A NEW CONSTITUENT OF THE ATMOSPHERE. 193 
obtained sufficient of themselves to prove that the atmosphere contains a previously 
unknown gas. 
But although the method of diffusion was capable of deciding the main, or at any 
rate the first question, it held out no prospect of isolating the new constituent of the 
atmosphere, and we therefore turned our attention in the first instance to the con- 
sideration of methods more strictly chemical. 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” with the constituent of nitric acid is due 
to CAVENDISH, whose method consisted 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.* This tube (M) was only about ;/5 inch in diameter, and the column of 
gas was usually about 1 inch in length. After describing some preliminary trials, 
CAVENDISH proceeds :—“ I introduced into the tube a little soap-lees (potash), and then 
let up some dephlogisticatedt and common air, mixed in the above mentioned 
proportions which rising to the top of the tube M, divided the soap-lees into its two 
legs. As fast as the air was diminished by the electric spark, I continued adding more 
of the same kind, till no further diminution took place: after which a little pure dephlo- 
gisticated air, and after that a little common air, were added, in order to see whether 
the cessation of diminution was not owing to some imperfection in the proportion of 
the two kinds of air to each other; but without effect. The soap-lees being then 
poured out of the tube, and separated from the quicksilver, seemed to be perfectly 
neutralised, and they did not at all discolour paper tinged with the juice of blue 
flowers. Being evaporated to dryness, they left a small quantity of salt, which was 
evidently nitre, as appeared by the manner in which paper, impregnated with a 
solution of it, burned.” 
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 microscopical quantities of material, and by operations extending 
over days and weeks, he thus established one of the most important facts in 
chemistry. And what is still more to the purpose, he raises as distinctly as we 
* “Wixperiments on Air,” ‘Phil. Trans.,’ vol. 75, p. 372, 1785. 
[+ The explanation of combustion in CayenpisH’s day was still vague. It was generally imagined 
that substances capable of burning contained an unknown principle, to which the name ‘ phlogiston’ 
was applied, and which escaped during combustion. Thus, metals and hydrogen and other gases were 
said to be ‘ phlogisticated ’ if they were capable of burning in air. Oxygen being non-inflammable was 
named ‘ dephlogisticated air,’ and nitrogen, because it was incapable of supporting combustion or life 
was named by Priestipy ‘ phlogisticated air,’ although up till CaynnpisuH’s time it had not been made to 
unite with oxygen. 
The term used for oxygen by Cayenpisu is ‘ dephlogisticated air,’ and for nitrogen, ‘ phlogisticated 
air.’—April, 1895.] 
MDCCCXCV.—A. 6) 
