from Pyrites and Clay. 67 



arch were apertures two inches in diameter, which could 

 be opened and shut at pleasure. At the top of the vault 

 was another, of an ohlong form, conducting to a wooden 

 channel a foot and a half wide, but which, on account of 

 want of room, was only twelve feet long, and terminated 

 in a chest three feet in diameter. Such was the imperfect 

 apparatus with which I made my first experiment. 



A quintal of pyrites, triturated and washed, were mixed 

 with half their weight of clay, and formed into balls, which 

 \yere gently dried. Another quintal of clay was likewise 

 formed into balls, which were dried and baked, but only 

 till the clay had lost its unctuosity, and was therefore more 

 proper to receive the vapours of the sulphuric acid. The 

 balis of the pyrites were placed in the furnace, on about a 

 cubic foot of wood, intended for kindling the fire. The 

 aperture in front was closed, and only those on the sides 

 were left open : the balls of clay were exposed in the canal 

 and in the chest to the vapours of the sulphuric acid. The 

 combustion of the pyrites continued fourteen hours, and 

 not a vestige of sulphur was deposited j that substance be- 

 came entirely volatilized under the form of sulphuric acid*. 

 The wooden channel was too short, as I had expected; the 

 greater part of the vapours escaped ; the trees and plants in 

 th,e garden contiguous to the laboratory withered, and their 

 leaves fell off. I was therefore convinced that the pyrites 

 were completely oxidated in my apparatus. As soon as the 

 operation was ended, the balls of clay were covered with 

 an efiervescence of alum, which, mixed with 4 per cent, of 

 alkali, yielded alum. 



But as the greatest part of the acid was mixed with the 

 alimiine, without being saturated with it, I left the balls iu 

 a shed, exposed to the action of the air, from August 2, 

 179U, till the 3d of April the following year. At the ex- 

 piration of that time 1 obtained an earthy mass, entirely 

 covered with an efflorescence, and mixed with sulphate of 

 alumine ; being treated in the usual manner, it yielded three 

 poiuuls and a half of alum. 



'riiis experiment convinced me of the possibility of ob- 

 taining alum by this process, and that in a very cftco'nomical 

 Tuanner: but, to insure siicccss, the tube should be mads 

 liuich longer than mine. The remaining pyrites laav after- 

 wards be employed iu the manufacture of vitriol. 



• We cannot hf!p here suspecting the accuracy of M. Lampadius. It 

 «-<Tn» likely iliat by l:u ilic i^rcattr part of the vapours would be iii the state 

 •I" iu/^/jKf'jj/i acid- loir. 



r> 2 XII. Twe?ili/- 



