188 ANIMAL AMIDES. 



beak shut up, and let it remain at rest for 24 hours. A quan- 

 tity of cream collects on the surface, which is separated by allow- 

 ing the clear solution to pass through the funnel, retaining the 

 cream. Pour into this clear liquid a little sulphuric acid. A 

 curdy precipitate falls, consisting of casein combined with sul- 

 phuric acid. Wash this precipitate, heat it in water mixed with 

 a very small quantity of carbonate of potash, scarcely sufficient 

 to dissolve all the matter. We obtain a mucilaginous liquid, 

 which, while still hot, must be mixed with its own bulk of alco- 

 hol. No precipitate should fall till 24 hours after the mixture. 

 The precipitate consists of butter, sulphate of potash, and a por- 

 tion of casein. Let the liquid be passed through a cloth. We 

 obtain a transparent liquid, which, when evaporated to dryness, 

 leaves pure casein.* 



When the aqueous solution of casein is left to itself it gradu- 

 ally alters, gives out the smell of old cheese, and becomes ammo- 

 niacal. 



When alcohol is poured upon casein, dried in a low heat, it 

 becomes opaque, and assumes the aspect of coagulated albumen. 

 The alcohol abstracts the water with which it was united, and 

 thus occasions the alterations. At the same time the alcohol 

 dissolves a portion of the casein, which remains when the alco- 

 holic liquid is evaporated to dryness. Casein is still more solu- 

 ble in boiling alcohol. The excess precipitates as the liquid cools. 

 By this solution the characters of the casein are not in the least 

 altered. 



Anhydrous casein, or casein digested or dissolved by alcohol, 

 swells in water, and gradually dissolves into a mucilaginous fro- 

 thy mass, which becomes transparent and liquid when heated, 

 and then assumes the original characters of casein dissolved in 

 water. 



Acids act upon casein very nearly as upon albumen. With 

 a little acid it forms a compound soluble in water ; but when 

 the quantity of that acid is increased, the compound becomes 

 little soluble. By washing with water we may remove this excess, 

 and thus render it again soluble in water. The precipitate by 

 acetic acid may be again dissolved. But much more acid is ne- 

 cessary for that purpose than is required for albumen or fibrin. 

 Solutions of casein in acids are precipitated by prussiate of po- 



* Ann. de Chim. et de Phys. liii. 343. 



