90 On Plaister of Paris. 



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 u^ts.foj 



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 (arising from vvhatever cause, 

 be it the escape of air, or dissipation of its water of 

 chry stall ization) is considerable, it is good. If it be 



pair of mill stones. This circumstance, and the appearance 

 oi the petrii actions, have occasioned a beliei, that they ^v ere 

 formed by collections of plaister, mixed with the feed, and 

 taken in therewith by the horses, from time to time. This 

 opinion may not be well fomided ; as calculi are produced 

 in animals i'rom other causes. But such calculi consist gene- 

 rally of urinous partxles ; and are found in the bladder or 

 kidneys. They have not commonly foreign matter for their 

 basis; though it sometimes happens otherwise. The bare pos- 

 sibility oi it should produce circumspection, to avoid the dan- 

 ger of such accidents.* 



(oj [Vide ChaptaPs Chemistry vol, 1, page 212.] Where 

 the analysis o: the gyps is g ven, and it is said that it loses 20 

 per cent^ by calcination. Chemists say it loses only its water 

 of chrystallization. 



• Since I have discovered the violently purgative quality of the plaister, I doubt that these cal- 

 culi were fonnedof the calcareous, or other, part of the gj'psum. Let those better qualified decide. 



R. P. 

 September^ 1810. 



