3/4 PRINCIPLES OF AGRICULTURAL, CHEMISTRY 



Cellulose may be dissolved in a solution of copper oxide in am- 

 monia. It also dissolves in concentrated sulphuric acid. If the 

 solution is immediately diluted with water, a jelly-like mass is 

 precipitated. If digested for some time with the acid, and the 

 solution then diluted and boiled for some time, sugar is produced. 

 The product is glucose from cotton and many other celluloses, 

 but d-mannose is secured from some other celluloses, such as 

 those from the coffee bean and sesame seed. The function of 

 cellulose in plants is to form the structure of plant cells. In seeds 

 it acts as a reserve material. Digested cellulose appears to be 

 equal in value to other carbohydrates. Cellulose contains 44.4 

 per cent, carbon. 



Lignin. This is the term applied to the incrusting substances 

 which accompanies the cellulose in wood and woody cells. Crude 

 fiber is largely composed of this mixture or, perhaps compounded 

 of cellulose and lignins. The chemical nature of the lignins is 

 not clearly known. They do not appear to belong to the group 

 of carbohydrates, but contain 55-60 per cent, carbon. Cutin con- 

 tains 68-70 per cent, carbon. 



The quantity of lignins in the plant increases with the age of 

 the plant tissue. Young woody tissue may contain little lignin, 

 while old woody tissue may be composed largely of it. The 

 greater the quantity of lignin in the material, the lower its value 

 for feeding purposes. 



Hemicelluloses. This term has been proposed for the carbo- 

 hydrates of the cell walls which are insoluble in water, but, un- 

 like cellulose, are brought in solution by dilute acids or alkalies. 

 Such carbohydrates are of extensive occurrence. The sugars pro- 

 duced by their hydrolysis are both pentoses and hexoses. 

 Hydrated celluloses, formed by the union of cellulose with water, 

 are largely dissolved by acids or alkalies, and hence would be 

 classed with the hemicelluloses. 



Pentosans. Pentosans may be defined as carbohydrates insol- 

 uble in water, which yield pentose sugars on hydrolysis. The 

 reaction resulting in the formation of furfural when pentosans 

 are boiled with strong acids, is used for their estimation. The 



