VAEIOUS METHODS OF PREPARING CASEIN. 23 



of moisture, it is broken down into small lumps, which are 

 spread out thinly on cloths stretched on fnire . These are 

 placed in a drying-room, kept at a temperature o. about 86 F., 

 until the casein is perfectly free from water and will crumble 

 down to powder under the pressure of the finger. 



When thoroughly dry, casein can be packed and stored 

 in a dry room for an indefinite period, without undergoing 

 alteration. On the other hand, the presence of even the 

 smallest quantity of moisture enables micro-organisms to 

 develop in the casein and cause putrefaction of the whole 

 mass. The following method is a good one to adopt in 

 packing casein. The dried product is spread on cloths 

 and sprayed over with a small quantity of pure 95 per cent, 

 alcohol, after which it is immediately packed tightly into 

 square cardboard boxes, with a strip of paper pasted round 

 the edge of the lid when closed. The minute quantity of 

 spirit introduced into the casein volatilises, and forms an 

 atmosphere in which no micro-organisms can develop. 



Casein prepared in this manner will gradually swell up, 

 in very dilute solutions of caustic alkalies or their carbonates, 

 to a transparent mass, and eventually pass into solution. 

 The same result can be obtained without drying the casein, 

 the solution keeping well and having the advantage of being 

 ready for use without waiting for the solid casein to swell 

 and dissolve. With this object the washed casein is mixed 

 in the vat with sufficient water to form a thick cream, and 

 adding to this mixture about a quarter of a pint of aqueous am- 

 monia per pound of dry curd present. This can be calculated 

 approximately from the weight of milk taken in the first 

 place, the average casein content being 3' 2 per cent. After 

 adding the ammonia the vat is covered up and the stirrers 

 kept in motion for some time ; whereupon, if sufficient 

 ammonia has been used, the casein will be found to have 

 dissolved to a clear viscous liquid, of a faint yellow tinge. 



