Chemical Analysis of Milk and Its Products. 253 



a deep violet color will be obtained in the presence of 

 salicylic acid. 



304. e. Formaldehyde (a forty-per cent, solution in 

 water) . 



The following method by Hehner is stated to show 

 the presence of one part of formaldehyde in 200,000 

 parts of milk: the milk is diluted with an equal volume 

 of water, and strong H 2 S0 4 (sp. gr. 1.82-1.84) is added. 

 A violet ring is formed at the junction of the two 

 liquids if formaldehyde is present ; if not, a slight green- 

 ish tinge will be seen. The violet color is not obtained 

 with milk containing over .05 per cent, formaldehyde. 1 



The same color reaction is obtained in the Babcock 

 test and is easily recognized by persons familiar with 

 milk testing when their attention has once been called 

 to the characteristic color. 



An adulteration of milk, with formaldehyde may be 

 readily detected by the following method, which will 

 show the presence of 'only a trace of formaldehyde in 

 the milk. 5 cc. of milk is measured into a white porce- 

 lain dish, and a similar quantity of water added. 10 

 cc. of HC1 containing a trace of Fe 2 Cl 6 is added, and 

 the mixture is heated very slowly. If formaldehyde is 

 present, a violet color will be formed. 



1 Chem. News, 1896. No. 71 ; Milchzeitung, 1896, 491 ; 1897, 40. 

 667 ; The Analyst, 1895, 152, 154, 157 ; 1896, 285. 



