Page:Popular Science Monthly Volume 19.djvu/259

Rh 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 polarization of the electrodes as a symptom of previous electrolysis. Another sign of electrolytic conduction is, that liquids brought between two different metals produce an electro-motive 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 conduction with the galvanometer, and even these only at temperatures near to their melting-point. It is nearly impossible to shelter the quadrants of a delicate electrometer 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 substances or adhering 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 electrolyte. 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 startling to everybody who knows the mighty power of chemical 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 attraction which the poles of a battery of two Daniell's cells show. Nevertheless, this little apparatus is able to decompose 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 voltameter, give scarcely any visible traces of gases. At present we can give definite numbers. The result is, that the electricity of one milligramme of water, separated and communicated to two balls one kilometre distant, would produce an attraction between them equal to the weight of twenty-five thousand kilos.

The total force exerted by the attraction of an electrified body upon another charged with opposite electricity is always proportional