58 THE VEGETABLE PROTEINS 



NITROGEN AS AMMONIA IN PER CENT. OF THE PROTEIN. 



1 Figures given in preceding table. 



2 Distilled in vacua at 40. 



Is the Nitrogen Yielded as Ammonia Amide Nitrogen? 



As the amino-acids which result from protein hydrolysis yield no 

 ammonia by long boiling with strong hydrochloric acid, this ammonia 

 must arise from some other form of binding of the nitrogen in the 

 protein molecule. That this nitrogen may be in amide union seems 

 probable from the following experiments in which five portions of 

 gliadin, each weighing I gramme, were dissolved in 50 c.c. of 20 per 

 cent, hydrochloric acid, and the solutions boiled for the times indicated 

 in the following table : 



Boiled for 30 min., nitrogen as NH 3 = 4-30 per cent. 

 Boiled for i hour, nitrogen as NH 3 = 4-35 per cent. 

 Boiled for 2 hours, nitrogen as NH 3 = 4-33 per cent. 

 Boiled for 3 hours, nitrogen as NH 3 = 4*33 per cent. 

 Boiled for 4 hours, nitrogen as NH 3 = 4-33 per cent. 

 Boiled for 6 hours, nitrogen as NH 3 = 4-40 per cent. 



When treated with strong hydrochloric acid at 20 for two hours, 

 only o - 22 per cent, of nitrogen as ammonia was obtained, while after 

 seventeen hours at the same temperature i - 67 per cent, was found. 

 Under similar conditions asparagine yielded 1*4 per cent, of nitrogen 

 as ammonia after seventeen hours at 20 and one-half of its nitrogen 

 after boiling for thirty minutes. 



In regard to the accuracy of the figures given for the nitrogen pre- 

 cipitated by phosphotungstic acid we are able to form some judgment, 

 since the only strongly basic amino-acids yielded by proteins are 

 arginine, histidine and lysine, and these are, therefore, precipitated from 

 a dilute solution by phosphotungstic acid. The nitrogen thus precipi- 

 tated should, consequently, be equal to the nitrogen contained in these 

 three basic amino-acids, if no other basic substances are present among 

 their decomposition products. That such an agreement actually exists 

 is shown from the following table : 



