152 ORGANIC AGRICULTURAL CHEMISTRY 



of this character. In the soil this inorganic food is present in 

 the form of salts, principally as nitrates, phosphates, chlorides 

 and sulphates of potassium, sodium, calcium and magnesium. 

 These salts constitute what is termed the soil plant food. 

 They are also the constituents of substances used to supply an 

 abundance of soil plant food in the form of manure or commer- 

 cial fertilizers, the latter being mostly of three kinds, viz. 

 nitrate, phosphate and potassium salts. All of this relationship 

 of the plant to the soil and to fertilizers is part of the study of 

 Inorganic Agricultural Chemistry. We shall, therefore, not 

 say anything further in regard to the inorganic constituents of 

 plants and give only slight references to the inorganic constit- 

 uents of animals. The chapters which follow will deal pri- 

 marily with the organic constituents and will endeavor to show, 

 by general and well-established facts, how these constituents 

 are produced, what their function is and how this function is 

 carried out. 



EXPERIMENT STUDY XXVI 



Organic and Inorganic Constituents of Plants and Animals 



(i) Organic or Volatile Constituents, {a) Place i.o g. of pure dry 

 wheat starch or potato starch in a porcelain crucible or evaporating 

 dish. Heat the dish gradually with low flame. Note charring of 

 the starch, indicating free carbon. As fumes are given off hold a test 

 tube, dry on outside but half full of cold water, in the vapor. Note 

 deposit of water vapor. Increase the heating, and hold in the vapor 

 a glass tube that has been dipped in limewater. A cloudy appear- 

 ance of the limewater on the tube shows presence of carbon dioxide 

 in the vapor. Continue to heat with full flame until all free carbon 

 has disappeared. What is the source of carbon ? What has become 

 of it? What other elements are shown to have been present in the 

 starch? Is there any ash left? {b) Repeat the experiment, using 

 pure fat, e.g. lard or cottonseed oil. (c) Repeat again, using pure 

 protein, e.g. white of egg or wheat gluten. 



(2) Inorganic or Nonvolatile Constituents, (a) Weigh a small 

 porcelain evaporating dish that has been previously cleaned, dried 



