690 SCIENCE PROGRESS 



split off as ammonia, and is determined by distilling off the 

 ammonia with magnesia. 



2. Diamino-N. The fluid, free from ammonia, is precipitated 

 by phosphotungstic acid, and the nitrogen present in the pre- 

 cipitate determined. This represents the nitrogen of most of 

 the diamino acids, such as histidine and arginine. 



3. Monoamino-N is estimated in the residual fluid after 

 removal of the amide and diamino-N. 



Although this method is not absolutely correct, it has never- 

 theless furnished most valuable information when applied to 

 different animal and vegetable proteins, as is shown in the 

 following table from the analyses of Osborne : 



Zein (maize) 

 Hordein (barley) 

 Gliadin (wheat) . 

 Glutenin (wheat) 

 Globulin (wheat) 

 Leucosin (wheat) 

 Edestin (hemp) . 

 Excelsin (Para nut) 

 Caseinogen (milk) 



These figures show interesting differences between other- 

 wise similar proteins. New characteristics are given for some 

 protein groups, e.g. the alcohol soluble vegetable proteins, which 

 possess a high amide-N :and low diamino-N. In Osborne's 

 analyses (not given) of various so-called edestins, great differ- 

 ences of the diamino-N was revealed. The method has also 

 proved useful for the differentiation of albumoses (Pick), and 

 interesting deductions as to the food value of various pro- 

 teins were drawn from its results (Blum). As 80 to 90 per 

 cent, of the carbon of proteins (according to Kossel) is 

 present in combination with nitrogen, the method is likely 

 to give important clues as to the constitution of different 

 proteins. 



Cleavage Products. — The following is a list of the main sub- 

 stances so far met with among the hydrolytic products of 

 proteins ; they are classified roughly under the divisions of 

 Hausmann's method, and in each case the constitutional name 

 and discoverer of these substances are given : 



