The chemistry of plant and animal life

Front matter

s

THE CHEMISTRY

OF

Preface To First Edition

This book is the outgrowth of instruction in chemistry given in the School of Agriculture of the University of Minnesota. At first the classes were small, and individual work with blackboard exercises and references to the literature in the school library was possible. With increased number of students, mimeographed notes were supplied, until finally the size of the classes and the volume of the notes have necessitated their publication in book form. The work was first given, in 1 891, to a class of seven students, while in 1903 they numbered 150.

The students to whom this instruction has been given have been mostly earnest workers who attended school mainly from personal choice and who desired to make as much progress as possible. Numerous questions have been asked by them relating to the application of chemistry to farm and everyday life, and for a number of years the author kept a box in which were placed the more important of these questions together with notes of the difficulties experienced in the laboratory : and in developing the work from year to year these questions and difficulties have been considered.

This work was originally outlined as Agricultural Chemistry, but as special features have been developed and published, as "Soils and Fertilizers," and "The Chemistry of Dairying," this part of the subject has gradually developed into " The Chemistry of Plant and Animal Life," and includes the composition of plant and

VI PREFACE TO FIRST EDITION

animal bodies, the chemistry of the plant and of its food and growth, the chemistry of human foods and animal nutrition, the digestibility and value of foods and the laws governing their economic use. A few topics of an industrial nature but closely related to plant and animal life are also included.

Before taking up the parts relating to the chemistry of plant and animal bodies, the elements and the simpler compounds present in plants and animals, together with the laws governing their combinations, are considered so as to prepare the way for a more intelligent study of the subject, and to show the relation which exists between chemistry and plant and animal life. Laboratory practice forms an important feature, and questions are asked in connection with each experiment. Many of the experiments and problems are given to illustrate some special phase of the composition of plant and animal bodies. The illustrations, with the exception of a few as noted, are original.

It has been the aim throughout to present the topics

in such a way that they would be easily understood and to

develop the reasoning powers of the student so that he

would be able to make the best use of his chemistry in

everyday life affairs.

HARRY SNYDER.

St. Anthony Park, St. Paul, Minn.

First edition, March i, 1903.

Second edition, Nov. 11, 1903.

Preface To' Revised Edition

In revising this work it has been the aim to retain the individuality as expressed in the preface of the first edition, with such changes and additions as are in accord with recent investigations.

It has been deemed best to make a sharper division between the first part, which deals with the elementary principles of chemistry from an agricultural viewpoint, and the second part, dealing more distinctively with the chemistry of plant and animal life.

Many colleges in which this subject is taught give more extended courses in general chemistry than is presented in Part I of this work, in which case the student is already prepared, with a special review, to begin Part II. In other institutions the time allotted to chemistry is so limited as to necessitate a brief course, and then Part I or its equivalent should be given before undertaking Part II.

The problems, laboratory practice, and collateral reading as suggested, are essentials of the work, and sufficient time should be allotted in the curriculum, to permit a rational study of the subject. It should be the aim to master the principles which form the basis of the subject so as to intelligently apply them to the solution of the new problems which continually present themselves.

HARRY SNYDER.

Minneapolis, Minn.

May, 19 1 3.

vii

Chapter II

Properties of Elements and Compounds. — Physical properties ; Chemical properties ; Symbols of the elements ; Formulas of compounds ; Atomic weights ; Molecular weights ; Law of definite proportion ; Valence ; Combination of elements ; Problems on combination of elements; Experiments and questions. Pages 9-18.

Chapter III

Laboratory Manipulation. — Importance of laboratory practice ; Names and uses of apparatus ; Cutting glass tubing ; Bending glass tubing ; Perforating corks ; Weighing ; Measuring liquids ; Obtaining reagents from bottles ; Filtering ; Laboratory notebook ; Breakage of apparatus ; Care of sinks and plumbing ; How to accomplish the best results in the laboratory. Pages 19-29.

Chapter VII

Carbon. — Occurrence ; Preparation ; Properties ; Coal ; Allotropism ; A reducing agent ; Combustion ; ' Spontaneous combustion ; A decolorizer and deodorizer ; Products of combustion ; Compounds of carbon ; Importance ; Experiments and questions ; Part taken in plant and animal life. Pages 45-53.

Chapter VIII

Water. — Chemical composition ; Physical properties ; Water of crystallization ; Natural waters ; Impurities and relation to diseases ; Location of wells ; Mineral impurities ; Contamination of drinking water ; Methods of improving drinking waters ; Water filters ; Experiments and questions. Pages 54-62.

Chapter IX

Air. — A mechanical mixture ; Carbon dioxid ; Ammonium compounds ; Moisture ; Atmospheric constituents present in small amounts ; Liquid air ; Organic impurities and ventilation of rooms ; Air, a source of plant food ; Sources of contamination of air ; Experiments and questions ; Importance of air in plant and animal life. Pages 63-68.

CONTENTS XI

Chapter X

Acids, Bases, Salts, and Neutralization. — Classification of elements ; Acids ; Bases ; Salts ; Radicals ; Naming of acids ; Naming of bases ; Naming of salts ; Double salts ; Acid salts ; Basicity of acids ; Two series of salts. Pages 69-75.

Chapter XI

Hydrochloric Acid, Chlorin, and Chlorids. — Occurrence ; Preparation ; Properties ; Preparation of chlorin ; Properties ; The chlorin group of elements ; Chlorids ; Problems ; Experiments and questions. Pages 76-81.

Chapter XII

Nitric Acid and Nitrogen Compounds. — Occurrence ; Preparation ; Properties ; Importance ; Ammonia ; Occurrence ; Preparation ; Properties ; Uses ; Oxids of nitrogen ; Anhydrids ; Law of multiple proportion ; Utilization of atmospheric nitrogen ; Importance of the nitrogen compounds ; Problems ; Experiments and questions. Pages 82-88.

Chapter XVI

Oxids of Carbon, Carbonates, and Carbon Compounds. — Carbon dioxid ; Carbon monoxid ; Marsh gas ; Hydrocarbons ; Petroleum ; Use of gasoline ; Illuminating gas ; Mineral oils ; Oil of turpentine ; Creosote ; Benzene or benzol ; Aliphatic and aromatic series of compounds ; Carbon disulfid ; Cyanids ; Carbids ; Fuels; B. T. U. value of fuels ; Foods ; Production of organic compounds in plants ; Decay of organic compounds; Experiments. Pages 1 02-1 14.

Chapter XVII

Writing Equations. — Importance ; Common errors in writing equations ; Impossible reactions ; A knowledge of reacting compounds and products necessary ; Equations for classroom work. Pages 1 15-120.

Chapter XVIII

Potassium, Sodium, and their Compounds. — Occurrence of potassium ; Potassium hydroxid ; Potassium nitrate ; Potassium carbonate ; Potassium chlorate ; Potassium sulfate ; Miscellaneous potassium salts ; Occurrence of sodium ; Sodium chlorid ; Sodium nitrate ; Sodium carbonate ; Sodium hydroxid ; Sodium phosphate ; Miscellaneous sodium salts ; Experiments. Pages 1 21-127.

Chapter XIX

Calcium, Magnesium, and their Compounds. — Occurrence of calcium ; Calcium carbonate ; Calcium oxid ; Calcium hydroxid ; Calcium sulfate ; Calcium chlorid ; Bleaching powder ; Calcium phosphate ; Mortar ; Glass ; Occurrence of magnesia ; Magnesium salts ; Experiments. Pages 128-132.

Chapter XX

Iron, Aluminum, and their Compounds. — Occurrence of iron ; Reduction of iron ores ; Wrought iron ; Steel ; Rusting of iron ; Iron Compounds ; Occurrence of aluminum ; Alums ; Pottery ; Experiments. Pages 133-140.

CONTENTS X1U

Chapter XXI

Copper, Zinc, Lead, Tin, Arsenic, Mercury, their Compounds and Alloys. — Commercial importance ; Occurrence of copper and its metallurgy ; Copper sulfate ; Bordeaux mixture ; Occurrence of zinc ; Compounds of zinc ; Galvanized iron ; Occurrence of tin ; Tin salts ; Occurrence of lead ; Oxids of lead ; Lead carbonates ; Lead salts ; Uses of lead ; Occurrence of arsenic ; Paris green ; Occurrence of mercury ; Compounds of mercury ; Experiments. Pages 141-146.

Chapter XXII

The Water Content and Ash of Plants. — Water ; Dry matter ; Plant ash ; Form of the ash elements ; Amount of ash in plants ; Importance of ash elements ; Water culture ; Sand culture ; Occurrence and function of ash elements ; Potassium ; Sodium ; Calcium ; Magnesium ; Aluminum ; Iron ; Phosphorus ; Sulfur ; Silicon ; Chlorin ; Experiments; Problems. Pages 149-167.

Chapter XXIII

The Non-nitrogenous Organic Compounds of Plants. — Organic matter ; Non-nitrogenous and nitrogenous organic compounds ; Classification of non-nitrogenous compounds ; Carbohydrates ; General characteristics ; Cellulose ; Occurrence ; Physical properties ; Chemical properties ; Function and value ; Food value ; Amount of cellulose in plants ; Crude fiber ; Starch ; Occurrence ; Physical properties ; Chemical properties ; Function and value ; Food value of starch ; Amount of starch in plants ; Dextrin ; Structural formulas ; Sugar ; Classification of sugars ; Occurrence of sucrose ; Physical and chemical properties of sucrose ; Milk-sugar ; Maltose ; Inversion of sucrose ; Refining of sugar ; Occurrence of dextrose ; Chemical and physical properties ; Levulose ; Miscellaneous sugars ; Optical properties of sugar ; Sugar-beets ; Food value of sugar ; Gums ; Pentosans ; Pectin bodies ; Nitrogen-free extract ; Fats ; Presence in plants ; Physical properties ; Chemical composition ; Stearin ; Palmitin ; Olein ; Miscellaneous fats ; Sa-

XIV CONTENTS

ponification ; Fatty acids ; Waxes ; Food value of fat ; Amount of fat in plants and foods ; Ether extract ; Organic acids ; Occurrence in plants ; Tartaric acid ; Malic acid ; Succinic acid ; Oxalic acid ; Citric acid ; Tannic acid ; Function and food value of the organic acids ; Essential oils ; General properties ; Occurrence ; Chemical composition and properties ; Essential oils of agricultural crops ; Synthetic production of essential oils ; Amount of essential oils in plants ; Food value ; Miscellaneous compounds in plants ; Relationship of non-nitrogenous compounds of plants ; Food value of the non-nitrogenous compounds ; Experiments and questions. Pages 168-203.

Chapter XXIV

Nitrogenous Organic Compounds of Plants. — Amount of nitrogenous matter in plants ; Different terms applied to nitrogenous compounds ; Complexity of composition ; Classification of nitrogenous compounds ; Proteids ; General composition ; Occurrence ; Physical properties ; Chemical properties ; Classification of proteids ; Albumins ; Globulins ; Albuminates ; Peptones and proteoses ; Insoluble proteids ; Food value of proteids ; Amount in plants ; Crude protein ; Albuminoids ; Composition ; Nuclein ; Gelatin ; Mucin ; Elastin ; Food value of albuminoids ; Amides and amines ; Composition and properties ; Formation and Occurrence in plants ; Formation and occurrence of amides in animals ; Food value ; Amount in foods ; Protein production and disintegration ; Alkaloids ; General composition ; Plant alkaloids ; Animal alkaloids ; Food value and production ; Mixed nitrogenous compounds ; Lecithin ; Nitrogenous glucosides ; General relationship of the nitrogenous organic compounds of foods ; Problems and experiments. Pages 204-223.

Chapter XXV

Chemistry of Plant Growth. — Seeds ; Ash ; Non-nitrogenous compounds ; Nitrogenous compounds ; Chemical changes during germination ; Change of starch to soluble forms ; Change of fats to starch ; Change of insoluble proteids to soluble forms ; Germination of seeds and digestion of food compared ; Necessary conditions for germination ; Heavy- and light-weight seeds ; Movement of

CONTENTS XV plant juices ; Joint action of chemical and physical agents ; Porosity of tissues ; Osmosis ; Chlorophyl and protoplasm ; Chemical action in leaves of plants; Production of chlorophyl; Function; Production of organic matter; Experiments. Pages 224-234.

Chapter XXVI

Composition of Plants at Different Stages of Growth. — Composition and stage of growth ; Assimilation of mineral food by the wheat plant ; Assimilation of nitrogen by the wheat plant ; Clover ; Rapidity of growth ; Flax ; Rapidity of growth ; Maize (corn) ; Importance ; Roots ; Stalks ; Leaves ; Tassel ; Husks ; Ripening period. Pages 235-244.

Chapter XXVII

Factors which influence the Composition and Feeding Value of Crops. — Seed ; Soil ; Climate ; Stage of maturity ; Method of preparation as food ; Improving the feeding value of forage crops. Pages 245-249.

Chapter XXVIII

Composition of Coarse Fodders. — Coarse fodders ; Straw ; Timothy hay ; Hay similar to timothy ; Oat hay ; Hay similar to oat hay ; Bromus inermis ; Clover hay ; Alfalfa and fodders similar to clover ; Rape ; Pasture grass ; Corn fodder and stover ; Silage. Pages 250-258.

Chapter XXIX

Wheat. — Structure of kernel ; Proteids of wheat ; Relation of nitrogen in wheat to nitrogen content of flour ; Influence of fertilizers upon composition of wheat ; Variations in composition of wheat ; Storage in elevators ; Manufacture of flour ; Composition of unsound wheat ; Composition of different varieties ; American and foreign wheats ; Wheat as animal food ; As human food ; Experiments and questions. Pages 259-272.

XVI CONTENTS

Chapter XXX

Maize (Indian Corn). — Structure of the kernel; Composition; Proteids ; Nitrogenous and non-nitrogenous corn ; Varieties ; Moisture content of corn ; Corn products ; Corn as a food ; Experiments. Pages 273-278.

CHAPTER XXXI Oats, Barley, Rye, Buckwheat, Rice, and Miscellaneous Seeds

Structure of the oat kernel ; Composition of oats ; Oats as human and animal foods ; Barley ; Rye ; Rice ; Buckwheat ; Millet seed ; Peas and beans ; Grading of grains ; Experiments. Pages 279-290.

Chapter XXXII

Mill and By-products. — Sources ; Wheat by-products ; Wheat bran ; Wheat shorts ; Wheat germ ; Wheat screenings ; Linseed meal ; Cottonseed cake and meal ; Oat feed ; Gluten meal ; Malt sprouts ; Miscellaneous by-products ; Inspection of feeding stuffs ; Problems and experiments. Pages 291-298.

Chapter XXXIII

Roots, Tubers, and Fruits. — General composition ; Potatoes ; Carrots ; Parsnips ; Mangel wurzels ; Apples ; Oranges ; Lemons ; Strawberries ; Grapes ; Olives ; Dried fruits ; Miscellaneous fruits ; Food value. Pages 299-303.

Chapter XXXIV

Fermentation. — Insoluble ferments ; Soluble ferments or enzymes ; Aerobic and anaerobic ferments ; Conditions necessary for fermentation ; Soil ferments ; Ferments in seeds ; Ferments in bread-making ; Ferment action and food digestion ; Ferments and food preservation; Ferments in butter- and cheese-making; Disease-producing organisms; Beneficial organisms; Experiments. Pages 304-310.

Chapter XXXV

Chemistry of Digestion and Nutrition. — Digestion, a biochemical process ; Digestion experiments ; Caloric value of foods ; Available

CONTENTS XV11

energy of foods ; Net energy of foods ; Digestion of proteids ; Digestion of the carbohydrates ; Digestion of fats ; Oxygen necessary for digestion ; Factors influencing digestion ; Mechanical condition ; Combination of foods ; Amount of food consumed ; Palatability; Individuality; Miscellaneous factors influencing digestibility ; Application of digestion coefficients ; Digestible nutrients of foods; Problems. Pages 311-327.

Chapter XXXVI

Rational Feeding of Animals. — Balanced rations ; A maintenance ration ; Standard rations ; Food requirements of animals ; Food supply at different stages of growth ; Food requirements of horses ; Selection of food for horses ; Foods required for beef production ; Selection of foods for beef production ; Food requirements of dairy cows ; Selection of foods for dairy cows ; Food requirements of swine ; Food requirements of sheep ; Calculation of balanced rations ; Nutritive ratio ; Comparative cost and value ; Caloric value of rations ; Sanitary conditions ; Problems. Pages 328-347.

Chapter XXXVII

Composition of Animal Bodies. — Water and dry matter ; Mineral matter ; Fat ; Nitrogenous matter ; Proteids of meat ; Albumin ; Myosin ; Syntonin ; Hemoglobin ; Insoluble proteids ; Peptones ; Keratin ; Albuminoids ; Gelatin ; Influence of food upon the composition of animal bodies ; Composition of human body. Pages

348-355-

Chapter Xxxviii

Rational Feeding of Men. — Similarity of the principles of human and animal feeding ; Dietary standards ; Amount of food consumed per day ; Calculating a balanced ration ; Comparative cost and value of foods ; Factors influencing digestibility ; Requisites of a ration ; Dietary studies ; Chemical changes in the cooking of foods ; Refuse and waste matters ; Loss of nutrients in the preparation of foods ; Mineral matter in a ration ; Digestibility of foods ; Digestibility of animal foods ; Digestibility of vegetable foods ; Relation of food to health ; Tables of composition of human foods. Pages 356-380.

XVI CONTENTS

CHAPTER XXX

Maize (Indian Corn). — Structure of the kernel; Composition; Proteids ; Nitrogenous and non-nitrogenous corn ; Varieties ; Moisture content of corn ; Corn products ; Corn as a food ; Experiments. Pages 273-278.

CHAPTER XXXI

Oats, Barley, Rye, Buckwheat, Rice, and Miscellaneous Seeds. —

Structure of the oat kernel ; Composition of oats ; Oats as human and animal foods ; Barley ; Rye ; Rice ; Buckwheat ; Millet seed ; Peas and beans; Grading of grains; Experiments. Pages 279-290.

CHAPTER XXXII

Mill and By-products. — Sources ; Wheat by-products ; Wheat bran ; Wheat shorts ; Wheat germ ; Wheat screenings ; Linseed meal ; Cottonseed cake and meal ; Oat feed ; Gluten meal ; Malt sprouts ; Miscellaneous by-products ; Inspection of feeding stuffs ; Problems and experiments. Pages 291-298.

CHAPTER XXXIII

Roots, Tubers, and Fruits. — General composition ; Potatoes ; Carrots ; Parsnips ; Mangel wurzels ; Apples ; Oranges ; Lemons ; Strawberries ; Grapes ; Olives ; Dried fruits ; Miscellaneous fruits ; Food value. Pages 299-303.

CHAPTER XXXIV

Fermentation. — Insoluble ferments ; Soluble ferments or enzymes ; Aerobic and anaerobic ferments ; Conditions necessary for fermentation ; Soil ferments ; Ferments in seeds ; Ferments in bread-making ; Ferment action and food digestion ; Ferments and food preservation ; Ferments in butter- and cheese-making ; Disease-producing organisms; Beneficial organisms; Experiments. Pages 304-310.

CHAPTER XXXV

Chemistry of Digestion and Nutrition. — Digestion, a biochemical process ; Digestion experiments ; Caloric value of foods ; Available

CONTENTS XV11

energy of foods ; Net energy of foods ; Digestion of proteids ; Digestion of the carbohydrates ; Digestion of fats ; Oxygen necessary for digestion ; Factors influencing digestion ; Mechanical condition ; Combination of foods ; Amount of food consumed ; Palatability; Individuality; Miscellaneous factors influencing digestibility ; Application of digestion coefficients ; Digestible nutrients of foods ; Problems. Pages 311-327.

CHAPTER XXXVI

Rational Feeding of Animals. — Balanced rations ; A maintenance ration ; Standard rations ; Food requirements of animals ; Food supply at different stages of growth ; Food requirements of horses ; Selection of food for horses ; Foods required for beef production ; Selection of foods for beef production ; Food requirements of dairy cows ; Selection of foods for dairy cows ; Food requirements of swine ; Food requirements of sheep ; Calculation of balanced rations ; Nutritive ratio ; Comparative cost and value ; Caloric value of rations; Sanitary conditions; Problems. Pages 328-347.

CHAPTER XXXVII

Composition of Animal Bodies. — Water and dry matter ; Mineral matter ; Fat ; Nitrogenous matter ; Proteids of meat ; Albumin ; Myosin ; Syntonin ; Hemoglobin ; Insoluble proteids ; Peptones ; Keratin ; Albuminoids ; Gelatin ; Influence of food upon the composition of animal bodies ; Composition of human body. Pages

348-355-

CHAPTER XXXVIII

Rational Feeding of Men. — Similarity of the principles of human and animal feeding ; Dietary standards ; Amount of food consumed per day ; Calculating a balanced ration ; Comparative cost and value of foods ; Factors influencing digestibility ; Requisites of a ration ; Dietary studies ; Chemical changes in the cooking of foods ; Refuse and waste matters ; Loss of nutrients in the preparation of foods ; Mineral matter in a ration ; Digestibility of foods ; Digestibility of animal foods ; Digestibility of vegetable foods ; Relation of food to health ; Tables of composition of human foods. Pages 356-380.

INTRODUCTION

Plant life and animal life are dependent upon the changes which are continually taking place in nature. The laws of nature, as far as they are known, are set forth in the various sciences, among which chemistry occupies a prominent place. In everyday life affairs, chemistry takes an important part because it is the science which treats of the composition and uses of substances found in nature. Plant and animal foods which are essential for life are simply mechanical mixtures of various forms of matter which are constantly undergoing changes and exemplifying the laws of chemistry. In agriculture, chemistry takes an important part, the term Agricultural Chemistry being applied to that branch of the science which concerns itself with the practical application of the laws of chemistry to the science of agriculture.

In the cultivation of the soil, production of crops, feeding of animals, manufacture of farm products, preparation and use of human foods, and in all life processes, numerous chemical changes take place, and it is in part the province of chemistry to investigate these changes so as to assist nature in rendering the plant food of the soil more available, and to produce crops of the highest nutritive value, as well as to indicate ways in which the best possible use can be made of farm products in the feeding of animals and men. Before these subjects can

xix

XX INTRODUCTION

be considered in an intelligent way, a fundamental knowledge must be obtained of some of the basic principles and laws of chemistry, since they are as essential to future work along special lines as is a good foundation to a building, or a scaffold during its construction. In the household, arts, industries, and professions, constant use is made of products formed from the soil, air, and water. In order to understand more perfectly the nature of the substances dealt with so as to make the most intelligent use of them, it is necessary to have a practical knowledge of some of the laws of chemistry and of the properties of the elements and the compounds which enter into the composition of plant and animal bodies.

To the student who begins the study of chemistry, it is imperative that the first part of the subject should be thoroughly mastered. Chemistry is different in its nature from many subjects. It cannot be studied in disconnected parts, but must be undertaken systematically. It cannot be absorbed by listening to lectures, but must be studied. If the first part of the work is neglected, failure is almost inevitable. If particular attention is given to the elements and their combinations, to the composition of matter, to laboratory manipulations, and to the classification of the elements, and if the experiments are performed regularly, the student experiences a keen enjoyment in the subject, the work ceases to be drudgery and becomes a pleasure.

Should it be desired to begin the laboratory practice with the classroom study, Sections 15 to 21 of Chapter 2 may be deferred or studied with Chapters 4, 5, and 6.

The student should make an effort to learn how to study ; the memorizing of chemical formulas and equations is not studying chemistry; he should master the

INTRODUCTION XXI

principles governing the combination of elements and then the memorizing of chemical formulas becomes unnecessary. In the preparation of the lessons, there are a number of reference books which should be consulted occasionally. For example, if difficulty is experienced with the subject of valence and radicals, the interesting chapter upon these topics in Ellen H. Richards' " Chemistry of Cooking and Cleaning " should be read. Remsen's " Chemistry," Hart's " Chemistry for Beginners," Storer and Lindsay's " Elementary Manual of Chemistry," as well as many others, will be found valuable. In studying the parts relating to foods, crops, and animal feeding, Henry's " Feeds and Feeding," Jordan's " Feeding of Farm Animals," Armsby's " The Principles of Animal Nutrition," Johnson's " How Crops Grow," and " How Crops Feed," and the bulletins of the U. S. Department of Agriculture and of the several stations should be available. The student should early acquire the habit of consulting other works, as frequently a topic is presented more clearly in one work than in another.

He who studies chemistry from the professional point of view, as medical chemistry, pharmaceutical chemistry, or agricultural chemistry, should remember that because of the limited time for the subject in professional schools, he is receiving at the best only a very abridged course in the science. Hence the necessity of supplementing it by collateral reading and study ; otherwise he comes in contact with but one phase of the subject, and while he receives a technical education, he may obtain only a limited and narrow view of the science of chemistry.

In the study of the " Chemistry of Plant and Animal Life," it is the aim to bring the student into close contact with nature. This is one of the requisites for perfect agri-

XX11 INTRODUCTION

culture. Although not all of the laws relating to the chemistry of plant and animal life have been discovered, many of those relating to soils and foods, particularly human foods, are known and can be applied, to everyday life affairs.

PART I

CHAPTER I Composition of Matter

i. Physical and Chemical Changes. — All substances in nature are subject to change in form and composition. At a low temperature water is converted into ice, and by the application of heat, into steam. The three forms which water assumes, solid, liquid, and vapor, are merely the different conditions in which it is capable of existing. When water is changed to steam or ice, nothing is added to or taken from the particles of water, simply a change of form or a physical change takes place. When, however, an electric current is passed through water, the water is decomposed and two gases are produced. When such a change occurs the water particles are subjected to a change in composition called a chemical change.

Limestone may be pulverized until it is as fine as wheat flour, and when examined with a microscope, each fragment is in all respects like the original piece, except in size. The crushing has resulted merely in dividing the limestone into a large number of particles. If, however, a piece of limestone is burned in a lime kiln, the product is entirely different in its properties from the original lime rock. When water is added to burned lime, the lime slakes, heat is generated, and steam is given off, while, when water is added to lime rock, no appreciable change takes place.

Changes which affect the form but not the composition of matter are known as physical changes. The production of steam from water, the freezing of water, the pulverizing of limestone, and similar changes which do not affect the composition of the material are physical changes. When milk sours, fruits decay, or wood is burned, a different kind of change takes place. The smallest particles of which the material is composed undergo change in composition. The products formed are entirely different in character from the original substances. Such changes affect the identity or individuality of a material, and are chemical changes.

2. Physics is the science which concerns itself with the changes which matter undergoes when the ultimate particles of a material retain their identity or individuality.

Animal and plant life are to a great extent dependent upon the physical changes which take place in the soil. Rain is the result of the action of physical agencies, as is also the pulverization of rocks and soils. In all manufacturing operations, and as the result of all kinds of manual labor, particularly upon the farm and in the workshop, physical changes are continually taking place.

3. Chemistry is the science which deals with the changes which matter undergoes when the ultimate particles lose their identity or individuality, and the products formed are entirely different from the original material.

Chemical changes are continually taking place, and plant growth and animal life are dependent largely upon the chemical changes as well as upon the physical changes which occur in the soil and in the air. Life processes are intimately associated with chemical changes. Chemical and physical changes are closely related ; a chemical change is often dependent upon a physical change, and a physi-

COMPOSITION OF MATTER 5

cal change is, in turn, often dependent upon a chemical change. A chemical change necessarily brings about a physical change. While the sciences of chemistry and physics are, to a certain extent, closely related, each nevertheless deals with a different phase of change which matter undergoes.

4. Indestructibility of Matter. — When either a chemcal or a physical change takes place, no matter is destroyed or produced. It is not possible either to create or destroy matter. This is known as the law of indestructibility of matter.

Whenever a chemical change takes place, the parts which make up the substance are rearranged in a new and different way, or they are combined with other materials. When wood is burned, it is changed into gaseous products and ashes ; the materials which composed the wood are not lost to nature, they simply assume a different form. The law of indestructibility of matter is one of the foundation principles of chemistry. It was believed, at one time, that metals, as copper, could be changed to gold, and other substances to different forms of matter. After many centuries of experimenting, it was found that this could not be done, and as the result, the law of indestructibility of matter was established.