558 PHILOSOPHICAL TRANSACTIONS. [ANNO 1784. 



quantity of phlogiston than phlogisticated air does, because it has a greater spe- 

 cific gravity, and because it has more affinity with water. 



5. For many years I have entertained an opinion, that air was a modification 

 of water, which was originally founded on the facts that in most cases, wherein 

 air was actually made, which should be distinguished from those wherein it is 

 only extricated from substances containing it in their pores, or otherwise united 

 to them in the state of air, the substances were such as were known to contain 

 water as one of their constituent parts, yet no water was obtained in the pro- 

 cesses, except what was known to be only loosely connected with them, such as 

 the water of the crystallization of salts. This opinion arose from a discovery, 

 that the latent heat contained in steam diminished in proportion as the sensible 

 heat of the water from which it was produced increased ; or, in other words, 

 that the latent heat of steam was less when it was produced under a greater pres- 

 sure, or in a more dense state, and greater when it was produced under a less 

 pressure, or in a less dense state ; which led me to conclude, that when a very 

 great degree of heat was necessary for the production of the steam, the latent 

 heat would be wholly changed into sensible heat ; and that, in such cases the 

 steam itself might suffer some remarkable change. I now abandon this opinion 

 in so far as relates to the change of water into air, as I think that may be ac- 

 counted for on better principles. 



£). In every case, wherein dephlogisticated air has been produced, substances 

 have been employed, some of whose constituent parts have a strong attraction 

 for phlogiston, and, as it would appear, a stronger attraction for that substance 

 than humor has ; they should therefore dephlogisticate the water or fixed air, 

 and the humor thus set free should unite to the matter of fire and light, and 

 become pure air. Dephlogisticated air is produced in great abundance from 

 melted nitre. The acid of nitre has a greater attraction for phlogiston than any 

 other substance is known to have ; and it is also certain, that nitre, besides its 

 water of crystallization, contains a quantity of water as one of its elementary 

 parts, which water adheres to the other parts of the nitre with a force sufficient 

 to enable it to sustain a red heat. When the nitre is melted, or made red-hot, 

 the acid acts on the water and dephlogisticates it ; and the fire supplies the 

 humor with the due quantity of heat to constitute it air, under which form it 

 immediately issues. It is not easy to tell what becomes of the acid of nitre and 

 phlogiston, which are supposed to be united, as they seem to be lost in the 

 process. Dr. Priestley has lately made some experiments, with a view to ascer- 

 tain this point. He distilled dephlogisticated air from pure nitre, in an earthen 

 retort glazed within and without. He employed 2 oz. = g6o grs. of nitre : 

 the retort was placed in an air furnace, and, by means of an intense heat, he 

 obtained from the nitre in one experiment 7&7 > and in another experiment 800 



