Prof. Graham on the Law of the Diffusion of Gases. S57 



makes up the deficiency. A gas, however, of large diffusion - 

 volume escapes, in these circumstances, in a shorter time than 

 a gas of small diffusion-volume. Indeed, it was the conclusion 

 of the former paper, that gases diffuse more or less rapidly 

 according to some function of their densities, " apparently in- 

 versely as the square root of their densities." The advantage, 

 in illustrating the process of diffusion, of minute apertures or 

 channels of communication, such as we have in the stucco- 

 plug, depends upon the circumstance, that when a contraction 

 or expansion takes place in the gaseous contents of a diffusion- 

 instrument, any current in an outward or inward direction is 

 prevented by frictional resistance; so that the simple result of 

 diffusion is exhibited, not complicated by the effect of any 

 other force. 



The law at which we have arrived (which is merely a de- 

 scription of the appearances, and involves, I believe, nothing 

 hypothetic), is certainly not provided for in the corpuscular 

 philosophy of the day, and is altogether so extraordinary, that 

 I may be excused for not speculating further upon its cause, 

 till its various bearings, and certain collateral subjects, be fully 

 investigated. 



Supplementary Observations on the Law of the Diffusion of 



Gases. 



It is curious that intermixture takes place more rapidly in 

 the case of some gases than in that of others, although still in 

 conformity with the law of diffusion. Thus the process goes 

 on with much greater activity in the case of hydrogen, olefiant 

 gas and coal gas diffusing into air, than in the case of chlo- 

 rine, carbonic acid, carbonic oxide, &c, diffusing into the 

 same medium. This is very observable on comparing the 

 times as stated in describing the experiments on each gas. 



The circumstance of the apertures being in the upper part 

 of the diffusion-instruments, and opening upwards, may be sup- 

 posed to give the light gases an advantage in diffusing; but I 

 am disposed to attribute little of the inequality in question to 

 this cause. From a diffusion-bulb, in which the upper tube 

 was curved and bent downwards, hydrogen gas was found to 

 escape with its wonted rapidity. 



This inequality in the velocity of diffusion is strikingly il- 

 lustrated in the following results, obtained from experiments 

 with different gases, submitted in turn to diffusion from the 

 same instrument. In a certain time, the same in all the ex- 

 periments, a quantity of air entered, by diffusion, which varied 

 with the gas diffusing. 





