Appendix to Lecture of Jan. 22, 1915 819 



When a gas-bottle charged to 10 atmospheres with carbonic acid 

 was connected to the membrane box, Fig. 16 (&), the gas issued 

 from the exit tube of the gas-box at the rate of two or three bubbles 

 per minute. 



The variation with increasing pressure at constant temperature is 

 seen in Fig. 19. 



It is definitely not quite linear in the case of hydrogen ; and with 

 carbonic acid the rate increases at a very much greater proportion 

 than the pressure. Comparable experiments made at fractions of an 

 atmosphere reveal the same behaviour, though to a less degree. 

 Wroblewski's conclusion would, therefore, seem not to be strictly 

 true. 



CoMPOSiTiox OF Products of Air Diffusion through 

 Rubber. 



Since the different components of the atmosphere diffuse at 

 different rates through rubber, it is of interest to examine the 

 products obtained after an extended period of diffusion. The values 

 found for the increase of oxygen percentage may be tabulated as 

 follows : — 





The presence of helium, as well as neon and hydrogen, could be 

 readily detected in the gas passing through the membrane. For 

 this purpose charcoal cooled in liquid air was used to maintain a low 

 pressure behind the membrane by condensing the diffusing oxygen 

 and nitrogen. On the side of the charcoal further from the mem- 

 brane a sparking-tube of small volume was sealed, to afford the 

 means of detecting any helium or neon and hydrogen : they would 

 scarcely be diminished in amount by absorption in the small amount 

 of charcoal used. The more readily to accumulate a sufficient 

 pressure of these gases to give a good discharge, the free space in 

 the apparatus was kept as low as possible. It was found necessary 

 to dry the air coming into contact with the membrane, as otherwise 

 the narrow space in the charcoal tube in liquid air became plugged 

 with condensed ice from the water vapour diffused in from the air. 



The form of apparatus found most convenient is here figured. 



3 H 2 



