Oil the Chemical Properties of Soils. 
125 
mo likely that a dcfinito quantity of soil will rcinovo mon; 
ainirioiiia than from a smaller amount of liquid of the same 
strenf^th. 
1 have not, as yet, made many experiments in this direc- 
tion. These are urgently needed, for it is clear that we cannot 
calculate with any degree of certainty the amount of loss in 
ammtmia to which ammoniacal manures are subject in contact 
with soil, as long as we are not fully acquainted with the 
exact conditions under which this most interesting chemical 
property of soils manifests itself. 
Fifth Series. — Ammonia Retention Experiments. 
In the preceding experiments it has been shown that all the 
soils experimented upon possess the power of absorbing ammonia ; 
further, that all the soils absorbed more ammonia from a more 
concentrated than from a weaker solution ; and, lastly, that in no 
instance was the ammonia entirely removed from a solution 
brought into intimate contact with soil. Even in the case of 
heavy clay soils, and when A'ery dilute ammoniacal solutions were 
(Mnployed, ammonia invariably remained in solution. These facts 
not only explain the different results which must be obtained in 
experimenting upon the same kind of soil with solutions of 
different strength, but they also prove incontestably that the com- 
pounds which, no doubt, are produced in almost every descrip- 
tion of soil, when ammoniacal solutions are brought into contact 
with them, are not entirely insoluble, as has been supposed, but 
sufficiently soluble in water to benefit the growing crops, which 
we have no reason to suppose take up food from the soil in any- 
other than a soluble state. 
Notwithstanding the power of soils to absorb ammonia, this 
fertilizing constituent is not fixed by the soil so completely or 
permanently as to be of no avail to the growing plant. The 
possibility also exists that long-continued and heavy rains mav 
wash out more or less completely the ammonia previously 
absorbed by soils. Hence the invariable presence of ammonia 
in spring waters. 
An important question is naturally started by these curious 
properties of soils. It is this : Is the power of soils to retain 
ammonia greater, and if so to what extent, than the tendency to 
yield it again to water passed through the soil ? 
In order to facilitate the solution of this question I instituted 
a Fifth Series of Experiments, which, under the title of " Am- 
monia Retention Experiments," I shall now endeavour briefly to 
describe. 
