ATOMIC WEIGHTS 539 



THE HELIUM-AEGON" GEOUP. 



The five inert gases, lieli-um, neon, argon, krypton and xenon are ap- 

 parently incapable of forming compounds. Their atomic weights, there- 

 fore, can only be inferred from their densities, for which the following 

 data are available. 



For helium the earliest determinations by Eamsay ' are too high. He 

 obtained values ranging from 3.89 to 4.84, and later figures above 2.13, 

 when the density of oxygen, as the standard is put at 16. Langlet," a 

 little later, assigned to helium the density 3.00. Eamsay and Travers," 

 after the discovery of neon, krypton and xenon, with purer helium, 

 found its density to be 1.98, which is the best value now assignable to it. 



The density of argon has been inore carefully determined, both by 

 Eamsay * and by Eayleigh." 



Compared with an equal volume of oxygen weighing 2.62760 grammes, 

 Eayleigh found for argon the following weights : 



3.2710 

 3.2617 

 3.2727 

 3.2G52 

 3.2750 

 3.2748 

 3.2741 



Eayleigh accepts the last three determinations, which give 3.27463 in 

 mean. With = 16. the density of argon becomes 19. 9399, ±.0012. 

 Eamsay's figures, also referred to = 16, are as follows: 



19.904 

 19.823 

 19.816 

 19.959 

 19.969 

 19.932 



Eejeeting the second and tliivd of these determinations the four re- 

 maining values give in mean a density of 19. 941, ±.0099. Correcting 

 the figures for argon by the method of limiting densities, D. Berthelot " 

 assigns to ar^on the densitv 19.941. 



' Pi-oc. Roy. Soc, 58, SI. 1835. .Journ. Cheiii. Soc, 57, f>S4. 1895. 



''Zeitsch. anorg. Chein., 10, 289. 1895. 



"Proc. Roy. Soc, 67, 329. IfW). I'liil. Traii--., 197, A, 47. 1!X)0. 



^Phil. Trans., 186, 238. lfK)5. 



= Prof. Roy. Soc, 5.'), 201. 1896. 



eCompt. Rend., 126, 1.5(11. 



