CHAPTER III. 



VARIOUS METHODS OF PREPARING CASEIN. 



IN order to obtain white casein, free from the yellow tinge 

 attaching to that prepared with sulphuric acid, several dif- 

 ferent acids are used in succession as precipitants, a method 

 which also has the advantage of cheapness. The best plan 

 is to first throw down the casein as curd, with sulphuric 

 acid, then dissolve this curd in alkali, and reprecipitate with 

 acetic acid. According to the German patent specification 

 of R. Hatmaker (dated May, 1901), about one and a half 

 parts by volume of sulphuric acid (density 66 B.), diluted 

 with seven of water, are sufficient to precipitate the curd 

 from 1,000 parts of milk. If the operation is performed at a 

 temperature of 100 to 120 F. the curd will come down 

 as large and solid lumps, which must then be thoroughly 

 washed with cold water. The curd from the above quantity 

 of milk can be dissolved in 350 parts of a 5 per cent, solution 

 of bicarbonate of soda, the process being accelerated by 

 warming the whole to 100 F. Acetic acid of about 29 per 

 cent, strength is used, and is added slowly till all the casein 

 has been thrown down and the separated aqueous liquid is 

 perfectly clear. After this liquid has been drawn off the 

 casein is thoroughly washed with cold water. 



A. Hall recommends that the milk should be curdled 

 with hydrochloric acid, the resulting casein being heated to 

 such a degree that the contained acid volatilises. A current 

 of air is also passed through the mass. 



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