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 roo c.c. 
of the sample are distilled with 1 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 flat 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 0.1 
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 
