1915] on Problems of Hydrogen and the Rare Gases 557 



beo:ins in the tube and rapidly intensifies and becomes deep pink, 

 characteristic of hydrogen, and on examining with the spectroscope a 

 well-developed spectrum of this gas is seen. Xow the heating is 

 repeated, after exhausting by the charcoal, but with the quartz tube 

 containing air covering the platinum tube. This time no discharge 

 will pass even after several minutes of heating as before. Other 

 gases can then be passed through the annular space between the 

 quartz tube and the platinum. Neither oxygen nor carbonic acid 

 will show any diffusion under such circumstances, although at a 

 somewhat higher temperature, obtained in some cases by passing a 

 strong electric current through the platinum tube instead of using 

 flame temperatures, there are indications that both carbonic acid and 

 water vapour will pass through, and possibly also carbonic oxide, a 

 gas which, as we have seen, readily passes through hot iron. Finally, 

 when hydrogen is passed through the quartz tube a strong discharge 

 is rapidly obtained. 



If a thoroughly cleaned quartz tube is subjected to direct heating 

 by the Meker flame, there is no certain indication of any gas trans- 

 ference. If the quartz tube, however, is attached to a McLeod 

 gauge, instead of to the electric discharge tube, and the heating 

 continued for a considerable time, then a definite increase of pressure 

 can be detected. On the addition of the external quartz tube, as 

 was done with the platinum tube, the arrangement can be made 

 more convenient, as the two quartz tubes can be sealed together 

 to form a double tube in one piece, as shown in Fig. 5. This 

 arrangement further enables the annular space between the tubes 

 to be well exhausted or filled to any required pressure with different 

 gases. If hydrogen be admitted and the tubes strongly heated, a 

 discharge can only be obtained after a long time, the rate of diffusion 

 being very slow. 



When helium and neon replace the hydrogen in the annular 

 space, then a discharge is readily obtained. The helium appears more 

 quickly than the neon, the discharge being sky-blue at first and 

 steadily modifying to tlie well-known peach-blossom tint of helium 

 and neon mixtures, and becoming a brilliant orange-pink as the neon 

 intensities. This affords an effective and ready manner of demon- 

 strating the transference of these gases through hot quartz. The 

 annular space was tilled to about four-tifths of an atmosphere at 

 ordinary temperature ; a good Meker flame is a sufficient source of 

 heat ; the inner quartz tube is approximately h mm. thick in the 

 walls and about 1| mm. bore. To prevent much loss by diffusion 

 into the air through the outer tube the quartz tube ought to be thick 

 in the wall. After charging the annular space the helium and neon 

 gasholder is sealed off. The measure of the rate of transference 

 of helium and neon by the use of a McLeod gauge has not yet 

 l>een made. 



Vol. XXI. (So. 109) 2 o 



