IN S SEN . SNS WANN \ AN LIM MAIR BD RCE ros eo. eh Ws AS WRAY taste A ————. de eltes gaeeeew ce 91 § 10. Recapitulation of the Atmospheric Supplies of Food to Crops........... 94 pen opinion of Atmospherie Foods: 2i(ccts 2055... d600ip edhe ade aeend 97 § 12. Tabular View of the Relations of the Atmospheric Ingredients to the A Gg: Sea ee eee Oe ere Maisie wreeiawearn ee 98 CHAP AH Rh Ler: THE ATMOSPHERE AS PHYSICALLY RELATED TO VEGETATION. § 1. Manner of Absorption of Gaseous Food by Plants..........2.ceeeceee see eIY DIVISION II. THE SOIL AS RELATED TO VEGETABLE PRODUCTION. CHAP THE: ~i. INTRODUCTORY. .2 360 ost bce Se er tee SR Uicetuad bestows eodutlet tests .,.104 2 VIII HOW CROPS FEED. CHAP Ti R at. ORIGIN AND FosMATION OF SOILS... 2.4.5. .:5 5.22 .se pes dun oe 106 § 1. Chemical Elements: of Rocks 52. 2..5.0 occ i. 4 ince teereree 121 CTENATCE.-03 hac. Jc Seah Poe eee acne 231 Grenic ACIO .27a)s.. ceteris 227, 229 WIG CAY eee cor cae als «slain cite eres ace 289 WelMWesCeNGe s,s. er Satine rel ree 163 MeSOrts: > acc oo ucierecte Fee ee 197% Mews eect aa oes eee 189, 195 Diffusion of gases. .o6 jas. ease 100 WIOVITC AS. ais oo ot cits eee eee 120 D010) erences MeeOn hoes ose 120 NOlOMILE!< hse Soseen ssc es 115, 121 DCBINTNO'.-< o.concpete css saste eee 185 Drain water, composition Ol aan 312 DTLb. eo. 36. jee = & Ses ze aoe Ree ees 144 Dye struts, fixin Oba ./. cope terres 174 Marth-eloset:.......ct.asicas ences 171 HIFCMACAUSIE): «...4-eesebes tt ary.2) Evaporation, produces cold........ 188 ee amount of, from soil.197 Mis AARON: joe eae aig neta 202, 206 Mxposute Of SO) 3.2.2) e as. «eae 195 MOIS ATs oh ctar.c4 Stans tia Sues eee 108 «growth of barley in.... ..160 MOanMeNtAT OM) oa,sc 40's le meets Uda eats 290 Fixtation of bases in the soil ...... 339 Frost, effects of, on rocks..... .... 124 = « SEAGH SOUST Occ 184, 185 MAROC el, ain ities sive asics weet 258 A808, absorbed by the plant....... 103 4 ‘* porous bodies. .167 “y ae ere SODASs opaie eee 165, 166 is UM MSION, Ofor ea sicitceistertaie 100 ee ORINORE VOL. ok, ort Lene: 102 ETIACIONS ; pic's cas easiows ues a ste ena 124 HOW CROPS FEED, Glycine... .. 25 cbs5 as ceeidtec mites 296 Glycocoll -..../7..shesesee eee 296 Gneiss.s. .vdeeekeeeee rae ats 119 Granite... ; sc.» sd0< ase Renee 118, 120 Gravel. -.:.....4. é2trasee-aee ie eeerennaa 152 “warmth /0f-.\.:. asses oan 195 GUANIN...,.....0<'s0\vesls s/s 296 Gypsum: 6.5532 28 nee 115 ‘** does not directly absorb water .....0%...0 125) pater “fixes smmibRiay... eee 244 Hardpan.. ..xcescean sen eee ee 156 Heat, absorption and radiation of.. 188, 193 ‘* developed in flowering....... 24 “Of SOil: 22. ae eae 187 Hippuri¢ acid), s. 4205-0, someon 295, 277 Hornblende.. (3.4 sae eee eee 112 Hydration of minerals... ......... 127 Hydraulic: cements. > ee) 2-5.) 122 Hydrochloric acid gas.............. 93 Hydrogen, supply of, to plants..... 95 ‘ in decay sc2 een see 291 Hydrous silicates, formation of... .352 Hygroscopic quality... grees) son 164 Humates®, - (42 seagate eee aie 230 Hunii¢ acid’ .2 ge asceee eee eee 226, 229 Humin.. ° 33 oct eee 236, 229 AumUs: 652232). eres eee 186, 224, 276 ‘© absorbent power for water. .162 ‘¢ absorbs salts from solutions.172 ‘action on mineralah=s eee 138 “chemical matoure‘of >. 7 aeons 138 ‘* does it feed the plant?...... 232 ‘* not essential to crops........ 288 "valle Olea noeeaterre Ceeee 182 Jodine in sea=walenion mca. ares 322 Isomorphism: 225 .nss ceteses oeeiiets i Kreatin |... 3.5)ccraeete sent eeeae 196 Kaolinites- pare eke Oe 113, 132 Latent heat. {oleae epee eee 188 Lawes’ and Gilbert’s wheat experi- ments, :. . .\clisebespleet eisai ieraens 312 Leucite \. . 0. “awe Mneilee eee Sees 113 Lime; effectS'0f-. wc... tee 184, 185 Limestone: ....cceesepeier teniee 121, 122 Loam..." . boas mesg eae kcaate ty mmnES 154 Lysimeter.;--2.¢22anch ee eer 314 Maonesite. ........... L's ao atten 115 Marble: o's: ss: Gkane ets ete nee 121 Mar). . 5. .)s:. Sac ecipietelele tener 155 Marsh gas... sien ese eee 91, 99 Mica. .\...0.) % ss esetnsas a eee 109 INDEX, 1 EAS Be eee Ae eee ae 119° 1. TD eo ee eee 106, 108 4s hydration of.... ... PSA rr ie 127 - ROMMIEON: Of e504 s tcae se eee 127 “ec variable composition of. ...110 Moisture, effect of, on temperature SOT Ne ts Aawrmrcteds aatenee 195 PNM te coors nit Su cree Aaton Salomly gee the 156 MoOorDed Pane ws. 242 foes ats s Sx s bs 157 WER Serre VEC ROU ae sie, shes See 155 Nitrate of ammonia........... 71, 73 ** - oa in atmosphere. 89 PRN GEAR es oo hss Nero sere sinda se 252 ef as food for plants.......... 271 “S formed in soil.... ..... 171, 179 sf PAI WREGES: -. Soe tae a Tes 270 bd ROIS OR) SS econ Sess a eee 270 $¢ reduction: of... 2... .- 13, 82, 85 s se SOU BOT hee Ss 268 = (ESSLIS Ty (0) pan ge eae SS Ee fel (3, PILPG RE ss eee A baie bee ens. he 7 Se ‘** as plant-food. .. ... .90, 98 es ** deportment towards the ROU eoe sss. Sade ae soot oe “in atmosphere. . 4.55... 86 = roe TAME WALeT eo fo 5 86 BP eu EE ROM N= 2b) oo fact otsts 251, 254 sae SS te't oe? BONECES (Olas rea. > 256 CURE SIG 5 128 geile dhs wees oS: 72 BNPLIEIG *PCrORIGG. Mosc etc cea fons eed 42 IN MEMCAEON «28 eds wae Te 252, 286 s conditions of...... 265, 292 Nitrogen, atmospheric supply to PIAS be ce te Mya es 2s 95 ne combined, in decay.291, 292 as * of the soil.. .2%5 : combined, of the soil, available pies Fs she 283 = combined, of the soil, TCTEAS b> oy ese Hee Ste 278 st combined, of the soil, quantity needed for crops.288 c free, absorbed by soil. . .167 ye ** assimilated by the ROU e ee al R. 259 ¢ SS MVSOU lec Ste 218 « * not absorbed by vegetation..... 26,99 es ** not emitted by liv- mg plantse.cd ss 23 Nitrogen-compounds, formation of, in atmosphere.75, 77, 1 | | ————— XIII Nitrogenous fertilizers, effect on cereals... 83 Nitrogenous organic matters of soil.274 UNTEEOUS |ACLOIS a0 os a ca wea cae "2 INGTPOUSYORIGE: = nes 13:55. 71, 93 Oohens ties em fence. Seine sacle 156 Oxidation, aided by porous bodies. 169, 170 Oxide of iron, a carrier of oxygen. .257 =e oe hydrated, in the soil.350 Oxygen, absorbed by plants........ 98 ie essential to growth. ..... 23 *t exhaled by foliage...... 25, 99 ee function of, in growth..... 24 a TBO! se-A eas enenere sees 218 cM SUPP] y: .cePese eit Sisal ae 94 ae weathering action of..... 131 ne seh e e Ota, oes oe 63 ** concerned in oxidation of ni- EEO DEN Le SS vee tee a= 82 ‘** formed by chemical action.66, 67 ‘* produced by vegetation.67, 84, 99 ‘** relations of, to vegetable nu- tHONs 4. sdais oc Sees ees 70 Pan: composition Of:..-...4-a5 se eooe Parasitic plants, nourishment of. . .235 REAL Soe ens ane at eee ie es 155, 224 PS CULPOCEN Ole acces eee 27 Phosphate of Jimes.y.i.8 dss Seen es 116 Phosphoric acid fixed by the soil... .357 os ** presence in soil water_ P82. 315 IPHOEPNOTIFE.. 5 bd, 1. Seb dan agi 2 116 Plant-food, concentration of... .....320 se maintenance of supply.371 Platinized: charcoal.\sens2-k Jeaeee 2 70 Platinnm sponge, condenses oxygen170 POR PDY RY. oa inoed DAE FI oho wanes oe 120 Potash, quantity in barley crop.....363 Provence drouths: of-2 wees. ee 198 WYTULESS Saks si Saw es 6 case es 115 Py TORENG SS atacicD ors Soa Se ees 112 UU CE? oe. coats Spree eee ae 120 Potrerachion ©: sje pes Meee eer 290 Ouarias 262 ae aero cot ee ee 108, 122 Rain-water, ammonia in......... 60, 88 ck nitric acid jn........: 86 ee phosphoric acid in.... 94 Ree Ree bottom, soil of...... arr ATS, Respiration of the plant............ 43 ROCKS 2 ork 50 yt eae es aes 106, 117 ‘* attacked by plants. ..........140 XTV Rocks, conversion into soils........ 122 Roots, direct action on soil........ 326 Saline incrustations................ 179 PILED OEGES J Aas coi a? os See Se Ome 252 Salts decomposed or absorbed by CHB BOM. ocd. kote eee ee ORME ee Riess thay ee be See ee ee 153, 162 SEES U1) eg Pi oes Ona 172 Sandstane. jo aici. cs ceasceee ee 121 BerpenuNest-Fi. se see se 114, 121 SehHish, MICACCOUS. |. <0: j.ss0 « eee 119 a THLCORE A. Oy. cctraoec ee eras 121 ee chlorite: ...:\. -aeaseecer sae 121 phaless.s. se eee 122 Sherry wine region.:.:......... 22: 192 Shrinking: of soilss..; : 5562 ewes 183 Silicate. Si esses ee eee 108 “function mthe soil, <2 e7ae 353 *“ of soil, liberated by strong ACIASLS. 4a. eRe eee 330 DUICAtES [0:7 . Ooo nee ee ee 109 Ss zeolitic, presence in soils. .349 Silicic acid, fixed in the soil........358 SKS MYCTOSCOPIGs 2... 0 7 eee eae 165 Soapstone ..j. vase periaaaes eee eee 121 Sod, teniperature of .2./)). 22.0322 199 DOM nots ea hs cee ve heme ee oe 104 ** absorptive power of......... =: 333 *aid- to Oxidation a) - 9. ae eee 170 ** aqueous solution of... .309, 323, 328 + Condenses!Cases; 53: uaa: 165, 166 <* Capacity for Neiaines. y Stranepomeds ai tien ee 143 2 TWIP Ole cc. shiek ol eet eee 158 Solubility, standards of............ 308 HOW CROPS FEED. Solution of soil in acids............ 370 a = to Waber,.. cs. s5--310 Steatite....-<:.2. Nae eemeeeere. s- .ss 121 Swamp muck:..s sce. eee ees sens 155 Sulphates, agents of oxidation..... 258 Sulphate of linte. 225022. eee. 115 Sulphur, in'deeay..-- see eee ee 0 e290 Sulphurous acid. - 2225 2o vara ese 94 Sulphydric*acid: 222-2 e eee te 94 Syenite:......cdie ces easier eeee 120 Tale... .cidiacteee ee Sea eee: 113 Temperature of soil....... 186, 187, 194 Transpiration. :t.2.20cev seer 202, 208 Trap rock.) cis. ec. ceeeeeeee esas 120 Ulmates. 200-2 eee ees beac 230 Ulmic acid: 4.22). 8ie eee 224, 226. 229 Ulm... 6d inns ee ea ee 224, 226, 229 Utea.2 oic1gt ee eee 294, 277 Uric aeid uct FER setae e 295, B77 Brine?:: '.3.4 wus ee eee eee 293 ‘* preserved fresh by clay....... 293 ‘* its nitrogenous principles as- similated by plants.... .... 296 Vegetation, antiquity of............ 138 = GeGay Oia ete. cs... as 137 eS action on soil.......... 140 Volcanic rocks, conversion to soil. .135 Wall frtite). {epee Seager 199 Water absorbed by roots....... 202, 210 ** functions of, in nutrition of plant..2 3:22... Seen 216 “imbibed by soils: ss eee 180 ‘“ movements in soil.... ..... 177 ‘* proportion of in plant, influ- enced by soil.) :-..3-2- 542. 213 ‘Of SOI Ae aes aes 315, 317 eS ‘. “bottom water. i--2n0- 200 **_ capillary’\)27-icsctssmentnes oe 200 “ - Hydroptatiey.es.5 ee ee Pec ‘* hygroscopic?.. Vasher ee 201 ‘* quantity favorable to crops. .214 Water-currentss.c- nc sess one ee 124 Water-vapor, absorbed by soil.161, 164 “ exhaled by plants.... 99 f not absorbed by plants.........85, 99 " of the atmosphere.... 34 Weathering. zs icy uc esiceinaeieee 131-134 Wilting, «. °. 2, geet eer 203 Wool, hygroseopie: ii). feoe sees 164 Zeolites. ........ isan ep onde veueney B49 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 thus the complement of the first-mentioned treatise. Whatever information may be needed as preliminary to an under. standing of this book, the reader may find in “ How Crops Grow.” * That crops grow by gathering and assimilating food is a conception with which all are familiar, but it is only by following the subject into its details that we can gain hints that shall apply usefully in Agricultural Practice. * It has been at least the author's aim to make the first of this series of booke prepare the way for the second, as both the first and the second are written te make possible an intelligible account of the mode of action of Tillage and of Fertilizers. which will be the subject of a third work. 17 18 HOW CROPS FEED. When a seed germinates in a medium that is totally destitute of one or all the essential elements of the plant, the embryo attains a certain development from the mate- rials of the seed itself (cotyledons or endosperm,) but shortly after these are consumed, the p'antlet ceases to in- crease in dry weight,* and dies, or only grows at its own expense. A similar seed deposited in ordinary soil, watered 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 fuld—in weight, runs 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 capa- ble of feeding plants, and, under purely natural conditions, do exclusively nourish 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 cellulose, 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 re- tained in the pores, all comparisons must be made on the @ry, i. e., watersree substance, See ** How Crops Grow,” pp. 53-5, INTROVUCTION. 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 mineral matters. In studying the nutrition of the plant in those stages of its growth that are subsequent to the exhaustion 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 variable 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 plainly 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 the soil involves a con- sideration of its origin and of its manner of formation. The productive soil commonly contains atmospheric 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 especially of its nitrates. These subjects have been recently submitted to extended investigations, and our treatise contains a large ainount of information 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 farm- er. It is through the soil that a supply of solar heat, with: 20 HOW CROPS FEED. out which no life is possible, is largely influenced. Water, whose excess or deticviency 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. 4 WeVIolON F. THE ATMOSPHERE AS RELATED TO VEGETATION. CHAPTER. y- 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 atmosphere. The general composition of the Atmosphere is familiar to all. It is chiefly made up of the two elementary ga-es, 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 weight. By volume. Ceyens cher: Soe pe, ln PAN ee 20.95 INSGPD EN i ae ays neds vj gs = ef OR hare ye 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 abbreviation H.C. G. &. “f IFGy 21 29 HOW CROPS FEED. cur or may occur in the air in minute and variable quanti- ties, viz.: Water, as.vapor...average proportion by weight, 1] 100 Carbonic acid gas as jae ®|10-000 Ammonia we ms ss 1150-000 000 2 Ozone ga ue . ‘¢ minute traces, Nitric acid “ce ce “ce “ce “cc a“ Nitrous acid “ee “cc ae ‘73 «cs ae -Marsh gas a cc “ “ “ce “ In me of Carbonic oxide, “e cc ce “ec ce ce 1 Sulphurous acid, iio s 3 ~ sg towns. Sulphydric acid cc «“c “cc 6“ er “ Miller gives for the air of England the following aver- age proportions by volume of the four most abundant in- eredients.—(Hlements of Chemistry, part IL., p. 30, 3d Ed.) OXSYPCH 2.062. 0 cass peepee beeen 20 61 Mitropen ... 2 s.ea! ss sxsies sel ae 77.95 Carbonic acid. ...: 5. is. csc -seanene mane .04 Water-Vapor, . . .« i0a0 0000s sms Gam eee 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 has, 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. § 2. ‘ RELATIONS OF OXYGEN GAS TO VEGETABLE NUTRITION. Absorption of Oxygen Essential to Growth.—The ele ment Oxygen is endowed with great chemical activity. This activity we find exhibited in the first act of vegeta ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 23 tion, 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., p. 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 manner: Several ‘woody twigs (of willow, oak, apple, ete.) cut in spring-time just before the | iy | Dy | buds should unfold were placed | under a bell-glass containing common air, asin 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. (Recherches sur la Vegetation, p. 115.) The same acute investigator found that oxygen is ab- sorbed by the roots of plants. Fig. 2 shows the arrange- ment by which he examined the effect of different gases on these organs. A young horse-chestnut plant, carefully lifted from the soil so as not to injure its roots, had the latter passed through the neck of a bell-glass, and the stem was then cemented air-tight into the opening. The bell 24 HOW CROPS FEED. was placed in a basin of mereury, C, D, to shut off its con- tents from the external air. So much water was intro- duced as to reach the ends of the principal roots, and the space above was occupied by com- mon or some other kind of air. In one experiment carbonic acid, in a second nitrogen, in a third hydro- gen, and in three others common air, was employed. In the first the roots died in seven or eight days, in the second ang third they perish- ed in thirteen or fourteen days, while in the three others they re- mained healthy to the end of three weeks, when the experiments were coneludel|. (Zecherenes, p. 104.) Flowers require oxygen for their development. Aquatic plants send their flower-buds above the water to blossom. De Saussure found Fig. 2. 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 experience in this process, a considerable r:se of temperature. Garrean, observing the spadix of Arum italicum, which absorbed 284 times its bulk of oxygen in one hour, found it 15° F. warmer than the surrounding air. In the ripening of fruits, oxygen is a!so absorbed in small quantity. The Function of Free Oxygen.—All 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 p'ant, and probably are not cases in which external inorgani¢ bo:lies are built up into ingredients of the vegetable struc- ture. Young seedlings, buds, flowers, and ripening fruits, ATMOSPHERIC AIR AS THE FUOD OF PLANTS. oh have no power to increase in mass at the expense of the atmosphere and soil; they have no provision for the ab- sorption of the nutritive elements that surround them ex- ternally, but grow at the expense of other parts of the plant (or seed) to which they belong. The function of free gaseous oxygen in vegetable nutrition, so far as can be judged from our existing knowledge, consists in 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 oxygea which j is absorbed by the plant, or, at least, a corresponding quantity, is evolved avain, either in the un- combined state or in union with carbon as carbonic acid. Exhalation of Oxygen from Foliage.—The relation of the leaves and green purts 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 light, exhule oxygen. This interesting fact is illustrated TTT by a simple experiment. Fill a glass funnel with any kind of fresh leaves, nnd place it, inverted, in a wide glass containing water, fig. 3, so that it shall be completely immersed, and displace all air from its interior by agitation. Close the neck of the funnel air-tight by | a cork, and pour off a_ portion of the water from the outer vessel. Expose now the leaves to strong sunlight. Observe that very soon minute bubbles of air will gather on the leaves. These will graduilly inGrease in size and detach themselves, and after an hour or two, enough gas will accumulate in the neck of the funnel to enable the experimenter to 2 26 HOW CROPS FEED. prove that it consists of oxygen. For this purpose bring the water outside the neck toa level with that inside; have ready a splinter of pine, the end of which is glow. ing hot, but not in flame, remove the cork, and insert the ignited stick into the gas. It will inflame and burn much more brightly than in the external air. (See H. C. G., p. 35, Exp. 5.) To this phenomenon, one of the most im: portant connected with our subject, we shall recur under the head of carbonic acid, the compound which is the chief source of this exhaled oxygen. Sie RELATIONS OF NITROGEN GAS TO VEGETABLE NUTRITION. Nitrogen Gas not a Food to the Plant.—Nitrog n in the free state appears to be indifferent to vegetation. Priestley, to whom we are much indebted for our knowl- edge of the atmosphere, was led to believe in 1779 that free nitrogen is absorbed by an: feeds the plant. But this philosopher had no adequate means of investigating the subject. De Saussure, twenty years later, having command of better methods of analyzing gaseous mix- tures, concluded from his experiments that free nitrogen does not at all participate in vegetab'e nutrition. Boussingault’s Experiments,—The question rested un- til 1837, when Boussingault made some trials, which, how- ever, were not decisive. In 1851-1855 this ingenious chemist resumed the study of the subject and conducted a large number of experiments with the greatest care, all of which lead to the conclusion that no appreciable amount of free nitrogen is assimilated by plants. His plan of experiment was simply to canse plants to grow in circumstances where, every other condition of de- velopment being supplied, the only source of nitrogen at ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 27 their command, besides that contained in the seed itself, should be the free nitrogen of the atmosphere. For tlris purpose he prepared a soil consisting of pumice-stone and the ashes of stable-manure, which was perfectly freed from all compounds of nitrogen by treatment with acids and in- tense heat. In nine of his earlier experiments the soil thus prepared was placed at the bottom of a large glass globe, B, fig. 4, of 15 to 20 gallons’ capacity. Seeds of cress, dwarf beans, or lupins, were deposited in the soil, and a proper supply of water, purified for the purpose, was add- ed. After germination of the seeds, a glass globe, D, of about one-tenth the capacity of the larger vessel, was filled with carbonic acid (to supply carbon), and was secured air- tight to the mouth of the latter, com- munication being had between them by the open neck at C. The apparatus was then disposed in a suitably lighted place in a garden, and left to itself for a period which va- ried in the different experiments from 14 to 5 months. At 4 the conclusion of the trial the plants were iM lifted out, and, to- gether with the soil from which their roots could not be entirely separated, were subjected to chemical analysis, to determine the amount of nitrogen which they had assimilated during growth. The details of these trials are contained in the subjoined . ~ 28 HOW CROPS FEED. Table. The weights are expressed in the gram and its fractions. es, 2 = purain S| Pao) Be een : TAUWON | hs) WS 2S 6 Bice Sy 3| Kind of Plant. of (iss ss | SS | &s ‘$38 tls § Experiment. $4 SR SS | FB Iss" S gs =| rixits ~ SO ee 1} Dwarf bean. ........|2 months 1 0 780 | 1.87 |0.0349 0.0340 —0.0009 AW OES EU eg, PU MOn SWE ee |2 2 10 | 0.377 | 0.54 0.0078 0.0067/\—0.0011 Se CAD SoS ea oes. Pee 13 Be 1 | 0.530! 0.89 (0.0210 0.0189 —0.0021 4) Vy wal Sapte et Siac 1 | 0.618 | 1.13 |0.0245 0.0226'—0.0019 Bie TOM Ss hss, eee ae [Uy ri 4 | 0.139 | 0.44 |0.0031 0.0030 —0.0001 liad) Diy ov 0c lercpe ey Sears ee a (14% ‘ 2 | 0.825 | 1.82 |0.0430'0.0483)-+-0.0003 7 eer Be Ch Sosat 2 °F 6 | 2.202} 6.73 |0.1282)0.1246|—0.0036 8 St) eer peace ayes aes . 7 weeks 2 | 0.600} 1.95 0.0349 0.0339 —0.0010 9 Me, ashi sie acate cee eee 1 | 0.343 | 1 05 |0.0200 0.0204|+-0.0004 10 peO Pe ee oe er 16 hg 2 | 0.686 | 1.53 |0.0399 0.0397|—0.0002 11) Dwart, bedis 2: =... \2 months 1 | 0.792) 2.35 |0.0354 0.0360)-+-0.0006 12 be SS. Wea brahmnwe thee 2% & 1 | 0.665 | 2.80 0. DR —0.0021 i) CLEBBe ote ces ietdoee |344 ° 3 | 0.008 eS * bs ey See eee as manure 10 | 0.026 { 0.65 De tas 0.0000 FAGAN 5652 got hoa 5 months 2 | 0.6271 » x ‘gn|__ ‘ Pie Pee tee | eee asmanure | 8 | 2.5124 5.716 eit ie 3 0.0130 14| Sum ciao RE he eRe Meee Wipes og tane ..../11.%20 | 30.11 |0.6135!0.5868|—0.0247 While it must be admitted that the unavoidable errors of experiment are relatively large in working with such small quantities of material as Boussingault here employed, we cannot deny that the aggregate result of these trials is de- cisive against the assimilation of free nitrogen, since there was a loss of nitrogen in the 14 experiments, amounting to 4 per cent of the total contained in the seeds; while a gain was indicated in but 3 trials, and was but 0.18 per cent of the nitrogen concerned in them.—(Boussingault’s Agronomie, Chimie Agricole, et Physiologie, Tome I, pp- 1-64.) The Opposite Conclusions of Ville.—In the years 1849, 50, °51, and 752, Georges Ville, at Grenelle, near Paris, experimented upon the question of the assimilability of free nitrogen. His method was similar to that first employed by Boussingault. The plants subjected to his trials were cress, lupins, colza, wheat, rye, maize, sun-flowers, and to- bacco. They were situated in a large octagonal cage mide of iron sashes, set with glass-plates. The air was ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 29 constantly renewed, and carbonic acid was introduced in proper quantity. The experiments were conducted ona larger scale than those of Boussingault, and their result was uniformly the reverse. Ville indeed thought to have established that vegetation feeds on the free nitrogen of the air. To the conclusions to which Boussingault drew from the trials made in the manner already described, Ville objected that the limited amount of air contained in the glass globes was insufficient for the needs of vegetation; that plants, in fact, could not aitain a normal development under the conditions of Boussingault’s experiments.— (Ville, Recherches sur la Vegetation, pp. 29-58, and 53-98.) Boussingault’s Later Experiments,—The latter there- upon instituted a new series of trials in 1854, in which he proved that the plants he had previously experimented upon attain their full development in a confined atmosphere under the circumstances of his first experiments, provided they are supplied with some assimi'able compound of ni- trogen. He also conducted seven new experiments in an apparatus which allowed the air to be constantly renewed, and in every instance confirmed his former results.— (Agronomie, Chimie Agricole et Physiologie, Tome I, pp. 65-114.) The details of these experiments are given in the follow- ing Table. The weights are expressed in grams. e | ¢ Ss Ss & xg a lS oe fe pen emt x SSi xv 2S : Ss S| Kind of Plant. yg jasizs | se) 8s | eile S Experiment. SR! SB fe S2 | => | S25 = E = | = is | °~ = x A | 1 | SQh VU Se ee tee ae ee 10 weeks | 1 | 0.337 | 2.140:0.0196 0.0187 —0. 0009 = ee 10 * 1 | 0.720 | 2.000/0.0322 0.0325 +0.0003 Rye ant ont or es ee 12“ 1 | 0.748 | 2.847 0.0335 0.0341 +0. 0006 Sle 4 1 | 0.755 | 2.240 0.0339 0.0329 —6.0010 eat peewee 13 * 2 | 1.510 | 5.150,0.0676 0.0666 —0.0010 g « 1: 1 BO fo LO ee eee + se tamsinteol cca aer ree 730/0.0858 0.0824 —0 O08 Bar otkasnas a aint PER ee Ted 0.100 | 0.583 0. 0046 0.0052 +0, 0006 | |___— {asmanure! 12 Sum .4.780 | 16.64,0.2269 0.2240 —0.0035 30 HOW CROPS FEED. * Inaccuracy of Ville’s Results—In comparing the in- vestigations of Boussingault and Ville as detailed in their own words, the critical reader cannot fail to be struck with the greater simplicity of the apparatus used by the former, and his more exhaustive study of the possible sources of error incidental to the investigation—facts which are greatly in favor of the conclusions of this skillful and experienced philosopher. Furthermore Cloéz, who was employed by a Commission of the French Academy to oversee the repetition of Ville’s experiments, found that a considerable quantity of ammonia was either generated within or introduced into the apparatus of Ville during the period of the trials, which of course vitiated all his results. Any further doubts with regard to this important sub- ject have been effectually disposed of by another most elaborate investigation. Research of Lawes, Gilbert, and Pugh.—In 1857 and 58, the late Dr. Pugh, afterward President of the Penn- ‘ees Agricultur: a College, associated himself with Messrs. Lawes and Gilbert, af Rothamstead, England, for the purpose of investigating all those points con- nected with the subject, which the spirited discussion of the researches of Boussingault and Ville had suggested as possibly accounting for the diversity of their results. Lawes, Gilbert, and Pugh, conducted 27 experiments on graminaceous and leguminous plants, and on buckwheat. The plants vegetated within large glass bells. They were cut off from the external air by the bells dipping into mercury. They were supplied with renewed portions of purified air mixed with carbonic acid, which, being forced into the bells instead of being drawn through them, ef fectually prevented any ordinary air from getting access to the plants. To give an idea of the mode in which these delicate investigations are conducted, we give here a figure and concise description of the appara- = All wi iin i eee i v i mlb i NY 2 a 9 v a Zi Is o ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 59 Do Healthy Plants Exhale Ammonia ?—The idea having been advanced that in the act of vegetation a loss of ni- trogen may occur, possibly in the form of ammonia, Knop made an experiment with a water-plant, the Zypha lati- folia, a species of Cat-tail, to determine this point. The plant, growing undisturbed in a pond, was enclosed in a glass tube one and a half inches in diameter, and six feet long. The tube was tied to a stake driven for the purpose ; its lower end reached a short distance below the surface of the water, while the upper end was covered air-tight with a cap of India rubber. This cap was penetrated by a narrow glass tube, which communicated with a vessel filled with splinters of glass, moistened with pure hydro- chloric acid. As the large tube was placed over the plant, anarrow 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 Jast named. To guard against any ammonia that possibly might arise from decaying matters in the water, a thin stratum of oil was made to float on the water with- in the tube. Through this arrangement a slow stream of air was passed for fifty hours. At the expiration of that time the hydrochloric acid was examined for ammonia; but none was discovered. Our tests for ammonia are so delicate, that we may well assume that this gas is not ex- haled by the Typha latifolia, The statements to be found in early authors (Sprengel, Schiibler, Johnston), to the effect that ammonia is exhaled by some plants, deserve further examination. 60 HOW CROPS FEED. The Chenopodium vulvaria exhales from its foliage a body chemically related to ammonia, and that has been mistaken for it. This substance, known to the chemist as trimethylamine, is also contained in the flowers of Cra- teegus oxycantha, and is the cause of the detestable odor of these plants, which is that of putrid salt fish.* (Wicke, Liebig’s Ann., 124, p. 338.) Certain fungi (toad-stools) emit trimethylamine, or some analogous compound, (Lehmann, Sachs’ Hxperimentai Physiologie der Pflanzen, 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 folinge when they are sheltered from dew and rain. Such, at least, is the result of certain experi- ments. Boussingault (Agronomie, Chimie 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 watered 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: Weight of seéds:..Scies. 445 4.965 grm’s, - “* “ary, Harvest >....25- 18, 750 -- Nitrogen in harvest and soil.. .2499 ‘“ = I BECOS Saas satus: oe 5 Uy ies 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 * Trimethylamine CgsHyN = N (CH3)3 may be viewed as ammonia NHsg, in which the three atoms of hydrogen are replaced by three atoms of. methy\ . CH. It is a gas like ammonia, and has its pungency, but accompanied with the odor of stale fish. It is prepared from herring pickle, and used in medicine un- der the name propylamine. ‘ ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 61 soil, or upon the foliage of a cultivated field, they bring down to the reach of vegetation in a given time a quantity of ammonia, far greater than what is diffused throughout the limited volume of air which contributes to the nour- ishment of plants. The solubility of carbonate of ammo- nia in water has already been mentioned. In a rain-fall we have the atmosphere actually washed to a great de- gree of its ammonia, so that nearly the entire quantity of this substance which exists between the clouds and the earth, or in that mass of atmosphere through which the rain passes, is gathered by the latter and accumulated within a small space. Proportion of Ammonia in Rain-water, ete.—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 result of their accordant investigations is as follows: In rain-water the quantity of ammonia in the entire fall is very variable, ranging in the country from 1 to 33 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. * In all quantitative statements regarding ammonia, NH3 is to be understood, and not NH,0. 62 HOW CROPS FEED. Boussingault found in the first tenth of a slow-falling rain (24th Sept., 1853) 66 parts of ammonia, in the last three-tenths but 13 parts, to 10 million of water. In dew he found 40 to 62; in fog, 25 to 72; and in one extraordi- nary instance 497 parts in ten million, Boussingault found that the average proportion of am- monia in the atmospheric waters (dew and fogs included) which he was able to collect at Liebfrauenberg (near Stras- burg, France) from the 26th of May to the 8th of Nov. 18538, was 6 parts in 10 million (Agronomie, 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- Radeon: Vol. 3, p. 120.) Pincus ne Roéllig obtained from the atiitodplient wa- ters collected at Inster burg, 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, 54; and in 1866, 73 parts. paix oe d. Deanilectest ious 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, etce.—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 3900 of an acre, the entire rain-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 94 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, g 7, OZONE. When lightning strikes the earth or an object near its surface, a person in the vicinity at once perceives a peculiar, so-called “ sulphureous” odor, which must belong 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 produced is termed ozone, froma Greek word signifying to smell. It is a colorless gas, possessing most remarkab!e 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 HOW 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 isa metal which totally refuses to combine with oxygen under ordinary circumstances, as shown by its maint:ining its brilliancy without symptom of rust or tarnish when exposed to pure air at common or at greatly elevated temperatures. When a slip of moistened silver is placed in a vessel the air of which is charged with ozone, the metal after no long time becomes coated with a black crust, and at the same time the ozone 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 pigments, such as indigo, litmus, ete., are speedily bleached by ozone. This action, also, is simply one of oxidation. Gorup-Besanez (Ann. Ch. u. Ph., 110, 86; also, Physiologische Chemie) has examined the deportment of a number of organic bodies towards ozone. He finds that egg-albumin and casein of milk are rapidly altered by it, while flesh fibrin is unaffected. Starch, the sugars, the organic acids, and fats, are, when pure, 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. Dry substances are unaffected by it. The peculiar deportment towards ozone of certain volatile oils will be presently noticed, * Babo and Claus (Ann. Oh. u. Ph., 2d Sup., p. 804) prepared a mixture of oxy: gen and ozone containing nearly 6 per cent of the latter. ATMOSPHERIC AIR AS THE FOOD OF PLANTS, 65 Tests for Ozone.—Certain phenomena of oxidation that are attended with changes of color serve for the recognitiou of ozone. We havealready seen (H. C. G., p. 64) that starch, when brought in contact with iodine, at once assumes a deer 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 a mixture of starch-paste and solution of iodide of potassium,* we have a test of the presence of ozone, at once most characteristic and delicave. Such paper, moistened and placed in ozonous ¢ air, is speedily turned blue by the action of the liberated iodine upon the starch. By the use of this test the presence and abundance of ozvne ir the atmosphere has been measured. Ozone is Active Oxygen.—That ozone is nothing more or less than oxygen in a peculiar, active condition, is shown by the following experiment. When perfectly pure and dry oxygen is enclosed in a glass tube containing moist metallic silver in a state of fine division, it is possible by long-continued transmissicn of electrical discharges to cause the gaseous oxygen entirely to disappear. On heat- ing the silver, which has become blackened (oxidized) by the process, the original quantity of oxygen is recovered in its ordinary state. The oxygen is thus converted under the influence of electricity into ozone, which unites with the silver and disappears in the solid combination. The independent experiments of Andrews, Babo, and Soret, demonstrate that ozone has a greater density than oxygen, since the latter diminishes in volume when elec- trized. Ozone is therefore condensed oxygen,{ i. e., its molecule contains more atoms than the molecule of ordi- “nary oxygen gas. * Mix 10 parts of starch with 200 parts of cold water and 1 part of recently fused iodide of potassium, by rubbing them together in amortar; 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. + I. e., charged with ozone. ¢ Recent observations by Babo and Claus, and by Soret, show that the density f ozone is one and a half times greater than that of oxygen, 66 HOW CROPS FEED. Allotropism.—This occurrence of an element in two or ever more forms is not without other illustrations, and is termed Allotropism, Phosphorus occurs in two conditions, viz., red phosphorus, which erys- tallizes in rhombobedrons, and like ordinary oxygen is comparatively inactive in its affinities; and colorless phosphorus, which crystallizes in octahedrons, and, like ozone, has vigorous tendencies to unite with other bodies. Carbon is also fotind in three allotropic forms, viz., diamond, plumbago, and charcoal, which differ exccedingly in their chemical and physical characters. Ozone Formed by Chemical Action.—N ot only is ozone produced by electrical disturbance, but it has likewise been shown to originate from chemical action; and, in - fact, from the very kind of action which it itself so vig- orously manifests, viz., oxidation. When a clean stick of colorless phosphorus is placed at the bottom of a large class 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 portion escapes combination and is recognizable in the surrounding air. The ozone thus developed is mingled with other bodies, (phcsphorous 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 *|,,,, of the weight of the air,—is still sufficient to exhibit all the reactions that have been described. Schinbein has shown that various organic bodies which are susceptible of oxidation, viz., citric and tartaric acids, when dissolved in water and agitated with air in the sun- hight for half an hour, acquire the reactions of ozone. Ether and alcohol, kept in partially filled bottles, also be- come capable of producing oxidizing effects. Many of the ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 67 vegetable oils, as oil of turpentine, oil of lemon, vil 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 isa highly probable hypothesis that ozone may be formed in many or even all cases of slow oxidation, and that although the chief part of the ozone thus developed must unite at once with the oxidable substance, a portion of it may diffuse into the atmosphere and escape immediate combination. Ozone is likewise produced 1 a variety of chemical re- actions, whereby oxygen is liberated from combination at ordinary temperatures. When water is evolved by gul-. vanic electricity into free oxygen and free hydrogen, the former is accompanied with 2 small proportion of ozone. The same is true in the electrolysis of carbonic acid. So, too, when permanganate of potash, binoxide of barium, or chromic acid, is mixed with strong sulphuric acid, ox- ygen gas is disengaged which contains an admixture of ozone.* Is Ozone Produced by Vegetation ?—It is an interesting questicn whether the oxygen so freely exhaled from the foliage of plants under the influence of sunlight is accom- panied by ozone. Various experimenters have occupied * It appears probable that ozone is developed in all cases of rapid oxidation at high temperatures. This has been long suspected, and Meissner obtained strong indirect evidence of the fact. Since the above was written, Pincus has announ- ced that ozone is produced when hydrogen burns in the air, or in pure oxygen gas. The quantity of ozone thus developed is sufficient to be recognized by the odor. To observe this fact, a jet of hydrogen should issue from a fine orifice and burn with a small flame, not exceeding %g-inch in length. A clean, dry, and cold beaker glass is held over the flame for a few seconds, when its contents will smell as decidedly of ozone as the interior of a Leyden jar that has just been discharg- ed. (Vs. St., IX, p. 473.) Pincus has also noticed the ozone odor in similar ex- periments with alcohol and oil (Argand) lamps, and with stearine candles. Doubtless, therefore, we are justified in making the generalization that in all cases of oxidation ozone is formed, and in many instances a portion of it diffuses into the atmosphere and escapes immediate combination. 68 HOW CROPS FEED. themselves with this subject. The most recent investiga tions of Daubeny, (Journal Chem. Soc., 1867, pp. 1-28,) lead to the conclusion that ozone is exhaled by plants, a conclusion previously adopted by Scoutetten, Poey, De Luca, and Kosmann, from less satisfactory data. Dau- beny found that air deprived of ozone by streaming through a solution of iodide of potassium, then made to pass the foliage of a plant confined in a glass bell and ex- posed to sunlight, acquired the power of blueing iodide- of-potassium-starch-paper, even when the latter was shield- ed from the light.* Cloéz, however, obtained the contrary results in a series of experiments made by him in 1855, (Ann. de Chimie et de Phys., L, 326,) in which the oxy- gen, exhaled both from aquatic and land plants, contained in a large glass vessel, came into contact with iodide-of- potassium-starch-paper, situated in a narrow and blackened - glass tube. Lawes, Gilbert, and Pugh, in their researches on the sources of the nitrogen of vegetation, (Phil. Trans., 1861) examined the oxygen evolved from vegetable matter under the influence of strong light, without finding evidence of ozone. It is not impossible that ozone was really pro- duced in the circumstances of Cloéz’s experiments, but spent itself in some oxidizing action before it reached the test-paper. .In Daubeny’s experiments, however, the more rapid stream of air might have carried along over the test- paper enough ozone to give evidence of its presence, Al- though the question can hardly be considered settled, the evidence leads to tle belief that vegetation itself is a source of ozone, and that this substance is exhaled, to- gether with ordinary oxygen, from the foliage, when acted on by sunlight. Ozone in the Atmosphere, — Atmospheric electricity, slow oxidation, and combustion, are obvious means of im- pregnating the atmosphere more or less with ozone. If * Light alone blues this paper after a time in absence of ozone, ATMOSPHERIC AIR AS THE FOOD OF PLANTS. .- 69 the oxygen exhaled by plants contains ozone, this sub- stance must be perpetually formed in the atmosphere over a large share of the earth’s surface. The quantity present in the atmosphere at any one time must be very small, since, from its strong tendency to unite with and oxidize other substances, it shortly disappears, and under most circumstances cannot manifest its peculiar properties, except as it is continually reproduced. The ozone present in any part of the atmosphere at any given moment is then, not what has been formed, but what re- mains after oxidable matters have been oxidized. We find, accordingly, that atmospheric ozone is most abundant in winter; since then there not only occurs the greatest amount of electrical excitement * in the atmosphere, which produces ozone, but the earth is covered with snow, and thus the oxidable matters of its surface are prevented from consuming the active oxygen. In the atmosphere of crowded cities, in the vicinity of manure heaps, and wherever considerable quantities of or- ganic matters pervade thie air, as revealed. by their odor, there we find little or no ozone. There, however, it may actually be produced in the largest quantity, though from the excess of matters which at once combine with it, it cannot become manifest. That the atmosphere ordinarily cannot contain more than the minutest quantities of ozone, is evident, if we accept the statement (of Schénbein ?) that it communica‘es its odor distinctly to a million times its weight of air. The attempts to estimate the ozone of the atmosphere give varying results, but indicate a proportion far less than sufficient to be recognized by the odor, viz., not more than 1 part of ozone in 13 to 65 million of air. (Zwenger, Pless, and Pierre.) These figures convey no just idea of the quantities of * The amount of electrical disturbance is not measured by the number and violence of thunder-storms: these only indicate its intensity. 70 HOW CROPS FEED. ozone actually produced in the atmosphere and consumed in it, or at the surface of the soil. We have as yet indeed no satisfactory means of information on this point, but may safely conclude from the foregoing considerations that ozone performs an important part in the economy of nature. Relations of Ozone to Vegetable Nutrition.—Of the direct influence of atmospheric ozone on plants, nothing is certainly known. ‘Theoretically it should be consumed by them in various processes of oxidation, and would have ultimately the same effects that are produced by ordinary oxygen. Indirectly, ozone is of great significance in our theory of vegetable nutrition, inasmuch as it is the cause of chem- ical changes which are of the highest importance in main- taining the life of plants. This fact will appear in the section on Nitric Acid, which follows. 4 § 8. COMPOUNDS OF NITROGEN AND OXYGEN IN THE ATMOS- PHERE. Nitric Acid, NO,H.—Under the more common name Aqua fortis (strong water) this highly important sub- stance is to be found in every apothecary shop. It is, when pure, a colorless, usually a yellow liquid, whose most obvious properties are its sour, burning taste, and power of dissolving, or acting upon, many metals and other bodies. When pure, it isa half heavier than its own bulk of water, and emits pungent, suffocating vapors or fumes; in this state it is rarely seen, being in general mixed or di- luted with more or less water; when very dilute, it evolves no fumes, and is even pleasant to the taste. It has the properties of an acid in the most eminent de- gree; vegetable blue colors are reddened by it, and it ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 71 unites with great avidity to all basic bodies, forming a long list of nitrates. ) f It is volatile, and evaporates on exposure to air, though not so rapidly as water. Nitric acid has a strong affinity for water; hence its vapors, when they escape into moist air, condense the moisture, making therewith a visible cloud or fume. For the same reason the commercial acid is always more or less dilute, it being difficult or costly to remove the water en- tirely. Nitric acid, as it occurs in commerce, is made by heat- ing together sulphuric acid and nitrate of soda, when nitric acid distils off, and sulphate of soda remains behind. Nitrateof Sulphuric Bisulphate of Nitric soda. acid. soda. acid. NO,Na + HSO, = HNaSO, + NO,H Nitrate of soda is formed in nature, and exists in im- mense accumulations in the southern part of Peru, (see p. 252.) Anhydrous Nitric Acid, N,O;, is what is commonly under- stood as existing in combination with bases in the nitrates. It isa crystallized body, but is not an acid until it unites with the elements of water. Nitrate of Ammonia, NH, NO,H, or NH, NO,, may be easily prepared by adding to nitric acid, ammonia in slight excess, and evaporating the solution. The salt read- ily crystallizes in long, flexible needles, or as a fibrous mass. It gathers moisture from the air, and dissolves in about halt its weight of water. If nitrate of ammonia be mixed with potash, soda, or lime, or with the carbonates of these bases, an exchange of acids and bases takes place, the result of which is ni- trate of potash, soda, or lime, on the one hand, and free ammonia or carbonate of ammonia on the other. Nitrous Oxide, N,.O.—When nitrate of ammonia is heated, it 72 HOW CROPS FEED. melts, and gradually decomposes into water and nitrous oxide, 1 “Jaughing gas,’’ as represented by the equation :— NH, NO; = 2H,0: +:N,O Nitric acid and the nitrates act as powerful oxidizing agents, i. e., they readily yield up a portion or all their oxygen to substances having strong affinities for this ele- ment. If, for example, charcoal be warmed with strong nitric acid, it is rapidly acted upon and converted inta carbonic acid. If thrown into melted nitrate of soda ot saltpeter, it takes fire, and is violently burned to carbonid acid. Similarly, sulphur, phosphorus, and most of the 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 with water, is colorless and permanent. It is nitric oxide. By exposure to air it unites with oxy- gen, and forms red, suffocating fumes of nitric peroxide, or, if the oxygen be not in excess, nitrous acid is formed. Nitric Peroxide, (hyponitric acid,) NO,, appears as a dark yellowish-red gas when strong nitric acid is poured upon copper or tin exposed to the air. It is procured in a state of purity by strongly heating nitrate of lead: by a cold approaching zero of Fahrenheit’s thermometer, it may be condensed to a yellow liquid or even solid. : Nitrous Acid, (anhydrous,) N,O,, is produced when nitric peroxide is mixed with water at a low temperature, nitric acid being formed at the same time, Nitrous acid, a anhydrous. 4NO, + 0,0 = 2 NBO. 2 It may be procured as a blue liquid, which boils at the freezing point of water. é Nitric peroxide. Water. Nitric aci ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 13 When nitric peroxide is put in contact with solutions of an alkali, there results a mixture of nitrate and nitrite of the alkali. Nitric Hydrate of Nitrate of Nitrite of ain Water. peroxide. potash. potash. potash. eNO. +. 2KO:. =, NKO...+ NKO,.+ HO 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 : MET NOS 3) CRO oe 2 This decomposition is, however, not complete. A por- tion of ammonia escapes in the vapors, and nitrous acid accumulates in the residual liquid. (Pettenkofer.) Addi- tion of a strong acid facilitates decomposition; an alkali retards it. When a dilute solution, 1 : 500, is boiled, but a small portion of the salt is décomposed, and a part of it is found in the distillate. Very dilute solutions, 1 : 100,00, may be boiled without suffering any alteration whatever. (Sché yen. ) Schénbein 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 ef potish and soda may be procured by strongly heating the corresponding nitrates, whereby oxygen gas is expelled. The Mutual Convertibility of Nitrates and Nitrites is illustrated by various statements already made. There are, in fact, numerous substances which reduce nitrates to nitrites. According to Schénbein, (Jow. Prakt. Ch., 84, 207,) this reducing effect is exercised by the albuminoids, by starch, glucose, and milk-sugar, but not by cane-sugar. _ 74 HOW CROPS FEED. It is also manifested by many metals, as zine, iron, and lead, and by any mixture evolving hydrogen, as, for ex- ample, putrefying organic matter. On the other hand, ozone instantly oxidizes nitrites to nitrates. Reduction of Nitrates and Nitrites to Ammonia, — Some of the substinces which convert nitrates into nitrites may also by their prolonged action transform the latter into ammonia. When smull fragments of zine and iron mixed together are drenched with warm solution of caustic potash, hydrogen is copiously disengaged. Ifa nitrate be added to the mixture, it is at once reduced, and ammonia escapes. If to a mixture of zinc or iron and dilute chlor- hydric acid, such as is employed in preparing hydrogen gas, nitric acid, or any nitrate or nitrite be added, the evolution of hydrogen ceases, or is checked, and ammonia is formed in the solution, whence it can be expelled by lime or potash. Nitric acid. Hydrogen. Ammonia. Water. NOH +. 8H..=. Nj eae The appearance of nitrous acid in this process is an in- termediate step of the reduction. Further Reduction of Nitric and Nitrous Acids—Un- der certain conditions nitric acid and nitrous acid are still further deoxidized. Nesbit, who first employed the reduc- tion of nitric acid to ammonia by means of zine and dilute chlorhydric acid as a means of determining the quantity of the former, mentions (Quart. Jour. Chem. Soc., 1847, p- 283,) that when the temperature of the liquid is allowed to rise somewhat, nitric owide gas, NO, escapes. From weak nitric acid, zinc causes the evolution of ni- trous oxide gas, N,O. As already mentioned, nitrate of ammonia, when heated to fusion, evolves nitrous oxide, N,O. Emmet showed that by immersing a strip of zine in the pa salt, nearly pure nitrogen gas is set free. ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 45 When nitric acid is heated with lean flesh (fibrin), nitric. oxide and nitrogen gases both 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 Nitric and Nitrous Acids, — The fact that these substances often occur in extremely minute quantities renders it needful to employ very delicate tests for their recognition. Price's Test.—F ree nitrous acid decomposes iodide of potassium in the same manner as ozone, and hence gives a blue color, with a mixture of this salt and starch-paste: Any nitrite produces the same effect if to the mixture dilute sulphuric acid be added to liberate the nitrous acid. Pure nitric acid, if moderately dilute, and dilute solutions of nitrates mixed with dilute sulphuric acid, are without immediate effect upon iodide-of-potassium-starch-paste. If the solution of a nitrate be min- gled with dilute sulphuric acid, and agitated for some time with zine filings, reduction to nitrite occurs, and then addition of the starch-paste, ete., gives the blue coloration. According to Schénbein, this test, first proposed by Price, will detect nitrous acid when mixed with one-hund- red-thousand times its weight of water. It is of course only applicable in the absence of other oxidizing agents. Green Vitriol Test.—A very characteristic test for nitric and nitrous acids, and a delicate one, though less sensitive than that just describ- ed, is furnished by common green vitriol, or protosulphate 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 sulphuric 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 Nitrogen Compounds in the Atmosphere. —a. From free nitrogen, by electrical ozone. Schénbein 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- 76 HOW CROPS FEED. tricity directly, but the ozone developed by it, accom- plishes this oxidation. It has long been known that nitric peroxide decomposes with water, yitiding nitric and ni- trous acids thus: 2NO, + H,O .=. NOT +23 It is further known that nitrous acid, both in the free state and in combination, is instantly oxidized to nitric aci:l by contact with ozone. Thus is explained the ancient observation, first made by Cavendish in 1734, 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 Boussingault, that visible or andible 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 sélent electrical discharges develop more ozone than flashes of lightning. Meissner has shown that the electric spark causes the copious formation of nitric peroxide in its im- mediate path by virtue of the heat it excites, which in- creases the energy of the ozone simultaneously produced, and causes it to expend itself at once in the oxidation of nitrogen. Boussingault informs us that in some of the tropical regions of South America audible electrical dis- charges are continually taking place throughout the whole year. In our latitudes electrical disturbance is perpetu- ally occurring, but equalizes itself mostly by silent dis- charge. The ozone thus noiselessly developed, though operating at a lower temperature, and therefore more ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 77 slowly than that which is produced by lightning, must really oxidize much more nitrogen to nitric acid than the latter, because its action never ceases. Formation of Nitrogen Compounds in the Atmosphere, —b. From free nitrogen (by ozone?) in the processes of ,) combustion and slow oxidation. At high temperatures.—Saussure first observed (Ann. de Chimie, 1xxi, 282), that in the burning of a mixture of oxygen and hydrogen gases in the air, the resulting water contains »mmonia. He had previously noticed that nitric acid and nitrous acid are formed in the same process. Kolbe (Ann. Chem. u. Pharm., cxix, 176) found that when a jet of burning hydrogen was passed into the neck of an open bottle containing oxygen, reddish-yellow va- pors of nitrous acid or nitric peroxide were copiously pro- duced on atmospheric air becoming mingled with the burning gases. Bone Jones (Phil. Trans., 1851, il, 399) discovered ni- tric (nitrous ?) acid in the ie oe from the burn- ing of alcohol, hydrogen, coal, wax, and purified coal-gas. By the use of the iodide-of-potassium-starch test (Price’s test), Boettger (Jour. fiir Prakt. Chem., \xxxv, 396) and Schénbein (ibid., lxxxiv, 215) 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 simultancously formed, that, in fact, nitrite of ammonia is generated in all cases of rapid combustion. Meissner ( Untersuchungen 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. u. Ph., xxx, 54) in a series of careful experiments, found that when alcohol, il- luminating gas, and hydrogen, burn in the air, nitrous said and ammonia are very frequently, but not always, formed. 78 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 eme- 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 Schénbein, 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 temperatures.—Schonbein was the first to observe that nitric acid may be formed at moderately elevated or even ordinary temperatures. He obtained several grams of nitrate of potash by adding carbonate of potash to the liquid resulting from the slow oxidation of phosphorus in the preparation of ozone. More recently he believed to have discovered that ni- trogen compounds are formed by the simple evaporation of water. He heated a vessel (which was indifferently of * Meissner rejected Price’s test in the belief that it cannot serve to distinguish nitrous acid from peroxide of hydrogen, Hz Og. He therefore made the liquid to be exareined alkaline with a slight excess of potash, concentrated to small bulk and tested with dilute sulphuric acid and protosulphate of iron. (Unters. ii. a. Sauerstoff, p. 233). Schénbein had found that iodide of potassium is decom- posed after a little time by concentrated solutions of peroxide of hydrogen, but is unaffected by this body when dilute, (Jour. fir prakt. Chem., \xxxvi, p. 90). Zabelin agrees with Schénbein that Price’s test is decisive between peroxide of hydrogen and nitrous acid. (Ann. Chem. u. Ph., CXXX, p. 58.) ATMOSPHERIC AIR AS THE FOOD OF PLANTS, 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 vollected 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 ae of acidified iodide-of- potassium-starch-paste upon it, the reaction of nitrous acid was 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 with the above named test. Lastly, nitrous 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 tem»:ratures, in the open air or in a closed vessel. (Jour. fir Prakt. Chem., \xvi, 131.) These ex- periments of SchSnbein are open to criticism, and do not furnish perfectly satisfactory evidence that nitrous acid and ammonia are generated under the circumstances men- tioned. Bohlig has objected that these bodies might be gathered from the atmosphere, where they certainly exist, though ; in extremely minute quantity. eae in the paper before referred to (Ann. Ch. Phe 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 Ness- 80 HOW CROPS FEED. ler’s test,* which is of extreme delicacy, and which he con- stantly employed in his investigations. Zabelin 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- p2per or shreds of linen) yielded no ammonia to Nessler’s test when heated in a current of air at temperatures of 120° to 160° F. Lastly, he found that when cellulose and pure water to- gether were exposed to a current of air at the tempera- tures just named, ammonia was at once indicated by Nessler’s test. Nitrous acid, however, could be detected, if at all, in the minutest traces only. Views of Schinbein.—The reader should observe that Boettger and Schinbein, 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 sensitive litmus test-paper, concluded that the nitrous acid was united with some base in the form of a neutral salt. Af- terward, the detection of ammonia appeared to demon- strate the formation of nitrite of ammonia. We have already seen that nitrite of ammonia, by ex- posure to a moderate heat, is resolved into nitrogen and water. Schénbein assumed that under the conditions of * See p. 54 ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 81 his experiments nitrogen and water combine to form ni- trite of ammonia. 2N + 2H,O = NH, NOH This theory, supported by the authority of so distin- guished a philosopher, has been almost 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 water, or lastly in close proximity to the ames 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 Schénbein’s experiments prevail at all times and at all places, so far as these substances are con- cerned. The discovery of Zabelin that ammonia and nitrous acid do not always appear in equivalent quantities or even simultaneously, while difficult 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 Schénbein in case of urine. 4* 82 HOW CROPS FEED. command for experimental study, will establish or disprove them by suitable investigations. He believes, from the existing evidence, that free nitro- gen can, in no case, unite directly with water, but in the conditions of all the foregoing experiments, it enters com- bination by the action of ozone, as Schénbein formerly maintained and was the first to suggest. We have already recounted the evidence that goes to show the formation of ozone in all cases of oxidation, both at high and low temperatures, p. 67. In Zabelin’s experiments we may suppose that ozone was formed by the oxidation of the cellulose (linen and paper) he employed. In Schénbein’s experiments, where paper or linen was not employed, the 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 nitrous acid is formed, but is afterward reduced to ammonia, as has been already explained, p. 74. Zabelin, in the article before cited, refers to Schénbein as authority for the fact that various organic bodies, viz., all the vegetable and animal albuminoids, gelatine, and most of the carboliydrates, 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 Schénbein’s papers to which we have had access, it is entirely credible and in accordanee with numerous analogies. If, as thus appears extremely probable, ozone is devel- oped in all cases of oxidation, both rapid and slow, then ey a ve % ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 83 every flame and fire, every decaying plant and animal, the organic matters that exhale from the skin and lungs of living animals, or from the foliage and flowers of plants, especially, perhaps, the volatile oils of cone-bearing trees, are, indirectly, means of converting a portion of free n1- 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 Nitrogen Compounds in the Atmosphere. —c. From free nitrogen by ozone accompanying the oxy- gen exhaled from green foliage in sunlight. The evidence upon the question of the emission of ozone by plants, or of its formation in the vicinity of foliage, has been briefly presented on page 68. The present state of investigation does not permit us to pronounce definitely upon this point. There are, however, some facts of agri- culture which, perhaps, find their best explanation by as- suming this evolution of ozone. Tt has long been known that certain crops are especially aided in their growth by nitrogenous fertilizers, while oth- ers are comparatively indifferent to them. Thus the cereal grains and grasses are most frequently benefited by appli- cations of nitrate of soda, Peruvian guano, dung of ani- mals, fish, flesh and blood manures, or other matters rich in nitrogen. On the other hand, clover and turnips flour- ish best, as a rule, when treated with phosphates and alka- line substances, and are not manured with animal fertiliz- ers so economically as the cereals. It has, in fact, become a rule of practice in some of the best farming districts of England, where systematic rotation of crops is followed, to apply nitrogenous manures to the cereals and _phos- phates to turnips. Again, it is a fact, that whereas nitro- genous manures are often necessary to produce a good wheat crop, in which, at 30 bu. of grain and 2,600 Ibs. of straw, there is contained 45 lbs. of nitrogen; a crop of clover may be produced without nitrogenous manure, in 84 HOW CROPS FEED. which would be taken from the field twice or thrice the above amount of nitrogen, although the period of growth of the two crops is about the same. Ulbricht found in his investigation of the clover plant (Vs. S¢., IV., p. 27) that the soil appears to have but little influence on the content of nitrogen of clover, or of its individual organs. These facts admit of another expression, viz.: Clover, though containing two or three times more nitrogen, and requiring correspondingly larger supplies of nitrates and ammonia than wheat, 7s able to supply itself much more easily than the latter crop. In parts of the Genesee wheat region, it is the custom to alternate clover with wheat, be- cause the decay of the clover stubble and roots admirably prepares the ground for the last-named crop. The same preparation might be had by the more expensive process of dressing with a highly nitrogenous manure, and it is scarcely to be doubted that it is the mitrogen gathered by the clover which insures the wheat crop that follows. It thus appears that the plant itself causes the formation in its neighborhood of assimilable compounds of nitrogen, and that some plants excel others in their power of accom- plishing this important result. On the supposition that ozone is emitted by plants, it is plain that those crops which produce the largest mass of foliage develop it most abundantly. By the action of this ozone, the nitrogen that bathes the leaves is convert- ed into nitric acid, which, in its turn, is absorbed by the plant. The foliage of clover, cut green, and of root crops, maintains its activity until the time the crop is gathered ; the supply of nitrates thus keeps pace with the wants of the plant. In case of grain crops, the functions of the fo- liage decline as the seed begins to develop, and the plant’s means of providing itself with assimilable nitrogen fail, although the need for it still exists. Furthermore, the clover cut for hay, leaves behind much more roots and stubble per acre than grain crops, and the cloyer stubble ATMOSPHERIC AIR AS THE FOOD OF PLANTS, 85 is twice as rich in nitrogen as the stubble of ripened grain. This is a result of the fact that the clover is cut when in active growth, while the grain is harvested after the roots, stems, and leaves, have been exhausted of their own juices to meet the demands of the seed. . Whatever may be the value of our explanations, the fact is not to be denied that the soil is enriched in nitrogen by the culture of large-leaved plants, which are harvested while in active growth, and leave a considerable propor- tion of roots, leaves, or stubble, on the field. On the other hand, the field is impoverished in nitrogen when grain crops are raised upon it. Formation of Nitric Acid from Ammonia,—Ammonia (carbonate of ammonia) under the influence of ozone is converted into nitrate of ammonia, (Baumert, Houzeau). The reaction is such that one-half of the ammonia is oxid- ized to nitric acid, which unites with the residue and with water, as illustrated by the equation : pa OO ONE NOD HO In this manner, nitrate of ammonia may originate in the atmosphere, since, as already shown, ammonia and ozone are both present there. Oxidation and Reduction in the Atmosphere. — The fact that ammonia and organic matters on the one hand, and ozone, nitrous and nitric acids on the other, are pres- ent, and, perhaps, constantly present in the air, involves at first thought a contradiction, for these two classes of sub- stances are in a sense incompatible with each other. Organic matters, ammonia, and nitrous acid, are converted by ozone into nitric acid. On the contrary, certain or- ganic matters reduce ozone to ordinary oxygen, or destroy it altogether, and reduce nitric and nitrous acids to am- monia, or, perhaps, to free nitrogen. The truth is that the substances named are being perpetually composed and decomposed in the atmosphere, and at the surface of the 86 HOW CROPS FEED, soil. Here, or at one moment, oxidation prevails; there, or at another moment, reduction preponderates. It is only as one or another of the résults of this incessant ac- tion is withdrawn from the sphere of change, that we can give it permanence and identify it. The quantities we measure are but resultants of forces that oppose each oth- er. The idea of rest or permanence is as foreign to the chemistry of the atmosphere as to its visible phenomena. Nitric Acid in the Atmosphere,—The occurrence of ni- tric acid or nitrate of ammonia in the atmosphere has been abundantly demonstrated in late years (1854-6) by Cloez, Boussingault, De Luca, and Kletzinsky, who found that when large volumes of air are made to bubble through solutions of potash, or to strgam over fragments of brick or pumice which have been soaked in potash or carbonate of potash, these absorbents gradually acquire a small amount of nitric acid. In the experiments of Cloez and De Luca, the air was first washed of its ammonia by con- tact with sulphuric acid. Their results prove, therefore, that the nitric acid was formed independently of ammonia, though it doubtless exists in the air in combination with this base. Proportion of Nitric Acid in Rain-water, etc.—In at- mospheric waters, nitric acid is found much more abund- antly than in the air itself, for the reason that a small bulk of rain, etc., washes an immense volume of air. Many observers, among the first, Licbig, have found ni- trates in rain-water, especially in the rain of thunder- storms. The investigations of Boussingault, made in 1856-8, have amply confirmed Barral’s observation that nitric acid (in combination) is almost invariably present in rain, dew, fog, hail, and snow. Boussingault, (Agronomie, etc., 11, 825) determined the quantity of nitric acid in 134 rains, 31 snows, 8 dews, and 7 fogs. In only 16 instances out of these 180 was the amount of nitric acid too small ee ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 87 to detect. The greatest proportion of nitric acid found in rain occurred in a slow-falling morning shower, (9th Octo- ber, 1857, at Liebfrauenberg), viz., 62 parts * in 10 million of water. In fog, on one occasion, (at Paris, 19th Deec., 1857,) 101 parts to 10 million of water were observed. Knop found in rain-water, collected near Leipzig, in July, 1862, 56 parts; in rain that fell during a thunder- storm, 98 parts in 10 million of water. Boussingault found in rain an average of 2 parts, in snow of 4 parts, of nitric acid to 10 million of water. Mr. Way, whose determinations of ammonia in the at- mospheric waters collected by Lawes and Gilbert, at Rothamstead, during the whole of the years 1855-6, have already been noticed, (p. 63,) likewise estimated the nitric acid in the same waters. He found the proportion of ni- tric acid to be, in 1855, 4 parts, in 1856 44 parts, to 10 million of water. Bretschneider found at Ida-Marienhiitte, Prussia, for the year 1865-6 an average of 8} parts, for 1866-7 an average of 44 parts, of nitric acid in 10 million of water. At Regen- walde, Prussia, the average in 1865-6 was 25 parts, in 1866-7, 22 parts. At Proskau, the average in 1864-5 was 31 parts. At Kuschen, the average for 1864-5 was 6 parts; in 1865-6, 7; in 1866-7, 8 parts. At Dahme, in 1865-6, the average was 12 parts. At Insterburg, Pincus and Rollig obtained in 1864-5, an average of 12 parts; in 1865-6, an average of 16 parts of nitric acid in 10 million of water. The highest monthly average was 280 parts, at Lauersfort, July, 1864; and the lowest was nothing, April, 1865, at Ida-Marienhiitte. Quantity of Nitric Acid in Atmospheric Water,—The total quantity of nitric acid that could be collected in the rains, ete., at Rothamstead, amounted in 1855 to 2.98 lbs., and in 1856 to 2.80 Ibs. per acre. * In all the quantitative statements here and elsewhere, anhydrous nitric acid, Nez O05, (O=16, formerly NO5, O=8) is to be understood. 88 HOW CROPS FEED. This quantity was very irregularly distributed among the months. In 1855 the smallest amount was collected in January, the largest in October, the latter being nearly 20 times as much as the former. In 1856 the largest quantity occurred in May, and the smallest in February, the former not quite six times as much as the latter. The following table gives the results of Mr. Way entire. (Jour. Roy. Ag. Soc. of Hng., XVII, pp. 144 and 620.) AMOUNTS OF RAIN AND OF AMMONIA, NITRIC ACID, AND TOTAL NITROGEN therein, collected at Rothamstead, Eng., in the years 1855-6—calculated per acre, according to Messrs. Lawes, Gilbert, and Way. Quantity of Rain Ammonia | Nitric | Total Ni- in Imperial Gal- acid in \trogen in sagea Meg r.) ee g rains. grains. g? "ins. 1855 | 1856 /1855| 1856 /1855)1856) 1855) 1856 PAAR YS AAW SS ss ok y Shain = BS 13.523) 62.952 1244) 5005 230 1561/1084 4526 WRAY 5 255 on oes iys eee ie 22.473). 30.586/2337| 4175 | 944! 544.2169] 3579 CU | Miah y Sate Oe: Ea haa 52.484) 22.722/4513 2108 |1102 806 3995 1945 EE Re aah ea PL Sean 9.281| 59.083 1141) 8614 | 3251063 1024) 7369 Me tec ein eats ae 52.575 106.474/4206 18313 |1840 3024/3939 15863 TiS OR es eR? oi aaa 41.295) 43.253'5574! 4870 (3303) 2046/5447) 4540 EN AS AA ie Os eR 157.713 33.561 9620) 2869 |2680 1191/8615) 2670 Ra Te es Ae ee 59.622, 59.859 4769) 4214 [3577 2125/4870) 4021 LEE EC 2s eae a et eS 34.875] 47.477 3313] 5972 | 732 1'756 2917) 5373 Memabier! 3205, cde eltee A 124.466 65.033 7592) 3921 |4480 2075/7414) 3767 Marember 2.) ney aoe k 59.950 32.181 3021} 2591 |1007,1371 2749, 2489 Wiectmubide 405 Baede< 2705 39.075) 50.870 2438] 4070 | 664 2035 2180) 3352 Thi oe *. 6.2. ios aes | 663.332) 616.051.7.11| 9.58 |2.98 2. =r s 63| 8.31 | gall’s. | gall’s. ilbs.| Ibs. ilbs.!Ibs./Ibs.| Ibs. According to Pincus and Rillie, 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. The quantity of nitrogen that fell as 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% Ibs. of nitric acid per acre of surface. In Bretschneider’s investigation. the amount of nitrogen eee ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 89 brought down per acre in the form of ammonia was 9.936 Ibs.; that in the form of nitric acid was 0.974 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- tralblatt, August, 1866.) Relation of Nitric Acid to Ammonia in the Atmos- phere,—The foregoing results demonstrate that there is in the aggregate an excess of ammonia over the amount required to form nitrate with the nitric acid. (In nitrate of ammonia (NH, NO,), the 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 (Compt. Rendus, 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 exceptionally 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 is doubtless 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 atmosphere, and * In evaporating large quantities of rain-water to dryness, there are often found in the residue nitrates of lime and soda. In these cases the lime and soda come from dust suspended in the air. 90 HOW CROPS FEED. until in some way chemically decomposed, belongs to the soil or to the rivers and seas. Nitrous Acid in the Atmospheric Wuters.—In most of the researches up- on the quantity of nitric acid in the atmosphere and meteoric waters, nitrous acid has not been specially regarded. The tests which serve to detect nitric acid nearly all apply equally well to nitrous acid, and no discrimination has been made until recently. According to Schénbein and Bohlig, nitrates are sometimes absent from rain-water, but nitrites never. They occur, however, in but minute proportion. Pineus and Réllig observed but traces of nitrous acid in the waters gathered at Insterburg. Reichardt found no weighable quantity of nitrous acid in a sample of hail, the water from which contained in 10 million parts, 32 parts ammonia and 5g parts of nitric acid. It is evident, then, that nitrous acid, if produced to any extent in the atmosphere, does not re- min 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. The 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. Nitric 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 they 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. ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 91 The nitrates do not appear to be absorbed by the plant to any great extent, except through the medium of the soil, since 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. 271. In § 10, p. 96, “Recapitulation of the Atmospheric Supplies of Food to Crops,” the inadequacy of the at- mospheric nitrates will be noticed. § 9. OTHER INGREUVIENTS OF THE ATMOSPHERE; viz., Marsh Gas, Carborie Oxide, Nitrous Oxide, Hydrochloric Acid, Sulphurous Acid, Sulphydrie Acid, Organic Vapors, Suspended Solid Matters. There are several other gaseous bodies, some or all of which may oc- cur in the atmosphere in very minute quantities, but whose relations to vegetation, in the present state of our knowledges, 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. Marsh Gas,* C H,.—This substance is a colorless and nearly odorless gas, which is formed almost invariably when organic matters suffer decomposition in absence of oxygen. When a lump of coal ora billet of wood is strongly heated, portions of carbon and hydrogen unite to form this among several other substances. It is accordingly one of the ingredients of the gases whose combustion forms the flame of all fires and lamps. It is also produced in the decay of vegetable mat- ters, especially when they are immersed in 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 gaseous 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 Methane. 92 HOW CROPS FEED. The mode of ifs origin at once suggests its presence in the atmos- phere. Saussure observed that common air contains some gaseous com- pound or compounds of carbon, besides carbonic acid; and Boussin- gault found iu 1834 that the air at Paris contained a very small quantity (from two to eight-millionths) of hydrogen in some form of combina- tion besides water. These facts agree with the supposition that marsh gas is anormal though minute and variable ingredient of the atmosphere. Relations of Marsh Gas to Vegetation.—Whether this gas is absorbed and assimilated by plants isa point on which we have at present no information. It might serve as a source both of ear- bon and hydrogen; but as these bodies are amply furnished by carbonic acid and water, and as it is by no means improbable that marsh gas it- self is actually converted into these substances by ozone, the question of its assimilation is one of little importance, and remains to be inves- tigated. Schultz (Johnston’s Lectures on Ag. Chem., 2d Ed., 147) found on sey- eral occasious that the gas evolved from plants when exposed to the sun- light, instead of being pure oxygen, contained a combustible admixture, so that it exploded violently on contact with a lighted taper. This observation shows either that the healthy plants evolved a large amount of marsh gas, which forms with oxygen an explosive mixture (the fire-damp of coal-mines), or, as is most probable, that the vegetable matter entered into decomposition from too long cortinuance of the experiment. Boussingault has, however, recently found a minute proportion of marsh gas in the air exhaled from the leaves of plants that are exposed to sunlight when submerged in water. It does not appear when the leaves are surrounded by air, as the latest experiments of Boussingault, Cloez, and Corenwinder, agree in demonstrating. Carbonic Oxide, CO, isa gas destitute of color and odor. It burns in contact with air, with a flame that has a fine blue color. The result of its combustion is carbonic acid, CO + O = CO,. This gas is extremely poisonous to animals. Air containing a few per cent of it is unfit for respiration, and produces headache, insensi- bility, and death. Carbonic oxide may be obtained artificially by a variety of processes. If carbonic acid gas be made to stream slowly through a tube containing ignited charcoal, it is converted into carbonic oxide, CO, + C = 2 CO. Carbonic oxide is largely produced in all ordinary fires. The air which draws through a grate heaped with well-ignited coals, as it enters the bottom of the mass of fuel, loses a large portion of its oxygen, which there unites with carbon, forming carbonic acid. This gas is carried up into the heated coal, and there, where carbon is in excess, it takes up an- other proportion of this element, being converted into carbonic oxide, At the summit of the fire, where oxygen is abundant, the carbonic oxide burns again with its peculiar blue color, to carbonie acid, provided the heat be intense enough to inflame the gas, as is the case when the mass ~ ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 93 of fuel is thoroughly ignited. When, on the other hand, the fire is cov- ered with cold fuel, carbonic oxide escapes copiously into the atmos- phere. When crystallized oxalic acid is heated with oil of vitriol, it yields water to the latter, and falls iuto a mixture of carbonic acid and carbonic oxide. c, 8,0, 20,0""=- €0; ‘+-:CO' + “3 HO. Carbonic oxide may, perhaps, be formed in small quantity in the de- cay of organic matters; though Corenwinder (Compt. Rend., LX, 102) failed to detect it in the rotting of manure. Relations of Carbonic Oxide to Vegetation.— asde | LOO4=OT | ADs o> ||Greee Abbe * 4 te re Se), 2 Shs -6 hh Gs8L. <2) 5.383 478s" Regenwalde, near Stettin, SO 2. O64 5 Fila. 09k 252 |Sthe abe es s of ‘eg. | 1865-61/10.38 “* [4,358,053 °° Ida-Marienhiitte, near Breslau, Silesia, ‘‘ ....| 1865* {11.83 ‘* |4,877.545 ‘ Proskan, Silesia. oe) 1864-55/20. 98. 8: 4208L-7See. 5 Dahme, Province Brandenburg, es oq. estos: 36.60)" (3-868:64m) NADIE ea ee a each Sle shee Se SOAs kee ee 8.76 lbs./4.867.0%5 lbs. Direct Atmospheric Supply of Nitrogen Insufficient for Crops.—To estimate the adequacy of these atmos- pheric supplies of assimilable nitrogen, we may compare their amount with the quantity of nitrogen required in the 96 WOW CROPS FEED. composition of standard crops, and with the quantity con- tained in appropriate applications of nitrogenous fertil- izers. The average atmospheric supply of nutritive nitrogen in rain, ete., for 12 months, as above given, is much less than 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 454 lbs.; that in 23 tons of meadow hay is 56 lbs. The nitrogen in a crop of clover hay of 24 (long) tons is no less than 108 lbs. Ob- viously, therefore, the atmospheric waters alone are in- capable of furnishing crops with the quantity of nitrogen they require. On the other hand, the atmospheric supply of nitrogen by rain, etc., is not inconsiderable, compared with the amount of nitrogen, which often forms an effective manur- ing. Peruvian guano and nitrate of soda (Chili saltpeter) each contain about 15 per cent of nitrogen. The nitrogen of rain, estimated by the average above given, viz., 8? Ibs., corresponds to 58 lbs. of these fertilizers. 200 lbs. of gua- no is for most field purposes a sufticient application, and 400 lbs. is a large manuring. In Great Britain, where ni- trate of soda is largely employed as a fertilizer, 112 Ibs. of this substance is an 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 different 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 14 lbs., and in October nearly as much more was brought down; the least fell in January. In 1856 the largest amount, 2} Ibs., fell in May; the next, 1 lb,, in ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 97 April; and the least in March. At Ida-Marienhiitte, Kuschen, and Regenwalde, in 1865-6, nearly half the year’s atmospheric nitrogen came down in summer; but at Insterburg only 30 per cent fell in summer, while 40 per cent came gdre Oxy- acid Water... — oxide ~ gen. Ay gen. COQ, + HO =)..CO. 4° .0Riee In this reaction the oxygen set free is identical in bulk with the carbonic acid involved, and the residue retained in the plant, COH,, multiplied by 12, would give 12 molecules of carbonic oxide and 24 atoms of hydrogen, which, chemically united, might constitute either glucos_ or levulose, C,, H,, O,,, from which by elimination of H,O would result cane sugar and Arabic acid, while sepa- ration of 2H,O would give cellulose and the other mem- bers of its group. Whether the real chemical process be this or a different and more complicated one is at present 2 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 finished. TABULAR VIEW OF THE RELATIONS OF THE ATMOSPHERIC INGREDIENTS TO THE LIFE OF PLANTS. OXYGEN, by roots, flowers, ripening fruit, and by all | growing parts. CARBONIC ACID, by foliage and green parts, but only in the light. Absorbed ; AMMONIA, as carbonate, by foliage, probably at all times. by Plants. | WATER, as liquid, through the roots. Nitrous Acip ) united to ammonia, and dissolved in wa- [ozone Aci § ter through the roots, OZONE ) uncertain. Marsu Gas J THE ATMOSPHERE AS RELATED TO VEGETATION. 99 Not absorbed by Plants. NITROGEN. WATER in state of vapor. OXYGEN, | ee foliage and green parts, but only in the ieee Exhaled by | 02082! light. Plants , MARSH Le in traces by aquatic plants ? ‘ fovea as vapor, from surface of plant at all times. CaRBONIC ACID, from the growing parts at all times. CHAPTER IL. THE ATMOSPHERE AS PHYSICALLY RELATED TO VEGETATION. o£ 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 nced to remark somewhat upon the physical properties of gases in rela- tion to vegetable life; so far, at least, as may give some idea of the means by which they gain access into the plant. Physical Constitution of the Atmosphere.—That the atmosphere is a mixture and not a chemical combination of its elements isa fact so evident as scarcely to require discussion. As we have seen, the proportions which sub- sist among its ingredients are not uniform, although they are ordinarily maintained within very narrow limits of va- riation. This is a sufficient proof that it is a mixture. The remarkable fact that very nearly the same relative quantities of Oxygen, Nitrogen, and Carbonic Acid, steadily exist in the atmosphere is due to the even balance which obtains between growth and decay, between life and death. The equally remarkable fact that the gases 100 HOW CROPS FEED. which compose the atmosphere are uniformly mixed to- gether without regard to their specific gravity, is but one result of a law of nature which we shall immediately notice. Diffusion of Gases——Whenever two or more gases are brought into contact in a confined space, they instantly begin to intermingle, and continue so to do until, in a longer or shorter time, they are both equally diffused throughout the room they occupy. If two bottles, one 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 sha!l 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 porous diaphragm between two gases of different densities, we may visibly exhibit the fact of their ready and unequal diffusion. For this purpose the dia- phragm must offer a partial resistance to the movement of the gases. Since the lighter gas passes more rapidly into the denser than the reverse, the space on one side of the membrane will be overfilled, while that on the other side will be partially emptied of gas. In the accompanying figure is represented a long glass © tube, 6, widened above into a funnel, and having cemented upon this an inverted cylindrical enp of unglazed porce- lain, a. The funnel rests in a round aperture made in the horizontal arm of the support, while the tube below dips beneath the surface of some water contained in the wine- glass. The porous cup, funnel, and tube, being occupied with common air, a glass bell, ¢, is filled with hydrogen gas and placed over the cap, as shown in the figure. _In- 7 “ a a i 68 «& THE ATMOSPHERE AS RELATED TO VEGETATION. 101 stantly, bubbles begin to escape rapidly from the bottom of the tuhe through the water of the wine-glass, thus demonstr sung that hydrogen passes into the cup faster Fig. 7. than air can escape outwards through its pores. If the bell be removed, the cup is at once bathed again externally in common air, the light hydrogen floating instantly upwards, and now the water begins to rise in the tube in consequence of the return to the outer atmosphere of the hydrogen which before had diffused into the cup. It is the perpetual action of this diffusive tendency which maintains the atmosphere in a state of such uniform mixture that accurate ana- lyses of it give for oxygen and nitro xen almost identical figures, at all t mes 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 amount the usual proportion of the former gas. If in a limited volume of a mixture of several gases a solid or liquid body be placed, which is capable of chemic- ally uniting with, or otherwise destroying the aeriform condition of one of the gases, it will at once absorb those particles of this gas which lie in its immediate vicinity, and thus d'sturb the uniformity of the re:naining 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 102 HOW CROPS FEED. keep pace with each other until all the absorbable air is removed from the gaseous mixture, and condensed or fixed in the absorbent. In this manner, a portion of the atmosphere enclosed in a large glass vessel may be perfectly freed from watery vapor and carbonic acid by a small fragment of caustic potash. By standing over sulphuric acid, ammonia is taken from it; a piece of phosphorus will in a few hours absorb all its oxygen, and an ignited mass of the rare metil titanium will remove its nitrogen. Osmose of Gases.—By this expression is understood the passage of gaseous bodies through membranes whose pores are too small to be discoverable by optical means, such as the imperforate wall of the vegetable cell, the green cuticle of the plant where not interrupted by stomata, vegetable parchment, India rubber, and animal membranes, like bladder and similar visceral integuments. If a bottle filled with air have a thin sheet of India rubber, or a piece of moist bladder tied over its mouth and then be placed within a bell of hydrogen, evidence is at once had that gases penetrate the membrane, for it swells outwards, and may even burst by the pressure of the hydrogen that rapidly accumulates in the bottle. Gaseous Osmose is Diffusion Modified by the Influence of the Membrane.—The rapidity of osmose* is of course influenced by the thickness of the membrane, and the character of its pores. An adhesion between the mem- brane and the gases would necessarily increase their rate of penetration. In case the membrane should attract or have 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 ree 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. 354. THE ATMOSPHERE AS RELATED TO VEGETATION. 1638 other in penetrating it. In case a membrane is moistened with water or other liquid, or by a solution of sclid mat- ters, this would still further modify the result. Absorption of Gases by the Plant.—A few words will now suffice to apply these facts to the absorption 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. 239. The cells, or some portions of their contents, absorb or condense carbonic avid and ammonia in a similar way, or at least with the same effect, as potash absorbs carbonic acid. As rapidly as these bodies are removed from the atmosphere surrounding or occupying the cells, they are re-supplied by diffusion from without ; so that although the quantities of gaseous plant-food con- tained in the air are, relatively considered, very small, they are by. this grand natural law made to flow in con- tinuous streams toward every growing vegetable cell, DIVISION IL. THE SOIL AS RELATED TO VEGETABLE PRODUCTION. CHAPTER I INTRODUCTORTZ, 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 affect the growth of plants are indeed in themselves beyond our control. We cannot modify them in kind or amount; but we can influence their subserviency to our purposes through the medium of the soil by a proper un- derstanding of the characters of the latter. 104 INTRODUCTORY. 105 The General Functions of the Soil are of three kinds: 1. The ashes of the plant whose nature and variations have been the subject of study in a former volume (H. C. G., pp. 111-201,) are exclusively derived from the soil. The latter is then concerned in the most direct manner with the nutrition of the p!ant. The substances which the plant acquires from the soil, so far as they are nutri- tive, may be collectively termed so/l-food. 2. The soil is a mechanical support to vegetation. The roots of the plant penetrate the pores of the soil in all directions sidewise and downward from the point of their junction with the stem, and thus the latter is firmly braced to its upright position if that be natural to it, and in all cases is fixed to the source of its supplies of ash-in- gredients. 3. By virtue of certain special (physical) qualities to be hereafter enumerated, the soil otherwise contributes to the well-being of the plant, tempering and storing the heat of the sun which is essential to the vital processes ; regulating the supplies of food, which, coming from itself or from external sources, form at any one time but a mi- nute fraction of its mass, and in various medes ensuring the co-operation of the conditions which must unite to produce the perfect plant. Variety of Soils.—In nature we observe a vast varicty of soils, which differ as much in their agricultural value as they do in their external appearance. We find large tracts of country covered with barren, drifting sands, on whose arid bosom only a few stunted pines or shriveled grasses find nourishment. Again there occur in the high- lands of Scotland and Bavaria, as well as in Prussia, and other temperate countries, enormous stretches of moor land, bearing a nearly useless growth of heath or moss. In Southern Russia occurs a vast tract, two hundred mil- lions of acres in extent, of the tschornosem, or black earth, 5 106 HUW CROPS FERED. 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, are other examples of peculiar soils; while on every farm, almost, may be found numerous gradations from clay to sand, from vege- table mould to gravel—gradations in color, consistence, composition, and produc iveness. 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- vable 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. If. The Mineralogical Elements of Rocks. III. The Rocks themselves—their Kinds and Special Characters. IV. The Conversion of Rocks into Soils; to which 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., the constituents of the minerals which go to form rocks, include all the simple bodies known to science. Those, which, from their universal distribution and uses in agriculture, concern us immediately, are with one exception the same that have been noticed in a former volume as composing the ash of agricultural plants, viz., Chlorine, Sulphur, Carbon, Silicon, Potassium, Sodium, Calcium, Magnesium, Iron, and Man- ganese. The description given of these elements and of their most important compounds in “ How Crops Grow ” will suffice. It is only needful to notice further a single element. Aluminum, Symbol Al, Aé. wt. 27.4, is a bluish silver- white metal, characterized by its remarkable lightness, having about the specific gravity of glass. It is now manufactured on a somewhat large scale in Paris and New- castle, and is employed in 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 chloridz 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 NaCl + 2 Al. By combining with oxygen, this metal yields but one oxide, which, like the highest oxide of iron, is a sesqui- oxide, viz.: Alumina, Al, O,, Eq. 102.8—When alum (double sul- phate of alumina and potash) is dissolved in water and ammonia added to the solution, a white gelatinous body separates, which is alumina combined with water, Al, O,, 3H,O. By drying and strongly heating this hydrated ‘alumina, a white powder remains, which is pure alumina, 108 HOW CROPS FEED. In nature alumina is found in the form of emery. The sapphire and ruby are finely colorcd crystallized varieties of alumina, highly prized as gems. Hydrated alumina dissolves in acids, yielding a numer- ous class of salts, of which the sulphate and acetate are largely employed in dyeing and calico-printing. The sul- phate of alumina anl potash is familiarly known under the name of alum, with which all are acquainted. Other compounds of alumina will be noticed presently. § 2. MINERALOGICAL ELEMENTS OF ROCKS. The mineralogical elements or minerals * which compose rocks are very numerous. But little conception can be gained of the appearance of : 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. +26-) 134 Feldspar (field-spar) is, next to quartz, the most abund- * The word mineral, or mineral ‘‘ species,’ here implies a definite chemical compound of natural occurrence. ORIGIN AND FORMATION OF SOILS. 109 ant mineral. J¢ ts a compound of silica with alumina, and with one or more of the alkulies, and sometimes with lime. Mineralogists distinguish several species of feld- spar according to their composition and crysta‘lization. eldspar is found in crystals or crystalline-masses usually of a white, yellow, or flesh color, with@ somewhat pearly luster on the smooth and level aces which: it presents on fracture. It is scratched by,* d In the subjoined Table are given the mineralogical nantes and analyses of the principal varieties of feldspar. Ac- companying each analysis is its locality and the name of the analyst. ORTHOCLASE. ALBITE. OLIGOCLASE. LABRADORITE. Common or potash Soda fedspar. Soda-lime feldspar. Lime-soda Seddspar. Séldspar. New Rochelle, N. Y. Unionville. Pa. Haddam, Conn. Drummond, C. W. S. W. Johnson. M. C. Weld. G. J. Brush. Tis. Hunt. Silica, 64.23 66.86 64.26 54.70 Alumina, 20.42 21.89 21.90 29.80 Potash, 12.47 — 0.50 0.33 Soda, 2.62 8.78 9 99 2.44 Lime. trace 1.79 2.15 11-42 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 varicties, viz.: Musco- vite, Phlogopite, and Biotite. They are silicates of alumi- na with potash, magnesia, lime, iron, and manganese, Mica bears the common name “‘isinglass.” It readily splits into thin, elastic plates or leaves, has a brilliant luster, and a great variety of colors,—white, yellow, brown, green, and black. Muscovite, or muscovy glass, is some- times found in transparent sheets of great size, and is used in stove-doors and lamp-chimneys. It contains much alumina, and potash, or soda, and the black varieties oxide of iron. Phlogopite and Biotite contain a large percentage of magnesia, and often of oxide of iron. 110 HOW CROPS FEED. The following analyses represent these varieties. MUSCOVITE. PHLOGOPITE. BIOTITE. SSS OS SSS ee Litchfield, Mt.Leinster, Edwards, N. Burgess, Putnam Co., Conn. Ireland. Ne Canada. IN: ay, Siberia. Smith & Brush. Haughton. W.J.Craw. T.S.Hunt. Smith & Brush. H. Rosé, Silica, 44.60 44.64 40 . 36 40.97 39.62 40.00 Alumina, 36.23 30.18 16.45 18.56 17.35 12.67 Oxide ofiron, 1.34 6.35 trace oa 5.40 - 19.03 Oxide of 0.63 manganese, Magnesia, 0.37 0.72 29 .55 25.80 23.85 15.70 Lime, 0.50 — — -_-—_ oo 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 5.382 0.95 1.00 1.41 — Variable Composition of Mineralsx—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 aaa of iron than the first. Again, the second contains 12.4°|, of potash, but no soda and no Heute while the first reveals on analysis 4°|, of soda and 0.5°|, of lime, and contains correspondingly less potash. Similar differences are remarked in the other anal- yses, especially in those of Biotite. In fact, of the analyses 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 amphiboles and pyroxenes presently to be noticed. In accordance with this variation in composition we notice extraordinary diversities in the color and ap- pearance of different specimens of the same mineral. This fact may appear to stand in contradiction to the statement above made that these minerals are definite combinations. In the infancy of mineralogy great per- plexity arose from the numerous varieties of minerals that were found—varieties that agreed together in certain char- acteristics, but widely differed in others. ORIGIN AND FORMATION OF SOILS. L¥4t Isomorphism.—In 1830, Mitscherlich, a Prussian phi- losopher, discovered that a number of the elementary bodies are capable of replucing each other in combination, from the fact of their natural 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, which are all protoxide-bases, form one group, each of whose members may take the place of the other. Alumina (Al, O,) and oxide of iron (Fe, O,) be- long to another group of sesguioxide-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 mincral amphibole, for example, there are known a great number of varieties; some pure white in color, con- taining, in addition to silica, magnesia and lime; others pale green, a small portion of magnesia being replaced by protoxide of iron; others black, containing alumina in place of a portion of silica, and with oxides of iron and minganese in large proportion. All these varieties of amphibole, however, admit of one expression of their constitution, for the amount of oxygen in the bases, no matter what they are, or what their proportions, bears a constant relation to the oxygen of the silica (and alumina) they contain, the ratio being 1: 2. If the protoxides be grouped together under the gen- eral symbol MO (metallic protoxide,) the composition of the amphiboles may be expressed by the formula MO Si0O., In pyroxene the same replacements of protoxide-bases on the one hand, and of silica and alumina on the other, occur inextreme range. (See analyses, p. 112.) The gen- eral formula which includes all the varieties of pyroxene is the same as that of amphibole. The distinction of am- phibole from pyroxene is one of crystallization. 112 HOW CROPS FEED. We might give in the same style formule for all the minerals noticed in these pages, but for our purposes this is unnecessary. Amphibole is an abundant mineral often met with in distinct crystals or crystalline and fibrous masses, varying in color from pure white er gray (tremolite, asbestus), 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 alkalies. Silica, Magnesia, Lime, Protoxide of iron, Protoxide of manganese, Alumina, Soda, Potash, Water, White. Gray. Ash-gray. Black. Gouverneur, Lanark, Cummington, Brevig, 1 Canada. Mass. Norway. Rammelsberg. T.S. Hunt. Smith & Brush. Plantamour, 57.40 55.30 50.74 46.57 24.69 22.50 10.31 5.88 13.89 13.36 trace 5.91 1.36 6.30 33.14 24.38 trace LT 2.07 1.38 0.40 0.89 3.41 a 0.80 0.54 7.79 —_— 0.25 trace 2.96 0.40 0.30 3.04 — Leek green. Waldheim, Saxony. Knop. 58.71 10.01 11.53 5.65 0.50 Pyroxene is of very common occurrence, and consider- ably resembles hornblende in colors and in composition. Gray- White. Bathurst, Canada. T. S. Hunt. T.S. Hunt. Silica, Magnesia, Lime, Protoxide of iron. Sesquioxide of iron, Protoxide of manganese, Alumina, Soda, Potash, Water, White. Ottawa, Canada. 54.50 18.14 25.87 1.98 51.50 17.69 23.80 Green. Lake Champlain. Seybert. 50.38 6.83 19.35 20.40 Black. Orange Co., N.Y. Smith & Brush. 2.98 10.39 30.40 Black. Wetterau, Gmelin. 56.80 5.05 4.85 12.06 a el ORIGIN AND FORMATION OF SOILS. $93 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 compcsition, though in general it has a grayish or brownish-green color, and contains magnesia, alumina, and iron, united with silica. See analysis below. Leucite is an anhydrous silicate of alumina found chiefly in voleanic rocks. It exists in white, hard, 24-sid- ed crystals. It is interesting as being formed ata 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 usual temperature. Form- ed in this way, in a more or less impure state, it consti- tutes the mass of white porcelain clay or kaolin, which is largely used in making the finer kinds of pottery. It ap- pears in white or yellowish crystalline scales of a pearly luster, or as an amorphous translucent powder of extreme fineness. Ordinary clay isa still more impure kaolinite. CHLORITE. LEUCITE. KAOLINITE. Steele Mine, N.C. Vesuvius, Summit Hill, Chaudiere Eruption of 1857. Pa. Falls. Canada. Genth. Rammelsberg. 8S. W. Johnson. T.S. Hunt. Silica, 24.90 57.24 45 .93 46.05 Alumina, 1.7 22.96 39.81 38.37 Sesquioxide of iron, 4.60 — — — Protoxide of iron, 7A.21 —— — — Protoxide of manganese, 1.15 — —— — Magnesia, 12.78 —— —— 0.63 ~ Lime, — 0.91 a 0.61 Soda, — 0.93 —— —— Potash, — 18.61 —— Water, 10.59 — 14.02 14.00 Tale is often found in pale-green, flexible, inelastic scales or leaves, but much more commonly in compact gray masses, and is then known as soapstone. It is very soft, 114 HOW 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, ete. It is also a hydrous silicate of magnesia. See analysis. Chrysolite is a silicate of magnesia and iron, which is found abundantly in lavas and basaltic rocks. It is a hard, glassy mineral, usually of an olive or brown-green color. See analysis below. TALC. SERPENTINE. ._ CHRYSOLITE. Bristol, Conn. New Haven, Conn. Bolton, Mass. Dr. Lummis. G. J. Brush. G. J. Brush. Silica, 64.00 44.05 40.94 Alumina, oe sae 0.27 Protoxide of iron, 4.%5 2.53 4 37 Magnesia, 27.47 39.24 50.84 Lime, — —— 1.2% Water, 4.30 13.49 3.28 Zeolites.—Under this general name mineralogists are in the habit of including a number of minerals which have recently acquired considerable agricultural interest, since they represent certain compounds which we have strong reasons to believe are formed in and greatly influence the properties of soils. They are hydrous silicates of alum- ina or lime, and alkali, and are remarkable for the ease with which they undergo decomposition under the influ- ence of weak acids. We give here the names and compo- sition of the most common zeolites. Their special signif: icance will come under notice hereafter. We may add that while they all occur in white or red crystallizations, often of great beauty, they likewise exist in a state of division so minute that the eye cannot recognize them, and thus form a large share of certain rocks, which, by their disintegration, give origin to very fertile soils is ded ; ORIGIN AND FORMATION OF SOILS. Kia ANALCIME. CHABASITE. NATROLITE. SCOLECITE. THOMSONITE. Lake Superior. Nova Scotia. Bergen Hill, Ghaut’s Tun- Magnet Nid’: 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 29.42 Potash, —— 0.98 0.35 0.30 —_— Soda, 8.52 0.71 15.44 0.17 3.91 Lime, 3.00 Gs 0.41 13.97 13.95 Magnesia, — — —— — — Sesquioxide ore aes >? eee ae rn ale 118 HOW CROPS FEED. clay into granite. These rocks, which are the result of the united action of heat and water, are termed meta- morphic (i. e., metamorphosed) rocks. One of the most obvious division of rocks is into Crys- talline and Fragmental. Crystalline Rocks are those whose constituents crystal- lized at the time the rock was formed. Here belong both the igneous and metamorphic rocks. These are often - plainly crystalline to the eye, i. e., are composed of readily perceptible crystals or crystalline grains, like statuary marble or granite; but they are also frequently made up of crystals so minute, that the latter are only to be recog- nized by tracing them into their coarser varieties (basalt and trap.) Fragmenta! Rocks are the sedimentary rocks, formed by the cementing of the fragments of other older rocks existing as mud, sand, ete. THE CrystTaLttInE Rocks may be divided into two great classes, viz., the silicious and calcareous ; the first class containing silica, the latter, lime, as the predomina- ting ingredient. The silicious rocks fall into three parallel series, which have close relations to each other. 1. The Granitic series ; 2, The Syenitic series; 3. The Zalcose or Magnesian series. In all the silicious rocks quartz or feldspar is.4 prominent ingredient, and in most cases these two minerals _ are associated together. To the above are added, in the granitic series, mica ; in the syenitic series, amphibole or pyroxene ; and in the talcose series, tale, chlorite, or ser- pentine. The proportions of these minerals vary indef- initely. Tue Granitic SERIES consisting principally of Quartz, Feldspar, and Mica. Granite.— A hard, massive* rock, either finely or + Rocks are massive when they have no tendency to split into slabs or plates * as a ORIGIN AND FORMATION OF SOILS. 119 coarsely crystalline, of various shades of color, depending on the color and proportion of the constituent minerals, usually gray, grayish white, or flesh-red. In common granite the feldspar is orthoclase (potash-feldspar). A variety contains albite (soda-feldspar). Other kinds (less common) contain odigoclase and labradorite. Gneiss differs from granite in containing more mica, and in having a banded appearance and schistose* structure, due to the distribution of the mica in more or less parallel layers. It is cleavable along the planes of mica into coarse slabs. Mica-slate or Mica-schist contains a still larger pro- portion of mica than gneiss; it is perfectly schistose in structure, splitting easily into thin slabs, has a glistening appearance, and, in general, a grayish color. The coarse whetstones used for sharpening scythes, which are quar- ried in Connecticut and Rhode Island, consist of this min- eral. Argillite, Clay-slaie, is a rock of fine texture, often not visibly crystalline, of dull or but slightly glistening surface, and having a great variety of colors, in general black, but not rarely red, green, or light gray. Argillite has usually a slaty cleavage, i. e., it splits into thin and smooth plates. It is extensively quarried in various local- ities for roofing, and writing-slates. Some of the finest varieties are used for whetstones or hones. Other Granitic Rocks.—Sometimes mica is absent; in other cases the rock consists nearly or entirely of feldspar alone, or of guartz alone, or of mica and quartz. ‘The rocks of this series often insensibly gradate into each oth- er, and by admixture of other minerals run into number- less varieties. * Schésts or schistose rocks are those which have a tendency to break into slabs or plates from the arrangement of some of the mineral ingredients in layers. } HOW CROPS FEED. THe SyEniTic SERIES consisting chiefly of Quartz, Keldspar, and Amphibole. Syenite is granite, save that amphibole takes the place of mica. In appearance it is like granite; its color is usu- ally dark gray. Syenite isa very tough and durable rock, often most valuable for building purposes. The famous Quincy granite of Massachusetts is a syenite. Syenitic Gneiss and Hornblende Schist correspond to common Gneiss and Mica Schist, hornblende taking the place of mica. Tue Voucanic SERIES consisting of Feldspar, Amphibole or Pyrowene, and Zeolites. Diorite is a compact, tough, and heavy rock, common- ly greenish-black, brownish-black, or grayish-black in color. It contains amphibole, but no pyroxene, and is an ancient lava. Dolerite or Trap in the fine-grained varieties is scarcely to be distinguished from Diorite by the appearance, and is well exhibited in the Palisades of the Hudson and the East and West Rocks of New Haven. It contains pyrox- ene in place of amphibole. Basalt is like dolerite, but contains grains of chrysolite. The recent lavas of volcanic regions are commonly basaltic in composition, though very light and porous in texture. Porphyry.—Associated with basalt occur some feld- spathic lavas, of which porphyry is common. It consists of a compact base of feldspar, with disseminated crystals of feldspar usually lighter in color than the mass of the rock. Pumice is a vesicular rock, having nearly the composi- tion of feldspar. Tur Macnestan SERIES consisting of Quartz, Keldspar and Talc, or Chlorite. Talcose Granite differs from common granite in the substitution of tale for mica. Is a fragile and more easily ~. Set Raa id . ORIGIN AND FORMATION OF SOILS. 121 decomposable rock than granite. It passes through tadcose gneiss into Talcose Schist, which resembles mica-schist in colors and in facility of splitting into slabs, but has a less glis- tening luster and a soapy feel. Chloritic Schist resembles talcose schist, but has a less unctuous feel, and is generally of a dark green color. Related to the above are Steatite, or soapstone,—nearly pure, granular talc; and Serpentine rock, consisting chiefly of serpentine. The above are the more common and wide-spread si- licious rocks. By the blending together of the different members of each series, and the related members of the different series, and by the introduction of other minerals into their composition, an almost endless variety of si- licious rocks has been produced. ‘Turning now to the CRYSTALLINE CaLcarreous 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 monumental marble. Dolomite has all the appearance of granular limestone, but contains a large (variable) amount of carbonate of magnesia. Tue FRAGMENTAL oR SEDIMENTARY Rocks are as fol- lows: Conglomerates have resulted from the consolidation of rather coarse fragments of any kind of rock. According to the nature of the materials composing them, they may be granitic, syenitic, calcareous, basaltic, etc., etc. They pass into Sandstones, which consist of small fragments (sand), are generally sidicious in character, and often are nearly 6 122 nHUW CROPS FEED. pure quartz. The freestone of the Connecticut Valley is a granitic sandstone, containing fragments of feldspar and spangles of mica. Other varieties are calcareous, argillaceous (clayey), basaltic, ete., ete. 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 arg illite. Limestones of the sedimentary kind are soft, compact, nearly lusterless rocks of various colors, usually gray, blue, or black. They are sometimes nearly pure carbon- ate of lime, but usually contain other substances, and are often highly impure. When containing much carbonate of magnesia they are termed magnesian limestones. They pass into sandstones through intermediate calciferous sand rocks, and into shales through argillaceous lime- stones. ‘These impure limestones furnish the hydraulic cements of commerce. | § 4. 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. b ORIGIN AND FORMATION OF SOILS. 123 The first step towards the formation of a soil must have been the pulverization of the 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 indced stupendous when contrasted with the narrow experience of a single human life, but are really trifling compared with the magnitude of the earth itself, for the soil forms upon the surface of our globe, whose di- ameter is nearly 8,000 miles, a thin coating of dust, meas- ured in its greatest accumulations not by miles, nor scarcely by rods, but by feet. The conversion of rocks to soils has been performed, Ist, by Changes of Temperature ; 2d, by Moving Water or Ice ; 38d, by the Chemical Action of Water and Air ; Ath, by the Influence of Vegetable and Animal Life. 1.—CuanGrEs OF TEMPERATURE. The continued cooling of the globe after it had become enveloped ina 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, the first oc- casion of the breaking down of the rocks. The fact that 124 HOW CROPS FEED. many rocks consist of crystalline grains of distinct min erals more or less intimately blended, is a point of weak- ness in their structure. The grains of quartz, feldspar, and mica, of a granite, when exposed to changes of tem- perature, must tend to separate from each other; because the extent to which they expand and contract by alterna- tions of heat and cold are not absolutely equal, and be- cause, as Senarmont has proved, the same crystal expands or contracts unequally in its different diameters. Action of Freezing Water.—lIt 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 ;'; of its bulk, and the force thus exerted is sufficient to burst vessels of the strongest materials. In cold latitudes or altitudes this agency working through many years accomplishes stupen- dous results. The adventurous explorer in the higher Swiss Alps fre- quently sees or hears the fall of fragments of rock thus loosened from the peaks. Along the base of the vertical trap cliffs of 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.—Movine Water or Icr. Changes of temperature not only have created differ- ences of level in the earth’s surface, but they cause a con- / Sr - ORIGIN AND FORMATION OF SOILS. 125 tinual transfer of water from lower to higher levels. The elevate:l lands are cooler than the valleys. In their re- gion occurs a continual condensation of vapor from the atmosphere, which is as continually supplied from tie heated valleys. In the mountains, thus begin, as rills, the streams of water, which, gathering volume in their descent, unite below to vast rivers that flow unceasingly into the ocean. | These streams score their channels into tlie firmest rocks. Each grain of loosened material, as carried downward by the current, cuts the rock along which it is dragged so long as it is In motion. The sides of the channel being undermined and loosen- ed by exposure to the frosts, fall into the stream. In time of floods, and always, when the path of the river has a rapid descent, the mere momentum of the water acts pow- erfully upon any inequalities of surface that oppose its course, tearing away the rocky walls of its channel. The blocks and grains of stone, thus set in motion, grind each other to smaller fragments, and when the turbid waters clear themselves in a lake or estuary, there results a bed of gravel, sand, or svil. Two hundred and sixty years ago, the bed of the Sicilian river Simeto was obstructed by the flow across it of a stream of lava from Etna. Since that time the river, with but slight descent, has cut a chan- nel through this hard basalt from fifty to several hundred feet wide, and in some parts forty to fifty deep. But the action of water in pulverizing rock is not com- pleted when it reaches the sea. The oceans are in perpet- ual agitation from tides, wind-waves, and currents like the Gulfstream, and work continual changes on their shores. Glaciers.— W hat happens 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 appear like motion- * tae 125 HOW CROPS FEED. less ice-fields, but they are frozen rivers, rising in perpet ual snows and melting into water, after having reached half a mile or a mile below the limits of frost. The snow that accumulates on the frozen peaks of high mountains, which are bathed by moist winds, descends the slopes by its own weight. The rate of descent is slow,—a few inches, or, at the most, a few feet, daily. The motion it- self is not continuous, but intermittent by a succession of pushes. In the gorges, where many smaller glaciers unite, the mass has often a depth of a mile or more. Under the pressure of accumulation the snow is compacted to ice. Mingled with the snows are masses of rock broken off the higher pinnacles by the weight of adhering ice, or loosened by alternate freezing and thawing, below the line of perpetual frost. The rocks thus falling on the edge of a glacier become a part of the latter, and partake its mo- tion. When the moving mass bends over a convex sur- face, it cracks vertically to a great depth. Into the ere- vasses thus formed blocks of stone fall to the bottom, and water me!ted from the surface in hot days flows down and finds a channel beneath the ice. The middle of the glacicr moves most rapidly, the sides and bottom being retarded by friction. The ice is thus rubbed and rolled upon itself, and the stones imbedded in it crush and grind each other to smaller fragments an: to dust. The rocky bed of the glacier is broken, and ploughed by the stones frozen into its sides and bottom. The glacier thus moves until it descends so low that ice cannot exist, and gradually dis- solves into a torrent whose waters are always thick with mud, and whose course is strewn with worn blocks of stone (boulders) for many miles. The Rhone, which is chiefly fed from the glaciers of the Alps, transports such a volume of rock-dust that its muddy waters may be traced for six or seven miles after they have poured themselves into the Mediterranean, 3.—CHEMIcAL AcTION OF WATER AND AIR, - +. ma 2 ORIGIN AND FORMATION OF SOILS. 127 Water acts chemically upon rocks, or rather upon their constituent minerals, in two ways, viz., by 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 pyroxene, are minerals which have been artificially produced in the slags or linings of smelting furnaces, and thus formed they have been found totally destitute of wa- ter, as might be expected from the high temperature in which they originated. Yet these minerals as occurring in nature, even when broken out of blocks of apparently unaltered rock, and especially when they have been di- rectly exposed to the weather, often, if not always, con- tain a small amount of water, in chemical 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 with water, chloride of calcium, which is very soluble, being separated from the nearly insoluble phosphate of lime. The minerals which compose silicious rocks are all acted on perceptibly by pure water. This is readily observed when the minezals are employed in the state of fine powder. If pulverized feldspar, amphibole, ete., 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. Si., V, 404, 1848) found that by continued digestion of pure water for a week, with powdered feldspar, horn- blende, chlorite, serpentine, and natrolite,+ these minerals yielded to the solvent from 0.4 to 1 per cent of their weight. In nature we never deal with pure water, but with wa- ter holding in solution various matters, either derived from the air or from the soil. These substances modify, and in most cases enhance, the solvent power of water. Action of Carbonic Acid.—This gaseous substance is 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, protoxide of iron, and protoxide of manganese. The salts just named are as good as insoluble in pure water, but they exist in considerable quantities in most natural waters. The spring and well waters of limestone regions are hard on account of their content of carbonate of lime. Chalyb- cate waters are those which hold carbonate of iron in solution. When carbonated water comes in contact with silicious minerals, these are decomposed much more rapidly than by pure water. The lime, magnesia, and iron they contain, are partially removed in the form of carbonates. Struve exposed powdered phonolite (a rock composed of feldspar and zeolites) to water saturated with carbonic * Glass is a silicate of potash or soda, + Mesotype. e ORIGIN AND FORMATION OF SOILS. 129 acid under a pressure of 3 atmospheres, and obtained a solution of which a pound* contained: Carbonate of soda, 22.0 grains. Chloride of sodium, 8S aR Sulphate of potash, Lif Gag _ “ soda, 4.8 -_°* Carbonate of lime, y BS ed a “* magnesia, A ae Silica, 7 a Phosvhoric acid and manganese, traces Total, 37.1 grains. In various ‘natural springs, water comes to the surface so charged with carbonic acid that the latter escapes copiously in bubbles. Such waters dissolve large quantities of mineral matters from the rocks through which they emerge. Examples are seen in the springs at Saratoga, N. Y. According to Prof. Chandler, the “Saratoga Spring,” whose waters issue directly from the rock, con- tains in one gallon of 231 cubic inches : Chloride of Sodium (common salt) 398.561 grains. = ** Potassium, 9.698 " Bromide of Sodium, 0.571 se Todide of Sodium, 0.126 ss Sulphate of Potash, 5.400 Li Carbonate of Lime, 86.483 « sg ‘* Magnesia, 41.050 oh - ** Soda, 8.948 = e ‘* Protoxide of iron, .879 ; os Silica, 1.283 oe Phosphate of lime, trace ec Solid matters, fox toe Ss Carbonic acid gas, (407.647 cubic inches at 52° Fah.) Water, 58,317.110 = The waters of ordinary springs and rivers, as well as those that fall upon the earth’s surface as rain, are, indeed, * The Saxon pound contains 7,680 Saxon grains. 6* 130 HOW 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 Baumhauer, 40 to 90 Ske: o G 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 ammonia and of soda, however, it is taken up in considerable quantity. Solution of nitrate of ammonia 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, tale, and serpentine, invariably contain these prot- oxides in notable proportion. In the fe!dspars they exist, indeed, in very minute quantity, but are almost never en- tirely wanting. Sulphide of iron (iron pyrites), in many of its forms, is also disposed to oxidize its sulphur to sul- phurie 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, metallic iron is said to occur in minute proportion,* and in a state of fine division. The oxidation of these substances materially hastens the disintegration of the rocks containing them, since the higher oxides of iron and of manganese occupy more space than the metals or lower oxides. This fact is well illustrated by the sulphate of protoxide of iron (cop- peras, or green-vitriol), which, on long keeping, exposed to the air, is converted from transparent, glassy, green crys- tals to a bulky, brown, opaque powder of sulphate of sesquioxide of iron. Weathering.—The conjoined influence of water, car- * This statement rests on the authority of Professor Henry Wurtz, of New York. 1382 HOW CROPS FEED. bonic acid, oxygen, and the salts held in solution by the atmospheric waters, is expressed by the word weathering. This term may likewise include the action of frost. When rocks weather, they are decomposed or dissolved, and new compounds, or new forms of the original mat- ter, result. The soil is a mixture of broken or pulverized rocks, with the products of their alteration by weathering. a. Weathering of Quartz Rock.—Quartz (silicic acid), as occurring nearly pure in quartzite, and in many sand- stones, or as a chief ingredient of all the granitic, horn- blendic, an 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 varieties, 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. 6. 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 exceedingly durable. The decomposition results in completely breaking up the hard, 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, Aaolinite, a hydrated silicate of alumina,(the analysis of which has been given already, p. 113,) mixed ORIGIN AND FORMATION OF SOILS. 133 with hydrated silica, and ofien with grains of undecompos- 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. ANUMAIAD ces iors 6 18 3 18 3 0 STL a ee 64.8 23.0 41.8 IPOUAS Biro. vo ooo, 3 16.9 16.9 ERE ge eae es 6.4 6.4 100 47.7 58.7 64 It thus appears that, in the complete conversion of 100 parts of potash feldspar into kaolinite, there result 47.7 parts of the latter, while 58.7°|, of the feldspar, viz: 41.8°|, of silica and 16.9°|, of potash, are dissolved out. The potash, and, in case of other feldsp:rs, 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. ec. Other Silicious Minerals, as Leucite, (Topaz, Scapo- lite,) ete., yield kaolin by decomposition. It is probable that the micas, which decompose with difficulty, (phlogo- * We have seen (H C. G., p. 121) that silica, when newly set free from combi- nation, is, at first, freely soluble in water. 134 HOW CROPS FEED. pite, perhaps, excepted,) and the amphiboles 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 Clays, 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 minerals. Fresenius deduces from his analyses of several Nassau clays the existence in them of a compound having the symbol Al, O, 3 SiO,+H,O, and the follow- ing composition per cent. Silica, 57.14 Alumina, 31.72 Water, 11.14 100.00 Other chemists have assumed the existence of hydrated silicates of alumina of still different composition in clays, but kaolinite is the only one which occurs in a pure state, as indicated by its crystallization, and the existence of the others is not perfectly established. (S. W. Johnson and J. M. Blake on Kaolinite, etc., Am. Jour. S7i., May, 1867, pp. 351-362.) d. The Zeolites readily suffer change by weathering ; little is known, however, as to the details of their disinte- gration. Instead of yielding kaolinite, they appear to be transformed into other zeolites, or retain something of their original chemical constitution, although mechanically dis- integrated or dissolved. We shall see hereafter that there ée ORIGIN AND FORMATION OF SOILS. 135 is strong reason to assume the existence of compounds analogous to zeolites in every soil. e. Serpentine and Magnesian Silicates are generally slow of decomposition, and yield a meager soil. J. 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 flow over them with carbonate of lime. g. Argillite and Argillaceous Limestones, which have resulted from the solidification of clays, readily yield clay again, either by simple pulverization or by pulverization and weathering, according as they have suffered more or less change by metamorphism. § 5. tNCORPORATION OF ORGANIC MATTER WITH THE SOIL AND ITS EFFECTS. Antiquity of Vegetation.— Geological observations lead to the conclusion that but small portions of the earth’s surface-rocks were formed previous to the existence of. vegetation. The enormous tracts of coal found in every quarter of the globe are but the residues of preadamite forests, while in the oldest stratified rocks the remains of plants (marine) are either most distinctly traced, or the abundance of animal forms warrants us in assuming the existence of vegetation previous to their deposition. The Development of Vegetation on a purely Mineral Soil.—The mode in which the original inorganic soil be- came more or less impregnated with organic matter may be illustrated by what has happened in recent years upon the streams of lava that have issued from volcanoes. The lava flows from the crater as red-hot molten rock, often in masses of such depth and extent as to require months to cool down to the ordinary temperature, For many years 136 HOW CROPS FEED. the lava is incapable of bearing any vegetation save some almost microscopic forms. During these years the surface of the rock suffers gradual disintegration by the agencies of air and water, and so in time acquires the power to support some lichens that appear at first as mere stains upon its surface. These, by their decay, increase the film of soil from which they sprung. The growth of new generations of these plants is more and more vigor- ous, and other superior kinds take rvot among them. After another period of years, there has accumulated a tangible soil, supporting herbaceous plants and dwarf shrubs. Henceforward the increase proceeds more rapid- ly; shrubs gradually give place to trees, and in a century, more or less, the once hard, barren rock has weathered to a soil fit for vineyards and gardens. Those lowest orders of plants, the lichens and mosses, which prepare 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, particles of the stone itself are detached. Many of the old marbles of Greece are incrusted with oxalate of lime left by the decay of lichens which have grown upon their surface. Humus.—By the decay of successive generations of plants the soil gradually acquires a certain content of dead organic matter. The falling leaves, seeds and stems of vegetation do not in general waste from the surface as rapidly as they are renewed. In forests, pastures, prai- ries, and marshes, there accumulates on the surface a brown or black mass, termed Aumus, of which leaf-mold, swamp- muck, and peat are varieties, differing in appearance as in ORIGIN AND FORMATION OF SOILS. 137 the circumstances of their origin. In the depths of the soil similar matters are formed by the decay of roots and other subterranean parts of plants, or by the inversion of sod and stubble, as well as by manuring. Decay of Vegetation.—When a plant or any part of a plant dies, and remains exposed to air and m»isture at the common temperatures, it undergoes a series of cliemical and physical changes, which are largely due to an oxida- tion of portions of its 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 asmall proportion of albuminous and mineral substances. By decay, the white or light- colored and tough tissues of plants become converted into brown or black friable substances, in which less or none of the organized structure of the 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 acid and water, proceeds without interruption, though more and more slowly, until nearly all the carbon and hydrogen of the vegetable matters are oxidized to the above-named products, and little more than the ashes of the plant reinains. With limited access of air the process rapidly runs through a first stage of oxidation, when it becomes checked by the formation of substances which are themselves able, to a good degree, to resist further oxidation, especially under the circum: stances of their formation, and hence they accumulate in considerable quantities. This happens in the lower layers of fallen leaves in a dense forest, in compost and manure heaps, in the sod of a meadow or pasture, and especially in swamps and peat-bogs. The more delicate, porous and watery the vegetable 138 HOW SROPS FEED. | matter, and the more soluble substances and albuminoids it contains, the more rapidly does it decay or humify. It has been shown by a chemical examination of 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 (CH,). Carbonic oxide gas (CQ) is proba- bly also produced in minute quantity. The nitrogen of the vegetable matter is to a considerable extent liberated in the free gascous state; a portion of it unites to hydro- gen, forming ammonia (NH,), 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 of moisture. 6. Organic matters furnish copious supplies of carbonte acid, the action of which has already been considered ORIGIN AND FORMATION OF SOILS. 139 (p. 128). Boussingault and Lewy (Mémoires de Chimie Agricole, etc., p. 369,) have analyzed the air contained in the pores of the soil, and, as was to be anticipated, found it vastly richer in carbonic acid than the ordinary atmos- phere. The following table exhibits the composition of the air in the soil compared with that of the air above the soil, as observed in their investigations, Carbonic acid in 10,000 parts of air (by weight). Wamhary abmonplere: Vs. 6.04.22. eek). ee A 8 6 Air from sandy subsoil of forest...............000¢ 38 Sh NA OT i re Seat 124 Re UPERRO BOG ei rks aba gaggia é 150 edaaala: a ee MIEN RUO Sc ecs vane aedee 146 By iat as ** old asparagus bed....... 122 a Ae “ eg: ‘* newly manured. 233 re yale 3 ot) PCT. iiss 5 oon eg ech 270 poe Tielt Mm lames: 223.20! ol ea 545 hes Ra f newly manured sandy field, ; during dry weather....... 393 =, as newly manured sandy field, during wet weather....... 1415 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, bemg 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. ce. 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 HOW CROPS FEED. ly with other bases, as lime, oxide of iron, etc. These alkali-salts, then, should attack the minerals of the soil in a manner similar to carbonic acid. The same is probably ~ true of crenic and apocrenic acids. d. It scarcely requires mention that the ammonia salts and nitrates yielded by the decay of plants, as well as the organic acids, oxalic, tartaric, etc., or acid-salts, and the chlorides, sulphates, and phosphates they contain, act upon the surface soil where 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 lygroscopic humus left by their decay, maintains the surface in a state of saturation by moisture. The carbonic acid produced in living roots, and to some extent, at least, it is certain, excreted from them, adds its effect to that derived from other sources. 2. Organie Acids within the Plant.—According to Zoller, (Vs. St. V. 45) the young roots of living plants (what plants, is not mentioned) contain an acid or acid- salt which so impregnates the tissues as to manifest a strong acid reaction with (give a red color to) blue litmus- paper, which is permanent, and therefore not due to car- bonic acid. This acidity, Zoller informs us, is most in- tense in the finest fibrils, and is exhibited when the roots are 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 Zoller, Salm Horst- mar (Jour. fiir. Prakt. Chem. XU, 304,) having found in the ashes of ground pine (Lycopodium complanatum), 38° |, of ORIGIN AND FORMATION OF SOILS. 141 alumina, while in the ashes of juniper, growing beside the Lycopodium, this substance was absent, examined the rootlets of both plants, and found that the former had an acid reaction, while the latter did not affect ltmus- paper. Salm Horstmar supposed that the alumina of the soil finds its way into the Lycopodium by means of this acid. Ritthausen has shown that the Lycopodium contains malic acid, and since all the alumina of the plant may be extracted by water, it is probable that the acid reaction of the rootlets is due, in part at least, to the presence of acid malate of alumina. (Jour. fiir. Prakt. Chem. LITi. 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 lrydrochloric acid, vinegar, citric acid, bitartrate of potash, etc.; the open end of each tube was then closed by a piece of moistened bladder tied tightly over, and various salts, in- soluble in water, as phosphate of lime, phosphate of am- monia and magnesia, cte., were strewn on the bladder. After a short time it was found that the ingredients of these salts were contained in the liquid in contact with the under surface of the bladder, having been dissolved by the dilute acid present in the pores of the membrane, ond absorbed through it. This is an ingenious illustra- tion of the mode in which the organic acids existing In the root-cells of plants may act directly upon the rock or soil external to them. By such action is doubtless to be explained the fact mentioned by Liebig in the following words: “We frequently find in meadows smooth limestones with their surfaces covered with a network of small fur- rows. When these stones are newly taken out of the ground, we find that each furrow corresponds to a rootlet, which appears as if it had eaten its way into the stone.” (Modern Ag p. 43.) 142 HOW CROPS FEED. This direct action of the living plant is probably ex- erted by the lichens, which, as has been already stated, grow upon the smooth surface of the rock itself. Many of the lichens are known to contain oxalate of lime to the extent of half their weight (Braconnot). According to Goeppert, the hard, fine-grained rock of the Zobtenberg, a mountain of Silesia, is 1: all cases softened at its surface where covered with lichens (Acarospora smar- agdula, Imbricaria olivacea, etc.), while the bare rock, closely adjacent, is so hard as to resist the knife. On the Schwalbenstein, near Glatz, in Silesia, at a height of 4,500 feet, the granite is disintegrated under a covering of li- chens, the feldspar being converted into kaolin or washed away, only the grains of quartz and mica remaining unal- tered.* CHAPTER IIL. KINDS OF SOILS—THEIR DEFINITION AND CLASSIFI- CATION. g A 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 serve to give a certain degree of precision to language, and enable us to discriminate in some measure the different kinds of soils, which offer. great diversity in origin, composition, external characters, * See, also, p. 136, KINDS OF SOILS. 1438 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 Trunsported. The lat- ter are subdivided into Drift, Alluvial, aud Colluvial soils. | Sedentary Soils, or Sozls 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 probable agricultural value; because the still unweathered 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 rivers, soils in place are not abundant as compared with the entire area. Nevertheless they do occur in many small patches. Thus the red-sand- stone of the Connecticut Valley often crops out in that part of New England, and, being, in many localities, of a friable nature, has crumbled to soil, which now lies undis- turbed in its original position. So, too, at the base of trap- bluffs may be found trap-soils, still full of sharp-angled fragments of the rock. | Transported Soils, (subdivided into drift, alluvial, and colluvial), are those which have been removed to a dis- tance from the rock-beds whence they originated, by the 144 HOW CROPS FEED. action of moving ice (glaciers) or water (rivers), and de- posited as sediment in their present positions. Drift Soils (sometimes called diluvial) are characterized by the following ;articulars. 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, from sand- grains up to immense rock-masses of many tons in weight. This kind of soil is usually distinguished from all others by the rounded rocks or boulders (“hard heads”) it con- tains, which are promiscuously scattered through it. The “ Drift” has undoubtedly been formed by moving ice in that period of the earth’s history known to geolo- gists as the Glacial Epoch, a perio: when the present sur- face of the country was covered to a great depth by fields of ice. In regions like Greenland and the Swiss Alps, which reach above the line of perpetual snow, drift is now ac- cumulating, perfectly similar in character to that of New England, or has been obviously produced by the melting of glaciers, which, in former geological ages and under a colder climate, were continuations on an immense scale of those now in existence. A large share of the northern portion of the country from the Arctic regions southward as far as latitude 39°, or nearly to the southern boundaries of Pennsylvania and to the Ohio River, including C:nada, New England, Long Island, and the States west as far as Iowa, is more or less covered with drift. Comparison of the boulders with the undisturbed rocks of the regions about show that the materials of the drift have been moved southwards or southeast wards to a distance generally of twenty to forty miles, but sometimes also of sixty or one hundred miles, from where they were detached from their original beds. _KINDS OF SOILS. 145 + The surface of the country when covered with drift is often or usually irregular and hilly, the hills themselves being conical heaps or long ridges 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 moraines of the Swiss Alps. Drift is accordingly not confined to the valleys, but the northern slopes of mountains or hills, whose basis is unbroken rock, are strewn to the summit with it, and immense blocks of transported stone are seen upon the very tops of the Catskills and of the White and Green Mountains. Drift soils are for these reasons often made up 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 waters 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 movmg 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 running water (rivers and tides). Since small and light particles are more readily sustained in a current of water than 7 ' 146 HOW CROPS FEED. heavy masses, alluvium is always more or less stratified or arranged in distinct layers: stones or gravel at the bottom and nearest the source of movement, finer stones or finer gravel above and further-down in the path of flow, sand and impalpable matters at the surface and at 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. Colluvial Soils, lastly, are those which, while consisting in part of drift or alluvium, also contain sharp, angular fragments of the rock from which they mainly originated, thus demonstrating that they have not been transported to any great distance, or are made up of soils in place, more or less mingled with drift or alluvium. § 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 iia iii = KINDS OF SOILS. 14% mechanical ingredients, or from other highly obvious qualities. , The distinctions thus established, though very vague scientifically considered, are extremely useful for practical purposes, and the grounds upon which they rest deserve to be carefully reviewed for the purpose of appreciating their deficiencies and giving greater precision to the terms employed to define them. The farmer, speaking of soils, defines them as gravelly, sandy, clayey, loamy, calcareous, peaty, ochreous, ctc. Mechanical Analysis of the Soil.—Before noticing these various distinctions in detail, we may appropriately study the methods which are employed for separating the mechanical ingredients of a soil. It is evident that the epithet sandy, for exainple, 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 finer and especially by the finest particles. Mechanical analysis serves therefore to compare together different 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 practical purposes; but in any serious attempt to define a soil precisely, for the purposes of science, its mechanical analysis must be made with care. Mechanical separation is effected by sifting and wash- ing. Sifting serves only to remove thie stones and coarse sand. By placing the soil in a glass cylinder, adding wa- ter, and vigorously agitating for a few moments, then letting the whole come to rest, there remains suspended in the water a greater or less quantity of matter in a sta*e 148 HOW CROPS FEED. of extreme division. This fine matter is in many cases clay (kaolinite), or at least consists of substances resulting from the weathering of the rocks, and is not, or not chiefly, rock-dust. Between this impalpably fine matter and the grains of sand retained by a sieve, there exist numberless gradations of fineness in the particles. By conducting a slow stream of water through a tube to the bottom of a vessel, the fine particles of soil are carried off andl may be received in a pan placed beneath. Increasing tl:e rapidity of the current enables it to remove larger particles, and thus it is easy to separate the soil in- to anumber of portions, cach of which contains soil of 2 different fineness. Various attempts have been made to devise precise means of separating the materials of soils mechanically into a definite number of grades of fineness. This may be accomplished in good measure by washing, but constant and accurate results are of course only at- tained when the circumstances of the washing are uniform throuzhout. The method adopted by the Society of Agricultural Chemists of Germany is essentia'ly the fol- lowing ( Versuchs Stationen, VI, 144): The air-dry soil is gently rubbed on a tin-plate sieve with round holes three millimeters in diameter; what passes is weighed as jfine-earth. What remains on the sieve is washed with water, dried, weighed, and designated as gravel, pebbles, stones, as the case may be, the size of the stones, etc., being indicated by comparison with the fist, with an egg, a walnut, a hazelnut, a pea, etc. Of the fine- earth a portion (80 grams) is now boiled for an hour or more in water, so as to completely break down any lumps and separate adhering particles, and is then left at rest for some minutes, when it is transferred into the vessel I of the apparatus, fig. 8., after having poured off the turbid water with which it was boiled, into 2, This washing ap- paratus (invented by Ndbel) consists of a reservoir, 4, . + a KINDS OF SOILS. 149 made of sheet metal, capable of holding something more than 9 liters of water, and furnished at 4 with a stop-cock. By means of a tube of rubber it is joined to the series of Fig. 8. vessels, 1, 2, 8, and 4, which are connected to each cther, as shown in the figure, the recurved neck of 2 fitting water-tight into the nozzle of I at a, ete. These vessels are made of glass, and together hold 4 liters of water; their relative volume is nearly fe Ole 764) or =)": 273s 4 5 is a glass vessel of somewhat more than 5 liters, capacity. The distance between } and ¢ is 2 feet. The cock, J, is opened, so that in 20 minutes exactly 9 liters of water 150 HOW CROPS FEED, piss it. The apparatus being joined together, and the cock opened, the soil in 1 is agitated by the stream of wa- ter flowing through, and the finer portions are carried over into 2, 3, 4, and 5, Asa given amount of water requires eight times longer to pass through 2 than 1, its velocity of motion and buoyant power in the neck of 3 are corre- spondingly less. After the requisite amount of water has run from A, the cock is closed, the who'e left to rest sev- eral hours, when the contents of the vessels are separately rinsed out into porcelain dishes, dried and weighed.* The contents of the several vessels are designated as follows :f. Gravel, fragments of rock. Coarse sand. . Fine sand. . Finest or dust sand. Clayey substance or impalpable matter. ot 99 20 In most inferior soils the gravel, the coarse sand, and the fine sand, are angular fragments of quartz, feldspar, amphibole, pyroxene, and mica, or of rocks consisting of these minerals. It is only these harder and less easily decomposable minerals that can resist the pulverizing agencies through which a large share of our soils have passed. In the more fertile soils, formed from sedimen- tary limestones and slates, the fragments of these strati- fied rocks occur as flat pebbles and rounded grains, The finest or dust-sand, when viewed under the micro- scope, is found to be the same rocks in a higher state of pulverization. * See, also, Wolff’s ‘‘ Anleitung zur Untersuchung landwir. Mla niin dStoffe,”’ 1867, p. 5. + These names, applied by Wolff to the results of washing the sedentary soils of Wirtemberg, do not always well apply to other soils. Thus Grouven, (3¢er Salz- minder Bericht, p. 32), operating on the alluvial soils of North Germany, desig- nated the contents of the 4th funncl as ‘clay and loam,” and those of the 5th vessel as ‘Slight clayand humus.” Again, Schéne found (Bulletin, ete., de Moscou, p. 402) by treatment of a certain soil in Nébel’s apparatus, 45 per cent. of ** coarse sand’ remaining in the 2d funnel. The particles of this were for the most part smaller than 1-10th millimeter (1-250th inch), which certainly is not coarse sand ! Wee - L KINDS OF SOILS. 151 What is designated as clayey substance, or impalpable matter, is oftentimes largely made up of rock-dust, so fine that it is supported by water, when the latter is in the gentlest motion. In what are properly termed clay-soils, the finest parts consist, however, chiefly of the hydrous silicate of alumina, already described, p. 113, under the mineralogical name of kaolinite, or of analogous com- pounds, mixed with gelatinous silica, oxides of iron, and carbonate of lime, as well as with finely divided quartz and other granitic minerals. So gradual is the transition from true kaolinite clay through its impurer sorts to mere impalpable rock-dust, in all that relates to sensible char- acters, as color, feel, adhesiveness, and plasticity, that the term clay is employed rather loosely in agriculture, being not infrequently given to soils that contain very little kaolinite or true clay, and thus implies the general physi- eal qualities that are usually typified by clay rather than the presence of any definite chemical compound, like kaolinite, in the soil. Many soils contain much carbonate of lime in an im- palpable form, this substance having been derived from lime rocks, as marble and chalk, from the shells of mollusks, or from coral; or from clays that have originated by the chemical decomposition of feldspathic rocks containing much lime. Organic matter, especially the debris of former vegeta- tion, is almost never absent from the impalpable portion of the soil, existing there in some of the various forms as- sumed by humus. As Schone has shown, (Bulletin dela Societé des Natura- listes de Moscou, 1867, p. 368), the results obtained by Nobel’s apparatus are far from answering the purposes of science. The separation is not carried far enough, and no simple relations subsist between the separated portions, as regards the dimensions of their particles. Ifthe soil were composed of spherical particles of one kind of matter, or 152 HOW CROPS FEED. having all the same specific gravity, it would be possible by the use of a properly constructed washing apparatus to separate a sample into fifty or one hundred parts, and to define the dimensions of the particles of each of these parts. Since, however, the soil is very heterogeneous, and since its particles are unlike in shape, consisting partly of nearly spherical grains and partly of plates or scales upon which moving water exerts an unequal floating effect, it is difficult, if not impossible, to realize so perfect a mechanic- al analysis. It is, however, easy to make a separation of a soil into a large number of parts, each of which shall ad- mit of precise definition in terms of the rapidity of flow of a current of water capible of sustaining the particles which compose it. Instruments for mechanical analysis, which provide for producing and maintaining at will any desired rate of flow in a stream of water, have been very recently devised, indepe::dently of each other, by E. Schone » (loc. cit., pp. 334-405) and A. Muller (Vs. S¢., X, 25-51). The employment of such apparatus promises valuable re- sults, although as yet no extended investigations made with its help have been published. Gravelly Soils are so named from the abundance of small stones or pebbles in them. This name alone gives but little idea of the really important characters of the soil. Simple gravel is nearly valueless for agricultural purposes; many highly gravelly soils are, however, very fertile. The fine portion of the soil gives them their crop- feeding power. The coarse parts ensure drainage and store the solar heat. The mineralogical characters of the pebbles in a soil, as determined by a practised eye, may often give useful indications of its composition, since it is generally true that the finer parts of the soil agree in this respect with the coarser, or, if d fferent, are not in- ferior. Thus if the gravel of a soil contains many pebbles of feldspar, the soil itself may be concluded to be well supplied with alkalies; if the gravel consists of limestone, KINDS OF SOILS. 153 we may infer that lime is abundant in the soil. On the other hand, if asoil contains a large proportion of quartz pebbles, the legitimate inference is that it is of compara- tively poor quality. The term gravelly admits of various qualification. We may have a very gravelly or a mod- erately gravelly soil, and the coarse material may be char- acterized as a fine or coarse gravel, a slaty gravel, a granitic gravel, or a diorite gravel, according to its state of division or the character of the rock from which it was formed. But the closest description that can thus be given of a gravelly soil cannot convey a very precise notion of even its external qualities, much less of those properties upon which its fertility depends. Sandy Soils are those which visibly consist to a large degree, 90°|, or more, of sand, i. e., of small granular fragments of rock, no matter of what kind. Sand usually signifies grains of quartz; this mineral, from its hardness, withstanding the action of disintegrating agencies beyond any other. Considerable tracts of nearly pure and white quartz sand are not uncommon, and are characterized by obdurate barrenness. But in general, sandy soils are by no means free from other silicious minerals, especially feldspar and mica. When the sand is yellow or red in color, this fact is due to admixture of oxide or silicates of iron, and points with certainty to the presence of ferruginous minevals or their decomposition-products, which often give considera- ble fertility to the soil. Other varieties of sand are not uncommon. In New Jersey occur extensive deposits of so-called green sand, containing grains of a mineral, glauconite, to be hereafter noticed as a fertilizer. Lime sand, consisting of grains of carbonate of lime, is of frequent occurrence on the shores of coral islands or reefs. The term sandy-soil is obviously very indefinite, including nearly the extremes We 154 HOW CROPS FEED. of fertility and barrenness, and covering a wide range of variety as regards composition. It is therefore qualified by various epithets, as coarse, fine, etc. Coarse, sandy soils are usually unprofitable, while fine, sandy soils are often valuable. Clayey Soils are those in which clay or impalpable mat- ters predominate. They are commonly characterized by extreme fineness of texture, and by great retentive power for water; this liquid finding passage through their pores with extreme slowness. When dried, they become crack- ed and rifted in every direction from the shrinking that takes place in this process. It should be distinctly understood that a soil may be clayey without being clay, i e., it may have the external, physical properties of adhesiveness and impermeability to water which usually characterize clay, without containing those compounds (kaolinite and the like) which constitute clay in the true chemical sense. On the other hand it were possible to have a soil consist ing chemically of clay, which should have the physical properties of sand; for kaolinite has been found in erys- tals sana of an inch in breadth, and destitute of all cohesive- ness or plasticity. Kaolinite in such a coarse form is, how- ever, extremely rare, and not likely to exist in the soil. Loamy Soils are those intermediate in character between sandy and clayey, and consist of mixtures of sand with clay, or of coarse with impalpable matters. They are free from the excessive tenacity of clay, as well as from the too great porosity of sand. The gradations between sandy and clayey soils are roughly expressed by such terms and distinctions as the following : “ss ~ 1 Uk Sees col KINDS OF SOILS. 155 Clay or impalpable matters. Sand. Heavy clay contains 75—90° |, 10— 25°|, Clay loam oa 60—75 20— 40 Loam 6. 40—60 40— 60 Sandy loam“ 25—40 60— 75 Light sandy loam contains 10—25 Ta— 90 Sand . 0—10 90—100 The percentage composition above given applies to the dry soil, and must be received with great, allowance, since the transition from fine sand to impalpable matter not physically distinguishable from clay, is an impercep- tible one, and therefore not well admitting of nice discrim- ination. It is furthermore not to be doubted that the difference between a clayey soil and a loamy soil depends more on the form and intimacy of admixture of the ingredients, than upon their relative proportions, so that a loam may exist which contains less sand than some clayey soils. Calcareous or Lime Soils are those in which carbonate of lime, is a predominating or characteristic ingredient. They are recognizable by effervescing vigorously when drenched with an acid. Strong vinegar answers for test- ing them. They are not uncommon in Europe, but in this country are comparatively rare. In the Northern and Middle States, calcareous soils scarcely occur to an extent worthy of mention. While lime soils exist containing 75°|, and more of car- bonate of lime, this ingredient is in general subordinate to sand and clay, and we have therefore caleareous sands, caleareous clays, or calcareous loams. Marls 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 New Jersey, green sand mari, or marl simply, is the name applied to the green sand employed as a fertilizer. Shed marl isa name designating nearly pure carbonate of lime found in swamps. 156 HOW CROPS FEED. vegetable matter in bogs and marshes. A soil is peaty or mucky when containing vegetable remains that have suf- fered partial decay under water. Vegetable Mold is a soil containing much organic mat- ter that has decayed without submergence in water, either resulting from the leaves, etc., of forest trees, from the roots of grasses, or from the frequent application of large doses of strawy manures. Ochery or Ferruginous Soils are those containing much oxide or silicates of iron; they have a yellow, 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. ‘hese terms mostly explain tlhem- selves. When, at the dcpth 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 CHARACTERS OF THE SOIL. 157 pacted 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, we may proceed to a somewhat extend- ed notice of the properties of the soil as influencing fertil- ity. These divide themselves into physical characters— those which externally affect the growth of the 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 pa!pable 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 ch:r- 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. . Power of fixing Solid Matters from their Solutions, Permeability to Liquid Water. Capillary Power. Changes of Bulk by Drying, ete. Adhesiveness. . Relations to Heat. DIMM 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 Agricultural Society, and reproduced in altered form in a Lecture given at the Smithsonian Institution, Dec., 1859. gm 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 (=438,560 cubic feet). WEIGHT OF SoILs per cubic foot __per.acre to depth of one foot. Dry silicious or calcareous sand......... about 110 Ibs. 4,792,000 Half sand and half clay....:....°.....< 2 95° 4,182,000 Common:arable land *. 255 ..ciee bed: ‘© 80 to 90 ‘* 3,485,000 to 3,920,000 CAV Glave ote caltna soak ee homesite tees oe {6 ee 3,267,000 Garden mold, rich in vegetable matter... “ nO 2 3,049,000 1 APES HT =/ O11 ROS payee me DE ey Men, Sen was 9 ..-. “* 80to 50 “ 1,307,000 to 2:1'78:000 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 3,768,000 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 mind, Boussingault found to weigh 81 Ibs. ay. per cubic foot Bi 3 kilos per liter). This would be per acre, one foot deep, 3,528,000 Ibs. te “ee PHYSICAL CHARACTERS OF THE SOIL. 159 nourishment to crops as the latter, since they present one- half more absolute weight in a given space. Peat soils are light in both senses in which this word is used by agriculturists. The Specific Gravity of Soils is the weight of a given bulk compared with the same bulk of water. A cubic foot of water weighs 624 lbs., but comparison of this num- ber with the numbers stated in the last table expressing the weights of a cubic foot of various 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. Schéne has recently determined with care the specific gravity of 14 soils, and the figures range from 2.93 to 2.71. The former density is that of a soil rich in humus, from Orenberg, Russia; the latter of a lime soil from Jena. The density of sandy and clayey soils free from humus is 2.65 to 2.69. (Bulletin de la Soc. Imp. des Naturalistes de Moscou, 1867, p. 404.) This agrees with the density of those minerals which constitute the bulk of most soils, as seen from the 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 OF 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 it; 160 HOW CROPS FEED. if it is reduced to a very fine dust and duly watered, even the cereal grains will grow and perfect fruit on it. Magnus (Jour. fiir prakt. Chem., LL, '70) caused barley . to germinate in pure feldspar, which was in one exper:- ment coarsely, in another finely, pulverized. In the coarse feldspar the plants 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 inches, and produced four seeds. It is true, as a general rulc, that a’l fertile soils contain a large proportion of fine or impalpable matter. The soil of the “Ree Ree Bottom,” on the Scioto River, Ohio, re- markable for its extraordinary fertility, which has remained nearly undiminished for 60 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. Sci., 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 which it exposes. The finer the particles, the more abundantly will the p'ant 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 contact with such an extent of surface that they are able to dissolve the soil-ingredients in as Jarge 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- PHYSICAL CHARACTERS OF THE SOIL. 161 ing roots. have in which to expand themselves, and the more abundantly are they able to present their absorbent surfaces to the supplies which the soil contains. The fine- ness of the particles may, however, be excessive. They may fit each other 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 appear that other very important prop- erties of the soil are more or less related to its state of mechanical division. ee 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 property of a soil is of the utmost agricultural im- portance, because, Ist, 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 experiments carried out by Schiibler, 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 hours by the previously dried soil from air confined over water, and hence nearly saturated with vapor. ReEL is PONS, CONGR. cass va ci va alae via Sento + acoso ue 0 Le SR MR de Bide A a aera Bae BI Ane eae te ! PME SIO so Meas aie Riot See teee oes pe Me She bs} Berar) ARAM och Syahid ain Folge Tes, | taiufarlaa dial sh aie sie'o 6 paiaiwnuss 2 23 ise, One tener CENE Clby } .. . sig cask veda vat ca oaks line « 28 Pee MEER uc Soa science aha mle Si ewe eee a cee ane 30 tf OS Gs 162 HOW CROPS FEED. Hine carbonate.of lime. .....,.. 0is+ cas iiesmwrenee wes oa ee eee * Heavy clay soil, (80 per cent clay)... ......5..e8senmeee . 41 Garden mold, (7 per cent humus)... ......o. sean eee 52 Pure Clay is. 5! os ad ce ann obs O's om oe pee 49 Carbonate of magnesia (fine powder) «. ......-e.sassneene 82 TITITUS “oii a op .0is 0 p.05es anys sipersice p= 5 © noo sel 120 Davy found that one thousand 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 heath. ..:........sseeekee aan 3 Coarse Sand... 2. .scsc snes éwiew 02 a0 56 Os als 6 heen 8 Wine sand). . 3.04260 ass vnee sags mae os 40lciss 2 le eee 1 Soil from Mersey, Hssex. . .S. i.e... ain's ) eat 13 Very fertile alluvium, Somersetshire. .....2.. .2-ee eee 16 Extremely fertile soil of Ormistor, East Lothian......... 18 An obvious practical result follows from the facts 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 be 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 does 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. Tlis 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 a8 i PHYSICAL CHARACTERS OF THE SOIL. 163 from want of moisture; when, however, they occur as fine dust, they form too wet a soil, in which planis suffer from the opposite cause.”—(/lamnv’s Lindwirthschaft.) 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 perfectly clean and dry surface, is coated with a film of moisture. Ifa piece of glass be weighed on avery delicate balance, and then be wiped with a clean cloth, it will be found to weigh perceptibly 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 water an adhesive attraction. Certain compounds familiar to the chemist attract water with great avidity and to a large 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 example, is perfectly freed from vapor of water by slowly traversing a tube containing lumps of dried chloride of calcium, or phosphoric acid, or by bubbling repeatedly throug’ ol 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 deliquescent. Certain compounds, such as urea, the char- acteristic ingredient of human urine, deliquesce in moist air and dry away again in a warm atmosphere. Allusion has been made in “How Crops Grow,” p. 55, 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 CROPS FEED. only dependent on the nature of the substance and its amount of surface, but is likewise influenced by externa) conditions. The rapidity 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 unaffected 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 whieh 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 th2 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. oe 66° “cc 11.9 74 ce ce a4 <4 if fa oe 10.2 oe “ 74 ce ce 88° ce 8.7 74 cc 74 6c Knop calcul:utes on the basis of his numerous observa- tions that hair and wool, which are more hygroscopic than most vegetable and mineral substances, if allowed to ab 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. 6c 55° 6c 15.5 6c 6 “cc 32° ce 19.3 ‘T4 “ce PHYSICAL CHARACTERS OF THE SOIL. 165 Silk is sold in Europe by weight with suitable allowance for hygroscopic moisture, its variable conteut of which is carefully determined by experiment in each important transaction. It is plain that the circumstances of sale may affect the weight of wool to 10 or more per cent. § 4, CONDENSATION OF GASES BY THE SOIL. Adhesion.—In the fact that soils and porous bodies gen erally have a physical absorbing power for the vapor of water, we have an illustration of a principle of very wide application, viz., Zhe surfuces of liquid and solid matter attract the particles of other kinds of matter. This force of adhesion, as it is termed, when it acts up- on gaseous bodies, overcomes to a greater or less degree their expansive tendency, and coerces them into a smaller space—condenses them. Absorbent Power of Charcoal, ete.—Charcoal serves to illustrate this fiict, and some of its most curious as well as useful properttes depend upon this kind of physical peculiarity. Charcoal is prepared from wood, itself ex- tremely porous,* by expelling the volatile constituents, whereby the porosity is increased to an enormous extent. When charcoal is kept in a damp cellar, it condenses so much vapor of water in its pores that it becomes difficult to set on fire. It may even take up one-fourth its own weight. When exposed to various gases and volatile matters, it absorbs them in the same manner, though to very unequal extent. De Saussure was the first to measure the absorbing power of charcoal for gases. In his experiments, boxwood charcoal was heated to redness and plunged under mer- * Mitscherlich has calculated that the cells of a cubic inch of boxwood have no less than 73 sauare feet of surface. 166 HOW CROPS FEED. eury to cool. Then introduced into the various gases named below, it absorbed as many times its bulk of them, as are designated by the subjoined figures: e PAUMMMOMED 5 op oie 0 wort ble 90 Hydrochloric acid....... 85 Sulphurous acid......... 65 Hydrosulphurie acid..... 55 Protoxide of nitrogen....40 Carbonic acid........ a ee CPR OOM Jo csatataeess out 9144. -Curbonic oxide Joye ceee 916 Pplvatets 125 Ft es ave os 13% Nitrogen... ses 05 ese Ug 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 has experimented in the same di- rection. From these researches we learn that the power in question is exerted towards different gases with very - unequal effect, and that different kinds of charcoal exert very different condensing power. Stenhouse found that one gramme of dry charcoal ab- sorbed of several gases the number of cubic centimeters given below. Kind of Charcoal. Name of Gas —— SSeS Wood. Peat. | Anétmal. Ly) es |e | apres VANONIIMNTIT ED Soo disor dota «18 nates & = 9.928 m jaro eee wdislapere ee 98.5 96.0 | 435 FIVUPOGRIGNIC ACLGS. 22 i2\5 32. tinh. ist pape aoe 45.0 60.0 | FIVArOsSnIPBUNIC: BCIGGS 22) sen see dainw nase. eee eee | 30.0 28.5 90 SHIPRUVORS, ACOs 6.45.3 arp yes po atedenss eee ee | 32.5 27.5 17.5 CAPPODIC ACI... recess sen Uses toa sees emits ; 14.0 10.0 5.0 OPEN OND OF 2.) a 7ale asta ee > Dem = tk, se See ae 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, hydrochlorie acid). Condensation of Gases by the Soil.—Reichardt and Blumtritt have recently made a minute study of the kind and amount of gases that are condensed in the pores of various solid substances, including soils and some of their PHYSICAL CHARACTERS OF THE SOIL. 167 ingredients. (Jour. fir prakt. Chem., Bd. 93, p. 476.) Their results relate chiefly to these substances as ordinarily occurring exposed to the atmosphere, and therefore more or less moist. The following Table includes the more im- portant data obtained by subjecting the substances to a temperature of 284° F.,and measuring and analyzing the gas thus expelled. 100 Grams 19 Vols. 109 Vols. of Gas contained : Ee yielded gas yielded — ———_——— Substance an vols. Nitro- Oxy- Carbon- Car- > C. C. gas. gen. gen. tcacid. bonic : oxide. Charcoal, air-dry, 164 — 100 0 0 0 of moistened and dried again, 140 59 85 2 9 3 Peat, 162 — dt 5 51 0 Garden soil, moist, 14 20 64 3 24 9 me “air-dry, 38 54 65 2 33 0 Hydrated oxide of iron, air-dry, 375 309 25 4 79 0 Oxide of iron, ignited, 52 83 13 4 0 Hydrated alumina, air-dry, 69 82 41 0 59 —— Alumina, dried at 212°, au! 14 §3 17 0 — Clay, 3: — 65 21 14 — ** Jong exposed to air, 26 39 8 5 23 — ‘© moistened, 29 Bi) 60 6 34 — River silt, air-dry, 40 48 68 0 18 14 = ‘** moistened, 24 29 67 0 31 2 a ‘© again dried, 26 30 67 9 16 i Carbonate of lime (whiting,) 1864, 43 52 100 0 0 _— i Shs. a 1865, 39 48 74 16 10 — $ “eS precipitated, 1864, 65 a 81 19 0 a , = otis oe 1865, 51 52 U7 15 8 — Carbonate of magnesia, (29 125 64 7 29 — Gypsum, pulverized, 17 _ 81 19 0 — From these figures we gather: 1. The gaseous mixture which is contained in the pores of solid substances rarely has the composition of the at- mosphere. In but two instances, viz., with gypsum and precipitated carbonate of lime, were only oxygen and ni- trogen absorbed in proportions closely approaching those of the atmosphere. 2. Nitrogen appears to be nearly always absorbed in greater proportion than oxygen, and is greatly condensed in some cases, as by peat, hydrated oxide of iron, and car- bonate of magnesia. 168 HOW CROPS FEED, 3. Oxygen is often nearly or quite wanting, as in char- coal, oxide of tron, alumina, river silt, and whiting. 4, Carbonic acid, though sometimes wanting entirely, is usually abundant in the absorbed gases. 5. In the pores of charcoal and of soils containing de- caying organic matters, carbonic acid is often partially re- placed by carbonic oxide. The experiments, however, do not furnish proof that this substance is not formed under the influence of the high temperature employed (284° F.) in expelling the gases, rather than by incomplete oxidation of organic matters at ordinary temperatures. 6, A substance, when moist, absorvs less gas than when dry. Inaccordance with this observation, De Saussure no- ticed that dry charcoal saturated with various gases evoly- ed a good share of them when moistened with 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. The extremely variable figures obtained by Blumtritt when operating with the same substance (the figures given in the table are averages of two or tliree usually discordant results), result from the general fact that the proportion in which a number of gases are present in a mixture, in- fluences the proportion of the individual gases absorbed. Thus while charcoal or soil will absorb a large amount of ammonia from the pure gas, it wiil 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 condense 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 a PHYSICAL CHARACTERS OF THE SOIL. 169 is absorbed by porous bodies in the largest quantity. This not only displaces other gases from their adhesion to solid surfaces, but by its own attractions modifies these adhesions. Reichardt and Blumtritt take no account of water-gas, except in the few experiments where the substances were purposely moistened. In all their trials, however, moist-_ ure was present, and had its quantity been estimated, doubtless its influence on the extent and kind of absorp- tion would have been strikingly evident throughout. Ammonia and carbonate of ammonia in the gaseous form are absorbed from the air by the dry soil, to a less degree than by a soil that is moist, as will be noticed fully hereafter. Chemical Action 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 piece 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 effuvium that ordinarily arises from decaying flesh. The metal platinum exhibits a remarkable condensing power, which is manifest even with the polished surface of foil or wire; but is most striking when the metal is 8 r) t 170 HOW CROPS FEED. brought to the condition of sponge, a form it assumes when certain of its compounds (e. g. ammonia-chloride of platinum) are decomposed by heat, or to the more finely divided state of platinum black. The latter is capable of condensing from 100 to 250 times its volume of oxygen, according to its mode of preparation (its porosity ?); and for this reason it possesses intense oxidizing power, so that, for example, when it is brought into a mixture of oxygen and hydrogen, it causes them to unite explosively. A jet of hydrogen gas, allowed to play on platinum sponge, is almost instantly ignited—a fact taken advantage of in Dobereiner’s hydrogen lamp. The oxidizing powers of platinum are much more vig- orous than those of charcoal. Stenhouse has proposed the use of platinized charcoal (charcoal ignited after moist- ening with solution of chioride 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, heing able to take up or “‘ occlude” 900 times its volume of the gas, (Graham, Proceedings Roy. Soc., 1868, p. 422.} oy ABSORBENT POWER OF SOILS. vel odor, by burying them for a few days in the earth. The Indians of this country are said to sweeten the carcass of the skunk by the same process, when needful, to fit it for their food. Dogs and foxes bury bones and meat in the ground, and afterward exhume them in a state of com- parative freedom from offensive odor, When human excrements are covered with fine dry earth, as in the “ Earth Closet ” system, all odor is at once suppressed and never reappears. At the most, besides an “earthy” smell, an odor of ammonia appears, resulting from decomposition, which appears to proceed at once to its ultimate results without admitting of the formation of any intermediate offensive compounds. Dr. Angus Smith, having frequently observed the pres- ence of nitrates in the water of shallow town wells, sus- pected that the nitric acid was derived from animal mat- ters, and to test this view, made experiments on the action of filters of sand, and other porous bodies, upon solutions of different animal and vegetable matters. He found that in such circumstances oxidation took place most rap- idly—the nitrogen of organic matters being converted. in- to nitric acid, the carbon and hydrogen combining with oxygen at the same time. Thus solution of yeast, which contained no nitric acid, after being passed through a filter of sand, gave abundant evidence of salts of this acid. Colored solutions were in this way more or less decolor- ized. Water, rendered brown by peaty matter, was found to be purified by filtration through sand.* § 5. POWER OF SOILS TO REMOVE DISSOLVED SOLIDS FROM THEIR SOLUTIONS. Action of Sand upon Saline Solutions.—It has long been known that simple sand is capable of partially re- * This account of Dr. Smith’s experiments is quoted from Prof. Way’s paper ‘On the Power of Soils to Absorb Manure.” (Jour. Roy. Ag. Soc. of England, XL, p. 317.) 172 HOW CROPS FEED. moving saline matters from thcir solutions in water. Lord Bacon, in his “Sylva Sylvarum,” speaks of a method of obtaining fresh water, which was practised on the coast of Barbary. ‘“‘Digge a hole on the sea-shore somewhat above high-water mark and as deep as low-water mark, which, when the tide cometh, will be filled with water fresh and potable.” He also remarks ‘to have read that trial hath been made of salt-water passed through earth through ten vessels, one within another, and yet it hath not lost its saltness as to become potable;” but when “drayned through twenty vessels, hath become fresh.” Dr. Stephen Hales, in a paper read before the Royal Society in 1739, on “Some attempts to make sea-water wholesome,” mentions on the authority of Mr. Boyle God- frey that “sea-water, being filtered through stone cisterns, the first pint that runs through will be pure water having no taste of the salt, but the next pint will be salt as usual.” Berzelius found upon filtering solutions of common salt through sand, that the portions which first passed were quite free from saline impregnation. Matteucci extended this observation to other salts, and found that the solu- tions when filtered through sand were diminished in den- sity, showing a detention by tlhe sand of certain quantities of the salt operated upon.* Action of Humus on Saline Solutions.—Heiden (Hoff- mani’s Juhresbericht, 1866, p. 29) found that peat and various preparations of the humic acids, when brought in- to solutions of chloride of potassium and chloride of am- monium, remove a portion of these salts from the liquid, leaving the solutions perceptibly weaker. The removed salts were for the most part readily dissolved by a small quantity of water. W. Schumacher (Hoff. Jahres., 1867, p- 18) observed that humus, artificially prepared by the * These statements of Bacon, Hales, Berzelius, and Matteucci, are derived from Prof. Way’s paper ‘*On the Power of Soils, etc.” (Jour. Roy. Ag. Soc. @ Eng., XI, 216.) Bt e ABSORBENT. POWER OF SOILS. ie action of oil of vitriol on sugar, when placed in ten times its quantity of solutions of various salts (containing about + per cent of solid mutter) absorbed of sulphates of soda and ammonia, and chlorides of calcium and ammonium, about 2 per cent; of sulphate of potash 4 per cent; and of phosphate of soda 10 per cent. Schumacher also noticed that sulphate of potash is able to expel sulphate of ammo- nia from humic acid which has been saturated with the latter salt, but that the latter cannot displace the former. In Schumacher’s experiments, pure water freely dissolved the salts absorbed by the humic acid. Explanation.—Let us consider what occurs in the ac} of solution and in this separation of soluble matters from aliquid. The difference between the solid and the liquid state, so far as we can define it, lies in the unequal cohe- sion of the particles. Cohesion prevails in solids, and op- poses freedom of motion among the particles. In liquids, cohesion is not altogether overcome but is greatly weak- ened, and the particles move easily upon each other When a lump of salt is put into water, the cohesion that otherwise maintains its particles in the solid state is over- come by the attraction of adhesion, which is mutually ex- erted between them and the particles of water, and the salt dissolves. If now into the solution of salt any in- soluble solid be placed which the liquid can wet (adhere to) its particles will exert adhesive attraction for the par- ticles of salt, and the tendency of the latter will be to concentrate somewhat upon the surface of the solid. If the solid, thus introduced into a solution, be excecd- ingly porous, or otherwise present a great amount of sur- face, as in case of sand or humus, this tendency is propor- tionately heightened, and a separation of the dissolved substance may become plainly evident on proper examina- tion. When, on the other hand, the solid surface is rela- tively small, no weakening of the solution may be percep- tible by ordinary means. Doubtless the glass of a bottle 174 HOW CROPS FEED. containing brine concentrates the latter where the two are in contact, though the effect may be difficult to dem- onstrate. Defecating Action of Charcoal on Solutions,—Char- coal manifests a strong surface attraction for various solid substances, and exhibits this power by overcoming the adhesion they have to the particles of water when dis- solved in that fluid. If ink, solution of indigo, red wine, or bitter ale, be agitated some time with charcoal, the color, and in the case of ale, the bitter principle, will be taken up by the charcoal, leaving the liquid colorless and comparatively tasteless. Water, which is impure from putrefying organic matters, is sweetened, and brown sugars are whitened by the use of charcoal or bone-black.. In case of bone-black, the finely divided bone-earth (phos- phate of lime) assists the action of the charcoal. Fixing of Dye-Stuffs,—The familiar process of dyeing depends upon the adhesion of coloring matters to the fiber of textile fabrics. Wool steeped in solution of indigo at- taches the pigment permanently to its fibers. Silk in the same way fastens the particles of rosaniline, which consti- tutes the magenta dye. Many colors, e. g. madder and logwood, which will not adhere themselves directly to cloth, are made to dye by the use of mordants—substances ~ like alumina, oxide of tin, ete.—which have adhesion both wo the fabric and the pigment. Absorptive Power of Clay.—These effects of charcoal and of the fibers of cotton, etc., are in great part identical with those previously noticed in case of sand and humus. Their action is, however, more intense, and the effects are more decided. Charcoal, for example, that has ab- sorbed a pigment or a bitter principle from a liquid, will usually yield it up again to the same or a stronger solvent. {n some instances, however, as in dyeing with simple col- ers, matters are fixed in a state of great permanence by ABSORBENT POWER OF SOILS. 175 the absorbent; and in others, as where mordants are used, chemical combinations supervene, which possess extraordi- nary stability. Many facts are known which show that soils, or certain of their ingredients, have a fixing power like that of char- coal and textile fibers. It is a matter of common expe- rience that a few feet or yards of soil intervening between a cess-pool or dung-pit, and a well, preserves the latter against contamination for a longer or shorter period. J. P. Bronner, of Baden, in a treatise on “‘ Grape Cul- ture in South Germany,” published in 1836, first mentions that dung liquor is deodorized, decolorized, and rendered nearly tasteless by filtration through garden earth. Mr. Huxtable, of England, made the same observation in 1848, and Prof. Way and others have published extended in- vestigations on this extremely important subject. Prof. Way informs us that he filled a long tube to the depth of 18 inches with Mr. Huxtable’s light soil, mixed with its own bulk of white sand. “Upon this filter-bed a quantity of highly offensive stinking tank water was poured, The liquid did not pass for several hours, but ultimately more than 1 ounce of it passed quite clear, free from smell or taste, except a peculiar earthy smell and taste derived from the soil.” Similar results were obtain- ed by acting upon putrid human urine, upon the stinking water in which flax had been steeped, and upon the water of a London sewer. Prof. Way found that these effects were not strikingly manifested by pure sand, but appeared when clay was used. He found that solutions of coloring matters, such as logwood, sandal-wood, cochineal, litmus, etce., when fil- tered through or siaken up with a portion of clay, are entirely deprived of color. (Jour. Roy. Ag. Soc. of Fing., XI, p. 364.) These effects of clay or clayey matters, like the fixing power of cotton and woolen stuffs upon pigments, must 176 HOW CROPS FEED, be regarded for the most part as purely physical. There are other results of the action of the soil on saline solu- tions, which, though perhaps influenced by simple physical action, are preponderatingly chemical in their aspect. These effects, which manifest themselves by chemical de- compositions and substitutions, will be fully discussed in a subsequent chapter, p. 333. § 6. 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 is 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 pores 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 percoiates them. When, instead of running through, the water is largely absorbed and held by the soil, the latter is said to possess great capillary power ; such a soil has many and minute pores. 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 will be curved or concave. In a very narrow tube the liquid will rise to a considerable height. In these cases the surface attraction of the glass for the water neu- tralizes or overcomes the weight of (earth’s attraction for) the latter. The pores of a sponge raise and hold water in them, in the same way that these narrow (capillary *) tubes sup- * From capillus, the Latin word for hair, because as fine as hair; (but a hair is no tube, as is often supposed.) ia PERMEABILITY OF SOILS TO LIQUID WATER. 177 port it. When a body has pores so fine (surfaces so near eich other) that their surface attraction is greater than the gravitating tendency of water, then the body will im- bibe and hold water—will exhibit capillarity; a lump of salt or sugar, a lamp-wick, are familiar examples. When the pores of a body are so large (the surfaces so distant) that they cannot fill themselves or keep themselves full, the body allows the water to run through or to percolate. Sand is most easily permeable to water, and to a higher degree the coarser its particles. Clay, on the other hand, is the least penetrab!e, 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 fall upon it quickly soak through, and it shortly becomes dry. On such a soil, the manures that may be applied in the spring are to some de- gree washed down below the reach of vegetation, and in the droughts of summer, plants suffer or perish from want of moisture. ; When the texture of a soil is too fine,—its pores too small_—as happens in a heavy clay, the rains penetrate it too slowly; they flow off the surface, if the latier be in- clined, or remain as pools for days and even weeks in the hollows. In a soil of proper texture the rains neither soak off into the under-earth nor stagnate on the surface, but the soil always (except in excessive wet or drought) maintains the moistness which is salutary to most of our cultivated plants. Movements of Water in the Soil.—If a wick be put into a lamp containing oil, the oil, by capillary action, gradually permeates its whole length, that which is above as well as that below the surface of the liquid. When the lamp is set burning, the oil at the flame is consumed, and as each particle disappears its place is supplied by a new one, until the lamp is empty or the flame extinguished, gs 178 HOW CROPS FEED. Something quite analogous occurs in the soil, by which 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 wick, and the matter stands thus: Let us suppose dew or rain to have saturated the ground with moisture for some depth. On recurrence of a dry atmosphere with sunshine and wind, the surface of the soil rapidly dries; but as each particle of water es- capes (by evaporation) into the atmosphere, its place is supplied (by capillarity) from the stores below. The as- cending water brings along with it tle soluble matters of the soil, and thus the roots of plants are situated in a stream of their appropriate food. The movement proceeds in this way so long as the surface is drier than the deeper soil. When, by rain or otherwise, the surface is saturated, it is like letting a thin stream of oil run upon the apex of the Jamp-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 which do not enter vegetation accumulate on or near the surface of the ground; when a rain falls, they are washed down again to a certain depth, and thus are kept constantly changing their place with the water, which is the vehicle of their distribution. In regions where rain falls periodically or not at all, this upward flow of the soil- PERMEABILITY OF SOILS TO LIQUID WATER. 179 water often causes an accumulation of salts on the surface of the ground. Thus in Bengal many soils which in the wet season produce the most luxuriant crops, during the rainless portion of the year become covered with white crusts of saltpeter. The beds of nitrate of soda that are found in Peru, and the carbonate of soda and other salts which incrust the deserts of Utah, and often fill the air with alkaline dust, have accumulated in the same manner. So in our western caves the earth sheltered from rains is saturated with salts—epsom-salts, Glanber’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 supplies of food. As before ex- p'ained, the materials of the soil are always undergoing decomposition, whereby the silica, ime, phosphoric acid, potash, etc., of the insoluble fragments of rock, become soluble in water and accessible to the plant. Water charged with carbonic acid and oxygen is the chief agent in these chemical changes. The more extensive and rapid the circulation of water in the soil, the more matters will be rendered soluble in a given time, and, other things be- ing equal, the less will the soil be dependent on manures to keep up its fertility. Capacity of Imbibition. Capillary Power.—No mat- ter how favorable the structure of the soil may be to the 180 HOW CROPS FEED. circulation of water in it, no continuous upward movement can take place without evaporation. The ease and rapid- ity of evaporation, while mainly depending on the condi- tion of the atmosphere and on the sun’s heat, are to a cer- tain degree influenced by the soil itself. We have already seen that the soil possesses a power of absorbing watery vapor from the atmosphere, a power which is related both to the kind of material that forms the soil and to its state of division. This absorptive power opposes evaporation. Again, different soils manifest widely different capacities for imbibing liquid water—capacities mainly connected with their porosity. Obviously, too, the quantity of liquid in a given volume of soil affects not only the rapidity, but also the duration of evaporation. The following tables by Schiibler illustrate the peculi- arities of different soils in these respects. The first col- umn gives the percentages of liguid water absorbed by the completely dry soil. In these experiments the soils were thoroughly wet with water, the excess allowed to drip off, and the increase.of weight determined. In the second column are given the percentages of water that evaporated during the space of four hours from the satu- rated soil spread over a given surface: Quvarizisands: 2.6 6. . oes. diGis . ease ee eee 25 88.4 GV RUINS 2 oa obijare n-a.r sy 08 * synced bosca’s ak oe aaah 27 Aw Dame SA... . 0 Fa fad 6:08 = hte < god A ep oa 29 75.9 SLY WAT. oe reece cee ek bak on ele ee 34 68.0 Clay soil, (sixty: per cent clay,):d iss. 0... deus eee 40 52.0 MIB a8 once boo bo eters done wa aa a ee 51 45.7 Plo ge Ww NG. o.oo wc ss x vis «0's mein oy ts eee ee 52 32.0 Heavy clay, (eighty per cent clay,)..:.<.......%. 61 34.9 Pate craycliyss. Hoc. 6 isis ks Bee 70 319 Fine, earbenate, of m6 ccs «miss buss an 85 28.0 arden WO Ae 4.655 2 aco ois Vent oes on pe eee 89 24.5 TAMING. 35 cone set dads a6 coe mesic wo ses ate een 181 25.5 Fine carbonate of magnesia. ........1.. poured upon the soil in which a white hyacinth was blos- soming, was absorbed by the plaut, and in one to two hours dyed the flowers of its own color. After two or three days, however, the red color disappeared, the flow- ers becoming white again. From the facts just detailed, we conclude that some kinds of organic matters may be absorbed and chemically changed (certain of them assimilated) by agricultural plants. We must therefore hold it to be extremely probable that various forms of humus, viz., soluble humates, ulmates, crenates, and apocrenates, together with the other soluble organic matters of the soil, are taken up by plants, and decomposed or transformed, nay, we may say, assimilated by them. 238 HOW CROPS FEED. A few experiments might easily be devised which would completely settle this point beyond all controversy. Organic Matters as Indirect Sources of Carbon to Plants,—The decay of organic matters in the soil supplies to vegetation considerably more carbonic acid in a given time than would be otherwise at the command of crops. The quantities of carbonic acid found in various soils have already been given (p. 219). The beneficial effects of such a source of carbonic acid in the soil are sufficiently obvious (p. 128). Organic Matters not Essential to the Growth of Crops.—Although, on the farm, crops are rarely raised without the concurrence of humus or at least without its presence in the soil, it is by no means indispensable to their life or full development. Carbonic acid gas is of it- self able to supply the rankest vegetation with carbon, as has been demonstrated by numerous experiments, in which all other compounds of this element have been excludeé (p. 48). g 4. THE AMMONIA OF THE SOIL. In the chapter on the Atmosphere as the food of plants we have been led to conclude that the element nitrogen, — so indispensable to vegetation as an ingredient of albumin, etc., is supplied to plants exclusively by its compounds, and mainly by ammonia and nitric acid, or by substances which yield these bodies readily on oxidation or decay. i We have seen further that both ammonia and nitric acid exist in very minute quantities in the atmosphere, are dis- solved in the atmospheric waters, and by them brought into the soil. It is pretty fairly demonstrated, too, that these bodies, as occurring in the atmosphere, become of appreciable use By yee THE AMMONIA OF THE SOIL. 239 to agricultural vegetation only a‘ter their incorporation with the soil. Rain and dew are means of collecting them from the atmosphere, and, as we shall shortly see, the soil is a storehouse for them and the medium of their entrance into vegetation. | This is therefore the proper place to consider in detail the origin and formation of ammonia and nitric acid, so far as these points have not been noticed when discussing their relations to the atmosphere. Ammonia is formed in the Soil either in the decay of organic bodies containing nitrogen, as the albuminoids, ete., 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, ete., or that set free from water in the oxidation of certain metals, as iron and zine, has been completely disproved by Will. (Ann. d. Ch. u. Ph., 45, pp. 106-112.) The ammonir encountered in such experiments may have been, Ist, that pre-existing in the pores of the substances, or dissolved in the wa- ter operated with. Faraday (Researches in Chemistry and Physics, p. 145) has shown by a series of exact experiments that numerous, we may say all, porous bodies exposed to the air have a minute amount of ammonia adhering to them; 2d, that which is generated in the process of testing or experimenting (as when iron is heated with potash), and formed by the action of an alkali on some compound of nitrogen occurring in the materials of the experiment; or, 3d, that which results from the reduc- tion of a nitrite formed from free nitrogen by the action of ozone (pp. 77-83). The Ammonia of the Soil.—a. Gaseous Ammonia as Carbonate.—Boussingault and Lewy,in their examination of the air contained in the interstices of the soil, p. 219, 240 HOW CROPS FEED. tested it for ammonia. In but two instances did they find sufficient to weigh. In all cases, however, they were ab‘e 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; on 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 fouud 52 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 physically condensed in the Soil.—Many porous bodies condense a large quantity of ammonia gas. Charcoal, which has an cxtreme porosity, serves to illus- trate this fact. De Saussure found that box-wood char- coal, freshly ignited, absorbed 98 times its volume of ammonia gas. Similar results have been obtained by Sten- house, Angus Smith, and others (p. 1€6). 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 cooling the hot charcoal in mer- cury which does not penetrate it, or in a vacuum, and then bringing it directly into the pure ammonia gas. The charcoal thus saturated with ammonia loses the latter rap- idly on exposure to the air, and Stenhouse has found 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 growth is moist or wet. The water of the soil which covers the particles of earth, rather than the particles themselves, must contain any absorbed ammonia. Thirdly, there are THE AMMONIA OF THE SOIL. 241 in fertile soils substances which combine chemically with ammonia. That the soil does contain a certain quantity of ammo- nia adhering to the surface of its particles, or, more prob- ably, dissolved in the hygroscopic water, is demonstrated by the experiments of Boussingault and Lewy just alluded to, in all of which ammonia was detected in the air in- cluded in the cavities of the soil. In case ammonia were physically condensed or absorbed, a portion of it would be carried off in a current of air in the conditions of Boussingault and Lewy’s experiments,—nay, all of it would be removed by such treatment sufficiently prolonged. Brustlein (Boussingault’s Agronomie, et:., 1, p. 152) records that 100 parts of moist earth placed in a vessel of about 24 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 that soil placed in a confined atmos- phere containing very limited quantities of ammonia can- not condense the latter completely. In an experiment similar to those just described, 100 parts of earth (tena- cious calcareous clay) and 0.019 parts of ammonia were ~ left together 5 days. At the conclusion of this period 0.016 parts of the latter had been taken up by the earth. The remainder was found to be dissolved in the water that had evaporated from the soil, and that formed a dew on the interior of the glass vessel. Brustlein proved further that while air may be almost entirely deprived of its ammonia by traversing a long column of soil, so the soil that has absorbed ammonia readily gives up a large share of it to a stream of pure air. He caused air, charged with ammonia gas by being made to bubble through water of ammonia, to traverse a tube 1 ft. long filled with 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 through the soil, ammonia began to escape unabsorbed. The earth thus saturated contained 0.192°|, of ammonia. A current of pure air was now passed through the soil as long as ammonia was removed by it in notable quantity, about 38 cubic feet being required. By this means more than one-half the ammonia was displaced and carried off, the earth retaining but 0.084’ |. Brustlein ascertained 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 with 187 parts of water containing 0.889 parts of ammonia. The earth absorbed 0.157 parts of ammonia. It was now drained from the liquid and allowed to dry at a low tem- perature, which operation required eight days. It was then moistened and allowed to dry again, and this was re- peated four times. The progressive loss of ammonia is shown by the following figures. 100 parts of ‘soul absorbed’) ..bo% .2.2 cscs. ees Cee 0.157 parts of ammonia, Ke 66 86 contained after thefirst. (dryine,s-eeee 0.083 =," 55 a oe se “é ee ss se ee second vie) 0.066 “se ee 4s “ce se oe “sé “ce ee ec third A ae 0.054 ae “ “ “c “ce ee &e oe Lad “ce fourth ee - .. 20.041 ac “ce “ce “ec “se se “ec ee es ee fifth Ce) ee 0.039 “ec ae “se In this instance the loss of ammonia amounted to three: fourths the quantity at first absorbed. The extent to which absorbed ammonia escapes from the soil is greatly increased by the evaporation of water. Brustlein found that a soil containing 0,067°|, of ammo- nia suffered only a trifling loss by keeping 43 days ina dry place, whereas the same earth lost half its ammonia in a shorter time by being thrice moistened and dried. According to Knop (Vs, S¢., HI, p. 222), the single THE AMMONIA OF THE SOIL. 243 proximate ingredient of soils that under ordinary cir- cumstances exerts a considerable surface attraction for ammonia gas is 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, 1. 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. ce. Chemically combined Ammenia.—The reader wiil 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, Ist, 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 ulmic, humic, and apocrenic acids for ammonia is so strong that they can only be freed from it by evaporation of their sulutions to dryness with caustic potash. Boiling with carbouate of potash or carbonate of soda will not suffice to decompose their ammonia-salts. We ho!d it more likely that the ammonia which requires an alkali for its expulsion is generated by the decomposition of the organic acid itself, or, if that be desti- tute of nitrogen, of some nitrogenous substance admixed. According to Bous- singault, ammonia is completely removed from humus by boiling wicm water and caustic magnesia, “i - +e LS ee ee . oe ee 244 HOW 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, oxide of manganese, and alumina, the latter being in preponderating quantity, there are formed double compounds which are insoluble or slightly soluble. Since the humic, ulmic, crenic, and 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. teserving for a subsequent chapter a further discussion of the causes of the chemical retention of ammonia in the soil, we may now appropriately recount the observations thit have been made regarding the condition of the am- monia of the soil as regards its volatility, solubility, ete. Volatility of the Ammonia of the Soil.— We have seen that ammonia my escape from the soil as gaseous carbonate. The fact is not only true of this substance as- physically absorbed, but also under certain conditions of that chemically combined. When we mingle together equal bulks of sulphate 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 mixture be drenched with water, the odor of ammonia at once ceases to be perceptible, and if, after some time, the mixture 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; while the liquid that has passed 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, odorless, THE AMMONIA OF THE SOIL. 945 crystalline solid. Double decomposition has 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 becounes evident again—carbonate of ammonia, in fact, escaping by volatilization, while sulphate of lime is reproduced. It is a general law in chemistry that when a number of acids and bases are together, those which under the circum- stances can produce by their union a volatile body will unite, 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 1s the circumstances which determine in what mode these bodies combine. In presence of much 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- bonie acid being then volatile, 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 so:la, 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 yive off at the 246 HOW CROPS FEED. surface in dry weather a portion of the ammonia which before was chemically retained within it. Solubility of the Ammonia of the Soil,—The distine- tions between physically adhering and chemically combin- ed ammonia are difficult, if not impossible, to draw with accuracy. In what follows, therefore, we shall not attempt to consider them separately. When ammonia, carbonate of ammonia, or any of the 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 remoyed 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., Ist, the soil cannot absorb ammo- nia completely from its solutions ; 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, caleareous, sandy garden soil, when placed in twice its weight of pure water for 24 hours, yielded to the latter ;)59 of its weight of ammonia (=0.0002" |,). 100 parts of the same soil left for 24 hours in 200 parts of a solution of chloride of ammonium (containing 2.182 of sal-ammoniac =0.693 part of ammonia), absorbed 0,112 part of ammonia. Half of the liquid was poured off and its place supplied with pure water, and the whole left for 24 hours, when 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 was that the water added dis- THE AMMONIA OF THE SOIL. 247 volved out nearly one-half the ammonia which the earth at first absorbed. The Ist dilution removed from thesoil ............... 0.010 aS ee ce AONE Wee CPR ey ON Me Re: 0.009 eon * ts isbn) Nene AMR te EEA PNG OE 0.014 ag Sl “ Set Sew CEM owe alg taki tet 0.011 6 agit. Se ‘ oh Be AR ae re se es toe 0.009 ERATE a eae tS a a ee hal cee Ba 0.053 Deducting 0.053 from the quantity first absorbed, viz., 0.112, there remains 0.059 part retained by the soil after five dilutions. Knop, in 11 decantations, in which the soil was treated with 8 times its weight of water, removed 93°|, of the ammonia which 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 ammonia 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 avid. 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 instead 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 948 HOW CROPS FEED. acids, whereby bodies result which are no longer soluble in water, and which, as such, are probably innutritious 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- position ammonia is reproduced. These indifferent nitrog- enous matters appear to be analogous to a class of sub- stances known to chemists as amides, of which asparagin, acrystallizable body obtained from asparagus, young peas, etc., and urea and uric acid, the characteristic ingredients of urine, are examples. Further account of these matters will be given subsequently, p. 276. Quantity of Ammonia in Soils,—Formerly the amount of ammonia in soils was greatly overestimated, as the re- sult of imperfect methods of analysis. In 1846, Krocker, at Liebig’s instigation, estimated the nitrogen of 22 soils, and Liebig published some ingenious speculations 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 1855, the writer examined several soils in Liebig’s laboratory. The soils were boiled for some hours with water and caustic lime, or caustic potash. The ammonia that was set free, distill- ed off, and its amount was determined by alkalimetry. It was found that however long the distillation was kept up, ammonia continued to come over in minute quantity, and it was probable that this substance was not simply expelled from the soil, but was slowly formed by the ac- tion of lime on organic matters, it being well known to chemists that many nitrogenous bodies are thus decom- posed. The results were as follows: Ammonia. White sandy loam distilled with caustic lime gave in two Eyp's. | 9.0186 a ae “ cs “c 6 ‘ 0.0047 ‘ Yellow clay os “os Fe | 0.0051 ** 66 ‘6 ‘“ sc sc potash 6 ‘“ one “ 0.00% ** Black garden soil ¥ 2s * . lime.<*.' * ee | o.09s3 \ THE AMMONIA OF THE SOIL. Q49 The fact that caustic potash, a more energetic decom- posing agent than lime, disengaged more ammonia than the latter from the yellow clay, strengthens the view that ammonia is produced and not merely driven off under the conditions of these experiments, and that accordingly the figures are too high. Other chemists employing the same method have obtained similar results. Boussingault (Agronomie, T. ILI, p. 206) -was the first to substitute magnesia for potash and lime in the estima- tion of ammonia, having first demonstrated that this sub- stance, so feebly alkaline, does not perceptibly decompose gelatine, albumin, or asparagine, all of which bodies, espe- cially the latter, give ammonia when boiled with milk of lime or solutions of potash. The results of Boussingault here follow. , Localities. Quantity of Ammonia per cent. Liebfrauenberg, JRISHIIA™ ie atee oe sroten Sate ec oo ets 0.0022 Bischwiller, Seep eee EL are ck AB as 0.0020 Merckwiller, i i Pte eee ne te Ay wae 2 O0012 Bechelbronn, ee dhs Maite a cian art iwi) ti Sarai alo see a rere = 0.0009 Mittelhausbergen, ogee Teas aes eS. 2 aboot eet 0.0007 HemNapolcan. Mnlhouses 3) e's 6.2 esas tos so eede eee eoe ek ce 0.0006 RPP CMTE CIUTIG LS wy ges Wie fy vasarstnsie omc oiascintr einicesinia qeivis wise 0.0060 Gucsnoy-sur-Dewles Nord, § Pits es sir. eb clos ails «dine See 2 0.0012 Rio Madeira, Ameneae 4S doin. Seutocteeeaie ne den es 0.0090 Rio Trombetto, MS ee eae Se tuid acinar aot ema ee ee 0.0030 Rio Negro, os Oe MO fm 6 eee bak Oe Reda eC ae 0.0038 Santarem, ee eee et ee aoe Meer 0.0083 Tle du Salut, Teo, Ligue love bapalelatac Saxe bow Slava lerstseotssiene orate 0.0080 Martinique, Seni tRa le ate tanec Strats ches See 0.0085 ro oupart, (ert mold.) °° 7, us tade Seco hex chee ocatek's 0.0525 Peat, API Gter CR ls eos cea a neo oe ee 0.0180 The above results on French soils correspond with those obtained more recently on soils of Saxony by Knop and Wolff, who have devised an ingenious method of estimat- ing ammonia, which is founded on altogether a different principle. Knop and Wolff measure the 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 bromine © and caustic soda. lif Oa - aee e- 250 HOW CROPS FEED. Azotometer. (Chemisches Centralblatt, 1860, pp. 243 and 534.) By this method, which gives accurate results when ap- plied to known quantities of ammonia-salts, Knop and Wolff obtained the following results: Ammonia in dry soil, Very light sandy soil from birch forest............ 0.00077? |, Rich lime soil from beech forest. -.........ceseuee 0.00087 Sandy loum, forestseil. ... 0.4. 5. svicc. 2s eee eee 0.00012 Pofest 500). i... on Te. in de Rees 0.00080 Meadow soil, red sandy Joam.....3,. «02 sss ae 0.00027 AVerawte. ¢ sits gh3s cee ee 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 oS. Ge ia May <4 0.019 ce 66 “ The simple standing of the moistened soil for two months sufficed in this case to double the content of am- monia. The quantitative fluctuations of this constituent of the soil has been studied further both by Boussingault and by Knop and Wolff. The latter in seeking to answer the ! - THE NITRIC ACID OF THE SOIL. 251 question—“ How great is the ammonia-content of good manured soil lying fallow ?”—made repeated determina- tions of ammonia (17 in all) in the same soil (well-ma- nured, sandy, calcareous loam exposed to all rains and dews but not washed) during five months. The moist soil varied in its proportion of ammonia with the greatest irregularity between the extremes of 0.0008 and 0.0003° |, Similar observations were made the same summer on the loamy soil of a field, at first bare of vegetation, then cov- ered with a vigorous potato crop. In this case the fluctu- ations ranged from 0.0009 to 0.0003°|, as irregularly as in the other instance. Knop and Wolff examined the soil last mentioned at various depths. At 3 ft. the proportion of ammonia was scarcely less than at the surface. At 6 ft. this loam, and at a somewhat greater depth an underlying bed of sand, contained no trace of ammonia. This observation ac- cords with the established fact that deep well and drain- waters are destitute of ammonia. Boussingault has discovered (Agronomie, 3, 195) that the addition of caustic lime to the soil largely increases its content of ammonia—an effect due to the decomposing ac- tion of lime on the amide-like substances already noticed.. NITRIC ACID (NITRATES, NITROUS ACID, AND NITRITES) OF THE SOIL. Nitric acid is formed in the atmosphere by the action of ozone, and is brought down to the soil occasionally in the free state, but almost invariably in combination with ammonia, by rain and dew, as has been already described (p. 86). It is also produced in the soil itself by processes whose nature—considerably obscure and little understood —will be discussed presently. 952 HOW CROPS FEED. In the soil, nitric acid is always combined with an alkali or alkali-earth, and never exists in the free state in appreciable quantity. We speak of nitric acid instead of nitrates, because the former is the active ingredient com- mon to all the latter. Before considering its formation and nutritive relations to vegetation, we shall describe those of its compounds which may exist in the soil, viz., the nitrates of potash, soda, lime, magnesia, and iron. Nitrate of Potash (K NO,) is the substance com- mercially known as niter or saltpeter. When pure (refin- ed saltpeter), it occurs in colorless prismatic crystals. It is freely solub‘e in water, and has a peculiar sharp, cooling taste. Crude saltpeter contains common salt and other impurities. Nitrate of potash is largely procured for in- dustrial uses from certain districts of India (Bengal) and from various caves in tropical and temperate climates, by simply leaching the earth with water and evaporating the solution thus obtained. It is also made in artificial miter- beds or plantations in many European countries. It is likewise prepared artificially from nitrate of soda and caustic potash, or chloride of potassium. The chief use of the commercial salt is in the manufacture of gunpowder and fireworks. Sulphur, charcoal, (which are ingredients of gunpow- der), and other combustible matters, when heated in con- tact with a nitrate, burn with great intensity at the ex- pense of the oxygen which the nitrate contains in large proportion and readily parts with. Nitrate of Soda (Na NO.) occurs in immense quantities in the southern extremity of Peru, province of Tarapaca, as an incrustation or a compact stratum several feet thick, on the pampa of 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 ' THE NITRIC ACID OF THE SOIL. 253 yellow or reddish color. When pure, it is white or color- less. From the shape of the crystals it has been called cubic * niter; it is also known as Chili saltpeter, having been formerly exported from Chilian ports, and is some- times termed soda-saltpeter. In 1854, about 40,000 tons were shipped from the port of Iquique. Nitrate of soda is hygroscopic, and in damp air be- comes quite moist, or even deliquesces, and hence is not suited for making gunpowder. It is easily procured arti- ficially by dissolving carbonate of soda in nitric acid. This salt is largely employed as a fertilizer, and for pre- paring nitrate of potash and nitric acid. Nitrate of Lime (Ca2NO,) may be obtained as a white mass or as six-sided crystals by dissolving lime in nitric acid anil evaporating the solution. It absorbs water from the air and runs to a liquid. Its taste is bitter and sharp. Nitrate of lime exists in well-waters and accompanies nitrate of potash in artificial niter-beds. Nitrate of Magnesia (Mg2NO.,) closely resembles _ni- trate of lime in external characters and occurrence. It may be prepared by dissolving magnesia in nitric acid and evaporating the solution. Nitrates of Iron.—Various compounds of nitric acid and iron, both soluble and insoluble, are known. In the soil it is probable that only insoluble basic nitrates of sesquioxide can occur. Knop observed (V. S¢., 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 are, in fact, rhomboidal, ~ o's i paid) Mita "- 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- ficular. The nitrates are usually not fixed by the soil, but remain freely soluble in water, so that washing readily and completely removes them. The nitrates of ammonia and potash are decomposed in the soil, the alkali being retain- ed, while the nitric acil may be removed by washing with water, mostly in the form of nitrate of lime. Nitrate of soda is partially decomposed in the same manner, Free nitric acid unites with lime, or at least is found in the washings of the soil in combination with that base. As just remarked, Knop has observed that certain soils containing much organic matters and sesquioxide of iron, appeared to retain or decompose a small portion of nitric acil (put in contact with them in the form of nitrate of potash). Knop leaves it uncertain whether this result is simply the fault of the method of estimation, caused by the formation of basic nitrate of iron, which is insoluble in water, or, as is perhaps more probable, due to the de- composing (reducing) action of organic matters. Nitrification is the formation of nitrates. When vege- table and animal matters containing nitrogen decay in the soil, nitrates of these bases presently appear. In Bengal, during the dry season, when for several months rain sel- dom or never falls, an incrustation of saline matters, chiefly nitrate of potash, accumulates on the surface of those soils, which are most fertile, and which, though culti- vated in the wet season only, yield two and sometimes three crops of grain, ete., yearly. The formation of ni- trates, which probably takes place during the entire year, appears to goon most rapidly in the hottest weather. THE NITRIC ACID OF THE 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 rich soils, but do not accumulate to any extent, unless in caves or positions artificially sheltered from the rain. Boussingault’s examination of garden earth from Lieb- frauenberg (Agronomie, etc., T. II, p. 10) conveys an idea of the progress which nitrification may make in a soil un- der cultivation, and lighly charged with nitrogenous ma- nures. About 2.3 Ibs. of sifted and well-mixed soil were placed ina heap on aslab of stone under a glazed roof. From time to time, as was needful, the earth was moist- ened with water exempt from ammonia. The proportion of nitric acid was determined in a sample of it on the day the experiment began, and the analysis was repeated four times at various intervals. The subjoined statement gives the per cent of nitrates expressed as nitrate of potash in the dry soil, and also the quantity of this salt contained in an acre taken to the depth of one foot.* Ter cent. Ibs. per acre. 1857— 5th August, 0.01 34 “ —17th s 0.06 222 “« — 2d September, 0.18 654 * —17th us 0.22 760 ‘* — 2d October, 0.21 728 The formation of nitrates proceeded rapidly during the heat of summer, but ceased by the middle of September. Whether this cessation was due to the lower temperature or to the complete nitrification of all the matter existing in the soil capable of this change, or to decomposition of nitric acid by the reducing action of organic matters, * The figures given above are abbreviated from the originals, or reduced tc English denominations with a trifling loss of exactness. 256 HOW CROPS FEED. 2 further researches must decide. The quantities that ac- cumulated in this experiment are seen to be very consider- able, when we remember that experience has shown that 200 Ibs. per acre of the nitrates of potash or soda isa large dressing upon grain or grass. Had the earth been exposed to occasional rain, its analysis would have indi- cated a much less percentage of nitrates, because thie salt would have been washed down far into, and, perhaps, out of, the soil ut 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 during this time. When the rain ceased, the soil contained but 38 lbs. per acre. In September, rain fell 15 times, and to the amount of four inches. On the 10th of October, after a fortnight of hot, 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 Ibs. 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 than 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 St., V, 143). Nitrates are almost invariably found in all well and river waters, and in quantities larger than exist in rain. We may hence as- sume that nitrification is a process universal to all soils, and that nitrates are normal, though, for the reasons stat- ed, very variable ingredients of cultivated earth. The Sources of the Nitric Acid which is formed within the Soil,—Nitric acid is produced—a, from ammonia, THE NITRIC ACID OF THE SOIL. 257 either that absorbed by the so'l from the atmosphere, or that originating in the soil itself by the decay of nitrog- enous organic matters. Knop made an experiment with a sandy loam, as follows: The earth was exposed ina box to the vapor of ammonia for three days, was then mixed thoroughly, spread out thinly, moistened with pure water, and kept sheltered from rain 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, while 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 pace at the expense of the ammonia which the earth had absorbed. The conversion of ammonia into nitric acid is an oxidation expressed by the statement 2 NH xt #0 = NH NO, :+>H,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 ofiron. This compound (Fe, O,) readily yields a portion of its oxygen to bodies which are inclined to oxidize, be- ing itself reduced thereby to protoxide (FeO) thus :— Fe, O, = 2 FeO0 + 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 which 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 fabrics 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 but 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 a condition to be oxidized, a ie. § LZ . ™ 258 HOW CROPS FEED. ficient time this oxidation extends so fur as to leave the board Joose upon the nail, as may often be seen on old, unpainted wooden buildings. Direct experiments by Knop ( Versuchs St., II, 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 directly 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 Rendus, XLILX, 289) that a nitrogenous substance obtained by him from rotten dung and called fumie 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 humate of ammonia. THE NITRIC ACID OF THE SOIL. 259 face charged with sulphides (sulphur-springs). Water containing sulphates in solution often acquires an odor of sulphuretted hydrogen by being kept bott!ed, the cork or other organic matters deoxidizing the sulphates. The earth just below the paving-stones in Paris contains con- siderable quantities of sulphides of iron and calcium, the gypsum in the soil being reduced by organic matters. (Chevreul.) These sulphides, when exposed to air, speed- ily oxidize to sulphates, to suffer reduction again in con- tact with the appropriate substances, and under certain conditions, operate continuously, to gather and impart oxygen. One of the causes of the often remarkable and inexplicable effects of plaster of Paris when used as a fer- tilizer may, perhaps, be traced to this power of oxidation, resulting in the formation of nitrates. This point requires and is well worthy of special investigation. c. Lastly, the free nitrogen of the atmosphere appears to be in some way involved in the act of nitrification—is itself to a certain extent oxidized in the soil, as has been maintained by Saussure, Gaultier de Claubry, and others (Gmelin’s Hand-book of Chemistry, Ii, 388). The truth of this view is sustained by some of Bous- singault’s researches on the garden soil of Liebfrauenberg (Agronomie, etc., T., 1, 318). On the 29th of July, 1858, he spread out thinly 120 grammes of this soil in a shallow glass dish, and for three months moistened it daily with water exempt from compounds of nitrogen. At the end of this time analysis of the soil showed that while a small proportion of carbon (0.825°|,) had wasted by oxidation, the quantity of nitrogen had slightly increased. The gain of nitrogen was but 0.009 grm. = 0.008"| .. In five other experiments where plants grew for several months in small quantities of the same garden soil, either in the free air but sheltered from rain and dew, or ina confined space and watered with pure water, analyses 260 HOW CROPS FEED. were made of the soil and seed before the trial, and of the soil and crop afterwards. The analyses show that while in all cases the plants gained some nitrogen beyond what was originally contain- ed in the seed, there was in no instance any loss of nitro- gen by the soil, and in three cases the soil contained more of this element after than before the trial. Here follow the results. No. of Exp. Weight of Crop, Quantity of Soil. Gain of Nitrogen. the seed taken as 1. —————— by plant. by soil. 1. Lupin,* 3% 130 grms. 0.0042 grms. 0.0672 grms. 2. Lupin, 4 5B: | ae 0.0047: D:O05E = 5 3. Hemp, 5 sy 0.00389: ~ ** . -* 5. Lupin,* 3 130 * 0.0217 “ 0.0454 ‘ That the gain of nitrogen by the soil was not due to direct absorption of nitric acid or ammonia from the at- mosphere is demonstrated by the fact that it was largest in the two cases (Exps. 1 and 5) where the experiment was conducted ina closed vessel, containing throughout the whole time the same small volume, about 20 gallons, of air. 3 In Exp. 4, where the soil at the conclusion contained no more nitrogen than at the commencement of the trial, it is scarcely to be doubted that the considerable gain of ni- trogen experienced by the plant came through the soil, and would have been found in the latter had it borne no crop. The experiments show that the quantity of nitrogen assimilated from the atmosphere by a given soil is very variable, or may even amount to nothing (Exp. 3); but they give us no clue to the circumstances or conditions which quantitatively influence the result. 1t must be ob- served that this fixation of nitrogen took piace here in a soil very rich in organic matters, existing m the condition of humus, and capable of oxidation, so that the soil itself * Experiments made in confined air. a THE NITRIC ACID OF THE SOIL. 261 lost during three summer montlis eight-tenths of one per cent of carbon. In the numerous similar experiments made by Boussingault with soils destitute of organic mat- ter, no accumulation of nitrogen occurred beyond the merest traces coming from condensation of atmospheric ammonia. Certain experiments executed by Mulder more than 20 years ago (Chemistry of Animal and Vegetable Physi- ology, p. 673) confirm the view we have taken. Two of these were ‘‘made with beans which had germinated in an atmosphere void of ammonia, and grown, in one case, in ulmic acid prepared from sugar, and also free from am- monia; and, in the other case, in charcoal, both being moistened with distilled water free from ammonia, The ulmic acid and the charcoal were severally mixed up with 1 per cent of wood ashes, to supply the plants with ash- ingredients. I determined the proportion of nitrogen in three beans, and also in the plants that were produced by three other beans. The results are as follows :— Whéte beans in ulmic acid. Brown beans in charcod. Weight. Nitrogen. Weight. Nitrogen. Beans, 1.465 grm. 50 cub. cent. 1.27¢7 27 cub. cent. Plants, 4.167, * 160.2" *f gre ae wh The white beans, therefore, whilst growing into plants in substances and an atmosphere, both of which were fiee of ammonia, had obtained more than thrice the quantity of nitrogen that originally existed in the beans; in thie brown beans the original quantity was doubled.” Mulder believed this experiment to furnish evidence that ammonia is produced by the union of atmospheric nitrogen with hydrogen set free in the decay of organic matters. To this notion allusion has been already made, and the con- viction expressed that no proof can be adduced in its favor (p. 239). The results of the experiments are fully explained by assuming that nitrogen was oxidized in nitri- fication, and no other explanation yet proposed accords with existing facts. 262 HOW CROPS FEED. As to the mode in which the soil thus assimilates free nitrogen, several hypotheses. have been offered. One is that of Schénbein, to the effect that in the act of evapora- tion free nitrogen and water combine, with formation of nitrite of ammonia. In a former paragraph, p. 79, we have given the results of Zabelin, which appear to render this theory inadmissible. A second and adequate explanation is, that free nitrogen existing in the cavities of the soil is directly oxidized te nitric acid by ozone, which is generated in the action of ordinary oxygen on organic matters, (in the same way as happens when ordinary oxygen acts on phosphorus, ) or is, perhaps, the resu't of electrical disturbance. Experiments by Lawes, Gilbert, and Pugh (Ad. Trans., 1861, II, 495), show indeed that organic matters in certain conditions of decay do not yield nitric acid under the influence of ozone. They caused air highly impregnated with ozone to pass daily for six months through moist mixtures of burned soil with relatively large quantities of saw-dust, starch, and bean meal, with and without lime—in all 10 mixtures —hut in no case was any nitric acid produced. It would thus appesxr that ozone can form nitrates in the soil only when organic matters have passed into the comparatively stable condition of humus, That nitrogen is oxidized in the soil by ozone is highly probable, and in perfect analogy with what must happen in the atmosphere, and is denonstrated to occur in Schén- bein’s experiments with moistened phosphorus (p. 66, also Ann. der Chem. u. Pharm., 89, 287), as well as in Zabelin’s investigations that have been already recounted. (See pp. 75-83.) he fact, established by Reichardt and Blumtritt, that humus condenses atmospheric nitrogen in its pores (p. 167), doubtless aids the oxidation of this element. The third mode of accounting for the oxidation of THE NITRIC ACID OF THE SOIL. 263 free nitrogen is based upon the effects of a reducible body, like sesquioxide of iron or sulphate of lime, to which attention has been already directed. In a very carefully conducted experiment, Cloez * trans- mitted atmospheric air purified from suspended dust, and from nitric acid and ammonia, through a series of 10 large glass vessels filled with various porous materials. Vessel No. 1 contained fragments of unglazed porcelain; No. 2, calcined pumice-stone; No. 3, bits of well-washed brick. Each of these three vessels also contained 10 grms. of car- bonate of potash dissolved in water. The next three vessels, Nos. 4, 5, and 6, included the above-named porous materials in the same order; but instead of carbonate of potash, they were impregnated with carbonate of lime by soaking in water, holding this compound in suspension. The vessel No. 7 was occupied with Meudon chalk, washed and dried. No. 8 contained a clayey soil thoroughly washed with water and ignited so as to carbonize the organic matters without baking the clay. No. 9 held the same earth washed and dried, but not calcined. Lastly, in No. 10, was placed moist pumicé-stone mixed with pure car- bonate of lime and 10 grms. of urea, the nitrogenous princi- ple of urine. Through these vessels a slow stream of puri- fied air, amounting to 160,000 liters, was passed, night and day,for 8 months. At the conclusion of the experiment, vessel No. 1 contained a minute quantity of nitric acid, which, undoubtedly, came from the atmosphere, having escaped the purifying apparatus. The contents of Nos. 2,4, and 5, were free from nitrates. Nos. 8 and 6, con- taining fragments of washed brick, gave notable evidences of nitric acid. Traces were also found in the washed chalk, No. 7, and in the calcined soil, No. 8. In No. 9, filled with washed soil, niter was abundant. No. 10, * Recherches sur la Nitrification—Lecons de Chimie professées en 1861 ala Société Chimique de Paris, pp. 145-150. 264 HOW CROPS FEED. containing pumice, carbonate of lime, and urea, was desti- tute of nitrates. Experiments 2, 4, and 5, demonstrate that the concourse of nitrogen gas, a porous body, and an alkali-carbonate, is insufficient to produce nitrates. Experiment No. 10 shows that the highly nitrogenous substance, urea,* dif- fused throughout an extremely porous medium and expos- ed to the action of the air in moist contact with carbonate of lime, does not suffer nitrification. In the brick (ves- sels Nos. 3 and 6), something was obviously present, which determined the oxidation of free atmospheric ni- trogen. Cloez took the brick fresh from the kiln where it was burned, and assured himself that it included at the beginning of the experiment, no nitrogen in organic combination and no nitrates of any kind. Cloez believes the brick to have contained some oxidable mineral sub- stance, probably sulphide of iron. The Gentilly clay, used in making the brick, as well as some iron-cinder, added to it in the manufacture, furnished the elements of this compound. The slight nitrification that occurred in the vessels Nos. 7 and 8, containing washed chaik and burned soil, likewise points to the oxidizing action of some mineral matter. In vessel No. 9, the simply washed soil, which was thus freed from nitrates before the trial began, un- derwent a decided nitrification in remarkable contrast to the same soil calcined (No. 8). The influence of humus is thus brought out in a striking manner. It may be that apocrenic acid, which readily yields oxygen to oxidable matters, is an important agent in * Urea (COH4 N.) contains in 100 parts: Carbon, 20.00 Hydrogen, 6.67 Nitrogen, 46.67 Oxygen, 26.66 100.00 - THE NITRIC ACID OF THE SOIL. 265 nitrification. As we have seen, this acid, according to Mulder, passes into crenic acid by loss of oxygen, to be reproduced from the latter by absorption of free oxygen. The apocrenate of sesquioxide of iron, in which both acid and base are susceptible of this transfer of oxygen, should thus exert great oxidizing power. (See p. 228.) The Conditions Influencing Nitrification have been for the most part already mentioned incidentally. We may, however, advantageously recapitulate them. a. The formation of nitrates appears to require or to be facilitated by an elevated temperature, and goes on most rapidly in hot weather and in hot climates. b. According to Knop, ammonia that has been absorbed by a soil suffers no change so long as the soil is dry; but when the soil is moistened, nitrification quickly ensues. Water thus appears to be indispensable in this process. ce. An alkali base or carbonate appears to be essential for the nitric acid to combine with. It has been thought that the mere presence of potash, soda, and lime, favors nitrification, “ disposes,” as is said, nitrogen to unite with oxygen. JBoussingault found, however (Chimie Agri- cole, III, 198), that caustic lime developed ammonia from the organic matters of his garden soil without favoring nitrification as much as mere sand. The caustic lime by its chemical action, in fact, opposed nitrification; while pure sand, probably by dividing the particles of earth and thus perfecting their exposure to the air, facilitated this process. Boussingault’s experiments on this point were made by inclosing an earth of known composition (from his garden) with sand, etc., in a large glass vessel, and, after three to seven months, analyzing the mixtures, which were made suitably moist at the outset. Below are the results of five experiments. I. 1000 grms. of soil and 850 grms. sand acquired 0.012 grms. ammonia and 0.482 grms. nitric acid. iI. 1000 grms. of soil and 5500 grms. sand acquired 0.035 grms. ammonia and 0.545 grms. nitric acid. 12 266 HOW CROPS FEED. III. 1000 grms. of soil and 500 grms. marl acquired 0.002 grms. ammonia and 0.360 grms. nitric acid. . IV. 1000 grms. of soil and 2 grms. carbonate of potash acquired 0.015 grms. ammonia and 0.290 grms. nitric acid. V. 1000 grms. of soil and 200 grms. quicklime acquired 0.303 grms. ammonia and 0.099 grms. nitric acid. The unfavorable effect of caustic lime is well pronounce- ed and is confirmed by other similar experiments. Car- bonate of potash, which is strongly alkaline, but was used in sma!l quantity, and marl (carbonate of lime), which is but very feebly alkaline, are plainly inferior to sand in their influence on the development of nitric acid. The effect of lime or carbonate of potash in these ex- periments of Boussingault may, perhaps, be thus explain- ed. Many organic bodies which are comparatively stable of themselves, absorb oxygen with great avidity in pres- ence of, or rather when combined with, a caustic alkali. Crenic acid is of this kind; also gallic acid (derived from nut-galls), and especially pyrogallic acid (a result of the dry distillation of gallic acid). The last-named body, when dissolved in potash, almost instantly removes the oxygen from a limited volume of air, and is hence used for analysis of the atmosphere.* We reason, then, that certain organic matters in the soil of Bonsdcuees garden, became ¢o altered by treat- ment with lime or carbonate of potash as to be susceptible of a rapid oxidation, in a manner analogous to what hap- pens with pyrogallicacid. Dr. I. Angus Smith has shown (Jour. Roy. Ag. Soc., XVII, 456) that if a soil rich in or- ganic matter be ade alkaline, moist, and warm, putre- factive decomposition may shorily set in, This 1s what happens in every we!l-managed compost of lime and peat. By this rapid alteration of organic matters, as we shall see (p. 268), not only is nitric acid not formed, but nitrates added are reduced toammonia. It is not improbable that * Not all organic bodies, by any means, are thus affected. Lime hinders the alteration of urine, flesh, and the albuminoids. 4 THE NITRIC ACID OF THE SOIL. 267 smaller doses of lime or alkali than those employed by Boussingault would have been found promotive of nitri- fication, especially after the lapse of time sufficient to allow the first rapid decomposition to subside, for then we should expect that its presence would favor slow oxida- tion, This view is in accordance with the idea, universally received, that lime, or alkali of some sort, is an indispensa- ble ingredient of artificial niter-beds. The point is one upon which further investigations are needed. d. Free oxygen, i. e., atmospheric air, and the porosity of so:l which ensures its contact with the particles of the latter, are indispensable to nitrification, which is in ali cases a process of oxidation. When sesquioxide of iron oxidizes organic matters, its action would cease as soon as its reduction to protoxide is complete, hut for the atmos- pheric oxygen, which at once combines with the protoxide, constantly reproducing the sesquioxide. In the saltpeter plantations it is a matter of experience that light, porous soils yield the largest product. The operations of tillage, which promote access of air to the deeper portions of earth and counteract the tendency of many soils to “cake” to 4 comparatively impervious mass, must also favor the formation of nitrates. Many authors, especially Mulder, insist upon the physic- al influence of porosity in determining nitrification by condensed oxygen. The probability that porosity may assist this process where compounds of nitrogen are con- cerned, is indeed great; but there is no evidence that any porous body can determine the union of free nitrogen and oxygen. Knop found that of all the proximate ingredi- ents of the soil, clay alone can be shown to be capable of physically condensing gaseous ammonia (humus combines with it chemically, and if it previously effects physical condensation, the fact cannot be demonstrated). The observations by Reichardt and Blumtritt on the condensing effect of the soil for the gases of the atmos- 268 HOW CROPS FEED. phere (p. 167) indicate absorption both of oxygen and nitrogen, as well as of carbonic acid. The fact that char- coal acts as an energetic oxidizer of organic matters has been alluded to (p. 169). This action is something very remarkable, although charcoal condenses oxygen but to a slight extent. The soil exercises a similar but less vigorous oxidizing effect, as the author is convinced from experi- ments made under his direction (by J. J. Matthias, Esq.), and as is to be inferred from tle well-known fact tuat the odor of putrefying flesh, etc., cannot pass a certain thickness of soil. But charcoal is unable to accomplish the union of oxygen and nitrogen at common temperatures, or at 212° F., either dry, moistened with pure water, or with solution of caustic soda. (Experiments in Sheffield labo- ratory, by Dr. L. H. Wood.) Putrefying flesh, covered with charcoal as in Stenhouse’s experiment (p. 169) gives off ammonia, but no nitric acid is formed. Dumas has indeed stated ( Comptes Rend., X XII) that ammonia mixed with air is conyeried into nitric acid by a porous body—chalk—that has been drenched with caustic potash and is heated to 212° I’. But this is an error, as Dr. Wood has demonstrated. It is true that platinum at a high temperature causes ammonia and oxy- gen to unite. Even a platinum wire when heated to red- ness exerts this effect in a striking manner (Kraut, Ann. Ch. u. Ph., 136, 69); but spongy platinum is without ef- fect on a mixture of air and ammonia gas at 212° or lower temperatures. (Wood.) e. Presence of organic matters prone to oxidation. Ke- duction of nitrates to ammonia, etc., in the soil—As we have seen, the organic matters (humus) of the soil are a source of nitric acid. Dut it appears that this is not al- ways or universally true. In compact soils, at a certain depth, organic matters (their hydrogen and carbon) may oxidize at the expense of nitric acid itself, converting the latter into ammonia. Pelouze (Comptes Rendus, XLIV, THE NITRIC ACID OF THE SOIL. 269 118) has proved that putrefying animal substances, as al. bumin, thus reduce nitric acid with formation of ammonia. For this reason, he adds, the liquor of dung heaps and putrid urine contains little or no nitrates. Boussingault (Agronomie, II, 17) examined a remarkably rich alluvial soil from the junction of the Amazon with the Rio Cupari, made up of alternate layers of sand and partially decayed leaves, containing 40°|, of the latter. This natural leaf- compost contained no trace of nitrates, but an exception- ally high quantity of ammonia, viz., .05°|.. Kuhlmann (Ann. de Chim. et de Phys., 3 Ser., XX) was the first to draw attention to the probability that ni- tric acid may thus be deoxidized in the lower strata of the soil, and his arguments, drawn from facts observed in the laboratory, appear to apply in cases where there exist much organic matters and imperfect access of air. In a soil so porous as is demanded for the culture of most crops these conditions cannot usually occur, as Grouven has taken the trouble to demonstrate (Zeitschrift fir _ Deutsche Landwirthe, 1855, p. 341). In rice swamps and peat bogs, as well as in wet compost heaps, this reduction must proceed to a considerable extent. In some, if not all cases, the addition of much lime or other alkaline substance to a soil rich in organic matters sets up rapid putrefactive decomposition, whereby nitrates are at once reduced to ammonia (p. 266). In one and the same soil the conditions may exist at different times that favor nitrification on the one hand, and reduction of nitrates to ammonia’on the other. A surplus of moisture might so exclude air from a porous soil as to cause reduction to take place, to be succeeded by rapid nitrification as the soil becomes more dry. It is possible that nitrates may undergo further chemi- cal alteration in the presence of excess of organic matters. That nitrites may often exist in the soil is evident from what has been written with regard to the mutual convert- 270 HOW CROPS FEED. ibility of nitrates and nitrites (p. 73). According to Goppelsrider (Dingler’s Polytech. Jour., 164, 388), certain soils rich in humus possess in a high degree the power to reduce nitrates to nitrites. It is not unlikely that further reduction may occur—that, in fact, the deoxidation may be complete and free nitrogen be disengaged. This isa question eminently worthy of study. Loss of Nitrates may occur when the soil is saturated with water, so that the latter actually flows through and away from it, as happens during heavy rains, the nitrates (those of sesquioxide of iron, perhaps, excepted) being freely soluble and not retained by the soil. Boussingault made 40 analyses of lake and river water, 25 of spring water, and 35 of well water, and found nitric acid in ey- ery case, though the quantity varied greatly, being largest in cities and fertile regions. Thus the water of the upper Rhine contains one millionth, that of the Seine, in Paris, six millionths, and that of the Nile four millionths of ni- tric acid. The Rhine daily removes from the country supplying its waters an amount of nitric acid equivalent to 220 tons of saltpeter. The Seine carries daily into the Atlantic 270 tons, and the Nile pours 1,100 tons into the Mediterranean every twenty-four hours. In the wells of crowded cities the proportion of nitrates is much higher. In the older parts of Paris the well wa- ters contain as much as one part of niter (or its equiva- lent of other nitrates) in 500 of water. The soil may experience a loss of nitrates by the com- plete reduction of nitric acid to gaseous nitrogen, or by the formation of inert compounds with humus, as will be noticed in the next section. Loss of assimilable nitrogen by the washing of nitrates from the soil may be hindered to some extent In compact soils by the fact just noticed that nitric acid is liable to be converted into ammonia, which is at once rendered com- paratively insoluble, pif if THE NITRIc AvID OF THE SOIL. 271 Nitric Acid as Food to Plants.—Experiments demon- strating that nitric acid is capable of perfectly supplying Sih vegetation with SS Pee nitrogen were = f a first made by aa UNG Boussingaul t ! oe (Agronomie, Mt _ Chimie Agri- cole, etc., 1, 210). _ We give an ac- count of some of these. Two seeds of adwarfSunflow- er (L7elianthus argophyllus), were planted in each of three pots, the soil of which, consist- ing of a mixture of brick - dust and sand, as well as the pots them- selves, had been thoroughly freed from all ni- trogenous com- pounds by igni- tion and wash- ing with distill- Fig. 9. ed water. To the soil of the pot A, fig. 9, nothing was added save the two seeds, and distilled water, with which all the plants were watered from time to time. With the soil of pot C, were incorporated small quantities of phosphate of lime, yy AY NAN NG WN NEW S \ r IA WS Waiting WANE \\\ VN \ ANY Ri Qn \\) A) 272 HOW CROPS FEED. of ashes of clover, and bicarbonate of potash, in order that the plants growing in it might have an abundant supply of all the ash-ingredients they needed, Finally, the soil of pot D received the same mineral matters as pot C, and, in addition, a small quantity (1.4 gram) of nitrate of pot- ash. The seeds were sown on the 5th of July, and on the 30th of September, the plants had the relative size and appearance seen in the figure, where they are represented in one-eighth of the natural dimensions. For the sake of comparison, the size of one of the largest leaves of the same kind of Sunflower that grew in the garden is represented at D, in one-eighth of its natural dimensions. Nothing can be more striking than the influence of the nitrate on the growth of this plant, as exhibited in this experiment. The plants A and C are mere dwarfs, al- though both carry small and imperfectly developed flow- ers. The plant D, on the contrary, is scarcely smaller than the same kind of plant growing under the best con- ditions of garden culture. Here follows a Table of the results obtained by the examination of the plants. i) a ' - ad Ss 2 ? SS =X R§ Acquired by the ‘ri | os S (plants in 86 days Ss SSN ° = 8 ss Sx of vegetation. ae be Ss s = S ES aS (cm. ee) SOR Sore os Nitro- ESS} RS OB \Carbon.| gen. cubic rm. cent. orm, grm. A—nothing added to the soil......... | 38.6 | 0.285 2.45 | 0.114 | 0.0023 C—ashes, phosphate of lime, and bi- carbonate of potash, added to the} / Set Sas eR Fen ees ie in | 4.6 | 0.391] 38.42 | 0.156 | 0.0027 D—ashes, phosphate of lime, and ni- | | | trate of potash, added to the soil..| 198.3 | 21.111 | 182.00 | 8.444 | 0.1666 We gather from the above data: 1. That without some compound of nitrogen in the soil vegetation cannot attain any considerable development, notwithstanding all requisite ash-ingredients are present ~ oe ‘ THE NITRIC ACID OF THE SOIL. 273 in abundance. Observe that in exps. A and C the crop attained but 4 to 5 times greater weight than the seed, and gathered from the atmosphere during 86 days but 24 milligrams of nitrogen. The crop, supplied with nitrate of potash, weighed 200 times as much as the seed, and assimilated 66 t:mes as much nitrogen as was acquired by A and C from external sources. 2. That nitric acid of itself may furnish ad/ the nitrogen requisite to a normal vegetation. In another series of experiments (Agronomie, etc., I, pp. 227-233) Boussingault prepared four pots, each containing 145 grams (about 5 oz. avoirdupois) of calcined sand with a little phosphate of lime and ashes of stable-dung, and planted in each two Sunflower seeds. To three of the pots he added weighed quantities of nitrate of soda— to No. 3 twice as much as to No. 2, and to No. 4 three times as much as to No. 38; No.1 received no nitrate. The seeds germinated duly, and the plants, sheltered from rain and dew, but fully exposed to air, and watered with water exempt from ammonia, grew for 50 days. In the subjoined Table is a summary of the results. ea er ed eee $3 |S8s [SS3s_ Sg S ara = = 2g ,j@a. s 2). 2 bee = San a © | 8Sss |$es~ > ae a : a wdso SSN SSS S z Se, > a S+ SRxe |e wele~=s Ss = Ss LE SS SS & Sos RD Ba a Ss 83 8 SS | SSe | S88 lSS eee = S xs | S82 [S888 rs SES S| os zs S& S | 288 | SES |SESs Sakae | grms. grms. grms.,. grms. | grms. corms. anme grms. — a —_——_—— — —_—— 1..! 0.0033 | 0.0000 | 0.0033 | 0.0053 | 0.0020+ | 0.397 1 1 2..| 0.0033 | 0.0033 | 0.0066 | 0.0063 | 0.0002 | 0.720 1.8 2 3..' 0.0033 | 0.0066 | 0.0099 | 0.0097 | 0.0002t | 1.130 2.8 3 4..| 0.0038 | 0.0264 | 0.0297 | 0.0251 0.0046¢ | 3.280 8.5 9 * N=Nitrogen. In the first Exp. a trifling quantity of nitrogen was gathered (as ammonia?) from the air. In the others, and especially in the last, nitrate of soda remained in the soil, 12* 274 HOW CROPS FEED. not having been absorbed entirely by the plants. Observe, however, what a remarkable coincidence exists between the ratios of supply of nitrogen in form of a nitrate and those of growth of the several crops, as exhibited in the last two columns of the Table. Nothing could demon- strate more strikingly the nutritive function of nitric acid than these admirable investigations. Of the multitude of experiments on vegetable nutrition which have been recently made by the process of water- culture (ZZ. C. G., p. 167), nearly all have depended upon nitric acid as the exclusive source of nitrogen, and it has proved in all cases not only adequate to this purpose, but far more certain in its effects than ammonia or any other nitrogenous compound. § 6. NITROGENOUS ORGANIC MATTERS OF THE SOIL. AVAILABLE NITROGEN.—QUANTITY OF NITROGEN REQUIRED FOR CROPS. In the minerals and rocks of the earth’s surface nitrogen is a very small, scarcely appreciable ingredient. So far as we now know, ammonia-salts and nitrates (nitrites) are the only mineral compounds of nitrogen found in soils. When, however, organic matters are altered to humus, and become a part of the soil, its content of nitrogen ac- quires significance. In peat, which is humus compara- tively free from earthy matters, the proportion of nitrogen is ofien very considerable. In 32 specimens of peat ex- amined by the author (Peat and its Uses us Fertilizer and Fuel, p. 90), the nitrogen, ealeulated cn the organic mat- ters, ranged from 1.12 to 4.81 per cent, the average being 2.6 per cent. The average amount of nitrogen in the air- dry and in some cases high'y impure peat, was 1.4 per cent. This nitrogen belongs to the organic matters in % NITROGENOUS ORGANIC MATTERS OF THE SOIL. 278 great part, but a small proportion of it being in the form of ammonia-salts or nitrates. Tn 1846, Krocker, in Liebig’s laboratory, first estimated the nitrogen in a number of soils and marls (Ann. Ch. u. Ph., 58, 887). 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 0.085 per cent. Numerous examinations have since been made by An- derson, Liebig, Ritthausen, Wolff, and others, with simi- lar results. In all but his latest writings, Liebig has regarded this 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, 0.261 per cent. Ammonia, OD: 002 ii: 2» Nitric acid, 0.00034 “ “ The subjoined Table includes the results of Boussin- gault’s examinations of a number of soils from France and South America, in which are given the quantities of am- monia, of nitric acid, expressed as nitrate of potash, and of nitrogen in organic combination. These quantities are stated both in per cent of the air-dry soil, and in lbs. ay. 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. (Agronomie, T II, pp. 14-21.) 276 HOW CROPS FEED. AmmoniA, NITRATIS, 2ND OnGANnic NITROGEN OF VARtIous Sorzs. 2- ; Nitrate 9 Nitrogen in \:x Ammonia. peers |ong. combi'n.| = Soils Mee, wth : pare . Ibs. Ibs. Ibs |g $§ per | per per |per|| per | per |§S2 | cent. jacre|} cent |acrel| cent. | acre |R5$ o { Liebfrauenberg, light gard. soil |0.0022| 100||0.0175*| 875)| 0.259) 12970) 1:9.3 = J Bischwiller, light garden soil... |0.0020) 100) /0.1526 |7630)| 0.205) 14755) 1:9.7 @ | Bechelbronn, wheat field clay. |0.0009| 45) 0.0015 %5\| 0.138 6985) 1:3.2 f | Argentan, rich pasture......... \(0.0060) 300 0.0046 | 280)! 0.513) 25650) 1:8 a {Rio Madeira, sugar field, clay|0.0090) 450/'0.0004 | 20)| 0.148) 7140) 1:6.3 £ | Rio Trombetto,forest heavy do. |0.0030) 183) |0.0001 5)| 0.119) 5955) 1:4.9 ® | Rio Negro, prairie v. fine sand. |0.003S) 190) /0.0001 5|| 0.0C8} 3140) 1:5.6 = J Santarem, cocoa plantation... |0.00S83) 415 (0.0011 5d)|| 0.649} 32450) 1:11 < | Saracca, near Amazon, loam.. |0.0042} 210,| none | 0.152} 9100) 1:8.2 oad Rio Cupari, rich leaf mould... . 0.0525 2875 | iH | 0.685} 34250) 1:18.8 = | Iles du Salut, French Guiana... 0.0980} 409 0.0643 |3215)| 0.543) 27170) 1:11.7 7a | Martinique, gucar ficld....< <<: 10.0055| 275 10.0186 930!| 0.112] 5590! 1:8 * The same soil whose partial analysis has just been given, but examined for | nitrates at another time. It is seen that in all cases the nitrogen in the forms of ammonia + and nitrates { is much less than that in organic conibination, and in most cases, as in the Liebfrauenberg garden, the disparity is very great. Nature of the Nitrogenous Organic Matters, Amides. —Hitherto we have followed Mulder in assuming that the humic, ulmic, ecrenic, 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 + Ammonia contains 82.4 per cent of nitrogen. } Nitrate of potash contains 13.8 per cent of nitrogen, “NITROGENOUS ORGANIC MATTERS OF THE SOIL. 277 suppose that it is generated by the action of the alkali, In fact, there are a large number of bodies which manifest a similar deportment. Many substances which are pro- duced from ammonia-compounds by heat and otherwise, and called amides, to which allusion has been already made, p. 276, are of this kind. Oxalate of ammonia, when heated to decomposition, yields oxamide, which contains the elements of the oxalate minus the elements of two molecules of water, viz., Oxalate of ammonia. Oxamide. Water. tt) a) = BN. AO OW 2 2 EO On boiling oxamide with solution of potash, ammonia is reproduced by the taking up of two molecules of water, and passes off as a gas, while oxalate of potash remains in the liquid. Nearly every organic acid known has one or several amides, bearing to it a relation similar to that thus sub- sisting between oxalic acid and oxamide. | Asparagine, a crystallizable body found in asparagus and many other plants, already mentioned as an amide, is thought to be an amide of malic acid. Urea, the principal solid ingredient of human urine, is an amide of carbonic acid. Uric acid, hippuric acid, gua- nine, found also in urine; kreatin and kreatinine, occurring in the juice of flesh; thein, the active principle of tea and coffee; and theobromin, that of chocolate, are all regard- ed as amides. Amide-like boaies are gelatine (glue), the organic sub- stance of the tendons and of bones, that of skin, hair, wool, and horn. The albuminoids themselves are amide- like, in so far that they yield ammonia on heating with solutions of caustic alkalies, Albuminoids a Source of the Nitrogen of Humus.— The organic nitrogen of humus may come from the albu- minoids of the vegetation that has decayed upon or in the Paar cet Ser og 278 HOW CROPS FEED. soil. In their alteration by decay, a portion of nitrogen assumes the gaseous form, but a portion remains in an in- soluble and comparatively unalterable condition, though in what particular compounds we are unable to say. The loss of carbon and hydrogen from decaying organic mat- ters, it is believed, usually proceeds more rapidly than the waste of nitrogen, so that in humus, which is the residue of the change, the relative proportion of nitrogen to car- bon is greater than in the original vegetation. Reversion of Nitric Acid and Ammonia to inert Forms, —It is probable that the nitrogen of ammonia, and of ni- trates, which are reducible to ammonia under certain con- ditions, may pass into organic combination in the soil. Knop ( Versuchs St., IIT, 228) found that when peat or soils containing humus were kept for several months in contact with ammonia in closed vessels, at the usual tem. perature of summer, the ammonia, according to its quan- tity, completely or in part disappeared. There having been no such amount of oxygen present a8 would be necessary to convert it into nitric acid, the only explanation is that the ammonia combined with some organic substance in the humus, forming an amide-like body, not decomposable by the hypochlorite of soda used in Knop’s azometrical anal. ysis. Facts supporting the above view by analogy are not wanting. When gelatine (a body of animal origin closely related to the albuminoids, but containing 18 instead of 15°|, of nitrogen) is boiled with dilute acids for some time, it yields, among other products, sugar, as Gerhardt has demonstrated. Prof. T. Sterry Hunt was the first to suggest (Am. Jour. Sci. & Arts, 1848, Vol. 5, p. 76) that gelatine has nearly the composition of an amide of dextrin or other body of the cellulose group, and might be regard- ed as derived chemically from dextrin (or starch) by the union of the latter with ammonia, water being eliminated, VIZ. < NITROGENOUS ORGANIC MATTERS OF THE Son. 279 Carbohydrate. Ammonia. Water. Gelatine. Hs O- --2NG.'='8 £0 + 2(C; EB: Ni: O;). Afterwards Dusart, Schiitzenberger, and P. Thenard, in- dependently of each other, obtained hy exposing dextrin, starch, and glucose, to a somewhat elevated temperature (800-360°F.), in contact with ammonia-water, substances containing from 11 to 19°|, of nitrogen, some soluble in water and having properties not unlike those of gelatine, others insoluble. It was observed, also, that analogous compounds, containing less nitrogen, were formed at lower temperatures, as at 212° F. Payen had previously observed that cane sugar underwent entire alteration by prolonged action of ammonia at common temperatures. “These facts scarcely leave room to doubt that ammonia, as carbonate, by prolonged contact with the humic acids or with cellulose, and bodies of like composition, may form combinations with them, from which, by the action of alkalies or lime, ammonia may be regenerated. It has already been mentioned that when soils are boil- ed with solutions of potash, they yield ammonia continu- ously for a long time. Boussingault observed, as has been previously remarked, that lime, when incorporated with the soil at the ordinary temperature, causes its content of ammonia to increase, Soil from the Liebfrauenberg garden, mixed with ‘|, its weight of lime and nearly } its weight of water, was placed in a confined atmosphere for 8 months. On open- ing the vessel, a distinct odor of ammonia was perceptible, and the earth, which originally contained per kilogram, 11 milligrams of this substance, yielded by analysis 303 mgr. (See p. 265, for other similar results.) Alteration of Albumineids in the Seil,—Albuminoids are carried into the soil when fresh vegetable matter is in- corporated with it. They are so susceptible to alteration, however, that under ordinary conditions they must speed- 280 HOW CROPS FEED. ily decompose, and cannot therefore themselves be consid- ered as ingredieuts of the soil. Among. the proximate products of their decomposition are organic acids (butyric, valeric, propionic) destitute of nitrogen, and the amides leucin (C, H,, NO,) and tyrosin (C, H,, NO,). These latter bodies, by further decompo- sition, yield ammonia. As has been remarked, it is proba- ble that the albuminoids, when associated as they are in decay with cellulose and other carbohydrates, may at once give rise to insoluble amide-like bodies, such as those whose existence in humus is evident from the consider- ations already advanced. Can these Organic Bodies Yield Nitrogen Directly to Plants 3—Those nitrogenous organic compounds that exist in the soil associated with humus, which possess something of the nature of amides, though unknown to us in a pure state, appear to be nearly or entirely incapable of feeding vegetation directly. Our information on this point is de- rived from the researches of Boussingault, whose papers on this subject (De la Terre végétale considérée dans ses effets sur la Veéegétation) are to be found in his Agronemie, etc., Vols. I and IL. Boussingault experimented with the extremely fertile soil of his garden, which was rich in all the elements needful to support vegetation, as was demonstrated by the results of actual garden culture. This soil was especially rich in nitrogen, containing of this element 0.26°|,, which, were it in the form of ammonia, would be equivalent to more than 7 tons per acre taken to the depth of 13 inches; or, if existing as nitric acid, would correspond to more than 43 tons of saltpeter to the acre taken to the depth just mentioned. This soil, however, when employed in quantities of 40 to 130 grams (1} to 44 oz. av.) and shielded from rain and dew, was scarcely more capable of carrying lupins, beans, maize, or hemp, to any considerable development, AVAILABLE NITROGEN OF THE SOIL. 281 than the most barren sand. In eight distinct trials the crops weighed (dry) but 3 to 5 times, in one case 8 times (average 4 times), as much as the seed; while in sand, pumice, or burned soil, containing no nitrogen, Boussin- gault several times realized a crop weighing 6 times as much as the seed, though the average crop of 38 experi- ments was but 3 times, and the lowest result 14 times the weight of the seed. The fact that the nitrogen of this garden soil was for the most part inert is secktnaly shown on a comparison of the crops yielded by it to those obtained in barren soil with aid of known quantities of nitrates. In a series of experiments with the Sunflower, Boussin- gault (Agronomie, etc., I, p. 233) obtained in a soil desti- tute of nitrogen a crop weighing (dry) 4.6 times as much as the seeds, the latter furnishing the plants 0.0033 grm. of nitrogen. In a second pot, with same weight of seeds, in iaek the nitrogen was doubled by adding. 0.0035 grm. in form of nitrate of soda, the weight of crop was eles doubled—was 7.6 times that of seeds. In a third pot the nitrogen was trebled by adding 0.0066 grm. in form of ni- trate, and the crop was nearly trebled also—was 11.3 times the weiglt of the seeds, In another experiment (p. 271) the addition of 0.194 grm. of nitrogen as nitrate of potash to barren sand with needful mineral matters, gave a crop weighing 198 times as much as the seeds. But in the garden soil, which con- tained, when 40 germs. were employed 0.104 grm., and when 130 grms. were used 0.338 grm. of nitrogen, the result of growth was often not greater than in a soil that contained no nitrogen, and only in a single instance surpassed that of a soil to which was added but 0.0033 grm. The fact is thus demonstrated that but a very small proportion of the nitrogen of this soil was assimilable to vegetation. I’rom these beautiful investigations Boussingault deems it highly probable that in this garden soil, and in soils 282 HOW CROPS FEED. generally which have not been recently manured, ammonia and nitric acid are the exclusive feeders of vegetation with nitrogen. Such a view is not indeed absolutely demon- strated, but the experiments alluded to render it in the highest degree probable, and justify us in designating the organic nitrogen for the most part as inert, so far as vege- table nutrition is concerned, until altered to nitrates or ammoni.-salts by chemical. change. To comprehend the favorable results of garden-culture in such a soil, it must be considered what a large quantity of earth is at the disposal of the crop, viz., as Boussingault ascertained, 57 lbs. for each hill of dwarf beans, 190 lbs. for each hill of potatoes, 470 lbs. for each tobacco plant, and 2,900 lbs. for every three hop-plants. The quantity and condition of the nitrogen of Boussin- gault’s garden so:l are stated in the subjoined scheme. Available § Ammonia_ 0.00220 per cent = Nitrogen 0.00181 per cent {0.0019 per ct. nitrogen | Nitric acid 0.000384 ‘* “ = 0.00009 ‘+ ** Inert nitrogen—of organic compounds...........-..20-ceeceee seen ee 0.2581 > Fr Total nitrogen...... fase hs cio 2% eee - o, eter ereee 0.2610 per ct. Calculation shows that in garden culture the plants above named would have at their disposal in this soil quan- tities of inert and available nitrogen as follows: Weight of soil. Inert nitrogen. Available nitrogen. Bean (dwarf) hill 57 Ibs. 75 grams.* 1 gram. Potato, és 190 ‘‘ 242 te 3 grams. Tobacco, single plant, 470 ** 555 fs eos Hop, three plants, 2900 ‘* 34388 % 4 «= * {gram — 15 grains avoirdupois nearly. 17 grams 1 oz. re 4 983 sh 1 lb es bh Indirect Feeding of Crops by the Organic Nitrogen of the Soil.—tIn what has been said of the oxidation of the organic matters of the soil, (whereby it is probable that their nitrogen is partially converted into nitric acid,) and of the effect of alkalies and lime upon them, (whereby ammonia is generated,) is given a clue to the understand- AVAILABLE NITROGEN OF THE SOIL. 283 ing of their indirect nutritive influence upon vegetation. By these chemical transformations the organic nitrogen may pass into the two compounds which, in the present state of knowledge, we must regard as practically the ex- clusive feeders of the plant with nitrogen. The rapidity and completeness of the transformation depend upon circumstances or conditions which we understand but im- perfectly, and which are extremely important subjects for further investigation. Difficulty of estimating the Available Nitrogen of any Soil.—The value of a soil as to its power of supplying plants with nitrogen isa problem by no means easy to solve. The calculations that have just been made from the analytical data of Boussingault regarding the soil of his garden are necessarily based on the assumption that no alteration in the condition of the nitrogen could take place during the period of growth. In reality, however, there is no constancy either in the absolute quantity of nitrogen in the soil or in its state of availability. Por- tions of nitrogen, both from the air and from fertilizers, may continually enter the soil and assume temporarily the form of insoluble and inert organic combinations. Other portions, again, at the same time and as continually, may escape from this condition and be washed out or gathered by vegetation in the form of soluble nitrates, as has al- ready been set forth. It is then manifestly impossible to learn more from analysis, than how much nitrogen is avail- able to vegetation at the moment the sample is examined. To estimate with accuracy what is assimilable during the whole season of growth is simply out of the question. The nearest approach that can be made to this result is to ascertain how much a crop can gather from a limited vol- ume of the soil. Bretschneider’s Experiments.— W e may introduce here a notice of some recent researches made by Bretschneider in Silesia, a brief account of which has appeared since the 284 HOW CROPS FEED. foregoing pines writtens (Juhresbericht i. Ag. Chem., 1865, 29.) 3retschneider’s experiments were made for the purpose of estimating how much ammonia, nitric acid, and nitro- gen, exist or are formed in the soil, either fallow or occu- pied with various crops during the period of growth. For this purpose he measured off in the field four plots of ground, cach one square rod (Prussian) in area, and sepa- rated from the others by paths a yard wide. The soil of one plot was dug out to the depth of 12 inches, sifted, and after a board frame 12 inches deep had been fitted to the sides of the excavation, the sifted earth was filled in again. This and another—not sifted—plot were planted to sugar bects, another was sown to vetches, and the fourth to oats. At the end of April, six accurate and concordant anal- yses were made of the soil. Afterwards, at five different periods, a cubic foot of soil was taken from each plot, and from the spaces between that bore no vegetation, for de- termining the amounts of nitric acid, ammonia, and total nitrogen. The results of this analytical work are given in the following Tables, being calculated in pounds for the area of an acre, and to the depth of 12 inches (English measures”) : TABLE I. AMOUNT OF AMMONIA. Beet plot, pret plot. Vetch plot. Oatplot. Vacant plot. sifted sod. End of April, 59 59 59 59 59 12th June, 15 48 41 32 28 30th June, 12 41 24 40 32 22d July, 9 29 39 22 29 13th August, 8 15 16 11 43 0 16 16 7 23 9th September, * It is plain that when the results of analyses made on a small amount of soil are calculated upon the 3,500,000 lbs. of soil (more or less) contained in an acre to the depth of one foot (see p. 158), the errors of the analyses, which cannot be absolutely exact, are enormously multiplied. What allowance ought to be made in this case we cannot say, but should suppose that 5 per cent would not be too much, On this basis differences of 200-300 lbs, in Table TV should be overlooked. “ ~ sah ee AVAILABLE NITROGEN OF THE SOIL. 285 TABLE II. AMOUNT OF NITRIC ACID. Beet plot, poet plot. Vetch plot. Oat plot. Vacant plot. sifted soi. End of April, 56 56 56 56 56 12th June, 281 270 102 28 106 30th June, 328 442 15 93 318 22d July, 116 89 58 0 43 18th August, 53 6 71 14 81 Qth September. 0 0 12 0 0 - TABLE IU. TOTAY ASSIMILABLE NITROGEN (OF AMMONIA AND NITRIC ACID). . clad a Beet plot. Vetch plot. Oat plot. Vacant plot. End of April, 63 63 63 63 63 12th June, 84 109 | 60 33 50 30th June, 95 148 23 57 108 22d Juty, 37 Aq 31 18 35 18th Angust, 21 14 31 13 56 9th September, 0 13 16 6 19 TABLE IV. TOTAL NITROGEN OF THE SOIL, cited edi, Beet plot. Vetch plot. Oat plot. Vacant plot, End of April, 4652 4652 4652 4652 4652 12th June, 4861 5209 5606 6140 4720 30th June, 4667 5744 5688 5514 4482 22d July, 5398 5485 4724 4924 13th August. 5467 6316 6316 6266 4412 9th September, 5164 4656 6522 5004 4294 From the first Table we gather that the quantity of ammonia, which was considerable in the spring, dimin- ished, especially in a porous (sifted) soil until September. In the compact earth of the uncultivated path, its diminu- tion was less rapid and less complete. The amount of nitric acid (nitrates), on the other hand, increased, though not alike in any two cases. It attained its maximum in the hot weather of June, and thence fell off until, at the close of the experiments, it was completely wanting save in a single instance. The figures in the second Table do not represent the absolute quantities of nitric acid that existed in the soil . 286 HOW CROPS FEED, throughout the period of experiment, but only those amounts that remained at the time of taking the samples. What the vegetation took up from the planted plots, what was washed out of the surface soil by rains, or otherwise removed by chemical change, does not come into the reckoning. Those plots, the surface soil of which was most occupied by active roots, would naturally lose the most nitrates by the agency of vegetation; hence, not unlikely, the vetch and oat plots contained so little in June. The results up- on the beet, and vacant ground plots demonstrate that in- that month a rapid formation of nitrates took place. It is not, perhaps, impossible that nitrification also proceeded vigorously in the loose soils in July and August, but was not revealed by the analysis, either because the vegetation took it up or heavy rains washed it out from the surface soil. In the brief account of these experiments at hand, no information is furnished on these points. Since mois¢- ure is essential to nitrification, it is possible that a period of dry weather coming on shortly before the soil was analyzed in July, August, and September, had an influence on the results. It is certainly remarkable that with the ex- ception of the vetch plot, the soil was destitute of nitrates on the 9th of September. This plot, at that time, was thickly covered with fallen leaves. : We observe further that the nature of the crops influ- enced the accumulation of nitrates, whether simply be- cause of the different amount of absorbent rootlets pro- duced by them and unequally developed at the given period, or for other reasons, we cannot decide.* From the third Table may be gathered some idea of the total quantity of nitrogen that was present in the soil in_ * It is remarka)le that the large-leaved beet plant had a great surplus of ni- trates, while the oat plot was comparatively deficient in them. Has this fact any connection with what has been stated (p. 84) regarding the unequal power of plants to provide themselves with nitrogenous food ? AVAILABLE NITROGEN OF THE SOIL. 287 a form available to crops. Assuming that ammonia and nitric acid chiefly, if not exclusively, supply vegetation with nitrogen, it is seen that the greatest quantity of available nitrogen ascertained to be present at any time in the soil was 148 Ibs. per acre, taken to the depth cf one foot. This, as regards nitrogen, corresponds to the follow- ing dressings :— lbs. per acre. Saltpeter (nitrate of potash) ka 1068 Chili saltpeter (nitrate of soda) : 898 Sulphate of ammonia - Sy trek Re 909 Peruvian guano (14 per cent of nitrogen) 1057 The experience of British farmers, among whom ali the substances above mentioned have been employed, being that 2 to 3 ewt. of any one of them make a large, and 5 ewt. avery large, application per acre, It is plain that in the surface soil of Bretschneider’s trials there was Jormed during the growing season a large manuring of nitrates in addition to what ras actually consumed by the crops. The assimilable nitrogen increased in the beet plots up to the 30th of June, thence rapidly diminished zs it did in the soil of the paths. In the oat and vetch plots the soil contained, at none of the times of analysis, so much assimilable nitrogen as at the beginning of the experi- _ ments. In September, all the plots were much poorer in available nitrogen than in the spring. Table IV confirms what Boussingault has taught as to the vast stores of nitrogen which may exist in the soil. The amount here is more than two tons per acre. We ob- serve further that in none of the cultivated plots d:d this amount at any time fall below this figure; on the other hand, in most cases it was considerably increased during the period of experiment. In the uncultivated plot, perhaps, the total nitrogen fell off somewhat. This difference may have been due to the root fibrils that, in spite of the ut 288 HOW CROPS FEED. most care, unavoidably remain in a soil from which grow- ing vegetation is removed. The regular and great increase of total nitrogen in the vetch plot was certainly due in part to the abundance of leaves that fell from the plants, and covered the surface of the soil. But this ni- trogen, as well as that of the standing crops, must have come from the atmosphere, since the soil exhibited no diminution in its content of this element. We have here confirmation of the view that ammonia, as naturally supplied, is of very trifling importance to vegetation, and that, consequently, nitrates are the chief natural means of providing nitrogen for crops. The fact that atmospheric nitrogen becomes a part of the soil and enters speedily into organic and inert combinations, also appears to be sustained by these researches. Quantity of Nitrogen needful for Maximum Grain Crops.—Hellriegel has made experiments on the effects of various quantities of nitrogen (in the form of nitrates) on the yield of cereals. The plants grew in an artificial soil consisting of pure quartz sand, with an admixture of ash-ingredients in such proportions as trial had demon- strated to be appropriate. All the conditions of the ex- periments were made as nearly alike as possible, except as regards the amount of nitrogen, which, in a series of eight trials, ranged from nothing to 84 parts per 1,000,000 of soil. The subjoined Table contains his results. EFFECTS OF VARIOUS PROPORTIONS OF ASSIMILABLE NITROGEN IN THE SOIL. Nitrogen in| Yield of Grain, in lbs. 1,000,000 lbs. of soil. Wheat. Rye. | Oats. Found | Calculated | Found | Calculated | Found | Calculated 0 0.002 —— 0.218 — 0.380 — Increase Increase Increase q 0.553 0.926 0.832 0.966 0.929 1.168 14 1.708 1.851 1.944 1.9838 2.605 2.336 21 2.767 MAT Grieg 2.669 2.899 8.845 8.503 28 3.763 3.708 4.172 3.866 6.211 4.671 42 6.065 5.554 5.162 , 5.798 7.039 7.007 56 7.198 7.406 7.163 %.732 9.052 9.342 84 9.257 9.257 8.698 8.698 9.342 « 9.342 DECAY OF NITROGENOUS BODIES. 289 From numerous other experiments, not published at this writing, Hellriegel believes himself justified in assum- ing that the highest yield thus observed, with 84 lbs. of nitrogen in 1,000,000 of soil, might have been got with 70 lbs. of nitrogen in case of wheat, with 63 Ibs. in case of rye, and with 56 lbs. in case of oats. On this assump- tion he has calculated the yield of each of these crops, and the figures obtained (see Table) present on the whole a remarkable coincidence with those directly observed. § 7, DECAY OF NITROGENOUS BODIES. We have incidentally noticed some of the products of the decay of nitrogenous bodies, viz., those which remain in the soil. We may now, with advantage, review the subject connectedly, and make our account of this as more complete. It will be needful in the first place to give some ex- planations concerning the nature of the familiar trans- formations to which animal and vegetable matters are subject. By the word decay,as popularly employed, is under- stood a series of chemical changes which are very differ- ent in their manifestations and results, according to the circumstances under which they take place or the kinds of matter they attack. Under one set of conditions we have slow decay, or, as Liebig has fitly designated it, eren ausis ;* under others fermentation; and under still others putrefaction. Eremecausis* is a slow oxidation, and requires the constant presence of an excess of free oxygen. It pro- ceeds upon vegetable matters which are comparatively *¥From the Greek, signifying slow combustion. 13 290 HOW CROPS FEED, difficult of alteration, such as stems and leaves, consist- ing chiefly of cellulose, with but little albuminoids, and both in insoluble forms. What is said in a former paragraph on the “ Decay of Vegetation,” p. 137, applies in general to eremecausis. Fermentation is a term commonly applied to any seemingly spontaneous change taking place with vegeta, ble or animal matters, wherein their sensible qualities suffer alteration, and heat becomes perceptible, or gas 1s rapidly evolved. Chemically speaking, fermentation is the breaking up of an organic body by chemical decom. position, which may go on in absence of oxygen, and is excited by a substance or an organism called a ferment. There are a variety of fermentations, viz., the vinous, acetic, lactic, ete. In vinous fermentation, the yeast-fungus, Torvula cerevisie, vegetates in an impure solution of sugar, and causes the latter to break up into alcohol and carbonic acid with small quantities of other products. In the acetic fermentation, the vinegar-plant, Mzycoderma vini, is believed to facilitate the conversion of alcohol into acetic acid, but this change is also accomplished by platinum sponge, which acts as a ferment. In the lactic fermentation, a fungus, Lenicilium glaueum, is thought to de- termine the conversion of sugar into lactic acid, as in the souring of milk. The transformation of starch into sugar has been termed the saccha- rous fermentation, diastase being the ferment. Putrefaction, or putrid fermentation, is a rapid internal change which proceeds in comparative absence of oxygen. It most readily attacks animal matters which are rich in albuminoids and other nitrogenous and sulphurized prin- ciples, as flesh, blood, and urine, or the highly nitrogenous parts of plants, as seeds, when they are fully saturated with water. Putrefying matters commonly disengage stinking gases. According to Pasteur putrefaction is oc- casioned by the growth of animalcules ( Vibrios). Fermentation is usually and putrefaction is always a reducing (deoxidizing) process, for either the ferment it- self or the decomposing substances, or some of the prod- ucts of decomposition, are highly prone to oxidation, and om DECAY OF NITROGENOUS BODIES, 291 in absence of free oxygen may remove this element from reducible bodies (Traube, Fermentwirkungen, pp. 63-78). In a mixture of cellulose, sugar, and albuminoids, ere- mecausis, fermentation, and putrefaction, may all proceed simultaneously. When the albuminoids decay in the soil associated with carbohydrates and humus, the final results of their altera- tion may be summed up as follows: 1. Carbon unites mainly with oxygen, forming carbonic acid gas, which escapes into the atmosphere. With im- perfect supplies of oxygen, as when submerged in water, carbonic oxide (CO) and marsh gas (CH,) are formed. A portion of carbon remains as humus. 2. Hydrogen, for the most part, combines with oxygen, yielding water. In deficiency of oxygen, some hydrogen escapes as a carbon compound (marsh-gas), or in the free state. If humus remains, liydrogen is one of its con- stituents. 3. a. Nitrogen always unites to a large extent with hydrogen, giving ammonia, which escapes as gaseous car- bonate in considerable quantity, unless from presence of carbohydrates much humus is formed, in which case it may be nearly or entirely retained by the latter. Lawes, Gilbert, and Pugh, (Phil. Trans. 1861, II., p. 501) made observations on the decay of wheat, barley, and bean seeds, either entire or in form of meal, mixed with a large quantity of soil or powdered pumice, and exposed in vart- ous conditions of moisture to a current of air for six months. They found in nine experiments that from 11 to 58°|, of the nitrogen was converted into ammonia, al- though but a trifling proportion of this (on the average but 0.4°|,) escaped in the gaseous form. b. In presence of excess of oxygen, a portion of mtro- gen usually escapes in the free state. Reiset proved the escape of free nitrogen from fermenting dung. DBoussin 292 HOW CROPS FEED. gault, in his investigations on the assimilability of free nitrogen, found in various vegetation-experiments, in which crushed seeds were used as fertilizers, that nitrogen was lost by assuming some gaseous form. This loss prob- ably took place to some slight extent as ammonia, but chiefly as free nitrogen. Lawes, Gilbert, and Pugh, found in thirteen out of fifteen trials, including the experiments just referred to, that a loss of free nitrogen took place, ranging from 2 to 40 per cent of the total quantity con- tained originally in the vegetable matters submitted to decomposition. In six experiments the loss was 12 to 13 per cent. In the two cases where no loss of nitrogen oc- curred, nothing in the circumstances of decay was discoy- erable to which such exceptional results could be at- tributed. Other experiments (PAil. Trans. 1861, IL, p. 509) demonstrated that in absence of oxygen no nitrogen was evolved in the free state. c. Nitric acid is not formed from the nitrogen of or- ganic bodies in rapid or putrefactive decay, but only in slow oxidation or eremecausis of humuified matters. Pelouze found no nitrates in the liquor of dung heaps. Lawes, Gilbert, and Pugh, (/oc. cit.).found no nitric acid when the seed-grains decayed in ordinary air, nor was it produced when ozonized air was passed over moist bean- meal, either alone or mixed with burned soil or with slaked lime, the experiments lasting several months. It thus appears that the carbon and hydrogen of organic matters have such an affinity for oxygen as to prevent the ~ nitrogen from acquiring it in the quicker stages of decay. More than this, as Pelouze has shown (Comptes Rendus, XLIV., p. 118), putrefying matters rob nitric acid of its oxygen and convert it into ammonia. We have already remarked that putrefaction and fermentation are reducing processes, and until they have run their course and the organic matters have passed into the comparatively stable forms of humus, their nitrogen appears to be incapable of ae » 4 THE NITROGENOUS PRINCIPLES OF URINE. 293 oxidation. So soon as compounds of carbon and hydrogen are formed, which unite but slowly with free oxygen, so that the latter easily maintains itself in excess, then and not before, the nitrogen begins to combine with oxygen. 4, Finally, the sulphur of the albuminoids may be at first partially dissipated as sulphuretted hydrogen gas, while in the slower stages of decay, it 1s oxidized to sul. phuric acid, which remains as sulphates in the soil. § 8. > On 2 ‘ THE NITROGENOUS PRINCIPLES OF URINE. The question “ How Crops Feed ” is not fully answered as regards the element Nitrogen, without a consideration of certain substances—ingredients of urine—which may become incorporated with the soil in the use of animal manures. Professor Way, in his investigation on the “ Power of Soils to Absorb Manure,” describes the following remark- able experiment: “ Three quantities of fresh urine, of 2,000 grains each, were measured out into similar glasses. With one portion its own weight of sand was mixed ; with another, its own weight of white clay ; the third being left without admixture of any kind. When smelt immediately after mixture, the sand appeared to have had no effect, whilst the clay mixture had entirely lost the smellof urine. The three glasses were covered light- ly with paper and put in a warm place, being examined from time to time. In a few hours it was found that the urine containing sand had become slightly putrid; then followed the natural urine; but the quantity with which clay had been mixed did not become putrid at all, and at the end of seven or eight weeks it had only the pecu- liar smell of fresh urine, without the slightest putridity. The surface of the clay, however, became afterwards coy- Ts we ma a 294 HOW CROPS FEED. ered with a luxuriant growth of confervee, which did not happen in the other glasses.” (Jour. Roy. Ag. Soe. of Eing., X1., 366.) Professor Way likewise found that filtering urine through clay or simply shaking the two together, allow- ing the liquid to clear itself, and pouring it off, sufficed to prevent putrefaction, and keep the urine as if fresh for a month or more, Cloez found, as stated on p. 264, that in a mixture of moistened pumice-stone, carbonate of lime, and urea (the nitrogenous principle of urine), no nitrates were formed during eight months’ expesure to a slow current of air. These facts make it necessary to consider in what state the nitrogen of urine is absorbed and assimilated by vegetation. Urine contains a number of compounds rich in nitro- - gen, being derived from the waste ot the food and tissues of a numa: which require a brief notice. Urea (CO N,H,)* may be obtais.ed from the urine of man as a white crystalline mass or in distinct transparent rhombic crystals, which remain indefinitely unaltered in dry air, and have a cooling, bitterish taste like saltpeter. It is a weak base, and chemists have bat si its nitrate, oxalate, phuephate ete. Urea constitutes 2 to 3 per cent of healthy human urine, and a ies and robust man excretes of it about 40 grams, or 1"|, oz. ay. daily. When urine is left to itself, it shortly emits a putrid odor; after a few days or hours the urea it contained en- tirely disappears, and the liquid smells powerfully of am- monia. Urea, when in contact with the animal matters # CArDONG... se tetee e 20.00 Hydrogen......... 6.67 NUP OROR . o< ocns 7 hs 46.67 Oxygen: 23%. 5.5 ee 26.66 100.00 THE NITROGENOUS PRINCIPLES OF URINE. 295 of urine, suffers decomposition, and its elements, combin- ing with the elements of water, are completely transformed into carbonate of ammonia. Urea. Water. Carbonate of Ammonia. CO NH, + 2H,O = 2(NH,), H,O,CO,,. As we have learned from Way’s experiments, clay is able to remove from urine the “‘ ferment” which occasions its putrefaction. Urea is abundant in the urine of all carnivorous and herbivorous mammals, and exists in small quantity in the urine of carnivorous birds, but has not been detected in that of herbivorous birds. Uric acid (C,H,N,O,)* is always present in healthy human urine, but in very minute quantity. It is the chief solid ingredient of the urine of birds and reptiles. Here it exists mainly as urate of ammonia.** The urine of birds and serpents is expelled from the intestine as a white, thickish liquid, which dries to a chalk-like mass. From this, uric acid may be obtained in the form of a white powder, which, when magnified, is seen to consist of mi- nute crystals. By powerful oxidizing agents uric acid is converted into oxalate and carbonate of ammonia, and urea. Peruvian guano, when of good quality, contains some 10 per cent of urate of ammonia. Hippuric acid (C,H,NO,)t is commonly abundant in the urine of the ox, horse, and other herbivorous animals. By boiling down fresh urine of the pastured or hay-fed cow to ‘|, its bulk, and adding hydrochloric acid, hippuric acid crystallizes out on cooling in four-sided prisms, of- ten two or three inches in length. * Carbon... .......d0.12 SF .Carboi. 5... 2...d840. .. 7 Catbott.....i0%d2e% 60.74 Hydrogen........ 2.38 Hydrogen...... 3.78 Hydrogen......... 4.96 Nitrogen...... ...33.33 Nitraren-seo kiss 7.84 *Nitrogen ......... 7.82 SPRV CU: bs on 5c wan 28.57 GEV OCR os 50210: 25.95 Gaver. oi ae 26.48 296 HOW CROPS FEED. Glycocoll or Glycine* is a sweet substance that re- sults from the decomposition of hippuric acid under the influence of various agents. It is also a product of the action of acids on gelatine and horn. Guanine (C,H,N.O)+ occurs to the extent of about "|, per cent in Peruvian guano, and is an ingredient of the liver and pancreas of animals, whence it passes into the excrement in case of birds and spiders. By oxidation it yields among other products urea and oxalic acid. Kreatin (C,H,N,O,) { is an organic base existing in very minute quantity in the flesh of animals, and occa- sionally found in urine. Cameron was the first, in 1857, to investigate the assimi- lability of urinary products by vegetation. His experi- ments (Chemistry of Agriculture, pp. 189-144) were made with barley, which was sown in an artificial soil, destitute of nitrogen. Of four pots one remained without a supply of nitrogen, another was manured with sulphate of ammonia, and two received a solution of urea. The pot without nitrogen gave plants 8 inches high, but these developed no seeds. The pot with sulphate of ammonia gave plants 22 inches high, and 300 seeds. Those with urea gave respectively stalks of 26 and 29 inches height, and 252 and 270 seeds. The soil in neither case contained ammonia, the usual decomposition-product of urea. Dr. Cameron justly concluded that urea enters plants un- changed, is assimilated by them, and equals ammonia-salts as a means of supplying nitrogen to vegetation. The next studies in this direction were made by the au- thor in 1861 (Am. Jour, Science, XLI., 27). Experiments were conducted with uric acid, hippuric acid, and guanine. © OCarpon.cestoce. eee B0.io. St Carbon’ 29 (ates 32.00. . { Carbone. see . .86.64 Hydrogen.......... Sol = Hydraren.’.....5.5 6.6% Hydrogen .:o. cic 6.87 Nitrogen. c.5 eset 46.36 Nitrogen.......... 18.67 Nitrogen! 4 2) yin 32.06 OXYGED. wes. vce ess 10.60 Oxygen........ .» 42.66 Onypen tote 24.43 100.00 100.00 100.00 THE NITROGENOUS PRINCIPLES OF URINE. 297 Washed and ignited flower-pots were employed, to con- tain, for each trial, a soil consisting of 700 grms. of ignited and washed granitic sand, mixed with 0.25 orm. sulphate of lime, 2 grms. ashes of hay, prepared in a muffle, and 2.75 grms. bone-ashes. This soil was placed upon 100 grms. of clean gravel to serve as drainage. | In each of four pots containing the above soil was des posited, July 6th, a weighed kernel of maize. The pots were watered with equal quantities of distilled water con- taining a scarcely appreciable trace of ammonia. The seeds germinated in a healthy manner, the plants devel- oped slowly and alike until July 28th, when the addition of nitrogenous matters was begun. To No. 1, no solid addition was made. To No. 2 was added, July 28th, 0.420 erm. uric acid. To No. 3 was added 1.790 grm. hippuric acid, at four different times, viz: July 28, 0.358 orm., Aug. 26th, 0.358 grm., Sept. 16th, 0.716 grm., Oct. 3d, 0.358 grmm. To No. 4 was added 0.4110 grm. hydrochlorate of gua- nine, viz: July 28th, 0.0822 grm., Aug. 26th, 0.0822 grm., Sept. 16th, 0.1644 grm., Oct. 3d, 0.0822 grm. The nitrogenous additions contained in each case, 0.140 grm. of nitrogen, and were strewn, as fine powder, over the surface of the soil. The plants continued to grow or to remain healthy (the lower leaves withering more or less) until they were re- moved from the soil, Nov. 8th. The plants exhibited striking differences in their devel- opment. No. | (noadded nitrogen) produced in all seven slender leaves, and attained a height of 7 inches. At tlie close of the experiment, only the two newest leaves were perfectly fresh ; the next was withered and dead through- out one-third of its length. The newer portions of this plant grew chiefly at the expense of the older parts. No sign rat organs appeared, Uae yee 298 HOW CROPS FEED. No. 2, fed with uric acid, was the best developed plant of the series. At the conclusion of the experiment, it bore ten vigorous leaves, six of which were fresh, and two but partly withered. It was 14 inches high, and carried two rudimentary ears (pistillate flowers), from the upper one of which hung tassels 6 inches long. No. 3, supplied with hippuric acid, bore eight leaves, four of which were withered, and two rudimentary ears, one of which tasseled. Height, 12 inches. No. 4, with hydrochlorate of guanine, had six leaves, one withered, and two ears, one of which was tasseled. Height, 12 inches. The weight of the crops (dried at 212° F.), exclusive of the fine rootlets that could not be removed from the soil, was ascertained, with the subjomed results. 1 2 3 4 Without Hippuric Nitrogen. Uric Acid. Acid. Guanine. Weight of dried crop, 0.1925 grm. 1.9470 grm. 1.0149 grm. 0.9820 grm. " “ seed, 0.1644 “ 1725 ‘* | OUR AS) | aGpe es gain, 0.0201 “* L.7145 “"“OSaat >= | eee We thus have proof that all the substances employed contributed nitrogen to the growing plant. This is con- clusively shown by the fact that the development of pis- tillate organs, which are especially rich in “nitrogen, occurred in the three plants fed with nitrogenous com- pounds, but was totally wanting in the other. The rela- tion of matter, new-organized by growth, to that derived from the seed, is strikingly seen from a comparison of the ratios of the weight of the seed to the increase of organs ized matter, the former being taken as unity. The ratio is approximatively for No. 1, 1° ee var ae 1 1 ST gee 1 age.” 1; 48 THE NITROGENOUS PRINCIPLES OF URINE. 299 The relative gain by growth, that o* No. 1 assumed as unity, is for No.1, — 1 ee 2. cea CS et Bh > Om a AS 3 OB The crops were small, principally because the supply ofunitrogen was very limited. These experiments demonstrate that the substances asded, in every case, aided growth by supplying nitro- gen. They do not, indeed, prove that the organic fertil- izers entered as such into the crop without decomposition, but if urea escapes decomposition in a soil, as Cameron and Cloez have shown is true, it is not to be anticipated that the bodies employed in these trials should suffer al- teration to ammonia-salts or nitrates. Hampe afterwards experimented with urea and uric acid by the method of Water-Culture ( Vs. S¢.,; VII., 308 ; VITI., 225; TX., 49; and X.,175). He succeeded in pro- ducing, by help of urea, maize plants as large as those growing in garden soil, and fully confirmed Cameron’s conclusion regarding the assimilability of this substance. Tampe demonstrated that urea entered as such into the plant. In fact, he separated it, in the pure state, from the stems and leaves of the maize which had been pro- duced with its aid. Hampe’s experiments with uric acid in solution showed that this body supplied nitrogen without first assuming the form of ammonia-salts, but it suffered partially if not entirely a decomposition, the nature of which was not determined. Uric acid itself could not be found in the crop. Hampe’s results with hippuric acid were to the effect that this substance furnishes nitrogen without reversion to ammonia, but is resolved into other bodies, probably ~ benzoic acid and glycocoll, which are formed when hip- 300 HOW CROPS FEED. puric acid is subjected to the action of strong acids or ferments. Hampe, therefore, experimented with .glycocoll, and from his trials formed the opinion that this body is di- rectly nutritive. In fact, he obtained with it a crop equal to that yielded by ammonia-salts. Knop, who made, in 1857, an unsuccessful experiment with hippuric acid, found, in 1866, that glycocoll is as- similated (Chem. Centralblatt, 1866, p. 774). In 1868, Wagner experimented anew with hippuric acid and glycocoll. His results confirm those of Hampe. Wagner, however, deems it probable that hippuric acid enters the plant as such, and is decomposed within it into benzoic acid and glycocoll ( Vs. S¢., XI., p. 294). Wagner found, also, that kreatin is assimilated by vegetation. The grand result of these researches is, that the nitrog- enous (amide-like) acids and bases which are thrown off in the urinary excretions of animals need not revert, by decay or putrefaction, to inorganic bodies (ammonia or nitric acid), in order to nourish vegetation, but are either immediately, or after undergoing a slight and easy altera: tion, taken up and assimilated by growing plants. As a practical result, these facts show that it is not necessary that urine should be fermented before using it as a fertilizer. § 9, COMPARATIVE NUTRITIVE VALUE OF AMMONIA-SALTS AND NITRATES. The evidence that both ammonia and nitric acid are ca- pable of supplying nitrogen to plants has been set forth. It has been shown further that nitric acid alone can per- fectly satisfy the wants of vegetation as regards the ele- ment nitrogen. In respect to ammonia, the case has not VALUE OF AMMONIA AND NITRIC ACID. 301 been similarly made out. We have learned that ammonia -occurs, naturally, in too small proportion, either .in the atmosphere or the soil, to supply much nitrogen to crops. In exceptional cases, however, as in the leaf-mold of Rio Cupari, examined by Boussingault, p. 276, as well as in lands manured with fermenting dung, or with sulphate or muriate of ammonia, this substance acquires importance from its quantity. On the assumption that it is the nitrogen of these sub- stances, and not their hydrogen or oxygen, which is of value to the plant, we should anticipate that 17 parts of ammonia would equal 54 parts of nitric acid in nutritive effect, since each of these quantities represents the same amount (14 parts) of nitrogen. The ease with which ammonia and nitric acid are mutually transformed favors this view, but the facts of experience in the actual feed- ing of vegetation do not, as yet, admit of its acceptance. In earlier vegetation-experiments, wherein the nitro- genous part of an artificial soil (without humus or clay) consisted of ammonia-salts, it was found that these were decidedly inferior to nitrates in their producing power. This was observed by Ville in trials made with wheat planted in calcined sand, to which was added a given quantity of nitrogen in the several forms of nitrate of potash, sal-ammoniac (chloride of ammonium), nitrate of ammonia, and phosphate of ammonia. Ville’s results are detailed in the following table. The quantity of nitrogen added was 0.110 grm. in each case. Nitrogen Straw and Average jin average Source of Nitrogen. Roots. |Grain.}| crop. crop. ES eS ee ow et = a Nitrate of Potash.............0. {an 70:98 7:30 | «-26-71| 0.921 / oO Sal-ammoniac..........0.. 2.0006 Vit 7'34| Sea} ---28-88| 0.142 9 90' 2 Oo Nitrate of ammonia............. 1 BS pate 5 86 .. 18.32] 0.133 9 aR] 2 4 Phosphate of ammonia.......... 1 as 15891 pies ..18.40} 0.1388 302 HOW CROPS FEED. It is seen that the ammonia-salts gave about one-fourth less crop than the nitrate of potash. The potash doubt- less contributed somewhat to this difference. The author began some experiments on this point in 1861, which turned out unsatisfactorily on account of the want of light in the apartment. In a number of these, buckwheat, sown in a weathered feldspathic sand, was ma- nured with equal quantities of nitrogen, potash, lime, phosphorie acid, sulphuric acid, and chlorine, the nitrogen being presented in one instance in form of nitrate of potash, in the others as an ammonia-salt—sulphate, muriate, phos- phate, or oxalate. Although the plants failed to mature, from the cause above mentioned, the experiments plainly indicated the inferiority of ammonia as compared with nitric acid, Explanations of this fact are not difficult to suggest. The most reasonable one is, perhaps, to be found in the circumstance that clayey matters (which existed in the soil under consideration) “‘ fix ” ammonia, 7. é., convert it into a comparatively insoluble compound, so that the plant may not be able to appropriate it all. On the other hand, Hellriegel (Ann. d. Landw., VIL., 53, u. VIIL, 119) got a better yield of clover in artificial soil with sulphate of ammonia and phosphate of ammonia than with nitrate of ammonia or nitrate of soda, the quan- tity of nitrogen being in all cases the same. As Sachs and Knop developed the method of Water- Culture, it was found by the latter that ammonia-sadts did not effectively replace nitrates. The same conclusion was arrived at by Stohmann, in 1861 and 1863 (Henneberg’s Journ., 1862, 1, and 1864, 65), and by Rautenberg and Kiihn, in 1863 (Henneberg’s Journ., 1864, 107), who ex- perimented with sal-ammoniac, as well as by Birner and Lucanus, in 1864 (Vs. S¢., VIII., 152), who employed sulphate and phosphate of ammonia. The cause of failure lay doubtless in the fact, first noticed VALUE OF AMMONIA AND NITRIC ACID. 3038 by Kiihn, that so soon as ammonia was taken up by the plant, the acid with which it was combined, becoming free, acted as a poison. In 1866, Hampe (Vs. Sé., [X., 165), using phosphate of ammonia as the single source of nitrogen, and taking care to keep the solution but faintly acid, obtained a maize-plant which had a dry weight of 18 grams, includ- ing 36 perfect seeds; no nitrates were formed in the solution. The same summer Kiihn (Vs. S¢., [X., 167) produced two small maize-plants, one with phosphate, the other with sulphate of ammonia as the source of nitrogen, but his experiments were interrupted by excessive heat in the glass-house. In 1866, Beyer ( Vs. S¢., [X., 480) also made trials on the growth of the oat-plant in a solution containing bi- carbonate of ammonia. The plants vegetated, though poorly, and several blossomed and even produced a few seeds. Quite at the close of the experiments the plants suddenly began to grow, with formation of new shoots. Examination of the liquid showed that the ammonia had been almost completely converted into nitric acid, and the increased growth was obviously connected with this nitrifi- cation. In 1867, Hampe ( Vs. S¢., X., 176) made new experi- ments with ammonia-salts, and obtained one maize-plant 2’|, ft. high, bearing 40 handsome seeds, and weighing, dry, 25'|, grams. In these trials the seedlings, at the time of unfolding the sixth or seventh leaf, after consum- ing the nutriment of the seeds, manifested remarkable symptoms of disturbed nutrition, growth being sup- pressed, and the foliage becoming yellow. After a week or two the plants recovered their green color, began to grow again, and preserved a healthy appearance until mature. Experiment demonstrated that this diseased state was not affected by the concentration of the nour- 304 HOW CROPS FEED. ishing solution, by the amount of free acid or of iron present, nor by the illumination. Hampe observed that from these trials it seemed that the plants, while young, were unable to assimilate ammonia or did so with diffi- culty, but acquired the power with a certain age. In 1868, Wagner (Vs. S¢., XI, 288) obtained exactly the same results as Hampe. 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. S¢., 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 Hampe, 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 impossible 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 growing in a solution or in pure quartz sand is in abnormal circumstances, in so far 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 before this point can be definitely settled. It is, however, a matter CONSTITUTION OF THE SOIL. 305 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. SI, GENERAL VIEW OF THE CONSTITUTION OF THE SOIL AS RELATED TO VEGETABLE NUTRITION. Inert, Active, and Reserve Matters,—In all cases the soil consists in great part of matters that are of no direct or present use in feeding the plant. The chemical nature of this inert portion may vary greatly without correspond- ingly influencing the fertility of the soil. Sand, either quartzose, calcareous, micaceous, feldspathic, hornblendic, or augitic; clay in its many varieties; chalk, ocher (oxide of iron), humus; in short, any porous or granular material that is insoluble and little alterable by weather, may con- stitute the mass of the soil. The physical and mechanical characters of the soil are chiefly influenced by those ingre- dients which preponderate in quantity. Hence Ville has quite appropriately designated them the “mechanical agents of the soil.” They affect fertility principally as they relate the plant to moisture and to temperature. They also have an influence on crops by gradually assum- ing more active forms, and yielding nourishment as the resuat of chemical changes. In general, it is probable i Ss em 306 HOW 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 Ibs. 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 weight 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 Ibs. of the purest quartz sand, and sow the usual amount of seed upon it, maintain~ ing it in the proper state of moisture, etc., we could not produce a crop; we could not even recover the seed. Such a soil would be sterile in the most emphatic sense. But should we incorporate with such a soil a few thousand Ibs. of the mineral ingredients of agricultural plants, to- gether with some nitrates in the appropriate combinations and proportions, we should bestow fertility upon it by this addition and be able to realize a crop. Should we add to our acre of pure quartz the ashes of a hay crop, 400 Ibs., and a proper quantity of nitrate of potash, we might also realize a good crop, could we but ensure contact of the roots of the plants with all the added matters. But in this case the soil would be fertile for one crop only, and after the removal of the latter it would be as sterile as CONSTITUTION OF THE SOIL, 307 before. 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 previous chapter we have traced the formation of the soil from rocks by the conjoint agencies of mechanical and chemical disintegration. It is the perpetual operation of these agencies, especially those of the chemical kind, which serves to maintain fertility. The fragments 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 thet occur within it. We cannot, therefore, dissect the soil and decide what and how much is immediately available, and what is not. Furthermore, the soil is chem- ically so complex, and its relations to the plant are so com- plicated by 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. Nevertheless, what we have attained of knowledge and insight in this direction is full of value and encouragement. Deportment of the Soil towards Solvents,x—When we 308 HOW CROPS FEED. put a soil in contact with water, certain matters are dis- solved in this liquid. It has been thought that the sub- stances taken up by water at any moment are those which at that time represent the available plant-food. This no- tion was based upon the supposition that the plant cannot feed itself at the roots save by matters in solution. Since Liebig has brought into prominence the doctrine that roots are able to attack and dissolve the insoluble ingredients of the soil, this idea is generally regarded as no longer tenable. Again, it has been taught that the reserve plant-food of the soil is represented by the matters which acids (hydro- chloric or nitric acid) are capable of bringing into solu- tion. This is true ina certain rough sense only. The action of hydrochloric or nitric acid is indeed analogous to that of carbonic acid, which is the natural solvent; but between the two there are great differences, independent of those of degrec. 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 Selubility.—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 statc- ment is plain; it is simply that salt is readily recognized to be soluble and that glass is not ordinarily perceived to dissolve. The statement that glass is insoluble is, however, only true when the ordinary standards of solubility are re- ferred to, The glass bottle which may contain water for ee IZ 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 finest dust, and thus extend the sur- face of glass many thousand or million times; weigh the glass-powder accurately, then agitate it for a few minutes with water, remove the liquid, dry and weigh the glass again. We shall thus find that the glass has lost several per cent of its original weight (Pelouze), and by evapo- rating the water, it will leave a solid residue equal in weight to the loss experienced by the glass. § 2. AQUEOUS SOLUTION OF THE SOIL. The soil and the rocks from which it is formed would commonly be spoken of as insoluble in water. They are, however, soluble to a slight extent, or rather, we should say, they contain soluble matters. The quantity that water dissolves from a soil depends upon the amount of the liquid and the duration of its contact; it is therefore necessary, in order to estimate properly any statements respecting the solubility of the soil, to know the method and conditions of the experi- ment upon which such statements are based. We subjoin the results of various investigations that exhibit the general nature and amount of matters soluble in water, In 1852 Verdeil and Risler examined 10 soils from the - grounds of the Institut Agronomique, 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, oy and after standing several hours with Sy agitation os the water was poured off; this process wag repented to the third time. The ola faintly yellow solutions- thus obtained were evaporated to dryness, and the ‘residues-~ were analyzed with results as follows, pey cent+~ AQUEOUS SOLUTION OF THE SOIL. 309 — 310 HOW CROPS FEED. Per cent of Ash. Nameof Field, ~ .. esl 8) 8.15 1 ¢ [eae sts WI SS5| 3 | SA) 85) SS) 3s] F (S28) 8 8s SS3] 3] 4s/ Ss] Esl SE] S Sse] B les] & Mall ...[Walk| 43.00|57.00/48.92/25.60| 4.27) 1.55) 0.62] 7.63] 5.49/3.77| — Pheasant %0.50/29.90/31.4935.29| 2.16] 0.47) trace | 3.55|13.67/4.23] — ete ce ee cate 35.00/65.00|48.45| 6.08) 2.75) 1.21; — 6.19/25. 715.06) — gre Ave..} 44.0056.00/48.75! 6.08) 6.32) 2.00 trace | 14.45|15.61/4.13) — itchen Gard.) 37.00)63.00/26.60 12.35,11.20 trace trace | 18.51,19.60]7.23 trace Satory..[Galy! 33.00/67.00|18.70 24.25/18.50| 3.72) 0.50] — |21.60/4.65) — Clay ‘soil of | 48.00'52.U0/18.75/45.61| 3.83] 0.95] 1.55) 9.14) 5.00!7.60) 7.60 Lime soil, do.| 47.00/53.00|17.21/48.50| 9.00)trace | — 6.21) 5.50} — | 8.32 Peat bog..... 46.00 54.00/24.43 30.61) 0.92| 5.15|trace | 6.06) 8.75)7.45) — Sand pit..... 47 .04/52.06122.31/34.59! 8.10! 1.02] — | 4.05/15.58/6.47] — Here we notice that in almost every instance all the mineral ingredients of the plant were extracted from these soils by water. Only magnesia and chlorine are in any case missing. We are not informed, unfortunately, what amount of soluble matters was obtained in these experiments. We next adduce a number of statements of the pro- portion of matters which water is 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, Seitendorf, 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). spy, eC ey AQUEOUS SOLUTION OF THE SOIL. $11 Vil. Garden soil, Heidelberg—3-fold amount of cold water (Grouven). VUI. 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, Moldau Valley, Bohemia, treated with twice its weight of water (R. Hoffmann). XI. Salt meadow, Stollhammer, Oldenburg (Harms). 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 PARTS OF VARIOUS SOILS. : ; = " > : 5 8 < eg les SS} eh] eRe] S |ax}] & [S8x[Sa] & Ba Pree. 18 2 18 8 2 Sel Oe a PR 5 | 53) 134 Ln Sy See 5 214! 3 5l4\trace |trace |trace 41%, 64%} 24) 51 (eee 6 te 4 4 — |trace 1 2 2 23] 43 1D ae 10 |trace | 1 2 — |trace 1 11 3 18} 46 Witeet sens 34 fae es. 13 — 9 22 — 36) 136 VE ay eal 9 v¢ 1 i 214) 64) 138% 1 22) 87 Ad ion seseeea 23 eA ayy 4, 5b boas A 1 38 2 30) 110 Skee. 2 8 ¥,| %| 3%|trace 1 1%|. 20 | — | 10] 45 1 1 Re ea 33%| 31%| 4% 5 Stel trace | — 70| 147 2 OF 164 1 |4% 12 |trace 3 302 |trace WT | 449/1095 ¢ Oa 92 44 /21 24 trace |trace 11 1 2 | 230) 425 xii 1 214| 2 1 trace jtrace |trace |trace | — 33} 39% 2 "9 43 |16 | 476 — | 407 | 144 58 — | 170)1393 D.C Seree 19 opie 5 1 4 4 20 3 88} 150 be 5 3 4 a 5 3 165 2 83) 147 <5 Paes 6%; 2 {1 3 yy Dili ayeh 12 7 12) 53 Boe 8 216%! 1 ifal «te 1%! 17. | 12] 55% 312 HOW CROPS FEED. The foregoing analyses (all the author has access to that are sufficiently detailed for the purpose) 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, 1X, 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 number of cases essential elements of plant- food, viz., phosphoric acid and sulphuric acid, are wanting, or their presence was overlooked by the analyst. Composition of Drain-Water.— Before further discus- ~ ‘sion of the above data, additional evidence as to the kind and extent of aqueous action on the soil will be adduced, The water of rains, falling on the soil and slowly sinking through it, forms solutions on the grand scale, the study of which must be instructive. Such solutions are easily gathered in their full strength from the tiles of thorough- drained fields, when, after a period of dry weather, a rain- fall occurs, sufficient to saturate the ground. Dr. E. Wolff, at Moeckern, Saxony, made two analyses of the water collected in the middle of May from newly laid tiles, when, after a period of no flow, the tiles had AQUEOUS SOLUTION OF THE SOIL. 313 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 3.2 Carbonate of lime, 21.9 4.4 “6 ‘* magnesia, : 1.4 s ‘* potash, 0.3 0.5 “ ‘* soda, £9 1.4 Chloride of sodium, 2.3 trace Sulphate of potash, £3 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 waters were collected from the pipes (4-5 ft. deep) of thorough-drained fields in December, 1855, and in most cases were the first flow of the ditches after the autumn rains. The soils, with exception of 7 and 8, were but a few years before in an impoverished condition, but had been brought up to a high state of fertility by ma- nuring and deep tillage. (Jour. Roy. Ag. Soc., XVII, 133.) IN 100,000 PARTS OF DRAIN-WATER. 1 2 3 4 5 6 7 Wheat | Hop | Hop | Wheat | Wheat | Hop | Hop field. | field. | field.| field. | field. | field. | field. SGA atte, bode isles 25 trace |trace | 0.03 | 0.07 trace ; 0.31 |trace BM es pits x esd cso xs 1.43 | 3.10 | 3.238 | 1.24 2.03 |-2.00 | 4.57 PGs Sab sae Seki dare ake 6.93 |10.24 | 8.64] 2.28 8.60 | 8 31 |18.50 Pea a ons bp os 0.97 | 3.31 | 3.54] 0.58 0.30 | 1.33 | 3.57 Oxide of iron and alumina.| 0.59 { 0.07] 0.14} none | 1.85 | 0.50 | 0.71 =f Pe < ee ete deo 020400078 | 1a 2.57 | 0.93 | 1.21 Gmiorine:3.7../22.2-. Jae eee OO. |! ASSES hs 84s (pete 1g 1.80 | 1.73 | 3.%4 SOIpNEFIGACIG. 6 os). Ss... 22. 2.80 | 7.385 | 6.28 | 2.44 1.84 | 4.45 |13.58 Puosphoric acide...) 72s. trace | 0.17 |trace | trace | 0.11 {| 0.09 | 0.17 WELT SUGIEL bod eis, wn oe ne o>) 10.24 |21.05 /18.17 |} 2.78 4.93 |11.50 |16.35 PORIGRELG i) onc ner aoe eae: 0.025 | 0.025) 0.025) 0.017 | 0.025 | 0.025) 0.009 Soluble organic matter..... 10.00 {10.57 |17.85 | 8.00 8.14 | 8.28 10.5% Total...... ..........| 34.885 158.095160.525! 21.297 | 97.195 ‘39.455 72.979 14 314 HOW CROPS FEED. Krocker has also published analyses of drain-waters collected in summer from poorer soils. He obtained IN 100,000 PARTS: a b c d é = Organic matters, 2.5 2.4 1.6 0.6 6.3 5.6 Carbonate of lime, 8.4 8.4 12.7% "9 ye | 8.4 Sulphate of lime, 20.8 21.0 11.4 Att a %.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 2.4 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 33.7 15.3 25.8 24.7 Krocker remarks (Jour. fiir Prakt. Chem., 60-466) that phosphoric acid could bé detected in all these waters, though its quantity was too small for estimation. aand 6 are analyses of water from the same drains—a gathered April Ist, and 6 May Ist, 1858; ¢ is from an ad- joining field; d, froma field where the drains run con- stantly, where, accordingly, the drain-water is mixed with spring water; e¢ and fare of water running from the sur- face of a field and gathered in the furrows. Lysimeter-W ater.— Entirely similar results were ob- tained by Zoller in the analysis of water which was col- lected in the Lysimeter of Fraas. The lysimeter* con- sists of a vessel with vertical sides and open above, the upper part of which 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 water. The vessel is imbedded in the ground to within 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, while the water which percolates the soil gathers in the reseryoir * Measurer of solution, AQUEOUS SOLUTION OF THE SOIL. 315 below. Dr. Zoller analyzed the water that was thus col- lected from 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 0.56 0.74 2.37 0.60 Lime, 14.58 5.76 7.08 6.84 9.23 Magnesia, 2.05 0.89 0.18 0.29 0.51 Oxide of iron, 0.01 0.63 0.83 0.57 0.43 Chlorine, 5.75 0.95 2.08 3.94 3.52 Phosphoric acid, 0.22 -- — — — Sulphuric acid, 1.05 2.71 2.78 2.93 3.35 Silica, 1.04 1.13 1.75 _. 0.95 0.93 Bete master, willl comet 99 47 12.59 13.67 12.08 10.19 nitric and carbonic acids, Total, 47.23 25.46 29.26 30.52 29.15 The foregoing analyses of drain and lysimeter-water ‘exhibit a certain general agreement in their results. They agree, namely, in demonstrating the presence in the soil-water of all the mineral food of the plant, and while the figures for the total quantities of dissolved matters vary considerably, their average, 363 parts to 100,000 of water, is probably about equally removed from the ex- tremes met with on the one hand in the drainage from a very highly manured soil, and on the other hand in that where the soil-solution is diluted with rain or spring water, It must not be forgotten that in the analyses of drain- age water the figures refer to 100,000 parts of water; whereas, in the analyses on p. 311, they refer to 100,000 parts of 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 ? —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- } 316 HOW CROPS FEED. er nutritive elements, viz., chlorine and sulphuric acid, in the Table, p.311, leads to the question, May not the aqueous solution of the soil be altogether lacking in some es- sential kinds of mineral plant-food in certain instances? May it not happen 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 capable of dissolving from the soil all the sub- stances that it contains which serve as the food of plants. The absence of one or several substances in the analytical statement would seem to be no proof of their actual ab- sence in the solution, but indicates simply that the sub- stance was overlooked or was too small for estimation by the common methods of analysis in the quantity of solu- tion which the experimenter had in hand. It would ap- pear probable that by employing enough of the soil and enough water in extracting it, solutions would be easily obtained admitting of the detection and estimation of ey- ery ingredient. Knop, however, asserts (Chem. Central- blatt, 1864, 168) that he has repeatedly tested aqueous solutions of fruitful soils for phosphoric acid, employing the soils in quantities ranging from 2 to 22 lbs., and water in similar amounts, without in any case finding any traces of it. On the other hand Schulze mentions having inva- riably detected it in numerous trials; and Von Babo, in the examination of seven soils, found phosphoric acid in every instance but one, which, singularly enough, was that of 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. (Hof mann’s Jahresbericht der Ag. Chem., I. 17.) So Heiden, in answer to Knop’s statement, found and estimated phosphoric acid in four instances in proportions PTE Oe AQUEOUS SOLUTION OF THE SOIL. 317 ranging from 2 to 6 parts in 100,000 of soil. (Jahresbe- richt der Ag. Chem., 1865, p. 34.) It should be remarked that Knop’s failure to find phos- phoric acid may depend on the (uranium) method he em- ployed, a method different from that commonly used. Can the Soil-water supply Crops with Food ?— As- suming, then, that all the soil-food for plants exists in solu- tion in the water of the soil, the question arises, Does the water of the soil contain enough of these substances to nourish crops? In case of very fertile or highly manured fields, this question without doubt should be answered af- firmatively. In respect of poor or ordinary soils, how- ever, the answer has been for the most part of late years in the negative. While to decide such a question is, per- haps, impossible, a closer discussion of it may prove ad- vantageous, Russell (Journal Highland and Ag. Soc., New Series, Vol. 8, p. 5384) and Liebig (Ann. d. Chem. u. 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 falls escapes through the drains, and the rest is got rid of by evaporation.+ An inch of rain falling on an English acre weighs rather more than a hundred tons; hence in the course of a year, there must pass off by the drains about 1,000 tons of drainage water, carrying with it, out of the reach of plants, such substances as it has dissolved, and * On drain-waters, see p 313. + From Parke’s measurements, Jour. Roy. Ag. Soc., Hng., Vol, XVII, p. 127. =~ 318 HOW CROPS FEED. 1,500 tons must remain to give to the plant all that it holds in solution. These 1,500 tons of water must, if they have the same composition as that which escapes, contain only two and a half pounds of potash and less than a pound of ammonia, It may be alleged that the water which re- mains lying longer in contact with the soil may contain a larger quantity of matters in solution; but even admit- ting 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, perhaps, 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. = = | Ss Ses Ss 3 Nsiss8/]o8 | 3S || 28 | 38 q B N = 1 300 0.303 0.129 || 0.329 | 0.056 0.012 0.121 | 0.110 0.049 1%| 200! 0.455 | 0.193 0.488 | 0.120 | 0.011 0.034 | 0.105 | 0.030 - We observe that the soil not only retained no sulphuric acid, but gave up a small quantity to the solution. Of the ammonia a little more than one-half in one case, and three-eighths in the other, was absorbed, and in the solu- tion its place was supplied chiefly by lime, but to some extent also by potash, soda, and magnesia, which were dissolved from the soil. It is also to be noticed that in - the two cases—unlike quantities of the same soil and \ ABSORPTIVE POWER OF THE SOIL. ; 341 solution having been employed—the bases were displaced in quantities that bear to each other no obvious relation. Another fact which follows from the rule just illustra. ted, is the following: Any base that has been absorbed by the soil, may be released from combination partly or en- tirely by any other. Peters subjected a soil which had been saturated with potash and subsequently washed copiously with water to the action of various solutions. The results, which exhib- it the principle just stated, are subjoined. The soil was employed in portions of 100 grams, each of which con- tained 0.204 gram of absorbed potash. These were di- gested for three days with 250 c.c. of solutions (of ni- trates) of the content below indicated. For sake of comparison the amount of matters taken up by distilled water is added. Dissolved by the solution. . Content of ; Magne- Ammo-| Absorbed alison. Lime. ae: Potash.| Soda. nae. by the soil. gram. 0.2808 soda. 0.0671(?)| 0.0006 | 0.0983 | 0.2197 0.0611 soda. 0.2165 ammonia.|| 0.0322 —— | 0.1455 | 0.0024 | 0.1596 ||0.0569 ammonia. 0.2996 lime. 0.2380 | 0.0020 | 0.1252 | 0.0252 | —— |/0.0616 lime. 0 2317 magnesia.|| 0.0542 | 0.1726 | 0.1224 | 0.0245 | —— | 0.0591 magnesia, Dist. water. trace —— | 0.0434 | 0.0004 | —— |; —— We notice that while distilled water dissolved about *|, 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 base (potash and lime were tried) increases the absorbent power for other bases, and on the other hand, treatment with acids, which removes absorbed bases, diminishes their absorptive power. “3 { 342 HOW CROPS FEED. Tkis fact is made evident by the following data furnish- ed by Peters. The soils employed were No. 1. Unaltered Soil. No. 2. Soil heated with hydrochloric acid for some time, then thoroughly 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 solution 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 three days. The results are subjoined: ssolv is Nistnber|\_ 1. Dissolned ‘by the souiion ee of soil. Lime. Magnesia. Soda. Chlorine. by the soil. Bec cega7 '| 0.0940 0.0084 0.0261 0.4482 0.1841 “haere 0.0136 0.0004 0.4444 0.0227 Ot ee 0.0784 0.0024 0.0019 0.4452 0.0882 ae 0.0560 0.0094 0.0024 0.4452 0.1243 Sirti tease 0.1176 0.0094 0.0019 0.4425 0.1378 Woh othe I] 0.1456 0.0074 ars 0.4404 0.2011 It is seen that the soil which had been washed with acid, absorbed but one-ninth as much as the 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 had 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 — ABSORPTIVE POWER OF THE SOIL. 343 is diminished or even destroyed by burning or 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 0.0202 Loam, 0.1841 0.1200 - The Cause of the Absorptive Power of Soils for Bases when combined with chlorine, sulphuric, 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 soda containing water was prepared, which possessed ab- sorptive 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 essential ingredient. 344 HOW CROPS FEED. _ This compound is analogous in constitution to the 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 alumina. On digesting this soda-silicate of alumina with a solu- tion of any salt of lime, Way found that it was decom- posed, its soda was eliminated, and a Jime-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 manner, ammonia and magnesia-silicates were gener- ated. In case of the ammonia-compound, 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- 7 ce Oz) ce see potash “ ‘“ eed The ammonia- ‘* “1.06. “ —“ sxumogia Seep 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 artificially, 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 replace 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 ‘ . . . a -_ Be — _ 5 = wv a ee eae ee ABSORPTIVE POWER OF THE SOIL. 845 replaces those ranged to its left in the above series, but none of those on its right. Way remarks, that “ of course the reverse of this action cannot occur.” Liebig (Ann. 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 either 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 these 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 researches of Eichhorn, ‘‘ Ueber die Einwirkang ver- diinnter Salzlésungen auf Ackererde,” (Landwirthschaft- liches Centralblatt, 1858, ii, 169, and Pogg. Ann., No. 9, 1858), served to clear up the discrepancies of Way’s in- vestigation, and to confirm and explain his facts. _As Way’s artificial silicates contained about 12 per cent of water, the happy thought occurred to Eichhorn to test the action of saline solutions on the hydrous silicates (zeolites) which 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* 846 HOW CROPS FEED, acted evidently in two or three days. Chloride of barium and nitrate of cadmium were slower in their effect. Chlo- rides of zine 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 (1,) and of the same after the action of chloride of sodium (11,) were as follows: I. II. Silica, 47.44 48.31 Alumina, 20.69 21.04 Lime, 10.37 6.65 7. 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 mineral was thus substituted by soda. A loss of water also occurred. The solution 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 cc. of water) for 10 days, the mineral was altered, and contained 3.33 per cent of am- monia. Digested 21 days, the 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 ABSORPTIVE POWER OF THE SOIL. 847 monia, in order fo ascertain whether the formation of a soluble salt of the displaced 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. Eichhorn found that the artificial soda-chabazite re-ex- changed soda for lime when digested in a solution of chloride of calcium; in solution of chloride of potassium, both soda and lime were separated from it and replaced by potash. So, the ammonia-chabazite in solution of chlo- - ride of calcium, exchanged ammonia for lime, and in so- lutions of chlorides of potassium and sodium, both am- monia and lime passed into the liquid. The ammonia- chabazite in solution of sulphate of magnesia, lost ammo- nia but not lime, though 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 replace each other, time being the only element of difference in the 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 zeolitic minerals stilbite, thomsonite, and prehnite. (Che- mie der Ackerkrume, I, 396). He has also artificially prepared hydrous silicates, having properties like those of Way, and has noticed that sesguioxide 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 game substitutions when acted upon by saline solutions, 348 HOW CROPS FEED. The precipitate he operated with, contained (water-free) in 100 parts: RINGS... oc: dears bw nerd ona} Sh pawns See Per ok - 49.0 ABD, oi an. son nscinin 0 ,00ie vac ote mip w a'e erties ao ae pe Oxide Of ifOD 6... i csc ca cccec scene agoutay oie aun 21.9 Lime. .. oo 2. o 0 osc cabs ce uwese cc td wate obiecneete nena 6.9 Mi aomesida nice. (5). 0.0/0 010 aie d vines dino Aietatpie lien Bien an i Insoluble matters with traces of alkalies, ete.......... 10.0 100.0 On digesting portions of this substance with solutions of sulphates of soda, potash, magnesia, ammonia, for a single hour, all the 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 (Henneberg’s Jour. fiir Landwirthschaft, 1862, pp. 405-454), and Knop (Vs. St., VI, 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.: Quartz sand. Be | eolinite (purified kaolin.) | Carbonate of lime (chalk.) | These bodies have no absorptive effect, either 1 Humus (decayed wood.) f separately or together. ee oxide of iron. Hydrated alumina. Humate of lime, magnesia, and alumina. Pe Phosphate of alumina. _ Gelatinous silica. | id ** dried in the air. Rautenberg. These observers, together with Heiden (Jahresbericht tiber Agriculturchemie, 1864, p. 17), made experiments on soils to which hydrated silicates of alumina, and soda, or of lime, etce., were added, and found their absorptive power thereby increased. Rautenberg and Heiden 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 oa ABSORPTIVE POWER OF THE SOIL. 349 ide of iron which the soils yielded to hydrochloric acid. Heiden traced a similar relation between the silica set free by the action of acids on eleven soils and their absorptive power. Rautenberg and Heiden further confirmed what Way and Peters had 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 sulphates, nitrates, etc., and since these bodies do not ordinarily exist as such 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 the absorptive agent. That the absorbing compound is not necessarily hydra- ted, is indicated by the fact that calcination, which must remove water, though it diminishes, does not always alto- gether destroy the absorptive quality of a soil. (See p. 343.) Eichhorn, as already stated, found that the anhy- drous silicates, chlorite and labradorite, were acted upon by saline solutions, though but slowly. Do Zeolitic Silicates, hydrated or otherwise, exist in the Soil 2—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 quantity (several per cent.) of matter which, 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 uncombined silica, afterwards yields to the proper solvent (hot solution of carbonate of soda) a considerable quantity. This is our best evidence of the presence in the soil of easily decom- ‘ Sie OF ee ee - ~ pa 350 HOW CROPS FEED. j posable silicates. A number of analyses which illustrate - these facts are subjoined: : 2. 3. 4. 5. 6. White | Bed | “tain | Pottery Sandy Loum. Clay. Clay. Clay. | Clay: HEIDEN. RAUTENBERG. Way. ——— eee OO ee WV RiP Res we Rae wine ba eee 1.613 | 1.347 |. 6.15 6.39 | 10.36 6.18 Oreanie matter... :....05. 2.3887 | 2.003 | none | none | none | none Sand and insoluble silicates.| 89.754 | 88.782 | 58.08 | 80.51 89.46 | 58.72 (Clay, kaolinite)... 2. 0.052... (10.344) | (5.762) GUE ES ie eee SrIe Ff 2.630*| 4.199 | 18.73 6.80 0.04¢ | 18.41 wf oxide Mf IPOH... s... ..-- 1.87 1.680 |} 2.11 0.90 0.14 5. Pil SANTINO LEG wale Spiele acc 1.152 | 1.288 | 12.15 4.35 F 13.90 ; el ree 0.161 122") Ore 0.38 0.12 0.61 a ROMEME: 25 aes ,2)4 vs. 0.201 | 0.240} 0.29 0.17 0.08 0.43 et POUAED «5 ok \aisisc veins aa ee 0.242 0.212 0.86 J ete eee eae 0.034 | 0.141 | 1.41 ©, | Phosphoric acid........ 0.083 | 0.034 0.50: 1.37 a | Sulphuric acid,......-.. 0.007 0.021 | none : : = Bebe acid, chlorine, 3 and Mossi esse 2s tice ans 0.047 | 0.095 | none | 100.000 |100.006 |100.00 |100.00 |100.20 1100.00 * This soil yielded to solution of carbonate of soda before treatment with acid, 0.340 °|, silica. + The silica in this case is the small portion held in the acid solution. The first three analyses especially, show that the soils 4 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 shown by treatment with solu- tion of carbonate of soda, but it appears difficult, if not impossible, to ascertain its quantity. Again, hydrated oxide of iron (according to A. Miiller and Knop) and hy- ~ drated alumina* (Knop) may also exist, as can be made evident by digesting the soil in solution of tartrate of soda and potash (Miller, Vs. Sé., ZV, p. 277), or in a mix- ture of tartrate and oxalate of ammonia (Knop, Vs. St. VITT, p. 41). Finally, organic acids occur to some ex- tent in insoluble combinations with iron, alumina, lime, ® More probably, highly basic carbonates, or mixtures of hydrates and car bonates., ABSORPTIVE POWER OF THE SOIL. 351 &c. This complexity of the soil effectually prevents an 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 which 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 through 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 Daubrée has shown (Ann. des Mines, 5me., Série, 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, harmotome, 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 quantities of these substances that could be formed there must be distributed throughout twenty, fifty, or more times their weight 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 which the evaporation of water containing dissolved salts has left a solid residue of sili- cates. Thus, Kersten has described (Jour. fiir prakt. Chem., 22,1) a hydrous silicate 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 pumps. Kersten and Berzelius have no- 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. (Bischof’s Chem. Geology, Cav. Ed., Vol. 1, p. 5). Bischof (/oc. e/t., 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 combine when adverse affinities do not prevent, 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, etc.) was treated with strong hydro- chloric acid, whereby it was decomposed and in part dis- solved, and then with ammonia, (which neutralized and re- ABSORPTIVE POWER OF THE SOIL. 353 moved the acid,) the 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 ordinary 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- water, 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 Dict. of Solubilities, p. 551.) The fact that free bases, as ammonia, potash and lime, are absorbed by and fixed in soils or clays that contain no organic acids, and to adegree different, usually greater than, when presented in combination, would indicate that they directly unite 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 carbonate of lime, or of other lime-salts with the soil, usually enhances its absorbent power, is not improbably due, as Rautenberg 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 from 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, an 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 HOW CROPS FEED. proportions, extremely important to the soil, and espe- cially so when existing in combinations admitting of the remarkable changes which have come under our notice. That we cannot decide as to the precise composition of the zeolitic compounds which may exist in the soil, is plain from what has been stated. We have the certainty of their analogy with the well-defined silicates of the miner- alogist, which have been termed zeolites, an analogy of chemical composition and of chemical properties ; we know further that they are likely to be numerous and to be in perpetual alteration, as 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 potash or other base is accompanied by a chemical decomposition, which Way, Rautenberg, Heiden, and Knop’s researches conclusively connect with certain hydrous silicates whose presence 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 porous 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, for bases in combination, re- sides in the chemical action of zeolitic silicates, the facts just mentioned indicate that the physical properties of the - soil may also exert an influence. Indeed, the fixation of Sree bases by the soil may be in all cases partially due to this cause, as Brustlein has made evident in case of am- monia (Boussingault’s Agronomie, ete., T., II, p. 153). ABSORPTIVE POWER OF THE SOIL. 355 Peters concludes the account of his valuable investiga- tion with the following words: “ Absorption is caused by the surface attraction which the particles of earth exert. In the absorption of bases from salts, a chemical trans- position with the ingredients of the soil is necessary, which is made possible through céoperation of the surface. attraction of the soil for the base.” (Vs. St., II, p. 151.) If we admit the soundness of this conclusion, we 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, though they have undeniably a chiefly chemical 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 strength 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 been 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 the soil. Veelcker was the first to notice an absorption of sulphuric acid and chlorine. In his papers on “ Farm Yard Manure,” etc., (Jour. Roy. Ag. Soc., XVIIL, p. 140,) 356 HOW CROPS FEED, and on the “ Changes which Liquid Manure undergoes in contact with different Soils of Known Composition” (idem XX., 184-57), he found, in seven experiments, that dung liquor, after contact with various soils, lost or gained acid ingredients, as exhibited by the following figures, in grains per gallon: (loss is indicated by —, gain by +): 1 2. 8 .4. (53900 Chloride of Potassium —8.81 +9.17 —2.74 +2.14 —2.74 +2.55 —1.10 Chloride of Sodium...—3.95 —2.43 —7.04 —1.12 —1.10 —1.24 +3.66 —1.89 +19.05 Sulphuric Acid........ $2.32 —4.21 —1.06 —1.21 —0.27 +1.24 +3.44 +2.26 —0.42 Bilicie Acid: ob. vs. +1.63 +10.83 —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 —%.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 differences as due to the unavoid. able errors of experiment, and it is certain that in Veelck- er’s results similar allowance must be made. Neverthe: less, these errors can hardly account for the large loss of chlorine observed in 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 solutiox 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 r a - 4 . Z a eee ABSORPTIVE POWER OF THE SOII. DDT retained rather than altered to ammonia or some other compound, The fixation of acids in the 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 chlorides, nitrates, sulphates, silicates, phosphates and carbonates of these oxides. Whether such compounds can be actually produced 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 free 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 disappeared 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 phosphorite 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 ieee x ei 358 HOW CROPS FEED. contact with the soil, the base may be withdrawn by the absorbent silicate, and the acid may unite to lime or mag- nesia. The phosphates of lime and magnesia thus formed are, 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 phosphate of lime (J. Lawrence Smith). Vcelcker, in a number of ex- periments on the deportment of the soluble 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 than with clays or sands. . All observers agree that phosphoric acid is but slowly fixed 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 acid, it may also, as solid hydrate, unite slowly with the oxides of iron and with alumina (see Kers- ten’s observations, p. 852). When occurring in solution, as silicate of an alkali, as happens in dung liquor, it would 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 POWER OF THE SOIL. 359 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 Silicates.—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, which, however, in contact 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 solution of its bicarbon- ate, forming a nearly insoluble silicate of magnesia. 2. It has long been known that hydrated owide of iron and hydrated alumina may unite with and retain free ammonia, potash, etc. Rautenberg experimented with both these substances as freshly prepared by artificial means, and found that, under similar conditions, 10 grms. of hydrated 10 grms. of hydrated ~ oxide of i iron, alumina. Avarbed of free ammonia 0.046 grm. 0.066 grm. & “ free potash - 0.147 “ 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 sufficient to have appreciable effect in absorbing free alkalies is extremely improbable. Liebig has shown (Ann. Ch. u. Ph. 105, p. 122,) ‘that hydrated alumina unites with silicate of potash with great 360 HOW CROPS FEED. 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 grms. of anhydrous alumina, absorbed from a liter of solution of silicate of potash containing 1.185 grm. 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 that these compounds unite readily to other earthy* 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, their 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 made by the author, a sample of Peat from the New Haven Beaver Meadow was 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 saniple 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 ammonia are alkalies or alkali-bases. Lime, magnesia, and alumina are earths or earthy bases, and oxide of iron and oxide of manganese are metallic bases. ' REVIEW AND CONCLUSION. 361 peat contained humate of lime, which was not affected by the pure ammonia, but in contact with carbonate of am- monia yielded carbonate of lime and humate of ammonia, In these cases the ammonia was én excess, and the chemical changes were therefore, in some particulars, unlike those which occur when the humus preponderates. Brustlein, Liebig and others have observed that soils rich in organic matter (forest mold, decayed wood,) have their absorptive power much enhanced by mixture with carbonate of lime. Although Rautenberg has shown (Henneberg’s Journal 186, p. 439,) that silicate of lime is probably formed when ordinary 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 appropriately close the volume. There are 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 must contain.—Jn order to feed crops, 16 ; 362 HOW CROPS FEED. the soil must contain the ash-ingredients of plants, together with assimilable nitrogen-compounds in proper quantity gad 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 inches deep. Insoluble silica, quartz, 57.646 51.706 55.372 Soluble silica, 2.340 2.496 2.286 Alumina, 1.830 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 0.128 Potash, 1.026 * 1.430 1.521 Soda, 1,972 2.069 1.937 Ammonia,* 0.060 0.078 0.0%5 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, 12402 1.302 1.418 Humic acid, 2.798 3.991 3.428 Crenic acid, 0.771 0.731 0.037 Apocrenic acid, 0.107 0.160 0.152 Other organic matters, and com- bined water (nitrates ?), 8.324 7.700 9.348 Logs in analysis, 0.540 0.611 0.753 100.000 100.000 100.000 A glance at tlle above analyses shows the unusual rich- ness of this soil in all the elements of plant-food, with 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 this * The figures are probably too high for ammonia, because, at the time the analy- ses were made, the methods of estimating this substance in the soil had not been studied sufficiently, and the ammonia obtained was doubtless derived in great part from the decomposition of humus under the action of an alkali. =- REVIEW AND CONCLUSION. 363 . quantity to weigh 3,500.000 lbs., (p. 158,) are as follows; lbs. Soluble silica 81.900 Lime, 143.220 Potash, 35.910 Soda, 68,920 Ammonia, 2.100 Phosphoric acid, 16.310 Sulphuric 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. They are here reproduced, EFFECTS OF VARIOUS PROPORTIONS OF AVAILABLE POTASH * IN THE SOIL ON THE BARLEY CROP. Yield Potash in | |——-—————— Fo — 1,000.000 dds. of soél.| of Straw and Chaff. of Grain. Total. 0 0.798 —-—— ——— 6 3.869 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 wher 71 parts of potash were present in 1,000.000 lbs. of scil, A * Other conditions were in all respects as nearly alike as possible. 364 HOW CROPS FEED. larger quantity depressed the yield. It is probable that less than 71 lbs. would have produced an equal effect, since 47 lbs. gave so nearly the same result. The ash composition of bar ley, grain, and straw, in 100 parts, is as follows, according to Zoeller, (H. C. G., pp. 150 to 151): Grain. Straw. Potash, 18.5 12.0 Soda, 3.9 46 Magnesia, 7.0 30 Lime, 2.7 7.3 Oxide of iron, 0.7 1.9 Phosphoric acid, 32.4 6.0 Sulphuric acid, 2.8 2.8 Silica, 31.1 59 7 Chlorine, 1.1 26°-* The proportion of ash in the air-dry grain is 24 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 Ibs., and one ton of straw,* we have in the bariey crop of an acre the following quantities of ash-ingtedients: ze ‘ 2 aie : > "3 poe gS s 8 © § $8 33. 9.7 s & 8 By > Ce gee eee Barley Grain, 43% 81 1% B81 12 08 142 190008 Straw, 100.00 120 46 30 73 19 60 28 26 | | | | Total, 143.75 20.1 6.3 6.1 8.5 2.2 20.4 4.0 3.1 In the account of Hellriegel’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 Ibs. each per acre. This is more than 4} times the yield above assumed. The above figures show that 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 figures are employed by Anderson, and are based on Scotch statistics REVIEW AND CONCLUSION, 365 while lime is bat one-half 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 crop 44 times greater than can ordinarily he produced under agricultural conditions, the same quantity of phosphoric acid, and less than half that amount of lime, 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 Hellricgel (1), and the quantities needed for the average crop of 33 bushels (2). The amounts of nitrogen are those which Hellriegel found adequate to the wheat crop. See p. 289. 1 2 lbs. lbs. Potash, 248 55 Soda, 78 17 Magnesia, 76 17 Lime, 105 23 Phosphoric acid, 250- 55 Sulphuric acid, 49 at Chlorine, 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 maximum _ 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 barley crops. Potash oc 44 “c “ 648 “ rT: “ Phosphoric acid sn, 5" v« “ 999 «6 ‘ “ Sulphuric 6 ae | “ “ ogg & “ cd Nitrogen in ammonia ‘‘ 7 6 «“ 31. «6 ‘ “ We give next the composition of one of the excellent 366 HOW CROPS FEED. wheat soils of Mid Lothian, analyzed by Dr. Anderson. The air-dry surface-soil contained in 100 parts: PRCA: 5 oss aise oases dle'a wiele ou c plnea mle eet eae 71.552 ALOMINA,. 055 2 sise sos nieve o.06 cela exc oe 6.935 Peroxide of lron..:.,....2....cs2«.sieeeeeeee 5.173 DAMNG ys oe vis oo ont weed Bede a tdanlee Oe 1.229 Magnesia. «5.6. oh ak aids saan se beeen 1.082 Potash soi: sac cas deccnsae octet ae oe eee 0.354 * SOG goin so dep ea ons vie de’ sa-cine w oi apie lee 0.4383 Sulphuric acid... .\.. 2.0. .00k uae sce dn ee en een 0.044 Phosphoric acid... 0500 .+50. 0 see aes cee 0.480 CUIGFIIB oes Scr cle 6 0c dn Sadie s 4 ould Be traces Organie matter... 2... .-.02c0>.008 550 5h 10.198 WIE. oc Si wau's »aks sc ckee sedeee sued sce es aan 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 phosphoric 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.” PRE OR es ncaliie ois Sind o 2.0 an.len Sede Oye ae 0.585 Organic matter. ...<).2. 260052464500 ss ake 1.850 LTC: in An I Co 0.016 Oxide of iron and alumina. .>.5....00% sas) eee 1.640 Lime). pies cn'ss edie o-wiand eed sere wl ce 0.096 Magnesia... .. . oes cee - cies sa se nlsnuens 5 trace Carbonie 9eid .. ho... soa 5 2s ae trace Phosphoric acid. . 2... .200 500.5 nse’ aoe trace Chlorine... oo. csc od soak os Cam's ee ae trace AE a he Ss ake topes ay a none Quartz and insoluble silicates...'.......e0.sesssene 95. 863 100.000 Here we note the absence in weighable quantity of magnesia and phosphoric acid, while potash could not even és in REVIEW AND CONCLUSION. 367 be detected by the tests employed. This soil was mostly naked and destitute of vegetation, and its composition shows the absence of any crop-producing power. Relative Importance of the Ingredients of the Soil. —From the general point of view of vegetable nutrition, all those ingredients of the soil which act as food to the plant, are equally important as they are equally indispens- able. Absence of any one of the substances which water- culture demonstrates must be presented to the roots of a plant so that it shall grow, is fatal to the productiveness of a soil. Thus regarded, oxide of iron is as important as phos- phoric acid, and chlorine (for the crops which require it) is no less valuable than potash. Practically, however, the relative importance of the nutritive elements is meas- ured by their comparative abundance. Those which, like oxide of iron, are rarely deficient, are for that reason less prominent among the factors of a crop. If any single substance, 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 may safely state that, on the whole, availa- ble nitrogen and phosphoric acid are the most important ingredients of the soil, and potash, perhaps, takes the next rank. These are, most commonly, the substances whose absence or deficiency impairs fertility, and are those which, when added as fertilizers, produce the most frequent and remarkable increase of productiveness. In a multi- tude of special cases, however, sulphuric acid or lime, or magnesia, assumes the chief prominence, while in many in- stances it is scarcely possible to make out a greater crop- producing value for one of these substances over several others. Again, those ingredients of the soil which could be spared for all that they immediately contribute to the 368 HOW CROPS FEED. nourishment of crops, are often the chief factors of fer- tility on account of 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 assimilablé nitrogen. Again, gravel may not be in any sense nutritious, yet because it acts as a reservoir of heat and promotes drainage it may be one of the most import- ant components of a soil. What the Soil must Supply,—It is not sufficient that the soil contain an adequate amount of the several ash-in- gredients of the plant and of nitrogen, but it must be able to give these over to the plant in due quantity and pro- portion. The chemist could without difficulty compound _ an artificial soil that should include every element of plant-food in abundance, and yet be perfectly sterile. The potash of feldspar, the phosphoric acid of massive apatite, the nitrogen of peat, are nearly innutritious for crops on account of their immobility—because they are locked up in insoluble combinations. Indications of Chemical Analysis.—The analyses by Baumhauer of soils from the Zuider Zee, p. 362, give in a single statement their ultimate composition. We are in- formed how much phosphoric acid, potash, magnesia, etc., exist in the soil, but get from the analysis no clue to the amount of any of these substances which is at the dispo- sition of the present crop. Experience demonstrates the productiveness of the soil, and experience also shows that a soil of such composition is fertile; but the analysis does not necessarily give proof of the fact. A nearer approach to providing the data for estimating what a soil may sup- ply to crops, is wade by ascertaining what it will yield toe acids, REVIEW AND CONCLUSION. 369 Boussingault has analyzed in this manner a soil from Calvario, near Tacunga, in Equador, South America, which nossesses extraordinary fertility. He found its composition to be as follows: Nitrogen in organic combination, 0.243 Nitric acid, 0.975 Ammonia, 0.010 Phosphoric acid, 7} 0.460 Chlorine, 0.395 Sulphuric acid, 0.023 Carbonic acid, : : traces Potash and Soda, { Soluble in acids. 1.030 Lime, 1.256 Magnesia, 0.875 Sesquioxide of iron, 2.450 Sand, fragments of pumice, and clay insoluble in acids, 88.195 Moisture, 3.150 Organic matters (less nitrogen), undetermined substances, and loss, 5.938 100.000 This analysis is much more complete in reference to nik trogen and its compounds, than those by Baumhauer al. ready given (p. 362), 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 the soils from Zuider Zee. The method of analysis is a guarantee that the one per cent of potash and soda does not exist in the insoluble form of feldspar. Boussingault found fragments of pumice by a microscopic examination. This rock is vesicular feld- spar, or has at least a composition similar to feldspar, and the same insolubility in acids. The inert nitrogen of the humus is discriminated from that 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. 16* 370 HOW CROPS FEED. 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 (lter & 3ter Salemiinder Berichte) 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 lowertemperature. The follow- - ing statement shows the composition of each extract, cal- culated on 100 parts of the soil. EXTRACT OF SOIL OF SALZMUNDE. Hot strong acid. Hot dilute acid. Cold dilute acid. Potash, 635 116 -029 Soda, .127 067 .020 Lime, 1.677 1.046 1.098 Magnesia, .687 .5389 237 Oxide of iron and alumina, 7.931 3.180 AC Dae ; Oxide of manganese, .030 .086 O71 - Sulphuric acid, .059 .039 .020 Phosphoric acid, 059 -091 057 Silica, é 1.785 . 234 1% Total, 12.990 5.398 2.357 The most interesting fact brought out by the above fig- _ ures, is that strong and weak acids do not act on all the ingredients with the same relative power. Comparing the quantities found in the extract by cold dilute acid with those which the hot dilute acid took up, we find that the latter dissolved 5 times as much of oxide of iron and alumina, 4 times as much potash, 3 times as much soda, REVIEW AND CONCLUSION. 371 twice the amount of magnesia, sulphuric acid, and phos- phoric acid, and the same quantity of lime. These facts’ show how very far chemical analysis in its present state is from being able to say definitely what any given 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 that 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 particular soil is able to give to crops? is one for which we not only have no chemical answer at the present, but one that for many years, and, perhaps, always can be answered only by the method of experience—by appealing to the crop and not to the soil. Chemical analysis is competent to inform us very accurately as to the ultimate composition of the soil, but as regards its proximate composition or its chemical 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 atmosphere and the soil, the latter keeps up its store of available nutritive matters. The difficultly soluble silicates slowly yield alkalies, lime, and magnesia, in soluble forms; the sulphides are converted into sulphates, and, generally, the minerals of the soil are disintegrated and fluxed under the influence of the oxy- gen, the water, the carbonic acid, and the nitric acid of the air, (pp. 122-135). Again, the atmospheric nitrogen is assimilated by the soil in the shape of ammonia, ni- trates, and the amide-like matters of humus, (pp. 254-265). The rate of disintegration as well as that of nitrifica- tion depends in part upon the chemical and physical char- acters of the soil, and partly upon temperature and mete- oie HOW CROPS FEED. orological conditions. In the tropics, both these processes go on more vigorously than in cold climates. Every soil has a certain inherent capacity of production in general, which is 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 which was 15 bushels per acre, the last 174 bushels, and the average of all 16} bushels. (Jour. Roy. Ag. Soc. of Hng., XXV, 490.) The same investigators also raised barley on the same field for 16 years, each year applying the same quan- tity and kinds of manure, and obtaining in the first 8 years (1852-59) an average of 441 bushels of grain and 28 cwt. of straw; for the second 8 years an average of 512 bushels of grain and 29 cwt. of straw; and for the 16 years an average of 48} bushels of grain and 28} ewt. of straw. (Jour. of Bath and West of Eng. Ag.Soc., XV1,214.) The wheat experiments show the natural capacity of — the Rothamstead soil for producing that cereal, and de- meonstrate that those matters which are annually removed by a crop of 164 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, Holkham in Nor- folk, and Rodmersham in Kent, the experiments extending over periods of 8, 3, and 4 years, respectively, shows that these soils were, for the wheat crop, rela- tively deficient in assimilable nitrogen. The crop on the unmanured soil was therefore a measure of nitrification rather than of mineral disintegration. na | \ REVIEW AND CONCLUSION. 373 that this native power of producing wheat will last unim- paired for years, or, perhaps, centuries, provided the depth of the soil is sufficient. In time, however, the silicates and other compounds whose disintegration supplies alka- lies, phosphates, etc., must become relatively less in quan- tity compared with the quite inert quartz and alumina- silicates which cannot in any way feed plants. Then the crop will fall off, and ultimately, if sufficient time be al- lowed, the soil will be reduced to sterility. Other things being equal, this natural and durable pro- ductive power is of course greatest in those soils which contain and annually supply the largest proportions of plant-food from their entire mass, those which to the great- est extent originated from good soil-making nfaterials. Soils formed from nearly pure quartz, from mere chalk, or from serpentine (silicate of magnesia), are among those least capable of maintaining a supply of food to crops. These poor soils are often indeed fairly productive for a few years when first cleared from the forests or marshes; but this temporary fertility is due to a natural manuring, the accumulation of vegetable remains on the surface, which contains but enough nutriment for a few crops and wastes rapidly under tillage. Exhaustion of the Soil in the language of Practice has a relative meaning, and signifies a reduction of producing power below the point of remuneration. A soil is said to 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 ‘ S74 HOW CROPS FEED. point of remuneration, but the sterility thus induced is of a kind that easily y ‘elds to rest or other meliorating agen- cies, and is far from resembling in its permanence that which depends upon original poverty of constitution. Significance of the Absorptive Quality.—Disintegration and nitrification would lead to a waste of the resources of fertility, were it not for the conserving effect of those physical absorptions and chemical combinations and re- placements which have been described. The two least abundant ash-ingredients, viz., potash and phosphoric acid, if liberated by the weathering of the soil in the form of phosphate of potash, would suffer speedy removal did not the soil itself fix them both in combinations, which are at once so soluble that, while they best serve as plant-food, they cannot ordinarily accumulate in quantities destruct- ive to vegetation, and so insoluble that the rain-fall cannot wash them off into the ocean. The salts that are abundant in springs, rivers, and seas, are 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-- able salt, enters somewhat into nearly insoluble combina- | tion and liberates a corresponding quantity of other bases. “The great bencficent law regulating these absorptions appears to admit of the following expression: those bodies which are most rare and precious to the growing plant are REVIEW AND CONCLUSION. 37D by the soil converted into, and retained in, a condition not of absolute, but of relative insolubility, and are kept avaitl- able to the plant by the continual circulation in the soil of the more abundant saline matters. “ The soil (speaking in the widest sense) is then not only the ultimate exhaustless source of mineral (fixed) food, to vegetation, but it is the storehouse and conservatory of this food, protecting its own resources from waste and from too rapid use, and converting the highly soluble matters of animal exuvie 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 American Journal of Science and Arts, May, 1859, (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. 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Contents:—Natural History.—History of Cultivation.—Choice of Location.—Preparing the Ground.—-Planting the Vines.—Manage- ment of Meadows.—Flooding.—Enemies and Difficulties Overcome. —Picking.—Keeping.—Profit and Loss.—Letters from Practical Growers.—Insects Injurious to the Cranberry. By Joseph J. White, a practical grower. Illustrated. Cloth,12mo. New and revised edition. ~ 1.25 Fuller’s Practical Forestey. A Treatise on the Propagation, Planting and Cultivation, with a description and the botanical and proper names of all the indigen- ous trees of the United States, both Evergreen and Deciduous, with Notes on a large number of the most valuable Exotic Species. By Andrew S. Fuller, author of “Grape Culturist,” “Small Fruit Cul- turist,” ete. 1.56 Stewart’s Irrigation for the Farm, Garden and Orchard. This work is offered to those American Farmers and other cultiva- tors of the soil who, from painful experience, can readily appre- ciate the losses which result from the scarcity of water at critical periods. By Henry Stewart. Fully illustrated. Cloth,]2mo. 1.50 Quinn’s Money in the Garden. By P. T. Quinn. The author gives in a plain, practical style, in- structions on three distinct, although closely connected branches of gardening—the kitchen garden, market garden, and field culture, from successful practical experience for a term of years. Ilustra- ted. Cloth, 12mo. 1.50 (Gee & STANDARD BOOKS. . % Roe’s Play and Profit in My Garden. By E. P. Roe. The author takes us to his garden on the rocky hill- sides in the vicinity of West Point, and shows us how out of it, after four years’ experience, he evoked a profit of $1,000, and ‘this while carrying on pastoral and literary labor. It is very rarely that so much literary taste and skill are mated to so much agri- cultural experience and good sense. Cloth, 12mo. 1.50 The New Onion Culture. By T. Greiner. This new work is written by one of our most suc- cessful agriculturists, and is full of new, original, and highly valu- able matter of material interest to every one who raises onions in the family garden, or by the acre for market. By the process here . described a crop of 2000 bushels per acre can be as easily raised as 500 or 600 bushels in the old way. Paper, 12mo. .50 The Dairyman’s Manual. By Henry Stewart, author of “The Shepherd’s Manual,” ‘Irriga- tion,’ etc. A useful and practical work, by a writer who is well known as thoroughly familiar with the subject of which he writes. Cloth, 12mo. 2.00 Allen’s American Cattle. Their History, Breeding and Management. By Lewis F. Allen. This book will be considered indispensable by every breeder of live stock. The large experience of the author in improving the character of American herds adds to the weight of his observations and has enabled him to produce a work which will at once make good his claims as a standard authority on the subject. New and revised edition. Illustrated. Cloth, 12mo. 2.50 Profits in Poultry. Useful and ornamental Breeds and their Profitable Management. © This excellent work contains the combined experience of a num- ber of practical men in all departments of poultry raising. It is profusely illustrated and forms a unique and important addition to our poultry literature. Cloth, 12mo. 1.00 The American Standard of Perfection. The recognized standard work on Poultry in this country, adopted by the American Poultry Association. It contains a complete de- scription of all the recognized varieties of fowls, including turkeys, ducks and geese; gives instructions to judyzes; glossary of technical terms and nomenclature. It contains 244 pages, handsomely bound in cloth, embellished with title in gold on front cover. $1.00 Stoddard’s An Egg Farm. By H. H. Stoddard. The management of poultry in large numbers, being a series of articles written for the AMERICAN AGRICULTUR- Ist. Dlustrated. Cloth, 12mo. pe) 8 STANDARD BOOKS, Stewart’s Shepherd’s Manual. A Valuable Practical Treatise on the Sheep for American rarmers and sheep growers. It isso plain that a farmer or a farmer’s son who has never kept a sheep, may learn fromits pages how to manage a flock successfully, and yet so complete that even the ex- perienced shepherd may gather many suggestions from it. The results of personal experience of some years with the characters - of the various modern breeds of sheep, and the sheep raising capa- bilities of many portions of our extensive territory and that of Canada—and the careful study of the diseases to which our sheep are chiefly subject, with those by which they may eventually be affiicted through unforseen accidents—as well as the methods of management called for under our circumstances, are carefully described. By Henry Stewart. Illustrated. Cloth, 12mo. 1.50 Wright’s Practical Poultry-Keeper. By L. Wright. A complete and standard guide to the management of poultry, for domestic use, the markets or exhibition. It suits at once the plain poulterer, who must make the business pay, and the chicken fancier whose taste is for gay plumage and strange, bright birds. Illustrated. Cloth, 12mo. $2.00 Harris on the Pig. New Edition. Revised and enlarged by the author. The points of the various English and American breeds are thoroughly discussed, and the great advantage of using thoroughbred males clearly shown. The work is equally valuable to the farmer who keeps but few pigs, and to the breeder on an extensive scale. By Joseph Harris. Illustrated. Cloth, 12mo. 1.50 The Farmer’s Veterinary Adviser. A guide to the Prevention and Treatment of Disease in Domestic Animals. This is one of the best works on this subject, and is es- pecially designed to supply the need of the busy American Farm- er, who can rarely avail himself of the advice of a Scientific Veter- inarian. It is brought up to date and treats of the Prevention of Disease as wellas of the Remedies. By Prof. Jas. Law. Cloth. Crown, 8vo. 3.00 Dadd’s American Cattle Doctor. By George H. Dadd, M. D., Veterinary Practitioner. To help every man to be his own cattle-doctor; giving the necessary information ~ for preserving the health and curing the diseases of oxen, cows, sheep and swine, with a great variety of original recipes, and val- uable information on farm and dairy management. Cloth, 12mo. 1.50 ‘Cattle Breeding. By Wm. Warfield. This work is by common consent the most valuable and pre-eminently practical treatise on cattle-breeding ever published in America, being the actual experience and ob- servance of a practical man. Cloth, 12mo. 2.06 ‘ s . York _ anaes Loney ph J62 An on Oi iy rater — 3 5185 5708 . el ae 7 ary Sl ein matte,