CHAP, xi.] ELECTRICITY AND MAGNETISM. 



387 



their appearance at the electrodes only, are salient 

 facts. 



The hypothesis put forward in 1805 by Grotthuss 

 serves fairly, when stated in accordance with modern 

 terms, to explain these facts. Grotthuss supposes that, 

 when two metal plates at different potentials are placed 

 in "a cell, the first effect produced in the liquid is that 

 the molecules of the liquid arrange themselves in in- 

 numerable chains, in which every molecule has its 

 constituent atoms pointing in a certain direction ; the 

 atom of electropositive substance being attracted toward 

 the kathode, and the fellow atom of electronegative 

 substance being attracted toward the anode. (This 

 assumes the constituent atoms grouped in the molecule 

 to retain their individual electric properties.) The 

 diagram of Fig. i 56 shows, in the case of Hydrochloric 



Fig. 156. 



Acid, a row of molecules i, i, at first distributed at 

 random, and secondly (as at 2, 2,) grouped in a chain 

 as described. The action which Grotthuss then sup- 

 poses to take place is that an interchange of partners 

 goes on between the separate atoms all along the line, 



