aN ELECTRICITY IN MOTION. 675 



solids nor of fluids, and they must be of three different kinds, possessed of 

 different powers of conducting electricity; but whether the difference of 

 their conducting powers is of any other consequence than as it accompanies 

 different chemical properties, is hitherto undetermined. Of these three 

 substances, two must possess a power of acting mutually on each other, while 

 the other appears to serve principally for making a separate connexion between 

 them: and this action may be of two kinds, or perhaps of more ; the one is 

 oxidation, or the combination of a metal or an inflammable substance with a 

 portion of oxygen derived from water or from an acid, the other sulfuration, 

 or a combination with the sulfur contained in a solution of an alkaline sulfuret. 



We may represent the effects of all galvanic combinations, by considering the 

 oxidation as producing positive electricity in the acting liquid, and the sulfuration 

 as producing negative electricity, and by imagining that this electricity is always 

 communicated to the best conductor of the other substances concerned, so as 

 to produce a circulation in the direction thus determined. For example, when 

 two wires of zinc and silver, touching each other, are separately immersed in an 

 acid, the acid, becoming positively electrical, imparts its electricity to the silver, 

 and hence it flows back into the zinc: when the ends of a piece of charcoal 

 are dipped into water and into an acid, connected together by a small tube, 

 the acid, becoming positive, sends its superfluous fluid through the charcoal 

 into the water; and if a wire of copper be dipped into water and a solution 

 of alkaline sulfuret, connected with each other, the sulfuret, becoming nega- 

 tive, will draw the fluid from the copper on which it acts; and in all these 

 cases the direction of the current is truly determined, as it may be shown 

 hy composing a battery of a number of alternations of this kind, and either 

 examining the state of its different parts by electrical tests, or connecting 

 wires with its extremities, which, when immersed into a portion of water, 

 will exhibit the production of oxygen gas where they emit the electric fluid, 

 and of hydrogen where they receive it. These processes of oxidation and 

 of sulfuration may be opposed to each other, or they may be combined in 

 various ways, the sum or difference of the separate actions being obtained by 

 their union; thus it usually happens that both the metals employed are oxid- 

 able in some degree, and the oxidation, which takes place at the surface of the 

 better conductor, tends to impede the Avhole effect, perhaps by impeding 

 the passage of the fluid through the surface. The most oxidable of the 



