF THE SOIL TO HEAT. Trtie relations of tlio soli to heat are of tlie utmost im- portafice Mn affecting its fertility. The distribution of plants general, determined by differences of mean temperature. In the same climate and locality, however^ Ave find the farmer distinguishing between cold and Avarm soils. The Temperature of (he Soil varies to a certain depth Avith that of the air; yet its changes occur more slowly, are confined to a considerably narrower range, and dimin- ish downward in rapidity and amount, until at a certain depth a point ii reached where the temperature is invari- able. In summer the temperature of the soil is higher in day- time than that of the* air ; at night the temperature of the surface rapidly fills, especially Avhon the sky is clear. In temperate climates, at a de})th of three feet, the tern ]>erature remains unchanged from day to night ; at a depth of 20 feet the annual tem]>erature varies but a degree or two ; at 75 feet below the surface, the thermometer re- mains perfectly stationary. In the vaults of the Paris Observatory, 80 feet deep, the temperature is 50° Fahren- heit. In tropical regions the point of nearly unvarying temperature is reached at a depth of one foot. RELATIONS OF THE SOIL TO HEAT. 187 The mean annual temperature of the soil is the same as, or in higher latitudes a degree above, that of the air. The nature and position of the soil must considerably influence its temperature Sources of the Heat of the Soil* — The sources of that heat which is found in the soil are tliroe, viz. : First, tlie original heat of the earth ; second, the chemical process of oxidation or decay going on within it; anowerfiil sun. Since, however, the soil was moist, the wilting could only aiise from the inability of the roots to absorb water as rapidly as it exhaled from the leaves, owing to the low temperature. Further ex- periments showed that warming the soil in which the wilted plants stood, restored the foliage to its proper tur- gidity in a short time, and by surrounding the soil of a fresh plant with snow, the leaves wilted in three or four hours. Cabbages, winter colza, and beans, similarly circum- stanced, did not wilt, showing that different plants are un- equally affected. The general rule nevertheless appears to be established that within certain limits the root absorbs more vigorously at high than at low temperatures. The Amount of Loss of Water of Vegetation in Wilt- ing has been determined by Hesse ( Vs, I, 248) in case of sugar-beet leaves. Of two similar leaves, one, gathered at evening after several days of dryness and sun- shine, contained 85.74® 1^ of water; the other, gathered the mext morning, two hours after a rain storm, yielded 89.57® Iq. The difference was accordingly 3.8® |^. Other observations corroborated this result. Is Exhalation Indispensable to Plants] — It was for a long time supposed that transpiration is indispensable to the life of plants. It was taught that the water which the plant imbibes from the soil to replace that lost by ex- halation, is the means of bringing into its roots the min- eral and other soluble substances that serve for its nutii- ment. There are, however, strong' grounds for believing that tlie current of water which ascends through a plant moves independently of the matters that may be in solution, either without or within it;' and, moreover, the motion of soluble matters from tlie soil into the plant may go on, THE FREE WATER OF THE SOIL. 207 although there he no ascending aqueous current. (H. C. G., pp. 288 and 340.) In accordance with these views, vegetation grows as well in the confined atmosphere of green-houses or of W ardian Cases, where the air is for the most part or entirely satu- rated with vapor, so that transpiration is reduced to a mini- mum, as in the free air, where it may attain a maximum. As is well known, the growth of field crops and garden vegetables is often most rapid during damp and showery weather, when the transpiration must proceed with com- parative slowness. While the above considerations, together with the asser- tion of Knop, that leaves lose for the first half hour nearly the same quantities of water under similar exposure, whether they are attached to the stem or removed from it, whether entire or i i fragments, would lead to the con- clusion that transpiration, which is so extremely variable in its amount, is, so to speak, an accident to the plant and not a process essential to its existence or vvelfare, there are, on the other hand, facts which appear t ) indicate the contrary. In certain experiments of Sachs, in which the roots of a bean were situated in an atmosphere nearly saturated with aqueous vapor, the foliage being exposed to the air, although the plant continued for two months fresh and healthy to appearance, it remained entirely stationary iu its development. ( Vfi, St.^ I, 237.) Knop also mentions incidentally ( I, 192) that beans, lupines, and maize, die when the whole pi ^At is kept confined in a vessel over water. It is not, however, improbable that the cessMion of growth in the one case and the death of the plants in the other were due not so much to the checking of transpira- tion, which, as we have seen, is never entirely suppressed under these circumstances, as to the exliaustion of oxygen or the undue accumulation of carbonic acid in the narrow 208 HOW CROPS FEED. and confined atmosphere in which these results were noticed. On the whole, then, we conclude from the evidence be- fore us that transpiration is not necessary to vegetation, or at least fulfills no very important offices in the nutrition of plants. The entrance of wate r into the plant and the steady maintenance of its proper content of this substance, under all circumstances is of the utmost moment, and leads us to notice in the next place the Direct Proof that Crops can Absorb from the Soil enough Hygroscopic Water to Maintain their Life.^-Sachs suffered a young bean-plant standing in a pot of very reten- tive (clay) soil to remain without watering until the leaves began to wilt. A high and spacious glass cylinder, having a layer of water at its bottom, was then provided, and the pot containing the wilting plant was supported in it, near its top, while the cylinder was capped by two semicircular plates of glass which closed snugly about the stem of the bean. The pot of soil and the roots of the plant were thus enclosed in an atmosphere which was constantly sat- urated, or nearly so, with watery vapor, while the leaves were fully exposed to the free air. It was now to be ob- served whether the water that exhaled from the leaves could be supplied by the hygroscopic moisture which the soil should gather from the damp air enveloping it. This proved to be the case. The leaves, previously wilted, re- covered their proper turgidity, and remained fresh during the two months of June and July. Sachs, liaving shown in other experiments that plants situated precisely like this bean, save that the roots are not in contact with soil, lose water continuously and have no power to recover it from damp air (p. 3G) thus gives us demonstration that the clay soil which condenses vapor in its pores and holds it as hygroscopic water, yields it again to the plant, and thus becomes the medium through which THE FREE WATER OF THE SOIL. 209 water is continually carried from the atmosphere into vegetation. In a similar experiment, a tobacco plant was employed which stood in a soil of humus. This material was also capable of supplying the plant with water by virtue of its hygroscopic power, but less satisfactorily than the clay. As already mentioned, these plants, while remaining fresh, exhibited no signs of growth. This may be due to the consumption of oxygen by the roots and soil, or possibly the roots of plants may require an occasional drenching with liquid water. Further investigations in this direc- tion are required and promise most interesting results. What Proportion of the Capillary and Hygroscopic Water of the Soil may Plants Absorb, is a question that Dr. Sachs has made the only attempts to answer. When a plant, whose leaves are in a very moist atmosphere, wilts or begins to wilt in the night time, when therefore trans- piration is reduced to a minimum, it is because the soil no longer yields it water. The quantity of water still con- tained in a soil at that juncture is that which the plant cannot remove from it, — is that which is unavailable to vegetation, or at least to the kind of vegetation experi- mented with. Sachs made trials on this principle with tobacco plants in three different soils. The plant began to wilt in a mixture of hlaclc humus (from beech-wood) and sand^ when the soil contained 12.3® Ij, of water.* This soil, however, was capable of holdw 46®!^ of capillary water. It results therefore tiiat of its mghest content of absorbed water 33.7® (=46—12.3) was available to the tobacco plant. Another plant began to wilt on a rainy night, while the loam it stood in contained 8®| ^ of water. This soil was able to absorb 52.1®|^of water, so that it might after • Ascertained by drying at 212*. 210 HOW CROPS FEED. sntuiation, furnish the tobucco plant Avith 44.1® of its weiglit of water. A coarse sand that could hold 20.8® of water was found to yield all but 1.5® to a tobacco plant. From these trials Ave g’ather Avith at least approximate a^pcuracy the poA^rer of the plant to extract Avater from these several soils, and by difference, the quantity of wa- ter in them that Avas unavailable to the tobacco plant. How do the Roots take Hygroscopic Water from the Soil ? — The entire plant, when living, is itself extremely hygroscopic. Even the dead plant retains a certain pro- portion of A\ ater with great obstinacy. Thus wheat, maize, starch, straw, and most air-dry vegetable substances, contain 12 to 15®}^ of water; and Avhen these matters are exposed to damp air, they can take up much more. Ac- cording to Trommer {Bodenkunde^ p. 270), 100 j^arts of the following matters, when dry, absorb from moist air in 12 24 48 72 hours. Fine cut barley straw, 15 34 34 45 pai*ts of water. U U 41 ^ 30 27 29 “ “ “ ‘‘ whit« nnsized paper, * 8 12 17 19 “ As already explained, a body is hygroscopic because there is attraction between its particles and the particles of water. The form of attraction exerted thus among different kinds of matter is termed adhesiA^e attraction, or simply adhesion. Adhesion acts only through a small distance, but its in- tensity varies greatly within this distance. If we attempt to remove hygroscopic water from starch or any similar body by drying at 212°, Ave shall find that the greater part of the moisture is easily expelled in a short time, but Ave shall also notice that it requires a relatively much longer time to expel the last portions. A general law of attraction is that its force diminishes as the distance be- tween the attracting bodies increases. This has been ex- THE FREE WATER OF THE SOIL. 211 aetly demonstrated in case of the force of gravity and electrical attraction, which act through great intervals of space. We must therefore suppose that when a mass of hygro- scopic matter is allowed to coat itself with water by the exercise of its adhesive attraction, the layer of aqueous particles which is in nearest contact is more strongly held to it than the next outer layer, and the adhesion diminish- es with the distance, until, at a certain point, still too small for ns to perceive, the attraction is nothing, or is neutralized by other opposing forces, and further adhesion ceases. Suppose, now, we bring in contact at a single point two masses of the same kind of matter, one of which is satu- rated with hygroscopic water and the other is perfectly dry. It is plain tliat the outer layers of water-particles adhering to the moist body come at once within the range of a more powerful attraction exerted by the very surface of the dry body. The external particles of water attached to the first must then pass to the second, and they must also distribute themselves equally over the surface of the latter; and this motion must go on until the attraction of the two surfaces is equally satisfied, and the water is equally distributed according to the surface, i. e., is uni- form over the whole surface. If of two difierent bodies put in contact (one dry and one moist) the surfaces be equal, but the attractive force of one for water be twice that of the other, then motion must go on until the one has appropriated two-thirds, and the other is left with one-third the total amount of water. When bodies in contact have thus equalized the water at their disposal, they may be said to be in a condition of hygroscopic equilibrium. Any cause which disturbs this equilibrium at once sets up motion of the hygrosco[)ic water, which always j^roceeds from the more dry to the less dry body. 2!2 HOW CROPS FEED. The application of these principles to the question be- fore us is apparent. The young, active roots that are in contact with the soil are eminently hygroscopic, as is de- monstrated by the fact that they supply the plant with large quantities of water when the soil is so dry that it has no visible moisture. They therefore share with the soil the moisture which the latter contains. As water evaporates from the surface of the foliage, its place is supplied by the adjacent portions, and thus motion is es- tablished within the plant which propagates itself to the roots and through these to the soil. Each particle of water that flies ofl* in vapor from the leaf makes room for the entrance of a particle at the root. If the soil and air have a surplus of water, the plant will contain more ; if the soil and air be dry, it will contain less. Within certain narrow limits the supply and waste may vary without detriment to the plant, but wlien the loss goes on more rapidly than the supply can be kept up, or when the absolute content of water in the soil is re- duced to a certain point, the plant shortly wilts. Even then its content of water is many times greater than that of the soil. The living tobacco plant cannot contain less than 80" 1^, of water, while the soils in Sachs’ experiments contained but 12.3®j^ and 1.5" 1^^ respectively. When fully air-dry, vegetable matter retains 13" to 15® 1^^ of water, while the soil similarly dry rarely contains more than The plant therefore, especially when living, is much more hygroscojnc than the soil. CMT If roots are so hygroscopic, why, it may be asked, do they not directly absorb vapor of water from the air of the soil ? It cannot be denied that both the roots and fo- liage of plants are capable of this kind of absorption, and that it is taking place constantly in case of the roots. The experiments before described prove, however, that the higher orders of plants absorb very little in this way, THE FBEE WATER OF THE SOIL. 213 too little, in fact, to be estimated by the methods hitherto * employed. Sachs explains this as follows : Assuming that the roots have at a given temperature as strong an attrac- tion for water in the state of vapor as for liquid water, the amount of each taken up in a given time under the same circumstances would be in proportion to the weight of each contained in a given space. A cubic inch of water yields at 212° nearly a cubic foot (accurately, 1,696 times its volume, the barometer standing at 29.92 inches) of vapor. We may then U'^sumo that the absorption of liq- uid or hygroscopic water proceeds at least one thousand times more rapid y than that of vapor, a difference in rate that enables us to comprehend why a plant may gain water by its roots from the soil, when it would lose water by its roots were they simply stationed in air saturated with vapor. Again, the soil need not be more hygroscopic than roots, to supply the latter with water. It is important only that it present a sufficient surface. As is well known, a plant requires a great volume of earth to nourish it properly, and the root-surface is trilling, compared to the surface of the particles which compose the soil. Boussingault found by actual measurement that, accord- ing to the rules of garden culture as practiced near Stras- burg, a dwarf bean had at its disposition 5T pounds of soil; a potato plant, 190 pounds; a tobacco plant, 470 pounds ; and a hop plant, 2,900 pounds. , These weights correspond to about 1, 3, 7, and 50 cubic feet respectively. The Quantity of Water in Teg^etation is influenced by lat of the Soil. — De Saussure observed that plants grow- Lg in a dry lime soil contained less water than those from loam. It is well known that the grass of a wet summer is taller and more succulent, and the green crop is heavier than that from the same field in a dry summer. It does not, however, make much more hay, its greater weight consisting to a large degree of water, which is lost in dry* 214 now CROPS FEED. ing. Ritthausen gives some data concerning two clover crops of the year 1854, from a loamy sand, portions of which were manured, one with ashes, others with gypsum. The following statement gives the produce of the nearly* fresh and of the air-dry crops. Weight in pounds per acre. Fresh. Air-dry. Water lost in drying. Crop I, manured with ashes, 14,903 5,182 9,721 “ “ uiimanured, 12,380 6,418 6,962 Crop II, manured with gypsum. 22,256 4,800 17,456 “ “ unmanured, 18,815 6,190 13,625 It is seen that while in both cases the fresh manured crop greatly outweighed the unmanured, the excess of weight consisted of water. In fact, the unmanured plots yielded mo7^e hay than the manured. The manure ! : ^ c parts. Car- bonic add. Ox- ygon. Nitro- gen. 50820! 12 0.025 20.945 79.030 The percentage, as well as the absolute quantity of car- bonic acid, is seen to stand in close relation with the or- ganic matters of the soil. The influence of the recent application of manure rich* in organic substances is strik- ingly shown in case of the asparagus bed and the sandy soil. The lowest percentage of carbonic acid is-10 Jimes that of the atmosphere a few feet above the surface of the * earth, as determined at the same time, while the highest percentage is -EQOjbimes that proportion. Even in the sandy subsoil the quantity of free carbonic acid is as great as in an equal bulk of the atmosphere ; and in the cultivated soils it is present in from 6 to 95 220 HOW CROPS PEED. times greater amount. In other words, in the cultivated soils taken to the depth of 14 inches, there was found as much carbonic acid gas as existed in the same horizontal area of the atmosphere through a height of 7 to 110 feet. The accumulation of such a percentage of carbonic acid gas in the interstices of the soil demonstrates the rapid formation of this substance, which must as rapidly diffuse off into the air. The roots, and, what is of more signifi- cance, the leaves of crops, are thus far more copiously fed with this substance than were they simply bathed by the free atmosphere so long as the latter is un agitated. When the wind blows, the carbonic acid of the soil is of less account in feeding vegetation compared with that of the atmosphere. Wlien the air moves at the late of two feet per second, the current is just plainly perceptible. A mass of foliage 2 feet high and 200 feet * long, situated in such a current, would be swept by a volume of atmos- phere, amounting in one minute to 48,000 cubic feet, and containing 12 cubic feet of carbonic acid. In one hour it would amount to 2,280,000 cubic feet of air, equal to 720 cubic feet of carbonic acid, and in one day to 69,120,000 cubic feet of air, containing no less than 17,280 cubic feet of carbonic acid. In a brisk wind, ten times the above quantities of air and carbonic acid would pass by or through the foliage. It is plain, then, that the atmosphere, which is rarely at rest, can supply carbonic acid abundantly to foliage with- out the concourse of the soil. At the same time it should not be forgotten that the carbonic acid of the atmosphere is largely derived from the soil. Carbonic Acid in the Water of the Soil# — Notwith- standing the presence of so much carbonic acid in the air of the soil, it appears that the capillary soil-water, or so ♦ A square field containing one acre is 208 feet and a few inches on each side. THE AIR OF THE SOIL. 221 much of it as may be expressed by pressure, is not nearly saturated with this gas. De Saussure {Recherches Chimiques sur la Vegetation^ p. 168) filled large vessels with soils rich in organic mat- ters^ poured on as much water as the earth could imbibe, allowing the excess to drain oif and the vessels to stand five days. Then the soils were subjected to powerful pressure, and the water thus extracted was examined for carbonic aci(l. It contained but 2®|g of its volume of the gas. Since at a medium temperature (60° F.) water is capa- ble of dissolving 100® (its own bulk) of carbonic acid, it would appear on first thought inexplicable that the soil- water should hold but 2 per cent. Henry and Dalton long ago demonstrated that the relative proportion in which the ingredients of a gaseous mixture are absorbed by wa- ter depends not only on the relative solubility of each gas by itself, but also on the proportions in which they exist in the mixture. The large quantities of oxygen, and especially of nitrogen, associated with carbonic acid in the pores of the soil, thus act to prevent the last-named gas being taken up in gi*eater amount ; for, while carbonic acid is about fifty times more soluble than the atmos- pheric mixture of oxygen and nitrogen, the latter is pres« ent in fifty times (more or less) the quantity of the former. Absorption of Carbonic Acid by the Soil, — ^According to Van den Broek, {Ann. derChemie u. Ph.^ 115, p. 87) certain wells in the vicinity of Utrecht, Holland, which are exca- vated only a few feet deep in the soil of gardens, contain water w^hich is destitute of carbonic acid (gives no precipi- tate with lime-water), while those which penetrate into the underlying sand contain large quantities of carbonate of lime in solution in carbonic acid. Van den Broek made the following experiments with garden-soil newly manured, and containing free carbonic acid in its interstices, which could be displaced by a cur- 222 HOW CROPS FEED. rent of air. Tlirough a mass of this earth 20 inches deep and 3 inches in diameter, pure distilled water (free from carbonic acid) was allowed to filter. It ran through without taking up any of the gas. Again, water contain- ing its own volume of carbonic acid was filtered through a similar body of the same earth. This water gave up all its carbonic acid while in contact loith the soil. After a certain amount had run off, however, the subsequent por- tions contained it. In other words, the soils experiment- ed with were able to absorb carbonic acid from its aqueous solution, even when their interstices contained the gas in the free state. These extraordinary jfiienomena deserve further study. § 3 . NON-NITROGENOUS ORGANIC MATTERS OF THE SOIL.— CARBOHYDRATES, VEGETABLE ACIDS. VOLATILE ORGANIC ACIDS. HUMUS. Carbohydrates, or Bodies of the Cellulose Group,— The steps by which organic matters beconie incorporated with the soil have been recounted on p. 135. When plants perish, their proximate principles become mixed with the soil. These organic matters shortly begin to decay or to pass into humus. In most circumstances, however, the soil must contain, temporarily or periodically, unalter- ed carbohydrates. Cellulose, especially, may be often found in an unaltered state in the form of fragments of straw, etc. De Saussure {Recherches^ p. 174) found that water dis- solved from a rich garden soil that had been highly ma- nured for a long time, several thousandths of organic matter, giving an extract, which, when concentrated, had an almost syrupy consistence and a sweet taste, was neither acid nor alkaline in reaction, and comported itself not unlike an impure mixture of glucose and dextrin. ORGANIC MATTERS OF THE SOIL. 223 Yerdeil and Risler have made similar observations on ten soils from the farm of the Institut Agronomique^ at Ver- sailles. They found that the water-extract of these soils contained, on the average, of organic matter, wliich, wlien strongly heated, gave an odor like burning paper or sugar. These observers make no mention of crenates or apocrenates, an not inconsiderable quantities. When the earth is turned over by the plow, two essentially different processes fol- low each other: oxidation, where the air has free access; reduction, v here its access is more or less limited by the adhesion of tlie partic’es and especially by moisture. In the loose, dry earth apocrenic acid is formed ; in the firm, ORGANIC MATTERS OF THE SOIL. 229 moist soil, and in every soil after rain, crenic acid is pro- duced, so that the action or effects of these substances are alternately manifested.” The Humus Bodies Artificially Produced, — When sugar, cellulose, starch, or gum, is boiled with strong hy- drochloric acid or a strong solution of potash, brown or black bodies result which have the greatest similarity with tlie ulmin and humin, the ulmic and humic acids of peat and of soils. By heating humus witli nitric acid (a vigorous oxidizing agent), crenic and apocrenic acids are formed. The pro- duction of these bodies by sucli artificial means gives in- teresting confirmation of the reality of t’leir existence, and demonstrates the correctness of the views which have been advanced as to their origin. While the precise composition of all these substances may well be a matter of doubt, and from the difficulties of obtaining them in the pure state is likely to remain so, their existence in the soil and their importance in agricul- tural science are beyond question, as we shall shortly have o])portunity to understand. The Condition of these Humus Bodies in the Soil requires some comment. The organic substances thus noticed as existing in the soil are for the most pai*t acids, but they do not exist to much extent in the free state, ex- cept in bogs and morasses. A soil that is fit for agricul- tural purposes contains little or no free acid, except car- bonic acid, and oftentimes gives an alkaline reaction with test-papers. Regarding ul.nic and humic acids, which, as we have stated, are extracted by solution of carbonate of soda from humus, it appears that they do not exhibit acid char- acters before treatment with the alkali. They appear to be altered by the alkali and converted through its influ- ence into acids. Only those portions of tliese bodies 230 now CROP3 FEED. which are acted upon Ly the carbonates of potash, soda, and lime, that become ingredients of the soil by the solution of rocks, or by carbonate of ammonia brought down from the atmosphere or produced by decay of ni- trogenous matters, acquire solubility, and are, in fact, acids ; and these portions are acids in combination (salts), and not in the free state. The Salts of the Humus Acids that may exist in the soil, viz., the ulmates, humates, apocrenates, and crenatcs of potash, soda, ammonia, lime, magnesia, iron, manga- nese, and alumina, require notice. The ulmates and humates agi*cc closely in their cha:*:ic- ters so far as is known. The ulmates and humates of the alkalies (potash, soda, and ammonia) are freely soluble iu water. They arc formed v hen the alkalies or their carbonates come in contact 1st, with the ulmic and liumic jicids themselves ; 2d, with the ulmates and humates of lime, magnesia, iron, and mang:i- nese; and 3d, by the action of the alkalies and their car- bonates on humin and ulmin. Their solutions are yellow or brown. The ulmates and humates of lime, magnesia, iron, man- ganese, and alumina, are insoluble^ or but very slightly soluble in water. From ordinary soils where these earths and oxides pre- dominate, water removes but traces of humates and ulmates. From peat, gar^len earth, and leaf-mould, which contain excess of the humic and ulmic acids, and carbonate of ammonia resulting from the decay of nitrogenous matters, water extracts a perceptible amount of these acids render- ed soluble by the alkali. There appear to exist double sedis of humic acid and o ulmic acid, i. c., salts containing the acid combined with two or more bases. By adding solutions of compounds (e. g., sulphates) of lime, magnesia, iron, manganese, and alumina ORGANIC MATTERS OP THE SOIL. 231 to solutions of humates or ulmates of the alkalies, precipi- tates are formed in which the acid is combined both with an alkali and an earth or oxide. These double salts are insoluble or nearly so in water. Solutions of alkalies and alkali carbonates decompose them into soluble alkali humates or ulmates, and the earths or oxides are at least partially held in solution by* the resulting compounds. Mulder describes the following experiments, which justify the above conclusions. “Garden-soil was extracted with dilute solution of car- bonate of soda, the soil being in excess. The solution was filtered and ])recipitated by addition of water, and the precipitate was washed and dis- solved in a little ammonia. Thus was obtained a dark-brovrn solution of neutral hiimate of ammonia. The solution was rendered perfectly colorless by addition of caustic lime — basic humate of lime is therefore perfectly insoluble in water. “Chloride of calcium rendered the solution very nearly colorless — neutral humate of lime is almost entirely insoluble. “Calcined magnesia decolorized the solution perfectly. Chloride of magnesium made the solution very nearly colorless. “The sulphates of protoxide aiul peroxide of iron, and sulphate of manganese, decolorized the solution perfectly. “These decolorized liquids were made brown again by agitating them and the precipitated humates with carbonate of ammonia.” Apocrenates and €renates, — According to Mulder, the crenates and apocrenates of the soil nearly always contain ammonia — are, in fact, double salts of this alkali with lime, iron, etc. The apocrenates of the alkalies are freely soluble ; those of the oxides of iron and manganese are moderately soluble; those of lime, magnesia, and alumina, are in- soluble. The . crenates of the alkalies, of lime, magnesia, and protoxide of iron, are soluble ; those of jjrotoxide of iron and manganese are less soluble; crenate of alumina is insoluble. All the salts of these acids that are insoluble of them- selves are decomposed by, and soluble in, excess of the alkali-salts. 232 HOW CIJOPS FEED. to 1 ' 4 > Do the Organic Matters of the Soil Directly IVourish Veg'etation I — This is a question which, so far as humus is concerned, has been discussed with great earnestness by the most prominent writers on Agricultural Science. De Saussure, Berzelius, and Mulder, have argued in the aflirmative ; while Liebig and his numerous r.dherents to- tally deny to humus the possession of any nutritive value. It is probable that humus m^y bo directly absorbed by, and feed, plants. It is certain, also, that it does not con- tribute largely to the sustenance of agricultural crops. To ascertain the real extent to which humus is taken up by plants, or even to demonstrate that it is taken up by them, is, perhaps, impossible from the data now in our possession. We shall consider the probabilities. There have not been wanting attempts to ascertain ex- perimentally Avhether humus is capable of feeding vegeta- tion. Hartig, De Saussure, Wiegmann ai>d Polstorf, and Soubeiran, liave observed the growth of plants whose roots were immersed in solutions of humus. The experi- ments of Hartig led this observer to conclude that humate of potash and water-extract of peat do not enter the roots cf plants. Not having had access to the original account of this investigation, the writer cannot, perhaps, judge properly of its merits. It appears, however, that the roots of the plants operated with were not kept constantly moist, and their extremities wei*e decomposed by too great concentration of the liquid in which they were immersed. Under such conditions accurate results were out of the question. De Saussure i^Ann. Ch. u, 42, 275) made two ex- periments, one with a bean, the other with Polygonum Persicaria^ in which these plants were made to vegetate with their roots immersed in a solution of humate of jpot- ash (prepared by boiling humus with bicarbonate of pot- ash). In the first case the bean plant, orierinally weighing 11 gi-ains, gained during 14 days G grins., while the ORGANIC MATTERS OF THE SOIL. 233 weic^ht of tlie humus decreased 9 millioframs. The Polygonum during 10 days gained 3,5 grms., and tlie solution lost 43 milligrams of humus. These experi- ments Liebig considers undecisive, because an alkali- humate loses weight by oxidation (to carbonic acid and water) when exposed in solution to the air. Mulder, how- ever, denies that any appreciable loss could occur in such a solution during the time^of experiment, and considers the trials conclusive. In a third experiment, De Saussure placed the roots of Polygonum Perslcaria in the water-extract of turf con- taining no humic acid but crenic and apocrenic acids, where they remained nine days in a very flo irishing state, putting forth new roots of a healthy white color. An equal quantity of the same extract was placed in a simi- lar vessel for purposes ot* coin|)arison. It was found that the solution in which the plants were stationed became paler in color and remained perfectly clear, while the other solution retained its original dark tint and became tuibid. The former left after evaporation 33 mgrms., the latter 39 ingrms. of solid residue. The differen *e of G mgrms., De Saussure believes to have been absorbed by the plant. Wiegmann and Polstorf [Ueher die un^rganischeu Be- standthelle der VJlanzen) experim nted in a similar man- ner with Mentha und^data^ a kind < f mint, and Polygonum Perslcaria^ using two plants of 8 inches height, whose roots were well developed and perfectly healthy. The plants grew for 30 days in a wine-yehow water-extract of leaf compost (containing 148 mgrms. ol‘ solid sub- stance — organic matter, carbonate of lime, etc., — in 100 grams of extract), the roots being shielded from light, and during the same time an equal quantity of the same solution stood near by in a vessel of the same dimensions. The plants grew well, increasing 6^ inches in length, and put forth long roots of a healthy white color. On the 18th of July the plants were removed from the solution, 234 HOW CROPS FEED. and 100 grams of the solution left on evafforation 132 mgrms. of residue. The same amount of humus extract, that had been kept in a contiguous vessel containing no plant, left a residue of 136 mgims. The disappearance of humus from the solution is thus mostly accounted for by its oxidation. De Saussure considers that his experiments demonstrate that humic acid and (in his third exp.) the matters ex- tracted from peat by water (crenic and apocrenic acids) are absorbed by plants. Wiegmann and Polstorf attrib- ute any apparent absorption in their trials to the una- voidable errors of experiment. Tlie quantities that may have been absorbed were indeed small, but in our judg- ment not smaller than ought to be estimated witli certainty. Other experiments by Soubeiran, Malaguti, and Mulder, are on record, mostly agreeing in this, viz., that agricul- tural plants (beans, oats, cresses, peas, barley) grow well when their roots are immersed in, or watered by, solutions of humates, ulmat(‘S, crenates, and apocrenates of ammo- nia and potasl). Tliese experiments are, however, all un- adapted to demonstrate that humus is absorbed by plants, and the trials of De Saussure and of Wiegmann, and Pol- storf, are the only ones that have been made under condi- tions at all satisfactory to a just criticism. These do not, perhaps, conclusively demonstrate the nutritive function of humus. It is to be observed, however, that what evi- dence they do furnish is in its favor. They prove effec- tually that humus is not injurious to plants, though Liebig and Wolff have strenuously insisted that it is poisonous. Let us now turn to the probabilities bearing on the question. In the first place there are plants — those living in bogs and flourishing in dung-heap liquor — which throughout the whole ])eriod of their growth must tolerate^ if not ab- sorb, somewhat strong solutions of humus. Again, the cultivated soil invariably yields some humus ORGANIC MATTERS OP THE SOIL. 235 (we use this word as a general collective term) to rain- water, and the richer the soil, as made so by manures and judged of by its productiveness, the larger the quantity, up to certain limits, of humus it contains. If, as we have seen, plants always contain silica, though this element be not essential to their development (H. C. G., p. 186), is it probable that they are able to reject humus so constantly presented to them under such a variety of forms? Liebig opposes the view that humus contributes directly to the nourishment of plants because it and its compounc is are insoluble; in the same book, however, {Die Chemie in ihrer Ayiwenduag auf Agricultur luid PhysloJogie^ 7th Ed., 1862) he teaches the doctrine that all the food of the agricultural plant exists in the soil in an insoluble form. This old objection, still m lintained, tallies poorly with his new doctrine. The old objection, furthermore, is baseless, for the humates are as soluble as phosphates, which are gathe: ed by every plant and from all soils. It lias been the habit of Liebig and his adherents to teach that the plant is nourished exclusively by the last products of the destruction of organic matter, viz., by car- bonic acid, ammonia, nitric acid, and water, together with the ingredients of ashes. While no one denies or doubts that these substances chiefly nourish agricultural plants, no one can deny that other bodies may and do take part in the process. It is well established that various organic substances of animal origin, viz., urea, uric acid, and gly- cocoll, are absorbed by, and nourish, agricultural plants ; while it is universally known that the principal food of multitudes of the lower orders of plants, the fungi, includ- ing yeast, mould, rust, brand, mushrooms, are fed entirely, so far as regards their carbon, on organic matters. Thus, yeast lives upon sugai-, the vinegar plant on acetic acid, the Peronospora infestans on the juices of the potato, etc. There are many parasitic plants of a higher order common in our forests whose roots are fastened upon and 236 HOW CROPS FEED. absorb the juices of the roots of trees ; such are the beech drops {Epiphegua)^ pine drops {Pterospora)^ Indian pipe {Monotropa) ; the last-named also grows upon decayed vegetable matter. The dodder ( Cv.scuta) is parasitic upon living plants, especially upon flax, whose juices it appropriates often to the destruction of the crop. It is indeed true that there is a wide distinction between most of these parasites and agricultural plants. The former are mostly destitute of chlorophyll, and appear to be totally incapable of assimilating carbon from cai-bonic acid.* The latter acquire certainly the most of their food from carbonic acid, but in their root-organs they contain no chlorophyll ; there they cannot assimilate carbon from carbonic acid. They do assimilate nitrogen from the or- ganic principles of urine ; what is to hinder their obtain- ing carbon from the soluble portions of humus, from the organic acids, or even from unaltered carbohydrates? De Saussuro, i;i his investigation just quoted from, says further: “After having thus demonstrate 1 f the absorp- tion of humus by the roots, it remains to speak of its as- similation by the plant. One of the indications of this assimilation is derived from the absence of the ])eculiar color of humus in the interior of the plant, which has ab- sorbed a strongly colored solution of humate of potash, as compared to the different deportment of coloring matters * Dr. Lack {Ann. Chem. u. Pharm., 78, 85) has indeed shown that the mistle- toe ( Viscum album) decomposes carbonic acid in the sunlight, but this plant has greenish-yellow leaves contaiidng chlorophyll. t We take occasion liere to say explicitly that the only valid criticism of De Saussure’s experiment on the Polygonum supplied with humate of potash, is Liebig’s, to the effect that the solution lost humic acid to the amount of 43 milli- grams not as a result of absorption hy the jilaiit, but by direct oxidation. Mulder and Soubeiran both agree that such a solution could not lose perceptibly in this way. That De Saussure was satisfied that such a loss could not occur, would appear from the fact that he did not attempt to estimate it, as he did in the subsequent (ixperiment with water-extract of peat. If, now. Liebig be wrong in his objection (and he has furnished no proof that his statement is true), then De Saussure has demonstrated that humic acid is absorbed by plants. ORGANIC MATTERS OF THE SOIL. 237 (sucli as ink) which cannot nourish the plant. The latter (ink, etc.) leave evidences of their entrance into the plant, while the former are changed and partly assimilated. A bean 15 inches high, whose roots were placed in a decoction of Brazil-wood (to which a little alum had been added and which was filtered), was able to absorb no more than the fifth part of its weight of this solution without wilting and dying. In this process four-fifths of its stem was colored red. Polygonum Ferslcaria (on occasion an aquatic or bog plant) grew very well in the same solution and absorbed its coloring matter, but the color never reached the stem. The red principle of Brazil-wood being partially assimilat- ed by the Polygonum^ underwent a chemical change; while in the bean, which it was unable to nourish, it suf- fered no change. The Polygonum itself became colored, and withered when its roots were immersed in diluted ink.” Biot {Comptes Pendus^ 1837, 1, 12) observed that the red juice of Phytolacca decandra (poke-weed), when poured upon the soil in which a white hyacinth was blos- soming, was absorbed by the plant, and in one to two hours dyed the flowers of its own color. After two or three days, however, the red color disappeared, the flow- ers becoming white again. From the facts just detailed, we conclude that some kinds of organic matters may be absorbed and chemically changed (certain of them assimilated) by agricultural plants. We must therefore hold it to be extremely probable that various forms of humus, viz., soluble humates, ulmates, crenates, and apocrenates, together with the other soluble organic matters of the soil, are taken up by plants, and decomposed or transformed, nay, we may say, assimilated by them. 238 HOW CROPS FEED. A few experiments might easily be devised which would completely settle this point beyond all controversy. Organic Matters as Indirect Sources of Carbon to Plants. — The decay of organic matters in the soil supplies to vegetation considerably more carbonic acid in a given time than would be otherwise at the command of crops. The quantities of carbonic acid found in various soils have already been given (p. 219). The beneficial effects of such a source of carbonic acid in the soil are sufficiently obvious (p. 128). Organic Matters not Essential to the Growth of Crops. — Although, on the farm, crops are rarely raised without the concurrence of humus or at least without its presence in the soil, it is by no means indispensable to their life or full development. Carbonic acid gas is of it- self able to supply the rankest vegetation with carbon, as has been demonstrated by numerous experiments, in which all other compounds of this element have been excluded (p. 48).^ § 4 . THE AMMONIA OF THE SOIL. J In the chapter on the Atmosphere as the food of plants we have been led to conclude that the element nitrogen^ so indispensable to vegetation as an ingredient of albumin, etc., is supplied to plants exclusively by its compounds^ and mainly by ammon ia and nitric acid^ or by substances w^hich yield these bodies readily on oxidation or decay. ^ We have seen further that both ammonia and nitric acid exist in very minute quantities in the atmosphere, are dis- solved in the atmospheric waters, and by them brought into the soil. It is pretty fairly demonstrated, too, that these bodies, as occurring in the atmosphere, become of appreciable use THE AM^^O^IA OF THE SOIL. 239 to agricultural vegetation only a' ter tlieir incorporation with the soil. Rain and dew are means of collecting them from the atmosphere, and, as we shall shortly see, the soil is a storehouse for them and the medium of their entrance into vegetation. This is tlierefore the proper place to consider in detail the origin and formation of ammonia and nitric acid, so far as these points have not been noticed when discussing their relations to the atmosphere. Ammonia is formed in the Soil either in the decay of organic bodies containing nitrogen, as the albuminoids, etc., or by the reduction of nitrates (p. 74). The former process is of universal occurrence since both vegetable and animal remains are constantly present in the soil; the latter transformation goes on only under certain condi- tions, which will be considered in the next section (p. 269). The statement tliat ammonia is .generated from the free nitrogen of the air and the nascent hydrogen of decom- posing carbohydrates, as cellulose, starch, etc., or that set free from v/ater in the oxidation of certain metals, as iron and zinc, has been completely disproved by Will. (Ann, d, Ch. u, Ph,^ 45, i^p. 106-112.) The ammonia encountered in such experiments may have been, 1st, that pre-existini^ in the i)ores of the substances, or dissolved in the wa- ter operated with. Faraday {Uesearches in Chemistrij and Physics^ p. 143) has shown by a series of exact experiments that numerous, we may say all, porous bodies exposed to the air have a minute amount of ammonia f adhering to them ; 2d, that which is generated in the process of Testin;^ or experimenting (as when iron is heated with potash), and formed by the action of an alkali on some compound of nitrogen occurring in the materials of the experiment; or, 3d, that which results from the reduc- tion of a nitrite formed from free nitrogen by the action of ozone (pp. 77-83). The Ammonia of the Soil. — a. Gaseous Ammonia as Carbonate , — Boussingault and Lewy, in their examination of the air contained i:i the interstices of the soil, p. 219, 240 HOW CROPS FEED. tested it for ammonia. In but two instances did they find sufficient to weigh. In all cases, however, they were able to detect it, though it was present in very minute quanti- ty. The two experiments in which they were able to Aveigh the ammonia were made in a light, sandy soil from which potatoes had been lately harvested. On the 2d of September tlic field was manured Avith stable dung; on the 4tli the first experiment Avas made, the air being taken, it must be inferred from the account giAmn, at a depth of 14 inches. In a million parts of air by weight Avere found 32 parts of ammonia. Five days subsequently, after rainy AA^eather, tlie air collected at the same place contained but 13 })arts in a million. b. Ammonia physically condensed in the Soil, — Many porous bodies condense a large quantity of ammonia gas. Charcoal, which has an extreme porosity, serves to illus- trate this fact. De Saussure found that box- wood char- coal, freshly ignited, absorbed 98 times its volume of ammonia gas. Similar results have been obtained by Sten- house, Angus Smitli, and others (p. 1C6). The soil cannot, however, ordinarily contain more than a minute quantity of pliysically absorbed ammonia. The reasons are, first, a porous body saturated with ammonia loses the greater share of this substance when other gases come in contact with it. It is only ])Ossible to condense in charcoal 93 times its volume of ammonia, by cooling the hot charcoal in mer- cury Avhich does not penetrate it, or in a vacuum, and then bringing it directly into the pure ammonia gas. The charcoal thus saturated with ammonia loses the latter rap- idly on exposure to the air, and Stenhoiise has found by actual trial that charcoal exposed to ammonia and after- wards to air r(‘tains but rninute traces of the former. Secondly, the soil when adapted for vegetable groAvth is moist or Avet. The water of the soil Avhich covers the particles of earth, rather than the particles themselves, must contain any absorbed ammonia. Thirdly, there are THE AMIMONIA OF THE SOIL. 241 in fertile soils substances which combine chemically with ammonia. That tlie soil does contain a certain quantity of ammo- nia adhering to tlie surface of its particles, or, more prob- ably, dissolved in the hygroscopic water, is demonstrated by the experiments of Boussingault and Lewy just alluded to, in a:l of which ammonia was detected in the air in- cluded in the cavities of the soil. In case ammonia were physically condensed or absorbed, a portion of it would be carried off in a current of air in the conditions of Boussingault and Lewy’s experiments, — nay, all of it would be removed by such treatment sufficiently prolonged. Brustlein (Boussingault’s Agronomis^ et\^ 1, p. 152) records that 100 parts of moist earth placed in a vessel of about 2^ quarts caj)acity containing 0,9 parts of (free) ammonia, absorbed during 3 hours a little more than 0.4 pai ts of the latter. In another trial 100 parts of the same earth dried, placed under the same circumstances, absorb- ed 0.28 parts of a nmonia and 2.G parts of water. Brustlein found that soil placed in a confined atmos- phere containing very limited quantities of ammonia can- not condense the latter completely. In an experiment similar to those just described, 100 parts of earth (tena- cious calcareous clay) and 0.019 parts of ammonia were left together 5 days. At the conclusion of this period 0.016 parts of the latter had been taken up by the earth. Tlie remainder was found to be dissolved in the water that had evaporated from the soil, and that formed a dew on the interior of the glass vessel. Brustlein proved further that while air may be almost entirely deprived of its ammonia by traversing a long column of soil, so the soil that has absorbed ammonia readily gives up a large share of it to a stream of pure air. He caused air, charged with ammonia gas by being made to bubble through water of ammonia, to traverse a tube 1 ft. long filled with smnll fragments of moist soil. The 11 242 HOW CROPS FEED, ammonia was completely absorbed in the first paii; of the experiment. After about 7 cubic feet of air had streamed through the soil, amn)onia began to escape unabsorbed. The earth thus saturated contained 0.192® of ammonia. A current of pure air was now passed through the soil as long as ammonia was removed by it in notable quantity, about 38 cubic feet being required. By this means more than one-half the ammonia was displaced and carried off, the earth retaining but 0.084® 1^^, Brustlein ascertained farther tliat ammonia which has been absorbed by a soil from aqueous solution escapes easily when the earth is exposed to the air, especially when it is repeatedly moistened and allowed to dry. 100 parts of the same kind of soil as was employed in the experiments already described were agitated with 187 parts of water containing 0,889 parts of ammonia. The earth absorbed 0.157 parts of ammonia. It was now drained from the liquid and allowed to dry at a low tem- perature, which operation required eight days. It was then moistened and allowed to dry again, and this was re- peated four times. The progressive loss of ammonia is shown by the following figures. 100 parts of soil absorbed 0.157 parts of amitjonla. contained after the first drying 0,083 “ “ “ “ “ second “ ,0.0fi6 “ “ “ “ “ third ‘‘ 0.054 “ “ “ “ “ ‘‘ ‘‘ “ “ “ fourth 0.041 “ “ ‘‘ “ “ ‘‘ fifth ‘‘ 0.039 ‘‘ ‘‘ In this instance the loss of ammonia amounted to three^ fourths the quantity at first absorbed. The extent to which absorbed ammonia escapes from the soil is greatly increased by the evaporation of water. Brustlein found that a soil containing 0.067® of ammo- nia suffered only a trifling loss by keeping 43 days in a dry place, whereas the same earth lost half its ammonia in a shorter time by being thrice moistened and dried. According to Knop ( Vs. Ill, p. 222), the single THE AMMONIA OF THE SOIL. 243 proximate ingredient of soils that under ordinary cir- cumstances exerts a considerable surface attraction for ammonia gas is day, Knop examined the deportment of ammonia in this respect towards san10X1 A OF THE SOIL. 249 The fact that caustic potash, a more energetic decom- posing agent than lime, disengaged more ammonia than the latter from the yellow clay, strengthens the view that ammonia is produced and not merely driven off under the conditions of these experiments, and that accordingly the figures are too high. Other chemists employing the same method have obtained similar results. Boussingault (Agronomie^ T. Ill, p. 206) was the first to substitute magnesia for potash and lime in the estima- tion of ammonia, having first demonstrated that this sub- stance, so feebly alkaline, does not perceptibly decompose gelatine, albumin, or asparagine, all of which bodies, espe- cially the latter, give ammonia when boiled with milk of lime or solutions of potash. The results of Boussingault here follow. Lccalities. Liebfnmenberg, Alsatia Bischwiller, “ Merck wilier, “ Bechelbronn, “ Miltellmasbergen, “ He Napoleon, Miilhouse, Ar^entan, Orne, Que«noy-snr-I)eule, Nord, Rio Madeira, America, Rio Trombetto, . “ Rio Negro, “ Santarem, “ He dn Saint, “ Martinique, “ Rio Cupari, (leaf mold,) “ Peat, Paris, Quantity of Ammonia per cent : 0.002*2 0.0020 0.0011 0.0009 O.OOOT 0.0006 0.0060 0.0012 0.0090 0.0030 0.0038 0.0083 0.0080 0.0085 0.0525 0.0180 The above results on French soils correspond with those obtained more recently on soils of Saxony by Knop and Wolff, who have devised an ingenious method of estimat- ing ammonia, which is founded on altogether a different principle. Knop and Wolff measure the nitrogcm gas which is set free by the action of chloride of soda (Ja- velle water*) in a specially constructed apparatus, the * More properly hypochlorite of soda^ whicli is used in mixture with bromine and caustic soda. 11 * 250 HOW CROPS FEED. Azotometer. [Cheynisches Centralblatt^ 1860, pp. 243 and 534.) By this method, which gives accurate results when ap- plied to known quantities of ammonia-salts, Knop and Wolff obtained the following results: Ammonia in dry soil. Very sandy soil from birch forest 0.00077o|o Rich lime soil from beech forest 0.00087 Sandy loam, forest soil 0.00012 Forest soil 0.00080 Meadow soil, red sandy loam 0.00027 Average 0.00056 The rich alluvial soils from tropical America are ten or more times richer in ready-formed ammonia than those of Saxony. These figures show then that the substance in question is very variable as a constituent of the soil, and that in the ordinary or poorer classes of unmanurcd soils its percentage is scarcely greater than in the atmospheric waters. The Quantity of Ammonia fluctuates. — Boussi igault has further demonstrated by analysis what we have insist- ed upon already in this chapter, viz., that the quantity of ammonia is liable to fluctuations. He estimated ammonia in garden soil on the 4th of March, 1860, and then, moist- ening two samples of the same soil with pure water, ex- amined them at the termination of one and two months respectively. He found, March 4th, 0.009® of ammonia. April “ 0.014“ “ May “ 0.019 “ “ “ The simple standing of the moistened soil for two months sufticed in this case to double the content of am- monia. The quantitative fluctuations of this constituent of the soil has been studied further both by Boiissingault and by Knop and Wolff. The latter in seeking to answer the THE NITRIC ACID OF THE SOIL. 251 question — “ How great is the ammonia-content of good manured soil lying fallow?” — made repeated determina- tions of ammonia (17 in all) in the same soil (well-ma- nured, sandy, calcareous loam exposed to all rains and dews but not washed) during five months. The moist soil varied in its proportion of ammonia with the greatest irregularity between the extremes of 0.0008 and 0.0003® Similar observations were made the same summer on the loamy soil of a field, at first bare of vegetation, then cov- ered with a vigorous potato crop. In this case the fluctu- ations ranged from 0.0009 to 0.0003® as irregularly as in the other instance. Knop and Wolff examined the soil last mentioned at various depths. At 3 ft. the proportion .of ammonia was scarcely less than at the surface. At 6 ft. this loam, and at a somewhat greater depth an underlying bed of sand, contained no trace of ammonia. This observation ac- cords with the established fact that deep well and drain- waters are destitute of ammonia. Boussingault has discovered [Agronomie.^ 3, 195) that the addition of caustic? lime to the soil largely increases its content of ammonia — an effect due to the decomposing ac- tion of lime on the amide-like substances already noticed. § S- NITRIC ACID (NITRATES, NITROUS ACID, AND NITRITES) OF THE SOIL. Nitric acid is formed in the atmosphere by the action of ozone, and is brought down to the soil occasionally in the free state, but almost invariably in combination with ammonia, by rain and dew, as has been already described (p. 86). It is also produced in the soil itself by processes whose nature — considerably obscure and little understood - — will be discussed presently. 252 HOW CROPS FEED. In the soil, nitric acid is always combined with an alkali or alkali-earth, and never exists in the free state in appreciable quantity. We speak of nitric acid instead of nitrates, because the former is the active ingredient com- mon to all the latter. Before considering its formation and nutritive relations to vegetation, we shall describe those of its compounds which may exist in the soil, viz., the nitrates of potash^ soda^ llme^ magnesia^ and iron. Nitrate of Potash (K NO3) is the substance com- mercially known as niter or saltpeter. When pure (refin- ed saltpeter), it occurs in colorless prismatic crystals. It is freely solub’e in water, and has a peculiar sharp, cooling taste. Crude saltpeter contains common salt and other impurities. Nitrate of potash is largely procured for in- dustrial uses from certain districts of India (Bengal) and from various caves in tropical and temperate climates, by simjdy leaching the earth with water and evaporating tlie solution thus obtained. It is also made in artificial niter- beds or plantations in many European countries. It is likewise prepared artificially from nitrate of soda and caustic potash, or chloride of potassium. The chief Tise of the commercial salt is in the manufacture of gunpowder and fireworks. Sulphur, charcoal, (which are ingredicmts of gunpow- der), and other combustible matters, when heated in con- tact with a nitrate, burn with great intensity at the ex- pense of the oxygen which the nitrate contains in large proportion and readily parts with. Nitrate of Soda (Na NO3) occurs in immense quantities in the southern extremity of Peru, province of Tarapaca, as an incrustation or a compact stratum several feet thick, on the pampa of Tamar ugel, an arid plain situated in a region where rain never falls. The salt is dissolved in hot water, the solution poured off from sand and evaporated to the crystallizing point. The crude salt lias in general a THE NITRIC ACID OP THE SOIL. 253 yellow or reddish color. When pure, it is white or color- less. From the shape of the crystals it has been called cubic* niter; it is also known as Chili saltpeter, having been formerly exported from Chilian ports, and is some- times termed soda-saltpeter. In 1854, about 40,000 tons were shipped from the port of Iquique. Nitrate of soda is hygroscopic, and in damp air be- comes quite moist, or even deliquesces, and hence is not suited for making gunpowder. It is easily procured arti- ficially by dissolving carbonate of soda in nitric acid. This salt is largely employed as a fertilizer, and for pre- paring nitrate of potash and nitric acid. Kitrate of Lime (Ca2NO g) may be obtained as a white mass or as six-sided crystals by dissolving lime in nitric acid and evaporating the solution. It absorbs water from the air and runs to a liquid. Its taste is bitter and sharp. Nitrate of lime exists in well-waters and accompanies nitrate of potash in artificial niter-beds. IVitrate of Magnesia (Mg 2 N 03 ) closely resembles ni- trate of lime in external characters and occurrence. It may be prepared by dissolving magnesia in nitric acid and evaporating the solution. Nitrates of Iron. — Various compounds of nitric acid and iron, both soluble and insoluble, are known. In the soil it is probable that only insoluble basic nitrates of sesquioxide can occur. Knop observed ( Vi Y, 151) that certain soils 'when left in contact with solution of ni- trate of potash for some time, failed to yield the latter en- tirely to water again. The soils that manifested this anomalous deportment were rich in humus, and at the same time contained much sesquioxide of iron that could be dissolved out by acids. It is possible that nitric acid entered into insoluble combinations here, though this hypothesis as yet awaits proof. ♦ The crystals are, in fact, rhomboidal. 254 HOW CROPS FEED. Nitrates of alumina are known to the chemist, but have not been proved to exist in soils. Nitrate of ammonia has already been noticed, p. 71. Nitric Acid not usually fixed by the Soil, — In its deport- ment towafils the soil, nitric acid (either free or in its salts) differs in most cases from ammonia in one important par- ticular. The nitrates are usually not fixed by the soil, but remain freely soluble in water, so that washing readily and completely removes them. The nitrates of ammonia and potash are decomposed in the soil, the alkali being retain- ed, while the nitric acid may be removed by washing with water, mostly in the form of nitrate of lime. Nitrate of soda is partially decomposed in the same manner. Free nitric acid unites with lime, or at least is found in the washings of the soil in combination with that base. As just remarked, Knop has observed that certain soils containing much organic matters and sesquioxide of iron, appeared to retain or decompose a small portion of nitric acid (put in contact with them in the form of nitrate of potash). Knop leaves it uncertain whether this result is simply the fault of the method of estimation, caused by the formation of basic nitrate of iron, which is insoluble in water, or, as is perhaps more probable, due to the de- composing (reducing) action of organic matters. Nitrification is the formation of nitrates. When vege-^ table and animal matters containing nitrogen decay in the soil, nitrates of these bases presently appear. In Bengal, during the dry season, when for several months rain sel- dom or never falls, an incrustation of saline matters, chiefly nitrate of potash, accumulates on the surface of those soils, which are most fertile, and which, though culti- vated in the wet season only, yield two and sometimes three crops of grain, etc., yearly. The formation of ni- trates, which probably takes place during the entire year, appears to go on most rapidly in the hottest weather. THE NITETC ACID OF THE SOIL. 255 The nitrates accumulate near the surface when no rain falls to dissolve and wash them down — wlien evaporation causes a current of capillary water to ascend continually in the soil, carrying with it dissolved matters which must remain at the surface as the water escapes into the atmos- phere. In regions where rain frequently falls, nitrates are largely formed in ricli soils, but do not accumulate to any extent, unless in caves or positions artificially sheltered from the rain. Boussingault’s examination of garden earth from Lieb- frauenberg {Agronomie^ etc., T. II, p. 10) conveys an idea of the progress which nitrification may make in a soil un- der cultivation, and liighly charged with nitrogenous ma- nures. About 2.3 lbs. of sifted and well-mixed soil were placed in a heap on a slab of stone under a glazed roof. From time to time, as was needful, the earth was moist- ened with water exempt from ammonia. The proportion of nitric acid was determined in a sample of it on the day the experiment began, and the analysis was repeated four times at various intervals. The subjoined statement gives the per cent of nitrates expressed as nitrate of potash in the dry soil, and also the quantity of this salt contained in an acre taken to the depth of one foot.* Per cent. Lbs. per acre. 1857— 5th August, 0.01 34 “ —17th 0.06 222 “ — 2d September, 0.18 634 “ —17th 0.22 760 “ — 2d October, 0.21 728 The formation of nitrates proceeded rapidly during the heat of summer, but ceased by the middle of September. Whether this cessation was due to the lower temperature or to the complete nitrification of all the matter existing in the soil capable of this change, or to decomposition of nitric acid by the reducing action of organic matters, * The figures "iven above are abbreviated from the originals, or reduced tc English denominations with a trifling loss of exactness. 256 now CROPS FEED. further researches must decide. The quantities that aC’ cumulated in this experiment are seen to be very consider- able, when we remember that experience has shown that 200 lbs. per acre of the nitrates of potash or soda is a large dressing upon grain or grass. Had the earth been exposed to occasional rain, its analysis would have indi- cated a much less percentage of nitrates, because the salt would have been washed down far into, and, perhaps, out of, the soil but no less, probably even somewhat more, would have been actually formed. In August, 1856, Boussingault examined earth front the same garden after 14 days of hot, dry wc*ather. He found the nitrates equal to 911 lbs. of nitrate of potash per acre taken to the depth of one foot. From the 9th to the 20th of August it rained daily at Liebfrauenberg, more than two inches of water falling during this time. When the rain ceased, the soil contained but 38 lbs. per acre. In September, rain fell 15 times, and to the amount of four inches. On the 10th of October, after a fortnight of hot, Avindy weather, the gar- den had become so dry as to need watering. On being then analyzed, the soil was found to contain nitrates equiv- alent to no less than 1,290 lbs. of nitrate of potash per acre to the depth of one foot. This soil, be it rememberee converted into ammonia, which is at once rendered com- paratively insoluble. THE NITRIC At;ID OF THE SOIL. 271 Nitric Acid as Food to Plants#— Experiments demon- strating that nitric acid is capable of perfectly supplying vegetation with nitrogen were first made by Bouss i n g a u 1 1 {AgronomiG , Chimie Ajrl- ccle^ etc,^ 1 , 210 ). We give an ac- count of some of these. Two seeds of a dwarf Sunflow- er [Ilelianthus argophylliis)^ were planted in each of three pots, the soil of which, consist- ing of a mixture of brick - dust and sand, as well as the jDots them- selves, had been thoroughly freed from all ni- trogenous com- pounds by igni- tion and wash- ing witli distill- Fig. 9. ed water. To the soil of the pot A, fig. 9, nothing was added save the two seeds, and distilled water, with which all the plants were watered from time to time. With the soil of pot C, were incorporated small qunntities of phosphate of lime, 272 now CROPS FEED. of ashes of clover, and bicarbonate of potash, in order that the plants growing in it might have an abundant supply of all the ash-ingredients they needed. Finally, the soil of pot D received the same mineral matters as pot C, and, in addition, a small quantity (1.4 gram) of nitrate of pot- ash. The seeds were sown on the 5th of July, and on the 30th of September, the plants had the relative size and appearance seen in the figure, where they are represented in one-eighth of the natural dimensions. For the sake of comparison, the size of one of the largest leaves of the same kind of Sunflower that grew in the garden is represented at D, in one-eighth of its natural dimensions. Nothing can be more striking than the influence of the nitrate on the growth of this plant, as exhibited in this experiment. The plants A and C are mere dwarfs, al- though both carry small and imperfectly developed flow- ers. The plant D, on the contrary, is scarcely smaller than the same kind of plant growing under the best con- ditions of garden culture. Here follows a Table of the results obtained by the examination of the plants. oo SI I'i |3 \ Acquired by the pLarits in 86 days of 'Vegetation. - si S’® Carbon. 1 Nitro- A — nothing added to the soil 3.6 grm. 0.285 cubic cent. 2.45 grm. 0.114 grm. 0.0023 C— ashes, phosphate of lime, and bi- carbonate of potash, added to the soil ! 4.6 0.391 i 1 3.42 j 0.156 ! ! 0.0027 D — ashes, phosphate of lime, and ni-! trate of potash, added to the soih.i 198.3 21.111 182.00 8.444 1 0.1666 We gather from the above data : 1. That without some compound of nitrogen m the soil vegetation cannot attain any considerable development, notwithstanding all requisite ash-ingredients are present THE NITRIC ACID OP THE SOIL. 273 in abundance. Observe that in exps. A and C the crop attained but 4 to 5 times greater weight than the seed, and gathered from the atmosphere during 86 days but 2^ milligrams of nitrogen. The crop, supplied with nitrate of potash, weighed 200 times as much as the seed, and assimilated 63 times as much nitrogen as was acquired by A and C from external sources. 2. That nitric acid of itself may furnish all the nitrogen requisite to a normal vegetation. In another seiies of experiments {Agronomic^ etc,^ I, pp. 227-233) Boussingault prepared four pots, each containing 145 grams (about 5 oz. avoirdupois) of calcined sand with a little phospliate of lime and ashes of stable-dung, and planted in each two Sunflower seeds. To three of the pots he added weighed quantities of nitrate of soda — to No. 3 twice as much as to No. 2, and to No. 4 three times as much as to No. 3; No. 1 received no nitrate. The seeds germinated duly, and the plants, sheltered from rain and dew, but fully exposed to air, and watered with water exempt from ammonia, grew for 50 days. In the subjoined Table is a summary of the results. 1 Experiment | 1 * N. added as ni- trate of soda. Total N'. at dis- posed cf plants. Total N. of crop. 1 II % « «+t ^ e § Vegetable matter 07‘ganized in 50 da7js grenjoth. Eelatixe weights of matter organized}^ that of first Exp. 1 taken as vnity. Itl - p.l grms. grms. grms. grins. grms. grms. grms. grms. 1.. 0.0033 0.0000 0.0033 0.0053 1 0.0020t 0.397 1 1 2.. 0.0033 0.0033 0.0066 0.0063 i 0.0002$ 0.720 1.8 2 3.. 0.0033 0.0066 0.0090 0.0097 i 0.0002$ 1.130 2.8 3 4.. 0.0033 0.0264 0.029T 0.0251 1 0.0046$ 3.280 8.5 9 ♦ Nz^Nitro^cn. In the first Exp. a trifling quantity of nitrogen was gathered (as ammonia?) from the air. In the others, and especially in the last, nitrate of soda remained in the soil, 19 * 2T4 now CROPS FEED. not having been absorb 'd entii-ely by the plants. Observe, however, what a remarkable coincidence exists between the ratios of supply of nitrogen i.i form of a nitrate and those of growth of the several crops, as exhibited in the last two columns ot* the Table. Nothing could demon- strate more strikingly the nutritive function of nitric acid than these admirable investigations. Of the multitude of experiments on vegetable nutrition wliich have been recently made by the process of water- culture {JS, C. 6r., p. 167), nearly all have depended upon nitric acid as the exclusive source of nitrogen, and it has proved in all cases not only adequate to this purpose, but far more certain in its effects than ammonia or any other nitrogenous compound. NITROGENOUS ORGANIC MATTERS OF THE SOIL. AVAILABLE NITROGEN.— QUANTITY OF NITROGEN REQUIRED FOR CROPS. In the minerals and rocks of the earth’s surface nitrogen is a very small, scarcely appreciable ingredient. So far as we now know, ammonia-salts and nitrates (nitrires) are the only mineral compounds of nitrogen found in soils. When, however, organic matters are altered to humus, and become a part of the soil, its content of nitrogen ac- quires significance. In peat, which is humus compara- tively free from earthy matters, the proportion of nitrogen is often very considerable. In 32 specimens of peat ex- amined by the author {Peat and its Uses as Fertilizer and Fuel^ p. 90), the nitrogen, calculated on the organic mat- te s^ ranged from 1.12 to 4.31 per cent, the average being 2.6 per cent. The average amount of nitrogen in the air- dry and in some cases highly impure peat, was 1.4 per cent. This nitrogen belongs to the organic matters in NITKOGl:XOU3 Or.GANIC MATTERS OF THE SOIL. 275 great part, but a small proportion of it being in the form of ammonia-salts or nitrates. In 1846, Krocker, in Liebig’s laboratory, first estimated the nitrogen in a number of soils and marls (Ami. Ch. w, jP 4., 58, 387). Ten soils, which were of a clayey or loamy character, yielded from 0.11 to 0.14 per cent; three sands gave from 0.025 to 0.074 per cent; seven marls contained 0.004 to 0.083 per cent. Numerous examinations have since been made by An- derson, Liebig, Ritthausen, Wolff, and others, with simi- lar results. In all but his latest writings, Liebig has regarded thiis. nitrogen as available to vegetation, and in fact designated it as ammonia. Way, Wolff, and others, have made evi- dent that a large portion of it exists in organic combina- tion. Boussingault (Agronomie^ T. I) has investigated the subject most fully, and has shown that in rich and highly manured soils nitrogen accumulates in considerable quantity, but exists for the most part in an insoluble and inert form. In the garden of Liebfrauenberg, which had been heavily manured for centuries, but 4°!^ of the total nitrogen existed as ammonia-salts and nitrate^. The soil itself contained — Total nitrogen, 0.2C1 per cent. Ammonia, 0.0022 “ “ Nitric acid, . 0.00034 “ “ The subjoined Table includes the results of Boussin- gault’s examinations of a number of soils from France and South America, in which are given the quantities of am- monia, of nitric acid, expressed as nitrate of potash, and of nitrogen in organic combination. These quantities are stated both in per cent of the air-dry soil, and in lbs. av. per acre, taken to the di^pth of 17 inches. In another column is also given the ratio of nitrogen to carbon in the organic matters. (Agronomic.^ T II, p^D. 14-21.) 270 now CKOPS FEED. Ammonia, Nitrates, ^nd Organic Nitrogen or various Soils. Soils, Ammonia. • Nitrate of potash. Nitrogen in org. combVn. i-i "" i ^ per cent. lbs. per acre per cent lbs. per acre per cent. lbs per acre II s III G) r Licbfrauenl)erg, light gard. soil 0.0022 100 0.0175* 875 0.259 12970 1:0.3 cJ 1 Bischwillcr, light garden soil... 0.0020 100 0.1526 7630 0.295 14755 1:9.7 I 1 Bechelbronn, wheat field clay. 0.0009 45 0.0015 75 0.139 6985 l:h2 ^ 1 [Argentan, rich pasture 0.0060 300 0.0046 230 0.513 25650 1:8 cS 1 fRio Madeira, sugar field, clay 0.0090 450 0.0004 20 0.143 7140 1:6.3 o Rio Trombetto, forest heavy do. 0.0030 183 0.0001 5 0.119 5955 1:4.9 o Rio Negro, prairie v. fine sand. 0.0038 190 0.0001 5 0.068 3440 1:5.6 s J Santarem, cocoa plantation. . 0.0083 415 0.0011 55 0.649 32450 1:11 Saracca, near Amazon, loam.. 0.0042 210 none 0.182 9100 1:8.2 Rio Cupari, rich leaf mould 0.0525 2875 0.685 34250 1:18.8 c Ile« du Salut, French Guiana... 0.0080 400 0.0643 1 3215 0.543 27170 1:11.7 ^Martinique, sugar field 0.0055 275 1 0.0186 1 930 0.112 5590 1:8 * The same soil whose partial analysis has just been given, but examined for nitrates at another time. It is seen that in all cases the nitrogen in the forms of ammonia f and nitrates J is much less than that in organic combination, and in most cases, as in the Liebfraucnberg garden, the disparity is very great. Nature of the Nitrogenous Organic Matters, Amides, -Hitherto we have followed Mulder in assuming that the humic, ulmic, crenic, and apocrenic acids, are destitute of nitrogen. Certain it is, however, that natural humus is never destitute of nitrogen, and, as wo have remarked in case of peat, contains this element in considerable quanti- ty, often 3 per cent or more. Mulder teaches that the acids of humus, themselves free from nitrogen, are nat- urally combined to ammonia, but that this ammonia is with difficulty expelled from them, or is indeed impossible to separate completely by the action of solutions of the fixed alkalies. In all chemistry, beside, there is no example ^ of such a deportment, and we may well doubt whether the ammonia that is slowly evolved when natural humus is boiled with potash is thus expelled from a hum ate of ammonia. It is more accordant with general analogies to t Ammonia contains 82.4 per cent of nitro'ren. X Nitrate of potash contains 13.8 pjr cent of nitrogen. fslTROGENOUS OEOAXIG MATTERS OE THE SOIL. 277 supjDOse that it is generated by the action of the alhalL In fact, there are a large number of bodies which manifest a similar deportment. Many substances which are pro- /diiced from ammonia-compounds by heat and otherwise, and called amides^ to which allusion has been already made, j). 276, are of this kind. Oxalate of ammonia, when heated to decomposition, yields oxamide, which contains the elements of the oxalate minus the elements of two molecules of water, viz.. Oxalate of ammonia, Oxamide, ^ater, 2 (X II,) C, O, = 2 (N C, O, + 2 H,0 On b(uling oxamide with solution of potash, ammonia is reproduced by the taking up of two molecules of water, and passes oiT as a gas, while oxalate of potash remains in the liquid. Nearly every organic acid known has one or several amides, bearing to it a relation similar to that thus sub- sisting between oxalic acid and oxamide. Asparagine, a crystallizable body found in asparagus and many other plants, already mentioned as an amide, is thought to be an amide of malic acid. Urea, the principal solid ingredient of human urine, is an amide of carbonic acid. Uric acid, hippuric acid, gua- nine, found also in urine; kreatin and kreatinine, occurring in the juice of flesh; thein, the active principle of tea and cofiee ; and theobromin, that of chocolate, are all regard- ed as amides. Amide-like boaies are gelatine (glue), the organic sub- stance of the tendons and of bones, that of skin, hair, wool, and horn. The albuminoids themselves are amide- like, in so far that they yield ammonia on heating with solutions of caustic alkalies. Albuminoids a Source of the Nitrogen cf Humus. — The organic nitrogen of humus inav come from the albu- minoids of the vegetation that hns decayed upon or in the 278 now CHOPS FEED. soil In their alteration by decay, a portion of nitrogen assumes the gaseous form, but a portion remains in an in- soluble and comparatively unalterable condition, though in what particular compounds we are unable to say. The loss of carbon and hydrogen from decayifig organic mat- ters, it is believed, usually proceeds more rapidly than the waste of nitrogen, so that in humus, which is the residue of the change, the relative proportion of nitrogen to car- bon is greater than in the original vegetation. } Rerersi®!! of IVitric Acid and Ammonia to inert Forms. — It is probable that the nitrogen of ammonia, and of ni- trates, which a’c reducible to ammonia under certain con- ditions, may pass into organic combination in the soil. Knop ( Versuchs St.^ Ill, 228) found that when peat or soils containing humus were kept for several montlis in contact with ammonia in closed vessels, at the usual tem^ perature of summer, the ammonia, according to its quan- tity, completely or in part disappeared. Tlierc h iving been no such amount of oxygen present as would be necessary to convert it into nitric acid, the only explanation is that the ammonia combined with some organic substance in the humus, forming an amide-like body, not decomposable by the hypochlorite of soda used in Knop’s azometrical anal ysis. Facts supporting the above view by analogy are not wanting. When gelatine (a body of animal origin clos dy related to the albuminoids, but containing 18 instead of 15” Ij, of nitrogen) is boiled with dilute acids for some time, it yields, among other produids, sugar, as Gerhardt has demonstrated. Prof. T. Sterry Hunt was the first to suggest {Am. Jour. Sci. dt Arts, 1848, Vol 5, p. 76) that gelatine has nearly the composition of an amide of dextri or other body of the cellulose group, and might be regai n, ed as derive! chemically from dextrin (or starch) by the union of the latter with ammonia, water being eliminated, viz. : NITROGENOUS ORGANIC MATTERS OP THE SOIL. 279 Carbohydrate. Ammonia. Water. Gelatine. C., 0.„ + 4 NH 3 = 6 II 3 O + 2 (G 3 N 3 O 3 ). Afterwards Dusart, Schiitzenberger, and P. Thenard, in- dependently of each other, obtained i>y exposing dextrin, starch, and glucose, to a somewhat elevated temperature* (300-360°F.), in contact with ammonia-water, substances containing from 11 to 19®]^ of nitrogen, some soluble in' water and having properties not unlike those of gelatine, others insoluble. It was observed, also, that analogous compounds, containing less nitrogen, were formed at lower temperatures, as at 212° F. Payen had previously observed that cane sugar underwent entire alteration by prolonged action of ammonia at common temperatures. These facts scarcely leave room to doubt that ammonia, as carbonate, by prolonged contact with the humic acids or with cellulose, and bodies of like composition, may form combinations with them, from which, by the action of alkalies or lime, ammonia may be regenerated. It has already been mentioned that when soils are boil- ed with solutions of potash, they yield ammonia continu- ously for a long time. Boussingault observed, as has been previously remarked, that lime, when incorporated with the soil at the ordinary temperature, causes its content of ammonia to in(Tease. Soil from the Liebfrauenberg garden, mixed with its weight of lime and nearly ^ its weight of water, was placed in a confined atmosphere for 8 months. On open- ing the vessel, a distinct odor of ammonia was perceptible, and the earth, which originally contained per kilogram, 11 milligrams of this substance, yielded by analysis 303 mgr. (See p. 265, for other similar results.) Alteration of Albuminoids in the Soil.— Albuminoids are carried into the soil when fresh vegetable matter is in- corporated with it. They are so susceptible to alteration, however, that under ordinary conditions they must speed- 280 now CROPS FEED. ily decompose, and cannot therefore themselves be consid- ered as ingredients of the soil. Among the proximate products of their decomposition are organic acids (butyric, valeric, propionic) de statiite o f nitrogen, and the amides leucin (C^ H^g NO^) and tyrosin (Cg Hjj N^Og). These latter bodies, by further decompo- sition, yield ammonia. As has been remarked, it is^pr^S- hie that the albuminoids, when associated as they are in decay with cellulose and other carbohydrates, may at once give rise to insoluble amide-like bodies, such as those whose existence in humus is evident from the consider- ations already advanced. Can these Organic Bodies Yield Nitrogen Directly to Plants ? — Tliose nitrogenous organic compounds that exist in the soil associated with humus, which possess something of the nature of amides, though unknown to us in a pure state, appear to be nearly or entirely incapable of feeding vegetation directly. Our information on this point is de- rived from the researches of Boiissingault, whose papers on this subject (^De la Terre vegetale consideree dans ses effets svr la Vegetation) are to be found in his Agronomie^ etc,^ Vols. I and II. Boussingault experimented with the extremely fertile soil of his garden, which was rich in all the elements needful to support vegetation, as was demonst’ ated by ihe results of actual garden culture. This soil was especially rich in nitrogen, containing of this element 0.26° |g, which, were it in the form of ammonia, would be equivalent to ir.ore than 7 tons per acre taken to the depth of 13 inches ; or, if existing as nitric acid, would correspond to more than 43 tons of saltpeter to the acre taken to the d(‘pth just mentioned. Tliis soil, however, wlien emjdoyed in quantities of 40 to 130 irrams (1^ to 44 oz. av.) and shielded from rain a!id dew, was scarcely more capable of carrying lu])ins, beans, maize, or hemp, to any considerable development, AVAILABLE NITROGEN OF THE SOIL. 281 til an the most barren sand. In eight distinct trials the crops weighed (dry) but 3 to 5 times, in one case 8 times (average 4 times), as much as the seed; while in sand, pumice, or burned soil, containing no nitrogen, Boussin- gault several times realized a crop weighing 6 times as much as the seed, though the average crop of 38 experi- ments was but 3 times, and the lowest result times the weight of the seed. The fact that the nitrogen of this garden soil was for the most part inert is strikingly shown on a comparison of the crops yielded by it to those obtained in barren soil with aid of known quantities of nitrates. In a series of experiments with the Sunflower, Boussin- gault {Agronomie^ etc,^ I, p. 233) obtained in a soil desti- tute of nitrogen a crop Aveighing (dry) 4.6 times as much as the seeds, the latter furnishing the plants 0.0033 grm. of nitrogen. In a second pot, with same weight of seeds, in which the nitrogen was doubled by adding 0.0033 grm. in form of nitrate of soda, the weight of crop was nearly doubled — Avas 7.6 times that of seeds. In a third pot the nitrogen was trebled by adding 0.0066 grm. i \ form of ni- trate, and the crop was nearly trebled also — was 11.3 times the weight of the seeds. In another experiment (p. 271) the addition of 0.194 grm. of nitrogen as nitrate of i)otash to barren sand with needful mineral matters, gave a crop Aveighing 198 times as much as the seeds. But in the garden soil, which con- tained, Avhen 40 grms. were employed 0.104 grm., and when 130 grms. were used 0.338 grm. of nitrogen, the result of growth was often not greater than in a soil that contained no nitrogen, and only in a single instance surpassed that of a soil to which Avas added but 0.0033 gi-m. The fact is thus demonstrated that but a very small proportion of the nitrogen of this soil Avas assimilable to vegetation. From these beautiful investigations Boussingault deems it highly probable that in this garden soil, and in soils 232 II^^V CROPS FEED. generally which have not been recently manured, ammonia and nitric acid are the exclusive feeders of vegetation with nitrogen. Such a view is not indeed absolutely demon- strated, but tlie experiments alluded to render it iu the highest degree probable, and justify us in designating the organic nitrogen for the most part as inert, so far as vege- table nutrition is concerned, until altered to nitrates or ammonia-salts by chemical change. To compreliend the favorable results of garden-culture in such a soil, it must be considered what a large quantity of earth is at tlie disposal of the crop, viz., as Bous^ingault ascertained, 57 lbs. for each hill of dwarf beans, 190 lbs. for each hill of potatoes, 470 lbs. for each tobacco plant, and 2,900 lbs. for every three hop-plants. The quantity and condition of the nitrogen of Boussin- gault’s garden soil are stated in the subjoined scheme. Available I Ammonia 0.00220 per cent = Nitrogen 0.00181 per cent I ^ nitrogen 1 Nitric acid 0.00034 ‘‘ “ = “ 0.00009 ^ U.UUi.J per ct. Inert nitrogen — of organic compounds 0.2591 “ “ Total nitrogen. 0.2610 per ct. Calculation shows ti at in garden culture the plants above named wonl I have at their disposal in this soil quan- tities of inert and available nitrogen as follows: Weight of soil. hurt nitrogen. Bean (dwarf) hill 57 lbs. 75 grams.* Potato, ” 190 “ 242 T'obacco, single plant, 470 “ 555 “ Hop, three jdants, 2900 “ 3438 “ AvaUaUe nitrogen. 1 gram. 3 grams. 1 “ 44 “ * 1 gram = 15 grains avoirdupois nearly. 17grams=: 1 oz. ** “ 233 “ = lib. Indirect Feeding of Crops by the Organic Nitrogen of the Soil. — In what has been said of the oxidation of the organic matters of the soil, (whereby it is probable that their nitrogen is partially converted into nitric acid,) and of the effect of alkalies and lime upon them, (whereby ammonia is generated,) is given a clue to the understand- AVAILABLE NITROGEN' OF THE SOIL. 283 in:^ of their indirect nutritive influence upon ve getation. By these chemical transformations the organic nitrogen may pass into the two compounds which, in the present state of knowledge, we must regard as practically the ex- clusive feeders of the plant with nitrogen. The rapidity and completeness of the transformation depend upon circumstances or conditions which we understand but im- perfectly, and which are extremely important subjects for furt h er investigation. Difficulty of estimating the Available IVitrogcn of any Soil# — The value of a soil as to its power of supplying plants with nitrogen is a problem by no means easy to solve. The calculations that have just been made from the analytical data of Boussingault regarding the soil of his garden are necessarily based on the assumption that no alteration in the condition of the nitrogen could take ])]ace during the period of growth. In reality, however, there is no constancy either in the absolute quantity of nitrogen in the soil or in its state of availability. Por- tions of nitrogen, both from the air and from fertilizers, may continually enter the soil and assume temporarily the form of insoluble and inert organic combinations. Othe r ])ortions, again, at the same time and as continually, may escape from this condition and be washed out or gathered by vegetation in the form of soluble nitrates, as has al- ready been set forth. It is then manifestly impossible to learn more from analysis, than how much nitrogen is avail- able to vegetation at the moment the sample is examined. To estimate with accuracy what is assimilable during the whole season of growth is simply out of the question. 1 The nearest approach that can be made to tliis result is to ascertain how much a crop can gather from a limited vol- ume of the soil. Bretschueider^s Experiments. — We may introduce here a notice of some recent researches made by Bretschneider in Silesia, a brief account of which h;is appeared since the 284 HOW CROPS FEED. foregoing paragraphs were written. {Jahresbericht il. Ag. Chem.^ 18G5, 29.) Bretschneider’s experiments were made for the purpose of estimating how much ammonia, nitric acid, and nitro- gen, exist or are formed in the soil, either fallow or occu- pied with various crops during the period of growth. For this purpose he measured off in the field four jdots of ground, each one square rod (Prussian) in area, and sepa- rated from the others by paths a } ard wide. The soil of one plot was dug out to the depth of 12 inches, sifted, and after a board frame 12 inches deep had been fitted to the sides of the excavation, the sifted earth was filled in again. This and another — not sifted — plot were planted to sugar beets, another Avas sown to vetches, and the fourth to oats. At the end of April, six accurate and concordant anal- yses Avere made of the soil. Afterwards, at five r OF THE SOIL. 305 of little practical importance, since ammonia is so sparse- ly supj)lied by nature, and the ammonia of fertilizers is almost invariably subjected to the conditions of speedy nitrification. ') CHAPTER VI, THE SOIL AS A SOURCE OF FOOD TO CROPS.— IHGRE. DIEHTS WHOSE ELEMENTS ARE DERIVED FROM ROCKS, . 1 - GENERAL VIEW OF THE CONSTITUTION OF THE SOIL AS RELATED TO VEGETABLE NUTRITION, Inert, Active, and Reserve Matters, — In all cases the soil consists in great part of matters thnt are of no direct or present use i:i feeding the plant. The chemical nature of this inert portion may vary greatly without correspond- ingly influencing the fertility of the soil. Sand, either quartzose, calcareous, micaceous, feldspathic, hornblendic, or augitic; clay in its many varieties ; chalk, ocher (oxide of iron), humus ; in short, any porous or granular material that is insoluble and little alterable by weather, may con- stitute the mass of the soil. The physical and mechanical characters of the soil are chiefly influenced by those ingre- dients which preponderate in quantity. Hence Viile has quite appropriately designated them the ‘‘mechanical agents of the soil.” They affect fertility principally as they relate the plant to moisture and to temperature. They also have an influence on crops by gradually assum- ing moie active forms, and yielding nourishment as the resiiit of chemical changes. In general, it is probable 806 HOW CROPS FEED. that 99 per cent and more of the soil, exclusive of water, does not in the slightest degree contribute directly to tlie support of the present vegetation of our ordinary field products. The hay crop is one that takes up and removes from the soil the largest quantity of mineral matters (ash- ingredients), but even a cutting of 2^ tons of hay car- ries olf no more than 400 lbs. per acre. From the data given on page 158, we may assume the weiglit of the soil upon an acre, taken to the depth of one foot, to be 4,000,000 lbs. The ash-ingredients of a heavy hay crop amount therefore to but one ten-thousandth of the soil, admitting the crop to be fed exclusively by tlie 12 inches next the surface. Accordingly no less than 100 full crops of hay would require to be taken oif to consume one per cent of the weight of the soil to this depth. We confine our calculation to the ashdngredients because we have learned that the atmosphere furnishes the main sup- ply of the food from which the combustible part of the crop is organized. Should we spread out over the surface of an acre of rock 4,000,000 lbs. of the purest quartz sand, and sow the usual amount of seed upon it, maintain- ing it in the proper state of moisture, etc., we could not produce a crop ; we could not even recover the seed. Such a soil would be sterile in the most emphatic sense. But sliould we incorporate with such a soil a few tliousand lbs. of the mineral ingredients of agricultural plants, to- gether with some nitrates in the appropriate combinations and proportions, we should bestow fertility upon it by this addition and be able to realize a crop. Should we add to our acre of pure quartz the ashes of a hay crop, 400 lbs., and a proper quantity of nitrate of potash, we might also realize a good crop, could we but ensure contact of the roots of the plants with all the added matters. But in this case the soil would be fertile for one crop only,'and after the removal of the hitter it would be as sterile Jis COXSTITUTIOX OF THE SOIL. 307 before. We gather, then, that there aretliree items to be regarded in the simplest view of the chemical compo- sition of the soil, viz., the inert mechanical hasis^ the presently available nutritive ingredients^ and the reserve matters from which the available ingredients are supplied as needed, 111 a previous chapter we have traced the formation of the soil from rocks by the conjoint agencies of mechanical and chemical disintegration. It is the perpetual operation of these agencies, especially those of the chemical kind, wliich serves to maintain fertility. The fragments of rock, and the insoluble matters generally that exist in the soil, arc constantly suffering decomposition, whereby the ele- ments that feed vegetation become available. What, therefore, we have designated as the inert basis of the soil, is inert for the moment only. From it, by perpetual change, is preparing the available food of crops. Various attem}>t3 have been made to distinguish in fact between these three classes or conditions of soil-ingredients; but the distinction is to us one of i^lea only. Yv^e cannot realize their separation, nor can we even define their peculiar con- ditions. We are ignorant in great degree of the power of the roots of plants to imbibe their food ; we are equally ignorant of the mode in which the elements of the soil are associated and combined ; we have, too, a very imperfect knowledge of the chemical transformations and decomposi- tions that occur within it. We cannot, therefore, dissect the soil and decide what and liow much is immediately available, and what is not. Furthermore, the soil is chem- ically so complex, and its relations to the plant are so com- plicated by i^hysical and physiological conditions, that wo may, perhaps, never arrive at a clear and unconfused idea of the mode by vdiich it nourishes a crop. Nevertheless, what we have attained of knowledge and insight in this direction is full of value and encouragement. Deportment of the Soil towards Solvents. — When we 308 HOW CROPS FEED. put a soil in contact with water, certain matters are dis- solved in this liquid. It has been thought that the sub- stances taken up by water at any moment are those which at that time represent tlie available plant-food. This no- tion was based upon the supposition that the plant cannot feed itself at the roots save by matters in solution. Since Liebig has brought into prominence the doctrine that roots arc able to attack and dissolve the insoluble ingredients of the soil, this idea is generally regarded as no longer tenable. Again, it has been taught tliat the reserve plant-food of the soil is represented by the matters which acids (hydro- chloric or nitric acid) are capable of bringing into solu- tion. This is true in a certain rough sense only. The action of hydrochloric or nitric acid is indeed analogous to that of carbonic acid, which is the natural solvent; but between tlie two there are great differences, independent of those of degree. Although we liave no means of learning with positive accuracy what is the condition of the insoluble ingredients of the soil as to present or remote availability, the deport- ment of the soil towards water and acids is highly in- structive, and by its study we make some approach to the solution of this question. Standards ef Solubility. — Before proceeding to details, some words upon the limits of solubility and upon what is meant by soluble in water or in acids will bo appropri- ate,. The terms soluble and insoluble are to a great de- gree relative as applied to the ingredients of the soil. When it is affirmed that salt is soluble in water, and that glass is insoluble in that liquid, the meaning of the state- ment is plain; it is simply that salt is readily recognized to be soluble and that glass is not ordinarily perceived to dissolve. The statement that glass is insoluble is, however, only true when the ordinary standards ofsoluhillty arc re- ferred to. The glass bottle v/hich may contain water fot AQUEOUS SOLUTION OF THE SOIL. 309 years without perceptibly yielding aught of its mass to the liquid, does, nevertlieless, slowly dissolve. We may make its solubility perceptible by a simple expc^dient. Pulver- ize the bottle to tlie finest dust, and thus extend the sur- face of glass many thousand or million times ; weigh the glass-powder accurately, then agitate it for a few minutes with water, remove the liquid, dry and weigh the glass again. We shall thus find that the glass has lost several per cent of its original weight (Pelouze), and by evapo- rating the water, it will leave a solid residue equal in weight to the loss experienced by the glass. 2 . AQUEOUS SOLUTION OF THE SOIL. The soil and the rocks from which it is formed would commonly be spoken of as insoluble in water. They are, however, soluble to a slight extent, or rather, we should say, they contain soluble matters. The quantity that water dissolves from a soil depends upon the amount of the liquid and the duration of its contact ; it is therefore necessary, in order to estimate properly any statements respecting the solubility of the soil, to know the method and conditions of the experi- ment upon which such statements are based. We subjoin the results of various investigations that exhibit the general nature and amount of matters soluble in Avater. In 1852 Verdeil and Risler examined 10 soils from the grounds of the Instltut A^jronomlque^ at Versailles. In each case about 22 lbs. of the fine earth were mixed with pure lukewarm Avatcr to the consistence of a thin pap, and after standing several hours Avith frequent agitation the Avatcr Avas poured off; this process was repeated to the third time. The clear, faintly yellow solutions thus obtained Averc evaporated to dryness, and the residues were analyzed with results as folloAvs, per cent v 310 now CROPS FEED. Name of Fields etc. Per cent of Ai^h. Sidphaie 1 of Lime. Carbonate of Lime. b II < 1 1 1 ® • 1 ! ^ 1 “ Mall ...[Walk 43.00 57.00 48.92,25.(50 4.27 1.55i 0.02 7.63 5.40 3.77 — Pheasant 70.50 29.93 31.49,35.29 2!i6 0.47, trace 3.55 13.67 4.23 i ~ Turf 35.00 05.00 48.45 G.08 2.75 1.2l| — G.19 25.71 5.06 Queen’s Ave.. ^t.OO 5(5.00 43.751 G.08 (5.32 2.00 trace 14.45 15.61 4.13 i — Kitchen Card. 37.00 03.00 3(5. (50 ; 12. 35 11.20 trace trace 18.51. 19.60 7.23 trace Satory. . [Galy 33.03 07.00 18.70:24.25 18.50 ! 3.72 0.50 — j 21.60 4.65 — Clay soil of 43.00' 52.no 18.75 45. (51 3.83 0.95 1.55 9.14 5 00 7.60 7.60 Lime soil, do. 47.00,53.00 17.21 48.50 9.00 trace — 6.21 5.50 — 8.32 Peat 1)0^^ 4(5.00 154.00 24. 43 1 30. G1 0.92 5.15 trace 6.06 8.75 7.45 — Sand pit 47. 04152. 0« 22.31 134.59 8.10 1.02 — 4.05 115.58 6.47 — Here we notice that in almost every instance all the mineral ingredients of the plant were extracted from these soils by water. Only magnesia and chlorine are in any case missing. We are not informed, unfortunately, what amount of soluble matters was obtained in these experiments. We next adduce a number of statements of the pro- portion of matters which water is capab^.e of extracting from earth, statements derived from the analyses of soils of widely differing character and origin. I. Very rich soil (excellent for clover) from St. Martin’s, ITl)per Austria, treated with six times its quantity of cold water (Jarriges). II. Excellent beet soil (but clover sick) from Schlnn- stacdt, Silesia, treated with 5 times its quantity of cold water (Jarriges). III. Fair wheat soil, Seitendorf, Silesia, treated with 5 times its weight of cold water (Peters). lY. Inferior wheat soil from Lampersdorf, Silesia — 5-fold quantity of water (Peters). V. Good wheat soil, Warwickshire, Scotland — 10-fold quantity of hot water (Anderson). VI. Garden soil, Cologne — 3-fold amount of cold water (Grouven). AQUEOUS SOLUTION OE THE SOIL. 311 VIT. Garden soil, Heidelberg — 3-fold amount of cold water (Grouveii). Yin, Poor, sandy soil, Bickendoi’f — 3-fold amount of cold water (Grouven). IX. Clay soil, beet field, Liebesnitz, Bohemia, extract- ed with 9.6 times its weight of water (R. Hoffmann). X. Peat, Meronitz, Bohemia, extracted with 16 times its weight of water (R. Hoffmann). XI. Peaty soil of meadow, extracted with 8 times its weiglit of water (R. Hoffmann). XII. Sandy soil, Moldau Valley, Bohemia, treated with twice its weight of water (R. Hoffmann). XIIL Salt meadow, Stollhammer, Oldenburg (Harms), XIY. Excellent beet soil, Magdeburg (Hellriegel). XV. Poor beet soil, but good grain soil, Magdeburg (Hellriegel). < XVI. Experimental soil, Ida-Maiienhiltte, Silesia, treat- ed with 2 ^ times its weight of cold water (Kullenberg). XVH. Soil from farm of Dr. Geo. B. Loring, Salem, Mass., treated with twice its weight of water (W. G. Mixter). MATTEKS DISSOLVED BY WATER FROM 100,000 PARTS OF VARIOUS SOILS, S Magnesia. § § '1 O § i ^ • Oxide of Iron and Alumina, Organic 1 Matters. Total. I 18 2 13 8 • 2 1 5 11 5 53 \ 134 II 5 3 5K trace trace trace 4K' ^K 24 ! 51 Ill 0 1 4 4 — trace ^ i 2 2 23 ! 43 IV 10 trace 1 2 — trace 1 11 3 IS 1 40 V S4 7 8 13 — 7 9 22 — 30 130 VI 17 3 0 7K 5 2K <>K, 13K 1 22 ! S7 VII 23 IK 7 4K IK IK 1 38 2 SOI •110 VIII 8 K K 3K trace 1 IK 20 — 10 45 IX ssy^ 4K 9 5 3K 18 trace — 70 147 X 164 11 47 12 trace 33 302 truce 77 449 1095 XI 02 44 21 24 trace trace 11 1 2 230 425 XII 1 2i/o 2 1 trace trace trace* trace — 331 39K XIII 70 43 - K) 476 — 407 144 58 — 170 1393 XIV 19 3 3 5 1 4 4 20 3 88 150 XV 20 5 3 4 1 5 3 15 2 83 147 XVI 2 1 3 K 5K 3K 12 7 12 53 XVII 8 2 OK 1 *]i» 7K IK 17 12 55K » , HOW CHOPS PEKD. V' 'Rie feregoihg analyses (all the author has access to" that are sufficiently detailed for the purpose) indicate 1. Tliat the quantity of soluble matters is greatest — 400 to 1,400 in 100,000— in wet, peaty soils (X, XI, XIII), though their aqueous solutions, are not rich in some of the most important kinds of plam-food, as, for example, phos- phone acid. 2. That poor, sandy soils (Vm, XII) yield to water the least amount of soluble matters, — 40 to 45 in 100,000. 3. That very rich soils, and rich soils especially when recently and heavily manured as for the hop and beet crops (I, II, V, VI, YII, IX, XIV, XV, XVI), vield, in general, to water, a larger proportion of soluble matters than poor soils, the quantity ranging in the instances be- fore us from 50 to 150 parts in 100,000. 4. It is seen that in most cases phosphoric acid is not present in the aqueous extract in quantity sufficient to be estimated; in some instances other substances, as mag- nesia, chlorine, and sulphuric acid, occur in traces only. 5. In a number of cases essential elements of plant- food, viz., phosphoric acid and sulphuric acid, are wanting, or their presence was overlooked by the analyst. Composition of Drain-Water.— Before further discus- sion of the above data, additional evidence as to the kind and extent of aqueous action on the soil will be adduced. The water of rains, falling on the soil and slowly sinking through it, forms solutions on the grand scale, the study of which must be instructive. Such solutions are easily gathered in their full strength from the tiles of thorough- drained fields, when, after a period of dry weather, a rain- fall occurs, sufficient to saturate the ground. Dr. E. Wolff, at Moeckern, Saxony, made two analyses of the 'water collected in the middle of May from newly laid tiles, when, after a period of no flow, the tiles had AQUEOUS SOLUTIOT^ OF THE SOIL. 313 been running full for several i hours in consequence of a heavy rain. The soil was of good quality. He found : IN 100,000 PARTS OF DR AIN- WATER. Rye field. Meadow. Organic matters, 2.6 3.2 Carbonate of lime. 21.9 4.4 “ “ magnesia, 3.1 1.4 “ “ potash, 0.3 0.5 “ “ soda, 1.9 . 1.4 Chloride of sodium, trace Sulphate of potash. ^2 V f # i# w trace Alumina, ) 0.8 0.6 Oxide of iron, ) Silica, 0.7 0.4 Phosphoric acid. trace 1.9 — — 34.8 13.8 Prof. Way has made a series of elaborate examinations on drain-waters furnished by Mr. Paine, of Farnham, Surrey. The waters were collected from the pi[)es (4-5 ft. deep) of thorough-drained fields in December, 1855, and in most cases were the frst flow of the ditches after the autumn rains. The soils, with exception of 7 and 8, were but a few years before in an impoverished condition, but had been brought up to a high state of fertility by ma- nuring and deep tillage. {Jour. Roy. Ay. Soc., XVII, 133.) IN 100,000 PARTS OF DRAIN-WATER. 1 Wheat field. 2 Hop field. 3 Hop fHd. 4 Wheat field. 5 Wheat \neld. 6 Hop field. 7 Hop field. Potash trace trace 0.03 0.(!7 trace 0.31 t race Soda 1.4.3 6.93 3.10 3.23 1.24 2.03 2. CO 4.57 Lime 10.24 8.64 2.23 3.00 8 31 18.50 Maj^iiesia 0.9T 3..^1 3.54 0.58 0.30 1.33 3.57 Oxide of iron and alumina. Silica . 0.59 1.35 o.or O.Cl 0.14 0.78 none 1.71 1.85 2.57 0.50 0.C3 0.71 1.21 Chlorine 1.00 1.57 1.84 1.16 1.80 1.73 3.74 Sulphuric acid 2.35 7.35 6.28 2.44 1.84 4.45 13.58 Phosphoric acid trace 0.17 trace trace 0.11 0.09 0.17 Nitric acid 10.^ 21.(5 18.17 2.78 4.93 11.50 16.35 Ammonia Soluble organic matter. . . . . 0.025 10.00 0.025 10.57 0.025 17.85 0.017 8.00 0.025 8.14 0.025 8.28 0.009 10.57 Total 1 34.885 158.095 60.5251 21.227 1 27.195 39.455: 72. 979 14 314 now CROPS FEED. Krocker has also published analyses of d rain-waters collected in summer from poorer soils. He obtained IN 100,000 PARTS : a b c d e / Organic matters, 2.5 2.4 1.6 0.6 6.3 5.6 Carbonate of lime, 8.4 8.4 12.7 7.0 7.1 8.4 Sulpliate of lime, 20.8 21.0 11.4 1.7 7.7 7.2 Nitrate of lime. 0.2 0.2 0.1 0.2 0.2 0.2 Carbonate of magnesia, 7.0 6.9 4.7 2.7 2.7 1.6 Carbonate of iron, 0.4 0.4 0.4 0.2 0.2 0.1 Potash, 0.2 0.2 0.2 9.2 0.4 0.6 Soda, 1.1 1.5 1.3 1.0 0.5 0.4 Chloride of sodium. 0.8 0.8 0.7 0.3 0.1 0.1 Silica, 0.7 0.7 0.6 0.5 0.6 0.5 Total, 42.1 42.5 a3.7 15.3 25.8 24.7 Krocker remarks {Jour, f llr Praht, Chem,,^ 60-46C) that phosphoric acid could be detected in all these y^aters, tliougli its quantity was too small for estimation. a and h are analyses cf water from the same drains — a gathered April 1st, and h May 1st, 18d3; c is from an ad- joining held; c?, from a held Avhere the drains run con- stantly, where, accordingly, the drain-water is mixed with spring water ; e and f arc of water running from the sur- '"face of a held and gathered in the furroAvs. Lysimeter- Water. — Entirely similar results vrcrc ob- tained by Zoller in the analysis <^f Avater Ayhich was col- lected in the Lysimcter of Fraas. The lysimeter^* con- sists of a A^essel A\dth Axrtical sides and open aboAm, the upper part of Avhich contains a layer of soil (in these ex- periments G inches deep) supported by a perforated shelf, Avhilc below is a reservoir for the reception of Avater. The vessel is imbedded in the ground to Avithin an inch of its upper edge, and is tlicn hlled from the diaphragm up Avith soil. In this condition it remains, the soil in it being exposed to the same inhuences as that of the held, Avhilc the Avatcr AA'hicli percolates the soil gathers in the reservoir * Measurer of solution. 315 AQUEOTTS SOEUTION OF THE SOIL. below. Dr. Zoller analyzed the water that was thus col- lected from a number of soils at Munich, in the half yeai , April 7th to Oct. 7th, 1857. He found IN 100,000 OF LYSIMETER-WATER: Potasli, Soda, 0.65 0.71 0.24 0.56 0.20 0.74 0.55 2.37 Lime, 14.58 5.76 7.08 6.84 Magnesia, 2.05 0.89 0.13 0.29 Oxide of iron, 0.01 0.63 0.83 0.57 Chlorine, 5.75 0.95 2.08 3.94 Phos])horic acid. 0.22 — Sulphuric acid. Silica, 1.75 1.04 2.71 1.13 2.78 1.75 2.93 0.95 Organic matter, with some j- 20.47 12.59 13.67 12.08 nitric and carbonic acids. — 0.38 0.00 9.23 0.51 0.43 3.53 3.35 0.93 10.19 Total, 47 23 ^ 25.46 \ • 29.26 30.52 29.15 The foregoing analyses of drmn and lysimeter-watcr exhibit a certain general agreement in their results. They agree, namely, in demonstrating the presence in the soil-water of all the mineral food of the plant, and while the figures for the total quantities of dissolved matters vary considerably, their average, 36|- parts to 100,000 of water, is probably about equally removed from the ex- tremes met with on the one hand in the drainage from a very highly manured soil, and on the other hand in that where the soil-solution is diluted with rain or spring water. It must not be forgotten that in the analyses of drain- age water the figures refer to 100,000 parts of water; whereas, in the anjalyses on p. 311, they refer to 100,000 parts of soil, and hence the two scries of data cannot bo directly compared and are not nocesgarily discrepant. Is Soil-Water destitute of certain Nutritive Matters? —Wo notico that in tho natural solutions which •flow off from the soil, phosphoric acid in nearly every case exists in quantity too minute for estimation ; and when estimat- ed, as has been done in a nuinber of instances, its propor- tion does not reach 2 parts in 100,000. This fact, together with the non-appearance of the same substance and of oth- ^ \ i / 316 // HOW CROPS FEED. ^ ^er nutritive elements, viz., chlorine and sulphuric acid, in the Table, p.311, leads to the question, May not the aqueous solution of the soil be altogether lacking in some es- sential kinds of mineral plant-food in certain instances? May it not happen iu case of a rather poor soil that it will support a moderate crop, and yet refuse to give up to water all the ingredients of that crop that are derived from the soil? The weight of evidence supports the conclusion that water is capable of dissolving from the soil all the sub- stances that it contains which serve as the food of plants. The absence of one or several substances in the analytical statement would seem to be no proof of their actual ab- sence in the solution, but indicates simply that the sub- stance was overlooked or was too small for estimation by the common methods of analysis in the quantity of solu- tion which the experimenter had in hand. It would ap- pear probable that by employing enough of the soil and enough water in extracting it, solutions would be easily obtained admitting of the detection and estimation of ev- ery ingredient. Knop, however, asserts (CAem. Central- hlatt^ 1864, 168) that he has repeatedly tested aqueous solutions of fruitful soils for phosphoric acid, employing the soils in quantities ranging from 2 to 22 lbs., and water in similar amounts, without in any case finding any traces of it. On the other hand Schulze mentions having inva- riably detected it in numerous trials ; and Von Babo, in the examination of seven soils, found phosphoric acid in every instance but one, which, singularly enough, was that of Q. recently manured clay soil In no case did he fail to detect lime, potash, soda, sulphuric acid, chlorine, and nitric acid ; magnesia he d’d not look for. {Hoff- mann'^s Jahreshericht der Ag, Chem.^ I. 17.) So Tleiden, in answer to Knop’s statement, found and estimated phosphoric acid in four instances in proportions AQUEOUS SOLUTION OF THE SOIL. 317 ranging from 2 to 6 parts in 100,000 of soil, {Jahreiibe-‘ richt der Ag. Chem.^ 1865, p. 34.) It should be remarked that Knop’s failure to find phos- phoric acid may depend on the (uranium) method he em- ployed, a method different from that commonly used. Can the Soil-water supply Crops with Food] — As- suming, then, that all the soil-food for plants exists in solu- tion in the water of the soil, the question arises. Does the water of the soil contain enough of these substances to nourish crops ? In case of very fertile or highly manured fields, this question without doubt should be answered af- firmatively. In respect of poor or ordinary soils, how- ever, the answer has been for the most part of late years in the negative. W^hile to decide such a question is, per- haps, impossible, a closer discussion of it may prove ad- vantageous. Russell {Journal Highland and Ag. Soc., New Series, Vol. 8, p. 534) and Liebig {Ann. d. Chem. u. Fharm., CV, 138) were the first to bring prominently forward the idea that crops are not fed simply from aqueous solutions. Dr. Anderson, of Glasgow, presents the argument as follows (his Ag. Chemistry^ p. 113) : ‘‘In order to obtain an estimate of the quantity of the substances actually dissolved, we shall select the results obtained * by Way. The average rain-fall in Kent, where the waters he examined were obtained, is 25 inches. Now, it appears that about two-fifths of all the rain which falls escapes through the drains, and the rest is got rid of by evaporation. f An inch of rain falling on an English acre weighs rather more than a hundred tons; hence in the course of a year, there must pass off by the drains about 1,000 tons of drainage water, carrying with it, out of the reach of plants, such substances as it has dissolved, and * On drain-waters, see p 313. t From Parke’s measurements, Jour. Roy. Ag. Soc.., Eng.., Vot XVII, p. IST. 318 HOW CROPS FEED. 1,500 tons must remain to give to tlie plant all that it )\olds in solution. These 1,500 tons of water must, if they have the same composition as that Avhich escapes, contain only two and a half pounds of potash and less than a pound of ammonia. It may be alleged that the water which re- mains lying longer in contact with the soil may contain a larger quantity of matters in solution ; but even admit- ting tliis to be the case, it cannot for a moment be sup- posed that they can ever amount to more than a very small fraction of what is required for a single crop.” The objection to this conclusion which Anderson al- ludes to above, but wliich he considers to be of little mo- ment, is, perhaps, a serious one. The soil is saturated with water sufficiently to cause a flow from drains at a depth of 4 to 5 ft., for but a small part of the grow- ing season. The Indian corn crop, for example, is })lanted in Xew England i:i the early part of June, and is liarvest- ed the first of October. During the four months of its growth, the average i-ain-fall is not enough to make a flow from drains for more, perliaps, tlian one day in seven. During six-seventlis of the time, then, there is a current of water ascending in the soil to supply the loss by evapora- tion at the surface. In tliis way the solution at the sur- face is concentrated by the carrying upward of dissolved matters. A heavy rain dilutes this solution, not having time to saturate itself before reacliing the drains. Ac- cordingly we find that the quantity of matters dissolved by water acting tlioroughly on the surface soil is greater than that washed out by an equal amount of drain- water ; at least such is the conclusion to be gathered from the experiments of Eichhorn and Wunder. These chemists have examined the solution obtained by leaving soil in contact with sufficient water to saturate it for a number of days or weeks. ( Vs, St,, II, pp. 107- 111 .) The soil examined by Eichhorn was from a garden near AQUEOUS SOLUTIOJf OF THE SOIL. 319 Bonn, Prussia, not freshly manured, and was treated with about one-third its weight (36.5 per cent) of cold water for ten days. Wunder employed soil from a field of the Experiment Station, Chemnitz, Saxony. This soil had not been re- cently manured, and was of rather inferior quality (yield- ed 15 bushels wheat per acre, English). It Avas also treated with about one-third its weight (34.5 per cent) of water for four weeks. The solutions thus procured contained in 100,000 parts, Bonn. Chemnitz. Silica, 4 80 2.57 Siill)huric acid, 10.03 — Phosphoric acid. 3.10 ^ traces Oxide of iron and alumina, trace 1.17 Chloride of sodium. 5. 80 4.76 Lime, 12.80 8.36 Magnesia, 3.84 3.74 Pota>h, 11.54 0.75 Soda, 1.10 3.04 If we assume with Anderson that 1,500 tons (= 3,360,000 lbs.) of water remain in these soils to feed a crop, and that this quantity makes solutions like those Avhose composition is given above, Ave have dissolved (in pounds per English acre) from the soil of Bonn. Chemnitz. Silica, 161 86 Sulphuric acid, 343 -- Phosphoric acid. 104 ? Oxide of iron and alumina. 39 Chloride of sodium, 197 160 Lime, 430 281 Magnesia, 139 126 Potash, . 387 25 Soda, 37 103 These results differ widely from those based on the com- position of drain-water. Eichhorn, by a similar calcula- tion, was led to the conclusion that the soil he operated with was capable of nourishing the heaviest crops Avith 320 HOW CROPS FEED. its aqueous solution. Wunder, on the contrary, calculat- ed that the Chemnitz soil yields insufficient matters for the ordinary amount of vegetation ; and we see that as respects potash, the wants of grass and root crops could not be satisfied with the quantities in our computation, while sulphuric acid and phosphoric acid arc nearly or en- tirely wanting. We do not, liowever, regard such calcu- lations as decisive, either one Avay or the other. The quantity of water which may stand at the actual service of a crop is beyond our power to estimate with anything like certainty. Doubtless the amount assumed by Ander- son is too large, and hence the calculations relative to the Bonn and Chemnitz soils as above interpreted^ convey an exaggerated notion of the extent of solution. Proper Concentration of Plant-Food, — Let us next inquire what strength of solution is necessary for the sup- port of plants. As has been shown by Nobbe ( T^s, St^ VIII, p. 337), Birner & Lucanus ( Vb, St.^ VIII, p. 134), and Wolff ( Vs. /St.^ VIII, p. 192), various agricultural plants flourish to extraordinary perfection when their roots are immersed in a solution containing about one part of ash-ingredients (together witli nitrates) to 1,000 of water. The solutions they employed contained the following substances in the proportions stated (approximately) be- low : 100,000 i)arts of Water. Nobbe. Birner &> Lucanus. Wolff. Lime, 16 19 19 Magnesia, 3 Potash, 81 16 16 Phosphoric acid, 7 21 14 Chlorine, 21 none 2 Sulphuric acid. 5 13 4 Oxide of iron, X Nitiic acid. 36 51 116 115 109 Nobbc found further that the vigor of vegetation in his AQUEOUS SOLUnOJ^' OF THE SOIL. 321 solution was diminished either by reducing the proportion of solid matters below 0.5, or increasing it to 2 parts in 1,000 of water. The proper dilution of the food of plants for most vigorous growth and most perfect development is thus approximately indicated. ( We notice, however, considerable latitude as regards the proportions of some of the most important ingredients whicli are usually present in least quantity in the aqueous solution of the soil. Thus, phosphoric acid in one case is thrice as abundant as in the other. We infer, therefore, that the minimum limit of the individual ingredients is not fixed by the above experiments, especially not for or- dinary growth. Birner and Lucanus communicate other results ( Vs. VIII., p. 154), which tlirow much light on the question un- der discussion. They compared the gro wth of the oat plant, when nourished respectively by a rich garden soil, by ordinary cultivated land, by a solution the composition of which is given above, and lastly by a natural aqueous solution of soil, viz., a wellrwater. Below is a statement of the weight in grams of an average plant, produced in these various media, as well as that of the grain yielded by it. Weiirlit of aver- Weiiiht of Dry crops compared with seed, the latter aj^e plant, dry. dry Grain. taken as unity. Garden 5.27 1.23 193 Field 1.75 0.63 61 Solution 3.75 1.53 137 Well-water 2.91 1.25 106 W e gather from the above figures that well-water, in quantities of one quart for each plant, renewed weekly, gave a considerably heavier plant, straw, and grain, than a field under ordinary culture ; the yield in grain being djyble that of the latter^ and equal to that obtained in a rich garden soiL 14 * 322 HOW CROPS FEEI>. Tlie analysis of the well-water shows that the nntritiYe solution need not contain the food of plants in greater proportion than occurs in the aqueous extract of ordinary soils. The well-water contained, in 100,000 parts, Lime, - - - - 15.14 Magnesia, 1.53 Potash, - . . . 2.13 Phosphoric acid, ... - 0.16 Sulphuric acid, ... 7.45 Nitric acid, - - . . - 6.02 We thus have demonstration that a solution containing but one-and-a-hrdf parts of phosphoric acid to ten million of water is competent, so far as this substance is concern- ed, to support a crop bearing twice as much grain as an ordinary soil could produce under the same circumstances of weather. Do we thus rc^ach the limit of dilution ? We cannot answer for agricultural plants, but in case of- some other forms of vegetation, the reply is obvious and striking. Various species of Fucus^ Lccminaria^ and other ma- rine plants, contain iodine in notable quantities. Tliis element, so much used in photography and medicine, is made exclusively from the ashes of these sea-weeds, one establishment in Glasgow producing 85 tons of it annu- ally. The iodine must be gathered from the water of the ocean in which these plants vegetate, and yet, although the starch-test is so delicate th.it one part of iodine can be detected when dissolved in 300,000 parts of water, it is not possible to recognize iodine in the bitterns ” Avhic h remain when sea-water is concentrated to the one-hund- reth of its original bulk, so that its proportion must be less tlian one part in thirty millions of water ! ( Otto*s Lehrbach der Chemle^ pp. 743-4.) AQUEOUS SOLUTION OF THE SOIL. 323 Mode whereby dilute solutions may nourish Crops.— There are other considerations which may enable us to reconcile extreme dilution of the nutritive liquid of the soil, with the conveyance by it into the plant of the req- uisite quantity of its appropriate food. It is certain that the amount of matters found in solution at any given moment in the water of the soil by no means repre- sents its power of supplying nourishment to vegetation. If the water which has saturated itself with the solu- ble matters of the soil be deprived of a portion or all of these matters, as it might be by the absorptive action of the roots of a plant, the water would immediately act anew upon the soil, and in time would diss(dve another similar quantity of the same substance or substances, and these being taken up by plants, it would again dissolve more, and so on as long and to such an extent as the soil itself would admit. In other words, the same water may act over and over again in the soil, to transfer fi*om it to the crop the needful soluble matters. It has been shown that the substances dissolved i:i water may diffuse through \ animal and vegetable tissues independently of each other, and independently of the water itself. {II. C. G., p. 340.) ^ Deportment of the Soil to renewed portions of Water. — It remains to satisfy ourselves that the soil is capable of yielding soluble matters continuously to renewed por- tions of water. The only observations on this point that the writer is acquainted with are those made by Schulze and Ulbricht. Schulze experimented on a rich soil from Goldberg, in Mecklenburg ( Vs, St.^ Vl., 411). This soil, in a quantity of 1,000 grams (= 2.2 lbs.) was slowly leached with pure water, so that one liter 1.056 quart) of liquid passed it in 24 hours. The extraction was con- tinued during six successive days, and each portion was separately examined for total matters dissolved, and for phosphoric acid, which is, in general, the least soluble of the soil-ingredients. 324 HOW CROPS FEED. The results were as follows, for 1,000 parts of extract, Portion of aqueous extract. Total matters dissolved. Organic and volatile. Inorganic. Phosphoric acid. 1 0.535 0.340 0.195 0.0056 2 0.120 0.057 0.063 0.0083 3 0.261 0.101 0.160 0.00S8 4 0.203 0.083 0.120 0.0075 5 0.260 0.082 0.178 0.0069 6 0.200 0.077 0.123 0.0044 1.579 0.740 0.839 0.0414 We see that each successive extraction removed from the soil a scarcely diminished quantity of mineral mat- ters, including phosphoric acid. In case of a poor soil, we should not expect results so striking, as regards quan- tity of dissolved matters, but doubtless they would be similar in kind. This is shown by the investigations that follow. Ulbricht gives ( Vs, V., 207) the results of the simi- lar treatment of four soils. 1,000 grains of each were put in contact with four times as much pure water f r three days, then two-tliirds of the solution was poured off for analysis, and replaced by as much pure water; tliis was repeated ten times. Partial analyses were made of some of the extracts thus obtained ; we subjoin the pub- lished results : Dissolved by 40,000,000 parts of water from 1,000,000 parts of — Loamy Sand from Heiiisdorf. 1st 2d 3d 1 4tli 1 7th loth Extract. Extract. Extract. Extract. Extract Extract. Potash 30X 15 15 8 1 4 Soda 34 14 • 21 18 11 Lime 95 39 38 39 Magnesia 30 12 10 10 Phosphoric acid. . trace. IK 3 3 Total 190 81 K 87 1 78 1 1 AQUEOUS SOLUTIO?^ OF THE SOIL. 325 Loamy Sand from Wahlsdorf. 1 * 0 1 ash Soda Lime Magnesia Phosphoric acid.. 33 26 116 36X 13 16 43 15 3 13 20 39 14 4 6 16 43 13 4 48 14 4 6 Total 308X 89 90 80 Loamy ferruginous Sand from Dabme, containing 4 }^ of hum us. Potash 7 6 7 7 3 Soda 41 11 26 17 8 Lime 96 70 55 48 62 Map'll esia 14 10 9 7 8 Phosphoric acid.. ti-ace. 3 trace. 1 Total 158 99 97 80 Pine Sandy Loam from Palkcnberg. Potash 15 11 13 9 9 Soda 47 13 8 Lime 47 27 19 18 Magnesia 17 8 5 6 Phosphoric acid.. 3 2 trace. trace. Total 139 60 45 41 1 As Schulze remarks, it is practically impossible to ex- haust a soil completely by water. This liquid will still dissolve something after the most prolonged or frequently renewed action, as not one of the components of the soil is jiossessed of absolute insolubility, although in a sterile soil the amount of matters taken up would presently be- come what the chemist terms “ traces,” or might be such at the outset. The two analyses by Krocker, a and 5, p. 314, made on water from the same drain, gatliercd at an interval of one month, further show that water, rapidly percolating the soil, continuously finds and takes up new portions of all its ingredients. In addition to the simple solution of matters, the soil sulfers constantly the chemical changes which have been already noticed, and are expressed by the term weather* 326 HOW CROPS FEED. ing. Matters insoluble in water to-day become soluble to-morrow, and substances that to-morrow resist the action of water are taken up the day after. In this way tliere is no limit to the solution of the soil, and we cannot there- fore infer from what the soil yields to water at any given moment nor from what is taken out of it by any given amount of water, the real extent to which aqueous action operates, during the long period of vegetable growth, to present to the roots of a crop the indispensable ingredi- ents of its food. The discussion of the question as to the capacity of water to dissolve from the soil enough of the various in- gredients to feed crops, while satisfactorily establishing this capacity in case of rich soils, and making evident that in poor soils most of the inorganic matters are pre- sented to vegetation by water in sufficient quantity, does not entirely satisfy us in reference to some of the needful elements of the jdant, especially phosphoric acid. It is therefore appropriate, in this place, to pursue fur- , ther inquiries into the mode by which vegetation acquires \ food from the soil, although to do so will somewhat inter- ^ Vife t the general plan of our chapter. * T)ircct action of Roots upon the Soil. — In noticing the means by which rocks are converted into soils, the yj\^action of the organic acids of the living plant has been meniioned. Since that chapter was written, further evi- dence has been obtained concerning the influence of the plant on the soil, whicli we now proceed to adduce. Sachs {JExperimental Physiologie^ 189) gives an ac- count of observations made by him on the action of roots on marble, dolomite (carbonate of lime and magnesia), magnesite (carbonate of magnesia), osteolitc (phosphate of lime), gypsum, and glass. Polished plates of these substances were placed at the bottom of suitable vessels and covered several inches in depth with fine quartz sand. Seeds of various plants were planted in the sand and kept DIRECT ACTION OF ROOTS UPON THE SOIL, 327 moist. The roots penetrated the sand and came in coi> tact with the plates below^ and branched horizontally on their surfaces. After several days or weeks the plates were removed and examined. The plants employed were the bean, maize^ squash, and wheat. The carbonates of lime and magnesia and the phosphate of lime were ])laim ly corroded where they had been in contact with the * roots, so that the course of the latter could be traced with- out difficulty. Even the action of the root-hairs was mani- fest as a faint roughening of the surface of the stone either side of the path of the root. Gypsum and glass were not perceptibly acted on. Dietrich has made a scries of experiments [JSq^mann^s Jakresbericht^ VI, 8) on the amount of matters made solu- ble from basalt and sandstone, both coarsely powdered, and kept watered with equal quantities of distilled. water, when supporting and when free from vegetation. Tlie crushed rocks were employed in quantities of 9 and 11 lbs. ; they were well washed before the trials with dis- tilled water, and access of dust was prevented by a layer of cotton batting upon the surface. After removing the plants, at the termination of the experiments, each sam- ple of rock-soil was washed with the same quantity of Water, to which a hundredth of nitric acid had been added. It was found that the plants employed, especially lupins, peas, vetches, spurry, and buckwheat, assisted in the decomposition and solution of the basalt and sand- stone. Kot only did these plants take up mineral mat- ters from the rock, but the latter contained besides, Ui larger amount of soluble matters than was found in the experiments where no plants were made to grow. The cereal grains had the same elfect, but in less degree. In the subjoined table we give the total quantities of sub- stances dissolved under the influence of the growing vegetation. These figures were obtained by adding to what was found in the washings of the rock-soils the ash 328 HOW CROPS FEED. of the crops, and subtracting from that sum the ash of the seeds, together with the matters made soluble in the same soils, which had sustained no plants, but which had been treated otherwise in a similar manner. ^ MATTERS DISSOLVED BY ACTION OF ROOTS. V. - On 9 lbs. of On 11 lbs. of sandstone. basalt. Of' 31upin plants . . . 0.608 ^rams. 0.749 j L;;rara&. “ 3 pea “ ..i i 0.481 (C 0.713 u “ 20spiirry “ ...0.2C8 t( 0.365 u “ 10 buckwh’t “ . .1 0.232 0.327 n “ 4 vetch “ ..j ........0.221 0.251 (( “ 8 wheat ‘‘ .1 0.027 0.196 8 rye i- 0.014 0.133 n These trials appear to show conclusively that plants exert a decided effect on the soil. We are not informed, however, what particular substances are rendered soluble* under this influence. We conclude, then, that the direct action of the roots of a crop may in all cases contribute toward supplying it with food, and in many instances ihay be absolutely essential to its satisfactory growth. . ; ^ Further Notice of Matters Soluble in Water.— The analyses we have quoted show that every chemical ele- ment of the soil m.ay pass into aqueous solution. They also show that some substaixces arc dissolved more easily and in greater quantity than others. In general, chlorine^ nitric acid^ and sulphuric acid^ are most readily and completely taken up by water, and, for the most part, in combination with llme^ soda^ and, magnesia. In some cases, sulphuric acid appears to exist in a difficultly soluble condition ( Van Bemrhelen., Vs. St., VIII., 263). Potash., ammonia., oxide of iron., cdumina., silica., and phosphoric acid., are the substances winch arc usually soluble in but small proportion. These, together with ACID SOLUTION OF THE SOIL. 329 lime, magnesia, and soda, it is difficult or impossible to wash out completely from a soil of good quality. Very poor soils may be deficient in soluble^ forms of any or several of the above ingredients, and therefore readily admit of nearly complete extraction by a small amount of water. Certain soils contain soluble salts of iron and alumina (sulphates and humates) in considerable quantity, and are for that reason unproductive. Such are many marsh lands, as well as upland soils containing bisulphide of iron (iron pyrites), of the kind that readily oxidizes to sulphate of protoxide of iron (copperas). SOLUTION OF THE SOIL IN STRONG ACIDS. The strong acids, hydrochloric (muriatic), nitric, and sulphuric, by virtue of their vigorous affinities, readily remove from the soil a considerable quantity of all its mineral ingredients. The quantity thus taken up is greatly more than can be dissolved in water, and is, in general, the greater, the more fertile the soil. Exceptions are 'soils consisting largely of carbonate of lime (chalk soils), or compounds of iron (ochreous soils). The differ- ent acids above^ named exercise very unlike solvent effects according to their concentration, the time of their action, the temperature at which they are applied, and the chemi- cal nature and state .of division of the soil. The deportment of the minerals which chiefly constitute the soil towards these acids will enable us to under- stand their action upon the soil itself. Of these miaerals quartz, feldspar, mica, hornblende, augite, talc, steatite, kaolinite, chrysolite, and chlorite, when not altered by weathering, nearly or altogether resist the action of even hot and moderately strong hydrochloric and nitric acidSe 830 now CROPS PEED. On the other hand, all carbonates, sulphates, and phos- phates, are completely dissolved, while the zeolites and serpentine, are decomposed, their alkalies, lime, etc., enter- ing into solution, and the silica they contain separating, for the most part, as gelatinous hydrate. According to the nature of the soil, and the concentra- tion of the reagent, hydrochloric aci 1, the solvent usually employed, takes up from two to fifteen or more per cent. Very dilute acids remove from the soil the bases, lime, magnesia, j^otash, and soda, in scarcely greater quantity than they are united with chlorine, and with sulphuric, phosphoric, carbonic, and nitric acids. Treatment with stronger acids takes up the bases above mentioned, par- ticularly lime and magnesia, in greater proportion than the acids specified. We find that, by the stronger acids, silica is displaced from combination (and may be taken up by boiling the soil with solution of soda after treat- ment with the acid). It hence follows that silicaj*©e^^^h as are decomposable by acids, (zeolites) although we cannot recognize them dii'Utl^Dy inspec- tion even with the help of the microscop^^.' To this point we shall subsequently recur. ^ § PORTION OF SOIL INSOLUBLE IN ACIDS. When a soil has been boiled with concentrated hydro- chloric acid for some time, or until this solvent exerts no further action, there may remain quartz, feldspar, mica, hornblende, augite, and kaolinite (clay), together witli other similar silicates, which, in many cases, are ingredients of the soil. Treatment with concentrated sulphuiic acid at very high temperatures (Mitscherlich), or syrupy phos- phoric acid (A. Muller), decomposes all these minerals, quartz alone excepted. By making, therefore, in the first CHEMICAL ACTION IN THE SOIL. 331 place, a mechanical analysis, as described on page 147, and subjecting the fine portion, which consists entirely or in great part of clay, to the action of these acids, the quan- tity of clay may be approximately estimated. Or, by melting the portion insoluble in acids with carbonate of soda, or acting upon it with hydrofluoric acid, the whole may be decomposed, and its elementary composition be ascertained by further analysis. Notwithstanding an immense amount of labor has been expended in studying the composition of soils, and chiefly in ascertaining what and how much, acids dissolve from them, we have, unfortunately, very few results in the way of general principles that are of application, either to a scientific or a practical purpose. In a number of special cases, however, these investigations have proved exceed- ingly instructive and useful. § 5 . REACTIONS BY WHICH THE SOLUBILITY OF THE ELEMENTS OF THE SOIL IS ALTERED. SOLVENT EFFECT OF VARIOUS SUBSTANCES THAT ARE COxMMONLY BROUGHT TO ACT UPON SOILS. THE AB- SORPTIVE AND FIXING POWER OF SOILS. Chemical Action in the Soil. — Chemistry has proved that the soil is by no means the inert thing it appears to be. It is not a passive jumble of rock-dust, out of which air and water extract the food of vegetation. It is not simply a stage on which the plant performs the drama of growth. It is, on the contrary, in itself, the theater of ceaseless activities; the seat of perpetual and complicated changes, A large share of the rocks now accessible to our study at the earth’s surface have once been soil, or in the condi- tion of soil. Not only the immense masses of stratified limestones, sandstones, slates, and shales, that cover so 332 HOW CROPS FEED. large a part of the Middle State?, but most of the rocks of New England liave been soil, and have supported vege- table and animal life, as is proved by the fossil relics that have been disinterred from them. We have explained the agencies, mechanical and chemi- cal, by which our soils have been formed and are forming from the rocks. By a reverse metamorphosis, involving also the cooperation of mechanical and chemical and even of vital influcmces, the soils of earlier ages have been so- lidified and cemented to our rocks. Nor, indeed, is this process of rock-making brought to a conclusion. It is going on at the present day on a stu})endous scale in vari- ous parts of the world, as the observations of geologists abundantly demonstrate. If we moisten sand with a so- lution of silicate of soda or silicate of potash, and then drench it with chloride of calcium, it shortly hardens to a rockdike mass, possessing enough firmness to answer many building purposes (Ransome’s artificial stone). A mixture of lime, sand, and water, slowly acquires a simi- lar hardness. Many clay-limestones yield, on calcination, a matei’ial (water-lime cement) which hardens speedily, even under water, and becomes, to all intents, a rock. Analogous changes proceed in the soil itself. Hard pnn, which forms at the plow-sole in cultivated fields, and moor-bed pan, which makes a peat basin impervious to water in beds of sand and gravel, are of the same nature.. The bonds which hold together the elements of feldspar, of mica, of a zeolite, or of slate, may be indeed loosened and overcome by a superior force, but they are not de- stroyed, and reassert their power when the proper cir- cumstances concur. The disintegration of rock into soil is, for the most ])art, a slow and unnoticed change. So, too, is the reversion of soil to rock, but it nevertheless goes on. The cultivable surface of the earth is, liowever, on the whole, far more favorable to disintegration than to petrifaction. Nevertheless, the chemical affinities and ABSORPTIVE POWER OF THE SOIL. 333 physical qualities that oppose disintegration are inherent in the soil, and constantly manifest themselves in the kind, if not in the degree, involved in the making of rocks. The fourteen elementary substances that exist in all soils are capable of forming and tend to form a multitude of combinations. In our enumeration of the minerals from which soils originate, we have instanced but a few, the more common of the many which may, in fact, contribute to its formation. The mineralogist counts by hundreds the natural compound! s of these very elements, com- pounds which, from their capability of crystallization, occur in a visibly distinguishable shape. The chemist is able, by putting together these elements in different pro- portions, and under various circumstances, to identify a further number of their compounds, and both mineralogy and chemistry daily attest the discovery of new combi- nations of these same elements of the soil. We cannot examine the soil directly for many of the substances which most certainly exist in it, on account of their being indistinguishable to the eye or other senses, even when assisted by the best instruments of vision. We have learned to infer their existence either from analo- gies with what is visibly revealed in other spheres of ob- servation, or from the changes we are able to bring about and measure by the art of chemical analysis. Absorptive Power of the Soil. — We have already drawn attention to the fact tliat various substances, when put in contact with the soil, in a state of solution in water, are withdrawn from the liquid and held by the soil. As has been mentioned on p. 175, the first appreciative rec- ord of this fact appears to have been published by Bronner, in 1836. In his work on Grape Culture occur the following passages : “ Fill a bottle which has a small hole in its bottom with fine river sand or half-dry sifted garden ea^th. Pour gradually into the bottle thick and putrefied dung-liquor until its contents are saturated. The 334 HOW CROPS FEED. liquid that flows out at the lower opening appears almost odorless and colorless, and has entirely lost its original properties.” After instancing the facts that wells situ- ated near dung-pits are not spoiled by the latter, and that the foul water of the Seine at Paris becomes potable af- ter filtering through porous sandstone, Bronner contin- ues : These examples sufficiently prove that the soil, even sand, possesses the property of attracting and fully absorbing the extractive matters so that the xoater which subsequently passes is not able to remove them ; even the soluble salts are absorbed-^ and are only washed out to a small extent by nev) quantities of water It was subsequently observed in the laboratory of Liebig, at Giessen, that water holding ammonia in solu- tion, when poured upon clay, lan through deprived of this substance. Afterward, Messrs. Thompson and llux- table, of England, repeated and extended the observa- tions of Bronner, and in 1850, Professor Way, then chemist to the Roy. Ag. Soc. of Eng., published in tlio Journal of that Society, Vol. XL, pp. 313-370 an accour.t of a most laborious and fruitful investigation of the sub- ject. Since that time many chemists have studied the phenomena of absorption, and the results of these labors will be briefly stated in the paragraphs that follow. There are two kinds of absorptive power exhibited by soils. One is purely physical, and is the consequence of adhesion or surf ice-attraction, exerted by the particles of certain ingredients of the soil. The other is a chemical action, and results from a play of affinities among certain of its components. The ])hysical absorptive power of various bodies, im eluding the soil, has been already noticed in some detail (pp. 161-176). In experiments like those of Bronner, just alluded to, the absorption of the coloring and odor- ous ingredients of dung-liquor is doubtless a pliysical prococs. These substances are separated from solution by ABSORPTIVE POWER OF THE SOIL. 335 the soil just as a mass of clean wool separates indigo from the liquor of a dye-vat, or as bone-charcoal removes the brown color from syrup. Chemical absorptions depend upon tlie formation of new compounds, and in many cases occasion chemical decompositions and displacements in such a manner tliat while one ingredient is absorbed, and becomes in a sense fixed, another is released from combination and becomes soluble. Brief notice has already been made of the chemical absorption of ammonia by tlie soil (p. 243). We shall now enter upon a fuller discussion of this and allied phenomena. When solutions of the various soluble acids and bases existing in the soil, or of their salts, are put in contact with any ordinary earth for a short time, suitable exami- nation proves that in most cases a chemical change takes place, — a reaction occurs between the soil and the substance. If we provide a number of tall, narrow lamp-chimneys or similar tubes of glass, place on the flanged end ot'cach a disk of cotton-batting, tying over it a piece of muslin, then support them vertically in clamps or by strings, and fill each of them compactly, two-thirds full of ordinary loamy soil, which should be free from lumps, we have an arrangement suitable for the study of the absorptive power in question. Let now solutions, containing various soluble salts of the acids and bases existing in the soil, be pre- pared. These solutions should be quite dilute, but still admit of ready identification by their taste or by simple tests. We may employ, for example, any or all of the following compounds, viz., saltpeter, common salt, sul- phate of magnesia, phosphate of soda, and silicate of soda. If we pour solution of saltpeter on the soil, which should admit of its ready but not too rapid percolation, we shall find that the first portions of liquid which pass 836 HOW CROPS FEED. are no longer a solution of nitrate of potash, but one of nitrates of lime, magnesia, and soda. The potash lias disappeared from, solution'*^ and become a constituent of the soil, while other bases, chiefly lime, have been dis- placed from the soil, and now exist in the solution Avith the nitric acid. If we operate in a similar manner on a fresh tube of soil with solution of salt (chloride of sodium), Av'e shall find by chemical examination that the soda of the salt is absorbed by the soil, Avhile the chlorine passes through in combination with lime, magnesia, and potash. In case of sulphate of magnesia, magnesia is retained, and sul])hatesof lime, etc., pass through. With phosphates and silicates Ave find that not onlAyth^Jj^e, but also these^^ acids are retained. Law of Absorption and Displacement. — From a great number of experiments made by Way, Liebig, Brustlein, ^ Henneberg and Stohmann, Rautenberg, Peters, Weinhold, ^ Ktillenberg, Heiden, Knop, and others, it is established as a general fact that all cultivable soils are able to de- • compose salts of tlie alhalies and alkali earths in a state of solution, in such a manner as to retain the base together j with phosphoric and silicic acids, Avhile chlorine, nitric ] acid, and sulphuric acid, remained dissolved, in union with J some other base or bases besides tlie one Avith which they ^ were originally combined. The absorptive poAver of the v soil is, hoAvever, limited. After it has removed a certain quantity of potash, etc., from solution its action ceases, it has become saturated, and can take up no more. If, therefore, a large bulk of solution be filtered through a small volume of earth, the liquid, after a time, passes through unaltered. * The absence of potash may be shown by aid of stronir, cold solution of tartariz acld^ which will precipitate bi tartrate of ])otash (cream of tartar) from the ori'^inal solution, if not too dilute, but not from that which has filtered thromrh the soil. The presence of lime in the liquid that ])asses the soil may be shown by adding to it either carbonate or oxalate of ammonia. % ABSORPTIVE POWER OF THE SOIL. 337 Experiments to ascertain how much of a substance the soil is able to absorb are made by putting a known amount of the dry soil (c. g. 100 grms.) in a bottle with a given volume (e. g. 500” cubic cent.) of solution whose content of substance has been accurately determined. The solu- tions are most conveniently prepared so as to contain as many grms. of the salt to the liter of water as corresponds to the atomic weight or equivalent of the former, or one-half, one tenth, etc., of that amount. The soil and solution are kept in contact with occasional agitation for some hours or days, and then a measured portion of the liquid is ■ filtered off and subjected to chemical anal3^sis. The absorptive power of the soil is exerted unequally towards individual suhstancesi Thus, in Peters’ experi- ments ( Vs. aS^.,IL, 140), the soil lie operated with absorb- ed the bases in quantities diminishing in the following order : Potash, Ammonia, Soda, Magnesia, Lime. Another soil, experimented upon by Ktillenberg {Jahreshericht uher A gricultur. Chemie., lb;65, p. 15), ab- sorbed in a different order of quantity, as follows : Ammonia, Potash, Magnesia, Lime, Soda. As might be expected, different soils e^ert absorptive power tovmrds the same substance to an unequal extent. Rautenberg {IJenneberg^ s Jour, fur La^idwirthschaff 1862, p. C2), operated with nine soils, 10,000 parts of which, under precisely similar circumstances, absorbed quantities of ammonia ranging from 7 to 25 parts. The time required for absorption is usually short. . Way found that in most cases the absorption of ammonia was complete in half an hour. Peters, however, observed that 48 hours were requisite for the* saturation of the soil he employed with potash, and in the experiments of Hen- neberg and Stohmann {Henneberg' s Journal.^ 1859, p. 35), ‘ phosphoric acid continued to be fixed after the expii ation of 24 hours. The strength of the solution influences the extent of absorption. The stronger the solution.^ the more substance is taken up from it by the soil. Thus, in Peters’ experi- 15 338 HOW CROPS FEED. merits, 100 grms. of soil absorbed from 250 cubic centi- meters of solutions of chloride of potassium of vaiious degrees of concentration, as follows: strength of Solution. Designa- Quantity of pot.ash in 250 c.c. tion. of solution. 80 equiv, = 0.1472 gram, ■ =:r 0.2044 = 0.5888 - 1.1TT7 ‘‘ “ = 2.3555 Potash absorbed by 100 parts By 10.000 parts in Proportion of soil. round numbers. absorbed. 0.98^ o :rain. 10 ^(3 0.1381 14 0.1990 20 Ms 0.3124 “ 31 M 4 0.4503 ‘‘ 45 A glance at the right-hand column shows that although absolutely potash is absorbed from a weak solution than from a strong one, yet the weak solutions yield relatively more than those which are concentrated. The quantity of base absorbed in a given time, also de- pends upon the relative mass of the solution and soil. In these experiments Peters treated a soil with various bulks of solution of chloride of potassium. The results are subjoined : — From 250 c.c. of solution 10,000 parts of soil absorbed 20 parts. u 500 “ “ “ 25 “ 1,000 “ 29 “ The quantity of a substance absorbed by the soil de- pends somewhat on the state of eombinatlon it is in, i. e., on the substances with which it is associated. Peters found, for example, that 10,000 parts of soil absorbed from solutions of a number of potash-salts, each containing 23 of an equivalent of that base expressed in grams, to the liter, the following quantities of potash : — From phosphate, 49 parts. 4 ; hydrate, 40 “ u carbonate, 32 “ u bicarbonate, 00 ii nitrate, 25 “ u sulphate, 21 “ u chloride* and carbonate, 21 u chloride, 20 “ * Chloride of Potust^iuin, KC!. ABSORPTIVE POWER OF THE SOIL 339 We observe that potash was absorbed in this case in largest proportion from the phosphate, and in least from the chloride. Henneberg and Stohmann, operating on a garden soil, observed a somewhat different deportment of it towards ammonia-salts. 10,000 parts of' soil absorbed as follows : — From phosphate, 21 parts, hydrate, 13 “ sulphate, 12 “ hydrate and chloride,* 11' I 2 “ chloride, 11 nitrate, 11 Fixation neither complete nor permanent,— A point of the utmost importance is that none of the bases are ever completely absorbed even from the most dilate solu- tions. Liebig indeed, formerly believed that potash is en- tirely removed from its solutions. We find, in fact, that when a dilute solution of potash is slowly filtered through a large body of soil, the first portions contain so little of this substance as to give no indication to the usual tests. These portions are similar in composition to drain-waters, and like the latter they contain potash in very minute though appreciable quantity. In accordance with the above fact, it is found that water will dissolve and remove a portion of the potash, etc., which a soil has absorbed. Peters placesphoric acid is about the same. The’ amount of sulphuric acid is but one-twentieth that in the Holland soil, and is accordingly enough for 15 good bar- ley crops. Lastly may be instanced the author’s analysis of a soil from the Upper Palatinate, which was characterized by Dr. Sendtner, who collected it, as “ the most sterile soil in Bavaria.” Water 0.535 Organic matter 1.850 Silica •. . .0.016 Oxide of ii’on and alumina 1.640 Lime 0.096 Magnesia trace Carbonic acid trace Pliosplioric acid trace Chlorine trace Alkalies none Quartz and insoluble silicates 95.863 100.000 Here we note the absence in weighable quantity of magnesia and phosphoric acid, while potash could not even REVIEW AND CONCLUSION. 867 be detected by the tests employed. This soil was mostly naked and destitute of vegetation, and its composition shows the absence of any crop-producing power. Relative Importance of the Ingredients of the Soil. ^From the general point of view of vegetable nutrition, all those ingredients of the soil which act as food to the plant, are equally important as they are equally indispens^ able. Absence of any one of the substances which water- culture demonstrates must be presented to the roots of a plant so that it shall grow, is fatal to th*e productiveness of a soil. Thus regarded, oxide of iron is as important as phos- phoric acid, and chlorine (for the crops which require it) is no less valuable than potash. Practically, however, the relative importance of the nutritive elements is meas- ured by their comparative abundance. ' Those which, like oxide of iron, are rarely deficient, are for that reason less prominent among the ^factors of a crop. If any single substance, he it phosphoric acid, or sulphuric acid, or pot- ash, or magnesia, is lacking in a given soil at a certain time, that substance is then and for that soil the most im- portant ingredient. From the point of view of natural abundance, we may safely state that, on the whole, availa- ble nitrogen and phosphoric acid are the most important ingredients of the soil, and potash, perhaps, takes the next rank. These are, most commonly, the substances whose absence or deficiency impairs fertility, and are those which, when added as fertilizers, produce the most frequent and remarkable increase of productiveness. In a multi- tude of special cases, however, sulphuric acid or lime, or magnesia, assumes the chief prominence, while in many in- stances it is scarcely possible to make out a greater crop- producing value for one of these substances over several others. Again, those ingredients of the soil which could be spared for all that they immediately contribute to the 368 HOW CROPS FEED. nourishment of crops, are often the chief factors of fer- tility on account of th(‘ir indirect action, or because they supply some necessary physical conditions. Thus humus is not in any way essential to the growth of agricultural plants, for plants have been raised to full perfection with- out it; yet in the soil it has immense value practically, since among other reasons it stores and supplies water and assimilable nitrogen. Again, gravel may not be in any sense nutritious, yet because it acts as a reservoir of heat and promotes drainage it may be one of the most import- ant components of a soil. What the Soil must Supply. — It is not sufficient that the soil contain an adequate amount of the several ash-in- gredients of the plant and of nitrogen, but it must be able to give these over to the plant in due quantity and pro- portion. The chemist could without difficulty compound an artificial soil that should include every element of plant-food in abundance, and yet be perfectly sterile. The potash of feldspar, the phosphoric acid of massive apatite, the nitrogen of peat, are nearly innutritions for crops on account of their immobility — because they are locked up in insoluble combinations. Indications of Chemical Analysis. — The analyses by Baumhauer of soils from the Zuider Zee, p. 362, give in a single statement their ultimate composition. We are in- formed how much phosphoric acid, potash, magnesia, etc., exist in the soil, but get from the analysis no clue to the amount of any of these substances which is at the dispo- sition of the present crop. Experience demonstrates the productiveness of the soil, and experience also shows that a soil of such composition is fertile ; but the analysis does not necessarily give proof of the fact. A nearer approach to providing the data for estimating what a soil may sup- ply to crops, is made by ascertaining what it will yield to acids. REVIEW AI^D OONCLUSIOH. 369 Boiissiligault has analyzed in this manner a soil from Calvario, near Tacunga, in Equador^ South America, which possesses extraordinary fertility. He found its composition to be as follows: Nitrog;en in organic combinatiou. 0.243 Nitric acid. 0.975 Ammonia, 0.010 Phosphoric acid, 0.460 Chlorine, 0.395 Sulphuric acid, 0.023 Carbonic acid, traces Potash and Soda, -Soluble io acids. 1.030 Lime, 1.256 Magnesia, 0.875 Se-quioxide of iron. 2.450 Sand, fragments of pumice, and clay insoluble in acids. 83.195 Moisture, 3.150 Organic mutters (less nitrogen), undetermined substances. and loss, 5.938 100.000 This analysis is much more complete in reference to ni- trogen and its compounds, than those hy Baumliauer al- ready given (p. 362), and therefore has a peculiar value. As regards the other ingredients, we observe tliat phos- phoric acid is present in about the same proportion ; lime, alkalies, sulphuric acid, and chlorine, are less abundant, while magnesia is more abundant than in the soils from Zuider Zee. The method of analysis is a guarantee that the one per cent of potash and soda does not exist in the insoluble form of feldspar. Boussingault found fragments of pumice by a microscopic examination. Tliis rock is vesicular feld- spar, or has at least a composition similar to feldspar, and the same insolubility in acids. The inert nitrogen of the humus is discriminated from that whicli in the state of nitric acid is doubtless all assim- ilable, and that which, as ammonia, is probably so for the most part. The comparative solubility of the two per cent of lime and magnesia is also indicated by the analysis. 16 ^ 370 now CROPS FEED. Boussing-ault does not state the kind or concentration, or temperature of the acid employed to extract the soil for tlie above analysis. These are by no means points of indiiference. Gronven {^ter & Ster Sulzmilnder J^erichte) has extracted the same earth with hydrochloric acid, con- centrated and dilute, hot and cold, with gi'catly different results as was to be anticipated. In 1862, a sample from an experimental field at Salzmunde was treated, after be- ing heated to redness, with boiling concentrated acid for 3 hours. In 1867 a sample was taken from a field 1,000 paces distant from the former, one portion of it was treat- ed with boiling dilute acid (1 of concentrated acid to 20 of water) for 3 hours. Another portion was digested for three dnys with the same dilute acid, but without applica- tion of heat. In each case the same substances were ex- tracted, but the quantities taken up were less, as the acid was weaker, or acted at a lower temperature. The follow- ing statement shows the composition of each extract, cal- culated on 100 parts of the soil. EXTRACT OP SOIL OP SALZMUNDE. Sot strong add. Potash, .635 Soda, .127 Lime, 1.677 Magnesia, .687 Oxide of iron and alumina, 7.931 Oxide of manganese, .030 Sulphnric acid, .(^9 Phosphoric acid, .059 Silica, 1.785 Hoi dilute add. .116 .067 1.046 .539 3.180 .086 .039 .091 .234 Cold dilute add. .029 .020 1.098 .237 .650 .071 .020 .057 .175 Total, 12.990 5.398 2.357 The most interesting fact brought out by the above fig- ures, is that strong and weak acids do not act on all the ingredients with the same relative power. Comparing the quantities found in the extract by cold, dilute acid with those which the hot dilute acid took up, we find that the latter dissolved 5 times as much of oxide of iron and alumina, 4 times as much potash, 3 times as much soda, EEVIEW AND CONCLUSION. 371 twice the amount of magnesia, sulphuric acid, and phos- phoric acid, and the same quantity of lime. These facts show how very far chemical analysis in its present state is from being able to say definitely what any given s^ >11 can supply to crops, although we owe nearly all our pre- cise knowledge of vegetable nutrition directly or indi- rectly to this art. The solvent efiect of water on the soil, and the direct action of roots, have been already discussed (pp. 309 to 328). It is unquestionably the fact that acids, like pure water in TJlbricht’s experiments (p. 324), dissolve the more the longer they are in contact with a soil, and it is evident that the question : How much a particular soil is able to give to crops ? is one for which we not only have no chemical answer at the present, but one that for many years, and, perhaps, always can be answered only by the method of experience — by appealing to the crop and not to the soil. Chemical analysis is competent to inform us very accurtitely as to the ultimate composition of the soil, but as regards its proximate composition or its chemical consti- tution, there remains a vast and difiicult Unknown, which will yield only to very long and laborious investigation. Maintenance of a Supply of Plant-food, — By the recip- rocal action of the atmos})here and the soil, the latter keeps up its store of available nutritive matters. The difficultly soluble silicates slowly yield alkalies, lime, and magnesia, in soluble forms ; the sulphides are converted into sulphates, and, generally, the minerals of the soil are disintegrated and fluxed under the influence of the oxy- gen, the water, the carbonic acid, and the nitric acid of the air, (pp. 122—135). Again, the atmospheric nitrogen is assimilated by the soil in the shape of ammonia, ni- trates, and the amide-like matters of humus, (pp. 254-265). The rate of disintegration as well as that of nitrifica- tion depends in part upon the chemical and physical char- acters of the soil, and partly upon temperature and mete- 372 HOW CROPS FEED, orological conditions. In the tropics, both these processes go on more vigorously than in cold climates. Every soil has a certain inherent capacity of production in general, which is cliiefly governed by its power of sup- plying plant-food, and is designated its natural strength.” The rocky hill ranges of the Housatonic yield once in 30 years a crop of wood, the value of which, for a given locality and area, is nearly uniform from century to cen- tury. Under cultivation, the same uniformity of crop is seen when the conditions remain unchanged. Messrs. Lawes and Gilbert, in their valuable experiments, have obtained from ‘‘ a soil of not more than average wheat- producing quadty,” without the application of any ma- nure, 20 successive crops of wheat, the first of which was 15 bushels per acre, the last 17^ bushels, and the average of all 16| bushels. {Jour, Roy, Ag, Soc, of JEng,^ XXY, 490.) The same investigators also raised barley on the same field for IG years, each year app’ying the same quan- tity and kinds of manure, and obtaining in the first 8 years (1852-59) an average of 44|^ bushels of grain and 28 cwt. of straw ; for the second 8 years an average of 5 If bushels of grain and 29 cwt. of straw; and for the 16 years an average of 48]- bushels of grain and 28 V cwt. of straw. {Jour, of Bath and West of Eng,Ag,SoG.^ XVI,2:*4.) The wheat experiments show the natural capacity of the Rothamstead soil for producing that cereal, and de- monstrate that those matters which are annu.dly removed by a crop of 16^ bushels, are here restored to availability by weathering and nitrification. The crop is thus a measure of one or both of these processes.* It is probable * 111 the experiments of Lawes and Gilbert it was found that phosphates, sul- phates, and carbonates of lime, potash, mai,mesia, and soda, raised the iirodiice of wlieat but 2 to 3 bushels per acre above the yield of the uiimanured soil, while sulphate and muriate of ammonia increased the crop G to 10 bushels. This, re- sult, ol)tained on three soils, viz., at Rothamstead in Herts, llolkham in Nor- folk, and Rodmcrsham in Kent, the experiments extending: over periods of 8. 3, and 4 years, respectively, shows that these soils were, for the wheat crop, reJa- tively deficient in assiniilahle nitroofen. The crop on the unmanurc'd soil was therefore a measure of nitrification rather than of mineral disinte^^ration. REVIEW AND CONCLUSION. 373 that this native power of producing wheat will last unim- paired for years, or, perhaps, centuries, provided the depth of the soil is sufficient. In time, however, the silicates and other compounds whose disintegration supplies alka'- lies, phosphates, etc., must become relatively less in quan- tity compared with the quite inert quartz and alumina- silicates which cannot in any way feed plants. Then the crop will fall off, and ultimately, if sufficient time be al- lowed, the soil will be reduced to sterility. Other things being equal, this natural and durable pro- ductive power is of course greatest in those soils which contain and annually supply the largest proportions of plant-food from their entire mass, those wffiich to the great- est extent originated from good soil-making materials. Soils formed from nearly |)urc quartz, from mere chalk, or from serpentine (silicate of magnesia), are among those least capable of maintaining a supply of food to crops. These poor soils are often indeed fairly productive for a few years when first cleared from the forests or marshes ; but this temporary fertility is due to a natural manuring, the accumulation of vegetable remains on the surface, which contains but enough nutriment for a few crops and wastes rapidly under tillage. Exhaustion of the Soil in the language of Practice has a relative meaning, and signifies a reduction of producing power below the point of remuneration. A soil is said to bo exhausted when the cost of cropping it is more than the crops are worth. In this sense the idea is very indef- inite since a soil may refuse to grow one crop and yet may give good returns of another, and because a crop that re- munerates in the vicinity of active demand for it, may be worthless at a little distance, on account of difficulties of transportation. The speedy and absolute exhaustion of a soil once fertile', that has been so much discussed by spec- ulative writers, is found in their writings only, and does not exist in agriculture. A soil may be cropped below the 374 HOW CROPS FEED. point of remuneration, but the sterility thus induced is of a kind that easily yields to rest or other meliorating agen- cies, and is far from resembling in its permanence that which depends upon original poverty of constitution. Significance of the Absorptive Quality,— Disintegration and nitrification would lead to a waste of the resources of fertility, were it not for the conserving effect of those physical absorptions and chemical combinations and re- placements which have been described. The two least abundant ash-ingredients, viz., potash and phosphoric acid, if liberated by the weathering of the soil in the form of phosphate of potash, would suffer speedy removal did not the soil itself fix them both in combinations, which are at once so soluble that, while they best serve as plant-food, they cannot ordinarily accumulate in quantities destruct- ive to vegetation, and so insoluble that the rain-fall cannot wash them off into the ocean. The salts that are abundant in springs, rivers, and seas, are natui-ally enough those for which the soil has the least retention, viz., nitrates, carbonates, sulphates, and hydro- chlorates of lime and soda. The constituents of these salts are either required by vegetation in but small quantities as is the case with chlo- rine and soda, or they are generally speaking, abundant or abundantly formed in the soil, so that their removal does not immediately threaten the loss of productiveness. In fact, these more abundant matters aid in putting into circulation the scarcer and less soluble ingredients of crops, in accordance with the general law established by the researches of Way, Eichhorn, and others, to the effect that any base brought into the soil in form of a freely sol- uble salt, enters somewhat into nearly insoluble combina- tion and liberates a corresponding quantity of other bases. “ The great beneficent law regulating these absorptions appears to admit of the following expression : those bodies which are most rare and precious to the growing plant are REVIEW AND CONCLUSION. 875 hythe soil converted into^ and retained in^ a condition y{oi of absolute^ bat ( f relative InsolabUity ^ and are kept avail- able to the plant by the continual circulation in the soil of the more abundant saline matters, “ The soil (speaking in the widest sense) is then not only tlie ultimate exhaustless source of mineral (fixed) food, to vegetation, but it is the storehouse and conservatory of this food, protecting its own resources from waste and from too rapid use, and converting the highly soluble matters of animal exuviae as well as of artificial refuse (manures) into permanent supplies.”^ By absorption as well as by nitrification the soil acts therefore to prepare the food of the plant, and to present it in due kind and quantity. * The author quotes here the concluding^ pai*agraphs of an article by him ‘*On Some points of Agricultural Science,*’ from the American Journal of Sdjence and Arts, May. 1850. (p. 85). whieli have historic ijiterest in beiii". so far as he is aware, the earliest^ broad and accurate generalization on record, of the facts of soil-absorption, NOTICE TO TEACHERS. At the Author’s request, Mr. Louis Stiidtmuller, of New Haven, will uudertake to furnish collections of the niiuerdls and rocks which chiefly compose soils (see pp. 108-122), suitable for study and illustration, as also the apparatus and materials needful lor the chemical experiments described iu ** How Crops Grow,” / A ValnaMe Periodical lor eyeryOody ii city, Village, aad country. JhE AfflBPican A gricnltuPigi (ESTABLISHED 1842.) fHE LEADING INTERNATIONAL PUBLICATION FOR THE FARM, GARDEN, AND HOUSEHOLD. 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In other wmrds it tells how to manage a co-operative store, farm or factory, and co-op- erative dairying, banking and fire insurance, and co-operative farmers* and women’s exchanges for both buying and selling. The directions given are based on the actual experience of successful co-operative en- terprises in all parts of the United States, llie character and useful- ness of the book commiend it to tlie attention of all men and women who desire to better their condition. 12mo. Cloth 1.50 STANDARD BOOKS. 7 Batty’s Practical Taxidermy and Home Decoration. By Joseph H. Batty, taxidermist for the government surveys and many colleges and museums in the United States. An entirely new and complete as well as authentic work on taxidermy — giving in detail full directions for collecting and mounting animals, birds, rep- tiles, fish, insects, and general objects of natural history. 125 illus- trations. Cloth, 12mo 1.50 Stewart’s Irrigation for the Farm, Garden, and Orchard. New and Enlarged Edition. This work is offered to those American Farmers, and other cultivators of the soil, who from painful expe- rience can readily appreciate the losses whicli result from the scarcity of water at critical periods. By Henry Stewart. Fully illustrated. Cloth, 12ino - 1.50 Johnson’s How Crops Grow. New Elation, entirely rewritten. A Treatise on the Chemical Compo- sition, Structure, and Life of the Plant. Revised Edition. This booK is a guide to the knowledge of agricultural plants, their composition, their structure, and modes of development and growth ; of the com plex organization of plants, and the use of the parts ; the germination of seeds, and the food of plants obtained both from the air and the soil. The book is an invaluable one to all real students of agricul- ture. With numerous illustrations and tables of analysis. By Prof. Samuel W. Johnson, of Yale College. Cloth, 12mo * 2.00 Johnson’s How Crops Feed. A treatise on the Atmosphere and the Soil, as related in the Nutrition of Agricultural Plants The volume — the companion and complement to “How Crops Grow,” — has been welcomed by those who appreciate scientific aspects of agriculture. Illustrated. By Prof. Sami^el W. Johnson. Cloth, 12mo 2.00 Warington’s Chemistry of the Farm. Treating with the utmost clearness and conciseness, and in the most popular manner possible, of the relations of Chemistry to Agriculture, and providing a welcome manual for those, who, while not having time to systematically study Chemistry, will gladly have such an idea as this gives them of its relation to operations on the farm. By R. Warington, F. C. S. Cloth, 12mo- 1.00 French’s Farm Drainage. The Principles, Process, and Effects of Draining Land, with Stones, Wood, Ditch-plows, Open Ditches, and especially with Ties ; includ- ing Tables of Rainfall, Evaporation, Filteration, Excavation, Capacity of Pipes, cost and number to the acre. By Judge French, of New Hampshire. Cloth, 12mo 1.50 Hunter and Trapper. The best modes of Hunting and Trapping are fully explained, and Foxes, Deer, Bears, etc., fall into his traps readily by following his directions. By Halsey Thrasher, an old and experienced sportsman. Cloth, 12mo - ,75 The American Merino. For Wool or for Mutton. A practical and most valuable work on the selection, care, breeding and diseases of the Merino sheep, in all sections of the the United States. It is a full and exhaustive treatise upon this one breed of «heep. By Stephen Powers. Cloth, 12mo 1.* 8 STANDARD BOOKS. Armatage’s Every Man His Own Horse Doctor. By Prof. George Armatage, M. R. C. V. S. A valuable and compre- hensive guide for both the professional and general reader with the fullest and latest information regarding all diseases, local injuries, lameness, operations, poisons, the dispensatory, etc , etc., with practi- cal anatomical and surgical Illustrations. New Edition. Together with Blaine’s “'Veterinary Art,” and numerous recipes. One large 8vo. volume, 830 pages, half morocco 7.50 Dadd’s Modern Horse Doctor. Containing Practical Observations on the Causes, Nature, and Treat- ment of Diseases and Lameness of Horses— embracing recent and im- proved Methods, according to an enlightened system of Veterinary Practice, for Preservation and Restoration of Health. Illustrated. By Geo. H. Dadd, M. D. V. S., Cloth, 12mo 1.50 The Family Horse, Its Stabling, Care, and Feeding. By Geo. A. Martin. A Practical Manual, full of the most useful information. Illustrated. Cloth, 12mo - - - 1.00 Sander’s Horse Breeding. Being the general principles of Heredity applied to the Business of Breeding Horses and the Management of Stallions, Brood Mares and Foals, ^i'he book embraces all that the breeder should know in regard to the selection of stock, management of the stallion, broodmare, and foal, and treatment of diseases peculiar to breeding animals. By J. H. 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Cloth cover .50 American Bird Fancier. Or how to breed, rear, and care for Song and Domestic Birds. This valuable and important little work for all who are interested in the keeping of Song Birds, has been revised and enlaiged, and is now a compile manual upon the subject. All who own valuable birds, or wish to do so, will find the new Fancier indispensable. New, revised and enlarged edition. By D. J. Browne, and Dr. Fuller Walker. lUus- trated, paper cover ^ %