58 MILK 



that the well-known test for nitrites (sulfanilic 

 acid and alphanaphthylamine) reacts in the 

 presence of formaldehyde. The reactions are 

 obtained in fresh samples and in those that have 

 stood for twenty-four hours. 



Determination of Formaldehyde. — In the case 

 of milk the proportion of formaldehyde is almost 

 always small and it may be in great part removed 

 from milk by distillation especially in a current 

 of steam. B. H. Smith found that if loo c.c. 

 of the sample are distilled with i c.c. of dilute 

 sulfuric acid (1:3), one-third of the formaldehyde 

 present will come over with the first 20 c.c. 

 Distillation of milk is troublesome owing to 

 bumping, but Smith found that it could be safely 

 conducted with a fiat evaporating burner. It is 

 advisable to put a few pieces of pumice into the 

 flask. 



Shrewsbury and Knapp recommend the fol- 

 lowing method for estimation of formaldehyde. 

 An oxidizing reagent is prepared by mixing o.i 

 gram of pure nitric acid (sp. gr. 1.52) with 100 c.c. 

 of strong hydrochloric acid are mixed. This 

 mixture should be freshly made. 



5 c.c. of milk are treated with 10 c.c. of the 

 reagent, the mixture well shaken and kept for ten 

 minutes in a water-bath at 50°. The depth of 

 color is proportional to the amount of formalde- 

 hyde present and by means of milk containing 



