SALTS OF ALBUMIN WITH BASES 



101 



The study of the caseinates has been particularly useful in 

 increasing our knowledge of the alkali proteins. Casein, the 

 insoluble protein of milk, can be prepared in a state of great 

 and constant purity practically free from ash by Hammer- 

 sten's method. It gives an apparently well-defined salt when 

 titrated with alkali and phenol phthalein, the hydrion concen- 

 tration of the product approximating to absolute neutrality in 

 a i per cent, solution. According to Laqueur and Sackur,* 

 who made the first determination on the caseinates in which 

 modern physico-chemical methods were employed, i gm. of 

 casein is neutralised by 8-8 c.c. of N/io sodium hydroxide, when 

 phenol phthalein is used as indicator. In the light of more 

 recent and more detailed researches! the physico-chemical 

 properties of the caseinates deserve a short discussion at this 

 point. In the first place, a fact which is extremely important 

 and, indeed, decisive for the evaluation of the older observations, 

 must be emphasised ; that is, that even at great dilution 

 solutions of neutral alkali caseinates show no hydrolytic dis- 

 sociation which would disturb conductivity measurements. 

 This is shown by electrometric tests made by Pauli and Matula, J 

 which gave no relative increase in the OH 7 ion concentration on 

 large and progressive dilution. 



0-009 



Table 48. 

 NaOH (saturated with casein). 



These results give a firm foundation to the analogy between 

 the behaviour of the alkali caseinates and that of the neutral 

 salts of fairly strong acids. In consequence we can deal 

 intelligently with the results obtained some time ago by 

 Laqueur and Sackur, as also with the conductivity measure- 



* Beitr. z. Chem. Phys. Path., 1903, 3, 193. 



f Pauli and J. Matula, Biochem. Zeitsch., 1919, 99, 219. 



I Pauli, Biochem. Zeitsch., 1915, 70, 489. 



