CASEIN. 187 



ost and albumen, which Scheele had from his observations pro- 

 nounced identical. 



I do not know who first applied to the curdy part of milk the 

 name casein. But it occurs in the 27th volume of the Diction- 

 naire des Sciences Medicales, published in 1818. The word case- 

 us, applied to the same substance, is found in the Dictionnaire de 

 C/timie of Klaproth and Wolff, the French translation of which 

 appeared in 1810. 



Casein may be obtained from cow's milk by the following pro- 



Mix skimmed milk with dilute sulphuric acid. The casein 

 and acid unite and precipitate in the state of a white curd. Let 

 the curd be collected on a filter, and well washed with water to 

 remove the whey which it contains. Thus cleaned, it is to be 

 mixed with water and digested over carbonate of barytes. The 

 sulphuric acid unites with the barytes, while the casein set at li- 

 berty dissolves in the water. When this liquid is filtered to free 

 it from the sulphate of barytes and the excess of carbonate em- 

 ployed, it has a pale yellow colour, and resembles in consistence 

 a solution of gum. When heated in an open vessel it emits the 

 smell of boiling milk, and a white pellicle forms on the surface, 

 similar to that which is formed on the surface of boiling milk.' 

 When the liquid is evaporated to dryness in a gentle heat we 

 obtain the casein in the state of an amber-coloured mass, which 

 is still soluble in water. The aqueous solution is coagulated by 

 all acids, even by the acetic, especially when assisted by heat 

 This property distinguishes casein from albumen ; which last is 

 not precipitated by acetic acid. 



Braconnot assures us that casein obtained by the above process 

 is not quite free from impurity. He recommends -the following 

 process as better. Take 400 parts of curd formed by rennet, 

 and well washed in boiling water to get red of the whey. Mix 

 them with one part of bicarbonate of potash in crystals, and a 

 sufficient quantity of water. Heat the mixture, an effervescence 

 takes place, and the curd and alkali combine and dissolve in the 

 water. When this solution is cautiously evaporated to dryness 

 it constitutes the soluble casein of Braconnot, a substance which 

 he recommends for a variety of useful purposes. 



To obtain pure casein, dissolve a quantity of soluble casein 

 in boiling water. Pour the solution into a funnel, having its 



