Mr. Graham's Recent Discoveries. 



453 



tube. The following numbers represent the velocity with whicli 

 the rubber is penetrated by different gases in equal times : — 



Mtrogen 1 



Carbonic oxide 1*113 



Atmospheric air 1*149 



Marsh gas 2*148 



Oxygen 2*55 



Hydrogen 5*50 



Carbonic acid . . . • . .13*58 



Air being a mechanical mixture of 21 per cent, of oxygen 

 and 79 per cent, of nitrogen, the constituents of atmospheric 

 air are carried through a film of rubber into a vacuum nearly 

 in the same relative proportion as the same gases penetrate it 

 singly, hence the composition of air " dialyzed " by the india- 

 rubber septum is deducible by calculation — 



Oxygen . 21 x 2-556 = 53*676 = 40*46 

 Nitrogen . 79 X 1 =79* = 59*54 



In the experiment with 

 the Torricellian vacuum, 

 air entering through the 

 rubber was found to have 

 the composition indicated 

 by theory — 40 per cent, 

 oxygen and 60 per cent, 

 nitrogen. 



Dr. Sprengel's Mercu- 

 rial Exhauster (Fig. 1) is 

 now used instead of the 

 Torricellian vacuum. It 

 possesses the advantage 

 of simultaneously main- 

 taining the space vacuous, 

 and delivering for exami- 

 nation any air entering 

 through the septum. 



The flow of mercury, 

 from the funnel, a, 

 through the fall tube, c b, 

 is regulated by the clip 

 which compresses the 

 caoutchouc tube, c. The 

 receiver to be exhausted 

 is connected with the fall 

 tube by a branch arm, x. 



The descending stream 

 of mercury draws the air 



100*00 



