880 Mr. Napier on the Decomposition of the 



influence to another I need hardly say is absurd ; and it is well 

 known that the conducting medium in any fluid is the sub- 

 stance decomposed. It is certain that the free cyanide of po- 

 tassium, which is added with the idea of giving conduction, is 

 not decomposed. The question then occurs, what part does 

 it take in these operations? I have observed that, whilst en- 

 deavouring to deposit from the neutral salt, the positive elec- 

 trode, although brightly polished previous to being put into 

 the solution, instantly assumed a chalky aspect. It appeared 

 probable that this was owing to the formation of cyanide of 

 silver, which, being insoluble in the neutral salt, olastructed 

 the current of electricity by its coating. To prove this, I 

 placed a quantity of crystallized cyanide of potassium and 

 silver, dissolved in water, in a long shallow vessel, kept 

 the two electrodes at a considerable distance apart, and con- 

 nected them with a battery of 20 pairs of plates for forty- 

 eight hours: there was a considerable deposit of silver upon 

 the cathode, the solution around it was strongly alkaline, and 

 the precipitate formed by adding a drop of nitrate of silver 

 was easily redissolved ; whilst that part of the solution round 

 the anode remained neutral, the anode was covered over with 

 a grayish-white powder, which being washed exhibited every 

 character of cyanide of silver. The use of the addition of free 

 cyanide of potassium to the silver solution was now evident, 

 not to facilitate the passage of the current, but to dissolve the 

 cyanide of silver formed upon the electrode. To make this 

 the more certain, I dissolved 2 equivalents of the cyanide of 

 potassium, or twice 200 grains, and put them into a vessel di- 

 vided by a porous diaphragm : into the division in which the 

 anode was placed I put an equivalent of cyanide of potassium, 

 or 6Q grains ; the electrodes being previously weighed, were 

 connected with a battery of 4 pairs, deposition immediately 

 took place; the current was continued for twelve hours; to- 

 wards the end of the operation hydrogen gas began to be 

 evolved from the cathode, and a powder to appear upon the 

 anode; the experiment was then stopped ; the anode being 

 washed and weighed indicated a loss of 108'7 grains; the so- 

 lution in which it was placed was neutral, and on being eva- 

 porated and fused yielded 214''3 grains of silver; the cathode 

 had gained 107'4 grains in weight; the solution in which it 

 was placed had a powerful alkaline reaction, smelled strongly 

 of hydrocyanic acid, and on being tested scarcely indicated the 

 presence of silver. This last circumstance attracted particular 

 attention, and induced me to repeat the experiment under 

 various modifications, also with gold, copper and zinc, all of 

 which gave similar results. 



