PROCEEDINGS 



OF THE 



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On the relative velocities of diffusion in aqueous solution 

 of rubidium and caesium chlorides. By G. R. Mines, B.A., 

 Fellow of Sidney Sussex College. (From the Physiological 

 Laboratory, Cambridge.) 



[Bead 24 January 1910.] 



In the course of some physiological work with the chlorides of 

 the alkali metals certain results led me to inquire as to the 

 relative rates of diffusion of these salts in aqueous solution. While 

 many data are available regarding the salts of lithium, sodium, 

 and potassium, I have been unable to find any figures relating 

 the two rarer members, rubidium and caesium, to the rest of the 

 group. 



The method I have used offers certain advantages in the 

 simplicity of the manipulations involved and the small quantity 

 of material needed for a determination. I therefore publish this 

 short account in the hope that it may be of use to others. 

 Graham* showed nearly fifty years ago that sodium chloride 

 diffuses in a gelatine jelly as quickly as in distilled water. 

 Voigtlanderf found that the rate of diffusion of salts in agar- 

 agar was unaffected by changes in the strength of the jelly 



from l7o-57o- 



My plan has been to keep a solution of salt of known concen- 

 tration in contact with a free surface of jelly, and to ascertain the 

 rate of progress of the salt by measurement of the electrical 

 conductivity at a fixed distance below the surface of the jelly. 



* Thomas Graham, Phil. Trans. 1861, p. 183. 



+ Voigtlander, Zeitschr. Physik. Ghem, ill, 1889, p. 316. 



VOL. XV. PT. V. 25 



