38 CHEMICAL STATICS 



acetic acid diluted to 1 litre) is carefully added until the casein 

 separates completely, after which the clear solution is removed 

 by syphon as soon as the precipitate settles. Distilled water is 

 then added, the mixture stirred vigorously and the precipitate 

 allowed to settle, after which the wash water is syphoned off. 

 Water is again added, and the casein is dissolved by adding, for 

 each litre of milk used, 1 litre of dilute NH 4 OH (6 cc. of strong 

 reagent diluted to 1 litre). When the solution is complete the 

 whole is filtered through a thick layer of absorbent cotton. The 

 casein is then precipitated again with dilute acetic acid; the 

 precipitate is allowed to settle, and is then washed, redissolved 

 in dilute NH 4 OH and filtered, the process of precipitation, wash- 

 ing, dissolving, etc., being repeated not less than four times. 

 Finally an excess of strong NH 4 OH (10 cc.) is added and then 

 20 cc. of a saturated solution of ammonium oxalate. The mix- 

 ture is allowed to stand twelve hours or more. Calcium is pre- 

 cipitated as oxalate in very finely divided condition, too fine to 

 permit its satisfactory removal by ordinary methods of filtration. 

 Better aggregation of the precipitate can, however, be effected 

 by means of centrifugal force. The centrifuged mixture is then 

 filtered through double thickness of filter paper. The filtered 

 solution is next treated with dilute HC1 (10 cc. HC1, sp. gr. 1.20 

 diluted to 1 litre) until the casein is precipitated. The precipi- 

 tate is washed with distilled water until free from chloride and is 

 then placed on a hardened filter paper in a Buchner funnel, as 

 much water as possible being now removed by suction. The mass 

 is next transferred to a large mortar and thoroughly triturated 

 with 95 per cent alcohol. The alcohol is then removed by suc- 

 tion on a Buchner funnel and the casein is placed in a mortar 

 and triturated with absolute alcohol. Most of the alcohol is 

 removed and the casein treated twice with ether in a mortar 

 by trituration, the ether being removed each time by means of 

 suction on a Buchner funnel. The material is then placed in a 

 large evaporating dish and spread out in a layer as thin as possible, 

 allowed to stand twelve hours or more in a warm place, and 

 then finely ground in a mortar until the particles pass through a 

 40-mesh sieve and dried for two days over H 2 S04 in a desiccator 

 under diminished pressure. 



Casein prepared in this manner contains only 0.71 per cent of 

 phosphorus; corresponding almost exactly to the theoretical per- 



