New York AGRICULTURAL EXPERIMENT STATION. 211 
pounds even when they are practically absent. Phosphotungstic 
acid, on the other hand, completely precipitates peptones, but 
also precipitates some of the amido-acid compounds that are 
present in cheese and milk, and the consequence is that the 
amount of amido-acid compounds found is too low. Bromine 
is open to both objections,— it fails to precipitate peptones com- 
pletely and at the same time does precipitate some of the amido- 
acid compounds. While these two sources of error might tend 
to offset each other under certain conditions, we cannot depend 
upon such a method for reliable quantitative results. 
In our judgment, it is desirable, for best results, to use phos- 
photungstic acid to separate peptones and amido-acid com- 
pounds, when the amount of amido-acid compounds is relatively 
small as compared with peptones or when they consist mostly 
of monoamido compounds. This condition occurs in the early 
stages of cheese ripening and persists longer in cheese cured at 
low temperatures; it occurs also in milk and cheese acted upon 
by pepsin enzymes, especially in the presence of chloroform. 
Tannin-salt solution can be relied upon to give better results 
than phosphotungstic acid, when amido-acid compounds are 
present in proportions that are relatively large compared with 
peptones or when they consist largely of diamido compounds. 
The former condition prevails in normal cheese cured under 
usual conditions, especially after the first few weeks of curing. 
10. DETERMINATION OF NITROGEN IN THE FORM OF AMMONIA. 
We distil with magnesium oxide 100 ce. of the filtrate from the 
tannin-salt precipitation, passing the distillate into a standard- 
ized acid and titrating in the usual way. In our early work the 
cheese-mass itself, suspended in water, was used for distillation, 
giving slightly higher results than the method jnst described. 
The small increase is generally accounted for as coming from the 
proteids themselves present in the solution. Theoretically, it is 
.true that when such bases are present as putrescine and cadav- 
erine, they might distil with the ammonia. In one case where 
a large quantity of cheese was subjected directly to distillation 
with magnesium oxide and the distillate examined for these 
bases, none was found, the distillate consisting entirely of the 
