222 MILK HYGIENE 



their food, these are frequently present in water in small 

 quantity. The presence of nitrates or nitrites in the 

 milk, therefore, shows, with certainty, that water has 

 been added. However, the lack of nitrates does not ex- 

 clude this, as all water does not contain nitrates. Even 

 a very small quantity of nitrates and nitrites can be 

 detected as follows : 



1.5 c.c. of a 20 per cent, calcium chloride solution is added to 

 100 c.c. of milk; the mixture is boiled and filtered. A little of the 

 filtrate is mixed with enough of a 2 per cent, solution of diphenylamin 

 in sulphuric acid to make it milky ; a little concentrated sulphuric acid 

 is poured into a test tube and the mixture is added slowly, so that 

 the fluids do not mix; if nitric acid or nitrous acid is present, a blue 

 zone is formed at the plane of contact. (Soxhlet.) 



[A simpler test for nitrates is that devised by Richmond. The 

 following description of this test is from Farrington and Woll. 55 

 " Place a small quantity of diphenylamin at the bottom of a porcelain 

 dish, and add to it about 1 c.c. of pure, concentrated sulphuric acid; 

 allow a few drops of the milk serum (obtained by adding a little 

 acetic aci'd to the milk and warming) to flow down the sides of 

 the dish and over the surface of the acid. If a blue color develops in 

 the course of ten minutes, though it may be faint, it shows the 

 presence of nitrates, after ten minutes a reddish-brown color is 

 always developed from the action of the acid on the serum. There 

 should be no difficulty in detecting an addition of 10 per cent, of 

 water to the milk by this test, if the water added contained 5 parts 

 of nitric acid, or more, per 100,000." L. P.] 



c. The skimming of whole milk in conjunction with 

 the addition of water, or the addition of skimmed milk 

 as well as water, are common methods of adulteration. 

 It is easily understood that the fat content is consid- 

 erably lessened in this way, and that also the solids not 

 fat decrease ; it is evident, besides, that the percentage 

 of solids not fat (p) is lessened and, consequently, the 



65 Farrington and Woll. Testing Milk and its Products, 13th 

 edition. Madison, 1904. 



