750 



Professor Sir James Be war 



[June 7 



On immersing the charcoal bulb in liquid air, the nitrogen was 

 rapidly absorbed and the discharge finally was that due to helium and 

 neon. Now the helium spectrum contains two very prominent lines, 

 one in the yellow and one in the green, and at very low pressures the 

 green predominates. In another tube, the initial pressure was con- 

 siderably reduced, and the green coloration was very strikingly 

 displayed. 



The intense red colour given out by neon vacuum tubes is now 

 well known. On immersing one end of such a neon tube in liquid 

 hydrogen, the gas was immediately differentiated, the more con- 

 densable and heavier neon sinking to the lower end of the tube, 

 where it revealed itself by its orange-ruddy glow, while the upper 

 end of the tube retained the yellow colour of the helium discharge, 

 thus demonstrating that the gas in the tube was a mixture of helium 

 and neon. 



Yelocity of Absokptiox of Air by Charcoal at -185°C. 

 UNDER Small Pressures. 



For this purpose a long horizontal glass tube, A, Plate I., over an 

 inch in diameter having either platinum electrodes sealed in at the 

 ends or external tin foil electrodes, had a charcoal condenser immersed 

 in liquid air attached, B, together with a means, after the vacuum was 

 so high that no discharge would pass, of allowing a definite small 

 volume of dry air to enter between two stop-cocks C. On opening 

 the stop-cock D to the charcoal condenser, rapid exhaustion took 

 place, which was measured at definite periods, after shutting off 

 the charcoal, by the McLeod gauge E, which had no india-rubber 

 joints or tubes used in its construction. 



In the course of observations in high vacua it was found that 

 metallic electrodes are unreliable because they occlude gas. For 

 this reason, therefore, it was necessary to work with external tin-foil 

 electrodes. 



The rate of exhaustion may be gathered from the fact that 20 

 grammes of charcoal cooled in liquid air was able to reduce the pres- 



sure of air in the tube of 2000 c.c. capacity from one thre e- hundred - 

 and-fiftieth of an atmosphere to one three-millionth of an atmosphere 



