516 On the Absorption of Gas in a Crookes Tube, 



One sample, bought as soft Jena from the dealers, ran down 

 very quickly the first time it was used, until about 120 c.c. 

 at a pressure o£ 1 mm. had been absorbed, when no further 

 fall in pressure occurred although the discharge passed for 

 several days. The tube was then left exposed to atmospheric 

 pressure for several weeks. When the discharge was again 

 passed a further quantity of gas disappeared, but this was 

 •considerably less than in the first case. That a tube can be 

 made which shows a limited capacity for absorption, seems to 

 point clearly to the action being a chemical one. 



Tubes made of soda- and Jena-glass were treated with hot 

 acids, but this was not found to influence the absorption. 



Mylius * has shown that if glass be soaked in water for 

 several days and then heated to 300°-4G0° C, it is rendered 

 less liable to be acted on chemically. This treatment applied 

 to soda-glass produced no difference in the rate of running 

 down; but a soft Jena-glass tube was made to run down much 

 •more slowly, although the quantity of gas that it finally 

 absorbed was unaltered. 



Jena-glass further differed from soda-glass in that hydrogen 

 was scarcely absorbed at all. If a Jena-glass tube which 

 refused to absorb more gas was heated, a small quantity came 

 off, but this could not be reabsorbed as in the case of soda- 

 glass. 



To summarize : It appears from the experiments that most, 

 if not all, of the gas absorbed is to be accounted for by a 

 chemical combination with the glass ; that if tabes are desired 

 in which the pressure remains constant they should be made 

 of Jena-glass in preference to lead-glass, and of lead-glass 

 rather than of soda-glass; and finally, that in the first two 

 cases hydrogen is absorbed to a far less extent than air or 

 nitrogen, the last two gases showing little difference. 



14. One or two effects noticed during the experiments may 

 ; be added here. 



It was frequently noticed that when a battery of voltage 

 just insufficient to start the discharge was connected to a 

 tube, a double reversal by means of a commutator frequently 

 enabled the discharge to pass. 



When running tubes with a striated positive column con- 

 tinuously with a battery, I have often observed the following : 

 at a distance of two or three stria3 away from the anode a 

 well-defined dark deposit (aluminium ?) appears round the 

 whole circumference of the tube, just opposite the bright part 

 of a striation, to which it is equal in width. This gradually 



* Chem. Soc. Abs. 1889, p. 549. 



