82 THE CHEMISTRY OF CATTLE FEEDING 



of mela-phosphoric acid has been added. The soluble nitro- 

 genous compounds (amides) which are not coagulated by this 

 treatment are then filtered off. The residue which contains the 

 true, coagulated proteins, is well washed with the precipitating 

 reagent to complete the separation, and the nitrogen is 

 determined in it as before. In Stutzer's method, the soluble 

 proteins are precipitated by warming with moist cupric hydrate 

 instead of being coagulated with phenol ; but in other respects 

 it is the same in principle as that described above. 



The nitrogen in the coagulated residue multiplied by the 

 factor 6*25 gives the true protein. The difference between 

 this and the total nitrogenous matter or crude protein is often 

 rendered in analytical reports as amides. The value so 

 obtained, it will be seen, does not correspond to any particular 

 compound ; it is merely the non-protein or amidic nitrogen 

 multiplied by 6' 25. Sometimes this non-albuminoid nitrogen 

 is calculated as asparagine or other typical amide. Vegetable 

 matter, particularly roots, often contains a certain amount of 

 nitrogen as nitrates, which, of course, must be determined 

 separately. 



For further information see " Chemistry of Proteides " by 

 Mann. 



