Decompositions hy a Single Pair of Plates, 41 



compositions were effected at a:, and occasionally, indeed ge- 

 nerally, a galvanometer was introduced into the circuit at^: 

 its place only is here given, the circle at g having no refer- 

 ence to the size of the instrument. Various arrangements 

 were made at ^, according to the kind of decomposition to be 

 effected. If a drop of liquid was to be acted upon, the two 

 ends were merely dipped into it; if a solution contained in the 

 pores of paper was to be decomposed, one of the extremities 

 was connected with a platina plate supporting the paper, whilst 

 the other extremity rested on the paper, e, fig. 12 : or some- 

 times, as with sulphate of soda, a plate of platina sustained 

 two portions of paper, one of the ends of a and c resting upon 

 each piece, <r, fig. 14-. The darts represent the direction of 

 the electric current (66T.). 



900. Solution of iodide of 'potassium^ being placed in moist- 

 ened paper at the interruption of the circuit at jr, was readily 

 decomposed. Iodine was evolved at the anode, and alkali at 

 the cathode, of the decomposing body. 



901. Protochloride of tin, when fused and placed at x, was 

 also readily decomposed, yielding perchloride of tin at the 

 anode {119.\ and tin at the cathode, 



902. Fused chloride of silver, placed at x, was also easily 

 decomposed; chlorine was evolved at the anode, and brilliant 

 metallic silver, either in films upon the surface of the liquid, 

 or in crystals beneath, evolved at the cathode, 



903. Water acidulated with sulphuric acid, solution of 

 muriatic acid, solution of sulphate of soda, fused nitre, and 

 the fused chloride and iodide of lead were not decomposed by 

 this single pair of plates, excited only by dilute sulphuric acid. 



904'. These experiments give abundant proofs that a single 

 pair of plates can electrolyze bodies and separate their ele- 

 ments. They also show in a beautiful manner the direct re- 

 lation and opposition of the chemical affinities concerned at 

 the two points of action. In those cases where the sum of 

 the opposing affinities at x was sufficiently beneath the sum 

 of the acting affinities in v, decomposition took place ; but in 

 those cases where they rose higher, decomposition was effec- 

 tually resisted and the current ceased to pass (891.). 



905. It is, however, evident, that the sum of acting affinities 

 in V may be increased by using other fluids than dilute sul- 

 phuric acid, in which latter case, as I believe, it is merely the 

 affinity of the zinc for the oxygen already combined with hy- 

 drogen in the water that is exerted in producing the electric 

 current (919.): and when the affinities are so increased, the 

 view I am supporting leads to the conclusion, that bodies 

 which resisted in the preceding experiments would then be 

 decomposed, because of the increased difference between their 



Third Series, Vol.6. No. 31. Jan. 1835. G 



