283 



gives a great number of examples ; but although the processes for 

 that purpose are easy, the difficulty consists wholly in findir.g the 

 proper method of treating each individual case. The author hopes to 

 lay before the Society, on a future occasion, an account of the prin- 

 ciples on which this branch of analysis is founded. 



Mr. Faraday's Eighth Series of Experimental Researches in Elec- 

 tricity was resumed and read in continuation. 



June 19, 1834. 

 FRANCIS BAILY, Esq., Vice-President, in the Chair. 



The reading of Mr. Faraday's Eighth Series of Experimental Re- 

 searches in Electricity was resumed and concluded. 



This series is devoted to an investigation of the source, character 

 and conditions of the electricity of the voltaic instrument, and is di- 

 vided into five parts. In the first part, simple voltaic circles are con- 

 sidered ; and at the outset, the great question of" whether the elec- 

 tricity is due to contact or chemical action r" is investigated and de- 

 cided* by apparently very conclusive evidence in favour of the latter. 

 One principal experiment in favour of this decision is the following : 

 A plate of zinc and a plate ofplatina were prepared; one end of each 

 of these was put into a vessel containing a little dilute sulphuric acid 

 or sulpho-nitric acid, and between the other ends was placed a piece 

 of bibulous paper moistened in a solution of iodide of potassium : the 

 two plates did not touch each other anywhere, but still the action of 

 the end at the one extremity was able to induce the electro-chemical 

 decomposition of the iodide of potassium at the other. That this de- 

 composition was due to the chemical action of the acid was proved by- 

 removing the latter ; for then the decomposition ceased. It was also 

 farther proved by the appearance of the iodine against the platina ; 

 for it went there in consequence of the passage of a current (induced 

 by the action of the acid) having the opposite direction to that which 

 the solution of iodide would have produced had it been the only ex- 

 citing body, and metallic contact had been allowed. 



The opposition of the chemical affinities at the two places where 

 the acid and the solution of the iodide are placed, is shown when the 

 metal plates are allowed to touch each other in the middle ; for then 

 two opposite electric currents are produced, but that occasioned by 

 the acid is the stronger. This opposition is farther shown in the 

 manner in which the weaker set of affinities are overcome by the 

 stronger (that is, those of the iodide and zinc by those of the acid and 

 zinc) ; and this dependence and relation of the two explains at once 

 the value of metallic contact ; for if the solution of iodide of potassium 

 be placed between platina and platina, one of those pieces of metal 

 touching the zinc which is immersed in the acid, then the solution of 

 iodide does not tend to throw an electric current into circulation, 

 because it exerts no chemical action in either direction ; and therefore 



