124 PROCEEDINGS OF SECTION B. 
-air freed from carbon dioxide to consist of 79:16 of nitrogem 
(phlogisticated air) and 20-84 of oxygen (dephlogisticated 
air), results that surprise us by their close approximation te 
the results of the most accurate modern analyses.” 
Priestley had found that the volume of air was diminished 
by the passage of electric sparks. Cavendish repeated these 
experiments, and reasoned out carefully that the nitrous 
acid produced was the result of the combination of the two 
airs, oxygen and nitrogen; then he proceeds to raise the 
doubt . . . . “whether there are not in reality many 
different substances confounded together by us under the 
name of dephlogisticated air (oxygen).” “I therefore made 
an experiment,’ he continues, ‘‘to determine whether the 
whole of a given portion of the phlogisticated air (nitrogen) 
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.” He 
kept adding oxygen and sparking to reduce it down, neutral- 
ising with caustic potash, and finally absorbing’ the excess 
of oxygen added, and found still a little bubble left, the 
volume of which was estimated. He draws this remarkable 
conclusion—remarkable and most interesting when viewed 
in the light of recent discovery—‘“ So that, if there is any 
part of the phlogisticated air (nitrogen) 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 1-120th 
part of the whole.” By burning a large quantity of common 
air with hydrogen, he found that the dew so often noticed 
im the tube was really water, and “ that almost all the in- 
flammable, and about one-fifth of the common 4air, are 
turned into pure water.” 
Lord Rayleigh found that nitrogen, separated from atmo- 
spheric air, was about 1-200th heavier than the purest nitro- 
gen obtained from other sources by chemical means. As 
this difference could not be accounted for by errors of experi- 
ment, the suspicion was at once aroused that “atmospheric 
nitrogen’ contained some other constituent than nitrogen, 
possibly a smaller portion of a heavier gas. 
With the assistance of Professor Ramsay as chemist, a 
vigorous campaign by physicist and chemist was entered 
upon to clear up the discrepancy. |The able investigation 
that ensued, laborious, painstaking, and skilfully carried out, 
is fresh m the memories of all. The long-neglected endio- 
metric analyses of Cavendish were unearthed, and repeated 
with all modern refinements, and the existence of that re 
manent bubble “not more than 1-120th” of the original 
