344 Absorption of Potash by Soils of known Composition. 
degree than the marly soil, which it will be noticed absorbed 
from the same solution more than three times as much potash. 
The residue obtained on evaporating the filtered liquid, con- 
tained 50 - 847 grains of sulphuric acid, of which 
4G - 855 were united with potash 
2'917 „ „ lime and 
T075 „ „ magnesia 
50-847 
Before nitration, the solution contained 55*540 of sulphuric 
acid. It would appear, therefore, that sulphuric acid, as well as 
potash, was absorbed in this experiment. This, however, is not 
the case ; for, on making a separate sulphuric acid determination 
in another portion of the solution after contact with soil, and 
avoiding previous evaporation to dryness, I find in 8 decigallons 
56*368 grains of sulphuric acid, that is, a slight excess over the 
quantity of sulphuric acid in the 120'S of sulphate of potash, 
which were dissolved in 8 decigallons of distilled water. It 
is evident, therefore, that the evaporation to dryness of the 
filtered liquid and heating of the residue, had the effect of dis- 
sipating a considerable proportion of sulphuric acid. But as the 
filtered liquid had no acid reaction, the acid could not be present 
in a free state, and the question arises in what state of com- 
bination did it exist? 
The experimental soil, it may be mentioned, had received 
rather a heavy dressing of Peruvian guano. Digested with 
water, it gave a brownish-coloured solution, which afforded 
distinct indications of the presence of ammonia. A portion of 
sulphuric acid, originally united with potash, doubtless passed 
into the filtered liquid in combination with ammonia. 
As sulphate of ammonia, like all salts of ammonia, is 
volatile at a high temperature, the evaporated and strongly- 
heated residue of the filtered liquid could not contain any 
sulphate of ammonia ; the analysis of this residue consequently 
yielded less sulphuric acid than the liquid from which it was 
obtained. A careful determination of the amount of ready- 
formed ammonia in this soil showed that it contained 403 per 
cent, of ammonia. As 1 lb. of soil was used in the filtration 
experiment, this evaporation of ready-formed ammonia in the 
soil is quite sufficient to combine with the quantity of sulphuric 
acid that escaped on heating the solid matter left on evaporation 
of the filtered liquid. 
The result of this experiment is interesting in several respects. 
1. On comparing the results obtained in passing a solution of 
sulphate of potash through the soil, it will be noticed that much less 
potash was retained than was the case when caustic potash was 
