60 THE VEGETABLE PROTEINS 



time of boiling. The deficiency found for casein may be caused by 

 diamino-tri-oxy-dodecanic acid which Fischer has shown to be precipi- 

 table by phosphotungstic acid. 



It is evident from the figures given in the table that in most cases 

 the agreement between the nitrogen in arginine, histidine and lysine 

 and that precipitated by phosphotungstic acid is so close that Haus- 

 mann's method can be employed for controlling the results of deter- 

 minations of the bases by the method of Kossel, Kutscher and Patten ; 

 for where a wide difference between the nitrogen obtained by these 

 two methods is found the accuracy of the direct determination of the 

 bases can be established by careful repetition. 



The accuracy of the determinations of the individual bases, that is, 

 the completeness with which they can be separated from one another, 

 as well as from other substances, is shown by the evident purity of the 

 products obtained in the course of analysis. The arginine copper ni- 

 trate double salt separates completely from its solution on slow eva- 

 poration, leaving no trace of any other substance in the final liquid. 

 The histidine solutions readily yield pure histidine dichloride, and the 

 character of the crystallisation of the lysine picrate, in which form this 

 substance is weighed, is such as to leave no doubt of its purity, which 

 can, moreover, be further established by analysis of the product in the 

 form in which it is actually weighed. The agreement between dupli- 

 cate determinations of the several bases made on one and the same 

 protein is further evidence of their accuracy. 



Ratio of Ammonia to Glutaminic and Aspartic Acids. 



The work of Emil Fischer has made it almost if not quite certain 

 that the amino-acids are for the most part united in the protein mole- 

 cule in polypeptide union ; that is by the union of the NH 2 group of 

 one amino-acid with the carboxyl group of another ; thus 



CH 8 CH COOH 

 NH NH 2 

 CO CH CH 2 COOH 



which represents a peptide of alanine and aspartic acid. The dibasic 

 acids would therefore afford carboxyl groups with which nitrogen 

 might unite in amide union, as shown by the following formula, which 

 represents the amide of the peptide just mentioned : 



CH 3 CH COOH 

 NH NH 2 

 CO CH CH 2 CON H. 



