CASEINOGEN 7 



ogen and albumin may also be precipitated by the addition of a 

 solution of calcium chloride if the milk is previously heated to 

 35° to 45° C. All three proteids are soluble in alkalies and 

 insoluble in alcohol and ether: their copper, mercury, and other 

 salts of the heavy metals are insoluble, and aU the lacto proteids 

 are completely precipitated by tannin and phosphotungstic acids. 



Caseinogen, when pvu-e, is a white, amorphous, odourless, 

 and tasteless substance which is practically insoluble in water. 

 The specific gravity is 1.257. Owing to the stability of the 

 additive compoimd which calcium caseinogenate forms with 

 calcium phosphate, in which form it is present in milk, the 

 preparation of pure caseinogen is a matter of considerable dif- 

 ficulty, and it is probable that at least a portion of the differ- 

 ences in composition found by various observers is due to this 

 factor. Repeated precipitation and solution remove the 

 greater part of the calcium but the last traces are extremely 

 difficult to eliminate (Van Slyke and Bosworth^). Caseinogen 

 is easily precipitated by the addition of a few drops of glacial 

 acetic acid to milk diluted with an equal volume of water, and 

 the precipitate may be redissolved by the addition of caustic 

 alkahes, alkaline earths, ammonia, carbonates, bicarbonates, or 

 phosphates, even in minute quantities. Scluyver^ has shown 

 that if the caseinogen produced by precipitation with acetic 

 acid is allowed to remain in contact with the excess of acid 

 (1 in 1000) at rooni temperature, or is heated with water to 

 37° C, a product is formed the solubility of which in lime water 

 is only about one-third that of natural caseinogen. This has 

 been designated as "metacaseinogen," the solution of which in 

 half satm-ated lime water is opalescent but not opaque. Meta- 

 caseinogen can be reconverted into caseinogen by solution in 

 sodium hydrate and precipitation with acetic acid providing 

 that the contact with the acid is not unduly prolonged. Meta- 

 caseinogen is identical in composition with caseinogen: the 

 following are some of the more authentic analyses of caseinogen. 



Most of the analyses given were obtained from material 

 prepared by Hammerstein's method, i.e., by repeated precip- 



