VOL. LXXIV.] PHILOSOPHICAL TRANSACTIONS. 557 



violence, they become red-hot, and on cooling totally disappear. When the 

 vessel is cooled, a quantity of water is found in it equal to the weight of the air 

 employed. This water is then the only remaining product of the process, and 

 water, light, and heat, are all the products," unless there be some other matter 

 set free which escapes our senses. " Are we not then authorised to conclude, 

 that water is composed of dephlogisticated air and phlogiston, deprived of part of 

 their latent or elementary heat; that dephlogisticated or pure air is composed of 

 water deprived of its phlogiston, and united to elementary heat and light; and 

 that the latter are contained in it in a latent state, so as not to be sensible to the 

 thermometer or to the eye; and if light be only a modification of heat, or a cir- 

 cumstance attending it, or a component part of the inflammable air, then pure 

 or dephlogisticated air is composed of water deprived of its phlogiston and united 

 to elementary heat ?" 



4. " It appears, that dephlogisticated water," or, which may be a better name 

 for the basis of water and air, the element Mr. De Luc calls humor, " has a 

 more powerful attraction for phlogiston than it has for latent heat, but that it 

 cannot unite with it, at least not to the point of saturation, or to the total ex- 

 pulsion of the heat, unless it be first made red-hot," or nearly so. " The electric 

 spark heats a portion of it red-hot, the attraction between the humor and the 

 phlogiston takes place, and the heat which is let loose from this first portion heats 

 a second, which operates in a like manner on the adjoining particles, and so con- 

 tinually till the whole is heated red-hot and decomposed." Why this attraction 

 does not take place to the same degree in the common temperature of the atmos- 

 phere, is a question I am not yet able to solve; but it appears, that, in some 

 circumstances, " dephlogisticated air can unite, in certain degrees, with phlo- 

 giston without being changed into water." Thus Dr. Priestley has found, that 

 by taking clean filings of iron, which alone produce only inflammable air of the 

 purest kind, and mercurius calcinatus per se, which gives only the purest dephlo- 

 gisticated air, and exposing them to heat, in the same vessel, he obtained neither 

 dephlogisticated nor inflammable air, " but in their place fixed air." Yet it is 

 well known, that a mixture of dephlogisticated and inflammable air will remain 

 for years in close vessels in the common heat of the atmosphere, without suffer- 

 ing any change, the mixture being as capable of deflagration at the end of that 

 time as it was when first shut up. These facts the Doctor accounts for, by sup- 

 posing that the 1 kinds of air, when formed at the same time in the same vessel, 

 can unite in their nascent state; but that, when fully formed, they are incapable 

 of acting on each other, unless they are first set in motion by external heat. 

 Phlogisticated air seems also to be another composition of phlogiston and dephlo- 

 gisticated air; but in what proportions they are united, or by what means, is 

 still unknown. It appears to be very probable, that fixed air contains a greater 



