C 289 2 
XV. Experiments made with the View of decompounding Fixed 
Air , or Carbonic Acid. By George Pearson, M.D. F.R.S. 
Read May 24, 1792. 
From a Paper read to the Philosophical Society of Edinburgh, 
in 1755, published in the second volume of the Physical and 
Literary Essays, Doctor Black appears to have discovered the 
affinities between an aeriform substance, which he called fixed 
air, and alkalies, quick-lime, and magnesia. His experiments 
also shewed, that many properties of these bodies depended 
upon the union and separation of this air. The discovery of 
these facts established this elastic fluid to be a peculiar species 
of substance. 
Mr. Cavendish, Dr. Brownrigg, Dr. Priestley, Sir Tor^- 
bern Bergman, Mr. Bewley, Mr. Kirwan, and other che- 
mists, afterwards extended, very considerably, the history of 
fixed air. The question, whether it was a simple or compound 
body, was discussed ; and by many persons it was believed to have 
been proved, that fixed air was composed of phlogiston and re- 
spirable air. But some of the principal facts, upon which this 
belief was founded, being afterwards demonstrated to be erro- 
neous ; and the production of fixed air being, to the apprehen- 
sion of many chemists, more satisfactorily accounted for by the 
new principles of chemistry, this doctrine of its composition 
became no longer tenable. As the science of chemistry ad?- 
