[ 379 ] 



LXV. Observations upon the Decomposition of the Double 



Cyanides by an Electric Current. By Mr. James Napier*. 

 ipOR some time past I have considered that there were phae- 

 -*■ nomena presenting themselves in my daily operations of 

 depositing metals by a galvanic current of sufficient scientific 

 interest to warrant their being collected and given in detail to 

 this Society. In anticipation of doing so, I carefully noted 

 down what seemed most interesting, in hopes of being pre- 

 pared to give them as a short series of papers next session : 

 I say series, because so far as I have observed, all the double 

 cyanides, even when they have the same constitution, do not 

 comport themselves in the same manner, giving rise to differ- 

 ent results, all of which could not be given in the compass of 

 one paper. But these anticipations have been somewhat 

 changed by the circumstance, that a paper upon a similar 

 subject has lately been read by Prof Daniell to the Royal 

 Society. The facts brought forward in that paper are as yet 

 unknown to me, further than that certain metals are not trans- 

 ferred from one pole of the galvanic circuit to the other by 

 means of the current ; this is one of the facts to which my at- 

 tention has been directed for a long time, and 1 am induced 

 to bring this paper forward to-night, not with any desire of 

 sharing the honours due to the discovery, but in hopes that, 

 while noticing this in connection with other facts which 1 hope 

 to have the honour of laying before you next session, I may 

 have a little more claim upon your attention, from its having 

 been original on my part. 



The present paper is more particularly devoted to cyanide 

 of potassium and silver, — a double salt of general use in elec- 

 tro-metallurgical operations, and one of a class eminently fitted 

 to exhibit some of the most interesting facts in connection with 

 electrical decompositions. It is known to those engaged in 

 the deposition of silver from this salt, that if it be used pure, 

 or in a neutral state, with a positive electrode of silver, no 

 deposition of metal is obtained unless a battery of great power 

 be used; but if a little cyanide of potassium be added to the 

 solution, a very weak current of electricity is sufficient to give 

 a deposit. The usual explanation of these facts is, that pure 

 or neutral cyanide of potassium and silver is a bad conductor 

 of electricity, and that the addition of free cyanide of potas- 

 sium gives it conducting power, either as being the conduct- 

 ing medium, or by a kind of disposing influence which it im- 

 parts to the salt decomposed. That one fluid imparts such an 



* Communicated by the Chemical Society; having been read May 6, 

 1844. 



