TOL. LXXIX.] PHILOSOPHICAL TRANSACTIONS. 605 



till there remained only 14-oz. measure, and of this -§.|. oz. measure was fixed air. 

 In 6 oz. measures of dephlogisticated air, of the standard of 0.2, he melted iron 

 till it was reduced to ^ of an ounce measure, of which 4- was fixed air, and the 

 remainder completely phlogisticated. Again, he melted iron in 74- oz. measures 

 of dephlogisticated air, of the same purity with that in the last experiment, 

 when it was reduced to 1-i-oz. measure, and of this -f was fixed air, and the 

 remainder phlogisticated. In this case Dr. P. carefully weighed the finery cinder 

 that was formed in the process, and found it to be 9 grains, so that the iron that 

 had been melted, being about -|- of this weight, had been about 6 grains. 



When the dephlogisticated air is more impure, the quantity of fixed air will 

 always be less in proportion. Thus, having melted iron in 7 oz. measures of 

 dephlogisticated air of the standard of O.65, it was reduced to 1.6 oz. m.; and 

 of this only 4- of an ounce measure was fixed air. This however is much more 

 than can come from the plumbago in the iron ; but as the production of this 

 fixed air is by many ascribed to this plumbago, it may be worth while to show by 

 computation that it is impossible that it should have this origin. Both the quan- 

 tity of plumbago in iron, and the quantity of fixed air in plumbago, are much 

 too small for the purpose. From half an ounce of the purest plumbago. Dr. P. 

 first got, in a coated glass retort, 13 oz. measures of air, of which only 3 oz. 

 measures were fixed air, the rest being inflammable; then putting it into an 

 earthen tube, he kept it some hours in as great a heat as he could produce, and 

 got 22 oz. m. more; and of this also only 3 were fixed, and the rest inflam- 

 mable, and the last portion was wholly so. 



But instead of supposing the fixed air that he got to be that which was expelled 

 from the plumbago in the iron, he would suppose that even the whole of this 

 plumbago aflforded only ] of the elements of the fixed air, viz. phlogiston, or 

 that which the French chemists call carbone; and that this principle, by its. 

 union with the dephlogisticated air in the vessel, forms the fixed air, yet on thia 

 most unfavourable and improbable supposition the quantity will be found to be 

 insufficient. If 100 gr. of iron contain, according to M. Bergman, 0.12 gr. of 

 plumbago, 7 gr. would contain only 0.0084 gr. of plumbago ; and if we suppose, 

 with Mr. Kirwan, that 100 cubic inches of fixed air contain 8.14 gr. of phlo- 

 giston, the fixed air produced in one of the above-mentioned processes (viz. -f 

 of an ounce measure) would contain .032 gr. of phlogiston, which is above 3 

 times more than the plumbago in the iron could furnish. It is evident therefore, 

 that the quantity of fixed air that he found must have been formed by phlogiston 

 from the iron uniting with the dephlogisticated air in the vessel. 



Another argument against the antiphlogistic doctrine may be drawn from an 

 experiment which Dr. P. made on Prussian blue; if the small quantity of fixed 

 air, that may be expelled from it by heat, be compared with the much greater 



