PROTEINS AND AMIDES 151 



mixture heated to boiling. Substances containing 

 much starch should be heated on the water-bath for ten 

 minutes. A quantity of the cupric hydroxide reagent 

 containing 0-5 to 0-8 gram Cu(0H)2 is added to the 

 mixture, which is stirred well and allowed to cool. The 

 precipitate, which contains copper and the true proteins, 

 is filtered off, washed, dried, and the nitrogen estimated 

 by Kjeldahl's process. Nx6-25 (or the same factor 

 used for the crude protein) = Protein. 



To substances such as oilcakes, crushed seeds, etc., 

 which contain phosphates, it is advisable to add a few 

 cubic centimetres of a concentrated alum solution before 

 using the cupric hydroxide reagent. This decomposes 

 alkaline phosphates ; otherwise alkali may be set free 

 from the phosphates and cupric phosphate formed, some 

 of the albuminoids being dissolved. 



(/) Non-Protein Nitrogenous Material. 



These substances, consisting chiefly of amides and amino- 

 acids, etc. (see 11, p. 18), are present in considerable quantity in 

 some feeding stuffs, e.g. mangolds. Their nutritive value is not as 

 great as that of the proteins, and consists largely in conserving the 

 true proteins. 



The non-protein nitrogenous matter is obtained by 

 difference from the crude protein and the true protein, 

 estimated as above. 



Non-Nitrogenous Constituents. 

 144. {g) Crude Fibre. 



The residue from the ether extract, or another 

 portion of fat-free substance, is boiled for half an hour 

 with 200 cc. of 1-25 per cent, sulphuric acid, washed free 

 from acid on a calico filter, and then boiled for another 

 half-hour with 1-25 per cent, caustic soda. The 

 digestion should be carried out in a large flask fitted 

 with a reflux tube, as considerable frothing is liable to 



