The Ground Water. 
43 
entering into the answer which are not known with sufficient defi¬ 
niteness. The same may be true of the off-flow water, but this water 
is the same that flowed onto the soil, and, after having been in con¬ 
tact with it for a certain length of time, flowing over it for a dis¬ 
tance of 600 feet in this case, was collected for examination. The 
water as it flowed onto the soil contained onlv traces of nitrates; the 
first portions that flowed off contained 1.970 and 1.077 parts per 
million respectively ; the last portions that flowed off contained 
0.3590 and a trace respectively. 
§ 123. The ground water in two instances showed an increase 
in the nitrates from 1.970 and 2.513 to 3.231 and 7.628 parts per 
million respectively. In two other instances a slight decrease was 
observed. 
• 
§ 124. The rapid diminution in the amount of the nitrates 
removed by the off-flowing water shows that their removal by the 
water flowing over the soil is very limited, probably confined to the 
very surface of the soil. In this connection I would recall the fact 
that comparatively large quantities of nitrates existed in the upper 
two inches of this soil. It is evident that the water upon coming 
in contact with the soil wets the uppermost portion before flowing 
over it; this takes place even when there is a good head of water. 
This wetting means a downward movement of the water at first, 
which may carry the nitrates not somewhat firmly held by the soil, 
down into the soil and beyond the action of the succeeding, over¬ 
flowing portions of water. 
§ 125. It is stated above that two instances of a decrease in 
the nitric acid were observed after irrigation. This decrease was 
in wells B and D and amounted to 0.1840 and 1.0870 parts per 
million respectively. In the case of D, which was near the point 
at which the water was brought onto the plot and where the soil 
was a sandy loam, it may be that the irrigation water may have 
found its way into the well more directly than it was intended it 
should, or it may be that the amount of water received at this point 
sufficed to produce leaching, but I am very doubtful of this. 
§ 126. The water, especially the ditch water, used for irrigat¬ 
ing, contained an unusual amount of nitrous acid. Whence it came 
I did not attempt to ascertain, and it was probably not true of the 
water after it had been running for some hours. Some of the water 
used was what we designate as seepage water, and contained 0.2340 
parts nitrous acid per million. The off flow was from 3 to 8 times 
as rich in nitrous acid as the ground water after irrigation. The 
amount of the off-flow was comparatively small. What relation it 
bore to the amount applied, I did not determine, nor have I any 
means of estimating how long the water collected was in contact 
