130 CHEMICAL STATICS 



duction of coagula irresistibly suggests that this phenomenon is 

 dependent upon the formation of anhydrides * analogous to the 

 diketopiperazines {vide Chap. I) and of the general formula: 



r:" I or r; )r 



^ CO ^ CO.HN ^ 



Such bodies may exist either in the keto form, illustrated by 

 the above formulae, or in the enol form, such as: 



r( )r 



If this be granted then the fact that alcohol throws down the 

 protein salts in an unaltered condition (vide Chap, IV) lends 

 strong support to the view which I have advanced (Chap. I) 

 regarding the mode of formation and structure of the protein 

 salts, since according to that view the metal ions in a protein- 

 metal compound would be bound up in — COH.N— groups pre- 

 viously to dehydration, which could only affect terminal — NH2 

 or — NH3OH and — COOH groups and would leave the union be- 

 tween the protein and the metal unaffected. 



In this connection, and with reference to the "solvate" theory 

 of Jones, it is of interest to note that the relative efficacy of the 

 various salts in bringing about the coagulation of electronegative 

 protein is exactly their relative efficacy in bringing about dimi- 

 nution of the solubility of phenylthiocarbamid (69) (53). On the 

 other hand, evidence of the affinity of proteins for water is afforded 

 by the observation of Pauli and Samec (59) that the solubility 

 of highly soluble inorganic salts, such as ammonium chloride, 

 magnesium chloride or ammonium sulphocyanate in water is 

 diminished by the presence of gelatin or of blood-serum proteins. 

 The solubility of very slightly soluble substances (calcium sul- 

 phate, phosphate, or carbonate and uric acid) is, however, defi- 

 nitely increased. 



As regards the precipitation of proteins by salts; it appears 

 probable that acid and alkali protein react with salts as follows: 



* Cf. also Gustav Mann (46). 



