MILK. 291 



solution until a permanent pink appears. In this way the equivalent or 

 combining weight of the casein may be found very closely. It is over 



IOOO. 



The alkali salt of the casein forms a somewhat viscid solution. If ex- 

 posed to the air it dries down to a gummy mass which is very adhesive 

 and acts like a mucilage. In the arts similar, but crude, solutions are 

 used as sizing material and as a constituent of certain paints. These 

 products are made from the cheap whey from the creameries. 



Ex. While the alkali salts of casein are readily soluble in water the 

 heavier metal combinations are not. This may be shown by adding to 

 the alkali solution as obtained above solutions of salts of other metals. 

 Precipitates are formed readily with most of them. The calcium salt is 

 moderately soluble, as may be shown by rubbing up some casein with 

 calcium carbonate and water. On filtering and adding a drop of acetic 

 acid to the nitrate a casein precipitate comes down. 



Ex. The lactalbumin may be shown by boiling the decanted liquid from 

 the first acetic acid precipitation given above. A coagulum forms as in 

 a dilute white of egg solution to which a little acid had been added. 



The phosphorus in casein appears to be combined in at least 

 two forms. On digesting casein with pepsin and hydrochloric 

 acid a product known as pseudo-nuclein is separated because 

 of its failure to digest. In long continued digestion some 

 phosphorus seems to pass into the form of orthophosphoric 

 acid, while another portion remains in the albumoses formed, 

 in the organic condition. The digestion residue, however, is 

 not nucleinic acid, which distinguishes the casein from the true 

 nucleo-proteids. In the precipitation of casein from milk by 

 the treatment given above the combined phosphorus, whether 

 in acid or organic combination, does not appear to be touched. 

 The mineral phosphates are separated, however, but not com- 

 pletely, as the finally washed and dried casein always contains 

 some ash, a part of which is calcium phosphate. 



Milk Sugar. This crystallizes with one molecule of water, 

 C 12 H 22 O ll + H 2 O, and yields glucose and galactose on inver- 

 sion. It is separated in large quantities from the whey of 

 cheese factories and is employed in the manufacture of invalid 

 and infant foods. The general properties of the sugar have 

 already been given. 



The Mineral Substances in Milk. In the analyses quoted 

 at the beginning of the chapter the ash of the milk is given as 



