VOL. LXXIX.] PHILOSOPHICAL TRANSACTIONS. 550 



expulsion of dephlogisticated air, it is evident that it contains 2 principles in 

 close affinity with each other, and that nothing is necessary to render either of 

 them conspicuous besides the absence of the other. 



It is also natural to suppose that, for the same reason that the dephlogisticating 

 principle, as it may be called, is expelled, the phlogisticating principle should 

 enter; so that the purification of the air in contact with the acid may be a ne- 

 cessary consequence of the expulsion of the pure air contained in it, the whole 

 tending, as it were, to an equilibrium in this respect. It is therefore by no 

 means difficult to conceive, that phlogiston should be extracted from the con- 

 tiguous air at the same time that the dephlogisticated air not pure, that is con- 

 taining a mixture of phlogisticated air, is driven out of it; for the acid always 

 containing phlogistion, whatever air is contained in it, and expelled from it, may 

 necessarily contain phlogiston or phlogisticated air; but the purer air may be 

 emitted, and the less pure air be imbibed, till the whole come to be of the same 

 quality. It may however perhaps follow from the emission of impure dephlo- 

 gisticated air, and the imbibing of phlogisticated air at the same time, that the 

 former does not consist of dephlogisticated and phlogisticated air loosely mixed, 

 but of some intimate union of dephlogisticated air with phlogiston, though they 

 may be separated by a mixture of nitrous air, and other processes, in the very 

 same manner as dephlogisticated air may be separated from a loose mixture of 

 phlogisticated air. It is evident from these experiments, that a red heat is not 

 necessary to the conversion of nitrous acid into pure air, though this process, as 

 appeared by my former experiments, produces this effect most quickly and effec- 

 tually. 



I cannot help considering the experiments above recited to be favourable to 

 the doctrine of the phlogiston, and unfavourable to that of the decomposition 

 of water, though not decisively so ; for since the red vapour of spirit of nitre un- 

 questionably contains the same principle that has been termed phlogiston, or the 

 principal element in the constitution of inflammable air, and according to the 

 antiphlogistians this is one constituent part of water, they must suppose, that the 

 water in this acid is decomposed by a much more moderate heat than in most 

 other cases. In general I believe they have thought a red heat to be necessary 

 for this purpose. It is evident, that the conversion of water into steam by 

 boiling, or by any heat that can be given to it under the strongest pressure, has 

 no tendency whatever to decompose it. But if the mere boiling of water in 

 nitrous acid could produce this effect, I do not see why the same should not be 

 the case when water alone is boiled. I think it will also be more difficult to ex- 

 plain the purification of the incumbent atmospherical air on the antiphlogistic 

 than on the phlogistic hypothesis, whatever be the constitution of phlogistica- 

 ted air. 



