342 Dr. Faraday's Experimental Researches in Electricity. 



between the metal and acid is allowed in the first to what 

 would occur in the second. 



1009. When the extreme plates of the arrangement just 

 described, fig. 18, are connected metallically through the 

 galvanometer g, then the whole represents a battery consisting 

 of two pairs of zinc and platina plates urging a current for- 

 ward, which has, however, to decompose water unassisted by 

 any direct chemical affinity before it can be transmitted across 

 the cell iii, and therefore before it can circulate. This de- 

 composition of water, which is opposed to the passage of the 

 current, may as a matter of convenience be considered as 

 taking place either against the surfaces of the two platina 

 plates which constitute the electrodes in the cell iii, or against 

 the two surfaces of that platina plate which separates the cells 

 ii and iii, fig. 19, from each other. It is evident that if that 

 plate were away, the battery would consist of two pairs of 

 plates and two cells, arranged in the most favourable position 

 for the production of a current. The platina plate therefore, 

 which being introduced as at x, has oxygen evolved at one 

 surface and hydrogen at the other (that is, if the decomposing 

 current passes), may be considered as the cause of any ob- 

 struction arising from the decomposition of water by the elec- 

 trolytic action of the current; and I have usually called it 

 the interposed plate. 



1010. In order to simplify the conditions, dilute sulphuric 

 acid was first used in all the cells, and platina for the inter- 

 posed plates ; for then the initial intensity of the current which 

 tends to be formed is constant, being due to the power which 

 zinc has of decomposing water; and the opposing force of de- 

 composition is also constant, the elements of the water being 

 unassisted in their separation at the interposed plates by any 

 affinity or secondary action at the electrodes (744.), arising 

 either from the nature of the plate itself or the surrounding 

 fluid. 



1011. When only one voltaic pair of zinc and platina plates 

 were [was] used, the current of electricity was entirely stopped 

 to all practical purposes by interposing one platina plate, fig. 

 20, i. e. by requiring of the current that it should decompose 

 water, and evolve both its elements, before it should pass. 

 This consequence is in perfect accordance with the views be- 

 fore given (910. 917. 973.). For as the whole result depends 

 upon the opposition of forces at the places of electric excite- 

 ment and electro-decomposition, and as water is the substance 

 to be decomposed at both before the current can move, it is 

 not to be expected that the zinc should have such powerful 

 attraction for the oxygen, as not only to be able to take it from 



