MIN'ERAL C0XSTITUEXT8. 39 



from the clear ethereal solution, which is separated by filtration, 

 washed with strong alcohol and afterwards with ether, and dried 

 in the air at the ordinary temperatuie. Storch found that if the 

 cream was mixed with water at 35° C. and separated in a cream 

 separator, and this process repeated several times, the protein could 

 be prepared from the washed cream. This method was, however, 

 more difficult than that involving the use of cane sugar solution. 



The density of the mucoid substance containing 642 per cent, 

 of mucoid protein and 1-03 per cent, ash was found to be 1-0228 

 at 15° C. 



This substance appears to be identical with a product described 

 some years ago as /3-casein by Struve ; he separated it from his 

 a-casein by dissolving in ammonia, when the /3-casein wasMt; 

 it was found in traces only in milk. 



Mineral Constituents. — On burning milk a white ash is left : 

 this contains the mineral constituents of milk, altered, however, 

 to some extent by the oxidation of some of the compounds 

 present in milk ; thus tlio phosphorus and sulphur of the proteins 

 give rise to phosphoric and sulphuric acids; and carbon clioxido 

 is also formed by the oxidation of organic carbon. The ash 

 does not truly represent the mineral constituents of milk. 



The average composition of the ash of milk is — 



Lime, . . .... 



Magnesia, 

 Putasli, 

 Soda, . 



Phosplioiic a'iil, 

 Chlorine, 

 Caibon dioxide 

 Sulphuric acid, . 

 Ferric oxide, &e., 



Less = U1 



1(1,1 iiij 



The amount of insoluble ash— j.e., ash insoluble in hot water- 

 amounts to about 0-5'2 per cent, of the milk ; and the soluble 

 ash to 0-23 per cent. The soluble ash consists mainly of the 

 chlorides of the alkalies, with a little carbonate and a mere trace 

 of phosphates. 



The insoluble ash is mainlv composed of double phosphates 

 of the formula CaKPO,, the" lime being partially replaced by 

 magnesia and the potash by soda ; double carbonates of the 

 formula CaNa,(CO.,l., also exist in traces: these compounds are 

 insoluble in water, and this accounts for the fact that the insolubl' 

 ash is always higher than the sum of the calcium and magnesium 

 phosphates. 



