VOL. LXXIV.] PHILOSOPHICAL TRANSACTIONS. 565 



of them appears by every test to be the same, when freed from accidental impurities. 

 To this argument it is answered, that it is not any particular species of earth 

 which is the basis of air, but elementary or simple earth, which is contained in 

 all of them. If this were the matter of fact, would not that earth be found 

 after the decomposition of the air ? 



Mr. Scheele has formed an hypothesis en this subject, in which he supposes 

 heat to be composed of dephlogisticated air united to phlogiston, and that this 

 combination is sufficiently subtile to pass through glass vessels. He affirms, 

 that the nitrous and other acids, when in an ignited state, attract the phlogiston 

 from the heat, and set the dephlogisticated heat at liberty; but he does not seem 

 to have been more successful than myself in explaining what becomes of the acid 

 of nitre and phlogiston in the case of the decomposition of nitre by heat. And 

 since we know, from the late experiments, that water is a composition of air, or 

 more properly humour and phlogiston, his whole theory must fall to the ground, 

 unless that fact be otherwise accounted for, which it does not seem easy to do. 



lfj. To return to the experiment of the deflagration of dephlogisticated and 

 inflammable air, it appears from the two airs becoming red-hot on their union, 

 that the quantity of heat contained in one or both of them, is much greater 

 than that contained in steam ; because, for the first moments after the explosion, 

 the water deposited by the air remains in the form of steam, and consequently 

 retains the latent heat due to that modification of water. This matter may be 

 easily examined by firing the mixture of dephlogisticated and inflammable air in 

 a vessel immersed in another vessel containing a given quantity of water of a 

 known heat, and after the vessel in which the deflagration is performed is come 

 to the same temperature with the water in which it is immersed, by examining 

 how much heat that water has gained, which being divided by the quantity of 

 water produced by the decomposition of the airs, will give the whole quantity of 

 elementary or latent heat which that water had contained, both as air and as 

 steam ; and if from that quantity we deduct the latent heat of the steam, the 

 remainder will be the latent or elementary heat contained more in air than in 

 steam. This experiment may be made more completely by means of the excel- 

 lent apparatus which Messrs. Lavoisier and De la Place have contrived for similar 

 purposes. 



Till direct experiments are made, we may conclude, from those which have 

 been made by the gentlemen just named, on the decompositions of air by burn- 

 ing phosphorus and charcoal, that the heat extricated during the combustion of 

 inflammable and dephlogisticated air is much greater than it appears to be; for 

 they found that one Paris oz. (= 5/6 Parisian grs.) of dephlogisticated air, when 

 decomposed by burning phosphorus, melted 68.634 oz. of ice ; and as, according 

 to another of their experiments, ice, on being melted, absorbs 135° of heat bv 



