ADULTEKATION OF MILK. 355 



solution, and about 120 c.c. of water. The mixture is kept 

 on the water hath for 15 minutes and filtered through a small 

 filter paper or a Gooch's crucible. The precipitated cuprous 

 oxide is thoroughly washed with boiling water, next with 

 alcohol, and finally with ether. The precipitate is then dried, 

 transferred to a weighed porcelain crucible, and strongly 

 ignited with free access of air, so as to oxidise it completely to 

 cupric oxide. The amount of hydrated milk sugar correspond- 

 ing to the weight of the cupric oxide is then ascertained, best 

 by reference to a table, or approximately, by multiplying the 

 weight of the precipitate by O6024. 



Adulteration of Milk. The commonest adulterant is w^ater. 

 Direct proof of the presence, in a sample of milk, of added 

 water is very difficult unless the water happens to contain some 

 substance not naturally present in milk, e.g., nitrates. In such 

 cases the detection of nitrates in the milk, say by the reaction 

 with diphenylamine and sulphuric acid, becomes at once proof 

 of the addition of water, though in some cases this may be 

 due to the small quantities employed in rinsing out the milk 

 cans, &c. The usual way of estimating the amount of added 

 water is from a determination of the amount of solids not fat. 

 By assuming that this, in genuine milk, never falls below 8'5%, 

 the percentage of added water is given by the expression 



100 ^ Xlo 



8^' 



in which S percentage of solids not fat. This gives the 

 probable minimum amount of added water. 



Another method of calculating the probable percentage of 

 added water is based on the assumed constancy of the sum of 

 the ''lactometer degrees" (i.e., sp. gr. x 1000 1000) and the 

 percentage of fat. This sum is generally about 36 and rarely 

 falls below 7 34-5. Accepting this latter value as the minimum 

 in genuine milk, the percentage of added water is then given 

 by the expression 



~34 T 5 ' 

 where G = " lactometer degrees" and F = percentage of fat." 



* Richmond, Dairy Chemistry. 



AA 2 



