188 Professor Sir James Deivar [Jan. 20, 



operation. In this way 50 litres of air can be treated in a short 

 time, supplying sparking tubes showing brilliantly the complete 

 spectra of the volatile constituents of the air. 



The results derived from the treatment of Bath gas in this way 

 <are interesting. This gas, consisting mainly of nitrogen and yoVoti^ 

 part helium, when subjected to the action of the charcoal condenser 

 in liquid air, gives no high vacuum. All the nitrogen and any other 

 constituents are absorbed, and a spectrum of helium and hydrogen 

 showing much less neon than exists in the volatile residue from 

 atmospheric air is the result. A sample of argon prepared from Bath 

 gas treated in the same way, gives a tube showing the helium 

 .and neon spectrum ; and one prepared from atmospheric air gives a 

 similar result, but the helium spectrum is the stronger in the Bath 

 argon, whereas with the atmospheric argon the neon spectrum is the 

 most pronounced. 



Illustrations of various Applications of Charcoal in Experimental 

 Investigations. 



The gaseous products from minerals containing helium, hydrogen, 

 -etc., also the products from radium compounds, may be treated by 

 the charcoal method. As an example I have applied this method to 

 the crude gases got by heating the mineral Fergusonite. During the 

 €Ooling of the charcoal the nitrogen and hydrogen spectra were 

 marked, but in a short time nothing could be seen but the Hues of 

 hydrogen and helium. It is needless to say that the charcoal 

 method of exhaustion can be applied to the manufacture of in- 

 candescent lamps and Rontgen radiation tubes, and that the method 

 can be conveniently employed to produce and maintain high 

 vacuum for the purpose of distilling bodies under low pressures. 

 Many experiments with the radiometer can be carried out by 

 the use of the charcoal method of exhaustion. If a charcoal 

 capsule is sealed to the bulb of a radiometer full of air under 

 relatively high pressure, on directing a beam of light on the vanes 

 •of the radiometer they remain at rest, showing that the density of the 

 air is too great for motion to take place. When, however, the charcoal 

 capsule is immersed in a vessel containing liquid air, the vanes im- 

 mediately commence a rapid rotation. On removing this liquid air 

 bath their motion slackens, and finally they come to rest as the char- 

 coal returns to the temperature of the room. 



It is known that dry phosphorus does not enter into chemical com- 

 bination witli pure oxygen at ordinary temperature and pressure. A 

 bulb of from 100 to 200 c.c. filled with pure oxygen, having a side 

 tube sealed on of 2 mm. cross section containing fused phosphorus, 

 the whole being connected by means of a quill tube to a charcoal 

 capsule , containing in part also a good layer of phosphoric anhydride, 

 and the latter immersed in liquid air, the charcoal gradually absorbs 



