222 PHILOSOPHICAL TRANSACTIONS. [aNNO 1792, 



sist of a psciiliar basis, and respirable air; and on the ground of analogy it was 

 concluded, that all other acids were composed in a similar manner. Fixed air 

 having been shown, by Mr. Bcwley, and by Bergman, to be an acid, of course 

 its composition was considered, in the new system of chemistry, to be similar to 

 that of all other acids. On examining facts already well ascertained, and by 

 various experiments discovering others, no clear instance could be perceived of 

 the formation of fixed air, but in those cases where charcoal was applied red-hot 

 to respirable air. Mr. Lavoisier at last established this interesting fact, by a con- 

 clusive experiment, published in a vol. of the Memoirs of the Acad, of Sciences 

 in 1781, and in his Traile Elementaire in 1789, by which he demonstrated that 

 charcoal of wood, except a minute portion of residue, as might reasonably be 

 expected, combined with respirable air, and composed fixed air only. This is 

 the date therefore of the discovery by synthesis, of the composition of fixed air; 

 or, as I would rather call it, with Mr. Lavoisier, carbonic acid. The proof by 

 analysis however was required, to render the demonstration of the composition 

 of this elastic fluid complete. The honour of the first analytical experiments on 

 carbonic acid is due to Mr. Tennant, f. r. s., who, in a paper read to this Society, 

 in March, 1791, and contained in vol. 81, of tlie Phil. Trans., asserted, that 

 charcoal and phosphoric acid were produced by applying phosphorus to red-hot 

 marble, from which he inferred, that the carbonic acid of the marble was decom- 

 pounded. Tliis decomposition, the ingenious author conceives to be eflected by 

 the united powers of affinity between phosphorus and the respirable air of the 

 carbonic acid in the calcareous earth, and between the phosphoric acid, thus 

 composed, and the quick-lime of the calcareous earth. That the black matter 

 produced is really charcoal, the author has proved by adequate experiments. The 

 inference however does not appear to me to be just, that the charcoal and phos- 

 phoric acid are the necessary result of the agency of the affinities, as stated by 

 Mr. Tennant. For the well known fact, that phosphorus cannot be produced 

 from bone-ashes by the application of charcoal and heat, I think, only proves 

 that the powers of affinity between respirable air and phosphorus, together with 

 the affinity between the compound formed by their union (namely, phosphoric 

 acid) and quick-lime, are not inferior to the joint affinities between the respirable 

 air, in the phosphoric acid, and charcoal, and between the compound of respir- 

 able air and charcoal (namely, carbonic acid) and quick-lime. Hence, from the 

 principle referred to, it could not be concluded, that carbonic acid, combined 

 witli quick-lime, would be decompounded by phosphorus attracting its respirable 

 air, and the phosphoric acid, thus formed, attracting the quick-lime. Experi- 

 ence only could determine the result of these affinities, but no proof has been 

 given, from the examination of the mixture, after applying phosphorus to red-hot 

 ni'uble; such as finding tluit carbonic acid was really decompounded, because 



