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



the diffusiometer, was, for air 1210 seconds, for hydrogen 321 



seconds. 



Air 1310 _o. 7fiq 



Hydrogen .... W^ 769 - 



The time, again, from 736 to 685 millims. (29 to 27 inches) 

 was, for air 685 and 684 seconds; mean 684*5 seconds; and 

 for hydrogen 183, 183, and 184 seconds; mean 183*3 seconds. 



Air 684-5 „„... 



Hydrogen .... 183^5 ~ d ' 754 ' 



The stoneware was evidently of a much closer texture than 

 stucco, and the ratio appears again less influenced by capillary 

 transpiration. In fact the molecular ratio of 1 to 3*80 is ap- 

 proached within 1 per cent. Biscuitware therefore appears to 

 be but little inferior to graphite for such experiments, a circum- 

 stance which is important, as the latter is not easily procured 

 and cannot be converted into tubes and other convenient forms 

 like plastic clay. 



Further, the rate of passage of gas through the plate of gra- 

 phite appears to be closely proportional to the pressure. The 

 resistance was increased by augmenting the thickness of the 

 plate to 2 millims. ; and with air and hydrogen at a pressure 

 maintained constant at 50 and 100 millims,, the time was ob- 

 served that the gas took to enter 10 linear millimetre divisions 

 of the tube. 



Seconds. Ratio. 

 Air under pressure of 100 millims. . . 1925 1 

 Air under pressure of 50 millims. . . 3880 2*015 

 Hydrogen under pressure of 100 millims. 497 1 

 Hydrogen under pressure of 50 millims. 1022 2*056 



By halving the pressure, the time of passage is doubled, or 

 increased somewhat more. Greater pressures might probably 

 give a rate of passage corresponding more exactly with the 

 pressure. 



The ratio between the comparative times of the two gases in 

 the last experiments may also be noticed, the observations having 

 been made in similar circumstances as to pressure and tempe- 

 rature. 



Barom. 760 millims. ; At pressure Barom. 760 millims. ; At pressure 

 Therm. 12°'9 C. of 50 millims. Therm. 12°'9 C, of 100 millims. 

 Air. . . . 3880 Air. . . 1925 



Hydrogen . . 1022 ~ 6 ™" Hydrogen . "497 ~ 6 b76 ' 



