'250 PHILOSOPHICAL TRANSACTIONS. [ANNO 1782. 



no acid is capable of decompounding inflammable air. Lastly, respirable air 

 cannot be said to be the basis of inflammable air, unless we suppose that respir- 

 able air enters into the composition of metals; for Dr. Priestley has, by solar heat, 

 extracted inflammable air from them in a vessel full of mercury, into which 

 respirable air had no access, and even in vacuo. Besides respirable air and phlo- 

 giston form other compounds very different from inflammable air, viz. fixed and 

 phlogisticated airs, as will presently be seen. 



It may also be fairly urged against all these suppositions, that they are not 

 founded on any direct experiment, nor any known analogy, but merely gra- 

 tuitous, or at least deduced from experiments inadequate to their support; 

 whereas the opinion that inflammable air is nothing else than phlogiston thrown 

 into a fluid form by elementary fire, is directly founded on that experiment by 

 which inflammable air is separated from metals by mere solar heat in the most 

 perfect vacuum, just as fixed air united to marble and in a concrete state (in which 

 it is nearly of equal density with gold) is separated from the marble, and thrown 

 into a permanently fluid form by heat alone. 



In favour of the existence of an acid in inflammable air, it has been said, 

 that if this air be passed through water tinged blue by litmus, it reddens 

 instantly. I have seen this frequently happen when inflammable air has been 

 extracted from iron by spirit of vitriol; but if this air be washed, by passing it 

 through lime-water, and then passed through, or agitated in, an infusion of 

 litmus, it will not discolour it in the least: this I have seen done by Mr. Fontaua 

 in June 1779- It has also been said, that inflammable air and alkaline air, 

 mixed together, form a cloud; but this has been fully disproved by 

 Dr. Priestley, in the 4th volume of his observations. That an earth of any kind 

 is essentially requisite to the constitution of inflammable air, seems to me utterly 

 improbable; nor do I know of any experiment whence it can be inferred. That 

 metallic substances may be held in solution by inflammable air is certain; but it 

 is equally so, that they no way contribute to its inflammability, and are quite 

 distinct from it. 



But the opinion, that inflammable air consists of respirable air super saturated 

 with phlogiston, is grounded on very specious arguments, drawn from experi- 

 ments to be found in various parts of Dr. Priestley'6 works, which deserve so 

 much the more attention as the facts mentioned by that excellent philosopher are 

 not to be questioned. I shall endeavour to state them with accuracy; but shall 

 at the same time accompany them with such remarks as seem to invalidate the 

 conclusion that has been drawn from them. 



In the first volume of Dr. Priestley's observations it appears, that a quantity 

 of strong inflammable air, having been agitated in a glass jar immersed in a 

 trough of water, the surface of which was exposed to the common atmosphere, 



