£8 Dr. Austin’s Experiments cn 
peared after long boiling in ftrong nitrous acid. More experi- 
ments, than it is in my power to make at prefent, are neceflary 
to determine fully the nature of it. 
The analogy between the heavy inflammable air and char- 
coal is illuftrated by the formation of hepatic air from charcoal 
and fulphur. Thefe fubftances, heated in a fmall glafs retort, 
yield hepatic air in great abundance. The blue vegetable co- 
lour is turned green by expofure to this air. After hepatic air 
had been generated for a long time from the fame materials, 
without admitting any common air into the retort, ninety-nine 
parts in a hundred of the air which came over laft were ab- 
forbed by water. The infallible part appeared to be phlogifti- 
cated air. Thus fulphur and charcoal, heated in a glafs retort,, 
yield hepatic air, phlogifticated air, and volatile alkali, or a 
fubftance very analogous to it. 
As far as I have been able to difeover by experiments, the 
heavy inflammable air and charcoal conflft of the fame ele- 
ments in different proportion. The application of heat to pure 
charcoal confirms this opinion ; for the produdlion of heavy 
inflammable air from charcoal, by mere heat, is conftantly ac- 
companied with a production alfo of phlogifticated air. I ap- 
prehend, that in thefe cafes the charcoal is decompofed and 
refolved into thefe two parts. Whenever charcoal, or any, 
fubftance containing k, is decompofed by heat only, the phlo- 
gifticated and heavy inflammable airs are produced ; and when 
the heat is intenfe, Dr. Higgins has obferved% thatr the air 
produced from thefe fubftances becomes rarer ; as I imagine,, 
in conference of a portion of the heavy inflammable air itfelf 
being refolved by heat into its co-nftituent parts. I would not 
lay much ftrefs on the appearance of phlogifticated air from 
*■ Higgins on Acetous Acid, p, 2.93. 
the 
