240 



J. M. Lewis : 





sJ3 



SVrwXi^v*. 



- z- 



Fig. 2. 



(After Lehfeldt) 



The sum of the differences thus shown is 1.1 volt, which is the 

 known voltage of the Daniell cell. 



Concentration Battery 



Knowing the laws which govern the production of e.m.f. it 

 is possible to set up an arrangement known as a " concentration 

 cell," in which both electrodes consist of the same metal. These- 

 are made to dip into vessels containing a solution of a salt of 

 the metal at differing concentrations. Electrical connection is 

 made between the vessels by suitable means. The arrangement 

 shown below may be employed, where a suitably bent glass tube 

 contains the solutions, means being employed at c to prevent 

 rapid diffusion. Let the electrodes at a, and b, for example, 

 consist of silver, and the solutions be of some salt of that metal. 



If, now, the electrodes be connected with a galvanometer, an 

 e.m.f. will become apparent, which, as far as the external circuit 

 is concerned, is directed toward that electrode which dips into the 

 more dilute solution. 



