CASEIX. 



33 



On boiling milk -with the quantity of acid just sufficient to 

 curdle, the whole of the casein is not precipitated ; thus the author 

 found that 2'91 per cent, was thrown down out of a total of 

 3-05 per cent. 



Casein on treatment with strong sulphuric acid gives off carbon 

 monoxide. 



Preparation of Casein. — Casein is prepared from milk by 

 diluting it to about five times its volume, and adding sufficient 

 acetic acid to give O'l per cent, of the acid in the solution ; the 

 casein is precipitated, carrying down with it the fat ; the pre- 

 cipitate is well washed by decantation some ten times, collected 

 on a cloth filter, washed on the filter, and then dried, as far as 

 possible, by pressure. This precipitate is dis.solved in the least 

 possible excess of ammonia, the solution allowed to staiul for 

 some time (to allow the fat to rise), then syphoned off and filtered, 

 and the filtrate precipitated, as before, by acetic acid ; the 

 ])recipitat(' washed and redissolved in ammonia ; and this treat- 

 ment repeated three or four times. The casein is now rubbed 

 up in a mortar with 80 per cent, alcohol, and tin- alcohol poured 

 off ; the treatment with alcohol is repeated several times, using. 

 finally, absolute alcohol ; it is then treated two or three times 

 with ether which has been freshly distilled from some reagent 

 which removes aldehydes (e.g., casein, sodium phenyl-hydrazine- 

 sulphonate) in the same maimer, and then extracted for some 

 hours in a Soxlilct extractor to renio\-e the fat, and tlie ethei 

 e\-aporated off at as low a ti-mperature as possible. This c-iseiii 

 iriav, if a very pure product is required, lie redissolved. lepi-i'- 

 cipitated, and the treatment with alcohol and ether repeated ; 

 the casein is finally dried at loo to 10.")- (_'., and is then a white 

 amorphous powder ; if casein containing water is dvii'd it forms 

 horny masses. 



Products of Hydrolysis of Casein. — The following eomposition 

 is gi\ en l)v Chittenden and Painter to the products of hydrolysis 

 of casein : — 



C.A.SI'IOSKS PRODUlKD liY THl-: Al-TIOX OF PePSIN. 



