184- Pro£ Graham on the Law off he Diffusion of Gases. 



At the beginning of the experiment, the instrument con- 

 tained 855 measures hydrogen, saturated with vapour at 62° ; 

 in three minutes a contraction of 95 measures took place, and 

 in the course of an hour the diffusion was sensibly at an end. 

 The instrument, however, was exposed for two hours longer, 

 that the diffusion might certainly be complete. During in- 

 tervals so short uniformity of temperature might be counted 

 upon, with certain precautions ; and the variations in atmo- 

 spheric pressure were generally so minute, that they might 

 be neglected with impunity. Corrections for temperature and 

 pressure might therefore be dispensed with, which was a great 

 advantage. 855 measures hydrogen were found eventually 

 to be replaced by 226*5 measures air, both saturated with va- 

 pour at 62°. 



855 



= 3*774? = diffusion- volume of hydrogen. This 



determination is somewhat below the theoretical diffusion- 

 volume, 3*79, while the preceding determination was in ex- 

 cess. 



Exp. S. — Another diffusion-instrument of the form B, with 

 a dense plug, one tenth of an inch in thickness, was filled with 

 water, which was then poured into a counterpoised phial, and 

 found to weigh 1085*7 grains. When filled over water, 1085*7 

 grain-measures of gas are therefore introduced into this in- 

 strument, and in this way we express most correctly its capa- 

 city. The instrument, after the plug was dried, was entirely 

 filled with hydrogen gas, as in the preceding experiment, 

 thermometer 61°. The bulk of the diffusion appeared to be 

 over in an hour and a half, but five hours were allowed to the 

 experiment. Thereafter the water which had entered the in- 

 strument was poured into a counterpoised phial, and found 

 to weigh 800*6 grains. This last quantity represents the con- 

 traction, and subtracting it from 1085*7, we have the return- 

 air equal to 285*1 grain measures. Now, 



1 08 %'7 



= 3*808 = diffusion-volume of hydrogen gas. 



285*1 J & & 



Exp. 4. — Same bulb, circumstances the same, but thermo- 

 meter 62°. Time allowed for the diffusion four hours. 



1085*7 measures hydrogen were replaced by 286*1 mea- 

 sures air. 



1085*7 



286*1 



3*795 = diffusion-volume of hydrogen. 



Exp. 5. — Same bulb, &c. thermometer 61°. Time five 

 hours. 



