f)24 Prof. H. F. Weber's Researches on 



methods of investigation ; and I succeeded in discovering one 

 which affords the possibility of making within a feio hours an 

 extremely delicate trial of the correctness of Fields elementary 

 law of diffusion, and determining within any fraction of an 

 hour the quantity of the constant of diffusion. By this proce- 

 dure the influences of the temperature and concentration upon 

 the course of the diffusion can be investigated in a way as 

 much more exact as it is more convenient. It is as follows : — 

 A plane, circular, amalgamated zinc plate forms the bottom 

 of a shallow glass cylinder about 12 centims. wide. Upon three 

 places at the margin of this plate bits of a plane-parallel hard- 

 gum plate, each of 0*52 centim. thickness, are put, which have 

 to support a second amalgamated zinc plate exactly similar to 

 the lower one. The slight interspace between the two parallel 

 zinc plates is filled up with a solution of zinc sulphate of any 

 degree of concentration : in the following experiments concen- 

 trations between 0*20 and 0*38 were employed. Wires are 

 soldered to the two zinc plates in order to send a galvanic 

 current through the system consisting of the plates and the 

 the solution, or to insert it in the circuit of a galvanometer. If 

 before the experiment the two zinc plates are rubbed down 

 and then rinsed with solution of zinc sulphate of the same 

 concentration as that which is to fill the interspace between 

 them, the system of plates and solution shows itself absolutely 

 without any difference of potential when both plates have the 

 same temperature ; only when the two have not exactly the 

 same temperature does a slight deflection appear on a sensitive 

 galvanometer in the circuit of which the system is inserted. 

 Hereupon a galvanic current, maintained constant, is sent 

 through the combination thus prepared, entering through the 

 lower plate and issuing through the upper one. By the 

 migration of the ions the salt-solution becomes more concen- 

 trated in the boundary layer at the lower zinc plate (the 

 anode), and more dilute in the boundary layer at the upper 

 (the cathode). These alterations of concentration of the 

 boundary layers are proportional to the intensity and the dura- 

 tion of the current. Now, as soon as through the action of 

 the galvanic current these alterations of concentration com- 

 mence, the diffusion-current develops itself, which tends to 

 counterbalance the action of the galvanic current. By the 

 cooperation of the galvanic and the diffusion-current a 

 stationary condition of the distribution of concentration 

 between the two electrodes is striven after, in which exactly 



as much salt is carried in unit time bv the diffusion < c > 



( from J 



