6 THE CHEMICAL CONSTITUTION OF THE PROTEINS 



The Biuret Base. 



In 1883 Curtius first prepared glycine ester by decomposing glycine 

 ester hydrochloride with silver oxide. It was a colourless, strongly 

 basic oil, very unstable, and only capable of preservation in dry ether. 

 If it were allowed to stand in the air, it underwent decomposition and 

 was converted into an insoluble anhydride, 



CH / | 

 \CO 



and a soluble base, which gave the biuret reaction and was called the 

 biuret base. Further investigations upon the nature of these compounds 

 were made by Curtius and Goebel in 1888, who found that the glycine 

 anhydride separated when the ester was allowed to stand for a few days 

 with four volumes of water, and that from the analysis of its silver and 

 copper compounds it had the formula 



/NH /N 



CH 2 / I or possibly CH 2 / || 



\CO N C(OH) 



No result could be arrived at concerning the biuret base, which was 

 prepared by keeping pure glycine ester in a sealed tube, when it changed 

 into a white, crystalline mass. Curtius and Schulze, in 1890, by molecular 

 weight determinations found that the formula of the anhydride must be 

 doubled, and it was probably represented by 



/NH co\ 

 CH 2 ( \CH 2 , 



\CO NH/ 



which was ultimately proved by Fischer and Fourneau in 1901. 



This anhydride or biuret base was investigated again in 1894 by 

 Lilienfeld, who prepared it by heating glycine ester with solid potassium 

 bisulphate on the water bath, and who gave it the formula C 4 H 9 N 3 O 2 , 

 and the constitution 



/CO.NH 2 .CH 2 

 NH/ 



\CO.NH 2 . CH 2 



since he also obtained dimethyl am ine, ethyl ether and carbonic acid in 

 its preparation. 



When he heated it with water, Lilienfeld obtained a flocculent pre- 

 cipitate, just as Curtius and Goebel had observed ; this formed a gelat- 

 inous mass after filtering which contracted like gelatin and behaved, 

 in fact, very like glutin. In a similar manner Lilienfeld condensed 



