H. P. Armsby—Absorption of Bases by the Soil. 29 
Nos. CaQin1le.c.of sol. Wt. of silicate. Vol.ofsolution. Absorption. 
VI. 3. 0001683 grms. 10 grms. 200c.c. 0°2996 grms. 
4, eo oe 5 66 pen 0°2 “ 
Marit ark Sewce 2°5 - e 071217.“ 
Le are 1°25 em ghie 00673 “ 
(as 0°625 =“ at 0°0338 “ 
Dee bac es Og125. .< pine o°0198 “ 
VIL 5. 0°000841 grms. 2% grms. 200¢.¢.  0°1151 grms. 
. ee aceien i gs ag fe 00663 “ 
qe ee Se 0625 — ie 070359 “ 
eee ee 0°3125 “ mp 070187 “ 
It will be seen that the same variations occur here as in soil- 
of replaceable bases in the soil. A similar limit seems to have 
been reached in some of these experiments. In experiment 
II, 8, about two-thirds of the soda of the silicate has been 
replaced by lime, and an increase of concentration seems un- 
able to carry the replacement further. e same is seen in 
VII, 7, and the corresponding ones of the other series, while 
In those experiments where this limit is not reached the 
absorption increases with the concentration in the same wa 
in soil-absorption. For the same reason, apparently, the ab- 
Sorption in the last four experiments of (V) and the last three 
of VI, decreases proportionally to the soil, seemingly unable to 
pass this limit of two-thirds, © That the rest of the soda cannot 
be displaced is not probable, but it is evidently more difficultly 
replaceable. The high absorption of (VI, 8) is perhaps an 
error of experiment. 
Since, now, it has been shown that the absorption of bases by 
tion there would seem to be no reason why the latter should not 
be considered to be due chiefly to these silicates in the soil. That 
other agents may also be concerned to some extent, especially in 
the absorption of free bases, is doubtless true, but that any form of 
Surlace-attraction can decompose simple salts is yet to be proved. 
Jn regard to the chemical or physical nature of absorption it 
will hardly be denied, in view of the results of Way, Eichhorn 
and Heiden, that the reaction between the hydrous silicates and 
a salt is essentially a chemical process consisting in a partial ex- 
Change of bases. The reason why the exchange is not com 
plete would seem to be the same as the reason why, e. g., I Cl 
i O when heated together are not completely converted into 
20 and Cl, or the reverse ; or why, when two salts are mixed 
