Chemistry and Physics. . 261 
To decompose sulphate of lime, and obtain from it sulphuric and pul 
i: a acids, and free lime, I proceed in the following ma poll 
have a fire-clay cylinder of close texture, and of any convenient size, 
placed vertically in a furnace, and provided with openings at the top 
- and bottom, for charging and discharging, which openings are capable 
of being closed air-tight. To the top of, this cylinder I adapt an es- 
cape tube of fire-clay, for conveying off the acid vapors; and to the 
bottom, for the admission of the steam, I adapt another clay pipe, con- 
nected witha _— boiler, by a series of fire-clay tubes, which are to 
be kept at a red heat. In order to diminish the corrosion of the e cylin- 
der by the sulphate of lime or the lime itself, I line it with a coating of 
native carbonate of magnesia, applied in a manner similar to the usual 
clay linings of chemical furnaces. a4 the mi cin with pieces of 
sulphate of lime, about a quarter of an inch in diameter, and having 
luted the on air-tight, I heat xe eylibdee and its contents toa 
high red heat. I then pass steam from the boiler, through the red hot 
clay tubes, into the bottom of the cylinder, and up through the charge. 
The heated steam, in its passage through the pieces of sulphate of lime, 
carries off the acid in the state of sulphurous acid and oxygen, with 
sometimes a little sulphuric acid mixed with it. The acid vapors pass 
off by the escape tube at the top of the cylinder, and I convey them by 
stone-ware tubes into a leaden chamber, in order to combine them into 
priees acid by the usual means. I ee care that the heat is not rais- 
ed so high at first as to melt the sulphate of lime in the cylinder, but I 
veying off the acid vapors from the top of the cylinder, by means of 
which [ examine the vapors from time to time, and from the relative 
acidity of these, ascertained by the usual tests, I judge ‘of the progress 
of the operation. I regulate by a stop-cock the quantity of steam pass- 
takes place at a much lower temperature than that of sulphate of lime, 
(a low red heat is sufficient,) and a considerable part of the acid is giv- 
en off in the state of sulphuric acid. When the charge has been treat- 
ed as _— the residue will be found to consist chiefly of caustic 
magnes 
When t wish: to decompose - sulphates of baryta and strontia, I 
operate upon them in a reverberating furnace. This mode is less ad- 
Seconp Serres, Vol. VI, No. 17, ae 1848. 34 
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