ADULTERANTS. 41 



above. By standing, or immediately on boiling, the 

 rotatory power falls to the point mentioned. In pre- 

 paring solutions from the solid milk sugar, care must 

 be taken to bring them to the boiling point, previous 

 to making up to a definite volume. This precaution 

 is unnecessary when operating upon milk. 



MIIvK ADULTERANTS. 



Water. The addition of water to milk is usually 

 detected by the diminution in the amount of 

 solids. Since nitrates are absent from normal milk, and 

 almost invariably present in surface and subsoil waters, it 

 may be possible to detect the addition of water by the 

 application of one of the delicate tests for nitrates. The 

 value of this method is considerably impaired by the 

 fact that small amounts of nitrates may be introduced 

 into the milk by the water used in rinsing the cans. 

 Nevertheless, the presence of notable quantities of ni- 

 trates will be ground for grave suspicion. The test is 

 applied as follows : Several grains of diphenylamin 

 are placed in a test-tube and dissolved in two or three 

 c. c. of strong, pure sulfuric acid. A small quantity of 

 milk is then added carefully, so as to form a layer on 

 the surface of the acid. If nitrates be present, a blue 

 color is formed at the junction of the two layers. 



With any given sample of milk, addition of water de- 

 creases the gravity, while abstraction of fat increases it. 

 It is possible, therefore, by carrying out both methods 

 of adulteration carefully, to maintain the same gravity 

 as in the original sample, so that this datum alone will 



D 



