MILK. 369 



longer period. The process of ripening is a partial decomposi- 

 tion (decay and putrefaction) of the casein, and the value of 

 cheese depends mainly upon the nature of the products formed 

 during this decomposition. 



Adulterations of milk. Of these, the most commonly practised 

 are removal of cream, addition of water, or both. Sometimes 

 sodium carbonate, sugar, and even chalk are added, but these 

 latter adulterations are fortunately but rarely practised by milk- 

 dealers. The question whether or not milk has been tampered 

 with is generally decided by ascertaining whether cream has 

 been removed or water added. It is, therefore, chiefly the 

 quantity of total solids which has to be determined in order to 

 decide the purity of milk. But it has been shown by the above 

 tables of milk analysis that the quantity of these solids varies 

 considerably, and a minimum of total solids- should therefore 

 be adopted legally. While no such minimum quantity is offi- 

 cially recognized in most States of this country, it is safe to say 

 that milk containing less than 11 per cent, of total solids may 

 be looked upon as adulterated. (The above given lowest quan- 

 tity of 9.8 per cent, of total solids in cow's milk is very abnor- 

 mal.) The methods for detecting such fraud will be considered 

 below. 



Testing milk. There is, unfortunately, no instrument which 

 will indicate the purity or quality of milk directly. An instru- 

 ment heretofore used for that purpose (especially in France), 

 and known as the lactometer, is simply a hydrometer which indi- 

 cates the specific gravity of milk. There are, however, in milk 

 substances which have a tendency to increase the specific gravity, 

 such as lactose, salts, and casein, whilst there is at the same 

 time one substance, the fat, which is specifically lighter than 

 water. The specific gravity of milk ranges from 1027 to 1034, 

 the average being about 1030. If water be added to milk, the 

 specific gravity will become lower, but the same effect may be 

 obtained by adding fat or cream. Again, if cream be removed, 

 the specific gravity will be higher, and in order to bring the 

 milk back to the standard of 1030, water ma} 7 be added. In 

 other words, cream may be removed from and water added to 

 the same milk and the specific gravity will be unchanged; or a 



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