The Fixation oe Nitrogen. 31 
The soil designated as Laboratory No. 989a, was very brown 
on its surface, and when exposed to the atmosphere, after drying at 
ioo°, absorbed enough moisture to cause it to adhere so tena¬ 
ciously that one could press it into clumps in the hand which re¬ 
tained the form of the fingers. The aqueous extract had a brownish 
yellow color which became decidedly brown on evaporation. This 
color continued to go into solution even after the chlorids and 
sulfates had been completely washed out. The color could scarcely 
have been due to humus in the presence of such quantities of lime 
salts, besides the soil is poor in humus and the strong brown color 
on the surface of this soil is not due to this cause. It would have 
been difficult to have obtained a sample of this soil entirely free 
from the azotobacter pigments in which to determine the humus. 
Prof. Sackett has obtained cultures showing that the azotobacter 
pigments are soluble in water. This accounts for the deportment 
of this sample. 
The mechanical analysis given for Laboratory No. 1067 is 
quite as applicable to the sample No. 989 as to the one of which 
it was made and likewise the agricultural chemical analysis is 
quite as applicable to 1067. The localities are probably as much as 
two miles apart but the soils are similar in location and character. 
ANALYSIS XXXVIII 
Soil, top four 
inches 
laboratory 
No. 989 
Percent 
Sand . 59.993 
Silicic acid (sol.) . 15.000 
Sulfuric acid . 0.430 
Carbonic acid . 3.450 
Chlorin . 1.561 
Phosphoric acid . 0.220 
Lime . 4.890 
Magnesia . 1.783 
Potash . 0.794 
Soda. 1.557 
Ferric oxid . 3.542 
Aluminic oxid. 2.189 
Manganic oxid . 0.370 
Water at 100° C. 0.500 
Ignition . (4.072) 
Sum .100.351 
O. equivalent to chlorin . 0.351 
Total . 100.000 
Total nitrogen . 0.118 
The ordinary agricultural analysis of this sample indicates 
that it is an excellent soil, which inference would be further 
justified by the mechanical analysis of No. 1067. While these 
inferences are fully justified by the analytical results and even 
further by the fact that all that was said of the preceding case, 
