CASEIN. 379 



According to more recent investigations purified casein contains 

 0'85% of sulphur. 



In casein, precipitated by acetic acid, and washed with alcohol 

 and ether, Ruling* found 1'015^ of sulphur; but in casein which 

 had been precipitated by acetic acid, dissolved in carbonate of 

 soda, and again precipitated by the acid, the quantity was only 

 0-850-JS- ; Waltherf found 0'933, and VerdeilJ 0'842 of sulphur in 

 casein, which had been treated with hydrochloric acid and car- 

 bonate of soda. 



According to Mulder, casein is nothing more than his hypo- 

 thetical protein combined with sulphamide. No formula for 

 casein can, however, be established till the question is definitively 

 settled whether it be a simple or a compound body. 



Casein that has not been treated with acids contains about 6 

 of phosphate of lime ; more, consequently, than is contained in any 

 of the protein-compounds we have hitherto considered. 



Preparation. We obtain soluble casein by evaporating skimmed 

 milk, extracting the residue with ether, and dissolving it in 

 water ; we then throw down the casein from the aqueous solution 

 by the addition of alcohol, with which we must also carefully wash 

 the precipitate. 



Berzelius precipitates the casein from skimmed milk by sul- 

 phuric acid, rinses the white coagulum with water, and decomposes 

 the sulphate of casein with carbonate of lime, or (which s better) 

 with carbonate of lead; the casein which is dissolved in water 

 always contains a little lead, which, however, may be removed from 

 the solution by sulphuretted hydrogen. 



Simon removed the fat, by means of alcohol and ether, from 

 casein precipitated by sulphuric acid, before decomposing it with 

 carbonate of lime. 



Mulder prepared casein for elementary analysis by precipita- 

 ting it from skimmed milk, by warming it with acetic acid, washing 

 and thoroughly rinsing the precipitate with water, separating the 

 fat by boiling alcohol, and finally, by drying at 130. 



According to Rochleder's method skimmed milk is coagulated 

 with dilute sulphuric acid, (acetic acid or hydrochloric acid may 

 however be used in its place;) the precipitate is then duly pressed 

 and again dissolved in a dilute solution of carbonate of soda ; this 



* Ann. d. Ch. u. Pharm. Bd. 38, S. 309. 



f Ibid. Bd. 37, S. 316. 



% Ibid. Bd. 38, S. 319. 



Ibid. Bd. 45, S. 253-256. 



