26 H. P. Armsby—Absorption of Bases by the Soi. 
do away with the variability of absorption as ordinarily deter- 
mined nor rob that variability of its force as an argument for 
the physical nature of absorption, since as Pillitz himself says 
even the most dilute solution is not exhausted, which must be 
the case were the variations due simply to a lack of sufficient 
material to saturate the soil. 
In view of the interest attaching to this question it seemed to 
me desirable to compare the behavior of the soil in this respect 
with that of pure hydrous silicates. If it should be found that 
the exchange of bases between these compounds and neutral 
salts showed the same variations as soil-absorption, then, what- 
ever view might be held as to the cause of these variations, all 
possible objections to the theory which considers soil-absorp- 
tion to be such an exchange of bases between the salt and the 
hydrous silicates known to exist in the soil would seem to be 
removed. 
As illustrating the variations of soil-absorption the following 
determinations made in the laboratory of Prof. Knop in Leipzig 
may be adduced. ‘T'wo soils were used: No. 1, Deposit of the 
Nile. No. 2, A loamy soil from the vicinity of Leipzig. 
The absorptive power of these soils for ammonia was deter- 
mined by Knop’s method (Bonitirung der Ackererde, 49) by 
digesting the soil in the cold with a solution of NH,Cl of 
known strength for forty-eight hours and determining the am- 
monia remaining in the fluid by means of the azotometer. 
The results denote the c. c. of nitrogen at 0° C. and 760 m.m 
pressure contained in the ammonia absorbed, and the concen- 
tration of the solution employed is stated in the same way. I 
was found more convenient to vary the amount of the soil than 
of the solution. 
Absorption 
Nos. Ninle.c of Sol. Wt. of Boil. Soil No. 1. Soil No. 2. 
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