246 Testing Milk and Its Products. 



watered (126). Normal fresh milk does not contain 

 nitrates, while common well-water, particularly on 

 farms where precautions to guard against contamina- 

 tion of the water supply have not been taken, in gen- 

 eral contains appreciable amounts of nitrates, nitrites 

 and ammonia compounds, and watered milk will, there- 

 fore, in such cases also contain nitrates.^ The method 

 for detection of small amounts of nitrates in milk, as 

 given by Richmond^ is as follows: Place a small quan- 

 tity of diphenylamin at the bottom of a porcelain dish, 

 and add to it about 1 cc. of pure HaSOj (cone.) ; allow 

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

 little acetic acid 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 de- 

 veloped 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. 



The following test for nitric acid is proposed by Mc- 

 Kay and Bouska: About 5 ec. of milk is placed in a 

 test tube. Some Kaniss' reagent (about 1 part formal- 

 dehyd in 500 cc. C. P. HgSO^) is poured down the side 

 of the tube so it will form a layer under the milk. If 

 nitrates or nitrites are present, a violet ring will form 

 at the place of contact. This is Hehner's test for for- 

 maldehyd reversed, see (304). 



1 UfEelmann, Deutsche Vierteljahresschr. f. off. Ges.-pfl., 15, p. 663. 

 ' The Analyst, 1893, p. 272. 



