decompounding fixed Air. 307 
The resemblance betwixt phosphorus and sulphur, induced 
me to consider whether carbonic acid, combined with alkalies 
and earths, might not be decompounded by sulphur. Experi- 
ence, however, did not favour the supposition of a decomposi- 
tion in these instances ; for it is well known that hepar may 
be formed by applying charcoal to tartar of vitriol, Glauber's 
salt, vitriolic selenite, and ponderous spar : and therefore that 
the affinity between charcoal and respirable air is superior to 
the joint affinities between respirable air and sulphur, and be- 
tween vitriolic acid and fixed alkalies, lime, and barytes ; con- 
sequently, if sulphur be applied to carbonic acid, united to 
these alkalies and earths, the affinity between sulphur and 
respirable air cannot disengage charcoal from the carbonic acid 
in mild alkalies and absorbent earths. This conclusion would, 
however, only be just, provided no other agents interfered; 
and as we cannot be absolutely certain that they could not, I 
repeated the above experiments with sulphur instead of phos- 
phorus ; by which I produced a blackish powder, that had 
the properties of reducing calx of lead, and changing vitriolic 
salts into hepars : but as it did not burn on red hot iron, and 
deflagrate with nitre, I cannot pronounce it to be charcoal ; 
thinking it most prudent to reserve this matter for future exa- 
mination. 
Leicester-Square, September 20, 1792. 
P. S. In consequence of some observations published in the 
Annales de Chimie, Juin, 1792, Tome XIII. by Mr. Fourcroy, 
it is thought proper to add, that although the above paper was 
not read till May last, it was presented to the Society in March 
