Absorptive Properties of Soils. 
513 
absorbed without liming is either greater than when this agent 
has been employed, or so nearly the same as to forbid the notion 
that it has had any effect upon them. The exceptions are, 
however, those of the surface, cultivated soils. 
One circ umstance is certainly worthy of great attention, namely, 
tlie very large quantity of ammonia which a soil, whether in its 
natural state or after treatment with lime, is able to absorb from 
an atmospliere containing it. As a matter of course such results 
as those now given can never occur in practice, because centuries 
probably would be required for a soil to absorb from the atmos- 
pliere containing only traces of ammonia the same cjuantity of 
the alkali which it acquires in a few hours from air highly 
charged with it. Still, as the measure of a power which is 
always in operation, and which is only limited by the extent of 
subdivision of the soil, and the fiequency with which the air in 
its pores is changed, these numbers are very interesting. They 
afford at once an encouragement to abundant tillage of the land, 
and an explanation of the fertility which almost invariably 
follows it. Take for instance the soil No. 17 or No. 15, and we 
find that in eitlier case ammonia to the extent of 3 tons per acre, 
equal to 20 tons of guano, would be absorbed before the power 
to absorb it ceased. 
But a further suggestion is conveyed by the result of these 
experiments. Lime is capable of liberating one half of the 
ammonia contained in a soil. Is it now possible that for profit- 
able agi-icultural use the ammonia of the soil is too tightly 
locked up in it ? Can we suppose that the very powers of the 
soil to unite with and preserve the elements of manure are, 
however excellent a provision of nature, yet in some degree 
opposed to the growth of the abnormal crops which it is the 
business of the farmer to cultivate ? Tiiere is no absolute reason 
why such should not be the case. A provision of nature must 
relate to natural circumstances; for instance, compounds of 
ammonia may be found in the soil capable of giving out to the 
agencies of water ami air quite enough of ammonia for the growth 
of ordinary plants and the preservation of their species ; but this 
supply may be totally inadequate to the necessities of man. It may 
be argued that the earth was made for man, and consequently that 
there can be no natural law interfering directly with the welfare 
of his kind ; but a population of greater civilisation and greater 
requirements also presupposes one of greater powers and appli- 
ances. It is the function of man to make use of the laws of 
nature to modify the natural conditions. Now it is not impossible 
that the laws which preserve the supply of vegi?table nutrition in 
the soil are too stringent for the requirements of an unusual and 
excessive vegetation, such as the cultivator must promote. 
