224 Testing Milk and Its Products. 



to the Beichert-Wollny method, as already explained 

 under Detection of Artificial Butter (270). 1 



TESTS FOR ADULTERATION or MILK AND CREAM. 



281. The nitric acid test may prove useful as corrobora- 

 tive evidence that a sample of milk has been watered 

 (123). Normal fresh milk does not contain nitrates, 

 while common well-water, particularly on farms where 

 precautions to guard against contamination of the 

 water supply have not been taken, in general contains 

 appreciable amounts of nitrates, nitrites and ammonia 

 compounds, and watered milk will, therefore, in such cases 

 also contain nitrates. 2 The method for detection of 

 small amounts of nitrates in milk, as given by Eich- 

 mond 3 is as follows: Place a small quantity of diphenyl- 

 amin at the bottom of a porcelain dish, and add to it 

 about 1 cc. of pure H 2 SO 4 (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 

 developes 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 ct. of 

 water to the milk by this test, if the water added con- 

 tained 5 parts of nitric acid, or more, per 100,000. 



Besides by the methods given in the preceeding (pp. 

 101-107), watering or skimming of milk may be detected 



1 See Arb. Kais. Ges.-Amt., 14, 506-598. 



2 Uffelmann, Deutsche Vierteljahresschr. f. off. Ges.-pfl. 15, p. 663. 



3 The Analyst, 1893, p. 272. 



