VOL. LXXIV.] PHILOSOPHICAL TRANSACTIONS. 567 



120 grs. of inflammable air with 576 grs. of dephlogisticated air, extricates 9265 

 of heat. 



18. In the experiment on the deflagration of nitre with charcoal, by Messrs. 

 Lavoisier and De la Place, 1 oz. of nitre and 4. of 1 oz. of charcoal melted 12 

 oz. of ice. Supposing the ounce of nitre to have produced a. an oz. of dephlo- 

 gisticated air, it ought to have consumed 0.1507 oz. of ice; and I suppose it fell 

 short of its effect by the heat not being sufficiently intense to decompose the 

 nitre perfectly. 



19. By the above gentlemen's experiment 1 oz. of charcoal required for its 

 combustion 3.3167 oz. of dephlogisticated air, and produced 3.6715 oz. of fixed 

 air ; therefore there was united to each oz. of air, when changed into fixed air, 

 6l.5 grs. of phlogiston, and 3988 of heat were extracted. It appears by these 

 facts, that the union of phlogiston, in different proportions, with dephlogisticated 

 air, does not extricate proportional quantities of heat. For the addition of 6 1. 5 

 grs. produces 3988 , and the union of 120 grs. produces 9265 . This difference 

 may arise from a mistake in supposing the specific gravity of the inflammable air 

 Dr. Priestley employed to have been only T ig. of that of dephlogisticated air ; for 

 if it be supposed that its specific gravity was a little more than -£- of that of the de- 

 phlogisticated air, then equal additions of phlogiston would have produced equal 

 quantities of heat :* this matter should therefore be put to the test of experiment, 

 by deflagrating dephlogisticated air with inflammable air of a known specific gra- 

 vity, or by finding how much dephlogisticated air is necessary for the combustion 

 of 1 oz. of sulphur, the quantity of phlogiston in which has been accurately de- 

 termined by Mr. Kirwan ; or by finding the quantity of phlogiston in phosphorus, 

 the quantity of dephlogisticated air necessary for its decomposition being known 

 from Messrs. Lavoisier and De la Place's experiments. 



On considering these latter gentlemen's experiments on the combustion of 

 charcoal, a difficulty arises, to know what became of the remainder of the oz. 

 of charcoal ; for the dephlogisticated air, in becoming fixed air, gained only the 

 weight of 0.3548, or about J- of 1 oz. ; about f of 1 oz. are therefore unac- 

 counted for. The weight of the ashes of 1 oz. of charcoal is very inconsider- 

 able ; and, by some experiments of Dr. Priestley's, charcoal, when freed from 

 fixed air, and other air which it imbibes from the atmosphere, is almost wholly 

 convertible into phlogiston. The cause of this apparent loss of matter, I doubt 



* Or it may arise from my being mistaken, in supposing that the same quantity of heat is disen- 

 gaged by the union of dephlogisticated air with phlogiston, in the form of inflammable air, as is by 

 its union with the phlogiston of phosphorus or sulphur ; and there appears to be some reason why 

 there should not; because in these latter cases the water, being united to the acids, cannot retain so 

 much elementary heat as it can do when left in the form of pure water, which is the case when the 

 inflammable air is used. — Orig. 



