THE ELEMENTS OF THE CHEMIST 137 



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 pos- 

 sessed 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 phlogisticated 

 air. I therefore made an experiment to determine whether the 

 whole of a given portion of the phlogisticated air of the atmo- 

 sphere 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 original bulk. I then, in order to decompound as 

 much as I could of the phlogisticated 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 solution of liver of sulphur to absorb the dephlo- 

 gisticated air ; after which only a small bubble of air remained 

 unabsorbed, which certainly was riot more than T ^ 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 T ^ part of the whole.' " 1 

 The authors repeated this experiment of Cavendish with the 

 advantage of modern apparatus, and they found that on spark- 

 ing air with added oxygen in the presence of potash the residue 

 which remained unabsorbable was in proportion to the amount 

 of air operated on. An examination of this residue with the 

 spectroscope showed that the gas left was not nitrogen, but had 

 a spectrum of its own. 



1 Cavendish's " Experiments on Air," Philosophical Transactions of the Royal 

 Soc., 1785. 



