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 i 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 



