414 Mr. T. Graham on the Molecular Mobility of Gases. 



ever, show a close relation to the square roots of the densities of 

 the respective gases, as is seen in the last Table ; and they so far 

 agree with theoretical times of diffusion usually ascribed to the 

 same gases. 



These results were obtained by means of the graphite diffusio- 

 meter already referred to, which was a plain glass tube about 

 22 millims. in diameter, closed at one end by the graphite 

 plate. In order to conduct gas to the upper surface of the 

 graphite plate, a little chamber was formed above the plate, to 

 which the gas s was conveyed in a moderate stream by the entrance- 

 tube e (fig. 3) ; while the gas brought^ in excess was constantly 

 escaping into 

 the air by the 

 open issue- 

 tube i. The 

 chamber was 



formed of a short piece of 

 glass tube, about 2 inches in 

 length, cemented over the 

 upper end of the diffusio- 

 meter. The upper opening 

 of this short tube was closed 

 by a cork perforated for the 

 entrance- and exit -tubes. It 

 will be observed that by this 

 arrangement the upper sur- j f-||| 



face of the graphite plate was 

 constantly swept by a stream 

 of gas, which was under no 

 additional pressure beyond 

 that of the atmosphere, a free 

 escape being allowed by the 

 exit- tube. The gas also was 

 always dried before reaching 

 the chamber. The diffusio- 

 meter stood over mercury, 

 and was raised or lowered by 

 the lever movement intro- 

 duced by Professor Bunsen 

 in his very exact experiments 

 upon gaseous diffusion*. To 

 obtain the pressure of 100 

 millims. of mercury, the dif- 

 fusiometer was first entirely 

 filled with mercury and then 



* Bunsen's 'Gasometry, 5 by Roscoe. 



