50 THE GENERAL CHARACTERS OF THE PROTEINS 



Many similar results with, however, some marked contrast, have 

 been obtained by Hardy in his investigation on serum-globulin ; 

 these analogies and contrast will be referred to later. 



The Salt Formation of Caseinogen (Lacqueur and Sackur). 



W. A. Osborne showed that the salts of caseinogen could be 

 divided into two classes, viz., those of the alkaline earths and those 

 of the alkalis, which can be distinguished from one another by the 

 facts that the former form opalescent solutions and cannot be 

 filtered through a Martin gelatin filter, whilst the latter form quite 

 clear solutions and can be filtered through gelatin. Osborne clearly 

 recognised the acid character of caseinogen and its salt - forming 

 capacity. 



Various attempts have been made to determine quantitatively the 

 amount of different bases necessary to neutralise a given amount of 

 caseinogen, 1 but the most accurate determinations are due to Lac- 

 queur and Sackur. They showed that the discrepancies of the 

 different observers are due to the fact that the calculations as to com- 

 bining weights are made with reference to the air-dried caseinogen, 

 instead of the substance dried at 110 C. This is important when 

 it is remembered that caseinogen preparations are somewhat hy- 

 groscopic. 



Lacqueur and Sackur confirmed other investigators in their 

 statement of the fact that solutions of caseinogen in alkali, which are 

 alkaline to litmus, are acid to phenpl phthalein. They showed further- 

 more that with phenol phthalein perfectly sharp neutralisation points 

 could be obtained with various alkalis, both by direct titration and 

 by the addition of alkali in excess, and subsequent titration of this 

 excess with acids. They found as a means of several concordant 

 experiments that I gram of caseinogen (calculated as free from 



N 

 water) was capable of neutralising 8'8i c.c. of sodium hydroxide 



solution. The amount of water in each sample titrated was esti- 

 mated by drying at no C. ; the percentages of water were found to 

 vary between 8 '2 and 15*5. 



Lacqueur and Sackur also determined the electrolytic conduc- 

 tivity of solutions of caseinogen, which has been neutralised by 

 sodium hydroxide in the presence of phenol phthalein in various 

 dilutions, with a view of ascertaining the basicity of the acid casein- 

 ogen, as Ostwald and Walden have shown that the more polybasic 

 an acid is, the greater is the decrease in the amount of dissociation 

 when the solution of its sodium salt is concentrated. This dissocia- 

 tion influences, of course, the conductivity, and if A^ represent the 

 equivalent conductivity at dilution z/ x and A v the equivalent con- 

 ductivity at dilution z/ 2 , then between dilutions 32 and 512 (*>., I 

 gram equivalent in 32 litres and I gram equivalent in 512 litres) 



1 A 2 has the following average values : for dibasic acids 0*15, 



-"i 

 for tribasic acids o'22, for tetrabasic acids 0*29, for pentabasic acids 



0*35, and for hexabasic acids 0*39. 



1 The reference to these earlier investigations is given in Lacqueur and Sackur's 

 paper. 



