UNIVERSITY OF CALIFORNIA 
 
 LOS ANGELES 
 
 GIFT OF 
 
 U. C. Library
 
 THE 
 
 CHEMISTRY OF AGRICULTURE 
 
 FOR STUDENTS AND FARMERS 
 
 BY 
 
 CHARLES W. STODDART, PH.D. 
 
 DEAN, SCHOOL OF THE LIBERAL ARTS, PENNSYLVANIA STATE COLLEGE 
 
 SECOND EDITION, THOROUGHLY REVISED 
 ILLUSTRATED WITH 83 ENGRAVINGS AND 1 PLATE 
 
 LEA & FEBIGER 
 
 PHILADELPHIA AND NEW YORK 
 1921
 
 COPYRIGHT 
 
 LEA & FEBIGER 
 
 1921
 
 38 b 
 
 . 
 
 PREFACE TO THE SECOND EDITION 
 
 IN preparing the second edition some changes have been 
 made, notably the omission of the summary at the end of 
 each chapter and the addition of a list of suggestive exercises 
 designed to make the student think. The subject-matter 
 presented in the text can, in this way, be brought more 
 forcefully to the attention of the reader and the facts applied 
 to practical conditions. There have also been added sections 
 on new fertilizer materials, showing the development of 
 our own potash resources as a result of the Great War, and 
 also of synthetic nitrogenous fertilizers. 
 
 More material has been inserted where it seemed desirable; 
 parts have been rewritten to make the subject clearer; and 
 an attempt has been made to eliminate errors that crept into 
 the first edition. The order of the first three chapters has 
 been changed to facilitate the teaching of the subject- 
 matter. 
 
 The questions at the end of the chapters, many criticisms, 
 and some of the additional material have been the work of 
 Professor M. W. Lisse. To him the author wishes to express 
 his gratitude and esteem. 
 
 C. W. S. 
 STATE COLLEGE, PA. 
 
 (v) 
 
 480546
 
 PREFACE TO THE FIRST EDITION 
 
 THERE is at present need for a text on general agricultural 
 chemistry which will cover the field briefly, in a logical 
 manner, giving only the facts, and not consisting of a dis- 
 connected series of quotations and tables from the very 
 extended literature of the subject. The need for such a 
 text has been particularly marked in teaching large classes 
 of students at The Pennsylvania State College. As a con- 
 sequence the present book has been written. While it is 
 intended primarily for students who have had previous 
 training in Botany, Chemistry, Geology and Physics, it is 
 sufficiently elementary to make it of value to any intelligent 
 person. 
 
 Concerning some of the statements made in the text it 
 is well known that a difference of opinion exists among 
 authorities, but it is deemed better to present them as facts 
 rather than to give the various arguments or to omit them 
 altogether. 
 
 Since the raising of crop plants is the fundamental business 
 of agriculture, and since on them depend the life and growth 
 of animals, there is discussed first the plant, its germination, 
 growth, and products. Then are taken up the various 
 conditions necessary for plant growth, such as the atmos- 
 phere, soil, fertilizers, and spray materials. A short chapter 
 on the gas engine is inserted at this point, since the increasing 
 use of power on the farm in the raising and marketing of 
 
 (vii)
 
 Vlll PREFACE TO THE FIRST EDITION 
 
 crops makes some knowledge of the chemistry of gasoline 
 and carburetion important. Finally the animal is considered, 
 together with its food, digestion, and products. 
 
 The references at the end of each chapter give the principal 
 sources of information used in the preparation of this text. 
 While the lists are by no means complete, they will be of 
 help for any who desire to pursue the subject further. 
 
 The thanks of the author are due to the German Kali 
 Works, "La Hacienda," Great Western Sugar Co., Economy 
 Silo and Manufacturing Co., Chilean Nitrate Propaganda, 
 American Coal Products Co., C. Tennant Sons & Co., 
 American Cyanamid Co., and the Avery Co., for many 
 of the illustrations. Particularly is the author indebted 
 to Dr. M. B. MacDonald, Mr. F. P. Weaver, and Mr. 
 R. U. Blasingame for helpful suggestions, and to Messrs. 
 C. A. Smith and E. DeTurk for some of the drawings* 
 
 C. W. S. 
 STATE COLLEGE, PA.
 
 CONTENTS 
 
 PART I 
 THE PLANT 
 
 CHAPTER I 
 PLANT COMPOUNDS 17 
 
 CHAPTER II 
 GERMINATION OF THE SEED 72 
 
 CHAPTER III 
 GROWTH OF THE PLANT 80 
 
 CHAPTER IV 
 CROPS 102 
 
 PART II 
 FACTORS IN PLANT GROWTH 
 
 CHAPTER V 
 THE AIR 125 
 
 CHAPTER VI 
 THE SOIL: ORGANIC MATTER 132 
 
 CHAPTER VII 
 THE SOIL: INORGANIC MATTER 153 
 
 CHAPTER VIII 
 
 FERTILIZERS 186 
 
 (ix)
 
 x CONTENTS 
 
 CHAPTER IX 
 NITROGENOUS FERTILIZERS 192 
 
 CHAPTER X 
 PHOSPHATE FERTILIZERS 206 
 
 CHAPTER XI 
 POTASH FERTILIZERS 216 
 
 CHAPTER XII 
 LIME 224 
 
 CHAPTER XIII 
 FARM MANURE 241 
 
 CHAPTER XIV 
 
 SOIL AND FERTILIZER ANALYSIS 256 
 
 CHAPTER XV 
 INSECTICIDES AND FUNGICIDES 264 
 
 CHAPTER XVI 
 
 THE GAS ENGINE . 279 
 
 PART III 
 THE ANIMAL 
 
 CHAPTER XVII 
 THE CHEMISTRY OF ANIMAL PHYSIOLOGY 287 
 
 CHAPTER XVIII 
 FOOD AND DIGESTION 304 
 
 CHAPTER XIX 
 MILK AND DAIRY PRODUCTS , 318
 
 THE CHEMISTRY OF AGRICULTURE 
 
 PART I 
 
 THE PLANT 
 
 CHAPTER I 
 PLANT COMPOUNDS 
 
 THERE are a very large number of organic compounds 
 produced during the growth of plants. Some plants form 
 one kind, some another. Many of the compounds have no 
 value commercially, and no known value physiologically. 
 Some are evidently merely by-products, whereas others 
 undoubtedly serve some useful purpose to the plant. Since 
 many of these compounds are of great importance to the 
 human race, it is necessary to know something of their proper- 
 ties and uses outside of the plant. In the following discussion 
 only those plant compounds which are of known physiological 
 importance to the plant, and particularly those which are of 
 economic importance to mankind, will be considered. For 
 convenience the various compounds will be grouped as 
 follows : 
 
 I. Carbohydrates 
 II. Fixed Oils and Waxes 
 
 III. Volatile Oils and Resins 
 
 IV. Nitrogenous Compounds 
 
 V. Organic Acids and their Salts 
 2 (17)
 
 18 PLANT COMPOUNDS 
 
 I. CARBOHYDRATES 
 
 1. General Definition. The most abundant group of 
 organic compounds is that of the carbohydrates or sac- 
 charides, comprising about 75 per cent, of the dry matter 
 of plants. Popularly, a carbohydrate is defined as a com- 
 pound containing carbon, hydrogen, and oxygen, with the 
 hydrogen and oxygen in the same proportion as in water; 
 or, a compound of carbon and water, thus: Dextrose = 
 6C+6H 2 O. This definition, while not exactly correct, will 
 hold in a majority of cases and serves very well to dis- 
 tinguish the group. The exceptions to this statement are 
 principally acetic acid, whose empirical formula is C2H 4 O2, 
 but whose graphic formula is CH 3 COOH, showing the acid 
 or carboxyl group; and lactic acid, C 3 H 6 3 , but otherwise 
 written CH 3 .CHOH.COOH. 
 
 A carbohydrate may be defined more accurately as a 
 compound containing always one or more hydroxyl (OH) 
 groups, and usually either an aldehyde 
 
 H o 
 
 II , I II I 
 
 ( c c=O) orketone ( c c C ) group. 
 
 I I I 
 
 The presence of the aldehyde group indicates that the 
 carbohydrate is easily oxidized, whereas the presence of the 
 ketone group usually, though not always, indicates that the 
 carbohydrate is not easily oxidized. The principal carbo- 
 hydrates contain carbon atoms to the number of six or a 
 multiple of six. The carbohydrates are divided into two 
 general classes, the Sugars including the monosaccharides 
 and disaccharides; and the Non-Sugars or Polysaccharides. 
 
 2. Sugars. As a class the sugars are colorless, odor- 
 less, crystalline compounds, soluble in water, and, ordinarily, 
 sweet in taste. Their most characteristic property is that 
 of optical activity, that is, they rotate the plane of polarized
 
 CARBOHYDRATES 19 
 
 light either to the right or to the left. 1 The simple sugars, 
 or monosaccharides, contain from two to nine carbon atoms, 
 and are named according to the number of carbon atoms in 
 the molecule: Dioses, trioses, tetroses, etc. Each molecule 
 consists of a single "sugar" group of atoms. The only 
 important monosaccharides are the hexoses, or sugars con- 
 taining six carbon atoms, CeH^Oe. Dextrose and levulose 
 are the best examples of hexoses. The disacckarides are 
 formed by the condensation of two molecules of a monosac- 
 charide with the elimination of one molecule of water. Each 
 molecule of a disaccharide, then, consists of two single 
 "sugar" groups of atoms. Sucrose and maltose are the 
 principle disaccharides found in plants. 
 
 1 Optical Activity : An ordinary ray of light is supposed to consist of 
 particles vibrating in every direction at right angles to the direction of the 
 ray. When such a ray is passed through a properly cut crystal of Iceland 
 spar called a Nicol prism, it is separated into two rays, one of which is 
 reflected out to one side of the prism, and the other passes through, its 
 particles now vibrating in only one plane. This ray is said to be polarized, 
 and substances which have the power of rotating this plane of polarized 
 light in one direction or the other are said to be optically active, either 
 dextrorotatory ( +) or levorotatory ( ) as they turn the plane of polarized 
 light to the right or to the left. The amount of rotation depends on the 
 specific property of the substance and the number of molecules through 
 which the light passes. The amount of rotation can be measured, and by 
 calculation the percentage composition of sugar or other substance can be 
 determined in a solution. The instrument for measuring the amount of 
 rotation is called a polariscope, or, since it is used mostly for the determina- 
 tion of sugar, a saccharimeter. It consists essentially of a tube containing 
 at one end a polarizing prism which polarizes a ray of light from some source, 
 and an analyzing prism at the other end mounted on a revolving disk gradu- 
 ated into degrees. Between the two prisms is a trough in which may be 
 placed a tube, closed at both ends with glass, containing the solution to be 
 examined. The polarized light if undisturbed passes through the analyzer 
 and illuminates the field of vision through an eye-piece. If the ray is rotated 
 by an optically active substance, the light does not pass through the analyzer 
 and the field of vision is darkened. If the analyzer is now rotated to the right 
 or left, as the case may be, just as much as the substance rotates the polarized 
 ray, the field of vision, will again be brightly illuminated. There are many 
 modifications of this polariscope tending to increase the accuracy of obser- 
 vation, but the principle is the same in all of the instruments. For com- 
 paring the rotatory power of different substances, there is used the term 
 specific rotation which is the amount of dextro- or levorotation of plane 
 polarized sodium light caused by a solution 10 cm. long, each cubic centi- 
 meter of which contains one gram of substance, at a temperature of 20 C.
 
 20 
 
 3. Dextrose, Glucose, Grape Sugar. CeH^Oe, graphically: 
 
 H 
 
 H C O H 
 
 This constitutes what may be termed a single "sugar" 
 group of atoms, hence, monosaccharide. It is found free in 
 nature in all parts of the plant, but for the most part it occurs 
 associated with an equal quantity of levulose in such sweet 
 fruits as grapes, cherries, and pears. It is also found in 
 onions. Dextrose occurs in glucosides 1 in combination with 
 different kinds of compounds such as alcohols, acids, and 
 aldehydes, which hydrolyze naturally under the action of 
 enzymes to form glucose and the other compounds. It is 
 formed in nature (Section 62) by the condensation of for- 
 maldehyde in the leaf, and by hydrolytic enzyme (Section 
 46) action on such storage forms of carbohydrates as starch 
 and sucrose (Section 63). 
 
 1 The formation of a glucoside can best be seen from a graphic formula: 
 H H 
 
 H C O H H C O H 
 
 I I 
 
 H C O H H C O H 
 
 H C O H + H 
 H C O H 
 H C O H 
 
 H C 
 
 = 
 
 O R = H C 1 + H 2 O 
 
 O R 
 
 R represents the alkyl group of an alcohol, acid, aldehyde, or ketone.
 
 CARBOHYDRATES 21 
 
 Physiologically dextrose is the usual transport form of 
 carbohydrates, but occasionally it is the storage form, as in 
 the onion. Dextrose is a nearly white solid, easily soluble 
 in water and in hot alcohol, insoluble in ether, crystallizes 
 as a hydrate, CeH^Oe.I^O, from water, and in the dehydrated 
 form from alcohol (Fig. 1). It is not as sweet as ordinary 
 sugar. It is dextrorotatory, from which fact it gets the name 
 
 Fro. 1. Crystals of anhydrous dextrose. Magnified. Drawing l>y 
 C. A. Smith. 
 
 dextrose, "right sugar." The specif c rotation of ordinary 
 dextrose is +52.5. Since it contains the aldehyde group 
 it is easily oxidized to various compounds. This oxidation is 
 measured by the equivalent reduction of what is called 
 Fehling's solution 1 and this reduction of Fehling's solution 
 is a characteristic reaction for dextrose. Dextrose also 
 
 1 Fehling's solution is made by mixing equal parts of a solution of copper 
 sulphate with a solution of sodium potassium (artrate (Rochelle salts) 
 in sodium hydroxide. The sodium hydroxide forms copper hydroxide which 
 dissolves to a deep blue color in the sodium potassium tartrate. The copper 
 hydroxide in solution is the reacting compound. It is reduced according 
 to the following equation: 
 
 4 Cu(OH)a = 4 CuOH + 2 H 2 O + Oj. 
 
 On boiling the solution the yellow cuprous hydroxide, 4 CuOH, changes 
 to the brick red cuprous oxide and water, CmO+HaO. The amount of 
 red precipitate is a measure of the amount of dextrose in solution.
 
 22 PLANT COMPOUNDS 
 
 unites with calcium hydroxide and barium hydroxide to 
 form compounds which might be called "dextrates" or 
 "dextroxides," C 6 HiiO 6 .CaOH and CeHnOe.BaOH. 1 They 
 are soluble in water but insoluble in alcohol. Dextrose 
 is easily changed, or fermented, by fungi and bacteria to 
 alcohol and carbon dioxide, as follows: CeH^Oe = 2C 2 H 5 OH 
 + 2CO 2 ; to lactic acid, as follows: C 6 H 12 O 6 = 2CH 3 .CHOH.- 
 COOH; and to butyric acid, carbon dioxide, and hydrogen, 
 as follows: C 6 H 12 O 6 = CH 3 .CH 2 .CH 2 .COOH + 2CO 2 + 2H 2 . 
 Pure dextrose can be made by the hydrolysis of starch or 
 sucrose with dilute hydrochloric acid, and recrystallization 
 from hot alcohol. Commercial glucose is made in this country 
 by boiling cornstarch under pressure with hydrochloric acid, 
 neutralizing the acid with sodium carbonate, and clarifying 
 the liquid with bone charcoal. The product is sold as a thick, 
 amber-colored liquid containing 30 to 40 per cent, of dextrose, 
 the rest being dextrins and other impurities. By boiling the 
 mass longer more dextrins are converted to dextrose and a 
 crystallizable product containing 70 to 80 per cent, dextrose 
 is obtained. Glucose is used largely in making candy, 
 jellies, preserves, table syrup, etc. 
 
 1 Their formation can be best illustrated graphically. The exact location 
 of the hydroxyl group which combines with the base is not known, but the 
 one chosen will at least illustrate the reaction : 
 
 H H 
 
 I I 
 
 H C O H H C O H 
 
 H C O H H C O H + H.O 
 
 H C O H = H C O H 
 
 I I 
 
 H C O H H C O H 
 
 H C O+H + H O v H C O Ca O H 
 
 I \/ 
 
 I I >Ca 
 
 H C=O H O/ H C=O
 
 CARBOHYDRATES 23 
 
 4. Levulose, Fructose, Fruit Sugar. CeH^Oj, graphically: 
 
 This constitutes another single "sugar" group of atoms. 
 Levulose is found in plants, particularly the sweet fruits, 
 and nearly always with dextrose. Honey is almost wholly 
 a mixture of levulose and dextrose. Levulose is formed 
 naturally by the enzyme hydrolysis of sucrose, or arti- 
 ficially by hydrolysis of sucrose with dilute hydrochloric 
 acid. In either case there are produced equal quantities 
 of dextrose and levulose. Physiologically it probably plays 
 the same role as dextrose. Levulose is a white solid, crystal- 
 lizable with considerable difficulty, very soluble in water 
 and in hot alcohol. It is much more strongly levorotatory 
 than dextrose is dextrorotatory, the specific rotation being 
 92.5. Hence it is called levulose, "left sugar." It is 
 sweeter than dextrose. Although it does not contain an 
 aldehyde group it is easily oxidized, that is, it reduces 
 Fehling's solution. Levulose forms compounds with calcium 
 hydroxide and barium hydroxide "levulates" insoluble in 
 water and in alcohol. It is fermented by fungi and bacteria 
 like dextrose. One way to make it is to boil sucrose with 
 hydrochloric acid and thereby change the sucrose to dextrose 
 and levulose. On treating the cold solution with an excess 
 of calcium hydroxide, the crystals of calcium levulate 
 are precipitated and can be filtered. On decomposing the 
 precipitate with oxalic acid, and concentrating the filtered 
 solution, levulose will crystallize out. Aside from its use
 
 24 PLANT COMPOUNDS 
 
 as a food in fruit and honey, where it occurs naturally, 
 levulose has no economic importance. 
 
 5. Sucrose, Saccharose, Cane Sugar. C^H^On, graphi- 
 cally: 
 
 H 
 
 H ( 
 H ( 
 Hf 
 
 3 H H 
 
 : o H H c o H 
 
 1 
 
 - f) TT n r\ 
 
 H ( 
 
 3 O H 
 
 H C O H 
 
 H C O H 
 TT C" C 
 
 H C O H 
 > r. 
 
 H C O H 
 
 This constitutes a double "sugar" group of atoms or the 
 union of two single groups. Hence it is a disaccharide. It 
 is very widely distributed in plants, being found particularly 
 in sweet fruits, stalks of corn and sugar cane, in seeds, roots, 
 bulbs, and the sap of maple, birch, and other trees. Sugar 
 cane and sugar beets are the principal sources of sucrose, 
 the former containing about 20 per cent., the latter, 15 
 per cent. Fig. 2 illustrates the harvesting of a crop of 
 sugar cane, and Fig. 2 a growing crop of sugar beets. 
 From the physiological point of view, sucrose is a storage 
 form of carbohydrates, particularly in roots and tubers such 
 as beets and sweet potatoes, it being formed in all proba- 
 bility by a condensation of dextrose and the elimination of 
 water. 
 
 Sucrose is a colorless solid, crystallizing in large, clear crys- 
 tals (Fig. 3). As it is usually purchased, it consists of very 
 small crystals, the mass of which appears white because 
 of reflected light. It is easily soluble in water, slightly 
 soluble in hot absolute alcohol, more easily soluble in dilute 
 alcohol, insoluble in ether and in cold absolute alcohol. It 
 is dextrorotatory, the specific rotation being +66.5. Its 
 sweetness is too well known to need description.
 
 CARBOHYDRATES 
 
 25 
 
 =
 
 26 PLANT COMPOUNDS 
 
 Sucrose does not reduce Fehling's solution, that is, it is 
 not easily oxidized. It melts at about 160 C. From 170 
 up to 190 C. it decomposes, by losing water, to a mixture 
 of unknown condensation products, the mass turning brown 
 in color and having a peculiar, agreeable flavor. Caramel 
 is the name given to the material. Caramel is soluble in 
 water, reduces Fehling's solution, and is used to a large 
 extent as flavoring for candy and ice-cream. 
 
 FIG. 3. Crystal of sucrose. Natural size. Drawing by C. A. Smith. 
 
 Under the action of an enzyme (Section 46) called inver- 
 tase, sucrose hydrolyzes to equal parts of dextrose and levu- 
 lose. 1 This is the way it changes naturally in plants. Arti- 
 
 1 The hydrolytic change of sucrose into equal parts of levulose and dex- 
 trose is shown best by the graphic formula, and illustrates very well the 
 glucoside-like character of the sucrose molecule. (See footnote on p"age 20.) 
 In fact it may be considered a " levulo-glucoside, " or "levulin. " 
 H H 
 
 I I 
 
 H H C O H H 
 
 H O C H H C O H H O C H 
 O C H H C O H H O C H 
 
 H O C H = H C O H + H O C H 
 H O C H H C O H H O C H 
 C H C=O O=C 
 
 H O C H H O C H 
 
 I I 
 
 H H 
 
 Sucrose. Dextrose. Levulose. 
 The hydrogen and oxygen of water enter the sucrose molecule as indi- 
 cated by the heavy letters, and the molecules of dextrose and levulose 
 result.
 
 CARBOHYDRATES 27 
 
 ficially, sucrose can be hydrolyzed by boiling with a dilute 
 mineral acid like hydrochloric, the products of this acid 
 hydrolysis being the same as with invertase. The mixture of 
 levulose and dextrose thus produced is known as invert sugar, 
 because the levorotatory power of levulose is greater than the 
 dextrorotatory power of dextrose, the net result being levo- 
 rotation. The specific rotation of invert sugar is 20 V 
 Fungi and bacteria containing invertase change sucrose to 
 dextrose and levulose, and can then ferment to the usual 
 products of alcohol, carbon dioxide, etc. It is not directly 
 fermentable in most cases. 
 
 With alkalies and alkaline earths sucrose forms saccha- 
 rates, or "sucroxides," those of calcium being the most im- 
 portant. There are three compounds with calcium : Mono- 
 calcium saccharate, Ci 2 H 2 iOu.CaOH; dicalcium saccharate, 
 Ci2H 2 oOn.2CaOH; tricalcium saccharate, C^HigOu.SCaOH. 
 The monocalcium compound is readily soluble in water, the 
 tricalcium compound difficultly soluble. The latter is used 
 commerically in the separation of sucrose from beet molasses. 
 The molasses is treated with freshly burned lime. The 
 resulting precipitate of tricalcium saccharate is filtered, 
 washed with cold water and decomposed by carbon dioxide 
 in aqueous suspension. The reaction is as follows: 
 
 C^HnOn.SCaOH + 3COj = ciiHaOu + 3CaCO 3 . 
 
 Many other saccharates are also formed, such as those of 
 iron, aluminium, nickel, and copper. Those of iron are used 
 medicinally. 
 
 Pure sucrose is prepared by precipitating it from a solu- 
 tion of commercial sucrose with cold, absolute alcohol, and 
 
 1 The specific rotation of levulose is 92.5 and of dextrose is + 52.5, but 
 that of invert sugar is not 40, but 20, since specific rotation is the 
 angular rotation of a column 10 centimeters long which contains 1 gram of 
 substance in 1 cubic centimeter (footnote p. 19), and 1 gram of invert 
 sugar consists of i gram of dextrose and J gram of levulose, thus giving 
 only $ the angular difference between the specific rotations of levulose and 
 dextrose.
 
 28 
 
 PLANT COMPOUNDS 
 
 washing the fine crystals with absolute alcohol. Commercial 
 sucrose is made from sugar cane by squeezing out the juice 
 in mills, clarifying with lime to remove impurities, evapo- 
 rating the filtrate, and finally crystallizing out the sucrose. 
 Fig. 4 shows the interior of a sugar factory where the cane 
 juice is being evaporated. Further solution, treatment 
 with lime and bone black, and recrystallization yields the 
 pure granular sugar (sucrose) of commerce. Brown sugar 
 
 FIG. 4. Boiling cane juice in a sugar factory at Guadaloupe. 
 
 is obtained by evaporating to dryness the mother liquor 
 from which no sucrose will crystallize. Brown sugar origin- 
 ally contained some caramel because the evaporation of the 
 syrup was carried on in vats heated by a free flame, and part 
 of the material, being overheated, caramelized. Modern 
 evaporators are steam-heated vacuum pans, and thus 
 caramelization is avoided. 
 
 From the sugar beet, sucrose is made by slicing the beets 
 and soaking them in water, thus allowing the sucrose to
 
 CARBOHYDRATES 29 
 
 diffuse gradually out of the beet cells. The concentrated 
 juice is clarified and purified much as in the case of sugar 
 cane juice. Beet sugar is exactly the same as cane sugar, 
 although when first made methods of purification were not 
 perfect, and the admixed impurities made its quality poorer 
 than that of cane sugar. 
 
 The various uses of cane sugar are too well known to 
 need description. 
 
 6. Maltose, Maltobiose, Malt Sugar. Ci^H^On, graphi- 
 cally : 
 
 This constitutes another double "sugar" group. It is 
 one of the most widely distributed sugars in plants, but 
 since it is never a storage form of carbohydrates it is not 
 found in any quantity, as are the other sugars. It is one 
 of the transition forms from starch to dextrose, and is 
 formed to a large extent in the germinating seed (Section 47). 
 Of itself, however, it may serve as a transport form of 
 carbohydrate without undergoing a change to dextrose. 
 It is a white, crystalline solid, readily soluble in water; 
 slightly soluble in cold alcohol; not as sweet as sucrose. 
 It is dextrorotatory, the specific rotation being +138. 
 Maltose reduces Fehling's solution, since it belongs to the 
 aldehyde group. Under the action of an enzyme called mal- 
 tase, it is hydrolyzed to dextrose, one molecule of maltose
 
 30 PLANT COMPOUNDS 
 
 breaking up into two molecules of dextrose. 1 It is also 
 hydrolyzed to dextrose on boiling with a dilute mineral acid 
 like hydrochloric. Maltose ferments only as it is hydro- 
 lyzed to dextrose by enzymes (Section 46) in the fungi and 
 bacteria. It forms compounds with alkalies and alkaline 
 earths, but they are of no importance. 
 
 Maltose is prepared by treating starch paste with malt 
 extract (Section 47) at 60 C., and extracting the maltose thus 
 formed with successive portions of hot 87 per cent, alcohol, 
 finally evaporating and allowing it to crystallize. It is 
 recrystallized from hot methyl alcohol, after purifying with 
 bone black. 
 
 Commercially it occurs in malt and malt products which 
 are made from germinating barley (Section 96, a). It also 
 occurs mixed with dextrin (Section 8) as a thick syrup or 
 solid. In a rather pure form as a syrup it is used to some 
 extent as a substitute for cane sugar, particularly during the 
 shortage of sugar caused by the Great War. 
 
 7. Non-sugars or Polysaccharides. These compounds are 
 usually colorless or white, odorless, and amorphous, with 
 little or no taste, and insoluble in water and in alcohol. 
 They are formed by the condensation of a great many 
 molecules of a monosaccharide with the elimination of 
 water, thus: 
 
 n C6Hi 2 O n H 2 O = (C 6 HioO 6 ) n. 
 
 1 As in the case of sucrose this hydrolytic change shows the glucoside-like 
 character of maltose, it being a " gluco-glucoside, " or "glucolin." Thus: 
 H H 
 
 H C O H O=C H H C O H 0=C H 
 
 I I I I 
 
 H C O H H O C H H C O H H O C H 
 
 H C O 1 H O C H = H C O H + H O C H 
 
 I I I 
 
 H O C H H C O H H O C H 
 
 I I I 
 
 H O C H H C O H H O C H 
 
 C H H C=O H O C H 
 
 H H 
 
 Maltose Dextrose Dextrose
 
 CARBOHYDRATES 31 
 
 Each molecule consists of a large number of single "sugar" 
 groups. Starch and cellulose are the principal polysac- 
 charides. 
 
 8. Starch. (CeHioOs)^?). The exact graphic formula 
 is not known. Starch occurs in all parts of the plant as 
 a storage form of carbohydrate material, being a condensed 
 anhydride, and insoluble. It occurs to a great extent in 
 seeds and tubers as follows: 
 
 Approximate per cent. 
 Crops. starch. 
 
 Corn .... 62 
 
 Wheat 64 
 
 Oats 54 
 
 Rice 70 
 
 Potatoes . 20 
 
 Starch occurs in plant cells in the form of very small, 
 white grains, the size and shape of which vary with the 
 plant which manufactures it. Figs. 5 to 9 show various 
 kinds of starch grains, and it is to be noted that those of the 
 potato are comparatively large, while those of rice are very 
 small. The size varies from about 0.002 mm. to 0.2 mm. in 
 diameter. These grains are composed of very thin cellulose 
 walls, with contents of powdery material called granulose 
 or amylose. They are insoluble in cold water, alcohol, and 
 ether, but on treatment with boiling water the cellulose 
 envelope ruptures and the escaping granulose dissolves 
 in the water to form a more or less gelatinous solution, 
 slightly cloudy from the insoluble cellulose walls. This 
 semisolution is called starch paste. It is strongly dextro- 
 rotatory, and will not reduce Fehling's solution. Its most 
 characteristic reaction is to turn blue in the cold with a 
 solution of iodine (in alcohol or potassium iodide). The 
 compound formed is supposed to be (C24H4oO2<J)4.HI, which 
 breaks up on heating, but which reforms again when the 
 solution is cooled down. 
 
 Under the action of enzymes (Section 46), diastase for 
 example, starch hydrolyzes to maltose (Section 6), thus: 
 
 2(CHioO 6 )n + nH 2 O
 
 32 
 
 PLANT COMPOUNDS 
 
 In so doing, however, it passes through a series of hydro- 
 lytic compounds, named successively: Amylodextrin, colored 
 
 FIG. 5. Potato starch. 
 
 FIG. 6. Wheat starch.
 
 CARBOHYDRATES 
 
 33 
 
 blue by iodine; erythrodextrin, colored red by iodine; achro- 
 odextrin, not colored by iodine; maltodextrin, not colored 
 
 FIG. 8. Oat starch.
 
 34 
 
 PLANT COMPOUNDS 
 
 by iodine; maltose, not colored by iodine. These various 
 dextrins differ from starch in containing a smaller number of 
 CeHioOg groups in their molecules. They are colorless, 
 soluble in water to a gelatinous consistency, and dextro- 
 rotatory. They can also be made from starch by roasting 
 it in ovens with about 0.2 per cent, nitric acid to 110-170 
 C., and dissolving out the so-called Dextrin or British Gum, 
 which is used in the textile industries for thickening colors, 
 as mucilage on stamps, envelopes, etc. 
 
 FIG. 9. Rice starch. 
 
 FIGS. 5 to 9. Starch grains. Bureau of Chemistry, United States 
 Department of Agriculture. 
 
 On boiling starch with mineral acids such as hydrochloric 
 or sulphuric, the same hydrolytic changes take place except 
 that maltose is still further changed into dextrose. If starch 
 is treated with cold, dilute hydrochloric acid it is changed 
 to a substance called soluble starch, which is probably amylo- 
 dextrin, the first compound formed in the hydrolysis of starch. 
 It is soluble in water and colored blue by iodine. 
 
 Commercial starch is prepared from corn by grinding 
 and separating the starch from the other material by gravity
 
 CA RBOH YDRA TES 35 
 
 in water; from potatoes by scraping or pulping, filtering 
 off the fiber, and washing to separate the starch. It is used 
 for a great variety of purposes, such as for food in pud- 
 dings, for laundry work, for sizing in paper and textiles, 
 for cosmetics, etc. 
 
 9. Cellulose. (C 6 HioO 6 )n (n greater than 200). The graphic 
 formula is not well understood, but the following has been 
 assigned to it as the unit group which occurs a large 
 number of times: 
 
 H O H H O H 
 
 \ / \ / 
 
 C C H 
 
 O = C C 
 
 \ / \ 
 
 C C H 
 
 / \ / \ 
 
 H O H H O H 
 
 Cellulose comprises about one-half of the dry matter of 
 plants. 1 It forms their framework, being the chief con- 
 stituent of cell-walls and supporting fibers. Usually it 
 occurs in combination, either weakly chemical or physical, 
 with so-called "encrusting substances" derived from it, 
 such as lignin and pentosans. In the pure form it occurs 
 naturally only in the cotton plant as a mass of seed hairs, and 
 in a very few other plants. It is derived from dextrose by 
 dehydration, thus: 
 
 nCsHizO* nHjO = (CsHioOb)n. 
 
 Its function is to provide a somewhat elastic, but fairly 
 rigid envelope for plant cells. Where heavy walls are 
 needed and heavy weights are to be supported, as in trees, 
 
 1 Different plant materials contain the following approximate amount 
 of cellulose: 
 
 Per cent. 
 
 Wood 60 
 
 Straw 40 
 
 Seeds (including husks) 15 
 
 Roots , . , ... 10
 
 36 PLANT COMPOUNDS 
 
 these walls become "lignified" or thickened, filling the cell 
 almost completely. This thickened part forms the encrusting 
 substances mentioned above. 
 
 Physically, cellulose is a white, amorphous or fibrous 
 solid, insoluble without decomposition in all solvents. 
 Cuprammonium hydroxide solution (cf. Section 204, I, c), 
 called Schweitzer's reagent, dissolves cellulose to a thick, 
 viscous, dark blue liquid in which the cellulose exists as a 
 complex compound with the copper and ammonia. From 
 this solution it may be reprecipitated in the amorphous 
 form by acidification with hydrochloric or sulphuric acid. 
 A strong solution of zinc chloride in concentrated hydro- 
 chloric acid also dissolves cellulose to a complex compound 
 from which it may be recovered on treatment with alcohol. 
 Cold, concentrated sulphuric acid dissolves cellulose. In 
 so dissolving it is changed to a cellulose sulphuric acid 
 compound from which the cellulose can not be recovered. 
 On diluting such a solution and boiling it, the cellulose is 
 hydrolyzed to dextrose. 
 
 If cellulose is treated with a cold solution of sodium 
 hydroxide stronger than 10 per cent., a compound is formed 
 which has a formula something like this: CeHgOsXa. On 
 washing with water the cellulose is regenerated as the hydrate, 
 (C6HioO 5 ) 2 .H 2 O. If cotton cloth is stretched on a frame and 
 treated in this way there is obtained a cloth of silky appear- 
 ance called "mercerized cotton." The treatment results 
 in a shrinking of the cotton fibers, and a resultant gloss if 
 the cloth is kept taut during the shrinking process. 
 
 If the above mentioned soda-cellulose is treated with 
 carbon disulphide a compound is formed called "viscose," 
 
 s=c 
 \ 
 
 S Na 
 
 which is soluble in water to a viscous liquid. On spon- 
 taneous decomposition in the air, viscose loses carbon 
 disulphide and sodium hydroxide. The former disappears
 
 CARBOH YDRA TES 37 
 
 by volatilization and the latter may be washed out. A 
 hard, transparent, vitreous mass of cellulose is left. This 
 is called "viscoid" or "cellophane" and finds a variety of 
 uses. On treating cotton with nitric and sulphuric acids 
 there are obtained, according to conditions, a trinitrate 
 of cellulose, OeHioOsCNOs^, or a dinitrate of cellulose, 
 CeHioOaCNOsV The former, insoluble in alcohol and ether, 
 is known as guncotton, the explosive; the latter, soluble in 
 alcohol and ether, is called pyroxylin or soluble cotton. The 
 solution of pyroxylin in alcohol and ether is known as collo- 
 dion which finds a variety of uses in surgery as a dressing for 
 wounds, and in photography for making films. If pyroxylin 
 is intimately mixed with camphor, celluloid results. 
 
 The thick viscous solutions of cellulose in ammoniacal 
 cupric hydrate, of viscose, and of collodion, all serve as 
 materials for making artificial silk. By squeezing the thick 
 liquid through exceedingly fine holes, and winding the 
 resulting filaments into a thread, a lustrous imitation silk 
 is made after regenerating the cellulose. In the case of the 
 ammoniacal copper hydrate solution the cellulose is formed 
 by treating the threads with dilute sulphuric acid and 
 washing; in the case of viscose, by simple drying and wash- 
 ing; and in the case of collodion by denitrating with alkaline 
 sulphides. 
 
 Under proper conditions cellulose will unite with acetic 
 acid to form a tetra-acetate CeHeO^HsC^, soluble in 
 nitrobenzol. On evaporation of the solvent there is formed 
 a transparent film that is used for photographic purposes. 
 It is also a superior insulating material for electric wires. 
 
 From the above discussion it can be seen that cellulose 
 has both acid and basic properties, since it forms compounds 
 with bases like sodium and copper hydroxides, on the one 
 hand, and with nitric and acetic acids, on the other. On 
 the whole, however, it is exceedingly inert, resisting all 
 ordinary decomposition and decay. It is not fermentable. 
 It finds its chief use on account of this decay-resistant 
 property in the manufacture of rope, cotton cloth, linen 
 cloth, paper, and other articles, all of which are made of 
 cellulose from different sources.
 
 38 
 
 PLANT COMPOUNDS 
 
 Cotton fiber (Fig. 10) is the purest form of cellulose, 
 but even that must be treated with alkali, acid, alcohol, and 
 ether to remove impurities attached to it, such as proteins 
 and fats. In the case of flax used for linen, and hemp used 
 for rope, various processes are employed to free the crude 
 cellulose fibers from their encrusting substances. In making 
 paper from wood, the lignin and other impurities are dis- 
 solved away by a weak caustic soda solution (Soda Process), 
 or an acid sulphite solution (Sulphite Process). The remain- 
 ing cellulose fibers, which, by the way, are much shorter 
 
 Fio. 10. Cotton fiber. Magnified. Drawing by C. A. Smith. 
 
 than cotton and linen fibers, are sized, loaded, and matted 
 into paper of various kinds. If unsized paper, that is, 
 pure, matted, cellulose fibers, are dipped in fairly strong 
 sulphuric acid for an instant and then plunged into water, 
 the cellulose assumes a tough, parchment-like texture, and 
 is used as a substitute for sheepskin. This material is called 
 "amyloid," since it is starch-like in character, giving a blue 
 color with iodine. 
 
 10. Lignin and Pentosans. These "encrusting sub- 
 stances" are derived from cellulose apparently, but differ
 
 CA RBOH YDRA TES 39 
 
 from it in chemical composition. Lignin contains less oxygen 
 than cellulose, and in addition contains methyl (CH 3 ) groups. 
 It is soluble with decomposition in hot dilute alkali, acid 
 sulphite, and some other solvents. It is easily decomposed 
 by chlorine and bromine. It forms a large part of the woody 
 fiber of trees, and hence its name, lignin. Pentosans are 
 compounds of the general formula (CsHgO^n which are 
 hydrolyzed by acids to pentoses, CsHioOs. Xylan and araban, 
 hydrolyzing to xylose and arabinose, are examples. Pento- 
 sans form some 10 per cent, of the dry matter of coniferous 
 trees and 20 per cent, of deciduous trees. 
 
 1 1 . Inulin. (CeHioOsV This carbohydrate occurs natur- 
 ally as a storage form of carbohydrate in the roots of such 
 plants as dandelion, dahlia, and chicory. It is derived 
 undoubtedly as are the other anhydride forms of dextrose 
 by a dehydration process: GCeH^Oe 6H 2 O=(C6HioO 6 )6. It 
 is a white, crystalline substance easily soluble in water, 
 insoluble in alcohol. It does not reduce Fehling's solution, 
 and is levorotatory. It hydrolyzes under the action of 
 dilute mineral acids and of the enzyme (Section 46), inulase, 
 to levulose. It is not fermentable. 
 
 12. Gums. These are amorphous substances of unknown 
 composition, but are probably glucosides of organic acids. 
 They are soluble in \vater, or at least gelatinize in it, insoluble 
 in alcohol, and hydrolyze with acids to hexoses and pentoses. 
 Gum arable, used in making mucilage, and various wood 
 gums, are examples. 
 
 13. Pectins. Pectins are amorphous, white substances 
 found in most fruit juices, soluble in water, but insoluble 
 in alcohol. They are related to the gums and are probably 
 carbohydrates. By enzyme action (Section 46) they are 
 derived from insoluble pectose which gives hardness to unripe 
 fruit. The pectins in turn are changed to pectic acid by 
 enzymes (Section 46) as the fruit ripens, and the calcium salt 
 of pectic acid is what makes the juice of fruits like apples, 
 plums, and grapes, solidify to a jelly.
 
 40 PLANT COMPOUNDS 
 
 II. FIXED OILS AND WAXES 
 
 14. General Definition. The name oil is given to liquid 
 substances which are characterized by their slippery or 
 greasy feel, and by the fact that they leave a grease spot, 
 or permanent translucent spot on paper. These properties 
 are the same whether the oils are the so-called mineral 
 oils, hydrocarbons occurring naturally in the earth, or are 
 vegetable oils, called fixed oils or fats, or are volatile oils 
 also found in plants. 
 
 The fixed oils are always esters of glycerine and fatty acids, 
 or glycerides of fatty acids. Glycerine being a trihydric 
 alcohol can combine with one, two, or three monobasic 
 fatty acids, and most fixed oils are mixtures of compounds 
 of glycerine with more than one fatty acid. The name oil 
 usually signifies a liquid compound, fat being the name 
 usually given to a fixed oil which is solid at ordinary tempera- 
 tures. When found in plants the fixed oils are sometimes 
 called vegetable oils to distinguish them from the so-called 
 animal oils which are found in animals. The present dis- 
 cussion will be confined to fixed oils of plants, or vegetable 
 oils, although the general characteristics are the same for 
 both classes of fixed oils. 
 
 15. Properties. Fixed oils when pure are colorless or 
 pale yellow. When impure they are frequently darker in 
 color, sometimes even greenish in shade from the presence 
 of small amounts of chlorophyl. With few exceptions they 
 have no particular odor or taste. They are lighter than 
 water, their specific gravity varying from 0.875 to 0.970. 
 
 They will not distill unchanged. On heating they de- 
 compose into various compounds depending on the tem- 
 perature. They are insoluble in water and in cold alcohol, 
 somewhat soluble in hot alcohol, easily soluble in ether, 
 chloroform, carbon tetrachloride, carbon disulphide, and 
 other volatile solvents. They "saponify" on treatment with 
 alkaline hydroxides, that is, they break up into glycerine 
 and the alkaline salt of the fatty acid, called a soap (Section 
 17). They hydrolyze to glycerine and fatty acids on treat-
 
 FIXED OILS AND WAXES 41 
 
 ment with steam, and also under the influence of lipases 
 (Section 48). 
 
 They are found for the most part in the seeds of plants, 
 where they serve as reserve material for respiration, or from 
 which to make carbohydrates (Sections 48 and 71 ). Fixed oils 
 are, however, found in all living cells of plants and apparently 
 play a necessary part in the functioning of protoplasm. 
 
 The fixed oils are "drying" or "non-drying" in character. 
 That is, on exposure to the air some of them absorb oxygen 
 and harden more or less, while others remain perfectly liquid. 
 This is a property of the fatty acid radicle. The non-drying 
 oils on exposure to the air slowly become rancid, that is, 
 oxidation takes place, helped by the action of bacteria, which 
 gives the oils a disagreeable smell and taste, and makes them 
 acid to litmus. This is caused by the formation of free fatty 
 acids with some other products. 
 
 16. Methods of Extraction. An old way of extracting 
 fixed oils from seeds and other plant substances was to crush 
 them and boil with water. The oil rising to the top could 
 be skimmed off. Another way is to extract the oil with 
 volatile solvents which can later be distilled off, leaving the 
 oil behind. This process, however, is expensive and the 
 product contains other compounds which dissolve out in 
 the solvent and remain as impurities in the oil. 
 
 The most common method is to clean and decorticate the 
 seeds, place them in bags and squeeze the oil out by heavy 
 presses. The first expression is made in the cold which gives 
 a better quality of oil. The pulp is then expressed hot and 
 more oil is obtained, but it is not so pure. The material 
 remaining is called "press cake,'' and when ground is sold 
 for cattle food and fertilizers. 
 
 17. Soap. The saponifying property of fixed oils is 
 made use of in the manufacture of soap. If potassium 
 hydroxide is used a soft soap results, if sodium hydroxide, 
 a hard soap. Both kinds are soluble in water, but the potash 
 salt of the fatty acids is a soft substance, whereas the soda 
 salt is a hard substance. The oil or fat is boiled with the 
 alkali until saponification is complete. If a hard product 
 is being made, the soap is separated from the resulting
 
 42 PLANT COMPOUNDS 
 
 glycerine and the excess of alkali by the addition of common 
 salt. The soap is insoluble in this solution, and can be 
 separated, further treated, and made into cakes. 
 
 18. Glycerine. From the residue after the removal of 
 soap, glycerine may be obtained by special processes in- 
 cluding purification by distillation under reduced pressure. 
 Glycerine is a thick, oily liquid, hygroscopic, miscible with 
 water in all proportions, and has a very sweet taste. Its 
 formula is C3H 5 (OH) 3 , graphically: 
 
 H 
 
 H C O H 
 H C O H 
 H C O H 
 H 
 
 It is used in the manufacture of nitroglycerine and dyna- 
 mite; as a solvent in confectionery on account of its hygro- 
 scopic qualities which keep candy soft; in printing inks, etc. 
 
 19. Classification of the Fatty Acids. The drying property 
 of oils depends on the existence of double bonds in the fatty 
 acid radical ; or to express it in another way, on the existence 
 of unsaturated carbon atoms which readily take up oxygen. 
 On this basis the fatty acids of the fixed oils may be classified 
 as saturated or unsaturated compounds as follows: 
 
 (a) SATURATED FATTY ACIDS. C n H 2n +iCOOH. Stearic 
 acid, CnH 35 COOH, melting point 69 C. 
 
 . CH3.(CH 2 )i 6 .COOH 
 
 Palmitic acid, CisHsiCOOH, melting point 62 C. 
 
 CH 8 .(CH2)i4.COOH 
 
 (6) UNSATURATED FATTY ACIDS. (1) With one double bond, 
 C n H 2 n-iCOOH. Oleicacid, CnHsgCOOH, melting point 14 C. 
 
 CH,.(CH 2 )7.CH:CH.(CH 2 )7.COOH 
 
 (2) With two double bonds, C n H 2n -3COOH. Linoleic acid, 
 CnHsiCOOH, melting point below- 18 C. 
 
 CH,.(CH 2 ).CH:CH.CH:CH.(CH 2 ),.COOH
 
 FIXED OILS AND WAXES 43 
 
 (3) With three double bands, C n H 2n -5COOH. Linoleic 
 acid, CnHagCOOH, liquid at ordinary temperatures. 
 
 CH.(CH,),.CH:CH.CH:CH.CH:CH.(CH),.COOH 
 
 The presence of more than one double bond in the fatty 
 acid is necessary for a true drying oil of commercial value. 
 One double bond in the acid radical does not allow enough 
 oxygen to be absorbed does not harden sufficiently. 
 
 The glycerides are named according to the fatty acid 
 radical, thus: Olein for a glyceride of oleic acid, palmitin, 
 for one of palmitic acid, stearin for one of stearic acid, etc. 
 
 In the above classification it is to be noted that palmitic 
 and stearic acids are solid at ordinary temperatures, and 
 oils containing a large proportion of these acids are solid 
 at ordinary temperatures. They are called fats. The other 
 acids mentioned are liquid at ordinary temperatures and oils 
 containing them are usually liquid. This property of being 
 solid is more or less characteristic of the saturated group, 
 and of being liquid more or less characteristic of the unsatu- 
 rated group, although not exclusively so. Some acids of the 
 first group are liquid at ordinary temperatures, and some 
 acids of the second group are solid. 
 
 In most cases the plant fixed oils are liquid and contain 
 a larger proportion of the liquid fatty acids than do animal 
 fixed oils which are called fats. The latter contain as a 
 rule more stearic and palmitic acids. 
 
 Oils containing oleic acid have a slight drying power. 
 Those containing linoleic and linolenic ' are much better 
 "driers." The "drying," it should be remembered, is an 
 oxidation process, resulting in the formation of a hard, resin- 
 ous compound, and not a desiccation which is the case in 
 true drying. Non-drying oils may be used as lubricants, 
 but drying oils are not suited for this purpose, since the 
 "drying" would make them lose their lubricating qualities. 
 
 20. Some Common Fixed Oils. (a) CASTOR OIL is a thick, 
 viscous, transparent, colorless or slightly yellow oil of dis- 
 agreeable taste. It is pressed from the seeds of the castor 
 bean which contain about 50 per cent, of oil, and is composed 
 of small amounts of stearin but principally of ricinolein, the
 
 44 PLANT COMPOUNDS 
 
 latter being the glyceride of ricinoleic acid, a hydroxy-acid 
 with one double bond, Ci/H^OH.COOH. It is used in 
 medicine; for making soap; and as a lubricant for heavy 
 machinery, since it is very viscous and does not "dry" 
 appreciably. 
 
 (6) CORN OIL is a pale yellow, fluid oil, with a smell of 
 corn meal. It is composed mostly of olein and linolein 
 and is a semi-drying oil. It is derived by pressing the germs 
 which have been removed from corn kernels previous to 
 the manufacture of starch (Fig. 19). It is used largely in 
 making soap, oil-cloth, and as an adulterant of edible oils. 
 The press cake is an excellent cattle food. 
 
 (c) COTTONSEED OIL, when purified, is a straw colored, 
 pleasant tasting oil, composed of palmitin, stearin, olein, 
 and linolein. It is made from husked or decorticated cotton 
 seeds by pressure when hot, and the resulting oil, 18 per cent, 
 yield, is clarified. By cooling below 12 C. the solid fats, 
 palmitin and stearin, separate out and can be obtained by 
 pressing. "Cottonseed stearin" is used in making butter 
 substitutes, such as oleomargarine. The original oil is used 
 as a substitute for olive oil and to adulterate olive oil, 
 but principally in soap making. The press cake is used for 
 cattle food. 
 
 (d) LINSEED OIL is obtained by cold pressing or hot press- 
 ing the seeds of the flax plant (Fig. 26 shows a field of flax 
 in blossom) . The seeds contain from 30 to 40 per cent, of 
 oil. The cold pressed product is clear and yellow, containing 
 less solid glycerides and hence is a better drying oil. It 
 is also used as a food in some countries, whereas the hot 
 pressed oil is brown and unfit to use as a food. The pressed 
 oil is allowed to stand for some time to allow impurities to 
 settle, and it is also further purified and bleached. It contains 
 about 58.5 per cent, isolinolenin (isolinolenic acid has the 
 same empirical formula as linolenic acid, but a different 
 structural formula), 13.5 per cent, linolein, 13.5 per cent, 
 linolenin, 4.5 per cent, olein, and 10 per cent, of solid glycer- 
 ides, stearin, palmitin, and myristin (from myristic acid, 
 saturated, CisH^COOH). 
 
 Linseed is the principal drying oil and has been used for
 
 FIXED OILS AND WAXES 45 
 
 hundreds of years in the paint and varnish industry. Its 
 usefulness lies in the fact that a thin layer of it dries or 
 oxidizes to a hard, transparent, more or less glossy skin 
 which serves as varnish when uncolored or as a paint when 
 mixed with pigments. If linseed oil is boiled first it dries 
 more quickly on exposure to the air. Also if the oil is boiled 
 with "driers" such as lead oxide, lead resinate, manganese 
 borate, and manganese resinate, the drying process is 
 hastened, probably by the metallic salts acting as catalytic 
 agents in the oxidation. Raw, or unboiled oil is used for 
 making soap, some kinds of paints and varnishes, and for 
 rubber substitutes by "vulcanizing" with sulphur or sulphur 
 monochloride. The boiled oil is used for paints, printer's 
 inks, oil-cloth, linoleum, etc. 
 
 The oxidation process which drying oils undergo develops 
 considerable heat. Cotton waste or similar material soaked 
 in linseed oil has been known to take fire spontaneously, the 
 loose mass of material preventing the radiation of the heat 
 which gradually increases to the "flash point." 
 
 Press cake from hot pressed linseed oil makes an excellent 
 cattle food. The cold pressed cake is more apt to poison 
 cattle because of the presence of a hydrocyanic acid glucoside 
 which is acted upon by an enzyme (Section 46) in the presence 
 of water with consequent hydrolysis to hydrocyanic acid and 
 glucose. The former is the poison. Hot pressed cake on the 
 other hand has had the enzyme destroyed by heat and no 
 hydrolytic action takes place, the glucoside itself being 
 harmless. 
 
 (e) OLIVE OIL is made by pressing the fruit pulp and the 
 seeds. The cold pressed oil from the former is the better 
 grade and is employed as a condiment. The oil expressed hot 
 from the original cake and from the seeds is less pure and is 
 used for lubricating purposes and soap making. The color 
 of the oil varies from a pale yellow to a greenish or brownish 
 shade. It contains about 72 per cent, olein and 28 per cent, 
 palmitin. Thin films dry slowly. Cotton seed oil is the 
 principal adulterant. 
 
 (/) PEANUT OIL is obtained from peanuts, and is a light 
 greenish-yellow oil, although colorless when refined. It is
 
 46 PLANT COMPOUNDS 
 
 used as an adulterant for olive oil, as a salad oil under 
 its own name, and for making butterine and soap. It con- 
 tains olein, linolein, palmitin, stearin, and some less known 
 glycerides. 
 
 (0) RAPESEED OIL OR COLZA OIL is obtained from rapeseed 
 by hot pressing. The purified oil is light colored and used 
 as a condiment under the name of colza oil, rape seed oil 
 being applied to the darker colored oil which is used as a 
 lubricant and to some extent as a burning oil. Both kinds, 
 containing mostly olein, stearin, and brassin, are very 
 viscous, and on exposure to the air, become gummy, but 
 do not dry. 
 
 (K) SUNFLOWER OIL is obtained from the seeds of the 
 sunflower. It is pale yellow and of pleasant taste, being 
 used in cooking. Less pure grades are used for soap making 
 and as an adulterant for linseed oil, although it does not dry 
 as quickly. It is composed principally of olein, palmitin and 
 linolein. 
 
 21. Waxes. These compounds are allied to the fixed 
 oils in that they have many of the properties of oils, and are 
 esters of fatty acids, but the acids are combined with mono- 
 hydric alcohols of high molecular weight, and not with 
 glycerine. In the plant they serve as a protective water- 
 proof coating on the stems, leaves, and fruit of many plants. 
 The "bloom" on plums is a wax. The surface of corn stalks 
 and sugar cane is covered with a thin layer of wax. The 
 waxes may be liquid or solid and are found in animals as 
 well as in plants. 
 
 Carnauba Wax is the principal plant wax. It ife a very 
 hard substance, usually of sulphur yellow color and obtained 
 from the leaves of a certain kind of palm tree in Brazil by 
 scraping the surface of the leaves, melting and collecting it 
 in boiling water. It contains an ester of so-called myricyl 
 alcohol, CsoHeiOH, and cerotic acid, C25H 6 iCOOH, and some 
 other similar esters. It is used in making candles, polishing 
 pastes, and phonograph cylinders. 
 
 22. Lecithin. While this compound is not a wax or fat, 
 it is allied to them in chemical composition. It is an ester
 
 VOLATILE OILS AND RESINS 47 
 
 of glycerine and choline with fatty acids and phosphoric 
 acid. Its formula may be as follows: 
 H 
 
 .CHj.CH,.N i 
 OH OH 
 
 This would be called a stearo-palmito-phosphate of glycerine 
 and choline. Other fatty acids may replace the two given. 
 It is a yellowish-white, waxy substance, soluble in alco- 
 hol, and other organic solvents. In water it forms an 
 opalescent emulsion or solution. Since it contains certain 
 fat radicals, a reduced nitrogen group, and phosphoric acid, 
 it may be useful in the formation of fats or of proteins. It 
 is found in cereal grains, peas, and beans, to a larger extent 
 than in other plants, although present in most plant cells. 
 
 m. VOLATILE OILS AND RESINS 
 
 23. General Definition. The name oil signifies a liquid 
 having certain characteristic properties as noted in Section 
 14, but the volatile oils, also called essential or ethereal oils, 
 are less greasy in character than the fixed oils, and are 
 volatile on exposure to the air; so that the spot they leave 
 on paper will disappear in time. Chemically they are of 
 several different kinds of compounds, to be noted later 
 (Section 26). They are to be found free or as glucosides 
 in all parts of plants, except in the seeds where the fixed 
 oils predominate. The glucosides hydrolyze under certain 
 conditions with the help of enzymes to glucose and the 
 volatile oil. The volatile oils apparently serve no true 
 physiological function in plants, being for the most part 
 by-products or end-products in metabolism. They frequently 
 serve as valuable helps to the plant, however, in attracting 
 insects whereby fertilization is effected; or as repellents 
 to keep off harmful insects.
 
 48 PLANT COMPOUNDS 
 
 24. Properties. Volatile oils are usually colorless or 
 yellow when fresh, but darken on standing. They have very 
 characteristic odors and tastes and are valuable commercially 
 for these properties. Most of them are lighter than water, 
 varying in specific gravity from 0.850 to 0.990, although a 
 few are less than 0.850 and many of the more common oils 
 are heavier than water. They will for the most part distill 
 unchanged, especially under reduced pressure. They are 
 slowly volatile at ordinary temperatures, hence the dis- 
 tinction in names between the fixed oils, which are not 
 volatile, and the volatile oils, which are like their name. 
 Their boiling points are rather high. Volatile oils are 
 insoluble in w r ater, although many of them dissolve to a 
 slight extent, imparting the characteristic odor and taste 
 to the water. They are readily soluble in cold alcohol as 
 well as in hot alcohol, and in ether, chloroform, carbon 
 tetrachloride, and carbon disulphide. They are also mis- 
 cible in all proportions with fixed oils. Only those which are 
 esters saponify. 
 
 25. Methods of Extraction. There are several ways of 
 obtaining the volatile oils for commercial use : 
 
 (a) BY EXPRESSION, very much as in the case of the fixed 
 oils. 
 
 (6) BY DISTILLATION WITH WATER OR STEAM whereby 
 the crushed material to be extracted is either boiled with 
 water or has a current of steam passed through it. The 
 volatile oil is carried over with the steam and condensed. 
 The oil and water can easily be separated because of their 
 insolubility in each other and because of the difference in 
 their specific gravities. 
 
 (c) BY HYDROLYSIS AND DISTILLATION. Some oils occur 
 as glucosides not only of the oil but also of other compounds. 
 Occurring with them in the plant is an enzyme which under 
 favorable conditions of moisture and temperature acts on the 
 glucosides, forming in addition to glucose the volatile oil 
 and the other compound if it is present. Commercially the 
 oil is obtained by crushing the material in water, allowing 
 the enzyme to act, and distilling off the oil.
 
 VOLATILE OILS AND RESINS 49 
 
 (d) BY SOLUTION IN A FIXED OIL, such as olive oil or lard. 
 The product is used as a perfumed oil or an unguent. 
 
 (e) BY EXTRACTION WITH A SOLVENT much more volatile 
 than the oil. The solvent is removed by distillation. This 
 method is applicable only for such oils as have high boiling 
 points. 
 
 26. Classification. The volatile oils as obtained from 
 plants are not single chemical compounds, but are very 
 frequently mixtures of several chemical individuals, and the 
 difficulty often experienced in obtaining an extracted oil 
 which resembles the original is due either to a failure to 
 obtain every compound, or to obtain them in the proper 
 proportions. Each oil, however, generally contains one 
 principal compound to which are due most of the odor and 
 taste. For convenience, these compounds may be classified 
 into three groups: 
 
 (a) CARBON-HYDROGEN COMPOUNDS. These constituents 
 belong to that class of hydrocarbons called terpenes ring 
 compounds which have a general formula, CioHie, or a mul- 
 tiple thereof. They may be terpenes proper, CioHie, or. 
 sesquiterpenes, CisH 2 4. 
 
 (6) CARBON-HYDROGEN-OXYGEN COMPOUNDS. -- These 
 constituents may be alcohols, aldehydes, or ketones of the 
 aliphatic or carbocyclic series, or esters of any of the 
 alcohols and acids. 
 
 (c) CARBON-HYDROGEN-SULPHUR COMPOUNDS. In addi- 
 tion these compounds sometimes contain nitrogen. They are 
 usually organic sulphides, or thiocyanates. The constitu- 
 ents containing oxygen or sulphur have much stronger odors 
 and flavors than the terpenes, and are more useful for these 
 properties than are the commoner terpenes. 
 
 27. Some Common Volatile Oils. (a) OIL OF BITTER 
 ALMONDS. This oil is benzaldehyde, CeHsCHO, occurring in 
 the almond kernel as a glucoside of hydrocyanic acid and ben- 
 zaldehyde, called amygdalin. The fixed oil is first expressed, 
 and the cake is crushed, soaked in water until the enzyme, 
 emulsin, hydrolyzes the glucoside to benzaldehyde, hydro- 
 cyanic acid, and dextrose. The mixture is then distilled. 
 Hydrocyanic acid is a very powerful poison and care must
 
 50 PLANT COMPOUNDS 
 
 be taken in the distillation. Moreover, the distillate must 
 be carefully freed from hydrocyanic acid before use. Apricot 
 and peach seeds also contain amygdalin and most of the 
 commercial oil of bitter almonds is obtained from the former. 
 It is a white liquid when pure, heavier than water, and is 
 used in making dyes and for flavoring purposes. 
 
 (6) OIL OF CINNAMON. This oil consists mostly of 
 cinnamic aldehyde and eugenol, represented below, 
 
 CH 2 .CH:CH 2 
 CH:CH.CHO 
 
 ^ ; O.CH, 
 
 OH 
 
 with some other compounds. It is obtained by distillation 
 from the bark of the cinnamon tree, and is a yellow oil, 
 heavier than water, and is used in flavoring, for perfumes, 
 and in pharmacy. 
 
 (c) OIL OF CLOVES, This oil is practically all eugenol 
 with a little sesquiterpene. It is obtained from the dried, 
 unopened flower buds of the clove tree, growing in the East 
 and West Indies. It is a yellow oil, heavier than water, and 
 is used in pharmacy,, perfumery, and for flavoring. 
 
 (d) OIL OF LEMON. This is mostly a terpene, limonene, 
 CioHie, with less than 10 per cent, of citral, 
 
 ,\ 
 
 >C:CH.CHz.CH2.C:CH.CHO 
 CH/ I 
 
 CH 3 
 
 to which the odor is due, and many other compounds such 
 as terpenes, alcohols, aldehydes, and esters. It is obtained 
 from the rind of lemons either by rupturing the oil cells over 
 a sponge, or rolling in a vessel lined with spikes, or by dis- 
 tillation, or expression. The two latter methods do not 
 yield as good an oil as the sponge method. It is a pale 
 yellow oil, lighter than water, and its uses are the same as 
 for clove and cinnamon oils.
 
 VOLATILE OILS AND RESINS 51 
 
 (e) OIL OF MUSTARD. This oil is chiefly allyl isothio- 
 cyanate, CH2:CH.CH 2 .N:C:S, with some carbon disulphide 
 and allyl cyanide. In nature it occurs in the seeds of black 
 mustard as a glucoside of potassium acid sulphate and allyl 
 isothiocyanate, called potassium myronate which is hydro- 
 lyzed by a naturally occurring enzyme when water is present. 
 The seeds are first expressed for the fixed oil, then treated 
 with water, and digested in the cold when the enzyme 
 myrosin converts the glucoside into glucose, potassium 
 acid sulphate, and allyl isothiocyanate. The latter is then 
 distilled off. It is a colorless or a pale yellow oil, heavier than 
 water, with pungent odor and burning taste. It is used in 
 medicine largely. 
 
 (/) OIL OF ONION consists principally of allyl-propyl- 
 
 disulphide, 
 
 CH S :CH.CH 2 .S 
 
 CHj.CHj.CH s .S 
 
 and some other sulphides. It is obtained by distillation 
 from onions. It is not of much value commercially, but 
 is the compound which gives to onions and garlic their 
 characteristic odor and taste. 
 
 (g) OIL OF PEPPERMINT contains a great number of differ- 
 ent compounds in small amounts terpenes, alcohols, esters, 
 acids, and aldehydes, but principally menthol, a closed-chain 
 compound but not a benzene compound : 
 
 CH 2 .CH CHj 
 
 / \ / 
 
 CH,.CH CH.CH 
 
 \ / \ 
 
 CHj.CH CH, 
 
 I 
 
 OH 
 
 This is a white, crystalline solid at ordinary temperatures 
 and can be obtained from peppermint oil by freezing. It 
 is used in medicine. The peppermint oil itself is obtained by 
 steam distillation of the peppermint plant and is a pale 
 greenish-yellow oil which darkens on standing. It is lighter 
 than water and is used in medicine and for flavoring to a 
 very great extent.
 
 52 PLANT COMPOUNDS 
 
 (Ji) OIL OF ROSES, called attar or otto of roses. This oil is 
 composed of geraniol, CioHnOH, and citronellol, CioH^OH, 
 both open-chain or aliphatic alcohols. There are also some 
 esters and paraffins present. It is obtained by distillation 
 of roses which are grown for the most part in Bulgaria 
 and Roumania, "the rose garden of the world." It is a 
 pale yellow oil, lighter than water, with a very delicate odor. 
 Attar of roses is very high priced and is frequently adul- 
 terated with geranium oil which resembles it somewhat. 
 
 (i) OIL OF SASSAFRAS consists of safrol, 
 
 CH 2 .CH:CH2 
 
 and a number of terpenes, etc. It is obtained by distilling 
 the root bark of the sassafras tree which is very common in 
 the United States. It is usually a reddish-yellow liquid, 
 heavier than water, and is used for scenting cheap soaps and 
 in flavoring. It is one of the cheaper oils, 
 (j) OIL OF THYME is chiefly thymol, 
 
 \/ /OH 
 
 CH,.CH.CH 
 
 and carvacrol, isomeric phenols. The former is obtained 
 from thyme oil, and is used as an antiseptic. It is a crystal- 
 line solid. The other constituents of thyme oil are esters, 
 hydrocarbons, etc. Thyme oil is yellowish-red when impure, 
 due to action of the phenols on the iron stills; and light 
 yellow when pure. It is lighter than water; used in medi-
 
 VOLATILE OILS AND RESINS 
 
 53 
 
 cine, and as a cheap perfume for soaps. It is distilled from 
 the leaves and flowers of an herb that grows largely in Spain 
 and France. 
 
 FIG. 11. The proper way to collect crude turpentine. Forest Service, 
 United States Department of Agriculture. 
 
 (k) OIL OF TURPENTINE is a terpene, usually pinene, 
 CioHie, with some other isomers. It is obtained by steam dis- 
 tillation of the resinous exudate of the long-leaf pine tree.
 
 54 
 
 PLANT COMPOUNDS 
 
 This sticky liquid which flows from cuts in the trees is com- 
 posed of a resin, colophony (Section 29,6), and an essential 
 oil which is volatile with steam. The resin is left in the 
 still. The turpentine, which is lighter than water, is drawn 
 off and sold as oil or spirits of turpentine. Figs. 11 and 12 
 illustrate the process of collection and distillation of tur- 
 pentine. The best grades come from this country and 
 France. Russia produces some oil of poorer quality. It is 
 
 FIG. 12. Distilling turpentine. Forest Service, United States 
 Department of Agriculture. 
 
 a colorless, mobile liquid with a faint, pleasant, ethereal 
 odor when pure. On standing there is formed an oxidized 
 compound, probably an aldehyde, which is said to give 
 turpentine its peculiar, pungent odor. It dissolves sulphur, 
 rubber, phosphorus, and resins. It burns with a very 
 smoky flame, and on exposure to the air it absorbs oxygen, 
 and hardens, much like the drying oils. For this reason it 
 is used very largely in making paints and varnishes. It is 
 also employed to some extent in medicine.
 
 VOLATILE OILS AND RESINS 55 
 
 (/) OIL OF WINTERGREEN is practically all methyl salicylate, 
 
 OH 
 
 /\ 
 
 .COO.CHj 
 
 
 It is distilled from the wintergreen plant, or teaberry, and 
 from the bark of the sweet birch, both native to America. 
 The oil is yellow, heavier than water, and has a very pleasant 
 taste and odor. It is used in pharmacy to conceal the taste 
 of nauseous drugs, as a meaicine, and for flavoring. Since 
 methyl salicylate can be prepared synthetically, the artificial 
 product is largely sold in place of the true oil. 
 
 28. Resins. These compounds are yellow or brown 
 solid substances, more or less transparent, brittle, and 
 found as natural or induced exudations from plants. Some 
 of them are supposed to be derived by oxidation of terpenes. 
 Their function in plants may be to serve as a protective 
 coating for wounds and cuts. This prevents evaporation 
 and decay until new cells can be formed to permanently 
 cover the wound. As resins ooze out of the plant, usually 
 from special tubular "resin ducts," they are sticky, thick 
 liquids, but on exposure to the air they change either by 
 oxidation or evaporation of some natural volatile solvent, 
 like an essential oil. Resins are insoluble in water, soluble 
 as a rule in alcohol and in other organic solvents. They 
 decompose on heating away from the air, and burn with a 
 smoky flame. Their chemical composition is very complex, 
 some of them consisting mostly of esters, others of acids, 
 and still others of uncertain compounds classed under the 
 name of resen.es. In addition to being of a complex nature 
 when purified, they frequently occur in nature as an exudate 
 mixed with gums and called Gum-resins, which emukify 
 with water; with volatile oils called Oleo-resins, which are 
 softer than the resins proper; and with volatile oils together 
 with benzoic or cinnamic acid, in which case they are properly 
 called Balsams.
 
 56 PLANT COMPOUNDS 
 
 29. Some of the Common Resins. (a) AMBER is a fossil 
 resin found mostly on the shore of the Baltic Sea, frequently 
 buried in the earth. It is the hardest resin known, varying 
 in color from yellow to black, sometimes clear and trans- 
 parent, sometimes cloudy. Chemically amber consists of 
 acids and esters. On heating in a retort above 287 C., it 
 melts and decomposes, forming water, succinic acid, a little 
 volatile fatty acid, oil of amber, and some other compounds. 
 The succinic acid and oil of amber are used in pharmacy. 
 Amber is used mostly for ornamental purposes, although 
 formerly it was employed in the manufacture of the more 
 expensive varnishes. 
 
 (6) COLOPHONY OR ROSIN is the solid residue remaining 
 after oil of turpentine (Section 27, k] has been distilled 
 off. It occurs naturally as an exudate with turpentine 
 from certain pine trees. It is a brittle, yellow to brown solid, 
 chemically consisting largely of an acid. It unites on boiling 
 with sodium or potassium hydroxide to form a deliquescent 
 substance called resinate used in making soaps and for sizing 
 paper. On fusing with manganese or with lead oxides it 
 forms resinates soluble in linseed oil and used as driers in 
 making varnish. On dry distillation colophony breaks 
 up into hydrocarbons, acids, and aldehydes. Commercially 
 two products are obtained rosin spirit, boiling at 80 to 
 250 C. and rosin oil, boiling at over 300 C. Rosin spirit 
 is a colorless liquid composed of hydrocarbons, and resem- 
 bling oil of turpentine for which it is used as a substitute. 
 Rosin oil is a heavy, viscid liquid, colorless to brown, com- 
 posed mostly of high boiling point hydrocarbons. It is used 
 in making rosin-grease by mixing with milk of lime, for 
 lubricating axles, and for making printer's ink. Colophony 
 or rosin itself is used in making varnishes, in pharmacy, 
 and in the preparation of resinates, rosin spirit, and rosin oil. 
 
 (c) COPAL is a name applied to a number of valuable 
 resins. Some are obtained from living trees in Java, Sumatra, 
 and the Philippines. Others are found as fossils in West 
 Africa, Madagascar, and East Indies. Copal resins may be 
 white, yellow, red, brown, or brownish black. The softer 
 varieties are the recent resins and are readily soluble in the
 
 VOLATILE OILS AND RESINS 57 
 
 usual solvents. The harder kinds are the fossil resins and 
 are practically insoluble in the usual solvents until they 
 have been melted and partly decomposed, when they dis- 
 solve in hot turpentine or linseed oil. The latter copals 
 are the more valuable. They are complex in composition, 
 consisting largely of acids and resenes. They are used in 
 making the better grades of varnish. 
 
 (d) DRAGON'S BLOOD is found in Sumatra, and is a clear, 
 deep red resin composed of resenes and esters. It is soluble 
 in alcohol and ether, and is used in making red varnishes. 
 
 (e) LAC OR SHELLAC is either a secretion of the lac insect 
 or produced from the plant sap by the sting of this insect 
 on the twigs of certain East Indian trees. It is sold in sticks 
 as "stick lac;" melted, purified, and poured on cold surfaces 
 to cool in thin plates as "shellac;" or poured into moulds to 
 form " button lac." It is pale orange or red when pure, much 
 darker when impure. The red shade is due to a dye secreted 
 by the insect. Bleached shellac is made by passing chlorine 
 through a solution of lac in alkali. This precipitates white 
 lac which is melted and pulled. It is soluble in alcohol and 
 alkalies, partly soluble in ether. Lac is composed of resenes 
 and acids. It is used extensively in varnishes, for stiffening 
 hats, as a constituent of sealing wax, etc. 
 
 (/) MASTIC AND SANDARAC are similar resins found in Africa 
 and Australia, occurring in the form of "tears" or "solid 
 drops" of rather yellow, translucent material. They are 
 partly soluble in alcohol and turpentine, completely soluble 
 in ether. They are composed of acids, resenes, and bitter 
 principles, probably alkaloids. They are used in varnishes 
 and pharmacy, in the latter for tooth cements and plasters. 
 
 30. Some of the Gum-resins, (a) ASAFETIDA is found on 
 the roots of certain plants in Thibet and Turkestan in the 
 form of tears and masses. It is usually yellowish or brownish 
 in color, and has an unpleasant garlic odor and bitter char- 
 acteristic taste. Asafetida is composed of about 25 per cent, 
 of gum and the rest resin ester with a little volatile oil and 
 some other compounds in small amounts. Its use is restricted 
 now largely to veterinary practice, although it is used to 
 some extent in India and Persia as a flavoring agent in sauces.
 
 58 PLANT COMPOUNDS 
 
 (6) FRANKINCENSE OR OLIBANUM is found on certain trees 
 in Arabia and Africa as yellow-brown tears, with aromatic 
 odor. It is composed of resin, gum, some volatile oil, and 
 bitter principle. It is used somewhat in pharmacy, but 
 more generally in preparing incense. 
 
 (c) GAMBOGE is found on trees in the East Indies as an 
 orange-red substance which is soluble in alcohol. It is 
 composed of an ester, an acid, and a gum. It is used in 
 medicine and as a pigment. 
 
 (d) MYRRH is found on a shrub growing in Arabia and some 
 other eastern countries. It occurs in reddish-brown lumps 
 of oily fracture, fragrant odor, and bitter taste. It is com- 
 posed of resin, gum, bitter principle, and volatile oil, being 
 used in medicine and in making incense. 
 
 31. Some of the Oleo-resins and Balsams. (a) BENZOIN 
 is a balsam and comes from Sumatra and Siam, that from 
 the latter place being of the better quality. It occurs in tears 
 or masses usually reddish-brown in color, having a very 
 pleasant, aromatic odor, and is soluble in alcohol. Benzoin 
 consists of a volatile oil, benzoic acid esterified with a resin 
 alcohol, and some other compounds. It is used in medicine 
 as an antiseptic and in perfumery. 
 
 (6) CANADA BALSAM is incorrectly named, for it is not a 
 true balsam, since it contains no benzoic or cinnamic acid. 
 It is an exudate from the balsam fir, and is a thick liquid, 
 yellowish in color, clear and transparent, with very high 
 refractive index, hardening on exposure to the air. It is 
 composed of a volatile oil and two resins, and is used in 
 medicine, in preparing flexible collodion, and in mounting 
 microscopic specimens. 
 
 (c) CRUDE TURPENTINE is the thick, viscous, yellowish 
 liquid which exudes from cuts in pine trees, usually the long 
 leaf pine, in the United States. This material is collected 
 in boxes made in the trees or better in cups hung on the 
 trees. Fig. 11 shows the best modern method for collecting 
 crude turpentine. The first year's flow called "virgin dip" 
 is the best. "Yellow dip" is the yield *of subsequent years, 
 and "scrape" is the hardened material which is scraped from 
 the trees. This last is the poorest of all. The crude tur-
 
 VOLATILE OILS AND RESINS 59 
 
 pentine is placed in copper stills and distilled with steam to 
 separate the volatile oil of turpentine (Section 27, k). Colo- 
 phony or rosin is left in the still (Section 29, 6). The 
 oleo-resin itself has no value except as a source of oil of 
 turpentine and rosin. Fig. 12 illustrates the distillation 
 of turpentine. 
 
 (d) TOLU comes from South America as a nearly solid 
 mass, yellow-brown in color, of aromatic odor and taste. It 
 contains both benzpic and cinnamic acids, probably united 
 with resin alcohols, and in addition a few other compounds. 
 It is largely used in medicine. 
 
 32. Compounds Similar to the Resins. (a) RUBBER OR 
 CAOUTCHOUC. Many trees contain besides the so-called sap 
 and other liquids, a milky juice called latex, flowing in 
 special elongated cells or tubes. The function of this latex 
 may be to carry food material in an emulsified form, or to 
 serve as a protection w r hen the tree is w'ounded. It oozes 
 out of cut surfaces, hardens on exposure to the air, and 
 serves to keep out water and bacteria just as do the 
 resins (Section 28). This latex is an emulsion of fats, Waxes, 
 resinous substances, and proteins in a watery fluid. Certain 
 trees, more particularly in South America, contain in the 
 latex minute liquid drops of a hydrocarbon, having the 
 general formula of a terpene, CioHie, but supposed to be a 
 chain compound and not a ring compound like a terpene. 
 These drops coagulate on exposure to the air. In practice 
 this coagulation is hastened by the smoke of burning palm- 
 nuts, or by the addition of salt water, wood-ash lye, or alum. 
 The resulting mass forms the crude rubber of commerce. 
 To obtain the latex the trees are cut and the latex gathered 
 much as is maple sap in the United States. The pure hydro- 
 carbon is nearly white when fresh but darkens on exposure 
 to the air. It is soluble in chloroform, benzine, and toluene, 
 and is rendered hard and brittle after a time by oils. Chlorine, 
 bromine, and strong acids destroy it. The commercial 
 material is practically black from smoke and dirt, containing 
 in addition to the rubber proper, or the hydrocarbon, some 
 fat, waxes, and proteins, which \vere originally in the latex. 
 In addition there are chips, bark, and dirt of various kinds 
 accidentally present or intentionally added.
 
 60 PLANT COMPOUNDS 
 
 The crude material is ground and washed, and for use 
 must be treated with sulphur, metallic sulphides, or metallic 
 oxides. The pure rubber is very sticky, but on heating with 
 5 to 10 per cent, of sulphur it loses its stickiness, becomes 
 more elastic, and is the usual form of soft rubber from 
 which so many articles are manufactured. When heated 
 with antimony pentasulphide it forms "red" or "antimony" 
 rubber. Red antimony trisulphide is formed, the rest of the 
 sulphur uniting with the rubber. If the pure rubber is 
 heated with 25 to 30 per cent, of sulphur, it forms on cooling 
 a hard, hornlike mass, called ebonite, or hard rubber, which 
 finds a great variety of uses too well known to need mention. 
 The sulphur may form a chemical compound with the 
 hydrocarbon or it may be merely a physical mixture of 
 sulphur and hydrocarbon. 
 
 (6) GUTTA PERCHA. This material is somewhat similar to 
 rubber, occurring in the latex of certain East Indian trees. 
 It is obtained and washed like crude rubber and is then a 
 fibrous white to brown mass, tough and inelastic when cold, 
 softening greatly on heating. It is soluble in carbon disul- 
 phide, chloroform, and warm benzine. In composition it 
 is a mixture apparently of a hydrocarbon, C 5 H 8 , .and two 
 resins which are oxygenated bodies. It is a very poor con- 
 ductor of electricity and finds its principal use as insulating 
 material for wires, etc. 
 
 (c) CHICLE is also a product of the coagulated latex of 
 certain South American trees, and is used in the United 
 States in the manufacture of chewing gum. It is composed 
 of a true gum soluble in water, resins, the hydrocarbon of 
 gutta percha, mineral constituents, and some other com- 
 pounds. The purified insoluble portion is used for making 
 chewing gum. 
 
 IV. NITROGENOUS COMPOUNDS 
 
 33. Nitrates and Ammonia. There is always present in 
 growing plants a certain amount of nitrates that has been 
 absorbed by the plant rootts. In some plants the amount 
 may be 1.5 to 3 per cent, of the dry weight, but this is excep-
 
 NITROGENOUS COMPOUNDS 61 
 
 tional. They are present only until the synthetic processes 
 are able to convert them into other compounds. This is 
 shown by the fact that as a rule most of the nitrates are in 
 the root, less in the stem and leaves, and none in the seed. 
 Nitrates are present only as they are absorbed by the roots. 
 Plants do not form nitrates from other compounds of nitro- 
 gen. Ammonia is sometimes present in small amounts as an 
 absorbed constituent, for some plants can use ammonium 
 salts as well as nitrates in the manufacture of proteins. 
 Moreover, it may occur as a decomposition product of pro- 
 tein hydrolysis (Section 49), or as an intermediate product 
 in the synthesis of proteins (Section 69). 
 
 34. Amino-acids and Amides. After absorption by the 
 plant, nitrates or ammonia are changed to amino-acids and 
 amides. Amino-acids, sometimes called amido-acids, are 
 organic acids in which one of the alkyl hydrogen atoms 
 is replaced by NH 2 . A common one is amino-acetic acid, 
 CH 2 (NH 2 )COOH, or glycocoll. The amino-acids as a group 
 are crystalline substances soluble in water. They will unite 
 with acids to some extent on account of their amine group 
 and with bases on account of their carboxyl group. Amides, 
 sometimes called acid amides, are organic acids in which the 
 hydroxyl of the carboxyl group is replaced by XH 2 , a common 
 amide being acet-amide, CH 3 COXH 2 . Acids having more 
 than one carboxyl group may have one or all of the hydroxyl 
 groups replaced by XH 2 . They are, as a rule, crystalline 
 substances and more or less soluble in water. They are 
 basic in character, forming salts with acids. 
 
 Apparently the formation of these compounds is in most 
 cases transitory; they are merely intermediate products, 
 existing in but small amounts at any one time. There are 
 a number of these amides and amino-acids found in plants, 
 but the more common ones, and ones which illustrate these 
 compounds very well, are as follows: 
 
 (a) ASPARAGINE is found in considerable quantities in pea 
 and bean seedlings, 
 
 CHz.CO.NHj 
 
 I 
 
 NHj.CH.COOH 
 
 It is also called amino-succinamide.
 
 62 PLANT COMPOUNDS 
 
 (b) GLUTAMINE occurs to a large extent in cucumber and 
 other seedlings. It is the monamide of amino-glutaric acid, 
 
 CHa.CONHz 
 
 CH 2 
 I 
 NH2.CH.COOH 
 
 (c) ARGENINE occurs largely in coniferse or trees of the 
 pine order, and possesses a more complicated structure than 
 the others mentioned, 
 
 NH 2 
 NH:C/ ' 
 
 NH.CH2.CH2.CH2.CH.COOH 
 
 NH 2 
 
 (d) TYROSINE is an amino-acid of the carbocyclic series, 
 found in many plants, 
 
 CH2.CH.COOH 
 
 NHs 
 
 OH 
 
 35. Proteins. Proteins are compounds containing carbon, 
 hydrogen, oxygen, and nitrogen, usually sulphur, and some- 
 times phosphorus. They are the most complex compounds 
 known, and probably the most important, since they are a 
 necessary constituent of every living cell, whether plant or 
 animal, and compose most of the dry matter of animals 
 except the bones. Moreover, plant proteins are important 
 not only to plants themselves, but also to animals, since. the 
 latter are dependent for the most part on the ready-made 
 proteins of plants for their own body nitrogenous compounds. 
 The name itself is significant, being derived from a Greek 
 word signifying "preeminent." 
 
 Chemically proteins are combinations of alpha-amino- 
 acids or their derivatives. Alpha-amino-acids are amino-
 
 NITROGENOUS COMPOUNDS 63 
 
 acids in which the amine group is attached to the carbon 
 atom next to the carboxyl group (note the position of XH 2 
 in the formulas given in Section 34). The composition of 
 proteins is about as follows: Carbon, .50 to 55 percent.; 
 hydrogen, 6 to 7.3 per cent..; oxygen, 19 to 24 per cent.; 
 nitrogen, 15 to 19 per cent.; sulphur, 0.3 to 2.5 per cent.; and 
 phosphorus, if present, 0.4 to 0.8 per cent. A protein molecule 
 is known to be exceedingly large, the molecular weight of 
 different proteins being estimated at from 4000 to 16,000 in 
 round numbers. A formula which has been proposed for 
 zein an example of a typical plant protein will give some 
 idea of the complexity of the molecule: 
 
 Most of the knowledge of proteins is based on studies 
 of the animal proteins. Plant proteins in general, however, 
 are very similar, although not so numerous. 
 
 The various proteins differ somewhat in solubility, some 
 of them being soluble in water, others in dilute alcohol, 
 others in salt solutions, and still others in very dilute acids 
 and in alkalies. Strong acids and alkalies dissolve proteins 
 on heating, but with decomposition. On heating with 
 strong sulphuric acid the nitrogen of proteins is converted to 
 ammonium sulphate, from which ammonia can be evolved 
 with sodium hydroxide. This is the basis of the quantita- 
 tive estimation of proteins (Section 92) since they are built 
 up from a series of amino-acids or their derivatives from which 
 ammonia is easily split off. On hydrolytic decomposition 
 they generally break down into amino-acids. 
 
 For the most part proteins are noncrystallizable, belong- 
 ing to that peculiar class of compounds called colloids. 
 Solutions of proteins are levorotary. One of the com- 
 monest tests for a protein is to dissolve it in concentrated 
 nitric acid which gives a yellow r color, turning to orange on 
 the addition of ammonium hydroxide. This is known as 
 the xanthoproteic reaction or "yellow protein' reaction. 
 Chemists are familiar with the fact that strong nitric acid 
 stains the skin yellow. This is due to this action of nitric 
 acid on the proteins of the skin.
 
 64 PLANT COMPOUNDS 
 
 Some of the proteins in solution are precipitated unaltered 
 by saturating the solution with sodium chloride, ammonium 
 sulphate, or magnesium sulphate, a process called "salting 
 out;" others are thrown down in a changed form by salts 
 of the heavy metals; while still others are precipitated as 
 insoluble salts by tannin. No single reaction is common to 
 all proteins. According to their properties proteins have 
 been classified into some eighteen groups which serve to 
 distinguish them and aid in their study. 
 
 36. Alkaloids. These are plant compounds containing 
 nitrogen and possessing strongly basic properties. They 
 differ from the other organic bases, like amines and amides, 
 in being more complex in structure (the exact formula is 
 unknown in most cases) and more basic in reaction. They 
 differ from the proteins in being less complex. Their most 
 characteristic property is their very powerful physiological 
 action on animals. They are strong medicines or strong 
 poisons. As a rule, they are colorless or white, crystalline 
 solids, and contain oxygen in addition to carbon, hydrogen, 
 and nitrogen. Nicotine is an exception being a liquid and 
 containing no oxygen. Most of the alkaloids are only slightly 
 soluble in alcohol. They dissolve in acids with the formation 
 of salts. From their solutions they are as a rule precipitated 
 by tannin, phosphomolybdic acid, and some other reagents. 
 In the plant they occur in the bark of the stem or root, in 
 seeds, and in the fruit rind. Their function is not definitely 
 known, being considered by some authorities as end products 
 of metabolism waste compounds stored where they are 
 most easily removed; other authorities, however, claim that 
 alkaloids are intermediate or transitory compounds necessary 
 for the growth of the plant. They do not occur in all plants, 
 being confined for the most part to the poppy and legume 
 families. They occur as salts of malic, oxalic, succinic, tannic, 
 or some other plant acid, and are extracted by dissolving 
 out these salts with appropriate solvents, and separating 
 the alkaloid from the acid. Ordinarily this is done by using 
 a mineral acid like sulphuric or hydrochloric, since it is in 
 this form that the alkaloids are used commercially; for 
 example, quinine sulphate, cocaine hydrochloride, etc.
 
 NITROGENOUS COMPOUNDS 65 
 
 37. Some of the Common Alkaloids. (a) ATROPINE, 
 CnHwOsN, is a white crystalline solid with a bitter, acrid 
 taste and is very poisonous. It is used as the sulphate for 
 spasmodic affections, and for dilating the pupil of the eye. 
 Antidotes are emetics, tannin, or charcoal. 
 
 FIG. 13. The cultivated variety of the opium poppy. 
 
 (6) CAFFEINE OR THEINE, CsHuC^N^ is a white, silky solid 
 with bitter taste. It occurs in tea and coffee in combination 
 with a complex organic acid, the compound being soluble in 
 water and is hence extracted when tea and coffee are treated 
 with water for beverages. The alkaloid, occurring to the 
 5
 
 66 PLANT COMPOUNDS 
 
 extent of 1 per cent, in coffee and 2 per cent, in tea, exerts 
 the stimulating effect of these drinks. In addition, however, 
 there are also extracted tannin (in tea only), volatile oil 
 of tea or of coffee, gum, and dextrin, all of which serve to 
 modify the effect of the alkaloid. Pure caffeine is used in 
 medicine as a stimulant, and to cure somnolence. 
 
 (c) COCAINE, CnlLiCXN, is a colorless, crystalline solid 
 with bitter taste, and producing numbness. Used medicin- 
 ally usually as the hydrochloride, CnH^iCXN.HCl, it is a local 
 anaesthetic. It is, however, a dangerous drug to use. Anti- 
 dotes are morphine, alcohol, ammonia, and applications of 
 ice to the head. 
 
 (d) MORPHINE, CnHigOaN, occurs in colorless, shining 
 crystals, with bitter taste, and is used in medicine ordinarily 
 as the sulphate, (CnHigOsN^.H^SCX. It is the chief con- 
 stituent of opium which is obtained from the unripe seed 
 capsules of the poppy (Fig. 13). Morphine is one of the 
 most valuable narcotics known, but it is a very dangerous 
 drug to use on account of its habit-forming properties and 
 its general harmful effect on the mind and body when the 
 habit is once formed. Antidotes to morphine poisoning are 
 potassium permanganate, tannic acid, and emetics. 
 
 (e) NICOTINE, CioHi4N2, is a colorless liquid turning brown 
 on exposure to the air, with acrid taste. It is one of the 
 most virulent poisons known. In small doses it has been 
 used in medicine as a sedative. It is found in tobacco, varying 
 in amounts from 1 to 8 per cent. The pleasant as well as 
 the exceedingly disagreeable effects of smoking and chewing 
 tobacco are probably ascribable to nicotine. In the impure 
 form it is used as an insecticide. 
 
 (/) QUININE, C2oH 2 4O 2 N2, is usually a white, amorphous 
 powder, although it can be obtained in silky needles, and has 
 a very bitter taste. It is used in medicine as the sulphate, 
 (C2oH24O2N 2 )2.H 2 SO4, being particularly efficacious in malaria, 
 and as a tonic and stimulant. 
 
 (g) STRYCHNINE, C 2 iH 2 2O 2 N2, is a white crystalline powder, 
 with very bitter taste, and is a powerful poison. It is used 
 in medicine in very small doses as a nerve stimulant. Anti- 
 dotes are potassium permanganate, emetics, and sedatives.
 
 ORGANIC ACIDS AND THEIR SALTS 67 
 
 (K) THEOBROMINE, CyHgQzN^ is a white crystalline powder 
 of bitter taste. It is the active principle of chocolate and 
 cocoa, occurring to the extent of about 1 per cent, in the 
 cocoa bean. It is used medicinally to some extent, its effect 
 being similar to that of caffeine. 
 
 V. ORGANIC ACIDS AND THEIE SALTS 
 
 38. General. In discussing the various plant compounds, 
 it has been found that there are a large number of organic 
 acids present in one form or another. The fixed oils (Section 
 14) are glyceryl salts of various fatty acids of high molecular 
 weight; some of the volatile oils (Section 26) are esters of 
 organic acids both of the chain and carbocyclic series; 
 some of the resins (Section 28) are composed largely of very 
 complex acids or their salts; alkaloids (Section 36) exist in 
 combination with organic acids of various kinds. But in 
 none of these cases do the acids display the properties which 
 are usually ascribed to them, namely, that of a sour taste 
 and distinctly acid reaction. There are, however, in many 
 plants, chiefly in the fruits, acids w T hich respond to these 
 tests. As mentioned in Section 67, acids may be in part at 
 least the products of imperfect oxidation, or intermolecular 
 respiration. They may be in part waste products (compare 
 oxalic acid below), or they may serve some definite, physio- 
 logical function. 
 
 39. Some of the Common Organic Acids. (a) CITRIC ACID 
 
 CH 2 .COOH 
 HO.C.COOH 
 CH2.COOH 
 
 is found in the free state in lemons, limes, currants, goose- 
 berries, cranberries, etc. It is obtained from lemons and 
 limes for commercial purposes, and is used in medicine and 
 for calico printing. It forms large rhombic crystals with 
 one molecule of water of crystallization, and is soluble in 
 water and in alcohol. On boiling with lime a tricalcium 
 salt is precipitated. 
 (6) MALIC ACID, 
 
 HO.CH.COOH 
 
 CHs.COOH
 
 68 PLANT COMPOUNDS 
 
 occurs free in unripe apples, grapes, gooseberries, and in many 
 other fruits; as the acid potassium salt in some cherries and 
 rhubarb; and as the acid calcium salt in mountain ash 
 berries. It is prepared from the latter, and used to some 
 extent in medicine. It forms deliquescent crystals, soluble 
 in alcohol. The normal calcium salt is insoluble in alcohol. 
 
 (c) OXALIC ACID, 
 
 COOH 
 
 I 
 
 COOH 
 
 is found in very many plants, frequently as the insoluble 
 calcium salt in the form of crystals (Fig. 17, d). It occurs 
 as the soluble acid calcium salt as well as the soluble acid 
 potassium salt in sorrel and rhubarb. It forms monoclinic, 
 efflorescent prisms with two molecules of water of crystal- 
 lization. It is soluble in water and alcohol. 
 
 (d) TARTARIC ACID, 
 
 HO. CH. COOH 
 
 I 
 
 HO. CH. COOH 
 
 is found as the acid potassium salt in grapes; and as the 
 acid potassium and acid calcium salts in pineapples. When 
 grapes are made into wine, crude acid potassium tartrate, 
 called " argol," is precipitated in the vats. When purified it is 
 called "cream of tartar." If it is treated with sulphuric 
 acid and recrystallized, tartaric acid is produced. The neutral 
 calcium salt is insoluble in water. The acid potassium salt 
 is soluble in water but practically insoluble in alcohol. 
 Tartaric acid crystallizes in large monoclinic prisms, soluble 
 in water and in alcohol. The sodium potassium tartrate is 
 Rochelle salts, and potassium antimonyl tartrate is tartar 
 emetic, both of which are used in medicine. 
 
 (e) TANNIC ACID, commonly known as tannin, is extracted 
 from gall nuts (Section 40, i), and forms usually a light, 
 yellowish-buff, amorphous powder or small scales, soluble in 
 water and in alcohol, insoluble in ether, and of acid reaction. 
 It has an astringent, sour taste, precipitates some proteins,
 
 ORGANIC ACIDS AND THEIR SALTS 09 
 
 notably gelatine (Section 216), and forms a blue-black pre- 
 cipitate with ferric salts. Its formula is : 
 
 O OH 
 
 \ C O / \ OH 
 
 digallic acid 
 
 COOH 
 
 On boiling with dilute mineral acids it hydrolyzes to 
 two molecules of gallic acid : 
 
 COOH 
 
 HO k ) OH 
 
 Tannic acid is used in making inks with ferric salts and as 
 an astringent in medicine. 
 
 40. Tannins. These are a group of compounds found in 
 various plants, and in all parts of plants, namely, roots, 
 bark, stem, leaves, flowers, and fruit. They derive their 
 name from the fact that they will tan hides to make leather. 
 They are obtained by extracting the various materials with 
 water and subsequent purification. The extracts contain in 
 addition to the tannins soluble carbohydrates, coloring mat- 
 ter, gums, and other water soluble materials. In fact their 
 value for tanning frequently lies partly in the extractive 
 material other than the tannins. 
 
 Chemically they are very complex and not well known. 
 Some of them contain digallic acid (Section 39, e)\ some 
 contain compounds of gallic acid with dextrose, as glucosides; 
 while others contain various acids derived from gallic acid 
 or from protocatechuic acid, 
 
 COOH 
 
 OH 
 OH
 
 70 
 
 PLANT COMPOUNDS 
 
 Their properties are about the same as those of tannic 
 acid. The property of precipitating gelatine makes them 
 valuable for tanning hides, and that of precipitating metallic 
 salts, for dyeing. Their principal use is in tanning hides, 
 in calico printing, dyeing, and making inks. 
 
 The following are a few of the principal kinds of tannin- 
 containing materials : 
 
 (a) Root of CANAIGRE, a beet-like plant, growing in south- 
 western United States, and Mexico. It contains 30 per 
 cent, of tannin. 
 
 (6) Wood of QUEBRACHO, a tree from South America, con- 
 taining 24 per cent, of tannin; and of CATECHU or CUTCH, 
 an Indian tree. 
 
 FIG. 14. Hemlock bark and logs to be used for tanning. (Rhoads.) 
 
 (c) Wood and bark of CHESTNUT, containing 8 to 12 per 
 cent, of tannin, and of HEMLOCK, 10 to 14 per cent, of tannin. 
 Fig. 14 shows hemlock bark and logs being collected for 
 tanning purposes. 
 
 (d) Bark of OAK, containing 5 to 15 per cent, of tannin; 
 and of MANGROVE, a West African tree, 9 to 30 per cent, of 
 tannin.
 
 EXERCISES 71 
 
 (e) Leaves of SUMACH, containing 15 to 30 per cent, of 
 tannin; and of GAMBIER, an Indian shrub. 
 
 (/) Fruit of Divi-Divi, a West Indian tree, containing 
 30 to 50 per cent, of tannin; and of MYROB ALANS, an Indian 
 and Chinese tree, 20 to 40 per cent, of tannin. 
 
 (</) Acorn cups, called VALONIA, of a certain kind of oak, 
 containing 25 to 35 per cent, of tannin. 
 
 (h) Dried sap, called KINO, from Indian and African 
 trees, containing 75 per cent, of tannin. 
 
 (i) GALLS, or NUT GALLS, a diseased excrescence on cer- 
 tain Persian and Turkish oak trees, caused by the sting of an 
 insect. Galls contain 60 to 75 per cent, of tannin. Tannic 
 acid is the purified form of tannin extracted from these galls. 
 
 EXERCISES 
 
 1. In tabular form compare two monosaccharidcs, two disaccharides and 
 two polysaccharides as follows: Formula; solubility; action with Fehling's 
 test; whether aldose or ketose; action with iodine; optical activity; products 
 of hydrolysis; whether storage or transport form. 
 
 2. Given a mixture of dextrose, levulose, sucrose, starch and cellulose 
 in solid form, how can the presence of each be proved? 
 
 3. What diffeience if any exists between the action of diastase and dilute 
 hydrochloric acid on starch? 
 
 4. Can you differentiate corn starch from potato starch physically and 
 chemically? 
 
 5. Differentiate in tabular form between a fixed oil and a volatile oil with 
 respect to their chemical composition, physical properties, functions in the 
 plant and commercial use. 
 
 6. How many points of similarity can be 'found in the hydrolysis of starch 
 and of proteins? Name them. 
 
 7. Find samples of the statement: "The higher the molecular weight 
 in a series of compounds, the greater the insolubility." 
 
 8. How can the presence of each of the following compounds be proved 
 in a mixture of stearin, zein, cellulose, benzaldehyde? 
 
 9. What is the meaning of each of the following words used in this chapter: 
 Physiologically, empirical, condensation, hydrolytic, decorticate, alkyl, 
 reduction, transport form, storage form, hydrate, fermentable, amorphous, 
 anhydride, trihydric, monobasic, ester, unsaturated, carboxyl, mineral acid, 
 aliphatic, carbocyclic. 
 
 (Forming the habit of using a dictionary or a reference book as soon 
 as a word is used whose meaning is not definitely understood is imperative.) 
 
 REFERENCES 
 
 Allen. Commercial Organic Analysis, 4th ed., vols. i, ii, iii, iv, v, and vi. 
 Browne. Handbook of Sugar Analysis. 
 Cross and Bevan. Cellulose. 
 
 Haas and Hill. The Chemistry of Plant Products. 
 Parry. The Chemistry of Essential Oils. 
 
 Rogers. Manual of Industrial Chemistry, Chapters 24, 25, 28, 29, 31-37, 
 43, 44, 47. 
 
 Thorp. Outlines of Industrial Chemistry, pp. 317-395, 521-532.
 
 CHAPTER II 
 GERMINATION OF THE SEED 
 
 THE seed of a plant contains besides the growing part or 
 embryo, food material to nourish the seedling until it can pro- 
 duce enough roots and leaves to be independent. The food 
 is stored away in a very concentrated form either in seed 
 leaves called cotyledons, which are part of the embryo, or 
 in a special depository called the endosperm which is merely 
 connected with the embryo. Peas and beans are good ex- 
 amples of seeds with food in cotyledons; corn and wheat, of 
 those with food in endosperms. The food material in the 
 cotyledons or in the endosperm consists of starch, oil, and 
 protein, the relative amounts of which vary with the kind 
 of seed. Fig. 19 shows the interior of a corn kernel and the 
 distribution of these foods. 
 
 41. Conditions for Germination. In germinating, a seed first 
 sends out a primary root which starts down into the soil, 
 then it puts forth toward the light a seed bud or plumule, 
 with or without its attendant cotyledons as the case may be. 
 Only under certain conditions, however, will a seed germinate, 
 and these conditions are: Presence of a certain amount of 
 water, oxygen, and heat. All three of the conditions must be 
 fulfilled or no growth will result. If seeds are kept dry, even 
 though they may be in a warm place and surrounded by 
 air which contains all the oxygen ever needed by plants, 
 they will not sprout. They will, however, retain their 
 vitality for a long time, several years being the ordinary 
 maximum, although some seeds have grown after being 
 kept fifty or one hundred years. So also, if seeds are placed 
 in water freed from air, and kept warm, no germination 
 results, because the water prevents oxygen from reaching 
 the seed. Under these conditions, however, seeds will decay 
 (72)
 
 WATER 73 
 
 in a short time, because of the influence of bacteria which 
 act in the presence of moisture, but not otherwise. This 
 indicates the importance of planting seeds in aerated soil, 
 not in soil saturated with water. Seeds under the latter 
 condition will decay. And finally if seeds are supplied with 
 sufficient moisture and are well aerated, but kept cold, no 
 germination will occur. It is absolutely necessary that there 
 be present sufficient water, oxygen, and heat. 
 
 42. Water. The food material packed away in the 
 cotyledons or endosperm is anhydrous and insoluble. To 
 be transported from the cells in which it is stored to the 
 growing root and plumule where it can be used in manufac- 
 turing new cells, this food material must be changed to a 
 soluble form. The chemical change which makes starch, 
 oil, and protein soluble- is hydrolytic in character; that 
 is, water is necessary to break down the insoluble mole- 
 cules of stored food into soluble molecules of transportable 
 food. Certain catalytic agents or enzymes are necessary 
 for this hydrolytic action. There must be in addition 
 enough water to dissolve the soluble compounds, and to 
 keep the new cells properly distended as fast as they are 
 formed. 
 
 A seed in the air dry condition contains about 10 per cent, 
 of water, but to start germination there must be present 
 about 30 per cent. The water is imbibed in part through 
 the seed coat, but mostly through small openings where the 
 seed was attached to the parent plant and adjacent to the 
 embryo. This absorption or imbibition of water is apparently 
 caused by an attraction which the contents of the seed have 
 for water. Starch, for example, will take on water and form a 
 weak chemical union with it, something like water of crystal- 
 lization. Other parts of the seed also have an affinity for 
 water, a sort of molecular attraction for it. This causes the 
 water to enter the seed. 
 
 There are several factors which affect the absorption of 
 water by the seed. Within reasonable limits the higher the 
 temperature the more rapidly water is absorbed. This is 
 because the attraction of the seed contents for water is 
 increased with rising temperature, as is true of very many
 
 74 GERMINATION OF THE SEED 
 
 chemical reactions. Another factor affecting the intake of 
 water by the seed is the amount of salts dissolved in the 
 water. The more salts in solution, the less water is absorbed, 
 for the salts have a counter-attraction for water and pre- 
 vent its entering the seed so readily. Strong salt water 
 or too much soluble fertilizer around seeds will prevent 
 their germination. This is the reason why seeds do not 
 germinate in some of the "alkali soils" of the west there 
 is too much soluble salt in the soil moisture. Some salts, 
 of course, are poisonous to seed plants and so cause death, 
 but ordinarily harmless salts, if present in excessive amounts, 
 act only by keeping water from the seed. It is doubtful 
 if seeds can absorb enough water from saturated air to 
 germinate, hence direct contact with water films is necessary; 
 and a third factor in the amount of water absorbed by seeds 
 is the amount of seed surface in contact with water. The 
 finer the soil particles in the seed bed, the more points of 
 contact with the seed, and since each soil particle is sur- 
 rounded by a water film, therefore the more water in contact 
 with the seed. 
 
 43. Oxygen. In forcing the roots down into the soil as 
 well as the plumule up through the soil, and in forming 
 compounds from which new tissue is constructed, the ger- 
 minating seed requires energy. This energy is derived from 
 the oxidation of oils, carbohydrates, and possibly of protein 
 materials. Just as in a steam engine where oxidation of 
 coal or wood results in various forms of energy such as heat 
 and work, and just as in the animal where oxidation of oils 
 and carbohydrates results in various forms of energy such 
 as heat, work, and formation of compounds, so in the germ- 
 inating seedling oxidation of material results in the various 
 forms of energy necessary to produce a plant. This oxida- 
 tion, or respiration as it is called, requires the presence of 
 free oxygen, and the products of combustion are carbon 
 dioxide and water in the case of starch and sugars. In the 
 case of oils, probably a sugar is first formed. Both oils and 
 carbohydrates contain carbon, hydrogen, and oxygen, but 
 carbohydrates contain a much larger proportion of oxygen 
 than do oils. It is highly probable that intermediate products
 
 HEAT 75 
 
 are formed in part before carbohydrates are completely 
 converted to carbon dioxide and water. Germinating seeds, 
 then, absorb not only water, but oxygen, and give off or 
 respire carbon dioxide and water. The water formed in 
 respiration remains for the most part in the cells where it 
 is formed, and serves as solvent water or chemical water 
 in changing insoluble compounds to soluble compounds. 
 Temperature is a very important factor in oxidation, and 
 within limits the higher the temperature the faster the 
 oxidation. 
 
 Unlike ordinary chemical oxidation or combustion, respira- 
 tion in seeds is not a direct union of oxygen with another 
 substance. Variations in quantity or pressure of oxygen 
 have little effect on the rate of oxidation, as they have in the 
 case of true combustion. Moreover, outside of the seed, 
 substances like starch do not oxidize except at high tempera- 
 tures, and yet in the seed oxidation goes on at relatively low 
 temperatures. Oxidation in the seed is due rather to the 
 presence of certain catalytic agents, or enzymes, which act 
 as aids in making oxygen unite with seed materials. 
 
 Oxidation in the seed causes loss of material, as might be 
 expected. In corn grain, for example, it has been noted that 
 half of the reserve food material has disappeared in three 
 weeks, due to oxidation. Energy produced by this oxidation 
 can be observed in the movements of root and plumule, 
 in the formation of new compounds, and in the production 
 of heat. A mass of seeds enclosed in a non-conducting vessel 
 has been observed to raise the temperature 5 to 10 C. 
 during germination. This production of heat in the germin- 
 ating seed is of value in stimulating the solution of food 
 material and, in general, in quickening the germination. 
 
 44. Heat. It has been noted how temperature or amount 
 of heat affects germination. Seeds can germinate over a 
 wide range of temperature; some seeds, wheat, for example, 
 will germinate at nearly C., but most seeds at not less 
 than 5 C. The upper limit of germination is about 40 C., 
 although cucumber seeds will germinate at 46 C. Each 
 seed, however, has an optimum temperature, and although 
 this varies for different seeds, it is not far from 30 C. Not
 
 76 GERMINATION OF THE SEED 
 
 all of the necessary heat need come from without; vigorous 
 respiration of the germinating seed will produce some of the 
 necessary heat, as noted in the preceding section. 
 
 45. Food for the Seedling. The insoluble compounds 
 which supply nourishment to the growing seedling, and which 
 furnish material for oxidation, are starch (Section 8), oil 
 (Section 14), and proteins (Section 35). The chemical 
 changes taking place in these compounds are: First, the 
 hydrolytic action which makes them soluble; and second, 
 the oxidation reaction which changes starch and oil ulti- 
 mately to carbon dioxide and water. It was stated in 
 Sections 42 and 43 that these reactions were brought about 
 by certain catalytic agents called enzymes. 
 
 46. Enzymes. Enzymes are amorphous substances made 
 by living cells, but which can act independently of the 
 living cell. They are not organized bodies, that is, they 
 have no life in themselves. They are soluble in glycerine and 
 in water, insoluble in alcohol, and can be obtained from 
 living tissue by pulverization, extraction with glycerine or 
 water, and purified by alternate precipitation with alcohol 
 and solution in water. Chemically they are protein-like 
 in character, although they have never been obtained pure 
 enough to have their constitution accurately determined. 
 The mode of action is catalytic, that is, they start a reaction 
 or change its rate. In most cases it is thought that a given 
 reaction in the seed will go on by itself, but so slowly as 
 to be almost imperceptible. A catalytic agent hastens the 
 reaction so that the changes take place quickly. The catalytic 
 agent suffers no permanent change by the reaction, and a 
 small amount of catalyst under optimum conditions can cause 
 an almost indefinite amount of chemical change. Catalytic 
 agents are not confined to enzymes. An example of an 
 inorganic catalyst is manganese dioxide in the generation of 
 oxygen from potassium chlorate. Manganese dioxide comes 
 out of the reaction unchanged ; potassium chlorate is reduced 
 to potassium chloride. The manganese dioxide serves to 
 hasten the reaction and to make it take place at a lower 
 temperature than if the potassium chlorate were decomposed 
 alone. Another example is platinized asbestos in the contact
 
 AMYLASES 
 
 77 
 
 process for sulphuric acid, causing sulphur dioxide and oxygen 
 to unite easily, remaining unchanged itself. 
 
 Enzymes are specific in their activity. There are numerous 
 classes, each one causing or hastening a particular reaction, 
 and no other. The principal classes that are effective in 
 changing insoluble stored food to soluble, movable foods 
 in the seed are ami/loses, Upases, and proteases. Enzymes 
 which cause oxidation are called oxidases. 
 
 FIG. 15. Starch grain acted upon by diastase, showing progressive 
 solution. Much magnified. Drawing by C. A. Smith from microscopic 
 observation. 
 
 47. Amylases. These enzymes, commonly known as 
 starch splitters, are the best known of the seed enzymes. 
 Diastase is a general name for certain members of this 
 group which occur in plants. In the presence of water and 
 sufficient heat, and from the energy derived by oxidation, 
 the embryo cells, for the most part, produce quantities 
 of these diastatic enzymes which pass through the cell 
 walls into the starch packed cells of the endosperm or 
 cotyledons. There they cause the starch to unite with water 
 and, after going through a series of changes, form maltose as 
 an end product. In some cases, although not so often in
 
 78 GERMINATION OF THE SEED 
 
 seeds, dextrose is formed from maltose by another enzyme. 
 Apparently there is a different kind of diastase causing each 
 change. Maltose and dextrose are soluble and diffusible. 
 They are the forms in which carbohydrate food is trans- 
 ported to the growing root and plumule and utilized in the 
 formation of new cells. Fig. 15 shows how a starch grain is 
 gradually broken down and dissolved away by the action 
 of diastase and water. 
 
 48. Lipases. There is not much known of these enzymes, 
 except that they do exist and have the property of splitting 
 up oil by hydrolysis. There are produced glycerine and the 
 fatty acid or acids which were combined with the glycerine 
 to form the oil. Glycerine is soluble and diffusible. The 
 fatty acids are insoluble, but probably unite with such 
 compounds as potash within the cell to form soap. From 
 glycerine and the fatty acids, carbohydrates are formed 
 in the growing cells, probably by oxidation. 
 
 49. Proteases. These enzymes, called also protein split- 
 ters, have the power of hydrolyzing protein substances and 
 changing them to simpler bodies such as albumoses, peptones, 
 amino-acids, and even ammonia compounds. These are all 
 soluble and diffusible. After transport to the growing points 
 the simpler bodies are again united to form proteins. 
 
 50. Oxidases. Respiration or oxidation, not being a 
 case of simple combustion, is probably due to the activity 
 of these enzymes which have the power of causing oxygen 
 to unite with various compounds. Under their influence, 
 starch and maltose are oxidized to carbon dioxide and water; 
 oils, as well as glycerine and fatty acids, are oxidized to 
 carbohydrates and possibly directly to carbon dioxide and 
 water. 
 
 EXERCISES 
 
 1. Is hydrolysis of a fat sufficient to change it to a transport form? Why 
 or why not? 
 
 2. Of what use is each of the following to germination: Hydrolysis, 
 oxidation, dextrose, starch, enzymes? 
 
 3. What three kinds of reactions does a germinating seed use? What is 
 the purpose of each? 
 
 4. Is it usually somewhat warmer next to a germinating seed than it is 
 at a little distance from it? If so, why?
 
 REFERENCES 79 
 
 5. What is the meaning of the following words: Embryo, cotyledon, 
 endosperm, plumule, anhydrous, energy, diffusible, carbohydrate, protein, 
 maltose and chemical energy? 
 
 6. What two substances that you have studied undergo hydrolysis in 
 steps? Name the steps in each case. 
 
 7. In what respect is the burning of coal in a furnace similar to a reaction 
 necessary for the germination of a seed? What is the most essential product 
 in each case? Are there any waste products? 
 
 8. Which requires the more oxygen for its complete oxidation, 100 grams 
 of stearin or 100 grams of starch, and how much more? 
 
 9. What is the reaction of the germinating seed upon litmus paper? How 
 is the compound which causes this reaction produced? 
 
 10. Would you think it possible to have too much soluble plant food 
 around a germinating seed? Why or why not? Answer the same questions 
 for water. 
 
 REFERENCES 
 
 Bergen and Davis. Principles of Botany. 
 Coulter, Barnes, and Cowles. Text-book of Botany, vol. i. 
 Curtis. Nature and Development of Plants. 
 Czapek. Chemical Phenomena in Life. 
 Duggar. Plant Physiology. 
 Ganong. The Living Plant. 
 
 Jost. Plant Physiology, translated by R. J. H. Gibson. 
 Pfeffer. Physiology of Plants, translated by A. J. Ewart. 2d ed., vol. i 
 Strasburger, Jost, Schenk, and Karsten. A Text-book of Botany, trans- 
 lated by W. H. Lang. 10th English ed.
 
 CHAPTER III 
 GROWTH OF THE PLANT 
 
 As soon as the plumule rises above the surface of the 
 soil it turns green, leaves rapidly form, and the young plant 
 begins to live independently of the food laid up for it in the 
 seed by the parent plant. It now obtains all the material 
 it needs for the manufacture of new tissue from the air 
 through the leaves, and from the soil through the roots. 
 
 I. PLANT FOOD 
 
 51. Definition. Plant food is material which enables a 
 plant to build new tissue and may still further be defined as 
 substances supplying an element or elements by means of 
 which a plant can carry on its normal functions of growth 
 and reproduction. Some elements thus supplied become a 
 constituent part of the cells. Other elements merely help 
 in this formation of cellular substance. Plant foods may 
 exist in forms readily taken up by the plant, in which case 
 they are called available foods, or in forms not easily taken 
 up by plants, in which case they are called unavailable foods. 
 The latter must go through certain changes before they 
 become available. To be available a plant food must be in 
 a water soluble form. 1 
 
 52. Essential Elements. For its normal development 
 every crop plant must be supplied with food containing 
 the following ten chemical elements: Carbon, hydrogen, 
 oxygen, phosphorus, potassium, nitrogen, sulphur, calcium, 
 iron, and magnesium. Most plants contain in addition 
 silicon, sodium, and chlorine. These latter elements have 
 
 1 To the botanist true plant food is material elaborated by the plant and 
 then used in building cellular tissue. It is not material supplied from the 
 outside. These substances might be called plant food materials. But to the 
 agriculturist the definition in the text is the most rational and satisfactory. 
 (80)
 
 PLANT FOOD 
 
 81 
 
 not been proved essential, although in many cases plants 
 seem to do better with them than without them. The first 
 ten, however, are absolutely essential to the plant. 
 
 53. Composition of the Plant. About three-fourths of 
 the total weight of a green plant is water. The remaining 
 one-fourth of dry matter is manufactured by the plant and 
 is made up largely of fundamental organic substance con- 
 
 FIG. 16. Diagram showing the distribution of water and dry matter in 
 plants. Drawing by E. DeTurk. 
 
 taining only carbon, hydrogen, and oxygen. There is further 
 some organic substance which includes part of the nitrogen, 
 sulphur, and phosphorus. The remainder of the dry matter, 
 containing potassium, calcium, magnesium, iron, and some 
 of the nitrogen, sulphur, and phosphorus, in organic and 
 inorganic form, is necessary for the formation of funda- 
 mental substance, although not a part of it. 
 
 Fig. 16 gives a graphic illustration of how water and dry 
 6
 
 82 GROWTH OF THE PLANT 
 
 matter are distributed in plants, and of what the dry matter 
 is ultimately composed. The percentages are general 
 averages of green plants. 
 
 54. Form in which the Elements are Absorbed. Carbon 
 enters the plant in the form of carbon dioxide through the 
 leaves. Oxygen, as an element, enters the plant for the most 
 part through the leaves, but also through the roots and 
 stems. This is the only one of the essential elements which 
 is taken up by the plant in the elemental form. As such, 
 however, it is not used in making compounds, but in 
 destroying compounds by the production of energy through 
 the oxidation of plant substance. The same thing has 
 been noted in the case of the germinating seed. For manu- 
 facturing plant substance oxygen is absorbed in combina- 
 tion with carbon as carbon dioxide, or in combination with 
 hydrogen as water, the latter being taken up through the 
 roots from the soil. Water also supplies the hydrogen 
 necessary for plant life. 
 
 All the other elements enter the plant from the soil through 
 the roots. Phosphorus, nitrogen, and sulphur are absorbed 
 as phosphates, nitrates, and sulphates respectively of one of 
 the basic elements, usually calcium. Potassium commonly 
 enters the plant as carbonate or bicarbonate, but also as a 
 salt of one of the acid elements that is, as a phosphate, 
 nitrate, or sulphate. Calcium and magnesium are absorbed 
 as bicarbonate, phosphate, nitrate, and sulphate; and iron 
 as hydrated ferric oxide. 
 
 It is to be noted that these compounds are all in a highly 
 oxidized form. Lower oxidized compounds such as phos- 
 phites, nitrites, and sulphites are not plant foods. They 
 are rather plant poisons. The same thing is true of other 
 lower oxidized compounds. Ammonia may serve as a plant 
 food in some cases, but in this form it is a base and not an 
 acid. It is generally true, however, that nitrates are the 
 best form of nitrogen for crop plants, and usually are the 
 only form which can be utilized. Gaseous nitrogen of the 
 air for legumes is a special case, and will be discussed later 
 (Section 125). 
 
 All of the plant foods must be inorganic in nature and
 
 PLANT FOOD 83 
 
 must dissolve in water before the plant can absorb them. 
 It is not necessary, however, that they be very soluble. A 
 weak solution is even better for a plant than a strong one. 
 In the case of iron, for example, enough of the hydrated 
 ferric oxide dissolves in the soil moisture to nourish plants, 
 although hydrated ferric oxide is usually regarded as a 
 comparatively insoluble compound. 
 
 55. How Absorbed. As stated above, part of the plant 
 food is absorbed through the leaves from the. air and part 
 through the roots from the soil. Considering first the ab- 
 sorption from the soil, it is to be noted that not all of the 
 roots of plants spreading through the soil will absorb water 
 and plant food. Only the very fine root hairs, located near 
 the growing tips and extending but a short distance back of 
 them, act as absorbers of plant food matter. The remainder 
 of the roots is covered with a hard, corky layer which is 
 impervious to water. Since the growing tip keeps pushing 
 forward, the feeding ground is constantly changing. 
 
 The root hairs are long, slender, single cells. The walls 
 are very thin, composed largely of cellulose, and are easily 
 pervious to liquids. Lining the inside of these cells is a 
 layer of protoplasm which serves as a regulator for the 
 entrance and exit of water and soluble material. Under 
 normal conditions of growth, water passes into the root 
 hairs together with the dissolved plant food. These materials 
 pass from cell to cell until they reach the long conducting 
 tubes on the interior of the root and stem called tracheae. 
 Here the stream of liquid is forced up to the leaves and other 
 parts of the plant. The passage of any particular plant food 
 from cell to cell is always from the region of greater con- 
 centration of that particular food to the region of less con- 
 centration. Water passes into the root hairs and from cell 
 to cell regardless of the concentration of any one plant food, 
 but from the region of less total concentration to the region 
 of greater total concentration. 
 
 56. Selective Action by the Roots. The protoplasmic 
 lining of the root hairs, as well as of other cells, exhibits 
 a certain amount of selective action, permitting the entrance 
 of some substances and keeping out others. To a limited
 
 84 GROWTH OF THE PLANT 
 
 extent this means that as the plant needs this or that 
 plant food the root hairs absorb it. For example, at any 
 one time nitrates may pass in freely and phosphates may 
 not. Later this proceeding may be reversed; or both may 
 enter. On the other hand this selective action does not seem 
 very perfect, for most soluble inorganic compounds will 
 enter a plant* even when very harmful. Still further, the 
 protoplasmic layer may exert a sort of decomposing action 
 on a salt like sodium nitrate, absorbing the nitrate radical 
 and leaving behind the sodium, combined probably as a 
 carbonate. Or potassium sulphate may be split up, the 
 potassium being absorbed in some other form, possibly as 
 the carbonate, and the sulphate left behind, probably as 
 sulphuric acid. Moreover, it prevents such cell contents as 
 sugar and soluble proteins from passing out. In general, 
 soluble organic compounds do not pass through the root 
 hair wall or protoplasm in either direction. In other words, 
 crop plants can not absorb organic compounds of the essential 
 elements, and organic compounds such as acids are not 
 excreted by the plant root hairs. The acid action of root 
 hairs is due to the excretion of carbon dioxide which in water 
 forms carbonic acid, capable of dissolving certain substances. 
 This excretion of carbon dioxide is the result of respiration 
 or oxidation of material within the root cells. 
 
 57. Withdrawal of Water from the Roots. Under abnormal 
 conditions, such as when the soil moisture becomes too 
 concentrated in plant food, water passes out of the root 
 hairs instead of into them. This movement of water extends 
 back from cell to cell and results, if not remedied, in the 
 ultimate death of the plant. Too much fertilizer around the 
 roots of plants; strong brine solution, as when the ice-cream 
 freezer is emptied on the grass; white alkali in the west; 
 all these are familiar causes of this effect of withdrawing 
 water from a plant, resulting in its death. This outflow of 
 water, however, does not prevent the dissolved salts from 
 entering the plant at the same time. In some instances the 
 salts themselves, passing into the plant in excessive quanti- 
 ties, stop the vital activity of the cells. The so-called black 
 alkali or sodium carbonate of the west is one of these 
 poisonous salts, unless in very dilute solution.
 
 UTILIZATION OF PLANT FOOD 85 
 
 58. Function of Roots. Roots serve not only as an anchor- 
 age for the plant, to hold it upright and prevent its being 
 blown down or knocked over easily, but also as ports of 
 entry for water and plant food through the root hairs, and as 
 "aqueducts" or water carriers for the rest of their course. 
 The corky layer on the greater part of the roots prevents 
 loss of water and plant food on their way up into the plant. 
 
 H. UTILIZATION OF PLANT FOOD 
 
 59. Use of Inorganic Material. Unlike animals, plants 
 manufacture carbonaceous or organic matter from inorganic 
 raw materials. All that the plant absorbs are inorganic 
 compounds dissolved in water. From these it makes its cells 
 and their contents, which latter are very complex and of many 
 different kinds. The basis of all the organic compounds in 
 plants is composed of carbon, hydrogen, and oxygen, and is 
 manufactured in the leaves for the most part. Energy for 
 this chemical synthesis is derived from the sun's rays. That 
 is, the energy of light waves is transformed into potential 
 energy in the form of chemical compounds. Only a few of 
 the light waves are useful in this work and of the sun's total 
 energy only 1 to 2 per cent, is utilized. 
 
 60. The Spectrum. The sun's rays are composed of 
 many kinds of light waves, some short and some long, some 
 visible and some not. Those that are visible can be separated 
 by a prism into a so-called spectrum which shows the colors 
 of the different waves from violet to red. The red waves 
 are almost twice as long as the violet waves. It is the 
 waves near the red part of the spectrum that are absorbed 
 and changed to potential energy. 
 
 61. Chlorophyl. To absorb these light waves the plant 
 must have chlorophyl, which is a green substance manufac- 
 tured by the plant as soon as the plumule emerges into the 
 light. It is composed of two pigments, blue and yellow, if 
 not more. One of these pigments at least contains nitrogen 
 and phosphorus. They may be separated by appropriate 
 means, but their chemistrv is little understood. This
 
 86 
 
 GROWTH OF THE PLANT 
 
 chlorophyl is located in small bodies called chloroplasts, 
 principally within the cells of the leaves (see Fig. 18, c). 
 Leaves are particularly well adapted to their purpose of 
 absorbing light waves, being broad and flat, thus exposing 
 a large surface to the light. Moreover, they are so distrib- 
 uted that light can fall on them to the best advantage; 
 as can be seen by examining the grouping of leaves on 
 plants a grapevine for example. 
 
 FIG. 17 
 
 FIG. 18 
 
 FIGS. 17 and 18. Section of a leaf. Much magnified. 
 
 FIG. 17. Across the whole leaf, a, epidermis; b, palisade cells showing 
 chloroplasts, c; d, crystals of calcium oxalate; e, spongy parenchyma also 
 showing chloroplasts, c; f, air spaces; g, stoma. 
 
 FIG. 18. Single cell, c, chloroplasts; s, starch grains; n, nucleus; p, 
 protoplasm. Drawing by C. A. Smith. 
 
 Chlorophyl itself does not develop in the dark. Potato 
 sprouts, for example, that grow in a dark cellar may be of 
 considerable size and small leaves may develop, but they are
 
 UTILIZATION OF PLANT FOOD 87 
 
 white or yellowish in color. Grass leaves that have grown 
 under a board or stone are lacking in chlorophyl. 
 
 62. Manufacture of Carbohydrate. The raw materials, 
 combining to form the chemical compounds which store 
 this energy, are carbon dioxide and water. The water, as 
 has been noted, comes up from the soil through the roots 
 and stems. The carbon dioxide enters the leaves through 
 small openings on the under side, called stomata (Fig. 17, g). 
 This gas passes into the air spaces (Fig. 17, /) between the 
 cells and finally through the cell wall, dissolving in the cell 
 sap to form carbonic acid. Under the action of the light 
 waves absorbed by the chlorophyl, carbonic acid probably 
 breaks up into formaldehyde and oxygen according to this 
 equation : 
 
 H 2 CO 3 = CH 2 O + O 2 . 
 
 The oxygen is given off through the cell walls into the air 
 spaces and out through the stomata. The formaldehyde, 
 dissolved in water, of course, is almost instantly condensed 
 to dextrose, thus: 
 
 6CH2O = CsHisOs. 
 
 The dextrose is acted upon by an enzyme which subtracts 
 water from it and forms starch (Fig. 18, s), thus: 
 
 n CsHnOe n H 2 O = (C 6 HioO 6 )n. 
 
 Starch is usually the first visible compound formed in this 
 process of photosynthesis, as the process of chemical synthesis 
 by means of light is called. In some cases, however, the 
 dextrose is changed to sucrose. This process of starch manu- 
 facture goes on during the day only. No synthesis takes 
 place in the dark. 
 
 63. Transfer of Carbohydrates. Starch in the leaf is 
 only the temporary form of manufactured material. During 
 the day carbonaceous matter is synthesized more rapidly 
 than it can be removed, and the cells would be clogged with 
 soluble food if it were not changed to an insoluble, concen- 
 trated form for temporary storage. At night w r hen no car-
 
 bonaceous matter is being formed, the starch is acted upon 
 by amylases and is changed probably to dextrose. It is 
 thus passed from cell to cell by diffusion through the 
 cell walls and plasmatic linings until it passes out of the leaf 
 into the main conducting channels of the plant. These 
 channels are the so-called sieve tubes located outside of the 
 tracheae, or passages for the upward current of water and 
 plant food. 
 
 Dextrose moves to that part of the plant needing new 
 material, such as newly expanding leaves, growing tips, 
 flowers, or roots. At these points other changes take place 
 in the dextrose. It may be reconverted into starch for 
 storage, or into cellulose for cell walls, or into oils, or into 
 any other of the numerous plant compounds. 
 
 64. Amount of Carbohydrate Synthesized. Averaging the 
 results of several experiments, it can be said that during 
 daylight on a bright day one square meter of leaf surface 
 manufactures about one gram of carbohydrate material in 
 one hour. For an acre of corn about the time of tasseling, 
 there is manufactured about 170 pounds of carbohydrate 
 in one day. 
 
 65. Respiration. As has been shown, the manufacture 
 of carbohydrates is brought about by the energy of light 
 waves, and the process is called photosynthesis. The manu- 
 facture of all other products is brought about by the energy 
 released on the oxidation of plant material, and the process 
 is called chemosynthesis. Oxidation or respiration is common 
 to the growing plant just as it is to the germinating 'seed, 
 although not to so great an extent. It is dependent on the 
 activity of oxidases in the presence of oxygen. This results 
 in the production of carbon dioxide and water, and a con- 
 sequent loss of plant substance. In other words the leaves 
 of plants are not only taking in carbon dioxide through their 
 stomata, making carbohydrates with water and giving off 
 oxygen, but they are also absorbing oxygen, oxidizing car- 
 bohydrates, producing water, and giving off carbon dioxide. 
 The gain of plant substance through photosynthesis, 
 however, is much greater than the loss through respiration, 
 for it is obvious that a growing plant gains in weight of dry
 
 UTILIZATION OF PLANT FOOD 89 
 
 matter. It does not lose weight. Experiments have shown 
 that the material assimilated may amount to thirty times 
 that lost by respiration. 
 
 66. Products of Respiration. The gases of respiration, 
 oxygen and carbon dioxide, can pass from cell to cell by 
 diffusion, being dissolved in water and transported like other 
 soluble compounds. The greater part of these gases, however, 
 exists in the intercellular spaces which have access to the 
 outer air through the stomata on the leaves, and the lenticels 
 in the bark and roots. The oxidation of material liberates 
 in the plant several forms of energy. First, heat is generated 
 to a noticeable extent in germinating seeds, flowers, and 
 buds, though for the most part it is dissipated by radiation, 
 plants having a much larger radiating surface in proportion 
 to their mass than do animals. Second, work results, such 
 as movements of various organs; of the entire plant; or 
 of protoplasm within the cells. Food is also transported. 
 Third, chemical changes are brought about, such as the 
 formation of new compounds, the solution of some, and the 
 precipitation of others. 
 
 67. Intermolecular Respiration. In addition to ordinary 
 respiration which takes place only in the presence of free 
 oxygen, there occurs, especially under conditions where 
 oxygen is wanting, a process of oxidation at the expense of 
 other molecules by their reduction. That is, energy for 
 certain processes may be derived by a reaction between 
 molecules in the same cell, resulting in the temporary 
 release of oxygen from one of them. This may be called 
 intermolecular respiration. The products of such oxidation 
 are, besides carbon dioxide and water, ethyl alcohol, higher 
 alcohols, acids, aromatic compounds, and even hydrogen. 
 This sort of oxidation, it must be remembered, means as 
 much reduction as oxidation. Where one molecule gains 
 an atom of oxygen another molecule loses it. Plant cells, 
 however, cannot live for any length of time by means of 
 intermolecular respiration alone. All crop plants must 
 have free oxygen for their development. 
 
 68. Manufacture of Oil. Particles or films of oil seem 
 to be a necessary constituent of plant cells and this material
 
 90 
 
 is made from carbohydrates probably dextrose. Since 
 oils contain less oxygen than dextrose or other carbohydrates, 
 the process must be one of reduction possibly a result of 
 intermolecular respiration. 
 
 69. Manufacture of Protein. By far the most important 
 chemical work done by the plant is the making of proteins, 
 the most complex compounds known. Just how these 
 compounds are manufactured from raw materials is not 
 thoroughly understood. Starting with carbohydrates 
 probably dextrose nitrates, sulphates, and sometimes 
 phosphates, the cells of plants build up a compound which 
 in no way resembles its constituents. The nitrogen and 
 sulphur are no longer in the oxidized condition, in fact, 
 just the reverse. In other words, the nitrates and sulphates 
 are reduced, possibly to ammonia and free sulphur. Then 
 they are combined with carbon, hydrogen, and oxygen from 
 carbohydrates to gradually build up the complex protein. 
 One of the first nitrogen compounds to be formed seems to 
 be an amino-acid. It has been suggested that nitrates and 
 sulphates are reduced by carbohydrates, as a result of 
 intermolecular respiration, whereby the carbohydrates are 
 oxidized in part to oxalic acid. This acid unites with the 
 bases of the reduced nitrates or sulphates, namely, calcium, 
 potassium, or sodium. Later the soluble oxalates of potas- 
 sium and sodium are changed to insoluble calcium oxalate 
 (Fig. 27, d). This excess of calcium may possibly be furnished 
 by calcium phosphate, since the phosphoric acid radical is 
 used in making some proteins. The remainder of the oxi- 
 dized carbohydrates, in the form of some other acids, may 
 unite with the ammonia to form amino-acids. A number 
 of these amino-acids uniting together with sulphur and 
 sometimes phosphorus gradually construct a protein. 
 
 Proteins are made to a great extent in leaves, but their 
 formation is not restricted to the leaves. Other parts of the 
 plant make these compounds from the raw materials. Light 
 is not directly essential for their formation. The necessary 
 energy is derived from oxidation of carbohydrates and is a 
 chemosynthesis as in the case of oils. The presence of 
 carbohydrates is, of course, required since they are the source
 
 UTILIZATION OF PLANT FOOD 91 
 
 of carbon for the proteins, and inasmuch as formation of 
 carbohydrates depends on light, protein synthesis takes 
 place usually more rapidly in the light. 
 
 70. Transfer of Oil and Protein. Just as starch is rendered 
 soluble and transported throughout the plant to parts needing 
 new material, so are oils and proteins changed. Lipases and 
 proteases are not confined to the seeds. They exist anywhere 
 in the plant that oil and protein splitting is essential. Oils 
 are hydrolyzed to glycerine and fatty acids, the latter to 
 soap just as in the seed. Proteins are hydrolyzed to simpler 
 compounds such as albumoses, peptones, amides, etc. It 
 is not known whether the breaking down of proteins goes 
 through the same changes in reverse order as the synthesis, 
 but possibly it does. The course of dissolved oils and pro- 
 teins through the plant is the same as that of dextrose, or 
 dissolved carbohydrates. 
 
 71. Functions of Carbohydrate, Oil, and Protein. For 
 respiration and the consequent production of energy in the 
 plant, carbohydrates are principally used. Oils and proteins, 
 however, may serve this purpose. For the manufacture 
 of cell walls, carbohydrates are employed. As was seen in 
 Section 63, soluble material like dextrose is changed to 
 cellulose. For the manufacture of protoplasm, and as 
 storage material for the crop of the following year, all three 
 kinds of material are important. 
 
 72. Protoplasm. This is the material which plays the 
 most active role in all of these chemical changes, and which 
 must be constantly renewed in old cells and increased for 
 new cells (Fig. 18, p). Its appearance is not the same in 
 different cells but in general it is a more or less soft, spongy, 
 slimy, granular mass, practically colorless, and suspended 
 in water. Embedded in it are always the nucleus or real 
 seat of life, and varying with conditions, chloroplasts 
 or chlorophyl cells, particles of starch, droplets of oil, and 
 many other substances of more or less temporary nature. 
 The approximate chemical composition of the dry matter 
 of protoplasm is as follows : 
 
 50 to 66 per cent, proteins. 
 
 25 to 17 per cent, oils and carbohydrates.
 
 92 GROWTH OF THE PLANT 
 
 25 to 17 per cent, organic acids, particularly amino-acids, 
 organic bases, and mineral salts of potassium, magnesium, 
 calcium, and iron. 
 
 73. Seeds. In providing for a continuation of itself the 
 following year the plant has several ways of storing up 
 food to be used before new roots and leaves can provide 
 bodily substance for the new plant. Sooner or later crop 
 plants bear seeds which contain carbohydrates, oils, and 
 proteins, all in the most concentrated and dehydrated 
 form. Carbohydrates occur in the form of starch (Fig. 20, 
 c and d); and proteins occur in the granular or crystalline 
 form usually called aleurone grains (Fig. 20, 6). The oils 
 are packed away as minute drops (Fig. 20, /). There is 
 little water present in the seed (Sections 42 and 95), and but 
 little space is occupied by the food materials. During the 
 formation of seeds most of the plant activities are devoted 
 to the solution and transportation of material from the 
 leaves and stems, where it has been temporarily lodged, 
 to the seeds, where it is changed to the insoluble form and 
 packed away. Dextrose is dehydrated and made into 
 starch, or reduced and made into oils; in some cases largely 
 starch, as in cereals, in others largely oils, as in cottonseed. 
 Peptones and proteoses are dehydrated and made into 
 proteins. 
 
 74. Roots, Bulbs, and Tubers. Some plants do not bear 
 seeds the first year, but go into a resting stage for a time and 
 the following year produce seed. These are the so-called 
 biennials. To get a start the second year they must have a 
 store of material from which to build new plant substance 
 before roots and leaves can do their work. Consequently 
 they form enlarged fleshy roots, like the beet; underground 
 stems or tubers, like the potato; or enlarged stalks called 
 bulbs, like the onion. In these storage organs the car- 
 bohydrates, oils, and proteins are not usually packed away 
 in a dry, concentrated form. In the beet carbohydrates 
 take the form of sucrose; in the onion, of dextrose; but in 
 the potato, of starch. Oils and proteins are not present to 
 any extent. If the latter are present, however, they occur 
 not as aleurone grains, but in a more hydrolyzed form, even
 
 UTILIZATION OF PLANT FOOD 
 
 93 
 
 
 
 
 
 iHi 
 
 5 a Iffl II 'US sms^ 
 
 FIG. 19 
 
 FIG. 20 
 
 FIGS. 19 and 20. Section of corn kernel. 
 
 FIG. 19. Across the whole kernel. Magnified, a, epidermis; 6, layer of 
 cells containing protein; c, hard starch cells; d, soft starch cells; e, plumule; 
 /, cotyledon or "germ;" g, primary root. 
 
 FIG. 20. Detail of various parts of kernel. Much magnified, a, epi- 
 dermis; 6, cells containing protein or aleurone grains; c, hard starch cells; 
 d, soft starch cells; /, cells containing oil drops. Lettering to correspond 
 to Fig. 19. Drawing by C. A. Smith.
 
 94 
 
 amides, etc. Another class of plants is called perennials, 
 which live on from year to year, bear seeds from time to 
 time, and also maintain life by means of succulent storage 
 organs. Trees are plants of this kind. Their reserve car- 
 bohydrates and other material are stored just under the 
 bark in the so-called cambium layer. 
 
 m. FUNCTIONS OF THE ESSENTIAL ELEMENTS 
 
 75. Value of a Study of These Functions. In the previous 
 discussion of plant growth something has been said about 
 how the principal plant compounds are manufactured, 
 but only in part has been noted the specific function played 
 by each of the essential elements in this process. 
 
 A study of the physiological function of each of the essential 
 elements is of practical importance in the proper feeding 
 of a crop with fertilizers. It is possible by judicious feeding 
 to produce special, desirable results, and the more facts 
 known about the effect of fertilizers, the more economically 
 can they be applied. As yet our knowledge of the subject is 
 not very extensive, although some progress has been made. 
 
 76. Carbon. This element is the principal constituent 
 (45 per cent.) of the dry matter of plants. All of the com- 
 pounds manufactured by plants contain carbon. Every 
 naturally occurring organic compound owes its carbon content 
 directly or indirectly to the activity of plants. Whether 
 these compounds are tissues of the animal body, or coal 
 and oil in the earth, all of them are originally from plants. 
 Animals use as food either other animals or plants, and thus 
 directly or indirectly are dependent on plants as the source 
 of carbon. Coal and oil in the earth are decomposed remains 
 of plants. The very numerous "coal tar derivatives" were 
 originally plant compounds, decomposed in part by heat 
 and pressure within the earth, in part by the chemist. 
 
 77. Hydrogen. This is another of the elements which is an 
 essential constituent of plant compounds. Every organic com- 
 pound in plants, except neutral oxalates, contains hydrogen. 
 And yet in spite of its wide distribution, plants average only
 
 FUNCTIONS OF THE ESSENTIAL ELEMENTS 95 
 
 6.5 per cent, of hydrogen. This is because of its extreme 
 lightness, being the lightest of all the elements. 
 
 78. Oxygen. This element is second to carbon as a 
 constituent of the dry matter of plants, occurring to the 
 extent of 42 per cent., and entering into the composition 
 of most plant compounds. In addition it is necessary for 
 respiration, or for the oxidation of material, which results 
 in energy for the growing plant (Section 65). Combined 
 with hydrogen it forms water which may be considered 
 here with respect to its physiological functions, although 
 it is not an element. 
 
 79. Water. This compound serves a variety of purposes 
 in the plant, (a) It provides a medium in which plant food 
 is dissolved and by which food can be transported through- 
 out the plant. (6) It is a reagent which helps break down 
 insoluble compounds to form soluble compounds (Sections 
 42, 63, and 70). (c) By filling the cells and pressing against 
 their walls, it gives rigidity to the plant structure and keeps 
 it erect. This filling out of the cells is called "turgor." 
 (d) By its evaporation from the leaves, water reduces the 
 temperature of plants and thus prevents overheating due 
 to the sun's rays. 
 
 80. Phosphorus. (a) As a necessary constituent of some 
 proteins phosphorus is required for the building up of 
 certain plant compounds. Cell nuclei, for example, contain 
 phosphorus. Hence this element is necessary for cell division 
 and new growth. (6) It stimulates the growth of seedlings 
 markedly. This is to be noted in the practice of drilling a 
 soluble phosphate with corn. Although they did not know 
 it, it was also the cause of better corn growth when the early 
 New England Indians planted a dead fish in each hill, and 
 so advised the Pilgrims, (c) Phosphorus is important in the 
 ripening of grain. A plentiful supply hastens maturity and 
 also increases the yield of grain over straw or stover (Fig. 21). 
 (d) A plentiful supply of available phosphorus in the soil 
 increases root growth. This increase in root growth is 
 important for crops, especially during a dry season when a 
 generous root system permits plants to get subsoil water 
 more easily. This fact has been noticed particularly in the
 
 96 
 
 GROWTH OF THE PLANT 
 
 growth of cereals in South Australia, (e) Plenty of phos- 
 phorus reduces the content of nitrogen in seeds of grains. 
 
 FIG. 21. Effect of phosphorus on seed development. Corn. The shock 
 on the right came from a phosphate-treated plat. (Soils Department 
 Wisconsin Station.) 
 
 81. Potassium. (a) For the manufacture of carbo- 
 hydrates, potassium is necessary. It seems probable that 
 the condensation of formaldehyde to dextrose takes place 
 only in the presence of some potassium compound, organic 
 in nature. (6) For the hydrolysis of starch, potassium 
 seems necessary, possibly forming a suitable solution in 
 which the amylases can best act. (c) The presence of potas- 
 sium is necessary for the production of cellulose, since it 
 gives rigidity to stems. A lack of potassium is shown in
 
 FIG. 22 
 
 FIG. 23 
 
 FIGS. 22 and 23. Effect of potassium on development of roots containing 
 carbohydrate. Sugar beets. KPN, potassium, phosphorus, nitrogen. PN, 
 phosphorus, nitrogen. 
 
 7
 
 98 GROWTH OF THE PLANT 
 
 weak, brittle stems, where there is insufficient cellulose for 
 the cell walls. Potassium helps the plant to resist attacks 
 of fungous diseases such as the rust. Fungous hyphae can 
 not readily penetrate strong cell walls, (d) It serves also 
 to cause good leaf development, (e) It gives enlarged 
 yields of potatoes, which are a starchy crop. (/) It also 
 increases the yield of sugar in beets (Figs. 22 and 23). 
 This is very well illustrated at the Rothamsted Station, 
 England, w^here a mangold crop fertilized with nitrogen and 
 phosphorus produced 1594 pounds of sugar, but when fertil- 
 ized with potassium, in addition to nitrogen and phosphorus, 
 produced 4446 pounds, (g) Potassium also is the base which 
 neutralizes or partly neutralizes the acids produced during 
 plant growth. 
 
 82. Nitrogen. (a) Nitrogen is a necessary constituent 
 of all proteins, and proteins play a very considerable part 
 in the formation of protoplasm, chlorophyl, and many other 
 compounds (Section 72). (6) It is important in the growth 
 of new tissue, such as stems and leaves (Fig. 24), producing 
 a bright green color in the leaves (effect on chlorophyl). 
 In case an excess is present such a vigorous growth of foliage 
 is produced as to delay maturity of the seed. The ripening 
 of the seed is a process of translocation of food material 
 which does not take place while active assimilation and 
 vegetative growth are going on. This effect of delaying 
 maturity is just the opposite of the effect of phosphorus which 
 hastens it. (c) Excess of nitrogen also causes such rapid 
 vegetative growth that the stems are weakened, and lodging 
 in the case of grain may result. Apparently the cells of the 
 growing stem are multiplied more rapidly than proper cell 
 walls can form, and large cells with weakened walls result. 
 (d) In the case of leafy crops, such as lettuce and cabbage, 
 or of a stem crop like celery, this excess of nitrogen is 
 advantageous. Seeds are not wanted, (e) This effect of 
 too much nitrogen on growth renders plants susceptible to 
 disease. Wheat crops over-stimulated with nitrogen are 
 liable to rust. Greenhouse crops which are always grown 
 on soils rich in nitrogen are peculiarly sensitive to diseases. 
 Shrubbery and young trees which have been forced too
 
 FUNCTIONS OF THE ESSENTIAL ELEMENTS 99 
 
 rapidly with nitrogen are also more easily attacked by fungi. 
 The cause is due not only to a cell wall less resistant to the 
 passage of the fungous hyphae, but also in all probability 
 to a change in the composition of the cell sap which is more 
 favorable to the growth of the fungi. 
 
 FIG. 24. Effect of nitrogen on leaf development. Rape. Jar 5, no nitrate 
 Jar 12, nitrate. Wisconsin Station. 
 
 83. Sulphur. (a) This is a necessary constituent of most 
 proteins. (6) It is also a part of some of the flavoring oils 
 in mustard, onion, cabbage, and horseradish. 
 
 84. Calcium. (a) Like potassium, calcium has some 
 part to play in the solution and transportation of starch, 
 probably by forming a proper medium for the -activity 
 of the amylases. (6) It also takes part in the development 
 of strong cell walls, and numerous root hairs, (c) It serves 
 as a base to precipitate oxalic acid which is formed during 
 respiration and some other activities (Section 69), and which 
 is poisonous to the plant if allowed to accumulate. Crystals 
 of calcium oxalate occur frequently in plants (Fig. 17, d).
 
 100 GROWTH OF THE PLANT 
 
 (d) It is also supposed to be a necessary constituent of the 
 proteins of the cell nuclei. 
 
 85. Iron. This element is necessary for the manufacture 
 of chlorophyl, although not a constituent part of the ehloro- 
 phyl compound. Plants which fail to absorb iron, or which 
 do not absorb enough to keep pace with growth, produce 
 white leaves, a diseased condition known as chlorosis. 
 
 86. Magnesium. (a) The production of chlorophyl is 
 dependent on magnesium, which is a necessary constituent. 
 (6) Protein formation is helped by this element, and par- 
 ticularly in the assimilation of phosphorus, (c) The forma- 
 tion of seeds is also dependent on the activity of magnesium, 
 possibly as a carrier of phosphorus in the plant. 
 
 87. General Distribution in Seed Crops. The staple crops 
 in agriculture are the grains, typical seed plants, which 
 are of value both for their seeds and for their stems and 
 leaves. The distribution of the essential elements, and 
 particularly of the fertilizing elements, in such plants is of 
 importance, not only in connection with their physiological 
 functions, but also with respect to their use on the soil and 
 their economic value. Carbon, hydrogen, and oxygen need 
 not be considered. 
 
 Taking the mature plant as harvested, it is to be noted 
 that phosphorus and nitrogen move to the seeds during 
 ripening to such an extent that there are two to three times 
 as much phosphorus and nitrogen in the seeds as in the 
 leaves and stems. Potassium and calcium, on the other 
 hand, being necessary parts of the assimilating mechanism, 
 remain in the stems and leaves where two to three times as 
 much potassium, and nearly eight times as much calcium, 
 are found as in the seeds. Sulphur is more evenly dis- 
 tributed, being a trifle more in the stems and leaves than 
 in the seeds, except in the corn plant. Iron, being necessary 
 for the formation of chlorophyl, is found in the leaves and 
 stems to a greater extent than in the seeds. Magnesium 
 is more evenly distributed, with a trifle more in the seeds 
 than in the stems and leaves of most grains except corn. 
 
 For the distribution of fertilizing constituents in fruits and 
 vegetables the reader is referred to Table III, Chapter IV.
 
 REFERENCES 101 
 
 The commercially valuable part of these crops differs with 
 the kind of plant, thus making any general discussion 
 impossible. For example, the apple, pear, squash, and pump- 
 kin are raised for the fleshy seed coverings; celery and rhubarb 
 for their thickened stems; the carrot and beet for their 
 thickened root; and spinach and lettuce for their leaves. 
 
 EXERCISES 
 
 1. In detail show the relation that exists between oxidation within the 
 plant cell and photosynthesis. 
 
 2. Starting with carbon dioxide, water, nitrates, phosphates and sulphates 
 build up the following compounds: Dextrose, maltose, sucrose, starch, 
 cellulose, lignin, protein, fat. In doing so, show that dextrose is the initial 
 organic substance formed by the plant for the elaboration of other organic 
 substances. 
 
 3. What are the intermediate and end-products of the hydrolysis of 
 starch, fat and proteins in a plant? 
 
 4. Compare hydrolysis and condensation physically, chemically, and as 
 to their function in plants. 
 
 5. What is the purpose of oxidation in the plant? Name the three prod- 
 ucts usually formed by such action. Which one is of use to the plant? 
 
 6. What do the following prefixes and suffixes mean: yl, ase, ose, ide, ate, 
 ol, um? Dp they usually or always have this meaning? 
 
 7. Name the ten essential plant elements. In four words describe the form 
 in which they are absorbed. What part does the protoplasmic lining of the 
 root hairs play in this absorption? 
 
 8. State why a good nurse will take plants from the sick room at night 
 and return them in the daytime. 
 
 9. Do plants breathe oxygen? If so, why? 
 
 10. Explain in detail how water by its evaporation from the leaves of 
 plants reduces the temperature of plants and prevents the overheating 
 caused by the sun's rays. 
 
 11. What plant poison composed only of carbon, hydrogen and oxygen is 
 formed during plant growth? How does the plant prevent its doing any 
 damage? 
 
 12. If a substance outside the root hairs is soluble and inorganic does 
 that mean it will be absorbed? If not, why not? 
 
 13. Into what kind of energy is the energy of the sun changed during 
 photosynthesis? 
 
 REFERENCES 
 See References at end of Chapter II.
 
 CHAPTER IV 
 CROPS 
 
 THE so-called crop plants those plants which are of 
 value to the farmer owe their importance to certain of 
 their constituents. For example, the grains are valuable for 
 the starch, fixed oils, and proteins, which they contain; 
 potatoes for their starch; nuts for their oils; peas and beans 
 for their proteins; and beets for their sugar. Since most of 
 the ordinary crop plants are raised almost entirely as food 
 for stock or for man, it is of interest to know something of 
 the amounts, not only of the valuable, but also of the useless 
 food constituents in the various crops. 
 
 The determination of the different individual plant com- 
 pounds discussed in Chapter I involves considerable 
 difficulty, and although many of the determinations can be 
 made with accuracy, the time consumed is very great even 
 if only a partial analysis is made. For scientific stock 
 feeding it is only necessary to know the amount of all the 
 carbohydrates that are reasonably digestible; the amount 
 of those carbohydrates which are indigestible; the amount 
 of total protein material; of total oil; and of total mineral 
 matter. Consequently there is employed a method which 
 serves to differentiate the classes of constituents rather 
 than the compounds in each class. 
 
 The determinations are more or less conventional and in 
 some cases only approximate, but on the whole they are 
 reasonably accurate. This general method of analysis is 
 known as the "Weende Method" since it was the method 
 employed at the Weende Experiment Station, Germany, 
 by Dr. W. Henneberg, and reported by him in 1864. With 
 some modifications it is still in use. A very brief description 
 of the following determinations will help to make clear the 
 meaning of terms which are referred to very frequently in 
 any discussion of foods. 
 (102)
 
 CROP CONSTITUENTS AND DETERMINATION 103 
 
 I. CROP CONSTITUENTS AND THEIR DETERMINATION 
 
 88. Water or Moisture. This is the loss in weight of the 
 material which takes place when it is dried at the temperature 
 of boiling water, a little under 100 C. usually, and sometimes 
 in an atmosphere of hydrogen or in vacuo. If the tempera- 
 ture is lower, not all of the water will be driven off; if it is 
 higher, organic compounds begin to break up and the results 
 will be high. It is in some cases necessary to make the deter- 
 mination in an atmosphere of hydrogen or in vacuo, because 
 many crops contain "drying" or "semidrying" oils, which 
 would absorb oxygen if dried in the air, and the results for 
 moisture would be incorrect. 
 
 89. Crude Fat. This constituent is obtained by extracting 
 the dried material with dry, alcohol-free ether. The extract 
 is dried carefully at the temperature of boiling water to 
 remove the ether, and then weighed. If water is present 
 in the sample, or if it is present in the ether, or if alcohol 
 is present in the ether, there is danger of dissolving some 
 of the carbohydrates and ash constituents. Crude fat 
 consists of fixed oils, volatile oils, waxes, resins, chlorophyl, 
 and other pigments, if present, and possibly some other 
 ether-soluble compounds. This accounts for the fact that 
 it is called crude fat, for it is an approximate method at best, 
 although in most of our crop plants the constituents other 
 than fixed oils are very small in amount. 
 
 90. Crude Fiber. The material which has been dried and 
 extracted with ether is boiled first with dilute sulphuric 
 acid, then with dilute sodium hydroxide, giving it a thorough 
 washing after each treatment. The amount of acid and 
 alkali, as well as the strength and time of boiling are very 
 carefully regulated. By drying and weighing the residue, 
 igniting and weighing the remaining ash, the difference in 
 weight will give the crude fiber which consists of cellulose, 
 lignin, and possibly some proteins. The treatment with 
 acid and alkali is supposed to remove all soluble sugars; 
 starch which is hydrolyzed to dextrose and washed out; 
 proteins which are hydrolyzed and removed; and any other 
 constituents rendered soluble by these reagents.
 
 104 CROPS 
 
 91. Ash. By burning the material and continuing to 
 heat it until all the organic matter has been destroyed, the 
 weighed residue will constitute the ash or the mineral con- 
 stituents of the plant substance. These mineral constituents 
 will not occur in the ash in the same form as in the plant, 
 for the bases which were originally united with organic acids 
 will be present in the ash as sulphates, phosphates, silicates, 
 and carbonates. Sulphur and phosphorus in proteins will 
 occur here as sulphates and phosphates of the bases. Silicon, 
 which may or may not have been present in the plant in 
 organic combination, will occur in the ash as silicates. 
 The excess of inorganic basic elements over inorganic acid 
 elements will be present in the ash as carbonates. The ash 
 residue from the crude fiber determination will not serve 
 in this determination, since much of the inorganic material 
 has been removed by the treatment with acid and alkali. 
 
 92. Crude Protein. By using a well known method for the 
 determination of total nitrogen (Section 35) and multiplying 
 the result by 6.25 the percentage of crude protein is obtained. 
 This is based on the assumption that proteins contain on the 
 average 16 per cent, of nitrogen. The assumption is only 
 approximately correct. This method, however, does not 
 take into consideration the presence of nitrogen in other 
 than protein form. In some cases there is a considerable 
 amount of this non-protein nitrogen which is of importance 
 in feeding. Consequently it is customary in most cases to 
 determine the so-called "Albuminoid Nitrogen" or protein 
 nitrogen and calculate this to proteins. The method is 
 based on the fact that proteins are precipitated by copper 
 hydroxide, whereas amides, ammonia, and nitrates are not. 
 After washing the precipitate of proteins and copper 
 hydroxide the total nitrogen is determined and the result 
 multiplied by 6.25 as before. The difference between the 
 total nitrogen and protein nitrogen, is multiplied by 4.7 
 and called amides, on the assumption that amides are 
 asparagine and contain 21.2 per cent, of nitrogen a very 
 broad generalization. 
 
 93. Nitrogen-free Extract, or Digestible Carbohydrates. 
 This is merely the difference between 100 per cent, and the
 
 CLASSIFICATION AND ANALYSES OF CROPS 105 
 
 sum of all the other constituents. It comprises starch, the 
 sugars, and any other compounds not determined elsewhere. 
 Most of the analyses now in use give this determination only, 
 but it is customary at present, in most work of a careful 
 nature, to make separate determinations of sucrose; of 
 reducing sugars, such as dextrose, levulose, and maltose; 
 of starch; and of the pentosans. 
 
 H. CLASSIFICATION AND ANALYSES OF CROPS 
 
 94. Classification. The classification of crops is always 
 more or less arbitrary, particularly so since the popular 
 names for kinds of crops differ from the scientific names. 
 For example, the botanical term for the matured ovary and 
 its contents is fruit, no matter whether the part of the 
 plant in question belongs to corn, or walnut, or apple, or 
 pumpkin. Popularly the term fruit is restricted to those soft, 
 fleshy seed coverings of the apple, pear, and similar plants. 
 
 In the present classification an attempt has been made to 
 arrange the crops in the main according to the part of the 
 plant from which the money value is obtained, and with some 
 regard for popular terminology. The Seed Crops are those 
 which are raised primarily for the seeds themselves, and they 
 are subdivided into Grains, Legumes, and Miscellaneous. 
 The stems and leaves of the ripe grains are also included 
 here for comparison. 
 
 The Fruit Crops are those which are raised for their 
 fleshy seed coverings and are particularly sweet. 
 
 The Stem and Leaf Crops or the Fodder Crops are those 
 which are used only for the stems and leaves. In some cases, 
 corn fodder, for example, the crop may be used when green 
 as fodder, or when ripe as a seed crop. The composition of 
 these crops is given at the time of cutting, not when cured 
 for hay. For the latter see Section 101, and Table IV. 
 
 The Vegetable Crops are all those "garden crops" which 
 are popularly called vegetables. They are valuable for their 
 succulent or juicy parts, and may be conveniently sub- 
 divided into Stem, Leaf, Root, and Fruit Vegetables. It
 
 106 
 
 CROPS 
 
 is to be noted that potatoes are classed with the Root 
 Vegetables, although they are really underground stems, 
 not roots. 
 
 95. Analyses. Table I gives the percentage composition 
 of a number of crop's in each class. Table II gives the 
 yields in pounds per acre of each crop as a whole, and of the 
 several constituents of each crop. Table III gives the per- 
 centage composition of these same crops in the three chief fer- 
 tilizing constituents nitrogen, phosphoric acid, and potash. 
 
 TABLE I. PERCENTAGE COMPOSITION OF CROPS 
 
 Grains. 
 Barley: 
 
 Seed . . 
 
 Straw . 
 Corn : 
 
 Seed . . 
 
 Stover . 
 Oats: 
 
 Seed . . 
 
 Straw . 
 Rye: 
 
 Seed . . 
 
 Straw . 
 Wheat: 
 
 Seed . . 
 
 Straw . 
 
 Legumes. 
 Cowpea . 
 Soja Bean 
 
 Miscellaneous. 
 Cotton Seed 
 Flax Seed 
 
 Water. 
 
 10.9 
 14.2 
 
 10.6 
 
 22.8 
 
 11.0 
 9.2 
 
 11.6 
 7.1 
 
 10.5 
 9.6 
 
 14.8 
 10.8 
 
 10.3 
 9.2 
 
 SEED CROPS 
 
 Nitrogen- 
 Crude Crude free 
 Ash. protein. fiber. extract. 
 
 2.4 
 
 5.8 
 
 1.5 
 4.9 
 
 3.0 
 5.1 
 
 1.9 
 3.2 
 
 1.8 
 4.2 
 
 3.2 
 
 4.7 
 
 3.5 
 
 4.2 
 
 12.4 
 3.5 
 
 10.3 
 5.5 
 
 11.8 
 4.0 
 
 10.6 
 3.0 
 
 11.9 
 3.4 
 
 20.8 
 34.0 
 
 18.4 
 22.6 
 
 2.7 
 36.0 
 
 2.2 
 25.6 
 
 9.5 
 37.0 
 
 1.7 
 38.9 
 
 1.8 
 38.1 
 
 4.1 
 
 4.8 
 
 23.2 
 7.1 
 
 69.8 
 39.0 
 
 70.4 
 39.9 
 
 59.7 
 42.4 
 
 72.5 
 46.6 
 
 71.9 
 43.4 
 
 55.7 
 
 28.8 
 
 24.7 
 23.2 
 
 Crude 
 fat. 
 
 1.8 
 1.5 
 
 5.0 
 1.3 
 
 5.0 
 2.3 
 
 1.7 
 1.2 
 
 2.1 
 1.3 
 
 1.4 
 16.9 
 
 19.9 
 33.7 
 
 FRUIT CROPS 
 
 Nitrogen- 
 
 
 
 
 Crude 
 
 Crude 
 
 free 
 
 Crude 
 
 
 Water. 
 
 Ash. 
 
 protein. 
 
 fiber. 
 
 extract. 
 
 fat. 
 
 Apples .... 
 
 84.6 
 
 0.3 
 
 0.4 
 
 1.2 
 
 13.0 
 
 0.5 
 
 Blackberries . 
 
 86.3 
 
 0.5 
 
 1.3 
 
 2.5 
 
 8.4 
 
 1.0 
 
 Cherries .... 
 
 80.9 
 
 0.6 
 
 1.0 
 
 0.2 
 
 16.5 
 
 0.8 
 
 Currants .... 
 
 85.0 
 
 0.7 
 
 1.5 
 
 12 
 
 .8 
 
 
 Grapes .... 
 
 77.4 
 
 0.5 
 
 1.3 
 
 4.3 
 
 14.9 
 
 1.6 
 
 Peaches .... 
 
 89.4 
 
 0.4 
 
 0.7 
 
 3.6 
 
 5.8 
 
 0.1 
 
 Pears 
 
 84.4 
 
 0.4 
 
 0.6 
 
 2.7 
 
 11.4 
 
 0.5 
 
 Raspberries, black . 
 
 84.1 
 
 0.6 
 
 1.7 
 
 12, 
 
 6 
 
 1.0 
 
 Strawberries 
 
 90.4 
 
 0.6 
 
 1.0 
 
 1.4 
 
 6.0 
 
 0.6
 
 CLASSIFICATION AND ANALYSES OF CROPS 107 
 
 TABLE I PERCENTAGE COMPOSITION OF CROPS (Continued) 
 
 STEM AND LEAF CHOPS 
 
 Water. 
 
 Alfalfa, green . . 71.8 
 
 Alsike clover, green 74.8 
 
 Corn fodder, green . 79.3 
 
 Orchard grass, green 73.0 
 
 Red clover, green . 70.8 
 
 Timothy, green . . 61.6 
 
 Alfalfa, hay . . . 8.4 
 
 Alsike clover, hay . 9.7 
 
 Corn fodder, cured . 42.2 
 
 Orchard grass, hay . 9.9 
 
 Red clover, hay . 15.3 
 
 Timothy, hay . . 13.2 
 
 
 
 
 Nitrogen- 
 
 
 
 Crude 
 
 Crude 
 
 free 
 
 Crude 
 
 Ash. 
 
 protein. 
 
 fiber. 
 
 extract. 
 
 fat. 
 
 2.7 
 
 4.8 
 
 7.4 
 
 12.3 
 
 1.0 
 
 2.0 
 
 3.9 
 
 7.4 
 
 11.0 
 
 0.9 
 
 1.2 
 
 1.8 
 
 5.0 
 
 12.2 
 
 0.5 
 
 2.0 
 
 2.6 
 
 8.2 
 
 13.3 
 
 0.9 
 
 2.1 
 
 4.4 
 
 8.1 
 
 13.5 
 
 1.1 
 
 2.1 
 
 3.1 
 
 11.8 
 
 20.2 
 
 1.2 
 
 7.4 
 
 14.3 
 
 25.0 
 
 42.7 
 
 2.2 
 
 8.3 
 
 12.8 
 
 25.6 
 
 40.7 
 
 2.9 
 
 2.7 
 
 4.5 
 
 14.3 
 
 34.7 
 
 1.6 
 
 6.0 
 
 8.1 
 
 32.4 
 
 41.0 
 
 2.6 
 
 6.2 
 
 12.3 
 
 24.8 
 
 38.1 
 
 3.3 
 
 4.4 
 
 5.9 
 
 29.0 
 
 45.0 
 
 2.5 
 
 VEGETABLE CROPS 
 
 Crude 
 
 Water. Ash. protein. 
 
 Stem vegetables: 
 
 Asparagus . . 94.0 0.7 1.8 
 
 Celery .... 94.5 1.0 1.1 
 
 Rhubarb . . . 94.4 0.7 0.6 
 
 Leaf vegetables: 
 
 Cabbage . . . 91.5 1.0 1.6 
 
 Lettuce . . . 94.7 0.9 1.2 
 
 Onions . . . 87.6 0.6 1.6 
 
 Spinach . . . 92.3 2.1 2.1 
 
 Root vegetables: 
 
 Beets .... 87.5 1.1 1.6 
 
 Carrots . . . 88.2 1.0 1.1 
 
 Parsnips . . . 83.0 1.4 1.6 
 
 Potatoes . . . 78.3 1.0 2.2 
 
 Turnips . . . 89.6 0.8 1.3 
 
 Fruit vegetables: 
 
 Cucumbers . . 95.4 0.5 0.8 
 
 Squash . . . 88.3 0.8 1.4 
 
 Tomatoes . . . 94.3 0.5 0.9 
 
 Watermelons . 92.4 0.3 0.4 
 
 Nitrogen- 
 Crude free 
 fiber. extract. 
 
 0.8 2.5 
 
 3.3 
 1.1 2.5 
 
 1.1 
 0.7 
 0.8 
 0.9 
 
 0.9 
 1.1 
 2.5 
 0.4 
 1.3 
 
 4.5 
 2.2 
 9.1 
 2.3 
 
 8.8 
 
 8.2 
 
 11.0 
 
 18.0 
 
 6.8 
 
 0.7 2.4 
 
 0.8 8.2 
 
 0.6 3.3 
 
 6.7 
 
 Crude 
 fat. 
 
 0.2 
 0.1 
 0.7 
 
 0.3 
 0.3 
 0.3 
 0.3 
 
 0.1 
 0.4 
 0.5 
 0.1 
 0.2 
 
 0.2 
 0.5 
 0.4 
 0.2 
 
 It also gives the yields of these constituents in pounds per 
 acre. This latter part of the table illustates the distribution 
 of these essential elements as discussed in Section 87. The 
 seed and fodder crops are reported as harvested ; the fodder 
 crops also as cured. Fruit and vegetable crops are reported 
 on the edible portion only, except for blackberries, currants, 
 asparagus, spinach, and tomatoes which are reported as 
 purchased. The yields of the fruit and vegetable crops 
 have also been calculated to the edible portion, except in
 
 108 
 
 CROPS 
 
 the cases just mentioned. In the case of the analyses of 
 nitrogen, phosphoric acid, and potash, all crops are reported 
 as harvested, except cherries, peaches, and squash, which 
 are reported as edible portion. Here the yields of only these 
 two crops are calculated on this basis, otherwise as harvested. 
 
 TABLE II YIELD OF CROPS (!N POUNDS PER ACRE) 
 SEED CROPS 
 
 Nltrogen- 
 At Dry Crude Crude free Crude 
 
 Grain. 
 
 harvest. 
 
 matter 
 
 . Ash. 
 
 protein. 
 
 fiber. 
 
 extract. 
 
 fat. 
 
 Barley (35 bushels) : 
 
 
 
 
 
 
 
 
 Seed .... 
 
 1,680 
 
 1,497 
 
 40 
 
 208 
 
 46 
 
 1,173 
 
 30 
 
 Straw .... 
 
 3,000 
 
 2,574 
 
 174 
 
 105 
 
 1,080 
 
 1,170 
 
 45 
 
 Corn (50 bushels) : 
 
 
 
 
 
 
 
 
 Seed .... 
 
 2,800 
 
 2,503 
 
 42 
 
 288 
 
 62 
 
 1,971 
 
 140 
 
 Stover .... 
 
 2,500 
 
 1,930 
 
 122 
 
 138 
 
 640 
 
 998 
 
 32 
 
 Oats (40 bushels) : 
 
 
 
 
 
 
 
 
 Seed .... 
 
 1,280 
 
 1,139 
 
 38 
 
 151 
 
 122 
 
 764 
 
 64 
 
 Straw .... 
 
 1,800 
 
 1,634 
 
 92 
 
 72 
 
 666 
 
 763 
 
 41 
 
 Rye (20 bushels) : 
 
 
 
 
 
 
 
 
 Seed .... 
 
 1,120 
 
 990 
 
 21 
 
 119 
 
 19 
 
 812 
 
 19 
 
 Straw .... 
 
 2,200 
 
 2,044 
 
 70 
 
 66 
 
 856 
 
 1,025 
 
 27 
 
 Wheat (20 bushels) : 
 
 
 
 
 
 
 
 
 Seed .... 
 
 1,200 
 
 1,074 
 
 22 
 
 143 
 
 22 
 
 862 
 
 25 
 
 Straw .... 
 
 2,000 
 
 1,808 
 
 84 
 
 68 
 
 762 
 
 868 
 
 26 
 
 Legumes. 
 
 
 
 
 
 
 
 
 Cowpea (20 bu.) 
 
 1,200 
 
 1,022 
 
 38 
 
 250 
 
 49 
 
 668 
 
 17 
 
 Soja Bean (20 bu.) 
 
 1,200 
 
 1,070 
 
 56 
 
 408 
 
 58 
 
 345 
 
 203 
 
 Miscellaneous. 
 
 
 
 
 
 
 
 
 Cotton Seed 
 
 850 
 
 762 
 
 30 
 
 156 
 
 197 
 
 210 
 
 169 
 
 Flax Seed . . . 
 
 560 
 
 509 
 
 23 
 
 127 
 
 40 
 
 130 
 
 189 
 
 
 
 FRUIT 
 
 CROPS 
 
 
 
 
 
 Nitrogen- 
 
 
 At 
 
 Dry 
 
 
 Crude 
 
 Crude 
 
 free 
 
 Crude 
 
 
 harvest. 
 
 matter. 
 
 Ash. 
 
 protein. 
 
 fiber, extract. 
 
 fat. 
 
 Apples 
 
 18,750 
 
 2,888 
 
 56 
 
 75 
 
 225 
 
 2,438 
 
 94 
 
 Blackberries . 
 
 3,000 
 
 411 
 
 15 
 
 39 
 
 75 
 
 252 
 
 30 
 
 Cherries 
 
 3,800 
 
 726 
 
 23 
 
 38 
 
 8 
 
 627 
 
 30 
 
 Currants . 
 
 4,000 
 
 600 
 
 28 
 
 60 
 
 512 
 
 
 
 Grapes 
 
 6,000 
 
 1,356 
 
 30 
 
 78 
 
 258 
 
 894 
 
 96 
 
 Peaches 
 
 30,750 
 
 3,260 
 
 123 
 
 215 
 
 1,107 
 
 1,784 
 
 31 
 
 Pears .... 
 
 27,000 
 
 4,212 
 
 108 
 
 162 
 
 729 
 
 3,078 
 
 135 
 
 Raspberries 
 
 2,850 
 
 453 
 
 17 
 
 48 
 
 359 
 
 
 29 
 
 Strawberries . 
 
 5,700 
 
 547 
 
 34 
 
 57 
 
 80 
 
 342 
 
 34 
 
 STEM AND LEAF 
 
 CROPS 
 
 , CURED 
 
 
 
 
 Alfalfa . . . 
 
 10,000 
 
 9,160 
 
 740 
 
 1,430 
 
 2,500 
 
 4,270 
 
 220 
 
 Alsike clover . 
 
 5,000 
 
 4,515 
 
 415 
 
 640 
 
 1,280 
 
 2,035 
 
 145 
 
 Corn fodder . 
 
 20,000 
 
 11,560 
 
 540 
 
 900 
 
 2,860 
 
 6,940 
 
 320 
 
 Orchard grass 
 
 4,000 
 
 3,604 
 
 240 
 
 324 
 
 1,296 
 
 1,640 
 
 104 
 
 Red clover 
 
 5,000 
 
 4.235 
 
 310 
 
 615 
 
 1,240 
 
 1,905 
 
 165 
 
 Timothy . . . 
 
 5,000 
 
 4,340 
 
 220 
 
 295 
 
 1,450 
 
 2.250 
 
 125
 
 CLASSIFICATION AND ANALYSES OF CROPS 109 
 
 TABLE II YIELD OF CROPS (Continued) 
 
 VEGETABLE CROPS 
 
 At Dry Crude 
 
 harvest, matter. Ash. protein. 
 
 Nitrogen- 
 Crude free Crude 
 fiber. extract, fat. 
 
 Stem vegetables: 
 
 
 
 
 
 
 
 
 
 
 
 Asparagus 
 
 4,000 
 
 240 
 
 28 
 
 
 72 
 
 
 32 
 
 
 100 
 
 8 
 
 Celery .... 
 
 8,000 
 
 440 
 
 80 
 
 
 88 
 
 264 
 
 8 
 
 Rhubarb . 
 
 12,000 
 
 672 
 
 84 
 
 
 72 
 
 
 132 
 
 
 300 
 
 84 
 
 Leaf vegetables: 
 
 
 
 
 
 
 
 
 
 
 
 Cabbage . 
 
 25,500 
 
 2,167 
 
 255 
 
 
 408 
 
 
 281 
 
 
 1,147 
 
 76 
 
 Lettuce 
 
 12,750 
 
 676 
 
 115 
 
 
 153 
 
 
 89 
 
 
 281 
 
 38 
 
 Onions 
 
 21,600 
 
 2,678 
 
 130 
 
 
 346 
 
 
 172 
 
 
 1,965 
 
 65 
 
 Spinach . . . 
 
 10.000 
 
 770 
 
 210 
 
 
 210 
 
 
 90 
 
 
 230 
 
 30 
 
 Root vegetables: 
 
 
 
 
 
 
 
 
 
 
 
 Beets .... 
 
 13,440 
 
 1.680 
 
 148 
 
 
 215 
 
 
 121 
 
 
 1,182 
 
 14 
 
 Carrots 
 
 10,000 
 
 1,180 
 
 100 
 
 
 110 
 
 
 110 
 
 
 820 
 
 40 
 
 Parsnips . 
 
 12,000 
 
 2,040 
 
 168 
 
 
 192 
 
 
 300 
 
 
 1,320 
 
 60 
 
 Potatoes . 
 
 9,600 
 
 2,083 
 
 96 
 
 
 211 
 
 
 38 
 
 
 1,728 
 
 10 
 
 Turnips 
 
 12,600 
 
 1,310 
 
 101 
 
 
 164 
 
 
 164 
 
 
 856 
 
 25 
 
 Fruit vegetables: 
 
 
 
 
 
 
 
 
 
 
 
 Cucumbers 
 
 10,625 
 
 489 
 
 54 
 
 
 85 
 
 
 74 
 
 
 255 
 
 21 
 
 Squash 
 
 9,000 
 
 1,053 
 
 72 
 
 
 126 
 
 
 72 
 
 
 738 
 
 45 
 
 Tomatoes . 
 
 24,000 
 
 1,368 
 
 120 
 
 
 216 
 
 
 144 
 
 
 792 
 
 96 
 
 Watermelons . 
 
 9,744 
 
 741 
 
 30 
 
 
 39 
 
 652 
 
 20 
 
 TABLE III FERTILIZING 
 
 CONSTITUENTS OF VARIOUS 
 
 CROPS 
 
 
 Percentage composition. 
 
 Pounds per acre. 
 
 
 N 
 
 P.O 6 
 
 KiO 
 
 N 
 
 P,Oj 
 
 K,O 
 
 Barley: 
 
 
 
 
 
 
 
 
 
 
 
 Seed .... 
 
 1.75 
 
 0.75 
 
 0. 
 
 ->(> 
 
 
 2!>. 
 
 4 
 
 12 
 
 .6 
 
 8.4 
 
 Straw .... 
 
 0.60 
 
 0.20 
 
 1. 
 
 10 
 
 
 IS. 
 
 
 
 6 
 
 .0 
 
 33.0 
 
 Corn: 
 
 
 
 
 
 
 
 
 
 
 
 Seed .... 
 
 1.65 
 
 0.65 
 
 0. 
 
 -10 
 
 
 46. 
 
 2 
 
 is 
 
 .2 
 
 11.2 
 
 Stover .... 
 
 1.04 
 
 0.29 
 
 1. 
 
 -10 
 
 
 20. 
 
 
 
 7 
 
 .3 
 
 35.0 
 
 Oats: 
 
 
 
 
 
 
 
 
 
 
 
 Seed .... 
 
 2.00 
 
 0.80 
 
 0. 
 
 GO 
 
 
 2.-, . 
 
 6 
 
 10 
 
 .2 
 
 7.7 
 
 Straw .... 
 
 0.60 
 
 0.20 
 
 1. 
 
 2.-> 
 
 
 10. 
 
 8 
 
 3 
 
 .6 
 
 22.5 
 
 Rye: 
 
 
 
 
 
 
 
 
 
 
 
 Seed .... 
 
 1.70 
 
 0.85 
 
 0. 
 
 r,o 
 
 
 19. 
 
 
 
 9 
 
 .5 
 
 6.7 
 
 Straw .... 
 
 0.50 
 
 0.30 
 
 0. 
 
 85 
 
 
 11. 
 
 
 
 6 
 
 .6 
 
 18.7 
 
 Wheat: 
 
 
 
 
 
 
 
 
 
 
 
 Seed .... 
 
 2.00 
 
 0.85 
 
 0. 
 
 ->o 
 
 
 21. 
 
 
 
 10 
 
 .2 
 
 6.0 
 
 Straw .... 
 
 0.50 
 
 0.15 
 
 0. 
 
 (i() 
 
 
 10. 
 
 
 
 3 
 
 .0 
 
 12.0 
 
 Cowpea .... 
 
 3.10 
 
 1.00 
 
 1. 
 
 20 
 
 
 :>>7 . 
 
 2 
 
 12 
 
 .0 
 
 14.4 
 
 Soja bean 
 
 5.30 
 
 1.80 
 
 2. 
 
 00 
 
 
 83. 
 
 6 
 
 21 
 
 .6 
 
 24.0 
 
 Cotton seed . 
 
 3.15 
 
 1.25 
 
 1. 
 
 IT, 
 
 
 26. 
 
 8 
 
 10 
 
 .6 
 
 9.8 
 
 Flax seed 
 
 4.35 
 
 1.60 
 
 0. 
 
 <).-, 
 
 
 24. 
 
 4 
 
 9 
 
 .0 
 
 5.3 
 
 Apples (fmit) 
 
 0.05 
 
 0.02 
 
 0. 
 
 10 
 
 
 12. 
 
 5 
 
 5 
 
 .0 
 
 25.0 
 
 Blackberries (fruit) . 
 
 0.22 
 
 0.06 
 
 0. 
 
 2:5 
 
 
 6. 
 
 6 
 
 1 
 
 .8 
 
 6.9 
 
 Cherries (fruit pulp) 
 
 0.17 
 
 0.04. 
 
 0. 
 
 20 
 
 
 6. 
 
 5 
 
 1 
 
 .5 
 
 7.6 
 
 Currants (fruit) . 
 
 0.30 
 
 0.12 
 
 0. 
 
 30 
 
 
 12. 
 
 
 
 4 
 
 .8 
 
 12.0 
 
 Grapes (fruit) 
 
 0.15 
 
 0.07 
 
 0. 
 
 30 
 
 
 12 
 
 
 
 5 
 
 .6 
 
 34.0
 
 110 CROPS 
 
 TABLE III FERTILIZING CONSTITUENTS (Continued) 
 
 Percentage composition. 
 
 Pounds per acre. 
 
 
 N 
 
 PiO 6 
 
 K 2 O 
 
 N 
 
 P 2 6 
 
 K,O 
 
 Peaches (fruit pulp) 
 
 0.08 
 
 0.04 
 
 0.20 
 
 24.6 
 
 12.3 
 
 61.5 
 
 Pears (fruit) 
 
 0.05 
 
 0.02 
 
 0.10 
 
 15.0 
 
 6.0 
 
 30.0 
 
 Raspberries (fruit) . 
 
 0.20 
 
 0.10 
 
 0.25 
 
 6.0 
 
 3.0 
 
 7.5 
 
 Strawberries (fruit) 
 
 0.15 
 
 0.06 
 
 0.25 
 
 9.0 
 
 3.6 
 
 15.0 
 
 Alfalfa (green) . 
 
 0.60 
 
 0.15 
 
 0.50 
 
 60.0 
 
 15.0 
 
 50.0 
 
 Alsike clover (green) 
 
 0.50 
 
 0.12 
 
 0.30 
 
 25.0 
 
 6.0 
 
 15.0 
 
 Corn fodder (green) 
 
 0.41 
 
 0.15 
 
 0.33 
 
 82.0 
 
 30.0 
 
 66.0 
 
 Orchard grass (green) 
 
 0.45 
 
 0.15 
 
 0.55 
 
 18.0 
 
 6.0 
 
 22.0 
 
 Red clover (green) . 
 
 0.55 
 
 0.13 
 
 0.50 
 
 27.5 
 
 6.5 
 
 25.0 
 
 Timothy (green) 
 
 0.50 
 
 0.25 
 
 0.75 
 
 25.0 
 
 12.5 
 
 37.5 
 
 Asparagus (young 
 
 
 
 
 
 
 
 shoots) 
 
 0.35 
 
 0.10 
 
 0.25 
 
 14.0 
 
 4.0 
 
 10.0 
 
 Celery .... 
 
 0.25 
 
 0.20 
 
 0.75 
 
 25.0 
 
 20.0 
 
 75.0 
 
 Rhubarb .... 
 
 0.10 
 
 0.04 
 
 0.35 
 
 20.0 
 
 8.0 
 
 70.0 
 
 Cabbage (head) 
 
 0.30 
 
 0.10 
 
 0.40 
 
 90.0 
 
 30.0 
 
 120.0 
 
 Lettuce .... 
 
 0.25 
 
 0.08 
 
 0.45 
 
 37.5 
 
 12.0 
 
 67.5 
 
 Onions .... 
 
 0.23 
 
 0.09 
 
 0.22 
 
 55.2 
 
 21.6 
 
 52.8 
 
 Spinach .... 
 
 0.50 
 
 0.15 
 
 0.25 
 
 50.0 
 
 15.0 
 
 25.0 
 
 Beets 
 
 0.25 
 
 0.10 
 
 0.50 
 
 42.0 
 
 16.8 
 
 84.0 
 
 Carrots .... 
 
 0.23 
 
 0.13 
 
 0.53 
 
 28.8 
 
 16.3 
 
 66.3 
 
 Parsnips .... 
 
 0.22 
 
 0.20 
 
 0.65 
 
 33.0 
 
 30.0 
 
 97.5 
 
 Potatoes . 
 
 0.35 
 
 0.15 
 
 0.50 
 
 42.0 
 
 18.0 
 
 60.0 
 
 Turnips .... 
 
 0.25 
 
 0.10 
 
 0.45 
 
 45.0 
 
 18.0 
 
 81.0 
 
 Cucumbers . 
 
 0.10 
 
 0.06 
 
 0.20 
 
 12.5 
 
 7.5 
 
 25.0 
 
 Squash (edible 
 
 
 
 
 
 
 
 portion) 
 
 0.22 
 
 0.08 
 
 0.05 
 
 18.0 
 
 7.2 
 
 4.5 
 
 Tomatoes 
 
 0.20 
 
 0.07 
 
 0.35 
 
 48.0 
 
 16.8 
 
 84.0 
 
 Watermelons . . 0.17 0.06 0.30 40.8 14.4 72.0 
 
 m. CROP CHEMISTRY 
 
 96. Seed Crops. As a class the seeds of the seed crops 
 are relatively low in water, about 10 per cent. During the 
 process of seed formation the soluble sugars are transported 
 to the seed where dehydration takes place in the deposition 
 of starch. This extra water is eliminated during the drying 
 or curing of seeds. The same change of hydrolyzed com- 
 pounds to dehydrated compounds takes place in the case 
 of proteins (Section 73). The leaves and stems of seed 
 crops are also low in water inasmuch as they have dried out 
 and are practically dead before they are harvested. The 
 seeds are low in ash, much lower than any other part of the 
 plant. Considered from the standpoint of plant economy 
 the seeds need very little of the mineral elements. Food 
 for the seedling is ready made in the seed, only needing
 
 CROP CHEMISTRY 111 
 
 solution to make it immediately available. By the time 
 the seedling rises into the light where it can begin the 
 manufacture of food, the roots have begun to absorb from 
 the soil necessary quantities of inorganic elements for the 
 synthetic processes. Straw and stover, on the other hand, 
 are high in ash which consists largely of the unessential 
 element silicon together with lime and potash. The stems 
 and leaves, it will be remembered (Section 87), are the seat 
 of synthetic processes requiring the help of mineral elements. 
 
 Compared to other crops, seeds are high in crude protein, 
 crude fat and nitrogen-free extract, or carbohydrates, as 
 would be expected, since these are the stored foods for the 
 next generation. The carbohydrates are chiefly starch. 
 Straw and stover, on the other hand, are very high in crude 
 fiber, which goes to make cell walls and strengthening fibers, 
 not living matter. 
 
 (a) GRAINS. Considering the grains separately, it is to 
 be noted that barley seed is of importance chiefly for its 
 nitrogen-free extract starch and the very active starch 
 splitting enzyme, diastase, which is produced on germination. 
 These are made use of in the malting of barley and the sub- 
 sequent "mashing." Barley grains are soaked in water 
 and allowed to germinate. This results in the evolution of 
 heat (Section 43) and the production of diastase in large 
 quantities. All seeds during germination produce diastase 
 of some kind to dissolve the starch (Section 47), but barley 
 diastase is particularly active. When the sprouts have well 
 started they are killed by heat and removed, appearing on 
 the market as "malt sprouts," a feeding stuff. The barley 
 grains, now called malt, are still very rich in starch but have 
 in addition quantities of diastase. The malt is next heated 
 with water when the diastase converts the starch to maltose, 
 a process called mashing. Diastase can act on the starch 
 of other grains as well as on that of barley, and in brewing 
 it is used for the hydrolysis of large amounts of corn starch. 
 The maltose is removed in solution, and fermented with 
 yeast, producing beer. The grain that is left behind is sold 
 as "brewers' grains" for feeding purposes. The presence of 
 much protein in the seed interferes with the malting process.
 
 112 
 
 CROPS 
 
 Corn seed is rich in starch and fat. The starch is used 
 as such, or converted into glucose (Section 3). The fat is 
 extracted and forms corn oil (Section 20, 6). Sweet corn 
 contains a considerable portion of its carbohydrate in the 
 form of sucrose. Corn is low in ash. 
 
 Oat seed is higher in crude fiber and ash than the other 
 grain seeds due to its very considerable hull. It is corre- 
 spondingly lower in digestible carbohydrates. The proportion 
 of fat is also high, being equalled only by that of corn. 
 
 Rye seed has a relatively low protein content like corn 
 seed, and is low in fat like barley. 
 
 FIG. 25. Seed crop: Wheat. Agronomy Department, Pennsylvania 
 
 Station. 
 
 Wheat seed (Fig. 25) has no particularly noticeable con- 
 stituent as far as percentage goes. Its starch is the chief 
 constituent of flour and one of its proteins deserves particular 
 mention in this connection. It is a protein called gliadin, to 
 which wheat flour owes its stickiness or tenacity when mixed 
 with water, and on which the baking qualities depend, serving 
 to keep the baked loaf light. Carbon dioxide formed by the 
 yeast puffs out the sticky mass into many minute cells, the
 
 CROP CHEMISTRY 
 
 113 
 
 gliadin giving tenacity to the cell walls. If it were not for 
 the gliadin the mass would be solid and hard. This is the 
 case with flour from other grain seeds containing no gliadin, 
 
 ' " -' *' 
 
 . .. 
 ':..* /< 
 
 >. V -v"' 
 .v . .'( . 
 
 .:.- : - ( >VU 
 
 H-/4' ' 
 
 \ " * 
 . l > 
 
 vW> . .-. .-, 
 
 /-r/-O. '- ; ^ 
 $*X.* ' -- - 
 
 :V : V--. ; '. 
 
 ^;:-:..- by <* 
 
 >:;$- -i^V ! - '-.-: * * 
 :<^..^:- ? ::V.-.^N^V 
 
 av;.v--v ;>'Vy-{*|*St. - 
 KS^ii^; .>..- *- /_ ;
 
 114 CROPS 
 
 or at least not enough to give good baking quality to bread 
 made from them. 
 
 The straws from these grains are not as a class very 
 digestible, except possibly barley and oats. The ash is high 
 in silica and potash. 
 
 (6) LEGUMES. These seeds are particularly high in protein 
 and correspondingly low in carbohydrates. The soja bean 
 contains considerable fat. 
 
 (c) MISCELLANEOUS. CottonSeedandFlaxSeed(ig. 26)are 
 very high in fat and are used for the oil which can be expressed 
 from them (Section 20, c and d). The press cake is used as 
 a feeding stuff and fertilizer on account of its high nitrogen 
 content. These seeds are also high in fiber and very low 
 in carbohydrates. 
 
 97. Fruit Crops (Fig. 27). These crops are remarkable 
 for the extremely large amounts of water which they contain. 
 A pound of peach pulp or of strawberries, for example, 
 contains more water than a pound (approximately pint) of 
 milk. It is this water content which makes fruit such a 
 valuable addition to the ordinary forms of food. The dry 
 matter of fruits contains, in some cases about as much protein 
 as the grains, in most cases more crude fiber, in many cases 
 more nitrogen-free extract. When the fruit is green, the 
 nitrogen-free extract consists largely of starch, which is 
 converted to such soluble sugars as sucrose and dextrose 
 during ripening. There are also present in the nitrogen-free 
 extract some acids or acid salts. Certain volatile flavoring 
 oils are included in the crude fat. The ash of fruits is very 
 largely basic in character and this makes fruit very valuable 
 as a food. Potash is an important constituent, being neces- 
 sary for the ripening process. 
 
 98. Stem and Leaf Crops. These crops when green are 
 high in water which is largely eliminated during the curing 
 process (Section 100). The dry matter of these crops is 
 high in ash and crude fiber, but low in nitrogen-free extract 
 and fat. They are not so high in crude fiber as the straws of 
 the grains, partly because they are cut before so much of 
 the starch and other digestible carbohydrates are changed to 
 crude fiber. The ash is rich in lime and potash, but not much
 
 CROP CHEMISTRY 
 
 115 
 
 silica is present. The changes that take place during the cur- 
 ing process, or haymaking, are discussed later (Section 100). 
 
 FIG. 27. Fruit crop: Apples. 
 
 99. Vegetable Crops. These crops, like the fruits, are 
 very high in water. 
 
 (a) STEM VEGETABLES as a class are the highest in water 
 content of all the crops, over 94 per cent. Of the dry matter,
 
 116 CROPS 
 
 nitrogen-free extract is the largest in amount, although 
 compared to the grain seeds this constituent is smaller; 
 ash, protein, fiber, and fat all being larger in amount. It is 
 the bases in the ash which make the vegetables an important 
 class of foods. 
 
 (6) LEAF VEGETABLES (Fig. 28). These do not differ much 
 in composition from the stem vegetables. Stems and leaves 
 have been classed together in the other crops. 
 
 FIG. 28. Leaf vegetable crop: Cabbages. Horticultural Department, 
 Pennsylvania Station. 
 
 (c) ROOT VEGETABLES (Fig. 29). Of these the beets are 
 noted for their sugar content, especially the sugar beet which 
 runs about 15 per cent, sucrose. Potatoes are much the 
 highest in nitrogen-free extract of any of the vegetables, and 
 this is mostly starch. 
 
 (d) FRUIT VEGETABLES. As would be expected these run 
 lower in ash than the other vegetables, although on a dry 
 basis this constituent is higher than it is in grain seeds. 
 The ash is largely potash. Crude fiber is less, fat is higher. 
 
 100. Hay. Stem and leaf crops, or fodder crops as they 
 are customarily called, do not keep well unless cured or 
 preserved in some way. One of the common methods is to 
 make hay out of them. The usual hay crops are timothy and 
 clover, although many other grasses and legumes, par-
 
 CROP CHEMISTRY 
 
 117 
 
 ticularly alfalfa (Fig. 30), are grown for this purpose. What- 
 ever the crop, the principle is the same, namely, to cut the 
 crop when it is in the best condition for making a valuable 
 hay, and to dry it or cure it. 
 
 FIQ. 29. Root vegetable crop: Potatoes. 
 
 101. Chemical Changes in Making Hay. As noted in 
 Table I, the fodder crops range in moisture content from 60 
 to 80 per cent., whereas hay runs from 8 to 15 per cent., 
 except in the case of cured corn fodder which contains
 
 118 
 
 CROPS 
 
 42 per cent, of water. In addition to a mere desiccation of 
 the crop there are changes which take place in the various 
 constituents. Table IV gives the changes that take place 
 
 FIG. 30. Hay crop: Alfalfa. 
 
 Agronomy Department, Pennsylvania 
 Station. 
 
 TABLE IV. CHANGES IN COMPOSITION DURING HAYMAKING 
 
 (Calculated to Dry Basis) 
 
 Alfalfa: 
 
 Green 
 
 Hay . . 
 Alsike clover: 
 
 Green 
 
 Hay . . 
 Corn fodder: 
 
 Green 
 
 Cured 
 Orchard grass: 
 
 Green 
 
 Hay . . 
 Red clover: 
 
 Green 
 
 Hay . . 
 Timothy: 
 
 Green 
 
 Hay . . 
 
 Ash. 
 
 9.6 
 8.1 
 
 7.8 
 9.3 
 
 5.6 
 4.7 
 
 7.4 
 6.7 
 
 7.2 
 7.3 
 
 Crude 
 protein. 
 
 17.0 
 15.6 
 
 15.3 
 14.2 
 
 9.6 
 9.0 
 
 15.3 
 14.5 
 
 Crude 
 fiber. 
 
 26.3 
 27.3 
 
 29.2 
 
 28.4 
 
 24.1 
 
 24.7 
 
 30.4 
 36.0 
 
 27.8 
 29.1 
 
 Nitrogen- 
 free 
 extract. 
 
 43.6 
 46.6 
 
 44.0 
 44.9 
 
 58.9 
 60.1 
 
 49.3 
 45.4 
 
 45.8 
 45.2 
 
 Crude 
 fat. 
 
 3.5 
 
 2.4 
 
 3.7 
 3.2 
 
 2.6 
 2.8 
 
 3.3 
 
 2.9 
 
 3.9 
 3.9
 
 CROP CHEMISTRY 119 
 
 during the making of hay from alfalfa, alsike and red clovers, 
 orchard grass and timothy, and in the curing of corn fodder. 
 The figures are all reduced to the dry basis so that they may 
 be compared. It is to be noted that a loss occurs uniformly 
 in the crude protein content, in nearly every crop in ash 
 and crude fat, whereas there is little change in the nitrogen- 
 free extract, and an increase in the crude fiber in nearly 
 every instance. 
 
 The drying of the crop is of the greatest importance in 
 haymaking, for the presence of large quantities of water will 
 promote the activities of fermentative bacteria, that is, the 
 hay will rot. This rotting is in large measure an oxidation 
 process caused by the action of bacteria. Moisture is 
 necessary for the life of the bacteria, and changes take place 
 which render the hay unfit for use as food. This bacterial 
 oxidation sometimes raises the temperature considerably, 
 occurring when the stack is not ventilated sufficiently, and 
 the heat is not conducted away. Moreover, too moist hay 
 encourages the growth of molds which destroy the value of 
 a hay as food. 
 
 During the drying process some changes take place, 
 probably of an enzyme nature, whereby compounds like 
 volatile oils develop, thus giving flavor and palatability 
 to the hay. This process undoubtedly continues to some 
 extent in the mow or stack. 
 
 The time of cutting hay is of importance. It must be 
 remembered that the stems and leaves are the valuable 
 portion. They should be harvested when they contain as 
 much valuable digestible constituents as possible, and yet 
 give as great a yield as is consistent with the other factors. 
 In the later stages of growth the proteins, fats, and carbo- 
 hydrates are moved to the seed. The stems and leaves 
 are exhausted of these constituents and at the same 
 time are provided with more cell wall material or crude 
 fiber. The seeds of grasses and of. the hay legumes are very 
 small and are easily shaken off when dry. In this way there 
 would be lost the most valuable part of the food, were the 
 hay to be made from mature crops. 
 
 Again, jn^ such crops as alfalfa most of the protein is in
 
 120 CROPS 
 
 the leaves. If the plant matures before cutting, the leaves 
 become brittle and are easily knocked off, and in this way 
 protein is lost. Also as a plant grows older, and the seeds 
 form, the ash elements which are of value to stock are gradu- 
 ally lost from the plant, largely by being exuded on the 
 surface of the leaves and washed off by rains. In addition, 
 the older a fodder crop gets, particularly timothy, the less 
 protein and fat, and the more crude fiber and nitrogen-free 
 extract there are in the dry material (See Table V). 
 
 TABLE V. CHANGES IN THE COMPOSITION OF TIMOTHY DURING 
 GROWTH 
 
 (Pounds in 100 of Dry Matter) 
 
 Nitrogen- 
 Crude Crude free Crude 
 Ash. protein. fiber. extract. fat. 
 Before bloom, 
 
 headed ... 7.7 11.3 26.3 50.9 3.8 
 
 In full bloom . . 5.7 7.9 29.9 53.6 2.9 
 
 Just after bloom . 5.7 7.1 30.9 53.2 3.1 
 
 In seed, nearly ripe 5.7 6.6 30.7 54.2 2.8 
 
 If cut too early, on the other hand, the crop will be too 
 small and not a maximum amount of inorganic material 
 will have been absorbed by the plant. In fact all of the 
 constituents will be small in amount. Although the time 
 of cutting hay will vary with the crop and the purpose to 
 which it is to be put, and will also depend somewhat on 
 weather and other conditions, the proper time, in general, 
 to cut hay crops is when they are beginning to bloom. 
 Later, of course, a larger yield will be obtained but the 
 quality will not be as good, and the palatability and color 
 will not be as desirable. 
 
 The proper methods of curing and storing hay are not 
 to be considered in a work of this kind, but there is one 
 practice which should be mentioned here. Some farmers 
 have a habit of mixing salt or lime with the hay in stacking, 
 with the idea of preserving it, especially if it has been neces- 
 sary to stack the hay a little wetter than usual. Salt and 
 lime may prevent the action of bacteria and fungi to some 
 extent, although no definite information is available. Cer- 
 tainly stock like salted hay, but that is on account of the
 
 CROP CHEMISTRY 121 
 
 salt. Lime, on the other hand, does not improve the taste 
 of the hay. The value of either of these materials as a 
 preservative is very questionable. 
 
 102. Silage. Inasmuch as haymaking is in large measure 
 a drying process the resulting material is dry, and for general 
 feeding purposes a certain amount of more succulent food 
 is desirable. Silage answers this purpose. It is usually 
 made from corn, but sometimes mixtures of corn and cow- 
 peas, corn and soja beans, oats and vetch are employed. 
 Those crops which do not field cure or dry readily are best 
 employed for silage. Corn is particularly well adapted for 
 this purpose because of its succulence and also because it is 
 an economical crop to use, for the more mature it becomes 
 the better is its composition from a feeding point of view. 
 Hay, on the other hand (Section 101), becomes less digestible, 
 containing less ash, protein, and fat, and more crude fiber. 
 The corn crop not only increases in weight with maturity, 
 but also improves in quality, containing more crude fat 
 and nitrogen-free extract, much less crude fiber, and not 
 very much less ash and crude protein (See Table VI). The 
 
 TABLE VI. CHANGES IN THE COMPOSITION OF CORN DURING 
 GROWTH 
 
 (Pounds in 100 of Dry Matter) 
 
 Nitrogen- 
 Crude Crude free Crude 
 Date of harvest. Ash. protein. fiber. extract. fat. 
 
 Aug. 15, ears beginning to form . 9.31 14.94 26.47 46.63 2.65 
 
 Aug. 28, a few roasting ears . .6.51 11.71 23.31 55.49 2.98 
 
 Sept. 4, all roasting ears . . . 6.19 11.36 19.69 59.74 3.02 
 
 Sept. 12, some ears glazing . . 5.57 9.58 19.33 62.59 2.93 
 
 Sept. 21, all ears glazed . . . 5.92 9.23 18.59 63.30 2.96 
 
 material for silage is cut fine and packed tightly in an air- 
 tight receptacle, called a silo (Figs. 31 and 74). The object 
 is to keep the material away from the air as much as possible. 
 Since it is a moist material the presence of air will hasten 
 bacterial action and cause putrefaction. 
 
 103. Chemical Changes in Silage Making. Decomposition 
 occurs to some extent. Some of the sugars, usually dextrose 
 in corn, are fermented by yeasts to alcohol, and the alcohol 
 is changed by acetic bacteria to acetic acid. Lactic bacteria
 
 122 
 
 CROPS 
 
 convert part of the sugar into lactic acid. There are also 
 small amounts of butyric and some other acids formed, the 
 total acidity amounting to not more than 2 per cent, nor 
 usually less than 1 per cent. It is sometimes stated that these 
 acid changes are due not to bacteria but to intermolecular 
 respiration in the plant cells. Whether caused by bacteria 
 or intermolecular respiration, the accumulation of acid 
 stops the process, thus accounting for the maxmium of 
 2 per cent. acid. 
 
 FIG. 31. Silos. 
 
 In addition to these changes there is also a loss of protein 
 and a formation of amides, possibly due to enzyme changes 
 analogous to the usual hydrolytic changes of protein within 
 the plant. Moreoever, some nitrogenous material decomposes 
 to ammonia, which forms salts with the acids present. Crude 
 fiber is softened and made more digestible, being partly 
 hydrolyzed in all probability. Other compounds in the 
 nature of volatile oils are formed, which add to the palata- 
 bility of the material. There is also a complete decomposition 
 of some of the organic material. There is oxidation to carbon 
 dioxide and water, either by bacteria or oxidases, resulting 
 in a loss of dry matter amounting to 10 or 15 per cent.
 
 REFERENCES 123 
 
 EXERCISES 
 
 1. Why is dried material extracted in a crude fat determination? Why 
 is alcohol-free ether used in this determination? What substances does the 
 ether extract? 
 
 2. List all the types of substances that are found in plants. In which of 
 the six groups of the Weende method does each fall? 
 
 3. Compare the analyses of seed and straw of barley by the Weende 
 method. To what extent are these figures relatively as you would expect 
 them to be from your former knowledge, and why? Compare wheat, straw 
 and potatoes in the same way. 
 
 4. Would a crop containing more crude protein than nitrogen-free extract 
 be a better crop to feed for energy production than one containing more of 
 the latter than of the former and why? Substitute crude fiber for crude 
 protein in the above question and then answer it. 
 
 5. Explain why calcium and potassium are so necessary for alfalfa and 
 red clover. 
 
 6. Given a rotation of corn, oats and hay (timothy and red clover), tell 
 which crops would remove nitrogen and phosphorus and but little potassium, 
 also which crops would remove potassium and but little nitrogen and 
 phosphorus. 
 
 7. How many samples must be weighed out in order to make a Weende 
 determination? 
 
 8. State whether plant food applied to the following crops should be com 
 paratively high in N, PjOs, or KjO: Potatoes, corn and strawberries. 
 Consider these plant foods functionally and then state whether or not the 
 figures found are what you would expect them to be. (See Table 111.) 
 
 9. State why or why not you would expect seeds to be low in ash. 
 
 10. Cucumbers contain 95.4 per cent, water. Explain why they are not 
 easily crushed. 
 
 1 1 . Write equations for the chemical changes that take place in hay mak- 
 ing and silage production. Why cannot equations be written for all of these 
 changes? 
 
 REFERENCES 
 
 Conn., Storrs, Agr. Expt. Sta., Bui. 70. Silage Fermentation. 
 
 Farmers' Bui. No. 578, U. S. Dept. Agr. Making and Feeding of Silage. 
 
 Halligan. Elementary Treatise on Stock Feeds and Feeding. 
 
 Kans. Bui. 155. Alfalfa. 
 
 Kans. Bui. 175. Grasses. 
 
 Office of Experiment Stations, Appendix Bui. 15, U. S. Dept. Agr. Com- 
 position of Various Crops. 
 
 Office of Experiment Stations, Bui. 28, U. S. Dept. Agr. Chemical Com- 
 position of American Food Materials. 
 
 Van Slyke. Fertilizers and Crops.
 
 PART II 
 
 FACTORS IN PLANT GROWTH 
 
 CHAPTER V 
 THE AIR 
 
 OF all the factors which influence plant growth, there is 
 one over which the farmer has no control and yet one which 
 is absolutely necessary to the life of both plants and animals. 
 This factor is the air. It is important not only because it 
 supplies plants and animals with certain essential elements, 
 but also because its constituents and the changes in these 
 constituents cause variations in climate. Moreover, the air 
 and its constituents have a very considerable effect on the 
 formation and decomposition of soils. It is, in short, of 
 such vital importance to the farmer that a short discussion 
 of its properties and constituents is advisable at this point. 
 
 104. Height of the Air. If the air were of the same 
 density throughout it would extend away from the earth for 
 five or six miles, but since its density becomes less as the 
 distance from the earth increases, it has been estimated that 
 our planet is enclosed within a gaseous envelope about 200 
 miles thick. 
 
 105. Pressure or Weight of the Air. At sea level, and 
 at C. the air exerts normally a pressure or weight of 1033 
 grams per square centimeter. This is 14.7 pounds per 
 square inch or 46,100 tons per acre. The pressure diminishes 
 with the altitude. At an elevation of about 18,000 feet the 
 pressure is one-half that at sea-level, and at 36,000 feet 
 about one-fourth. Since the average farm is not at sea- 
 level it would be reasonable, then, to say that the weight of 
 
 (125)
 
 126 THE AIR 
 
 the air on each acre is in round numbers 45,000 tons. The 
 pressure or weight of the air, however, is never constant; it 
 varies from day to day, from season to season, and from 
 latitude to latitude. It is lower, for example, at the poles 
 and at the equator than it is between these two latitudes. 
 
 106. Properties of the Air. The air is usually a trans- 
 parent, colorless, odorless, mechanical mixture of gases, 
 vapor, and solids, the latter existing in exceedingly fine 
 particles. 1000 cc. of air weigh 1.293 grams. By cooling 
 and pressure it can be condensed to a bluish, mobile liquid, 
 whose boiling point is about 195 C. Its specific gravity is 
 0.9. There exist in it particles of ice from frozen water, and 
 solid carbon dioxide. These can be removed by filtration. 
 
 107. Water Vapor. Ordinary air contains varying 
 amounts of water vapor, on the average about 1.3 per cent, 
 by volume or 0.84 per cent, by weight. There is a limit to 
 the amount of water vapor that the air will retain. When 
 that limit is reached water is condensed to drops and we 
 have rain, or snow if it is cold enough to freeze the drops. 
 The higher the temperature the more water vapor can be 
 held by the air. For instance, at C., 1 cubic meter of 
 air will hold 4.8 grams, whereas at 20 C., "ordinary room 
 temperature," 1 cubic meter will hold 17.1 grams. When the 
 air is saturated at any given temperature, a lowering in the 
 temperature will result in precipitation. A glass of ice water 
 " sweats," that is, moisture is condensed from the surrounding 
 air by a lowering of the temperature below which the moisture 
 can be retained. That temperature at which air begins to 
 deposit water is called the dew point and, of course, will 
 vary with the amount of water vapor present in the air. 
 Dew is deposited at night when objects are cooled off by 
 radiation to such an extent that their temperature is below 
 the dew point of the surrounding air. 
 
 108. Temperature of the Air. The presence of water 
 vapor in the air modifies the temperature to a very great 
 extent. Perfectly dry air absorbs practically no heat from 
 the sun's rays. They pass through and warm up the earth. 
 And in the same way at night, heat radiates from the earth, 
 passing through dry air with but little absorption. In the
 
 COMPOSITION OF THE AIR 127 
 
 dry regions of western United States, the days are very 
 hot. The sun's heat rays pass through the air unchecked. 
 At night, on the other hand, it is very cool, because the heat 
 has radiated away again. Water vappr and particles of 
 dust in the air absorb the heat. A cloud blanket does not 
 permit of radiation from the earth, nor does it permit much 
 heat to pass through to the earth. On a cloudy night there 
 is not so much danger of frost as on a clear night, since the 
 heat is not radiated off into space so rapidly. 
 
 Air is warmed by contact with its own water vapor, or 
 with the earth. When a surface of water is evaporating 
 heat is being absorbed; when water vapor condenses heat 
 is liberated. The specific heat of water is 1, whereas air 
 is only 0.240, and the weight of a given volume of air is ^-^ 
 of the weight of an equal volume of water. Thus when a 
 large body of water warms up one degree and evaporation 
 takes place, a volume of surrounding air equal to 3200 times 
 the volume of the body of water is cooled down one degree. 
 And, conversely, when a body of water cools down one degree, 
 the surrounding air to the extent of 3200 tunes the volume 
 of water is warmed up one degree. This accounts for the 
 modifying effect of large bodies of water on the climate of 
 nearby land. This accounts, also, for the mild climate of 
 western Europe which is washed by the warm Gulf Stream. 
 
 109. Composition of the Air. The constituents of the air 
 other than water vapor, which is exceedingly variable, are 
 arranged in Table VII in the order of their amounts : 
 
 TABLE VII. ATMOSPHERIC CONSTITUENTS 
 
 Per cent. Per cent. 
 
 Constituents. by volume. by weight. 
 
 Nitrogen . 78.03 75.51 
 
 Oxygen 
 
 Argon 
 
 Carbon dioxide 
 Hydrogen .... 
 Compounds of nitrogen 
 Bacteria .... 
 Dust, etc 
 
 20.99 23.14 
 
 0.94 1.29 
 
 0.03 0.05 
 
 0.01 0.001 
 
 Trace Trace 
 
 To give a striking illustration of the different amounts of 
 the constituents of the air, a slight modification of Graham's
 
 128 THE AIR 
 
 suggestion is interesting. If the air is imagined to be sepa- 
 rated into its several parts and these to be arranged around 
 the earth in the order of their specific gravities, water vapor 
 being condensed, there would be first a layer of water five 
 inches thick, then thirteen feet of carbon dioxide, next ninety 
 yards of argon, then a mile of oxygen, and finally four miles of 
 nitrogen, with possibly three or four feet of hydrogen on top. 
 
 (a) NITROGEN. The amount of nitrogen in the air varies 
 but little. It is the most constant of all the constituents. 
 It is a very inert gas, uniting with other elements only at 
 high temperatures. It acts in the air in part as a diluent, 
 rendering the activity of oxygen less energetic. It is the 
 ultimate source of all nitrogenous compounds. The means 
 by which it has been made to combine with other elements 
 is bacterial in nature (see Section 125). By these means 
 it is removed from the air, but is returned in small measure 
 in the free state by the decomposition of nitrogenous organic 
 matter, and by the burning of all kinds of fuel or other or- 
 ganic material containing nitrogen. The ordinary com- 
 bustion of one ton of coal releases from one to five pounds 
 of nitrogen. 
 
 (6) OXYGEN. This constituent, although fairly constant 
 in amount, has been known to vary from 20.53 per cent, by 
 volume to 21.03 per cent. Since a man consumes about 
 600 liters of oxygen in a day, and a ton of coal in burning 
 consumes about 1,500,000 liters, it can easily be seen that 
 the air of cities, which are densely populated and where 
 much manufacturing is carried on, has a lower percentage 
 of oxygen than the open country. And this is further empha- 
 sized by the fact that the country is where large numbers of 
 growing plants are to be found, and in photosynthesis oxygen 
 is given off by plants. Oxygen, as has been noted in Chapters 
 II and III, is necessary for the germination of the seed and the 
 growth of the plant. It is, moreover, absolutely necessary 
 for the life of man and other animals. 
 
 (c) CARBON DIOXIDE. Of the important constituents of 
 the air, carbon dioxide is the smallest in amount and the most 
 variable, with the exception of water vapor. Although 
 normal, pure air contains about 0.03 per cent, by volume,
 
 COMPOSITION OF THE AIR 129 
 
 city air contains 0.05 to 0.07 per cent.> and the carbon dioxide 
 in the air of crowded auditoriums may rise to 0.5 per cent. 
 At night the amount of carbon dioxide is greater than during 
 the day, because of the inactivity of plants in the dark. Since 
 one man exhales about 550 liters of carbon dioxide daily, 
 and a ton of coal gives off in burning about 1,500,000 liters 
 of carbon dioxide, it is easy to account for the higher pro- 
 portion of carbon dioxide in the air of cities. In the country 
 where there are many plants and a large area of leaf surface 
 absorbing carbon dioxide, the amount is naturally less (see 
 Frontispiece). An acre of corn, for example, at the height 
 of the growing season would absorb about 10,000 liters of 
 carbon dioxide per day, and it has been estimated that an 
 acre of forest uses up about 6000 liters per day. In addition 
 to these compensatory changes in the amount of carbon 
 dioxide in the air there are volumes poured into the air by 
 some volcanoes and other openings in the earth. The 
 decay of organic matter causes evolution of carbon dioxide; 
 the weathering of rocks on the other hand uses up some 
 carbon dioxide (Section 128). The amounts of carbon 
 dioxide absorbed do not balance the amounts given off into 
 the air. The ocean apparently acts as a regulator of the 
 amount. When there is any increase in the percentage of 
 carbon dioxide in the air this naturally increases the pressure 
 of carbon dioxide on the surface of the water and some is 
 dissolved and changed to bicarbonate of calcium. On the 
 other hand a diminution in the amount causes a lowering 
 in the pressure and some bicarbonate of calcium changes to 
 carbonate again and releases carbon dioxide. In this way 
 there is maintained a fairly uniform amount of carbon 
 dioxide in the air. 
 
 (d) ARGON AND HYDROGEN. Argon is one of the so-called 
 rare elements. It has no agricultural bearing, and is so 
 inert that it will unite with no other element. In fact its 
 name means that it will not work. In addition there are 
 several other rare gases existing in much smaller amounts, 
 but none of them is of any importance. Hydrogen, also, 
 although present in the air in fairly constant quantities, 
 is of no agricultural value and need not be considered. 
 9
 
 130 THE AIR 
 
 (e) COMPOUNDS OF NITROGEN. These compounds are of 
 importance as far as they go, but the amount present is very 
 small. They are principally oxides of nitrogen and am- 
 monia, occurring usually, perhaps, as nitrous and nitric 
 acids and ammonium nitrite, nitrate, carbonate, or sulphate. 
 The oxides of nitrogen are formed from oxygen and nitrogen 
 by lightning discharges. The intense heat in the immediate 
 vicinity of the electric spark causes a very small part of 
 these gases to unite. Ammonia is formed by the decomposi- 
 tion of organic matter, although free nitrogen is formed 
 under some conditions (Section 124). These compounds of 
 nitrogen can be used very well by plants after some changes 
 in the soil, but the amount is hardly worth considering 
 ordinarily. On the average there are about three pounds of 
 nitrogen brought to the surface of an acre in a year by rain 
 and snow. Occasionally this may amount to ten pounds, 
 but very rarely. 
 
 (/) BACTERIA. The solid particles of the air, besides the 
 nitrate, carbonate, and sulphate of ammonium mentioned 
 above, consist of bacteria and dust. Bacteria exist in count- 
 less numbers in the air, invisible, but nevertheless of great 
 importance, sometimes beneficial, sometimes harmful. The 
 bacteria which aid in decomposing organic matter in the 
 soil and in making nitrogen available are all carried in the 
 air and help the farmer very materially. Moreover, the 
 germs of many diseases are carried through the air and work 
 considerable harm. One proof of the presence of bacteria in 
 the air is to be found in the fact that if perfectly sterile milk 
 is exposed to the air for any length of time it will sour, due 
 to the lactic acid bacteria being carried to it by the air. 
 
 (g) DUST. Fine particles of dust are everywhere present 
 in the air, and consist of minute particles of organic matter, 
 bits of cotton, pieces of hair, and fragments of minerals. 
 There may also be pollen from flowers, and spores of fungi. 
 These particles of dust form nuclei for the precipitation of 
 water vapor and hence cause the formation of fog and clouds. 
 Dustless air would contain no fog. 
 
 (h) SULPHUR DIOXIDE is of very serious consequence in 
 some places. In the western part of the United States where
 
 REFERENCES 131 
 
 smelters have been erected for the treatment of sulphide 
 ores, large volumes of sulphur dioxide are discharged into 
 the air during the roasting of the sulphides. This has a 
 very harmful effect on vegetation and has led to legislative 
 action in a number of states. Not only does the gas itself 
 harm vegetation, but its solution in rain water as sulphurous 
 acid is poisonous. In large cities where much soft coal is 
 burned sulphur dioxide is present in the air and this accounts 
 in part for the weak, sickly appearance of trees and grass 
 in such centers of industrv. 
 
 EXERCISES 
 
 1. List the components of air. State the processes by which each com- 
 ponent serves in a beneficial or harmful way to agriculture, and how. 
 
 2. Explain why the temperature on the shores of the Great Lakes is 
 more constant than 150 miles inland. 
 
 3. Is moist or dry air the heavier? Why? What instrument in common 
 use can detect the difference? 
 
 4. Why is the farmer more uncomfortable while making hay on a moist 
 day than on a dry day of the same temperature? 
 
 5. Why are thunderstorms of any value to agriculture? 
 
 6. From what sources are the principal components of the air continually 
 derived? By what means are they removed? Why is the composition of 
 the air so nearly constant all over the earth? 
 
 7. What would be the result of making your animals work in an atmos- 
 phere whose nitrogen content was materially lessened? 
 
 8. Why is the farmer's wife at preserving time so very careful not to get 
 any unheated air into her preserves? 
 
 9. Why will freshly drawn milk spoil more quickly when kept exposed to 
 the atmosphere than when kept in sealed containers? 
 
 REFERENCES 
 
 McPherson and Henderson. General Chemistry. 
 
 Newth. Inorganic Chemistry. 
 
 Smith. General Chemistry for Colleges. 
 
 Any other good text-book on general chemistry.
 
 CHAPTER VI 
 THE SOIL: ORGANIC MATTER 
 
 THAT portion of the earth's crust which can support 
 vegetation, or can raise crops, is what the farmer terms the 
 soil. That loose mass of particles derived from rock dis- 
 integration and decay, and which covers most of the land 
 portion of the globe is the way the geologist defines the soil. 
 These definitions for the most part describe the same mate- 
 rial but geological soil is not always agricultural soil, for 
 not all loose rock particles will raise crops, and hence to the 
 farmer are not soil. 
 
 110. Composition of Soil. Soil agriculturally is composed 
 of fine and coarse particles of rock in all stages of decompo- 
 sition, of organic matter derived from decayed or decaying 
 plants and animals, of water, of bacteria, fungi, and other 
 forms of life, and of gases. 
 
 111. Function of the Soil. Soil serves not only as an 
 anchorage for plants, where they can spread out their roots 
 and maintain a position which will enable them to absorb 
 the sun's rays to the best advantage, but also serves as the 
 source of most of those elements which are essential to the 
 plant's growth. A perfect soil is one which maintains a 
 reserve supply of insoluble food material that cannot be 
 washed away; which produces enough soluble material to 
 feed the growing crop; which is so constructed that it can 
 supply sufficient water to the crop; which is capable of main- 
 taining the right temperature or of warming up quickly in 
 the spring; and which has a structure that permits of proper 
 root movement. 
 
 112. Soil Study. The study of the movements of water 
 in the soil, of its holding capacity for water, of the arrange- 
 ment of soil clusters, of the size of ultimate particles, of the 
 relations of soils to heat, and of the various methods of 
 
 (132)
 
 ORGANIC MATTER 133 
 
 working the soil, are all important factors for the farmer to 
 consider, but do not come within the scope of agricultural 
 chemistry. The study of the important compounds in the 
 soil and the changes which take place in them; in other 
 words the chemical reactions and their causes, which directly 
 or indirectly affect the growth of crops, do, however, com- 
 prise soil chemistry. The food of plants, from what derived, 
 how made soluble, how retained in the soil or made insoluble, 
 are particular points to be considered. 
 
 Plant food is derived from the rock particles and from the 
 organic matter. Soil moisture, organic matter, bacteria, 
 fungi, and gases are factors influencing the changes taking 
 place in plant food. The mineral particles, and the organic 
 matter to a small extent, supply the compounds containing 
 phosphorus, potassium, sulphur, calcium, magnesium, and 
 iron. The organic matter is the source of nitrogen. In 
 taking up the subject of plant food in soils it seems best 
 to discuss first the organic matter which has been very 
 truthfully called the life of the soil. It is probably the most 
 important single factor in making plant food soluble, except 
 of course water, the solvent medium itself. 
 
 113. Organic Matter. The soil is separated horizontally 
 into two portions as .it lies in the field : First, the surface 
 soil, or sometimes called merely soil, and second, subsoil. 
 For certain purposes, such as the scientific study of soils 
 in comparing types, it is advisable to arbitrarily assume that 
 the surface six, eight, or ten inches shall be the surface soil, 
 and all below that shall be the subsoil, but the natural 
 division lies at the place where the color of the soil changes, 
 frequently very abruptly, almost always very distinctly, 
 from dark to light (Fig. 32). This depth varies in different 
 soils, sometimes lying only a few inches below the surface 
 of the land, sometimes lying several feet below. 
 
 It is in this dark soil that crops can grow best. It frequently 
 happens that when a light colored subsoil is turned up, 
 crops will not grow. This may be due to several causes, but 
 one of them at least is the absence of organic matter which 
 gives the dark color to surface soil. Organic matter in the 
 soil is composed of particles of roots, leaves, bark and other
 
 134 
 
 THE SOIL: ORGANIC MATTER 
 
 plant debris, and fragments of animals, insects, and worms, 
 in all stages of decomposition, ranging from their original 
 condition and easily recognizable, down to the unrecognizable 
 pieces and the amorphous, waxy coating on soil grains. The 
 whole mass of soil material, which at one time or another was 
 a part of living organisms, is called organic matter. Organic 
 matter in the process of decomposition, which is changing 
 continually and breaking down into new compounds, may 
 be called active organic matter. That particular part of it 
 
 FIG. 32. Soil and subsoil, showing dark color due to organic matter. (Weir.) 
 
 which is much more decomposed, which has lost all resem- 
 blance to living matter, and which is indistinguishable among 
 the soil grains, except that it gives the dark color to them, 
 may be called inactive organic matter or humus. 
 
 114. Bacteria. As soon as a portion of a living organism 
 dies, whether it be a leaf, or bit of bark, or 1 mass of roots, it 
 is at once attacked by bacteria which are everywhere present 
 in the soil. Inasmuch as bacteria are of such vital impor- 
 tance to agriculture, both beneficially and otherwise, a brief 
 description of them is desirable.
 
 BACTERIA 135 
 
 Bacteria are one-celled plants which are composed of 
 cell walls of protein not cellulose cell contents or proto- 
 plasm and enzymes, but no nucleus. They are very much 
 like any of the simple cells in crop plants except for the 
 absence of nuclei. These bacterial cells require soluble 
 material which can diffuse through their walls and from which 
 can be built up the various components of the cell wall and 
 contents. They are thus permitted to reproduce themselves 
 by subdivision. The cells are small, about 1 micron (0.001 
 mm.) in diameter, or even smaller. Some bacteria are more 
 or less spherical, others are rod-shaped, perhaps two or three 
 times as long as they are wide, and some of them are spiral- 
 shaped. They consist of about 85 per cent, of water, and 
 of the dry matter some 8 per cent, is composed of inorganic 
 compounds. The rest is fat, carbohydrate, and protein 
 material largely, very much like the cell contents of any 
 plant. 
 
 Bacteria contain no chlorophyl, hence do not make their 
 organic food by means of the energy derived from the sun's 
 rays. The energy they use in synthesizing compounds is 
 derived by oxidation of various compounds, with or without 
 the aid of free oxygen, or by intermolecular decomposition, 
 which releases energy. Many bacteria, like crop plants, 
 oxidize organic compounds to carbon dioxide and water. 
 Some oxidize nitrogen, sulphur, iron, and other inorganic 
 elements (considering nitrogen an inorganic element) to 
 nitrites and nitrates, sulphuric acid, and ferric oxide. In 
 this way they derive energy. Others reduce highly oxidized 
 compounds like nitrates and sulphates, using the oxygen 
 thus derived to oxidize other compounds. And still others 
 merely decompose compounds without any oxidation, deriv- 
 ing such energy, for example, as is released when dextrose is 
 changed to lactic acid. . 
 
 The material which bacteria use as food for tissue-forming 
 purposes is largely organic in nature, although there are some 
 bacteria which live without any organic matter that is, 
 they use inorganic compounds entirely from which to make 
 their cell substance. The organic material that is most 
 frequently used is composed of the various carbohydrates,
 
 136 THE SOIL: ORGANIC MATTER 
 
 fats, and proteins of animal and plant origin. Those 
 compounds which are insoluble are rendered soluble by the 
 excretion of enzymes which acts hydrolytically usually, to 
 dissolve the compound. The soluble substance then diffuses 
 into the bacterial cell where further transformations take place. 
 
 Since enzymes act independently of the living cell which 
 produces them, they frequently form sufficient material to 
 kill, or at least to stop the activities of the bacteria as well 
 as of themselves. This is true of acid- and alcohol-forming 
 enzymes in particular. If the acid can be neutralized as 
 fast as it is formed, or if the alcohol is further changed, 
 the production of acid and alcohol will not cease. 
 
 Some bacteria use oxygen, while some do not. This fact 
 goes one step further in that many of the oxygen-using, or 
 aerobic bacteria, can not live at all in the absence of oxygen 
 or air, and in that many of those which do not use oxygen, or 
 anaerobic bacteria, cannot live in the presence of free oxygen 
 or air. 
 
 115. Decomposition of Organic Matter. In the soil, as 
 was stated above, are very many bacteria of all kinds. 
 Furthermore, the conditions under which they live are very 
 different, depending on the physical condition of the soil 
 and on the kind of organic matter from which they derive 
 nourishment. The principal difference, however, is the 
 presence or absence of air. In a soil that is fairly open and 
 aerated there are different products formed from those in a 
 water-logged or non-aerated soil. It is not easy, however, 
 to classify organic decomposition on this basis, for soils 
 vary gradually all the way from those containing no air at 
 all, like swampy lands under water, to those which are very 
 thoroughly penetrated by the air, like loose, sandy lands. 
 
 In a general way the products of decomposition can 
 be classified into two groups: First, those developed under 
 aerobic conditions; and second, those developed under 
 anaerobic conditions. Under aerobic conditions there will 
 be produced large quantities of carbon dioxide and water, 
 mineral salts (set free by oxidation of organic matter con- 
 taining inorganic elements), and nitrates, but not much 
 humus (Section 117). Under anaerobic conditions there
 
 FACTORS AFFECTING RATE OF DECOMPOSITION 137 
 
 will be produced small amounts of carbon dioxide and water, 
 considerable humus, and in addition methane and hydrogen 
 sulphide. In both cases there will be varying amounts of 
 organic acids, alcohols, higher hydrocarbons, waxes, etc. 
 
 The classification holds only in a general way. Of course, 
 where there is an excess of air, organic matter is largely 
 oxidized to carbon dioxide, water, residual inorganic salts, 
 and nitrates. As the amount of air available to the bacteria 
 becomes less, oxidation to carbon dioxide, water, nitrates, 
 and mineral salts, materially lessens. More acids and alcohols 
 form, as well as more of that black, amorphous product 
 called humus. As the air supply continues to decrease, less 
 and less carbon dioxide and water are produced, although 
 their formation never ceases entirely, for intermolecular 
 oxidation sets free small quantities. The production of 
 nitrates practically ceases in the absence of air, and products 
 that result from reduction, like methane and hydrogen 
 sulphide, begin to form. The reduction of one compound is 
 accompanied by a simultaneous oxidation of another com- 
 pound and the production of energy. Considerably more 
 acids, alcohols, and waxes are formed, since intermolecular 
 decomposition results in the formation of these compounds 
 rather than of the completely oxidized forms. At the 
 same time there is produced more and more of this curious, 
 amorphous mixture called humus. In soils which are 
 absolutely anaerobic, however, little humus is formed. In 
 fact under conditions where no air at all is present decom- 
 position is very slow. Organic matter is maintained in a 
 fairly well preserved condition. In peat bogs, for example, 
 the structure of the original plants, sphagnum moss in many 
 cases, is not destroyed. 
 
 The bacteria exist in soils for the most part in the upper 
 eight to ten inches, just under the surface. There are very 
 few on top of the ground, for direct sunlight kills most 
 bacteria. 
 
 116. Factors Affecting the Rate of Decomposition. The 
 extent to which decomposition of organic matter will take 
 place theoretically agrees with the above classification, but 
 the amount or rate of decomposition depends on two prin-
 
 138 THE SOIL: ORGANIC MATTER 
 
 cipal factors: First, the number of bacteria present; and 
 second, the kind of living matter undergoing decomposition. 
 
 (a) NUMBER OF BACTERIA IN SOILS. As to the number 
 of bacteria in soils, it will vary between very wide limits. 
 When "number of bacteria" is mentioned it means the 
 number of colonies of bacteria that can be cultivated from 
 a given amount of soil in an artificial nutrient solution and 
 subsequently counted. The supposition is that each colony 
 is developed from a single bacterium. The numbers vary 
 from 100,000 to 50,000,000 or even 100,000,000 per gram 
 of soil. The average cultivated land probably contains 
 several million per gram. The more bacteria present, the 
 more decomposition takes place and hence a greater pro- 
 duction of those various compounds mentioned above, 
 namely, carbon dioxide, water, mineral salts, and nitrogenous 
 compounds, but ordinarily less humus. 
 
 The number of bacteria is dependent on several factors, 
 the principal ones being: Temperature, moisture, food, and 
 reaction of the soil, whether acid or alkaline. 
 
 (1) Temperature. Bacteria thrive best between 15 and 
 25 C., although they do live from about to 40 C. Near 
 bacterial life is inactive although not dead. Above 40 
 the bacteria begin to die; at 100 C. most bacteria are killed, 
 although the spores are not. 
 
 (2) Moisture. It is claimed that the best moisture con- 
 ditions for bacteria vary from 8 to 10 per cent, in sandy 
 soils to 20 per cent, and even more in heavy clays. As 
 soils dry out the bacteria for the most part merely become 
 dormant, although some are killed outright. Excessive 
 water tends to kill off the aerobic bacteria but encourages 
 the growth of the anaerobes. Since for the most part the 
 beneficial bacteria are aerobes, aeration is essential to 
 optimum soil conditions. 
 
 (3) Food. This includes of course organic matter from 
 which most bacteria derive their sustenance. Being plants, 
 they must have inorganic salts as well, and there are neces- 
 sary such salts as sulphates, phosphates, lime, and potash 
 compounds, derived either from the organic remains or from 
 mineral particles in the soil.
 
 HUMUS 139 
 
 (4) Reaction of the Soil. Most beneficial bacteria require 
 for their optimum growth a neutral or alkaline medium in 
 which to work. The presence of an acid inhibits their 
 growth to a certain extent. Some bacteria produce mineral 
 or organic acids as a result of their own activities, and these 
 acids after reaching certain concentrations not only check 
 the growth of the bacteria which produce them, but that of 
 other bacteria as well. If there are sufficient acid-neutral- 
 izing compounds in the soil, such as calcium carbonates, 
 these acids are neutralized as fast as formed and bacterial 
 life is not suspended. 
 
 (6) KINDS OF LIVING MATTER. Although all portions of 
 vegetable and animal remains are attacked by one kind of 
 bacteria or another, and eventually can be entirely decom- 
 posed under ordinary soil conditions, some parts of these 
 remains resist decay more strongly than others. This is due 
 ordinarily to the few species of bacteria which can attack 
 these parts of the plant or animal body. 
 
 Cellulose and lignin that is, the hard, woody portion of 
 plants resist decay more strongly than the softer, more 
 succulent portions. Large roots, bits of bark, particularly 
 bark containing tannins, and wood in general, are more 
 resistant than leaves, soft stems, and fine roots like those of 
 grass. As a rule fats and waxes are less easily decomposed 
 than sugars and most of the proteins. In forests, however, 
 logs and stumps gradually decay and disappear entirely, 
 but here the conditions for one thing are most favorable 
 for rapid oxidation, and those bacteria and fungi which are 
 the most active oxidizers thrive. 
 
 Most animal remains decay rapidly, but such things as the 
 organic matter in bones, hair, or hide decompose very 
 slowly. 
 
 117. Humus. The accompaniment of almost all kinds 
 of organic decomposition in soils is the production of a black 
 or dark amorphous material which is called humus. It is 
 one of the products of decay, formed for the most part 
 where there is insufficient oxygen to allow complete destruc- 
 tion to carbon dioxide and water. From the original source, 
 whether it be root or leaf or stalk or animal, the humus is
 
 140 THE SOIL: ORGANIC MATTER 
 
 distributed among the soil grains with considerable uni- 
 formity within certain limits. That is, it does not ordinarily 
 extend to any great depth, nor does it extend laterally 
 over a field with uniformity, owing to changing conditions 
 in soil masses, but the grains themselves are fairly well 
 covered with the humus. It must therefore have been more 
 or less soluble in water, or in liquid form at one time or 
 another at least, to surround the particles. Its distribution, 
 moreover, is aided by the growth and final decay of the hyphse 
 or root-like hairs of certain fungi which feed on a decaying 
 bit of organic matter. It is no uncommon occurrence to 
 note the wide ring of darker soil surrounding a decaying 
 root. Earthworms also distribute humus throughout the 
 soil to a very great extent by passing soil through their bodies 
 and drawing after themselves into their burrows particles 
 of leaves and blades of grass. In some localities where 
 earthworms are fairly numerous, Darwin has estimated 
 that they work over in a year from 0.1 to 0.2 of an inch 
 of surface soil. Ants, burrowing insects, and animals, all 
 help to distribute organic matter and, subsequently, humus 
 throughout the soil. 
 
 118. Properties of Humus. If a dark soil containing 
 considerable humus be first treated with a dilute mineral 
 acid like hydrochloric, and then with ammonia, a black 
 liquid will be obtained. The soil residue after washing is 
 very much lighter in color, almost white in some cases. 
 By this means the humus has been dissolved from the soil 
 grains, although in many cases it may not be of exactly the 
 same composition as it was in the soil. If the water is 
 evaporated from this solution there remains a shiny black 
 material, rather hard and scaly, and absorptive of water. 
 If it is burned there remains behind an ash of inorganic 
 material. 
 
 Chemically, humus is by no means a single compound. 
 It is a mixture, probably a mechanical mixture, of many 
 substances. Research by the Bureau of Soils has shown that 
 it is composed of acids, carbohydrates, fats, waxes, hydro- 
 carbons, resins, nitrogenous compounds of various kinds, 
 black compounds or pigments, and undoubtedly many com-
 
 ACID HUMUS 141 
 
 pounds other than these few classes mentioned. Notwith- 
 standing this great complexity, the black material has, or 
 perhaps more correctly, these numerous compounds colored 
 black have certain general properties which afford sufficient 
 excuse for the term humus, and to consider them as a single 
 kind of material in the soil. 
 
 Using the term "humus," then, in this general and popular 
 sense, it can be said that it is composed of the same elements 
 as are plants, except that there is more carbon and nitrogen, 
 and less oxygen, hydrogen, and ash, or inorganic material. 
 Table VIII gives the percentage composition of cellulose, 
 grass, oak wood, decayed oak wood, and humus, showing the 
 changes in composition from fresh material to humus. 
 
 TABLE VIII. COMPOSITION OF HUMUS AND HUMUS-FORMING 
 MATERIALS 
 
 Decayed 
 Cellulose. Grass. Oak Wood. Oak Wood. Humus. 
 
 Carbon 44.2 50.3 50.6 56.2 54.5 
 
 Hydrogen .... 6.3 5.5 6.0 4.9 3.5 
 
 Oxygen .... 49.5 42.3] (41.5 
 
 43.4 38.9 
 
 Nitrogen 1.8J ( 0.5 
 
 Results on the ash of humus are not of sufficient number 
 for any definite statement to be made, but it can be said that 
 whereas plants on the whole contain 6.5 per cent, ash (Section 
 53), humus probably does not contain more than 2 per cent, 
 on the average. On the whole humus is insoluble in water 
 and organic solvents. 
 
 Humus can be divided into two kinds in the soil: Acid 
 humus, and neutral humus, both with the same physical 
 properties. 
 
 119. Acid Humus. Acid humus is formed in soils lacking 
 sufficient neutralizing materials. It is insoluble in water, acids, 
 and organic solvents. It combines with bases to form salts, 
 particularly those of the alkaline earths, which are insolu- 
 ble in water, and of the alkalies, which are soluble in water. 
 By treating a soil containing acid humus and for practical 
 purposes this means an acid soil with ammonium hydroxide 
 the acid humus reacts with the ammonium hydroxide, the re-
 
 142 THE SOIL: ORGANIC MATTER 
 
 suiting material dissolving in the solution present. A dark 
 or black liquid results. For the sake of convenience in dis- 
 cussing humus we can call the acid humus, humic acid, 
 remembering, however, that it is not a single acid by any 
 means but a mixture w T hich acts like an acid. The material 
 combined with ammonium hydroxide would then be called 
 ammonium humate. Sodium and potassium hydroxides 
 react like ammonium hydroxide. From a solution of alka- 
 line humate a mineral acid like hydrochloric precipitates 
 humic acid which separates out in black or brown flocks, 
 drying to shiny scales. 
 
 120. Neutral Humus. Where the soil contains sufficient 
 calcium or other carbonate, humic acid is neutralized as 
 fast as it is formed and the humus may then be said to be 
 calcium (or other basic element) humate. This neutral 
 humus is insoluble in water and organic solvents, unchanged 
 by ammonium hydroxide, but partly decomposed by sodium 
 and potassium hydroxides, forming the humates of the 
 alkalies, soluble in water. When treated with a mineral 
 acid like hydrochloric, the humus is decomposed, forming 
 humic acid insoluble in water, and calcium chloride soluble 
 in water. On further treatment of the soil with ammonium 
 hydroxide, the humic acid forms ammonium humate soluble 
 in water. 
 
 121. Functions of Organic Matter. In considering the 
 functions of the organic matter in the soil it should be re- 
 membered (Section 113) that there are really two kinds of 
 organic matter: First, the active or decomposing organic 
 matter which is constantly changing, with the production of 
 organic acids, carbon dioxide, water, and mineral salts, and 
 the release of nitrogen locked up in insoluble form; second, 
 the inactive organic matter or humus, which is a more or 
 less stable "compound" comparatively resistant to further 
 rapid decay. 
 
 (a) THE ACTIVE ORGANIC MATTER serves important pur- 
 poses in the production of chemical compounds active in the 
 decomposition of mineral particles; in the formation of 
 nitrates and soluble inorganic salts which serve as plant 
 foods; in increasing the moisture-holding capacity of the 
 soil; and in improving the structure of the soil.
 
 LOSS OF ORGANIC MATTER 143 
 
 (6) INACTIVE ORGANIC MATTER, OR HUMUS, serves as the 
 reserve nitrogen supply, decomposing but slowly, and thus 
 decreasing the loss of nitrogen as nitrates by leaching. Its 
 decomposition is ordinarily so slow that it does not serve to 
 any great extent as a source of organic acids, carbon dioxide, 
 and inorganic salts. Its principal function is physical, in 
 that it improves the water holding capacity very materially ; 
 increases the heat absorption and thus warms up the soil 
 earlier in the spring; improves the structure of the soil by 
 loosening heavy clays, and making sandy soils more compact. 
 
 In other words, active organic matter has a decided 
 chemical effect in the soil, while humus has an important 
 physical effect. This distinction is not absolutely definite, 
 but is generally true. 
 
 122. Loss of Organic Matter. The active decomposition 
 of organic matter in the soil is of vast importance to the 
 farmer. It is not wholly a question of piling up reserves of 
 organic matter, but rather of continually renewing the supply 
 which is undergoing constant decomposition, thus rendering 
 mineral particles soluble, freeing plant food from the organic 
 matter, and making nitrogen available. In addition, of 
 course, there must be a fair amount of humus, particularly 
 on sandy soils, for physical reasons. 
 
 Active decomposition and loss of organic matter and 
 this includes humus takes place most rapidly under in- 
 tensive cultivation, proper drainage, and application of 
 lime and commercial fertilizers. This is just what should 
 take place, but the supply must just as surely be renewed 
 by good applications of manure, and by plowing under grass, 
 clover stubble, and green manure crops. Manure by its 
 rapid decomposition does not ordinarily form humus to such 
 an extent as do the fine, numerous roots of grass. Humus 
 accumulates in pastures not only because of the fine roots 
 thoroughly spread throughout the soil, but also because the 
 soil is not cultivated and the organic matter is hence not so 
 completely oxidized. Even very heavy applications of 
 manure do not result in increased content of organic matter 
 and humus, and consequently are not economical. It is 
 better to put on reasonable applications (say 6 to 10 tons
 
 144 THE SOIL: ORGANIC MATTER 
 
 every two or three years) and supplement with hay stubble 
 or green manure. 
 
 123. Nitrification. As has been noted several times, 
 organic matter serves as the source of nitrogen for crop 
 plants. But before this organic nitrogen can be used by 
 plants it must undergo a change to nitrates (Section 54), 
 for most of the organic nitrogen is protein in character, and 
 hence insoluble and unavailable to crop plants. 
 
 The process by which organic nitrogen is changed to 
 nitrates, and thereby made available to crops, is bacterial 
 in character, and is generally called nitrification, although 
 it really takes place in three steps, the first called ammoni- 
 fication and the last two nitrification proper. Oxygen is 
 necessary for these changes to take place, hence the impor- 
 tance of thorough aeration to produce nitrates from the 
 nitrogen reserves in the soil. 
 
 (a) AMMONIFICATION is brought about by many of the 
 bacteria in the soil and is caused by the proteolytic enzymes 
 of the bacteria first breaking down the proteins into simpler 
 compounds, and further decomposing or hydrolyzing them 
 into ammonia among other products. Some of the bacteria 
 producing ammonia use it as a source of nitrogenous food, 
 others leave it merely as a by-product. 
 
 (6) NITRIFICATION PROPER is a distinct bacterial oxidation 
 of ammonia to nitrous acid, and of nitrous to nitric acid. 
 There are definitely known two kinds of organisms which 
 oxidize ammonia to nitrous acids, and they are called nitrous 
 or nitrite bacteria. The equation for this reaction may be 
 expressed as follows: 
 
 2NH 3 + 3O 2 = 2HNOj+ 2H 2 O. 
 
 There is only one kind of organism oxidizing nitrous acid 
 to nitric acid, called the nitric or nitrate bacteria. The 
 following equation represents the reaction: 
 
 2HNO 2 +O 2 =2HNO3. 
 
 The amount of ammonia or nitrous acid in the soil at any 
 one time is very small because the ammonia is changed very 
 rapidly to nitrous acid and the nitrous acid to nitric acid.
 
 DENITRIFICATION 145 
 
 Particularly is it difficult to detect traces of nitrous acid 
 because the nitrous and nitric organisms work together, the 
 latter using up nitrous acid as soon as it is formed. 
 
 It is claimed that there is one kind of bacteria which 
 oxidizes ammonia directly to nitric acid, but its identity is 
 not completely established. 
 
 These nitrifying organisms, the nitrous and the nitric, 
 obtain their energy by this oxidation process, and also utilize 
 the ammonia and nitrous acid respectively as food for 
 growth. When this happens, as whenever bacteria use soluble 
 nitrogenous compounds as food, some nitrogen is converted 
 into protein and rendered insoluble and unavailable to plants 
 until acted upon by bacteria, as in the first instance. More- 
 over, these bacteria utilize only inorganic food. From 
 carbon dioxide they manufacture their cellular substances of 
 an organic nature. The synthesis is brought about not by 
 chlorophyl but by the oxidation of ammonia and nitrous 
 acid. Hence organic matter is not essential for these bacteria, 
 and in fact too much soluble organic matter interferes with 
 their growth. This does not happen in ordinary farm soil, 
 but is a serious matter at times in soils very intensively 
 fertilized with manure and sewage, like greenhouse and 
 truck soils. 
 
 It is to be noted that the free acids themselves are the 
 products of these bacteria. In the presence of bases or basic 
 carbonates the acids are neutralized. Since calcium car- 
 bonate is the principal acid neutralizing substance in the 
 soil, nitric nitrogen occurs in most soils as calcium nitrate, 
 although some of the acid is neutralized by magnesium car- 
 bonate and potassium carbonate. If there is not sufficient 
 basic material to neutralize the acids as they are formed, the 
 bacteria are rendered inactive or are killed by the excess of 
 acid. Other conditions for their growth are much the same 
 as mentioned for bacteria in general (Section 116, a). 
 
 124. Denitrification. A process just the opposite of nitri- 
 fication is denitrification, which results in a loss of nitrogen. 
 Under anaerobic conditions and in the presence of large 
 quantities of easily decomposed organic matter, there are 
 
 several species of bacteria which can reduce nitrates to 
 10
 
 146 THE SOIL: ORGANIC MATTER 
 
 nitrites, to ammonia, and to free nitrogen. The following 
 equations illustrate the reactions: 
 
 2HNO 3 =2HNO 2 +O 2 
 4HNO 2 = 2H 2 O + 2N 2 +3O 2 
 HNO 3 + H 2 O = NHs + 2O 2 . 
 
 These bacteria can live under aerobic conditions, in which 
 case they use free oxygen for their respiration, but under 
 anaerobic conditions they use the oxygen removed from 
 nitrates. The oxygen, whether from the air or from nitrates, 
 they use in oxidizing organic matter which is necessary for 
 their growth. The denitrifiers occur in manure and on straw 
 to a considerable extent, but are not responsible for loss of 
 nitrogen under ordinary farming conditions. In cases of 
 excessive applications of manure in addition to nitrates, 
 or in greenhouses where soils are very moist and large 
 quantities of organic matter are present, nitrates may be 
 reduced. In any conditions where soils are compact or very 
 wet so there is no aeration, and where excessive quantities 
 of decomposing organic matter are present in addition to 
 nitrates, there denitrification may occur. It is, however, not 
 a condition that occurs frequently enough to cause anxiety 
 over loss of nitrogen. In any event, where only nitrites and 
 ammonia are the products, loss does not occur, for these 
 compounds may be later oxidized back to nitrates. Only 
 free nitrogen is a total loss. 
 
 125. Nitrogen Fixation. In the discussion of nitrogen 
 for the use of plants, it has been noted that the source of 
 nitrogen is the organic matter of the soil ; that in the decom- 
 position processes most of it is made available but some may 
 be lost to the air; that after entering the plant it is used 
 in tissue building and goes largely to the seed. After the 
 plant dies that part which is left on the field serves as organic 
 nitrogen for bacterial decomposition again. That part of 
 the plant which goes to feed animals returns to the soil 
 sooner or later in the form of manure, or dead animals, or 
 parts of animals. The nitrogen is continually travelling in 
 a circle with some loss. So far no mention has been made 
 of any gain.
 
 NITROGEN FIXATION 147 
 
 All nitrogen in combination on the earth came at one time 
 or another from the atmosphere. The nitrate of soda beds, 
 coal, and many other forms, all owe their nitrogen to the 
 air. In other words, there is and has been some natural 
 agency for combining atmospheric nitrogen. Nitrogen gas 
 is very inert and does not combine easily with other elements. 
 A small portion unites with oxygen under the influence of 
 lightning. But aside from this there exist in the soil 
 certain bacteria which can combine nitrogen from the air 
 with carbon, hydrogen, and oxygen, and so put it in a form 
 that can be used. This process by which atmospheric 
 nitrogen is fixed, or made into stable compounds, is called 
 nitrogen fixation, and is probably the most important single 
 process taking place in the soil, all things considered. 
 
 There are two kinds of bacteria which can fix nitrogen: 
 First, those which act independently of other living things, 
 like most of the soil bacteria; and second, those which act 
 most energetically when living with some other plant. In 
 both cases the bacteria derive energy for combining nitro- 
 gen from the oxidation of carbohydrates, and for their most 
 efficient work large quantities of soluble carbohydrates, 
 sugars probably, are necessary. The nitrogen so fixed is 
 then used by the bacteria in part, although more is fixed 
 than the bacteria need for their own growth. 
 
 (a) NON-SYMBIOTIC. Those bacteria which act indepen- 
 dently are non-symbiotic in character, that is, they do not 
 live with any other plant to the mutual advantage of both. 
 They occur in most soils apparently and are able to fix some 
 nitrogen which is left in the soil after their death. Not 
 very much is known about these bacteria, but it is not prob- 
 able that in ordinary farming they play much part in adding 
 nitrogen to the soil. 
 
 (6) SYMBIOTIC. This class is by far the more important 
 and is familiar to all farmers. The nodules on the roots of 
 leguminous plants like clover, alfalfa, peas, beans, and 
 vetch, are abnormal root growths formed to accommodate 
 the colonies of these nitrogen-fixing bacteria which are living 
 with the legumes to the mutual benefit of both (Figs. 33, 34, 
 35). The legumes supply the bacteria with soluble carbo-
 
 148 
 
 THE SOIL: ORGANIC MATTER 
 
 FIG. 33. Red Clover. 
 
 FIG. 34. Alfalfa. - 
 
 FIG. 35. Cowpea. 
 
 FIGS. 33 to 35. Nodules on legumes. Bureau of Plant Industry, United 
 States Department of Agriculture.
 
 NITROGEN FIXATION 
 
 149 
 
 hydrates, probably dextrose or maltose, and by the oxidation 
 of this material the bacteria fix nitrogen obtained from the 
 soil air through the nodules. They not only use some of the 
 resulting compounds for their own growth but apparently 
 pass on a large part of it for the use of the legumes. Fig. 36 
 shows the effect of these bacteria on clover growing in soil 
 containing no nitrates. 
 
 FIG. 36. Clover growing on soil containing no nitrates. /. No nitrogen 
 fixing bacteria. II. Supplied with bacteria. Soils Department, Wisconsin 
 Station. 
 
 Both the bacteria and the legumes can utilize nitrates in 
 the soil, but apparently the symbiotic relationship is better 
 for both. The bacteria do not fix nitrogen when supplied 
 with nitrate nitrogen, nor do the legumes accumulate the 
 nodules to any extent when there are sufficient nitrates 
 in the soil. 
 
 The bacteria are present in the soil to a considerable 
 extent, and although it is claimed they can, under suitable 
 conditions, fix nitrogen independently of legumes, they 
 apparently do not do it readily. When legume roots are 
 present in the soil these bacteria enter the root hairs, grow 
 into long gelatinous threads which penetrate the various 
 cells of the fine roots, and develop immense numbers of 
 bacteria. Their multiplication causes the peculiar nodule
 
 150 THE SOIL: ORGANIC MATTER 
 
 formation on the young roots. On clover and alfalfa the 
 nodules are very small like a pinhead or a small bean, but 
 on some beans and cowpeas they are very large, even reaching 
 the size of baseballs on the velvet bean. When the legume is 
 harvested and the roots die the nodules decompose, the 
 accumulated fixed nitrogen going back to the soil. The 
 bacteria remain for the most part inactive until more legumes 
 are grown. The amount of nitrogen added to the soil by 
 plowing under the legume crop varies considerably with the 
 crop, season, and condition of soil, but it is safe to say that 
 the ordinary clover crop adds 40 to 50 pounds per acre, and 
 alfalfa 75 to 100 pounds per acre. 
 
 Although there seems to be evidence that most of these 
 symbiotic bacteria belong to but one or two species, as a 
 matter of practical fact they are so differentiated by habit 
 of growth that there are several classes. For instance, the 
 bacteria which live on alfalfa roots are not fitted to live on 
 red clover roots, nor do the bacteria of beans live on vetch 
 roots. Not every legume has its own special bacteria, how- 
 ever, for alfalfa and sweet clover can interchange bacteria; 
 white, alsike, and red clovers apparently have the same 
 bacteria; the vetches all seem to use the same organism. 
 
 As far as crop plants are concerned only legumes have 
 nitrogen fixing bacteria on their roots, but there are some 
 plants such as the alder, New Jersey tea, buffalo berry, 
 sweet fern, and a few others which also have bacterial nodules 
 on their roots. The importance of this fact lies in the 
 ability of waste lands to accumulate nitrogen through the 
 agency of wild plants. 
 
 1 26. Inoculation. Practically all soils contain the nitrogen 
 fixing bacteria for the common clovers, peas, and beans, so 
 that a failure to have nodules develop on these legumes is 
 due rather to other causes than to lack of the bacteria in the 
 soil. For example, lime may be lacking, the soil may need 
 drainage, too much available nitrogenous compounds like 
 nitrates may be present, plant diseases may infect the 
 legumes. But where a new legume is tried, such as alfalfa 
 or serradella, and the crop fails under ordinarily beneficial 
 conditions, it may be necessary to inoculate the soil with 
 the proper bacteria.
 
 INOCULATION 
 
 151 
 
 This can be done by applying 200 to 500 pounds of surface 
 soil from some field where the crop in question has produced 
 nodules, or where a similar crop has succeeded. The soil 
 should be harrowed in at once to prevent the sunlight from 
 killing the bacteria. In the case of alfalfa, soil from a road- 
 side where sweet clover grows is satisfactory. This practice 
 of course may introduce weed seeds or plant diseases into 
 the soil and for that reason is not always satisfactory. 
 
 It is possible to get pure cultures of the bacteria at some 
 of the experiment stations, and from some commercial 
 sources (Fig. 37). These cultures can be mixed with water 
 and the seeds soaked in it before planting. The bacteria cling 
 
 
 FIG. 37. Cultures for Legume Inoculation. Bacteriological Department, 
 Virginia Station. 
 
 to the seeds and infect the roots when the seeds germinate. 
 The trouble with this method is to get cultures which are 
 fresh. Many preparations put out by commercial firms and 
 the scheme of the United States Department of Agriculture 
 for sending, out the bacteria dried on cotton have failed 
 because the bacteria were dead when inoculation was 
 attempted. 
 
 It must not be thought that inoculation alone is the easy 
 way to obtain nitrogen from the air and that it will work on 
 any crop. There are people who think it is a complete 
 fertilizer in vest pocket form; that corn or oats can be 
 inoculated and will gather their own nitrogen! It is not a 
 complete fertilizer and will not help any but leguminous
 
 152 THE SOIL: ORGANIC MATTER 
 
 crops, and then only if the inoculating material contains 
 living bacteria. The average farmer will probably never 
 need to inoculate his legume crop. Failure to get a crop is 
 usually due to some other cause more or less easily remedied. 
 
 EXERCISES 
 
 1. How could you isolate humus from an acid soil? from an alkaline soil? 
 
 2. In what two ways might the nitrogen of the air become a constituent 
 part of a legume protein? 
 
 3. Trace nitrogen from an atmospheric element until it becomes part of 
 an organic substance found in leguminous plants; thence until it becomes 
 nitrates in the soil; thence through protein formation in some plant other 
 than a legume; thence until it is deposited in the seed of some plant; thence 
 until it becomes atmospheric nitrogen. 
 
 4. How do carbon dioxide and water affect nitrification and nitrogen 
 fixation? 
 
 5. Distinguish among humus, organic matter, acid humus and neutral 
 humus. To what extent are these four materials alike or unlike chemically 
 and physically? 
 
 6. Why are nitrification and nitrogen fixation such important phenomena? 
 
 7. State five ways in which respiration differs from photosynthesis, and 
 three ways in which respiration differs from intermolecular respiration. 
 
 8. Show that the nitrogen applied as nitrates was once atmospheric 
 nitrogen. 
 
 9. Explain in detail how alfalfa differs from potatoes in the way it builds 
 up proteins. 
 
 10. In detail state how, when and where organic matter can be changed 
 into humus. 
 
 11. What condition is best for the soil, complete absence of oxygen, an 
 excess of oxygen, or a happy medium in respect to oxygen? In detail, 
 explain why. 
 
 12. To what extent are acid and neutral humus alike chemically and 
 physically? 
 
 13. What properties do proteins have that make their nitrogen not 
 directly available? 
 
 14. Define symbiosis. Just what do br.cteria give legumes and what do 
 the legumes give in return? Why this exchange? 
 
 REFERENCES 
 
 Bulletins of Bureau of Soils, U. S. Dept. of Agriculture. 
 
 Cameron. The Soil Solution. 
 
 Hall. The Soil. 
 
 Halligan. Soil Fertility and Fertilizers. 
 
 Hilgard. Soils. 
 
 Hopkins. Soil Fertility and Permanent Agriculture. 
 
 Lyon and Fippin. Soils. 
 
 Russell. Soil Conditions and Plant Growth/ 
 
 Van Slyke. Fertilizers and Crops. 
 
 Whitson and Walster. Soils and Soil Fertility.
 
 CHAPTER VII 
 THE SOIL: INORGANIC MATTER 
 
 IN the previous chapter the discussion of organic matter 
 in the soil brought out the fact that it was the immediate 
 source of nitrogen for plants. The other necessary elements 
 which are derived from the soil come, originally at least, 
 from the mineral particles or inorganic portion of the soil. 
 The organic matter in its decomposition furnishes acids which 
 are important agents in the solution of mineral particles. 
 Other factors in the changes of mineral particles are the 
 gases present in the soil. 
 
 127. Soil Gases. The pore spaces of a soil are filled, 
 part of the time with gases, and part of the time with water. 
 The latter condition happens only after a rain, and in a soil 
 of good structure does not last very long. The water running 
 down into the country drainage is followed by atmospheric 
 gases. From the decomposing organic matter gases are 
 added to those already present, and at the same time some 
 gases are withdrawn by absorption from the soil atmosphere. 
 Certain chemical reactions also involve changes in the 
 composition of soil atmosphere. It has been found that 
 nitrogen varies but little, existing in the soil in about the 
 same proportion that it does in the air, namely 78 per cent. 
 (Section 109). 
 
 Oxygen varies from 10 to 20 per cent., whereas in the 
 air it runs rather constantly at 21 per cent. This difference 
 is due to changing rates of oxidation resulting from bacterial 
 action on the organic matter, as well as to ordinary chemical 
 oxidation of minerals in the soil. The amount of carbon 
 dioxide varies inversely with the oxygen content, running 
 from about 11 to 1 per cent. As oxygen is used up in oxidiz- 
 ing organic matter, carbon dioxide is evolved. Ordinarily the 
 disappearance of oxygen causes the appearance of an equal 
 volume of carbon dioxide. Intermolecular or anaerobic 
 oxidation is not sufficient in ordinary soils to cause much 
 
 (153)
 
 154 THE SOIL: INORGANIC MATTER 
 
 change in the composition of the soil gases. In other words 
 the amount of oxygen and carbon dioxide together equal 
 21 per cent, rather constantly. In the air they amount 
 to 21.02 per cent. 
 
 Decomposing organic matter is the principal factor in the 
 variation in composition of soil gases, and to this cause also 
 is due, especially in soils more or less water-logged, the 
 presence of methane and hydrogen sulphide; but these gases 
 are rare constituents in any ordinary soil in good condition. 
 Other constituents are not worth considering. 
 
 As to the value of soil gases in decomposing mineral 
 particles, it will be found later that carbon dioxide and 
 oxygen are the most active agents. A solution of carbon 
 dioxide in water is by far the most active solvent for minerals 
 which the soil produces. Of course sulphuric and nitric 
 acids which result from decomposing organic matter are 
 more powerful reagents ordinarily, but their occurrence is 
 very slight compared to that of carbonic acid, which though 
 rated a weak acid is always present in large quantities in 
 practically all soils. -Decaying organic matter has been esti- 
 mated to supply through bacterial action to a depth of eight 
 inches, about 1 ton of carbon dioxide per acre per year. When 
 dissolved in water this makes a very respectable amount of 
 solvent. Organic acids, together with sulphuric and nitric 
 acids, are produced in very much smaller amounts, and 
 being very dilute have not the effect that carbon dioxide 
 has, although these reagents are to be reckoned with in 
 considering mineral decomposition and solubility. 
 
 128. Soil Solvents. The soil moisture which acts on the 
 mineral particles in the soil consists primarily, of course, of 
 water. Pure water dissolves ordinary minerals but slightly, 
 except gypsum and sodium chloride, of which the latter 
 occurs in normal soils more as a decomposition product 
 than as an original mineral. In the soil, however, water is 
 never pure. Carbon dioxide is always present from the decay 
 of organic matter. Living plant roots excrete carbon dioxide 
 because of respiration, and the soil moisture immediately 
 around such roots is fairly well concentrated in this con- 
 stituent. The growing of plants on a polished slab of 
 marble calcium carbonate or on one of feldspar leaves a
 
 SOIL MINERALS 155 
 
 fine tracery of the roots caused by the solvent action of the 
 carbon dioxide excreted. Carbon dioxide is soluble in pure 
 water to the extent of about 1 part in 600 parts of water. 
 The presence of soluble salts reduces its solubility. 
 
 Oxygen is very generally present in the moisture of well 
 aerated soils, attacking minerals containing ferrous iron, 
 like hornblende, and breaking them down with water and 
 carbon dioxide. It is soluble to the extent of about 1 part 
 in 20,000 parts of water. 
 
 Organic Acids like acetic, butyric, and others of a more 
 complex nature, all formed by the bacterial decay of organic 
 matter, particularly carbohydrates, dissolve in soil water 
 to a greater or less extent and act on many minerals. 
 
 Inorganic Acids like sulphuric and nitric, formed from 
 sulphur and nitrogen in organic matter, serve as very active 
 reagents. They are present, however, to a very small 
 extent at any one time. 
 
 Soluble Salts, derived from various minerals such as 
 chlorides, nitrates, and sulphates, all have a greater or less 
 effect on minerals. 
 
 129. Soil Minerals. In considering the chemical changes 
 by which inorganic plant food becomes available, it is 
 necessary to know some of the principal soil minerals which 
 are the source of these elements. They will be taken up and 
 discussed in groups according to the element or elements 
 which they supply. In addition there will be discussed 
 the minerals of a few elements which are thought not to be 
 essential and yet which occur very commonly in plants, 
 or which have some effect in the soil. 
 
 (a) PHOSPHORUS MINERALS. The principal mineral con- 
 taining phosphorus is apatite, Ca 5 (PO 4 ) 3 Cl or F. To show its 
 chemical structure better it may be written graphically: 
 
 O=P-O Ca^-Cl(F)
 
 156 THE SOIL: INORGANIC MATTER 
 
 It occurs in hexagonal prisms frequently of very small 
 size, almost like needles, and green or red in color. 
 
 This compound is practically insoluble in water but under 
 the action of water and carbon dioxide it slowly dissolves, 
 possibly according to the following equation: 
 
 2Cae(PO4)jCl + 12CO 2 + 12H 2 O = 3CaH 4 (PC>4) 2 + 6CaH 2 (C0 3 ) 2 + CaCk 
 
 Most of the phosphorus in soils, however, occurs in an 
 amorphous, secondary form possibly derived from apatite, 
 expressed by the formula Ca 3 (PO 4 )2 and called tricalcium 
 phosphate. This compound in the presence of small amounts 
 of carbon dioxide in water changes to the dicalcium phos- 
 phate, thus: 
 
 Ca 3 (PO4) 2 + 2CO 2 + 2H 2 O = Ca 2 H 2 (PO4) 2 + CaH 2 (CO 3 ) 2 . 
 
 In the presence of more carbon dioxide and water it decom- 
 poses to the monocalcium phosphate, thus: 
 
 Ca 3 (PO4) 2 +4CO 2 + 4H 2 O = CaH 4 (PO4) 2 + 2CaH 2 (COi.) 2 . 
 
 Tricalcium phosphate is practically insoluble in pure water, 
 1 part requiring 50,000 parts of water, whereas dicalcium 
 phosphate is soluble to the extent of 1 part in 7500 parts of 
 water, and monocalcium phosphate, 1 part in 100 of water. 
 
 Soil water, of course, is never pure water, having always 
 some substances dissolved in it, and these substances in 
 solution tend to modify the above solubilities to a slight 
 extent; but the figures serve to show the relative solubilities 
 of the three forms of phosphate. Dicalcium phosphate and 
 monocalcium phosphate, both of them, can be used by plants. 
 Since carbon dioxide is so generally prevalent in soil water 
 and can dissolve tricalcium phosphate, it is safe to say 
 that all compounds of phosphorus with calcium are available 
 forms of phosphorus for plant use. 
 
 Phosphorus also occurs as more or less indefinite com- 
 pounds of iron phosphate, FePO 4 , and aluminium phosphate, 
 A1PO4, both very insoluble in water, or in water and carbon 
 dioxide, or in any other ordinary soil solution, unless calcium
 
 SOIL MINERALS . 157 
 
 is present. Where calcium bicarbonate is in solution in the 
 soil water these phosphates are slowly changed as follows: 
 
 2FePOi + CaH s (COi) 2 -f- 4H 5 O = 2Fe(OH),+ CaH 4 (PO4)i+ 2COj. 
 
 This emphasizes the importance of having calcium carbonate 
 or lime in the soil. Aluminium phosphate acts similarly. 
 
 (6) POTASSIUM MINERALS. Since these minerals, and in 
 addition most of those of calcium, magnesium, and iron, 
 belong to that principal group of minerals called silicates, 
 it will help to understand their structure if a brief survey 
 is made of the silicic acids from which they are derived. 
 
 Silicic Acids. Normal or orthosilicic acid is H 4 SiO 4 , 
 written graphically : 
 
 H o O H 
 
 \ / 
 Si 
 
 / \ 
 
 H O O H 
 
 By the elimination of one molecule of water there is formed 
 metasilicic acid, thus: 
 
 H 4 SiO4 H 2 O =H 2 SiO 3 or: 
 O H 
 
 O = Si 
 
 O H 
 
 metasilicic acid. 
 
 By the elimination of three or more molecules of water from 
 two or more molecules of orthosilicic acid there are formed 
 polysilicic acids, of which the disilicic and trisilicic acids are 
 the commonest. They are formed thus : 
 
 1. 2H4SiOi 3H 2 O = H2Si 2 Os or: 
 O H 
 
 O=Si 
 
 O 
 
 O = Si 
 
 \ 
 
 O H 
 disilicic acid.
 
 158 THE SOIL: INORGANIC MATTER 
 
 2. 3H*SiO4 4H Z O 
 
 H O O H 
 
 \ / - 
 Si 
 
 / \ 
 O O 
 
 \ / 
 
 Si 
 
 / \ 
 O O 
 
 \ / 
 
 Si 
 
 / \ 
 
 H O O H 
 
 trisilicic acid. 
 
 These silicic acids are either unknown or but little known 
 in the free condition but their salts are very common among 
 the silicates which constitute most of the soil minerals. 
 
 The most important potassium silicate is a double tri- 
 silicate of potassium and aluminium called orthoclase or the 
 potash feldspar. Its formula is KaAUCSisOs^. It is frequently 
 written K 2 O.Al 2 O3.6SiO 2 which shows its composition but 
 not its chemical structure. Written graphically it is: 
 
 Al 
 
 It occurs in monoclinic crystals of flesh-red, yellow, or white 
 color. In pure water orthoclase is but very slighly soluble,
 
 SOIL MINERALS 159 
 
 but in water containing carbon dioxide it decomposes as 
 follows : 
 
 KtAh(Si*Os),+ COi+2H.O = Al 2 (OH)*SijOi + 4SiOi+ KjCOi. 
 
 Its solubility in pure water is 1 part in 37,000; in water 
 saturated with carbon dioxide, 1 part in 4000. 
 
 From the above equation it is to be noted that the potas- 
 sium goes into solution as potassium carbonate and it is 
 this form which supplies the plant with most of its potassium. 
 It is also to be observed that a new silicate is formed. This 
 is a hydrated disilicate of aluminium and is called kaolinitc, 
 the graphic formula of which is: 
 
 o H 
 / 
 
 O Al 
 
 / \ 
 
 O=Si O H 
 
 O 
 / 
 O=Si O H 
 
 \ / 
 
 O Al 
 
 \ 
 O H 
 
 It is a compact or mealy mass with greasy feel when wet, 
 very plastic, and white, yellow, brown, red, or blue in color. 
 This particular process of decomposition by which kaolinite 
 is formed is called kaolinization and is common to very many 
 silicates. It is one of the most important soil reactions, for 
 not only is plant food made available by it, but in addition 
 the soil structure is modified by kaolinite, the basis of clay. 
 The mechanical mixture of kaolinite and silica formed in 
 the above reaction is called kaolin or potter's clay. Varying 
 amounts of silica are present, some being dissolved and 
 washed away in the soil. 
 
 The potassium in orthoclase is also said to be made avail- 
 able by another reaction caused by calcium bicarbonate, thus : 
 
 KzAh(SiO 8 ) 2 + CaH(CO)j = CaAl 2 (SiiO 8 ) 2 + 2KHCO*. 
 
 This shows the importance of having calcium carbonate in 
 the soil. (Compare the effect of calcium bicarbonate on 
 iron phosphate, Section 129, a).
 
 160 THE SOIL: INORGANIC MATTER 
 
 Leucite is another potassium mineral which has the 
 formula KAl(SiO 3 )2 a metasilicate. It occurs in trans- 
 lucent to opaque grains of gray to white color. The potas- 
 sium becomes slowly available under the action of water 
 and carbon dioxide. 
 
 Another, potassium mineral that is very common and very 
 familiar to nearly everybody is potash mica or muscovite. 
 The thin, transparent leaves that very easily cleave are too 
 common to need description. This is the white mica. It is an 
 orthosilicate the formula for which is H 2 (K or Na)Al 3 (SiO 4 )3. 
 It might be called an acid salt since the hydrogen atoms 
 replace bases that is, they are true acid hydrogen atoms. 
 It is very resistant to the action of soil reagents but does 
 change very slowly under the action of water and carbon 
 dioxide, allowing potassium to go into solution. 
 
 (c) SULPHUR MINERALS. The principal sulphur mineral is 
 gypsum or land plaster, CaSO 4 .2H 2 O. It is soft, white, 
 granular, or compact, sometimes silky and fibrous. Occasion- 
 ally it is crystalline. It is soluble in water to the extent of 
 1 part in 400. On being heated to 130 C. it loses one mole- 
 cule of water and becomes "plaster of Paris," which has the 
 power of reabsorbing the lost molecule of water and "setting" 
 to gypsum again. This property is made use of in making 
 casts, etc. There is another sulphur mineral called anhy- 
 drite which is CaSO 4 . This is more or less common. 
 
 (d) CALCIUM MINERALS. Aside from apatite and gypsum 
 which contain calcium there are a number of important 
 calcium minerals. By far the most common is calcite, 
 CaCO 3 . This occurs as white or yellowish, transparent 
 crystals of many shapes, but the amorphous variety known 
 as limestone is the commonest, and is too well known to need 
 description. It occurs pure, and with magnesium, when it 
 is called dolomite, Ca.Mg(CO 3 )i: 
 
 O Ca O 
 
 / \ 
 
 O=C C=O 
 
 \ / 
 
 O Mg O 
 
 Calcium carbonate is soluble in pure water only to the extent 
 of 1 part in 20,000, but when the water contains carbon
 
 SOIL MINERALS 161 
 
 dioxide to saturation the calcium carbonate is soluble to the 
 extent of 1 part in 1000 of water, being changed to the acid 
 carbonate, thus: 
 
 CaCOs+ HiO + CO 2 = CaH s (CO)j. 
 
 This form of calcium is the most important in the soil, 
 although some of the more soluble silicates supply small 
 amounts of this element. 
 
 Anorthite or the lime-feldspar is an orthosilicate of calcium 
 and aluminium, CaAUCSiO^z, which slowly decomposes 
 under the action of water and carbon dioxide to kaolinite 
 and calcium bicarbonate. 
 
 (e) IRON MINERALS. Iron occurs largely as the hydrated 
 ferric oxide, Fe 2 O3.xH 2 O, in surface soils. There are a number 
 of minerals of this kind, of which limonite is the most common. 
 It is an amorphous, loose to compact, yellow or brown mineral, 
 occurring fairly well disseminated in soils. Its formula is 
 Fe 4 O 3 (OH) 6 , graphically: 
 
 /OH 
 
 HO Fe^ 
 
 o 
 
 HO Fe/ 
 O 
 
 HO Fe 
 
 O 
 
 HO Fe/ 
 
 X OH 
 
 Limonite is derived from silicate minerals containing iron, 
 hornblende for example. This occurs in columnar and gran- 
 ular crystals of green, brown, or black color. It is a meta- 
 silicate of any two or sometimes more of the following bases : 
 Calcium, magnesium, iron, and aluminium. The iron may 
 be ferrous or ferric. Under the action of water and carbon 
 dioxide, carbonates or bicarbonates of the bases are formed, 
 except ferric iron which is set free as such, usually in the 
 hydrated form and becomes limonite or similar minerals. 
 If the iron is ferrous it is changed to carbonate first but 
 11
 
 162 THE SOIL: INORGANIC MATTER 
 
 oxidizes almost instantly, if in aerated soils, to the hydrated 
 oxide. If, however, the decomposition takes place in sub- 
 soils and in water-logged soils, ferrous carbonate may remain 
 as siderite, FeCO 3 . Iron compounds give the yellow, red, 
 and brown color to soils when it is not masked by humus. 
 A phosphate mineral is mmanite, Fe3(P0 4 )2, a bluish-green, 
 earthy mass. 
 
 (/) MAGNESIUM MINERALS. Some of the magnesium in 
 soils is derived from dolomite, already mentioned under the 
 calcium minerals. There are also many silicates containing 
 magnesium, hornblende, already mentioned, and biotite or 
 black mica, an orthosilicate of aluminium, magnesium, hydro- 
 gen, and potassium, thus: (H or K) 2 (Mg or Fe) 2 Al 2 (Si04) 3 . 
 This mineral is similar to muscovite or white mica, except 
 as to color, which is dark green or black. 
 
 (0) SILICON MINERALS. All of the silicate minerals con- 
 tain silicon, of course, but quartz, or SiO 2 , is the only one to 
 be considered here. It is, next to feldspar, the most common 
 mineral in the earth's crust and occurs in many varieties 
 and all colors from transparent and white to red, blue, 
 green, and brown. Small quantities of impurities give the 
 color to it. Ordinarily, however, it is a hard, brittle mineral, 
 clear to white, and in hexagonal crystals of all sizes, although 
 frequently amorphous. Sandstone and quartzite are massive 
 varieties of quartz. It is ordinarily very insoluble, but some 
 varieties dissolve appreciably to the silicic acids. 
 
 (A) SODIUM MINERALS. Common salt, or halite, NaCl, is 
 the most familiar mineral of both sodium and chlorine, but 
 it does not occur to any extent in agricultural soil, being 
 confined to beds located in many parts of the world. Albite, 
 or the soda feldspar, is a silicate mineral of soda and is the 
 counterpart of orthoclase, being Na 2 Al 2 (SisO8)2. It occurs 
 in white granular masses or plates. Its solubility is similar 
 to that of orthoclase. 
 
 (1) CHLORINE MINERALS. Halite mentioned above is the 
 only one of importance. There is very little chlorine in 
 soils ordinarily. 
 
 (j) ALUMINIUM MINERALS. The feldspars and many 
 other silicates contain aluminium, and these break down as
 
 FACTORS OF SOLUBILITY 163 
 
 noted above to kaolinite, which is an aluminium mineral. 
 In addition there are bauxite, A1 2 O(OH)4, 
 
 OH 
 Al OH 
 
 o 
 
 / 
 
 Al OH 
 OH 
 
 rounded grains or clay-like masses, white or yellowish in 
 color; and wavellitc, A1 3 (OH) 3 (PO 4 )2, 
 
 \ 
 / )>Al OH 
 
 O=P <y 
 \ 
 
 >A1 OH 
 (X 
 
 / 
 O =P 
 
 \ >Al OH 
 
 radiating crystals occurring in hemispherical masses. 
 
 130. Factors of Solubility. From the above discussion of 
 the solubilities and decomposition products of soil minerals 
 it might be thought that solution was easy and the reactions 
 fairly simple. But it must be emphasized that under actual 
 conditions the reactions only approximate those indicated. 
 That is, only a part of any mineral actually decomposes as 
 far as stated. Reactions are not complete, and while in 
 the case of a feldspar, for example, some potassium car- 
 bonate and kaolinite are formed, and formed continually 
 although slowly, much of the mineral remains unaltered and 
 some of it decomposes only partly. Intermediate compounds 
 are formed. Other compounds interfere and react with the 
 original mineral or with its decomposition products. Much 
 more so is this true of more complex minerals. 
 
 Temperature has a decided effect on these reactions in the 
 soil. The higher the temperature the more active the
 
 164 THE SOIL: INORGANIC MATTER 
 
 decomposition by most solvents except carbon dioxide. 
 This compound is less soluble in warm water than in 
 cold. Then, too, the amount of water; the movement of 
 water, which removes decomposition products and exposes 
 fresh surfaces to the action of the solvents; the size of soil 
 particles; the arrangement of soil particles; the kind of soil 
 particles; all have a decided effect on the rate and amount 
 of decomposition. Some minerals like feldspar decompose 
 fairly readily ; others, like mica, decompose with considerable 
 difficulty. And again, small minerals like apatite may be 
 enclosed within other minerals, like quartz, for example, 
 and soil solvents cannot touch them. All these factors, of 
 course, are in addition to the amount of organic matter, the 
 rate of its decomposition, and the number of bacteria. 
 
 To sum up, then, the decomposition of mineral particles 
 in the soil, while it appears rather simple, is in reality depend- 
 ent on many factors which are only more or less controllable 
 by the farmer. But if he understands the ordinary progress 
 of favorable decomposition, he can modify his controllable 
 factors accordingly. He can cultivate, maintain the supply 
 of organic matter, and look after drainage or irrigation as 
 the case may be. 
 
 131. Absorption. From what has been said it might be 
 thought that when once a plant food becomes soluble it 
 undergoes no further change, and if not taken up at once by 
 the plant is in danger of being leached from the soil. The 
 danger of leaching is by no means as great as might be 
 expected, and any given plant food element undergoes a 
 great many changes before it meets its final fate in the 
 plant or in the drainage water. Compounds are constantly 
 going into solution or being made available, and going 
 out of solution or being made unavailable. Compounds 
 are also held in the soil by physical means. In other words 
 the soil not only makes plant food available from its reserve 
 stores, but it in large measure prevents them from being 
 removed from the soil by leaching. This process of retention 
 of soluble salts or of elements in soluble compounds is called 
 absorption, or sometimes fixation. The latter is not so good 
 a name since it may be confused with nitrogen fixation which
 
 CHEMICAL ABSORPTION 165 
 
 is a very different process (Section 125). Absorption, as 
 barely indicated above, is of two kinds, chemical and physical. 
 132. Chemical Absorption. Some elements are retained 
 in the soil by a chemical reaction which changes the element 
 from a soluble compound into an insoluble compound. This 
 may take place by double decomposition and subsequent 
 precipitation, or by simple precipitation. When, for example, 
 potassium sulphate or potassium carbonate in solution in the 
 soil moisture comes in contact with an insoluble compound 
 containing calcium, such as a silicate or a humate, there is 
 an interchange of bases, the- potassium remaining as the 
 silicate and the calcium leaching away as the sulphate 
 or carbonate (bicarbonate would be the soluble form), thus: 
 
 CaAl 2 (Si,O 8 )! + KzCOj + H 2 O +CO 2 = K 2 Ah(Si 3 O 8 )2+ CaH 2 (CO,) 2 . 
 
 Or take a compound like monocalcium phosphate. It is 
 precipitated by calcium bicarbonate or iron hydroxide as an 
 insoluble phosphate, thus: 
 
 CaH(PO4) 2 + 2CaH 2 (CO 3 ) 2 = Ca3(PO 4 )2 + 4H 2 O + 4CO 2 
 
 and 
 
 2Fe(OH)+ CaH 4 (PO) 2 + 2CO 2 = 2FePO 4 + CaH 2 (CO 3 ) 2 + 4H 2 O. 
 
 In some cases the reaction occurs directly between a solid 
 and a compound in solution. In other cases two substances 
 in solution react and an insoluble precipitate results. In 
 one case it is an exchange of bases, and in this connection 
 it must be noted that other bases than potassium and calcium 
 exchange places in this way. Sodium, magnesium, and 
 ammonium exchange with one another and with potassium 
 and calcium. In the other case it is the formation of an 
 insoluble salt of an acid. 
 
 There is still another case where the base of a salt is 
 absorbed and the acid radicle left behind as an acid. There 
 is no exchange of bases. For instance, a hydrated silicate 
 like kaolinite in the presence of a salt like potassium sulphate 
 and water will absorb the potassium, probably to form a 
 potassium silicate, and leave sulphuric acid. This applies 
 to salts like the chlorides and sulphates more particularly.
 
 166 THE SOIL: INORGANIC MATTER 
 
 Other things being equal it has been found that there is a 
 difference in the ability of one base to replace another. 
 Potassium will replace magnesium and be replaced by 
 ammonium in turn. Sodium will replace calcium and be 
 replaced by magnesium. In other words, the order of 
 replacing power beginning with the strongest is: Ammo- 
 nium, potassium, magnesium, sodium, calcium. Each element 
 will replace any of those following it and be replaced by any 
 of those preceding it. In the case of acid radicals, those 
 which form insoluble compounds the most readily are the 
 ones absorbed the quickest. Phosphates of calcium (tri) 
 and of iron and aluminium are insoluble. Calcium phosphate 
 forms soluble acid phosphates, but the others do not dissolve 
 easily. Carbonates of calcium and magnesium are insoluble, 
 but form soluble bicarbonates very readily. Sulphates, 
 except of barium, are rather soluble. Chlorides and nitrates, 
 particularly the latter, are all readily soluble and hence do 
 not form compounds which can be retained chemically. 
 
 But a part at least of the above discussion seems to be at 
 some variance with what has been said in Section 129 about 
 the solubility of soil minerals. The fact is that under some 
 conditions elements are rendered soluble and under other 
 conditions the same elements are rendered insoluble, even 
 when the reacting substances are exactly the same, and this 
 difference of reaction depends on the active mass of the 
 reacting substances. This is called the law of mass action. 
 
 133. Mass Action. To illustrate this important chemical 
 law, the equations for the solution of phosphorus and for 
 the fixation of phosphorus may be written together thus: 
 
 Cas(PO4)s+ 4CO 2 + 4H 2 O ~ CaH4(PO 4 )2+ 2CaH2(CO 3 )z. 
 
 This is called a reversible reaction, for it will go in either 
 direction depending on the active mass of the reacting sub- 
 stances. Tricalcium phosphate continues to go into solu- 
 tion as long as the supply of carbon dioxide is continuous, 
 and the monocalcium phosphate or calcium bicarbonate is 
 removed from the solution. In the soil, decomposition of 
 organic matter supplies carbon dioxide. Growing root hairs
 
 PHYSICAL ABSORPTION 167 
 
 or diffusion may remove the soluble compounds. The re- 
 action, then, continues to go from left to right, and phos- 
 phorus is made soluble. 
 
 But suppose the supply of carbon dioxide diminishes, 
 because organic matter for some reason does not decompose 
 very rapidly or not at all; or suppose no plant removes the 
 soluble phosphate; or suppose that a solution of monocal- 
 cium phosphate passing through the soil comes in contact 
 with considerable calcium bicarbonate; or, more than all 
 this, suppose fresh supplies of calcium bicarbonate are being 
 continually added to the solution from other places; under 
 these conditions, then, the reaction goes from right to left 
 and phosphorus is absorbed or fixed in the soil. Of course, 
 in all cases there must be enough water present to allow of 
 reactions in solution. 
 
 Starting with a fixed amount of the reacting substances 
 the reaction will proceed in a direction dependent upon the 
 masses until an equilibrium is reached, or until the masses 
 on one side of the equation balance in reacting velocity those 
 on the other side. This, however, is something that rarely 
 happens in a soil, for the composition of a solution is con- 
 stantly changing. Reactions in a soil are always in a state 
 of change. They are essentially dynamic and not static. 
 
 This reversible reaction and the resultant solubility or 
 absorption of plant food is applicable just as well in the case 
 of the reactions given for potassium in Sections 129, b, and 
 132, and for phosphorus and iron compounds in Sections 
 129, a, and 132. 
 
 134. Physical Absorption. Compounds of the plant food 
 elements are retained by the soil to a greater or less ex- 
 tent in an unchanged form. Certain solid substances in the 
 soil attract and hold on their surfaces compounds in solu- 
 tion. This process is called adsorption and may be defined 
 as that property of a solid which attracts dissolved substances 
 and causes the existence in such solutions as soil moisture 
 of two different concentrations of dissolved substances, the 
 greater lying immediately adjacent to the surface of a solid. 
 For example, iron and aluminium hydrated oxides have a 
 very decided affinity for potassium sulphate. Adsorption 
 is a purely physical phenomenon in that the compounds
 
 168 THE SOIL: INORGANIC MATTER 
 
 held are not chemically changed. They remain in their 
 original form, attached to the surface of the solid as by a 
 magnet, and the amount of adsorption depends very largely 
 on the surface exposed. Hence, the smaller the soil grains 
 the greater the adsorption because of more surface exposed. 
 Another factor in adsorption is the character of the solids 
 and of the substances in solution. Some solids have greater 
 attractive powers than others, and some dissolved substances 
 are more attracted than others. For example, humus, 
 hydrated iron and aluminium oxides, and hydrated silicates 
 or so-called zeolites, have greater adsorptive powers than 
 calcium carbonate and quartz. Potassium salts and phos- 
 phates are attracted more than sodium salts and nitrates. 
 Plant foods held by adsorption on the surfaces of solids are 
 available to plants if the root hairs come in contact with 
 them. Substances absorbed chemically are not available 
 to plants until they are dissolved again, as may or may 
 not happen. It must be understood, however, that in no 
 case is the whole of a substance in solution absorbed either 
 chemically or physically. No chemical reaction is complete 
 in the soil. Only a part of the monocalcium phosphate, 
 for example, is precipitated as iron phosphate at any one 
 time, but enough of it may be rendered insoluble to affect 
 the growth of crops. Moreover, some of it is lost by leaching. 
 
 135. Movements of Dissolved Substances. Having dis- 
 cussed how plant foods are made soluble and how they are 
 retained in the soil after being made soluble, the question 
 naturally arises as to how the compounds in solution move 
 from place to place. That plant foods do move is obvious, 
 for they are lost from soils in the drainage water and eventu- 
 ally are deposited in the ocean; and again they move up- 
 ward, for incrustations of salts which have been lifted by the 
 water appear on the surface of soils in arid countries (Sec- 
 tion 138, d). 
 
 Movement of plant food in the soil may take place in two 
 ways : First, by the movement of water; second, by diffusion. 
 
 (a) MOVEMENT BY WATER. Water moves in the soil in 
 two ways to affect substances in solution, by gravity and by 
 capillarity, or more properly by surface tension. When the 
 saturation point of soils is reached, water responds to the
 
 MOVEMENTS OF DISSOLVED SUBSTANCES 1G9 
 
 force of gravity which carries it downward through the pore 
 spaces and channels in the soil. This bodily movement of 
 water carries with it the substances in solution which are 
 not absorbed as they go. The water may go directly down 
 in a vertical direction or more nearly horizontally if any- 
 thing like an impervious subsoil or entrapped air deflects 
 its course. Gravitational movements cease as soon as the 
 excess water drains off and the surface tension overcomes the 
 force of gravity. It is by this movement that soils lose plant 
 foods which are not absorbed. 
 
 The surface of a liquid acts as if it exerted at all times a 
 certain tension or pressure on the liquid below. If a drop 
 of liquid is free to take any position, it assumes the spherical 
 form in w r hich the surface tension is uniform throughout, 
 that is, it is in equilibrium. When the surface of a liquid 
 is forced to assume various shapes, as in the case of film 
 water covering soil particles, there is exerted an unequal 
 tension. The more curved the surface the greater the 
 tension. In a soil the surfaces at the top are more curved 
 than they are lower down where the films are thicker. This 
 means that the pull of the surface tension at the top will 
 tend to raise water until the gravity pull balances the ten- 
 sion pull. As water evaporates, or plant roots absorb it, 
 the increasing tension caused by thinner films and consequent 
 greater curvatures, draws up more water. This movement 
 of water, of course, carries with it dissolved plant food. 
 Theoretically this movement can take place in any direction 
 and does so under some circumstances, but under ordinary 
 circumstances the increasing surface tension occurs on top 
 of the soil because of evaporation, and hence the water 
 movement is upward. 
 
 (6) MOVEMENT BY DIFFUSION. It is a property of sub- 
 stances, or rather of the molecules of such substances in 
 solution, to move within the solvent from a region of greater 
 concentration to one of less concentration in that particular 
 compound. That is, sodium nitrate, for example, tends to 
 move from that portion of the soil moisture where its con- 
 centration is considerable to other portions where there is 
 little or no sodium nitrate. This movement is called diffu-
 
 170 THE SOIL: INORGANIC MATTER 
 
 sion, and may take place in any direction. Within the soil 
 liquid, however, there is opposed to diffusion absorption 
 both chemical and physical. Moreover the bodily move- 
 ment of water caused by gravity or by surface tension 
 neutralizes the effect of diffusion in many cases. 
 
 As a matter of fact diffusion in soils does not play a very 
 important part. Movements of plant foods in solution take 
 place for the most part in a general direction up and down; 
 up by surface tension, down by gravity, and are caused by 
 bodily movements of water containing the plant foods. 
 Experiments have repeatedly demonstrated that plant foods 
 in the form of soluble fertilizers show no effect laterally 
 within a very short distance from the point of application. 
 That is, the plant foods apparently get no chance to diffuse, 
 for if they did the diffusion would be in every direction away 
 from the point of application and the effect would be shown 
 laterally from the fertilizers. 
 
 136. Composition of Soil Water. From the preceding 
 sections it has been seen what compounds exist in a soluble 
 form in the soil moisture; how they may be soluble part of 
 the time and insoluble part of the time because of chemical 
 change. The conditions affecting these various changes 
 have been studied. In addition to this information it may 
 be interesting to know how much soluble plant food material 
 there is in soils. Soil water which contains the soluble 
 compounds may be divided into two classes for convenience 
 of study: Film water and drainage water. 
 
 (a) FILM WATER is the liquid in the soil which surrounds 
 the soil grains with a thin film, and which furnishes plants 
 with their foods. It bathes the plant roots with their nutrient 
 fluid. Determining the amount of soluble material in this 
 film water is a matter of great difficulty, and the results so 
 far obtained can be considered only as roughly approximate, 
 and even then represent but a few soils. However, it can be 
 said that the following figures show the parts per million in 
 a solution that probably is not far from an average soil 
 solution : 
 
 N 2 O 5 P.O. K.O CaO 
 
 3 6 33 33
 
 COMPOSITION OF SOIL WATER 
 
 171 
 
 These figures have been calculated from data published 
 by the Bureau of Soils. They show that at any one time 
 phosphorous compounds and nitrates are present in con- 
 siderably less quantity than are potash and lime. It is true 
 that these two elements, nitrogen and phosphorus, are usually 
 the limiting essential elements in crop production, as this 
 
 FIG. 38. Waste water. Outlet of drain tile. (Elliott.) 
 
 might indicate; but on the other hand, if these concentra- 
 tions are maintained throughout the growing season there 
 will be enough of these foods supplied to nourish the crop. 
 It is not at all probable that this same concentration is 
 maintained in all soils and at all times. In fact quite the 
 contrary. The amount of material in the film water must
 
 172 THE SOIL: INORGANIC MATTER 
 
 vary from day to day and from soil to soil, depending on 
 daily temperature and moisture content, soil composition, 
 texture and structure, amount of organic matter, character 
 of the solvent, whether rich or poor in carbon dioxide and 
 organic acids. The figures given, however, show only what 
 have been obtained by very laborious methods from a few 
 soils, and give an idea of the amount of concentration. 
 
 (6) WASTE WATER is the excess water which flows away 
 from the soil as drainage or river water. Table IX gives 
 average analyses of these two kinds of waste water. Drain- 
 age water is that which has been obtained from drains under 
 cropped fields and represents that which comes directly from 
 the soil after having passed through the soil and subsoil 
 (Fig. 38). River water is that which flows into the sea 
 and has travelled for long distances from its sources, being 
 subjected to many changes after passing through the soil. 
 
 TABLE IX. COMPOSITION OF DRAINAGE AND RIVER WATERS. 
 
 Expressed in parts per million. 
 
 (Averages of numerous analyses except N 2 Os in the case of drainage water, 
 
 which is from Rothamsted figures. There are not many analyses 
 
 on this constituent.) 
 
 Drainage. Rivers. 
 
 Potash K 2 O 3.2 2.4 
 
 Soda Na 2 O 15.1 7.1 
 
 Lime CaO .107.6 43.2 
 
 Magnesia MgO 16.3 14.7 
 
 Silica SiO 2 8.5 * 16.4 
 
 Carbon dioxide .... CO 2 74.4 46.0 
 
 Phosphoric acid .... P 2 Os 0.5 0.3 
 
 Sulphuric acid .... SOs 60.8 8.0 
 
 Chlorine Cl 17.7 3.7 
 
 Organic matter 37.4 16.4 
 
 Nitric acid . . . . . N 2 0s 15.0 3.8 
 
 Total solids 352.6 168.6 
 
 Since the figures given for film water do not represent as 
 many types of soil as those in Table IX, comparison between 
 them is hardly proper. Contrasting drainage water with 
 river w r ater it is to be noted that in practically every case 
 the latter contains less of the various constituents. This is, 
 of course, to be expected, for after the drainage water has 
 entered an open stream and travelled considerable distances
 
 COMPOSITION OF SOIL WATER 173 
 
 much of the soluble material is deposited. Aeration, for 
 example, frees carbon dioxide from the solution and pre- 
 cipitates calcium carbonate and magnesium carbonate. 
 Inter-reactions of bases and acids with new compounds 
 remove many substances. Dilution of water charged with 
 soluble material by fairly pure water reduces the con- 
 centration. 
 
 Taking up drainage water alone, it is very noticeable 
 that potash is present in small quantities, whereas lime is 
 present in considerable amounts; and it will be remembered 
 (Section 132) that potassium is absorbed to a much greater 
 extent than calcium. Soda and magnesia are present in 
 nearly equal quantities. The acid radicles in the order of 
 increasing amounts are P2O 5 , SiO 2 , Cl, SO 3 , and CO 2 , with 
 N 2 O 5 probably about equal to Cl. Nitric acid, as nitrates, 
 of course, will be present in widely varying amounts, probably 
 more widely than any other radical, acid or basic, and 
 hence an average figure does not mean much. This arrange- 
 ment indicates that most of the salts in solution are calcium 
 and magnesium bicarbonates and sulphates, sodium chloride, 
 some silicates of the alkalies, and nitrates of different bases. 
 
 It may be said for nitrates that although the nitric acid 
 radical is the least absorbed of all, there is not such a great 
 loss of it from ordinary soils as might be expected. Rapid 
 growth of crops at the time when nitrates are formed in 
 greatest amount, and lack of moisture for nitrification later 
 in the season when crop grow r th practically ceases, are two 
 factors which tend to prevent loss of nitrates. The practice 
 of fallowing, which fortunately is not very common nowa- 
 days, always results in a heavy loss of nitrates. Conditions 
 are ideal for nitrification and there are no crops to remove 
 the nitrates. 
 
 Bicarbonates and sulphates of calcium and magnesium, 
 present in largest amounts in drainage water, are what 
 ordinarily make water "hard," although any soluble sub- 
 stance may be responsible for this condition. The hardness 
 of the water- depends, of course, on the nature of the soil 
 drained. A limestone country yields a very hard water. 
 The bicarbonates of calcium and magnesium give a water
 
 174 THE SOIL: INORGANIC MATTER 
 
 "temporary" hardness, because they decompose easily on 
 aeration or boiling and precipitate the carbonates. The 
 sulphates of calcium and magnesium give water "permanent" 
 hardness, since they are not so easily precipitated. 
 
 Of course in the case of drainage and river waters there is 
 a very wide variation in the content of dissolved material, 
 just as there is in the film water. A granitic or sandy country 
 will yield water that is very " soft" or almost pure, whereas 
 a limestone country gives just the opposite. Take two 
 fresh water lakes in Wisconsin, for example. One Devil's 
 Lake receives the drainage from a granitic region, the 
 other Lake Mendota receives that from a limestone 
 country. Table X gives the analyses of both lakes. 
 
 TABLE X. COMPOSITION OF LAKES. 
 (Expressed in parts per million.) 
 
 Fe,0, 
 SiO, AhO, CaO MgO SO, Cl 
 
 Lake Mendota 1.1 0.8 40.1 42.3 10.3 2.0 
 
 Devil's Lake 2.2 0.6 4.5 1.8 6.7 8.2 
 
 137. Soil-forming Rocks. To obtain some idea of the 
 composition of a soil, it is necessary to know something of 
 the rocks from which the soil is derived. Rocks are mineral 
 aggregates, that is, they are composed of two or more minerals 
 welded together either by heat or pressure. They are classi- 
 fied as igneous, formed by the cooling of molten masses; 
 sedimentary, laid down by water; and metamorphic, changed 
 by heat and pressure from their original forms. Knowing 
 the rocks in a general way will give an idea of the minerals 
 to be expected in a soil derived from any given rock, and also 
 the character of the compounds resulting therefrom. This 
 applies, of course, only to soils in place. Soils that have been 
 transported by water have been sorted more or less accord- 
 ing to the specific gravity of their various constituents and 
 therefore do not contain all of their original minerals. It is 
 impossible to describe all of the rocks or even the common 
 rocks from which soils are derived, but it may suffice to 
 mention a few characteristic soil-forming rocks,
 
 SOIL-FORMING ROCKS 
 
 175 
 
 (a) GRANITE. (Fig. 39). This is one of the most common 
 igneous rocks and many soils are derived from it. It is 
 usually composed of quartz, feldspar, mica, and hornblende. 
 
 FIG. 39. Soil-forming rock: Granite. United States Geological Survey. 
 
 The action of water, heat, and cold serve to break it down 
 into small particles. Aided by the chemical action of water 
 and carbon dioxide the feldspar changes in part to kaolinite
 
 176 THE SOIL: INORGANIC MATTER 
 
 and silica, or clay and potassium carbonate. Mica slowly 
 changes to clay and carbonates of the alkalies. Hornblende 
 forms hydrated oxides of iron and aluminium, clay, and 
 carbonates of calcium and magnesium. Quartz changes 
 but little except as to size of particles, these becoming 
 small grains which form sand. 
 
 If the decomposed material is not disturbed it forms a soil 
 of excellent texture and good composition. Apatite occurs 
 very commonly disseminated in small crystals throughout 
 granite, and supplies phosphorus to such a soil. All the 
 other essential elements are present. Sorted by water, 
 however, it separates into sand and clay soils with most of 
 the plant foods in the clay. 
 
 (6) BASALTS AND LAVAS form soils which may be very 
 sandy and barren, when silica predominates with only cal- 
 cium, magnesium, and aluminium for bases; or form good 
 soils, when bases predominate, which include potassium. 
 
 (c) LIMESTONE ROCKS consist for the most part of calcium 
 carbonate (and magnesium carbonate) which is leached out 
 very completely by the action of water and carbon dioxide 
 (Fig. 40). There is left to form soil only a very small per- 
 centage of impurities in the form of clay. Limestone is 
 laid down far out at sea in deep water, and there is entangled 
 with it the finer and lighter particles of clay which have 
 been washed out into the sea by rivers. This clayey im- 
 purity which forms soil from limestone may have been 
 derived from granite, in which case it would be fairly rich 
 in plant food. It may have been derived from barren 
 basalts, in which case it would be very poor. As a rule, 
 however, limestone soils are rich, except that they may be 
 lacking in calcium carbonate. At first thought it seems 
 strange that limestone soils are apt to be lacking in calcium 
 carbonate. But soil is derived from limestone only by the 
 solution and removal of calcium carbonate, soil material 
 being only the impurities present in the limestone rock. 
 Calcium carbonate is on the whole very soluble in soil w r ater, 
 compared to other rock constituents. Moreover, the particles 
 composing the clay are for the most part decomposition 
 products of silicates which may have originally contained
 
 KINDS OF SOIL 
 
 177 
 
 calcium, but which have lost a large part of this constituent 
 during decomposition. 
 
 Of course, there may be particles of limestone and calcium- 
 containing silicates left in the soil, and these serve as sources 
 of calcium for a time, but nevertheless, limestone soils are 
 among the first to become acid, because of lack of calcium 
 carbonate. 
 
 FIG. 40. Soil-forming rock: Limestone. 
 Survey. 
 
 United States Geological 
 
 (d) SANDSTONES AND SHALES form sandy and clayey soils, 
 respectively, containing more or less plant food according 
 to their original composition and derivation, for they are 
 secondary rocks derived from decomposition products of 
 others. Sandstones are more apt to yield poor soils unless 
 it happens that the binding material is of a clayey 
 nature. 
 
 138. Kinds of Soil. The number of different kinds of 
 
 soil is necessarily very great, and any attempt to classify 
 
 them is a very considerable undertaking. Ordinarily they 
 
 are divided according to their geological origin, but they may 
 
 12
 
 178 THE SOIL: INORGANIC MATTER 
 
 be classified on the basis of physical composition or of 
 chemical composition. It is not the place here to discuss 
 soil types and characteristics in detail, but it may be of some 
 help to briefly discuss general soil classifications, using as a 
 basis merely the common terms which are familiar to every 
 farmer, and not trying to adhere rigidly to some technical 
 basis which is of value only to the soil expert. The chemical 
 properties of soils in every case will form the basis of the 
 discussion. They can be discussed as: (a) Arid and humid 
 soils, which will distinguish in a general way those soils 
 which are located, on the one hand, where very little rain 
 falls, and on the other hand, where sufficient rain falls; 
 (6) sand, clay, loam, muck, and peat, names which are 
 very commonly used and which depend on physical and 
 chemical characteristics; (c) soil and subsoil, terms suffi- 
 ciently plain; (d) alkali soils or special soils that are very 
 important in certain arid regions of the United States 
 particularly an extreme type of arid soil. 
 
 (a) ARID AND HUMID SOILS. The principal chemical dif- 
 ferences between soils in an arid or dry region and those in 
 a humid or moist region is in the amount of available or 
 soluble plant food. In a humid climate the soil is continu- 
 ally subject to leaching and fixation of soluble compounds. 
 Decomposition takes place as indicated in Section 129. 
 In a region of little rain, the plant food made soluble by 
 decomposition remains in the soil for the most part as such. 
 Decomposition of rocks takes place largely by the action 
 of sudden extremes of heat and cold, and not to a very 
 great extent by the solvent action of soil moisture. As a 
 result arid soils are not only pulverulent and sandy in 
 texture, but the soluble compounds which are formed remain 
 in the soil. Little clay is formed from feldspars, because of 
 lack of water for hydration. This means a soil, coarse in 
 texture, as mentioned above. In other words kaolinization 
 is not marked in arid regions. Since there is little leaching, 
 calcium carbonate derived from limestone, or from silicate 
 rocks by slow decomposition, is not removed from the soil 
 and exerts its flocculent effect on what little clay is formed. 
 Arid soils are more fertile as a rule than humid soils if water
 
 KINDS OF SOIL 
 
 179 
 
 can be supplied and maintained. Fig. 41 shows the method 
 of supplying water to such soils. The lack of organic matter 
 is a serious drawback in arid soils, for it is easily "burned 
 out." Decomposition is very rapid, for the pulverulent soils 
 are naturally well aerated. 
 
 FIG. 41. Arid soil under irrigation. Sugar beets. 
 
 (6) 1. Sand Soils. The term sand is based on size of 
 soil particles and not on chemical composition, although 
 from the nature of its formation there is usually a distinct 
 chemical composition. Technically a sand soil consists of 
 any coarse material whether composed of pieces of lava, 
 coral, shell, or pure quartz. Since in humid regions, however, 
 sands are derived by the action of water and carbon dioxide 
 on rocks containing quartz, such soils are composed largely 
 of silica, SiOa, since this is the least soluble of any of the 
 ordinary minerals, and breaks up slowly largely by physical 
 agencies. There are present in addition pieces of feldspar, 
 mica, and hornblende. As a rule sandy soils do not contain 
 much organic matter for the reason given above they are 
 too well aerated. Fig. 42 shows the effect of organic matter
 
 180 THE SOIL: INORGANIC MATTER 
 
 on such soils. In humid regions the grains are rounded 
 from the rolling caused by water movements. In arid 
 regions the grains are angular and of any sort of material, 
 not necessarily of silica. 
 
 FIG. 42. Sand soil. Organic matter applied to plat on the left. Soils 
 Department, Wisconsin Station. 
 
 2. Clay Soils. Like the term sand, clay in soil nomen- 
 clature refers to size of particles, and is applied to soils, or 
 that portion of soils, having the very finest particles, regard- 
 less of composition. It has been truly said that clay is either 
 rock rot or rock flour. In the former case, and that is the 
 common occurrence, clay is derived from silicate rocks by the 
 decomposing action of water and carbon dioxide. It is largely 
 hydrated aluminium silicate. In the latter case clay is 
 merely very finely ground rock material made by the action 
 of glaciers, for example, and the composition will depend 
 on the kind of rock ground up. 
 
 3. Loam Soils. The term loam does not mean much 
 scientifically, but popularly it is a term applied to soils of 
 good texture and well supplied with organic matter. They 
 are sand or clay loams as they have more or less of the 
 qualifying constituent. Their chemical composition is very 
 general in nature.
 
 KINDS OF SOIL 181 
 
 4. Peat Soils. These are composed for the most part of 
 organic matter but little decomposed (Fig. 43). The tissue 
 of the plants of which they are composed is still plainly dis- 
 tinguishable. Unless these soils are in a limestone region 
 decomposition results in the production of a considerable 
 degree of acidity. The mineral matter present frequently 
 amounts to no more than 10 or 15 per cent. 
 
 FIG. 43. Peat soil. Soils Department, Wisconsin Station. 
 
 5. Muck Soils. These are soils containing large amounts 
 of organic matter, but which are in a more advanced state 
 of decomposition than peats. Plant tissue is quite indis- 
 tinguishable and there is very much more mineral matter 
 present. 
 
 6. General Composition. Table XI gives the approximate 
 composition of sand, clay, muck, and peat soils in three 
 principal constituents, nitrogen, phosphoric acid, and potash. 
 The figures, while not applicable in every case, will at least 
 give an idea of relative differences as they very commonly 
 occur. The weight of the surface eight inches of sand is 
 taken at 2,500,000 pounds, of clay at 2,000,000, of muck 
 at 1,000,000, and of peat at 350,000. 
 
 TABLE XI. COMPOSITION OF GENERAL SOIL TTPES. 
 
 Soil. 
 Sand 
 Clay 
 Peat 
 Muck 
 
 Per cent. 
 
 N. 
 
 Pounds 
 per acre. 
 
 Per cent. 
 P,O 4 . 
 
 Pounds 
 per acre. 
 
 Per cent. 
 K,O. 
 
 Pounds 
 per acre. 
 
 0.05 
 
 1250 
 
 0.01 
 
 250 
 
 1.5 
 
 37,500 
 
 0.15 
 
 3000 
 
 0.15 
 
 3000 
 
 2.0 
 
 40,000 
 
 2.50 
 
 8750 
 
 0.25 
 
 875 
 
 0.5 
 
 1,750 
 
 0.30 
 
 3000 
 
 0.30 
 
 3000 
 
 1.5 
 
 15,000
 
 182 THE SOIL: INORGANIC MATTER 
 
 (c) SOIL AND SUBSOIL. In humid regions there is a con- 
 siderable difference between the soil and the subsoil. The 
 most striking contrast is in the amount of organic matter. 
 In fact a common way of distinguishing between them is to 
 note the dividing line between the dark soil and the light 
 subsoil. It is frequently very sharply defined. This means 
 of course that there is more nitrogen in the soil than in the 
 subsoil. In addition there is found ordinarily more phos- 
 phoric acid and total lime in the soil than in the subsoil. 
 There is, however, less potash, ferric and aluminium oxides, 
 and calcium carbonate. The finer clay particles are washed 
 down into the subsoil, which results in subsoils of finer 
 texture than soils. This fact also accounts for the greater 
 amount of potash, ferric and aluminium oxides, and calcium 
 carbonate in the subsoil, since these constituents are more 
 rapidly weathered on the surface and washed into the 
 subsoil, where they are fixed. In the soil there are more 
 bacteria and bacterial food organic matter consequently 
 there are more organic acids and carbon dioxide. The latter 
 makes a stronger reagent of soil moisture and as a result 
 greater availability of plant food. Being more open and 
 porous and of better structure than subsoil, the soil is in better 
 physical condition for crop growth. Aeration being better, 
 all compounds are in a higher state of oxidation, iron, for 
 example, is all in the ferric form. This is not always the case 
 in subsoils. Iron may be in the ferrous form, and such 
 compounds as ferrous sulphate which may be derived from 
 the imperfect oxidation of iron sulphide or pyrites, are 
 poisonous to plants. It very often happens that when too 
 much subsoil has been turned up in plowing the crop is 
 very poor. This may be due to ferrous salts, to poor structure 
 too compact and badly aerated to lack of organic matter. 
 This latter lack reduces the rate of availability of plant 
 foods. 
 
 In arid regions there is very little difference between 
 soil and subsoil. Organic matter extends to considerable 
 depths, because of deep root penetration. There is no sharp, 
 dividing line. The structure is the same throughout, lack 
 of water causing little clay formation, and the soils are
 
 KINDS OF SOIL 183 
 
 pulverulent all the way down. Weathering is uniform and 
 production of water-soluble material is uniform. The sub- 
 soil will raise just as good crops as the soil. In many places 
 material thrown out in excavating for the cellar of a house 
 makes just as good a garden as the top soil. 
 
 (d) ALKALI SOILS. In certain parts of the arid west, as 
 well as of other arid regions of the world, there exist patches 
 of so-called alkali soil (Fig. 44). They are usually barren 
 of vegetation and are covered with white or black incrusta- 
 tions of soluble salts. The white salts are called "white 
 alkali" and the black salts "black alkali." Chemically 
 
 FIG. 44. Alkali soil, showing patches of white alkali. Agronomy Depart- 
 ment, California Station. 
 
 the white salts are not alkaline in character but consist 
 largely of sodium chloride and sodium sulphate with some 
 chlorides and sulphates of calcium and magnesium. "Black 
 alkali" is composed largely of sodium carbonate, the solution 
 of which dissolves from the soil through which it has passed 
 some of the humus, thus coloring the evaporated salts black. 
 As was noticed in Section 138 (a), the soluble salts formed 
 by decomposition of the minerals are not leached out of arid 
 soils, and under normal conditions are spread throughout 
 the soil and subsoil in amounts not at all injurious to plants; 
 but when there arise conditions which permit the accumula-
 
 184 THE SOIL: INORGANIC MATTER 
 
 tion of a large quantity of soluble salts in one spot, then the 
 "rise of alkali," as it is called, begins. For example, steady 
 drainage of soluble salts from a higher region to a lower, 
 with insufficient water to completely remove the salts in the 
 drainage water, results in the accumulation of salts in the 
 lower area. Where irrigation is practiced and there is used 
 water heavily charged with salts, but not enough water to 
 remove the salts into the country drainage, an accumula- 
 tion is apt to occur. And where excessive amounts of water 
 are used for irrigation in lands not properly provided with 
 underdrainage, the rising water table dissolves out the soluble 
 salts in the subsoil and brings them within capillary reach 
 of the surface. 
 
 In any case the salts in solution in the soil water rise to 
 the surface by capillarity and are left there by the evaporation 
 of the water. A rain dissolves them and carries them into 
 the soil for a greater or less distance depending on the 
 amount of rainfall, and they return to the surface when 
 surface tension is again established. 
 
 Many different kinds of compounds are made soluble by 
 the decomposition of rocks, but in passing through con- 
 siderable portions of soil, chemical absorption plays an 
 important selective part. As was seen in Section 132, 
 potassium and magnesium are retained more than sodium 
 and calcium. Phosphates are easily retained in an insoluble 
 form, carbonates, sulphates, chlorides less easily. As a 
 result it is to be expected that chlorides, sulphates, and 
 carbonates of not easily fixed bases will predominate in 
 alkali soils, and the chloride, sulphate, and carbonate of 
 sodium, sulphates of calcium and magnesium, and some 
 chlorides of calcium and magnesium prevail in such soils. 
 
 White alkali is not so injurious to vegetation as 
 black alkali, sodium sulphate being the least injurious, but 
 both kinds are very troublesome to farmers in some arid 
 regions. In addition to the harmful effects on crops, black 
 alkali or sodium carbonate has the puddling effect on soils 
 common to most alkaline solutions. Limiting strengths of 
 these salts in sandy loam soil for cereals have been found to 
 be about 0.1 per cent, of sodium carbonate, 0.25 per cent.
 
 REFERENCES 185 
 
 for sodium chloride, and 0.5 per cent, for sodium sulphate. 
 On clay soils this tolerance is less. Crops vary in their 
 ability to withstand the alkali, alfalfa, sugar beets, and 
 radishes being better able to withstand it than the grains 
 and celery. 
 
 Methods of reclaiming alkali soils are for the most part a 
 matter of rotation, culture, the growing of resistant crops, 
 prevention of evaporation, flooding, and underdrainage. 
 Black alkali can be remedied by the application of gypsum 
 or land plaster. This reacts with the sodium carbonate to 
 form calcium carbonate and sodium sulphate, the former 
 harmless and the latter relatively so. 
 
 EXERCISES 
 
 1. What is the chief -solvent? How is it made in the soil? State what 
 four reactions of this solvent you consider the most important. Why? 
 How are these reactions related to the phenomenon of absorption? 
 
 2. Why does drainage water contain less PjOs and K^O than CaO and N ? 
 
 3. State three reasons why a clay soil usually retains more soluble plant 
 food than a sandy soil. 
 
 4. State all the reactions that you have studied that are probably revers- 
 ible. Is reversibility the rule or the exception in plant and soil reactions? 
 For the accomplishment of how many reactions are enzymes necessary? 
 
 5. Examine the formulae and solubility of tricalcium phosphate, dicalcium 
 phosphate, monocalcium phosphate, pure limestone and calcium bicarbo- 
 nate. What general rule becomes apparent? 
 
 6. Other things being equal, will a soil in which much kaolinization has 
 taken place permit KC1 to leach away as readily as one in which this action 
 has not taken place? Why or why not? 
 
 7. What are the two chief functions of carbon dioxide from the farmer's 
 standpoint? 
 
 8. Suppose you added equal amounts of soluble compounds containing 
 the following radicals to the soil, NOj, NH4, PO4, Ca and K; place them 
 in an order that shows the increasing ability to leach. 
 
 9. Suppose a farmer added acid phosphate to a soil that was very poor 
 in organic matter but rich in lime; explain in detail what would happen to 
 the acid phosphate. 
 
 10. From what kind of organic matter can nitric and sulphuric acid be 
 produced in the soil? 
 
 11. Explain in detail why an acid soil is often lacking in available phos- 
 phorus. 
 
 12. Explain why little kaolinization takes place in an arid soil. 
 
 13. Why are soil minerals less soluble in warm water containing carbonic 
 acid than in cold water containing this solvent? 
 
 REFERENCES 
 See references at end of Chapter VI.
 
 CHAPTER VIII 
 FERTILIZERS 
 
 IT frequently happens that soils lose their ability to 
 raise good crops. They no longer continue to produce the 
 high yields which are characteristic of soils functioning 
 properly in accordance with the facts stated in the last two 
 chapters. This failure may be due to several causes: Poor 
 drainage, insufficient water, bad physical condition, not enough 
 organic matter, and lack of available plant food. Most of the 
 conditions can be remedied by the farmer. Insufficient water 
 cannot be prevented except by irrigation where a source 
 of water is convenient and it is possible to ditch the land. 
 All other factors can be modified. In this discussion of 
 the chemical phase of soil fertility only one factor can be 
 considered, namely, the supply of plant food, available or 
 total. 
 
 139. Plant Food in the Soil. When it is a question of 
 unavailable plant food, attention to such things as cultiva- 
 tion and the supply of organic matter will frequently remedy 
 the deficiency; but where these factors are insufficient, or 
 where plant foods are actually lacking, then it becomes 
 necessary to add them to the soil. 
 
 From Table III, p. 109, showing the number of pounds of 
 nitrogen, phosphoric acid, and potash removed from an acre 
 by various crops, it can readily be seen that there is a steady 
 drain on the reserve food supply in the soil, and no compensa- 
 tive natural return. In the case of nitrogen there is an addi- 
 tion of possibly 40 to 60 pounds of nitrogen in the roots and 
 stubble of one legume crop. This is in excess of the amount 
 removed from the soil and illustrates very forcibly the 
 necessity of growing a legume in the rotation. And yet, 
 compared to the total amount of nitrogen removed in the 
 (186)
 
 DEFINITION OF FERTILIZERS 187 
 
 other crops of a rotation, this is inadequate to make up the 
 loss 40 to 60 pounds returned, and 100 to 150 pounds 
 removed. 
 
 There may be added to the soil of one field more or less 
 fine soil blown from an adjoining field or roadway. This, of 
 course, adds some plant food such as potash and phosphoric 
 acid, but it is at best only "robbing Peter to pay Paul," since 
 this plant food may in turn be lost to the next field in the same 
 way. There is, of course, some plant food brought to the 
 surface soil by the rise of capillary or film water, and the 
 decay of roots and stubble may add plant food which has 
 been brought up from the subsoil by deeply penetrating 
 roots. But analyses show very conclusively that a long 
 period of cropping reduces all the plant food elements. As 
 much as one-third to one-half of the amount contained in the 
 virgin soil has been found to disappear during 50 to 60 
 years of cropping with no return in the way of manure or 
 fertilizers. . 
 
 It is a well-recognized fact among farmers who have the 
 experience of centuries to guide them that if plant food is 
 removed it must be returned. F. H. King in his " Farmers of 
 Forty Centuries" states that to each acre of the 20,000 
 square miles of cultivated land in Japan there are added 
 annually 60 pounds of nitrogen, 32 pounds of phosphoric 
 acid, and 48 pounds of potash. These people have been 
 farming for centuries and are still maintaining the fertility 
 of their soil only by a most rigorous return to the soil of the 
 plant food removed. 
 
 These facts all show that sooner or later plant food must 
 be added to the soil. 
 
 140. Definition of Fertilizers. The term fertilizer is ap- 
 plied not only to a compound which supplies a plant food 
 to the soil, but also to a compound which has other func- 
 tions in the soil, such as neutralizing acidity, making potash 
 available, etc. Hence, fertilizers may be defined as com- 
 pounds which are added to the soil to increase the yield of 
 crops to increase the fertility of the soil. 
 
 141. Direct Fertilizers. Compounds which supply plant 
 food to the soil and thus have a direct action on plant growth
 
 188 FERTILIZERS 
 
 are called direct fertilizers, and are usually compounds 
 containing nitrogen, phosphoric acid, or potash which are 
 the three elements most commonly lacking in soils, either 
 because of low total content like nitrogen and phosphoric 
 acid, or because of unavailability like potash. The addition 
 of the other essential elements is rarely necessary, with the 
 exception of calcium. 
 
 142. Indirect Fertilizers or Amendments. Compounds 
 which are not added primarily to supply plant food, but 
 which cause some other plant food to become available, and 
 which correct a harmful condition in the soil, or act as a 
 stimulant to plant growth by other causes than merely nutri- 
 tive, are called indirect fertilizers or amendments. Calcium 
 in various forms is usually called an indirect fertilizer, 
 although as noted in Chapter XII, calcium may frequently 
 serve as a plant food. Sodium chloride, manganese salts, and 
 sulphur, are all classed as indirect fertilizers or amendments. 
 
 143. Commercial Fertilizers. Under this head come all 
 those fertilizers which the farmer buys compounds which 
 are of great commercial importance. Compounds which are 
 produced on the farm, such as barnyard manure or green- 
 crop manures, are not rated as commercial fertilizers. 
 
 144. Complete Fertilizers. A complete fertilizer is one 
 which contains nitrogen, phosphoric acid, and potash. 
 These three constituents are the only ones which the farmer 
 needs to consider as being necessary to purchase for plant 
 food. Nitrogen and phosphoric acid exist in soils in very 
 small amounts and are hence very likely to be lacking in 
 sufficient quantity to nourish crops. Potassium on the other 
 hand is rarely lacking, but is very frequently present in such 
 unavailable form that certain plants cannot obtain enough for 
 normal growth. Of the other essential elements, none is 
 ever actually lacking in soil for the nutrition of the plant, 
 except calcium. But since calcium is usually referred to as 
 a soil amendment or indirect fertilizer, discussion of this 
 element as a plant food will be postponed. 
 
 In preparing a complete fertilizer for the market the 
 manufacturer makes use of various compounds of nitrogen, 
 phosphoric acid, and potash in forms that are immediately
 
 HOME MIXING 189 
 
 soluble, or will become soluble very quickly. The farmer 
 wants quick returns from his fertilizer and hence the various 
 ingredients must be readily available. Chapters IX, X, 
 and XI give the various sources of the individual elements. 
 An almost infinite number of combinations of the different 
 constituents can be made and the manufacturer uses many 
 of them, with phosphoric acid, however, predominating 
 in most of the fertilizers. In making the so-called high 
 grade fertilizers only compounds containing the maximum 
 amount of nitrogen, phosphoric acid, and potash are used, but 
 even here it is not possible to manufacture a product contain- 
 ing very much of the essential elements. Few nitrogenous 
 materials contain more than 15 per cent, nitrogen, or phos- 
 phate substances more than 16 to 18 per cent, available 
 phosphoric acid, or potash compounds more than 50 per cent, 
 potash. The rest of the product is worthless as a fertilizer, 
 but its presence can not be helped, for it is obviously impos- 
 sible to use elemental nitrogen, or phosphorus pentoxide, or 
 potassium oxide in a fertilizer (cf. Section 198). In making 
 low grade fertilizers, however, various diluents are used to 
 reduce the percentage composition; diluents, however, 
 which are harmless in themselves, although of course value- 
 less as fertilizers. These substances are gypsum, fine, dry 
 soil, peat (which does contain a small amount of nitrogen, 
 although not very available), sawdust, and other dry, cheap 
 substances. Sometimes it is necessary to add these materials 
 to a complete fertilizer to serve as driers, for some single 
 fertilizer ingredients, like sodium nitrate, absorb water and 
 make the mass sticky, or cause it to cake in hard lumps and 
 hence render it unfit for drilling purposes. 
 
 145. Incomplete Fertilizers. An incomplete fertilizer is 
 one which contains only one or two of the above named 
 three elements. Those containing only one are frequently 
 referred to as single fertilizers. 
 
 146. Home Mixing. It is not necessary for the farmer 
 to purchase ready mixed goods. He may buy single ferti- 
 lizers and do his own mixing before application, or he may 
 apply them singly to the soil. Each purchaser should decide 
 for himself which wav is the best for him. There are
 
 190 FERTILIZERS 
 
 advantages and disadvantages in the use of either form. 
 Ready mixed, complete fertilizers are easily purchased in 
 any quantity, with a wide variety of combinations in nitrogen, 
 phosphoric acid, and potash, and in a fine, dry condition 
 which will run readily through a fertilizer drill. The mixture 
 is uniform throughout. On the other hand, they are expensive 
 and the farmer does not know what the various ingredients 
 are. Particularly in the case of nitrogen, the farmer does 
 not know the source. It may be readily available and it 
 may not, although in a majority of cases it is in a reasonably 
 soluble form. 
 
 Home mixed goods are cheaper, the farmer knows the 
 source of his materials, and he can apply one element at a 
 time or only those which are necessary, without adding plant 
 food which is not needed in order to get that which is re- 
 quired. On the other hand, it is not always easy to get small 
 amounts of the separate ingredients and this is because 
 the manufacturer prefers to sell the single ingredients in 
 mixed form if possible. Again, it is not always easy to get 
 a uniform mixture and this may result in uneven yields. 
 Finally the mechanical condition may be such that the 
 material can not be drilled, and even if used otherwise it 
 must be broken up before use. This is due to absorption of 
 moisture as above indicated. 
 
 147. Mixtures to be Avoided. In mixing fertilizers care 
 must be taken not to put together two or more substances 
 which will cause loss of plant food or conversion to an 
 insoluble form. Lime in any form, or basic slag which 
 contains an excess of lime, or wood ashes, should not be 
 mixed with ammonium sulphate, or with organic nitrog- 
 enous materials, for loss of ammonia would occur. The 
 same compounds should not be mixed with acid phosphate 
 because reversion to the insoluble form takes place and the 
 fertilizer loses its immediate value. 
 
 Unless a mixture is to be used at once it is better not to 
 mix the basic compounds named above with sodium nitrate 
 or with potash salts, for the latter absorb moisture and the 
 whole mass will harden to a solid mass which requires 
 crushing before use.
 
 REFERENCES 191 
 
 148. Choice of Fertilizers. In the following discussion of 
 various fertilizers there are considered for the most part 
 only their effects on the plant, the soil, and on each other. 
 Their relative value as forms of plant food is considered 
 only on these grounds. But it must be remembered by the 
 farmer that the economical factor should enter into the choice 
 of a fertilizer. As a matter of scientific fact one form of 
 fertilizer may be better than another, but its cost may be 
 greater than the increased benefits derived from its use. 
 With a thorough knowledge of the several forms of each 
 element, of the effects of each crop to be grow r n, of the 
 soil, and of the cost, a farmer can decide for himself which 
 is the best kind to use under the circumstances. 
 
 EXERCISES 
 
 1. Give as many reasons as you can why substances containing Ca, N, P, 
 and K are the important fertilizers. 
 
 2. Would it be wise to mix the following: Sodium nitrate with lime; 
 ammonium sulphate with potassium chloride; lime with monocalcium 
 phosphate? If not, why not? How many mixtures to be avoided can you 
 give? 
 
 3. Would it be harmful to mix lime with ammonium sulphate in the soil? 
 Why or why not? 
 
 4. What condition of a crop would indicate the need of a nitrogenous 
 fertilizer; of a phosphatic fertilizer; of a potash fertilizer? 
 
 5. What kind of a fertilizer would you think most valuable for potatoes; 
 corn; cabbage; sugar beets; to mature a crop early; to give rapid vegetative 
 growth? Why? 
 
 6. What properties should a fertilizer have in order to be immediately 
 available; to be used as a spring dressing; to have residual effects? 
 
 7. A firm advertises a brand of rock phosphate containing 13 per cent. 
 P at $30 per ton. Another firm sells the same kind of fertilizer under a 
 different trade name, and guaranteed to contain 32 per cent. PjOs, for S31 
 per ton. Which fertilizer will give the greater amount of P for S10, and 
 how much more than the other? 
 
 REFERENCES 
 
 Hall. Fertilisers and Manures. 
 Halligan. Soil Fertility and Fertilizers. 
 Pranke. Cyanamid. 
 Van Slyke. Fertilizers and Crops. 
 Wheeler. Manures and Fertilizers.
 
 CHAPTER IX 
 NITROGENOUS FERTILIZERS 
 
 NITROGEN has usually been considered the most important 
 element in plant nutrition, and for several reasons: It 
 exists in the soil in only small quantities, rarely more than 
 0.2 per cent. It is so important in the vegetative growth of 
 plants that frequently nitrogen is the only fertilizing con- 
 stituent needed to produce large yields. In other words, the 
 increased growth of leaves and stems gives the plant more 
 power to forage for the other elements in the soil and so 
 produce a greater yield. It goes for the most part to the 
 seed, and thus, in the case of grain crops, is one of the ele- 
 ments that is removed from the soil. It is used by plants 
 to a greater extent than any other element. 
 
 As a matter of physiological fact, of course, no one element 
 is more important than another. All the essential elements 
 are equally necessary for the growth of the plant; some in 
 larger amounts than others, it is true, but not more necessary. 
 And yet, important as nitrogen is in many ways, it is the 
 only element which can be returned to the soil by natural 
 means, namely, by the agency of nitrogen-fixing bacteria on 
 the roots of legumes (Section 125). Clover, alfalfa, or some 
 other legume, is always a part of a good rotation system. 
 So that after all, nitrogen is not the important element for 
 the farmer to consider. 
 
 In taking up the different forms of nitrogen on the market 
 it is convenient to classify them according to the form of 
 chemical combination, and this order coincides with the 
 solubility, and roughly with the availability of the nitrogen 
 compounds. 
 (192)
 
 NITROGEN AS NITRATE 
 
 193 
 
 I. NITROGEN AS NITRATE 
 
 149. Sodium Nitrate, NaNO 3 . The best known and most 
 important of all the nitrogen fertilizers is sodium nitrate, 
 or more commonly, nitrate of soda, or "Chile saltpeter." 
 Saltpeter itself is potassium nitrate which is too expensive 
 for ordinary use as a fertilizer, although on account of the 
 fact that it contains both potassium and nitrogen it is a 
 plant food of great value. Nitrate of soda is a salt similar 
 to potassium nitrate in many of its properties, and because 
 most of the world's supply comes from Chile, it has received 
 the name of Chile saltpeter. 
 
 FIG. 45. Gathering caliche. 
 
 (a) How OBTAINED. The principal deposit of nitrate of 
 soda lies on a plateau some 3000 feet above sea-level in a 
 region where rain falls but once in two or three years. The 
 crude salt, called "caliche" (Fig. 45), is found in masses which 
 average about 3 feet thick. On top are strata of gravel and 
 rock several feet thick. The rock is composed largely of 
 sand and gypsum, while the caliche contains from 17 to 60 
 per cent, sodium nitrate mixed with various impurities such 
 as sodium chloride, calcium, magnesium, and sodium sul- 
 phates, some iodates and perchlorates. Dynamite is used 
 13
 
 194 NITROGENOUS FERTILIZERS 
 
 to loosen up the masses of caliche and to break up the 
 overlying strata. From the mines the crude material is 
 taken to the works where it is dissolved in hot water, trans- 
 ferred to evaporating tanks, and the sodium nitrate allowed 
 to crystallize out (Fig. 46). It is then dried and sacked 
 for shipment. As it comes on the market nitrate of soda 
 is coarsely granular material, brown, gray, or pink in color 
 and most of it is about 96 per cent, pure, containing in 
 addition to sodium nitrate, some moisture, sodium chloride, 
 calcium, magnesium, and sodium sulphates. The nitrogen 
 content is nearly 16 per cent. 
 
 FIG. 46. Nitrate of soda in crystallizing pans. 
 
 (6) AVAILABILITY. Since nitrate of soda is very soluble, 
 one part dissolving in about one part of water, and, more- 
 over, since its nitrogen is in the form which plants require, 
 it is an immediately available fertilizer. In addition to its 
 being very soluble it is not fixed or retained by the soil 
 to any extent, and is therefore easily lost by leaching. Con- 
 sequently applications of sodium nitrate should be made a 
 very short time before seeding, or as a top dressing. 
 
 (c) EFFECT ON THE SOIL. In the soil sodium nitrate serves 
 as an indirect fertilizer in that it reacts with insoluble potas- 
 sium compounds, making the potassium soluble. Experi-
 
 NITROGEN AS NITRATE 195 
 
 ments have shown that sodium nitrate in this way takes 
 the place of a potash fertilizer, in addition to supplying 
 nitrogen to the crop. Another effect of sodium nitrate in 
 the soil is to puddle heavy soils, if used continuously. This 
 is because plants absorb more of the nitrate radical than 
 they do of the sodium. The latter unites with carbon 
 dioxide in the soil forming sodium carbonate which de- 
 flocculates clay particles, giving the soil a very poor structure. 
 This fact of its leaving a residue of sodium carbonate 
 in the soil, however, makes sodium nitrate a valuable 
 fertilizer on acid soils, and thus saves the calcium carbonate 
 by supplying an additional base. 
 
 150. Synthetic Nitrates. Years ago when it was thought 
 that the Chilean nitrate beds were in serious danger of 
 rapid exhaustion, attention was directed to methods of 
 combining the nitrogen of the air with other elements, and 
 so to ward off inevitable destruction when no more nitrate 
 was to be procured. Although such a danger was very 
 much overrated it served the purpose of stimulating inven- 
 tion. More recently the Great War demonstrated the 
 necessity of making nitric acid from air nitrogen for explo- 
 sives. As a result Germany was able to make in this way 
 all the nitric acid necessary for military as well as for agri- 
 cultural purposes. In the Allied countries much was also 
 done in the way of making nitric acid from the nitrogen 
 of the air. In the United States several plants were started 
 but at present little is being done to operate them. They 
 have, however, demonstrated the possibilities. In times of 
 peace the products from such plants can be used largely 
 for fertilizers. 
 
 How MADE. It has been known for over a century that 
 nitrogen and oxygen would unite if heated to a sufficiently 
 high temperature, as by an electric spark. This fact is 
 made use of in a number of different processes, particularly 
 that of Birkeland and Eyde in Norway. The union of 
 nitrogen and oxygen is brought about in a specially con- 
 structed furnace (Figs. 47 and 48) which contains a large 
 and powerful electric arc through which air passes. Oxides 
 of nitrogen are formed which later are combined with water
 
 196 
 
 NITROGENOUS FERTILIZERS 
 
 to produce nitric acid. This acid can be neutralized with 
 lime or ammonia for fertilizer purposes. 
 
 FIG. 47. Manufacture of calcium nitrate. Interior view of furnace house 
 at Notodden, Norway. 
 
 FIG- 48. Interior of one of the fumaceg at Notodden.
 
 NITROGEN AS AMMONIA 197 
 
 Another method, the so-called Ilaber process, synthesizes 
 ammonia from pure nitrogen and pure hydrogen under great 
 pressure, at a moderate temperature and in the presence of 
 a catalyst. The ammonia can be oxidized to nitric acid 
 by being passed over red hot platinum gauze with an excess 
 of air. With part of the ammonia oxidized to nitric acid 
 and part unchanged, ammonium nitrate can be produced. 
 This compound may in time become valuable as a fertilizer, 
 although it is not used to any extent at present. 
 
 II. NITROGEN AS AMMONIA 
 
 151. Ammonium Sulphate. In addition to the nitrate 
 nitrogen mined as nitrate of soda and manufactured as 
 nitrate of lime, there is produced an ammonia nitrogen 
 fertilizer called ammonium sulphate, (NH^SO^ which 
 contains about 20 per cent, nitrogen as it appears on the 
 market. Ammonium sulphate is obtained for the most 
 part as a by-product in the destructive distillation of soft 
 coal. Coal contains from 1 to 2 per cent, nitrogen, of which 
 about 15 per cent, is recoverable. In other words, from one 
 ton of coal may be produced about twenty pounds of am- 
 monium sulphate. For years none of this valuable material 
 was saved, and even now not all of the amount produced is 
 recovered. 
 
 (a) How MADE. If soft coal is burned in the air all the 
 nitrogen escapes as elemental nitrogen and cannot be re- 
 covered, but if coal is heated in closed retorts, it undergoes 
 destructive distillation whereby coke and Combustible gases 
 are formed, the latter containing part of the nitrogen in the 
 form of ammonia. Soft coal is treated in this way in the 
 manufacture of coke, coal gas, or producer gas, and in any 
 one of these processes it is possible to save the ammonia. 
 The coke ovens have been the greatest source of loss, for in 
 the past no attempt was made to save any of the gases, 
 and even now not as many by-product coke ovens are in 
 use as should be, although the coke and steel concerns are 
 beginning to realize the advantage of saving the ammonia 
 (Figs. 49 and 50).
 
 198 
 
 NITROGENOUS FERTILIZERS 
 
 By proper appliances the escaping gases from coke ovens 
 or gas retorts are led through water in which the ammonia 
 
 FIG. 49 
 
 FIG. 50 
 
 FIGS. 49 and 50. Two views of by-product coke ovens.
 
 NITROGEN AS AMMONIA 199 
 
 is dissolved. It is then distilled by steam with the addi- 
 tion of lime to break up ammonium compounds, and led 
 into sulphuric acid. The solution of ammonium sulphate is 
 evaporated and the white or gray salt which results is dried 
 and sold as sulphate of ammonium, largely for fertilizing 
 purposes. 
 
 (6) AVAILABILITY. Ammonium sulphate is almost as solu- 
 ble as sodium nitrate, one part dissolving in about one and 
 one-third parts of water, but for most plants it is not the best 
 form of nitrogen. The ammonia nitrogen must first change 
 to nitrate nitrogen which it does very rapidly in the soil 
 by the process called nitrification (Section 123). Its ready 
 solubility and rapid change to nitrate make it only slightly 
 less readily available than sodium nitrate, and it is ranked 
 as a quick-acting fertilizer. In the early spring, however, to 
 start wheat, for example, ammonium sulphate is not good 
 because at that time of year bacterial action is very slow 
 and nitrification does not take place with sufficient rapidity 
 to feed the crop. A nitrate is better under these conditions. 
 
 Ammonia nitrogen is not leached from the soil as rapidly 
 as nitrate nitrogen, being absorbed both chemically and 
 physically (Section 131). Ammonia, held either in other 
 chemical combinations or absorbed by humus or hydrated 
 silicates, is just as easily nitrified as it is in the sulphate 
 form. Until nitrified, ammonium sulphate is not lost from 
 the soil, but nitrification is ordinarily so rapid that ammo- 
 nium sulphate is not a lasting nitrogenous fertilizer. 
 
 (c) EFFECT ON THE SOIL. Whereas sodium and calcium 
 nitrates tend to produce a residual alkaline condition of 
 the soil, ammonium sulphate tends to produce an acid con- 
 dition. Long continued use of this form of nitrogen results 
 in a very acid condition of the soil. On the fertilizer plats 
 of the Pennsylvania Experiment Station the use of 72 pounds 
 of nitrogen as ammonium sulphate per acre once in two years 
 for thirty years has resulted in a soil w y hich needs 19 times 
 as much lime to correct the acidity as do the check plats 
 receiving no fertilizer. 
 
 In nitrifying, the ammonia is changed to nitric acid, and 
 sulphuric acid is set free. Both acids require bases to
 
 200 
 
 NITROGENOUS FERTILIZERS 
 
 neutralize them, and thus there is twice as much lime or other 
 base needed for this fertilizer as is needed for other nitrog- 
 enous materials undergoing nitrification. Lime is used up 
 very rapidly and acidity results (Section 177). 
 
 m. NITROGEN AS AMINE OR PROTEIN 
 
 152. Cyanamid or Lime Nitrogen. The utilization of 
 atmospheric nitrogen in the manufacture of fertilizers is 
 successfully accomplished in another way than those men- 
 tioned in Section 150. The process depends on the fact that 
 nitrogen unites with calcium carbide to form calcium cyana- 
 mide at a temperature about 1000 C. in the soil this com- 
 pound changes gradually to nitrate. This fertilizer goes 
 under a variety of names. Cyanamid is the trade name of the 
 
 FIG. 51. Plant of American Cyanamid Co., Niagara Falls, N. Y. 
 
 American product manufactured at Niagara Falls (Fig. 51). 
 Calcium cyanamide is a common name for it, although as a 
 matter of fact the fertilizer contains only about 45 per 
 cent, of this compound. Lime nitrogen is another name; 
 also nitrolim which is the trade name of the fertilizer sold 
 in England.
 
 NITROGEN AS AMINE OR PROTEIN 201 
 
 (a) How MADE. Calcium carbide is first made by fusing 
 in an electric furnace a mixture of coke and lime. The 
 reaction is as follows : 
 
 CaO + 3C = CaCs + CO. 
 
 The carbide is removed, cooled, crushed to a fine powder 
 and placed in perforated steel cans set in brick oveng. A 
 carbon rod carrying a current of electricity, and passing 
 through the center of the can serves to heat up the carbide 
 to about 1100 C., when union takes place between the 
 carbide and a stream of pure nitrogen which is gently forced 
 into the can. The reaction is as follows: 
 
 CaCz + N 2 = CaCNs + C. 
 
 Pure nitrogen is obtained by passing air over red hot 
 copper when the oxygen unites with the copper to form 
 copper oxide and the nitrogen alone issues from the furnace. 
 The best process, however, is to fractionally distill liquid 
 air. Nitrogen boils at - 195.5 C. and oxygen at - 182.5 C. 
 The nitrogen comes off first and can be obtained very pure. 
 
 The nitrogenous product, which is really an impure calcium 
 cyanamide, is next cooled, pulverized, and treated with 
 water in rotating cylinders. About 30 per cent, of water 
 is taken up, the excess of calcium oxide is hydrated, and a 
 little carbide decomposed to acetylene and hydrated calcium 
 oxide. The material is then pressed into bricks and before 
 use is crushed and screened so that a granulated fertilizer 
 is obtained which is made use of almost exclusively in 
 manufacturing complete fertilizers. The cyanamid as it 
 comes on the market contains about 45 per cent, of calcium 
 cyanamide, 15 per cent, nitrogen, 27 per cent, calcium 
 hydroxide, and 13 per cent, free carbon, besides small 
 amounts of other constituents. 
 
 (6) AVAILABILITY. The fertilizing compound in cyanamid 
 is calcium cyanamide: Ca = NC = N. This compound is 
 soluble in water but not available to plants. Before its use 
 by plants it must be nitrified and this process takes place 
 in five stages as follows:
 
 202 NITROGENOUS FERTILIZERS 
 
 First, hydrolysis to cyanamide and calcium hydroxide, 
 helped probably by the adsorptive processes in the soil, thus : 
 
 CaCN 2 + 2H 2 O - H 2 CN Z + Ca(OH) 2 . 
 
 The calcium hydroxide is changed rapidly to carbonate. 
 
 Second, the hydrolysis of cyanamide with the aid of 
 colloidal catalysts to urea, thus: 
 
 H 2 CN 2 + H 2 O = CO(NH 2 ) 2 . 
 
 Third, the bacterial hydrolysis, or ordinary ammonifying 
 process, to ammonium carbonate, thus: 
 
 CO(NH 2 ) 2 + 2H 2 O = (NHOsCOi. 
 
 Fourth, nitrification to nitrous acid and nitrites. 
 
 Fifth, further nitrification to nitric acid and nitrates. 
 
 Cyanamid is ranked as a fairly quick acting fertilizer, 
 about as good as ammonium sulphate. 
 
 (c) EFFECT ON THE SOIL. Cyanamid while producing 
 nitric acid also carries considerably more calcium oxide than 
 is necessary to neutralize this acid. The residual effect is 
 like that of basic calcium nitrate, and is beneficial. Cases 
 have been reported where cyanamid has harmed crops, but 
 under ordinary farming conditions no danger from it need 
 be feared. 
 
 153. Dried Blood. By evaporating, drying, and grinding 
 animal blood from slaughter houses there is obtained a 
 product known as dried blood which is one of the best 
 organic nitrogenous fertilizers. It comes on the market in 
 two forms, red and black, the color depending on the processes 
 of manufacture. Red dried blood is the better of the two, 
 being more uniform in composition, containing more nitrogen 
 and being more available as a fertilizer. Its nitrogen content 
 is approximately 13 per cent. Black dried blood is not so 
 pure, being often mixed with hair, dirt, and other substances 
 which impair its value. Its nitrogen content varies greatly, 
 running from 6 to 12 per cent. It may also carry 3 or 4 
 per cent, of phosphoric acid.
 
 NITROGEN AS AM1NE OR PROTEIN 203 
 
 The availability of the best grades of dried blood is roughly 
 three-fourths that of sodium nitrate, although it varies with 
 soil conditions. Its nitrogen is in the protein form and must 
 undergo the complete process of ammonification and nitri- 
 fication before becoming available. In cold, acid soils this 
 process is not so rapid and as a result dried blood is not a 
 good fertilizer for such soils. The nitrogen is not lost from 
 soils since leaching cannot take place except as the protein 
 nitrifies, and this is not rapid enough to cause loss. 
 
 Dried blood has no marked effect on the soil, except that 
 its tendency is toward making a soil acid, it being organic 
 in nature and the decomposition of organic matter produces 
 organic acids. Nitrification also produces acids which must 
 be neutralized. But it must be remembered that the natural 
 tendency of cultivated and fertilized soils is toward acidity 
 and this condition should not be feared. Plenty of calcium 
 carbonate in the soil prevents acidity from appearing and 
 liming will overcome this condition if necessary (See Chapter 
 XII). 
 
 154. Dried Meat, Meat Meal. Refuse meat from slaughter 
 houses and packing houses, and waste from beef extract 
 factories are first rendered, that is, steamed under pressure 
 to remove fat, then dried and ground. Sometimes bones are 
 mixed with the meat before rendering, and in this case, 
 of course, the product contains phosphoric acid. The best 
 grades of dried meat carry 13 or 14 per cent, of nitrogen, 
 although many samples run less. 
 
 The availability of meat meal is not quite so high as dried 
 blood, but it makes a very satisfactory nitrogenous fertilizer 
 when rapid availability is not wanted. Its nitrogen is in the 
 protein form and like that of dried blood is not lost by 
 leaching. Its effect on the soil is similar to that of dried 
 blood. 
 
 155. Tankage. Besides the refuse meat there are other 
 waste animal products that are used as fertilizers. Tendons, 
 intestines, lungs, and hair, together with bones, horns, and 
 hoofs are treated with steam under pressure to remove fat 
 and gelatine, then dried and ground. If little or no bone is 
 present the product is called meat tankage. If considerable
 
 204 NITROGENOUS FERTILIZERS 
 
 bone is present it is called bone tankage. Tankage is very 
 variable in composition, sometimes containing as much as 
 12 per cent, nitrogen in meat tankage, and up to 9 per 
 cent, nitrogen with 17 per cent, phosphoric acid in bone 
 tankage. 
 
 Tankage is an excellent, rather slow acting fertilizer, its 
 value depending, especially in the case of bone tankage, on 
 fineness of grinding. The nitrogen is in the same form as in 
 dried meat and the effect on the soil is the same. 
 
 156. Dried Fish, Fish Scrap. The refuse material from 
 fish oil refineries, fish salting, or canning plants is dried 
 and ground, sometimes being treated with dilute sulphuric 
 acid to stop decomposition and partially dissolve the bones. 
 This fertilizer contains from 6 to 9 per cent, nitrogen and 
 5 to 9 per cent, phosphoric acid. Fish scrap is about as good 
 as the better grades of tankage, though slower acting than 
 dried blood. It contains the protein form of nitrogen. 
 
 157. Cottonseed Meal. The press cake which results from 
 the extraction of oil from cotton seed is used extensively 
 as a fertilizer. The decorticated meal made from seeds 
 which have had the husks removed before pressing, runs 
 about 6 per cent, nitrogen; the undecorticated meal carries 
 only 4 per cent, nitrogen. There are also small amounts 
 of phosphoric acid and potash. Since cottonseed meal is an 
 excellent cattle food, and since most of its fertilizing con- 
 stituents are recovered in the manure, it is much more 
 profitable to feed it first and use the manure as a fertilizer. 
 But it is, nevertheless, used to a very large extent directly 
 as a fertilizer, especially in the south. Moreover, its physical 
 condition is such that it improves the mechanical condition 
 of mixed fertilizers by absorbing moisture and preventing 
 caking. Its availability is about the same as dried blood 
 and the form of nitrogen is similar. 
 
 158. Castor-Bean Pomace. This is the ground press cake 
 from the manufacture of castor oil, and contains about 
 5 per cent, nitrogen with some phosphoric acid and potash. 
 It is a good fertilizer. 
 
 159. Leather, Hair, Wool Waste, Hoof, and Horn. These 
 materials are waste products from various industries and 
 are very slow acting, practically worthless forms of nitrog-
 
 EXERCISES 205 
 
 enous fertilizers when used without previous treatment. 
 Leather, hoof, and horn are sometimes steamed or roasted 
 and ground, and even treated with sulphuric acid, when they 
 make a fair grade of fertilizer. Leather contains about 8 
 per cent, nitrogen, hair 13 per cent., wool waste 5 to 10 
 per cent., horn and hoof 10 to 15 per cent. 
 
 Most of these materials, however, are used by the fertilizer 
 manufacturers in the preparation of "base goods." They are 
 treated with sulphuric acid along with rock phosphate. 
 The nitrogen is thereby partly converted to ammonium sul- 
 phate or some more available form of nitrogen than the 
 original non-decomposible protein form. This mixture of 
 acid phosphate and "chamber process" nitrogenous material 
 forms a " base" for fertilizer mixtures. 
 
 EXERCISES 
 
 1. What is the relative availability of the following fertilizers: sodium 
 nitrate, ammonium sulphate, dried blood, hair? Prove your statement 
 by showing that each in succession must undergo more changes than the 
 preceding one before it becomes available to plants. Which of these has a 
 tendency to leave the soil acid and why? 
 
 2. Describe briefly three widely different ways of changing the atmos- 
 pheric nitrogen into available plant food. 
 
 3. Why should nitrate and not dried blood be used in early spring? 
 Which makes the better top dressing and why? 
 
 4. Suppose a soil is lacking in available nitrogen and nitrogenous fertil- 
 izers are not to be had, state in detail how a crop of cabbage might suffer. 
 
 5. Is it wise to apply enough sodium nitrate to last for the four crops once 
 in a rotation of corn, oats, wheat and grass? Why or why not? 
 
 6. To what extent has man imitated Nature in the making of nitrogenous 
 fertilizers? 
 
 7. Which contains the most nitrogen per ton, sodium nitrate, 96 per cent, 
 pure, pure ammonium sulphate, or pure ammonium nitrate? 
 
 8. In how many respects is the process of making cyanamid available 
 similar to that of making a protein available? 
 
 9. Is cyanamid an organic compound? If so, what kind of an organic 
 compound? Is cyanamid a name descriptive of its composition? 
 
 10. Dried blood and hair both contain nitrogen in the protein form. 
 Why is there such a difference in their availability? 
 
 11. Refuse meats are first rendered in the making of meat meal. Why 
 does this process make a better fertilizer? 
 
 12. Can you suggest why the following are not mentioned as nitrogenous 
 fertilizers: Ammonium chloride, ammonium carbonate, potassium nitrate? 
 
 13. What crops remove the most nitrogen per acre? 
 
 REFERENCES 
 See references at end of Chapter VIII.
 
 CHAPTER X 
 PHOSPHATE FERTILIZERS 
 
 OF all the fertilizing elements which the farmer buys 
 phosphorus is the one which should and does cause him the 
 greatest concern. The soil contains no more phosphoric acid 
 than nitrogen, the average of good cultivated soil being not 
 far from 0.15 to 0.2 per cent. Phosphorus is necessary 
 for the production of seed, inducing early and full maturity. 
 It occurs for the most part in the grain at harvest and is 
 thereby sold from the farm, little being left in stems and 
 leaves to be returned to the soil as litter. Finally, phos- 
 phorus cannot be added to the soil by the growth of any 
 special crop. It is not like nitrogen which can be obtained 
 by legumes from the exhaustless atmospheric source. Phos- 
 phorus must be purchased and added to the soil, or the soil 
 becomes exhausted. Supplies brought up from the subsoil 
 either by capillarity or the growth of deep-rooted crops 
 are not sufficient to add materially to the amount in the 
 surface soil. Continued cropping and no return result in 
 a loss of phosphorus. Phosphate fertilizers, then, are of 
 prime importance. 
 
 160. Raw Bone. Bones when fresh contain about 40 
 per cent, of organic matter, 53 per cent, of inorganic matter 
 and 7 per cent, of water. The organic matter consists of 
 fat and ossein, the latter a protein. The inorganic matter 
 is mostly tricalcium phosphate, Ca 3 (P0 4 )2. It comes on 
 the market as raw bone-meal, and coarse ground bone, con- 
 taining about 4 per cent, nitrogen and 22 per cent, phos- 
 phoric acid. The presence of the fat makes fine grinding 
 impossible and it is not used much as a fertilizer. The 
 fat prevents bacterial action, thus checking nitrification, and 
 together with the ossein protecting the phosphate from being 
 acted upon by soil solvents, 
 (206)
 
 DISSOLVED BONE-BLACK 207 
 
 161. Steamed Bone, Bone-Meal. The fat in bone is 
 valuable for various commercial purposes and the ossein 
 can be converted into gelatine and glue. There are two 
 ways of removing fat: By extraction with a solvent like 
 benzine; or by treatment with boiling water or steam under 
 pressure. Subsequent cooling allows the fat to solidify on top 
 of the water, and to be removed. Steaming under pressure 
 also converts ossein to gelatine, soluble in water. The bone 
 that is left can be dried and easily ground fine. This material 
 is sold as steamed bone-meal or bone-meal. The best 
 grades contain 25 to 30 per cent, of phosphoric acid, but 
 frequently less than 1 per cent, nitrogen. The removal of 
 fat and ossein leaves the tricalcium phosphate in much 
 better physical condition both for grinding and subsequent 
 solution in the soil. Steamed bone-meal is a very excellent 
 phosphate fertilizer and fairly available. 
 
 Bone products have had a value as a fertilizer for centuries 
 and even now are considered by many to be superior to other 
 forms of phosphate, consequently the temptation to adulter- 
 ate bone-meal with worthless substances has been very 
 great. This fact together with differences in method of 
 treatment and quality of original bones makes the product 
 one of great variation in phosphoric acid content. The 
 figures given are average for a good product. 
 
 162. Bone-Black. When bones are subjected to destruc- 
 tive distillation, the organic matter is largely driven off and 
 there remains the inorganic matter and about 10 per cent, 
 of carbon. This material is known as bone-black, or animal 
 charcoal, and on account of its porosity and adsorptive power 
 is used after grinding for clarifying sugar solutions in sugar 
 refineries, and for other similar purposes. But little of it is 
 used as fertilizer in the freshly made form, most of it being 
 first employed as above stated. 
 
 After a time it loses its adsorptive or clarifying power and 
 then is sold as a fertilizer, although the presence of the 
 carbon prevents ready solution of the tricalcium phosphate. 
 It contains about 30 per cent, phosphoric acid. 
 
 163. Dissolved Bone-Black. If the spent bone-black 
 above mentioned is treated with sulphuric acid, it becomes a
 
 208 PHOSPHATE FERTILIZERS 
 
 readily available phosphate fertilizer, being converted into 
 monocalcium phosphate which is soluble in water, whereas 
 tricalcium phosphate is only slowly soluble in water and 
 carbon dioxide. The reaction may be expressed thus: 
 
 Cas(PO4) 2 + 2H 2 SO4 =CaH4(PO 4 )2+2CaSO4 
 
 1 1ts content of phosphoric acid is about 14 to 16 per cent. 
 
 164. Rock Phosphate, Floats. Originally the name "floats" 
 was applied to a particularly fine ground rock phos- 
 phate, so fine that it would float in the air. Now, however, 
 the term is loosely used for any finely ground rock phosphate. 
 Deposits of phosphate rock are found in many places. In 
 France, Belgium, Portugal, and North Africa there are 
 beds of greater or less thickness. The greatest supply, 
 however, comes from Florida, South Carolina and Ten- 
 nessee. Recently there have been discovered immense beds 
 in Idaho, Wyoming, and Montana. These constitute a 
 reserve supply of great importance since the older mines 
 are being rapidly exhausted. In South Carolina and 
 Florida the phosphate occurs largely as pebbles or boulders 
 in deposits resembling gravel beds (Fig. 52). In Tennessee 
 it occurs in veins or pockets. 
 
 The phosphorus occurs as tricalcium phosphate together 
 with varying amounts of iron and aluminium compounds 
 and calcium carbonate. The phosphoric acid content 
 varies from 25 to 40 per cent., iron and aluminium oxide, 
 2 to 6 per cent., and calcium carbonate from 1 or 2 per cent. 
 to 10 or 15 per cent. 
 
 As a fertilizer, rock phosphate is very slow acting when 
 applied alone. The finer it is, the more valuable it becomes, 
 but even very finely ground it is best used in connection 
 with decaying organic matter. Applied to acid peat or muck 
 soils it is especially good, and when mixed with manure 
 gives excellent results. Opinion is divided as to its value 
 compared to acid phosphate, even when mixed with manure. 
 Whether or not it is as good as, or better than, acid phosphate 
 when similarly mixed with manure, it is, nevertheless, a most 
 excellent phosphatic manure. Its cheapness recommends 
 it, as well as its high content of phosphoric acid.
 
 209
 
 210 PHOSPHATE FERTILIZERS 
 
 The fermenting mixture of rock phosphate and manure 
 has never showed any very greatly increased solubility of 
 phosphoric acid under laboratory conditions of extraction, 
 but field trials have abundantly proved that this mixture 
 is much better than rock phosphate alone or than manure 
 alone, showing that at least under field conditions the phos- 
 phoric acid is rendered sufficiently soluble for the growing 
 plant. 
 
 165. Acid Phosphate, Superphosphate. This is the best 
 known form of phosphate fertilizer. 
 
 (a) How MADE. To make rock phosphate available it 
 is treated with sulphuric acid which converts the tricalcium 
 phosphate to monocalcium phosphate according to the 
 equation given under Dissolved Bone-Black. The finely 
 ground rock phosphate together with the right amount of 
 approximately 65 per cent, sulphuric acid is placed in 
 mixing chambers provided with stirrers. After being 
 thoroughly mixed the material is dumped into "dens" 
 where the reaction is completed. Considerable heat is 
 developed, and the final product solidifies, because of the 
 formation of gypsum, CaSO 4 .2H 2 O. This mass after 
 standing for some time is crushed fine and is ready for 
 use. 
 
 In calculating the amount of acid to use, due regard is 
 paid to the ingredients other than tricalcium phosphate. 
 Calcium carbonate, of course, uses up sulphuric acid and so 
 do the iron and aluminium compounds. Iron compounds, 
 however, interfere with the formation of a good product, 
 if they are present in any considerable quantity over 4 or 
 5 per cent. The resulting mixture is in bad physical con- 
 dition on account of the formation of ferric sulphate and of 
 something like a hydrated, acid iron phosphate. It does 
 not dry sufficiently to pulverize easily. Moreover, insoluble 
 iron and aluminium phosphates are formed, which, of course, 
 are worthless as quick acting fertilizers. 
 
 Acid phosphate runs from 12 to 16 per cent, phosphoric 
 acid with 14 per cent, as the average content of available 
 phosphoric acid. In order to prevent any possible excess
 
 ACID PHOSPHATE, SUPERPHOSPHATE 211 
 
 of sulphuric acid it is customary to add somewhat less than 
 the theoretical amount. This results in the incomplete 
 conversion of all the tricalcium phosphate to monocalcium 
 phosphate. On standing, these two compounds unite to 
 form "reverted" or "gone back" phosphates. That is, 
 the water soluble monocalcium phosphate starts to revert 
 or go back to the tricalcium phosphate and forms dicalcium 
 phosphate. Since the latter is soluble in ammonium citrate 
 solution (Section 201), it is sometimes called citrate soluble 
 phosphoric acid. The equation is as follows: 
 
 CaH4(PO) z + Ca,(PO02 = 2Ca.tHt(PO t )!. 
 
 Reverted phosphate is almost as available as the mono- 
 calcium phosphate. 
 
 (6) AVAILABILITY. Acid phosphate is a quick acting fertil- 
 izer, readily available, and all things considered is the best 
 form of phosphate to use under ordinary conditions. 
 
 (c) EFFECT ON THE SOIL. In the soil acid phosphate 
 reverts very quickly to dicalcium and tricalcium phosphate. 
 Notwithstanding this reversion, which takes place before 
 the plant obtains much of the fertilizer, acid phosphate is 
 more readily available than tricalcium phosphate or rock 
 phosphate for two reasons : In the first place, acid phosphate 
 dissolves in the soil water and permeates the soil, so that 
 when it is precipitated it is thoroughly distributed. This 
 precipitate is much finer than any mechanically ground 
 material and, moreover, is much better mixed with the soil. 
 In the second place, freshly precipitated di- or tricalcium 
 phosphate is much more soluble in water and carbon dioxide 
 than is tricalcium phosphate which has been formed for a 
 long time, like the rock phosphate. 
 
 Acid phosphate is said to make a soil acid. This surely 
 is not due to the fact that it is an acid salt, for the plant in 
 the long run uses fully as much phosphoric acid as calcium, 
 and usually more, so that the residual effect could not be 
 acid. Moreover, although it may use up bases by reversion 
 in the soil, these bases are liberated again when the phosphate
 
 212 PHOSPHATE FERTILIZERS 
 
 redissolves in water and carbon dioxide. Some authorities 
 claim that the acidity is due to the presence of calcium 
 sulphate, a necessary by-product in the manufacturing 
 process. But it is doubtful if this has any more residual 
 acid effect than any ordinary fertilizer or than any normal 
 soil treatment. 
 
 166. Basic Slag, Thomas Slag. Basic slag is a very 
 popular fertilizer in Germany. 
 
 (a) How MADE. In the basic Bessemer process of making 
 steel from phosphatic iron, devised by Thomas and Gil- 
 christ, of England, the molten cast iron is placed in a con- 
 verter lined with calcium oxide or calcium and magnesium 
 oxides. By blowing a stream of air through the molten 
 mass, phosphorus and silicon are oxidized and unite with 
 the calcium to form a double, basic phosphate and silicate of 
 calcium. The molten slag is poured off and when cool is 
 broken up and finely ground. 
 
 (6) COMPOSITION. The exact compound of the phos- 
 phorus in basic slag is not known, but there have been 
 found crystals of so-called tetracalcium phosphate. Most 
 of the phosphorus, however, is probably in the form of a 
 pentacalcium silico-phosphate. These compounds may best 
 be compared with the other compounds of calcium and 
 phosphorus so far studied: 
 
 \..Monocalcium phosphate, CaO.(H 2 O) 2 .P2O 6 , found in 
 dissolved phosphates such as acid phosphate and dissolved 
 bone-black. 
 
 2. Dicalcium phosphate, (CaO) 2 .H 2 O.P 2 5 , found to some 
 extent with acid phosphate as the so-called reverted phos- 
 phate. 
 
 3. Tricaldum phosphate, (CaO) 3 .P 2 O 5 , found in rock 
 phosphate and bones. 
 
 4. Tetracalcium phosphate, (CaO)4.P 2 O5, and penta- 
 calcium silico-phosphate, (CaO) 5 .SiO 2 .P 2 O 5 . 
 
 The formulas for the first three have here been modified 
 from their usual form to bring out the differences between 
 them and the last two.
 
 BASIC SLAG 213 
 
 Now to illustrate their combination graphically: 
 
 H O 
 
 \ 
 
 H O P=O 
 
 O 
 
 Monocalcium phosphate Ca^ 
 
 O 
 
 \ 
 H O P=O 
 
 H O 
 
 H O 
 
 \ 
 H O P=O 
 
 O 
 Dicalcium phosphate 
 
 O 
 
 /(> P=O 
 Cs 
 
 /O 
 
 a< \ 
 X O P=O 
 
 Tricalcium phosphate Ca<^ 
 
 X) 
 
 \ 
 P=O 
 
 O O 
 
 / \ / \ 
 Ca P Ca 
 
 \ / 
 O O 
 
 Tetracalcium phosphate O 
 
 O 
 
 \ 
 
 O 
 
 \ 
 
 Ca P Ca 
 
 \ / \ / 
 O O
 
 214 
 
 PHOSPHATE FERTILIZERS 
 
 O 
 
 Ca 
 
 \ / \ 
 
 Ca 
 
 O O 
 
 Pentacalcium silico-phosphate O 
 
 O 
 
 / \ 
 Ca Si 
 
 Ca 
 
 \ 
 
 \ / \ 
 
 Ca 
 
 (c) AVAILABILITY. Basic slag is usually considered about 
 one-half as available as acid phosphate, although on acid 
 soils it is much more readily soluble and quick acting. It is 
 considered an excellent form of phosphate. In this country 
 its use is limited by few importations and relatively high 
 price. Iron ores in this country are too low in phosphorus 
 to produce a slag from steel that is valuable as a fertilizer. 
 In Europe, on the other hand, the slags are rich in phos- 
 phorus, the phosphoric acid content running from 10 to 
 20 per cent. 
 
 (d) EFFECT ON THE SOIL. Basic slag was formerly thought 
 to have considerable free lime, since it was basic in character 
 and was excellent on an acid soil. As a matter of fact it 
 contains only a few per cent, of free calcium oxide (1 to 6 
 per cent.). The decomposition of the basic slag in the soil, 
 however, results in the production of calcium carbonate. 
 The action of water and carbon dioxide produces di- or tri- 
 calcium phosphates and bicarbonate of calcium, in addition 
 to silicic acid or free silica. In this way basic slag acts as a 
 neutralizer of soil acidity, and an improver of soil texture. 
 There is not, however, enough calcium carbonate resulting 
 from an ordinary application of basic slag say 500 or 600 
 pounds to entirely correct the acidity of an ordinarily
 
 REFERENCES 215 
 
 sour soil. In such an application there probably would not 
 result more than 100 pounds of calcium oxide combined as 
 carbonate, not enough for any immediate effectiveness. 
 
 EXERCISES 
 
 1. Why is there a difference in the availability of rock phosphate, raw 
 bones and steamed bone meal? 
 
 2. Compare mono-, di-, and tri-calcium phosphate as to formula, solu- 
 bility and availability. How does industry change one into the other? 
 How does the soil accomplish the same thing? Can the soil accomplish 
 the opposite effect? Which is the better for the farmer to use and why? 
 
 3. In making acid phosphate from rock phosphate what components 
 are taken into account and why? 
 
 4. Suppose a soil was in such a state that available P2O was lacking, 
 and fertilizer was not to be had, state in detail how a crop of wheat might 
 suffer. 
 
 5. What is the value of mixing organic matter with rock phosphate? 
 
 6. Explain why an acid soil usually lacks available phosphorus. 
 
 7. Is much basic slag produced in this country? Why? 
 
 8. Is reversion of acid phosphate a phenomenon that is desirable? very 
 harmful? that can be prevented in an alkaline soil? that can happen in an 
 acid soil? that prevents leaching? that is an example of absorption? that 
 permits the addition of sufficient acid phosphate to a soil once in a rotation? 
 
 9. What crops remove the most phosphoric acid per acre? 
 
 REFERENCES 
 See references at end of Chapter VIII.
 
 CHAPTER XI 
 POTASH FERTILIZERS 
 
 THE third of the fertilizer trio is potassium or, as it is 
 usually called, potash. The element potassium occurs in 
 most soils to a very considerable extent (Section 138 6, 6), 
 but it is frequently present in an unavailable form. Some 
 plants, notably clover and alfalfa, require considerable 
 potassium; and other crops also remove it to no small 
 extent. Unlike nitrogen and phosphorus, however, potas- 
 sium is not sold from the farm in any considerable amount 
 except in hay, since it occurs for the most part in the stems 
 and leaves of plants. These are the portions of the crop 
 which usually remain on the farm, being fed as roughage or 
 used as litter. In this way the potassium gets back to the 
 soil. Its application, however, frequently results in increased 
 yields, and it is thus an important element in fertilizers. In 
 the past, however, there has been a tendency to use too much 
 potash, a fault corrected by the Great War which caused 
 a serious lack of potash fertilizers. Farmers have learned 
 that general farm crops, as a rule, need little or no potash. 
 Special crops like potatoes and tobacco and intensive crops 
 need some potash. 
 
 167. The German Potash Deposits. The most important 
 source of potassium in the world is located at Stassfurt in 
 northern Germany where there are today over one hundred 
 mines producing potash salts (Fig. 53) . For several centuries 
 common salt had been obtained from its salt springs and 
 wells. About the middle of the nineteenth century deep 
 borings revealed the presence of immense beds of rock salt 
 at a depth of about 1000 feet. Overlying these beds of salt, 
 however, were considerable deposits of potassium and 
 magnesium compounds. These salts were considered worth- 
 less at the time and were thrown away, but later their value 
 (216)
 
 THE GERMAN POTASH DEPOSITS 
 
 217 
 
 became apparent, until now the potash salts are the only 
 ones of value. Rock salt is no longer mined at Stassfurt.
 
 218 POTASH FERTILIZERS 
 
 It is believed that in past geologic ages there existed 
 here an immense inland sea which was probably fed inter- 
 mittently by inrushes of water from the ocean. The 
 climate of Europe at that time was tropical and evapora- 
 tion of water from this sea was consequently rapid. The 
 water became more and more concentrated in salts until 
 finally the least soluble were deposited. On top of these 
 compounds other salts were deposited layer by layer. 
 Intermittent additions of sea water from outside caused a 
 dilution of the water within, and deposition of salt was 
 consequently interrupted, causing alternate layers of less 
 soluble and more soluble compounds as evaporation went 
 on. Geologic changes brought about the deposition of 
 various sedimentary rocks and finally a layer of impervious 
 clay which protected the soluble salts from solution in rain 
 water. 
 
 The bottom layers of these beds are composed of anhydrite 
 (sulphate of calcium) and rock salt. Next comes the so-called 
 polyhalite region (sulphates of calcium, magnesium, and 
 potassium) ; then the kieserite region (magnesium sulphate) ; 
 and finally the carnallite region (chlorides of potassium and 
 magnesium). The last is a bed ranging from 50 to 130 
 feet in thickness, from which most of the potash salts are 
 obtained. Due to the intermittent deposition of salts, 
 partial solution from infiltration of rainwater, and redepo- 
 sition, the layers of salts are not perfectly distinct and not 
 always in the same order. For instance, layers of anhydrite 
 and rock salt intersperse the other salts, together with 
 minerals, such as sylvine (potassium chloride) and kainite 
 (sulphate and chloride of magnesium and potassium). 
 
 168. Muriate of Potash, Potassium Chloride, KC1. This is 
 the most widely used potash fertilizer. It is manufactured 
 from carnallite which occurs mixed with rock salt and other 
 minerals, and contains only 9 per cent, actual potash. 
 By dissolving carnallite in hot magnesium chloride solution, 
 boiling, and crystallizing, there is obtained a muriate con- 
 taining about 20 per cent, potash and called Potash Manure 
 Salt. On further evaporation and crystallization of the 
 mother liquor a pure carnallite (KCl.MgCl 2 .6H 2 O) is obtained
 
 MURIATE OF POTASH, POTASSIUM CHLORIDE 219 
 
 (Fig. 54). This salt on being treated just like the crude 
 carnallite yields the commercial muriate with one crystalli- 
 zation.
 
 220 POTASH FERTILIZERS 
 
 There are three grades of muriate on the market, 80 per 
 cent., 95 per cent., and 98 per cent., which contain respec- 
 tively 50.5 per cent., 60 per cent., and 61.9 per cent, potash 
 (K2O). The 80 per cent, muriate is the one usually sold, 
 however. 
 
 It is very generally stated that potassium chloride affects 
 the burning quality of tobacco and makes potatoes watery. 
 The former is probably true, but the latter is not always the 
 case, for excellent potatoes can be grown with the chloride, 
 provided, however, that lime has been applied to the soil. 
 The bad effects of the chlorine are apparently most pro- 
 nounced on acid soils. 
 
 The tendency of potassium chloride is to make a soil 
 acid (Section 177). Plants exercising their selective action 
 remove the base, potassium, from the soil and leave the 
 chlorine which is assimilated but little. This results in the 
 production of hydrochloric acid which neutralizes any basic 
 compound present in the soil, and this means usually calcium 
 carbonate. When the reserves of base are used up the soil 
 becomes acid. The calcium chloride thus formed is easily 
 leached from the soil. Potassium chloride removes calcium 
 from the soil in another way by reacting with calcium 
 silicates to form potassium silicates and calcium chloride 
 which is, of course, leached out. 
 
 169. Sulphate of Potash, Potassium Sulphate, K 2 SO 4 . This 
 fertilizer, although not used to so great an extent as the 
 muriate, is in many respects the best one to employ. It is 
 made by dissolving and concentrating a mixture of potassium 
 chloride and kieserite (magnesium sulphate). There is 
 precipitated the double sulphate of potassium and magnesium 
 (K 2 SO4.MgSO 4 ), which is also sold under the name of Double 
 Potash Manure Salt, containing about 27 per cent, potash. 
 This double salt is further dissolved with a certain amount 
 of potassium chloride and boiled. Potassium sulphate is 
 precipitated. Two grades are sold, 90 and 96 per cent, pure, 
 containing, respectively, 47 per cent., and 52.7 per cent, 
 potash. 
 
 Potassium sulphate has no bad effects on tobacco and 
 potatoes, and, furthermore, is not so apt to make a soil acid,
 
 NATURAL BRINES 221 
 
 since plants assimilate sulphur to a considerable extent. 
 The whole salt is thus absorbed and no residue left. This 
 fertilizer has an action on calcium silicates similar to that 
 of the chloride, but the resulting calcium sulphate is not so 
 soluble as calcium chloride, nor is it leached to so great an 
 extent. Loss of calcium from soils is hence not so great as 
 in the case of the chloride. 
 
 170. Kainite. This fertilizer was formerly the mineral 
 of the same name, the formula of which is KCl.MgSO 4 .6H 2 O, 
 but at present it is merely a name for a potash fertilizer 
 containing 12 per cent, potash, the form of the potassium 
 and the other compounds varying considerably. The per- 
 centage of potash only is constant. Since kainite always 
 contains chlorine in some form, it is open to the same 
 objection as is the muriate of potash, but it is nevertheless 
 a good low grade form of potash. 
 
 171. Wood Ashes. One of the oldest sources of potash is 
 wood ashes. When clean, hard wood is carefully burned, the 
 potash content may run up to 8 or 10 per cent., mostly in the 
 carbonate form. In addition there may be 1 or 2 per cent, of 
 phosphoric acid, and 30 per cent, of calcium compounds, 
 the calcium being in the oxide form when freshly burned, . 
 but changing to carbonate on exposure. The wood ashes 
 now on the market are of a very inferior grade, carrying 
 not more than 3 or 4 per cent, of potash in unleached ashes. 
 Leached ashes, that is, ashes which have been leached to 
 extract potash for other purposes than for fertilizers, or 
 ashes which have been exposed to the weather and leached 
 by rain, contain usually less than 1 per cent, potash. 
 
 Potassium carbonate in wood ashes is a good fertilizer 
 unless too much is applied, when it has a deflocculating 
 effect on soil grains and is poisonous to plants. This car- 
 bonate and the calcium carbonate in wood ashes are both 
 neutralizes of soil acidity and are valuable for this purpose. 
 
 172. Natural Brines. Certain lakes in Nebraska and 
 California are rich in potash salts, largely carbonate, but 
 some sulphate and chloride as well as similar sodium salts. 
 The water from these lakes is evaporated. The dried residue 
 contains 20 to 30 per cent. K 2 O. This is at present the 
 largest domestic source of potash.
 
 222 
 
 POTASH FERTILIZERS 
 
 173. Kelp and Alunite. The giant kelps or seaweeds 
 on the Pacific coast (Fig. 55), and alunite, a mineral found 
 to some extent in Utah, and consisting of a double sul- 
 
 Fia. 55. Giant kelp. 
 
 phate of potassium and aluminium, are also important 
 domestic sources of potash. The giant kelps grow rapidly' 
 and sometimes attain a length of hundreds of feet. Dry,
 
 REFERENCES 223 
 
 they contain 15 to 20 per cent, potash and their ashes 
 contain as much as 30 to 35 per cent, potash in the form 
 of the chloride. Alunite contains 10 per cent, potash, 
 but can be ignited and the potash content increased to 15 
 per cent., or ignited and the leeched potassium sulphate 
 evaporated, when the nearly pure potash salt can be obtained. 
 The latter process, however, is expensive. Both kelp and 
 alunite have given good results as a fertilizer with no treat- 
 ment other than drying in the case of kelp and pulverizing 
 in both cases. Used in this way, however, they are low- 
 grade fertilizers. 
 
 174. Cement Dust. The fine dust from cement works 
 and even from blast furnaces carries 2.5 to 9 per cent. K 2 O, 
 which is slowly available. This dust can be used just as it is or 
 it can be leached and a high grade sulphate obtained. Although 
 with proper appliances for collection this dust can be our 
 greatest source of potash, it is not yet used to any great extent. 
 
 175. Tobacco Waste. In some sections of the country 
 the stems, stalks, and other waste from harvesting the crop 
 and manufacturing tobacco products, can be obtained 
 easily. If ground fine this waste makes excellent fertilizing 
 material, being fairly available. The potash content varies 
 from 4 to 10 per cent., phosphoric acid less than 1 per cent., 
 and nitrogen from 2 to 4 per cent., sometimes as much as 
 half of it in the nitrate form. 
 
 EXERCISES 
 
 1. Suppose a soil is lacking in available potassium and potash fertilizers 
 are not to be had, state in detail how a crop of potatoes might suffer. 
 
 2. Tabulate all the fertilizers that are immediately available; that must 
 undergo nitrification; that leaves the soil acid; that leave it basic; that will 
 puddle the soil; that are high grade; that are low grade; that are slaughter- 
 house wastes; that can be made by the use of electricity; that are easily 
 leached; that are easily absorbed; that are easily adsorbed. 
 
 3. Compare the amounts of nitrogen, phosphoric acid and potash in the 
 average soil and in the film water. What do these figures indicate as to 
 the need for potash? 
 
 4. What crops remove the most potash per acre? 
 
 5. If potash fertilizers are absorbed in the soil, into what compound 
 might the potassium be changed? write equations. What conditions would 
 further its absorption? 
 
 6. What property studied in this text and displayed toward potassium 
 in sea-water is developed extremely by kelp? 
 
 REFERENCES 
 See references at end of Chapter VIII.
 
 CHAPTER XII 
 LIME 
 
 NITROGEN, phosphorus, and potassium compounds are 
 direct or food fertilizers primarily. It is for their food value 
 to the plant that they are purchased. Calcium compounds, 
 on the other hand, are usually considered as indirect ferti- 
 lizers or amendments. Calcium is, of course, an essential 
 element in the growth of plants, but the effects of compounds 
 of calcium on the soil, and the exploitation of these effects 
 has given calcium an importance for other than feeding 
 purposes. As a plant food, however, calcium is frequently 
 necessary in soils, especially for certain crops, and it is 
 necessary to consider calcium in this connection, without 
 at all minimizing its effect as an amendment. 
 
 176. Calcium Fertilizers as Plant Food. The total amount 
 of calcium in soils of course varies considerably, but on the 
 average is not as much as that of potassium 0.5 to 1.50 per 
 cent. In many cases it may be present in part as calcium car- 
 bonate which is fairly soluble in soil moisture, but most of 
 it is in silicate and organic form and may be very insoluble. 
 Since calcium carbonate is so soluble, it very frequently 
 happens that this compound is entirely lacking even in 
 limestone soils. As a result, soils may lack sufficient available 
 calcium for the nutrition of crops. 
 
 Some farm crops do not need very much calcium, it is 
 true, but other crops like clover and alfalfa do need large 
 quantities. Table XII shows the amount of calcium oxide 
 removed by various crops. Of course, this represents the 
 amount removed only, and not the whole amount needed, 
 for plants at harvest do not remove as much as they need 
 during their growth. 
 
 (224)
 
 SOIL ACIDITY 225 
 
 TABLE XII. AMOUNT OF CaO REMOVED BY VARIOUS CROPS 
 
 (Expressed in pounds per acre.) 
 
 Alfalfa 212 
 
 Cabbage 95 
 
 Corn 12 
 
 Clover 90 
 
 Oats . . . 11 
 
 Potatoes 31 
 
 Timothy 14 
 
 Tobacco 83 
 
 Wheat 8 
 
 In many cases, it is true, sufficient calcium is added in 
 the ordinary fertilizers to feed crops. Table XIII gives the 
 estimated amount of calcium oxide in 100 pounds of various 
 fertilizers. 
 
 TABLE XIII. AMOUNT OF CaO IN VARIOUS FERTILIZERS 
 
 Fertilizer. Form of Calcium. Per cent. CaO. 
 
 Acid phosphate Phosphate and sulphate . . . .21 
 
 Basic slag Phosphate, silicate, and oxide . . 48 
 
 Bone meal Phosphate 27 
 
 Rock phosphate Phosphate and carbonate ... 42 
 
 Wood ashes Carbonate and phosphate ... 34 
 
 It may happen, however, that a fertilizer application 
 does not add calcium and the crop becomes starved for lack 
 of this essential element. Particularly may this be true in 
 the case of clover and alfalfa, as mentioned above. An 
 application of lime, then, has the added benefit of feeding 
 the crop. 
 
 177. Soil Acidity. One of the most important effects of 
 adding lime to the soil is the neutralization of soil acidity or 
 to "sweeten a sour soil." This condition in the soil is very 
 common, may occur in all kinds of soils, and in fact is the 
 natural result of cropping. Its bad effect on crops is fre- 
 quently exaggerated, some crops preferring an acid soil and 
 even refusing to grow in neutral or alkaline soils. For 
 ordinary crops, however, in the usual farm rotation, a soil 
 which is neutral or slightly alkaline is preferable and should 
 be maintained. 
 
 The primary cause of soil acidity is the production of 
 acids or salts that are acid to litmus. These acids may be 
 organic or inorganic in nature and may vary in their harmful 
 15
 
 226 LIME 
 
 effect on crops. They may occur in the soil as a result of 
 natural changes which take place particularly when the soil 
 is cultivated and crops grown, or they may be the result 
 of the application of fertilizers, in which case soil acidity 
 may be said to be caused by artificial means! 
 
 (a) NATURAL ACIDITY. When organic matter in the soil 
 undergoes decomposition through bacterial action, organic 
 acids are some of the intermediate products. Decomposition 
 in the presence of air is an oxidation process, and with 
 thorough aeration results ultimately in the formation of 
 carbon dioxide, water, and inorganic salts, the last coming 
 from the combination of mineral elements with the organic 
 matter. Nitric acid, of course, is formed from nitrogenous 
 compounds and possibly mineral acids, but before complete 
 oxidation occurs, and especially in soils not thoroughly 
 aerated, organic acids are formed. These acids are some- 
 times fairly simple, like acetic, or butyric, or oxalic, but 
 more frequently they are very complex, and many of them 
 unknown. In the absence of air, as in water-logged soils, 
 acids are even more commonly produced as a result of 
 what may be called intermolecular oxidation, where one 
 compound is oxidized at the expense of another. 
 
 Another natural cause of acids is the removal of bases 
 from salts by plants and by certain hydrated compounds 
 in the soil. Plant root hairs exercise a so-called "selective 
 absorption" in taking up plant foods (Section 56). Sulphates 
 and chlorides, for example, are split up, the base element 
 entering the plant and the acid radical being left in the soil 
 as an acid. Certain colloidal materials like hydrated 
 silicates and humus produce this same result, the base 
 being adsorbed or perhaps chemically combined with the 
 colloid. It is possible that hydrolysis takes place previous 
 to the absortive phenomenon. This means the formation of 
 a hydroxide and an acid, thus: 
 
 KCl + HOH = KOH + HC1. 
 
 (6) ARTIFICIAL ACIDITY. The application of ammonium 
 sulphate results in the production of nitric acid from the 
 ammonia by the nitrifying bacteria, and of sulphuric acid
 
 SOIL ACIDITY 
 
 227 
 
 as the residue from the nitrification. Figs. 56 and 57 show 
 the effect of such acidity on corn and oats. Figs. 58 and 59 
 
 FIC.LU TTrT 
 
 t.r 1 1-UiM-Ar,. 
 
 lMui.l,ni ,. iMMLtv i..^'-, 
 
 ^.^rag^^^:.,* 
 
 ^aw^BSi 
 
 ?^ 
 
 FIG. 56. Effect of acidity resulting from use of ammonium sulphate. 
 Corn. General fertilizer plats, Department of Agronomy, Pennsylvania 
 Station.
 
 228 
 
 LIME 
 
 show the effect of the same treatment on corn and oats, 
 but in soil that contains enough limestone to neutralize the 
 acidity. Sulphate and particularly the muriate of potash 
 also tend to leave an acid residue, due to the absorption of 
 potassium by plants or colloids and the presence of the acids 
 sulphuric and hydrochloric. This of course is the same 
 phenomenon described under natural acidity, except that 
 it is more pronounced. 
 
 FIG. 57. Effect of acidity resulting from use of ammonium sulphate. 
 Oats. General fertilizer plats, Department of Agronomy, Pennsylvania 
 Station. 
 
 Whether or not a soil becomes acid from any or all of the 
 above mentioned causes depends on the absence or presence 
 of sufficient bases to neutralize the acids as they are formed. 
 In other words the causes above enumerated produce acids. 
 The effect is noticed if insufficient bases are present to 
 neutralize the acids (Figs. 56, 57, 58, and 59). The principal 
 basic material in the soil is calcium carbonate resulting from 
 limestone or from silicates containing calcium. Soils derived
 
 SOIL ACIDITY 
 
 229 
 
 from limestone contain particles of calcium carbonate which 
 slowly dissolve, yielding a solution which neutralizes any 
 acids resulting from organic decomposition or selective 
 absorption. Little calcium is, as a rule, present in silicate 
 
 FIG. 58. Effect of sufficient limestone in the soil to neutralize the acidity 
 from ammonium sulphate. Corn. General fertilizer plats, Department of 
 Agronomy, Pennsylvania Station. 
 
 form and hence little carbonate can be produced from this 
 source. In time all the calcium carbonate is dissolved out 
 and then the acid condition of the soil asserts itself. This 
 solution of calcium carbonate takes place rapidly and 
 completely.
 
 230 
 
 LIME 
 
 On the other hand, it frequently happens that soils derived 
 from silicate rocks containing calcium do not become acid 
 readily. This is because the calcium is slowly dissolved 
 out as calcium bicarbonate and but little is wasted due to 
 leaching. Practically all of it neutralizes acids or serves 
 some other valuable function. There is no excess at any 
 one time and, moreover, the total amount of calcium present 
 is very considerable. 
 
 
 
 ' 'i i' 
 
 v ! 
 
 w 
 
 FIG. 59. Effect of sufficient limestone in the soil to neutralize the acidity 
 from ammonium sulphate. Oats. General fertilizer plats, Department of 
 Agronomy, Pennsylvania Station. 
 
 But, nevertheless, the general tendency of all soils is to 
 lose the basic material and to produce acids from various 
 causes. This combination of changes results in' an acid or 
 sour soil. 
 
 Virgin soils may be temporarily acid, the latter being 
 caused by the accumulation of organic matter. Cultivation 
 will cause further oxidation and destruction of these acids 
 and also will cause increased solution of basic material and 
 hence neutralization of the acids.
 
 LIME 
 
 231 
 
 But whatever the cause may be, permanent soil acid, as 
 a rule, should be neutralized by certain calcium compounds, 
 loosely called "lime." 
 
 178. Lime. The chemical term lime is used for calcium 
 oxide, CaO. Agriculturally, however, lime is any compound 
 of calcium which will neutralize acids. The compounds 
 having this power are the carbonate, hydroxide, and oxide. 
 
 FIG. 60. Limestone quarry. Department of Experimental Agricultural 
 Chemistry, Pennsylvania Station. 
 
 (a) CALCIUM CARBONATE, CaC0 3 . This form of calcium 
 occurs in limestone, oyster shells, shell marl, and chalk, 
 all of which may contain as much as 95 to 98 per cent, 
 calcium carbonate, but frequently contain less (Fig. 60 
 shows a limestone quarry). Limestone very often is com- 
 posed of magnesium carbonate as well as calcium carbo- 
 nate, in amounts varying from a few per cent, up to 45 
 per cent. When the latter content of magnesium carbo- 
 nate is present the mineral is called dolomite. To be used 
 on the soil all forms of calcium carbonate should be ground 
 very fine, preferably so that 75 per cent, at least passes a 
 hundred mesh sieve. It must be remembered that it is the
 
 232 LIME 
 
 calcium oxide content only which is of value in neutralizing 
 acids. One hundred pounds of calcium carbonate contain 
 fifty-six pounds of calcium oxide, or to be more in accord 
 with the naturally occurring limestones, one hundred pounds 
 of 95 per cent, limestone contain fifty-three pounds of 
 calcium oxide. 
 
 FIG. 61. Lime kilns. Department of Experimental Agricultural Chem- 
 istry, Pennsylvania Station. 
 
 (6) CALCIUM OXIDE, called also BURNT LIME, STONE LIME, 
 LUMP LIME, ROCK LIME, CAUSTIC LIME, and QUICKLIME, 
 CaO. This is prepared from any of the forms of calcium 
 carbonate, although usually from limestone, by "burning," 
 either in specially built kilns (Fig. 61) or in piles in the field. 
 In either case the limestone is alternated with wood or coal 
 and the latter by burning produces sufficient heat to drive 
 off carbon dioxide from the limestone and leave calcium 
 oxide, thus: 
 
 CaCOs + heat = CaO + CO 2 . 4 
 
 If pure this form of lime is all valuable in neutralizing acids 
 and is the most concentrated form that can be obtained.
 
 AVAILABILITY OF LIME 233 
 
 It is in fact the only fertilizer which contains practically 
 100 per cent, of the valuable constituent. 
 
 (c) CALCIUM HYDROXIDE, SLAKED LIME, HYDRATED LIME, 
 Ca(OH) 2 . When water is added to a lump of calcium oxide 
 it swells, gives off heat, and finally crumbles to a fine, dry 
 powder. The process is called "slaking," and the product, 
 slaked lime. The reaction is expressed thus: 
 
 CaO+H 2 O=Ca(OH)i. 
 
 The volume of the calcium oxide is increased two or three 
 times, and the weight is increased one-third. To put it in 
 another way, 100 pounds of slaked lime contain about 75 
 pounds of calcium oxide. A solution of calcium hydroxide 
 in water is called lime water. A thin paste of the hydroxide 
 and water is called milk of lime. 
 
 (d) AIR-SLAKED LIME. When burnt lime is allowed to 
 remain exposed to the air it first takes on water and then 
 carbon dioxide until it finally becomes calcium carbonate, 
 thus: 
 
 CaO + H 2 O = Ca(OH) 2 . 
 Ca(OH) + COt = CaCO, + HjO. 
 
 A pile of burnt lime slakes first on the outside and the 
 lumps fall apart covering the pile with fine material and 
 filling up the interstices so as to protect the interior of the 
 pile from rapid change to carbonate (Fig. 62). The outside 
 changes very quickly to the carbonate. Without a chemical 
 analysis it would be impossible to tell how much calcium 
 oxide there is in a given lot of air-slaked lime, unless, of course, 
 the amount of burnt lime originally present is known. The 
 process, however, is very slow. For example, a sample 
 taken at a depth of 4 inches from the surface of a heap 
 exposed ten years contained 27 per cent, calcium carbonate 
 and 37 per cent, calcium hydroxide. 
 
 179. Availability of Lime. Under the best conditions 
 chemically pure calcium oxide is soluble as calcium hydroxide 
 at ordinary temperatures to the extent of one part in 1000 
 parts of pure water. Chemically pure calcium carbonate, 
 freshly precipitated, is very slightly soluble in pure water,
 
 234 
 
 LIME 
 
 but in water saturated with carbon dioxide at ordinary 
 temperature it is soluble as calcium bicarbonate to the 
 extent of one part in about 1000 parts. The less carbon 
 dioxide present, the less calcium carbonate is dissolved. Soil 
 moisture contains small quantities of carbon dioxide. This 
 would change calcium hydroxide dissolved in it to carbonate, 
 a change which takes place very quickly. Further quantities 
 of carbon dioxide would change the carbonate to bicarbonate 
 and so dissolve it. Since carbon dioxide is being constantly 
 produced in the soil, the change of hydroxide to carbonate 
 and bicarbonate is fairly rapid. On account of this double 
 
 FIG. 62. Pile of air-slaked lime. (Hibshman.) 
 
 change of hydroxide, it makes very little difference which 
 form is used on soils, whether fresh slaked lime, air-slaked 
 lime, or limestone. Burnt lime has a caustic effect on plant 
 growth, and is said to cause rapid decay of organic matter 
 in the soil; consequently it should be used with great care and 
 never should be applied near seeding time. Because of a 
 difference in physical condition, or more accurately stated, 
 because of a difference in molecular arrangement, there is 
 a difference in the solubility of various carbonates. Shell 
 marl, oyster shells, limestone, is the order of solubility of 
 these carbonates. For practical purposes, however, it may 
 be said again that the availability of all forms of lime is
 
 EFFECT OF LIME ON THE SOIL 
 
 235 
 
 about the same. In other words the farmer may apply 
 slaked lime, air-slaked lime, or ground carbonate in the form 
 of shell marl, oyster shells, or limestone, with equally good 
 results. It is the bicarbonate of lime in any event which 
 is the active form in the soil. All that he must remember 
 is that to get 100 pounds of calcium oxide he must use 100 
 pounds of burnt lime, 130 pounds of slaked lime, or 180 
 pounds of carbonate; of air-slaked lime he must know the 
 calcium oxide content. 
 
 FIG. 63. Lime and clover test. Check plat, yield of hay 980 pounds per 
 acre. Pennsylvania Station. 
 
 180. Effect of Lime on the Soil. Inasmuch as lime is 
 for the most part a soil amendment, the changes which it 
 occasions in the soil, and by which plants are benefited, 
 are of great importance. No other element has such a great 
 variety of uses in crop production, and yet it must not be 
 considered a universal panacea for all soil ills. Figs. 63, 64, 
 65, and 66 show that while lime is needed to correct acidity, 
 fertilizers also are needed. 
 
 (a) NEUTRALIZING ACIDS. This is perhaps the best known 
 function of lime, and the results are far reaching. Many 
 acids are poisonous to plants. That is, there is a direct 
 physiological effect, more particularly from the mineral 
 acids and from some organic acids, oxalic for example. Then
 
 236 LIME 
 
 again, acids check the activity of soil bacteria. Decompo- 
 sition is prevented. This means that the production of 
 carbon dioxide is limited, and hence, solution of soil 
 
 FIG. 64. Lime and clover test. Lime at rate of 1000 pounds per acre. 
 Yield, i960 pounds. Pennsylvania Station. 
 
 FIG. 65. Lime and clover test. Commercial fertilizer only at rate of 250 
 pounds per acre. Yield, 1560 pounds. Pennsylvania Station. 
 
 minerals is lessened and plant food thereby diminished. 
 Ammonification and nitrification are very seriously checked 
 by acids and the supply of nitrogen for plants is therefore 
 cut off. The activity of nitrogen-fixing bacteria is also
 
 EFFECT OF LIME ON THE SOIL 
 
 237 
 
 lessened by acids. Fig. 67 shows the effect of different 
 amounts of lime on the growth of clover in an acid soil. 
 
 FIG. 66. Lime and clover test. Lime and fertilizer. Same amounts as 
 . before. Yield, 2526 pounds per acre. Pennsylvania Station. 
 
 FIG. 67. Pot test of lime on clover in acid soil. Amounts indicated are 
 rates per acre, 5200 pounds CaCCb being needed to neutralize the soil 
 according to the Veitch method. Yields from left to right: 8.7 gms.; 8.8 
 gms.; 7.9 gms.; 2.3 gms.; gms. Department of Agronomy, Pennsylvania 
 Station. 
 
 By neutralizing soil acids lime prevents poisoning of 
 plants, hastens decomposition of organic matter, and in-
 
 238 LIME 
 
 creases nitrification and fixation. The fact that lime hastens 
 decomposition is frequently charged against it. This is a 
 great mistake, for decomposing organic matter is of very 
 great value to crops and should be encouraged, within 
 reason of course. Active organic matter helps to release 
 the stores of unavailable plant food. Organic matter in the 
 soil should be maintained so that it may be destroyed. A 
 mere piling up of organic matter in the soil, organic matter 
 that does not decay, is useless except for holding moisture 
 and improving soil structure. 
 
 (6) MAKING POTASSIUM AVAILABLE. Lime is said to 
 release potassium from insoluble silicates and humates, cal- 
 cium taking the place of potassium in these compounds and 
 potassium being made soluble as the carbonate. There 
 seems to be evidence now, however, which indicates con- 
 siderable doubt as to the ability of lime to make potash 
 available. 
 
 (c) MAKING PHOSPHORUS AVAILABLE. Lime also changes 
 iron and aluminium phosphates to calcium phosphate and 
 thereby makes the phosphorus compound soluble in the soil 
 moisture (Section 129, a). Also by maintaining a supply 
 of lime in the soil, phosphate fertilizers are prevented from 
 changing to iron and aluminium phosphates. 
 
 It must be borne in mind that valuable as lime is in free- 
 ing unavailable potassium and phosphorus, it does not add 
 either of these elements to the soil; it rather exhausts the 
 soil. This is of course beneficial the freeing of plant food 
 in the soil but additions must be made in the form of 
 phosphate fertilizers if the supply is to be maintained. 
 
 (d) IMPROVING THE PHYSICAL CONDITION. Lime also im- 
 proves the structure of soils by flocculating heavy clays and 
 binding together loose, sandy soils. 
 
 (e) CHECKING PLANT DISEASES. Lime destroys some fun- 
 gous diseases of plants, notably the club-root or finger-and- 
 toe disease of cabbage and turnips. 
 
 (/) HARMFUL EFFECTS. Lime, on the other hand> is favor- 
 able to potato scab. It prevents the growth of such crops as 
 the cranberry, watermelon, blueberry, and trailing arbutus. 
 It is not known why this is, whether they can live better
 
 WASTE LIME 239 
 
 on other forms of calcium than the bicarbonate or whether 
 they prefer an acid soil. Too heavy applications of caustic 
 or burnt lime particularly destroy organic matter to an 
 unreasonable extent, and also will injure germinating seeds 
 if applied too near to seeding. 
 
 181. Use of Magnesian Lime. Some limestones contain 
 magnesium, and small amounts do no harm. Large amounts 
 up to 45 per cent, (dolomite) are questionable. When burned, 
 such a lime slakes with difficulty, and may cause serious 
 harm to crops if the soil to which it is applied contains an 
 undue proportion of magnesium. Just what this proportion 
 should be varies with the crop and depends of course also 
 on the relative amounts of calcium and magnesium that are 
 dissolved in the soil moisture. On the other hand, magnesian 
 lime does no harm on soils not so well supplied with mag- 
 nesium. To be safe it is better to use a grade of lime high in 
 calcium carbonate. 
 
 182. Calcium Sulphate, Gypsum, Land Plaster, CaSO 4 .2H 2 O. 
 This material is used to some extent on soils as an amend- 
 ment. It frees potassium and phosphorus from insoluble 
 compounds, and is said to hasten the decomposition of 
 organic matter, but it has no neutralizing effect and is not 
 of much value. The other compounds of calcium have all 
 these effects plus the neutralizing effect. 
 
 183. Waste Lime. Lime is used in purifying coal gas and 
 in the manufacture of sugar from beets. Gas-lime should 
 be exposed to the air for some time before applying to the 
 soil, or should be added to the soil a long time before seeding 
 because it contains sulphides and sulphites from sulphur 
 compounds absorbed from the gas. These compounds 
 change to sulphates on exposure to the air and are thus 
 rendered harmless to plants. 
 
 Lime is a waste product in the manufacture of acetylene 
 gas, and should be exposed to the air before use to allow 
 the escape of traces of acetylene which is harmful to seeds. 
 
 Lime from these processes is usually a mixture of hydroxide 
 and carbonate and is valuable for agricultural purposes if 
 it can be obtained cheap and if the content of calcium 
 oxide is known.
 
 240 REFERENCES 
 
 EXERCISES 
 
 1. Is it better to use sodium nitrate, basic slag and wood ashes on an 
 acid soil, or ammonium sulphate, acid phosphate and muriate of potash 
 with lime in a rotation? Why? 
 
 2. Prove by calculation that 100 pounds of burnt lime are equivalent 
 to 130 pounds of slaked lime, and 180 pounds of carbonate. 
 
 3. In order of importance tabulate all the functions of lime. State why 
 you have placed them in this order. 
 
 4. On an acid soil, what crops would suffer most? Why would they 
 suffer? 
 
 5. Suppose you had a soil which turned litmus paper red, would not grow 
 clover, did not respond to an application of lime, what treatment would 
 you give it? 
 
 6. Show by equation what happens when limestone is burned; when the 
 resultant product is left piled exposed to the weather; when it is put in the 
 soil as an amendment. 
 
 7. Does carbonic acid make a soil acid? Why? 
 
 8. Under what conditions are the forms of lime of equal merit? 
 
 9. What different compounds of the same elements, other than the 
 forms of calcium carbonate, show a difference in solubility? 
 
 10. Which has the greater neutralizing power, 100 per cent, limestone 
 or a mixture of 70 per cent, calcium carbonate and 30 per cent, magnesium 
 carbonate? Which would you apply to an acid soil? Why? 
 
 REFERENCES 
 
 Penna. Agr. Expt. Sta. Report, 1899-1900, Pt. II, p. 15. The Agricul- 
 tural Use of Lime. 
 
 Van Slyke. Fertilizers and Crops. 
 Wheeler. Manures and Fertilizers.
 
 CHAPTER XIII 
 FARM MANURE 
 
 UP to the present time the fertilizers discussed have been 
 commercial products only, and many of them inorganic 
 materials of value only for the plant food which they con- 
 tain. There is one fertilizer, however, which is produced to a 
 greater or less extent on every farm, and which contains 
 not only the three principal plant foods, but which also 
 contains organic matter and bacteria, both of which are 
 valuable to the soil. This material is the excrement of 
 domestic animals mixed with straw or other litter. In this 
 discussion the term farm manure will be used to describe 
 the mixture of solid and liquid excrement of any domestic 
 animal with the litter of whatever character. There is 
 some tendency today to call the mixture of horse excrement 
 and litter, stable manure; and cattle excrement with litter, 
 barnyard manure. The term manure is sometimes applied 
 to any fertilizing material, but this practice is more common 
 in England than in the United States. 
 
 184. Solid Excrement. The solid excrement, or feces, 
 of an animal are the undigested portions of the food. This 
 material has been rather thoroughly comminuted by the 
 animal in the various processes of mastication, remastication 
 in the case of ruminants, and of churning movements in the 
 stomach and intestines. On account of the more complete 
 mastication and digestion in cattle, the feces of the latter 
 are more finely divided and more compact than those of 
 horses. Although the constituents of the feces have not 
 been digested and absorbed by the animal, more or less 
 decomposition has taken place, particularly in the case of 
 the proteins. Part of this change has occurred in the stomach 
 and intestines because of partial enzyme action, and part 
 16 (241)
 
 242 
 
 FARM MANURE 
 
 in the intestines due to bacteria. These bacteria are present 
 in very large numbers in the voided excrement and are 
 valuable in promoting further decomposition in the soil. 
 Although on this account feces contain plant food that is 
 more available than it was in the original animal food, never- 
 theless, it is not a quick acting fertilizer. All of the fertil- 
 izing constituents in feces have to undergo decomposition 
 to be soluble and available to plants. 
 
 The amount of the various fertilizer ingredients in solid 
 excrement varies with different animals. Table XIV gives 
 the average percentage composition of the excrement of the 
 common farm animals, horse, cow, pig, sheep, and hen. 
 The table also gives the amount voided per year for each 
 animal, taking the indicated weights as rough averages. 
 
 TABLE XIV. COMPOSITION AND AMOUNT OF ANIMAL EXCREMENT 
 
 
 Excrement. 
 
 
 
 
 Kind of 
 animal and 
 average 
 weight. 
 
 Kind. 
 
 Proportion 
 per cent. 
 
 Amount 
 voided per 
 year, pounds 
 per average 
 
 Nitrogen 
 per cent. 
 
 Phosphoric 
 acid 
 per cent. 
 
 Potash 
 per cent. 
 
 
 
 
 animal. 
 
 
 
 
 Horse, 1300 
 
 Solid 
 
 80 
 
 18,700 
 
 0.55 
 
 0.30 
 
 0.40 
 
 pounds 
 
 Liquid 
 
 20 
 
 4,700 
 
 1.35 
 
 Trace 
 
 1.25 
 
 Cow, 950 
 
 Solid 
 
 70 
 
 18,000 
 
 0.40 
 
 0.20 
 
 0.10 
 
 pounds 
 
 Liquid 
 
 30 
 
 7,600 
 
 1.00 
 
 Trace 
 
 1.35 
 
 Pig, 150 
 
 Solid 
 
 60 
 
 2,700 
 
 0.55 
 
 0.50 
 
 0.40 
 
 pounds 
 
 Liquid 
 
 40 
 
 1,800 
 
 0.40 
 
 0.10 
 
 0.45 
 
 Sheep, 120 
 
 Solid 
 
 67 
 
 1,000 
 
 0.75 
 
 0.50 
 
 0.45 
 
 pounds 
 
 Liquid 
 
 33 
 
 500 
 
 1.35 
 
 0.05 
 
 2.10 
 
 Hen, 4 
 
 
 
 35 
 
 1.00 
 
 0.80 
 
 0.40 
 
 pounds 
 
 
 
 
 
 
 
 It is to be noted that the solid excrement of the horse is 
 much drier than that of the cow, hence its decomposition 
 is more rapid and the temperature of the mass rises very 
 considerably. This fact is made use of in making "hot- 
 frames" in the early spring. Fermenting horse manure is 
 the source of heat. 
 
 185. Liquid Excrement. The liquid excrement, or urine, 
 of animals contains waste food material which has been
 
 LITTER 243 
 
 digested and absorbed, but which has also been utilized, 
 broken down, and eliminated. All of the material is soluble 
 and is quickly made available. Decomposition to inorganic 
 forms of plant food is rapid. Table XIV also shows the 
 relative amounts of liquid excrement. 
 
 186. Litter. By litter is meant the plant residues or 
 other materials used in stalls as bedding for animals and 
 which becomes mixed with excrement. As a part of farm 
 manure litter serves important functions, such as the ab- 
 sorption of urine, and of ammonia which escapes from ex- 
 crement on decomposition. It also makes manure easier 
 to handle and adds organic matter and plant food. 
 
 Table XV shows the number of pounds of water and 
 ammonia absorbed per 100 pounds of litter of various kinds. 
 
 TABLE XV. AMOUNT OF WATER AND AMMONIA ABSORBED BY 
 LITTER 
 
 Water Ammonia 
 pounds per pounds per 
 Kind of Utter. 100. 100. 
 
 Wheat straw 220 0.17 
 
 Partly decomposed oak leaves . . . . 162 .... 
 
 Pine sawdust 435 . 05 
 
 Peat 600 1.10 
 
 Peatmoss 1300 0.86 
 
 TABLE XVI. COMPOSITION OF LITTER 
 
 Nitrogen Phosphoric acid Potash 
 Kind of litter. per cent. per cent. per cent. 
 
 Straw 0.50 0.25 1.10 
 
 Leaves 0.80 0.30 0.30 
 
 Sawdust 0.45 0.30 0.70 
 
 Peatmoss .... 0.80 0.10 0.17 
 
 Peat 0.85 0.18 0.08 
 
 Table XVI shows the composition of various litters in the 
 fertilizing constituents. It is to be noted that straw, the 
 usual form of litter, contains about as much nitrogen, phos- 
 phoric acid, and potash as does excrement, so that as far 
 as actual plant food is concerned there is no dilution of the 
 amount present in excrement by mixing it with the litter. 
 Sawdust and shavings, however, which are used to a con- 
 siderable extent in cities, contain much less plant food, 
 and furthermore, they decompose very slowly in the soil,
 
 244 FARM MANURE 
 
 so that what plant food they do contain becomes available 
 to a very slight extent. But sawdust and shavings are good 
 absorbers of liquid, even better than straw, and are con- 
 sequently of considerable value. They do no harm in the 
 soil as is sometimes claimed. 
 
 187. Mixed Excrement. Considering the mixture of solid 
 and liquid excrement, exclusive of litter, it is found that 
 the composition varies with the age of the animal and the 
 kind of food eaten. An adult animal, working or fattening, 
 retains not more than 5 or 10 per cent, of the nitrogen, 
 phosphoric acid, and potash in the food. Cows giving 
 milk, and young animals, retain from 25 to 50 per cent, of 
 these constituents in their food. Taking the average excre- 
 ment produced on the farm, it may be said to contain 
 about 80 per cent, of the fertilizing constituents of the 
 food eaten. 
 
 The kind of food eaten will influence the composition 
 of excrement. If the food consists of press cake, grains, 
 bran, or other concentrated material, the excrement will 
 be much higher in nitrogen, phosphoric acid, and potash 
 than if the food were roughage, or ensilage, or beets (see 
 Table III). 
 
 188. Farm Manure. This product, as mentioned at the 
 beginning of the chapter, is a mixture of solid excrement, 
 liquid excrement, and litter. As can be readily seen from 
 what has been said about the causes of variation in the 
 composition of excrement, and what is known about variation 
 in the composition of litters, the amount of plant food in 
 farm manure is never constant. From the discussion which 
 follows as to the decomposition and losses of manure piles, 
 it is to be noted that these factors also affect the com- 
 position. For purposes of rough calculation, however, it is 
 somewhat generally agreed that the average farm manure 
 contains about 0.5 per cent, nitrogen, 0.25 per cent, phos- 
 phoric acid, and 0.5 per cent, potash; or, to put it more 
 plainly, a ton of farm manure contains 10 pounds of nitrogen, 
 5 pounds of phosphoric acid, and 10 pounds of potash. 
 
 189. Compounds in Fresh Farm Manure. When first 
 produced, farm manure contains in the solid excrement,
 
 DECOMPOSITION OF FARM MANURE 245 
 
 starch, cellulose, other carbohydrates, lignin, fat, proteins 
 in various stages of decomposition, mineral elements com- 
 bined organically, remains of intestinal juices, and other 
 compounds. The liquid portion contains organic and in- 
 organic salts, soluble nitrogenous compounds like urea, etc. 
 The litter, of course, contains the usual plant compounds 
 present in such materials. 
 
 190. Bacteria in Manure. Liquid excrement when first 
 voided contains no bacteria, but the solid excrement con- 
 tains exceedingly large numbers, determinations on various 
 excrements showing from 90,000,000 to 150,000,000 organisms 
 in one gram of material. In addition to this, litter contains 
 from 10,000,000 to 400,000,000 organisms. In the course 
 of time the number of organisms diminishes as food becomes 
 scarcer and the products of their activities increase sufficiently 
 to kill many of them. 
 
 191. Decomposition of Farm Manure. As a result of its 
 high bacterial content, manure commences to decompose as 
 soon as it is produced. Molds also help the decomposition. 
 The bacterial changes which take place in it are of consider- 
 able importance and can be discussed best under two heads: 
 Aerobic, where air has free access to the materials; and 
 anaerobic, where air is kept out. 
 
 (a) AEROBIC. The most important changes taking place 
 in manure are those affecting nitrogen. This element is 
 present in the urine largely as urea, CO(XHj) 2 , which is 
 attacked very easily by several kinds of bacteria. The 
 action is one of hydrolysis, thus : 
 
 CO(NH S ) 2 
 
 The ammonium carbonate readily breaks up on exposure 
 to the air, as follows: 
 
 (NHOsCO^NHj + COz + H 2 O. 
 
 This results, of course, in loss of nitrogen, for the ammonia 
 escapes into the air. The reaction is reversible, and in the 
 presence of plenty of carbon dioxide and water with no 
 circulation of air to remove the volatile products, ammonium 
 carbonate is not decomposed.
 
 246 FARM MANURE 
 
 In the solid excrement nitrogen is present in protein 
 forms which have resisted decomposition in the digestive 
 tract of the animal, and hence do not decompose very rapidly 
 in manure. In the litter the nitrogenous compounds are also 
 proteins, and although somewhat more easily broken down 
 than the proteins of the solid excrement, they are not decom- 
 posed very rapidly. Considering the nitrogen compounds in 
 the solid part of the manure, it can be said that they break 
 down in the presence of air with the formation of ammonia 
 which escapes into the atmosphere. Moreover, in the 
 presence of plenty of air, ammonia is further oxidized to 
 free nitrogen. True nitrification, that is, the formation of 
 nitrates, is not a common bacterial change in manure piles. 
 
 Aerobic decomposition results in a gradual change of 
 carbohydrates cellulose, starch, and pentosans and of fats, 
 as well as of proteins, to carbon dioxide and water, with 
 the intermediate production of organic acids. Compounds 
 containing potassium and other bases decompose with the 
 formation of carbonates of the bases. Phosphorus and 
 sulphur in proteins remain as phosphates and sulphates, 
 or more correctly speaking as phosphoric and sulphuric 
 acids which are neutralized by the bases present. As a 
 matter of fact, there is an excess of alkaline carbonates in 
 decomposing manure piles, whether the action is aerobic 
 or anaerobic. This is evidenced by the dark liquids which 
 may be seen draining from manure piles. This dark liquid 
 is an alkaline extract of humus, for humus, or at least humus- 
 like compounds, result from partial decomposition of the 
 organic matter, more particularly where there is not much 
 air present. 
 
 In general, aerobic decomposition of manure results in the 
 production of considerable heat. Horse and sheep manure 
 being more porous and drier, decompose very easily and 
 are called "hot" manures. The manure of pigs and cattle, 
 on the 'other hand, are more compact, contain more water, 
 and hence do not decompose so rapidly. They are called 
 " cold" manures. The loss of carbon dioxide and water from 
 manure, of course, results in loss of weight.
 
 LOSS 247 
 
 (6) ANAEROBIC. When air is not present in manure, 
 decomposition and loss of ammonia are not so rapid. While 
 urea may change to ammonium carbonate there is no op- 
 portunity for this compound to break up into ammonia, 
 carbon dioxide, and water. The proteins of the solid portion 
 are slowly changed to soluble compounds and some ammonia, 
 but the latter is not lost to any great extent. Moreover, 
 much of the nitrogen so changed is absorbed by the bacteria 
 themselves and retained in the manure as insoluble com- 
 pounds. 
 
 The non-nitrogenous portions of the manure are broken 
 down into organic acids, carbon dioxide to some extent, and 
 in addition considerable quantities of hydrogen and methane. 
 Sulphur is likely to be changed in part at least to hydro- 
 gen sulphide. Moreover, considerable quantities of black 
 "humus" are formed. The straw and other litter lose their 
 original fibrous condition and become a part of the dark, 
 fine mass of "well-rotted manure." Under anaerobic con- 
 ditions the loss of carbon dioxide, water, hydrogen, and 
 methane results in loss of weight. 
 
 192. Molds. Particularly in loose, dry manure, molds 
 develop and cause destruction of both nitrogenous and 
 non-nitrogenous compounds. "Fire fanging" is a result 
 of the growth of molds on horse manure, resulting in the 
 appearance of a white, powdery coating on the material. 
 
 193. Loss. The above mentioned changes are what take 
 place under special conditions. Considering now an ordinary 
 manure pile, such as is altogether too common even now, 
 it will be interesting to note what happens. Such a pile is 
 only moderately compact; loose on the outside at any rate, 
 and exposed to the weather. Both aerobic and anaerobic 
 decomposition take place. Urea changes rapidly to ammo- 
 nium carbonate and ammonia. Proteins are changing to 
 ammonia. Ammonia is being oxidized to free nitrogen as 
 well as passing off into the air. Carbon dioxide and water 
 are being formed in considerable quantities as well as some 
 hydrogen and methane. The pile shrinks in volume, losing 
 weight constantly. Humus-like substances form, many of 
 which are dissolved out by a solution of alkaline carbonates
 
 248 FARM MANURE 
 
 formed by the decomposition of organic compounds of 
 potassium and other alkalies, including some ammonium 
 carbonate. Rain leaches out these soluble compounds as 
 well as soluble phosphates. There is consequently a decided 
 loss of potassium and phosphorus by leaching; of nitrogen 
 by volatilization as free nitrogen and as ammonia; and a 
 decrease in amount of organic matter due to volatilization 
 of carbon dioxide, hydrogen, and methane, and to leaching 
 away of humus compounds. The most serious loss, however, 
 is that of nitrogen, phosphorus, and potassium, and amounts 
 under such conditions to more than half of the original 
 content of these elements. Moreover, they are in the best 
 form, being soluble and available to plants. 
 
 194. Prevention of Loss. From the preceding discussion, 
 it can be seen that the greatest loss of nitrogen occurs under 
 aerobic conditions, while the loss of phosphorus and potas- 
 sium and some of the nitrogen occurs only when leaching 
 takes place. Since it is possible to retain a large part of the 
 volatile ammonia by chemical means as well as by producing 
 anaerobic conditions, methods of preventing loss of the 
 fertilizing constituents can be grouped under two general 
 heads: Mechanical and chemical. 
 
 (a) MECHANICAL. Since phosphorus and potassium in the 
 solid excrement, after being rendered soluble under either 
 aerobic or anaerobic conditions, are lost only by being 
 washed out of the manure pile, it is sufficient only to prevent 
 leaching by keeping the pile under cover, or in a water-tight 
 receptacle; or piled in such a way that leaching is reduced 
 to a minimum. This may be accomplished by making the 
 pile decidedly concave on top to hold the water that falls, 
 and building the sides vertical. 
 
 Since a large part of the potassium and nitrogen are in the 
 urine and hence soluble, it is necessary to take precautions 
 which will prevent the urine from running off. Litter 
 accomplishes this purpose if employed in sufficient quantities, 
 and particularly if cut into short pieces a practice which 
 increases the absorptive capacity of straw two or three times. 
 Rock phosphate sprinkled in the stalls before adding the 
 bedding also makes an excellent absorbent material. This
 
 PREVENTION OF LOSS 249 
 
 practice not only reinforces the manure in phosphoric acid 
 content, but also serves to make the rock phosphate avail- 
 able to plants (Section 164). Three or four pounds to each 
 animal every day for horses and cattle is a good amount 
 to use. 
 
 In addition to the leaching away of soluble nitrogenous 
 compounds, a large part of the nitrogen is lost by volatiliza- 
 tion. Since this is due largely to aerobic bacterial action, 
 combined with free circulation of air which allows dissociation 
 of ammonium carbonate, a system which keeps the pile 
 compact and saturated with water, or at least with carbon 
 dioxide, will answer the purpose. This may be accomplished 
 by compacting either in piles or pits, or under the feet of the 
 animals by the so-called deep-stall system. 
 
 If a pile of manure is kept well packed down and 
 thoroughly though not excessively soaked with water or 
 surplus urine, air will not have access to the pile except on 
 the surface, and aerobic decomposition will be reduced to a 
 minimum. By this means nitrogen is not lost to any great 
 extent either as free nitrogen or as ammonia: 
 
 The deep-stall system consists in allowing the manure to 
 be compacted by the feet of animals in stalls where the 
 manure can accumulate and be well tramped down, litter 
 being liberally used. By this means the loss of nitrogen is 
 reduced to about 15 per cent., but the practice is not sani- 
 tary and although used to some extent in Europe is not to be 
 recommended. The saving of nitrogen in manure is not the 
 only thing to be considered in caring for stock. 
 
 (6) CHEMICAL. In preventing the loss of fertilizing con- 
 stituents from manure by chemical means there is only 
 nitrogen to be considered. Phosphorus and potassium 
 are easily retained by preventing leaching and this is a 
 mechanical means. Nitrogen, on the other hand, is volatile 
 as ammonia and free nitrogen, hence chemicals which 
 form non-volatile compounds of nitrogen, or which prevent 
 complete decomposition, are employed. 
 
 1. Gypsum, Land Plaster. By using gypsum, CaSO 4 , 
 at the rate of 100 pounds to the ton of manure, or better 
 yet by sprinkling three or four pounds in the stall of each
 
 I 
 
 250 FARM MANURE 
 
 animal per day and then adding litter, the ammonium car- 
 bonate is changed to ammonium sulphate, thus: 
 
 (NHOzCOs + CaSO4 = (NHOzSO* + CaCO 3 . 
 
 Ammonium sulphate is non-volatile, although it is soluble, 
 and must be prevented from leaching. The advantage is 
 that no ammonia escapes into the air. Gypsum is perfectly 
 safe to use because it has no harmful effect on the feet of the 
 animals. By itself it has no fertilizing effect on the soil, 
 but after reacting with ammonium carbonate, the resulting 
 calcium carbonate will neutralize soil acids, although there 
 is but little present at any one time. 
 
 2. Acid Phosphate. This material may be used at the 
 rate of 50 pounds per ton of manure, but on account of its 
 harmful effect on the feet of animals it is better to use it in 
 the gutters or with manure after the latter has been removed 
 from the stalls. The value of acid phosphate is two-fold. 
 It holds the ammonia as ammonium sulphate, due to the 
 calcium sulphate in the fertilizer. And furthermore, it rein- 
 forces the manure with phosphoric acid which is the deficient 
 element. It is stated that acid phosphate is the most 
 efficient holder of ammonia in use. 
 
 3. Potash Salts. The muriate and sulphate of potash, 
 kainite, or any of the salts of potash used as fertilizers, 
 except potassium carbonate (see below), are used at the 
 rate of 50 pounds per ton of manure. These compounds 
 are also injurious to the feet of animals and should be used 
 like acid phosphate. Ammonia is converted to ammonium 
 chloride or sulphate and is non-volatile, although soluble. 
 
 4. Sulphurous and Sulphuric Acids. These acids will 
 retain ammonia as the sulphite (later changing to the 
 sulphate) and the sulphate, but they are not to be recom- 
 mended, for their acid character renders them harmful to 
 the soil if they are not completely neutralized. 
 
 5. Preservatives. To check bacterial action and thus 
 prevent the formation of ammonium carbonate, such pre- 
 servatives or antiseptics as carbon disulphide and soluble 
 fluorides have been employed. Their use, however, should
 
 METHODS OF USE 251 
 
 be discouraged, for they are not only expensive, but by 
 interfering with the activity of bacteria in manure destroy 
 one of its most valuable functions, namely, that of supplying 
 microorganisms to the soil. 
 
 6. Lime Should Never be Used. In this connection it 
 must be emphasized that for the preservation of nitrogen 
 or absorption of liquid in stalls, lime should never be used. 
 It does not hold the ammonia, but rather causes its loss by 
 releasing it from any of its compounds. Ground limestone 
 is not so bad in this respect as burnt lime. Wood ashes 
 should never be used because the potassium carbonate will 
 drive off ammonia even more readily than burnt lime. 
 The use of lime in composting, however, is allowable, but 
 for a different purpose if proper precautions are taken 
 (Section 195, c). 
 
 195. Methods of Use. There are only a few points to be 
 brought out in a work of this kind. A more complete treat- 
 ment of the subject is better suited to a discussion of special 
 crops and methods of farming. 
 
 (a) FRESH MANURE. Experiments show conclusively 
 that better yields are secured on ordinary soils from manure 
 hauled fresh to the fields than from manure that has stood 
 in the pile for some time even under optimum conditions. 
 This is principally due to the fact that all the fertilizing 
 material has been retained and that the maximum effect 
 of bacteria in decomposing organic matter and dissolving 
 mineral plant food has been obtained. Manure which has 
 been hauled fresh to the fields can be spread on the surface 
 of the soil and allowed to lie exposed without danger of loss 
 of nitrogen, for the sun will check bacterial action directly, 
 and also by drying the manure will thus deprive the bacteria 
 of their necessary moisture. Fresh manure can be applied 
 on top of the snow with success. No loss of ammonia will 
 occur, and as the snow melts the soluble fertilizing ingredients 
 soak into the soil. This practice, however, is not safe on 
 frozen hillsides where there is danger of loss of these soluble 
 compounds by being washed away over the frozen soil. 
 
 (6) WELL DECOMPOSED MANURE. Sometimes, however, 
 it is not economical to spread manure at once. It may cost
 
 252 FARM MANURE 
 
 more to haul it fresh to the fields than the increase in crops 
 would be worth. In such cases the application of decomposed 
 manure should be followed at once by plowing or harrowing, 
 or be made just before a rain which will wash into the soil 
 ammonium carbonate previously formed. In the fresh 
 manure ammonium carbonate has not been produced, so 
 its loss need not be feared. 
 
 On light soils well decomposed manure has some advan- 
 tages over fresh manure, since the latter would make the soil 
 only more open and porous and would burn out quickly. The 
 nitrogen of well decomposed manure is not so available as 
 that of fresh manure, for much of it has been decomposed 
 to soluble compounds and back again to proteins in the 
 bodies of bacteria. The phosphorus and potash, on the 
 other hand, are more available. On account of these facts, 
 the action of well decomposed manure is more uniform and 
 under certain special conditions is desirable. 
 
 (c) COMPOSTED MANURE. This is a practice resorted to 
 by vegetable growers, largely to get the manure quickly into 
 a thoroughly decomposed and disintegrated condition. The 
 objects are to get the manure in a fine state of division for 
 easy mixing with the soil, and to make the fertilizing con- 
 stituents more uniformly available. As mentioned before, 
 fresh manure contains more available nitrogen than decom- 
 posed manure, and when used in large quantities fresh manure 
 produces too great a leaf growth on roots or other similar 
 crops, due to excess of nitrogen. The manure is piled in 
 alternate layers with some absorbent like soil. All sorts of 
 organic refuse can be added and sometimes bones, commercial 
 fertilizers, and lime. The pile should be well covered with 
 earth and kept reasonably moist. The alternate layers and 
 covering of soil adsorb ammonia which is generated freely 
 under these conditions, particularly if lime is present. The 
 pile is thoroughly turned over from time to time a practice 
 which hastens decomposition and the formation of nitrates. 
 The organic matter of bones in a compost heap is so de- 
 composed that they can be easily ground. If lime is used, 
 particular care must be exercised to keep plenty of absorbing 
 material in the pile, and to cover it well.
 
 VALUE OF MANURE 253 
 
 196. Manure an Unbalanced Fertilizer. As a complete 
 fertilizer manure is not well balanced. It contains 0.5 per 
 cent, of nitrogen, 0.25 per cent, of phosphoric acid, and 0.5 
 per cent, of potash. Proportionately expressed this is a 
 2-1-2 fertilizer. A common fertilizer for general farm crops 
 is a 1-6-4 combination (Section 201), and for garden crops a 
 4-8-10 fertilizer is used. Manure is very deficient in phos- 
 phoric acid, and in order to obtain enough of this con- 
 stituent it is necessary to apply in many cases more manure 
 than is economically profitable. While it is possible to 
 maintain the fertility of a soil for a long period of years, at 
 least with no other fertilizer than manure, it is not a practice 
 to be recommended. Manure reinforced with phosphoric 
 acid is more satisfactory and, better yet, a judicious use of 
 commercial fertilizers and manure, properly distributed in 
 a rotation according to the crops, is to be recommended. 
 It is by no means a good practice to add such excessive 
 amounts of manure as are used in some sections of the country 
 on tobacco land where an average of eighteen tons of manure 
 per acre have been applied annually. Under these con- 
 ditions the loss of the fertilizing constituents from the 
 surface soil has been enormous. 
 
 197. Value of Manure. The proper use of barnyard 
 manure is something to be earnestly recommended on every 
 farm. No other single material will do so much for the 
 soil, and no other material is so cheap and easily obtained 
 in most cases. Manure adds organic matter to the soil, 
 and organic matter, it will be remembered, improves the 
 physical condition of the soil, increases the moisture holding 
 capacity and the temperature of soils. Moreover, organic 
 matter is the source of carbon dioxide and organic acids 
 which aid in making mineral compounds soluble. This is 
 particularly true of fresh manure which decomposes easily. 
 Manure also adds large numbers of bacteria to the soil, 
 and the benefits to be derived from bacteria are too numerous 
 to mention. And finally manure adds nitrogen, phosphoric 
 acid, potash, and even calcium to the soil. Fig. 68 shows 
 the effect of manure on a soil which does not respond to 
 liming, although somewhat acid. It is probably the effect 
 of the plant food in the manure which is here most important.
 
 254 
 
 FARM MANURE 
 
 All these valuable properties of manure, moreover, are 
 lasting in effect. An application of manure shows by in- 
 creased yields for many years afterwards, whereas the effect
 
 REFERENCES 255 
 
 of commercial fertilizers lasts but a few years at most and 
 usually but one or two. 
 
 EXERCISES 
 
 1. Give all the reasons you can why it is not good practice to permit a 
 manure pile to remain exposed for months. 
 
 2. Why do nitrates form in a composted manure heap to a greater extent 
 than in an ordinary pile? 
 
 3. Should basic slag be mixed with manure to reinforce the phosphorus 
 content? Why? 
 
 4. What causes the color of the water leaching away from an exposed 
 manure pile? Explain in detail how these coloring substances were prob- 
 ably formed.^ 
 
 5. Why do you think the following statement is good or poor advice? 
 "Buy nitrogen in concentrated feeds rather than in commercial fertilizers." 
 
 6. Do you think that reinforcing manure with a phosphate is good farm 
 practice? If so, what phosphate would you use? 
 
 7. As components of what substances will N, P and K probably occur in 
 the solid and liquid excreta? 
 
 8. Is manure a balanced fertilizer? a complete fertilizer? a high-grade 
 fertilizer? a readily available fertilizer? a fertilizer that will leave a soil 
 acid? a necessary fertilizer? a lasting fertilizer? a commercial fertilizer? 
 
 9. Of the following which manure would you prefer: Produced by a 
 fattening animal; an animal giving milk; a growing animal; a mature, hard- 
 working animal; a mature animal not hard-working? 
 
 REFERENCES 
 
 Hall. Fertilisers and Manures. 
 Thorne. Farm Manures. 
 Van Slyke. Fertilizers and Crops. 
 Wheeler. Manures and Fertilizers.
 
 CHAPTER XIV 
 SOIL AND FERTILIZER ANALYSIS 
 
 THE analysis of soils and fertilizers is such an important 
 part, both of scientific and practical agriculture, that there 
 is necessary a brief discussion of the terms used, of the possi- 
 bilities and limitations of such work, and of the immediate 
 value. 
 
 198. How Analytical Results are Expressed. It is custom- 
 ary in ordinary analytical work to express results in terms 
 of the oxide of the element, thus: CaO, K 2 O, Fe 2 O 3 , P2O 5 . 
 This is not the form in which these elements occur, but 
 is a convenient and conventional means of expression. In 
 fertilizer work the elements usually determined are nitrogen, 
 phosphorus, and potassium, and reported as nitrogen, N, 
 phosphoric acid, P 2 O 5 , and potash, K 2 O. Phosphoric acid 
 
 . is not the correct name for the oxide of phosphorus P 2 O 5 
 but since the oxide is the acid oxide there is some excuse for 
 it. Furthermore, it is not consistent to express nitrogen 
 as the element, and phosphorus and potassium as the oxides. 
 There is a desire on the part of some chemists to express 
 these and other results in the elemental form. It is the 
 logical way to do, but since custom is so strong, and since 
 most farmers and scientists think in the conventional terms, 
 these inconsistent forms have been used here. 
 
 199. Soil Analysis. The popular conception of the pur- 
 pose of soil analysis is to ascertain the fertilizer deficiencies 
 of a soil. That is, by determining in some way the amount 
 of nitrogen, phosphoric acid, and potash, the need of a 
 soil for any particular element can be predicted. This 
 idea has resulted, of course, in the development of a large 
 number of methods, and in the analyses of a large number 
 
 (256)
 
 SOIL ANALYSIS 257 
 
 of soils, together with the publication of a large number of 
 predictions. Some of these predictions have proved correct ; 
 some of them incorrect; and some of them have never been 
 put to the proof. The difficulties in the way of determining 
 accurately fertilizer deficiencies of a soil are so many that 
 an analysis alone cannot give the information desired in a 
 great majority of cases. Fertilizer tests in the field are the 
 best single way to ascertain the plant food needs of a soil 
 (Fig. 69). 
 
 The total amount of each of the several constituents can 
 be determined accurately, and the result is a complete 
 inventory of the plant food supply in any given soil, pro- 
 vided the sampling has been done carefully. It is very 
 important to obtain a sample of soil which represents as 
 nearly as possible the soil of the whole field in question. 
 This information in connection with other data, such as 
 topography, physical condition of the soil, kind of seed, 
 cultivation, temperature, rainfall, and appearance of crop, 
 will give an expert a good idea of the needs of a given soil. 
 
 The difficulty with this kind of analysis in interpreting 
 plant food deficiencies is that by no means all of any par- 
 ticular element is available or will even become available 
 readily. A soil may contain a large amount of phosphoric 
 acid, but may have it in such unavailable form that plants 
 cannot obtain enough for normal growth, and a phosphate 
 fertilizer is actually needed. On the other hand, another 
 soil may contain a very small amount of phosphoric acid 
 and yet have it in readily available form. Of course, if 
 a constituent is present in ridiculously small amounts a 
 deficiency in that constituent may be suspected. 
 
 Various methods have been developed for determining 
 available or readily available plant food. Strong hydro- 
 chloric acid has been used more largely than any other 
 reagent to extract those constituents which it is assumed 
 will be most readily available to plants. Most of the soil 
 analyses published have been made by this method. But 
 the results mean very little for interpreting fertilizer de- 
 ficiencies. There is no accurate standard or minimum 
 amount known, below which a fertilizer need is indicated. 
 17
 
 258 
 
 SOIL AND FERTILIZER ANALYSIS 
 
 The minimum varies with kinds of soils, kinds of crops, 
 and many other factors. 
 
 Numerous weak organic acids and dilute mineral acids have 
 been proposed as solvents, and some methods seem reasonably
 
 LIME REQUIREMENT 259 
 
 good for certain special soils, but there are no methods 
 of general applicability. Pure water, or water charged with 
 carbon dioxide, might seem an excellent solvent, but against 
 this solvent as against others for that matter, though in 
 lesser measure, the power of chemical and physical absorp- 
 tion acts to prevent the extraction of plant food that may 
 be readily available to plants in the soil. Moreover, in all 
 these methods it is not the amount of plan; food available 
 at any one time which nourishes the crop, it is the plant 
 food available from day to day throughout the growing 
 season. It is the rate at which plant food becomes avail- 
 able that determines crop growth. 
 
 But soil analysis is of very great value to the soil chemist 
 in determining changes which take place in the soil under 
 certain conditions, and in comparing one soil with another, 
 all of which work is valuable in studying the effect of 
 fertilizers, the effect of changing physical conditions, and 
 the effect of cropping. The knowledge so obtained can later 
 be practically applied to help the farmer obtain better and 
 larger crops. 
 
 200. Lime Requirement. Since acidity is a very prevalent 
 condition of many soils, and since it needs correction in 
 most instances, numerous efforts have been made to deter- 
 mine the amount of acid in a soil ; or/ which is more direct, 
 to determine the amount of lime necessary to neutralize 
 acidity to a given depth. The method which has given the 
 best results is one devised by F. P. Veitch. Equal weights 
 of soil are treated with different amounts of lime water 
 until one amount is found which leaves the soil slightly 
 alkaline. Knowing the weight of soil in the sample, the 
 weight of lime applied, and the weight of an acre of soil to 
 the given depth, the amount of lime in pounds per acre 
 needed to correct the acidity can be calculated. The results 
 are only approximate at best, but the method serves to 
 compare the relative amounts of lime needed on different 
 soils, or on a soil under different treatments. It is not 
 sufficiently accurate to tell a farmer just how much lime to 
 put on a given field, although it may be a guide to the expert 
 in determining the amount.
 
 260 SOIL AND FERTILIZER ANALYSIS 
 
 There are two tests for telling whether or not a soil is 
 acid, but not how acid. One is by the use of blue litmus 
 paper. A strip of blue litmus paper is placed in the bottom 
 of a beaker or tumbler and on top of this a piece of filter 
 paper or clean white blotter cut to fit the bottom of the 
 vessel. The soil to be tested is added until the dish is half 
 full, and is then soaked with pure water. Another beaker 
 or tumbler is prepared the same way but no soil added. 
 This is to test the paper and water for acids. If the litmus 
 paper in the beaker containing the soil has turned red 
 after standing an hour, the soil is acid, the degree of acidity 
 depending on the amount and rapidity of coloration. At the 
 same time the litmus paper in the beaker containing no 
 soil must remain blue. If it turns red the paper or water 
 contains acid and a fresh test must be made using different 
 paper and water. 
 
 Another test is to add two or three ounces of soil to a 
 beaker or tumbler full of dilute ammonium hydroxide, 
 made by mixing one part of strong ammonia with five parts 
 of pure water. After standing some time an acid soil will 
 yield a brown or black color to the liquid, due to the solubility 
 of the humus acids in ammonium hydroxide (Section 119). 
 A neutral or alkaline soil will not yield a color to the liquid 
 beyond that which will be imparted to it by the fine soil 
 particles held in suspension. 
 
 201. Fertilizer Analysis. The total amount of plant food 
 in fertilizers can be determined accurately and, with the 
 possible exception of nitrogen, the available material can 
 also be determined. In buying a fertilizer a farmer ordina- 
 rily wants something which is quickly available to his crops. 
 State laws now require fertilizer manufacturers to give the 
 analysis with every fertilizer. This analysis usually consists 
 of total nitrogen; water soluble, citrate soluble, insoluble, 
 and total phosphoric acid; and water soluble potash. 
 
 There are methods which attempt to determine available 
 nitrogen, but except for the determination of nitrates and 
 ammonia which are satisfactory, there are no really good 
 methods. As a matter of fact, however, a determination 
 of total nitrogen is usually sufficient. The use of certain
 
 FERTILIZER ANALYSIS 261 
 
 materials, such as hair, wool waste, and leather is not per- 
 mitted by some states in making complete fertilizers unless 
 they are treated with sulphuric acid as in the manufacture 
 of "base goods." Their presence in the raw state can be 
 detected with a microscope, and the farmer is thus protected 
 against their use in this condition. 
 
 Water soluble phosphoric acid is monocalcium phosphate, 
 CaH 4 (PO 4 )2, citrate soluble phosphoric acid is the dicalcium 
 phosphate, Ca 2 H 2 (PO4) 2 . It is also called "reverted "phosphate 
 (Section 165, a). The name "citrate soluble" comes from 
 the fact that it is soluble in a neutral solution of ammonium 
 citrate. Both water soluble and citrate soluble phosphoric 
 acid are available to plants, so that analyses sometimes 
 give only the available phosphoric acid which includes 
 both forms. Insoluble phosphoric acid is tricalcium phos- 
 phate, Ca 3 (P0 4 ) 2 . 
 
 Water soluble potash is a simple determination, and 
 of course is that potash which is readily available to 
 plants. The guaranteed analysis does not state whether the 
 potash is in the chloride or sulphate form, or whether these 
 acid radicles are present. This is sometimes important 
 (Sections 168 and 169), and if so it would be necessary to 
 have the fertilizer analyzed further, or to buy known 
 materials. 
 
 In discussing fertilizers, and sometimes even in naming 
 them, it is customary to use the percentage figures only, 
 in the order of nitrogen, phosphoric acid, and potash. Thus, 
 a 1-6-4 fertilizer is one which contains 1 per cent, nitrogen, 
 6 per cent, phosphoric acid, and 4 per cent, potash. 
 
 In expressing the results of analyses it is sometimes custom- 
 ary to add: "Nitrogen equal to ammonia." This gives a 
 little higher figure and makes the fertilizer look richer than 
 it really is, unless the purchaser is in the habit of thinking of 
 nitrogen in terms of ammonia, the way the fertilizer manu- 
 facturers do. They buy all nitrogenous materials on the 
 ammonia basis. 
 
 In the same way phosphoric acid is sometimes referred to as 
 "bone phosphate of lime." Phosphoric acid is P 2 0s, bone 
 phosphate is Ca3(PO 4 )2. Hence the percentage is more than
 
 262 SOIL AND FERTILIZER ANALYSIS 
 
 doubled by expressing the amount of phosphorus in the 
 latter way. 
 
 Potash is sometimes called "equivalent to sulphate." 
 This also apparently increases the amount, almost doubling 
 the figures. 
 
 For example, a fertilizer containing 1 per cent, nitrogen, 
 6 per cent, phosphoric acid, and 4 per cent, potash would 
 be expressed on the higher basis as 1.21 per cent, ammonia, 
 13.08 per cent, bone phosphate of lime, and 7.40 per cent, 
 potassium sulphate, and yet it might contain no ammonia, 
 no bone phosphate, and no sulphate of potash. 
 
 In interpreting a fertilizer analysis the farmer need pay 
 attention only to the nitrogen, phosphoric acid, and potash, 
 and not be led astray by the more attractive higher figures. 
 It is only just to say, however, that most of the fertilizers 
 now offered for sale by reputable concerns are honest goods 
 with the guaranteed analysis well stated. 
 
 EXERCISES 
 
 1. How would you determine the fertilizer deficiencies of your farm? 
 
 2. State in detail just why a good soil should contain nitrogen, phosphorus, 
 potassium, calcium, humus and bacteria. 
 
 3. How test for the following: Dextrose, starch, protein, fat, a volatile 
 oil, cellulose, humus, soil acidity, an enzyme, a soluble phosphate, a nitrate, 
 an ammonium compound, a soluble potassium compound, organic matter 
 and limestone? 
 
 4. Given 750 pounds of acid phosphate containing 16 per cent, available 
 PiQ&, 167 pounds of muriate of potash containing 48 per cent, available 
 K2O, 607 pounds of sodium nitrate containing 16 per cent, available ammo- 
 nia and enough filler to make a ton of fertilizer, how much filler is used and 
 what is the formula of the fertilizer? 
 
 5. How many pounds of nitrate of soda containing 15 per cent. N, and 
 phosphate containing 7 per cent. P, and muriate of potash containing 42 
 per cent. K must be used to make a ton of a fertilizer selling as 3.5-4-6.3? 
 How many pounds of filler must be used to make this mixture equal to a 
 ton in weight? 
 
 6. About how many pounds of a complete fertilizer that sells as a 4-8-4 
 goods is it necessary to add in order to return to the soil the plant food 
 removed by an acre of corn? Would you recommend any other formula? 
 
 7. Answer Exercise 6 for an acre of potatoes; an acre of apples. 
 
 8. How much nitrogen, potassium and phosphorus is contained in a ton 
 of a 4-8-10 fertilizer? 
 
 9. Just why are the following used in the litmus paper test for soil acidity: 
 Two beakers, filter paper, water that is pure? 
 
 10. How is a sample of soil taken for a test by the Veitch method?
 
 REFERENCES 263 
 
 11. Which fertilizer would you buy, and why: One whose analysis is 
 2 per cent. N, 6 per cent. PjOi and 4 per cent. KjO or one that is marked 
 2.18 per cent. NH, 13 per cent, bone phosphate of lime and 6 per cent, 
 muriate of potash? 
 
 REFERENCES 
 
 Hilgard. Soils. 
 
 Van Slyke. Fertilizers and Crops.
 
 CHAPTER XV 
 INSECTICIDES AND FUNGICIDES 
 
 THE treatment of plants to destroy insect pests and 
 fungous diseases is now so important a factor in the growth 
 of crops that a short description of the compounds and 
 mixtures employed will be of value. No attempt will be 
 made to describe the various insects and fungi or to give 
 the proper treatment for each. All such details including 
 methods of application and proper dilution of spray material 
 should properly be taken up in connection with the pro- 
 pagation and growing of various plants. The present dis- 
 cussion will be limited to the chemistry of the more common 
 spray materials, noting first the chief characteristics of the 
 pests to be destroyed. Figs. 70, 71, and 72 illustrate the 
 method and results of spraying. 
 
 202. Insects. The insects which destroy crops are of 
 two kinds: First, those which have biting mouth parts for 
 chewing the plant tissues, such as grasshoppers, caterpillars, 
 and cucumber beetles. Second, those which have a beak 
 or apparatus for penetrating the skin of plant organs and 
 sucking up the juices. They do not chew and swallow any 
 of the tissue proper. The woolly aphis and San Jose scale 
 are examples of these insects. 
 
 For insects which eat plant tissue, it is usually sufficient 
 to sprinkle the surface of the leaves with a poison. This 
 kills the insects when the poison is taken internally. The 
 insects which do not eat tissue but suck out the plant juices 
 are not injured by this treatment. They penetrate the 
 skin for their nourishment and do not eat the poison on the 
 surface. Spray materials which kill by contact are efficacious. 
 They act by destroying the skin of the insects or by clogging 
 up their breathing pores, or by merely repelling them. 
 (264)
 
 FUNGI 265 
 
 203. Fungi. Fungi are plants which have no chlorophyl 
 and are consequently dependent on host plants for all their 
 food. They are propagated by spores which are produced 
 in great numbers and can be easily disseminated. When 
 the spores germinate on some suitable host, a little tube is 
 put forth, from which develops the mycelium. Some fungi 
 grow mostly under the surface, the spore tube entering by 
 
 FIG. 70. Spraying an orchard. Department of Experimental Pomology, 
 Pennsylvania Station. 
 
 the stomata or other openings in the leaf or stem. These are 
 fungi like the brown rot and grain smuts. Other fungi grow 
 on the surface, like the powdery mildew. Internal fungi 
 cannot be killed after they have gained entrance to the 
 host, but must be caught before the spore germinates, by 
 covering the plant with a poison which kills the spore or 
 germ tube. External fungi can be killed at any time because 
 they are always exposed.
 
 266 
 
 INSECTICIDES AND FUNGICIDES 
 
 FIG. 71. Unsprayed fruit. Department of Experimental Pomology, 
 Pennsylvania Station. 
 
 FIG. 72. Sprayed fruit. Department of Experimental Pomology, 
 Pennsylvania Station.
 
 INTERNAL INSECTICIDES 2G7 
 
 204. Insecticides. These spray materials may be divided 
 into two classes, internal, and external or contact insecti- 
 cides. 
 
 I. INTERNAL INSECTICIDES 
 
 (a) HELLEBORE is a powder made by grinding the dried 
 roots of the American hellebore (veratrum viride) or of 
 the white or European hellebore (veratrum album). The 
 active constituents are certain alkaloids, said to be some six 
 in number. 
 
 (6) LEAD ARSENATE is made by mixing sodium arsenate, 
 Na 2 HAsO 4 , with lead acetate, Pb(C 2 H 3 O 2 )2, or lead nitrate, 
 Pb(NO 3 ) 2 . The precipitate, depending on conditions of 
 temperature, concentration, and methods of mixing, consists 
 of neutral or triplumbic arsenate, Pb 3 (AsO 4 ) 2 , and acid lead 
 arsenate, PbHAsCX, in varying proportions. It comes on the 
 market as a paste or powder which forms a suspension on 
 mixing with water in the proper proportions for spraying. 
 When eaten by insects the arsenic in the compound is fatal. 
 
 Injury sometimes results to the leaves from the use of 
 lead arsenate. Since insoluble compounds do not harm foliage 
 it is certain that enough arsenic from lead arsenate goes, into 
 solution to penetrate the leaves and kill the tissues. Con- 
 sequently the amount of water soluble arsenic in commercial 
 preparations of lead arsenate is limited by the national 
 Insecticide Act of 1910 to 0.75 per cent, of water soluble 
 AsjAi. 1 But injury has resulted from the use of lead arsenate 
 that came well within the law, and as a result of investiga- 
 tion the following facts have been discovered: Triplumbic 
 arsenate or the neutral lead arsenate is insoluble in pure 
 water or water containing chlorides, sulphates, or carbon- 
 ates, and causes no harm to foliage. The acid arsenate, on 
 the other hand, is slightly soluble in pure water and much 
 more so in water containing the above named substances 
 in solution. Injury results when hard water, or "alkali" 
 
 1 Determined by soaking 1 gram of lead arsenate in 1000 c.c. of carbon 
 dioxide-free water for ten days, shaking eight times a day, and analyzing 
 the filtrate. Water soluble AssOs in Paris, green is determined in the same 
 way.
 
 268 INSECTICIDES AND FUNGICIDES 
 
 water, is used in the preparation of the spray from acid 
 arsenate, and when, furthermore, heavy dews or fogs keep 
 the foliage soaked with moisture part of the time, and so 
 dissolve enough arsenic to injure plant tissue. Rain would 
 wash off the dissolved arsenic and cause no harm. It is 
 possible to purchase lead arsenate at present which is guaran- 
 teed to be the neutral arsenate. 
 
 (c) PARIS GREEN, SCHWEINFURTH GREEN, is made by 
 boiling arsenous oxide, As 2 0s, with basic copper acetate, 
 Cu(C 2 H 3 O 2 ) 2 .CuO. The brilliant green precipitate is used 
 as a suspension in spraying. Its chemical name is copper 
 aceto-metarsenite, [Cu(AsO 2 ) 2 ]3.Cu(C 2 H 3 O2)2. The arsenic 
 content is the active poison for insects. 
 
 Leaf burning is very apt to result from the use of Paris 
 green, due to water soluble arsenic. The national Insecticide 
 Act of 1910 prohibits the sale of Paris green containing 
 more than 3.5 per cent, water soluble AS2O3. 1 In addition 
 to this, however, the action of water and carbon dioxide 
 will dissolve arsenic according to the following equation : 
 
 + 10H 2 O+ CO 2 = 
 6H 3 AsO 3 + CuCOs.Cu(OH)2+ Cu(C2H 3 O2)2.CuO. 
 
 This danger is so great that it is usually customary to mix 
 Paris green with lime or Bordeaux, the latter containing 
 an excess of lime. The free arsenic is neutralized by the 
 lime, thus: 
 
 2HsAsO3 + 3Ca(OH) 2 = Ca(AsOa)2 + 6H 2 O. 
 
 Sometimes Paris green is adulterated with worthless 
 articles like gypsum. It is easy to test for such adultera- 
 tion by treating the material with strong ammonia. Paris 
 green dissolves according to the following equation: 
 
 [Cu(AsO2)2]j.Cu(C2H 3 O2)2+ 36NH4OH = 
 4[Cu.(NHs)4.(OH)2] + 6(NH 4 )3AsO3 + 2NH4C 2 H 3 O 2 + 22H 2 O. 
 
 1 See footnote, page 267.
 
 EXTERNAL INSECTICIDES 269 
 
 The soluble copper compound called cuprammonium hydrox- 
 ide is written graphically, 
 
 Cu/ 
 
 NH NH, OH 
 NH NH OH 
 
 and is the same thing as Schweitzer's reagent used for 
 dissolving cellulose (Section 9). The gypsum is left as an 
 insoluble residue. So far as adulterations go, however, the 
 Insecticide Act of 1910 protects the farmer by limiting the 
 minimum amount of arsenous oxide to 50 per cent. 
 
 H. EXTERNAL INSECTICIDES 
 
 (a) HYDROCYANIC ACID GAS is a very violent poison to 
 man as well as to insects. The acid at ordinary tempera- 
 tures is a mobile, volatile liquid, with an odor of bitter 
 almonds and a boiling point of 26.5 C. It kills insects by 
 entering their breathing apparatus and putting a stop to 
 their vital functions. As used for fumigation it is prepared 
 by treating sulphuric acid with potassium cyanide. The 
 reaction is: 
 
 KCN+ H*SO4 - KHSO4+ HCN. 
 
 Potassium sulphate, K 2 SC>4, is not formed with the excess 
 of sulphuric acid necessary to get the maximum evolution 
 of gas. It is necessary to use enough water to hold the acid 
 potassium sulphate in solution after the reaction, especially 
 in the generators used for the purpose of producing the gas 
 on a large scale. The best proportion of cyanide, acid, and 
 water is a 1-1-3 formula, or 1 part potassium cyanide to 1 
 part of concentrated sulphuric acid (commercial concen- 
 trated acid is about 93 per cent, pure) and 3 parts of water. 
 The use of much stronger sulphuric acid results in the 
 decomposition of hydrocyanic acid and the formation of 
 ammonia and formic acid or carbon monoxide depending on 
 the strength of the sulphuric acid. The ammonia forms 
 ammonium sulphate with the acid.
 
 270 INSECTICIDES AND FUNGICIDES 
 
 The use of sodium cyanide is preferable in some ways, since 
 more hydrocyanic acid gas can be liberated from a pound 
 of sodium cyanide than from a pound of potassium cyanide, 
 because of the lower atomic weight of sodium. 100 parts of 
 sodium cyanide is equal to 132 parts of potassium cyanide 
 in theoretical effectiveness. The reaction is similar, but 
 the sodium acid sulphate is more soluble than the corre- 
 sponding potassium salt and a 3-4-6 formula is recommended. 
 
 The trouble which is sometimes experienced in obtaining 
 good results from the use of potassium cyanide is due in 
 part to the presence of sodium chloride. Sulphuric acid 
 sets free hydrochloric acid, and the latter forms ammonia, 
 later ammonium chloride, and formic acid. This reaction 
 of course reduces the yield of hydrocyanic acid gas. It is 
 not sufficient that the potassium cyanide have a guarantee 
 of 98 per cent, pure, for a mixture of potassium and sodium 
 cyanides would show 98 per cent, expressed as potassium 
 cyanide and yet have considerably more than 2 per cent, of 
 sodium chloride present. If possible the amount of sodium 
 chloride present should be known, and it is recommended 
 not to have more than 1 per cent. 
 
 Since the use of hydrocyanic acid gas is attended with 
 great danger to the operator, extreme pains should be taken 
 by him not to inhale the gas himself, or generate it where 
 others may run any risk. It is altogether too dangerous to 
 handle with impunity, and too much carelessness is displayed 
 in its use. 
 
 (6) KEROSENE EMULSION. Kerosene, or coal oil, as it is 
 sometimes called, is an excellent contact insecticide, killing 
 by entering the pores of the insect. Used in the pure state, 
 however, it is apt to harm vegetation, and is not much 
 employed. It is one of the fractional distillation products 
 from crude petroleum and consists of a mixture of paraffine 
 or methane hydrocarbons whose boiling points lie between 
 150 and 300 C. Kerosene is insoluble in water and hence 
 cannot easily be diluted, although attempts have been made 
 to agitate the two together so as to obtain a mechanical 
 mixture suitable for application to trees, but the mixture 
 separates too rapidly to be satisfactory. By thoroughly
 
 EXTERNAL INSECTICIDES 271 
 
 agitating kerosene with a solution of hard or soft soap, there 
 is obtained an emulsion which, when properly made, retains 
 its permanency for at least several days. 
 
 An emulsion is a mechanical mixture of two liquids in- 
 soluble in each other. One is usually an oil, the particles of 
 which are very finely divided and are held in suspension 
 in the other which is of a gelatinous or viscous nature. The 
 permanency of suspension is brought about partly because 
 the particles are very small and the friction in moving 
 through the suspending liquid is sufficient to prevent their 
 accumulating rapidly; and partly because the suspending 
 liquid exerts some physical if not chemical attraction for 
 the particles, thus helping to prevent their uniting with one 
 another. Moreover, each fine particle of oil is surrounded 
 by a coating of the gelatinous or viscous suspending liquid 
 and can not easily touch another particle to coalesce with it. 
 The finer the particles of oil, the more surface exposed, and 
 hence the greater the attraction of the suspending liquid for 
 the oil, and the more friction in moving. Kerosene and soap 
 solution are liquids of the character just described. 
 
 (c) LIME-SULPHUR BOILED is made by boiling together 
 for about an hour, or until the sulphur is dissolved, 50 
 pounds of pure lime and 100 pounds of finely ground 
 sulphur in 50 to 55 gallons of water. The lime is slaked 
 before actual boiling is begun. When properly made there 
 are formed the tetra- and pentasulphides of calcium and 
 calcium thiosulphate. The exact reaction is not known, 
 but the following is given as a possibility: 
 
 3Ca(OH)2 + 118= CaSsO* +CaS4 +CaS s +3H,O. 
 
 This reaction corresponds fairly well to the proportions 
 of lime to sulphur recommended, and to the amount of 
 sulphur in solution as thiosulphate and sulphides found 
 by analysis. 
 
 Lime containing magnesia should not be used, for mag- 
 nesium forms no compounds with the sulphur and only 
 serves to increase the amount of sediment. Long boiling 
 changes the thiosulphate to insoluble sulphite (Reaction 1);
 
 272 INSECTICIDES AND FUNGICIDES 
 
 oxidizes the sulphite to insoluble sulphate (Reaction 2); 
 and the sulphide to thiosulphate (Reaction 3), with a 
 separation of sulphur in each case except the second. Ex- 
 posure to the air causes the oxidation changes to take place. 
 The reactions are as follows: 
 
 1. CaS 2 Os=CaSO3+S 
 
 2. CaSO 3 +O=CaSO4 
 
 3. CaS4+3O=CaS 2 3 +2S 
 
 The active constituents as a contact insecticide are the 
 polysulphides which are caustic in nature, destroying the 
 skin of insects. The more sulphides in solution, the more 
 effective the spray; and much variation from the formula 
 given, or boiling too long, or use of impure materials, all 
 lessen the amount of sulphides formed. 
 
 Lime-sulphur is also a fungicide and in addition to the 
 sulphides, the thiosulphate has value for this purpose. 
 When sprayed on the trees and exposed to the air, the 
 thiosulphate and sulphides oxidize as indicated in Reactions 
 1 and 3. The insoluble sulphite and sulphur which are 
 formed are also useful as fungicides. The carbon dioxide 
 of the air also breaks up lime-sulphur as follows: 
 
 CaS4+CO2+H 2 O =CaCOj+H 2 S+3S 
 
 Injury to foliage from the use of this spray is due to the 
 caustic effect of the polysulphides, and occurs for the most 
 part when the sulphides occur in too great concentration 
 or when they penetrate the surface of the leaf through cracks 
 or stomata. Applied too thickly the drops coalesce and run 
 to the edge where by evaporation the solution becomes suffi- 
 ciently concentrated to destroy leaf tissue. Injury, however, 
 takes place only during the early part of the application, 
 for the longer the spray stays on the leaves the more the 
 sulphides are broken up as described above. 
 
 Although there is some evidence that lime-sulphur is an 
 internal as well as an external insecticide, its action in this 
 respect is not sufficiently pronounced for general use, and 
 it is advantageous if some internal insecticide can be mixed 
 with the lime sulphur, so that one spraying, or series of
 
 EXTERNAL INSECTICIDES 273 
 
 sprayings, may be useful for biting insects, sucking insects, 
 and fungi. Paris green is not satisfactory because it is 
 decomposed, freeing arsenous acid and injuring foliage. 
 Lead arsenate is the best material to use, and this in the 
 triplumbic form. The acid arsenate is not satisfactory, on 
 account of the formation of a soluble arsenic compound, 
 possibly arsenic acid. The reactions which take place when 
 lead arsenate is mixed with lime-sulphur are complex and 
 not well known. Apparently, among other compounds, lead 
 sulphide is formed, and there is an increase in the amount 
 of thiosulphate and sulphite. 
 
 Some commercial preparations of lime-sulphur, particularly 
 the dry powders which are to be dissolved in water, consist 
 largely of sulphides of sodium or potassium. These com- 
 pounds are fungicides not contact insecticides, and, further- 
 more, their use with arsenicals causes foliage injury due to 
 a greater solution of arsenic acid. 
 
 (d) MISCIBLE OR SOLUBLE OILS. Not only kerosene, but 
 crude petroleum also has valuable insecticidal properties. 
 Its use, however, like the use of kerosene in the pure state, 
 is not possible on account of its injury to trees. To facilitate 
 the proper dilution of these oils which can be so valuable, 
 the so-called miscible or soluble oils have been prepared. 
 
 For this purpose there is made first an "emulsifier" which 
 is essentially a soft, carbolated soap, made commonly by 
 boiling 10 gallons of menhaden oil, 8 gallons of carbolic acid, 
 and 15 pounds of caustic potash, then mixing with it 2 
 gallons of kerosene and 2 gallons of water. This emulsifier 
 is then mixed with varying amounts of other oils such as 
 crude petroleum, paraffine oil, rosin oil (Section 29, 6), 
 and more kerosene. This final solution is the miscible oil 
 and when mixed slowly with water according to the spray 
 requirements forms a milky emulsion that is reasonably 
 permanent if care is used in making and mixing. 
 
 (e) PYRETHRUM, PERSIAN INSECT POWDER, BUHACH, is 
 made by grinding the dried flowers of various species of the 
 pyrethrum plant. The active constituent is a volatile oil of 
 strong characteristic odor which can be extracted by ether. It 
 varies in amount from 5 to 10 per cent. It is green to brown 
 
 18
 
 274 INSECTICIDES AND FUNGICIDES 
 
 in color and on exposure to the air oxidizes to an inactive 
 .resin. This explains the necessity of keeping the powder 
 in air tight containers, otherwise it loses its efficacy. Pyre- 
 thrum is not poisonous to man. 
 
 (/) TOBACCO. An old remedy for certain delicate insects 
 like plant lice has been a simple decoction of tobacco leaves 
 or waste. The water extracts the alkaloid nicotine (Section 
 37, e) which is active in destroying insects. Besides a liquid 
 extract, powdered tobacco and the smoke of tobacco are 
 efficacious in some instances. The latter contains some 
 nicotine, but in addition decomposition products which 
 have some toxic effect. Commercial preparations are on 
 the market, many of them containing nicotine sulphate as 
 the active constituent. It will be remembered (Section 36) 
 that alkaloids are basic in character and will unite to form 
 salts with mineral acids. 
 
 (0) WHALE OIL SOAP. Only the name is left of what used 
 to be the soap made from whale oil. Now almost any kind 
 of cheap fish oil is used and saponified with potassium or 
 sodium hydroxide. The potash soap is soft; it is more 
 readily soluble in hot water, and the solution does not 
 harden when cold. It is also more penetrating and effective. 
 One pound of soap in 4 to 10 gallons of water are the pro- 
 portions ordinarily used. The sticky soap solution clogs 
 up the pores of the insects and causes death. 
 
 205. Fungicides. (a) AMMONIACAL COPPER CARBONATE 
 is a solution of basic copper carbonate, CuCO 3 .Cu(OH) 2 , or 
 
 /OH 
 
 Cu<^ 
 
 \ 
 yc=o 
 
 .0 
 
 Cu/ 
 X OH 
 
 dissolved in ammonia to form cuprammonium carbonate, 
 Cu(NH 3 )4CO 3 .H 2 O, 
 
 NHr NHj OH 
 
 Cu OH 
 
 \ / 
 
 NHi NH O C=O
 
 FUNGICIDES 275 
 
 Dilute ammonia dissolves more copper carbonate than strong 
 ammonia, so that it is better to use dilute ammonia in 
 dissolving the copper carbonate, rather than to use strong 
 ammonia for solution and to dilute it afterward. Excess 
 of ammonia harms vegetation, hence care must be used 
 in dissolving the copper carbonate. The soluble copper is 
 the active fungicide and in this form is not so dangerous to 
 foliage as is copper sulphate which is sometimes used in 
 dilute solution. 
 
 When diluted considerably, basic copper carbonate is 
 apt to precipitate out and in such cases an agitator can be 
 used in the spray, although if the spray is used immediately 
 after dilution, it can be brought on the plants before pre- 
 cipitation begins. 
 
 (6) BORDEAUX MIXTURE is usually made by mixing 
 equal parts of copper sulphate and burnt lime, the former 
 previously dissolved in water, and the latter slaked 
 and mixed with an equal quantity of water. The pro- 
 portions vary with the different uses of the fungicide. 
 Formerly the reaction was thought to be a simple one by 
 which copper hydroxide and calcium sulphate were formed, 
 but this is impossible. The mixture would gradually turn 
 black if copper hydroxide were formed. Copper hydroxide, 
 Cu(OH) 2 , blue, changes to Cu(OH) 2 .(CuO) 2 , and finally 
 CuO, black. The color is, however, very permanent and 
 there is some evidence to show that the compound formed 
 is a double basic sulphate of copper and calcium to which 
 has been given the formula, (CuO)i .SO 3 . (CaO) 4 .SO 3 . Graphi- 
 cally it can be written as follows: 
 
 O O 
 
 \ ^ 
 
 O Cu Cu Cu Cu Cu Cu Cu Cu Cu Cu O O 
 
 \/ \/ \/ \/ \/ \/ V \/ \/ 
 ooooooooo 
 
 Burnt lime which has been air-slaked and hydrated lime 
 which contains considerable carbonate are not recommended
 
 276 INSECTICIDES AND FUNGICIDES 
 
 for use in making Bordeaux unless the proportion of lime 
 is increased. Calcium carbonate does not form a compound 
 with copper sulphate. 
 
 The active agent in killing fungi is copper sulphate, but 
 the use of copper sulphate even in dilute solution is attended 
 with so much danger to foliage that Bordeaux, which is a 
 suspension of an insoluble copper salt in water, is far pre- 
 ferable. The bluish-white particles are distributed over the 
 surface of leaves, and under the action of water and carbon 
 dioxide very small quantities of copper sulphate are formed, 
 sufficient to kill fungous spores and germ tubes. Calcium 
 carbonate is also formed. 
 
 Under certain climatic conditions, such as long periods of 
 damp weather, but no rain, enough copper sulphate may be 
 formed to burn the leaves. Even under these conditions, 
 however, the presence of an excess of lime prevents this 
 danger. The formulas call for more lime than is necessary 
 to form the compound with copper. 
 
 Bordeaux may be mixed with arsenicals Paris green and 
 lead arsenate to good advantage so as to have both an 
 insecticide and a fungicide in the same spray. Paris green is 
 benefited by this mixing because the excess of lime neutralizes 
 the free arsenous acid so readily formed in plain Paris green 
 applications. 
 
 (c) CORROSIVE SUBLIMATE, MERCURIC CHLORIDE, JIgCl 2 , 
 is a very powerful fungicide and antiseptic. Furthermore, 
 it is very poisonous to human beings and should be used 
 with great care. A solution of 1 part sublimate to one 
 thousand parts of water is a common strength to employ. 
 Since mercuric chloride corrodes metal the solution should 
 be made in a wooden pail preferably. Sometimes it is 
 purchased in tablets mixed with ammonium chloride which 
 increases the solubility of the mercuric chloride by the forma- 
 tion of a double mercurammonium chloride, HgCl 2 .(NH 4 Cl) 2 . 
 
 (d) FORMALDEHYDE is a gas, CH 2 O, at ordinary tempera- 
 tures. It dissolves in water readily, and in commerce is 
 sold in the form of a solution containing approximately 
 38 per cent, by weight. Formalin is the trade name
 
 FUNGICIDES 277 
 
 of such a solution made by one German firm only. It 
 has no advantages whatever over any 38 per cent, solu- 
 tion made by other reputable manufacturers. Formal- 
 dehyde may be used in the liquid form by proper 
 solution or in the gaseous form by liberating it in a closed 
 room. The evolution of formaldehyde may be produced 
 by heating the solution under pressure; by simple evapora- 
 tion from large surfaces; by treatment with potassium per- 
 manganate whereby part of the formaldehyde is oxidized 
 and the heat of oxidation volatilizes the remainder; or 
 by burning the so-called formaldehyde candles. The latter 
 are made of paraform which is a condensation product 
 of formaldehyde made by spontaneous evaporation of the 
 solution. The compound is supposed to be trioxymethylene, 
 (CH 2 O) 3 . On heating this white solid, formaldehyde is 
 evolved. 
 
 (e) LIME-SULPHUR BOILED, being an insecticide as well 
 as a fungicide, was discussed under the former head 
 (Section 204 II, c). 
 
 (/) LIME-SULPHUR SELF BOILED is essentially a mechanical 
 mixture of sulphur and slaked lime. It is prepared 
 by adding, for example, 6 pounds of sulphur, finely 
 ground, to 6 pounds of lime which has just started to 
 slake. The mixture is stirred and more water added 
 until the mass boils, due to the slaking lime. The boiling 
 is continued five or ten minutes and then the remainder 
 of the water to equal 50 gallons in all is added. This 
 cools down the mass. The violent boiling has thoroughly 
 mixed the sulphur and slaked lime and formed very little 
 calcium sulphides. But at the strengths applied very little 
 sulphides are desired, or leaf burning results. This is why 
 the boiling is checked by the cold water. The mixture is of 
 course a suspension and must be applied with an agitator. 
 Lead arsenate and some other insecticides have been mixed 
 with the self-boiled lime-sulphur with good results. Some 
 chemical changes take place, due to the calcium sulphides 
 in solution.
 
 278 INSECTICIDES AND FUNGICIDES 
 
 EXERCISES 
 
 1. What is the name and formula of the acid of arsenic from which 
 Paris green is made? 
 
 2. Define the following terms: Alkaloid, spore, fungus, arsenical, emul- 
 sion, fractional distillation, hydrocarbon, viscous, the prefix thio and 
 antiseptic. 
 
 3. What arsenic compound found in sprays is soluble in hard water? 
 
 4. Show what each part of the chemical name for Paris green means. 
 
 5. Give a detailed explanation of how lead arsenate, kerosene emulsion, 
 Bordeaux mixture and hydrocyanic acid gas kill. 
 
 6. Show by calculation that 100 parts by weight of sodium cyanide are 
 equal in effectiveness to 132 parts by weight of potassium cyanide. 
 
 7. Mention the conditions under which leaf burning caused by the appli- 
 cation of an insecticide or fungicide might result. 
 
 REFERENCES 
 
 Bur. Ent., Bui. No. 90, Pt. I, U. S. Dept. Agr. Hydrocyanic Acid Gas 
 Fumigation in California. 
 
 Bur. Ent., Bui. No. 90, Pt. Ill, U. S. Dept. Agr. Chemistry of Fumiga- 
 tion with Hydrocyanic Acid Gas. 
 
 Bur. Ent., Bui. No. 116, Pt. IV, U. S. Dept. Agr. Lime-Sulphur as a 
 Stomach Poison for Insects. 
 
 Illinois Agr. Expt. Sta., Bui. No. 135. Bordeaux Mixture. 
 
 Iowa Agr. Expt. Sta., Research Bui. No. 12. Chemical Studies of Lime- 
 Sulphur-Lead Arsenate Spray Mixture. 
 
 New York, Cornell Agr. Expt. Sta., Bui. No. 288. Spray Injury In- 
 duced by Lime-Sulphur Preparations. 
 
 New York, Cornell Agr. Expt. Sta., Bui. No. 290. Studies of the Fungi- 
 cidal Value of Lime-Sulphur Preparations. 
 
 New York, Geneva Agr. Expt. Sta., Bui. No. 329. Chemical Investiga- 
 tions of Best Conditions for Making Lime-Sulphur Wash. 
 
 Penna. Agr. Expt. Sta., Bui. No. 86. Miscible Oils: How to Make 
 Them. 
 
 Penna. Agr. Expt. Sta., Bui. No. 110. The Control of Insects and 
 Diseases Affecting Horticultural Crops. 
 
 Penna. Agr. Expt. Sta., Bui. No. 115. Concentrated Lime-Sulphur Spray.
 
 ALTHOUGH not strictly a factor in plant growth, the gas 
 engine has become a very important factor in farm life. 
 For running tractors in plowing large farms rapidly (Fig. 73), 
 in furnishing power for pumping, silage cutting, cream 
 separating, and in moving products to market, as well as 
 providing rapid means of locomotion for the modern farmer, 
 the gas engine today occupies an almost essential place on 
 many farms. On this account a short discussion of the prin- 
 ciples of combustion, products obtained, fuels, and lubricants, 
 should fit in at this point. The subject of gas engines is too 
 large a one to treat from any standpoint except the chemical 
 one and should include only such other details as may be 
 necessary to fully understand the chemistry involved. 
 
 206. The Gas Engine. The gas engine is an appliance for 
 making use of the energy developed when a mixture of a 
 combustible gas and air explodes. When gases explode a 
 sudden pressure is produced. This pressure is directed against 
 a piston-head and the movement of the piston is trans- 
 mitted to a wheel by a connecting rod. In a steam engine, 
 steam is admitted first to one end and then to the other 
 end of the cylinder. This moves the piston back and forth 
 and by means of the connecting rod a wheel rotates. In a 
 gas engine a mixture of gas and air is admitted to one end of 
 the cylinder and at the proper moment is exploded, usually 
 by an electric spark. The pressure thus developed drives 
 the piston to the other end of the cylinder. Gas is not 
 exploded on the other end of the piston to drive it back, 
 but the momentum of a heavy fly-wheel attached to the 
 main shaft carries the piston back again. In one type of 
 engine, the so-called "four-cycle" type, the explosion comes 
 at every other inward movement of the piston, or once every 
 two revolutions of the fly-wheel. It is called four-cycle 
 because there are four strokes which complete the cycle: 
 
 (279)
 
 280 
 
 THE GAS ENGINE 
 
 An outward movement of the piston which draws gas and 
 air into the cylinder, or intake; inward movement and 
 explosion, or compression; outward movement and work, 
 or expansion; and inward movement, or exhaust. In the 
 other type, the "two-cycle," the explosion comes at every 
 inward movement of the piston, or once every revolution of 
 the fly-wheel. In this type the crank case is air tight, so 
 that air and gas can be admitted to the outer end of the 
 cylinder. A by-pass permits the mixture to go to the inner 
 end of the cylinder for the explosion. At the outward stroke 
 the gas and air are first compressed in the crank case and 
 
 FIG. 73. Gasoline tractor for plowing. 
 
 then as the by-pass is opened by the movement of the piston, 
 the mixture is forced into the inner end of the cylinder, 
 driving ahead of it the burned gas through a port. At the 
 inward movement of the piston the mixture is compressed 
 and the explosion takes place, and at the same time gas and 
 air are drawn in to the outer end of the cylinder; then the 
 cycle is repeated. 
 
 A very important part of the gas engine is the carburetor 
 or place where the air and gas are mixed. If the fuel is a 
 liquid at ordinary temperatures it is necessary to vaporize 
 it before an explosive mixture can be obtained. A liquid 
 like gaspline vaporizes very readily and it is only necessary
 
 CRUDE PETROLEUM 281 
 
 to convert it to a spray in the carburetor. The inflowing 
 air evaporates the fine particles of liquid and a gas mixture 
 results. Fuels like kerosene which do not vaporize so readily 
 at ordinary temperatures, should be heated before they are 
 admitted to the carburetor, in order to develop maximum 
 power. 
 
 The mechanical devices for admitting gas and air to the 
 carburetor, for regulating the inflow of explosive mixtures 
 to the piston, for removing the burned gas, and for the 
 numerous other necessary steps in the development of 
 maximum pow r er in a gas engine cannot be discussed here. 
 For such details the reader is referred to books on gas engines. 
 (See reference list at end of chapter). For the present pur- 
 pose, however, a brief description of fuels, their properties 
 and sources, may not be out of place. 
 
 207. Crude Petroleum. Crude petroleum is the source of 
 gas engine fuels. It is usually a heavy, dark, oily liquid 
 with peculiar characteristic odor, and found in porous rocks 
 at a depth of 300 to 3700 feet below the earth's surface. The 
 decomposition of organic matter within the earth is supposed 
 to be the origin of it. Since petroleum is an inflammable 
 liquid it can be used in the crude state as a fuel, but not of 
 course in a gas engine. To obtain the greatest value from 
 this material it is necessary to separate it into its various 
 components. This can be readily accomplished by fractional 
 distillation, since petroleum is essentially a mixture of par- 
 affine hydrocarbons of very many kinds. There are other 
 compounds in some petroleum, but in the better grades of 
 Pennsylvania oils from which the refined products are most 
 easily made, these compounds are present in very small 
 amounts and need not be considered. 
 
 The paraffme hydrocarbons have as empyrical formula 
 C n H 2n +2 and run from methane, CH 4 , to hexacontane, 
 CeoHm, from gases through liquids to solids. The more 
 carbon atoms in the molecule the greater the density and the 
 higher the boiling point. Without going into the details of 
 the distillation process it is sufficient to say that the crude 
 petroleum is charged into large stills and heated, the various 
 hydrocarbons coming off at different temperatures. By
 
 282 THE GAS ENGINE 
 
 changing receivers at any point in the boiling as many 
 fractions can be obtained as desired. 
 
 At first there are obtained only three or four fractions, the 
 first one called benzine distillate or crude naphtha (some- 
 times light naphtha and heavy naphtha), with a density of 
 80 to 58 Be. 1 Then come burning oils or kerosene with a 
 density of 58 to 43. Tar or residuum is left in the stills. 
 The temperature of distillation rises gradually to 300 or 
 400 C. From the crude naphtha several colorless fractions 
 are usually obtained by distilling again and purifying with 
 strong sulphuric acid and caustic soda. The liquid to be 
 thus treated is agitated with sulphuric acid of 66 Be., 
 then washed with water, agitated with caustic soda of 
 4 to 10 Be., and finally washed with water. The 
 acid and soda decompose or dissolve various impurities 
 and coloring matters in the petroleum products other than 
 the paraffine hydrocarbons. The spent acid which settles 
 to the bottom is drawn off as "sludge" acid and is used in 
 some places for making phosphatic fertilizers. The various 
 fractions have different names, not always uniform. They 
 are arbitrary at best, depending on the density. Some of 
 the names are gasoline; naphtha, A, B, C, grades; benzine; 
 petroleum ether, etc. It is not safe to buy by name for any 
 special purpose but by specific gravity (Baume scale) or by 
 boiling points. 
 
 The kerosene is redistilled into two or more nearly colorless 
 fractions, purified with acid and alkali as above described, 
 and sold as burning oils of various "tests." 2 Many of the 
 
 1 Baum6. This is an arbitrary standard of density for liquids. Hydrom- 
 eters are graduated for liquids heavier and lighter than water. For the 
 former, on the Baum6 scale is where the instrument sinks in pure water, 
 and 10 in a 10 per cent, solution of salt. For the latter is the point 
 to which the hydrometer sinks in a 10 per cent, salt solution, and 10 
 in pure water. The graduation is extended uniformly in both cases. The 
 temperature is 17.5 C. 
 
 2 For use in lamps particularly, kerosene must not be so volatile as to 
 cause an explosion when the wick is lighted. This volatility or "flash 
 point, " as it is called, is regulated by law. The flash point is the temperature 
 at which kerosene gives off enough vapor to ignite in a flash over the surface. 
 In most of our states 110 F. is the legal flash point. Flash tests are the 
 determinations which are made to show what the flash points are. Fire 
 tests, also made sometimes, are the determinations which show the tem- 
 perature at which the vapor will burn continuously. The fire point is 
 usually about 20 F. higher than the flash point.
 
 GASOLINE 283 
 
 above distillations are accomplished with steam, as the 
 steam distilled products are of better grade with less loss 
 and less danger of decomposition in the still. 
 
 The tar left in the stills is removed and destructively 
 distilled, yielding hydrocarbons of much higher density and 
 greater viscosity ; some even being solid at ordinary tempera- 
 tures. By redistillation, washing with sulphuric acid and 
 caustic soda, and chilling and pressing, there are obtained 
 heavy oils used for lubricating called lubricating and 
 paraffine oils paraffine, vaseline, and coke. 
 
 The very volatile products of low density are used for 
 solvents; intermediate products for fuel; kerosene for light- 
 ing purposes; lubricating oils for machinery; paraffine for 
 candles; vaseline for medicine; and coke for electric light 
 carbons. 
 
 208. Gasoline. Originally the name gasoline was applied 
 to a fraction whose density was somewhere between 90 and 
 80 Be., but now the product sold under the name of gasoline 
 maybe anything from 90 to 60 Be. or even less. Most of 
 the engine gasoline runs from 65 to 60 Be., 1 specific gravity 
 0.718 and 0.737, boiling point 120 to 150 C. It is a mixture 
 of hydrocarbons, having no constant composition. It is 
 possible to obtain any particular density by mixing light 
 and heavy fractions. The same result may be secured by 
 uniting a very light product with a very heavy one, or by 
 uniting two of more nearly equal densities. As a result the 
 mere specific gravity or Baume reading of a grade of gasoline 
 does not tell the purchaser just what he is getting. If a single 
 hydrocarbon liquid, having a density of 65 Be., is just suited 
 to a certain engine, a grade of material would not be as well 
 suited which consists of a mixture of very light hydrocarbon 
 with very heavy hydrocarbon, the resultant density of which 
 is 65 Be. The lighter material would vaporize too rapidly 
 and explode too easily, whereas the heavier portion would 
 vaporize very slowly or too slowly to make a proper explosive 
 mixture. In time it may be possible to buy gasoline, or 
 
 1 Instead of saying "65 or 60 Be. gasoline" it is usually customary to 
 speak of it as "65 or 60 test" gasoline.
 
 284 THE GAS ENGINE 
 
 at least a gas engine fuel, which has its constituents guaran- 
 teed, in order that the purchaser may obtain whatever grade 
 he wants for his particular purpose. Density alone is not the 
 best test ; a fractional distillation test should also be made. 
 
 It is important in using a gas engine to have the proper 
 amount of air mixed with the gasoline vapor. Too much 
 air dilutes the mixture and reduces the power. Too little 
 air does not permit of complete combustion, and this also 
 reduces the power and causes waste of fuel. Gasoline being 
 a mixture of hydrocarbons burns to carbon dioxide and 
 water when there is enough oxygen present. On this account 
 the exhaustion should not take place indoors for the large 
 quantities of carbon dioxide eliminated are detrimental 
 to health. The following may be taken as a typical reaction : 
 
 This means that one gallon of gasoline, assuming it to be 
 octane, CgHig, 64.8 Be., will require about 1180 cubic feet 
 of air at 62 F. When insufficient oxygen is present the 
 products of combustion are different, and include carbon. 
 The maximum amount of heat, and consequently power, is 
 developed only when combustion is complete. 
 
 209. Lubricants. The purpose of a lubricating oil is to 
 reduce friction between moving surfaces, and it should 
 have sufficient "body" or viscosity not to be squeezed out 
 from between the surfaces. Too viscous an oil will cause 
 friction of the oil itself and reduce efficiency. A lubricating 
 oil should not be so volatile that it will not last under the 
 temperature to which it is subjected. The flash test is useful 
 in determining this point. Neither should an oil have any 
 free acid present, such as sulphuric acid if a hydrocarbon oil ; 
 fatty acid, usually stearic, if an animal or vegetable oil. The 
 free acid corrodes the bearings. 
 
 From the tar or residuum left in the first distillation of crude 
 petroleum there are obtained (Section 207) a series of lubri- 
 cating oils which are of excellent character, and better 
 suited for most machinery than animal or vegetable oils, 
 though for some purposes the latter are better.
 
 REFERENCES 285 
 
 This is not the place to discuss the various grades of 
 lubricating oils and their properties and uses, but it may be 
 well to mention one fact and that is the necessity of using a 
 good grade of oil especially adapted for gas engine cylinders. 
 The contact surface of the piston in the cylinder must be 
 lubricated, of course, and since the temperature is very 
 high, the oil must be of a character that does not readily 
 carbonize or volatilize under the action of heat. An oi) 
 whose density is 26 to 28 Be., with a flash test of 400 to 
 475 F., has been recommended for some engines. Dealers 
 in engines can recommend the best cylinder oil for use in 
 their particular engine'. 
 
 EXERCISES 
 
 1. In what respects are the reactions that take place in a gas engine 
 like those that take place in a plant? 
 
 2. Show that the energy made in a steam engine has its source in the sun. 
 
 3. Compare the products of combustion of a hydrocarbon when sufficient 
 air is present to the combustion of the same material when insufficient 
 air is present. Which yields the more energy? Why? 
 
 4. What is meant by viscosity, Baume, coke, density, specific gravity, 
 paraffine, benzine and work? 
 
 5. Distinguish between fractional and destructive distillation. 
 
 6. Why must a gas engine be lubricated? 
 
 7. What in a plant corresponds in function to octane; to a lubricating 
 oil; to the exhaust; to the machine itself? 
 
 8. How many liters of pure oxygen under standard conditions are neces- 
 sary to completely use 1000 grams of pure octane by combustion? How 
 many liters of air under the same conditions would furnish as much oxygen? 
 
 9. Suppose in Exercise 8, 10 per cent, of the fuel forms carbon, how 
 many liters of air under standard conditions are necessary for its combustion? 
 How many liters of exhaust gases are formed under these conditions? 
 
 10. For what two reasons should a room in which a gas engine is running 
 be well ventilated? 
 
 REFERENCES 
 
 Hirshfeld and Ulbricht. Gas power. 
 Levin. The Modern Gas Engine and the Gas Producer. 
 Redwood. A Treatise on Petroleum, 3d ed., vol. ii. 
 Rogers and Aubert. Industrial Chemistry, Chapter XXIII. 
 Whitman. Gas Engine Principles.
 
 PART III 
 
 THE ANIMAL 
 
 CHAPTER XVII 
 THE CHEMISTRY OF ANIMAL PHYSIOLOGY 
 
 THE highest and most complex products of the farm are 
 animals (Fig. 74). Directly or indirectly animals are de- 
 pendent on plants for their sustenance. There are, of 
 course, many obvious differences between plants and animals, 
 but they are both living things that reproduce themselves. 
 They are composed largely of carbon compounds; that is, 
 they are organic in nature. For the proper elaboration of 
 these compounds, a few elements are necessary. But, 
 whereas plants absorb only soluble inorganic compounds and 
 from them build up their tissue, animals absorb compara- 
 tively little of such material but must have organic food 
 material previously elaborated by plants. This material 
 is taken into the animal and made soluble before being 
 absorbed and rebuilt into animal tissue. 
 
 210. Essential Elements for Animals. For animals there 
 are needed in compound form the following fifteen elements : 
 Carbon, hydrogen, oxygen, phosphorus, potassium, nitrogen, 
 sulphur, calcium, iron, magnesium, sodium, chlorine, iodine, 
 silicon, and fluorine. It is to be noted that the last five 
 elements, while essential for animals, are not essential for 
 plants. 
 
 211. Composition of the Animal. Like the plant, the 
 animal is composed largely of water, but not to so great an 
 extent. The average amount of water in farm animals is 
 not far from 50 per cent. In man it is about 70 per cent. 
 Of the dry matter of steers 60 per cent, is carbon, 14 per 
 
 (287)
 
 288 THE CHEMISTRY OF ANIMAL PHYSIOLOGY 
 
 cent, oxygen, 9 per cent, hydrogen, 6 per cent, nitrogen, and 
 11 per cent. ash. This analysis may be taken as fairly 
 representative. It shows (cf. Section 53) that there is a 
 much larger proporton of carbon to oxygen in animals than 
 
 FIG. 74. Farm animals. 
 
 in plants, and more nitrogen. This is because the dry 
 matter of animals consists mostly of fats and proteins, 
 whereas the dry matter of plants consists largely of carbo- 
 hydrates and crude fiber. The cell walls of plants are made 
 of cellulose, but the cell walls of animals are made of protein.
 
 MUSCULAR TISSUE 289 
 
 Table XVII shows the composition of various farm animals, 
 expressed for the most part on the same basis as the compo- 
 sition of plants in Table I, except that there is no crude 
 fiber or nitrogen-free extract. 
 
 TABLE XVII. COMPOSITION OF FARM ANIMALS 
 
 
 
 
 
 
 Contents of 
 
 
 Water 
 
 Fat 
 
 Protein 
 
 Ash 
 
 stomach and in- 
 
 Kind of animal. 
 
 per cent. 
 
 per cent. 
 
 per cent. 
 
 per cent. 
 
 testines, per cent. 
 
 Fat calf . . 
 
 . 63.0 
 
 14.8 
 
 15.2 
 
 3.8 
 
 3.2 
 
 Half fat ox . . 
 
 . 51.5 
 
 19.1 
 
 16.6 
 
 4.6 
 
 8.2 
 
 Fat ox ... 
 
 . 45.5 
 
 30.1 
 
 14.5 
 
 3.9 
 
 6.0 
 
 Fat lamb . . 
 
 . 47.8 
 
 28.5 
 
 12.3 
 
 2.9 
 
 8.5 
 
 Normal sheep . 
 
 . 57.3 
 
 18.7 
 
 14.8 
 
 3.2 
 
 6.0 
 
 Half fat sheep . 
 
 . 50.2 
 
 23.5 
 
 14.0 
 
 3.2 
 
 9.1 
 
 Fat sheep . 
 
 . 43.4 
 
 35.6 
 
 12.2 
 
 2.8 
 
 6.0 
 
 Normal pig 
 
 . 55.1 
 
 23.3 
 
 13.7 
 
 2.7 
 
 5.2 
 
 Fat pig . 
 
 . 41.3 
 
 42.2 
 
 10.9 
 
 1.6 
 
 4.0 
 
 In studying the animal it is necessary to know something 
 of the various parts of the body, their general composition, 
 their functions, and the reactions taking place in them. The 
 animal is obviously very complex in its structure and only 
 the very general points of physiology can be touched upon. 
 For further information the reader is referred to any good 
 text on animal physiology. (See references at end of chapter) . 
 
 212. Bones. The framework of the body about which 
 all the tissues are grouped, and which serves to give rigidity 
 and afford protection to the more delicate and sensitive 
 parts is composed of bones and is called the skeleton. 
 Chemically bones are composed of protein material called 
 osseous tissue, or ossein, permeated with tricalcium phos- 
 phate and calcium carbonate. The mineral and organic 
 part are present in about equal proportions (Section 160). 
 Bones are hollow to give greater strength to them, and are 
 filled with soft material called marrow, which consists largely 
 of fat and protein. Blood-vessels permeate the bones, and 
 the marrow is supposed to be the source of the red blood 
 corpuscles. Fig. 75 illustrates the appearance of bone tissue 
 under the microscope. 
 
 213. Muscular Tissue. The flesh of an animal, or muscular 
 tissue is composed usually of bundles of cells called fibers 
 
 19
 
 290 THE CHEMISTRY OF ANIMAL PHYSIOLOGY 
 
 FIG. 75. Transverse section of bone. Magnified. (Sharpey.) 
 
 FIG. 76. A, portion of a medium-sized human muscular fiber. Magnified 
 nearly 800 diameters; B, separated bundles of fibrils, equally magnified; 
 a, a, larger, and b, b, smaller collections; c, still smaller; d, d, the smallest 
 which could be detached. (Gray.)
 
 CONNECTIVE TISSUE 291 
 
 (Fig. 76). It causes motion in the animal, having the 
 power of contracting and expanding when stimulated 
 by the nerves. This contraction may be transmitted to 
 the bones and cause locomotion, or may be merely a rhyth- 
 mical contraction and expansion, causing the well-known 
 movements of the heart, lungs, and other organs. The 
 muscle substance is composed largely of proteins, but also of 
 some glycogen, dextrose, potassium phosphate, and nitrog- 
 enous extractives. 1 It is about 75 per cent, water and 
 25 per cent, solids. The principal protein is myosinogen, 
 liquid in living muscle, but changing to solid myosin in 
 dead muscle. Living muscle at rest is alkaline in character; 
 active and dead muscle are slightly acid due to the formation 
 of an isomer of lactic acid called sarcolactic acid. Muscles are 
 bathed in lymph and permeated with blood-vessels. When 
 a muscle does work, the dextrose is oxidized by the oxygen 
 brought to it in the blood stream, and carbon dioxide is 
 given off. Heat is also developed by this oxidation. 
 
 214. Fatty Tissue. Besides the fats or fixed oils which 
 constitute a part of all protoplasmic material, there are in 
 animals various deposits 6f fat in the muscles, bone marrow, 
 liver, and so-called adipose tissue (Fig. 77). The latter is a 
 mass of cells each composed mainly of a large globule of 
 fat. This adipose tissue usually lies just under the skin. 
 Chemically, fat is composed for the most part of glycerides 
 of stearic, palmitic, and oleic acids, as in the case of plants 
 (Section 14, et seq.}. 
 
 215. Epithelial Tissue. Epithelial tissue lines all the 
 surfaces of the body the skin on the outside and the 
 mucous membrane on the inside, such as the lining of the 
 alimentary canal and body cavities. Such epithelial cells 
 as the hair, nails, hoofs, etc., are composed largely of a 
 protein called keratin which is rich in sulphur. Epithelial 
 cells. of the mucous membrane are largely mucin, a protein 
 which gives this tissue its viscid character. 
 
 216. Connective Tissue. This material serves to bind 
 together the various body parts, and composes the tendons, 
 
 1 Nitrogen compounds, not proteins, soluble in water.
 
 292 THE CHEMISTRY OF ANIMAL PHYSIOLOGY 
 
 cartilage, and such substances. Collagen and elastin are 
 two proteins contained in connective tissue. Gelatine can 
 be prepared from collagen by boiling it in water. 
 
 FIG. 77. Adipose tissue, highly magnified, a, star-like appearance, from 
 crystallization of fatty acids. (Gray.) 
 
 217. Blood. This liquid serves to carry nutrient material 
 to all parts of the body, supplying the various tissues with 
 what they need for growth and repair. It also serves to 
 carry away the waste products of metabolic activity. The 
 blood may be compared roughly to the sap of plants in so 
 far as it supplies soluble food material to various parts of the 
 living organism. The sap of plants, it will be remembered 
 (Section 55), is forced through tracheae up the stem and 
 into the leaves by osmotic pressure or surface tension, or a 
 combination of both; whereas the blood is forced through 
 a system of open canals or vessels to all parts of the animal 
 body by the pressure of a pump which is called the heart. 
 A rhythmic expansion and contraction of muscles around the 
 heart pull the blood in and force it out, thus keeping up a 
 continuous circulation of blood through the vessels. The 
 main channels which bring blood to the heart are called veins, 
 while those carrying blood away from the heart are called
 
 BLOOD 293 
 
 arteries. All the tissues of the body are penetrated by a 
 system of very fine blood-vessels called capillaries, and it is 
 through the walls of these capillaries that the nutrient 
 material passes and thus feeds the cells of the tissues. 
 
 Physically, blood is an opaque, red liquid consisting of a 
 clear colorless solution called plasma holding in suspension 
 several kinds of solids, one of them red in color. These 
 red colored particles are so numerous that they give the 
 blood a red appearance. The suspended solids are red 
 corpuscles, white corpuscles and some other small bodies 
 which need not be considered. 
 
 (a) PLASMA is a clear, transparent, colorless or slightly 
 yellow, partly viscid liquid, consisting largely of water which 
 holds in solution or in suspension proteins, fats, dextrose, 
 lecithin, mineral salts, urea, uric acid, enzymes, and gases. 
 The proteins are principally serum albumin, which is the 
 most important constituent, and is probably the source of the 
 body proteins. Fibrinogen is another protein, and although 
 not present in a large amount, is very important. This will 
 be discussed later under coagulation. Fats are present in 
 minute globules. The inorganic salts are mostly sodium and 
 potassium chlorides, carbonates, sulphates and phosphates, 
 together with calcium and magnesium phosphates. The 
 reaction of the blood is slightly alkaline, because of sodium 
 carbonate and phosphate. Urea and uric acid are waste 
 products. 
 
 (6) RED CORPUSCLES, ERYTHROCYTES, occur in the blood to 
 the extent of about 5,000,000 per cubic millimeter in man. 
 They are disk- or bell-shaped, about 75 microns in diameter 
 (0.0075 mm.) and about 2 microns thick (0.002 mm.) (Fig. 78). 
 They consist of a framework of protein material called 
 stroma and coloring matter called haemoglobin. The latter 
 compound can combine with oxygen, carbon monoxide, and 
 some other gases. It will crystallize, acts as a weak acid, 
 and is composed of a protein called globin and an iron com- 
 pound which is the real coloring matter. Haemoglobin when 
 combined with oxygen is called oxyhsemoglobin. The union 
 is a weak chemical one in the proportion of one molecule 
 of haemoglobin to one molecule of oxygen. The union is
 
 294 THE CHEMISTRY OF ANIMAL PHYSIOLOGY 
 
 apparently a function of the iron, one atom of iron combining 
 with two atoms of oxygen. The oxygen can be removed by 
 means of reducing agents, by merely passing a neutral gas 
 like nitrogen through a solution containing haemoglobin, or 
 by exposure to a vacuum. Haemoglobin is darker red, more 
 purplish in color, than is oxyhaemoglobin, which is bright 
 red. Blood which flows in the veins is darker in color than 
 that which flows in the arteries, there being more haemoglobin 
 in the veins and more oxyhaemoglobin in the arteries. Haemo- 
 globin in the form of oxyhsemoglobin is the oxygen carrier 
 of the blood. As was noted above, carbon monoxide will 
 
 FIG. 78. Human red blood corpuscles. Highly magnified, a, seen from 
 the surface ; b, seen in profile and forming rouleaux ; c, rendered spherical 
 by water; d, rendered crenate by salt solution. (Gray.) 
 
 unite with haemoglobin and the combination is stronger than 
 the combination of oxygen with haemoglobin. Hence in an 
 atmosphere containing carbon monoxide, the oxygen is 
 driven out of combination with the haemoglobin and the 
 carbon monoxide takes its place. This is the cause of carbon 
 monoxide poisoning, since the carrying of oxygen by the 
 haemoglobin is a very necessary function of the blood. 
 
 (c) WHITE CORPUSCLES, LEUCOCYTES, occur in the blood 
 of man to the extent of about 5000 to 10,000 to the cubic 
 millimeter. They are more variable in size and form than 
 the red corpuscles, being 4 to 13 microns in diameter (0.004 
 to 0.013 mm.). They can move by their own processes,
 
 BLOOD 
 
 295 
 
 being somewhat amoeboid in character (Fig. 79). They can 
 pass through the walls of the capillaries and wander through 
 the tissue fluids. These leucocytes are composed of proteins, 
 glycogen, lecithin, fat, and phosphates. They are said to 
 serve as blood scavengers, carry- 
 ing away and absorbing undis- 
 solved substances in the blood 
 such as bacteria. Apparently 
 whenever a wound gives entrance 
 to bacteria the white corpuscles 
 swarm to that place and help to 
 destroy them. Although this fact 
 has not been definitely proved, it 
 is still a reasonable belief. 
 
 (d) COAGULATION. On expos- 
 ure to the air blood clots or coagu- 
 lates, and there is formed a mass 
 of corpuscles matted together 
 with a fibrous substance. The 
 cause of this clotting is not defi- 
 nitely known, but the theory has 
 been advanced that an enzyme 
 with the help of a calcium salt 
 acts on fibrinogen, a soluble pro- 
 tein, changing it to fibrin, an 
 insoluble protein. Fibrin is a 
 white, fibrous material which en- 
 tangles the corpuscles into a clot. 
 The liquid remaining after the 
 clot forms is called serum, and is 
 merely plasma without the fibrin- 
 ogen. By beating fresh drawn 
 blood the fibrin can be obtained 
 free from corpuscles. The speed 
 
 of coagulation is hindered by cold, by a 10 per cent, solution 
 of ammonium oxalate or of sodium chloride. It is hastened 
 by heat, ferric chloride, and alum. Speed of coagulation 
 also varies with animals. The blood of horses clots very 
 slowly. 
 
 FIG. 79. Small blood-vessel, 
 showing how leucocytes pene- 
 trate the wall. (G. Bachman.)
 
 296 THE CHEMISTRY OF ANIMAL PHYSIOLOGY 
 
 (e) GASEOUS EXCHANGE IN THE BLOOD. Reference has 
 been made occasionally to the fact that the blood in 
 one way or another carries oxygen and carbon dioxide. 
 The oxygen is necessary to oxidize 
 dextrose and supply energy to the 
 various tissues. Carbon dioxide is a 
 result of the oxidation of dextrose and 
 must be eliminated. The lungs are the 
 seat of exchange between the oxygen 
 and the carbon dioxide. They are a 
 mass of tissue containing very many 
 minute cells or alveoli surrounded by 
 capillaries. The venous blood coming 
 into the right side of the heart is charged 
 with carbon dioxide. It is forced from 
 there to the lungs where carbon dioxide 
 is given off and oxygen taken in. This 
 renewed blood passes then to the left 
 side of the heart where it is discharged 
 into the arterial system. Fig. 80 gives 
 in diagrammatic form the circulation 
 of the blood. 
 
 The lungs contract and expand by 
 involuntary muscular effort as they 
 exhale and inhale air. From Table 
 XVIII, which gives the composition 
 of 100 volumes of inspired and expired 
 air, it is' to be noted that the inspired air is richer in oxygen 
 than the expired air, and contains much less carbon dioxide 
 and water. 
 
 TABLE XVIII. COMPOSITION OF AIR 
 100 volumes 
 
 FIG. 80. Diagram of 
 blood circulation: L, 
 lung capillaries; c, other 
 capillaries; r, rV, right 
 compartments of heart; 
 /, IV, left compartments 
 of heart. 
 
 Inspired air. 
 
 Oxygen 20.80 
 
 Carbon dioxide. . . . trace 
 
 Nitrogen 79.20 
 
 Water .- .variable 
 
 Expired air. 
 
 Oxygen 16.02 
 
 Carbon dioxide . . . 4.38 
 
 Nitrogen 79.60 
 
 Water . . . . . saturated 
 Organic matter . . trace 
 
 From Table XIX, which gives the composition of 100 
 volumes of arterial and venous blood at and 760 mm.
 
 BLOOD 297 
 
 pressure it can be seen that the arterial blood contains more 
 oxygen and less carbon dioxide than the venous blood. 
 
 TABLE XIX. COMPOSITION OF GASES IN BLOOD 
 
 100 volumes 
 
 Arterial. Venous. 
 
 Oxygen 20 12 
 
 Nitrogen Ito2 Ito2 
 
 Carbon dioxide 40 45 
 
 The blood going into the lungs through the capillaries is 
 charged with carbon dioxide but it does not contain its full 
 quota of oxygen. The inspired air with which this blood 
 comes in contact contains on the other hand an excess of 
 oxygen and little or no carbon dioxide. Consequently, 
 oxygen passes through the capillary walls, dissolves in the 
 blood plasma, and then combines with the haemoglobin to 
 form oxyhsemoglobin. Carbon dioxide meanwhile has been 
 carried in the blood in the form of sodium bicarbonate and 
 dissolved to a slight extent in the blood plasma. The dis- 
 solved carbon dioxide passes through the capillary walls 
 into the lung cells and with the reduction in the amount 
 of dissolved carbon dioxide, sodium bicarbonate breaks up 
 into sodium carbonate and carbon dioxide, the latter pass- 
 ing into the lung cells, as above described. 
 
 The blood, now charged with oxygen and containing less 
 carbon dioxide, passes to the tissues where oxygen is needed. 
 The oxyhsemoglobin now breaks up, oxygen dissolving in the 
 plasma and passing through the capillaries. It oxidizes 
 dextrose with the elimination of carbon dioxide, which passes 
 through the capillaries, first dissolving in the plasma and 
 then combining with the sodium carbonate to form sodium 
 bicarbonate. 
 
 The above gaseous exchange in the lungs and in the 
 tissues is caused by a difference in the pressure of oxygen 
 and carbon dioxide, and is the result of mass action as can 
 be easily seen from the following reversible equations: 
 
 Haemoglobin + Oz ^ Oxyhsemoglobin 
 2NaHCOs ; Na 2 CO + COs + H S O.
 
 298 THE CHEMISTRY OF ANIMAL PHYSIOLOGY 
 
 The carbon dioxide in the veins is under greater pressure 
 than the carbon dioxide in the inspired air. Hence the 
 plasma loses carbon dioxide and sodium bicarbonate breaks 
 up. The partial pressure of the oxygen dissolved in the 
 plasma is less than that of the oxygen in the lungs. Hence 
 more oxygen is dissolved by the plasma and consequently 
 a combination of oxygen with haemoglobin takes place. 
 
 Chemically one volume of oxygen produces one volume of 
 carbon dioxide, but in the case of animal respiration the 
 amount of carbon dioxide evolved is normally less than the 
 amount of oxygen absorbed. This is because some oxygen 
 is used to oxidize the hydrogen of fat to water and to form 
 waste products from proteins like urea. Therefore it does 
 not appear as carbon dioxide. The ratio of carbon dioxide 
 to oxygen by volume is called the respiratory quotient. 
 
 218. Lymph. The tissues of the body are all bathed in a 
 liquid called lymph, or tissue fluid, which serves to bring 
 nutrient material in direct contact with the tissue cells and 
 to carry waste products away from the tissue cells. The 
 various tissues are all in a constant state of building up and 
 tearing down. Changes are constantly taking place. New 
 cells are forming and old ones wearing out. The blood 
 serves as the fluid which carries nutrient material from 
 one part of the body to another and transports waste 
 products of metabolism for elimination. It is carried within 
 the walls of the blood-vessels veins, arteries, and capillaries. 
 Water, soluble compounds, and leucocytes can pass through 
 the walls of the capillaries, and this fluid, which is practically 
 blood plasma, constitutes the lymph. 
 
 Not only are the tissues bathed in lymph but the tissue 
 spaces unite to form lymph vessels which are provided with 
 valves at frequent intervals to prevent the fluid from flowing 
 backward. These vessels permeate the body in every direc- 
 tion in a network, and combine sooner or later into the 
 thoracic duct (Fig. 82, th.d.), a large lymph vessel running 
 through the left side of the centre of the body and emptying 
 into the venous system at the left side of the base of the 
 neck. At intervals along the lymph vessels are enlargements 
 called lymph glands which serve among other things as a 
 principal source of white corpuscles.
 
 ANIMAL COMPOUNDS 299 
 
 Pressure caused by blood plasma being forced out of the 
 capillaries, possibly contraction of lymph vessels, and par- 
 ticularly muscular exercise, all serve to force lymph along 
 its vessels so that a continuous -stream is poured into the 
 veins from the thoracic duct. 
 
 Lymph being essentially blood plasma is a clear to opales- 
 cent liquid, slightly alkaline in character, containing proteins, 
 dextrose, sodium chloride and carbonate, some other salts, 
 white corpuscles, and a small amount of fibrinogen. It 
 also contains oxygen and carbon dioxide dissolved in it, 
 although part of the latter is combined with sodium car- 
 bonate. The proportion of the various constituents is not 
 quite the same as that in blood plasma and varies from 
 one part of the body to another according to the needs of 
 the body. 
 
 219. Animal Compounds. Many of the animal compounds 
 are the same as those in plants, but there are some differences, 
 enough to warrant a brief review of the subject. In this 
 discussion, of course, no attention is paid to compounds 
 eaten by the animal for food only those compounds 
 actually absorbed and utilized by the animal. For conveni- 
 ence in comparison, the same order will be observed as in 
 Chapter I on Plant Compounds. 
 
 (a) CARBOHYDRATES. Of the many carbohydrates known 
 only three are of importance in the animal. 
 
 1. Dextrose, already described, Section 3. It is found in 
 blood, liver, muscles, and other tissues, serving as a source of 
 energy by its oxidation, and also as a source of fat (Section 
 224, a). 
 
 2. Glycogen, Animal Starch (C6HioO 8 ) n . It is a white, 
 amorphous, tasteless powder, dissolving in water to an 
 opalescent solution, and giving a dark red color with iodine. 
 On hydrolysis with mineral acids or with amylolytic enzymes 
 it yields dextrose. The liver is the principal repository of 
 glycogen, containing from 1 to 4 per cent. The liver produces 
 glycogen from dextrose, levulose, and probably galactose, 
 the forms of soluble carbohydrates absorbed. As needed by 
 the body the liver reproduces dextrose. Glycogen is also 
 found in the muscles to a maximum extent of 1 per cent.
 
 300 THE CHEMISTRY OF ANIMAL PHYSIOLOGY 
 
 Like starch in the plant, glycogen in the body is the concen- 
 trated, dehydrated form of storage carbohydrate material in 
 the animal. 
 
 3. Lactose. This is found in milk and will be described 
 in Section 228, a. 
 
 4. Cellulose and Crude Fiber are not found in animals as in 
 plants. 
 
 (6) FATS. The fats are very much the same as in plants. 
 Their general properties are the same, but there are a few 
 animal fats and oils which deserve mention. 
 
 1. Tallow is the name given to certain animal fats, more 
 or less hard in character and extracted or "rendered" from 
 adipose tissue by melting out the fat to free it from the 
 protein membranes. It is almost white when pure and nearly 
 tasteless. It is composed of mixed glycerides of stearic, 
 palmitic, and oleic acids in varying proportions, the com- 
 mercial grades usually containing free fatty acids due to 
 hydrolysis of the glycerides. Beef tallow or beef fat is softer 
 than mutton tallow. The former is used for making oleomar- 
 garine (Section 232) and as an adulterant of lard in addition 
 to its use as a food. The latter is employed in the making 
 of soap, candles, and lubricants besides being used as a food. 
 
 2. Lard is the fat of pigs, and is obtained by rendering, 
 as in the case of tallow. It is composed of the glycerides of 
 stearic, palmitic, oleic, myristic, lauric, linoleic, and possibly 
 linolenic acids. 
 
 3. Neatsfoot Oil is made from the feet and shin bones of 
 cattle by boiling them in water. The oil rises to the surface and 
 is skimmed off. It is pale yellow in color, consisting chiefly 
 of olein with some palmitin and stearin. In leather dressing 
 and as a lubricant it finds its chief uses. 
 
 4. Codlicer Oil is extracted from the liver of the cod, pure 
 varieties being used in medicine, and other kinds in tanning. 
 Its composition is very complex, containing in addition to 
 the glycerides of myristic, palmitic, stearic, oleic, and erucic 
 acids, fats of two new acids. 
 
 5. Menhaden Oil is obtained from the whole body of the 
 menhaden fish by boiling in water and expressing. It finds 
 various uses, as in soap making and tanning.
 
 ANIMAL COMPOUNDS 301 
 
 6. Sperm Oil is not a true oil, being a liquid wax (Section 
 21), or compound of fatty acids, principally oleic, with 
 monohydric alcohols. It is obtained from the head cavities 
 of the sperm whale. On cooling it deposits crystals of sperm- 
 aceti, a solid wax. Sperm oil is a most excellent lubricant. 
 Spermaceti is used in making candles and in medicine. 
 
 7. Beeswax is the substance from which honey-comb is 
 made, being manufactured by the bees. It is a tough, com- 
 pact mass, yellow or brownish in color. It is not greasy 
 to the touch. In composition it is a wax, containing com- 
 pounds of palmitic, cerotic, and melissic acids with mono- 
 hydric alcohols, and in addition some higher hydrocarbons. 
 
 8. Volatile Oils are not found in animals. 
 
 (c) NITROGENOUS COMPOUNDS. These are for the most 
 part proteins, which differ somewhat from plant proteins. 
 Most of the knowledge of proteins is derived from a study 
 of these compounds in the animal. They have been classified, 
 their properties observed and tests described, but their 
 study is too complex and technical for a work of this kind. 
 As occasion arises various proteins will be named and briefly 
 described. Other nitrogenous compounds, as amino-acids 
 and ammonium compounds, occur as transition products. 
 
 (d) ORGANIC ACIDS are not a normal part of the animal 
 body, except as by-products of metabolic activity, as, for 
 example, sarcolactic acid in active muscle, and uric acid- 
 waste material in the blood. 
 
 (e) COMPOUNDS OF THE INORGANIC ELEMENTS. In the 
 plant inorganic compounds exist merely as transitory food 
 materials absorbed by the roots. The so-called inorganic 
 elements are combined organically for use by the plant 
 either as an integral part of its tissue or as a sort of helping 
 compound for tissue formation. In the animal, however, 
 inorganic compounds play a very important part. They can 
 best be taken up by elements. 
 
 1. Compounds of Phosphorus. Calcium phosphate, 
 Ca 3 (PO4)2, exists in bones and teeth, and CaH 4 (PO02 in 
 the tissue fluids. In the bones and teeth it gives solidity 
 to the organs. It is associated with magnesium phosphate, 
 Mg 3 (P0 4 ),.
 
 302 THE CHEMISTRY OF ANIMAL PHYSIOLOGY 
 
 Sodium phosphate, Na 2 HPO4, is found in all the solids 
 and fluids of the body, giving an alkaline reaction to the 
 latter. It is associated with potassium phosphate, K 2 HPO.i, 
 with similar properties. 
 
 2. Compounds of Potassium. Potassium chloride, KC1, 
 occurs together with sodium chloride in all the tissues and 
 fluids of the body, being present, however, to a greater 
 extent in the tissues than in the fluids. 
 
 Potassium carbonate, K 2 COs, is found with potassium 
 phosphate, which is mentioned above. 
 
 3. Compounds of Calcium. Calcium phosphate, mentioned 
 above. 
 
 Calcium carbonate, CaCO 3 , occurs together with calcium 
 phosphate in various parts of the body, and fulfills appar- 
 ently the same functions. In the tissue fluids it occurs as a 
 bicarbonate, CaH 2 (CO 3 ) 2 . 
 
 Calcium fluoride, CaF 2 , is found in the bones and teeth. 
 
 4. Compounds of Iron are organic in nature, occurring in 
 haemoglobin, in the lymph, bile, gastric juice, and in the 
 coloring matter of the eyes, hair, and skin. 
 
 5. Compounds of Sodium. Sodium chloride, NaCl, is 
 present in all the tissues and fluids of the body, particularly 
 in the latter. The blood contains 0.6 per cent., lymph 
 0.5 per cent. Its function apparently is to maintain osmotic 
 equilibrium between the cells and the fluids of the body, 
 regulating the intake of water to the former. In pure water 
 the tissue cells swell rapidly and die. The presence of sodium 
 chloride in water prevents too rapid entrance of water 
 to the cells. On this account in investigating living tissue 
 it is customary to use a physiological salt solution which 
 is a 0.6 per cent, solution of sodium chloride. Sodium 
 chloride is also the source of chlorine for potassium chloride 
 mentioned above and also for the hydrochloric acid of the 
 gastric juice mentioned below. 
 
 Sodium phosphate, mentioned above. 
 
 Sodium carbonate, Na 2 CO 3 , found together with sodium 
 phosphate, and serves also to give alkalinity to the tissue 
 fluids. When combined with carbon dioxide it exists in the 
 form of sodium bicarbonate, NaHCO 3 .
 
 REFERENCES 303 
 
 6. Compounds of Chlorine. Sodium chloride and Potassium 
 chloride, mentioned above. 
 
 Hydrochloric acid, HC1, is found in small amounts in the 
 gastric juice of the stomach where it aids in the enzyme 
 activity of digestion. 
 
 7. Compounds of Iodine are found in organic form in the 
 thyroid gland of man. 
 
 8. Compounds of Silicon occur in organic form in the hair. 
 
 EXERCISES 
 
 1. Which of the following are found only in plants, only in animals, in 
 both: Silicon, enzymes, iron, glycogen, urea, crude fiber, ossein, fibrinogen, 
 lymph, fats? 
 
 2. Do animals or plants contain more of each of the following: Water, 
 carbohydrates, fats, proteins and ash? 
 
 3. Are bones living material? Why or why not? 
 
 4. Suggest a possible function for each of the substances found in muscle 
 tissue. 
 
 5. Mention the differences in the properties of the protein that constitutes 
 epithelial tissue and that which constitutes muscle tissue. 
 
 6. What is the difference between blood and lymph? What is the chief 
 function of each? 
 
 7. Suppose blood was lacking in each of the following, what could it not 
 do: Leucocytes, a calcium salt, haemoglobin, sodium bicarbonate, dis- 
 solved carbon dioxide, dissolved oxygen, dextrose, amino-acids, fibrinogen 
 and urea? 
 
 8. What is the chief function of each of the following in animals: Glyco- 
 gen, protein, fat, compounds of metallic elements, and water? 
 
 9. Show by equations and calculations that the respiratory quotient of 
 carbohydrates is equal to 1 and that of fats to 0.7. 
 
 10. Can you suggest any value of the respiratory quotient? 
 
 REFERENCES 
 
 Brubaker. Text Book of Physiology. 
 Hawk. Practical Physiological Chemistry. 
 Smith. Manual of Veterinary Physiology. 
 Starling. Human Physiology.
 
 CHAPTER XVIII 
 FOOD AND DIGESTION 
 
 ONE of the principal differences between plants and 
 animals is the manner of food absorption. Plants must 
 have their food 'dissolved on the outside before they can take 
 it into their circulatory system. Animals can take in in- 
 soluble food and make it soluble within themselves before 
 absorbing it into their circulatory system. For a proper 
 understanding of the principles of feeding it is necessary to 
 know something of the chemical processes by which foods 
 are made soluble in the animal and of their functions after 
 absorption. 
 
 220. Food. Sherman defines food as "those substances 
 which supply the body either with material needed for its 
 substance, or with energy for its activities." Sometimes a 
 distinction is made between the food of human beings and 
 the food of animals. This is a distinction in terminology 
 only, food of domestic animals being called feed as distinct 
 from food which is applied to human foods only. Since the 
 processes of digestion and the main constituents of food 
 are the same for man as for domestic animals, no distinction 
 will be made in this chapter, all the material considered 
 being called food. 
 
 The tissues of the animal body are in a constant state of 
 change, new tissue being formed, old tissue being broken 
 down. These chemical processes of building up and tearing 
 down are called metabolism. Food supplies the material 
 for constructive metabolism anabolism. For the chemical 
 changes of metabolism in general, for the production of 
 heat and work in the animal, energy is necessary. Food 
 supplies the necessary material for this energy, which is a 
 result of destructive metabolism katabolism. A compara- 
 tively small part of the food required for animals is neces- 
 (304)
 
 DIGESTION 305 
 
 sary in repairing and building tissue, the greater portion of 
 the food being utilized in the production of energy. 
 
 221. Food Constituents. Food in general is composed of 
 different kinds of material, every one of which is separately 
 digested and absorbed in the animal and which serves 
 special functions in the body. These constituents are: 
 Carbohydrates, fats, proteins, and inorganic salts, not to 
 mention water which, strictly speaking, should be consid- 
 ered a food constituent; but since it is mixed with all food 
 constituents and since its presence is necessary for their 
 solution and absorption, it will not be necessary to consider 
 it separately. 
 
 222. Digestion. The processes by w r hich insoluble food 
 Materials are rendered soluble for absorption into the blood 
 of animals are called digestion. Digestion takes place in the 
 various parts of the alimentary canal, which consists prin- 
 cipally of the mouth, stomach, and small intestine. There 
 are connected with these various parts of the alimentary 
 canal certain appendages, which are necessary for the various 
 activities qf the food canal. Since digestion occurs in three 
 places and under three different kinds of conditions, it is ad- 
 visable to separate the discussion of these processes into three 
 parts: Salivary, gastric, and intestinal digestion. 
 
 (a) SALIVARY DIGESTION. The first process is one of masti- 
 cation, which serves to grind the solid food into more or less 
 fine particles so that the digestive juices can act on them to 
 better advantage. While the food is being masticated, there 
 is poured into the mouth from three different pairs of glands 
 a liquid called saliva, which serves mechanically to combine 
 the fine particles of food together so that they may be more 
 easily swallowed, and also to act chemically on some of the 
 food constituents. Saliva is a slightly turbid, opalescent, 
 somewhat viscid liquid which is composed almost entirely 
 of water, but with some soluble organic matter, inorganic 
 salts, and an enzyme called ptyalin. It is slightly alkaline 
 in character, due to the presence of sodium carbonate. The 
 enzyme ptyalin or salivary amylase is the active digestive 
 agent in the mouth. It acts on starch, changing it first to 
 dextrins and then to maltose. The process is hydrolytic in 
 20
 
 306 FOOD AND DIGESTION 
 
 character and in every way is similar to the amylolytic 
 action of diastase in seeds. The slightly alkaline character 
 of saliva is necessary for the activity of ptyalin. It does not 
 function in strong alkalies or acids. No other constituents 
 are acted upon in the mouth and not all of the starch is 
 rendered soluble. Food material, now united into a moist 
 ball, is swallowed and passes into the stomach where the 
 next change takes place. 
 
 (6) GASTRIC DIGESTION. In man, horses, and pigs, there is 
 but one stomach, but in the ruminants, like cattle and sheep, 
 there are four stomachs, or at least four compartments to the 
 stomach. Animals of this type "chew the cud," and food 
 passes from the mouth to the first and second compartments 
 of the stomach, is then forced back into the mouth for further 
 mastication, and then after swallowing is passed finally 
 through the third stomach into the fourth for final digestion. 
 The repeated mastication of food by these animals merely 
 serves to completely comminute the food and thoroughly 
 prepare it for digestion. In this way such animals are able 
 to digest fibrous material to a much greater extent than 
 other animals, like the horse. They can digest more crude 
 fiber and cellulose in this way because these insoluble food 
 constituents are so. thoroughly separated and ground up 
 that bacteria and possibly the digestive juices can act on 
 them successfully. In the following discussion of gastric 
 digestion, it will be understood that the processes described 
 apply in the case of ruminants to the fourth stomach only. 
 
 After the food reaches the stomach it is mixed with the 
 gastric juice, which is secreted by glands in the walls of the 
 stomach and is poured out when the food reaches the stomach. 
 The process of excretion of gastric juice is partly one of 
 response to a mechanical stimulus due to the contact of 
 food with the stomach; partly to psychic impulse caused by 
 the sight or odor of food; and partly in response to nerve 
 impulses when food is masticated. The gastric juice is 
 thoroughly incorporated with the food by to and fro move- 
 ments of the stomach. Gastric juice is a clear, colorless 
 liquid with a distinctly acid reaction, due to the presence of 
 about 0.2 per cent, hydrochloric acid. It consists largely of
 
 DIGESTION 307 
 
 water with a little organic matter and mineral salts besides 
 the hydrochloric acid just mentioned. In addition there 
 are present two enzymes: Pepsin and rennin. When the 
 food first enters the stomach it is alkaline in character due 
 to the admixture of saliva. The action of ptyalin continues 
 as long as the reaction is alkaline. As soon as the food 
 becomes thoroughly mixed with the acid gastric juice the 
 action of ptyalin ceases. 
 
 The enzyme pepsin, for the action of which the acid solution 
 is necessary, hydrolyzes proteins to proteoses and peptones 
 which are soluble decomposition products of proteins. Not 
 all of the proteins are acted upon in this way, for the food 
 does not remain in the stomach long enough for the com- 
 plete solution of all proteins to take place. This solvent 
 action of pepsin is also of secondary importance in that it 
 dissolves the protein cell walls of fats, thus disintegrating 
 fatty material and setting free the drops of fat. 
 
 Rennin, the other enzyme in the stomach, acts on the 
 caseinogen of milk (Section 228, c), which is a soluble com- 
 pound, changing it or "curdling" it to a solid compound, 
 casein. Just why this is necessary is not apparent. After 
 the change takes place the coagulated casein is dissolved by 
 the pepsin. No other food constituents are acted upon in 
 the stomach. There is no evidence that the hydrochloric 
 acid inverts sucrose, as might be expected (Section 5). 
 The combined action of water, hydrochloric acid, and pepsin, 
 together with the mixing and churning motions of the 
 stomach has now changed the solid elements of food material 
 to a semi-liquid form called chyme. 
 
 (c) INTESTINAL DIGESTION. The chyme is discharged into 
 the small intestine where the next processes of digestion 
 take place. The food material here is mixed with three 
 different fluids, intestinal juice, pancreatic juice, and bile. 
 
 Intestinal juice is secreted by certain glands in the walls 
 of the small intestine and is a watery, light yellow, slightly 
 opalescent, alkaline liquid, containing at least carbonates. 
 Because it is very difficult to obtain it in the pure state, its 
 composition is not accurately known except that it does 
 contain certain enzymes which are active in hydrolyzing
 
 308 FOOD AND DIGESTION 
 
 some of the carbohydrates. Inrertase changes sucrose to 
 dextrose and levulose; maltose changes maltose to dextrose; 
 and lactose changes lactose to dextrose and galactose. 
 
 Pancreatic juice is secreted by the pancreas, which is a 
 long flattened gland, and is discharged into the intestine 
 like the intestinal juice when food reaches the stomach. 
 Pancreatic juice is a clear, viscid, decidedly alkaline liquid, 
 containing in addition to water a little organic matter and 
 inorganic salts of which sodium carbonate is the most 
 important and which gives alkalinity to the juice. Pan- 
 creatic juice contains the principal digestive enzymes of the 
 alimentary canal. 
 
 Amylopsin is the pancreatic amylase which hydrolyzes 
 starch to maltose, being much more energetic in action than 
 ptyalin. An alkaline solution is necessary for it to act. 
 
 Steapsin is the pancreatic lipase which hydrolyzes fat 
 to glycerine and fatty acids. The fatty acids thus liberated 
 unite with the alkalies which are present in the juice of the 
 intestine to form soaps. It is not definitely known whether 
 all fats are thus hydrolyzed or whether a part of the fat is 
 so changed and the remainder emulsified in the soap solution. 
 The former is the more probable, however. This enzyme 
 also is only active in an alkaline solution. 
 
 Trypsin is the pancreatic protease which hydrolyzes 
 proteins in the alkaline medium and changes them to pep- 
 tones and usually to amino-acids. Trypsin is much more 
 energetic in its action than is pepsin in the stomach and the 
 probabilities are that it hydrolyzes the proteins more com- 
 pletely. 
 
 Bile is a fluid secreted by the liver and discharged into 
 the small intestine together with intestinal juice and pan- 
 creatic juice when food is received into the stomach. It is 
 a thin liquid somewhat viscid, of bitter taste, and very 
 alkaline due to the presence of sodium carbonate and sodium 
 phosphate. It varies in color from greenish yellow to 
 brownish red, depending on the animal. In herbivorous, or 
 plant-eating animals, it is greenish in color; in carnivorous, 
 or meat-eating animals, it is orange or brown. There are 
 present in the bile in addition to the normal secretory
 
 ABSORPTION OF FOOD CONSTITUENTS 309 
 
 compounds some excretory or waste compounds such as 
 cholesterin and lecithin. They are supposed to be decom- 
 position products of the nerve tissue and are eliminated 
 from the blood stream through the liver. The bile has no 
 direct solvent action on any of the food constituents, but 
 its action decidedly increases the power of the pancreatic 
 enzymes and it serves as the principal solvent for the fatty 
 acids in the formation of soaps. 
 
 In addition to the normal enzyme secretions of the body 
 which have a solvent action on food constituents, there are 
 ordinarily present in animals large numbers of bacteria, 
 principally in the intestines. Their presence is not necessary 
 for the decomposition and solution of food constituents, 
 but it is probable that their fermentative action is in some 
 cases of benefit in digesting food. 
 
 Food material which has been acted upon by the various 
 chemical agents is rendered soluble and ready for ab- 
 sorption. Not all of it, however, can be dissolved. Par- 
 ticularly do crude fiber and cellulose remain unattacked 
 except in the case of some of the domestic animals, more 
 particularly the ruminants, where these food constituents 
 are partly digested, due probably to the activity of bacteria. 
 The undigested portion of the food is discharged into the 
 large intestine for final elimination. 
 
 223. Absorption of Food Constituents. The absorption of 
 the various constituents of the food is limited almost wholly 
 to the small intestine, little if any being absorbed from the 
 mouth or stomach into the circulatory system. The interior 
 of the small intestine is covered with minute conical projec- 
 tions called mlli (Fig. 81), through which all the dissolved 
 material is absorbed. They serve the same purpose in the 
 animal that the root hairs do in the plant, but they differ 
 in that they are not each one a single cell but a large number 
 of cells containing blood capillaries and lymph vessels, which 
 carry the absorbed material into the general circulator}' 
 system. 
 
 The carbohydrates in the form of dextrose, levulose, and 
 possibly galactose are absorbed through the outer cells of the 
 villi into the capillaries, which finally unite into the portal
 
 310 
 
 FOOD AND DIGESTION 
 
 vein and discharge into the liver. In the liver the carbo- 
 hydrates are changed into glycogen until such time as 
 dextrose is needed in the blood, when the glycogen is trans- 
 formed into dextrose. Enzymes in the liver accomplish the 
 dehydration change to glycogen as well as the hydrolytic 
 change to dextrose. 
 
 Central lacteal 
 
 Artery 
 
 FIG. 81. Diagrammatic section through villi of small intestine. 
 Bohm and Davidoff, after Mall.) 
 
 (From 
 
 Fats are probably absorbed as glycerine and soaps, 
 although possibly also in the form of emulsified fats, and pass 
 through these outer cells of the villi into the lymph vessels or 
 lacteals. During the process of this absorption the glycerine 
 unites with the fatty acids of the soaps to form fats, so that 
 the lymph as it leaves the villi is charged with liquid globules 
 of fat to such an extent as to give it the appearance of milk. 
 The lymph vessels join the thoracic duct from which the 
 fatty particles are discharged into the veins and thus get 
 into the general circulatory system of the blood. 
 
 The proteins chiefly in the form of amino- acids are 
 absorbed into the blood-vessels of the villi, during which 
 process they combine to form the serum-albumin and globulin
 
 FUNCTIONS OF FOOD CONSTITUENTS 311 
 
 of the blood. These are the forms of protein which are trans- 
 ported through the body. The proteins pass into the portal 
 vein and through the liver, but are not arrested there as are 
 the carbohydrates, unless in excess when they are changed 
 to carbohydrate and urea. 
 
 Water and inorganic salts which have been set free from 
 their organic combination in foods by the various processes 
 of digestion are absorbed through the villi into the capillaries. 
 Under ordinary conditions no water is absorbed by the 
 lymph vessels. The progress of water and inorganic salts 
 is then like that of carbohydrates and proteins, through the 
 portal vein and the liver. Fig. 82 shows the routes of the 
 absorbed material. 
 
 224. Functions of Food Constituents. Various constituents 
 of the food after absorption into the body, serve each a more 
 or less distinct function in the activity of the animal and 
 can be discussed separately. 
 
 (a) CARBOHYDRATE. The only active form of carbohy- 
 drate in the body is dextrose and this material serves primarily 
 as a source of energy. Just as energy is derived in the steam 
 engine from the combustion of fuel so is the energy of the 
 body derived from combustion of fuel. This combustion 
 takes place within the tissues of the body and is caused 
 by enzymes, the final product being carbon dioxide and 
 water. Energy is set free in the form of heat and work. 
 When dextrose is present in larger quantities than is necessary 
 for fuel consumption it is transformed into fat and stored 
 away in the adipose tissue of the body. 
 
 (6) FAT serves also as fuel for body energy and is 
 the most concentrated source of fuel in the body, yielding 
 more energy per unit of weight than any other form of fuel. 
 Some of the fat absorbed is deposited in adipose tissue, and 
 there is some evidence that dextrose may be formed from fat. 
 
 (c) PROTEIN. The primary function of protein is, of 
 course, to supply the principal part of tissue material. It is 
 necessary for cell walls and protoplasmic contents of new 
 cells and also to replace worn out material in old cells. 
 Changes are constantly taking place in the body; old cells 
 wearing out, new cells being formed, in addition to increase 
 in the number of cells when an animal is growing. Protein
 
 FIG. 82. Diagram showing the routes by which the absorbed foods reach 
 the blood of the general circulation. (G. Bachman.) I. i., loop of small 
 intestine; int. v., intestinal veins converging to form in part, p. v., the portal 
 vein, which enters the liver and by repeated branchings assists in the forma- 
 tion of the hepatic capillary plexus; h. v., the hepatic veins carrying blood 
 from the liver and discharging it into, inf. v. c., the inferior vena cava; 
 int. I. v., the intestinal lymph vessels converging to discharge their contents, 
 chyle, into, rec. c., the receptaculum chyli, the lower expanded part of the 
 thoracic duct; th. d., the thoracic duct discharging lymph and chyle into the 
 blood at the junction of the internal jugular and subclavian veins; sup. v. c., 
 the superior vena cava. Brubaker's Physiology.
 
 HOW TO EXPRESS FOOD VALUE 313 
 
 also serves as a source of fuel in the body, particularly when 
 dextrose and fat are not present in sufficient amount. 
 The products of protein oxidation, however, in addition to 
 carbon dioxide and water, are nitrogenous compounds, 
 largely urea. The protein compounds can also be split 
 up in the body into a nitrogenous and a non-nitrogenous 
 residue. From the non-nitrogenous residue carbohydrates 
 can be formed and there is some evidence to show that fat 
 may also be formed. The nitrogenous residue is eliminated 
 as waste material. 
 
 (d) INORGANIC ELEMENTS. These constituents in mineral 
 form give rigidity to the skeleton. They serve also as neces- 
 sary constituents of protoplasm, sulphur and phosphorus, for 
 example, and are combined organically for this purpose. 
 Finally, these elements in the form of inorganic salts are 
 present in the fluids and tissues of the body, having an 
 influence upon the activities of the muscles and nerves, 
 supplying an alkaline or acid reaction as may be necessary, 
 and regulating the osmotic pressure of the cells. 
 
 225. How to Express Food Value. As has been stated 
 (Section 222, c), not all of the food taken in by the animal is 
 absorbed, and of course, that portion which is not digested is 
 of no use to the animal. It is customary to express the 
 amount of digestible material in each constituent in per- 
 centage. These "digestible coefficients," as they are called, 
 are determined by analyzing the original food and also by 
 analyzing all excreted waste products. The difference 
 between the two sets of results gives the percentage of food 
 digested, and hence serves as an indication of the amount 
 of tissue building or energy material in the food eaten. 
 The results, however, are not absolutely correct for several 
 reasons. In the first place the excreted material contains 
 protein and ether soluble material called fat, derived from 
 the intestinal juices and w r aste cells of the intestines. 
 In the second place, unless there is an analysis of all the 
 gas eliminated from the body there is a waste of some 
 material in this way that is unaccounted for. In the third 
 place, if it is desired to determine the value of the food for 
 the production of work or milk or fat, it is necessary to
 
 314 FOOD AND DIGESTION 
 
 take into consideration the food constituents which are 
 consumed by the involuntary activities of the body. An 
 animal absolutely at rest or asleep is constantly using up 
 food constituents. The beating of the heart, expansion and 
 contraction of the lungs, movements of the digestive ap- 
 paratus are going on constantly. When food is masticated 
 work is done and the oxidation of body fuel is necessary to 
 obtain this energy. 
 
 Most of the food taken in by the animal is used up in the 
 production of energy, and since energy can be expressed in 
 terms of heat, it is customary to value food on the basis of 
 heat equivalents. Since the combustion of food material 
 in the body results in the production of exactly as much 
 heat as is derived from the combustion of the same con- 
 stituents in the air, it is possible to determine the fuel value 
 of foods by well known methods of analysis. And, finally, 
 since an apparatus has been devised for determining the 
 energy value of foods in the animal, and at the same time 
 permitting a complete analysis of all food income and outgo, 
 it is possible to overcome in large measure the defects just 
 mentioned for determining the value of foods. 
 
 For the determination of the heat value of substances, 
 an instrument called a calorimeter is used, which consists 
 essentially of a closed chamber in which organic material 
 can be burned in an atmosphere of oxygen and the resulting 
 heat accurately measured by the rise in temperature of a 
 surrounding body of water after making certain necessary 
 corrections. Modern scientific ingenuity has gone one step 
 further and devised calorimeters which will contain a 
 living animal and in this way the amount of heat developed 
 by the combustion of food in the body can be accurately 
 measured. In addition these animal calorimeters are 
 equipped with elaborate apparatus for measuring the intake 
 of oxygen and the output of carbon dioxide and other gases. 
 These factors, together with the weighing and analyzing 
 of all foods consumed and all solid and liquid material 
 excreted, make it possible by a series of calculations to 
 arrive very accurately at the proper value of any food for 
 any particular animal. The respiration calorimeter devised
 
 HOW TO EXPRESS FOOD VALUE 
 
 315 
 
 by Armsby of the Pennsylvania Station is the most complete 
 apparatus of this kind in existence. Fig. 83 shows the 
 apparatus from the outside.
 
 316 FOOD AND DIGESTION 
 
 The unit for expressing food values in terms of heat is 
 the large Calorie which is the amount of heat necessary to 
 raise the temperature of 1000 grams of water 1 C. For many 
 purposes, however, this unit is not large enough for con- 
 venience and as a result the unit therm is now in use by 
 Armsby. A therm is the quantity of heat necessary to raise 
 the temperature of 1000 kilograms of water 1 C., and it is 
 customary in expressing the value of food to do so as therms 
 per 100 pounds. 
 
 226. Feeding Standards. Ever since the functions of the 
 various food constituents in animal metabolism have been 
 known there has been a desire to determine scientifically the 
 amount of these constituents necessary for various classes 
 of animals and for various purposes. As a result we have 
 the so-called "feeding standards," which are based on 
 analytical and experimental data. The accurate obser- 
 vations of Armsby with his respiration calorimeter now make 
 it possible to establish standards which are reasonably 
 correct. Although even so, our knowledge is not by any 
 means perfect. The question of the proper feeding of stock, 
 and what should be more important the proper feeding of 
 man, is too large a one to be considered here. For further 
 information along this line the reader is directed to the 
 references given at the end of the chapter. 
 
 EXERCISES 
 
 1. Does the action of ptyalin form diffusible products from starch? If 
 not, what enzyme does do so? Where is each secreted? What kind of a 
 medium is required by each? When will ptyalin stop acting and when 
 will the other enzyme begin acting? 
 
 2. What causes an animal's mouth to water? Of what value is this 
 phenomenon? 
 
 3. Is hydrolysis of fat sufficient to make diffusible products? Why or 
 why not? 
 
 4. Why is it wise to chew food? 
 
 5. Can you suggest whether or not drinking water at meal time is a good 
 practice? 
 
 6. What are the three functions of bile? 
 
 7. What happens to each of the six groups of the Weende method (Chap. 
 IV) in the passage of food through the digestive tract? 
 
 9. What is the function of digestion?
 
 REFERENCES 317 
 
 REFERENCES 
 
 Armsby. Principles of Animal Nutrition and The Nutrition of Farm 
 Animals. 
 
 Brubaker. Text Book of Physiology. 
 
 Halligan. Elementary Treatise on Stock Feeds and Feeding. 
 
 Henry. Feeds and Feeding. 
 
 Jordan. The Feeding of Animals. 
 
 McCollum: The Newer Knowledge of Nutrition. 
 
 Sherman. Chemistry of Food and Nutrition. 
 
 Smith. Manual of Veterinary Physiology. 
 
 Starling. Human Physiology.
 
 CHAPTER XIX 
 MILK AND DAIRY PRODUCTS 
 
 THE most valuable products of the animal are milk and its 
 derivatives. Most of these materials are used as food for 
 man. Milk in particular, as Hawk says, is the most satis- 
 factory individual food material elaborated by nature, in 
 that it contains protein, fat, and carbohydrate in addition 
 to mineral matter, all combined in such form and proportion 
 as to make it palatable, nourishing, and easily digested. 
 The following discussion applies solely to milk from CGWS, 
 since that has been most studied and since milk from other 
 animals differs from it only in the proportion of the various 
 constituents. 
 
 227. Physical Appearance. Milk is a white, opaque 
 liquid, the specific gravity of which is about 1.03, with a 
 slightly sweet, pleasing taste, and a freezing point of 0.56 C. 
 Its color is due to minute particles of fat in suspension and 
 also to the presence of a protein, caseinogen, in pseudo- 
 solution. 
 
 228. Chemical Composition. Milk is composed of a clear, 
 aqueous solution of carbohydrate, inorganic salts, and 
 protein, in which are suspended fat globules, calcium phos- 
 phate, and a protein in semi-suspension. The average com- 
 position is as follows: Water, 87.75 per cent.; fat, 3.4 per 
 cent.; protein, 3.5 per cent.; carbohydrate, 4.6 per cent.; 
 and inorganic salts, 0.75 per cent. 
 
 (a) CARBOHYDRATE. Lactose is the only carbohydrate 
 present in milk sugar. It is an aldose sugar whose formula is 
 Ci 2 H 22 On, graphically:
 
 CHEMICAL COMPOSITION 319 
 
 H C O H H C = O 
 
 I I 
 
 H C O H H C O H 
 
 I 
 
 H C O- 
 
 O H 
 
 H C O H 
 
 H C O H 
 
 I 
 H C O H 
 
 H C C H 
 
 I 
 
 It is dextrorotatory and reduces Fehling's solution, although 
 to a less extent than dextrose. It is hydrolyzed by enzymes 
 and acids to dextrose and galactose. It does not undergo 
 ordinary alcoholic fermentation except under the influence 
 of certain yeasts. The principal change in lactose is due 
 to the so-called lactic bacteria which hydrolyze it to lactic 
 acid, thus: 
 
 CizEtaOu + H 2 O = 4CsH 6 O3. 
 
 It is this lactic acid to which is due the taste of sour milk, 
 and it is produced so quickly that ordinary milk contains 
 about 0.2 per cent, of lactic acid. The taste is apparent 
 w T hen the proportion rises to 0.4 per cent., and at 0.7 per cent, 
 milk "curdles." Curdling is due to the coagulation of case- 
 inogen (see below). The percentage of lactic acid rarely 
 rises above 2 because in that amount the action of the 
 lactic acid bacteria is inhibited. Lactose is only one-tenth 
 as sweet as sucrose. 
 
 (6) FAT in milk is, of course, like other fixed oils 
 in that it is composed of glycerides of fatty acids. Milk 
 fat differs from other animal fat in that it contains the gly- 
 ceride of a number of lower fatty acids, there having been 
 found the following:
 
 320 MILK AND DAIRY PRODUCTS 
 
 Butyric, C 3 H 7 COOH 
 
 Caproic, C 5 H n COOH 
 
 Caprylic, C,H 15 COOH 
 
 Capric, aHuCOOH 
 
 Laurie, CnH 23 COOH 
 
 Myristic, C 13 H 27 COOH 
 
 Palmitic, C 15 H 31 COOH 
 
 Stearic, C 17 H 35 COOH 
 
 Oleic, C 17 H 33 COOH 
 
 Dihydroxystearic, C 17 H 33 (OH) 2 COOH 
 
 In general, oleic and palmitic acids are present to the greatest 
 extent. The fats from butyric, caproic, caprylic, and oleic 
 acids are liquid. The fats from the other acids are solid. 
 The first four mentioned fatty acids are soluble in water 
 and volatile in steam. All the acids are saturated with the 
 exception of oleic. Milk fat is soluble in the usual solvents : 
 Ether, carbon disulphide, acetone, and liquid hydrocarbons. 
 
 Milk fat occurs in small globules from 1.6 to 10 microns 
 in diameter (0.0016 to 0.01 mm.). They are liquid in the 
 animal, but solid at ordinary temperatures, the melting 
 point varying from 29.5 to 33 C. The fat globules in milk 
 are in the form of a true emulsion minute, oily particles 
 suspended in a slightly viscous medium (Section 204, II, 6), 
 the viscosity of the milk plasma being due to the soluble 
 proteins. Referring to the specific gravity of milk, it may 
 be noted that an increase in the amount of fat causes a 
 lowering of the specific gravity. ^ 
 
 (c) PROTEINS consist of caseinogen, lactalbumin, and one 
 or two others not of sufficient importance to deserve 
 mention. Caseinogen helps to give the opaque color to 
 milk, being present in a condition of pseudosolution. It 
 contains sulphur and phosphorus in addition to the ordinary 
 protein elements, carbon, hydrogen, nitrogen, and oxygen, 
 and is probably combined with calcium or with calcium 
 phosphate. Acids precipitate the casein by removing the 
 calcium, thus setting free the protein proper. The action of 
 rennin in precipitating casein is somewhat different. It splits 
 the caseinogen into two different soluble proteins, at the
 
 SECRETION 321 
 
 same time liberating the calcium phosphate. One of the 
 proteins unites with the liberated calcium phosphate to form 
 the insoluble curd. Casein is insoluble in water, alcohol, 
 ether, and dilute acids, but soluble in strong acids and in 
 alkalies. 
 
 Lactalbumin is coagulated by heat and precipitated by 
 tannin and saturated solutions of sodium and magnesium 
 sulphates. It contains carbon, hydrogen, oxygen, nitrogen, 
 and sulphur, but no phosphorus. 
 
 (d) INORGANIC SALTS are present in the form of chlorides 
 of sodium and potassium, mono- and dipotassium phos- 
 phates, dimagnesium phosphate, di- and tricalcium phos- 
 phates, calcium and magnesium citrates. All the salts 
 are present in solution except tricalcium phosphate, which 
 is suspended in finely divided form. It is to be noted that 
 some of the inorganic elements are combined with citric acid. 
 It may be noted that an increase in the amount of inorganic 
 salts raises the specific gravity. 
 
 (e) OTHER CONSTITUENTS. In addition to those substances 
 already mentioned, milk contains lecithin, cholesterol, pro- 
 teolytic enzymes, carbon dioxide, oxygen and other gases, 
 especially when the milk is fresh drawn, not to mention 
 various kinds of foreign matter including bacteria. The 
 amount of dirt and bacteria depends on the care with which 
 milk is handled. 
 
 229. Secretion. Milk is secreted in certain glands espe- 
 cially adapted for the purpose, and evidence points to the 
 fact that the various components of this fluid are elaborated 
 in these gland cells only and not merely filtered from the 
 blood plasma. Lactose, for example, is not found in the 
 blood stream, but must be manufactured, probably from 
 dextrose, in the milk glands. Milk fat and casein are not 
 found in any other part of the body. 
 
 The influence of breed of cow on the quality of milk 
 secretion is of much greater importance than that of food. 
 The Jersey, for example, produces large globules of milk 
 fat, which causes cream to rise rapidly and in considerable 
 quantities. The Holstein produces small globules of milk 
 fat and not so great a total quantity. Modifying the food 
 21
 
 322 MILK AND DAIRY PRODUCTS 
 
 has very little influence on the composition of milk. The 
 same food, for example, fed to different breeds produces 
 different kinds of milk, but changing the food for one par- 
 ticular breed does not change the kind of milk produced 
 by that breed. There are some exceptions to this statement, 
 but they are not of sufficient importance to be discussed 
 here. 
 
 230. Adulteration and Preservation. Since milk has be- 
 come such a very valuable food product, the temptation 
 to adulterate it is very great. The addition of water is the 
 commonest method of adulteration, detection of which is 
 not particularly easy. For example, the specific gravity of 
 milk might be used as a test for purity, but by removing 
 fat and adding water, the specific gravity can be made to 
 remain the same. It is, however, a requirement in some 
 states that milk shall not be sold under a certain content of 
 butter fat. This serves as a protection to the consumer, 
 but in some instances it works a hardship against the pro- 
 ducer for it is quite possible that perfectly pure milk may 
 contain less than the stated legal minimum amount of fat. 
 
 Milk is not only a perfect nutrient for man, but it is also 
 a perfect nutrient for bacteria, and exposure to the air for 
 any length of time permits the entrance of large numbers 
 of bacteria, many of them dangerous to health. No bacteria 
 are present in the milk within the animal, but as soon as it 
 is drawn bacteria begin to accumulate. Since bacteria thrive 
 best in warm milk, immediate cooling helps to some extent in 
 preventing their activity. 
 
 There are two ways of freeing milk from bacteria, which 
 are legitimate. One is by pasteurization which consists 
 in heating the milk to a temperature of 60 to 80 C. for 
 twenty minutes, and then cooling it. This treatment kills 
 practically all of the bacteria, and if carried out in sealed 
 containers no more bacteria can enter. Pasteurization does 
 not alter the taste or smell of the milk, and is practised 
 quite largely by the best dairies. 
 
 The other way of treating milk is by sterilization which 
 consists in heating the milk to 115 C., accomplished by 
 steam under pressure. This absolutely kills all bacteria,
 
 BUTTER 323 
 
 but it alters the taste and smell of the milk. Albumin is 
 precipitated, calcium citrate is deposited, and other changes 
 also take place which affect the quality of the milk. 
 
 It is unfortunately easier to stop the action of bacteria 
 by the addition of chemical preservatives, and the ones which 
 are most effective in killing bacteria are also the ones which 
 harm the consumer. Formaldehyde, boric acid, salicylic 
 acid, and benzoic acid, are compounds which have been 
 used, but the law in most states prevents their use at all, 
 so that at the present time the consumer is safe from such a 
 dangerous practice. 
 
 231. Cream. Cream consists merely of the greater part 
 of the milk fat separated from the remainder of the milk, 
 and is obtained by allowing the milk to stand quietly when 
 the fat globules, being lighter than the rest of the milk, rise 
 to the surface and can be skimmed off. Another way to 
 obtain cream is by use of the separator, which is a machine 
 where the fresh drawn milk can be subjected to centrifugal 
 force, the heavier part being thrown to the outside and the 
 lighter part rising in the centre. By appropriate devices 
 the two parts of the milk can be drawn off in separate streams 
 and by regulating the cream discharge pipe, cream of different 
 fat content can be obtained. The fat can be withdrawn 
 more completely from milk in this way than it can by the 
 old-fashioned skimming process, the former removing from 
 97 to 98 per cent, of the butter fat under the best conditions, 
 and the latter not more than 90 to 95 per cent. 
 
 232. Butter. Both butter and cream consist of milk fat, 
 but cream is mixed with more or less of the other con- 
 stituents of milk, whereas butter consists practically of milk 
 fat only. It is made by agitating cream in a churn whereby 
 the globules of milk fat coalesce into a mass. This is removed 
 and w r orked over to remove the last trace of buttermilk, which 
 consists of milk minus butter. Buttermilk usually contains 
 about 4 per cent, of lactic acid, giving it a sour taste. This 
 is because the best quality of butter is obtained from cream 
 which has been properly "ripened," or, to put it plainly, 
 which is somewhat sour. The souring, however, is not 
 permitted to take place spontaneously, because of the
 
 324 MILK AND DAIRY PRODUCTS 
 
 danger of introducing harmful bacteria, but is accomplished 
 by adding artificial lactic acid bacteria cultures. Butter 
 contains about 84 per cent, of fat, 13 per cent, of water, and 
 about 3 per cent, of lactose, albumin, and sodium chloride, 
 the latter having been added to improve the flavor and also 
 to serve as a preservative. Since it is possible to produce 
 butter which contains considerable water and thus sell an 
 adulterated product, it is not permitted in the United States 
 for butter to contain more than 16 per cent, of water. 
 
 Butter frequently becomes rancid, a condition which is 
 due probably to the action of bacteria, molds, light, and oxy- 
 gen. This combination -of factors results in the hydrolysis 
 of fat, which sets free some of the fatty acids, one of them 
 at least, butyric, being volatile, and some of them oxidizing 
 to aldehydes. 
 
 Oleomargarine. At this point it may be well to mention 
 one of the principal butter substitutes, which is a perfectly 
 nutritious article of food, but which not being butter should 
 not be sold as such. It is manufactured from beef fat by 
 rendering the latter and allowing the resultant product to 
 stand at a low temperature for some time, when part of the 
 solid fats crystallize. The soft mass is now subjected to 
 pressure, and a liquid oil consisting of olein and palmitin 
 principally is pressed out. This "oleo oil" is worked up 
 by itself or with lard, cottonseed oil, cocoanut and other 
 oils. It is then churned with milk, sometimes with a little 
 butter, after which it is worked and salted. 
 
 233. Cheese. This is one of the oldest articles of food, 
 being used 1000 years B. C., and still retaining its popularity 
 as a nutritious article of diet. It consists essentially of the 
 casein from milk with -considerable fat entangled with it 
 and some water, lactose, and inorganic salts. The solid 
 product is submitted to seasoning and ripening processes 
 which favorably affect its composition and flavor. Ordinary 
 American cheese contains about 34.4 per cent, water, 26.4 
 per cent, protein, 32.7 per cent, fat, 2.9 per cent, lactose, 
 and 3.6 per cent. ash. 
 
 Cheddar, or American cheese, is the commonest form of this 
 food. It is made by first ripening the milk with an artificial
 
 CHEESE 325 
 
 starter until it contains a small amount of lactic acid. Then 
 rennet is added. This is a preparation made from calves' 
 stomachs and contains the enzyme rennin which coagulates 
 the casein in the milk. The temperature is maintained at 
 about 30 C. until a curd settles, when it is raised somewhat 
 higher and maintained for one or two hours. After separating 
 the curd from the "whey," as the residual liquid is called, 
 the solid mass is ground, salted, and pressed into cakes, 
 after which it is placed in a curing room where it is kept 
 for some time at a temperature of 13 C. There should be 
 present also about 65 to 75 per cent, of moisture in the 
 curing room. If the temperature is too high fat exudes 
 from the cheese, and too much moisture is lost. The changes 
 which take place during ripening are not purely bacterial but 
 are largely due to enzymes. Some water is lost by vapori- 
 zation; lactose is converted to lactic acid; and proteins are 
 hydrolyzed, many of them to soluble products. Odor and 
 flavor are developed which impart quality to the cheese. The 
 result of the various changes is a decided improvement in 
 the palatability and digestibility of the material. 
 
 Cheshire cheese is made in England from fresh milk. The 
 method and care of cutting the curd and removal of the 
 whey is important. 
 
 Stilton cheese is made between March and September, from 
 the milk of cows fed only on natural pasture, and the rennet 
 is obtained from lambs' stomachs and not from calves. 
 
 Camembert and Brie are soft cheeses made in France by 
 somewhat similar processes, except that during the curing 
 mold develops on the outside and the enzyme changes 'are 
 more pronounced within. Proteins are broken down to a 
 greater extent. 
 
 Roquefort is made from sheep's milk and during ripening 
 a green mold grows throughout the mass of cheese, breaking 
 down the protein compounds so as to give it the characteristic 
 taste and odor. 
 
 Limburger was made in Belgium originally, but is now 
 considered strictly a German cheese. The curd is formed 
 at a high temperature, and it is ripened at a somewhat 
 higher temperature than usual, and in a very moist atmos-
 
 326 MILK AND DAIRY PRODUCTS 
 
 phere. Under these conditions bacterial changes take place 
 to such an extent that putrefactive fermentation sets in, 
 giving it the high odor for which it is noted. 
 
 234. Koumiss. Koumiss is a drink made properly from 
 mares' milk by the nomadic tribes of Asia Minor. Mares' 
 milk is richer in lactose than is cows' milk and on the addition 
 of old or dried koumiss part of the lactose ferments to alcohol 
 and carbon dioxide, some of it changing also to lactic acid. 
 
 Kephir is a somewhat similar drink prepared from cows' 
 milk by the inhabitants of the Caucasus. Fermentation is 
 caused by the addition of the so-called kephir grains, the 
 origin of which is not known, but which contain certain 
 microorganisms capable of causing the production of lactic 
 acid, alcohol, and carbon dioxide from lactose. Both of 
 these slightly alcoholic drinks are easily digested by invalids 
 and have assumed some importance as drinks for medicinal 
 purposes. 
 
 235. Condensed and Desiccated Milk. For the purpose of 
 keeping milk, it is condensed by evaporation in a partial 
 vacuum, with or without the addition of sugar, to a thick 
 consistency of one-third to one-fourth its original volume. 
 This substance can be sealed up in air-tight cans and kept for 
 a long time, being mixed with water in various proportions 
 just before use. Desiccated milk can be made by various 
 processes, one of which is to spray the milk against a rapidly 
 revolving hot plate which instantly drives off the water and 
 permits the collection of the dry milk powder. This resumes 
 
 its original condition when it is stirred up with water. 
 
 
 
 EXERCISES 
 
 1. What is meant by a pseudo-solution? Where else than in this chapter 
 has this word been used? What are the properties of such a solution? 
 How does it differ from a true solution? 
 
 2. How does the specific gravity of milk change if it is watered? If it 
 is skimmed? W r hy? 
 
 3. What is the difference between caseinogen and casein? What does 
 the suffix "ogen" mean? When else has it been used? 
 
 4. Can you explain why 2 per cent, is usually the maximum amount of 
 lactic acid found in sour milk? What other examples of a similar phenom- 
 enon have been studied? 
 
 5. How could you attempt to ascertain the percentage of fat in milk?
 
 REFERENCES 327 
 
 6. Compare milk, cheese, butter and buttermilk as to their composition; 
 as to their relative value as foods, pound for pound; as to the organ which 
 digests the major portion of the valuable constituents of each. 
 
 7. What substances found in milk produce the following effects: Sweeten 
 milk; help to make the bones of an infant; change when souring takes place; 
 gives milk its color; are without doubt made in the milk glands? 
 
 8. What properties common to proteins are mentioned in this chapter? 
 
 9. Is milk fat a compound? 
 
 10. Why is lactose called an aldose? 
 
 11. What fat is most characteristic of butter? 
 
 12. Write the graphic formula of butyrin and of the glyceryl ester of 
 butyric, lauric and oleic acids. 
 
 REFERENCES 
 
 Barthel. Milk and Dairy Products. 
 
 McKay and Larsen. Principles and Practice of Butter Making. 
 
 Leach. Food Inspection. 
 
 Richmond. Dairy Chemistry.
 
 INDEX 
 
 ABSORPTION of food constituents, 
 
 309 
 in soil, 164 
 
 chemical, 165 
 
 physical, 167 
 Achroodextrin, 33 
 Acid humus, 141 
 phosphate, 210 
 
 availability, 211 
 
 effect of, on soil, 211 
 
 with farm manure, 250 
 Acidity of soil, 225 
 
 artificial, 226 
 
 natural, 226 
 
 Active organic matter, 134, 142 
 Adipose tissue, 291 
 Adsorption, 167 
 Air, composition of, 127 
 
 inspired and expired, 296 
 properties of, 126 
 Air-slaked lime as fertilizer, 233 
 Albite, 162 
 Alkali soils, 183 
 
 reclamation of, 185 
 Alkaloids, 64 
 
 Allyl cyanide in oil of mustard, 51 
 isothiocyanate in oil of mustard, 
 
 51 
 
 Allyl-propyl-disulphide, 51 
 Aluminium minerals in the soil, 
 
 162 
 
 Alunite, 222 
 Amber, 56 
 Amendments, 188 
 American cheese, 324 
 Amides in plants, 61 
 Amino-acetic acid, 61 
 Amino-acids in plants, 61 
 Amino-succinamide, 61 
 Ammonia, formation of, in soil, 144 
 
 Ammonia, loss of, from farm 
 manure, 245 
 
 in plants, 60 
 
 Ammoniacal copper carbonate, 274 
 Ammonification, 144 
 Ammonium sulphate, 197 
 availability of, 199 
 cause of soil acidity of, 226 
 effect of, on soil, 199 
 Amylases, 77 
 Amylodextrin, 32 
 Amyloid, 38 
 Amylopsin, 308 
 Analyses of crops, 106 
 
 how expressed, 256 
 Anhydrite, 160 
 Animal, composition of, 287-289 
 
 compounds, 299 
 
 starch, 299 
 Anorthite, 161 
 Antimony rubber, 60 
 Apatite, 155 
 Araban, 38 
 Arabinose, 38 
 Argenine, 61 
 Argon in air, 129 
 Arid soils, 178 
 Arsenous oxide, use in making 
 
 Paris green, 268 
 Arteries, 293 
 Asafetida, 57 
 Ash in plants, 104 
 Asparagine, 61 
 Atropine, 65 
 Attar of roses, 52 
 Available plant food, 80 
 
 B 
 
 BACTERIA in air, 130 
 in farm manure, 245
 
 330 
 
 INDEX 
 
 Bacteria in intestines, 309 
 
 in milk, 322 
 
 in soils, 134 
 
 number of, 138 
 Balsams, definition of, 55 
 Barley seed, discussion of compo- 
 sition of, 111 
 Basalts, 176 
 Base goods, 205 
 Basic copper acetate, use of, in 
 
 making Paris green, 268 
 carbonate, use of, in making 
 fungicides, 274 
 
 slag, 212 
 
 availability of, 214 
 composition of, 212 
 effect of, on fertilizer mixtures, 
 
 190 
 
 on soil, 214 
 
 Baume" scale, 282 (footnote) 
 Bauxite, 163 
 Beeswax, 301 
 Benzaldehyde in oil of bitter 
 
 almonds, 50 
 Benzoin, 58 
 Biennials, 92 
 Bile, 308 
 Biotite, 162 
 Black alkali, 183 
 Blood, 292 
 
 clotting of, 295 
 
 exchange of gases in, 296 
 Bone phosphate of lime, 261 
 
 tankage, 204 
 Bone-black, 207 
 
 dissolved, 207 
 Bone-meal, 207 
 Bones, 289 
 
 raw, as a fertilizer, 206 
 Bordeaux mixture, 275 
 
 use of, with Paris green, 268 
 Brewer's grains, 111 
 Brewing, use of barley in, 111 
 Brie cheese, 349 
 British gum, 34 
 Brown sugar, 28 
 Buhach, 273 
 Bulbs, purpose of, 92 
 Burnt lime as fertilizer, 232 
 Butter, 323 
 Buttermilk, 323 
 Button lac, 57 
 By-product coke ovens, 197 
 
 CAFFEINE, 65 
 
 Calcite, 160 
 
 Calcium carbonate as fertilizer, 
 
 231 
 
 solution in soil moisture, 161 
 compounds in the animal, 302 
 cyanamide, 200 
 fertilizers as plant food, 224 
 function of, in plant, 99 
 hydroxide as fertilizer, 233 
 minerals in soil, 160 
 nitrate as a fertilizer, 195 
 
 in the soil, 145 
 oxide. See Lime. 
 
 amount of, in burnt lime, 
 
 235 
 in calcium carbonate, 232, 
 
 235 
 
 in slaked lime, 235 
 as a fertilizer, 232 
 saccharates, 27 
 sulphate as a fertilizer, 239 
 Caliche, 193 
 Calorie, 316 
 Calorimeter, 314 
 
 respiration, 314 
 Camembert cheese, 325 
 Canada balsam, 58 
 Canaigre, 70 
 
 Cane sugar, 24. See also Sucrose. 
 Caoutchouc, 59 
 Capillaries, 293 
 Caramel, 58 . 
 
 Carbohydrate, amount of, synthe- 
 sized by plants, 88 
 function of, in plant, 91 
 in milk, 318 
 Carbohydrates, absorption of, into 
 
 body, 309 
 
 amount of, in plants, 18 
 in the animal, 299 
 function of, 311 
 definition of, 18 
 manufacture of, 87 
 transfer of, in plants, 87 
 Carbon dioxide in air, 128 
 exhaled by man, 129 
 given off by burning coal, 
 
 129 
 
 how it gets out of the blood, 
 296
 
 INDEX 
 
 331 
 
 Carbon dioxide in the soil, 136, 
 
 137, 153 
 
 used by corn, 129 
 disulphide in oil of mustard, 51 
 
 use of, with farm manure, 250 
 function of, in plant, 94 
 monoxide poisoning, cause of, 
 294 
 
 Carburetor, 280 
 
 Carnauba wax, 46 
 
 Casein, 320 
 
 Caseinogen, 320 
 
 Castor oil, 43 
 
 Castor-bean pomace, 204 
 
 Catalytic agents, 76 
 
 Catechu, 70 
 
 Caustic lime as a fertilizer, 232 
 
 Cellophane, 37 
 
 Celluloid, 37 
 
 Cellulose acetate, 37 
 
 amount of, in different parts of 
 
 plants, 35 
 
 general description, 35 
 nitrates, 37 
 solvents for, 36 
 
 Cement dust, 223 
 
 Chalk as a source of lime, 231 
 
 Cheddar cheese, 324 
 
 Cheese, 324 
 
 Cheshire cheese, 325 
 
 Chestnut wood and bark for tan- 
 ning, 70 
 
 Chicle, 60 
 
 Chile saltpeter, 193 
 
 Chlorine compounds in the animal, 
 
 303 
 minerals in the soil, 162 
 
 Chlorophyl, 85 
 
 Chyme, 307 
 
 Cinnamic aldehyde in oil of cinna- 
 mon, 50 
 
 Citral in oil of lemon, 50 
 
 Citric acid, 67 
 
 Citronellol in oil of roses, 52 
 
 Clay soils, 180 
 
 Coagulation of blood, 295 
 
 Cocaine, 66 
 
 Cod-liver oil, 300 
 
 Cold manures, 246 
 
 Collagen, 292 
 
 Collodion, 37 
 
 Colophony, 56 
 
 Colza oil, 46 
 
 Commercial fertilizers, 188 
 
 Complete fertilizers, 188 
 
 Composted manure, 252 
 
 Condensed milk, 326 
 
 Connective tissue, 291 
 
 Copal, 56 
 
 Copper aceto-metarsenite, 268. See 
 
 Paris green. 
 Corn, changes in composition of, 
 
 during growth, 121 
 kernel, structure of, 93 
 oil, 44 
 seed, discussion of composition 
 
 of, 112 
 Corpuscles, red, 293 
 
 white, 294 
 
 Corrosive sublimate, 276 
 Cotton purification, 38 
 seed, composition of, 106 
 
 discussion of, 1 14 
 fertilizing constituents of, 109 
 meal as a fertilizer, 204 
 oil, 44 
 stearine, 44 
 yields, 108 
 Cream, 323 
 Crop chemistry, 110 
 
 yields, 108 
 
 Crops, analyses of, 108 
 classification of, 105 
 composition of, 106 
 Crude fat in plants, 103 
 fiber in plants, 103 
 petroleum, 281 
 
 use of, in making miscible oils, 
 
 273 
 
 protein in plants, 104 
 turpentine, 58 
 Cuprammonium carbonate as a 
 
 fungicide, 274 
 Curdling of milk, 319 
 Cutch, 70 
 
 Cyanamid, availability of, 201 
 effect of, on soil, 202 
 as a fertilizer, 201 
 Cylinder oil, 285 
 
 DEEP-STALL system of caring for 
 
 farm manure, 249 
 Denitrification, 145 
 Desiccated milk, 326
 
 332 
 
 INDEX 
 
 Dextrates, 22 
 
 Dextrin, 34 
 
 Dextrose in the animal, 299 
 
 condensation to, by formalde- 
 hyde, 87 
 
 general description of, 20 
 Dextroxides, 22 
 Diastase, 77 
 
 importance of, in brewing, 111 
 Dicalcium phosphate in fertilizers, 
 
 211, 222 
 in soils, 156 
 
 Diffusion in the soil, 169 
 Digallic acid, 69 
 Digestible carbohydrates, 104 
 
 coefficient, 313 
 Digestion, 305 
 Direct fertilizers, 188 
 Disaccharides, 19 
 Disilicic acids, 157 
 Dissolved bone-black, 208 
 Distribution of essential elements 
 
 in seed crops, 100 
 Divi-divi, 71 
 Dolomite, 160 
 
 as a fertilizer, 239 
 
 as a source of lime, 231 
 Double potash manure salt, 221 
 Dragon's blood, 57 
 Drainage-water, composition of, 
 
 172 
 
 Dried blood, availability of, 203 
 black, 202 
 as a fertilizer, 202 
 red, 202 
 
 fish, 204 
 
 meat as a fertilizer, 203 
 Driers for linseed oil, 44 
 Drying oils, constituents of, 43 
 
 definition of, 41 
 Dust in air, 130 
 
 EBONITE, 60 
 Elastin, 292 
 Elements, essential, for animals, 
 
 287 
 distribution of, in seed crops, 
 
 100 
 
 for plant growth, 80 
 function of, in plants, 94 
 
 Elements, form in which absorbed 
 
 by plants, 82 
 
 how absorbed by plants, 83 
 Emulsifier, 273 
 Emulsion, definition of, 271 
 Encrusting substances, 35, 38 
 Enzymes, 76 
 Epithelial tissue, 291 
 Erythrocytes, 293 
 Erythrpdextrin, 33 
 Essential oils, 47. See also Volatile 
 
 oils. 
 Ethereal oils, 47. See also Volatile 
 
 oils. 
 Eugenol in oil of bitter almonds, 49 
 
 of cloves, 50 . 
 
 Excrement, composition of, 242 
 liquid, of farm animals, 242 
 mixed, amount of plant food re- 
 covered in, 244 
 influence of animal on compo- 
 sition, 244 
 
 of food on composition, 244 
 solid, of farm animals, 241 
 
 F 
 
 FARM manure, action of molds in, 
 
 247 
 
 bacteria in, 245 
 composition of, 244 
 compounds in, 244-245 
 decomposition of, aerobic, 245 
 
 anaerobic, 245, 247 
 definition of, 241 
 fresh, how to use, 251 
 losses of, 247 
 
 prevention of, 248 
 chemical, 249 
 mechanical, 248 
 an unbalanced fertilizer, 253 
 value of, 253 
 well decomposed, how to use, 
 
 251 
 
 Fat in milk, 319 
 Fats, absorption into body, 310 
 animal, 300 
 
 composition of, 291 
 digestion of, in intestines, 308 
 function of, in the animal, 311 
 Fatty acids, classification of, 42 
 in milk, 320
 
 INDEX 
 
 333 
 
 Fatty acids, saturated, 42 
 unsaturatcd, 42 
 
 tissue, 291 
 Feces, 241 
 
 Feed, distinction from food, 304 
 Feeding standards, 316 
 Fehling's solution, 21 
 Feldspar, lime, 161 
 
 potash, 158 
 
 soda, 162 
 Fertilizer, analysis of; 260 
 
 mixtures to be avoided, 190 
 Fertilizers, choice of, 191 
 
 commercial, 188 
 
 .complete, 188 
 
 definition of, 187 
 
 direct, 188 
 
 incomplete, 189 
 
 indirect, 188 
 Fertilizing constituents of crops, 
 
 109 
 
 Fibrin, 295 
 Fibrinogen, 293, 295 
 Filnx water in the soil, 170 
 Fire point, 282 (footnote) 
 Fish scrap, 204 
 
 Fixed oils, general definition of, 40 
 methods of extraction of, 41 
 properties of, 40 
 Flash point, 282 (footnote) 
 Flax seed, composition of, 106 
 
 discussion of, 114 
 fertilizing constituents of, 109 
 yields of, 108 
 Floats, 208 
 Fluorides, use with farm manure, 
 
 250 
 Food constituents, 305 
 
 function of, in the animal, 311 
 
 definition of, 304 
 
 effect of, on quality of milk, 321 
 
 for seedling, 76 
 
 for soil bacteria, 138 
 
 value, expressions for, 313 
 Form in which plant food elements 
 
 are absorbed, 82 
 Formaldehyde candles, 277 
 
 formation of, in leaf, 87 
 
 as a fungicide, 276 
 Formalin, 276 
 
 Four-cycle type of gas engine, 279 
 Frankincense, 58 
 Fructose, 23. See also Levulose. 
 
 Fruit crops, composition of, 106 
 
 discussion of, 114 
 fertilizing constituents of, 109 
 yields of, 108 
 
 sugar, 23. See also Levuloee. 
 Fungj, how destroyed, 265 
 Fungicides, 274 
 
 GALLIC acid, 69 
 
 Galls, 71 
 
 Gam bier, 71 
 
 Gamboge, 58 
 
 Gas engine, 279 
 
 Gaseous exchange in the blood, 
 
 296 
 
 Gases in blood, composition of, 
 297 
 
 in soil, 153 
 
 Gas-lime as a fertilizer, 239 
 Gasoline, 283 
 Gastric digestion, 306 
 
 juice, 306 
 
 Geraniol in oil of roses, 52 
 German potash deposits, 216 
 Germination, conditions for, 52 
 
 of seed, 52 
 Gliadin, 112 
 Gluco-glucoside, 30 
 Glucolin, 30 
 Glucose, 20. See also Dextrose. 
 
 commercial, 22 
 Glucosides, definition of, 21 
 Glutamine, 62 
 Glycerine, 42 
 Glycocoll, 61 
 Glycogen, 299 
 Grains, composition of, 106 
 
 fertilizing constituents of, 109 
 
 yields of, 108 
 Granite, 175 
 
 Grape sugar, 20. See also Dex- 
 trose. 
 
 Gum arabic, 39 
 Gum-resins, definition of, 56 
 Gums, 39 
 Guncotton, 37 
 Gutta percha, 60 
 Gypsum as a fertilizer, 239 
 
 in the soil, 160 
 
 use of, with farm manure, 249
 
 334 
 
 INDEX 
 
 HEMOGLOBIN, 293 
 
 Hair as a fertilizer, 205 
 Halite, 162 
 Hard rubber, 60 
 
 water, 172 
 Hay, 116 
 
 chemical change hi making of, 
 117 
 
 crops, changes hi composition of 
 
 during making, 118 
 Heat caused by germination, 75 
 
 production in the animal body, 
 
 314 
 
 Height of air, 125 
 Hellebore, 264 
 
 Hemlock wood and bark for tan- 
 ning, 70 
 
 Home mixing of fertilizers, 189 
 Hoof as a fertilizer, 205 
 Horn as a fertilizer, 205 
 Hornblende, 161 
 Hot manures, 246 
 Humid soils, 178 
 Humus, 139 
 
 composition of, 141 
 
 properties of, 140 
 Hydrated lime as a fertilizer, 233 
 Hydrocarbons in crude petroleum, 
 
 281 
 
 Hydrocyanic acid gas, 269 
 in linseed press cake, 45 
 in oil of bitter almonds, 49 
 Hydrogen in air, 129 
 
 function of, in plant, 94 
 
 ICELAND spar, 19 
 
 Igneous rocks, 174 
 
 Inactive organic matter, 134, 143 
 
 Incomplete fertilizers, 189 
 
 Indirect fertilizers, 188 
 
 Inoculation of soils, 150 
 
 Inorganic acids in soil, 155 
 
 elements, function of, in animal, 
 313 
 
 material, use of, by plant, 85 
 Insecticides, external, 269 
 
 internal, 267 
 Insects, how destroyed, 264 
 
 Intermolecular respiration, 89 
 Intestinal digestion, 307 
 
 juice, 307 
 Inulin, 39 
 Invert sugar, 27 
 Invertase, 308 
 Iodine compounds in the animal, 
 
 303 
 Iron compounds in the animal, 302 
 
 function of, in plant, 100 
 
 minerals in soil, 161 
 
 K 
 
 KAINITE, 221 
 Kaolin, 159 
 Kaolinite, 159 
 Kaolinization, 159 
 Kelp, 221 
 Kephir, 326 
 Keratin, 291 
 Kerosene emulsion, 270 
 
 how made, 282 
 Kino, 70 
 Koumyss, 326 
 
 LAC, 57 
 
 Lactalbumin, 320 
 
 Lactase, 308 
 
 Lacteals, 310 
 
 Lactic acid production in milk, 319 
 
 Lactose, 318 
 
 Land plaster, 238. See Gypsum as 
 
 a fertilizer. 
 Lard, 300 
 Latex, 59 
 Lavas, 176 
 Lead acetate, use of, in making lead 
 
 arsenate, 267 
 arsenate, 267 
 
 use of, with Bordeaux mixture, 
 
 276 
 
 with lime-sulphur, 273 
 nitrate, use of, in making lead 
 
 arsenate, 267 
 Leaf, structure of, 86 
 Leather as a fertilizer, 205 
 Lecithin, description of, 46, 47 
 Legumes, composition of, 106
 
 INDEX 
 
 335 
 
 Legumes, discussion of composition 
 
 of, 114 
 
 fertilizing constituents of, 109 
 yields of, 108 
 Leucite, 160 
 Leucocytes, 294 
 Levulates, 23 
 Levulin, 27 
 Levulo-glucoside, 27 
 Levulose, general description of, 
 
 23 
 
 Lignification, 36 
 Lignin, 38 
 Limburger, 325 
 
 Lime, amount of, removed by 
 crops, 225 
 in fertilizers, 225 
 availability of, 233 
 in basic slag, 214 
 checking plant diseases, 238 
 definition of term, 231 
 effect of, on fertilizer mixtures, 
 
 190 
 
 harmful, 238 
 on soil, 235, 
 from acetylene plant as a fer- 
 
 tiizer, 239 
 
 improving soil texture, 238 
 making phosphorus available, 
 
 238 
 
 potassium available, 238 
 neutralizing acids, 235 
 nitrogen, 200 
 as a plant food, 224 
 requirement, how determined, 
 
 259 
 
 use of, with farm manure, 251 
 Limestone, 176 
 as a fertilizer, 231 
 soils become acid, 229 
 Lime-sulphur, boiled, 271 
 
 self-boiled, 277 
 Limonene in oil of lemon, 50 
 Limonite, 161 
 Linoleic acid, 45 
 Linolenic acid, 43 
 Linseed oil, 44 
 Li pases, 77 
 Litter, 243 
 amount of ammonia absorbed 
 
 by, 243 
 
 of water absorbed by, 243 
 composition of, 243 
 
 Loam soils, 180 
 Lubricants, 284 
 Lump lime as a fertilizer, 232 
 Lymph, 298 
 
 glands, 298 
 
 vessels, 298 
 
 M 
 
 MAGNESIAN lime, use of, 239 
 Magnesium, function of, in plant, 
 100 
 
 minerals in the soil, 162 
 Malic acid, 68 
 Malt sprouts, 111 
 
 sugar, 29. See also Maltose. 
 Maltase, 308 
 
 Maltobiose, 29. See also Maltose. 
 Maltodextrin, 33 
 
 Maltose, general description of, 29 
 Mangrove, 70 
 
 Manure. See Farm manure, 241, 
 et seq. 
 
 in formation of humus, 143 
 Marl as a source of lime, 231 
 Marrow, 289 
 Mashing, 111 
 Mass action, 166 
 Mastic, 57 
 Meat meal as a fertilizer, 203 
 
 tankage, 203 
 Menhaden oil, 300 
 
 use of, in making miscible oils, 
 
 273 
 
 Menthol in oil of peppermint, 51 
 Mercerized cotton, 36 
 Mercuric chloride as a fungicide, 
 
 276 
 
 Metamorphic rocks, 174 
 Metasilicic acid, 157 
 Methyl salicylate in oil of winter- 
 green, 55 
 
 Milk, adulteration and preserva- 
 tion of, 322 
 
 composition of, 318 
 
 digestion of, in stomach, 307 
 
 fat, 319 
 
 inorganic salts in, 321 
 
 physical appearance of, 318 
 
 secretion, 321 
 Minerals in soil, 155 
 
 factors of solubility of, 163
 
 336 
 
 INDEX 
 
 Miscible oils, 273 
 Moisture for soil bacteria, 138 
 Molds in farm manure, 247 
 Monocalcium phosphate in fertil- 
 izers, 210, 212 
 
 in soils, 156 
 Monosaccharides, 19 
 Morphine, 66 
 Movements of dissolved substances 
 
 in soil, 168 
 
 Muriate of potash, a cause of soil 
 acidity, 228 
 
 as a fertilizer, 218 
 Muscovite, 160 
 Muscular tissue, 289 
 Myosin, 291 
 Myosinogen, 291 
 Myrobalans, 71 
 Myrosin in oil of mustard, 51 
 Myrrh, 58 
 
 N 
 
 NAPHTHA, 282 
 Neatsfoot oil, 300 
 Neutral humus, 142 
 Nicol prism, 19 
 Nicotine, 66 
 
 sulphate, as an insecticide, 274 
 Nitrate of soda, as a fertilizer, 193 
 
 in tobacco waste, 223 
 Nitrates, formation of, in soil, 144 
 
 in plants, 60 
 Nitrification, 144 
 Nitrites, formation of, in the soil, 
 
 144 
 
 Nitrogen in air, 128 
 amount added to soil by clover 
 
 and alfalfa, 147, 150 
 in coal, 197 
 changes in farm manure, 245, el 
 
 seq. 
 
 compounds in the air, 130 
 equal to ammonia, 262 
 fixation, 146 
 
 non-symbiotic, 147 
 symbiotic, 147 
 function of, in plant, 98 
 importance of, in fertilizers, 192 
 loss of, in farm manure, 247 
 
 prevention of, 248, 249 
 in soil, 153 
 Nitrogen-free extract, 104 
 
 Nitrogenous extractives, 291 
 
 fertilizers, 192 
 Nutgalls, 71 
 
 OAK bark for tanning, 70 
 Oat seed, discussion of composi- 
 tion of, 112 
 Oil, 76 
 
 of amber, 56 
 
 of bitter almonds, 49 
 
 of cinnamon, 50 
 
 of cloves, 50 
 
 function of, in plant, .91 
 
 of lemon, 50 
 
 manufacture of, by plant, 89 
 
 of mustard, 51 
 
 of onion, 51 
 
 of peppermint, 51 
 
 of roses, 52 
 
 of sassafras, 52 
 
 of thyme, 52 
 
 transfer of, in plant, 91 
 
 of turpentine, 53 
 
 of wintergreen, 55 
 Oleic acid, 43 
 Olein, definition of, 43 
 Oleo oil, 324 
 Oleomargarine, 325 
 Oleoresin, definition of, 55 
 Olibanum, 58 
 Olive oil, 45 
 Optical activity, 19 
 Organic acids in animal, 301 
 in plants, 67 
 in soil, 137, 155 
 
 matter in arid soils, 178 
 
 decomposition of, in soils, 136 
 factors affecting rate of, 
 
 137 
 
 in sand soils, 179 
 in soils, 133 
 
 functions of, 142 
 loss of, 143 
 Orthoclase, 158 
 Ossein, 289 
 Otto of roses, 52 
 Oxalic acid, 68 
 Oxidases, 78 
 Oxygen in air, 128 
 
 consumed by burning coal, 128
 
 INDEX 
 
 337 
 
 Oxygen, function of, in plant, 95 
 
 for germination, 74 
 
 how it gets into blood, 296 
 
 in soil, 153, 155 
 
 used by man, 128 
 Oxyhsemoglobin, 293 
 Oyster shells as source of lime, 231 
 
 PALMITIC acid, 42 
 Palmitin, definition of, 43 
 Pancreatic juice, 308 
 Paper, 38 
 Paraform, 277 
 Paris green, 268 
 
 use of, with Bordeaux mixture, 
 
 276 
 
 with lime-sulphur, 273 
 Pasteurization of milk, 322 
 Peanut oil, 45 
 Peat soils, 181 
 Pectins, 39 
 
 Pentacalcium silico-phosphate, 212 
 Pentpsans, 38 
 Pepsin, 307 
 
 Persian insect powder, 273 
 Phosphate fertilizers, 206 
 Phosphoric acid, citrate soluble, in 
 
 fertilizers, 261 
 importance of, in fertilizers, 
 
 206 
 
 reverted, in fertilizers, 261 
 total, in fertilizers, 261 
 water soluble, in fertilizers, 
 
 261 
 Phosphorus, changes of, in farm 
 
 manure, 246 
 
 compounds in animal, 301 
 function of, in plant, 95 
 loss of, in farm manure, 247 
 
 prevention of, 248 
 minerals, 155 
 in soil, solution of, 156 
 Pinene in oil of turpentine, 53 
 Plant, composition of, 81 
 food, available, 80 
 definition of, 80 
 how absorbed by plant, 83 
 in soil, 186 
 unavailable, 80 
 Plasma, 293 
 Plaster of Paris, 160 
 
 Polariscope, 20 
 
 Polarized light, 19 
 
 Polysaccharides, 30 
 
 Potash equivalent to sulphate, 262 
 fertilizers, 216 
 
 importance of, in fertilizers, 216 
 manure salt, 218 
 salts, effect of, on fertilizer mix- 
 tures, 190 
 use of, with farm manure, 250 
 
 Potassium carbonate in soils, 159 
 
 in wood ashes, 221 
 changes in farm manure, 246 
 chloride as a fertilizer, 218 
 compounds in animal, 302 
 cyanide, use of, in making hydro- 
 cyanic acid gas, 270 
 function of, in plant, 96 
 loss of, in farm manure, 247 
 
 prevention of, 248 
 minerals in the soil, 157 
 
 solution of, 159 
 
 myronate in oil of mustard, 51 
 sulphate as a fertilizer, 220 
 
 Preservatives, use with farm man- 
 ure, 250 
 
 Press cake, 41 
 
 Pressure of air, 125 
 
 Products of oxidation in seeds, 75 
 
 Proteases, 78 
 
 Protein, function of, in plant, 91 
 manufacture of, by plant, 90 
 transfer of, in plants, 91 
 
 Proteins, absorption of, into body, 
 
 247 
 
 composition of, 62 
 digestion of, in intestines, 308 
 
 in stomach, 307 
 functions of, in animal, 311 
 in milk, 320 
 properties of, 62 
 
 Protoplasm, 91 
 composition of, 91 
 
 Ptyalin, 305 
 
 Pyrethrum, 273 
 
 Pyroxylin, 37 
 
 QUARTZ, 162 
 Quebracho, 70 
 Quicklime as fertilizer, 232 
 Quinine, 66
 
 338 
 
 INDEX 
 
 R 
 
 RAPESEED oil, 46 
 
 Raw bones as a fertilizer, 206 
 
 Red corpuscles, 293 
 
 rubber, 60 
 Rennin, 307 
 Resenes, 55 
 Resin ducts, 55 
 Resins, properties of, 55 
 Respiration calorimeter, 314 
 
 in plants, 88 
 products of, 89 
 
 in seeds, 74 
 
 due to oxidases, 78 
 Respiratory quotient, 298 
 Reversion of acid phosphate, 211 
 Ripening of cheese, 325 
 Rise of alkali, 184 
 River water, composition of, 172 
 Rock lime as fertilizer, 232 
 
 phosphate, 208 
 
 use of, with farm manure, 248 
 Rocks, soil forming, 174 
 Root hairs, 83 
 Roots, function of, 85 
 
 purpose of fleshy, 92 
 
 selective action by, 83 
 Roquefort cheese, 325 
 Rosin, 56 
 
 oil, 56 
 
 use of, in making miscible oils, 
 273 
 
 spirit, 56 
 Rubber, 59 
 Ruminants, gastric digestion of, 
 
 306 
 Rye seed, discussion of composition 
 
 of, 112 
 
 S 
 
 SACCHARATES, 27 
 
 Saccharimeter, 20 
 
 Saccharose, 24. See also Sucrose. 
 
 Safrol in oil of sassafras, 52 
 
 Saliva, 305 
 
 Salivary digestion, 305 
 
 Salting put proteins, 64 
 
 Sand soils, 179 
 
 Sandarac, 57 
 
 Sandstones, 177 
 
 Sarcolactic acid, 291 
 
 Sawdust, use as litter, 243 
 
 Schweitzer's reagent, 36 
 
 formula for, 269 
 Scrape, 58 
 
 Sedimentary rocks, 174 
 Seedling, food for, 76 
 Seeds, production of, 92 
 Selective action by roots, 83 
 Separator for cream, 323 
 Serum, 295 
 
 albumin, 293 
 Shales, 177 
 
 Shavings, use as litter, 243 
 Shellac, 57 
 Siderite, 162 
 Sieve tubes, 88 
 Silage, 121 
 
 making, chemical changes in, 
 
 121 
 
 Silicic acids, 157 
 Silicon compounds in animal, 303 
 
 minerals in soil, 162 
 Silk, artificial, 37 
 Slaked lime as fertilizer, 233 
 Sludge acid, use in making fertil- 
 izers, 282 
 Soap, 41 
 Soda cellulose, 36 
 
 process for making paper pulp. 
 
 38 
 
 Sodium arsenate, use of, in making 
 lead arsenate, 267 
 
 compounds in animal, 302 
 
 cyanide, use of, in making hydro- 
 cyanic acid gas, 270 
 
 minerals in soil, 162 
 
 nitrate, availability of, 194 
 effect of, on soil, 194 
 as a fertilizer, 193 
 Soil acidity, 225 
 
 how determined, 259. See 
 Lime requirement. 
 
 analysis, 256 
 
 and subsoil, 182 
 
 composition of, 132 
 
 distinction of, from subsoil, 182 
 
 functions of, 132 
 
 solvents, 154 
 Soils, composition of, 181 
 
 kinds of, 177 
 
 weight of, 181 
 Solubility of soil minerals, factors, 
 
 163 
 Soluble cotton, 36
 
 INDEX 
 
 339 
 
 Soluble oils, 273 
 
 Specific rotation, 20 
 
 Spectrum, 85 
 
 Sperm oil, 301 
 
 Starch, 76 
 animal, 299 
 amount of, in crops, 31 
 commercial, how made, 34-35 
 digestion of, in intestines, 308 
 
 in mouth, 305 
 
 formation of, from dextrose, 87 
 general description of, 31 
 grains acted on by diastase, 78 
 iodide, 31 
 paste, 31 
 
 Stassfurt potash deposits, 216 
 
 Steamed bone, 207 
 
 Steapsin, 308 
 
 Stearic acid, 42 
 
 Stearin, 43 
 
 Stem and leaf crops, composition 
 
 of, 107 
 
 discussion of, 114 
 fertilizing constituents of, 
 
 110 
 yields of, 108 
 
 Sterilization of milk, 322 
 
 Stick lac, 57 
 
 Stilton cheese, 325 
 
 Stone lime as fertilizer, 232 
 
 Strychnine, 66 
 
 Subsoil, 182 
 
 Succinic acid, 56 
 
 Sucrose, general description of, 24 
 pure, how made, 27-28 
 
 Sucroxides, 27 
 
 Sugar beet, sugar content of, 25 
 cane, sugar content of, 25 
 how made from sugar beets, 
 
 28-29 
 cane, 28-29 
 
 Sugars, 18 
 
 Sulphate of potash, cause of soil 
 
 acidity, 228 
 as a fertilizer, 220 
 
 Sulphite process for making paper 
 pulp, 38 
 
 Sulphur dioxide in air, 131 
 function in plant, 99 
 minerals in the soil, 160 
 
 Sulphuric acid, use with farm man- 
 ure, 250 
 
 Sumach leaves for tanning, 69 
 
 Sunflower oil, 46 
 
 Sun's rays, use of, in synthesizing 
 
 plant substances, 85 
 Superphosphate, 210. See also Acid 
 
 Phosphate. 
 
 TALLOW, 300 
 Tankage, 203 
 Tannic acid, 68 
 Tannins, 69 
 Tartaric acid, 68 
 Temperature of air, 126 
 
 for soil bacteria, 138 
 Tetracalcium phosphate in basic 
 
 slag, 212 
 Theine, 65 
 Theobromine, 67 
 Therm, 316 
 Thomas slag, 212 
 Thymol in oil of thyme, 52 
 Timothy, changes in composition 
 
 during growth, 120 
 Tobacco as an insecticide, 274 
 
 waste, 223 
 Tolu, 59 
 Tracheae, 83 
 Tricalcium phosphate, in bones, 
 
 289 
 
 in fertilizers, 206, 208, 212 
 in soils, 156 
 Trisilicic acids, 157 
 Trypsin, 308 
 Tubers, purpose of, 92 
 Two-cycle type of gas engine, 280 
 Tyrosine, 62 
 
 UNAVAILABLE plant food, 80 
 Urea in farm manure, decomposi- 
 tion of, 245 
 Urine, 242 
 
 VALONIA, 71 
 
 Vegetable crops, composition of, 
 
 107 
 discussion of, 115
 
 340 
 
 INDEX 
 
 Vegetable crops, fertilizing con- 
 stituents of, 110 
 
 yields of, 109 
 Veins, 292 
 Villi, 309 
 Virgin dip, 58 
 
 soils become acid, 230 
 Viscoid, 37 
 Viscose, 37 
 Vivianite, 162 
 Volatile oils, classification of, 49 
 
 definition of, 47 
 
 methods of extraction of, 48 
 
 properties of, 48 
 
 W 
 
 WASTE water in soil, 172 
 
 Water, absorption of, by seed, 74 
 amount of, in seeds, 73 
 determination of, in plants, 103 
 function of, in plant, 95 
 for germination, 73 
 passage of, into plant, 83 
 in soil, composition of, 170 
 soluble arsenic, 267 (footnote) 
 vapor in air, 126 
 withdrawal of, from roots, 84 
 
 Wavellite, 163 
 
 : Waxes, 46 
 
 Weende method for analyzing 
 foods, 102 
 
 Weight of air, 125 
 
 Well-rotted manure, 247 
 
 Wheat seed, discussion of compo- 
 sition of, 112 
 
 Whey, 325 
 
 White alkali, 183 
 corpuscles, 294 
 
 Wood ashes, 221 
 gum, 39 
 
 Wool waste as a fertilizer, 205 
 
 XANTHOPROTEIC reaction, 63 
 Xylan, 39 
 Xylose, 39 
 
 YELLOW dip, 58 
 Yields of crops, 108 
 
 ZEIN, 63
 
 UNIVERSITY OF CALIFORNIA, LOS ANGELES 
 
 THE UNIVERSITY LIBRARY 
 This book is DUE on the last date stamped below 
 
 MAY 2 Wffi 
 
 ex 
 
 DEC * 8 1953 
 
 REC'D LO-URC 
 U> 
 
 
 JAN 
 81979 
 
 Form L- 
 23m-tO,'41<24M) 
 
 THE LIBRARY
 
 3 1158 00413 3202 
 
 " " HI ii in in || | || I 
 
 A 001 131 532 2