Arc/on and its Companions. 



it was possible to remove the greater portion of the helium and neon 

 from this mixture of gases, leaving the argon behind. Many attempts 

 were made to separate the helium from the neon. Among these was 

 fractional solution in oxygen, followed by a systematic diffusion of the 

 two gases ; but it was not found possible to raise the density of the 

 neon beyond the number 9 - 16, and its spectrum still showed helium 

 lines. It was not until liquid hydrogen made by an apparatus designed 

 and built by one of us (M. W. T.) had been produced in quantity, that 

 the separation was effected ; the neon was liquefied or perhaps solidified 

 at the temperature of boiling hydrogen, while the helium remained 

 gaseous. A few fractionations serve to produce pure neon ; we 

 did not attempt to separate the helium in a pure state from this 

 mixture. 



That these are all monatomic gases was proved by determination of 

 the ratio of their specific heats by Kundt's method ; the physical pro- 

 perties which we have determined are the refractivities, the densities, 

 the compressibilities at two temperatures, and of argon, krypton and 

 .xenon the vapour-pressures and the volumes of the liquids at their 

 boiling points. 



The results are as follows : 



The compressibilities of these gases also show interesting features. 

 They were measured at two temperatures 11 '2 and 237'3 ; the value 

 of P.V. for an ideal and perfect gas at 11-2 is 17,710 metre-cubic- 

 centimetres, and at 237'3 to 31,800. This is, of course, on the 

 assumption that the product remains constant whatever be the varia- 

 tion in pressure. Now with hydrogen at 11 4 2 C. the product increases 

 with the rise of pressure ; with nitrogen, according to Amagat, it first 

 decreases slightly and then increases slightly. With helium the in- 

 crease is more rapid than with hydrogen ; with argon there is first a 

 considerable decrease followed at very high pressures by a gentle 



