The: Fixation of Nitrogen. 89 
of nitrogen.. In this climate I find that the thoroughly air-dried 
material presents almost as good a basis for comparison as is pos¬ 
sible for us to get, which would not be the case in a humid atmos¬ 
phere. 
When we consider the nitrification we find equally interesting 
results. As already stated, this sample of soil contained at the 
beginning of the experiment 0.0035 percent of nitrogen as nitrates, 
on the twenty-seventh day of the experiment the various samples 
gave the following: 
NITRIC NITROGEN IN SOIL SAMPLES INCUBATED FOR TWENTY- 
SEVEN DAYS. 
Percent in Soil Percent of Gain 
Sample A. 3/3 0.0055 54.29 
Sample B. 3/3 0.0057 62.85 
Sample C. 3/3 0.0060 71.43 
Sample D. 3/3 0.0065 85-71 
Sample E. 3/3 0.0036 - 
Sample F. 3/3 0.0043 22.85 
These results show clearly that both fixation and nitrification 
took place in all of the samples except E, in which nitrification is 
insignificant or zero, while the fixation amounted to 5.99 milli¬ 
grams per 100 grams of soil. At one time one of the dishes in the 
incubator smelled distinctly of butyric acid, but this odor disap¬ 
peared within a few days and all of the dishes had the pleasant odor 
of fresh soil when the samples were taken out of the dishes. 
The remaining portions of the samples, after having been 
thoroughly wetted with boiled, distilled water were returned to 
their original positions and only a little more water, not weighed, 
added till the forty-eighth day when this series of experiments was 
terminated. Four of the dishes were replaced in the incubator. 
One dish was covered and placed at the bottom, the other three 
dishes were not covered as in the first period except as each suc¬ 
ceeding one served as a cover for the one next below it. The top 
one of course was without any cover. Two beakers, containing 
water, were also placed in the incubator to aid in saturating the 
atmosphere with moisture and to lessen the evaporation from the 
soil. The moisture in the samples on the forty-eighth day was 
determined and found to be for A, 13.5, for B, 14.5, for C, 17.0, 
and for D, 20.0 percent. These are the four dishes placed in the 
incubator. Sample E, which was kept in a covered dish at the 
temperature of the room, contained 17.5 percent of water. The 
moisture in sample F, which was the original soil kept in a show- 
bottle, was not determined. 
