io The Colorado Experiment Station 
fixation of nitrogen and the formation of the nitrates in situ. I 
have already stated that the soil is a gypsiferous clay, and it follows 
that the amount of water-soluble found will depend almost alto¬ 
gether upon the amount of gypsum present and the persistency with 
which it is extracted with water. 
ANALYSIS OF WATER-SOLUBLE FROM BROWN SPOT. 
Silicic acid 
Calcic sulfate . . 
Calcic chlorid . . 
Magnesic chlorid 
Magnesic nitrate 
Potassic nitrate 
Sodic nitrate . . 
Percent 
0.206 
80.440 
3.835 
0.326 
7.766 
0.093 
7.334 
100.000 
The alkali incrustations, as well as the aqueous extracts of the 
surface soils, consist very largely of the sulfates of calcium, mag¬ 
nesium and sodium. The amount of the sodium sulfate varies ex¬ 
ceedingly but in this case we find a small amount of sodic salts and 
a relatively small amount of chlorin. The soluble portion is 115,- 
600.0 p. p. m., the chlorin is 3,112 and the nitric nitrogen is 3,120 
p. p. m. It is evident in this case that the nitric acid must be 
combined with other bases than sodium, but to make our statements 
uniform we will give the nitric nitrogen and chlorin as the sodic 
salts corresponding to.their respective quantities. The ratio of 
nitric nitrogen to chlorin in this case is 1 :1 and the corresponding 
amounts of sodic nitrate and chlorid are 18,720 and 4,979.2, or 
in the ratio of 1 :o.27. 
The soil first given with its large quantity of alkalis and no 
unusual quantities of nitrates, and this sample of a “brown spot” 
with large amounts of nitrates and small amounts of alkali, gypsum 
excepted, which in this case is clearly a portion of the clay, illus¬ 
trates the extreme difference between an alkali soil and a “brown 
spot” or nitre-area. I may add that I have seen a soil which is 
exceedingly rich in gypsum, so much so that it is ordinarily quite 
white, very strongly discolored with Azotobacter pigments and 
found it quite rich in nitric acid. This was in the immediate neigh¬ 
borhood of this “brown spot.” 
I answered this question of concentration fully in Bulletin 178 
and showed that the nitrates could not have come from the adjacent 
lands. I presented the whole case, the favorable and unfavorable 
features, so fully that persons conversant with our conditions cannot 
doubt the competency of the data given to present the conditions 
really obtaining, and they gave no support to the concentration 
theory. Concerning this case I stated, “There is not another in- 
