ee ee 
be Gd 
eal 
110 On Plaister of Paris. 
vous effects will be visible, as acids of all sorts are 
inimical to vegetation. | : : 
In this way we account for the different effects produc. 
ed by gypsum, and also for the gypsum, brought from 
certain places, being more valuable than that brought 
from others. In many cases its value will depend upon its 
containing more calcareous earth than acid. Upon lands, 
therefore, where no stimulating substance has been ap- 
plied, and which contain little or no calcareous earth 
in themselves, this sort of gypsum will be a good ma- 
nure; accordingly, in America, where the soil in. most. 
places is composed almost entirely of vegetable earth, 
arising from the decayed herbage, and the deciduous 
parts of the trees which have grown and decayed there 
since the creation, and where scar¢ely a particle of calca- 
reous earth is to be met with, this sort of gypsum will 
stimulate the soil, and produce good effects; even in this 
country, upon virgin soils, which contain no principles 
of that sort, its effects will be similar; but upon lands 
which have been long in a state of cultwation, which have 
been frequently manured with substances containing much 
alkaline matter, or which have received a due proportion 
of calcareous earth, its effects will not be perceptible, 
unless an enormous quantity be used. But in cases 
where the acid prevails, its bad effects will be visible at 
once. In all cases, therefore, where gypsum is intended 
to be used, it ought to be a matter of serious inquiry, 
first, whether the land has been previously limed? and 
next, whether the acid or calcareous earth prevails in 
its composition? If the land possesses in itself no cal- 
careous matter, the gypsum, which contains most of it, 
