% ^. p. ^tU pbrarg ^ortl; Car0ltna <^tale College Qr\66T J6 MSE^i^Si^i^^iS':^!f^s[^^ifjis?^^ 5731 This BOOK may be kept out TWO WEEKS ONLY, and is subject to a fine of FIVE CENTS a day thereafter. It is due on the day indicated below: ? Dec'48A 0> '^"V^^, H0¥ CROPS FEED. HOW CROPS FEED. A TREATISE ON THE ATMOSPHERE AND THE SOU AS RELATED TO THE Nutrition of Agricultural Plant? WITH ILLUSTRATIONS. SAMUEL W! JOHNSON, M.A., PKOFESSOB OP ANALYTICAL AND AGRICULTURAL CHKMISTRY IN THK SHBPFIELD 80IKNTIFI0 SCHOOL OF YALB COLLEGE ; CHEMIST TO THE CONNEC- TICUT STATE AGKICULTITRAL SOCIETY; MEMBER OF THE NATIONAL ACADEMY OF SCIENCES. NEW YORK: OKANGE JUDD COMPANY, 1910 (p^^^ 'I^ Entered according to Act of Congress, in the year 1870, by OI^ANGE JITDD & CO., Id th« Clerk's Office of the Dis^trict Court of the United States for the Soathem District ol New York ,575/ Printed in U. S. % 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 Editorsliip 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 Author, therefore, puts forth this volume — the com- panion and complement to the formei* — with the hope that it also will be welcomed by those who appreciate the sci- entific aspects of Agriculture, and are persuaded that a true Theory is the surest guide to a successful Practice. I 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 scientific discussion or experi- ment, nor has he attempted to make a show of revolution- izing liis subject by bold or striking speculations. His ofiice has been to digest the cumbrous mass of evidence, in which the truths of Vegetable Nutrition lie buried out 5 075/ ***'"<»llfGfUB»^»y. VI PUEFACE. of tlic roacli of the ordinary iuhatcs, agents of oxidation 258 Sulphate of lime 115 Sulphin-, in decay ..293 Sulphurous acid 94 Sulphydric acid 94 Syenite 120 Talc lis Temperature of soil 1S6, 187, 194 Transpiration 202, 208 Trap rock 120 Ulmates 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 1.38 " 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. 101, 164 " exhaled by plants.... 99 " not absorbed by plants 35, 99 " of the atmosphere 34 Weathering 131-134 Wilting 203 Wool, hygroscopic 164 Zeolites 114,349 HOW CROPS FEED. INTRODUCTION. In his treatise entitled " How Crops Grow," the author has described in detail the Chemical Composition of Agri- 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 infoimation may be needed as preliminary to an under, standing of this book, the reader may find hi "How Crops Grow." * That crops grow by g;ithering and assimilating food ia a conception with which all are familiar, but it is only by following the subject into its details that we cm 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 book* prepare tlie way for tlie second, as both the fir!«t and the second are written tu make possible an iiitelli<;ible aceonnt of tlie mode of action of Tillage and of Fertilizers, which will be the subject of a Mrd work. XT 18 HOW CROPS FKED. 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 cei'tain development from the mate- rials of the seed itself (cotyledons or endosperm,) hut shortly after these are consumed, the plantlet ceases to in- crease in dry weight,* and dies, or only grows at its own expense. A similar seed deposited in ordinary soil, Avatered with rain or spring water and freely exposed to the atmosphere, evolves a seedling which survives the exhaustion of the cotyledons, and continues without cessation to grow, forming cellulose, oil, starch, and albumin, increases many times — a hundred or two hundred fold— in weight, nms normally through all the stages of vegetation, blossoms, and yields a dozen or a hundred new seeds, each as perfect as the original. It is thus obvious that Air, Water, and Soil, are cai)a- ble of feeding plants, and, under purely natural conditions, do exclusively nourisli all vegetation. In the soil, atmosphere, and water, can be found no trace of the peculiar organic principles of plants. We look there in vain for celhilose, starch, dextrin, oil, or al- bumin. The natural sources of the food of crops consist of various salts and gases which contain the ultimate ele- ments of vegetation, but which require to be collected and worked over by the plant. The embryo of the germinating seed, like the bud of a tree when aroused by the spring warmth from a dormant state, or like the sprout of a potato tuber, enlarges at the expense of previously organized matters, supplied to it by the contiguous parts. As soon as the plantlet is weaned from the stores of the • Since vegetable matter may contain a variable amount of water, either that which belongs to the sap of the fresh plant, or that which is hygroscopically n- lained in the pores, all comparisons must be made on the dry, i. e., water-fret iubstaqce. See "How Crops Grow," pp. 53-5. IXTktOl^IrCTION. 19 mother seed, the materials, as well as the mode of its nu- trition, are for the most part completely changed. Hence- forth the tissues of the plant and the cell-contents must "be principally, and may be entirely, built up from purely inorganic or mhieral matters. In studying the nutrition of the plant in those stages^ of its growth that are subsequent to the exliaustioii of the cotyledons, it is needful to investigate separately the nu- tritive functions of the Atmosphere and of the Soil, for the important reason that the atmosphere is nearly con- stant in its composition, and is beyond the reach of human influence, while the soil is infinitely Aariable and may be exhausted to the verge of unproductiveness or raised to the extreme of fertility by the arts of the cultivator. In regard to the Atmosphere, we have to notice minutely the influence of each of its ingredients, including Water in the gaseous form, upon vegetable production. The evidence has been given in " How Crops Grow," which establishes what fixed earthy and saline matters are essential ingredients of plants. The Soil is i)lainly the exclusive source of all those elements of vegetation which cannot as- sume the gaseous condition, and which therefore cannot ex- ist in the atmosphere. The study of tlie soil involves a con- sideration of its origin and of its manner of formation. The productive soil commonly contains atmosjiheric elements, which are important to its fertility; the mode and extent of their incorporation with it are topics of extreme prac* tical importance. We have then to examine the signif- icance of its water, of its ammonia, and esjiecially of its nitrates. These subjects have been recently submitted to extended investigations, and our treatise contains a large amount of infoiTnation pertaining to them, which has never before appeared in any publication in the English tongue. Those characters of the soil that indirectly affect the growth of plants are of the utmost moment to the fann- er. It is through the soil that a supply of solar heat, with' 20 now CROPS FEED. out which no life is possible, is largely influenced. "Water, whose excess or deficiency is as pernicious as its proper quantity is beneficial to crops, enters the plant almost exclusively through its roots, and hence those qualities of the soil which are most favorable to a due supply of this liquid demand careful attention. The absorbent pow- er of soils for the elements of fertilizers is a subject which is treated of with considerable fullness, as it deserves. Our book naturally falls into two divisions, the first of which is devoted to a discussion of the Relations of the Atmosphere to Vegetation, the second being a treatise on the Soil. DIVISION I. THE ATMOSPHERE AS RELATED TO VEGETATION. CHAPTER I. ATMOSPHERIC AIR AS THE FOOD OF PLANTS. § 1- CHEMICAL COMPOSITION OF THE ATMOSPHERE. A multitude of observations has demonstrated that from ninety-five to ninety-nine per cent of the entire mass (weight) of agricultural plants is derived directly or indi- rectly from the atmosj^here. The general composition of the Atmosphei-e is familiar to all. It is chiefly made up of the two elementary gases, Oxygen and Nitrogen, which have been described in " How Crops Grow," pp. 33-39.* These two bodies are present in the atmosphere in very nearly, though not altogether, invariable proportions. Disregarding its other ingredients, the atmosphere contains in 100 parts By 7veight. By volume. Oxygen 23. 17 20. 95 Nitrogen 76.83 79.05 100.00 100.00 Besides the above elements, several other substances oc- * In our frequent references to this book we shall employ the abbreviatioa H. C. G. 21 22 now CROPS FEED. cur or may occur in tlie air in minute and variable quanti- ties, viz. : Water, as vapor. . .average proportion by weight, ' l,oo Carbonic acid gas " " " " •|io-ooo Ammonia " " " " ' Iso- ooo- ooo ? ' Ozone " " " «' minute traces. Nitric acid " " '< " " " Nitrons acid " " " " *' «' Marsh gas " " »' " " " In air of (^'^'■'^""''^''^i^^' " " " " -< Siili>liurous acid, " " " " *' " towns. ( g„ij,i,^^.(i,.j(. acid " " " " " " Miller gives for the air of England the following aver- age proportions by volume of the four most abundant in- gredients.— {Elements of Chemistry^ part II., p. 30, 3d Ed.) Oxygen 20.61 Nitrogen 77.95 Carbonic acid 04 Water- vapor 1.40 100.00 We may now appropriately proceed to notice in order each of the ingredients of the atmosphere in reference to the question of vegetable nutrition. This is a subject re- garding which unaided observation can teach us little or nothing. The atmosphere is so intangible to the senses that, without some finer instruments of investigation, we should forever be in ignorance, even of the separate exist- ence of its two principal elements. Chemistry lias, how- ever, set forth in a clear light many remarkable relations of the Atmosphere to the Plant, whose study forms one of the most instructive chapters of science. RELATIONS OF OXYGEN GAS TO VEGETABLE NUTRITION. Absorption of Oxygen Essential to Growtli,— The ele- ment Oxygen is endowed with great chemical activity. This activity we find exhibited in the first act of vegetar A^TMOSPIlEnK' AIR AS THE FOOD OP PLANTS. 23 tlon, viz.: in germination. We know that the presence of oxygen is an indispensable requisite to the sprouting seed, and is possibly the means of provoking to action the dor- mant life of the germ. The ingenious experiments of Traube (H. C. G., i\ 326.) demonstrate conclusively that free oxygen is an essential condition of the growth of the seedling plant, and must have access to the plumule, and especially to the parts that are in the act of elongation. De Saussure long ago showed that oxygen is needful to the development of the buds of maturer plants. He ex- perimented in the following mamier : Several woody twigs (of willow, oak, apple, etc.) cut in spring-time just before the buds should unfold were placed under a bell-glass containing common air, as in fig. 1. Their cut extremities stood in water held in a small vessel, while the air of the bell was separated from the external atmosphere by the mercury contained in the large basin. Thus situated, the buds opened 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. {Reeherches sur la Yegetatioii, \). 115.) The same acute investigator found tliat oxj'^gen is ab- sorbed by the roots of plants. Fig. 2 shows the arrange- ment by which he examined the effect of difierent 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 now CHOPS PEED. was placed in a basin ot'uiereury, 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 j^-iucipal roots, and the space above was occupied by com- mon or some other kind of air. lu one experiment carbonic acid, in a second nitrogen, in a third hydro- gen, and in three others common air, was employed. In the first the roots died in seven or eight days, in the SL'Cond an^l thii-d they perish- ed in thirteen or fourteen days, wliile in the three others they re- mained healthy to the end of three weeks, Avhen the experiments were concludeil. {Recherehes, 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. This absorption proceeds most energetically in the pistils and stamens. Flowers of very rapid growth expeiience in this process, a considerable rise of temperature. Garreau, observing the spadix of Arum itaUcum, which absorbed 28|^ times its bulk of oxygen in one hour, found it 15° F. wai'mer than the surroiuiding air. In the ripening of fruits, oxygen is also absorbed in small quantity. The Function of Free Oxyg^en. — AH those processes of growth to which free oxygen gas is a requisite appear to depend upon the transfer to the growing organ of mat- ters previously organized in some other part of the plant, and probably are not cases in which external inorgani(? bodies are built iip into ingredients of the vegetable struc- ture. Young seedlings, buds, flowers, and ripening fruits^ Fig. 2. ATMOSPHEllIC AlK As TlUi FoOD OF PLANTS. 2f» have no power to increase in mass at the expense of the atmosphere and soil ; tliey 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 c;m be judged from our existing knowledge, consists in effecting or aiding to effect the conversion of the materials 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 assimilation. Certain it is that the free oxygen which is absorbed by the j^lant, or, at least, a corresponding quantity, is evolved again, either in the un- combined state or in union witli carbon as carbonic acid. Exhalation of Oxygen from Foliai^e.— The relation of the leai^es 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 Mater, 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 accmnulate in the neck of the funnel to enable tlie experimenter to 2 96 rroAv was to supply them with water. The water which exhaled from the foliage and gathered on the inside of the shade ran off through 7i 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, B, C\ B, E. On opening the cock a b, A, water enters A, and Its pressure forces air through the bottles and tube into the shade Fy whence it finds its exit through the tube i k, and the bulb-apparatus Jf. In its passage through the strong sulphuric acid of B, C, and B, the air is completely freed from ammonia, while the carbonate of soda of £ re- moves any traces of nitric acid. The sulphuric acid of the bulh M puri- fies the small amount of air that might sometimes enter the shade through the tube i h, owing to cooling of the air in F-, when the curreut Al-aiOSPIIERlC AIU AS THE FOOD OF PLANTS. 06 was not passing. The outer ends of the tubes t and u were closed with caoutchouc tubes and glass plugs. In these experiments it was considered advisable to furnish to the plants lUDre carbonic acid than the air contains. This was accomplished by pouring hj-drochloric acid from time to time into the bottle T, which contained fragments of marble. The carbonic acid gas thus liberated joined, and was swept on by the current of air in C. E.Kperiments taught how much hydrochloric acid to add and how often. Tlie proportion of this gas was kept within tlie limits which previous experimenters had found permissible, and was not allowed to exceed 4.0 per cent, nor to fall below 0.^ per cent. In these experiments the seeds were deposited in a soil [uirilied from nitrogen-compounds, by calcination in a current of air and subsequent washing with pure water. To this soil was added about 0.5 per cent of the ash of the plant wliieh was to grow in it. Tlie water used for wa- tering the plants was specially purified from ammonia and nitric acid. The experiments of Lawes, Gilbert, and Pngh, fully confirmed those of Boussmgaiilt. For the numerous de- tails and the full discussion of collateral points bearing on the study of this question, we must refer to their elaborate memoir, " On the Sources of the Xitrogen of Vegetation." . — {Philosophical Transactions, 1831, II, pp. 431-579.) I\'iti-ogeiL Oils is not I^iiiitte«l l>y I.iiving' I'liiiits. — It was long supposed by vegetable physiologists that wlien the foliage of plants is exposed to the sun, free nitrogen is evolved by them in small quantitj'. In fact, when plants are placed in the circumstances which admit of coll-^cting the gases tliat exhale fi'om them under the action of light, it is found tliat besides oxj-gen a quantity of gas appears, which, unless special precautions arc observed, consists chieily of nitrogen, which was a iiart of tlie 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 Boussingault has recently (1863) done, this air be removed fpQm the plant and water, or rather if its quantity be'accurately determined and deducted from that obtained in the experiment, the result is tliat 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 unaljle to find marsh gas in tlie air exhaled from either aquatic or hind plants submerged in water, and in his most recent researches (186.5) Boussingault found none in the gases given tiflf from the foliaire of a living tree examined without submergence. The ancient conclusion of Saussure, Daubeuy, Draper, and others, that nitrogen is emitted from tlie substance of the plant, is thus showo to have been based on an inaccurate method of investigation. 2* I, IIOAV CROPS FEED. RELATIONS OF ATMOSPHERIC WATER TO VEGETABLE NUTRITION. Occurrence of Water in the Atmosphere.— If w ator be exposed to the uir in a sliallow, open vessel for some time, it is seen to decrease in quantity, and finally disapi)ears en- tirely ; it evaporates, vaporizes, or volatilizes. It is con- verted into vapor. It assmnes the form of air, and becomes a part of the atmosphere. The rapidity of evaporation is gi'eater the more eleva- ted the temperature of the water, and the drier the atmos- phere that is over it. Even snow and ice slowly suiFer 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 the other hand, a body or mixture whose tempera- ture is far lower thnn that of the atmosphere, condenses vapor from the air and makes it manifest in the form of water. Thus a glass of ice- water 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 warmed by the sun. Again, when the invisible vapor which fills a hot tea-kettle or steam-boiler issues into cold air, a visible cloud is immediately formed, which consists of mhiute droplets of water. In like man- ner, fogs and the clouds of the sky are produced by the cooling of air charged with vapor. When the cooling is sufficiently great and sudden, the droplets acquire such size as to fall directly to the ground ; the water assumes the form of rain. ATJIO.SPUKKIC AIU AS TIIK FOOD OF I LANTS. oO Water then exists in the atmosphere during the periods of vegetable activity as gas or vapor,* and as liquid. In the former state it is almost perpe'tually rising into the air, while in the latter form it frequently falls again to the ground. It is thus in a continual transition, back and forth, from the 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 cent ; but the amount is very variable, and is almost constantly fluctuating. It may range from less than one-hnlf to two and a half or three per cent, ac- cording to temperature and othei- 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 capable of taking up additional moisture, and thus ficilitates evaporation. Is Atmospheric Water Absorbed by Plants 1— It has long been supposed that growing vegetation has the power to absorb vapor of water from the atmosphere by its foliage, as well as to imbibe the liquid water which in the form of rain and dew may come in contact with its leaves. Experiments which have been instituted for the purpose of ascertaining the exact state of this question have, how- ever, demonstrated that agricultural plants gather little or no water from these sources. 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 rain or on the depo- sition of dew depends, not so much on the absorption by the foliasie, of the water that gathers on it, as it does * While there is properly no essential dift'orence between a gas and a vapor, the former term is commonly applied more especially to aeriform bodies which are not readily brought to the liquid state, and the latter to those which are easily condensed to liquids or solids. 36 HOW CROPS FEED. on the suppression of evaporation, whidi is a consequence of the saturation of the surrounding air with water. linger, and more recently Duchartre, have found, 1st, that plants lose weiglit (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 gain, but some- times lose weight 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 otlier hand, that leaves, either separate or attached to twigs, gain weight by continued imynersion in water, and not only recover what they may have lost by exposure, but absorb more tlian they orig- inally contained. ( Versuchs-Statlonen^ 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 grent degree, by the hairs or wax of the epidermis. Finally, 3d, Sachs has found that even the roots of plants appear incapable 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. St., II, 7.) A young camellia, having several fresh leaves, was taken from the loose soil of the pot in which it had been growing ; from its long roots all particles of earth were carefully remov- ed, and its weight was ascertained. The bottom of a glass cylinder was covered with water to a little depth, and the roots of the camellia were introduced, but not in contact with the water. The stem was supported at its ATMOSPHEnlC Ain AS THE POOD OP PLANTS. S? lower part in a hole in a glass cover,* that was cemented air-tight upon the vessel. The stem itself was cemented by soft wax into the liole, so that the interior of the ves- sel was completely cut off ffom direct communication with the external atmosphere. The plant thus situated had its roots in an atmospliere as neaily as possible saturated with vapor of water, while its leaves were exposed to the ex- ternal air. After four days had expired, the entire appa- ratus, plant included, had lost 1.823 grm. Thereupon the plant was removed from the vessel and weighed by itself; it had lost 2.188 grm. The loss of the entire apparatus was due to vapor of water, which had escaped through the leaves. The diiference between this loss and the los? which the plant had experienced could be attributed only to an exhalation of water through the roots, and amount ed to (2.188 — 1.823=) 0.365 grm. This exhalation of water into the confined and moist at- mosphere of the glass vessel is explained, according to Sachs, by the fact that the chemical changes proceeding within the plant elevate its temperature above that of the surrounding atmosphere. Knop, in experiments on the transpiration of plants, {Y. St., VI, 25.5,) obtained similar results. He found, however, that a moist piece of paper or wood also lost weight wlien kept for some time in a confined space over water. He therefore concludes that it is nearly impossible in the conditions of such experiments to maintain the air sat- urated with vapor, and that the loss of weight by the roots is due, not to the heat arising from internal chemical changes, but to simple evaporation from their surface. In one instance he found that a portulacca standing over night in a bell-glass with moistened sides, did not lose, but gained weight, some dew having gathered on its foliage. * The cover consisted of two semicircular pieces of ground glass, each of which had a small semicircular notch, so that the twoconld be brought togethei by their straight edges around the stem. 38 IIOAV CROPS FEEI>. The result of tliese investigations is, tliat while, perhaps, wilted foliage in a heavy rain may take u]) a small (juan- tity of water, and while foliage and roots may absoib some vajjor, yet in general and for the most part the at- mospheric water is not directly taken up to any great ex- tent by plants, and does not therefore contribute immedi- ately to their nourishment. itmospheric VFater Enters Crops through the Soil.— Jt is only after the water of the atmosphere has become in- corporated with tlie soil, that it enters freely into agricul- tiiial plants. The relations of this substance to proper ve'jetable nutrition may then be most appropriately dis- cussed in detail when we come to consider the soil. (See p. 199.) It is probable that certain air-plants (epiphytes) native to the tropics, ■which liave no connection with the soil, and are not rooted in a medium capable of yielding water, condense vapor from the air iu considerable quantity. So also it is pi'oved that the mosses and lichens absorb wafer )an;ely from moist air, and it is well known that they become dry and brittle in hot weather, recovering their freshness and flexibility when the air is damp. §5. RELATIONS OF CARBONIC ACID GAS TO VEGETABLE NUTRITION. Composition and Properties of Carbonic Acid, ~ When 12 grains of pure carbon are heated to redness in 32 grains of pure oxygen gas, the two boiiies unite to- gether, themselves completely disappearing, and 44 grains of a gas are pj-oduced which lias the same bulk as the oxygen had at the beginning of the experiment. The new gas is nearly one-half heavier than oxygen, and differs in most of its properties from both of its ingredients. It is carbonic acid. This substance is the jiroduct of the burn- ing of charcoal in oxygen gas, (H. C. G., p. 35, Exp. 6.) It is, in fact, produced whenever any organic body is ATMOSlniERIC AIR AS THE I^OOIl OF PLANTS. ,39 binned or decays in contact with the air. It is like oxy- gen, colorless, but it has a peculiar pungent odor and pleasant acid taste. The composition of carbonic acid is evident from what has been said as to its production from carbon and oxygen. It consists of two atoms, or 3:2 parts by weight, of oxygen, united to one atom, or 12 parts, of carbon. Its symbol is COjj. In the subjoined scheme are given its symbolic, atomic, and percentage composition. At. wt. Per cent. C = 13 27.27 Oo = 32 73.73 CO2 = 44 100.00 In a state of combination carbonic acid exists in nature in. immense quantities. Limestone, marble, and chalk, contain, when pure, 44 per cent of this acid united to lime. These minerals are in chemical language carbonate of lime. Common salteratus is a carbonate of potash, and soda- salasratus is a carbonate of soda. From either of these carbonates it is easy to separate this gas by tiie addition of another and stronger acid. For this purpose we may employ the Rochelle or Seidlitz powders so commonly used in medicine. If we mingle together in the dry state the contents of a blue paper, which contains carbonate of soda, with those of a white paper, which consist of tartaric acid, nothing is observed. If, however, the mixture be placed at the bottom of a tall bottle, and a little water be poured upon it, at once a vigorous bubbling sets in, which is caused by the liberated carbonic acid.* Some important properties of the gas thus set free may be raadily made manifest by the following experiments. a. If a burning taper or match be immersed in the gas, the flame is immediately extinguished. This happens because of the absence of free oxygen. 6. If the mouth of the bottle from which carbonic acid is escaping be held to that of another bottle, the gas can be poured into the second ves- sel, ou account of its density being one-half greater than that of the air. Proof that the invisible gas has thus been transferred is had by placing * Chalk, marble, or salaeratus, and chlorhydric (muriatic) acid, or strong vine- gar (acetic acid) can be equally well employed. 40 ttOtV CEOPS li-KEi). a burning; toper in the second bottle, when, if the exjieriment was rij^^ht- ]y conducted, the flume will be extinguished. c. Into a bottle filled as in the last experiment with carbonic acid, some lime-water is poured and agitated. The previously clear lime-wa- ter immediately becomes turbid and railliv from the formation oicarbcm- ate of lime, which is iieaily insoluble in water. Carbonic Acid iu the Atmospliere.— To show the pres- ence of carl)oi)ic acid in the atmosphere, it is only neces- sary to expose lime-water in an open vessel. But a little time elapses before the liqtiid is covered with a white film of carbonate. As already stated, the average proportion of carbonic acid in the atmosphere is 6-lOOOOths (l-16()0th nearly) by weight, or 4-lOOOOths (l-2500th) by bulk. Its quantity varies somewhat, however. Among over 300 analyses made by De Saussure in Switzerland, Verver in Holland, Lewy in New Granada, and Gilm in Austria, the extreme range was from 47 to 86 parts by weight in 100,000. Deportment of Carbonic Acid towards Water. — Water dissolves carljonic acid to a greater or less extent, accord- ing to the temperature and pressure. Under the best or- dinary conditions it takes up about its own volume of the gas. At the freezing point it may absorb nearly twice as much. This gas is therefore usually found in spring, well, and river waters, as well as in dew and rain. The consid- erable amount held in solution in cold springs and wells is a principal reason of the refreshing quality of their wa- ter. Under pressure the proportion of carbonic acid ab- sorbed by water is much larger, and when the pressure is removed, a portion of the gas escapes, resuming its gase- ous form and causing effervescence. The liquid that flows from a soda-fountain is an aqueous solution of carbonic acid, made under pressure. Bottled cider, ale, champagne, and all effervescent beverages, owe their sparkle and much of their refreshing qualities to the carbonic acid they con- tain. ATMOSl'UKUK FOOD OV PLANTS. 41 The Absorption of ( arbonic Acid by Plants. — In 1771 Priestley, in Eiigluud, found th;it tlie leaves of plants im- mersed in water, sometimes disengaged carbonic acid, sometimes oxygen, and sometimes no gas at all. A few years later Ingenbouss proved that the exhalation of car- bonic acid takes place in the absence, and that of oxygen in the presence, of solar light. Several years more elapsed before Sennebier first demonstrated that the oxygen which is exhaled by foliage in the sunlight comes from the car- bonic acid contained in the water in whicli the plants are immersed for the purpose of these experiments. It had been already noticed, by Ingenhouss, that in spring water plants evolve more oxygen than in river water. We now know that the former contains more carbonic acid than the latter. Where the water is by accident or purposely free from carbonic acid, no gas is evolved by foliage in the sunlight. The attention of scientific men was greatly attracted by these interesting discoveries ; and shortly Percival, in England, found that a |)lant of mint whose roots were stationed in water, flourished better when the air bathing its foliage was artificially enriched in carbonic acid than in the ordinary atmosphere. In 1840 Boussingault furnished direct proof, of what indeed was hardly to be doubted, viz.: the absorption of the carbonic acid of the atmosphere by foliage. Into one of the oiiflces iu a tbree-necked glass globe he introduced and fixed air-tight the brunch of a living vine bearing twenty leaves ; with another opening he connected a tube through which a slow current of air, containing, in one experiment, four-lOOOOths of carbonic acid, could be passed into the globe. This air after streaming over the vine leaves, at the rate of about 15 gallons per hour, escaped bj' the third neck into an arrangement for collecting and weighing the carbonic acid that remained in it. The experiment being set in process in the sun- light, it was found that the enclosed foliage removed from the current of air three-fourths of the carbonic acid it at first contained. Influence of the Relative Quantity of Carbonic Acid. — De Saussure investigated the influence of various propor- 42 now .Rops PKKD. tions of carbonic acid mixed with atmospheric air on the development of ^ egetation. lie found that young peas (4 inches high) when exposed to direct sunlight, endured for some days an atmosphere consisting to one-half of carbonic acid. When the proportion of tliis gas was increased to two-thirds or more, they speedily Avithered. In air con- taining one-twelfth of carbonic acid the peas flourished much better than in ordinary atmospheric air. The aver- age increase of each of the plants exposed to the latter for five or six hours daily during ten days was eight grains ; while in the former it amounted in the same time to eleven gi-aiiis. In the shade, however, Saussure found that increase of the proportion of carbonic acid to one-twelfth was detrimental to the plants. Their growth under these circumstances was but three-fifths of that experienced by similar plants exposed to the same light for tlie same time, but in common air. He also proved that foliage cannot long exist in the total absence of carbonic acid, w'hen exposed to direct sunlight. This result was obtained by enclosing young plants whose roots were immersed in water, or the branches of trees stationed in the soil, in a vessel which contained moistened quicklime. This substance rapidly absorbs and fixes carbonic acid, forming carbonate of lime. Thus situated, the leaves began in a few days to turn yel- low, and in two to three weeks they dropped ofi". In darkness the presence of lime not only did not de- stroy the plants, but they prospered the better for its presence, i. e., for the absence or constant removal of car- bonic acid. Boussingault has lately shown that pure carbonic acid is decomposed by leaves exposed to sunlight with extreme slowness, or not at all. It must be mixed with some other gas, and when diluted with either oxygen, nitrogen, or hy- drogen, or even when rarefied by the air-pum]) to a certain extent, the absorption and decomposition proceed as usual. Conclusioilt — It thus is proved list, that vegetatioa PHOPERTY OF 1' 1. u rni t Pnr \ \vxtktN!\ aTmospiikkk; aiu as tiii: food assing tlirough water. Tliis wash water is always found to contain a small quantity of ammonia, which may be cheaply utilized The exhalations of volcanoes and fumeroles likewise contain ammonia, which is probably formed in a similar manner. In the processes of combustion and decay the elements of the organic 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 themselves to form am- monia. Ammonia is a Stroni? Alkaline Base.— Those bases which have in general the strongest affinity for acids, are potash, soda, and ammonia. These bodies are very similar in many of their most obvious char.icters, 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. bonie acid, (by holding it inverted over a candle until the latter becomes extinguished when 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 Ain AS THE FOOD OF PLANTS. !)6 combine to a solid salt, llie 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 the so-called smelling-bot- tles. It rapidly vaporizes, exhaling the odor of ammonia very strongly, and is hence sometimes termed sal volatile. Like camphoi-, 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; hence it is im- possible that the latter should exist in the free state, and we must assume that it occurs there chiefly in combination with carbonic acid. The carbonate of ammonia, whether solid or gaseous, is readily soluble in water, and like free ammonia it evaporates from its solution with the first portions 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- parent 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 its existence. Its com- position is as follows : Symbol. At. wH. Pbr cent. NH3 17 21.5 H2O 18 23.8 CO2 44 55.7 NH3. H2O. CO2. 79 100.0 Tests for Amiuoiiia. — «. If salts of ammonia are rubbed to- gether with slaked lime, ^)e^^t witli the addition of a few drops of water, tht: ammouia is liberated in the gaseous st:-.te, and betrays itself (1) by its charaeteristic odor ; (2) by its reaction on moistened test-papers; and 54 now cnopt4 pkEd, (3) b J giving rise to the funnivfion oi white famea, wllcri nny object (c. ^.^ a glass rod) moistened witli hydrochloric iicid, is brouglit in contact with it. These fumes arise Irom the formation of solid ammoniucAl salts pro- duced by the contact of the gases. 6. Xensler's Text.—Yov the detection of e.vceedin-ly minute liuccs 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 tlie mixture stand lor some time, then filter; add to the filtrate 30 cub. cent, of pure concentrated solution of i)otassa(l : 4); and, should a precipitate form, filter again. If to this solution is added, in smnll quantity, a liquid containing ammonia or an ammonia-salt, a reddisli brown precipitate, or with exceedingly small quantities of ammonia, a yellow coloration is produced from the formation of dimercurammouic iodide, NHg2 I.OHj. c. Bohliff's Test. — According to Bohlig, chh^ride of mercury (corrosive sublimate) is the most sensitive reagent for ammonia, when in the free 6t;ite or as carbonate. It gives a white precipitate, or in very dilute so- lutions (even when containing but '|aoo,ooo of ammonia) a white turbidity, due to the separation of niercurammonie chloride, NH^ Ilg.Cl. In solu- tions of the salts of ammonia with other acids than carbonic, a clear solution of mixed carbonate of potassa and chloride of mercury must be employed, which is prcpaied by adding 10 drops of a solution of the purest carbonate of potassa, (1 of salt to 50 of water,) and 5 drops of a Bulution of chloride of mercury to 80 c. c. of water exempt from am- monia (such is the water of many springs, but ordinary distilled water rarely). This reagent may be kept in closed vessels for a time without change. It much more concentrated, oxide of mercury separates from it. Bj' its use the ammonia salt is first converted into carbonate by double decomposition with the carbonate of potassa, and the further reaction proceeds as before mentioned. Occurrence of Ainnionia in the Atmosphere. — The e.\- istence of ammonia in the atmosphere was first noticed by De Saussure, 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 whicli ammonia occurs in the atmosphere, but chiefly to the difficulty of collecting and estimating such small amounts, the state- ments of those who have experimented upon this subject are devoid of agreement. We present here a tabulated view of the most trust- worthy results hitherto published: ATMOSPIIEUIC AIR AS THE TOOD OF PLANTS. 55 1,000,000,000 parts of atinosplicric air contain of ammonia, according to Graeirer, at MiiliUiausen, Germany, averag:e, 333 parts. Fresenius, " Wiesbaden, " " 133 " Pierre, " Caen, France, 1851-52, " 3500 " " " " " 1852-53, " 500 " Bineau, " Lyons, " 1852-53, " 250 " " " Caliiire, " " wiuter, 40 " " " " " " summer, 80 " Ville, " Paris, " 1819-50, average, 24 " " Grenelle, " 1851, "" 21 " Graham lias shown by experhnent (Ville, Recherches sur la Vegetation, Paris, 1S53, p. 5,) that a quantity of ammonia like that found by Fresenius is sufficient to be readily detected by its eifect on a red litmus pai»er, which is not altered in the air. This demonstrates that the at- mosphere where Graham experimented (London) contained less than '"|j^„^^_^^^ths cf ammonia in the state of bicar- bonate. The experiments of Fresenius and of Grager were made with com[)aratively small volumes of air, and those of the latter, as well as those of Pierre, and some of Bineau's, were made in the vicinity of dwellings, or even in cities, where the results might easily be influenced by local emanations. Bineau's results were obtiuned by a method scarcely ailmitting of much accuracy. The investigations of Ville {Recherches, Paris, 1853,) are, perhaps, the most trustwoi'thy, 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, altliough 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 prolonged dry weather it would con- tain more than usual, since ammonia escapes from its solutions with the first portions of aqueous vapor. The Absorption of Amnioiiia by Vej?etation. — The gen- eral fact that ammonia in its compounds is appropriated 56 now CROPS FEED by plants as food is most abundantly established. 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 plants 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. Ville has stated, 1851-2, that vegetation in conserva- tories may be remarkably ])romoted by impregnating 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 gradually 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- aj^C. — 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 tliat according to Unger and Duchartre Avater enters the higher plants almost exclusively by the roots, after it has been absorbed by the soil. To Peters and Sachs ( Chem. Ackersmann, 6, 158) we owe an experiment which appears to de- monstrate that ammonia, like carbonic acid, is imbibed by the leaves of I' iy: ^'- plants. Tlie figure represents the ap- paratus employed. It consisted of a glass bell, resting below, AtMOSPHEIllC AIU AS TIIK 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. Tlirough an aperture in the centre of the glass ])late the stem of the plant experinienled on was introduced, so that its fo- liage should occupy the bell, while the roots were situated in a pot of earth 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 stems be- ing cemented tightly into the opening below, and through the tubes tlie foliage of each plant received daily the same quantities of mois^t atmosj)heric air mixed with 4-5 per cent of carbonic acid. One plant was supplied in addition with a quantity of carbonate of ammonia, w^hich Avas in- troduced by causing the air that was forced into the bell to stream through a dilute solution of this salt. Both plants grew well, until the experiment was terminated, on the 11th of August, when it Avas found that the plant Avhose foliage was not supplied with carbonate of ammo- nia weighed, dry, 4.14 gm., while the other, which Avas supplied Avith the A\apor of this salt, weighed, dry, 6.74 gms. Tlie fir>t plant had 20 full-sized leaves and 2 side slioots; the second Ixid 40 leaves and 7 shoots, besides a much larger mass of roots. The first contained 0.106 gm. of nitrogen; the second, double that amount, 0.208 gm. Other trials on various [»lants failed from the diffi- culty of making them groAV in the needful circumstances. Th#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* • Cheraie der Ackerkriime, A'ol. 2, p. 211. 3* 5ft now cRopfi PEEn. tural plants to tlic production of tlie albuniinokls.* We measure the nutritive efFoct of aminonia salts applied as fertilizers by tlie amount of nitrogen whicli vegetation as- similates from them. Effects of Ammonia on Vegetation. — 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 fruit. If, however, such plants are exposed 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 checked, and the activity of growth is transferred to stems and leaves, Avhich assume a new vigor and multiply with extraordinary luxuriance. If flowers are formed, they are sterile, and yield no seed. 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 belongs to a sickly or ill-fed growth. A third result is that not only the mass of vegetation is increased, but the relative proportion of nitrogen in it is heightened. This result was obtained in the experiment 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 prodaction of nicotine ; in coffee, of caffeine ; and in many other plants to analogous eubstances. Plants appear oflentiraes to contain small quantities of ammonia salts and nitrates, as well as of asparagin, (C4 Hs N2 03,)a substance first found in asjjaragus, and which is formed in manj plants when they vegetate in exclusion of light. ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 59 Do Healtliy Plants Exhale Ammonia ?— The idea having been advanced that in tlie act of vegetation a loss of ni- trogen may occur, possibly in the form of ammonia, Knop made an cxjieriment with a water-plant, the Typha latl- folia., a species of Cnt-tail, to determine this point. The plant, growing imdisturbed 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 uppiT 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 tlie large tube was placed over the plant, a narrow U-shaped tube was immersed in the water to 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 amuionia 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 Avell assume that this gas is not ex- haled by the Typha lati folia. The statements to be foi;nd in early authors (Sprengel, Schiibler, Johnston), to the effect tliat ammonia is exhaled by some plants, deserve further examination. 66 now crops PKED. The Chenopodium vuharla exhales from its foliage a body chemically related to ammonia, and that has been mistaken for it. This substance, known to the chemist as triinethylamine, is also contained in the flowers of Cra- ppgus oxycanthd^ and is the cause of the detestable odor of these plants, which is that of putrid salt fish.* (Wicke, Liehig's A/m., 124, p. 338.) Certain fungi (toad-stools) emit trimeth ylamine, or some analogous compound. (Lehmann, Sachs^ Experimental Plcyslolojie der I^anzen, 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 proper to the atmosphere has little effect upon plants through their foliage when they are sheltered from dew and rain. Such, at least, is the result of certain experi- ments. Boussingault (Agronomie, Chinile Agricole, et Physi-. 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. The 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: Weiglit of seeds 4.965 grin's. " dry harvest 18.730 " Nitrogea in harvest and soil.. .2499 " " " seeds 2307 " Gain of nitrogen 0192 grm's = 7.6 per cent of the total quantity. When rains fall, or dews deposit upon the surface of the * Triinethylamine CsHuN = N (01X3)3 may be viewed as ammonia NH3, in which the three atoms of liydro',aui are replaced by three atoms of methyl CH3. It is a jras like anmionia, and has its i)nn';ency, but accompanied with the odor of stale fish. It is prepared from herring pickle, and used iu medicine un- der the name ijropylamine. 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 tlum what is diifiised throughout the limited volume of air which contributes to the nour- ishment of plants. Tlie solubility of carbonate of ammo- nia in water has already been mentioned. In a rain-fall Ave have the atmosphere actually washed to a great de- gree of its ammonia, so tliat nearly the entire quantity of this substance which exists between the clouds and the earth, or in that mass of atmosphere through Avhich the rain passes, is gathered by the latter and accumulated within a small space. Proportion of Ammonia in Rain-water, etc. — The pro- portion of ammonia * which the atmospheric waters thus collect and bring down upon the surface of the soil, or upon the foliage of plants, has been the subject of inves- tigations by Boussingault, Bineau, Way, Knop, Bobiere, and Bretschneider. The general i-esiilt of their accordant investigations is as follows : In rain-water the quantity of ammonia in the entiiic fall is very variable, ranging in the country from 1 to 33 parts in 10 million. In cities the amount is larger, tenfold the above quantities having been observed. The first portions of rain that fall usually contain much more ammonia than the latter portions, for the reason that a certain amount of water 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. * III all (luaiilitative statemonis roj^'ardiui,' ammonia, NH3 is to be miderstoodi ftnauotNH^O. 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 atmosplieric waters (dew and fogs included) which he was able to collect at Liebfrauenborg (near Stras- burg, PVance) from the 26th of May to the 8th of Nov. 1853, was 6 parts in 10 million {Agyonomie, 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. ( Versuchs- 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 following 12 months was 9 parts in 10 million. Bretschneider found in the atmospheric waters collected by him at Ida-Marienhiitte, in Silesia, from April, 1865, to April, 1866, as the average of 9 estimations, 30 parts 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 Regenwalde, in 1865, 24; in 1867, 28; at Dahme, in 1865,17; at Kuschen, in 1865,5^; and in 1866, 7^ parts. {Preus. Ann. d. Layidwirthschaft, 1867.) The monthly averages fluctuated without regularity, but mostly within 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 raiu-fall (dews, etc., included) for those years. Prof. Way, at that time chem- ist to the Royal Ag. Soc. of England, analyzed the waters, and found that the total amount of ammonia contained in them was equal to 7 lbs. in 1855, and 9^ lbs. in 1856, for 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 March, 1865, Pincus and Rollig obtained 6.38 lbs. of ammonia per acre. Bretschneider found in the waters collected at Ida-Ma- rienhiitte 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. §7. When lightning strikes the earth or an object near its surface, a person in the vicinity at once perceives a peculiar, ; >called " sulphureous " odor, which must belono- to something developed in the atmosphere by electricity. The same smell may be noticed in a room in which an electrical machine has been for some time in vigorous action. The substance which is thus pioduced 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 only been obtained mixed with 64 HO-\V 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 lungs, 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 oxidizing power. Silver is a metal which totally refuses to combine ^^itii oxygen under ordinary circumstances, as shown by its maintaining its brilliancy without symptom of rust or tarnisli when exposed to piire 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 disappears. 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 vegetable pi<2;meuts, such as iiidiijo, litmus, etc., are speedily hleaclied by ozone. This action, also, is simply one of oxidation. Gorup-Besanez {Ann. Ch. u. /%., 110,86; also, rhysiologische Vfiemie) has examined the deportment of a number of orsxanic bodies towards ozone. He finds that egg-albumin and casein of milk are rapidly altered by it, while flesh fibrin is unaffected. Starch, the sugars, the organic acids, and fats, are, when ]nirc, unaf- fected by ozone. In presence 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. Dvy substances are unaffected by it. The peculiar deportment towards ozone of certain volatile oils will be presently noticed. * Babo and Claus (Ann. Ch. v. Ph.. 2d Sup., p. 304) prepared a mixture of oxy- gen and ozone coutaining nearly G per cent of the latter. ATMOSPIiHUIC AIU AS THE FOOD OF PLANTS. 65 Tests for Ozone.— Certain phenomena of oxidation tliat are attended with changes of color serve for the recognition of ozone. We liave alreiuly seen (II. C. G., p. 64) that starch, when brought in contact with iodine, at once assumes a dci-];- 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 paper be impregnated with i\ mi.xture of starch-paste and solution of iodide of potassium,* we have i^ test of the pi'esence of ozone, at once most chaiaeteristie and delicate. Sucli ]>apcr, moi.-tcned and placed in ozonoust air, is spcidi^j turnei\ blue by tiie action of the liberated iodine upon the starch. By the usq of this test the presence and abundance of oz<.>nte in tiiti atmosphere h;i^ been measured. Ozone is Active Oxygen. — That ozone is nothino; jnore or less than o.vygen in a peculiar, active condition, is shown by the following experiment. When perfectly pure and dry oxygen is enclosed in a glass tube containing moist metallic sih'er in a state of fine division, it is possible by long-continued transmissicn of electrical discharges to cause the gaseous oxj^gen entirely to disappear. On heat- ing the silver, which has boconie 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 e.^perimonts of Andrews, Babo, and Soret, demonstrate that ozone has a greater density than oxygen, since the latter diminislies 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. * Mis 10 parts of starch with 200 parts of cold water and 1 part of recently fused iodide of potassiiuu, by nibbing 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. c., charged with ozone. t Recent observations by Babo and Glaus, and by Soret, show that the density tf ozone is one and a half times greater than that of oxygen. DO now CnOPS FEED. Allotropism.— This occurrence of nn element in two or even .oore forms is not witliout otlier illustrations, and is termed Allotropism. Pliosphorus occurs in two conditions, viz., red pliosphorus, which crys- tallizes in rhonibohedrons, and like ordinary oxyjjen is coiniiaratively inactive in its affinities; and colorless phosphorus, which crystallizes in octahedrons, and, like ozone, has vigorous tendencies to unite with ottier bodies. Carbon is also found in three allotropic foims, viz., diamond, plumbago, and charcoal, which diflfer exceediugly in their chemical and physical characters. Ozone Formed by Chemical Action. — Not only is ozone produced by electrical disturbance, but it has likewise been sliown 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 modification ; 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 but ' |j3„„ of the weight of the air, — is still sufficient to exhibit all the reactions that have been described. Schuiibein has shown tliat 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 the reactions of ozone. Ether and alcohol, kept in partially filled bottles, also be- come capable of producing oxidizing efiects. Many of the ATMOSPUEllIC AIU AS THE FOOD OF PLANTS. 67 Tegetal)le 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 the cork of a partially filled turpentine bottle. It is a highly probable liypothesis that ozone may b i 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 oxi. nu'lts, and gTi.lir.ni.v decoiniiosc.s into wiitcr and nitrous oxide, Ji "langliiiiij s^is," as represented by the equation : — NH4 NO3 = 3 HoO + N,0 Xitric acid and the nitrates act as powerful oxidizing agents, i. e., tkey readily yield nj) a portion or all their oxygen to substances having strong affinities for tliis ele- ment. If, for example, charcoal he warmed with strong nitric acid, it is rapidly acted upon and converted into carbonic acid. If thrown into melted nitrate of soda oi saltpeter, it takes fire, and is violently burned to carbonid acid. Similarly, sulphur, phosphorus, and most of tlio metals, may be oxidized by this acid. When nitric acid oxidizes other substances, it itself loses oxygen and suffers reduction to compounds of nitrogen, containing less oxygen. Some of these compounds require notice. Nitric Oxide, NO. — ^When nitric acid somewhat diluted with water acts upon metallic copper, a gas is evolved, which, after washing Avith water, is colorless and permanent. It is nitric oxide. By exposure to air it tmites with oxy- gen, and forms red, suff.icating fumes of nitric peroxide, or, if the oxygen be not in excess, nitrous acid is formed. ]Vitric Peroxide, (hyponitric acid,) N0„, appears as a dark yellowish-red gas when strong nitric acid is ])Oured npon copper or tin exposed to the air. It is procured in a state of purity by strongly heating nitrate of lead : by a cold apjiroaching zero of Fahrenheit's thei'mometer, it may be condensed to a yelloAV liquid or even solid. Nitrous Acid, (anhydrous,) ^„0^, is produced when nitric peroxide is mixed with water at a low temperature, nitric acid being formed at the same time. mtric peroxide. Water. Nitric acid. ^'^T'i ''"''^' -' anhydrous. 4 NO, + H^ = 2 NHO3 + N, O, It may be procured as a blue liquid, which boils at the freezing point of water. ATMOSPnEi:i(; air a>; tiie food op plants. 73 When nitric peroxiJe is ])ut in cont:icL with solutions of an alkali, there lesults a mixture of nitrate and nitrite of the alkali. JVitric Hydnde of Nitrate of Nitrite of -rp-^^g^ peroxide. potash. potash. i)otash. 2 NO, + 2 IIKO = NKO3 + NKO, + II, O Nitrite of Ammonia, NH^ NO., is known to the 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 gas. This decomposition is represented by the following equa- tion: NH, NO, = 2 H,0 + 2 N This decomposition is, however, not complete, A por- tion of ammonia escapes in the vapors, ami 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 suifering any alteration whatever. (Schuyen.) 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 pot i'loyed in preparing hydrogen gas, nitric acid, or any nitrate or nitrite be added, the evolution of iiydrogen ceases, or is checked, and ammonia is formed in the solution, whence it can be expelled by lime or potash. Nitric acid. Hydrogen. Ammonia, 'Water. NO3H + 8H = NPI3 + 3Hp The appearance of nitrous acid in this process is an in- termediate step of the reduction. Further Reduction of Nitric and Nitrous Acids. — Tin- der certain conditions nit ric acid nnd nitrous acid are still further deoxidized. Nesbit, who first employed the reduc- tion of nitric acid to ammonia by means of zinc and dilute chlorhydric acid as a means of detL-rmining the cpiantity of the former, mentions {Quart. Jour. Ghem. Soc, 1847, p. 283,) that when the temperature of the liquid is allowed to rise somewhat, nitric oxide gas, NO, escapes. From weak nitric acid, zinc causes the evolution of ni- trous oxide gas, N'„0. As already mentioned, nitrate of ammonia, when heated to fusion, evolves nitrous oxide, N^O. Emmet showed that by immersing a strip of zinc in the melted salt, nearly pure nitrogen. gas is set free. AtMOSPIlKRir AIR AS TIIK FOOD OF PLANTS. 7") When nitric acid is heated with lean flesh (fibrin), nitric oxide and nitrogen g.ises botli appear. It is thus seen that by successive steps of deoxidation nitric acid may be gradually reduced to nitrous acid, ammonia, nitric oxide, nitrous oxide, and finally to nitrogen. Tests for I\iti'ic and Citrous Acids. — The fact that these substances (iften occur in extremely minute quantities renders it needful to employ very delicate tests for their recognition. Price's Test. — Free nitrous acid decomposes iodide of potassium in the Bame manner as ozone, and hence gives a blue color, witli a mixture of tliis salt and starch-piiste. Any niti'ite produces the same effect if to tlie mixture dilute sulphuric acid be added to liberate the nitrous acid. Pure nitric acid, if moderately dilute, and dilute solutions of nitrates mixed with dilute sulphuric acid, are without immediate efiFect upon iodide-of-pota-sium-starch-paste. If the solution of a nitrate be min- gled with dilute sulphuric acid, and ai^itated for some time witli zinc filiui^s, reduction to nitrite occurs, and then addition of the starch-paste, etc., gives the blue coloration. Accorditig to Seh6nl)ein, this test, first proposed by Price, will detect nitrous acid when mixed with one-hund- red-tliousand times its Aveight of water. It is of course only applicable in the absence of other oxidizing agents. 07-een 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 gieen vitriol, or protosulpliate of iron. Nitric oxide, the red gas which 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 sulj^hiiric acid, gives with green vitriol a peculiar blackish-brown coloration. To test for minute quantities of nitrous acid, mix the 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 with it. On standing, the coloration will be perceived where the two liquids are in contact. Nitric acid is tested as follows: 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 between 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* H now CROPS PEEf). 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, + HP = NO^H + 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. Tims 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 thunder- storms. It appears, however, from the analyses of both Way and Boussiugault, tliat 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 have demonstrated that silent 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, Avhich in- creases the energy of the ozone simultaneously produced, and causes it to expend itself at once in the oxidation of nitrogen. Boussiugault 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 ATMOSPIIKUIC AlU AS THE FOOD OF PLANTS. 77 slowly than that wlilch is produced by lightning, must really oxidize much more nitrogen to nitric acid than the latter, because its action never ceases. Formation of \itro^CD Compounds in the Atmosphere. — h. From tree nitrogen (by ozone ?) in the processes of combustion and slow oxidation. At high temperatures. — Saussure first observed {Ann. de Chimie., Ixxi, 'IS'l), that in the burning of a mixture of oxygen and hydrogen gases in the air, the resulting water contains .-immonia. He hud previously noticed that nitric acid and nitrous acid are formed in the same process. Kolbe {Ann. CJiem. 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 peroxide 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 ttie iodide-of potassium-starch test (Price's test), Boettger {Jour, far Prakt. Chem., Ixxxv, 396) and Schonbein (ibid., Ixxxiv, 21.5) have more recently confirm- ed the result of Jones, but because they could detect neitlier 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 aw.monia is generated in all cases of rapid combustion. Meissner ( Untersuchumjen Tiber den Sauerstoff^ 1863, p. 283) was unable to satisfy himself that either nitrous acid or ammonia is generated in combustion. Finally, Zabelin {Ann. Chem. x. 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. to HOW CROPS FEED. When the combustion is so perfect that the resulting wa- ter is colorless and pure, only nitrous acid is formed ; when, on the other hand, a trace of organic matters es- capes oxidation, less or no nitrous acid, but in its place ammonia, appears in the water, and this under circum- stances that preclude its absorption from the atmosphere. Zabelin gives no proof that the combustibles he etn<> ployed were absolutely free from compounds of nitrogen, but otherwise, his 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 simply because he employed a much less delicate test for nitrous acid than was used by Schonbein, 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 compounds 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. At low te?nperat((res. — 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 todistinjuish nitrous acid from peroxide of hydrogen, H2 O2. 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. {Uniers. u. d. Swiers'off, p. 233). Scliiinboin had found that iodide of potassium is decom- posed after a little time by concentrated sohitions of peroxides of hydrogen, but in unaff.'Ctcd by this body when dilute. {Jour, fur prakt. Chum., Ixsxvi, p. !)()). Zabelin agrees with Schonbein that Price's test is decisive between peroxide ol hydrogen and nitrous acid. {Ann. CItcin. u. Ph., cxsx, p. 5S.) ATMOSPHERIC AIU AS THE FOOii Of PLANl'S. 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 held the mouth of a cold bottle until a portion of the vapor was condensed in the latter. The water thus ■^'oUccted gave the reactions for nitrous acid and ammonia, sometimes quite intensely, again faint- ly, and sometimes not at all. By simply exposing a piece of filter-paper for a suffi- cient time to the vapors arising from pure water heated to boiling, and pouring a few drops of acidified iodide-of- potassium-ytarch-paste upon it, the reaction of nitrous acid Avas obtained. When paper which had been impregnated with dilute solution of pure potash was hung in the va- pors that arose from water heated in an open dish to 100° F., it shortly acquired so much nitrite of potash as to re- act WMth the above named test. Lastly, nitrons acid and ammonia 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, fiir Prakt. Chem., Ixvi, 131.) These ex- periments of Schonbein arc open to criticism, and do not furnish perfectly satisfactory eviilence 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 exist, 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 opinion, 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 Xess- 80 HOM' CROr.3 FEED. ler's test,* which is of cxtveino delicacy, and -wliich he con« stantly employed in his invostigntions. Zabelia operated in closed vessels. The apparatus he used consisted of two glass flasks, a larger and a smaller one, which were closed by corks and fitted with glass tubes, 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 that cellulose (clippings of filter, paper 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 :dl, in the minutest traces only. Views of SchOnbeiv. — Tiie 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 st iisitive 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 denion- Btrate 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. &4 I ATMOSPIIEUIC Allt AS THE FOOD OF PLANTS. 81 his experiments nitrogen and water combine to form ni- trite of ammonia. 2 N + 2 H,0 - Nil,, NO^H This theory, supported by the authority of so distin- guished a philosopher, has been ahnost universally credit- ed.* It has, however, 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 Avater, or lastly in close proximity to the flames of burning gases, then it 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 sul)stances are con- cerned. The discovery of Zabeliu that ammonia and nitrous acid do not always appear in equivalent quantities or even simultaneously, while difiicult to reconcile with Schon- 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 facts 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 Sch<>nbeiu in case of urine. 4* 82 UOW CROPS FEED. command for experimental study, will estaldish or disprove them by suitable investigations. lie believes, from the exi^tino; 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- bination by tlie action of ozone^ as Schonbein formerly maintain.ed and was the first to suggest. We have already recounted the evidence that goes to show tlie 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 emiiloyed. In Schimbein's experiments, where paper or linen was not employed, tlie dust of the air may have supplied the organic matters. The first result 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 niti'ous 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 which we have had access, it is entirely credible and in accordan«e with numerous analogies. If, as thus appears extremely probable, ozone is devel- oped in all cases of oxidavion, both rapid and slow, then ^TMOSPHEUIC AIU AS THE FOOD OF PLANTS. 83 every flame and fire, every dcicaying plant and animal, the organic matters that exhale from the; skin and Inngs of living animals, or from the foliage and flowers of plants, especially, i)erhaps, the volatile oils of cone-bearing trees, are, indirectly, means of converting a jiortion of free ni- trogen into nitrous and nitric acids, or ammonia. These topics will be recurred to in our discussion of Nitrification in the Soil, p. 254. Formation of Nitroi^en ('orapouii77'212.-> 4870 7321756,2917 4480 2075 7414 1(M7 137112749 664 203512180 2670 4021 5373 3767 According to Pincus and Rollig, the atmospheric water brought down at Insterburg, in the year ending with March, 1865, 7.225 lbs. av. of nitric acid per English acre of surface. j The quantity of nitrogen that fell ns ammonia was^ 3.628 lbs.; that collected in the form of nitric acid was 1.876 lbs. The total nitrogen of the atmospheric waters per acre, for the year, was 5.5 lbs. The rain-fall was 392,707 imperial gallons. Bretschneider found in the atmospheric waters gathered at Ida-Marienhiitte, in Silesia, during 12 months ending April 15th, 1866, 3|- lbs. of nitric acid per acre of surface. In Bretschneider's investigation, the amount of nitrogen ATMOSPHEiaO Aia aS THE T OP PLANTS. 80 brouglit down per acre in {ho form of ammonia was 9.93G lbs.; that in the ibrm of nitric acid Mas 0.9T4 lbs. The total nitrogen contained in the rain, etc., was accordingly 10.91, or, in round numbers, 11 lbs. avoirdupois. The rain-, fall amounted to 488.309 imperial gallons, (Wilda's Cen- tmlhlatt, August, 1866.) Relation of Nitric Acid to Ammonia in the Atmos- pliere. — The foregoing results demonstrate that there i8 in the aggregate an excess of ammonia over the amount required to form nitiate with the nitric acid. (In nitrate of ammonia (XH^ XO3)? ^^'^ acid and base contain the same quantity of nitrogen.) We are hence justified in assuming that the acid in question commonly occurs as ni- trate of ammonia * in the atmosphere. At times, however, the nitric acid may preponderate. One instance is on record (Journal de Pharmacie^ Apr., 1845) of the presence of free nitric acid in hail, which fell at Nismes, in June, 1842. This hail is said to have been perceptibly sour to the taste. Cloez ( Conipt. Mendus, lii, 527) found traces of free nitric acid in air taken 3 feet above the ground, especially at the beginning and end of winter. The same must have been true in the cases already giv- en, in which exception;dly large quantities of nitric acid were found, in the examinations made by Boussingault and the Prussian chemists. The nitrate of ammonia which exists in the atmosphere - d'Hibtless held there in a state of mechanical suspension. it is dissolved in the falling rains, and when once brought to the surface of the soil, cannot again find its way into the air by volatilization, as carbonate of ammonia does, but is permanently removed from the atmospheie, and * In evaporating large quantifies of rain-water to dryness, there are often found In the residue nitrates of lime and 6oda. In these cases the lime and soda come from dust suspended in the air. 00 now CROPS FEED. until in some way chemically decomposeil, belongs to the soil or to the rivers and seas, Mtrous Acid in the Atmospheric Waters. — In most of the researches up- on the quantity of nitric acid in tlie atmosphere and meteoric waters, tdtruus acid has not been specially i-egarded. The tests which serve to detect nitric acid nearly all apply equally well to nitrous acid, and n» di.-criiuiuatiun has been made until recently. According to Schonbein :md Bublig, nitrates are sometimes absent from rain-water, but nitrites never. They occur, however, in but minute proportion. Pincus and Rollig observed but traces of nitrous acid in the waters gathered at Iiistcrburg. Reichardt found no weii^hable quantity of nitrous acid in a samjile of hail, the water from which contained in 10 million parts, 33 parts ammonia and 5}4 parts of nitric acid. It is evident, then, that nitrous acid, if produced to any extent in the atmosphere, does not re- main as such, but is chiefly oxidized to nitric acid. In any case our data are probably not incorrect in respect to the quantity of nitrogen existing in both the forms of nitrous and nitric acids, although the former compound has not been separately estimated. Tlie methods employed for the estimation of nitric acid would, in gen- eral, include the nitrous acid, with the single error of bringing the latter into the reckoning as a part of the former. IVitric Acid as Food of Plants. — A multitude of obser- vations, both in the field and laboratory, demonstrate that nitrates greatly promote vegetable growth. The extensive use of nitrate of soda as a fertilizer, and the extraordinary fertility of the tropical regions of India, whose soil until lately furnished a large share of the nitrate of potash of commerce, attest the fact. Furthermore, in many cases, nitrates have been found abundantly in fertile soils of tem- perate climates. Experiments in artificial soil and in water-culture show not only that nitrates supply nitrogen to plants, but dem- onstrate beyond doubt that f/te^ alone are a sufficient source of this element, and that no other compound is so well adapted as nitric acid to furnish crops with nitrogen. Like ammonia-salts, the nitrates intensify the color, and increase, both absolutely and relatively, the quantity of nitrogen of the plant to which they are supplied. Their effect, when in excess, is also to favor the development of foliage at the expense of fruit. ATMOSPIIEIMC AIU as Till-: FOOD OF PLANTS. 91 The uiirates do not appear to be absorbed by the plant to any great extent, except through the medium of tlie soil, sinre they cannot exist in the state of vapor and are brought down to the earth's surface by atmospheric waters. The full discussion of their nutritive effects must there- fore be deferred until the soil comes under notice. See Division II, p. 371. In § 10, p. 96, "Recapitulation of the Atmospheric Supplies of Food to Crops," the inadequacy of the at- mospheric nitrates will be noticed. OTHER INGREDIENTS OF THE ATMOSPHERE; viz., 3farsh Gas, Carbonic Oxide, Mtroiis Oxide, Hijdrochloric Acid, Sulphurous Acid, Sulph'jdric Acid, Organic Vapors, Suspended Solid Matters. There are several other gaseous bodies, some or all of which may oc- cur in tlie atmosphere in very minute quantities, but whose relations to vegetation, in the present state of our knowledge, appear to be of no practical moment. Since, however, they have been the subjects of in- vestigations or disquisition by agricultural chemists, they require to be briefly noticed. IVInrsli «as,* C H4.— This substance is a coloiless and nearly odorless gas, whicli is formed almost invarialily when organic matters suffer decomposition in ab.-ence of oxygen. Wlien a lump of coal or a bilU't of wood is strongly heated, poi-tions of carbon and hydrogen unite to Conn this among several other substances. It is accordingly one of the ingredients of the gases whose combustion forms the flame of all fii-es and lamps. It is also produced in the decay of vegetal)le mat- ferrf, especially when they arc immer-ed iu water, as happens in swamps and stagnant ponds, and it often bubbles in large quantities from the bottom of ditches, when the mud is stirred. Pettenkofer and Voit have lately found that marsh gas is one of the f^aseous products of the respiration or nutrition of animals. It is combustible at high temperatures, and burns with a yellowish, faintly luminous flame, to water and carbonic acid. It causes no ill ef- fects when breathed by animals if it be mixed with much air, though of itself it cannot support respiration. * Known also to chemists under the names of Light Carburetted Hydrogen, Hydride of Methyl and Methauc. 02 now CROPS FEED. The mode or its Arisxin at once fu'^here, and has pub- lished an account of exiieriraents {Journal fiir Prakt. Chein., Vol. 59, p. 114) which, according to him, prove tliat it is absorbed by vegetation. Until nitrous oxide i< shown to be accessible to plmts, any fuither no- tice of it is unnecessary in a treatise of this kind. llydrocliloric Acid C«a<<», IICI, whose properties have been described in How Crops Grow, p. 118, i- found in minute quantity in the air over salt marshes. It doubtless proceeds from the decomposition of the chloride of magnesium of sea-water. Sprengel h:is surmised its ex- 94 HOW CROPS FEED. h;>Lation hy sea-shore pLints. It is found in the air near soda-works, be- ing a firoduct of the manufacture, and is destructive to vegetation. Niilpliiirou!i» Acid, SOo, and Siilpliydric Acid, HS, (see H. C. G., p. 115,) may exist in the atmosphere as local emanations. In lars^e quantities, as wlien escaping from smelting worlis, roasting lioaps, or manufactories, they often prove destructive to vegetation. In contact witli air tlicy qniclvly suffer oxid.ation to sulpiiurie acid, wliich, dissolv- ing in the water of rains, etc., becomes incorporated with the soil. Oi'g^iiiiic Iflattei-s of whatever sort that escape as vapor into the atmosphere and are tliere recognized I)y their odor, are rapidly oxidized and have no direct influenee upon vegetation, so far as is now Icnown. Suspended Solid IWLiitters iit tlie Alinowpliei'e. — The solid matters which are raised into the air by winds in the form of dust, and are often transported to great heights and distances, do not properly belong to the atmosphere, but to the soil. Their presence in the air explains the growth of certain plants {air-planU) when entirely disconnected from the soil, or of such as are found in pure sand or on the surface of rocks, incapable of performing the functions of the soil, except as dust accumulates upon them. Barral announced in 1863 {Jour. cTAg. pratique, p. 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. 10. RECAPITULATION OF THE ATMOSPHERIC SUPPLIES OF . FOOD TO CROPS. Oxyfi^en, whether required \n 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 atmos- phere. Carbon. — The carbonic acid of the atmosphere is a source of this element sufficient for the most rapid growth, ns is abundantly demonstrated by the experiments in wa- ter culture, made by Nobbe and Siegert, and by Wolff, (II. C. G., p. 170), in which oat and buckwheat plants were brought to more than the best agricultural develop)- ATMOSPHEKIC AIR AS THE FOOD OF PLANTS. 95 ment, Avith no other than tlic atmospheric sup2:>ly of carbon. HydrOfi^cn is adequately supplied to crops by water, which e(pially belongs to the Attnos|)here and the Soil, although it enters the plant chiefly fioui the latter. Nitrogen exists in immense quantities in tlie atmosphere, and we may regard the latter as the primal source of this element to the organic world. In the at i no -sphere, how- ever, nitrogen exists for the mjst part in the free state, and is, as such, so we must believe from existing evidence, un- assimilable by crops. Its assimilable compounds, ammo- iila and nitric 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 surface, a -cording to the determinations hitherto made in England and Prussia. Amount of Assimilable Nitrogen annually brought down by THE Atmospheric Waters. Locality. Tear. mtroqen per Acre. Wat^ ' per Acre. Rothamatead, Southern England 18.55* 1856* 1864-5t 1865-6t 1864-5t 1865-6t lS64-5t 1865-6t 1865* 1864-5+ 1865* 6.63 lbs. 8.31 '• 1.86 " 2.50 " 5.49 " 6.81 " 15.09 " 10.38 " 11.83 " ■i0.91 - 6.66 " 6.633,220 lbs. 6.160 510 '• Kuschen, Province Posen, Prussia lusterburg, near Koni^sberg, " Regenwalde, near Stettin, " Ida-Marienliiittc, near Brcslau, Silesia, " '.'.'.'. Proskau, Silesia. ■' Dahme, Province Brandenburg, " 2,680.086 " 4.008.491 " 6,2'22,461 " 5.383,4'r8 " 5,313,562 " 4,-358,053 " 4,877.545 " 4.(131, 7S2 " 3,868,646 " Averaqe 8.76 lbs. 4.867.075 lbs. * From Jan. to Jan. t From Apr. to Apr. % From May to May. Direct Atmospheric Supply of Nitrogen Insufficient for C^rops. — To estimate the ailequacy of tliese atmos- pheric supplies of assimilable nitrogen, Ave may compare their amount with the quantity of nitrogen required in the 96 llUAV CROPS FEED. eompositiou of standard crop;^, and with the (][uantity con- tained in appropriate applications of nitrogenous fertil- izers. The average atmosplieric supply of nutritive nitrogen in rain, etc., for 12 months, as above given, is much less tlian is necessary for ordinary crops. According to Dr. 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 50 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 hy rain, etc., is not inconsiderable, compared with the amount of nitrogen, which often forms an effective 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., 8f 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 au ordinary dressing, which has been known to double the grass crop. We notice, however, that the amount of nitrogen sup- plied in the atmospheric waters is quite variable, as well for ditferent localities as for different years, and for differ- ent periods of the year. At Kuschen, but 2-2^ lbs. were brought down against 21 lbs. at Proskau. At Regenwalde the quantity was 15 lbs. in 1864-5, but the next year it was nearly 30 per cent less. In 1855, at Rothamstead, the greatest 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; the next, 1 lb., ia ATMOSPIIEIIIC AIU AS THE FOOD OF PLANTS. 97 April; and the least in March. At Td.i-^Maiienliiitte, Kiischen, and Regenwaldc, in 1865-6, nearly half the year's atmosplieric nitrogen came down in summer ; but at Insterburg only 30 per cent fell in summer, while 40 •per cent came doAvn 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 s'.mmer than falls upon them in the same period ; while v.) Avinter, the water that falls is in excess of that which evaporates. But how much of the winter's fall comes to supply the summer's evaporation, is an element of the calculation likely to be very variable, and not as yet determined in any instance. We conclude, then, th:;t tlie direct atmospheric supply of assimilable nitrogen, though not miimportant, is insuf- ficient for crops. We must, therefore, look to the soil to supjdy a large share of this element, as well as to be the medium through which the assimilable .atmospheric nitrogen chiefly enters the plant. The Other Injfiedieiits of the Atmosphere, so far as we now know, are of no direct significance in the nutri- tion of agricultural i)lants. Indirectly, atmos])iieric 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 ATMOSPIIEPvIC FOOD. Boussingault lias 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 IIO-\V CROPS FEED. is absorbed and decomposed, and a nearly equal volume of oxygen is set free, — consists in the simultaneous deox- idation of c:irl)onic acid and of water, wliereby 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.: Gin-honh ^ Wate - —^ '"Thou I' Hydro- Oxy- acld ' oxide yen. yen. CO, + l\f> = CO + H, + O, In this reaction the oxygen set free is identical in bulk with the carbonic ncid involved, and the residue retained in the plant, COH^, multiplied by 12, would give 12 molecules of carbonic oxide and 24 atoms of hydrogen, Avhich, chemically united, might constitute either glucosj or levulose, C,^ 11^^ Oj„, from which by elimination of HjO would result cane sugar and Arabic acid, while sepa- ration of 211^0 would give cellulose and the other mem- bers of its group. Whether the real chemical jiroce^^s 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 finisheil. TABULAR VIEW OF THE RELATIONS OF THE ATMOSPHERIC INGREDIENTS TO THE LIFE OF PLANTS. [■ Oxygen, by roots, flowers, ripeiiiuj^ fruit, and by ;ili f^rowiirj.- jiarts. Carbonic Acid, by foliaire and rrreeu parts, but only in j the light. Absorbed J Ammonia, us carbonate, by folia<;e, probably at all times. by Pliints. 1 Watek, ax liquid, through the roots. Nitrous Aoid (^ united to ammonia, and dissolved in wa' Nitric Aciu ) ter through the roots. Ozone ) THK ATMOSrUEKE AS KKLATBD TO VEGETATION. 99 Not absorbed ( Nitrogen. by Plants. ( Water in state of vapor. (Oxygen, [ by folia;;e and green parts, but only in the Ozone? ) light. .. , _ M.\RSH Gas in traces by aquatic plants ? j Water, «.s- 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. § 1- 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 still 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 tliey gain access into the phmt. Physical Constitution of the Atmosphere.— That the atmosi)here 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 whicli 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^ Th« remarkable fact that very nearly the same relative quantities of Oxygen, Nitrogen, and Carbonic Acid, steadily exist in the atmosphere is due to tlie even balance which obtains between growth and decay, between life and death. The equally remarkable fact that .the gases 100 HOM' CROPS FEED. wliich compose the atmosphere are uiiiforinly 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 occuj^y. If two bottles, one filled with carbonic acid, the other with hydrogen, be con- nected by a tube no wider than a straw, and be placed so that the heavy carbonic acid is below the fifteen times lighter hydrogen, we sliall find, after the lapse of a few hours, that the two gases have mingled somewhat, and in a few days they will 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. By interposing a poious 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 flie 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, b, widened above into a funnel, and having cemented upon this an inverted cylindrical cup of imglazed porce- lain, a. The funnel rests in a round aperture inade in the horizontal arm of the support, wliile the tube below dips beneath the surface of some water contained in the wine- glass. The porous cup, funnel, and tube, being occujiied with common air, a glass bell, c, is filled with hydrogen gas and placed over the cap, as shown in the figure. In- THE ATMOSPITEKE AS RELATED rO VEGETATION. 101 stnntly, bubbles begin to escape rap:;lly from the bottom of the tube throiauh the water of the wine-glass, thus demonstiMiiiig that hydrogen ])asses into the cup faster ihan air can escMpe outwards ihrongli it-: porc-<. If tin- btll be removed, ihc cuj) is at once butlied Mgain externally in common air, the light hydrogen floating instantly uj)wards, and now the water begins to rise in the tube in consequence of the return to the outer atmosphere of the hydrogen which before had diffused into the cup. It is the i)erpetual action of tliis diffusive tendency which maintains the atniosplierc in a state of such uniform mixture that accurate ana- lyses of it give for oxygen and nitrogen almost identical figures, at all tnios 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 water than nitrogen, diminishes by a minute amoimt 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, which is capable of chemic- ally uniting witli, or otherwise destroying the aeriform condition of one of the gases, it will at once absorb those particles of this gas which 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 diffusion 103 now CROPS FKED. keep pace with each otLer until all the absorhable air is removed from the gaseous mixture, and condensed or fixed in tlie al)Sorbent. In tliis 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 from it ; a piece of phosphorus will in a few hours absorb all its oxygen, and an ignited mass of the rare met.il 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 rneanSy such as the imperforate wall of the vegetable cell, the green cuticle of the plant whore 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 })iece 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 DiiTusion llodified by the Influence of the Membrane. — The rapidity of osmose * is of coursa influenced by the thickness of tlie 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 haA 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 be separated from each ' The osmose of liquids is discussed in detail in "How Crops Grow," p. 854. THE ATMOSPHKKE AS TIELaTED TO VEGETATION. lOfi other in penetrating it. In case a meniLrane is moistened with water or other liquid, or by a solution of solid mat- ters, this would still further modify tlie I'csult. Absorption of (Jases by the Plant.— A few words will now suffice to ."ippiy tliese ficts to the abs()r[)tion of the nutritive gases by vegetation. The foliage of plants is freely permeable to gases, as has been set forth in " How Crops Grow,'' p. 289. The eells, or some portions of their contents, absorb or condense carbonic acid and ammonia in a similar way, or at least with tlie same effect, as potash absorbs carbonic acid. As rapidly as tliese bodies are removed from the atmosphere surrounding or occupying the cells, they are re-supplied by diifusion from without ; so that although the quantities of gaseous plant-food con- tained in the air nre, relatively considered, very small, they are by this grand natural law made to flow in con- tinuous streams toward every growing vegetable cell. DIVISION 11. THE SOIL AS RELATED TO VEGETABLE PRODUCTION. CHAPTER L 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 production, 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 afiect 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 INTUOUrCTORY. 105 The Cencral Fiiuctious 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 tlie most direct manner with tlie 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. Tlie 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 various 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 valuf 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 tem))erate 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 tsrhornosem, or black earth, 5* 100 1T(,\V C:nOPS FEED. which is remarkable for its extraordinary and persistent fertility. The prairies of our own West, the bottom lands of the Scioto and other rivers of Ohio, arc other examples of peculiar soils; while on every farm, almost, may bii found numerous gradations fi-om clay to sand, from ve<^e- 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- TDable 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 o.f Rocks. III. The Rocks themselves — their Kinds and Special Characters. IV. The Conversion of Rocks into Soils ; to wliich we may add : V. The Incorporation of Organic Matter with Soils. ORIGIN AND FORMATION' OF SOILS. 107 THE CHEMICAL ELEMENTS OF ROCKS. The chemical elements of rocks, i. e., ths constituents of the minerals which go to form rocks, include all the simple bodies known to science. Those, which, fiom their universal distribution and uses in agriculture, concern us immediately, are with one exception the same th:it have been noticed in a former volume as composing the ash of agricultural i)lants, viz., Chlorine, Sulphur, Carbon, Silicon, Potassium, Sodium, Calcium, Magnesium, lion, and Man- ganese. The description given of these elements and of their most important compounds in " IIow Crops Grow " Avill suffice. It is only needful to notice further a single element. Allliuinuin, Symbol Al., At. wt. 27.4, is a bluish silver- white metal, ciiaracterized 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 jewelry and ornamental work. It is prepared by a costly and complex process invented by Prof. Deville, of Paris, in 1854, which consists essen- tially in decomposing chlorido 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„ Cl^ + 6 Na = 6 Na CI + 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. — ^Vhen alum (double sul- phate of alumina and i)otash) is dissolved in water and ammonia added to the solution, a white gelatinous body separates, which is alumina combined with water, Al^ O3, 3 H^O. By drying and strongly heating this hydrated alumina, a white powder remains, which is pure alumina. 108 ilOW (HOPS FEEt). In nature alumina is found in tlie form of emery. The sappliire and ruby are tinely colored crystallized varieties of aluuiin:i, highly j^rized as gems. Hydrated alumina dissolves in acids, yielding a numer- ous class of salts, of which the sulj^hate 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 ac^quainted. Other compounds of alumina will be noticed presently. §2. MINERALOGICAL ELEMENTS OF ROCKS. The mineralogical elements or minerals * which compose rocks are very numerous. But little conception can be gained of the appearance of a 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 usually 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 implies a definite chemical comoouiid of natural occurrence. OEIGIX ANIJ FOU.MATIOX OF SOILS. 109 ant mineral. It is a cotnpound of silica with alumina^ and with one armor e of the alJcdies, and sometimes vrith lime. Mineralogists distinguish several species of feld- spar according to their composition and crystallization. Feldspar is found i:i crystals or crystalline masses xisually of a white, yellow, or flesh color, with a somewhat pearly luster on the smooth and level surfaces which it presents on fracture. It is scratched by, and docs not scratch quartz. In the subjt>ined Table are given the minefalogical names and analyses of the principal varieties of feldspar. Ac- companying each analysis is its locality and the name of the analyst. Orthoclase. A1.BITE. OUGOCLASE. Labradouite. Common or imtmh Soda feldspar. Soda-lirm feldspar Lime-soda feldspar. feldspar. NewRochellcN.Y. Unionville. Pa. Iladdam, Conn. Drummond, C. W. s . W. Johnson. M. C Weld. G. J. Brush. T. S. Hunt. Silica, 64.33 (56.86 64.26 54.70 Alumina, 20.42 21.80 21.00 39.80 Potash, 12.47 . 0.50 0.33 Soda, 2.62 8.78 9 99 2.44 Lime, trace 1.70 2.15 11.43 Magnesia, 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, — Avhite, 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. Phloyoplte and Biotite contain a large percentage of magnesia, and often of oxide of iron. 110 HOW CKOl'S FKED. The following analyses represent these varieties. Muscovite. Phlogopite. Biotite. Litchfield, Mt.Leiiistor, Edwards, N. Burgess, Putnam Co., Conn. Ireland. N. Y. Canada. N. Y. Siberia. Smith & Brush. IlaiiirP.ton. W.J.Craw. T.S.TIunt. Smith & Brush. H. Rosii. Silica. 44.f)0 44.64 40.. 36 40.97 39.62 40.00 Alumina, 36.23 30.18 16.45 18.56 17.35 13.67 Oxide of iron 1,1.34 6.35 trace. 5.40 19.03 Oxide of manganese — — — — — 0.63 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, 5.26 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 6°|„ more of alumina than the second, while the second contains 5° |„ more of oxide of iron than the first. Again, the second contains 12. 4" |^ of potash, but no soda and no lime, while the first reveals on analysis 4°|^ of soda and 0.5° 1,^ 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 analyst's of more than 50 micas which are given in mineralogical treatises, scarcely any two per- fectly agree. The same is true of many other minerals, especially of the ainphiboles and pyi'oxenes 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 th.it agreed togeilier in certain char- acteristics, but widely differed in others. ORIGIN AND FORMATION OF SOILS. Ill Isomorphism. — In 1830, Mitscherlich, a Prussian phi- losopher, discovered tliat a number of the elementary bodies are capable o^ replacing each other in, combination^ from the fact of their natur.d crystalline form being identic- al ; they being, as he termed it, isomorphous^ or of like shape. Thus, magnesia, lime, protoxide of iron, protoxide of manganese, whicli are all protovide-hases^ form one group, each of whose members may take the place of the other. Alumina (Al.^ OJ and oxide of iron (Fe, O3) be- long to another group of sesqui oxide-bases, 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 affect the composi- tion without altering the constitution of a mineral. Of the mineral amphibole, for example, there are known a great number of varieties ; some pure Avhite in color, con- taining, in addition to silica, magnesia and lime ; otliers 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 m inganese in large jiroportion. 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 r(>placements of j^rotoxide-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 ami)hibole. The distinction of am- phibole from pyroxene is one of crystallization. 112 HOW CROPS FEED. We might give in the same style formulpe for all the minerals noticed in these pages, but for our purposes tJiis is unnecessary, Amphibole is an abundant mineral often met with in distinct crystals or crystalline and fibrous masses, varying in color from pure white or gray {tretnoHte, asbestifs), light green {actinolite), grayish or brownish green {anthophyl- lite), 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 alkal'ies. White. Gray. Ash-gray. Black. Gouverneur, Lanark, Cuminington, Brevig, N. Y. Canada. Mass. Norway. Rammelsberg. T. S. Hunt. Smith & Brash. Plantamour. 57.40 a4.69 13.89 0.40 55.30 22.50 13.36 6.30 trace 0.40 0.80 0.25 0.30 50.74 10.31 trace as. 14 1.77 0.54 trace 3.04 46.57 5.88 5.91 24.38 2.07 3.41 7.79 2.96 Leekgreen. Waldheim, Saxony. Kuop. 58.71 10.01 11.53 Silica, Magnesia, Lime, Protoxide of iron, Protoxide of manganese, Alumina, Soda, Potash, Water, Pyroxene is of very common occurrence, and consider- ably resembles hornblende in colors and in composition. Green. Black. Black. Lake Orange Co., Wetterau, Cliamplain. N. Y. Seybert. Smith & Brush. Gmelin. 1.52 12.38 0.50 White. Gray- White. Ottawa, Batliurst, Canada. Canada. T. S. Hunt. T. S. Hunt. Silica, 54.50 51.50 50.38 39.. 30 56.80 Magnesia, 18.14 17.69 6.83 2.98 5.05 Lime, 25.87 23.80 19. a3 10.39 4.85 Protoxide 1.98 20.40 30.40 12.06 of iron. Sesquioxide 0.35 of iron. Protoxide of trace 0.67 3.72 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 1.95 ORIGIN AND FORMATION OF SOILS. 113 Chlorite is a common mineral occurring in small scales or plates which are brittle. It is soft, usually exists in masses, rarely crystallized, and is very variable in color and composition, though in general it has a grayish or brownisli-grcen color, and contains magnesia, alumina, and iron, united with silica. See analysis below. LeilCite is an anhydrous silicate of akimina 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 produced by the slow decomposition of feldspar under the action of air and water at the usu.il 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- pears 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. Steele Mine, N. C. Vesuvius, Summit Ilill, Chaudie'-e Eruption of 1857. Pa, Falls. Canada. Genth. Rammelsberg. S. W. Johnson. T. S. Hunt. Silica, 24.90 .57.24 45.9.3 46.05 Alumina, 21.77 22.9(5 ,■59.81 38.37 Sesquioxidc of iron, 4.()0 Protoxide of iron, 24.21 Protoxide of manj,'ane8e, 1.15 Magnesia, 12.78 0.63 Lime, 0.91 0.61 Soda, 0.93 Potash, 18.61 Water, 10. .59 14.02 14.00 Talc is often found in pale-green, flexil)le, inelastic scales or leaves, but much more commonly in compact gray masses, and is then known as soapstone. It is very soft, 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, Avhich is found abundantly in lavas and basaltic rocks. It is a hard, glassy mineral, usually of an olive or brown-green color. See analysis below. Talc. Seupentine. Chrysolite. Bristol, Conn. New Haven, Conn. Bolton, Mass. Dr. Lummis. G. J. Brush. G. J. Brush. Silica, 64.00 44.05 40.94 Alumina, 0.27 Protoxide of iron, 4.75 2.53 4.37 Magnesia, 27.47 39.24 50.84 Lime, 1.20 Water, 4.30 13.49 3.28 ZeoliteSi — Under this general name mineralogists are in the habit of including a number of minerals wliich 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 imder 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 crystallizntions, 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, Avhich, by their disintegration, give origin to very fertile soils OKIGIN AND FOUMATIOX OF SOILS. 115 Analcime. Chabasite. Natrolite. Scoi.ecite. Thomsokite. Lake Superior. Nova Scotia. Bergen Hill, Ghaut's Tun- Magnet N. J. nel, India. Cove, Ark. C. T. Jackson. Rammelsberg. Brush. P. Collier. Smith & Brush, Silica, 53.40 52.14 47.31 45.80 36.85 Alumina, 22.40 19.14 26.77 25.55 28.42 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 j 52 ^ of iron. Water, 9.70 19.19 9. at 14.28 13.80 Stilbite. Apophyi.lite. Pectolite. Laumontite. Leonhardite Nova Scotia. Lake Superior. Bergen Hill. Phippsburgh, Me. Lake Sup'r S.W. Johnson. J. L.Smith. J. D. Whitney. DuWnoy. Barnes. Silica, 57.63 52.08 55.60 51.98 55.04 Alumina, 16.17 1.45 21.12 22.34 Potash, 4.93 Soda, 1.55 8.89 Lime, 8.08 25.30 32.80 11.71 10.64 Water, 16.07 15.92 2.96 15.05 11.93 €alcite, 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 CurhonatQ of 31(Agiiesia, MgO C0„, oc- curs to a limited extent as a white massive or crystallized mineral, resembling carbonate of lime. Dolomite, CaO C0„ + MgO C'0„, is a compound of car- bonate of lime with carbonate of magnesia in Aariable 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. Gypsum, orllydrous Sulphate of Lime, CaO SO^ + Wfi^ is a mineral that is widely distril)uted and quite abundant in nature. When "boiled" to expel the water it is Plaster of Paris. Pyrites, or liisulphide 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 IIOAV ( ROI'S FKKH. is of almost universal occurrence in small quantities. Some forms of it easily oxidize when exposed to air, and furnish the green-vitriol (sulnliatc of protoxide of iron) of com- merce. Apatite aiiar and Talc, or Chlorite. Talcose Granite differs from common granite in the substitution of talc for mica. Is a fragile and more easily OmCIN AND Foli.MAHlON (»K SOILS. 1-1 decomposable rock than granite. It passes tlirougli talcose gneiss into Tak'OSC Schist, which resembles mica-scliist in colors and in facility of si>litiing into slabs, but has a less glis- tening luster and a soapy feel. C'hloritic Schist resembles talcose schist, but has a less unctuous feel, and is generally of u dark green color. Related to the above are Steatite, or soajystone, — nearly pure, granular talc; and Serpentine rOCk, consisting chiefly of serpentine. The above are tlie 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 minerals into their composition, an almost endless variety of si- licious rocks has been produced. Turning now to the Crystalline Calcareous Rocks, we have 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 mo?niinent(d marble. Dolomite has all the appearance of granular limestone, but contains a large (variable) amount of carbonate of magnesia. The Fragmental or Sedimentary Rocks are as fol- lows: Conj^lomerates 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, syenitic, calcareous, basaltic, etc., etc. They pass into Sandstones, wliich consist of small fragments (sand), are generally siliciovs in character, and often are nearly 6 162 iiuAV CROPS FEEb, pure quartz. The freestone of tlie Connecticut Valley la a granitic sandstone, containing fragments of feldspar 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 higlily impure. When containing much carbonate of magnesia they are termed raagnesian limestones. They pass into sandstones through intermediate calciferous sand rocks, and into sliales through argillaceovs lime- stones. These impure limestones furnish the hydraulic cements of commerce. CONVERSION OF ROCKS INTO SOILS. Soils are broken and decomposed rocks. 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 impalpa- 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. OKlGm AND r'or.^rAtioN^ oi;" soils. 123 The first step towards tlie formation of a soil must have been the pulverization of tlie rock. This has been 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 the narrow experience of a single human life, but are really trifling compared Avith 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 greatest accumulations not by miles, nor scarcely by rods, but by feet. The conversion of rocks to soils has been performed, 1st, by Changes of Temperature ; 2d, by 3Ioving Water or Ice J 3d, by the Chemical Action of Water and Air j 4th, by the Influence of Vegetable and An imal life. 1. — Changes of Tempekature. The continued cooling of tlie globe after it had become enveloped in a solid rock-crust 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 as 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 laminated structure of slaty rocks, which may be 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, tlie first oc- casion of the breaking down of the rocks. The fact that 124 HOW mors feed. many rocks consist of crystalline grains of tlistinct niin erals more or less intLmately blended, is a point of weak- ness in their structure. The grains of quartz, feldspar, and mica, of a granite, m lien exposed to changes of tem- perature, must tend to separate from each other; because the extent to which they expand and contiact by alterna- tions of heat and cold are not absolutely equal, and be- cause, as Senarmont has provdl, 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 j\ 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 residts. The adventurous explorer in the higher Swiss Alps fre- quently sees or hears the fall of fragments of i-ock thus loosened from the peaks. Along the base of the vertical trap cliffs of New 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- ORIGIX AND I'ORMATION OF SOILS. 1 '25 tinu.'il transf>-r of water froin lowrr to liiglier levels. The elevates! 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 vrvlleys. In the mountains, thus beo:in, 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 the firmest rocks. Each grain of loosened material, as carried downward by the current, cuts the rock along which it is di'agged so long as it is in motion. Tho sides of the channel being undermined and loosen- ed by exposure to the frosts, fall into the strejtm. In time of floods, and always, when the j^ath 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 stono, 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 i iver, 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 ]»ulverizing rock is not com- pleted when it reaches the sea. The oceans are in i)erpet- xial agitation from tides, wind-waves, and currents like the Gulf-stream, and work continual changes on their shores. Glaciers. — What liappens from the rapid 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 a])pear like motion- 126 uo^y CROPS feed. less ice-fields, but they are frozen rivers, rising in pei'pct^ 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 i:- 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 ioe, 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 moving 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 and finds a channel beneath the ice. The middle of the glacier moves most rapidly, the sides and bottom being retarded by fiiction. The ice is thus rubbed and 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 axd Aib, ORIGIN' AND FOKSIATIOX 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 in many instances a new compound, which, by being softer and more bulky than the original substance, is the first step towards further change. Mica, feldspar, amphibole, and pyioxene, are minerals whicli have been artificially produced in the slags or linings of smelting furnaces, and thus formed they have been fotuid totally destitute of wa- ter, as might be expected from the high temperature in wliich they originated. Yet these minerals as occurrino- 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 combination (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 Math water, chloride of calcium, Avhich is very soluble, being separated from the nearly insoluble phosphate of lime. The minerals Avhich compose silicious rocks are all acted on j^erceptibly by pure water. This is readily observed when the minerals are employed in the state of fine powder. If pulverized 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, which increases the surface 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 * finely 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 {Am. Jour. Sci.,Y, 4:0-1, 1848) found that by continued digestion of pure water for a week, with powdered feldspar, horn- blende, chlorite, serpentine, and natrolite,t these minerals yielded to the solvent fiora 0.4 to 1 per cent of their weiglit. In nature we never deal witli pure water, but witli 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 absorbed by or dissolved in all natural waters to a greater or less extent. At common temperatures and pressure 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 water, as we may designate this solution, has a high solvent power on the carbonates of lime, magnesia, pi'otoxide 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. Chalyb- eate 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 Musotj'pe. ORIGIN AND FORMATION OF SOILS^ 120 acid under a pressure of 0 atmospheres, and obtained a solution of -winch a pound* contained: Carbonate of soda, 22.0 grains. Cliloride of sodium, 3.0 " Sulphate i.f potash, 1.7 " " " soda, 4.8 " Carbonate of lime, 4.5 " " " magnesia, 1.1 " Silica, 0.5 " Phosohoric acid and manjranese, traces Total, oT.l gi'ains. In various natural springs, water comes to the surface so charged with carbonic acid that the latter escapes copiously in bubbles. Such waters dissolve laige quantities of mineral matters from the rocks through which they emerge. Examples are seen in the springs at Saratoga, N. Y. According to Prof Chandler, the '' Saratoga Spring," whose waters issue directly from the rock, con- tains in one sjallon of 231 cubic inches : Chloride of Sodium (common salt) 308. 3G1 " " Potassium, 9.098 Bromide of Sodium, 0.571 Iodide of Sodium, 0.126 Sulphate of Potash, 5.400 Carbonate of Lime, 86.483 " " Magnesia, 41.050 " " Soda, 8.948 " " Protoxide of i ron, .879 Silica, 1.28a Phospliatc of lime. trace 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 Avell as those tliat fall upon the earth's surface as rain, are, indeed, I'he Saxon pound contains 7,080 Saxc 6* 130 IIOM^ CROPS FEED. by no means fully charged with carbonic acid, and their solvent effect 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 Locality. Lampadius, 8 Country near Freiberg, Saxony. Mulder, 20 City of Utrecht, Holland. Von Buumbauer, 40 to 90 " " " " Peligot, 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 quantities are somewhat larger, but the carbonic acid exists chiefly in chemical com- bination as bicarbonates of lime, magnesia, etc. In the capillary water of soils containing much organic matters, more carbonic acid is dissolved. According to a single observation of De Saussure's, such water contains 2"! „ of the gas. In a subsequent paragraph, p. 221, is given the reason of the small content of carbonic acid in these waters. 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 have 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 pure water, or even car- bonated water, in their solvent and disintegrating action. Phosphate of lime, the earth of bones, is dissolved by pure water to an extent that is hardly appreciable ; in ORIGIN AND FORMATION OF SOILS. 131 salts of ammoTiia and of soda, however, it is taken up in considerable quantity. Solution of nitrate of aiiimonia dissolves lime and magnesia and their carbonates with great ease. In general, up to a certain limit, a saline so- lution acquires increased solvent power by increase in the amount and number of dissolved matters. This import- ant fact is one to which we shall recur at another time. Action of Oxygen. — This element, the great mover of chemical changes, which is present so largely in the at- mosphere, has a strong tendency to unite with certain bodies which are almost universally distributed in the 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 feldspars they exist, indeed, in very minute quantity, but are almost never en- tirely wanting. 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 or basaltic rocks, as at Bergen Hill, tnetalHe 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 more space than the metals or lower oxides. This fact is well illustrated by the sulphate of protoxide of iron (cop- jieras, 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. WeatherinjHf. — The conjoined influence of water, car- This statement rests on the authority of Professor Henry Wurtz, of New York. 132 HOW CROPS FEED. bonic acid, oxygen, and the salts held in solution by the atmospheric waters, is expressed by the word veathering. Tliis term may likewise include the action of frost. When rocks weather, they are decomposed or dissolved, 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 cliief 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- posed 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 absolutely insoluble, particularly in water containing alkali carbonates or sili- cates. In its less pure yarieti«s, and especially when as- sociated with readily decomposable minerals, it is acted on more rapidly. The quartz of granitic rocks is usually roughened on the surface when it has long been exposed to the weather. h. The Feldspars weather much more easily than quartz, though there are great differences among them. The soda and lime feldspars decompose most readily, while the potash feldspars are often exceeding!}^ durable. The decomposition results in completely breaking up the liard, glassy mineral. In its place there remains a white or yellowish mass, which is so soft as to admit of crush- ing between the fingers, and which, though usually, to the naked eye, opaque, and non-crystalline, is often seen, under a powerful magnifier, to contain numerous transparent crys- talline plates. The mass consists principally of the crys- talline mineral, ^Y/o/m/^e, ahydrated silicate of a]umina,(the analysis of which has been given already, p. 113,) mixed Or.ir.IN AND FOi:.Nf.\Tl<>\ ol' S(>ILS, lii'fi with liydrated silica, and often with grains of nndecomi>os- ed mineral. If we compare the composition of pure pot- ash feldspar with that of kaolinite, assuming, what is probably true, that all the alumina of the former remains in the latter, we find what portions of the feldspar have been removed and washed away by the water, which, to- gether with carbonic acid, is the agent of this change. Feldspar. Kaolinite. Liberated. Added. Alumina 18.3 18 3 0 Silica 64.8 23.0 41.8 Putasb 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 felds])ar into kaolinite, there result 47.7 parts of the hitter, while 58.7" |„ of the feldspar, viz: 41.8° |„ of silica and 16.9° |^ of potasli, are dissolved out. The potash, and, in case of other feldspars, soda, lime, and magnesia, are dissolved as carbonates. If much water has access during the decomposition, all the liberated silica is carried away.* It usually happens, however, that a por- tion of the silica is retained in the kaolin (perhaps in a manner similar to that in which 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 rocks, the fis- sures and cavities through which surface water finds its way downwards are often coated or filled with this sub- stance. c. Other Silicious Minerals, as Lencite, (Topaz, Scapo- lite,) etc., yield kaolin by decomposition. It is pi-obable that the micas, which decompose with difficulty, (phlogo- ♦ We have seen (H C. G., p. 121) that silica, when newly set free from combi- natiou, is, at tirst, freely soluble in water. 134 ilOAV CROPS PEED. pite, perhaps, excepted,) and the ampliiboles and pyrox- enes, which are often easily disintegrated, also yield kaolin ; but in the case of these latter minerals, the result- ing kaolinite 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 (lays, as pipe-clay, blue-clay, brick-clay, etc., are mixtures of kaolinite, 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 fragments or fine powder of undecom- posed mii'.erals. Fresenius deduces from his analyses of several Xassau clays the existence in them of a compound having the symbol Al„ O^ 3 SiO,+H,0, and the follow- ing composition joer 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 onh'^ 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. Sci., 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 ccmstitution, although mechanically dis- integrated or dissolved. We shall see hereafter that there OKIGIN AXD FOUMaTION OF SOILS. 13S is strong reason to assume tlie existence of compounds analogous to zeolites in every soil. e. Serpentine and Maja^ncsian Silicates are generally slow of decomposition, and yield a meager soil, /. The Limestones, when pure and compact, are very durable : as they become broken, or when impure, they often yield rapidly to the weather, and impregnate the streams which How 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 suffered more or less change by metamorphism. §5. JNCORPORATION 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 preadaraite 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 13(5 HOW CR0Pt5 FEED. the lava is incapable of bearing atiy vegetation save some almost microscopic forms. During these years the surface of the rock suttVrs gradual disintegration by tlie 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 from which they sprung. The growth of new generations of these p-lants 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 M'eathered 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 most insoluble rocks. They occur abund- antly on all our granitic and schistose rocks. 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 firmly to the rock that, on being forced off", ])articles 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 Avhich 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 aa rapidly as they fwe 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 F<>li.\[ATi():>l OF SOILS. 1^7 the circumstances of their oriL,Mn. Tii the depths of tlie soil sitiiilar inattars 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 VcifCtation. — When a plant or any part of a plant dies, and remains exposed to air and moisture at the common temi'.eratures, it undergoes a series of chemical and physical clianges, which are lai-gely due to an oxida- tion of portions of it)6 carbon and hydrogen, and the formation of new organic compounds. Vegetable matter is considerably variable in composition, but in all cases chiefly consists of cellulose and starch, or bodies of simi- lar character, mixed with a small proportion of albuminous and mineral substances. By decay, the white or light- colored and tough tissues of plants become conveited into brown or black friable substances, in which less or none of the organized structure of the fresh plant can be traced. The bulk and weight of the decaying matter constantly decreases as the process continues. With 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 nearlj'' 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 now onops FEEti. 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 what 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 (NHJ, 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 the in- fluence of alkalies and ammonia, it yields one or more bodies having acid characters, called humic and ulmic (also geic) acids. Further, by oxidation it gives rise to crenic and apocrenic 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 oi tnoisture. h. Organic matters furnish copious supplies of carbonic acid, the action of which has already been considered ORIGIN AND POUMATION OP SOILS. 139 (p. 128). Boussingault and Lewy {Memoires de CJiimie Agrk'ole, etc.^p. 369,) liave analyzed the air contained in the pores of the soil, and, as was to be anticipated, found it vastly riclier 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 atinospbeie 6 Air from sandy subsoil of forest 38 " " loamy " " " 134 " " surface-soil " " 130 " " " " vineyard 146 " " " " old asparagus bed 123 " " " " " " newly manured. 333 " " " " pasture 370 *' " *' rich in humus 543 " •' " newly manured sandy field, durinir 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 humus 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, have acid characters, in so far that they unite energetical- 140 now CROPS FEKD. ]y with other Lases, as lime, oxide of iron, etc. These alkali-salts, then, should attack the minerals of the soil in a manner similar to carbonic acid. The same is probably true of crenic and npoorenic 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 they 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 iu 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 ZuUcr, ( Vs. St. \. 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, Zuller informs us, is most in- tense in the finest fibrils, and is exhibited when the roots are simply 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 ZuUer, Salm Horst- mar {Jour. far. Prakt.Chem. XL. 304,) liaving found in the ashes of ground pine {Lycopodium, com^planatum), 38° j^, of ORIGIN AND FORMATION' OF SOILS. 141 alumina, while in the ashes of juniper, growing beside the Lycopodium, this substance was absent, examined the rootlets of both plants, and found that tlie former had an acid reaction, while the latter did not affect litmus- paper. Salm Ilorstniar supposed that the alumina of the soil finds its way into the Lycopodium by means of this acid. Ritthansen has shown that the Lycopodium contahis 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 raalate of alumina. {Joxr. fnr. Prakt. Chem. LIIL 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, bitartrato 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. A^ter 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 tlie dilute acid present in the pores of the membrane, and absorbed through it. This is an ingenious illustra- tion of the mode in which the organic aciils existing in the root-cells of plants may act directly upon the rock or soil external to tliem. By such action is doubtless to be explained the fact mentioned by Liebig hi 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." {31odern Ag p. 43.) 142 UOW CROPS FEED. This direct action of the living plant h 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 contahi 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 Avhere covered with lichens {Acarospora smar- agdula, Imhricaria oHvacea, etc.), while the bare rock, closely adjacent, is so hard as to resist the knife. On the Schwalbenstein, near Glatz, in Silesia, at a height of 4,500 feet, the granite is disintegrated under a covei-ing of li- chens, the feldspar being converted into kaolin or washed away, only the grains of quartz and mica remaining unal- tered.* CHAPTER III. KINDS OF SOILS— THEIR DEFINITION AND CLASSIFI- CATION. 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 we may profitably recount those defini- tions and distinctions that servo to give a certahi degree of precision to language, and enable us to discriminate in some measure the different kinds of soils, which offer great diversity in origin, comjiosition, external characteis, ♦ 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- ductive 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 from 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 })robable agricultural value; because the still un weathered rock reveals to the practised eye the nature of the min- erals, and thus of the elements, 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 rivets, 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 th« 144: HOW ( ROPS FEKD. 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 iiarticulars. They consist of fragments whose edges at least have been rounded by friction, if the fragments 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, fiom sand- granis up to iinmL-nse rock-masses of many tons in weight. This kind of soil is usually disdnguished from all others by the rounded rocks or boulders ("hard heads") it con- tains, which are jiromiscuously scattered through it. The "Drift" h:is undoubtedly been formed by moving ice in that period of the earth's history known to geolo- gists as the Glacial Epoch, a perioil 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 i)erpeLual 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 latitude 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 cf the drift have been moved southwards or southeastwards 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 tlie country when covered with drift is often or usually irregular and hilly, the hills themselves being conical heaps or long lidges of mingled sand, gravel, and boulders, the transported mass having often a great depth. These hills or ridges are parts of the vast trains of material left by the melting of preadamite glaciers or icebergs, and have their precise counterpart in the moralneA 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. Drift soils are for these reasons often made Tip of the most diverse materials, including all the kinds of rock and rock-dust that are to be found, or have existed for one or several scores of miles to the northward. 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 water. The great belts of yellow and red sand that 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 rumiing water (rivers and tides). Since small and light particles are more readily sustained in a current of water thaa 146 HOW CROPS FEED. heavy masses, alluvium is always more or less sti'atijied or arranged in distinct layers: stones or gravel at the bottom and nearest the soiirce of movement, finer stones or finer gravel above and furtlier down in the path of flow, sand and impalpable matters at the surface and at the 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, sand, and rock-dust detached from the slopes of neighboring mountains. Lakes and gulfs become filled with silt brought into them by streams. Alluvium is found below as well 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. ColIUTial Soils, lastly, are those which, while consisting in part of drift or alluvium, also contain sharp, angular fragments of the rock from wliich they mainly originated, thus demonstrating that they have not b('en transported to any great distance, or are made u]) of soils in place, more or less mingled with drift or alluvium. §2. 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, tliough very vague scientifically considered, are extremely useful for practical purposes, and the grounds upon which they rest deserve to be carefully reviewed for tlie purpose of api)reciating their deficiencies and giving greater jirecision to the terms employed to define them. The farmer, speaking of soils, defines them as gravelly^ sandy^ doyey^ loamy, calcareous, peaty, oehreous, etc. Mechanical Analysis of the Soil. — Befoie noticing these various distinctions in detail, we may appro] >riately Btudy the methods which are employed fi)r 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 necessary 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 finvr and especially by the finest particles. JMechanical 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 sufficient accuracy for all ordinary jjractical 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 i:i a glass cylinder, adding wa- ter, and vigorously agitating for a few moments, then letting the whole come to rest, there remains suspended in the water a greater or less quantity of matter iu a stJ»*Iarls are mixtures of clay or clayey matters, with finely- divided carbonate of lime, in something like equal propor- tions.* Peat or Swamp Muck is humus resulting from decayed * In Nuw .Tursey, green sand marl, or marl gimply, 13 tlie name applied to the green sand emi)l<)yed as a fertilizer. Shell marl is a uame desijjnatiug nearly pure carbonate of lime found in swamps. 15G How CHOPS FKED, vegetable matter in bogs and marshes. A soil is peaty or mucky wlien 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. Ochcry or Ferruginous Soils are those containing much oxide or silicates of iron ; they have a yellow, red, or brown color. Other divisions are current among practical men, as, for example, surface and subsoil, active and inert soil, tilth, and hard pan. These terms mostly explain them- selves. When, at the depth of four inches to one foot or more, the soil assumes a different color and texture, these distinctions have meaning. The surface soil, active soil, or tilth, is the portion that is wrought by the instruments of tillage — that which is moistened by the rains, warmed by the sun, permeated by the atmosphere, in which the plant extends its roots, gath- ers its soil-food, and which, by the decay of the subter- ranean organs of vegetation, acquires a content of humus. Subsoil. — Where the soil originally had the same char- acters to a great depth, it often becomes modified down to a certain point, by the agencies just enumerated, in such a manner that the eye at once makes the distinction into surface soil and subsoil. In many cases, however, such distinctions are entirely arbitrary, the earth changing its appearance gradually or even remaining uniform to a considerable depth. Again, the surface soil may have a greater downward extent than the active soil, or the tilth may extend into the subsoil. Hard pan is the appropriate name of a dense, almost impenetrable, crust or stratum of ochery clay or com- PHYSICAL. CUAKAOTEKS OF THE SOIL. 157 pactt'd gravel, often underlying a fairly fruitful soil. It is the soil reverting to rock. The particles once disjointed are being cemented together again by the solutions of lime, iron, or alkali-silicates and humates that descend from the surface soil. Such a stratum often separates the sur- face soil from a deep gravel bed, and peat swamps thus exist in basins formed on the most porous soils by a thin layer of moor-bed-pan. With these general notions regarding the origin and characters of soils, Ave may proceed to a somewhat extend- ed notice of the properties of the soil as influencing fertil- ity. These divide themselves into physicnl characters — those which externally affect the growth of llie plant ; and chemical characters — those which provide it with food. CHAPTER IV. PHYSICAL CHARACTERS OF THE SOIL. The physical characters of the soil are those which con- cern the form and arrangement of its visible or palpable particles, and likewise include the relations of these parti- cles to each other, and to air and water, as well as to the forces of heat and gravitation. Of these physical char- acters we have to notice : 1. The Weight of Soils. 2. State of Division. 3. Absorbent Power for Vapor of Water, or Hygro» scopic Capacity. 4. Property of Condensing Gases. 5. Power of fixing Solid JMatters from their Solutions. 6. Permeability to Liquid Water. Capillary Power. 7. Changes of Bulk by Drying, etc. 8. Adhesiveness. 9. Relations to Heat, 158 HOW CROPS FEED. In treating of the physical characters of the soil, the Writer employs an essay on this subject, contributed by him to Vol. XVI of the Transactions of the N. Y. State Axricultural Society, and reproduced in altered form in a Lecture given at the Smithsonian Institution, Dec, 1859, § 1- THE WEIGHT OF SOILS. The Absolute Weight of Soils varies directly with their porosity, and is greater the more gravel and sand they contain. In the following Table is given the weight per cubic foot of various soils according to Schiibler, and like- wise (in round numbers) the weight per acre taken to the depth of one foot (=43,560 cubic feet). Weight op Soils per cubic foot per acre to depth of one foot. Dry silicious or calcareous sand about 110 lbs. 4,792,000 Half sand and half clay " 96" 4,182,000 Common arable land * " SO to 90 " 3,485,000 to 3,920,000 Heavy clay " 75 " 3,207,000 Garden mold, rich in vegetable matter. . . " 70 " 3,049,000 Peat soil " 30 to 50 " 1,307,000 to 2,178,000 From the above figures we see that sandy soils, which are usually termed " light," because they are worked most easily by the plow, are, in fact, the heaviest of all ; while clayey land, which is called " heavy," weighs less, bulk for bulk, than any other soils, save those in which vegeta- ble matter predominates. The resistance offered by soils in tillage is more the result of adhesiveness than of gravity. Sandy soils, though they contain in general a less percent- age of nutritive matters than clays, may really offer as good * The author is indebted to Prof. Seely, of Middlebury, Vt., for a sample of one-fourth of a cubic foot of Wheat Soil from South Onondaga, New York. The cubic foot of this soil, when dry, weighs 86'/^ lbs. The acre to depth of one foot weighs 3,708,000 lbs. This soil contains a large proportion of slaty gravel. A rich garden soil of silicious sand that had been heavily dunged, time out of jnind. Boussingault found to weigh 81 lbs. av. per cubic foot (1.3 kilos per liter). This would be per acre, cue foot deep, 3,528,000 lbs. PHYSICAL CIIAUACTEKS OF THE SOIL. 159 nourisliment to crops as the latter, since they j)rcsent one- half more absolute weight in a given space. Peat soils are light in both senses in Avhich this word is used by agriculturists. The Specific Cravity of Soils is the weight of a given bulk compared with the same bidk of water. A cubic foot of water weighs 62^ lbs., but comparison of this num- ber with the numbers stated in the last table expressing the weights of a cubic foot of v.u'ious soils does not give us the true specific gravity of the latter, for the reason that these weights are those of the matters of the soil contained in a cubic foot, but not of a cubic foot of these matters themselves exclusive of the air, occupying their innumerable interspaces. When we exclude the air and take account only of the soil, we find that all soils, except those containing very much humus, have nearly the same density. Schone has recently determined with care the specific gravity of 14 soils, and the figures range from 2.53 to 2.71. The former density is that of a soil rich in humus, from Orcnbcrg, Tiussia ; the latter of a lime soil from Jena. The density of sandy and clayey soils free from humus is 2.65 to 2.G9. {Bulletin de la Soc. Imp. des JVatitrolistes de Moscou, 1807, p. 404.) This agrees with the density of those minerals which constitute the bulk of most soils, as seen from tlie following statement of their specific gravity, which is, for quartz, 2.65; feldspar, 2.62; mica, 2.75-3.10 ; kaolinite, 2.60. Calcite has a sp. gr. of 2.72 ; hence the greater density of calcareous soils. §2. STATE or DIVISION OF THE SOIL AND ITS INFLUENCE ON FERTILITY. On the surface of a block of granite only a few lichens and mosses can exist; crush the block to a coarse powder and a more abundant vegetation can be supported on itj 160 UOW CKOl'S FEED. if it is reduced to a very fine dust and duly watered, even the cereal gfains will grow and perfect fruit on it. Magnus {Jour, far prakt. Chem., L, 70) caused barley to germinate in pure feldspar, Avhich was in one experi- ment coarsely, in another finely, pulverized. In the coarse feldspar the i)lants grew to a height of 15 inches, formed ears, and one of them ripened two perfectly formed seeds. In the fine feldspar the plants were very decidedly strong- er. One of them attained a height of 20 i:iclics, and produced four seeds. It is true, as a general rule, that all fertile soils contain a large proportion of fine or impalpable matter. The soil of the " rJee Ree Bottom," on the Scioto River, Ohio, re- markable for its extraordinary fertility, which has remained nearly undiminished for GO years, though yielding heavy crops of wheat and maize without interruption, is char- acterized by the fineness of its particles. (D. A. Wells, Am. Jour. ScL, XIV, 11.) In what way the extreme di- vision of the particles of the soil is connected with its fer- tility is not difficult to understand. The food of the plant as existing in the soil must pass into solution either in the moisture of the soil, or in the acid juices of the roots of plants. In either case the rapidity of its solution is in direct ratio to the extent of surface wdiich it exposes. The finer the particles, the more abundantly will the plant be supplied with its necessary nourishment. In the Scioto valley soils, the water which surrounds the roots of the crops and the root-fibrils themselves come in contai-t wdth such an extent of surface that they are able to dissolve the soil-ingredients in as large quantity and as rapidly as the crop requires. In coarse-grained soils this is not so likely to be the case. Soluble matters (manures) must be applied to them by the farmer, or his crops refuse to yield handsomely. It is furthermore obvious, that, other things being equal, the finer the, articles of the soil the more space the grow PIIY£,:CAL CHARACTEUS OF THE SOIL. IGl ing roots have in whicli to expand themselves, and the more abundantly are they able to present their absorbent Burfaces to the supplies which the soil contains. The fine- ness of the particles may, however, be excessive. They may fit each otlier so closely as to interfere with the growth of the roots, or at least with the sprouting of the seed. The soil may be too compact. It will presently a})pear that other very important prop- erties of the soil are more or less related to its state of mechanical division. § 3. ABSORPTION OF VAPOR OF WATER BY THE SOIL. The soil has a power of withdrawing vapor of water from the air and condensing the same in its pores. It is. in other words, hygroscopic. This i^roperty of a soil i-; of the utmost agricultural im- portance, because, 1st, it is connected with the permanent moisture which is necessary to vegetable existence ; and, 2d, since the absorption of water-vapor to some degree determines the absorption of other vapors and gases. In the following table we have the results of a series of expeiiments carried out by Schablor, for the purpose of determining the absorptive power of different kinds of earths and soils for vapor of water. The column of figures gives in thousandths the (quantity of hygroscopic moisture absorbed in twenty-four liours by the previously dried soil from air confined over water, and hence nearly saturated with vaj)or. Quartz suud, course 0 Gypsum 1 Lime sand 8 Ploii.^h laud 2:^ Claj' soil, (60 per cent clay) 28 Slaty marl ;?3 Loam , 35 1C2 lIO-\V CKOPS FEED. Fine carbonate of lime 35 Heavy clay soil, (80 per cent clay) 41 Garden mold, (7 per cent liuraus) 53 Pure clay 49 Carbonate of mai::ncsi;i (fine jiowder) 83 Humus 130 Davy found that one tliousnnd parts of the soils named below, after having been dried at 212°, absorbed during one hour of exposure to the air, quantities of moisture as follows : Sterile soil of Bagshot h^ath 3 Coarse sand 8 Fine sand 11 Soil from Mersey, E.-sex 13 Very fertile alluvium, Somersetshire 16 Extremely fertile soil of Ormiston, East Lothian 18 An obvious practical result follows from the ficts ex- pressed in the above tables, viz.: that sandy soils which have little attractive force for watery vapor, and are there- fore dry and arid, may bo meliorated in this respect by admixture with clay, or better with humus, as is done by dressing with vegetable composts and by green manuring. The first table gives us proof that gypsum docs not exert any beneficial action in consequence of directly attracting moisture. Humus, or decaying vegetable matter, it will be seen, surpasses every other ingredient of the soil in absorbing vapor of water. This is doubtless in some de- gree connected with its extraordinary porosity or amount of surface. How the extent of surface alone may act is made evident by comparing the absorbent power of car- bonate of lime in the two states of sand and of an im- palpable powder. The latter, it is seen, absorbed twelve times as much vapor of water as the former. Carbonate of magnesia stands next to humus, and it is worthy of note that it is a very light and fine powder. Finally, it is a matter of observation that " silica and lime in the form of coarse sand make the soil in which they predominate so dry and hot that vegetation perishes PHYSICAL (JUAllACTEliS OP THE .SOIL. 10.') from want of moisture; when, however, they occur afijfue dust, they form too wet a soil, in which plants sufter from the opposite cause." — [Tlamni's Lindiclrthschaft.) Every body has a definite power of condensing moist- ure upon its surface or in its pores. Even glass, though presenting to the eye a jjerfectly clean and dry surface, is coated witli a film of moisture. If a piece of glass be weighed on :i very delicate balance, and then be wiped with a clean cloth, it will be found to weigh perceptibl}' less than before. Exposed to the air for an hour or more, it recovers the weight which it had lost by wiping; this loss was water. (Stas. Magnus.) The surface of the glass is thus proved to exert towards vapor of Avater an adhesive attraction. Certain compounds familiar to the chemist attract water with great avidity and to a lai'ge extent. Oil of vitriol, phosphoric acid, and chloride of calcium, gain weight rap- idly when exposed to moist air, or when placed contiguous to other substances which are impregnated with moisture. For this reason these compounds are employed for pur- poses of drying. Air, for exaniple, is perfectly freed from va})or of water by slowly traversing a tube containing lumps of dried chloride of calcium, or phosphoric acid, or by bubbling repeatedly througli oil of vitriol contained in a suitable apparatus. Solid substances, which, like chloride of calcium, carbon- ate of potash, etc., gather water from the air to such an extent as to become liquid, are said to deliquesce or to be dellques'ent. Certain compounds, such as urea, the char- acteristic ingredient of human urine, deliquesce in moist air and dry away again in a warm atmosphei'c. Allusion has been made in " How Crops Grow," p. 5.5, to the hygroscopic water of vegetation, which furnishes another striking illustration of the condensation of water in porous bodies. The absorption of vapor of water by solid bodies is not 164 HOW cuops fj:ed. only dependent on the natin-e of the substance and i'ibT amount of surface, but is likewise influenced by external conditions. The raj)idity of absorption depends upon the amount of vapor present or accessible, and is greatest in moist air. The amount of absorption is determined solely by tem- perature, as Knop has recently shown, and is unaflected 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 will do this the more speedily the more moist the surrounding atmosphere happens 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 tha quantity of water absorbed, as vapor, by the soil, we give Knop's observations on a sandy soil from Moeckern, Sax- ony : 1,000 parts of this soil absorbed At 55° F, 13 parts of hygroscopic water. " 66° " 11.9 " " " " " 77° " 10.:2 " " " " " 88° " 8.7 " " Knop calculates on the basis of his numerous observa- tions that hair and wool, which aie 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 87° Fah., 7.7 per cent. " 55° " 15.5 " " " 33° " 19.3 " " niYSK'AL CHAnAC'TEUS OP THE SOIL. 1 C5 Silk is sold ill Europe by weight with suitable allowance for hygroscopic moisture, its variable conti-nt of which is carefully (lelt-rmined 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 liave 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 kinds of matter. This force o? 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 tact, 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 Sanssure was the first to measure the absorbing power of charcoal for gases. In his experiments, boxwood chai'coal was heated to redness and plunged under mer- * Mitscherlich lias calculated that the cells of a cubic inch of boxwood have no less than 73 square feet of surface. 166 now CROPS feed. oury to cool. Then introduced into tlie various gases named below, it absorbed as many times its bulk of them, as are designated by the subjoined figures: Ammonia 90 Hydrochloric acid 85 Sulphurous acid G5 Hydrosulphuric acid 55 Protoxide of nitrogen 40 Carbonic acid 85 Oxygen 9}^ Carbonic oxide 9)^ Hydrogen 1% Nitrogen 7)^ According to De Saussure, the 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 lias 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 gi'amme of dry charcoal ab- sorbed of several srases the number of cubic centimeters given below. Name of Gas. Ammonia Hydrochloric acid Hydrosulphuric acid. Sulphurous acid Carbonic acid Oxygen A'ind of Charcoal. Wood. Peat. Animal. 98 5 96.0 43.5 45.0 GO.O 30.0 28.5 9 0 32.5 27.5 17.5 14.0 10.0 5.0 0.8 0.6 0.5 The absorption or solution of gases in water, alcohol, and other liquids, is analogous to this condensation, and 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 (iases 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 rHOPERTV OF KftM. COLLEGE LIBRARY. PHYSICAL fllARACTEnS OP HIE SOIL. 1(57 ingieclieuts. {Jour, filr prakt. Chem., 13d. 98, j). 476.) Their results relate chietly to these substances as ordinarily occurring exposed to the atmosphere, and therefore more or less moist. The following Tahle includes the more im- portant data obtained by subjecting tlie substances to a temperature of 284° F., and measuring and analyzing the gas thus expelled. 100 Gra7m 10 Vols. 100 Vols, of Gas contained: yielded gus yielded , Substance : in mis. Nitro- 0.ry- Cartmn- • Car- a c. gas. gen. gen. ic acid. bonic Charcoal, airclry. 164 _ 100 0 0 0 " moistened and dried i igain. , 140 5'J 85 2 9 3 Peat, 162 — 44 5 51 0 Garden soil, moist, 14 20 04 3 24 9 " " air-dry. 38 54 65 2 33 0 Hydrated oxide of iron, air -dry, 375 309 26 4 70 0 Oxide of iron, ignited. 30 52 83 13 4 0 Hydrated alumina, air-dry, 69 82 41 0 59 — Alumina, dried at 212'^, 11 14 83 17 0 _ Clay, 33 — 65 21 14 — " long exposed to air, 26 39 70 5 25 — " moistened, 29 35 60 6 Zi _ River silt, air-dry, 40 48 68 0 !■& 14 " moistened, 24 29 67 0 31 2 " " again dried. 26 30 67 9 16 7 Carbonate of lime (whiting ,) 1S64, 43 52 100 0 0 — 18G5, 39 48 74 16 10 _ " " " 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 apj^roaching those of the atmos])hei"e. 2. Xitrogeu ajjpears to be nearly always absorbed in greater proportion than oxygen, and is greatly condensed in some cases, as by peat, hydrated oxide of iron, and car- bonate of masrnesia. 168 now CROPS FEED. 3. Oxygen is often nearly or quite wanting, 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, wlien moist, absorbs less gas than when dry. In accordance with this observation, De Saussure no- ticed that dry charcoal saturated Avith various gases evolv- ed a good share of them when moistened Avith water. Ground (and burnt ?) coffee, as Babinet has lately stated, evolves so much gas when drenched with water as to burst a bottle in which it is confined. Tiie extremely variable figures obtained by Bluratritt wlien 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- iluences 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 with ammonia by ex- posure 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 CIIARACTKUS OF THE SOIL. 160 is iibijorbeil by })orous bodies in the largest quantity. This not only displaces otlier 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 liad 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 induced 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 which 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 may 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 or 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 ])olished surf ice of foil or wire : but is most striking when the metal is 170 now oitoi'S 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 poAver, so that, for example, when it is brouglit 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 escha- 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 ingre- 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 effluvia, 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. e. deprived of * Platinum does not condense hydrogen gas ; but the metal Palladium, 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 Roy. Hoc., 1868^ p. 432.J odor, by burying them for a few days in the earth. The Indians of this country arc 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 fi-om 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 reajipears. At the most, besides an "eartliy" smell, an odor of ammonia appears, resulting from decomi)osition, which appears to ])roc-eed 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 nitiic 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 different animal and vegetable matters. He found that in such circumstances oxidation ti)ok 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.* POWER OF SOILS TO REMOVE DISSOLVED SOLIDS FROM THEIR SOLUTIONS. Action of Sand upon Saline Solutions. — It has long been known that simple sn: Hoy. Ag. Soc. of Eng., XI, p. 364.) These efibcts of clay or clayey matters, like the fixing power of cotton ami woolen stulFs upon pigments, must 176 HOW CROPS FEED. be regarded for the most part as j^urely pliysical. There are other resuUs of the action of the soil on saline solu- tions, which, though j)erhaps influenced hy simple physical action, are prepondcratiugly chemical in their aspect. These effects, which manifest themselves by chemical de- compositions and substitutions, will be fully discussed in a subsequent chapter, p. 333. PERMEABILITY OF SOILS TO LIQUID WATER. IMBIBITION. CAPILLARY POWER. The fertility of the soil is greatly influenced by its de- portment toward water in the liquid state. A soil 1?, permeable to water when it allows that liquid to soak into or run through it. To be permeable is of course to be porous. On the size of the jjores depends its degree of permeability. Coarse sands, and soils which have few but large pores or interspaces, allow water to run through them readily — water ^:»ercota#es them. When, instead of runni-ng 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. The cause of capillarity is the same surface attraction which has been already under notice. When a narrow vial is partly filled 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 Avill be curved or concave. In a very narrow tube the liquid will rise to a considerable heiglit. 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 capilli/s, the Latin word fur hair, because as fine as hair; (but a hair la no tube, as is often supposed.) PERMEABILITY OF SOILS TO LIQUID WATEK. 177 port it. When a body has pores so fine (surfaces so near each other) that tlieir surface attraction is greater than the gravitating tendency of water, then the body will im- bibe and hohl water — will exhibit capillarity; a lump of salt or sugar, a lamp-wirk, 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 leachy or hungry. The rains that fdl 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 siiflfer 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 ]>enetrate it too slowly ; they flow oif 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 Hater 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 tlie liquid. Wlien 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 cuors fked. Sonietliuig quite analogous occurs in the soil, by wliicli the plant (corresponding to the flame in our illustration) is fed. The soil is at once lamp and wick, and the water of the soil represents the oil. Let evaporation of water from the surface of the soil or of the plant take the place of the combustion of oil from a Avick, and the matter stands thus : Let us suppose dew or rain to have saturated the ground with moisture fur some depth. On recurrence of a dry atmospliere with sunshine and wind, the surface of the soil rapidly dries ; but as each particle of Avater es- capes (by evaporation) into the atmosphei-e, its place is supplied (by capillarity) from the stores below. The as- cending water brings along with it the soluble matters of the soil, and thus the roots of plants are situated in a stream of their appropriate food, Tiie movement proceeds in this way so long as the surface is drier than the deeper soil. When, by rain or otlierwise, the surf^ice 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 water ; 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 cf 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 wliich 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 de})th, and thus are kept constantly changing their place with the Avater, which is the vehicle of their distribution. In regions Avhere rain falls periodically or not at all, this upward flow of the soil- termkability 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, have 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 plants 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 organs 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 sup])lies 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 rapi! HOVr CROPS FEEP. ■water are almost incapable of being warmed by heat ap- plied above them. Through the air, heat radiates without being absorbed. Solid bodies whicli have dull and porous surfaces absorb heat most rapidly and abundantly. The soil and solid bodies become warmed according to their individual capacity, and from them the air receives the heat which warms it. From the moist surface of the soil goes on a rapid evaporation of water, which consumes * a large amount of heat, so that the temperature of the soil is not rapidly but gradually elevated. The ascent of wa- ter from the subsoil to supply the plnce of that evaj^orat- ed, goes on as before described. When the sun declines, the process diminishes in intensity, and w^hen it sets, the reverse takes place. The heat that had accumulated on * When a piece of ice is placed in a vessel whose temperature is increasing, by means of a lamp, at tlie rate of one desree of the thermometer every minute, it will be found that the temperature of the ice rises until it attains 32°. When this point is reached, it begins to melt, but doos not suddenly become fluid : the melting goes on very gradually. A thermometer placed in the water remains constantly at 32° so long as a fragment of ice is present. The moment the ice disappears, the temperature begins to rise again, at the rate of one degree per minute. The time during which the temperature of the ice and water remains at 33° is 140 minutes. During each of these minutes one degree of heat enters the mixture, but is not indicated by the thermometer — the mercury remains sta- tionary ; 140° of heat have thus passed into the ice and become hidden, latent ; at the same time the solid ice has become liquid water. The dift'erence, then, between ice and water consists in the heat that is latent in the latter. If we now proceed with the above experiment, allowing the heat to increase with the same rapidity, we find that the temperature of the water rises constantly for ISO min- utes. The thermometer then indicates a temperature of 212°, (32+180,) and the water boils. Proceeding with the experiment, the water evaporartes away, but the thermometer continues stationary so long as any liquid remains. After the lapse of 972 minutes, it is completely evaporated. Water in becoming steam renders, therefore, still another portion, 972°, of heat latent. The heat latent in steam is indispensable to the existence of the latter. If this heat be removed by bringing the steam into a cold space, water is reproduced. If, by means ol pressure or cold, steam be condensed, the heat originally latent in it becomes sensible,/?-«A and capable of affecting the thermometer. If, also, water be con- verted into ice, as much heat is evolved and made sensible as was absorbed and made latent. It is seen thus that the processes of liquefaction and vaporization are cooling processes ; for the heat rendered latent by them must be derived from surrounding objects, and thus these become cooled. On the contrary, solidifica- tion, freezing, and vapor-condensation, are tvarminff processes, since in them large quantities of heat ce-ise to be latent and are made sensible, thus warming purroundiug bodies. KELATIONS OF TIIK SOIL TO HEAT. 1*^9 the surface of the earth radiates into the cooler atmos- phere aiid planetary sj^acc; the temperature of the surface rapidly diminishes, and the air itself becomes cooler by convection.* As the cooling goes on, the vapor suspend- ed in the atmosphere begins to condense upon cool objects, while its latent heat becoming free hinders the too sudden reduction of temperature. The condensed water collects ill drops — it is dew ; or hi the colder seasons it crystallizes as hoar-frost. The deposition of liquid water takes place not on the surface of the soil merely, but within it, and to that depth in which the temperature falls during the night, viz., 12 to 18 inches. (Krutzsch observed the temperature of a garden soil at the depth of one foot, to rise 3° F. on a May day, from 9 A. M. to 7 P. M.) Since the air contained in the interstices of the soil is at a little di'pth saturated with aqueous vapor, it results that the slightest reduction of temper;iture must at once occa- sion a deposition of water, so that the soil is thus supplied with moisture independently of its hygroscopic power. Conditions tliat Affect the Temperature of the Soil.— The special nature of the soil is closely connected with the maintenance of a uniform temperature, with the pre- vention of too great heat by day and cold by night, and with the watering of vegetation by means of dew. It is, however, in many cases only for a little space after seed- time that the soil is greatly concerned in these jjrocesses. So soon as it becomes covered with vegetation, the char- * Thoagh liquids and gases are almost perfect non-coiuliictors of heat, yet it can (Bffuse through them rapidly, if advantage be taken of the fact that by lieatiiig they' expand and therefore become specifically lighter. If heat be applied to the upper surface of liquids or gases, they remain for a long time nearly unaflected ; if it be applied beneath them, the lower layers of jjarticles become heated and rise, tlieir place is supplied by others, and so currents upward and downward are established, whereby the heat is rapidly and uniformly distributed. This process of convection can rarely have any influence in tlie soil. What we have stated concerning ft shows, however, in what way the atmosphere may coustantly act in removin'j heat from the surface of the soil. 190 HOAV CROPS FEED. acter of the latter determines to a certain degi-ee the na« tnre of the atmospheric changes. In case of many crops, the soil is but partially covered, and its peculiarities are then of direct influence on its temperature. Relation of Temperature to Color and Texture.— It is usually stated tliat black or dark-colored soils are sooner "warmed by the sun's rays than those of lighter color, and remain constantly of a higher temperature so long as the sun acts on them. An elevation of several degrees in the temperature of a light-colored soil may be caused by strewing its surface with peat, charcoal powder, or vege- table mould. To this influence may be partly ascribed the following facts. Lampadius was able to ripen melons, even in the coolest summers, in Freiberg, Saxony, by strewing a coating of coal dust an inch deep over the sur- face of the soil. In Belgium and on the Rhine, it is found tliat the grape matures best, when the soil is covered with fragments of black clay slate. According to Creuze-Latouche, the vineyards along the river Loire grow either upon a light-colored calcareous soil, or upon a dark red earth. These two kinds of soil often alternate with each other within a little distance, and the character of the wine produced on them is remark- ably connected with the color of the earth. On the light- colored soils only a weak, white wine can be raised to ad- vantage, while on contiguous dark soils a strong claret of fine quality is made. (Gasparin, Gours cT AgricultKre, 1, 103.) Girardin found in a scries of experiments ou the cultiva- tion of potatoes, that the time of their ripening varied eight to fourteen days, according to the color of the soil. He found on August 25th, in a very dark humus soil, twenty-six varieties ripe; in sandy soil, twenty; in clay, nineteen; and in white lime soil, only sixteen. It is not difticult, however, to indicate other causes that will at^ count in part for the results of Girardin, EELATIONS OF THE SOIL TO HEAT. 191 Schiibter made observations ou the temperatures at- tained by various dry soils exposed to the sun's raySj according as their surfaces were blackened by a thin sprinkling of latnp-black or whitened by magnesia. Ilis results are given in columns 1 and 2 of the following table {ride p. 196,) from which it is seen that the dark surf\ce was warmed 13° to 14° more than the white. We like- wise notice that the character of the very surface deter- mines the degree of warmth, for, under a sprinkling of lamp-black or magnesia, all the soils experimented with became as good as identical in their absorbing power for the sun's hent. The observations of Mnlaguti and Durocher prove that the peculiar temperature of the soil is not always so closely I'elated to color as to other qualities. They studied the thermometric characters of the following soils, viz. : Gai-den earth of dark gray color, — a mixture of sand and gravel with about five per cent of humus ; a grayish- white quartz sand ; a grayish-brown granite sand ; a fine light-gray clay (pipe clay) ; a yellow sandy clay ; and, finally, four lime soils of different physical qualities. It was found that Avhen the exposure was alike, the dark-gray granite sand became the warmest, and next to this th'' grayish-white quartz sand. The latter, notwith- standing its lighter color, often acquired a higher temper- ature at a depth of four inches than the former, a fact to be ascribed to its better conducting poAver. The black soils never became so warm as the two just mentioned. After the black soils, the others came in the following oi-- der : garden soil ; yellow sandy clay ; pipe clay ; lime soils having crystalline grains ; and, lastly, a pulverulent chalk soil. To show what different degrees of warmth soils may acquire, under the same circumstances, the following max- imum temperatures may be adduced : At noon of a July day, when the temperature of the air Mas 90°, a thermoni' 192 HOW CROPS FEED. eter placed at a depth of a little more than one inch, gave these results: In quartz sand 126* In crystalliue lime soil 115° In j!farflen soil 114° In yellow sandy cluy 100° In pipe clay 94° In chalk soil 87* Here we observe a difference of nearly 40° in the noon- day temperature of the coarse quartz and the chalk soil. Malaguti and Durochcr found that the temperature of the garden soil, just below the surface, was, on the average of day and night together, 6° Fahrenheit higher than that of the air, but that this higher temperature diminished at a greater depth. A thermometer buried four inches indi- cated a mean temperature only 3° above that of the at- mosphere. The experimenters do not mention the influence of wa- ter in affecting these results ; they do not state the degree of dryness of these soils. It will be seen, however, that the warmest soils are those that retain least water, and doubtless something of the slowness with which the fine soils increase in warmth is connected with the fact that they retain much water, which, in evaporating, appropri- ates and renders latent a large quantity of heat. The chalk soil is seen to be the coolest of all, its tem- perature in these observations being three degrees lower than that of the atmosphere at noonday. In hot climates this coolness is sometimes of gfeat advantage, as appears to happen in Spain, near Cadiz, where the Sherry vine- yards flourish. " The Don said the Sherry wine district was very small, not more than twelve miles square. The Sherry grape grew only on certain low, chalky hills, where the earth being light-colored, is not so much burnt ; did not chap and split so much by the sun as darker and heavier soils do. A mile beyond these hills the grape de- teriorates."— (Dickens' Household Words Nov. 13, 1858.) REJ.ATION.S OF THE SOIL Tu HEAT. 193 in Explanation of tliose ob.sci-vutions we must recall to TAmd the fact that all bodies are capable of absorbing and radiating as well as reflecting heat. These properties, al- though never dissoci;ited fi'oni color, are not necessarily dependent upon it. They chiefly depend upon the char- acter of the surface of bo lies. Smooth, polished surfaces absorb and radiate lieat least readily; they reflect it most perfectly. Ivadiation and absorption aie opposed to each other, and the power of any body to radiate, is precisely equal to its faculty of absorbing heat. It must be understood, however, that bodies may differ in their power of absorbing or radiating heat of different degrees of intensity. Lamp-blaclc absorbs and ra. 191.) Whi t-! Black- Differ- ened.l cned. | ence. 4 5 Surface. Wet. i 121. 3' I 12.G° I 95.2 13.7= 96.1 ■■rl 14.0" 97.3 ...0': 14.4° 97.7 ^■n.rrl 13.3' 9S.2 ir,.t) n.r I 9:).i 1-^1. ri 13.3° I 99.1' 100.2^! 122.9 11(1.3 j 124.3 1(17 99.3° 99.3° Dry. Differ- ence. 108. 7°| 13.5° 109.4°' 13.3° 110.5° 13.2° 111.7° 14.0° 111.4° 13.2' 112.6° 13.5° 112.1° 13.0° 112.1° 12.8° 112. 3°i 13.0° 113.0° 13.5° 113.5°! 14.0° 115.3') 13.5° 117. 3°| 13.7° Magnesia, pure white |133 Fine carbonate of lime, wiiitc. Gvpsiiri), liiiirlit \vhiti---rav I'!(.w l:ni(l. ^rav '.. . Sandv cl.iv.' vcilowisli (Quartz s^aud, bri-ht yellowi.-li-..,:-.;.,-. . . lO'i.!) Loam, yclliiwi.'^h .;..". 1(17. s' Lime saml, wliitish-trray Kiit.'.i Heavvclav soil. vi'll(nvisli-;,M-av 107.1 Piireclav.blnisb'-urav ' Kii; :; Oard.'H mould. blnrki'-li-Lrrav UN.:; 81nly mai-l, bniwiiisli-ivd. . .' los,;: Hiimiis. bnr.viiish-black Ids. .5 "We note that the difference in fovor of the dry earth is almost nniform.ly 13° to 14°. This difference is the same as obserA'ed between the whitened and blackened speci- mens of the ^ame soils. (Column 3.) We observe, liowever, that the wet soil in no case be- comes as warm as tlie same soil Avliitened. AVe notice further that of the wet soils, the dark-colored ones, humus and marl, are most highly he.ated. Further it is seen that coarse lime sand (carbonate of lime) acquires 3° higher temperature than fine carbonate of lime, both Avet, prob- ably because evaporation pi-oceeded more slowly from the coarse than from the fine materials. Again it is plain on com])aring columns 1, 2, and 5, that the gray to yellowish brown and black colors of all the soils, save the first three, assist the elevation of temperature, which rises nearly RELATIONS OP THE SOIL TO HEAT. 197 with the deepening of the color, until in case of humus it lacks but a few degrees of reaching the warmth of a sur- face of lamp-black. According to the observations of Dickinson, made at Abbot's Hill, Ilertfonlshire, England, and continued through eight years, 90 per cent of the Avater falling be- tween April 1st and October 1st evaporates from the sur- face of tlie soil, only 10 per cent finding its way into drains laid three and four feet deep. The total quantity of water ^hat fell during this time amounted to about 2,900,000 lbs. per acre; of this more than 2,000,000 evap- orated from the surface. It has been calculated that to evaporate artificially this enormous mass of water, more than seventy-five tons of coal must be consiimed. Thorough draining, by loosening the soil and causing a rapid removal from below of the surplus water, has a most decided influence, especially in spring time, in warming the soil and bringing it into a suitable condition for the support of vegetation. It is plain, then, that even if we knew with accuracy ■what are the physical characters of a surface soil, and if we were able to estimate correctly the influence of these characters on its fertility, still we must investigate those circumstances which afiect its wetness or dryness, whether they be an impervious subsoil, or springs coming to the surface, or the amount and frequency of rain-falls, taken in connection with other meteorological causes. We can- not decide that a clay is too wet or a sand too dry, until we know its situation and the climate it is subjected to. The gre'at deserts of the globe do not owe their barren- ness to necessary poverty of soil, but to meteorological influences — to the continued prevalence of parching winds, and the absence of mountains, to condense the atmospheric water and establish a system of rivers and streams. This is not the place to enter into a discussion of the causes that may determine or modify climate ; but to illustrate 198 HOW CROPS FEEi). the effect that may be iiroduced by means within human control, it may be stated that previous to the year 1821, the Frencli district Provence was a fertile and well-water- ed region. In 1822, the olive trees which were largely cultivated there were injured l)y frost, and the inhabitants began to cut them up root and branch. This amounted to clearing off a forest, and, in consequence, the streams dried up, and the productiveness of the country was seri- ously diminished. The Angle at which the Sun's Rays Strike a Soil is of great influence on its temperature. The more this ap- proaches a right angle the greater the heating effect. In the latitude of England the sun's heat acts most power- fully on surfaces having a southern exposure, and which are inclined at an angle of 25° and 30°. The best vine- yards of the Ehine and Neckar are also on hill-sides, so situated. In Lapland and Spitzbergen the southern side of hills may be seen covered with vegetation, while lasting or even perpetual snow lies on their northern in- clinations. The Influence of a Wall or other Reflecting Surface upon the warmth of a soil lying to the south of it was observed in the case of garden soil by Malaguti and Durocher. The highest temperature indicated by a ther- mometer placed in this soil at a distance of six inches from the wall, (iui-ing a series of observations lasting seven days (April, 1852), Avas 32° Fahrenheit higher at the surface, and 18° higher at a depth of four inches than in the same soil on the north side of the wall. The average temper- ature of the former during this time was 8° higher than that of the latter. In another trial in March the difference in average temperature between the southern and north- ern exposures was nearly double this amount in favor of the former. As is well known, fruits which refuse to ripen in cold climates under ordinary conditions of exposure may attaia The free water of the soil. 199 perfection when trained against the sunny side of a «all. It is tlius that in the nortli of England pears and pkims are raised in the most unfavorable seasons, and that the vineyards of Fontainehleau produce such delicious Chas- selas grapes fur the Paris market, the vines being trained against walls on the Tliomery system. In the Rhine district grape vines are kept low and as near the soil as possible, so that the heat of the sun may be reflected back upon them from the ground, and the ripen- ing is then carried through the nights by the heat radiated from the earth. — {Journal Highland and Agricidtural Society, July, I808, p. 347.) Vegetation. — Malaguti and Durocher also studied the effect of a sod on the temperature of the soil. They ob- served that it hindered the warming of the soil, and in- deed to about the same extent as a layer of earth of three inches depth. Thus a thermometer four inches deep in green-sward acquires the same temperature as one seven inches deep in the same soil not grassed. CHAPTER V. THE SOIL AS A SOURCE OF FOOD TO CROPS.— INGREDIENTS WHOSE ELEMENTS ARE OF ATMOSPHERIC ORIGIN. I § 1. THE FREE WATER OF THE SOIL IN ITS RELATIONS TO VEGETABLE NUTRITION. Water may exist free in the soil in three conditions, which we designate i-cspectively hydrostatic, capillary, and hygroscopic. Hydrostatic or Flowing* Water is water visible as I. e., capable of flowing. 300 now CROPS FEED. such to the eye, and free to obey the laws of gravity and motion. T\Tien the soil is saturated by rains, melting snows, or by overflow of streams, its pores contain liy- drost;itic water, whicli sooner or later sinks away into the subsoil or escapes into drains, streams, or lower situations. Bottom Water is permanent hydrostatic water ^ reached nearly always in excavating deep soils. The surface of water in a well corresponds with, or is somewhat below, the upper limit of bottom water. It usually fluctuates in level, rising nearer tlie surface of the soil in wet seasons, and receding during drought. In general, agricultural plants are injured if their roots be immersed for any length of time in hydrostatic water; and soils in which bottom water is found at a little depth during the season of growth are unprofitable for culture. If this depth be but a few inches, we have a bog, swamp, or sw\ale. If it is one and a half to three feet, and the surface soil be light, gravelly, or open, so as to admit of rapid evaporation, some plants, especially grasses, may flourish. If at a constant depth of four to eight feet under a gravelly or light loamy soil, it is favorable to crops as an abundant source of water. Heavy clays, which retain hydrostatic water for a long time, being but little permeable, are for the same reasons unfavorable to most crops, unless artificial provision be made for removing the excess. Rice, as we have seen, (H. C. G., p. 252), is a plant which grows well with its roots situated in water. Hen- rici's experiment with the raspberry (H. C. G., p. 254), and the frequent finding of roots of clover, turnips, etc., in cisterns or drain pipes, indicate that many or all agricultural plants may send down roots into the bottom water for the purpose of gathering a sufficient supply of this necessary liquid. Capillary Water is that which is held in the fine pores of the soil by the surface attraction of its particles, as oil TDK FUKK WATlCn OF T;iE SOIL. f20l is held in tlie Avick of ;i lamp. The adliesion of the water to the particles of eurLli suspends the flow of the liquid, and it is no longer subject to the laws of hydrostatics. Capillary water is usually designated as moisture, though a soil saturated with capillary water would be, in most cases, wet. The cai)illary power of various soils has al- ready been noticed, and is for coarse sands 25° |„ ; for loams and clays, 40 to 70° |„ ; for garden mould and humus, much higher, 90 to 300 °|„. (See p. 180.) I'^or a certain distance above bottom Avater, the soil is saturated with capillary water, and this distance is the greater, the greater the cajiillary power of the soil, i. e., the finer its pores. Capillary water is not visible as a distinct liquid layer on or between the particles of soil, but is still recogniza- ble by the eye. Even in the driest weather and in the driest sand (that is, when not shut off" from bottom water by too great distance or an intervening gravelly subsoil) it may b'3 found one or a few inches below the surface where the soil Jool:s moist — has a darker shade of color. Hygroscopic Water is that which is not perceptible to the senses, but is appreciated by loss or gain of weight in the boily which acquires or is deprived of it. (11. C. G., p. 54.) The loss experienced by an air-dry soil when kept for some hours at, or slightly above, the boiling point (212° F.,) expresses its content of hygroscopic water. This quantity is variable according to the character of the soil, and is constantly varying with the temperature; in- creasing during the night when it is collected from the at- mosphere, and diminishing during the day when it returns in part to the air. (See p. 104.) The amount of hygros- copic water ranges from 0.5 to 10 or more per cent. Value of these Distinctions. — These distinctions be- tween hydrostatic, capillary, and hygroscopic water, are nothing absolute, but rather those of degree. Hygroscopic water is capillary in all respects, save that its quantity is 202 ilow (R^ps pfiER. small, and its adhesion to the particles of soil more firm for that reason. Again, no precise boundary can always he drawn between capillary and hydrostatic water, espe- cially in soil having fine i)ores. The terms are neverthe- less useful in conveying an idea of the degrees of wet- ness or moisture in the soil. Roots Absorb Capillary or Hygroscopic Water,— It is from capillary or hygroscopic water that the roots of most agricultural plants chiefly draw a supply of this liquid, though not infrequently they send roots into wells and drains. The physical characters of soils that have been already considered suffice to explain how the earth acquires this water ; it here I'emains to notice how the plant is re- lated to it. As we have seen (pp. 35-38), the aerial organs appear incapable of taking up either vapor or liquid water from the air to much extent, and even roots continually exhale vapor without absorbing any, or at least without being able to make up the loss which they continually suffer. Transpiration of Water through Plants. — It is a most familiar fact that water constantly exhales from the surface of the ])lant. The amount of this exhalation is often very great. Hales, the earliest observer of this yjhenomenon, found that a sunflower whose foliage had 39 square feet of surface, gave off in 24 hours 3 lbs. of water. A cab- bage, whose surface of leaves equaled 19 square feet, ex- haled in the same time very nearly as much. Schleiden found the loss of water from a square foot of grass-sod to be more than 1^ lbs. in 24 hours. Schiibler states that in the same time 1 square foot of pasture-grass exhaled nearly 5^ lbs. of water. In one of Knop's more recent experiments, {Vs. St., VI, 239), a dwarf bean exhaled during 23 days, in September and October, 13 times its weight of water. In another trial a maize-plant transpir- ed 36 times its weight of water, from May 22d to Sept. 4th. According to Knop, a grass-plant will exhale its own TliE FREE WATEU OP THE SOIT.. 203 weight of water in 24 liours of hot and dry summer weather. Tlie water exhaled from tlie leaves must be constantly supplied by absorption at the roots, else the foliage soon becomes flabby or wilts, and finally dies. Except so far as water is actually formed or fixed within the plant, its absorption at the roots, its passage through the tissues, and its exhalation from the foliage, ai-e nearly equal in quantity and niutually dependent during the healthy ex- istence of vegetation. Circumstances that Influence Transpiration.— ^ Tlie structure of the leaf, including the character of the epi- dermis, and the number of stomata as they aflfect exhala- tion, has been considered in " How Crops Grow," (pp. 286-8). h. The physical conditions which facilitate evapora- tion increase the amount of water that passes through the plant. Exhalation of water-vapor proceeds most rapidly in a hot, dry, windy summer day. It is nearly checked when the air is saturated Avith moisture, and va- ries through a wide range according to the conditions just named. 0. The oxidations that are constantly going on, within the plant may, under certain conditions, acquire suflicient intensity to develop a jierceptible amount of heat and cause the vaporization of water. It has been repeatedly noticed that the process of flowering is accompanied by considerable elevation of temperature, (p. 24). In general, however, the opposite process of deoxidation preponder- ates with the plant, and this must occasion a reduction of tem.perature. These interior changes can have no apprecia- ble influence upon transpiration as compared Avith those that depend upon external causes. Sachs found in some of his experiments (p. 3G) that exhalation took place from plants confined in a limited space over water, Sachs be- 204- now eriods the opposite was noticed. f. Il^e temperature of the soil considerably affects the rate of transpiration by influencing the amount of absorp- tion at the roots. Sachs made a number of Aveighings up- on tAvo tobacco plants of equal size, potted in portions of the same soil and liaving their foliage exposed to the same atmosphere. After observing their relative transpiration when their roots Avere at the same temperature, one pot Avas Avarmed a number of degrees, and the result Avas in- variably observed that elevating the temjserature of the soil increased the transpiration. The same observer subsequently noticed the entire sup- pression of absorption by a reduction of temperature tc 41° to 43° F. A number of healthy tobacco and squash plants, rooted in a soil kept nearly saturated Avith Avater, were gioAving late in November in a room, the tempera- ture of which fell at night to the point just named. In the morning the leaves of these plants Avere so wilted that they hung doAvn like Avet cloths, as if the soil Avere 206 HOW CROPS FEED. completely dry, or tliey had been for a long time acted upon by a i)Owerful sun. Since, however, the soil was moist, the wilting could only arise 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 thj wilted plants stood, restored the foliage to its [jroper 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 diiferent plants are un- equally affected. The general rule nevertheless appears to be established that within certain limits the root absorbs mere vigorously at high than at low temperatures. The Amount of Loss of Water of Vea^etation in Wilt- ing has been determined by Ilesse ( Vs. St., I, 248) in case of sugai'-beet leaves. Of two similar leaves, one, gathered at evening after several days of dryness and sun- shine, contained 85.74°!^ of water; the other, gathered the next morning, two hours after a rain storm, yielded 89.57° |„. 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 i^lant 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 nutri- ment. There are, however, sti'ong grounds for believing that the current of water Avhich 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 the soil into the plant may go on, TUB FKEE WATEK OF THE SOIL. 207 although there be no ascending .-Kiueous curi-ent. (H. C. G., ijp. 288 and 340.) In accordance Avith these views, vegetation grows as Avell in the confined atniosplierc of green-houses or of Wardian Cases, Avhere tlie air is for tlie 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 'Tegetables 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 extreinely variable in its amount, is, so to speak, an accident to the plant and not a process essential to its existence or welfare, there are, on the other hand, facts which appear I > 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 ajjpearance, it remained entirely stationary in its development. ( Vs. St., I, 237.) Knop also mentions incidentally {Vs. St., I, 192) that beans, lupines, and maize, die when the whole pU^it is kept confined in a vessel over water. It is not, however, improbable that the cessfition of growth in the one case and the death of the plants in the other were due not so much to the checking of transpii-a- tion, which, as Ave have seen, is never entirely suppressed under these circumstances, as to the exhaustion of oxygen or the undue accumulation of carbonic acid in the narrow 208 HO"\v CKors feed. and confined atmosphere in wliich these results were noticed. On the whole, then, "\ve conclude from the evidence be- fore us that transpiration is not necessary to vegetation, or at least fulfills no very important oflices in the nutrition of plants. The entra'.K-e of water 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 sufiercd 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, Avas then provided, and the pot containing the Avilting 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. Tlie jiot of soil and the roots of the plant were thus enclosed in an atmosphere Avhich was constantly sat. urated, or nearly so, with w^atery vapor, while the leaves were fully exposed to the free air. It Avas now to be ob- served Avhether tlie water that exhaled from the leaves could be supplied by the hygroscopic moisture Avhich the soil should gather from the damp air enveloping it. This proved to be the case. The leaves, previously Avilted, re- covered their proper turgidity, and remained Iresh during^ the two months of June and July. Sachs, having shown in other experiments that plants situated precisely like this bean, save that the roots are not in contact with soil, lose Avater continuously and have no jiower to recover it from damp air (p. 3G) thus giA'cs us demonstration that the clay soil Avhich condenses vapor in its pores and holds it as hygroscopic water, yields it again to the plant, and thus becomes the medium through Avhich THE FKEK WATEK OF THE SOIL. 209 water Is continually carriccl 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 tlie 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 I'equire an occasional drenching with liquid water. Further investigations in this direc- tion are reqiiired 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 ])lant, 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 hlack huniKS (from beech-wood) and sand^ when the soil contained 12.3" |„ of water.* This soil, however, was capable of holding 46° |„ of capillary water. It results therefore that of its highest content of absorbed water 33.7" |„ (=46-12.3) was available to the tol>acco jjlant. 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 liy diyiiija'at 31 210 HOW CROPS FEED. saturation, furnish the tobacco }>lant with 44.1"!^ of its weiglit of water. A coarse sand that could hohl 20.8° ]„ of water was found to yield all but 1.5° ]„ to a tobacco plant. From these trials we gather with at least approximate accuracy the power of the plant to extract water fro:' these several soils, and by difference, the quantity of w;> ter in them that was unavailable to the tobacco plant. How do the Roots take Hyi^roscopic Water from the Soil ? — The entire plant, when living, is itself extremely hygroscopic. Even the dead plant letains a certain pro- portion of water with great obstinacy. Thus wheat, maize, starch, straw, and most air-dry vegetable substances, contain 12 to 15" |^ of water ; and when these matters are exposed to damp air, they can take up much more. Ac- cording to Trommer {Bodenkwide., p. 270), 100 parts of the following matters, when dry, absorb from moist air iu 12 24 4S 72 hours. Fine cut barley straw, 15 24 34 45 parts of water. " u rye 12 20 27 29 " " " " " white unsized 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 tlius among different kinds of matter is termed adhesive 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°, we shall find that the greater part of the moisture is easily expelled in a short time, but we 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 bo- tweeu the attracting bodies increases. This has been ex- THE FltEK ■WATJiU OK THE SOIL. 211 actly tlemonstrated 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 exeicise of its adhesive attraction, the Liver 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, itntil, at a certain point, still too small * for us to perceive, the attraction is nothing, or is neutralized by other opposing forces, and further adhesion ceases. Suppose, no\v, we bring in contact at a single point two masses of the same kind of matter, one of Avhich is satu- rated with hygroscopic water ;ind the other is perfectly dry. It is plain tliat the outer layers of water-particles adhering to the moist body come at once Avithin 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 o\'er the whole surface. If of two diff"erent 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 appiopriated 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 equWhv'ivm. Any cause which disturbs this equilibrium at once sets up motion of the hygroscopic water, which always j^roceeds from the more dry to thy less dry body. 212 HOAV CHOI'S FEED. The application of these principles to the question be- fore us is apparent. The young, active roots tliat 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 j^ropagates 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 Avlien 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 Avilts. Even then its content of water is many times greater than that of the soil. The living tobacco plant cannot contain less than 80°!^ of water, while the soils in Sachs' experiments contained but 12.3" |„ and 1.5° |„ respectively. When fully air-dry, vegetable matter retains IS'l^to 15° j^, of water, while the soil similarly dry rarely contains more thaq The plant therefore, especially when living, is much more hygroscopic than the soil. If roots are so hygroscopic, why, it may be asked, do they not directly absorb vapor of Avater from the air of the soil ? It cannot be denied that both tlie roots and fo- liage of plants are capable of ti)is kind of absorption, and that it is taking place constantly in case of the roots. The experiments before described prove, liowcver, tlat the higher oi'ders of plants absorb very little ia this W~^y« THE FREE WATEU OF THE SOn,. 213 too little, in fact, to l)o estimated by tlic methods hitherto employed. Sachs explains this as follows : Assuming that the roots have at a given temperature as strong an attrac- tion for Avater 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 pioportion to the weight of each contained in a given space. A cubic inch of water yields at 21'2° nearly a cubic foot (accurately, 1,696 times its volume, the barometer standing at 29.92 inches) of vapor. We may then a>u derChemie n. 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 which 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 ina- per, dryer portions of peat. When brown liumus remains wet and with imperfect access of air, it decomposes further, and in time is convert- ed into black humus. Black humus is invariably foimd in the soil beyond a little depth especially if it be com- pact, in the deeper layers of peat, in the interior of com- post heaps, in the lower portions of the leaf-mould of forests, and in the mud or muck of swamps and ponds. lllmic Acid aild lliuiiu, — The browu humus contains ORGANIC MATl'ERS OK TlIK SOIL. :i:iO (besules, perhaps, unaltered vegetable matters) ttvo char- acteristic ingredients, which have been designated tihnie add and ulmin, (so named from liaving been found in a brown mass that exuded from an ehn tree, vlmus being the Latin for ebu). These two bodies (lem:in0 now ( nop,; fkkd. which are acted upon Ly the carbonates of potash, soda, and lime, that become ini^redients of the soil by tlie solution of rocks, or by carbonate of ammonia brought down from the at\ 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 now CROPS PKEt>. and 100 grams of the solution left on evajjoration 13S mgrnis. of residue. The same amount of humus extract, that had been kept in a contiguous vessel containing no plant, left a residue of 136 mgrms. 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,) tlie 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 with 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, ulmates, crenates, and apocrenates of ammo- nia and potash. These 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 liumus. It is to be observed, however, that w^hat evi- dence they do furnish is in its favor. They prove eifec- 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 period of tiieir growth must tolerate^ if not ab- Borb, somewhat strong solutions of humus. Again, the cultivated soil invariably yields some humus ORGAN IC AtAlTKltS OP Til K SOIU S35 (we use this word ns a general collective term) to rain- water, and tlie richer the soil, as made so by manures and judged of by its productiveness, the larger ihe 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 (II. 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 nouiishment of plants because it and its compounds are insoluble; in the same book, however, {Die Chemle in Hirer Anwendung auf Agricultur und Physiol ogie^ 7th Ed., 18G2) he teaclies the doctrine that all the food of the agricultural plant exists in the soil in an insoluble form. This old objection, still m.iintained, tallies poorly with his new doctrine. The old objection, furthermore, is baseless, for the humates are as soluble as phosphates, which are gathered by every plant and from all soils. It has been the habit of Liehig and his adherents to teach that the plant is nourished exclusively by the last l^roducts of the destruction of organic matter, viz., by car- bonic acid, ammonia, nitric acid, and water, togetlier 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 sugar, the vinegar plant on acetic acid, tlie 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 tlOW CROPS FEED. absorb the juices of the roots of trees ; such are the beech drops {Epiphegus), pine drops (I-^erosporu), Indian pipe {3fo/io(rop(()/ the last-named also grows upon decayed vegL'table matter. The dodder ( Ct/scitti() 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 carbonic 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 Saussure, in his investigation just quoted from, says further: "After having thus demonstrated f the absor-p- ti(m of humus by the roots, it remains to speak of its as- similation by the jdant. One of the indications of this assimilation is derived from the absence of the peculiar color of humus in the interior of the ])lant, which has ab- sorbed a strongly colored solution of humate of potash, as compared to the different deportment of coloring matters * Dr. Luck (.Inn. C'hem. n. Pharm., 78, 85) has indeed ghown that the mistle- jw ( Visciim album) decomposes carbonic acid in the sunlight, but this plant has greenish-yellow leaves containing ddoroplnjll. t We take occasion here to say explicilly 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 by the plant, 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 experiment with water-extract of peat. If, now, Liebig be wrong in his ol)jection (and he has furnished no proof that his statement is true), then De Saussure lim demonstrated that humic acid is absorbed by plants. ORGANJC MATIKKS OF THE SOIL. 237 (such as Ink) which cannot nourish tlie 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 whicli 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. '•'•Polygomcm Persicaria (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, ixnderwent 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." Blot {Comptes Rendns, 1837, 1, 12) observed that the re8). Orjfanic Matters not Essential to the Growth of Crops. — Although, on the ianii, crops are rarely raised without the concurrence of humus or at least without its presence in the soil, it is by no meims 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). THE AMMONIA OV THE SOIL. In the chapter on the Atmosphere as the food of plants we have been led t) conclude that the element nitrogen., so indispensable to vegetation as an ingredient of albumin, etc., is supplied to p'ants exclusively by its compounds, and mainly by am,monia and nitric acid, or by substances which 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 tlie atmosphere, become of appreciable use THE AMMONIA OF THE SOIL. 239 to agricultural vegetation only after tlieir incorporation Avith the soil. Rain and dew are means of collecting tliem from the atmosphere, and, as Ave shall shortly see, the soil is a storehouse for them and the medium of their entrance into vegetation. This is therefore the ])roper place to consider in detail ilie origin and f )rmation of ammonia and nitric acid, so far as these points have not been noticed when discussing their relations to the atmosphere. Ammonia is formed iu tlic 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 that 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 water in the oxidation of certain metals, as iron and zinc, has been completely disproved by Will. (Ann. d. Ch. n. Ph., 4.5, pp. lOG-112.) Tlie ammonia eiicountei-ed in sucli experiments maj' liave been, 1st, tliat pi-e-existini^ in the pores of tlic substances, or dissolved in the wa- ter ()i)erated witli. Faraday {Researches in Chemistry and Physics, p. 143) has shown by a series of exact experiments tliat numerous, we may say all, porous bodies exposed to the air have a minute amount of ammonia adheriu;^ to them ; 2d, that which is generated in the process of testiu;^ or experimenting (as when iron is heated with potash), and formed by the action of an alkali on some compound oF nitrojien occurring in the materials of the experiment; or, 3d. that which results from tlie reduc- tion of a nitrite formed from free nitrogen by the action of ozone (pp. 77-83). Tlic Ammonia of the Soil. — a. Gaseous Ammonia as Garhonate. — Doussiugault and LcAvy, in their examination of the air contained la the interstices of the soil, p. 219, 24:0 HOW CPvOPS FEED. ' ' tested it for ammonia. In but two instances did tliey 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 weigh the ammonia were made in a light, sandy soil from which potatoes had been lately harvested. On the 2d of' September the field was manured with stable dung ; oni the 4th the first experiment was made, the air being taken, it must be inferred from the account given, at a depth of 14 inches. In a million parts of air by weight were found 32 parts of ammonia. Five days subsequently, after rainy weather, the air collected at the same place contained but 13 parts in a million. b. Ammonia phi/slcall^ 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 St en- house, Angus Smith, and others (p. 1G6). The soil cannot, however, ordinarily contain more than a minute quantity of physically 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 possible to condense in charcoal 98 times its volume of ammonia, by c(Joling the hot charcoal in mer- cury which does not penetrate it, or in a vacuum, and then bringing it directly into tlie ^:)r<>'e ammonia gas. The charcoal thus saturated with ammonia loses the latter rap- idly on exposure to the air, and Stenhouse has foimd by actual trial that charcoal exposed to ammonia and after- wards to air retains but minute traces of the former. Secondly, the soil when adapted for vegetable groAvth is moist or wet. The Avater of t!; > soil which covers the particles of carlh, ra'lur tliaii (lie particles themselves, must contai.i any absorbed auuuonia. Thirdly, there are THE AMMONIA OF THE SOIL. 241 in fertile soils substances which combiue chemically Avith ammonia. Tliat the soil does contain a certain quantity of ammo- nia adhering to the sjuiface of its particles, or, more prob- ably, dissolved in the hygroscopic water, is demonstrated by the experiments of Doussingault and Lewy just alluded to, in all of which ammonia was detected in the air in- cluded in the cavities of the soih In case ammonia Avere 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 Agronomie^ et ■., 1, p. 152) records that 100 parts of moist eartli i:)laced ia a vessel of about 2.]- quarts capacity containing 0.9 parts of (free) ammonia, absorbed during 3 hours a little more than 0.4 parts of the latter. In another trial 100 parts of the same earth dried, placed under the same circumstances, absorb- ed 0.28 parts of ammonia and 2.6 parts of water. Brustlein found th:it 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 jvist 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 O.OIG parts of the latter had been taken up by the earth. Tiie remainder was found to be dissolved in the Avater that had evaporated from the soil, and that formed a dew on the interior of the glass vessel Brustlein proved fui-ther 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 sliare 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 tilled with small fragments of moist soil. The 11 942 HOW CROPS FEED. ammonia was completely absorbed in the first part of the experiment. After about 7 cubic feet of air had streamed tlirough the soil, ammonia began to escape unabsorbed. The earth thus saturated contained 0.192" |„ of ammonia. A current of j^ure air was now passed through the soil as long as ammonia was removeii by it in notable quantity, about 38 cubic feet being required. By this means more than one-half the ammonia was displaced and carried oif, the earth retaining but 0.084" |^. Brustlein ascei'tained further that 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 witli 187 l^arts of water containing 0.889 parts of ammonia. The earth absoibed O.loT parts of ;immonia. It was now drained from tlie liquid :md 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 ammonia, " " " '• contained after the first dryini,' 0.083 " " " " " " " " " " second " 0.066 " " " " " " " " " " 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 wliich absorbed ammonia escapes from the soil is greatly increased by the evaporation of water. Bru.stlein 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 aTumonia in a sliorter time by being thrice moistened and dried. According to Knop ( Vs. /St., Ill, p. 222), the single THE AMMONIA OF THE SOIL. 243 proximate ingredient of soils that under ordinary cir- cunistances exerts a considerable surface attraction for ammonia gas is clay. Knop examined the deportment of ammonia in this respect towards sand, soluble silica, pure alumina, carbonate of lime, carbonate of magnesia, hy- drated sesquioxide of iron, sulphate of lime, and humus. To recapitulate, the soil contains carbonate of ammonia physically absorbed in its pores, i. e., adhering to the sur- faces of its particles, — as Knop believes, to the particles of clay. The quantity of ammonia is variable and con- stantly varying, being increased by rain and dew, or ma- nuring, and diminished by evaporation of water. The actual quantity of physically absorbed ammonia is, in general, very small, and an accurate estimation of it is, perhaps, impracticable, save in a few exceptional cases. c. Chemically combined Ammonia. — The reader will have noticed that in the experiments of Brustlein just quoted, a greater quantity of ammonia was absorbed by the soil than afterwards escaped, either when the soil was subjected to a current of air or allowed to dry after moist' ening with water. This ammonia, it is therefore to be be- lieved, was in great part retained in the soil in chemical combination in the form of compounds that not only do not permit it readily to escape as gas, but also are not easily washed out by water. The bodies that may unite with ammonia to comparatively insoluble compounds are, 1st, the organic acids of the humus group* — the humus acids, as we may designate them collectively. The salts of these acids have been already noticed. Their com- * Mulder asserts that the affinity of iihiiic, luimic, and apocrenic acids for ammonia is so strong tliat they can only be freed from it liy evaporation of their solutions to dryness with caustic potash. Boiling with carbonate of potash or carbonate of soda will not suffice to decompose their ammonia-salts. We hold it more likely that the ammonia which requires an alkali for its expulsion is generated by ihe decomposition of the organic acid itself, or, if that be desti- hite of nitrogen, of some nitrogenous substance admixed. According to Bous- eingault, ammonia is completely removed from humus by boiling vn.iu water au4 caustic magnesia, 244 IIOAV^ CROPS FEED. pounds with ammonia are freely soluble in water; hence strong solution of ammonia dissolves them from the soil. But when ammonia salts of these acids are put in contact with lime, magnesia, oxide of iron, oxiile of manganese, and alumina, the latter being in prej^onderating quantity, there are formed double compounds which are insoluble or slightly soluble. Since the humic, idmic, crenic, am, apocrenic acids always exist in soils which contain organic remains, there can be no question that these double salts are a chemical cause of the retention of ammonia in the soil. 2d. Certain phosphates and silicates hereafter to be no- ticed have the power of forming difficultly soluble com- pounds with ammonia. Reserving for a subsequent cliapter a further discussion of the causes of the chemical retention of ammonia in the soil, we may now appropriately recoimt the observations that have been made regarding the condition of the am- monia of the soil as regards its volatility, solubility, etc. Volatility of the Ammonia of the Soil. — We have seen that ammonia may esca])e from the soil as gaseous carbonate. The fact is not only true of this substance as physically absorbed, but also under certain conditicms of that chemically combined. When we mingle together equal bulks of suli)hale of lime (gypsum) and carbonate of ammonia, both in the state of fine powder, the mixture begins and continues to smell strongly of ammonia, owing to the volatility of the carbonate. If now the mixtuie be drenched with water, the odor of ammonia at once ceases to be perceptible, and if, after some time, the mixtuie be thrown on a filter and washed with water, we shall find that what remains undissolved contains a large proportion of carbonate of lime, as may be shown by its dissolving in an acid with effervescence; Avhile the liquid that has pnssed the filter contains sulphate of ammonia, as may be learned by the appropriate chemical tests or by evaporat- ing to dryness, when it will remain as a colorless, oiloi less. TTtK AMMONIA OF 'tU\t SOtt, ^45 crystalline solid. Double decomposition lias taken place between the two salts under the influence of water. If, again, the carbonate of lime on the filter be reunited to the liquid filtrate and the whole be evaporated, it will be found that when the water has so far passed off" that a moist, pasty mass remains, the odor of ammonia becomes evident again — carbonate of ammonia, in fact, escaping by volatilization, while sulphate of lime is reproduced. It is a general law in chemistry that wlien a number of acids and bases are together, those which under the circum- stances can produce by their union a volatile body will ixnite, and those which under the circumstances can form a solid body will unite. When carbonic and sulphuric acids, lime and ammonia, are in mixture, it is the circu instances which determine in what mode tliese bodies combine. In presence of nmch water carbonate of lime is formed be- cause of its insolubility, water not being able to destroy its solidity, and sulphate of ammonia necessarily results by the union of the other two substances. When the wa- ter is removed by evaporation, all the possible compounds between carbonic and sulphuric acids, lime and am- monia, become solid ; the compound of ammonia and car- bonic acid being then vohitile, this fact determines its formation, and, as it escapes, the lime and sulphuric acid can but remain in combination. To apply these principles : When carbonate of ammo- nia is brought into the soil by rain, or otherwise, it tends in presence of much water to enter into insoluble combi- nations so far as is possible. When the soil becomes dry, these compounds begin to undergo decomposition, provid- ed carbonates of lime, magnesia, potash, and soda, are present to transpose with them ; these bases taking the place of the ammonia, while the carbonic acid they were united with, forms with the latter a volatile compound. In this way, then, all soils, for it is probable that no soil exists which is destitute of carbonates, may give ofi'at th© 246 now CROPS fEEI). surface in dry weatlier a portion of the ammonia Avhich before was cliemically retained within it. Solubility of the Ammoiiia of the Soil.— The distinc- tions between physically adliering and cliemically combin- ed ammonia are difficult, if not impossible, to draw with acciuaey. In what follows, therefore, we shall not attempt to consider them separately. When ammonia, carbonate of ammonia, or any of tlie following ammoniacal salts, viz., chloride, sulphate, ni- trate, and phosphate, are dissolved in water, and the solu- tions are filtered through or agitated with a soil, we find that a portion of ammonia is invariably removed from so- lution and absorbed by the soil. An instance of this ab- sorbent action has been already given in recounting Brustlein's experiments, and further examples will be here- after adduced when we come to speak of the silicates of the soil. The points to which we now should direct at- tention are these, viz., 1st, the soil cannot absorb ammo- nia completely from its solittions ; and, 2d, the ammonia which it does absorb may be to a great degree dissolved out again by water. In other words, the compounds of ammonia that are formed in the soil, though comparatively insoluble, are not absolutely so. Henneberg and Stohmann found that a light, calcareous, sandy garden soil, when placed in twice its weight of pure water for 24 hours, yielded to the latter joVo of its weight of ammonia (=0.0002" |J. 100 parts of the same soil left for 24 hours in 200 parts i of a solution of chloride of ammonium (containing 2.182' of sal-ammoniac =0.693 part of ammonia), absorbed 0.112 j part of ammonia. Half of the liquid was poured off and its place supplied with pure water, and the whole left for 24 hours, Avhen half of this liquid was taken, and the process of dilution was thus repeated to the fifth time. In the portions of water each time removed, ammonia was estimated, and the result Avas that the water added dis- THE AMMONIA OF THE SOIL. 247 'olved out nearly one-half tlie ammonia whieli tlie earth at first absorbed. The 1st dilution removed from the soil 0.010 "2d " " " " " ...0.009 " 3d " " " " " 0.014 " 4tli " " " " " 0.011 " 5th " " " " " 0.009 Total 0.053 Deducting 0.053 from the quantity first absorbed, viz., 0.112, there remains 0.059 part retained by tlie soil after five dilutions. Knop, in 11 decantations, in which the soil was treated with 8 time* its weight of water, removed 93° !„ of the ammonia wliich the soil had previously ab- sorbed. We cannot doubt that by repeating the washing sufficiently long, all the ammonia would be dissolved, though a very large volume of water would certainly be needful. Causes which ordinarily prevent the Accumulation of Ammonia in the Soil. — The ammonia of the soil is con- stantly in motion or suffering change, and does not ac- cumulate to any great extent. In summer, the soil daily absorbs auimonia from the air, receives it by rains and dews, or acquires it by the decay of vegetable and animal matters. Daily, too, ammonia wastes from the soil — by volatili- zation— accompanying the vapor of water which almost unceasingly escapes into the atmosphere. When the soil is moist and the temperature not too low, its ammonia is also the subject of remarkable chemical transformations. Two distinct chemical changes are be- lieved to affect it ; one is its oxidation to nitric acid. This process we shall consider in detail in the next section. As a result of it, we never find ammonia in the water of or- dinary wells or deep drains, but inste-nd always encounter nitric acid united to lime, and, perhaps, to magnesia and alkalies. The other chemical change appears to be the alteration of the compounds of ammonia with the humus 248 nq\y chops pked. acids, wlicrel)}' hoJies result which arc no h)nger soluble in Avator, and which, as such, arc probably innutritions to plants. These substances are quite slowly decomposed when put in contact, especially when heated with alkalies or caustic lime in the presence of water. In this decom- jjosition ammonia is reproduced. These indifferent nitrog- enous matters appear to be analogous to a class of sub- stances known to chemists as amides, of Avhich asparagin, a crystallizable body obtained from asparagus, young peas, etc., and urea and \iric acid, the characteristic ingredients of urine, are examples. Further account of these matters will be given subsequently, p. 376. Quantity of Ammonia in Soils. — Formerly the amount of ammonia in soils Avas greatly overestimated, as the re- sult of imperfect methods of analysis. In 1846, Krocker, at Liebig's instigatiim, estimated the nitrogen of 22 soils, and Liebig published some ingenious speciilations in which all this nitrogen was incorrectly assumed to be in the form of ammonia. Later, various experimenters have attempt- ed to estimate the ammonia of soils. In 18."35, the writer examined several soils in Liebig's laboratory. The soils were boiled for some hours Avith water and caustic lime, or caustic potash. The ammonia that Avas set free, distill- ed off, and its amount Avas determined by alkalimetry. It Avas found that however long the distillation was kept up, ammonia continued to come over in minute quantity, and it Avas probable that this substance Avas not simply expelled from the soil, but Avas slowly formed by the ac- tion of lime on organic matters, it being Avell known to chemists that many nitrogenous bodies are thus decom- posed. The results Avere as follows : White sandy loam distilled with caustic lime gav« Yellow clav " •' " ' " " -'00047 iciiowciay (0.0051 " " " " " potash " " one " 0.0075 Black garden soil " " " lime " " ♦wo *' \ o 0951 THIO AMMONIA OK I'M K SOIL. 249 The fact that caustic potasli, 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 oif 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 {A(/ronomie, 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 anmionia when boiled with milk of lime or solutions of potash. The results of Boussingault here follow. Localities. Quantity of Ammonia per cent. Liebfrauenberg, Alsatia 0.0022 Bischwillor, " 0.0020 Merckwiller, " 0.0011 Bechelbronn, " 0.0009 Mittelhausbei-gen, " 0.0007 He Napoleon, Mulhouse, 0.0006 Argentan, Onie, 0.0060 Quesnoy-snr-Deule, Nord, 0.0012 Eio Madeira, America, 0.0090 Eio Trombetto, " 0.0030 RioNegro, " 0.0038 Santarem, " 0.0083 He du Salut, " 0.0080 Martinique, " 0.0085 Rio Cupari, (leaf mold,) " 0.0525 Peat, Paris, 0.0180 The above results on French soils correspond with those obtained more recently on soils of Saxony by Knop and Wolif, who have devised an ingenious method of estimat- ing ammonia, Avhich is founded on altogether a different l)rinciple. Knop and "Wolff measure the nitrogen 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, which is used in mixture with broimina Kud caustic soda. 11* 26(i now cuors feicix Azotometer. {Chemisc/ies Centralhlatt, 1860, pp. 243 and 534.) By this method, which gives accurate results when ap- phed to known quantities of ammonia-salts, Knop and Wolff obtained the following results : Ammonia in dry soil. Verj' li<,^ht sandy soil from birch forest 0. 00077" jo 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 unmanured soils its percentage is scarcely greater than in the atmospheric waters. The Quantity of Ammonia fluctuates, — Boussingault 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 sufficed in this case to double the content of am- monia. The quantitative fliuctuations of this constituent of the soil has been studied further both by Boussingault and by Knop and Wolff. The latter in seeking to answer the THE NITKK' ACID OF TIIK SOIt. 251 question — " IIow groat 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, calcar(>ous 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 iiregularly as in the other instance. Knop and WollF 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 tliat deep well and drain- waters are destitute of ammonia. Boussingault has discovered [Agrononiie, 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. NITRIC ACID (NITRATES, NITROUS ACID, AND NITRITES) OF THE SOIL. Nitric acid is formed in the atmospliere by the action of ozone, and is brought down to the soil occasionally in the free state, but almost invarial)ly 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. ^53 now mors fked. In the soil, nitric acid is always combined ■\vitli an alkali or alkali-earth, and never exists in the free state in apjireciable 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 vitrates of potash, coda, lime, magnesia, andiron. Nitrate of Potash (K NOJ is the substance com- mercially known as niter or saltpeter. When pure (refin- ed saltpeter), it occurs in colorless prismatic crystals. It is freely soluble in water, and lias 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 tropicil and tempei'ate climates, by^ simply leaching tlie earth with Avater and evaporating the solution thus obtained. It is also made in artificial niter- beds or jDlantations in many European countries. It is likewise prepared artificially from nitrate of sotia and caustic potash, or chloride of potassium. The chief use of the commercial salt is in the manufacture of gunpowder and fireworks. Sulphur, charcoal, (which are ingredients of gunpow- der), and other combustible matteis, 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 ]iampa of Tamarugel, 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 has in general a TIIK NITUIO ACID OK 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; il 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 ni 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. Nitrate of Lime (Ca^NO^) 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 i)otash in artificial niter-beds, IVitrate of Maj^nesia (Mg2N0J closely resembles ni- trate of lime in external chaiacters and occurrence. It may be prepared by dissolving magnesia in nitric acid and evaporating t.he sohition. 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 ( F! St., V, 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 arc, in fact, rhomboiUal, 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 towards 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 soii, 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 hme. 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 i:)robable, 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 apj)ear. 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 tliree 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 NiTiiic Aciij oy t:ik soil. 255 The nitrates accumulate near the surface when no rain falls to dissolve and wash them down — when 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 fiom Lieb- frauenberg [Agvonomie, etc., T. II, p. 10) conveys an idea of the progress which nitrification may make in a soil un- der cultivation, and highly 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 Mas repeated four times at various intervals. The subjoined statement gives the per cent of nitiatcs 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 " — irth 0.0(5 222 " — 2d September, 0.18 631 " -17th 0.22 760 " — 2d October, 0.21 728 The formation of nitrates proceeded rapidly during the h' at of summer, but ceased by the middle of September. T^hether this cessation was due to the lower temperature or to the complete nitrification of all the matter existing in the soil ca))able of this change, or to decomposition of nitric acid by the reducing action of organic matters, • The fi^rures jrivpn above arc abhrpvitited fn^iu the originals, or reduced tO Kuglisb dcnominatiouij witU a trifling loss of exactu^sij. 256 HOW 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 thaf 200 lbs. per acre of the nitrates of potash or soda is a large dressing upon grain or grass. Had tlie earth been exposed to occasional rain, its analysis Avould have indi- cated a much less percentage of nitrates, because the salt woidd have been Avashcd 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 from the same garden after 14 days of hot, dry weather. 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 29th of August it rained daily at Liebfrauenberg, more than two inches of water falling duiing 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, windy 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 remembered, was porous and sandy, and had been very heavily manur- ed with well-rotted compost for several centuries. Boussingault has examined more tiian sixty soils of ev- ery variety, and in every case but one found an apprecia- ble quantity of nitrates. Knop has also estimated nitric acid in several soils ( Versuchs jSt., V, 143). Nitrates are almost invariably found in all well and river waters, and in quantities larger thaii exist in rain. "We may hence as- sume that nitrification is a process universal to all soils, and that nitrates are normal, thougli, for the reasons stat- ed, very variable ingredients of cultivated earth. The Sources of the IVitric Acid which is formed within the Soilf — Nitric acid is produced — a, from ammonia^ THE NITIM oi'^ TU.: sui:.. '257 either that absorbed by the sol from the atmospliere, or tliat originating in the soil itself by the decay of nitrog- enous organic matters. Knoj) made an experiment with a sandy loam, as follows : The earth was exposed in a box to the vapor of ammonia for three days, was then mixed thoroughly, spread out thinly, moistened with pure water, and kept sheltered from rnin until it became dry again. At the beginning of the experiment, 1,000,000 parts of the earth contained 52 parts of nitric acid. During its exposure to the air, Avhile moist, the content of nitric acid in this earth increased to 591 parts in 1,000,000, or more than eleven times ; and, as Knop asserts, this increase took place at the expense of the ammonia which the earth had absorbed. The conversion of ammonia into nitric acid is an oxidation expi*essed by the statement 2 NH3 + 40 = NH, NO3 + 11,0. * The oxygen may be either ozone, as already explained, or it may be furnished by a substance which exists in all soils and often to a considerable extent, viz., sesquioxide of iron. This compound (Fe,^ O3) readily yields a portion of its oxygen to bodies which are inclined to oxidize, be- ing itself reduced thereby to pi-otoxide (FeO) thus : — Fe, O3 = 2 FeO + O. The protoxide in contact with the air quickly absorbs common oxygen, passing into sesqui- oxide again, and in this way iron operates as a carrier of atmospheric oxygen to bodies whicli cannot directly com- bine with the latter. The oxidizing action of sesquioxide of iron is proved to take place in many instances ; for ex- ample, a rope tied around a rusty iron bolt becomes " rot- ten," cotton and linen f ibrics are destroyed by iron-stains, the head of an iron nail corrodes away the wood sur- rounding it, when exposed to the weather, and after suf- * The above equation represents l)iit one-half of the ammonia as converted into nitric acid. In the soil the carbonates of lime, etc., would separate the nitric acid from the remaining ammonia and leave the latter in u condition to be oxidized. 258 HOW CROPS FEED. ficient time this oxidation extends so far as to leave the board loose upon the nail, as may often be seen on old, unpainted wooden buildings. Direct experiments by Knop ( Yersuchs St., Ill, 228) strongly indicate that ammonia is oxidized by the agency of iron in the soil. b. The organic matters of the soil, either of vegetable or animal origin, which contain nitrogen, suffer oxidation by directly combining with ordinary oxygen. As we shall presently see, nitrates cannot be formed in the rapid or putrefactive stages of decay, but only later, when the process proceeds so slowly that oxygen is in large excess. When the organic matters are so largely dilut- ed or divided by the earthy parts of the soil that oxygen greatly preponderates, it is probable that the nitrogen of the organic bodies is directlj^ oxidized to nitric acid. Otherwise ammonia is first formed, which is converted in- to nitrates at a subsequent slower stage of decay. Nitrogenous organic matters may perhaps likewise yield nitric acid when oxidized by the intervention of hydrated sesquioxide of iron, or other reducible mineral compounds. Thenard mentions {Comptes Mendus, XLIX, 289) that a nitrogenous substance obtained by him from rotten dung and called fumic acid* when mixed with carbonate of lime, sesquioxide of iron and water, and kept hot for 15 days in a closed vessel, was oxidized with formation of carbonic acid and noticeable quantities of nitric acid, the sesquioxide being at the same time reduced to protoxide. The various sulphates that occur in soils, especially sul- phate of lime (gypsum, plaster), and sulphate of iron (copperas), may not unlikely act in the same manner to convey oxygen to oxidable substances. These sulphates, in exclusion of air, become reduced by organic matters to sulphides. This often happens in deep fissures in the earth, and causes many natural waters to come to the sur- According to Mulder, impure liumate of ammoaia. TUB 2rL,'a-)ir ni;ittcrs in KITROGBNOUS ORGANIC MAITEIIS 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 {An?i. Ch. ic. PA., 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, Kitthausen, Wolff, and others, with simi- lar results. In all but his latest writings, Liebig has regarded thi\ 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 nitrates. The soil itself contained — Total nitrogen, 0.2G1 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 2)er cent of the air-dry soil, and in lbs. av. per acre, taken to the depth of 17 inches. In another column is also given the ratio of nitrogen to carbon in the organic matters. [Agfrononiie, T IT, pp. 14-21.) 27Q IIOAV CROPS FEED. Ammonia, Nitbates, ^yn Organic Nitkogen of various Boils. Ammonia. Nitrate of i potash. j\itroyen. in org. combfn. Soils. libs. lbs. lbs per per per per per per 111 cent, jacre cent acre cent. acre ^ fLicbfrauenbercr. lii:ht ?ard. soil 0.(i()i-J 100 0.0175* 8-5| 0.259 12970 1:9 3 " I Bischwillcr, li;,'lit j,'ardoa soil... .O.OOCdi 100 5 1 Bcchelbronn. wheal field clay, 'o.oood' 45 0.1,520 7(!30 0.295 14755 1:9.7 0.0015 75 0.139 69S5 1:8.2 ^ Armenian, rich T)asturc 0.(IO',:(F -150 O.0046 0.0004 230 20 ' 0.513 0.143 25050 1:8 «• fRio Madeira, sugar field, clay 7i;o! 1:0.3 ^ RioTromhctto.forestheavydo. o.oii-io, Is:! 0.0001 5 0.119 5955, 1:4.9 « 1 Rio Negro, prairie V. fine sand. (l.OO;;Si I'.io 0.0001 5 O.OOS 3440 1:5 « £ J Santarem, cocoa plantation.. O.00S3 •< j Saracca, near Amazon, loam.. lO.OO^'i 415 0.0011 55, 0.649 32450, 1:11 2io; none 1 0.102 9U;0 1:8.2 J3 RioCupari, rich leaf mould.... (). 0505 " 0.CS5 34250; 1:18.8 c lies du Salut, French Guiana... l).0:):^0 400 0.0043 13215 0.M3 27170, ]:11.T ,2 1 Martinique, suirar field |l).0055 275 O.OlKfi 1 900 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 Liebfrauenberg garden, the disparity is very great. Nature of the Nitrogenous Org.anic Matters. Amides. — Hitherto we have followed Mulder in assuming that the humic, ulmie, crenie, and apocrenic acids, are destitute of nitrogen. Certain it is, however, that natural humus is never destitute of nitrogen, and, as we 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 humate of ammonia. It is more accordant with general analogies to + .\mmonia contains 82.4 per cent of iiilroQ-on. ^ Nitrate ot ootash contains Ti.b pjr cent of nitrogea. NJTnOOKXOrfl OnCAXIC Jr.VTTET^S OP THE ROIL. 277 suppose that it is (joierated by the action of the alkali, In fact, there are a large number of bodies whicli manifest a similar depovjer with a certain age. In 1868, Wagner {Vs. >S?., XL, 288) obtained exactly' the same results as Ilampe. He found also that a maize- seedling, allowed to vegetate for two weeks in an artificial soil, and then placed in the nutritive solution, with phos- phate of ammonia as a source of nitrogen, grew nor- mally, without any symptoms of disease, Wagner ob- tained one plant weighing, dry, 26' |^ grams, and carrying 48 ripe seeds. In experiments with carbonate of ammonia, Wagner obtained the same negative result as Beyer had experienced in 1866. Beyer reports {Vs. St., XI., 267) that his attempts to nourish the oat-plant in solutions containing ammonia- salts as the single source of nitrogen invariably failed, although repeated through three summers, and varied in several ways. Even with solutions identical to those in which maize grew successfully for Ilampe, the oat seed- lings refused to increase notably in weight, every precau- tion that could be thought of being taken to provide favorable conditions. It is not imiDossible that all these failures to supply plants with nitrogen by the use of am- monia-salts depend not upon the incapacity of vegetation to assimilate ammonia, but upon other conditions, unfa- vorable to growth, which are inseparable from the meth- ods of experiment. A plant gro\ving in a solution or in pure quartz sand is in abnormal circumstances, in so for that neither of these media can exert absorbent power sufficient to remove from solution and make innocuous any substance which may be set free by the selective agency of the plant. Further investigations must be awaited befoi-e this point can be definitely settled. It is, however, a matter CONSTITUTIOX OK THE SOIL. 805 of little practical importance, since ammonia is so sparse- ly supplied 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.— INGRE. DIENTS WHOSE ELEMENTS ARE DERIVED FROM ROCKS. § 1. GENERAL VIEW OF THE CONSTITUTION OF THE SOIL AS RELATED TO VEGETABLE NUTRITION. Inert, Active, aaid Reserve Matters. — In all cases the soil consists in gre.at ])art of matters thnt are of no direct or present use iu feeding the plant. The cliemical nature of this inert portion may vary gre.atly Avithout coi-respond- ingly influencing the fertility of tho soil. Sand, either quartzose, calcareous, micaceous, fi'ldspatliic, hoi-nblendic, or augitic ; clay in its many varieties ; chalk, ocher (oxide of iron), humus ; iu short, any porous or granular material that is insoluble and little alterable by ^veather, may con- stitute the mass of the soil. The physical and mechanical characters of the soil are chielly influenced by those ingre- dients which preponderate in quantity. Hence Ville has quite appropriately desi^'nated them the "mechanical agents of the soil." They aifect fei'tility principally as they relate the plant to moisture and to temperature. They also have an influence on croj)S by gradually assum- ing moie active forms, and yielding nourishment as the result of chemical changes. In generalj it is probable 306 HOAV CROPS FEED. that 99 per cent and more of the soil, exclusive of water, does not in the slightest degree contribute directly to the 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 off no more than 400 lbs. per acre. From the data given on page 158, we may assume the weight 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 the 12 inches next the surface. Accordingly no less than 100 full crops of hay would require to be taken off to consume one per cent of the Aveight of the soil to this depth. "We confine our calculation to the ash-ingredients 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 2:)roper 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 should we incorporate with such a soil a few thousand 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. Sliould we add to our acre of pure quartz the ashes of a hay crop, 400 lbs., and a j^roper 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 he fertile for one crop only, and after the removal of the latter it would be as sterile aa CONSTITUTION^ OF THE SOIL. 3O7 fcefore. We gather, then, that there are three items to be regarded in the simplest view of the chemical compo- sition of the soil, viz., the inert mechanical basis, the presently available nutritive ingredients, and the reserve matters from which the available ingredients are supplied as needed. In a previons chapter we have traced the formation of the soil from rocks by the conjoint agencies of mechanical and chemical disintegration. It is the i>erpetual operation of these agencies, especially those of the chemical kind, which serves to maintain fertility. The /ragments of rock, and the insoluble matters generally that exist in the soil, are 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 attempts have been made to distinguish in fact between these three classes or conditions of soil-ingredients ; but the distinction is to us one of idea only. We 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 th?.t occur within it. We cannot, therefore, dissect the soil and decide what and how much is immediately available, and what is not. Furthermore, tlie soil is chem- ically so complex, and its relations to the plant are so com- plicated by physical and physiological conditions, that we may, perhaps, never arrive at a clear and unconfused idea of the mode by which it nourishes a crop. ISTevertheless, what we have attained of knowledge and insight in this direction is full of value and encoui-agemcnt. Deportment of the Soil towards Solvents,— When wo 308 HOW CROPS FEED. put a soil in contact with water, certain matters are dis- solved in this liqui'l. It has been thought that the sub- stances taken up by water at any moment are those which at that time represent the available plant-food. This no- tion was based upon the supposition that the plant cannot feed itself at the I'oots save by matters in solution. Since Liebig has brought into prominence the doctrine that roots are able to attack and dissolve the insoluble ingredients of the soil, this idea is generally regarded as no longer tenable, Agam, it has been taught that the reserve plant-food of the soil is represented by the matters whicli acids (hydro- chloric or nitric acid) arc c;ipable of bringing into solu- tion. This is true in a certain rough sense oidy. The action of hydrochloric or nitric acid is indeed analogous to that of carbonic acid, Avhich is the natural solvent ; but between the two there are great diiferences, independent of those of degree. Although we have 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 of 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 be 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 Avhen the ordinary standards of solubility arc re- ferred to. The glass bottle vrhich mav contain water f^r AQUEOUS SOKUTIOX OF THE SOIL. 309 years without perceptibly yielding aught of its mass to the liquid, does, nevertheless, slowly dissolve. We may make its solubility perceptible by a simple expedient. Pulver- ize the bottle to the fiiiest 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. 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 water. In 1852 Verdeil and Risler examined 10 soils from the grounds of the Instltut Agronomlque, at Versailles. In each case about 22 lbs. of the fine earth were mixed with pure lukewarm water to the consistence of a thin pap, and after standing several hours with frequent agitation the water vras poured ofi"; this process was repeated to the third time. The clear, faintly yellow solutions thus obtained were evaporated to dryness, and the residues were analyzed with results as folloAvs, per cent • 310 now CKOPS FEED, NameqfMdd, etc. Mall .-..[Walk Pheasant Turf Queen's Ave.. Kitchen Gard. S_''.tory..[Galy Clay soil of Lime soil, do. Peat boir Sand pit 43.00 70.50 3.5.00 44.00 37.00 33.00 57.00 29.90 65.00 5().00 03.00 67.00 48.00;52.U0 47.00 53.00 46.00 54.00 47.04153.06 Per cent of Ash. ■^^• 48.9:2 31.49' 4S.45| 43.75! 30.60 18.70 18.75 17.21 34.43 32.31 25.60 35.29 6.08 6.08 12.35 24.25 45.61 48.50 30.61 34.. 59 4.27 2.16 2.75 6.32 11.20 18.50 3 9.00 0.92 8.10 81 1..55i 0.62 0.474race I.21I - 2. 00, trace trace [trace 3.721 0.50 0.95 trace 5.15 1.02 1.55 ^■^.°s Here we notice that in almost every instance all the mineral ingi-edients 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 jo>-o- portio7i of matters which water is capable 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, Upper Austria, treated with six times its quantity of cold water (Jarriges). II. Excellent beet soil (but clover sick) from Schlan- staedt, Silesia, treated with 5 times its quantity of cold water (Jarriges). III. Fair wheat soil, Seltendorf, Silesia, treated with 5 times its weight of cold water (Peters). IV. 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 SOLUTIOT^ OF THE SOIL. Sll "Vn. Garden soil, Heidelberg — 3-fold amount of cold Water (Grouven). VIII. Poor, sandy soil, Bickendorf— 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 •weight of water (R. Hoffmann). XII. Sandy soil, JMoldau Valley, Bohemia, treated with twice its weight of water (R. Hoffmann). XIII. Salt meadow, Stollhammer, Oldenburg (Hai-ms). XIV. Excellent beet soil, Magdeburg (Hellriegel). XV. Poor beet soil, but good grain soil, Magdeburg (Hellriegel). XVI. Experimental soil, Ida-Marienhiitte, Silesia, treat- ed with 2^ times its weight of cold water (Kiillenberg). XVII. Soil from farm of Dr. Geo. B. Loring, Salem, Mass., treated with twice its weight of water (W. G. Mixter). MATTERS DISSOLVED BY WATER FROM 100,000 P.^RTS OF VARIOUS SOILS. I s.- «• •e i «^ 1 1 e ^•S i tg-^ 1 /„ 6'/, 13'/2 1 22 87 VII........ 2.3 l'/2 7 4'/2 l'/2 IH 1 38 2 30 110 VIII 8 % V„ 3'/, trace 1 l'/2 20 — 10 45 IX 33'/, 164 :;.. i'- 9 12 5 trace i" 18 302 trace trace — 70 147 X 449 i 1095 XI 92 1 44 2V„ 21 2 24 1 trace trace trace trace trace 1 trace 2 2:30) 425 XII 33| 39>/, XIII 79 43 16 476 — 407 144 58 — 170 1393 XIV 19 8 3 5 1 4 4 20 3 88 150 XV 26 5 3 4 1 5 15 2 S3 147 XVI 6'/i 2 1 3 Vi .5>/, 3>/2 12 7 12 53 XVII 8 2 6!4 1 '1,0 7'/2 l'/2 17 12! 55'/$ 312 HOW CROPS TEED. Tlie foregoing analyses (all the author has access to that are sufficiently detailed for the purj^ose) indicate 1. That 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 plant-food, as, for example, phos« phoric acid. 2. That poor, sandy soils (VIII, 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, VII, IX, XIV, XV, XVI), yield, 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 num.ber of cases essential elements of ])lant- food, viz., phosphoric acid and sulphuric acid, are wanting, or their j^resence 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 occuis, sufficient to saturate the ground. Dr. E. Wolff, at Moeckern. Saxony, made two analyses of the A\ater collected in the middle of May from newly \aid tiles, when, after a period of no flow, the tiles had AQtrEOUS SOLUTION OF THE SOIL. nis been running full for several hours in consequence of a heavy rain. The soil was of good quality. He found : IN 100,000 PARTS OF DRAIN-WATER. Rye field. Meadow. Organic matters, 2.6 3.3 Carbouate of lime, 21.9 4.4 " " magnesia, 3.1 1.4 " " potash, 0.3 0.5 " " soda, 1.9 1.4 Chloride of sodium, 2.3 trace Sulphate of potash, 1.2 trace Alumina, ) Oxide of iron, ) 0.8 0.6 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 wateis were collected from the pipes (4-5 ft. deep) of thorough-di-ained fields in December, 1855, and in most cases were the Jjrst 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. Hoy. Ag. jSoc, XVII, 133.) IN 100,000 PAHTS OP DRAIN-WATER. W/wat field. Hop Hop field. 4 Wheat field. 5 W/t^ai field. 6 1 Hop Hop field, field. Potash Soda Lime Maj^iiesia Oxide or iron and ahimina Silica Chlorine Sulphuric acid Phosphoric acid Nitric acid Ammonia Soluble organic matter Total ^ 14 trace 1.4.3 6.93 0.97 0.59 1.35 1.00 2.35 trace 10. ai 0.025 10. OU trace 3.10 10.24 3.. 31 O.OT 0.G4 1.57 7.35 0.17 21. ('5 0.025 10.57 158.1 0.03 3.23 8.64 3.54 0.14 0.78 1.84 6.23 trace 18.17 0.02c 17.85 0.(17 1.24 0!58 none 1.71 1.16 2.44 trace 2.78 0.017 8.00 trace 2.03 3.60 0..30 1.85 2.57 1.80 1.84 0.11 4.93 0.025 8.14 0.01 h-ace 2.00 4.57 8 31 18.50 1.33 I 3.57 0.50 0.93 1.73 4.45 0.09 11.50 0.025 O.T 1.21 3.74 13.58 0.17' 16.35 0.009 10.57 .5251 21.227 I 27.195 39.455172.979 814 TTO\r rnoPS TEKt). Krocker has also published analyses of drain- 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 7.9 7.1 8.4 Sulphate 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 aS.t 15.3 25.8 24.7 Krocker remarks {Joiir.far Praht. Chem., 60-466) that phosphoric acid could be detected in all these waters, though its quantity was too small for estimation. a and b are analyses of Avater from the same drains — a gatliered April 1st, and h May 1st, 1853 ; c is from an ad- joining field ; d, from a field whei-e the drains run con- stantly, where, accordingly, the drain-water is mixed with spring water ; e and f are of water running from the sur- face of a field and gathered in the furroAvs. Lysimeter-Water, — Entirely similar results Avere ob- tained by Zoller in the analysis of Avater AA^hich was col- lected in the Lysimeter of Fraas. The lysimeter * con- sists of a Aessel Avith A^ertical sides and open above, the upper part of AA'hich contains a layer of soil (in these ex- periments 6 inches deep) supported by a perforated shelf, while 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 then filled from the diaphragm up with soil. In this condition it remains, the soil in it being exposed to the same influences as that of the field, Avhile the water AA^hich percolates tiie soil gathers in the reservoir • Measurer of solution. AQtTTilOUS SOLUTION OP THK SOIL. 315 below. Dr. Zijller analyzed the water that was tbus col- lected fi'om a number of soils at Munich, in the half year, April 7th to Oct. 7th, 1857. He found IN 100,000 OF LYSIMETER- WATER: Potash, 0.65 0.24 0.20 0.55 0.38 Soda, 0.71 0.5G 0.74 2.37 0.60 Lime, 14.58 5.7G 7.08 6.84 9.23 Magnesia, 2.05 0.89 0.13 0.29 0.51 Oxiiie of iron. 0.01 0.G3 0.83 0.57 0.43 Chlorine, 5.75 0.95 2.08 3.94 3.53 Phosphoric acid, 0.22 — — — — Sulphuric acid, 1.75 2.71 2.78 2.93 3.35 Silica, 1.04 1.13 1.75 0.95 0.93 Organic matter, with some 1 20.47 12.59 13.67 12.08 10.19 nitric and carbonic acids. Total, 47.23 2,5.40 29.20 30.52 29.15 The foregoing analyses of drain and lysimeter-water exhibit a certain general agreement iu their results. They agree, namely, iu 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 Avith 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 wdth 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 analyses on p. 311, they refer to 100,000 parts ot soil, and hence the two series of data cannot be directly compared and are not necessarily discrepant. Is Soil-Water destitute of certain Nutritive Matters I — We notice that in the 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 number 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« SI 6 iTO-\V CROPS T'EED. er nutritive elements, viz., clilorine and sulphuric ncld, In the Table, ii,311 , leads to the question. May not the aqueous sohxtion of the soil be altogether lacking in some es- sential kinds of mineral plant-food in certain instances ? May it not happen in 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 caj^able 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 Avas 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 ( Chem. Central- hlatt, 1864, 168) that he has repeatedly tested aqueous solutions of fruitful soils for phosphoric acid, emj^loying 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 Yon Babo, in the examination of seven soils, found phosphoric acid in every instance but one, which, singularly enough, was ■that of a recently manured clay soil. In no case did he fail to detect lime, potash, soda, sulphuric acid, chlorine, and nitric acid ; magnesia he did not look for. {Hoff- mann's Jahresberirht der Ag. Chem., I. 17.) So Ileiden, in answer to Knop's statement, found and estimated phosphoric acid in four instances in proportions AQUEOUS SOLUTIOX OF THE SOIL. 31 7 ranging from 2 to 6 parts in 100,000 of soil. {Jahreshe- richt der Ag. Chem., 18G"), p. ?A.) It should be remnrkod that Knop's failure to find phos- phoric acid may depend on the (uranium) method he euj- ployed, a method different from that commonly used. Can the Soil-water supply Crops with Food I — 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. While to decide such a question is, per- haps, impossible, a closer discussion of it may prove ad- vantageous. Russell [Journal IIid and ^ig. iSoc., New Series, Vol. 8, p. 534) and Liebig {^Inn. d. Chem. ti. Pharm.., 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 fiills 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 watoi*, carrying with it, out of the reach of plants, such substances as it has dissolved, and * On (liaiii-water*, see p "13. t From Parke's measurcaicnts, Jour. Roy. Ag. Soc., Eny., Vol. X^'II, p. 137 318 HOW CROPS FEED. 1,500 tons must remain to give to the plant all that it liolds in solution. These 1,500 tons of water must, if they have the same composition as that which escapes, contain only- two and a lialf 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 this 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 which 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 planted in New England in the early part of June, and is harvest- ed the first of October. During the four months of its growth, the average rain-fall is not enough to make a flow from drains for more, perliaps, than one day in seven. During six-sevenths 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 this 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 reaching the drains. Ac- cordingly we find that the quantity of matters dissolved by water acting thoroughly 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 Just 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 SOLUTION OF THE SOIL. 319 Bonn, Prussia, not freshly manured, and was treated with about one-third its weiglit (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 rS bushels wheat per acre, English). It was 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 3.57 Sulphuric acid, 10.02 Phosphoric acid, 3.10 traces Oxide of iron and alumina. trace 1.17 Chloride of sodium, 5.86 4.76 Lime, 13.80 8.36 Magnesia, 3.84 3.74 Potash, 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 whose composition is given above, we 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, 89 Chloride of sodium, 197 160 Lime, 430 381 Magnesia, 139 126 Potash, 387 35 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 with 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 satiified with the quantities in our computation, while sulphuric acid and phosphoric acid are nearly or en- tirely wanting. We do not, however, regard such calcu- lations as decisive, either one way or the other. The quantity of water whicli may stand at the actual service of a crop is beyond our power to estimate witli 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 ahove interpreted, convey an exaggerated notion of the extent of solution. Proper Concentration of Plant-Food. — Let us next inquire what streiKjth of solution is necessary for the sup- port of plants. As has been shown by Nobbe ( Vs. St., VIII, p. 337), Birner & Lucanus {Vs. St., VIII, p. 134), and Wolff ( Fs. St., VIII, p. 102), various agricultural plants flourish to extraordinary perfection when their roots are immersed in a solution containing about one part of ash-ingredients (together with nitrates) to 1,000 of water. The solutions they employed contained the following substances in the proportions stated (apjiroximately) be- low: In 100,000 parts of Water. Nobbe. Birner & Lucanus. Wolff. Lime, 16 19 19 Magnesia, 3 QH ^'{ Potash, 31 16 16 Phosphoric acid, 7 24 14 Chlorine, 21 none 2 Sulpluiric acid, 6 13 4 Oxide of iron, M J-f X Nitric acid, 31X 36 51 Nobbe found further that the vigror of vesfetation in his AQUEOUS SOLUTION OF TH-E SOU,, 321 solution was diminished either by reducing the proportion of soHd 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 2^roportions of some of the most important ingredients Vhich 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. St., VIII., J). 154), which throw much light on the question un- der discussion. They compared the growth of the oat plant, when nourished respectively by a rich garden soil, by ordinary cultivated land, by a solution the composition of Avhich is given above, and lastly by a natural aqueous solution of soil, viz., a well-water. Below is a statement of the weight in grams of an average plant, produced iia these various media, as well as that of the grain yielded by it. Dry crops compared Weight of aver- Weiirht of with seed, the hitter age plant, dry. dry Grain. taken as unity. Garden 5.27 1.23 193 Field 1.75 0.63 &i Solution 3.75 1.53 137 Well-water 2.91 1.25 lOG We 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 dovble that of the latter, and equal to that obtained in a rich garden soil. 14* 322 HOW CROPS FEED. The analysis of the Avell-water sliows that the nutritive 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, 6.03 We thus have demonstration that a solution containing but one-and-a-hiilf jjarts of jjhosphoric 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 Aveather. Do we thus reach 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, Lam'niarla^ and other ma- rine plants, contain iodine in notable quantities. This element, so much used in photography and medicine, is made exclusively from the ashes of these sea-Aveeds, one establishment in Glasgow producing 35 tons of it annu- ally. The iodine must be gathered from the water of tlie ocean in which these plants Aegetate, and yet, although the starch-test is so delicate thnt 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" Avhirh remain when sea-water is concentrated to the one-hund- reth of its original bulk, so that its proportion must be less than one part in thirty millions of water! [Otto''s Lehrhich, der Cheni'e^ Ate, A>'Jf., \i\^. 743-4.) AQUEOL'S SOLUTIOJf OF TIIK SOIL. 323 Mode whereby dilute solutions may nourish Crops.— There are other considerations Mliicli niay en:il)lc 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 dissolve 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 from it to the crop the needful soluble matters. It has been shown that the substances dissolved in water may diffuse through animal and vegetable tissues independently of each other, and independently of the water itself. (11. C. G., p. 340.) Deportment of the Soil to renewed portions of Water. — ^It remains to satisfy ourselves tliat the soil is capa1)le of yielding soluble matters continuously to renewed por- tions of water. The only observations on this point that the writer is acquainted Avith are those made by Schulze and Ulbricht. Schulze ex[)erimented on a rich soil from Goldberg, in Mecklenburg ( Vs. St., YI., 411). This soil, in a quantity of 1,000 grams (= 2.3 11)S.) Avas slowly leached Avith 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. 824 HOW CROPS FEED. The results were as follows, for 1,000 j^arts of extract, Portion of aqueous extract. Total matters dissolved. Organic and Tolatile. Inorganic. Phosphoric acid. 1 0.535 0.340 0.195 0.0056 2 0.120 0.057 0.063 0.0082 3 0.261 0.101 0.160 0.0088 4 0.203 0.083 0.120 0.0075 5 0.260 0.082 0.178 0.0009 6 0.200 0.077 0.123 0.0044 1.579 "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 tliey would be similar in kind. This is shown by the investigations that follow. Ulbricht gives ( Vs. St.^ V., 207) the results of the simi- lar treatment of four soils. 1,000 grams of each were put in contact with four times as much pure water for three days, then two-thirds of the solution was poured off for analysis, and replaced by as much pure water; this 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 Heinsdorf. 1st Extract. 2d Extract. 3d Extract. 4th Extract. 7th Extract. 10th Extract. Potnsh 80K 95 30 1^ trace. 15 14 39 12 IK 15 21 38 10 3 8 18 39 10 3 4 Soda 11 Lime... Pliosphoiie acid... Total 190 sn4 1 87 1 78 ' AQUEOUS SOLUTIOX OP THE SOIL. 225 Loamy Sand from Wahleclorf. Potash 23 36 lie 12 16 43 15 3 13 20 ;;',) 14 4 6 16 42 12 4 48 14 4 Soda Lime.. . phosphoric acid.. Total 2081^ 89 90 80 1 Loamy ferruirinous Sand from Dahme, containing 4J^ of humus. Potash Soda Lime Magnesia Phosphoric acid.. Total. 7 6 7 7 1 41 11 26 17 96 70 55 48 62 14 10 9 8 trace. tnice. T 158 99 97 80 Fine Sandy Loam from Fallvcnberg. Potash 15 47 47 17 3 11 12 27 8 9 12 19 5 trace. 9 8 18 6 trace. Soda Lime Phosphoric acid.. Total 129 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 possessed 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 sueli at the outset. The two analyses by Krocker, a and i, p. 314, made on water from the same drain, gatliered 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 suffers constantly the chemical changes which have been already noticed, and are expressed by the term weather- 326 TiOW CROPS FEED. ing. Matters insoluLle in water to-day become soluble to-morrow, and substances that to-morrow icsist 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 Avater 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 tlie roots of a croj) 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- isented to vegetation by water in sufficient quantity, does not entirely satisfy us in reference to some of the needful elements of the ]ilant, 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- rupt the general plan of our chapter. Direct action of Roots upon the Soil. — In noticing the means by whicli rocks are converted into soils, the action of the organic acids of the living plant has been mentioned. Since that chapter was written, fuitlier evi- dence has been obtained concerning the influence of the plant on the soil, whicli we now proceed to adduce, Sachs [Experimental Physlologie^ 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), osteolite (phosphate of lime), gypsum, and glass. Polished plates of these substances were placed at the bottom of suitable vessels and covered several inches in dept'.i with fine quartz sand. Seeds of various plants were planted in the sand and kepi DIRECT ACTION* OF HOOTS UPON TIIE SOIL. 3^27 moist. The roots jienetrated the sand and came in con- 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 plain- ly corroded Avhere they had been in contact with the roots, so that tlie 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 tlie path of the root. Gypsum and glass were not perceptibly acted on. Dietiich has m:ide a series of experiments {SoffmanrCs tTahreshericlit^ VI, 3) 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. The 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 Nvater, to which a hundredtli 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. Not only did these plants take up mineral mat- ters from the rock, but the latter contained besides, a larger amount of soluble matters than was found in the experiments where no plants were made to grow. The cereal grains had the same effect, 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 washin. 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 acid, 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, potash, 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 silicates, such as are decomposable by acids, (zeolites) exist in the soil, although we cannot recognize them directly by inspec- tion even with the help of the microscope. To this point we shall subsequently recur. §4. 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 with other similar silicates, which, in many cases, are ingredients of the soil. Treatment with concentrated sulphuric acid at very high temperatures (Mitscherlich), or syrupy phos- phoric acid (A. Mailer), decomposes all these minerals, quartz alone excepted. By making, therefore, in the first cnEMirAT, ACTION- IN THE SOIT.. Jj5t 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 tliese 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 COMMONLY 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 tiOW CROPS FEED. large a part of the Middle State?, bxxt most of the rocks of New England have 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 influences, the soils of earlier ages have been so- lidified and cemented to our rocks. Xor, indeed, is this process of rock-making brought to a conclusion. It is going on at the present day on a stupendous 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 Avith chloride of calcium, it shortly hardens to a rock-like 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 material (water-lime cement) which hardens speedily, even under water, and becomes, to all intents, a rock. Analogous changes proceed in the soil itself Hard pan, 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 foi-ce, 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 part, 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, however, on the whole, far more favoi-able to disintegration than to petrifaction. Nevertheless, the chemical affinities and ABSORPTIVE POWEK 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 siihstances that exist in all soils are capable of forming and tend to form a multitude of combinations. In our enumeration of tlie 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 compounds of these verj^ 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 tlie 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 that various substances, when put in contact with the soil, in a stale 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 earth. Po;ir gradually into the bottle thick and putrefied dung-liquor until its contents are saturated. The S34 HOW CKOPS 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 tlie 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 water 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 waterP 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 IIux- 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 the Journal of that Society, Vol. XL, pp. 313-379 an account 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 surface-attraction, exerted by the particles of certain ingredients of the soil. The other is a chemical action, and results from a i)lay of affinities among certain of its components. I The physical absorptive power of various bodies, in- cluding the soil, has been already noticed in some detail (pp. lGl-176). In experiments like those of Bronner, just alluded to, the absorption of the coloring and odor- ons ingredients of dung-liquor is doubtless a physical process. These substances are separated from solution by ABSOIIPTIVK POWEU 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 that 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 the 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 of each 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 sohations should be quite dilute, but still admit of ready identification by their taste or by simple tests. We may emploj^ 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 li(piid which pasa 336 HOAV CR0P6 FEED. are no longer a solution of nitrate of potash, but one of nitrates of lime, magnesia, and soda. The potash has disappeared from sohition* 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 with the nitric acid. If we operate in a similar manner on a fresh tube of soil with solution of salt (chloride of sodium), we shall find by chemical examination that the soda of the salt is absorbed by the soil, while the chlorine passes through in combination with lime, magnesia, and potash. In case of sulphate of magnesia, magnesia is retained, and sul])hates of lime, etc., pass through. With jihospliatcs and silicates we find that not only the ba'^e, but also these acids are retained. Law of Absorption and Displacement. — From a great number of experiments made by AYay, Liebig, Brustlein, Henneberg andStohmann, Rautenberg, Pcteis, Weinhold, Ktillenberg, Ileiden, Knop, and others, it is established as a general fact that all cultivable soils are able to de- compose salts of the alkalies and alkali earths in a state of solution, in such a manner as to retain the base together with phosj^horic and silicic acids, while chlorine, nitric acid, and sulphuric acid, remained dissolved, in union with some other base or bases besides the one with which they were originally combined. The absorptive power of the soil is, however, 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 pofasli may be s^hown by aid of strong, cold solution of tartaric acid, which will precipitate bitartrate of jxitasli (cream of tartar) from the ori^'inal solution, if not too dilute, but not from that which lias filtered through the soil. Tlie prcs.ence of lime in tlie liquid that passes the soil may ba shown by adding to it either carbonate or oxalate of ammonia. ABSORrXIVE 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 tbc drij soil (e. 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 analysis. The absorptive power of tlio soil is exerted unequally towards individual substances. Thus, in Peters' experi- ments ( Vs. St., II., 140), the soil he operated with absorb- ed the bases in quantities diminishing in the following order : Potash, Ammonia, Soda, Magnesia, Lime. Another soil, experimented upon by Ktillenberg {Jahresbericht ilber Agricidtur. Chemie, 1865, p. 15), ab- sorbed in a different order of quantity, as follows : Ammonia, Potash, Magnesia, Lime, Soda. As might be expected, different soils evert ahsorptive •power toioards the same substance to an u)iequal extent. Kautenberg {Henneberg' s Jour, far Landicirthsrhaft, 18G2, p, 62), 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 absorjytion 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 ex2:)eriinents of Hen- neberg and Stohmann {Uenneberf s Jourmd.^ 1859, p. 35), phosplioric acid continued to be fixed after the cxpiiation of 24 hours. The strength of the solution influences the extent of absorjition. The stronger the solution., the more subsia)tce is taken up from it by the soil. Thus, in Peters' experi- 15 338 HOW CKOPS FEED. ments, 100 grms. of soil absorbed from 250 cubic centi- meters of solutions of chloride of potassium of various degrees of concentration, as follows: strength of Solution. Pota-ih absorbed by Designa- Quantity of potash in ^0 c.c. 100 parts By lO.OOO parts in ProjMrtion tion. of solution. of soil, round numbers. absorber/ |g„ equiv. = 0.1472 gram. 0.9S88 gram. 10 ^i^ \ta " — 0.2944 " O.iaSl '• 14 Mo a, " = 0.5888 " 0.1990 " 20 ' I3 1,0 " - 1.17-7 " 0..3124 " 31 'U U " = 2.3555 " 0.4503 " 45 ' U A glance at the right-hand column shows that although absolutely less potash is absorbed from a weak solution than from a strong one, yet the weak solutions yield relatively more than those wiiich 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 absorbud 20 parts. 500 " " " " " " " " 25 " " 1,000 " " " " " " " " 29 " The quantity of a substance absorbed by the soil de- pends somewhat on the state of combination it is in, i, e., on tlie 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 '1 ,3 of an equivalent of that base expressed in grams, to the liter, the following quantities of potash : — From phosphate, 49 parts. « hydrate, 40 « " carbonate, 32 " " bicarbonate, 28 " « nitrate, 25 « « sulphate, 21 « " chloride* and carbonate, 21 " « chloride, 20 « • ChloriUe of Potassium, KG!. ABSORPTIVE POWER OF THE SOIL 339 We observe that potash was absorbed m this case in largest proportion from the phosphate, and in least from the chloride. Ilenneberg 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 " " hydrateand chloride,* ir I, " « chloride, 11 " nitrate, U " 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 dilute solu- tions. Liebig indeed, formerly believed that potash is en- tirely removed from its solutions. We find, in lixct, 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 icater will dissolve and remove a portion of the potash, etc., which a soil has absorbed. Peters placed in 250 c.c. of a solution of chloride of potassium 100 grams of soil, which absorbed 0.2114 gram of potash. At the expiration of two days, one-half of the solittion was removed, and its place was supplied with pure water. After two days more, one-h:ilf of the liquid was again removed, and an equal volume of water added j ♦ Chloride of Ammonium, NH^Cl, 340 now CROPS FEED. and this process was repeated ten times, thus in the several washined by the soil. gram. 0.2808 soda. 0.2165 ammonia. 0.2996 lime. 0 2317 magnesia. Dist. water. 0.0671(?) 0.0322 0.2380 0.0542 trace 0.0006 0.0020 0.1726 0.0983 0.1455 0.1252 0.1224 0.0434 0.2197 0.0024 0.0252 0.0245 0.0004 0.1590 0.0611 goda. 0.0569 ammonia. I0.O6I6 lime. 1O.O59I magnesia. "We notice that while distilled water dissolved about ' j of the absorbed potash, the saline solutions took up two, three, or more times that quantity. We observe further that soda liberated lime and magnesia, ammonia liberated lime and soda, lime brought into solution magnesia and soda, and magnesia set free lime and soda from the soil itself. Again, Way, Brustlein, and Peters, have shown in case of various soils they experimented with, that the satura- ting of them, with one ha'^e (potasii and ' lime wore tried) increases the absorbent power for other bases, and on the other hand, treatment with a-ids, ichl-h remores absorbed ^ases, diminishes their absorptive power. 342 now r-Rors fkkb. This f:ict is made evident hy the following data furnish- ed by PctiTS. The soils employed were No. 1. Unaltered Soil. No. 2. Soil heated with hydrochloric acid for some time, then thorouglily washed with water. No. 3. No. 2, boiled with 10 grams of sulphate of lime and water, and washed. No. 4. No. 2, boiled with solution of 10 grams of chlo- ride of calcium, and well washed with water. No. 5. No. 2, boiled with water and 10 grams of car- bonate of lime. No. 6. No. 2, boiled with solutiou of bicarbonate of lime, and washed. Portions of 100 grams of each of the above were placed in contact with 250 c.c. of ' \^^ solution of chloride of po- tassium for tlirce days. Tlie results are subjoined: Number Dissolved by the solution. Potash absorbed of soil. Lime. Magnesia. Soda. Chlmine. by the sou. 1 0.0940 0.0084 0.0261 0.4482 1 0.1841 2 0.0136 0.0004 0.4444 ! 0.0227 3 0.0784 0.00-24 0.0019 0.4452 0.0883 4 0.05H0 0.0004 0.0024 0.4453 0.1343 5 O.llTtt 0.00i)4 0.0019 0.4425 1 0.1378 6 0.1456 0.0074 0.4404 ' 0.2011 It is seen that the soil which had been waslied with acid, absorbed but one-ninth as much as tlie unaltered earth. The treatment with the various lime-salts increas- ed the absorbent power, in the order of the Table, until in the last instance it surpassed that of the original soil. Here, too, we observe that the absorption of potash ac- companies and is made possible by the displacement of other bases, (in this case almost entirely lime, since the treatment with acid liad nearly removed the others). We observe further that the quantity of chlorine remained the same throughout (within the limits of experimental error,) not being absorbed in any instance. Way first showed that the absorptive power of the soil ABSOIIPTIVK POWER OP THE SOIL. 343 is diminished or even destroyed by burning o)' calcination. Peters, experimenting on this point, obtained the follow- ing results : Potash absorbed from solution of chloride of potassium by unburned burned Vegetable mould, 0.2515 0.0303 Loam, 0.1S41 0.1200 The Cause of the Absorptive Power of Soils for Bases when combined with chlorine, sul])huric, and nitric acids, has been the subject of several extensive investiga- tions. Way, in his papers already referred to, was led to conclude that the quality in question belongs to some pe- culiar compound or compounds that are associated with the clayey or impalpable portion of the soil. That these bodies were compounds of the bases of the soil with silica, was a most probable and legitimate hypothesis, which he at once sought to test by experiment. Various natural silicates, feldspars, and others, and some artificial preparations, were examined, but found to be destitute of action. Finally, a silicate of alumina and Boda containing water was prepared, which possessed ab- soi'ptive properties. To produce this compound, pure alumina was dissolved in solution of caustic soda on the one hand, and pure silica in the same solution on the other. On mingling the two liquids, a white precipitate separated, which, when washed from soluble matters and dried at 212°, had the following composition * : Silica, .46.1 Alumina, 26.1 Soda, 15.8 Water, 12.0 100.0 * Way gives the composition of the anhydrous salt, and says it contained, dried at 212% about 12 per cent of water. In the above statement this water is in- cluded, since it is obviously an essc'ntial ingredient. 344 sow CROPS FEED. This compound is analogous in constitution to tte zeolites, in so far as it is a highly basic silicate containing water, and is easy of decomposition. It is, in fact, de- composed by water alone, which removes from it silicate of soda, leaving insoluble silicate of ahimina. On digesting this soda-silicate of alumina witli a solu- tion of any salt of lime, Way found that it was decom- posed, its soda Avas eliminated, and a lime-silicate of alumina was produced. In several instances he succeeded in replacing nearly all the soda by lime. Potash-silicate of alumina was procured by acting on either the soda or lime silicate with solution of a potash-salt ; and, in a simi- lar mannei*, am,monia and m^agnesia-silicates were gener- ated. In case of the ammonia-compouml, however. Way succeeded in replacing only about one-third of soda or other base by ammonia. All of these compounds, when acted upon by pure water, yielded small proportions of alkali to the latter, viz. : The soda- silicate gave 3.36 parts of soda to 10,000 of water. The potash- '" " 2.27 " " potasli " " " " The ammonia- '• " 1,06 " " ammonia" " " " Way found furthermore that exposure to a strong heat destroyed the capacity of these substances to undergo the displacements we have mentioned. From these facts Way, concluded that there exist in all cultivable soils, compounds similar to those he thus pro- cured artificiall}^ and that it is their presence which oc- casions the absorptions and displacements that have been . noticed. Way gives as characteristic of this class of double sili- cates, that there is a regular order in which the common bases i-eplace each other. He arranges them in the fol- lowing series : Soda — Potash — Lime — Magnesia — Ammonia: and according to him, potash can replace soda but not the Other bases; while ammonia replaces them all : or each base ABSOUPTIVE POWKU OF THE SOIL. 345 replaces those ranged to its left in the above series, but none of tliose on its right. Way remarks, that " of course the reverse of this action cannot occur." Liebig {A)in. der Chem. u. Pharm., xciv, 380) drew attention to the fact that Way himself in the preparation of the potash-alumi- na-silicate, demonstrated that there is no invariable order of decomposition. For, as he asserts, this compound may be obtained by digesting cither the lime-alumina-silicate, or soda-alumina-silicate in nitrate or sulphate of potash, when the soda or lime is dissolved out and replaced by potash. Way was doubtless led into the mistake of assuming a fixed order of replacements by considering the?;e exchanges of bases as regulated after the ordinary manifestations of chemical affinity. His own experiments show that among these silicates there is not only no inflexible order of de- composition, but also no complete replacements. The researclics of Eichhorn, " Ueber die Einwirkung ver- dtinnter Salzlusungen auf Ackererde," {Landwirthschaft- liches Gentralblatt, 1858, ii, 169, and Potyg. Ann., No. 9, 1858), served to clear up the discrepancies of Way's in- vestigation, and to conflrm and explain his facts. As Way's artificial silicates contanicd about 12 per cent of water, the happy thought occurred to Eichhorn to test the action of saline solutions on the hydrous silicates (zeolites) whii-h occur in nature. He accordingly insti- tuted some trials on chabazite, an abstract of which is here given. On digesting finely pulverized chabazite (hydrous sili- cate of alumina and lime) with dilute solutions of chlo- rides of potassium, sodium, ammonium, lithium, barium, strontium, calcium, magnesium, and zinc, sulphate of magnesia, carbonates of soda and ammonia, and nitrate of cadmium, he found in every case that the basic ele- ment of these salts became a part of the silicate, while lime passed into the solution. The rapidity of the re- placement varied exceedingly. The alkali-chlorides re* 15* 546 no"\v cRors peed. acted evidently in two or tliree days. Chloride of barium and nitrate of cadtnium were slower in their effect. Chlo- rides of zinc and strontium at first, appeared not to react ; but after twelve days, lime was found in the solution. Chloride of magnesium was still tardier in replacing lime. Four grams of powdered chabazite were digested with 4 grams of chloride of sodium and 400 cubic centimeters of water for 10 days. The composition of the original mineral (i,) and of the same after the action of chloride of sodium (ii,) were as follows : Silica, 47.44 48.31 Alumina, 30.69 21.04 Lime, 10.37 6.65 Potash, 0.65 0.64 Soda, 0.42 5.40 Water, 20.18 18.33 Total, 99.75 • 100.37 Nearly one-half the lime of the original minei'al was thus substituted by soda. A loss of water also occurred. The sokition separated from the mineral, contained nothing but soda, lime, and chlorine, and the latter in precisely its original quantity. By acting on chabazite with dilute chloride of ammo- nium (10 grams to 500 c.c. of water) for 10 days, the mineral was altered, and contained 3.33 per cent of am- monia. Digested 21 days, tlie mineral yielded 6.94 per cent of ammonia, and also lost water. These ammonia-chabazites lost no ammonia at 212°, it escaped only when the heat was raised so high that water began to be expelled ; treated with warm solution of pot- ash it was immediately evolved. The ammonia-silicate was slightly soluble in water. As in the instances above cited, there occurred but a partial displacement of lime. Eichhorn made correspond- ing trials with solutions of carbonates of soda and am* At^soTiPTivK ro^v^:t^ of titk snTT,. fiAt monia, in order to asceitain whether tlie formation of a Bohible salt of the (lis[)laccd base limited the reaction; but the results were substantially the same as before, as shown by analyzing the residue after removing carbonate of lime by digestion in dilute acetic acid. Eichliorn found that the artificial soda-chabazite re-ex- changed soda for lune when digested in a solution of chloride of calcium ; in solution of chloride of potassium, both soda and lime were separated fiom it and replaced by pot:i8h. So, the ammonia-chabazito in solution of chlo- ride of calcium, exchanged ammonia for lime, and in so- lutions of chloi-ides of potassium and sodium, both am- monia and lime passed into the liquid. The ammonia- chabnzite in solution of sulphate of magnesia, lost ammo- nia but not lime, thougli doubtless the latter base would have been found in the liquid had the digestion been con- tinued longer. It thus appears that in the case of chabazite all the protoxide bases may mutually re})lace each other, time being the only element of difference in tlie reactions. Similar observations were made with natrolite (hydrous silicate of alumina and soda,) as well as with chlorite and labradorite, although in case of the latter difficultly de- composable silicates, the action of saline solutions was very slow and incomplete. Mulder has obtained similar displacements with the ZL'olitic minerals stilbite, thomsonite, and prehnite. {C/te- mie der Ackerkrume, T, 396). He has also artificially prepared hydrous silicates, having properties like those of Way, and has noticed tl:at sesquloxide of iron readily participates in the displacements. Mulder also found that the gelatinous zeolitic precipitate obtained by dissolving hydraulic cement in hydrochloric acid, precipitating by ammonia and long washing with water, underwent the same substitutions when acted upon by saline solutions. 348 Mow cuors feed. The precipitate he operated with, contained (water-free) in 100 parts: Silica 49.0 Alumina 11.1 Oxide of iron 21.9 Lime 6.9 Matrnesia 1.1 Insoluble matters -with traces of alkalies, etc 10.0 100.0 On digesting portions of this substance witli sohitions of sulphates of soda, potash, magnesia, ammonia, for a single hour, all tlie lime was displaced and replaced by- potash — two-thirds of it by soda and nearly four-fifths of it by magnesia and ammonia. Further investigations by Rautenberg {Henneherg^s Jour, fur Landiotrthschaft, 1862, pp. 405-454), and Knop ( Vs. St., VII, 57), which we have not space to re- count fully, have demonstrated that of the bodies possible to exist in the soil, those in the following list do not pos- sess the power of decomposing sulphates and nitrates of lime, potash, ammonia, etc., viz.: tlj f Quartz sand. "j S I Kaoliuite (purified kaolin.') i •S J Carbonate of lime (chalk.) I These liodies have no absorptive effect, either ^ 1 Iluinus (decayed wood.) f separately or together. g I Hydrated oxide of iron. 1 p5 (Hydrated alumina. I Hamate of lime, magnesia, and alumina. [Knop. Phosphate of alumina. Gelatinous silica. " dried in the air. These observers, together with Heiden [Jahresbericht lUber Agricultvrchemie, 1864, p. 17), made experiments on ' soils to which hydrated silicates of alumina, and soda, or of lime, etc., were added, and found their absorptive power thereby increased. Rautenberg and Ileiden also found an obvious relation to subsist between the absorptive powers of a soil and cer- tain of its ingredients. Rautenberg observed that the ab- sorptive power of the nine soils he operated with was closely connected with the quantity of alumina and oX' ABSORPTIVK POWER OF TUE SOIL. 349 ide of iron which llie soils yielded to hydrochloric acid. Heiden traced a similar relation between the silica set free by the action of acids on cluven soils and their absorptive power. Rautenberg and Heiden further confinued what Way and Peters Imd previously shown, viz., that treat- ment of soil with acids diminished their absorbent power. These facts admit of interpretation as follows : Since neither silica, hydrated alumina, nor hydrated oxide of iron, as such, have any absorptive or decomposing power on suljihates, nitrates, etc., and since these bodies do not ordinarily exist as sncli to much extent in soils, therefore the connection found in twenty cases to subsist between their amount (soluble in acids) in the soil, and the ab- sorptive power of the latter points to a compound of these (and other) substances (silicate of alumina, iron, lime, etc.), as tlie absorptive agent. That the absorbing compound is not necessarily hydra- ted, is indicated by the fact that calcination, wliich must Temove water, though it diminishes, does not always alto- gether destroy the absorptive quality of a soil. (See p. 343.) Eiciihorn, as already stated, found that the anhy- drous silicates, chlorite and labradorite, Avere acted upon by saline solutions, though but slowly. Do Zeolitic Silicates, hydrated or otherwise, exist in the Soil? — When a soil which is free from carbonates and salts readily soluble in water, is treated with acetic, hydrochloric, or nitric acid, there is taken up a quantit-y (several per cent.), of matter Avhich, while con- taining all the elements of the soil, consists chiefly of alumina and oxide of iron. Silica is not dissolved to much extent in the acid, but the soil which before treatment with acid contains but a minute amount of uncoinbined. silica, afterwards yields to the ))roper solvent (hot solution of carbonate of soda) a considerable quantity. This is our best evidence of the presence in the soil of easily decora* 850 HOW CROPS FEED. posable silicates. A number of analyses which illustratfl these facts are subjoined : Water Orsranic matter Siiiui and insoluble silicates. (Clay, kaoliiiite) f Silica (jD , Oxide of iron £. Alumina g. ' Lime 5- I Magnesia Potash Soda Phosiphoric acid Sulphuric acid Carbonic acid, clilorine, ^ and loss Sandy Loam. Heiden. 1.613 2.387 89.754 (10.344) 2.630* 1.8-2 1.152 o.ini 0.201 0.242 0.034 0.083 0.007 White Clay. 5. Porce- lain Vlay. Rautenbekg. Bed Clay. 6.15 none 58.03 18.73 2.11 12.15 0,27 0.29 0.86 1.41 none .095 I .(XW 1 6.80 0.90 4.35 89.46 0.04t 0.12 0.08 6. White Pottery Clay. Wat. 6.18 none 58.72 13.41 5.38 13.90 0.61 0.43 100.00 I100.20 lioo.oo • This soil yielded to solution of carbonate of soda before treatment with acid, 0.340 "u silica. + The eilica in this case is the small portion held in the acid solution. The first three analyses especially, show that the soils to which they refer, contained a silicate or silicates in which iron, alumina, lime, magnesia and the alkalies ex- isted as bases. How much of such silicates may occur in any given soil is impossible to decide in the present state of our knowledge. In the soil, free silica, is usually, if not always present, as may be shovvn by treatment with solu- tion of carbonate of soda, but it appears difficult, if not impossible, to ascertain its quantity. Again, hydratcd oxide of iron (according to A. Miiller and Knop) and hy- li'ated alumina* (Knop) may also exist, as can be made evident by digesthig the soil in solution of tartrate of .■^oda and potash (Mtillcr, Ys. St , IV, p. 277), or in a mi.x- ture of tartrate and oxalate of ammonia (Knop, Vs. St. VIII, p. 41). Finally, organic acids occur to some ex- tent in insoluble combinations with iron, alumina, lime, • Jl'ire probably, highly basic carbonates, or mixtures of hydrates and car bunates. ABSORPTIVE POWER OF THE SOIL. 351 &c. This complexity of the mW effectually ])revents au accurate analysis of its zeolitic silicates. If further evidence of the existence of zeolitic com- pounds in the soil were needful, it is to be found in con- sidering the analogy of the conditions whiirh there obtain with those under which these compounds are positively known to be formed. At Plombieres, in France, the water of a hot spring (temperature, 140" F.) has flowed over and penetrated throuo-h a mass of concrete, composed of bricks and sand- stone laid in lime, which was constructed centuries ago by the Romans. The water contains about nine ten-thou- sandths of solid matter in solution, a quantity so small as not to affect its taste perceptibly. As Daubree has shown {Ann. des Mifies, 5me., Serie, T. XIII, p. 242), the cavi- ties in the masonry frequently exhibit minute but well- defined crystals of various zeolitic minerals, viz, : chaba- site, apophyllite, scolezite, hnrraotome, together with hy- drated silicate of lime. These minerals have been pro- duced by the action of the water upon the bricks and lime of the concrete, and while a high temperature prevails there, which probably has facilitated the crystallization of the minerals, as it certainly has done the chemical altera- tion of the bricks and sandstone, the conditions otherwise are just those of the soil. In the soil, we should not expect to find zeolitic com binations crystallized or recognizable to the eye, because the small qu intities of these substances that could be formed there must be distrilmted throughout twenty, fifty, or more times their Aveight of bulky matter, which would mechanically prevent their crystallization or segregation in any form, more especially as the access of water is very abundant ; and the carbonic acid of the surface soil, which powerfully decomposes silicates, would operate antago- nistically to their accumulation. 352 HOW CROPS FEED. The water of the soil holds silica, lime, magnesia, alka» lies, and oxide of iron, often alumina, in solution. In- stances are numerous in Avhich the evaporation of water containing dissolved salts lias left a solid residue of sili- cates. Thus, Kersten has described {Jour, fur praki. Chem., 22, 1) a hydrous silvate of iron and manganese that occurred as a hard incrustation upon the rock, in one of the Freiberg mines, and was deposited where the water leaked from the pum2)s. Kersten and Berzelius have lio- ticed in the evaporation of mineral waters which contain carbonates of lime and magnesia, together with silica, that carbonates of these bases are first deposited, and finally silicates separate. {B's:hof^s Chem. Geolo^/y^ Car. Ed.^ Vol. 1, p. 5). Bischof (loc. cit., p, 6) has found that silica, even in its most inactive form of quartz, slowly decom- poses carbonate of soda and potash, forming silicate when boiled with their aqueous solutions. Undoubtedly, simple contact at ordinary temperature has the same effect, though more slowly and to a slight extent. Such facts make evident that silica, lime, the alkalies, oxide of iron and alumina, when dissolved in water, if they do not already exist in combination in the water, easily combhie when adverse affinities do not jirevent, and may react upon the ingredients of the soil, or upon rock dust, with the formation of zeolites. The " pan," which often forms an impervious stratum under peat bogs, though consisting largely of oxide of iron combined with organic acids, likewise contains consider- able quantities of hydrated silicates, as shown by the analyses of Warnas and Michielsen {Mulder'' s Chem. d. Ackerkrume, Bd. 1, p. 566.) Mulder found that when Portland cement (silicate of lime, alumina, iron, cte.) was treated with strong hydro- chloric, acid, whereby it was decomposed and in part dis- solved, and then with ammonia, (which neutralized and re* ABSOEPTIVE POWER OF THE SOIL. 353 moved the acid,) tlie gelatinous precipitate, consisting chiefly of free silica, free oxide of iron, free alumina, with smaller quantities of lime and magnesia, contained never- theless a portion of silica, and of these bases in combina- tion, because it exhibited absorbent power for bases, like Way's artificial silicates and like orilhiary soil. Mere contact of soluble silica or silicates, with finely divided bases, for a short time, is thus proved to be sufficient for chemical union to take place between them. Recently precipitated silicic acid being added to lime- Avater, unites with and almost completely removes the lime from solution. The small portion of lime that remains in the liquid is combined with silica, the silicate not being entirely insoluble. (Gadolin, cited in Storer's Diet, of Solubilities, p. 5.51.) The fict that free bases, as ammonia, potash and lime, are absorbed by and fixed in soils or clays that contain no organic adds, and to a degree different, usually greater th.in, when presented in combination, would indicate that they directly nnite either with free silica or with simple sili- cates. The hydrated oxide of iron and alumina are in- deed, under certain conditions, capable of retaining free alkalies, but only in minute quantities. (See p. 359.) The fact that an admixture of cai'b onate of lime, or of other lime-salts with the soil, usually enhances its absorbent ])Ower, is not improbably due, as liautenberg first suggest- ed, to the formation of silicates. A multitude of additional considerations from the his- tory of silicates, especially from the chemistry of hydraulic cements and fiom geological metamorphism, might be adduced, were it needful to fortify our position. Enough has been written, however, to make evident that silica, which is, so to speak, ;m accident in the plant, being unessential (we will not affirm useless) as one of its ingredients, is on account of its extraordinary capacity for chemical union with other bodies in a great variety of 354 now CKOPS feed. proportions, extremely important to the soil, and espe« cially 50 when existing in combinations admitting of the remaikable changes whicli liave come under our notice. That we cannot decide us to tlie precise composition of the zeohtic compounds which may exist in tlie soil, is plain from what lias been, stated. We have the certainty of their anah)gy with the well-defined sihcates of the miner- alogist, which have been termed zeolites, an analogy of chemical composition and of chemical properties ; we know further that they .ire likely to be numerous and to be in perpetual alteration, ac, they are subjected to the influence of one and another of the salts and substances that are brought into contact with them ; but more than this, at present, we cannot be certain of Physical agencies in the phenomena of absorption.— While the absorption by the soil of ])otash or other base is accompanied by a chemical decomposition, which Way, Rautenberg, Heiden, and Knop's researches conclusively connect Avith certain hydrous silicates whose j^resence in the soil cannot be doubted, it has been the opinion of Liebig, Brustlein, Henneberg, Stohmann and Peters, that the real cause of the absorption is physical, and is due to simple surface attraction (adhesion) of the jjorous soil to the absorbed substance. Brustlein and Peters have shown that bone and wood-charcoal, washed with acids, absorb ammonia and potash from their salts to some ex- tent, and after impregnation with carbonate of lime to as great an extent as ordinary soil. While the reasons al- ready given appear to show satisfactorily that the ab- sorbent power of the soil, /or bases hi combination^ re- sides in the chemical action of zeolitic silicates, the facts just mentioned indicate that the pliysical properties of the soil may also exert an influence. Indeed, the fixation of free bases by the soil may be in all cases pai'tially due to this cause, as Brustlein has made evident in case of am- monia {BoyssingaulCs Agronomie, etc., T., II, p. 153). ABSUKPTIVJi: roWKU OF THE SVlL. 355 Peters concludes the account of his valuable investiga- tion with the following words : " Absorption is caused by the surface attraction vhich the j)< articles of eurth esrert. In the absorption of bases from salts^ a chemical trans- position uith the ingredients of the soil is necessary, which is m.ade possible through cooperation of the surface attraction of the soil for the base:' (Ys. St., IT, p. 151.) If "we admit the soundness of tliis conclusion, Ave must also admit that in the soil the physical action is exerted in sufficient intensity to decompose salts, by the hydrated silicates alone. We must also allow that the displace- ments observed by Way and Eichhorn in silicates, are primarily due to mere physical action, thoiigh they have imdeniably a chiefly cliemical aspect. That the phenomena are modified and limited in certain respects by physical conditions, is to be expected. The facts that the quantity of solution compared with the amount of soil, the strengtli of the solution, and up to a certain point the time of contact, influence the degree of absorption, point unmistakably to purely physical in- fluences, analogous to those with whose action the chem- ist is familiar in his daily experience. Absorption of Acids. — It has been mentioned already that phosphoric and silicic acids are absorbed by soils. Absorption of phosphoric acid has been invariably observed. In case of silicic acid, excep- tions to the rule have baen noticed. In very few in- stances has the absorption of sulphuric and nitric acids or chlorine, from their compounds, been remarked hitherto by those who have investigated the ab- sorbent power of the soil. The nearly universal con- clusion has been that these substances are not subject in any way, chemical or physical, to the attraction of tlie soil. Yoelcker was the first to notice an absorption of sulphuric acid and chlorine. In his papers on " Farm Yard Manure," etc., (Jour. Roy. Ag. Soc.,XYIII,,p. 140,) 35ft HOW CROPS FEED. and on the "Changes which Liquid Manure undergoes in contact with different Soils of Known Composition" {idem XX., 134-57), he found, in seven experiments, that dung liquor, after contact with various soils, lost or gained acid ingredients, as exhibited l)y the following figures, in grains per gallon : (loss is indicated by — , gain by +) : 1 2 34567 A. B. Chloride of Potassium — S.Sl +9.17 —2.74 +2.14 —2.74 +2.55 —1.10 Chloride of Sodium. . .—3.05 —2.43 —7.04 —1.12 —1.10 —1.24 +3.CG -1.89 +19.05 Sulphuric Acid +3.32 —4.21 —1.06 —1.21 —0.27 +1.24 +3.44 +2.26 —0.42 Silicic Acid +1.63 +10.33 —1.64 +0.72 +2.76 —0.11 —0.07 undet. —1.57 Phosphoric Acid — — —4.23 —3.09 —2.91 —3.38 —0.13 —8.76 —7.71 We notice that chlorine was perceptibly retained in three instances, while in the other four it was, on the whole, dissolved from the soil. Sulphuric acid was re- moved from the solution in four instances, and taken up by it in three others. In four cases silica was absorbed, and in three was dissolved. In his first paper. Professor Way recorded similar experiments, one with flax-steep liquor and a second with sewage. The results, as regards acid ingredients, are included in the above table, A and B, where we see that in one case a slight absorption of chlo-. rine, and in the other of sulphuric acid, occurred. Way, however, regards these diiferences as due to the unavoid- able errors of experiment, and it is certain that in Vcelck- er's results similar allowance must be made. Neverthe- less, these errors can hardly account for the large loss of chlorine observed i:i 1 and 3, or of sulphuric acid in 2. Liebig found in his experiments "that a clay or lime- soil, poor in organic matter, withdrew from solution of silicate of potash, both silicic acid and potash, whereas one rich in humus extracted the potash, but left the silicic acid in solution." (Compare pp. 171-5.) As regards nitric acid , Knop observed in a single in- stance that this body could not be wholly removed by water from a soil to which it had been added in known quantity. He regards it probable that it was actually ABSORPnVE POWER OF THE SOIL. 357 retained rather than altered to ammonia or some other compound. The fixation of acids in tlie soil is unquestionably, for the most part, a chemical process, and is due to the for- mation of comparatively insoluble compounds. Hydrated oxide of iron and hydrated alumina are capable of forming highly insoluble compounds with all the mineral acids of the soil. The chemist has long been familiar with basic clilorides, nitrates, sulphates, silicates, phosphates and carbonates of these oxides. Whether such compounds can be actually jjroduced in the soil is, how- ever, to some extent, an open question, especially as re- gards chlorine, nitric and sulphuric acids. Their forma- tion must also greatly depend upon what other substances are present. Thus, a soil rich in these hydrated oxides, and containing lime and the other bases in minuter quan- tity (except as firmly combined in form of silicates,) would not unlikely fix free nitric acid or iree sulphuric acid as well as the chlorine of free hydrochloric acid. When the acids are presented in the form of salts, however, as is usually the case, the oxides in question have no power to displace them from these combinations. The acids, can- not, therefore, be converted into basic aluminous or iron salts unless they are first set free — unless the bases to which they were previously combined are first mastered by some separate agent. In the instance before referred to where nitric acid disappeaied from a soil, Knop sup- poses that a basic nitrate of iron may have been formed, the soil employed being, in fact, highly ferruginous. The hydrated oxides of iron and alumina do, however, form insoluble compounds with phosphoric acid^ and may even remove this acid from its soluble combinations with lime, as Thenard has shown, or even, perhaps, from its compounds with alkalies. Phosphoric acid is fixed by the soil in various ways. When a phosphate of potash, for example, is put in 358 IK^W CROPS FKEU. contact with tlie soil, the base may be withdrawn by tlie absorbent silicate, and the acid may iniite to lime or mag- nesia. The phosphates of lime and magnesia thus formed arc, however, insoluble, and hence the acid as well as the base remains fixed. Again, if the alkali-phosphate be present in quantity so great that its base cannot all be taken up by the absorbent silicate, then the hydrated oxide of iron or alumina may react on the phosphate, chemi- cally combining with the phosphoric acid, while the alkali gradually saturates itself with carbonic acid from the air. It is, however, more likely that organic salts of iron (cre- nates and apocrenates) transpose with the phosphate. So, too, carbonate of lime may decompose with phosphate of potash, producing carbonate of potash and pliosphate of lime (J. Lawrence Smith). Vadeker, in a number of ex- periments on the deportment of the sohible superphosphate of lime toward various soils, found that the absorption of phosphoric acid was more rapid and complete with soils containing much carbonate of lime tlian with clays or sands. All observers agree that phosphoric acid is but slowly fix;ed by the soil. Vcelcker found the process was not completed in 26 days. Its absorption is, therefore, mani- festly due to a different cause from that which completes the fixation of ammonia and potash in 48 hours. As to silicic ac'id^ it may also, as solid hydrate, unite slowly with the oxides of iron and with alumina (see Kers- ten's observations, p. 352). When occurring in solution, as silicate of an alkali, as happens in dung liquor, it Avould be fixed by contact with solid carbonate of lime, silicate of lime being formed (Fuchs, Kuhlmann), or by encoun- tering an excess of solutions of any salt of lime, magnesia, iron or ammonia. In presence of free carbonic acid in excess, a carbonate of the alkali would be formed, and the silicic acid would be separated as such in a nearly insoluble ABSORPTIVE fOWEll OF THE SOIL. 350 form. Dung liquor, rich in carbonate of potash, on the other hand, would dissolve silica from the soil. Sulphuric acid, existing in considerable quantities in dung liquor as a readily soluble salt of ammonia or potash, would be partially retained by a soil rich in carbonate of lime by conversion into sulphate of lime, which is com- paratively insoluble. Absorption of Bases, from their Hydrates, Carbonates and SilicateSi — 1. Incidentally it has been remarked that free bases, among which ammonia, potash, soda and lime are specially implied, may be retained by combining with undissolved silica. Potash, soda (and ammonia?) may at once form insoluble compounds if the silica be in large proportion ; otherwise they may produce soluble silicates, wliich, however, in contract with lime, magnesia, alumina or iron salts, will yield insoluble combinations. As is well proved, gelatinous silica and lime at once form a nearly insoluble compound. It is probable that gelatinous silica may remove magnesia from sobxtion of its bicarbon- ate, forming a nearly insoluble silicate of magnesia. 2. It has long been known that hydrated oxide of iron and hydrated alumina may unite with and retain free ammonia, j^otash, etc. Rautenberg experimented with both these substances as freshly prepared by artificial means, and found that, under similar conditions, 10 j,'rm9. ofbytlrated 10 grms. of hydrated oxide of iron. alumina. Absorbed of free ammonia 0.046 grm. 0.066 grm. " " free potash - 0.U7 " not det. Long continued washing with water removes the alkali from these combinations. That oxide of iron and alumina commonly occur in the soil in quantity suflicient to have appreciable effect in absorbing free alkalies is extremely improbable. Liebig has shown {Ann. Ch. u. Fh. 105, p. 122,) that hydrated alumina unites with silicate of potash with great 360 HOW CROPS PEEi). avidity (an insoluble double silicate being formed just as in the experiments of Way, p. 343). According to Liebig, a quantity of hydrated alumina equivalent to 2.696 gnns. of anhydrous alumina, absorbed from a liter of solution of silicate of potash containing 1.185 grra. of potash and 3.000 grm. of silica, fifteen per cent of the silicate. Doubt- less hydrated oxide of iron would behave in a similar manner. 3. The organic acids of humus are usually the most effective agents in retaining the bases when the latter are in the free state, or exist as soluble carbonates or silic- ates. The properties of the humates have been detailed on page 230. It may be repeated here that they form with the alkalies* when the latter preponderate, soluble salts, but th.nt tliese cumjjounds unite readily to other eartliy* and metallic* humates, forming insoluble com- pounds. Lime at once forms an insoluble humate, as do the metallic oxides. When, as naturally happens, the organic acids are in excess, ttieir effect is in all cases to render the soluble free bases or their carbonates nearly insoluble. In some cases, ammonia, potash and soda are absorbed more largely from their carbonates than from their hy- drates. Thus, in some experiments male by the author, a sample of Peat from the New Haven Beaver Meadow Avas digested with diluted solution of ammonia for 48 hours, and then the excess of ammonia was distilled off at a boiling heat. The peat retained 0.95° |^ of this alkali. Another portion of the same peat was moistened with diluted solution of carbonate of ammonia and then dried at 212° until no ammoniacal smell was perceptible. This sample was found to have retained 1.30" |„ of ammonia. This difference was doubtless due to the fact that the * In the customary language of Chemistry, potash, soda, and ammonim ara alkalies or alkali-bases. Lime, magnesia, and alumina are earths or earthy bases, and oxide of iron and oxide of maaganese are metallic bases. KEVIKW AND CONCLUSION. S61 peat contained hamate o/'^/me, which was not affected by tlio pure ainuionia, but in contact witli carbonate of am- monia yielded carbonate of lime and huniate of ammonia. In these cases the ammonia was la excess^ and the chemical changes were therefore, in some particulars, unbke those which occur when the humus preponderates. Brustlein, Liebig and others have observed that soils ricli in organic matter (forest mold, decayed wood,) have their absorptive power much enhanced by mixture with carbonate of lime. Although Rautenberg has shown {Henneherg''s Journal 186, p. 439,) that silicate of lime is probably formed when ordiaiary soils are mixed with carbonate of lime, it may easily happen, in the case of soils containing humus, that humate of lime is produced, which subsequently reacts upon the alkali-hydrates or salts with which absorption experiments are usually made. § 6. REVIEW AND CONCLUSION. The limits assigned to this work having been nearly reached, and the more important facts belonging to the present chapter brought under notice, with considerable fulness, it remains to sum up and also to adduce a few considerations which may appro2:>riately close the volume. There ai-e indeed a number of topics connected with the feeding of crops which have not been treated upon, such, especially as come up in agricultural practice ; but these find their place most naturally and properly in a discussion of the improvement of the soil by tillage and fertilizers, to which it is proposed to devote a third volume. What the Soil mast contain.— In order to feed crops, 16 362 BOW CROPS FEED. the soil must contaiu the ash-ingredieuts of plants, together with assimilable nitrogen-com[iounds in proper quantity and proportion. The composition of a very fertile soil is well exhibited by Baumhauer's analysis of an alluvial de- posit from the waters of the Rhine, near the Zuider Zee, in Holland. This soil, which produces large crops, con« tained — Surface. 15 inches deep. .30 itiches deep. Insoluble eillca, quartz, 57.646 51.706 55.372 Soluble silica, 2.340 2.496 2.286 Alumina, 1.&30 2.900 2.888 Peroxide of iron, 9.039 10.305 11.864 Protoxide of iron, 0.350 0.563 0.200 Oxide of manganese, 0.288 0.354 0.284 Lime, 4.092 5.096 2.480 Magnesia, 0.130 0.140 0.1-28 Potash, 1.026 1.430 1.521 Soda, 1.972 2.069 1.937 Ammonia,* 0.060 0.078 0.075 Phosphoric acid, 0.466 0..324 0.478 Sulphuric acid, 0.896 1.104 0.576 Carbonic acid, 6.085 6.940 4.775 Chlorine, 1.240 1.302 1.418 Humic acid, 2.798 3.991 3.428 Crenic acid, 0.771 0.731 0.037 Apocrenic acid, 0.107 0.100 0.152 Other organic matters, and com- bined water (nitrates ?), 8.324 7.700 9.348 Lobs in analysis, 0.540 0.611 0.753 A glance at the above analyses shows the unusual rich- ness of this soil in all the elements of plant-food, witli ex- ception of nitrates, which were not separately determined. The alkalies, phosphoric acid, and sulphuric acid, were present in large proportion. The absolute quantities of the most important substances existing in an acre of this soil taken to the depth of one foot, and assuming thia * The figures are probably too high for ammonia, because, at the time the analy- ses wore made, the methods of estimating this substance in the soil had not been Btudied sufficiently, and the ammonia obtained was doubtless derived in great part from the dfcomposition of humus under the action of au alkali. REVIEW A>fD CONCLUSION. 36^ quantity to weigh 3,500.000 lbs., (p. 158,) are as follows; Soluble silica 81.900 Lime, 143.2:20 Potasli, 35.910 Soda, 68,920 Ammonia, 2.100 Phosphoric acid 16.310 Sulpliuric acid, 31.360 Nitric acid, ? Quantity of Available Ash-ingredients necessary for a Maximum Crop. — We have already given some of the results of Hellriegel's experiments, made for the purpose of determining how much of the various elements of nu- trition are required to produce a maximum yield of cereals (pp. 215 and 288). This experimenter found that 74 lbs. of nitrogen (in form of nitrates) to 1,000.000 of soil was sufficient to feed the heaviest growth of wheat. Of his experiments on the ash-ingredients of crops, only those relating to potash have been published. Tiiey are here reproduced. EFFECTS OF VARIOUS PROPORTIONS OF AVAILABLE POTASH • IN THE SOIL ON THE BARLEY CROP. Yi£ld Potai^h in 1,000.000 »s.o/«ot;. Of straw and Chaff. Of Grain. Total. 0 0.798 6 3.809 2.993 6.802 12 5.740 4.695 10.435 24 6.859 7.851 14.710 47 8.195 9.578 17.773 71 9.. 327 10.097 19.424 94 8.693 9.083 17.776 141 8.764 8.529 17.293 282 8.916 8.962 17.878 It is seen that the greatest crop was obtained when 71 parts of potash were present in 1,000.000 lbs. of soil. A ♦ Other conditions were in all respects as nearly alike as possible. S64 HOW CROPS PEED. larger quantity depressed the yield. It is iirobable that less than 71 lbs. would have ])roduced an equal effect, since 47 lbs. gave so nearly the same result. The ash composition of barley, grain, and straw, in 100 parts, is as follows, according to Zoeller, (H. C. G., pp. 150 to 151) : Orain. Straio. Potash, 18.5 12.0 Soda, 3.9 4.6 Magnesia, 7.0 3 0 Lime, 2.7 7.3 Oxide of iron, 0.7 1.9 Phosphoric acid. 33.4 6.0 Sulphuric acid, 2.8 2.8 Silica, 31.1 59 7 Chlorine, 1.1 2.6 Tlie proportion of ash in the air-dry grain is 2^ per cent, that in the straw is 5 per cent, {Ann. Ch. u. Ph. CXII, p. 40). Assuming the average barley crop to be 33 bushels of grain at 53 lbs. per bushel = 1,750 lbs., and one ton of straw,* we have in the barley crop of an acre the following quantities of ash-ingredients : il 1 "fe^ 1 •£ S s| 1 1 1 ^1 !i i Grain, 43.75 8.1 1.7 3.1 1.3 0.3 14.2 1.2 0.5 Straw, 100.00 13.0 4.G 3.0 7.3 1.9 0.0 2.8 2.G _ . . — . — — . — — In the account of Ilellriegel's experiments, it is stated that the maximum barley crop in some other of his trials, corresponds to 8,160 lbs. of grain, or 154 bushels of 53 lbs. each per acre. This is more than 4^ times the yield above assumed. The above figures show th:it no essential ash-ingredi- ent of the oat crop is present in larger quantity than potash. Phosphoric acid is quite the same in amount, * These figuree are employed by Anderson, and are based on Scotch statistics REVIEW AND CO^'CLUSION, 365 while lime is but one-luilf as much, and the other acids and bases are still less abundant. It follows then that if 71 lbs. of available potash in 1,000.000 of soil are enough for a barley croj) 4.]- times greater than can ordinarily be produced under agricultural conditions, the same quantity of phosphoric acid, and less than half that amount of litne, .etc., must be ample. Calculating on this basis, we give in the following statement the quantities required per acre, taken to the depth of one foot, to produce the max- imum crop of Ilellriigel (1), and the quantities needed for the average crop of 33 l)ushels ('2). The amounts of nitrogen are those which liellriegel found adequate to the wheat crop. See p. 289. 1 s Potash, 248 55 Soda, 78 17 Magnesia, 76 17 Lime, 105 23 Pliospboric acid, 250 55 Sulplmric acid. 49 11 Clilorine, 38 8 Nitrogen, 245 54 If now we divide the total quantities of potash, etc., found in an acre, or 3,500.000 lbs. of the soil analyzed by Baumhauer, by the number of pounds thus estimated to be necessarily present in order to produce a maxinmra or an average yield, we have the following quotients, which give the number of maximum barley crops and the number of average crops, for which the soil can furnish the re- spective materials. The Zuider Zee soil contains enough Lime for 1364 maximum and 6138 average barlej- crops. Potash " 144 " " 648 " Phosphoric acid " 65 " " 292 " " " Sulphuric " " 64 " " 288 " Nitrogen in ammonia " 7 " " 31 " " " We give next the composition of one of the excellent 366 HOW CROl'S FEED. wheat soils of Mid Lothian, analyzed by Dr. Anderson. The air-dry surface-soil contained in 100 parts : Silica 71.553 Alumina 6.935 Peroxide of iron 5.173 Lime 1.229 Magnesia 1.082 Potash 0.354 Soda 0.433 Sulphuric acid 0.044 Phosphoric acid 0.430 Chlorine traces Organic matter 10.198 Water 2.684 100.116 "We observe that lime, potash, and sulphuric acid, are much less abundant than in the soil from the Zuider Zee. The quantity of ])hos2:)horic 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 iron and alumina 1.640 Lime 0.096 Magnesia trace Carbonic acid trace Phosphoric 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 phos})horic acid, while potash could not even REVIEW AND ( ONOIX'SIOX. 367 be detefted by the tests employed. This soil was mostly naked and destitute of vegetation, and ils composition shows tlie absence of any crop-producing 2>o\ver. Relative Importance of the In^^redients of the Soil. — From the general point of view of vegetable nutrition, all those ingredients of tlie 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 the productiveness of a soil. Thus regardeil, 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 ahundance. Those which, like oxide of irou, are rarely deficient, are for that reason less ])rominent among the factors of a crop. If any single substance, be 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 miy safely state that, on the whole, availa- ble nitrogen and phosphoric acid are the most imj^ortant ingredients of the soil, and potash, perhaps, takes the next rank. These are, most coaimoidy, the substances whose absence or deficiency impairs fertility, and are those which, when added as fertilizers, j^roduce the most frequent and remarkable increase of productiveness. In a multi- tuile of special cases, however, sulphuric acid or lime, or magnesia, assumes the chief prominence, Avhile 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 their 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 diffi'culty compound an artificial soil that should include every element of plant-food in abundance, and yet be perfectly sterile. The potash of feldspar, the pl)osphoric 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 Ziuder Zee, p. 362, give in a single statement their ultimate composition. We are in- formed how much phosphoric acie also shows that a soil of such composition is fertile ; but the analj^sis does not necessarily give proof of the f ict. A nearer approach to providing the data for estimat ing what a soil may sup- ply to crops, is made by ascertaining what it will yield to acids. Chlorine, Sulphuric acid, Carbonic acid, Potash and Soda, Lime, Magnesia, Scsquioxide of iron, REVIEW AND CONCLUSION. 369 Boussingault liua 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: Nitrogen in organic combination, 0.343 Nitric acid, 0.975 Ammonia, O.OIQ.^- Phosphoric acid, "j 0.460 * 0.395 0.023 traces - Soluble in acids. ^ q„q 1.256 0.875 2.450 Sand, fragments of pumice, and clay insolul)le in acids, 83.195 Moisture, 3.150 Organic miitters (less nit rogen), undetermined substances, and loss, 5.938 100.000 This analysis is much more complete in reference to ni. trogen and its compounds, than those by Baumhauer al' ready given (p, 36:2), and therefore has a peculiar value. As regards the other ingredients, we observe that 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 tlie 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. This rock is vesicsular feld- spar, or lias at least a composition similar to feldspar, and the same insolubility in acids. The inert nitrogen of the humus is discriminated from that which 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, 10* 370 HOW CROPS PEED. Boussingault does not state the kind or concentration, or temperature of the acid employed to extract the soil for the above analysis. These are by no means points of indifference. Grouven {Iter db 3ter Salzm under Herichte) has extracted the same earth with hydrochloric acid, con- centrated and dilute, hot and cold, with greatly different results as was to be anticipated. In 1862, a sample from an experimental field at Salzmiinde 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 days 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 OF SOIL OP SALZMtJNDE. not strong acid. IM dilute acid. Cold dilute acid. Potash, .635 .116 .029 Soda, .127 .067 .020 Lime, 1.677 1.046 1.098 Magnesia, .687 .539 .2.37 Oxide of iron and alumina , 7.931 3.180 .650 Oxide of manganese, .030 .086 .071 Sulpliui'ic acid, .059 .039 .020 Phosphoric acid, .059 .091 .057 Silica, 1.785 .234 .175 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 j^lumiua, 4 times as much potasli, 3 times as much soda, REVIEW AND CONCLUSION. 371 twice the amount of magnesia, sulphuric acid, and phos- phoric acid, and the same quantity of lime. These facts show liow very far chemical analysis in its present state is from being able to say definitely what any given soil 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 effect of water on the soil, and the direct action of roots, have been already discussed (pp. 309 to 328). It is unquestionably the fact tliat acids, like pure water in Ulbricht'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 pai'ticular 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 accurately as to the ultimate composition of the soil, but as regards its proximate composition or its cliemical consti- tution, there remains a vast and difficult 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 atmosphei-e 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 tlie air, (pp. 122-135). Again, the atmospheric nitrogen is assimilated by the soil in tlie sliape of ammonia, ni- trates, and the amide-like matters of humus, (pp. 254-265). Tlie 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 UOW CROPS FEED. orological conditions. In tte tropics, both ttese processes go on more vigorously than in cold climates. Every soil has a certain inherent capacity of production in general, which is chiefly 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 quality," without the application of any ma- nure, 20 successive crops of wheat, the first of Avhich was 15 bushels per acre, the last 17^ bushels, and the average of all 161 bushels. {Jovr. Roy. Ag. Soc. of Enrj., XX Y, 490.) The same investigators also raised barley on the same field for 16 years, each year applying the same quan- tity and kinds of manui-e, 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 51§ bushels of grain and 29 cwt. of straw ; and for the 16 years an average of 48j^ bushels of grain and 28^ cwt. of straw. {Jour, of Bath and West ofEnr/.Ag.Soc, XYI,214.) The wheat experiments show the natural capacity of the Rothamstead soil for producing that cereal, and de- monstrate that those matters which are annually 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 ♦ In the experiments of Lawes and Gilbert it was found that phosphates, sul- phates, and carbonates of lime, potash, magnesia, and soda, raised the produce of wheat but 2 to 3 bushels per acre above the yield of the unmanured soil, while sulphate and muriate of ammonia increased the crop 6 to 10 bushels. This re- sult, obtained on three soils, viz., at Rothamstead in Herts, Ilolklmm in Nor- folk, and Rodmersham in Kent, the experiments extending over periods of S. 3, and 4 years, respectivelj;. shows tliat tliese soils were, for the wheat croj). rela- tively deficient in assimilable nitroircn. The crop on tlie nnmanured soil was therefore a measure of nitrification rather tlian of mineral disintegration. REVIEW AND CONCLUSION. ^n tliat 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 atid 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 whioh contain and annually supply the largest proportions of plant-food from their entire mass, those which to the great- est extent originated from good soil-making materials. Soils formed from nearly [)ure 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, M'hich 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 be 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 now CROPS peed. point of remuneration, but the sterility thu5 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 nitrificntion 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, Avould suffer speedy removal did not the soil itself fix them both in combinations, which are at once so soluble that, while tliey 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 naturally 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 ^vecious to the (proving plant art HEVIBW AN1> CONCLUSION. 375 hythe soil converted into, and retained In, a condition not of absolute, bxt <>f relative insolubility, and are kept avail- able to the plant by the continual circulation in the soil of the more abundunt saline matters. " Tlie soil (spt'uking in the widest sense) is then not only tlie ultimate exhaustless source of mineral (fixed) food, to vegetation, hut 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 paragraphs of an article by him " On Some points of Agricultural Science," from the A?nerican Journal of Science and Arts, May. IRj-:). (p. 85). which have historic interest in being, 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 Stadtmuller, of New Haven, Conn., will undertake to furnish collections of the minerals and rocks which chiefly compose soils (see pp. 108-122), suitable for study and illustration, as also the apparatus and materials needful for the chemieal experiments described iu "How Crops Grow.^' TOOPERTY OF X'&M.C0llE6EUBIWRY. STANDARD BOOKS PUBLISHED BV ORANGE JUDD COMPANY ' NEW YORK CHICAGO 03d-Ui Lafayette Street Marquette Building "DOOICS sent to all parts of the world for catalog price. Discounts for large quantities on appli' cation. Correspondence invited. Brief descriptive catalog free. Large illustrated catalogs six cents. Soils By Charles William Burkett, Director Kansas Agri- cultural Experiment Station. The most complete and popular work of the kind ever published. As a rule, a book of this sort is dry and uninteresting, but in this case it reads like a novel. The author has put into it his individuality. The story of the properties of the soils, their improvement and manage- ment, as vi^ell as a discussion of the problems of crop growing and crop feeding, make this book equally valuable to the farmer, student and teacher. There are many illustrations of a practical character, each one suggesting some fundamental principle in soil manage- ment. 303 pages. 5J^ X 8 inches. Cloth. . ... . ,. $1.85 Insects Injurious to Vegetables By Dr. F. H. Chittenden, of the United States Depart- ment _ of Agriculture. A complete, practical work giving descriptions of the more important insects attacking vegetables of all kinds with simple and inexpensive remedies to check and destroy them, together with timely suggestions to prevent their recurrence. 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First-hand knowledge has been the policy of the author in his work, and every crop treated is presented in the light of individual study of the plant. If you have this book you have the latest and best that has been written upon the subject. Illustrated. 450 pages. 5J^ x 8 inches. Cloth $1.75 The Forage and Fiber Crops in America By Thomas F. Hunt, This book is exactly what its title indicates. It is indispensable to the farmer, student and teacher who wishes all the latest and most important information on the subject of forage and fiber crops. Like its famous com- panion, "The Cereals in America," by the same author, it treats of the cultivation and improvement of every one of the forage and fiber crops. With this book in hand, you hav» the latest and most up-to-date information available. Illus^ Irated. 428 pages. 5^ x 8 inches. Cloth. .... Sl.75 The Book of Alfalfa History. Cultivation and Merits. Its Uses as a Forage and Fertilizer. The appearance of the Hon. F. D. 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With the discussions on each disease are given its causes, symptoms, treatment and means of prevention. Every part of the book impresses the reader with the fact that its writer is thoroughly and practically familiar with all the details upon which he treats. All technical and strictly scientific terms are avoided, so far as feasible, thus making the work at once available to the practical stock raiser as well as to the teacher and student. Illustrated. 5x7 inches. 190 pages. Cloth $0.75 Spraying Crops — Why, When and How By Clarence M. Weed, D. Sc. The present fourth edition has been rewritten and reset throughout to bring it thoroughly up to date, so that it embodies the latest practical information gleaned by fruit growers and experiment station workers. So much new information has come to light since the third edition was published that this is practically a new book, needed by those who have utilized the earlier editions, as well as by fruit growers and farmers generally. Illustrated. 136 pages. 5x7 inches. Cloth. .,,,,,,,. I0.50 Farmer's Cyclopedia of Agriculture 0 j3 A Compendium of Agricultural Science and Practice on Farm, Orchard and Garden Crops, and the Feeding and Diseases of Farm Animals Bjf EARLEY VERNON WILCOX, Ph. B. ©nJ CLARENCE BEAMAN SMITH, M.S. Asiociate Bditors in the Office of Experiment Stations, United States "Department of Agriculture. I #w%'|HIS is a new, practical and complete pres- j Jl entation of the whole subject of agricul- ture in its broadest sense. It is designed for the use of agriculturists who desire up-to-date, reliable information on all matters pertaining to crops and stock, but more particularly for the actual farmer. The volume contains Detailed directions for the culture of every important field, orchard, and garden crop grown in America, together with descriptions of their chief insect pests and fungous diseases, and remedies for their control. It contains an account of modei;n methods in feeding land handling all farm stock, including poultry. The diseases which affect different farm animals and poultry are de- scribed, and the most recent remedies suggested for controlling them. Every bit of this vast mass of new and useful information is authoritative, practical, and easily found, and no effort has been spared to include all desirable details. There are between 6,000 and 7,000 topics covered in these references, and it contains 700 royal 8vo pages and nearly 500 superb half- tone and other original illustrations, making the most perfect Cyclopedia of Agriculture ever at- tempted. Handsomely bound in cloth, $3.50; half morocco (Verp sumptuous), $4.50, postpaid ORANGE JUDD COMPANY. ""I'a.^ffi'SS^Mr^fS." oSr""""" """-%".„«« HOW CROPS FEED A TREATISE ON ATMOSPHERE/