SOURCE OF ELECTRICITY IN THE VOLTAIC APPARATUS. 435 



919. When the circumstances connected with the production of electricity in the 

 ordinary voltaic circuit are examined and compared, it appears that the source of that 

 agent, always meaning the electricity which circulates and completes the current in 

 the voltaic apparatus, and gives that apparatus power and character (947. 996.), exists 

 in the chemical action which takes place directly between the metal and the body with 

 which it combines, and not at all in the subsequent action of the substance so pro- 

 duced with the acid present*. Thus, when zinc, platina, and dilute sulphuric acid are 

 used, it is the union of the zinc with the oxygen of the water which determines 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 combination with that oxide, produce any sensible portion of the current of elec- 

 tricity which circulates ; for the quantity of electricity is dependent upon the quantity 

 of zinc oxidized, and in definite proportion to it : its intensity is in proportion to the 

 intensity 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 action 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 limited still further, to such a state of com- 

 bination, 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 produce a current 

 of electricity, or act as a voltaic circle, 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 oxygen is not part of an electrolyte, 

 and cannot therefore conduct 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 electrolyte, so as to be capable of conduction during decomposi- 

 tion, and hence there is simple chemical action at the spot, and no electric current-f'. 



* WoLLASTON, Philosophical Transactions, 1801, p. 427. 



1 1 do not mean to affirm that 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. 



