bulletin 82. 
34 
water plane. Further, there must be a rapid diffusion of salts 
taking place between the two solutions represented by the ground 
water, which probably moves upward when the surface is first 
moistened, and the descending irrigation water. This diffusion 
may be greatly modified by the soil, but that some diffusion takes 
place can not be doubted. 
§ 60. I see no better way to present the general changes 
than to compare the ground water as actually found before and 
after irrigation. This varied in the different wells under observa¬ 
tion; it is usually a difference of degree rather than of character. 
While I know that in some respects I do violence to the facts 
from minor points of view, I think that by taking the averages 
of results found, we obtain a faithful view of the general results 
for the given irrigation and, while this does not answer many 
questions which arise, it seems the best approach that we can 
make to a knowledge of what takes place. As we estimate the 
amount of water applied at the rate of eight inches or two-thirds 
of an acre-foot, we will make our calculations for this amount 
throughout. The irrigation was begun on the 8th and the 
samples taken on the nth instant and, as we know that some 
diffusion must have taken place in these three days, we will as¬ 
sume that this took place completely with an equivalent of eight 
inches of the ground water. 
§ 61. The two-thirds acre-foot of irrigation water contained 
a total of 1,297 pounds of salts in solution; a like quantity of 
ground water before irrigation contained 5,139 pounds of salts and 
after irrigation, 9,550 pounds. The ground water as it was taken 
from the wells after irrigation showed an increase of 4,411 pounds 
in the salts held in each eight inches of water. If, however, we 
had mixed eight inches of the irrigation water with a like quan¬ 
tity of the ground water before irrigation, each eight inches 
should have contained 3,218 pounds. But we find 9,550 pounds 
which is an excess of 6,332 pounds in each eight inches, represent¬ 
ing the actual solution of 12,664 pounds of salts, which is prob¬ 
ably nearer correct than the 4,411 pounds. But as we wish to 
present conservative figures, we adopt the latter and assume that 
the eight inches of irrigation water applied, dissolved from the 
soil 4,411 pounds of salts which were previously not in solution. 
It would, however, be better to say that the result of the irrigation 
was to set this much salt free, that is, that whatever reactions inav 
have been induced between the salts within the soil, resulted in 
Fringing this additional amount into solution in the ground water. 
That the irrigation water acts not merely as a diluent is proven 
k>y the changed ratio of the salts present, which is best presented 
as follows: 
