TESTING MILK FOR ADULTERATIONS 147 



DETECTION OF FOREIGN SUBSTANCES IN MILK 



The foreign substances most frequently found in 

 milk are preservatives and coloring matters. The pre- 

 servatives in common use are formalin, boric acid, 

 borax and sodium bicarbonate. The coloring matters 

 generally used are annatto and coal-tar dyes (azo- 

 colors), which are added to milk to make it look rich, 

 and, especially in case of skimmed and watered milk, 

 to cover up the signs of such adulterations. 



Test for annatto. To 10 cc. of milk in a test-tube 

 add 10 cc. of ether, shake vigorously and let stand un- 

 til the ether separates on top of the milk. If annatto 

 is present, the layer of ether will be yellow, the depth 

 of color depending on the amount of annatto present. 



Test for Coal-Tar Dyes. The azo-colors, which 

 are the ones most commonly used in coloring milk, may 

 be detected by adding 10 cc. of milk to 10 cc. of strong 

 hydrochloric acid and mixing, when a pink coloration 

 appears. 



Tests for Formalin. Formalin, which is a 40 

 per cent, solution of formaldehyde, is commonly di- 

 luted and sold under such names as "Freezine," "Ice- 

 line," etc., which contain from 2 to 6 per cent, of for- 

 maldehyde. In making the Babcock test in milk, the 

 presence of formalin may be shown when a marked 

 violet layer forms at the junction of the acid and milk 

 just after pouring the acid into the test-bottle. The test 

 may also be performed by taking 10 cc. of milk in a 

 test-tube or Babcock test-bottle, and adding about 5 

 cc. of sulphuric acid, such as is used in the Babcock 

 test, pouring the acid down the side of the tube so 

 that it does not mix with the, milk. 



