pa 
90 On Plaist 
parts from being blown away, by damping it. But I 
do not find that it can, in this state, be so equally dis- 
tributed; it being apt, when thus damped, to collect in 
lumps. 
It should always be remembered, that calcination, 
however necessary it may be to make cement of plais- 
ter, lessens, if not destroys, its agricultural uses./o) 
We have a simple mode of trying the quality of 
plaister. We put a quantity pulverized, into a dry pot 
over the fire ; and when heated, it emits a sulphureous 
smell. If the ebullition (arismg from whatever cause, 
be it the escape of air, or dissipation of its water of 
chrystallization) is considerable, it is good. If it be 
pair of mill stones. This circumstance, and the appearance 
of the petriiactions, have occasioned a belief, that they were 
formed by collections of plaister, mixed with the feed, and 
taken in therewith by the horses, trom time to time. This 
opinion may not be well founded ; as calcul are produced 
in animals from other causes. But such calcul consist gene- 
rally of urinous particles ; and are iound in the bladder or 
kidneys. They have not commonly foreign matter for their 
basis; though it sometimes happens otherwise. The bare pos- 
sibility of it should produce circumspection, to avoid the dan- 
ger of such accidents.* 
(0) [Vide Chaptal’s Chemistry vol. 1, page 212.] Where 
the analysis of the gyps is given, and itis said that it loses 20 
per cent, by calcination. Chemists say it loses only its water 
of chrystallization. 
* Since I haye discoyered the violently purgative quality of the plaister, I doubt that these cal- 
culi were formed of the calcareous, or other, part of the gypsum. Let those better qualified decide. 
R. P. 
September, 1810. 
