VOL. LXXII.] PHILOSOPHICAL TRANSACTIONS. '24/ 



the acid obtained by deliquescence being never thoroughly dephlogisticated till 

 heated and vitrified, as Mr. Margraaf has shown ; or they are mineral substances, 

 as sulphur, from which inflammable air has been separated by means of fixed 

 alkalis, and, according to Dr. Priestley, also by means of marine air, or 

 bitumens or bituminous substances, all of which may be made to yield it ; or 

 metallic substances, as zinc and regulus of arsenic, both of which are inflam- 

 mable ; but neither of them is so when deprived of its inflammable air: this is 

 therefore the true and only principle of inflammability in any substance. I ac- 

 knowledge that the inflammable air, proceeding from almost all these substances, 

 is exceeding impure ; that it contains from some a mixture of aerial acid or of 

 oil, and from all some part of the substance which yields it or expels it, and 

 hence its smell is different, according to the class of the substances from which 

 it is extracted ; but it is equally true, that none of these substances contribute to 

 its inflammability ; on the contrary, it is so much the less inflammable (that is, 

 requires so much more air to be mixed with it before it flames) as it contains more 

 of these heterogeneous substances. Hence inflammable air of the morasses is 

 never totally consumed; and, on the contrary, inflammable air, from metals, 

 which is the purest of all, is also the most inflammable. 



Secondly, inflammable air is also the principle which reduces metallic earths 

 to a metallic state, and gives them their metallic splendour. This has been 

 proved analytically and synthetically, and therefore may be said to be as com- 

 pletely demonstrated as any thing in natural philosophy : thus Dr. Priestley has 

 extracted inflammable air from iron and zinc by heat alone; and the iron, thus 

 stripped of its phlogiston, lost its splendour, and was of a black colour, which 

 is that which iron, slightly dephlogisticated, always assumes, as appears by mar- 

 tial asthiops: so also zinc and regulus of arsenic, when once inflamed, lose their 

 metallic appearance: so also a mixture of lead and tin inflames in a moderate 

 heat, and then both are converted into a calx destitute of splendour and malle- 

 ability. On the other hand, if a current of inflammable air, in the act of com- 

 bustion, be directed on the calces of iron, lead, or mercury, they are immedi- 

 ately revived and restored to their metallic form, as appears by the experiment 

 of Mr. Chaussier. The following experiment is still more conclusive: if a 

 polished plate of iron be put into a saturate and dilute solution of copper in the 

 vitriolic or marine acids (I mention these because they are commonly used for 

 the production of inflammable air, though the result is the same when other acids 

 are used), no effervescence will arise, no inflammable air will be caught; but 

 the iron will be dissolved, and the copper precipitated in its metallic form. Here 

 inflammable air must be produced as usual, for the acid quits the copper and 

 dissolves the iron; but this inflammable air instantly loses its aerial form, and 

 unites to the copper, just as fixed air leaves alkalis to unite to lime without any 



