Organic agricultural chemistry

Front matter

Glass O j

Book jQ -

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Preface

Agricultural chemistry is a subject presenting two quite distinct lines of study. The study of soils and fertilizers, including the relation of the plant to its soil food, is almost wholly inorganic and physical. On the other hand, the study of plants and animals as living organisms is as distinctly organic and physiological, embracing the greater part of what is termed Bio-chemistry.

This has led the author to prepare one part of a textbook of General Agricultural Chemistry with this distinction in view, and to designate it as Organic Agricultural Chemistry — The Chemistry of Plants and Animals. The companion volume on Inorganic Agricultural Chemistry — The Chemistry of Soils and Fertilizers — is being prepared by the author's associate, Dr. Ernest Anderson.

The author believes that there is a place in our Agricultural Colleges for a course covering the work included in these two volumes with the definite aim of giving to students of practical agriculture enough general scientific instruction in chemistry to enable them to understand and correlate the broad problems of agricultural practice. The course covered by the two books has been planned to follow a course in general chemistry such as is given in the Freshman year in most colleges, and assumes a knowledge represented by such work.

The present volume does not pretend in any sense to replace the more thorough study of both organic and physiological chemistry by those students preparing to be chemists or other scientific workers in agriculture. Assuming that the student has not had a special course in systematic organic chemistry, there is included, as Section I, the essentials of such a study as related directly to agriculture. Following this systematic study of organic chemistry the treatment in Section II is largely

VL11 PREFACE

physiological, and centers around the general subjects of food and nutrition as applies to both animals and plants and photosynthesis in plants. In the last section on Crops, Foods and Feeding the effort has been to present the chemical basis for the valuation of animal foods, but without entering into the discussion of the practical operation and results of animal feeding.

In presenting the physiological chemistry of plants and animals a departure has been made from the usual custom, and the detailed study of animals and animal nutrition is considered before that of plants. The author believes that this procedure presents bio-chemistry in such a way that the student gains the correct view of plants and animals as living organisms. It also emphasizes the real differences between these two forms while retaining the idea of fundamental similarity.

There has been no effort to make the book a handbook of facts in regard to the subjects treated, and it is not a textbook of agricultural analysis, the methods mentioned being considered only as to the fundamental principles. The presentation is general and is in the lecture style with the underlying purpose of making a book of the most value to students as a text for class use. Laboratory experiments have been incorporated in the text as this has seemed to be desirable. Except in connection with the tables practically no references to literature have been cited, but at the end of each section a list is given of reference books which cover the subjects discussed. The author wishes to give full credit to all of these books as sources of the material presented.

The book is the result of five years' experience in giving a course in general agricultural chemistry to students in practical agriculture and horticulture in the Massachusetts Agricultural College, the work in the present volume being carried in a course of two lectures and one laboratory per week for one semester.

While intended primarily for use in Agricultural Colleges, the author hopes that the book may be found of value in other colleges where an elementary presentation of bio-chemistry is desired.

PREFACE ix

Finally the author wishes to acknowledge the assistance and cooperation of his associate, Dr. Ernest Anderson, and of all others who have in any way aided him in the work.

JOSEPH S. CHAMBERLAIN.

Massachusetts Agricultural College,

Amherst, Massachusetts.

November 15, 1915.

Table Of Contents

PAGES

Introduction 1-2

Chapter I. Hydrocarbons 5-17

Experiment Study I ; Hydrocarbons from wood and coal, 7. Methane, 7. Occurrence, properties, constitution, 7, 8. Structural formula, 8. Experiment Study II; Methane, 9. Substitution, 10. Synthesis of higher hydrocarbons, 13. Isomerism, 15.

Chapter II. Substitution Products of the Hydrocarbons 18-41 Halogen compounds, 18. Chloroform, iodoform, carbon tetrachloride, 18. Experiment Study III; Halogen substitution products, 19. Halogen ethanes, 19. Isomerism of di-brom-ethane, 20. Cyanides and amines, 21. Cyanamide, 23. Calcium cyanamide, 23. Experiment Study IV ; Cyanides, 25. Hydroxy substitution products or alcohols, 25. Alcohol series, 26. Experiment Study V; Distillation of alcohols, Fractional distillation, 26. Table I; Alcohol per cent and specific gravity, 28. Methyl alcohol, 29. Experiment Study VI; Methyl alcohol, 30. Ethyl alcohol, 31. Experiment Study VII; Ethyl alcohol, 31. Alcoholic fermentation, 32. Enzymes, zymase, 33. Experiment Study VIII ; Alcoholic fermentation, 34. Diastase, 34. Absolute alcohol, 36. Alcoholic beverages, 36. Industrial uses, 37. Taxation, 37. Denatured alcohol, 38. Higher alcohols, 39. Experiment Study IX; Amyl alcohol, 40. Polyhydroxy alcohols, 40. Glycol, 40. Glycerol, 41. Higher polyhydroxy alcohols, 41.

Chapter HI. Oxidation Products of Alcohols . . . 42-53 Aldehydes, 42. Formaldehyde (formalin), 43. Acetaldehyde, 44. Aldehyde reactions; addition compounds, oximes,

Xll TABLE OF CONTENTS hydrazones, 44. Experiment Study X; Aldehydes, 45. Acids, 46. Acetic acid series, 47. Formic acid, 48. Experiment Study XI; Formic acid, 48. Acetic acid, 49. Glacial acetic acid, 49. Vinegar, 50. Experiment Study XII; Acetic acid and vinegar, 51. Polycarboxy acids, 51. Oxalic acid, 52. Experiment Study XIII; Oxalic acid, 53. Succinic acid, 53.

Chapter IV. Derivatives of Alcohols and Acids . . 54-65

Ethers, 54. Ethyl ether, 54. Experiment Study XIV; Ether, 55. Acid chlorides and acid amides, 55. Esters, 56. Simple esters, 56. Fruit flavors, 56. Fats, oils and waxes,

57. Fatty acids, 57. Glycerol esters, 58. Esterification,

58. Hydrolysis, 59. Soap, 60. Saponification, 60. Important fats and oils, 60. Physical constants, 61. Chemical constants, 61. Table II; Fats and oils, 62. Experiment Study XV; Esters, 62. Experiment Study XVI; Fats and soap, 63.

Chapter V. Mlxed Compounds 66-81

Halogen-aldehydes, 66. Tri-chlor-aldehyde, chloral, 66. Halogen- acids, 67. Hydroxy-acids, 67. Lactic acid, 68. Stereoisomerism, 69. Optical activity, 69. Asymmetric carbon, 71. van't Hoff-Le Bel, 71. Tetrahedral theory, 72. Inactive lactic acid, 73. Dextro lactic acid, 74. Levo lactic acid, 74. Malic acid, 75. Tartaric acid, 76. Cream of tartar, 76. Rochelle salt, 77. Tartar emetic, 77. Stereoisomerism of tartaric acid, 78. Dextro-, levo-, racemic- and meso-tartaric acids, 78. Citric acid, 80. Experiment Study XVII ; Lactic, malic, tartaric and citric acids, 80.

Chapter VI. Amino-acids, Proteins, Urea, Uric Acid . 82-103

Amino-acids, 82. Glycine, 84. Hippuric acid, 84. Alanine, 85. Higher amino-acids, 85. Proteins, 87. Physical properties, 88. Chemical properties, 90. Composition, 90. Analysis, 90. Kjeldahl method, 90, 93. Molecular weight, 90. Hydrolytic decomposition, 91. Polypeptides, 92. Experiment Study XVIII; Proteins, 93. Urea, uric acid and purine bases, 97. Urea, 97. Biuret, 101. Experiment Study XIX; Urea, 101. Uric acid and purine bases, 102. Xanthine, caffeine, theobromine, 103.

TABLE OF CONTENTS Xlll

PAGES

Chapter VII. Carbohydrates 104-136

Composition, 104. Experiment Study XX ; General properties of carbohydrates, 105. Constitution, 105. Classification, 107. Trioses, 109. Pentoses, no. Experiment Study XXI; Pentosans and pentoses, no. Hexoses, no. Glucose, in. Determination, in. Fermentation of glucose, 113. Fructose, 113. Galactose, 114. Experiment Study XXII; Hexoses, 114. Disaccharoses, 115. Sucrose or cane sugar, 115. Hydrolysis, 117. Inversion, 117. Invert sugar, 117. Sugar analysis, 118. Maltose or malt sugar, 118. Lactose or milk sugar, 119. Experiment Study XXIII; Disaccharoses, 120. Polysaccharoses, 120. Hydrolysis, 120. Source of alcohol, 121. Starch, 121. Hydrolysis, 122. Source of glucose, 123. Determination, 123. Experiment Study XXIV; Starch, 123. Dextrin, Glycogen, 124. Inulin, Cellulose, 125. Paper, 126. Mercerized cotton and artificial silk, 127. Explosives and celluloid, 127. Experiment Study XXV; Cellulose, 128. Table III; Summary of carbohydrates, 129. Unsaturated compounds, 130. Conclusion, 134. References to Section I, 135.

Section II. Physiological . . 137

Chapter VIII. Enzymes and Enzymatic Action . . . 139-145 Enzymes and fermentation, 139. Definition, 140. General nature of enzymes, 140. Reactions brought about by enzymes, 141. Hydrolyzing enzymes, 141. Oxidizing enzymes, 142. Reducing enzymes, 142. Coagulating enzymes, 142. Decomposing and splitting enzymes, 142. Character of enzyme action, 142. Specific, 142. Reversible, 143. Zymogens, 143. Co-enzymes and anti-enzymes, 144. Names of enzymes, 144. Table IV; Enzymes, 145.

Chapter IX. Composition of Plants and Animals . . 146-153 Organic and inorganic constituents, 146. Volatile and nonvolatile constituents, 147. Ash, 149. Table V; Volatile and nonvolatile constituents, 150, 151. Experiment Study XXVI; Organic and inorganic constituents, 152.

Chapter X. The Living Cell and its Food . . . 154-158 Plant and animal cell alike, 154. Composition of the cell, 154. Cell energy and cell food, 155. Food as energy ma-

XIV TABLE OF CONTENTS terial, 155. Oxidation of food, 156. Heat and work, 156. Food as building material, 157. Function of food, 157. Plants and animals compared, 157.

Chapter XI. Animal Food and Nutrition; Digestion and

Absorption 159-189

Animal food, 159. Definition, 159. Utilization of food, 160. Mastication, 161. Digestion, 162. Digestive region, 163. Digestion of carbohydrates, 163. Monosaccharoses, final product of digestion, 164. Hydrolysis of di- and polysaccharoses, 164. The mouth, 165. Saliva, 165. Enzymes of saliva, 166. Ptyalin and maltase, 166. Conditions of salivary action, 167. Salts in saliva, 167. Organic compounds in saliva, 168. Experiment Study XXVII ; Salivary digestion, 168. The stomach, 169. The small intestine, 170. Pancreatic juice, amylopsin, 170. Intestinal juice, 170. Sucrase, maltase and lactase, 171. Digestion of proteins, 171. The stomach, 172. Gastric juice, 172. Rennin, 173. Pepsin, 173. Hydrochloric acid, 173. Experiment Study XXVIII; Gastric digestion, 174. The small intestine, 175. Pancreatic juice, 176. Hormones, 176. Pancreatic rennin, 177. Trypsin, 177. Trypsinogen, 177. Enterokinase, 177. Intestinal juice, 178. Erepsin, 178. Digestion of fats, 179. Hydrolysis of fats, 179. The stomach, gastric lipase, 180. The small intestine, pancreatic lipase, 180. The bile, 181. The large intestine, 182. Absorption of food, 183. Absorption of carbohydrates, 183. Absorption of proteins, 184. Absorption of fats, 185. Resume of digestion and absorption, 186. Time for food passage, 188.

Chapter XII. Animal Food and Nutrition; Metabolism 190-208 Metabolism, Anabolism, Katabolism, 190. Metabolism of carbohydrates, 191. Direct metabolism, 191. Glycogen, 192. Conversion of glycogen into glucose, 192. Amount of glycogen in the liver, 192. Oxidation of glucose, 193. Muscle glycogen, 194. Conversion of carbohydrates into fats, 195. Feeding experiments, 195. Respiratory quotient, 196. Metabolism of fats, 198. Body fat and milk fat, 199. Conversion of fats into carbohydrates, 200. Metabolism of proteins, 201. Amino-acids, 201. Polypeptide nucleus, 202. Serum albumin, 202. Body protein, 203. Oxidation of protein, 203. Katabolism of protein, 204. Katabolic products,

TABLE OF CONTENTS

XV

204. Nitrogen excretion in urine, 205. Formation of urea, etc., 205. Conversion of proteins into carbohydrates, 206. Conversion of proteins into fats, 207.

Chapter XIII. Milk, Blood and Urine .... 209-231 Milk, 209. Constituents, 209. Carbohydrates, 209. Fats, 210. Proteins, 211. Casein, 212. Lactalbumin, 212. Inorganic salts, 212. General properties, 214. Analysis, 215. Preservatives, 216. Butter, 216. Cheese, 217. Whey, 217. Food value, 218. Experiment Study XXIX; Milk, 218. Blood, 219. Properties, 220. Constituents, 220. Erythrocytes, 220. Haemolysis and haemagglutination, 220. Haemoglobin and oxyhaemoglobin, 221. Leucocytes, 222. Blood plasma, 223. Blood serum, 223. Serum albumin, 224. Fibrinogen and fibrin, 224. Clotting, 224. Experiment Study XXX; Blood, 226. Urine, 226. Constituents, 227. Nitrogen compounds, 227. Urea, 227. Isolation and determination, 227. Uric acid, 228. Creatinine, 228. Ammonia, 228. Hippuric acid, 229. Pathological constituents, 229. Glucose, 229. Albumin, 230. General properties, 230. Experiment Study XXXI ; Urine, 231.

Chapter XIV. Plant Physiology 232-258

Plants and animals compared, 232. Similarity, 232. Differences, 235. Exothermic and endothermic reactions,

235. Animals liberate energy, 236. Plants store energy,

236. Photosynthesis, 237. Source of energy, 237. Chlorophyll bodies and chlorophyll, 238. Products of photosynthesis, 238. Function of products of photosynthesis, 241. Carbohydrates, 241. Carbohydrates present in plants, 242. Metabolic transformations, 242. Sugars, 243. Translocation material, 243. Cell food, 243. Starch, 244. Reserve food, 244. Diastase and maltase, 244. Germination, 245. Experiment Study XXXII; Diastase and starch, 246. Building material, 246. Cell wall, 247. Cellulose, 247. Fats and proteins, 248. Synthesis of fats and proteins, 248. Location of fats, 249. Location of proteins, 249. Source of nitrogen, 249. Nitrogen cycle, 250. Fixation of atmospheric nitrogen, 251. Metallic nitrides, 251. Electrical discharges, 251. Nodule bacteria, 252. Reactions of nitrogen cycle, 254. Diagram of nitrogen cycle, 255. Resume, 255. References to Section II, 257.

XVI TABLE OF CONTENTS

PAGES

Section III. Crops, Foods And Feeding 259

Chapter XV. Occurrence and Uses of Important Constituents in Agricultural Plants 261-276

Carbohydrates, 261. Cellulose, 262. Forms of cellulose, 262. Normal celluloses, 262. Hemicelluloses, 263. Lignocelluloses, 264. Pectocelluloses, 264. Cellulose as food, 265. Crude fiber, 265. Table VI ; Cellulose content of crops, 266. Experiment Study XXXIII ; Cellulose and crude fiber, 267. Starch, 267. Starch as food, 268. Industrial uses, 268. Table VII; Starch content of crops, 269. Experiment Study XXXIV; Starch, 270. Dextrin, Glycogen, Inulin, Mannan, Galactan, 270. Pentosans, 272. Experiment Study XXXV; Pentosans, 273. Sugars, 274. Sucrose, 274. Maltose, 275. Monosaccharoses, 275. Table VIII; Sugar content of crops, 276.

Chapter XVI. Occurrence and Uses of Important Constituents est Agricultural Plants {Continued) . . 277-287

Fats and waxes, 277. Plant fats as food, 277. Occurrence, 277. Oil-yielding plants, 278. Table IX; Fat content of crops, 280. Lecithin and phytosterol, 280. Phytosterol and cholesterol, 280. Lecithin, 282. Physiological function, 283. Proteins, 283. Forms of protein, 283. Occurrence, 284. Table X; Protein content of crops, 285. Amino-acids, Alkaloids, Essential Oils, Terpenes, Tannins, etc., 286. End products of metabolism, 286.

Chapter XVII. Animal Foods and Feeding . . . 288-305

Food value, 288. Quantitative relation of food to energy, 288. Digestibility, 289. Coefficient of digestibility, 289. Table XI; Coefficients of digestibility, 290. Application of coefficients of digestibility, 291. Table XII; Digestibility of foods, 292. Energy value of food constituents, 293. Fuel value, 293. Bomb calorimeter, 293. Calorie, 294. Fuel values in calories, 294. Corrected fuel values, 295. Metabolizable or available energy, 295. Table XIII; Fuel values of food constituents, 296. Fuel values for cattle, 296. Table XIV ; Fuel values and metabolizable energy for cattle, 298. Food requirement, 298. Energy requirement, 298. Maintenance requirement, 298. Respira-

TABLE OF CONTENTS XVli tion calorimeter, 299. Production value, 299. Energy requirement for man, 300. Table XV; Production values for cattle, 301. Summary, 301. Table XVI; Digestibility and energy values for cattle, 302. Nutritive ratio, 302. Protein requirement, 303. References to Section III, 305.

Introduction

That part of Agricultural Chemistry which we may term Organic has to do with living plants and animals. Considered agriculturally as farm products, animals and plants have three general uses : (i) as servants of man in performing work, (2) as food for animals including man, (3) as material, or for furnishing material for the use of man in other ways than as food. A knowledge of the chemistry of plants and animals is of value in understanding their uses in these various ways and in showing how their economic value may be increased by greater production, greater conservation or the development of new uses.

The chemistry of living organisms is termed bio-chemistry and as a whole includes all of their physico-chemical relationships, especially those connected with the inorganic soil food of plants. This latter part of bio-chemistry we shall not consider, as it belongs to the inorganic division of agricultural chemistry.

The present study will treat of the composition of plants and animals and later of the physiological processes by which their body substance is built up and the energy of their living processes is produced. It will thus be largely physiological, with especial attention to the general subjects of food and nutrition and photosynthesis.

In order to understand the composition of plants and animals and the chemical reactions involved in their living processes, it is necessary to know the nature of the individual compounds of which they are constituted. As the greater part of these are what we term organic, and as these alone are related directly to the energy of the living organism, we shall take up first a brief study of systematic organic chemistry, discussing only such compounds as are directly related to agriculture.

We shall then be in a position to study the fundamental processes and reactions of living things and those particular physiological processes which differentiate plants from animals.

2 INTRODUCTION

Finally, as the agricultural problems with animals are largely those connected with animal feeding and as plants are the main food supply of domestic animals, we shall consider the distribution of food constituents in plants and the fundamental principles of animal foods and feeding together with the use of certain plants or plant products for other purposes than feeding, such as the manufacture of various materials of economic value.

Our entire study will thus be divided into three sections, as follows :

Section I. Systematic. The study of the composition, constitution, character and relationship of the more important organic compounds occurring in plants and animals.

Section II. Physiological. The study of the chemical reactions involved in the fundamental processes of living organisms, in the utilization of food by animals and in photosynthesis in plants.

Section III. Crops, Foods and Feeding. The study of the distribution of food constituents in agricultural crops and the principles of animal foods and feeding.

Section I Systematic

THE CHEMISTRY OF THE MORE IMPORTANT ORGANIC COMPOUNDS FOUND IN PLANTS AND ANIMALS

CHAPTER I HYDROCARBONS

A systematic study of organic chemistry directly connected with agriculture should embrace the study of those organic compounds which are of primary importance either as constituents of plants and animals or as products formed from them either naturally or artificially. In order to understand these compounds in their character and their relation to each other, it will be necessary to consider also a few typical ones which are not directly connected with plants or animals in any general agricultural sense.

Organic chemistry was originally so termed because the compounds included in it were produced by living organisms (plants and animals). With the development of this branch of the science of chemistry, many compounds have become known which are truly organic in their character and relationships, but have never been associated with either plants or animals; that is, they are still solely laboratory products. This has destroyed the original significance of the term organic. The word is still used, however, but in a broader sense.

All compounds which we class as organic are compounds of carbon, but a few carbon compounds are still held as truly inorganic, so that to term organic chemistry the chemistry of the compounds of carbon is not strictly true. However, all organic compounds are derivatives of certain fundamental compounds of carbon and hydrogen so that the best definition of organic chemistry is: the chemistry of the hydrogen compounds of carbon and their derivatives.

The hydrogen compounds of carbon will then be the starting point for the development of our study. As these compounds consist of the two elements, hydrogen and carbon, they are known as hydro-carbons. The hydrocarbons themselves are not found in either plants or animals. A few compounds of hydrogen and carbon do occur as plant constituents, e.g. turpentine, but these do not belong to the primary group of hydrocarbons.

The hydrocarbons are, however, a product of the decomposition of plant or animal substances. Plant and animal bodies consist largely of complex compounds of the elements carbon, hydrogen, oxygen, nitrogen, and sometimes sulphur and phosphorus. These compounds on decomposing, either by slow natural processes, as have taken place geologically in the formation of coal and petroleum, or by rapid artificial processes as in the distillation of wood, break down and yield eventually much more simple compounds. In the artificial distillation, some of the compounds obtained, e.g. wood alcohol and acetic acid, still contain carbon, hydrogen and oxygen, while others are gases containing carbon and hydrogen only, part of the oxygen going off in the form of water (H2O). The nitrogen is volatilized in the form of ammonia or ammonia-like compounds containing also carbon and hydrogen. In the natural geological decomposition of plant and animal substances the greater part of the carbon and hydrogen, however, remains in coal and petroleum and is easily volatilized from them, in the form of compounds containing only these two elements. Therefore we may say that petroleum, natural gas, coal and the gases formed by the natural decomposition of plant remains {marsh gas) , all contain, or at least yield by distillation, products which contain true hydrocarbons.

Although there are different theories as to the origin of such substances as petroleum, we may consider it as probably true that some at least of the petroleum and other materials, which are the sources of hydrocarbons, have been produced by the decomposition of plant and animal bodies from which the carbon and hydrogen have been derived.

EXPERIMENT STUDY I Hydrocarbons from Wood and Coal

(1) (a) Place a few dry wood shavings in a hard glass test tube. Fit the test tube with cork, glass and rubber tubing connections with a glass jet at the end. Heat the tube slowly and notice the moisture given off before the wood begins to char in case the wood was not perfectly dry. As the temperature becomes high enough to char the wood, notice the collection of moisture on the cool parts of the tube. This moisture comes from the decomposed wood. What two elements are, therefore, present in the wood? (&) When gas is being generated fast enough ignite it at the jet. Note character of flame, (c) Hold the burning jet inside a cool, dry, empty bottle. Let the jet burn in the bottle as long as possible. What does the moisture here prove? After the flame ceases to burn in the bottle pour into the bottle 25 c.c. limewater, and shake. The white precipitate proves that carbon dioxide (C0 2 ) is present. What does this mean? (d) Hold the burning jet against a cold piece of porcelain. What does this show? What do all these tests prove as to the elements contained in wood ?

(2) Repeat (1), using powdered soft coal instead of wood. The gas produced here is crude illuminating coal gas.

(3) Mix in a mortar 1 gram of wheat flour and an equal volume of fine soda lime. Heat the mixture in a test tube, and hold a piece of moist, red litmus paper at the mouth of the tube. Smell the gas given off. What is it ? What element does this prove to be present in the flour?

MARSH GAS — METHANE

Occurrence. — The gas rising from stagnant pools of water which contain decaying organic substances, commonly known as marsh gas, is known chemically as methane. It has also been obtained from petroleum and from coal and is found naturally in pockets and crevices in coal strata. It is prepared in the laboratory from a salt of acetic acid, a related compound, but it will not be necessary at this time to give the reactions involved in the preparation. (See Exp. II, 1, a.)

Properties. — By analysis the composition of methane has been shown to be 12 parts by mass of carbon to 4 parts by mass of hydrogen. Its molecular mass equals 16. It is represented, therefore, by the chemical formula CH 4 , or one atom of carbon to four atoms of hydrogen. It is a colorless gas lighter than air. It burns in the air with a yellow flame which deposits carbon on a cold surface. Mixed with air or with oxygen in the proportion of one volume of methane to two volumes of oxygen it explodes on ignition. Such an explosive mixture in coal mines is known as fire damp and is the cause of mine explosions.

Constitution. — It will not be necessary to consider in each case the proofs or reasons for conceptions which we shall bring forth, but merely state them, assuming that the proofs not here given have been fully developed.

In considering methane as a chemical compound three facts are at the foundation of our conceptions in regard to it, and these conceptions will lead to an understanding of the definite relationship between all of the organic compounds which we shall study. These three facts are as follows :

Methane, CH 4 , is (1) A saturated compound.

(2) A symmetrical compound, in which all four of the hydrogen atoms stand in exactly the same relation to the carbon atom.

(3) The carbon atom in methane and in practically all organic compounds is tetravalent, i.e. it has the power of holding four and only four hydrogen atoms, or any other univalent element, or group of elements, in combination.

Structural Formula. — The result of these facts is expressed in what is termed the structural or constitutional formula for methane, i.e. a formula which indicates the way in which the compound is built up or constituted. The geometrical figure which can represent perfect symmetry of one body joined to four others is the regular tetrahedron, and in all space relation formulas carbon is considered as being at the center of such a tetrahedron with one hydrogen (in the case of methane) situated at each apex.

Such a formula was suggested by van't Hofi" and is, because of the wonderful way in which it explains and agrees with facts, universally accepted as the complete structural or stereochemical (space relation) formula for methane. For the sake of expression on a plane surface in writing, this formula is modified to show only two dimensions, but retaining the ideas of symmetry, tetravalence and saturation :

H I

I

H

This formula is the plane structural formula to represent methane and to indicate the three facts previously mentioned : (1) saturation of carbon, (2) symmetry of the compound, i.e. all the hydrogen atoms are alike in relation to the carbon, and (3) tetravalence of carbon.

EXPERIMENT STUDY II

Methane, Marsh Gas

(1) (a) Mix in a mortar 10 grams fused, dry sodium acetate and 20 grams fine soda lime. Fill a test tube (hard glass) about half full, and hold horizontally and tap until the contents lie in the tube leaving a space along the top. Incline the tube slightly downward when heating. Connect the tube by means of glass and rubber tubing so as to generate gas and collect over water in small bottles or test

IO ORGANIC AGRICULTURAL CHEMISTRY

tubes. Heat the tube slowly and thoroughly until all the gas is evolved. Collect three or four bottles or tubes of gas. (b) While the gas is generating freely insert a glass jet at the end and ignite the gas, and repeat Experiment I, i, b. c. d.

(2) (a) Bring a flame to the mouth of one of the bottles of gas.

(b) Mix one bottle with an equal volume of air and ignite the mixture.

(c) Mix one volume of gas with ten volumes of air and ignite.

(d) Mix one volume of dry gas with two volumes of dry chlorine gas and ignite. Note character of flame and residue of carbon in the bottle after ignition. After ignition add a little water to the bottle and shake. Test water in bottle for hydrochloric acid, (e) Mix one volume of dry gas with two and one half volumes of dry chlorine gas. Allow the mixture to stand in the light for several days. Test for hydrochloric acid and examine for carbon residue. (Note. — These last two experiments are better performed in the lecture room. If they have been done there omit, but write up the results in the notebook.)

SUBSTITUTION

For the most part the hydrocarbons are characterized as inactive compounds. This is indicated by the name given to those similar to methane, viz. paraffins, from " parum affinitas" little affinity. This property of inactivity shows itself toward almost all ordinary reagents, such as acids, alkalies, oxidizing and reducing agents, etc. Toward only one group of elements does methane show any reactivity. The halogen elements, chlorine and bromine, do react with methane when brought in contact with it.

When chlorine reacts with methane suddenly at high temperatures, as when a mixture of the two gases is ignited, the methane is decomposed and all of the hydrogen unites with the chlorine, forming hydrogen chloride, and the carbon is left free. (See Exp. II, 2, d~) This is represented by the following reaction :

If, however, the action takes place slowly, as in case a mixture of the two gases is allowed to stand in diffused light, then

HYDROCARBONS II

another reaction takes place by which the four hydrogen atoms are removed by the chlorine atom by atom, and each time a hydrogen atom is removed a chlorine atom takes its place. (See Exp. II, 2, e.) The steps in this series of reactions are as follows :

3 CH3CI + 3 Cla -> 3 CH 2 C1 2 + 3 HC1 2 CH 2 C1 2 + 2 Cla -> 2 CHCI3 + 2 HC1 CHCI3 + Cl2-> CCI4 + HC1 or 4 CH4+ioC1 2 ->(CH 3 C1+CH 2 C1 2 +CHC13+CC1 4 ) + ioHC1

Such products formed from the hydrocarbons or other compounds by substituting for one or more of the hydrogen atoms an equivalent number of atoms of other elements are known as substitution products, and the phenomenon is called substitution. We shall find that numerous series of substitution products are known which have different groups acting as substitutes. The most important ones are those in which one of the halogen elements (CI, Br, I), the hydroxyl group (OH), the amino group (NH 2 ), the nitro group (N0 2 ), the sulphuric acid group (S0 2 OH), the cyanogen group (CN) become substituted for a hydrogen atom of a hydrocarbon. Also one oxygen atom (O) may take the place of two hydrogen atoms.