Absorptive Properties of Soils. 
493 
the structure ot" the plant that it operates. The other explana- 
tion — namely, tliat lime acts in liberatinj? alkaline bases from the 
remains of ancient rocks of the granitic type existing in soils — 
is more comprehensible, and is so far logical that it applies to a 
very much larger variety of cases than either of the others. All 
clays contain, in some form or other, compounds of potash, soda, 
and maijnesia, the origin of which must be traced to the granitic 
and basaltic rocks from which the clays have been formed, and 
the quantity of these alkalies is sometimes very considerable, 
although all appearance of the source from which they come is 
wanting. From such compounds lime would evidently set free 
in a gradual manner the alkaline bases, and so far its applica- 
tion would be equivalent to applying the alkaline substances 
themselves. But even then we have to ask ourselves whether a 
supply to the soil of the alkaline bases which lime is supposed 
to liberate would have the same effect as lime has ? It is very 
doubtful whether it would, and this is at once a weak point in 
the theory. In considering this great agricultural question of 
the use of lime, I have always thought that we wanted some 
theory of more universal application to account for the effects 
which follow its application— some cause which would account 
for its influence on soils of different character ; for where lime is 
judiciously applied it rarely fails of doing good, the case of 
that soil wliich it does not benefit being the exception rather 
than the rule. 
In the course of my experiments on the absorption by soils of 
different substances contained in manure, I found that lime was 
capable of playing a very important part in these phenomena. I 
will shortly I'ecapitulate a few of these results, in order that the 
reader may be in a position to understand how the action of lime 
is connected with them. Soils were found to possess, in a greater 
<n' less degree, the power of removing from solution in water 
certain animal and vegetable substances, but still more the 
alkaline bases, ammonia and potash, and the earths, magnesia 
and lime. These bases the soils were capable of separating 
from their salts, and retaining more or less, in spite of the action 
of water. It was afterwards discovered that a certain class of 
artificial double alkaline silicates had a similar power, and for 
several reasons it was concluded that it was to the presence of 
portions of these double silicates that soils owed the power in 
question. 
It was further observed that an ordinary soil had the power of 
collecting from the air and incorporating with itself gaseous car- 
a considerable per-centage of carbonate of lime in the state of fragments of chalk. 
On the (janlt clay also, which contains a very notable quantity of gypsum, lime 
acts most beneficially. 
VOL. XV. 2 K 
