44 MILK ANALYSIS 



Bevan has, however, noted the fact that the total sohds of 

 milk containing formaldehyde are always higher, and that the 

 increase is much greater than can be accounted for, even as- 

 suming that all the formaldehyde remains in the residue. 



The rate at which formaldehyde disappears from milk has 

 been investigated by Hehner, who found that at the end of a 

 week none could be detected in a sample to which had been 

 added i part in 100,000; after two weeks none could be de- 

 tected in a sample of i part in 50,000; after three weeks only 

 a trace could be detected with i part in 25,000. 



Detection of Boiled Milk. — Dupouy proposed the following 

 method: A few drops of a solution of 1-4-diamidobenzene in 

 water are added to 5 c.c. of the sample, and then a few drops 

 of hydrogen dioxid solution. Raw milk gives a blue color; 

 milk tliat has been heated to over 79° gives no color. The 

 solution of diamidobenzene must be freshly prepared. Rosier 

 has found that 1-3-diamidobenzene will serve, and that if the 

 blue milk be shaken with amyl alcohol, the blue color passes 

 into the latter and is more stable. These tests are applicable 

 for distinguishing between pasteurized and sterilized milks, 

 as the reactivity of milk is lost between 75° and 80°. 



Faber has shown that raw milk may be distinguished from 

 boiled milk or milk that has been heated above 75° by the fact 

 that such treatment coagulates or alters the albumin so that if 

 the liquid be saturated with magnesium sulfate, the albumin 

 is separated along with the albumin casein. 



Richmond & Boseley recommend the following methods to 

 distinguish new milk from milk which has been sterilized: 



(a) 100 c.c. of the sample are allowed to stand in a gradu- 

 ated cylinder for six hours at 15.5° and the percentage of cream 

 noted. If less than 2.5 per cent, of cream has risen for each i 

 per cent, of fat in the milk, the milk may be considered suspi- 

 cious; if the cream falls decidedly below 2 per cent, for each i 

 per cent, of fat, it is probable that sterilized milk is present. 



