1896.] On some Physical Properties of Argon and Helium. 207 



itself as to whether this conclusion might not be disturbed by the 

 presence in the Bath gas of helium, whose lightness would tend to 

 compensate the extra density of argon. 



An examination of the gas which had stood in my laboratory more 

 than a year having shown that it still contained no oxygen, it was 

 thought worth while to remove the nitrogen so as to determine the 

 proportion that would refuse oxidation. For this purpose 200 c.c. 

 were worked up with oxygen until the volume, free from nitrogen, 

 was reduced to 8 c.c. On treatment with pyrogallol and alkali the 

 residue measured 3*3 c.c, representing argon, and helium, if present. 

 On sparking the residue at atmospheric pressure and examining the 

 spectrum, it was seen to be mainly that of argon, but with an un- 

 mistakable exhibition of D 3 . At atmospheric pressure this line 

 appears very diffuse in a spectroscope of rather high power, but the 

 place was correct. 



From another sample of residue from the Bath gas, vacuum tubes 

 w r ere charged by my son, Mr. R. J. Strutt, and some of them showed 

 D 3 sharply defined' and precisely coincident with the line of helium 

 in a vacuum tube prepared by Professor Barnsay. 



Although the presence of helium in the Bath gas is not doubtful, 

 the quantity seems insufficient to explain the low density found in 

 October, 1894. In order to reconcile that density wnth the proportion 

 of residue (3'3/200 = O'OIG) found in the experiment just described, 

 it would be necessary to suppose that the helium amounted to 25 per 

 cent, of the whole residue of argon and helium. Experiment, how- 

 ever, proved that a mixture of argon and helium containing 10 per 

 cent, of the latter gas showed D 3 more plainly than did the Bath 

 residue. It is just possible that some of the helium was lost by 

 diffusion during the long interval betw r een the experiments whose 

 results are combined in the above estimate, 



Buxton Gas. 



Gfas from the Buxton springs, kindly collected for me by Mr. A 

 McDougall, was found to contain no appreciable oxygen. The argon 

 amounted to about 2 per cent, of the volume. When its spectrum 

 was examined, the presence of D 3 was suspected, but the appearance 

 was too feeble to allow of a definite statement being made. The 

 proportion of helium is in any case very much lower than in the 

 Bath gas. 



Is Helium Contained in the Atmosphere ? 



Apart from its independent interest, this question is important in 

 connection with the density of atmospheric argon. Since the spec- 

 trum of this gas does not show the line D 3 , we may probably conclude 



