248 THE POPULAR SCIENCE MONTHLY. 



to the quantity of electricity contained in the attracting as on the at- 

 tracted body, and therefore even the feeble electric tension of two 

 Daniell's elements, acting through an electrolytic cell upon the enor- 

 mous quantities of electricity with which the constituent ions of water 

 are charged, is mighty enough to separate these elements and to keep 

 them separated. 



We now turn to investigate what motions of the ponderable mole- 

 cules require the action of these forces. Let us begin with the, case 

 where the conducting liquid is surrounded everywhere by insulating 

 bodies. Then no electricity can enter, none can go out through its 

 surface, but ^^ositive electricity can be driven to one side, negative to 

 the other, by the attracting and repelling forces of external electrified 

 bodies. This process, going on as well in every metallic conductor, 

 is called " electrostatic induction." Liquid conductors behave quite like 

 metals under these conditions. Professor Wiillner has proved that 

 even our best insulators, exposed to electric forces for a long time, are 

 charged at last quite in the same way as metals would be charged in 

 an instant. There can be no doubt that even electro-motive forces 

 going down to less than yi^ I^aniell produce perfect electrical equilib- 

 rium in the interior of an electrolytic liquid. 



Another somewhat modified instance of the same effects is afforded 

 by a voltametric cell containing two electrodes of platinum, which are 

 connected with a Daniell's cell, the electro-motive force of which is 

 insufticient to decompose the electrolyte. Under this condition the 

 ions carried to the electrodes can not give off their electric charges. 

 The whole apparatus behaves, as was first accentuated by Sir W. Thom- 

 son, like a condenser of enormous capacity. 



Observing the polarizing and depolarizing currents in a cell con- 

 taining two electrodes of platinum, hermetically sealed and freed of all 

 air, Ave can observe these phenomena with the most feeble electro-mo- 

 tive forces of yoVo L^aniell, and I found that down to this limit the 

 capacity of the platinum surfaces proved to be constant. By taking 

 greater surfaces of platinum I suppose it will be possible to reach a 

 limit much lower than that. If any chemical force existed besides 

 that of the electrical charges, which could bind all the pairs of oppo- 

 site ions together, and require any amount of work to be vanquished, 

 an inferior limit to the electro-motive forces ought to exist, which forces 

 are able to attract the atoms to the electrodes and to charge these as 

 condensers. No phenomenon indicating such a limit -has as yet been 

 discovered, and we must conclude, therefore, that no other force re- 

 sists the motions of the ions through the interior of the liquid than the 

 mutual attractions of their electric charges. 



On the contrary, as soon as an ion is to be separated from its elec- 

 trical charge we find that the electrical forces of the battery meet with 

 a powerful resistance, the overpowering of which requires a good deal 

 of work to be done. Usually the ions, losing their electric charges, 



