VOL. LXXV.] PHILOSOPHICAL TRANSACTIONS. 21 



the nature of the phlogisticated part of onr atmosphere, than that it is not dimi- 

 nished by lime-water, caustic alkalis, or nitrous air; that it is unfit to support 

 fire, or maintain life in animals; and that its specific gravity is not much less 

 than that of common air; so that, though the nitrous acid, by being united to 

 phlogiston, is converted into air possessed of these properties, and consequently, 

 though it was reasonable to suppose that part at least of the phlogisticated air of 

 the atmosphere consists of this acid united to phlogiston, yet it might fairly be 

 doubted whether the whole is of this kind, or whether there are not in reality 

 many different substances confounded together by us under the name of phlo- 

 gisticated air. I therefore made an experiment to determine, whether the whole 

 of a given portion of the phlogisticated air of the atmosphere could be reduced 

 to nitrous acid, or whether there was not a part of a different nature from the 

 rest, which would refuse to undergo that change. The foregoing experiments 

 indeed in some measure decided this point, as much the greatest part of the air 

 let up into the tube lost its elasticity; yet, as some remained unabsorbed, it did 

 not appear for certain whether that was of the same nature as the rest or not. 

 For this purpose I diminished a similar mixture of dephlogisticated and common 

 air, in the same manner as before, till it was reduced to a small part of its ori- 

 ginal bulk. I then, in order to decompound as much as I could of the phlo- 

 gisticated air which remained in the tube, added some dephlogisticated air to it, 

 and continued the spark till no further diminution took place. Having by these 

 means condensed as much as I could of the phlogisticated air, I let up some solu- 

 tion of liver of sulphur to absorb the dephlogisticated air; after which only a 

 small bubbl of air remained unabsorbed, which certainly was not more than 

 T-l-5- of the bulk of the phlogisticated air let up into the tube; so that if there is 

 any part of the phlogisticated air of our atmosphere which differs from the rest, 

 and cannot be reduced to nitrous acid, we may safely conclude, that it is not 

 more than -^-1-^- part of the whole. 



The foregoing experiments show that the chief cause of the diminution which 

 common air, or a mixture of common and dephlogisticated air, suffers by the 

 electric spark, is the conversion of the air into nitrous acid; but yet it seemed 

 not unlikely, that when any liquor, containing inflammable matter, was in con- 

 tact with the air in the tube, some of this matter might be burnt by the spark, 

 and thereby diminish the air, as I supposed in the above-mentioned paper to be 

 the case. The best way which occurred to me of discovering whether this hap- 

 pened or not, was to pass the spark through dephlogisticated air, included be- 

 tween different liquors; for then, if the diminution proceeded solely from the 

 conversion of air into nitrous acid, it is plain that, when the dephlogisticated air 

 was perfectly pure, no diminution would take place; but when it contained any 

 phlogisticated air, all this phlogisticated air, joined to as much of the deplilogis- 



