502 l-HILOSOPHICAL TRANSACTIONS. [ANNO 1784. 



animal acids, are by burning reduced to fixed and phlogisticated air, and water, 

 and therefore contain more phlogiston, or less dephlogisticated air, than those 

 three substances. 



XIV. Remarks on Mr. Cavendish's Experiments on Air. By R. Kirtvan, 



Esq., F.R.S. p. 154. 



Having listened with much attention, and derived much useful information 

 from the very curious experiments of Mr. Cavendish, it is with peculiar regret 

 (says Mr. K.) I feel myself withheld from yielding an entire assent to all he has 

 advanced in his paper ; and it is with still greater that I find myself obliged, by 

 reason of the opposition of some of his deductions to those I had the honour to 

 lay before the Society about 2 years ago, to expose the reasons of my dissent 

 from them. In my paper I attributed the diminution of respirable air, observed 

 in common phlogistic processes, to the generation and absorption of fixed air, 

 which is now known to be an acid, and capable of being absorbed by several 

 substances. That fixed air was somehow produced in phlogistic processes, either 

 by separation or composition, I took for granted from the numerous experiments 

 of Dr. Priestley ; and among these I selected, as least liable to objection, the 

 calcination of metals, the decomposition of nitrous by mixture with respirable 

 air, the phlogistication of respirable air by the electric spark, and, lastly, that 

 effected by amalgamation. In each of these instances Mr. Cavendish is of opi- 

 nion, that the diminution of respirable air is owing to the production of water, 

 which, according to him, is formed by the union of the phlogiston, disengaged 

 in those processes, with the dephlogisticated part of common air ; and that fixed 

 air is never produced in phlogistic processes, except some animal or vegetable 

 substance is concerned in the operation, from whose decomposition it may arise. 

 To which of these causes the diminution of respirable air is to be attributed, I 

 shall now endeavour to elucidate. 



Of the calcination of metals. — I attributed the diminution of air by the calci- 

 nation of metals, to the conversion of the dephlogisticated part of common air 

 into fixed air, by reason of its union with the phlogiston of the metal, for this 

 plain reason, because I find it acknowledged on all hands, that the calces of all 

 the base metals yield fixed air, when sufficiently heated. Mr. Cavendish allows 

 the fact in general, but ascribes the fixed air found in them to their long expo- 

 sure to the atmosphere, in which he says fixed air pre-exists ; but that it exists 

 in common air in any quantity worth attending to, or is extracted from it in any 

 degree, I take the liberty of denying, grounded on the following facts. First, I 

 have frequently agitated 18 cubic inches of common air in 2 of lime-water, and 

 2 of common air in 18 of lime-water, but could never perceive the slightest 

 milkiness; and yet the I OOOth part of a cubic inch of fixed air would thus be 



