m Ley ae } % big 
On Plaister of Paris. 105 
and perhaps a better explanation, is, that in clay soils there 
is little or no calcareous earth, on which the plaister always -. 
operates the most favourably 3; as it finds, in these earths, the 
carbonic acid in the greatest plenty. 
Dr. Priestly, in a conversation I lately had with him, told 
me, he was preparing to analyze the gyps; with a view to 
farther discoveries of its nature and properties, both chemi- 
eal and agricultural. I wait, with much curiosity, to know 
the result of the experiments, of this able chemist and vene- 
rable philosopher. I am aware, that the doctor’s opinions, 
and those of the followers of Lavoisiere, in several points, 
differ very materially. I am neither qualified, nor inclined, — 
to determine which are right; though I have ventured to | 
make deductions, perhaps too hastily, from some of the new 
chemical theories. The Doctor asserts, that “some plants  _ 
>] Pp Sen } 
are chiefly nourished by Aydrogene or inflammable air, such 
as the willow, &c.” We see aquatic plants coarse, strong, and. 
capable of being sustained (if so they are) by air which is 
found the most plentifully in wet grounds, where-no tender 
plants, the occupants of dry soils, will grow. The air, nutritive 
to the one, may be poison to the other. Clover will not 
grow well in wet grounds, nor will plaister operate there ; 
so that clover and plaister seem to be made for each other. 
The Doctor thinks, that the infammable principle is the 
preyalent part of the nourishment of plants; and that they 
thrive the best in vitzated or phlogisticated air. It will be 
seen how much other eminent men differ with him, by 
what has been said by Ingenhausz, &c. The Doctor’s 
opinion of the carbonic acid being injurious to plants, is not 
in unison with that of Ingenhausz, Kirwan, and others. In 
Chaptal, page 117, vol. 1,it is said, ‘* The carbonic acid is 
improper for vegetation ; Dr. Priestly, having kept the roots 
of several plants in water impregnated with the carbonic 
acid, observed that they all perished ; and in those instances 
where plants are observed to vegetate in water, or in air which 
0) 
