1904.] Volatile Gases from Air without Liquefaction. 



129 



now beyond the striae stage. A further experiment starting with one- 

 fourth of an atmosphere gave a vacuum through which no discharge 



Finally, the 30 grammes of charcoal were replaced by only 1 gramme 

 and the initial pressure was reduced to 3 mm. of mercury. Now the 

 vacuum just reached the beginning of the phosphorescent stage. With 

 hydrogen, either a pressure of gas less than that of the atmosphere 

 had to be used at starting or a larger amount of charcoal employed in 

 order to get a vacuum well up in the striae stage. If, however, the 

 liquid air was cooled to - 210 C. by exhaustion, the tube just 

 reached the beginning of phosphorescence round the cathodes. 



With helium there was a very slight absorption, but neon did show 

 something more appreciably. Spectroscopic observations made during 

 the condensation of the gas in the charcoal showed the gradual dis- 

 appearance of the characteristic spectrum of oxygen, nitrogen and air, 

 as the high vacuum was reached and the discharge passed with great 

 difficulty. In tubes of this kind filled at atmospheric pressure I could 

 always see the F line of hydrogen and the neon yellow; but the 

 helium was not seen with any defmiteness. As the amount of neon in 

 the air cannot well exceed 1 /50,000th, the spectroscopic test is very 

 delicate. 



In order to bring in the helium lines it was necessary to concentrate 

 the volume of air in the space of the sparking tube six or seven times. 

 This was done by the use of an arrangement shown in fig. 2. A B is 



FIG. 2. 



the sparking tube with its small charcoal bulb C attached, capable of 

 being sealed off when required at G ; and D and E are larger charcoal 

 absorbers placed in vacuum tubes containing liquid air; the whole 

 being attached to a graduated gas-holder containing air. A series of 

 glass stop-cocks are attached at the points H, I, J and K in order to 

 facilitate manipulation. In determining the volume of air required to 

 bring in the helium lines only one charcoal absorber containing about 

 15 grammes of material was used. On allowing 200 c.c. of air from 

 the gas holder to be sucked into the charcoal (which had been previously 



