SCIENCE. 



with its electric equivalent or equivalents. At the sur- 

 face of the electrodes decomposition can take -place if 

 there is sufficient electromotive power, and then the 

 atoms give off their electric charges and become electri- 

 cally neutral. 



Now arises the question, Are all these relations be- 

 tween electricity and chemical combination limited to 

 that class of bodies which we know as electrolytes? In 

 order to produce a current of sufficient strength to collect 

 enough of the products of decomposition without produc- 

 ing too much heat in the electrolyte, the substance which 

 we try to decompose ought not to have too much resist- 

 ance against the current. But this resistance may be 

 very great, and the motion of the ions may be very slow, 

 so slow indeed that we should need to allow it to go on 

 for hundreds of years before we should be able to collect 

 even traces of the products of decomposition; neverthe- 

 less all the essential attributes of the process of elec- 

 trolysis could subsist. If you connect an electrified con- 

 ductor with one of the electrodes of a cell filled with oil 

 of turpentine, the other with the earth, ycu will find that 

 the electricity of the conductor is discharged unmistak- 

 ably more rapidly through the oil of turpentine than if 

 you take it away and fill the cell only with air. 



Also in this case we may observe polarisation of the 

 electrodes as a symptom of previous electrolysis. An- 

 other sign of electrolytic conduction is that liquids 

 brought between two different metals produce an elec- 

 tromotive force. This is never- done by metals of equal 

 temperature, or other conductors which, like metals, let 

 electricity pass without being decomposed. 



The same effect is also observed even with a great 

 many rigid bodies, although we have very few solid 

 bodies which allow us to observe this electrolytic con- 

 duction with the galvanometer, and even these only to 

 temperatures near to their melting-point. It is nearly 

 impossible to shelter the quadrants of a delicate elec- 

 trometer against being charged by the insulating bodies 

 by which they are supported. 



In all the cases which I have quoted one might suspect 

 that traces of humidity absorbed by the substance or ad- 

 hering to their surface were the electrolytes. I show 

 you therefore this little Daniell's cell, in which the 

 porous septum has been substituted by a thin stratum of 

 glass. Externally all is symmetrical at both poles ; there 

 is nothing in contact with the air but a closed surface 

 of glass, through which two wires of platinum penetrate. 

 The whole charges the electrometer exactly like a 

 Daniell's cell of very great resistance, and this it would 

 not do if the septum of glass did not behave like an elec- 

 trolyte. All these facts show that electrolytic conduction 

 is not at all limited to solutions of acids or salts. 



Hitherto we have studied the motions of ponderable 

 matter as well as of electricity, going on in an electrolyte. 

 Let us study now the forces which are able to produce 

 these motions. It has always appeared somewhat start- 

 ling to everybody who knows the mighty power of chem- 

 ical forces, the enormous quantity of heat and of 

 mechanical work which they are able to produce, and 

 who compares with it the exceedingly small electric at- 

 traction which the poles of a battery of two Daniell's cells 

 show. Nevertheless this little apparatus is able to de- 

 compose water. 



The quantity of electricity which can be conveyed by a 

 very small quantity of hydrogen, when measured by its 

 electrostatic forces, is exceedingly great. Faraday saw 

 this, and has endeavored in various ways to give at 

 least an approximate determination. The most powerful 

 batteries of Leyden jars, discharged through a volta- 

 meter, give scarcely any visible traces of gases. At 

 present we can give definite numbers. The result is that 

 the electricity of I m.grm. of water, separated and com- 

 municated to two balls, i kilometre distant, would pro- 

 duce an attraction between them, equal to the weight of 

 25,000 kilos, 



The total force exerted by the attraction of an electri- 

 fied body upon another charged with opposite electricity 

 is always proportional to the quantity of electricity con- 

 tained in the attracting as on the attracted body, and 

 therefore even the feeble electric tension of two Daniell's 

 elements, acting through an electrolytic cell upon the 

 enormous quantities of electricity with which the consti- 

 tuent ions of water are charged, is mighty enough to sep- 

 arate these elements and to keep them separated. 



We now turn to investigate what motions of the pon- 

 derable molecules require the action of these forces. Let 

 us begin with the case where the conducting liquid is 

 surrounded everywhere by insulated bodies. Then no 

 electricity can enter, none can go out through its surface, 

 but positive electricity can be driven to one side, negative 

 to the other, by the attracting and repelling forces of ex- 

 ternal electrified bodies. This process going on as well 

 in every metallic conductor is called "electrostatic induc- 

 tion." Liquid conductors behave quite like metals under 

 these conditions. Prof. Wullner 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 electromotive forces going down to less than 1-100 

 Daniell produce perfect electrical equilibrium in the in- 

 terior 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 Dan- 

 iell's cell, the electromotive force of which is insufficient 

 to decompose the electrolyte. Under this condition the 

 ions carried to the electrodes cannot give off their elec- 

 tric charges. The whole apparatus behaves, as was first 

 accentuated by Sir W. Thomson, like a condenser of 

 enormous capacity. 



Observing the polarizing and depolarizing currents in 

 a cell containing two electrodes of platinum, hermetically 

 sealed and freed of all air, we can observe these pheno- 

 mena with the most feeble electromotive forces of 

 1-1000 Daniell, and I found that down to this limit the 

 capacity of the platinum surfaces proved to be constant. 

 By taking greater surfaces ot 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 opposite ions 

 together, and require any amount of work to be van- 

 quished, an inferior limit to the electromotive 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 dis- 

 covered, and we must conclude, therefore, that no other 

 force resists 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 electrical charge we find that the electrical forces 

 of the battery meet with a powerful resistance, the over- 

 powering of which requires a good deal of work to be 

 done. Usually the ions, losing their electric charges, are 

 separated at the same time from the liquid ; some of them 

 are evolved as gases, others are deposited as rigid strata 

 on the surface of the electrodes, like galvanoplastic cop- 

 per. But the union of two constituents having powerful 

 affinity to form a chemical compound, as you know very 

 well, produces always a great amount of heat, and heat is 

 equivalent to work. On the contrary, decomposition of 

 the compound substances requires work, because it 

 restores the energy of the chemical forces, which has 

 been spent by the act of combination. 



Metals uniting with oxygen or halogens produce heat 

 in the same way, some of them, like potassium, sodium, 

 zinc, even more heat than an equivalent quantity of hy- 

 drogen ; less oxidisible metals, like copper, silver, pla- 

 tinum, less. We find, therefore, that heat is generated 

 when zinc drives'copper out of its combination with the 



