190 Prof. W. Bamsay and Dr. M. W. Travers. 



before it was complete. The gas under such conditions showed a trace 

 of the nitrogen spectrum. The portion last weighed was spectro- 

 scopically pure. 



Capacity of bulb. Temp. Pressure. Weight. Density. 



c.c. 



163-19 15-47 767-1 0-27235 19-935 



16-97 764-8 0-26985 19-914 



13-34 742-8 0-26591 19-952 



12-95 741-3 0-26586 19-961 



After the first of these determinations the gas was passed over a 

 mixture of red-hot magnesium and lime, and subsequently over red-hot 

 copper oxide, in order to remove hydrogen. But after determining the 

 density, the gas was examined spectroscopically, and was found to con- 

 tain hydrogen. The gas was therefore again sparked, when the density 

 19-952 was found. This specimen was also examined spectroscopically, 

 .and was found to be absolutely free from all visible traces of impurity. 

 The last weighing refers to the same sample of gas, and was made as a 

 control experiment. 



These results conclusively prove that the density of argon, purified 

 from its companions, does not differ greatly from that obtained by 

 Lord Rayleigh, viz., 19*94, nor by one of us, viz., 19'941. The true 

 density may, we think, be safely taken as the mean of the last two 

 determinations, viz., 19-957. 



This corresponds with the mean of the four reliable determinations 

 with the small bulb, viz., Nos. 2, 3, 5, and 6, which is 19*955. 



Refractivity of Argon. 



The refractivity of pure argon was next determined. The measure- 

 ments were made according to the plan suggested by Lord Rayleigh.* 

 The samples investigated were Nos. 1, 2, 5, and 6. The comparison 

 was made with air. 



(1) 0"9620 Contains neon and helium. 



(2) 0-9687 



(5) 0-9647 Mean, 0-9665. 



(6) 0-9660 



The refractivity of a previous sample of argon, obtained from the 

 middle of the 15 litres, during the second liquefaction, was 0*9679, a 

 number differing only slightly from that given above. 



The refractivity of argon containing krypton, which had a density 

 20*01, was much higher than the number given above for pure argon, 

 for it reached 1 -030 as a mean of two determinations. Evidently then 



* ' Roy. Soc. Proc.,' vol. 59, p. 201. 



