On Plaister of Paris. 
es 
contains this gas, the quantity of gas is very small.” Practical 
farmers know, that an overcharge of any manure is destruc- 
tive. I have killed plants with dung water, too highly impreg- 
nated; but have forwafded their growth surprisingly, with 
water moderately infused with dung. May not the water 
mentioned by Dr. P. have been too highly impregnated with 
the carbonic acid, when it destroyed the plants? It is allow- 
ed, that plants vegetated in such water, when “ the quantity 
of gas is very small.” Nature has provided, that plants shall, 
in ordinary operations, imbibe no more of their food than is 
proper for them. In extraordinary instances, a plant may, 
like an intemperate animal, be gorged with food, and, fall a 
sacrifice to excess. It may be, too, that carbonic acid is only 
‘a part oi the food; and requires to be corrected or aided 
by some other ingredients, to produce salutary effects. Ingen- 
hausz allows that ‘* Plants die in pure carbonic acid.” He 
says, oxygene, or pure respirable air, and heat, are necessary 
to vegetation. [Vide Ingenhausz on food of plants, pages 9, 
10, 11.] Plants absorb mephitic or phlogisticated air, and 
emit vital air. Man, on the contrary, is kept alive by vital 
air, and emits mephitic. Chaptal vol. 1, page 117. But Ingen- 
hausz. [tood of plants page 6.] pointedly asserts, that, ‘all airs, 
which cannot be easily changed or decomposed into_fixed air, 
as possessing no oxygene, are true poisons to plants, such as 
inflammable air, putrid air, and azote, contrary to Dr. Priestly 
and Mr. Scheele. He further says, that all “ other airs poi- 
sonous to vegetable life, are also destructive of animal life.” 
Such is even the carbonic acid, concentrated, or without a 
great proportion of respirable air. 
When I began to extract the accounts of the latest writers 
on chemistry, the food of plants, &c., it was under the idea, 
that the eypsum would be found to contain this food. Be 
this as it may, the theories I have mentioned may possibly 
afford amusement, if they are of no real use, to those who have 
not access to the works of the writers, who entertain, on this 
