REVIEW AND CONCLUSION. 361 
peat contained Aumate of lime, which was not affected by 
the pure ammonia, but in contact with carbonate of am- 
monia yielded carbonate of lime and humate of ammonia. 
In these cases the ammonia was in excess, and the chemical 
changes were therefore, in some particulars, unlike those 
which occur when the humus preponderates. 
Brustlein, Liebig and others have observed that soils 
rich in organic matter (forest mold, decayed wood,) have 
their absorptive power much enhanced by mixture with 
carbonate of lime. 
Although Rautenberg has shown (Hennebverg’s Journal 
186, p. 439,) that silicate of lime is probably formed when 
ordinary soils are mixed with carbonate of lime, it may 
easily happen, in the case of soils containing humus, that 
humate of lime is produced, which subsequently reacts 
upon the alkali-hydrates or salts with which absorption 
experiments are usually made. 
§ 6. 
REVIEW AND CONCLUSION. 
The limits assigned to this work having been nearly 
reached, and the more important facts belonging to the 
present chapter brought under notice, with considerable 
fulness, it remains to sum up and also to adduce a few 
considerations which may appropriately close the volume. 
There are indeed a number of topics connected with the 
feeding of crops-which have not been treated upon, such, 
especially as come up in agricultural practice; but these 
find their place most naturally and properly in a discussion 
of the improvement of the soil by tillage and fertilizers, 
to which it is proposed to devote a third volume. 
What the Soil must contain.—In order to feed crops, 
16 
