1905.] 



on New Low Temperature Phenomena. 



187 



spheric pressure, the F line of hydrogen and the neon yellow could 

 always be seen ; but the helium was not seen with any definiteness. 

 As the amount of neon in the air cannot well exceed 3-x7^xrT7th, the 

 spectroscopic test is very delicate. 



In order to get the helium spectrum the air in the sparking tube 

 had to be enriched six or seven times. This was attained by the 

 apparatus in Fig. 3. A B is the sparking tube, with its small char- 

 coal bulb attached, capable of being sealed off at G when required j 

 and D and E are larger charcoal absorbers placed in vacuum tubes 

 containing liquid air ; the whole being attached to a graduated gas- 

 holder, F, containing air. A series of glass stop-cocks are attached 

 at the points H, I, J, and K, to facilitate manipulation. 



In a preliminary experiment to determine the volume of air 

 necessary to bring in the helium lines, 200 c.c. of air were supplied 

 to one of the charcoal vessels D, containing 15 grm. of charcoal, 

 from which the residue was passed on to the sparking tube. This 

 tube gave the hydrogen lines C and F, the neon yellow and some of 



the orange lines, along with the helium yellow and green quite dis- 

 tinctly. Another tube with the residuary gas from a litre of air gave 

 all the helium lines as well as the neon yellow and the hydrogen F ; 

 from which we infer that by this means 5-owoth of helium can be 

 detected, so that the test is as delicate for helium as for neon. A 

 third tube, supplied from 3 litres of air, gave the neon and helium 

 spectra and a brilliant ruddy glow discharge. 



As 40 to 50 grammes of charcoal can absorb at the temperature of 

 liquid, air from 5 to 6 litres of air, it is easy to accumulate rapidly the 

 uncondensed gases in considerable quantities for spectroscopic examina- 

 tion. For this purpose it is convenient to use two charcoal condensers 

 in circuit. After the charcoal in the first one, marked E in figure, 

 was saturated, the stop-cock K was closed, while I and J were opened 

 for a short time to allow the less condensable gas in E to be sucked 

 into the second condenser D along with some portion of air. The 

 condenser E was then taken out of the liquid air, rapidly heated to 

 15° C. to expel the excluded air, and was thus ready to repeat the 



