Mr GRAHAM on the Law of the Diffusion of Gases. 223 



and if the gases are of unequal density, there is a consequent 

 accumulation on the side of the heavy gas, and loss on the side 

 of the light gas. In the case of air, for instance, on the one 

 side of the screen, and hydrogen gas on the other, a process of 

 exchanging 1 measure of air for 3.7947 measures of hydrogen, 

 through the apertures, is commenced, and continues till the 

 gases on both sides of the screen are in a state of uniform mix- 

 ture. Experiments on this principle can be made with ease and 

 precision, as will appear in the sequel, and afford an elegant de- 

 monstration of the law. 



There is a singular observation of DOEBEREINER, which che- 

 mists seem to have neglected as wholly inexplicable, on the 

 escape of hydrogen gas by a fissure or crack in glass-receivers, 

 which belongs to this subject, and from which I set out in the 

 inquiry. Having occasion, while engaged in his researches on 

 spongy platinum, to collect large quantities of hydrogen gas, he 

 accidentally made use of a jar which had a slight crack or fissure 

 in it. He was surprised to find that the water of the pneumatic 

 trough rose into this jar one and a half inches in twelve hours, 

 and that, after twenty-four hours, the height of the water was 

 two inches two -thirds above the level of the water-trough. 

 During the experiment neither the height of the barometer, nor 

 the temperature of the place, had sensibly altered. 



In other experiments, he substituted glass vessels of very dif- 

 ferent forms, tubes, bell-jars, flasks, all of which had fissures. In 

 every one of these vessels, filled with hydrogen, the water rose, 

 after some- hours, to a certain height. On covering one of these 

 vessels, containing hydrogen, by a receiver or on filling the 

 vessel with atmospheric air, oxygen or azote, instead of hydro- 

 gen he never observed a change in the original volume of the 

 gas. He thinks it probable that the phenomenon is due to the 

 capillary action of the fissure, and that the hydrogen only is at- 



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