14 
added, and the mixture incubated as before. After four and eight 
days, respectively, an additional gram of casein was added in certain 
instances and the ammonia and nitrate determined, as shown in the 
following table: 
Amount of nitrogen recovered from casein. 
[Average of 2 samples.] 
Amount of casein and period of incubation. 
N recovered N recovered 
asNH 3 . asN0 3 , 
Per cent of. 
total N 
converted 
intoNHs. 
1 gram 4 days 
1 gram 8 days 
1 gram 12 days 
1 gram 4 days+1 gram 4 days additional 
1 gram 4 days+1 gram 8 days additional 
1 gram 4 days+1 gram 4 days additional+1 gram 4 days 
Mg. 
72.1 
74.2 
60.2 
150.9 
138.9 
226.8 
Mg. 
12.5 
"e.'e' 
3.3 
57.3 
59.8 
58.6 
60.8 
57.1 
61.8 
Practically the same amounts of ammonia were formed from a 
given amount of casein in four days as in longer periods. The yields 
from 1 gram were 57.3 per cent in four days, 59.8 per cent in eight 
days, and 58.6 per cent in twelve days. By adding another gram 
on the fourth day and allowing the action to continue four days 
longer 60.8 per cent of the total nitrogen was converted into ammonia. 
The portions treated in the same way but allowed to stand eight days 
longer gave 57.1 per cent yield of ammonia. Finally when 1 gram 
was added at the beginning and after four and eight days, respectively, 
61.8 per cent of the total nitrogen was converted into ammonia. 
The above data show, therefore, in common with the preceding 
series, that increasing percentages of the total nitrogen were converted 
into ammonia when increasing amounts of casein up to 3 grams were 
acted upon, but whether this fact was due to partial suppression of 
the nonammonifying organisms can not be positively stated. There 
is evidence, however, that under the conditions of these experiments 
the organisms feed on the organic nitrogen of casein rather than on the 
ammonia after it has been formed. 
SERIES VIII— AMMONIFICATION OF CASEIN IN SILICA SAND. 
The amounts of ammonia recovered from casein in the preceding 
experiments usually did not exceed 60 per cent of the nitrogen added, 
and reached a maximum point by the fourth day. In order to throw 
further light on this subject a series of experiments was carried out 
with silica sand, ^provision being made for absorbing whatever 
ammonia was volatilized. The decomposition took place in closely 
stoppered bottles through which a slow current of air was drawn by 
means of a suction pump. The current of air was first drawn through 
sulphuric acid to remove traces of ammonia and after passing through 
