136 CHEMICAL DISCOVERY AND INVENTION 



might be formed in the first instance their life would probably 

 be short. On standing they might be expected to disappear, in 

 partial analogy with ozone. With this idea in view, a sample of 

 chemically prepared nitrogen was stored for eight months. But 

 at the end of this time the density showed no sign of increase, re- 

 maining exactly as at first. . . . 



" The simplest explanation in many respects was to admit 

 the existence of a second ingredient in air, from which oxygen, 

 moisture, and carbonic anhydride had already been removed. 

 The proportional amount required was not great. If the density 

 of the supposed gas were double that of nitrogen, \ per cent 

 only by volume would be needed ; or if the density were but 

 half as much again as that of nitrogen, then 1 per cent would 

 still suffice. But in accepting this explanation, even provision- 

 ally, we had to face the improbability that a gas surrounding us 

 on all sides, and present in enormous quantities, could have 

 remained so long unsuspected. . . . 



" And here the question forced itself upon us as to what 

 really was the evidence in favour of the prevalent doctrine that 

 the inert residue from air, after withdrawal of oxygen, water, 

 and carbonic anhydride, is all of one kind. 



" The identification of ' phlogisticated ' air 1 with the con- 

 stituent of nitric acid is due to Cavendish, whose method con- 

 sisted in operating with electric sparks upon a short column of 

 gas confined with potash over mercury at the upper end of an 

 inverted U tube. 



" Attempts to repeat Cavendish's experiment in Cavendish's 

 manner have only increased the admiration with which we 

 regard this wonderful investigation. Working on almost micro- 

 scopical quantities of material, and by operations extending 

 over days and weeks, he thus established one of the most im- 

 portant facts in chemistry. And, what is still more to the purpose, 

 he raises as distinctly as we could do, and to a certain extent 

 resolves, the question above suggested. The passage is so 

 important that it will be desirable to quote it at full length. 



" ' As far as the experiments hitherto published extend, we 

 scarcely know more of the nature of the phlogisticated part of 

 our atmosphere, than that it is not diminished by lime-water, 

 caustic alkalies, or nitrous air ; that it is unfit to support fire, 



1 That is deprived of oxygen. Phlogisticated air is in modern language 

 nitrogen ; dephlogisticated air was afterwards named oxygen by Lavoisier 



