, it was observed that the liquid which ran through, no
longer contained any of the ammonia or other salt employed. The soil
had, in some form or other, retained the alkaline substance, while the
water in which it was previously dissolved passed through.

Further, this power of the soil was found not to extend to the whole
salt of ammonia or potash, but only to the alkali itself. If, for
instance, sulphate of ammonia were the compound used in the experiments,
the ammonia would be removed from solution, but the filtered liquid
would contain sulphuric acid in abundance--not in the free or uncombined
form, but united to lime; instead of sulphate of ammonia we should find
sulphate of lime in the solution; and this result was obtained, whatever
the acid of the salt experimented upon might be.

It was found, moreover, that the process of filtration was by no means
necessary; by the mere mixing of an alkaline solution with a proper
quantity of soil, as by shaking them together in a bottle, and allowing
the soil to subside, the same result was obtained. The action,
therefore, was in no way referable to any physical law brought into
operation by the process of filtration.

It was also found that the combination between the soil and the alkaline
substance was rapid, if not instantaneous, partaking of the nature of
the ordinary union between an acid and an alkali.

In the course of these experiments, several different soils were
operated upon, and it was found that all soils capable of profitable
cultivation possessed this property in a greater or less degree.

Pure sand, it was found, did not possess this property. The organic
matter of the soil, it was proved, had nothing to do with it. The
addition of carbonate of lime to a soil did not increase its absorptive
power, and indeed it was found that a soil in which carbonate of lime
did not exist, possessed in a high degree the power of removing ammonia
or potash from solution.

To what, then, is the power of soils to arrest ammonia, potash,
magnesia, phosphoric acid, etc., owing? The above experiments lead to
the conclusion that it is due to the _clay_ which they contain. In the
language of Prof. Way, however,

"It still remained to be considered, whether the whole clay took any
active part in these changes, or whether there existed in clay some
chemical compound in small quantity to which the action was due. This
question was to be decided by the extent to which clay was a