176 Prof. Graham on the Law of the Diffusion of Gases. 



these gases, being the reciprocals of the square roots of the 

 densities, the density of air being assumed as unity. 



If the two gases are separated at the outset by a screen 

 having apertures of insensible magnitude, the interchange of 

 " equivalent volumes of 'diffusion " takes place through these 

 apertures, being effected by a force of the highest intensity ; 

 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 pro- 

 cess 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 uni- 

 form mixture. Experiments on this principle can be made 

 with ease and precision, as will appear in the sequel, and af- 

 ford an elegant demonstration of the law. 



There is a singular observation of Dcebereiner, 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 

 different 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, in- 

 stead of hydrogen — he never observed a change in the ori- 

 ginal volume of the gas. He thinks it probable that the phe- 

 nomenon is due to the capillary action of the fissure, and that 

 the hydrogen only is attracted by the fissures, and escapes 

 through them on account of the extreme smallness of its 

 atoms*. 



This explanation is rendered improbable by the circum- 

 stance, that hydrogen, of all the gases, was condensed and 



* Sw P Action capillaire des Fissures, $c. Annales de Chimie ct de Phy* 

 xique, torn. xxiv. pp. 332—334. 1823. 



