VOL. LXXXII.] PHILOSOPHICAL TRANSACTIONS. 231 



(c) The residuum (b) was exposed in a silver spoon red-hot; it soon ignited, 

 and sparkled; but though this heat was applied 6 minutes, on cooling, a blackish 

 matter remained, which weighed 1 .3 grs. 



(d) The 1.3 grs. of residue (c) under the flame applied with the blow-pipe, 

 gave some indications of fusion, yet it remained black : but 



(e) Being thrown into boiling nitre, a slight detonation ensued; this salt was 

 not coloured by it, and it was dissolved in water, leaving scarcely a visible quan- 

 tity of matter on the filter. 



I think I may safely conclude that but a small part of these 10 grs. of residue 

 was charcoal: and as the proportion is so much smaller than has been shown to 

 be afforded by an equal weight of alkali saturated with carbonic acid, this ex- 

 periment confirms the conclusion, that the charcoal produced in the preceding 

 experiments is from the decomposition of that elastic fluid. The small quantity 

 of charcoal in the above 10 grs. of residuum was perhaps intimately mixed with 

 phosphorus and alkali; but more experiments are required to determine satis- 

 factorily the nature of this compound. To corroborate the inference concern- 

 ing the source of the charcoal above described, I add, that not a grain of it 

 was produced by applying phosphorus to vegetable alkali and fossil alkali satura- 

 ted with vitriolic and marine acid. 



The resemblance between phosphorus and sulphur, induced me to consider 

 whether carbonic acid, combined with alkalis and earths, might not be decom- 

 pounded by sulphur. Experience, however, did not favour the supposition of a 

 decomposition 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 alkalis, lime, and barytes; consequently, if sulphur 

 be applied to carbonic acid, united to these alkalis and earths, the affinity be- 

 tween sulphur and respirable air cannot disengage charcoal from the carbonic 

 acid in mild alkalis and absorbent earths. This conclusion would however only 

 be just, provided no other agents interfered; and as we cannot be absolutely cer- 

 tain that they could not, I repeated the above experiments with sulphur instead 

 of phosphorus; 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 ihis matter for future examination. 



p. s. In consequence of some observations published in the Annales de Chimie, 

 Juin, 1792, tome 13, by M. Fourcroy, it is thought proper to add, that though 

 the above paper was not read till May last, it was presented to the Society in 

 March preceding; and the experiments were made during the author's autumnal 



