74 Mr. Graham's Experimental Researches 



sure, gives room for the professor to explain. If you should 

 think this description worth inserting in your Journal, you 

 will oblige 



Yours respectfully, 



Robert Greenhow. 



A short Account of Experimental Researches on the Diffusion 

 of Gases through each other, and their Separation by mecha- 

 nical means. By Thomas Graham, AJM., F.R.S.E., Lec- 

 turer on Chemistry, Glasgow. 



Fruitful as the miscibility of the gases has been in interesting 

 speculations, the experimental information we possess on the 

 subject amounts to little more than the well established fact, 

 that gases of a different nature, when brought into contact, do 

 not arrange themselves according to their density, the heaviest 

 undermost, and the lightest uppermost, but they spontaneously 

 diffuse, mutually and equably, through each other, and so re- 

 main in an intimate state of mixture for any length of time. 

 The beautiful illustrations of Mr. Dalton, by which this law 

 was first developed, have rendered it familiar to everyone. The 

 subsequent experiments of Berthollet were made with uncom- 

 mon care, and in most favourable circumstances, yet it is diffi- 

 cult to draw more from them than the same general fact ; 

 unless perhaps that hydrogen is much more penetrating and 

 diffusive than any of the other gases*. It is sufficiently 

 evident, however, from Berthollet's experiments, that, in cases 

 of gaseous mixture which are exactly similar, corresponding 

 results may be expected, or that the diffusion is not accidental, 

 but subject to fixed laws. 



In the prosecution of further inquiry into the laws of the 

 diffusion or miscibility of gases, much use was made of a 



* Berthollet's experimental paper is contained in the Mem. d'Arcueil, 

 vol. i. p. 463 ; but the whole experiments are given in a tabular form in 

 Dr. Thomson's System, vol. iii. p. 33. 



