18 
certain data have hitherto been offered for its ap- 
plication. 
There is, however, good ground for supposing, 
that the subject will be fully elucidated by che- 
mical inquiry. Those plants which seem most 
benefited by its application, are plants which 
always afford it on analysis. Clover, and most of 
the artificial grasses, contain it, but it exists in very 
minute quantity only in barley, wheat and turnips. 
Many peat ashes, which are sold at a considerable 
price, consist in great part of gypsum, with a little 
iron ; and the first seems to be their most active 
ingredient. I have examined several of the soils 
to which these ashes are successfully applied, and 
I have found in them no sensible quantity of 
gypsum. In general, cultivated soils contain 
sufficient of this substance for the use of the 
grasses ; in such cases, its application cannot be 
advantageous. For plants require only a certain 
quantity of manure ; an excess may be detrimental, 
and cannot be useful. 
The theory of the operation of alkaline sub- 
stances, is one of the parts of the chemistry of 
agriculture, most simple and distinct. They are 
found in all plants, and therefore may be regarded 
as amongst their essential ingredients. From their 
powers of combination, likewise, they may be 
useful in introducing various principles into the 
sap of vegetables, which may be subservient to 
their nourishment. 
The fixed alkalies, which were formerly re- 
garded as elementary bodies, it has been my good 
