452 DR. FARADAY'S EXPERIMENTAL RESEARCHES IN ELECTRICITY. 



showed that an electric current was passing, but there was no appearance of decom- 

 position at a, not even after a metallic communication at h was established. The expe- 

 riment was repeated several times, and I am led to conclude that in this case the cur- 

 rent has not intensity sufficient to cause the decomposition of the chloride of lead ; 

 and further, that, like water (974.), fused chloride of lead can conduct an electric 

 current having an intensity below that required to effect decomposition. 



979. Chloride of silver was then placed at a, fig. 15., instead of chloride of lead. 

 There was a very ready decomposition of the solution of iodide of potassium at h, and 

 when metallic contact was made there, very considerable deflection of the galvano- 

 meter needle at g. Platina also appeared to be dissolved at the anode of the fused 

 chloride at «, and there was every appearance of a decomposition having been effected 



there. 



980. A further proof of decomposition was obtained in the following manner. The 

 platina wires in the fused chloride at a were brought very near together (metallic 

 contact having been established at h), and left so ; the deflection at the galvanometer 

 indicated the passage of a current, feeble in its force, but constant. After a minute 

 or two, however, the needle would suddenly be violently affected, and indicate a cur- 

 rent as strong as if metallic contact had taken place at a. This I actually found to 

 be the case, for the silver reduced by the action of the current crystallized in long 

 delicate spiculse, and these at last completed the metallic communication ; and at the 

 same time that they transmitted a more powerful current than the fused chloride, 

 they proved that electro-chemical decomposition of that chloride had been going 

 on. Hence it appears, that the current excited by dilute sulphuric acid between zinc 

 and platina, has an intensity above that required to electrolyze the fused chloride of 

 silver when placed between platina electrodes, although it has not intensity enough 

 to decompose chloride of lead under the same circumstances. 



981. A drop of water placed at a instead of the fused chlorides, showed as in the 

 former case (970.), that it could conduct a current unable to decompose it, for de- 

 composition of the solution of iodide at h occurred after some time. But its con- 

 ducting power was much below that of the fused chloride of lead (978.). 



982. Fused nitre at a conducted much better than water : I was unable to decide 

 with certainty whether it was electrolyzed, but I incline to think not, for there was 

 no discoloration against the platina at the cathode. If sulpho-nitric acid had been 

 used in the exciting vessel, both the nitre and the chloride of lead would have suffered 

 decomposition like the water (906.). 



983. The results thus supplied of conduction without decomposition, and the ne- 

 cessity of a certain electrolytic intensity for the separation of the ions of differ- 

 ent electrolytes, are immediately connected with the experiments and results given 

 in § 10. of the Fourth Series of these Researches (418. 423. 444. 449.). But it will 

 require a more exact knowledge of the nature of intensity, both as regards the first 

 origin of the electric current, and also the manner in which it may be reduced. 



