

THE 



LONDON and EDINBURGH 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[THIRD SERIES.] 



MAY 1834. 



LIV. Observations on Mr. Graham's Law of the Diffusion of 

 Gases. By Thomas S. Thomson, Esq.* 



r |' , HE object of Mr. Graham's paper is to establish, with 

 -*- numerical exactness, the following law of the diffusion of 

 gases : "The diffusion or spontaneous intermixture of two gases 

 in contact, is effected by an interchange in position of indefi- 

 nitely minute volumes of the gases, which volumes are not ne- 

 cessarily of equal magnitude, being, in the case of each gas, in- 

 versely proportional to the square root of the density of that 

 gas." For the detail of Mr. Graham's beautiful experiments 

 I shall refer the reader to the original paperf, contenting my- 

 self with giving a brief sketch of his method of operating, and 

 of the results of his observations, which undoubtedly amount 

 to a rigorous demonstration of the above law. Mr. Graham 

 subjects to examination the diffusive powers of different gases; 

 but as the principle of operating is the same in all cases, it 

 will be sufficient to consider his first and most fully developed 

 example of the diffusion of hydrogen gas into the atmosphere. 

 The instrument used for this purpose consists of a bulb of 

 glass, two inches in diameter, blown on a tube of T %thS of an 

 inch. The upper extremity of the tube, above the bulb, was 

 closed with a stucco plug of plaster of Pari?, the porous me- 

 dium adopted for the exhibition of the mutual diffusion of the 

 gases. The instrument being filled with hydrogen gas, with 

 due precautions, is placed in a glass jar, with water in 

 the bottom ; and in proportion as the water rises in the tube 



* Communicated by the Author. 



t Edinb. Phil. Trans.: and Lond. and Edinb. Phil. Mug., vol. ii. p. 175. 

 Third Series. Vol. 4. No. 23. May 1834. 2 T 



