On Plaister of Paris. : 117 
5. On two others, ashes or lye. / ae 
The common salt must be applied at a distance 
from the gyps; plaister does not succeed on sea coasts, 
where the air is always impregnated with sea salt. 
This salt and that in plaister, by operating on each other, 
may change the qualities of both. Sulphuric acid forms 
sulphat of soda, or glauber salts, by decomposing ma- 
rine salt, and combining with the soda. Glauber salts, 
and all compounds containing su/phuric acid, are ma- 
nures, or auxiliaries to vegetation: but are not so effec- 
tual or cheap as the gypsum. The small quantities re- 
quired of the latter, and its rapid decomposition, will 
always give it the preference. 
Rv? 
6. Sprinkle, on two other lands, water, in which oil of 
vitriol is dissolved : this water will kill, or banish, bugs, 
flies, and other insects, from bedsteads, walls, &c., in our 
houses. If the plaister is an enemy to the fly, it is pro- 
bably by means of its vitrolic acid. If this could be 
proved by experience, Ingenhausz would render es- 
sential service, by his theory of the oi/ of vitriol. 
t would be well, if several farmers were to try some 
experiments of this sort; though at first they may seem 
whimsical. My fields, generally plaistered on the wheat, 
or on preceding crops of grain and clover, have been 
little infested by the fly. But I have attributed the 
safety of my wheat, to good tilth and manure. So that 
the crop may be sown late, and the ground throw up 
strong and vigorous plants, which resist the fly, when 
