56 MILK 
these conditions, milk, in the absence of for- 
maldehyde, gives a slight greenish tinge at 
the junction of the two liquids, while a violet 
ring is formed when formaldehyde is present 
even in so small a quantity as 1 part in 200,000 
of milk. The color is permanent for many 
hours. In the absence of formaldehyde, a 
brown ring may form in the course of a few 
hours, but it is below the junction line of the 
two liquids. 
Phenylhydrazin Test.—The following test 
avoids the fallacy of some other tests. A pinch 
of phenylhydrazin hydrochlorid is added to a 
few c.c. of the sample, the liquid shaken, then a 
drop of a fresh solution of sodium nitroprussid 
and a few drops of sodium hydroxid solution. 
A greenish tint is at once produced if formalde- 
hyde is present. If the test is applied to the 
liquid obtained by distilling milk the color will be 
deep blue. 
Phloroglucol Test—A small amount of a 1% 
solution of phloroglucol is added to the sample 
and then a considerable volume of sodium 
hydroxid solution. In the presence of formalde- 
hyde a distinct rose tint will be produced. It 
is best to add the phloroglucol by means of a 
tube passed to the bottom of the test-tube. 
Bonnet’s test utilizes the vapor of formalde- 
hyde, and avoids the fallacies of some of the 
