MANUAL OF CAITLE-FEEDING. 89 



by its slight solubility; neither dilute acids nor alkalies, 

 water, or any of the ordinary solvents, dissolve it. Hence, 

 it may be obtained by acting on vegetable matter with 

 various solvents till all other substances are removed. 



If cellulose be exposed for sonie time to the action of 

 strong oil-of- vitriol, or be boiled for some hours with dilute 

 acids or alkalies, it is converted iirst into dextrine and then 

 into grape-sugar. If treated with iodine and then with 

 strong sulphuric acid, it assumes a deep-blue color. This 

 reaction serves to identify cellulose under the microscope. 



Comjiodtlon. — Pure cellulose has exactly the same com 

 position as starch, viz. : 



Carbon 44.44 per cent. 



Hydrogen 6.17 '^ 



Oxygen .... 49.39 '' 



100.00 



As intimated above, however, it is seldom found pm*e, 

 except in the young and tender parts of plants, but is 

 usually more or less impregnated with substances to which 

 the collective name of lignin has been given, and the follow- 

 ing composition assigned : 



Caibon. 55,3 per cent. 



Hydrogen........ ^.8 '' 



Oxygen , 38. 9 " 



100.0 



This is, however, simply the inferred composition of 

 what is left after cellulose has been removed, and not the 

 result of direct analysis. But it is certain that lignin 

 (using the name in a collective sense) is richer in carbon 

 than cellulose, and as a membrane becomes impregnated 

 with the former, its percentage of that element increabCb. 



