DETECTION OF ADULTERATION 225 



cemed. Usually, the presence of nitrates is positive, 

 still it must not be forgotten that when the milk can is 

 rinsed a little water may be left, which, if it is rich in 

 nitrates, may cause the milk to show a slight reaction, 

 so that it might appear that water has been intentionally 

 added. Usually water does not contain such a quantity 

 of nitrates as to cause a suspicious reaction when the 

 milk has not really been adulterated. 



d. Adulteration of partly skimmed and skimmed 

 milk. In most cities no minimum limit is fixed for the 

 fat content of the half skimmed and the skinuned milk, 

 and the only form of adulteration to be considered in 

 this connection is the addition of water. This causes a 

 lowering of the specific gravity of the milk (from 1.030 

 to 1.036 to from 1.032 to 1.040) and whey, as well as a 

 diminution in the amount of solids. A possible trace of 

 nitrates proves that the milk has been watered. In 

 cities, in which the minimum limit of fat content for 

 partially skimmed milk or skimmed milk has been es- 

 tablished, the milk is, of course, considered adulterated 

 when it falls below this standard. [In some places there 

 is a standard of 9.25 per cent, total solids for skimmed 

 milk as provided by the U. S. Department of Agricul- 

 ture.] 



e. Adulteration of cream. Cream is sold in different 

 forms, with fat content varying between about 10 per 

 cent, and 30 per cent. (40 per cent.). In some cities, the 

 minimum content of different grades is defined, so in 

 such cases public control must be extended to determin- 

 ing the amount of fat in cream. Of the different aduL 

 terations, the addition of starch and flour are to be 

 mentioned particularly. This is done to make the cream 

 thicker and to give it the appearance of being better 

 than it really is. In raw cream, the proof by micro- 

 scopic examination is simple, as the starch grains are 



15 



