VOL. LXXII.] PHILOSOPHICAL TRANSACTIONS. 253 



mable air is never decomposed, unless the loss of its fire be called a decomposi- 

 tion ; but in the act of inflammation is totally transferred on the pure part of 

 respirable air to which it unites. Fifthly, to obtain still a clearer insight into 

 this matter, I entreated Mr. Cavallo, who is very expert in the management of 

 the blow-pipe, as well as in pneumatic experiments, to repeat this experiment in 

 my laboratory. We accordingly filled a tube 10.5 inches long, and J- of an inch 

 in diameter, with inflammable air from iron received over mercury, and having 

 made the tube red-hot throughout and black, and softened it so far as to en- 

 danger the escape of the air, we opened it on mercury. The air was diminished 

 only -fV, and inflamed with an explosion as loud as an equal quantity of the same 

 inflammable air that had not been heated. 



The only question that remains then is, whence the phlogisticated air pro- 

 ceeded which Dr. Priestley mentions to have found ? The circumstance of his 

 experiment would furnish a plausible answer ; but the doctor has lately informed 

 me, that he believes the air was really inflammable, but, being a very small 

 quantity, escaped before the flame could be applied. It seems, therefore suffi- 

 ciently proved, that inflammable air purified from the acids or other substances 

 that expel it from its basisj and also from all particles of the body to which it was 

 originally united, such as inflammable air from metals received on mercury, and 

 well washed in lime-water, is one and the same substance with phlogiston, differ- 

 ing only in quantity of fire, inflammable air containing nearly the same quantity 

 of this element as the same bulk of atmospheric air, as Dr. Crawford has found 

 by some late experiments, an account of which will soon be laid before the 

 public. This does not contradict that most important discovery of this ingeni- 

 ous philosopher, that fire and phlogiston repel each other : the meaning of this 

 being only, that the addition of phlogiston to any substance, as to respirable 

 air, dephlogisticated acids, metallic calces, expels part of the fire already con- 

 tained in such substance ; and, on the contrary, by the removal of phlogiston 

 from any substance, the quantity of fire absorbed by such substance is increased. 



It may appear extraordinary, supposing inflammable air and phlogiston to be 

 the same substance, that inflammable air should mix so easily with water, whereas 

 phlogiston constantly repels and is repelled by it ; but this entirely depends on 

 the state of this same substance, which, when fixed and concrete, is called 

 phlogiston, and, when rarefied and aeriform, inflammable air. In this latter 

 state it mixes with water in proportion to its rarefaction, as it even does in the 

 less dense forms of its concrete state : thus ether is totally absorbed by ]0 times 

 its weight of water. The animal oil of Dippel mixes entirely with water ; so 

 does pure Petrol, and essential oils frequently distilled, and the spiritus rector of 

 plants. Much more remains to be said of the different states of phlogiston from 

 its most rarefied known state, viz. that of inflammable air, to its most condensed 



