Source of Electricity in the Voltaic Apparatus. 127 



when zinc, platina, and dilute sulphuric acid are used, it is 

 the union of the zinc with the oxygen of the water which de- 

 termines the current; and though the acid is essential to the 

 removal of the oxide so formed, in order that another portion 

 of zinc may act on another portion of water, it does not, by com- 

 bination with that oxide, produce any sensible portion of the 

 current of electricity which circulates ; for the quantity of elec- 

 tricity is dependent upon the quantity of zinc oxidized, and in 

 definite proportion to it : its intensity is in proportion to the in- 

 tensity of the chemical affinity of the zinc for the oxygen under 

 the circumstances, and is scarcely, if at all, affected by the use 

 of either strong or weak acid (908. )• 



920. Again, if zinc, platina, and muriatic acid are used, the 

 electricity appears to be dependent upon the affinity of the 

 zinc for the chlorine, and to be circulated in exact proportion 

 to the number of particles of zinc and chlorine which unite, 

 being in fact an equivalent to them. 



921. But in considering this oxidation, or other direct ac- 

 tion upon the metal itself, as the cause and source of the 

 electric current, it is of the utmost importance to observe that 

 the oxygen or other body must be in a peculiar condition, 

 namely, in the state of combination', and not only so, but li- 

 mited still further, to such a state of combination, and in such 

 proportions as will constitute an electrolyte (823.). A pair of 

 zinc and platina plates cannot be so arranged in oxygen gas 

 as to f)roduce a current of electricity, or act as a voltaic cir- 

 cle, even though the temperature may be raised so highly as 

 to cause oxidation of the zinc far more rapidly than if the pair 

 of plates were plunged into dilute sulphuric acid, for the oxy- 

 gen is not part of an electrolyte, and cannot therefore con- 

 duct the forces onwards by decomposition, or even as metals 

 do by itself. Or if its gaseous state embarrass the minds of 

 some, then liquid chlorine may be taken. It does not excite 

 a current of electricity through the two plates by combining 

 with the zinc, for its particles cannot transfer the electricity 

 active at the point of combination, across to the platina. It 

 is not a conductor of itself, like the metals ; nor is it an elec- 

 trolyte, so as to be capable of conduction during decomposi- 

 tion, and hence there is simple chemical action at the spot, 

 and no electric current *. 



* I do not mean to affirm tiiat no traces of electricity ever appear in 

 such cases. What I mean is that no electricity is evolved in any way, due 

 or related to the causes which excite voltaic electricity, or proportionate 

 to them. That which does appear occasionally is the smallest possible 

 fraction of that which the acting matter could produce if arranged so as to 

 act voltaically, probably not the one hundred thousandth, or even the 

 millionth part, and is very probably altogether different in its source. 



