VOL. LXXII.] PHILOSOPHICAL TRANSACTIONS. 257 



be expelled out of it by mere heat. Nay, iron alone, exposed to common air, 

 over a vessel of water for 3 months, reduced this air -i- ; and being exposed to 

 dephlogisticated air, over a vessel of mercury, it reduced it -^ in 9 months. In 

 all these cases the fixed air could surely come from nothing else but the incum- 

 bent respirable air and the phlogiston of the metal. 



Secondly, it is well known, that if nitrous air be decomposed by respirable air 

 over lime-water, the lime will be precipitated. In this case also, the fixed air 

 must proceed from the respirable air and the phlogiston of the nitrous air ; for it 

 cannot proceed from the nitrous acid, as this acid is not decomposed, but is taken 

 up by the water over which the mixture of both airs is made, as Mr. Bewly has 

 undeniably proved : and hence it is, that unless a large quantity of lime-water 

 be used, so as to contain enough for both the nitrous and aerial acids to act on, 

 there will be no precipitation of lime, as Mr. Fontana has observed ; for the ni- 

 trous acid will seize on the lime preferably to the aerial. Dr. Priestley indeed 

 observed, that if a bladder, filled with nitrous air, be dipped in lime-water, it 

 occasions a precipitation of lime on the surface of the water. 1 Pr. 213. But 

 he elsewhere acknowledges, that this proceeds from the inability of the bladder 

 to confine nitrous air. 1 Pr. 76 and 128, which Mr. Baume also long ago ob- 

 served, without knowing any thing more of this air: Baume sur l'Ether, 285. 

 The phlogiston passes through the bladder, and unites to the common air con- 

 tiguous to it. Besides, nitrous air acts on the bladder itself, and extracts fixed 

 air from it. 1 Pr. 214. Hence also, if rain-water carefully boiled, and freed 

 from its own air, be made to absorb a quantity of nitrous air, it will again, on 

 boiling, yield it back as pure as at first ; but if common water be made to im- 

 bibe nitrous air in the same manner, it will, on boiling, yield also a portion of 

 fixed air. 3 Pr. 109. Does not this happen clearly because common water con- 

 tains atmospheric air, or air somewhat purer, which is converted into fixed air 

 by mixture with the nitrous air ? This experiment also shows, that water itself 

 never unites to phlogiston, since it does not take any from nitrous air, where the 

 union of phlogiston to the acid is of the laxest kind. 



Thirdly, if the electric spark be taken through common air, this air will be 

 diminished J-, and a solution of lime, if contiguous, will be precipitated, and a 

 solution of turnsole tinged red. 1 Pr. 184, 186. Whence could the fixed air 

 here produced proceed, but from the common air, and the phlogiston of the 

 metallic conductors ? This excellent philosopher has even shown it could pro- 

 ceed from nothing else ; for after that air had contributed all it could to that 

 production, that is, was diminished to the utmost, he changed the liquors, but 

 could produce no change in their colour, nor the least sign of fixed air. This 

 experiment has also been repeated in France, and the inside of the glass tube, 

 in which the common air was contained, was moistened with a solution of caustic 



vol. xv. L 1. 



