26 CASEIN. 



and slightly washed precipitate is purified by repeated solu- 

 tion in water containing sufficient commercial ammonium 

 carbonate to furnish a decidedly alkaline reaction, the filtered 

 solution being then neutralised with acetic acid. According 

 to Bechamp, this pure casein dissolves, when dried, in about 

 1,000 parts of water, as well as in alkalies and acids. 



The Hoppe - Seyler method of preparing casein, as 

 practised by Hammarsten, consists in treating milk with 

 acetic acid, and dissolving the precipitate in dilute ammonia 

 or sodium carbonate, an alkaline reaction being guarded 

 against. This operation is repeated, and the casein is 

 treated with alcohol and ether to completely eliminate the 

 contained fat, a second treatment with acetic acid and soda 

 being afterwards given. Provided a strongly alkaline reac- 

 tion is avoided, the casein is not decomposed. The removal 

 of fat can be facilitated by replacing new milk by skim. 



According to another report, pure casein is obtainable by 

 diluting milk with four times its own volume of water, and 

 then adding sufficient acetic acid to bring the acid content 

 of the mixture to O'075-O'l per cent. The precipitate is 

 purified by trituration under water, and then immediately 

 redissolved in very dilute potash, followed by reprecipitation 

 with acetic acid. The casein is washed in water, rubbed 

 down fine with 97 per cent, alcohol, drained and washed 

 with ether. 



Besana gives the following instructions for the prepara- 

 tion of casein for technical purposes : 



Skim milk from the separator is heated to about 95 F. 

 in a cheese vat or similar vessel, direct steam being used if 

 necessary. It is then treated with about 3 parts per mil. 

 of crude hydrochloric acid, previously diluted with 5 to 6 

 volumes of water, and curdled, the whey being drained off 

 and the curd spread out thinly on a sloping table to cool. 

 This done, the mass is washed with a spray of cold water or 



