6 SCIENTIFIC FEEDING OF ANIMALS 



oxygen, along with 0-3-2-3% of sulphur. In some 

 cases phosphorus is found, and in others a little 

 iron. 



When the proteins are pure and dry they form 

 a horny substance, which melts in the flame and 

 then burns to a black coal-like mass. At the same 

 time fumes, which have the smell of burning hair, 

 are given off. The products of such decomposition 

 vary considerably in their properties, according to 

 the substance which is heated. 



The proteins are further distinguished by the 

 ease or difficulty with which they dissolve in various 

 solvents, such as water, alcohol, salt solution, 

 caustic soda solution. They may be also charac- 

 terised by another set of properties, e.g. coagulation 

 on heating, precipitation from solution by metallic 

 salts or tannic acid, distinctive colouration when 

 acted upon by various reagents. 



It was thought for a long time that all the nitrogen 

 which is found in feeding-stuffs was present in the 

 form of albumin. For this reason, and also on 

 account of the impossibility of obtaining the pro- 

 teins from the plant or the animal in a sufficiently 

 pure state to be weighed, it has been the custom 

 to estimate the amount of nitrogen in a food, and 

 then calculate from this the percentage of protein 

 matter. The proteins were supposed to contain on 

 an average 16% of nitrogen, so by multiplying the 

 amount of nitrogen found by 6-25 the weight of 



