1887.] 



On the Electrodeposition of Alloys, fyc. 



387 



in progress in the laboratory of the Chemical Institute of the 

 University of Bonn, and we anticipate that the result will be the 

 preparation of bodies having the general formula R'OPCl 4 . 



XII. " Note on the Electrodeposition of Alloys and on the 

 Electromotive Forces of Metals in Cyanide Solutions." By 

 Silvanus P. Thompson, D.Sc, B.A. Communicated by 

 Professor G. Carey Foster, F.R.S. Received May 12, 

 1887. 



It is known that the electrodeposition of such alloys as brass, 

 bronze, and German silver is not practicable from mixed solutions of 

 ithe sulphates or chlorides of the constituent metals, but can be 

 accomplished by using cyanide solutions or neutral solutions con- 

 taining cyanide of potassium in excess, thereby apparently departing 

 from the law of Berzelius that out of a solution of mixed metals the 

 least electropositive metal is deposited first. 



To ascertain the cause of these facts the author has investigated — 



(a.) The electromotive forces of a number of metals in aqueous 

 solutions of cyanide of potassium. 



(6.) The dependence of these electromotive forces, in particular those 

 of copper and zinc, upon the degree of concentration of the solution. 



(c.) The variation of the electromotive forces of copper and zinc in 

 a standard solution of cyanide of potassium at varying temperatures. 



(d.) The electromotive forces of zinc and copper in a " brassing " 

 solution consisting of the mixed cyanides of zinc and copper, having 

 excess of cyanide of potassium present, and their variation at different 

 temperatures. 



It is found that the effect of higher concentration of the cyanide 

 solutions is invariably to increase the electromotive force of copper 

 more than it increases that of zinc. 



In a cold dilute solution of cyanide of potassium the electromotive 

 force of zinc against carbon is 1*158 volt, while that of copper against 

 ■carbon is 0*948 volt, or zinc is 0*210 volt higher than copper. In a 

 boiling saturated solution of cyanide of potassium, the electromotive 

 force of zinc against carbon is 0*768 volt, and that of copper 

 against carbon is 1*300 volt; or copper is 0*532 volt higher than 

 zinc. 



It is therefore possible to construct a voltaic battery containing one 

 metal only, namely copper, and one electrolyte only, namely an aqueous 

 solution of cyanide of potassium, kept hot at the anode and cold at 

 the cathode of the cell. 



In cyanide solutions containing about the following number of 



