The Ground Water. 
41 
there was enough downward moving water in the soil, even when 
the voids between the soil particles were not completely filled with 
water to carry the nitrates into the ground water. Such does not 
seem to be the case, for if it were, the ground water immediately 
after irrigation ought to be richer in nitrates than they were found 
to be, even after making liberal allowance for the fact that the irri¬ 
gation might effect a dilution of the ground water. In the case of 
the total solids we find a very decided increase, more salts having 
gone into solution than was necessary to maintain the degree of sat¬ 
uration. This is true, too, of the nitrates, at least in a measure. In 
the case of the irrigation applied August 31st and September 1st, 
1899, the results were not uniform in regard to the increase of the 
nitrates in the ground water, indeed an increase in their quantity 
was the exception. This result was probably due to the fact that I 
had a more liberal supply of water than in any previous irrigation 
.and the results were due to dilution of the ground water, owing to 
the addition of a large quantity of water in a short time. 
NITROUS ACID IN THE GROUND WATER, 
§ 118. I have given the limits found for the nitrous acid in 
the ground water, especially before and after irrigation, in a preced¬ 
ing paragraph. Our examination of the water did not as a rule ex¬ 
tend to the determination of this constituent except in studying the 
effects of irrigation upon the composition of the ground water, off- 
flow and drainage, under which topic the results observed will be 
given more fully. The results of the determinations made indicate 
that as a rule the nitrous acid present in the ground water of this 
plot was low, not exceeding 0.0837 part per million, except imme- 
- dialely after irrigation, when it rose to 0.1090 part per million. 
The least quantity of nitrous acid was found in the ground water 
from the alfalfa field west of our plot, in which we found only a 
trace. 
§ 119. The few samples of drain water which we examined 
were richer in nrtrous acid than the ground waters. The ground 
waters were richer in nitric than in nitrous acid ; while the reverse 
was the case with the drain waters. The cause of this might be a 
reduction of the nitrates in passing through the soil to the depth of 
the drain, which is about four feet, but the ratio of increase above 
that of the nitrates caused by irrigation suggests that it is rather 
due to the deportment of the salts of this acid toward the soil parti¬ 
cles. For while irrigation did not always increase the nitrates in 
the ground waters, it always increased the nitrites, and in those 
cases in which it caused an increase of the nitrates from 1J to 3 
times their previous amount, the nitrites were increased from 8 to 
30 or more times. It should be remembered that we always had 
very much smaller amounts of nitrites than of nitrates to deal with. 
