22 CASEIN. 



According to A. Spitteler, the alkali vsed ,in preparing 

 the casein should be replaced by an alkali carbonate, when a 

 colourless, tough casein is desired. In this case the reaction 

 proceeds more gradually. Should a transparent product be 

 desired, the separated substance should not be removed from 

 the solution until the latter begins to be transparent. 



K. Ruprecht states that the following method is employed 

 for producing technical casein : 



Skim milk is placed in a vat fitted with stirrers consisting 

 of a vertical shaft carrying several horizontal blades. These 

 stirrers are set going so as to bring the whole of the liquid 

 into rapid rotation, and dilute hydrochloric or acetic acid is 

 run in by degrees. The casein begins to separate immedi- 

 ately in the form of tender white flakes, and the quantity of 

 acid used is strictly limited to the amount necessary for pre- 

 cipitation; while continuing the stirring a sample of the 

 liquid is taken, filtered, and the clear filtrate tested with a 

 little of the acid. If it remains clear, the whole of the casein 

 has been precipitated. 



The liquid is then left alone until all the casein has settled 

 down, whereupon the clear liquid may be syphoned oft* by 

 means of a rubber tube fitted with a glass funnel, the mouth 

 of which is covered with fine gauze and is lowered into the 

 liquid until it reaches the curd, which is kept back by the 

 gauze sieve. The separated liquid contains albuminoid com- 

 pounds, salts and the whole of the milk sugar present in the 

 milk, for the recovery of which it can then be treated. 



The casein left in the vat is stirred up with water, left 

 to settle, the water run off, and the operation repeated two or 

 three times. The casein, thus sufficiently purified, is placed 

 in strong filter cloths and laid between wooden plates in a 

 screw press. Pressure is applied gradually and so long as 

 any liquid continues to drop. The casein is next taken out 

 of the cloths, and as it still contains a considerable amount 



