1 74 Dr. Faraday's Experimetital Researches in Electricity, 



of potassium when introduced into the circuit in the form of 

 apparatus already described (880.), fig. 1. Here no action of 

 acid or alkali on the oxide formed from the lead could supply 

 the electricity: it was due solely to the oxidation of the 

 metal. 



946. There is no point in electrical science which seems to 

 me of more importance than the state of the metals and the 

 electrolytic conductor in a simple voltaic circuit before a7id at 

 the moment when metallic contact is first completed. If 

 clearly understood, I feel no doubt it would supply us with a 

 direct key to the laws under which the great variety of voltaic 

 excitements, direct and incidental, occur, and open out va- 

 rious new fields of research for our investigation. 



947. We seem to have the power of deciding to a certain 

 extent in numerous cases of chemical affinity, (as of zinc with 

 the oxygen of water, &c. &c.) which of two modes of action of 

 the attractive power shall be exerted (996.). In the one mode 

 we can transfer the power onwards, and make it produce else- 

 where its equivalent of action (867. 917.); in the other, it is 

 not transferred, but exerted wholly at the spot. The first is 

 the case of volta-electric excitation, the other ordinary chemi- 

 cal affinity; but both are chemical actions and due to one 

 force or principle. 



948. The general circumstances of the former mode occur 

 in all instances of voltaic currents, but may be considered as 

 in their perfect condition, and then free from those of the se- 

 cond mode, in some only of the cases ; as in those of plates of 

 zinc and platina in solution of potassa, or of amalgamated 

 zinc and platina in dilute sulphuric acid. 



949. Assuming it sufficiently proved, by the preceding ex- 

 periments and considerations, that the electro-motive action 

 depends, when zinc, platina, and dilute sulphuric acid are 

 used, upon the mutual affinity of the metal zinc and the oxy- 

 gen of the water (921. 924.), it would appear that the metal, 

 when alone, has not power enough, under the circumstances, 

 to take the oxygen and expel the hydrogen from the combina- 

 tion ; for, in fact, no such action takes place. But it would 

 also appear that it has power so far to act, by its attraction 

 for the oxygen of the particles in contact with it, as to place 

 the similar forces already active between these and the other 

 particles of oxygen and the particles of hydrogen in the water, 

 in a peculiar state of tension or polarity, and probably also at 

 the same time to throw those of its own particles which are in 

 contact with the water into a similar but opposed state. 

 Whilst this state is retained, no further change occurs; but 

 when it is relieved, by completion of" the circuit, in which 



