ASH 19 



and Hart, the decomposition of the caseous matter produces free 

 casein. When about .5 per cent acid has developed in the milk, 

 the free casein combines with the acid and forms casein lactate. 

 The chemical composition of milk-sugar is C^IfeOn+H^O. 

 Were a perfect decomposition of milk-sugar into lactic acid to 

 take place, the following equation would represent the change: 



(Milk-sugar) (Lactic acid) 



Such an ideal change, however, never takes place. In such a 

 case, one gram of milk-sugar should produce one gram of lactic 

 acid. In a number of experiments carried on by one of the 

 authors of " The Analysis of Cream during Different Ripening 

 Stages," 1 the highest amount of acid produced from one gram of 

 milk-sugar was .8 of a gram. This indicates that there are 

 always accompanying by-products produced, besides lactic 

 acid, when milk-sugar is being decomposed in cream or milk. 

 The sourness of milk is due to this change. The by-products 

 which accompany the production of lactic acid are many 

 and various. The most important ones are gases of different 

 kinds, such as carbonic acid gas (CCfe); marsh gas (CH 4 ); 

 hydrogen (H); and nitrogen (N.) Small amounts of alcohol, 

 formic, acetic, and succinic acids are said to be normal 

 accompanying by-products also. These by-products may also 

 partially result from the breaking down of some of the other milk 

 components. 



As milk-sugar is in perfect solution, it follows the water of 

 milk, and in cheese-making nearly all of it passes into the 

 whey. Commercially and chemically it is prepared from whey. 

 It is a white, not very sweet powder, and is used for medicinal 

 purposes to dilute pure, powerful drugs. It is also used exten- 

 sively in the preparation of modified milk. 



Ash. The ash of milk is present in very small quantities, 

 and when viewed from such a standpoint it may first seem to be of 

 small importance. On account of the effect of the mineral con- 



thesis, I.S.C., Ames, la. 



