358 Prof. Graham on the Law of the Diffusion of Gases, 



In a given time, 

 With chlorine in the diffusion-tube 0*302 vol. air entered. 



With carbonic acid 0*623 — 



With hydrogen 1*277 



It appears, then, that the process of diffusion into air through 

 stucco is four times more rapid in the case of hydrogen than 

 in that of chlorine, and twice as rapid in the case of the former 

 gas as in carbonic acid. The process of diffusion might be said 

 to proceed at a uniform rate, if the same quantity of air en- 

 tered the instrument in the same time, whatever gas was dif- 

 fused, and although the quantity of gas which escaped was 

 variable of course, and proportional to the respective diffusion- 

 volume of the gas. But this exchange of diffusion-volumes 

 takes place more rapidly, it appears, in the case of some gases 

 than of others. 



A table of experiments is given in the body of the paper (p. 

 187) on the rate of passage of different gases through the pores 

 of stucco under the influence of pressure. The rate appears to 

 be the same in the case of air, nitrogen, oxygen, and carbonic 

 acid, from which carbonic oxide deviates in a small degree. 

 15 ut hydrogen, and, it is remarkable, olefiant gas and coal gas, 

 which contain hydrogen, are less resisted than the preceding 

 class. Upon reconsideration I am inclined to connect with 

 this fact the apparent deviation of hydrogen from the law of 

 diffusion, which is noticed in the paper. It is there shown 

 that more hydrogen passes out than the exact quantity pro- 

 portional to the return-air. The same deviation from the law 

 may be remarked in the experiments detailed on olefiant gas. 

 It is also very noticeable in the case of coal gas. But these 

 are gases which, like hydrogen, are less resisted than common 

 air in their passage through stucco. There appears to ex- 

 ist an inaptitude on the part of a stucco intermedium to exhi- 

 bit the exact effect of diffusion, in the case of gases, on either 

 side of it, which are not capable of permeating through it with 

 equal facility ; that gas which experiences least frictional re- 

 sistance diffusing through in a quantity somewhat greater than 

 it should do. 



There can be no doubt that the velocity of diffusion noticed 

 above, is likewise influenced by the variable resistance which 

 the gases experience in passing through the stucco. But I am 

 not prepared to say, that the variation depends entirely on this 

 cause, and is therefore accidental to the mode in which the 

 diffusion takes place. The diffusion or intermixture of light 

 gases appears to take place in all circumstances with greater 

 rapidity than that of heavy gases. 



Glasgow, Sept. 7, 1832. THOMAS GkAHAM. 



