32 CASEIN. 



with bases is 1,135, and its basicity is 4 to 6. The far higher 

 molecular weights of 5,000 to 6,000, found by Salkowski, 

 Hammarsten, Lehmann, Hempel and Soeldner, are based 

 partly on hydrolysis and partly on the investigation of acid 

 salts. Soeldner differentiates between two series of salts, 

 Courant three. In milk, casein is present as calcium caseate ; 

 and, according to Courant, not as the neutral salt, but as 

 calcium dicaseate, combined with calcium phosphate. This 

 point, however, is not yet properly decided. Calcium case- 

 ate may, per se, possess the property of maintaining in solu- 

 tion or suspension the neutral calcium phosphate also present 

 in the milk, or the milk may contain a true double salt of 

 calcium caseate and calcium phosphate ; in either case, the 

 calcium phosphate is thrown down when casein is precipi- 

 tated along with the total milk fat, the emulsification of 

 which is therefore due to calcium caseate. This again is the 

 reason of the great difficulty experienced in obtaining casein 

 free from fat and calcium phosphate. Whilst free casein is 

 perfectly insoluble in water, the neutral sodium and am- 

 monium salts are readily soluble. Even the acid salts of 

 casein are soluble in water, but the solutions are strongly 

 opalescent. Calcium caseate dissolves well, but the solution 

 has a distinctly milk-white appearance. Nutrose and plas- 

 mon are sodium caseate. Ammonium caseate is known as 

 " Eucasein ". 



Casein is precipitated from solutions of these salts, and 

 therefore also from milk, by very weak mineral acids or by 

 strong acetic acid, and is redissolved when the precipitating 

 acid is in excess. Precipitation of casein or its salts ensues 

 when the solution is saturated with common salt, magnesium 

 sulphate or sodium sulphate. For the bulk of the casein 

 the limits in the case of ammonium sulphate are 2'2 and 3'6, 

 though a slight cloudiness is already observed when 1*2 is 

 reached. In other respects casein behaves in acid, neutral 



