ANALYTICAL METHODS FOR DISTINGUISHING BETWEEN 

 NITROGEN OF PROTEIDS AND NITROGEN OF SIM- 

 PLER AMIDS OR AMIDO-ACIDS. 



DISCUSSION OF MATERIALS AND CONDITIONS. 



It is admitted by all who have had experience in the chemical analy- 

 sis of materials used as food that the common practice of determining 

 the total nitrogen in such materials by multiplying the result by 6.25 

 and calling the product so obtained "protein," is but a crude and 

 clumsy way of approximately representing the value of the material 

 under examination as respects its nitrogenous constituents. Besides 

 the substances which are properly designated as proteids there are 

 other nitrogenous constituents of food materials which differ widely 

 from these in nutritive value and some of which also differ greatly 

 from these and from each other in the proportion of nitrogen which 

 they contain. 



CLASSES OF NITROGENOUS CONSTITUENTS IN FOODS. 



The following classes of the nitrogenous constituents of food are 

 commonly recognized as requiring separate consideration. 



(1) Proteids proper (by some called albuminoids), and their closely 

 related derivatives, the proteoses and peptones. 



(2) Gelatinoids or collagens, and allied substances immediately 

 derived from them, such as gelatin, chondrin, etc. 



(3) Simpler amids, amido-acids, and allied substances, such as the 

 asparagin, glutamin, etc., of vegetable materials, and the "flesh 

 bases" (kreatin, kreatinin, etc.) of animal origin. 



(4) Alkaloids, or amine-like compounds of well-determined basic 

 character. 



(5) Ammonia and its salts. 



(6) titrates. 



To these, no doubt, should be added lecithin and analogous sub- 

 stances containing nitrogen but closely allied to the fats. 



The known and commonly used methods for determining nitrogen in 

 the forms of ammonia and nitrates, which occur but sparingly in food 

 materials, may be considered fairly satisfactory. Alkaloids in the 

 commonly accepted sense of the term demand attention only in con- 

 nection with such special accessories of food as tea, coffee, and similar 

 nervous stimulants, and the chief substances of alkaloidal character 

 admit of being separately dealt with in these special cases without 

 serious trouble and with a fair degree of accuracy. 



