MILK AND MILK PRODUCTS 39 



The following test, recently discovered by Bonnet, is due to 

 the vapor of formaldehyde, and avoids the fallacies of some of 

 the older tests. A solution is made by dissolving 0.035 gram 

 pure morphin sulfate in 10 c.c. of sulfuric acid. This solution 

 does not keep well. A convenient amount of the sample is 

 placed in a dish or beaker, a watch-glass containing i c.c. of the 

 above solution is floated on it, and the dish covered vsdth a glass 

 plate. The materials are allowed to remain undisturbed at 

 room-temperature for several hours. Formaldehyde is indicated 

 by the development of a color ranging from pink to dark blue. 

 A black discoloration is disregarded. Bonnet found that with 

 I part of formaldehyde to 25,000 parts of sample a distinct color 

 appeared in one hour. 



Formaldehyde may be obtained pure by distillation of the 

 sample, especially in a current of steam. B. H. Smith found 

 that if 100 c.c. of the sample be mixed with i c.c. of dilute 

 sulfuric acid (i : 3) and distilled, one-third of the formaldehyde 

 present will come over in the first 20 c.c. of distillate. The 

 distillation of milk is troublesome, owing to bumping and froth- 

 ing, but Smith found that it could be conducted safely by using 

 a flat evaporating burner. It is advisable also to put a few 

 small pieces of pumice-stone in the flask. 



In testing ice-cream and similar articles, it must be borne in 

 mind that some flavoring materials, such as vanillin, and 

 lemon and orange extract, being partially aldehydic in nature 

 may simulate formaldehyde. La Wall has obtained reactions 

 of this character from vanillin, and even from a commercial 

 table sugar. The phenylhydrazin and morphin sulfate tests are 

 the least liable to fallacy in this respect. 



Determination of Formaldehyde. — B. H. Smith, who also in- 

 vestigated the methods for this purpose, finds that the choice will 

 depend on the strength of the solution. For moderately strong 

 solutions the iodin method of Romijn is satisfactory. 



10 c.c. of the solution, which should be diluted so as not to 



