SALTS OF ALBUMIN AND ACIDS 85 



At 18 the dissociation constant of water K H2 o = 0-62 xio- 14 , 

 and if we vary the molecular weight of albumin between the 

 limits 1,000 and 10,000, for a i per cent, solution, v will vary 

 correspondingly between 100 and 1,000. The mean basic 

 dissociation constant K B of the albumin, calculated on a degree 

 of hydrolysis of 0-18 from equation i, gives the values 1-57 X 

 lo- 11 and 1-57 X io- 10 . Of these two figures the latter 

 probably approaches more nearly to the true value as the 

 molecular weight of the protein is nearer 10,000. The mean 

 value of KB thus obtained corresponds quite well in its order 

 of magnitude with what we should expect for a high poly- 

 peptide, for the value increases from 2-3 5-1 X io~ 12 for a 

 monoamino-acid (K. Winkelblech) to 2 3 X io- 11 for the 

 simplest dipeptide (H. Euler). 



In the formation of albumin salts with acids, the basic 

 valencies of the amino-group operate first according to the 

 equation previously proposed by W. B. Hardy and Wo. 

 Pauli : 



y2 /NH 2 HC1 



R/ + HC1 - > R< 



\COOH XXDOH 



The more recently propounded views of Robertson have failed 

 to hold the field in spite of many valuable suggestions, such as 

 that of the role of peptide linkage, or the possibility of reaction 

 in the enol-form, as no practical proof can be given. On the 

 other hand, it was necessary to decide the question whether 

 the terminal amino-groups, particularly in the diamino-acids, 

 lysin and arginin, are the sole places of combination with acids. 

 This point can be tested by the desamino-proteins which have 

 been deprived of these amino-groups. When acted on by 

 nitrous acid (sodium nitrite -{- glacial acetic acid) the amino- 

 groups react according to the equation : 



CH 2 NH 2 CH 2 OH 



| ' + HN0 2 - -> | + N 2 + H 2 0, 



COOH COOH 



a reaction which has also been successfully applied for the 

 determination of amino-nitrogen in proteins. Of, the desamino- 

 proteins the most useful for the study of physico-chemical 



