The Ground Water. 
37 
increase on the 8th was probably due to a rainfall which took place 
on the 5th and 6th and amounted to 0.78 of an inch. There were 
also slighter rainfalls on the 1st, 2d, 16th and 17th, but the total of 
these amounted to only .12 of an inch, the heaviest one was only 
.07 of an inch, too small an amount to produce an observable influ¬ 
ence. The comparatively small rainfall of .78 of an inch seems to 
have been the cause of the increase of the nitric acid in the ground 
water, for the increase in the four wells was simultaneous, though 
quite unequal; the greatest increase being 6 parts per million, the 
least 1 part per million. The effect of this rainfall was not great 
enough to show in well E, as the nitric acid was falling at a rapid 
rate and our samples were not taken often enough to show small 
variations in the rate of falling. 
§ 104. There was a slight change of the water table between 
the 6th and the 8th, amounting to a few hundredths, the greatest 
being 0.08 of a foot. The actual distance of the water table below 
the surface at this time was from 3.0 to 5.2 feet. Under these 
conditions there can scarcely be a thought of the nitric acid, 
nitrates, having been added to the ground waters by its direct wash¬ 
ing downward through the soil. The wells in which the water was 
the deepest below the surface showed the greatest increase. This 
is what we would expect if the rain water simply flowed through 
the soil, carrying the nitric acid or its equivalent nitrates down with 
it. This amgunt of rainfall, 0.78 of an inch, is, however, insuffi¬ 
cient to wet this depth of soil. As the surface of this soil was in an 
almost air dry condition at the time of the rainfall, it was probably 
not wet to a depth greater than two inches, which is a liberal esti¬ 
mate, but if we put the depth to which the rain water penetrated at 
four times this estimate, it would not account for the rise in the 
water table, nor for the washing downward of the nitric acid to a 
depth of a little more than 5 feet. I think that the oscillation in 
the water plane and the increase in the nitric acid in the water 
were both due to the effect of the rainfall upon the capillary condi¬ 
tions of the soil; the nitric acid, more explicitly the nitrates, exhib¬ 
iting a downward capillary movement. 
§ 105. A sample of water taken from well A on December 
7, 1898, showed only a trace of nitric acid. This determination was 
repeated to assure myself that no mistake had been made, but the 
results were the same, corroborating the first determination. This 
was the fourth instance that we had met with in which there was 
only a trace of nitric acid present in the water. These four instances 
were met with when the water plane was low, but not when it was 
at its lowest. 
§ 106. Well A was located in a portion of the plot where the 
incrustations formed most abundantly, where the mechanical con- 
