‘On Plaister of Paris. 
to a calcareous earth. This acid is well known to be 
as unfriendly to vegetation, as calcareous earth is favour- 
able to it, and, upon the proportion of it contained in 
gypsum, the value of that article, as a manure, depends. 
When calcareous earth is added to any of the acids, 
they unite, and compose earthy salts, differently named, 
according to the acid made use of. If this compound 
contains a due proportion of the acid and the calca- 
reous earth, it is said to be neutralized; but if either the 
acid or the calcareous earth predominate, the compound 
then possesses acid, or earthy properties. 
We suppose, therefore, that, in cases where calca- 
reous earth is the prevailing principle in gypsum, its 
beneficial effects as a manure willbe visible, because 
in that case, a portion of the earth will not be united 
with the acid, and will therefore be left at liberty to act 
upon the soil. 
In cases where these two ingredients. are equally 
balanced, the compound posseses very little solubility 
in water. It is, perhaps, in these cases where it produces 
little effect ; nor is it possible it can; because unless the 
parts of any substance are soluble in water, they generally 
can produce no effect on vegetation. 
Lastly, where the acid predominates in gypsum, of 
which, however, we recollect no instances, its mischie- 
Since this publication, the gypsum is used in England to 
profitable account. Its properties are better understood and 
I believe, the use of it is much encouraged. How whimsical 
and inapplicable is this theory! when we compare it with 
gacts generally known here. 
ROP. 
September, 1810. 
