and the feeming Converfon of Water into ■ Air, 41 5 
*rom them; and to mere opinions I have never fhewn mvfelf 
much attached. 
Having formerly obferved feveral remarkable changes in fluid 
ltibftances, in confequence of long expofure to heat in elafs 
veffels hermetically f'ealed (of which an account mav be foen 
in the fourth volume of my Philolophical Obfervatio.ua) ; I 
then formed a defign of expoiing all kinds of fohd fubfianeas 
to great heats, in a iim.il ar Hate of confinement; and for that 
purpofe provided rayfelf with a cark-iron veil. 1, which I could 
dole at one end, like a digeifer, and of iuch a length, that 
one of the ends might be red-hot, while the other was fum- 
cicntly cool to be handled. To this end there was a cock 
connected to a tube, by means of which I could let off foam, 
or air, in any period of tkeprocefs. 
I imagined, that when fubfomces confiding of parts fo vola- 
tile as to fly off before they had attained anv confiderable depree 
of heat, in the ufual preffure of the atmofpliere, w r ere com- 
pelled to bear great heats under a greater preffure, they might 
ail lime new forms, and undergo remarkable changes, limilar to 
what we may fuppofe to be the cafe within the bowels of the 
earth, where, bv means of fubterraneous fires, various fub- 
ldances bear great heats under very great preffures. 
I have had this inffrument lome years ; but it was fo ill con- 
ffrudfed, that I could not make the ufe of it that I had origi- 
nally intended. I therefore lately fitted up lome gun-barrels 
in the fame manner, and made my fir ft experiment with lime- 
ffone ; expefong, that when the fixed air, and other volatile 
matters, that might be contained in it, lhould be compelled to 
hear a red heat, without a poffibility of making their efcape, the 
fubffance itfelf might undergo fome change ; but I had no 
particular expectation concerning the nature of that change. 
Voi~ LXX 11 I. I i i I had. 
