212 Drs. W. Ramsay and J. Norman Collie. 



Less diffusible portion 



Volume of globe 162*843 c.c. 



Pressure at filling 663'8 mm. 



Temperature 19'93 



Weight 0-02902 gram 



Density 2'452 



Tlie less diffusible portion was next subjected to the process of 

 removing nine-tenths, the remaining tenth being collected apart. 

 This process was repeated three times, so that any portion of gas less 

 diffusible than the main bulk should thus be left as a residue. From 

 the more diffusible portion nine-tenths was also diffused out. The 

 more diffusible portions were then mixed, and the density was again 

 determined. 



Volume of globe 162'843 c.c. 



Pressure at filling 765' 7 mrn. 



Temperature 20'98 



Weight 0-02801 gram 



Density . 2*057 



This number is practically identical with that previously obtained, 

 viz., 2-049. 



It was of interest to follow the less diffusible gas, so as to ascertain 

 what impurity caused its higher density. Another set of fractiona- 

 tions was therefore carried out, and after five separate processes, 

 in each of which a residue was left, and that residue further diffused, 

 so as to separate all light gas as completely as possible, a few c.c. 

 of gas were collected, in which the spectrum of argon was strong. 

 Now we are certain that at no stage in the operations was any con- 

 siderable quantity of air admitted by leakage. It may safely be said 

 that the total amount of air could never have exceeded 5 c.c. And 

 inasmuch as the density of samples of helium from various sources, 

 which had undergone very little handling, differed by small amounts, 

 varying between 2*114 and 2'181, this must be ascribed to contami- 

 nation with argon, contained in the mineral from which the helium 

 had been obtained. Every effort was made to detect any unknown 

 lines in the spectrum of the residue, but in vain. With the jar and 

 spark-gap, the blue spectrum of argon was visible, and was compared 

 with that from a standard tube. 



If thus the increased density is due to argon, it is possible to calcu- 

 late the proportion of the latter ; first, in the lightest gas of density 

 2*117 found in samarskite ; second, in the residue in which the argon 

 had been concentrated, possessing the density 2*452, on the assump- 

 tion that helium possesses the density 2'042. The first must contain 

 0*42 per cent, of argon ; the second, 2'28 per cent. 



