40 
Bulletin 72. 
§ 115. The great difference in the amount of nitric acid in the 
first and second two inches of soil, suggested the question of a possi¬ 
ble reduction of the nitric acid from some cause. I had no reason 
to suspect the formation of ferrous salts, and the amounts of 
ammonia and nitrous acid found in the well and drain waters ex¬ 
amined for these constituents did not strongly support the idea of a 
reduction. The maximum amount of free ammonia found in the 
well waters before irrigation was 0.0850 part per million, and after 
irrigation 0.5780 part. The maximum quantity of nitrous acid 
found in the well waters before irrigation was 0.0837 part per mil¬ 
lion, and after irrigation 0.1000 part. The increase in the free 
ammonia present alter irrigation is not accompanied by a corre¬ 
sponding increase in the nitrous acid, but is greatly exceeded by the 
increase in albumenoidal ammonia, so that the probabilities are in 
favor of another source for it rather than that of the reduction of 
nitric acid. The nitric acid in these samples was, moreover, quite 
as high as the average, being 2.692 parts per million before irriga¬ 
tion and 7.628 parts per million after irrigation. 
§ 116. When we consider the large amount of nitric acid per 
acre, 293.14 pounds, existing in the uppermost two inches of this 
soil, and while the second two inches show less than a tenth as 
much, and further, that the ground waters are comparatively poor 
in it after as well as before irrigation, we are forced to the conclu¬ 
sion that there is a tendency in our soil to the concentration of this 
salt in the upper portions. Whether this is due to a very rapid 
formation of it at this point, or to the action of capillarity under 
our meteorological conditions, is an open question. Long continued 
cloudiness, with or without continued or heavy rains, which means 
impeded evaporation, is followed by a greater increase in the 
amount of nitric acid in the ground water than we have observed 
to be due to irrigation. In fact the increase due to irrigation has 
in no case been comparable to that observed after long rains. I 
have no explanation to offer for this fact unless we find one in the 
difference between the rate at which the nitrates tend to move up¬ 
ward, due to capillarity, whose effects are made more marked by 
our conditions, almost continuously favorable to a rapid evapor- 
may be washed 
downward by the amount of water used. It is well known that the 
nitrates appear in alkaline crusts under favorable conditions, some¬ 
times forming several per cent, of the mass, but I have not found it 
present in any incrustation collected in Colorado except in traces. 
§ 117. I expected to find relatively large quantities of nitrates 
n the ground water, owing to the fact that the soil is not usually 
credited with any great power of retaining them when solutions of 
these salts are passed through them, and I at first assumed that 
ation from the surface and that at which they 
