20 CASEIN. 



exhibits traces of a precipitate. As a rule ^ to | per cent, 

 of 40 per cent, nitric acid, mixed with 4 parts by weight of 

 water, will be sufficient. The casein separates out from the 

 milky liquid on standing and falls to the bottom. The super- 

 natant fluid is run off, the casein rinsed with fresh water, left 

 to settle, the water decanted, and the washing repeated till 

 the effluent water is perfectly neutral. 



To make the casein as dry as possible it is laid on filter 

 cloths to drain and afterwards pressed, preferably in a filter 

 press, this operation being followed by drying on trays in 

 drying chambers at a temperature of 120 to 140 F. The 

 finished product can either be worked up at once or stored in 

 a dry place for use later on. The small residual quantity of 

 butter fat in the casein could be entirely removed by digestion 

 with benzol or with an ether-alcohol mixture, but owing to the 

 troublesome nature of the process it is seldom practised. One 

 hundred parts of curd furnish 45 parts of purified casein, free 

 from lactic acid and butter fat. The material can be imme- 

 diately converted into a good glue by mixing it with 25 per cent, 

 of distilled water and 1 to 4 per cent, of bicarbonate of soda in 

 a mechanical stirring apparatus working at fifteen to twenty 

 revolutions per minute. Afterwards another 25 per cent, of 

 distilled water is added to complete the solution, and the 

 whole is left to stand for five to six hours. At the end of 

 that time the glue will be pliant and fit for use. An antiseptic 

 is added to prevent mould. 



