CHAPTER 1. 

 INTRODUCTION 



Agricultural chemistry concerns itself with the chemical com- 

 position of the food of plants and animals and with the chemical 

 changes involved in the processes of life. It has to deal with the 

 composition of soil, air, and water, of the bodies of plants and 

 animals, of manures and commercial fertilizers and with the 

 chemical changes which these substances undergo. 



Before beginning the study of the soil or air or the plant it 

 will be necessary for the student to learn something of the im- 

 portant elements concerned in agriculture and the meaning of 

 some of the common terms used in chemistry. 



The whole earth, so far as is known, is made up of about 

 eighty-one elements, a large proportion of which play little or 

 no part in the ordinary processes of plant and animal life. In- 

 deed a considerable proportion are found only in extremely small 

 quantities and are but curiosities to the student of chemistry. 

 From the standpoint of the farmer they possess no interest. They 

 are called elements for the reason that they are the simplest sub- 

 stances known, and cannot by any means yet discovered, be sep- 

 arated into simpler or different substances. Iron, gold, silver, 

 zinc, lead, and sulphur are examples of elements. 



The bodies of plants and animals are built up of compounds 

 of the following elements and these, therefore, become of the 

 first importance to the farmer : 



Oxygen Phosphorus Sodium 



Hydrogen Calcium Iron 



Carbon Magnesium Chlorine 



Nitrogen Potassium Silicon 

 Sulphur 



A short account of these elements will be given at this place. 

 Oxygen (0) is the most abundant and most important of the 

 elements. It forms about half the weight of the solid crust of 



