28 
Bulletin 72. 
at least, a difference due to the conditions which prevailed immedi¬ 
ately prior to the time of taking the sample. 
§ 78. Outside of these general features but little is shown by 
the composition of the ground waters as collected in the wells. The 
changes observed are not so great as were looked for, and when the 
variations due to changes in conditions immediately before the 
taking of the samples have been allowed for, the uniformity 
throughout the period of observation, a period of nearly three years, 
leaves but little doubt of the correctness of the conclusion that, 
while the total solids may vary in their quantity and in composi¬ 
tion, too, within narrow limits, they remain in all essential respects 
the same. 
THE GROUND WATERS DIFFERENT FROM ALKALIES-ALSO FROM THE 
DRAIN WATERS. 
§ 79. The total solids, obtained by evaporating the ground 
waters, represent a different mixture of salts than that which is 
obtained by continued treatment of the soil with frequently renewed 
portions of distilled water, until it is so thoroughly exhausted that 
no sulfuric acid can be found in the solution after standing in con¬ 
tact with the soil for not less than 12 hours. Attention was called 
to this fact in Bulletin 65, where some analyses of the water-soluble 
portions of this soil are given, together with their most characteristic 
features. 
§ 80. In the following comparison we shall not make any 
attempt to assign causes for the differences which are undoubtedly 
to be found in the complex reactions taking place between the 
different salts or their ions within the mass of the soil, and also to 
the formation of salts de novo, due to the action of water as such, 
and of solutions upon the rock particles in the soil. In Bulletin 65 
the suggested explanation was confined almost wholly to the latter 
phase of the question because it is the simplest feature of it and 
conveys a sufficiently extensive view of the subject without intro¬ 
ducing any of the more difficult questions involved in the theory of 
solutions. For a fuller and sufficient explanation of the facts 
recourse must be had to this branch of the subject, but I shall con¬ 
tent myself with as clear a statement of the facts as I may be able 
to make. 
§ 81. The samples which I have chosen are a sample of water 
from well C, the water soluble portions from two samples of soil C 
and a representative alkali incrustation. The designation well C 
and soil C is equivalent to stating that the sample of soil was taken 
as near to well C as we deemed advisable, which in this case was 
within 11 feet. 
