234 LORD RAYLEIGH AND PROFESSOR W. RAMSAY ON ARGON, 
redness, by which the black was changed to sponge, still no evidence of absorption 
was noticed. In all these experiments, absorption of half a cubic centimetre of argon 
could have at once been detected. 
We do not claim to have exhausted the possible reagents. But this much is 
certain, that the gas deserves the name “argon,” for it is a most astonishingly indif- 
ferent body, inasmuch as it is unattacked by elements of very opposite character, 
ranging from sodium and magnesium on the one hand, to oxygen, chlorine, and 
sulphur on the other. It will be interesting to see if fluorine also is without action, 
but for the present that experiment must be postponed, on account of difficulties of 
manipulation. 
It will also be necessary to try whether the inability of argon to combine at 
ordinary or at high temperatures is due to the instability of its possible compounds, 
except when cold. Mercury vapour at 800° would present a similar instance of 
passive behaviour. 
16. General Conclusions. 
It remains, finally, to discuss the probable nature of the gas or gases which we 
have succeeded in separating from atmospheric air, and which has been provisionally 
named argon. 
That argon is present in the atmosphere, and is not manufactured during the 
process of separation is amply proved by many lines of evidence. First, atmospheric 
nitrogen has a high density, while chemical nitrogen is lighter. That chemical 
nitrogen is a uniform substance is proved by the identity of properties of samples 
prepared by several different processes, and from several different compounds. It 
follows, therefore, that the cause of the high density of atmospheric nitrogen is due 
to the admixture with heavier gas. If that gas possesses the density of 20 compared 
with hydrogen as unity, atmospheric nitrogen should contain of it approximately 
1 per cent. This is found to be the case, for on causing the nitrogen of the atmos- 
phere to combine with oxygen in presence of alkali, the residue amounted to about 
1 per cent.; and on removing nitrogen with magnesium the result is similar. 
Second : This gas has been concentrated in the atmosphere by diffusion. It is true 
that it cannot be freed from oxygen and nitrogen by diffusion, but the process of 
diffusion increases relatively to nitrogen the amount of argon in that portion which 
does not pass through the porous walls. That this is the case is proved by the 
increase of density of that mixture of argon and nitrogen. 
Third: On removing nitrogen from “atmospheric nitrogen” by means of magne- 
sium, the density of the residue increases proportionately to the concentration of the 
heavier constituent. 
Fourth: As the solubility of argon in water is relatively high, it is to be expected 
that the density of the mixture of argon and nitrogen, pumped out of water 
along with oxygen should, after removal of the oxygen, exceed that of “atmos- 
pheric nitrogen.” Experiment has shown that the density is considerably increased. 
