246 PHILOSOPHICAL TRANSACTIONS. [ANNO 1/82. 



tion, the acid yielding its specific quantity of fire to the concrete fixed air, which 

 then assumes an aerial form, while the fixed air yields the substance it was com- 

 bined with to the acid. This is so true, that though a solution of lime in the 

 nitrous acid yields a considerable quantity of heat, yet a solution of chalk, in 

 that acid scarcely yields any ; for all the fire that is set loose, and rendered sen- 

 sible in the first case, is absorbed by the fixed air in the 2d case, being precisely 

 that which converts it into an aerial form. The separation of phlogiston from a 

 metallic earth, in the form of inflammable air, arises from the same cause, the 

 dissolving acid yielding its fire to the phlogiston, which then assumes an aerial 

 form, while the phlogiston yields the metallic earth to the acid. It is true, that 

 much sensible heat is produced on this occasion, for which 3 substantial reasons 

 may be assigned ; first, the proportion of fixed air in a given weight of crude 

 calcareous earth, is much greater than that of phlogiston in any metal, as will 

 hereafter be shown, it being in the former x of the whole, and that of phlo- 

 giston in the latter for the most part not even -f . Secondly, much of the phlo- 

 giston combines with the acid itself during the solution, and expels part of its 

 specific quantity of fire, as Dr. Crawford has shown, and as I have since expe- 

 rienced ; and this fire must occasion sensible heat. Thirdly, much of the phlo- 

 giston, during solution, unites to the surrounding atmosphere, expelling also 

 part of its specific fire, and this also must occasion sensible heat ; anil hence it 

 is, that metallic solutions in vacuo are generally attended with less heat, though 

 with a more violent effervescence, than in open air. The solution of metallic 

 calces is not attended with so much heat as that of their respective metals, not 

 only because neither the dissolving acids nor the surrounding air is much phlogisti- 

 cated ; but also because they contain an elastic fluid in a concrete state, which ab- 

 sorbs much of the fire given out by the dissolving acids, as it acquires an aerial state. 

 The origin and formation of inflammable air being thus explained, I now pro- 

 ceed to show its identity and homogeneity with phlogiston. By phlogiston is 

 generally understood that principle in combustible bodies on which their inflam- 

 mability principally depends ; that principle to which metals owe their malleability 

 and splendor ; that which combined with vitriolic acid forms sulphur ; that which 

 diminishes respirable air. Now inflammable air is that very principle which 

 alone is truly inflammable, as Mr. Volta has elegantly shown. In effect, com- 

 bustible substances are either animal or vegetable, as horn, hair, grease, 

 wood, &c. from all of which Dr. Hales has extracted inflammable air ; or char- 

 coal, from which Mr. Fontana has extracted it, as did Dr. Priestley from resin, 

 spirit of wine, and ether, in all which it is the only principle that is inflammable, 

 and they are inflammable only in proportion as they yield it; or phosphorus, from 

 whose acid Dr. Priestley has obtained this air by means of minium, for it was the 

 acid, and not the minium, that contained it, as Dr. Priestley rightly conjectured. 



