52 Mr. T. S. Thomson on the Diffusion of Gases. 



a minute to a day or more, according to the quantity of the 

 gavSes and the freedom of communication." 



Dr. Dalton proceeds further to discuss the rationale of ihe 

 action, and the result was (to use his own words), " In the 

 autumn of 1801 I hit upon an idea which seemed to be ex- 

 actly calculated to explain the phfenomena of vapour ; it gave 

 rise to a great variety of experiments, upon which a series of 

 essays were founded, which were read before the Literary and 

 Philosophical Society of Manchester, and published in the 

 fifth volume of their Memoirs, 1802. 



" The distinguishing feature of the new theory was, that the 

 particles of one gas are not elastic or repulsive in regard to 

 the particles of another gas, but only to the particles of their 

 own kind." 



The immediate result of the publication of this view of the 

 mutual relations of mixed elastic fluids was, a discussion be- 

 tween Dr. Dalton, Mr. Murray, Mr. Gough, &c., which ter- 

 minated in leaving the subject of " diffusion " in a state of in- 

 decision. 



Mr. Graham took up the subject experimentally in 1825, 

 and ascertained the arithmetical law of the rate of diffusion, 

 which he thus expresses : — " The mathematical relation which 

 subsists between the diffusion, volume and the density of a gas 

 is expressed thus: 



diffusion volume = —r, 



where d represents the specific gravity of the gas." — Elements 

 of Chemistry, p. 72.* 



Mr. Graham's experiments were performed with great care, 

 and are of undoubted accuracy. In 1834, through the me- 

 dium of your valuable Magazine, I offered to the public some 

 remarks upon Mr. Graham's Law of the Diffusion of Gases, 

 endeavouring to reconcile Mr. Graham's facts with Mr. Dal- 

 ton's theory. Mr. Graham, in his Elements of Chemistry, 

 p. 75, thus notices my remarks : — " The law of the diffusion of 

 gases has on this account been viewed by my friend, Mr. T. S. 

 Thomson of Clitheroe, as a confirmation of Dr. Dalton's 

 theory, that gases are inelastic tov.'ards each other f. It must 

 be admitted that the ultimate result in diffiision is in strict 

 accordance with Dalton's law, but there are certain circum- 

 stances which make me hesitate in adopting it as a true re- 

 presentation of the phsenomenon, although it affords a con- 



* [On the law of the diffusion of gases we refer those who may pursue 

 the subject to Faraday's Experimental Researches in Electricity, Series vi, 

 par. 659. — Edit.] 



t Phil. Mag. S. 3. vol. iv. p. 321. 



