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



diffusion action, as in the case of the pores of the stucco-plug, 

 and there follows a tendency to accumulation on the side ori- 

 ginally occupied by the carbonic acid. This accumulation is 

 limited by the increased facility with which the air-vessels can 

 empty themselves mechanically of a portion of their contents, 

 from their distended state. 



In the law of diffusion of gases, we have, therefore, a singu- 

 lar provision for the full and permanent inflation of the ulti- 

 mate air-cells of the lungs. 



But it is in the respiration of insects that the operation of 

 this law will be most distinctly perceived. The minute air- 

 tubes accompanying the blood-vessels to every organ, and like 

 them ramifying till they cease to be visible under the most 

 powerful microscope, are kept distended during the most lively 

 movements of the little animals, and the necessary gaseous 

 circulation maintained, wholly, we may presume, by the agency 

 of diffusion. 



In regard to the terms of the law of diffusion : " The dif- 

 fusion, or spontaneous intermixture of two gases in contact, is 

 effected by an interchange in position of indefinitely minute 

 volumes of the gases." My experiments, published on a former 

 occasion, on the diffusion of mixed gases (Quarterly Journal 

 of Science, Sept. 1829), afford the first demonstration of the 

 fact, that diffusion takes place between the ultimate particles 

 of gases, and not between sensible masses, and therefore that 

 diffusion cannot be the result of accident. For, in the case of 

 a mixture of two gases escaping from a receiver into the at- 

 mosphere, by apertures of 0'12 and 0*07 inch in diameter, it 

 was not so much of the mixture which left the receiver in a 

 given time, but a certain proportion of each of the mixed gases, 

 independently of the other, corresponding to its individual 

 diffusiveness. The same separation of mixed gases occurred 

 in diffusion through the pores of stucco, or the fissure of a 

 cracked jar. 



" Which volumes are not necessarily of equal magnitude, 

 being, in the case of each gas, inversely proportional to the 

 square root of the density of that gas." This may be demon- 

 strated, when different gases communicate by very narrow 

 channels, or by very small apertures, and when inequality of 

 pressure is guarded against. In the case of a gas communi- 

 cating with the air by a wide aperture, on the other hand, al- 

 though the diffusion or intermixture takes place precisely in 

 the same way, still the result is different; for where a contrac- 

 tion takes place from the process of diffusion, the air flows in 

 mechanical lv through the aperture, wholly unresisted, and 



