388 



On the Electrodeposition of Alloys, fyc. [June 16,. 



grams of cyanide to the litre, the following were the electromotive 

 forces observed with a carbon cathode : — 



Solution containing per litre 



99 '4 grams. 



191 *4 grams. 



1 '18 grams. 



Zinc 1-520 



Copper 1-425 



Brass 1-400 



German surer . . 1 05 



Gold -885 



Silver 0-845 



Lead 0-64 



Iron 0*47 



Steel 0*44 



Platinum 27 



Carbon 



Metals at 18° C. 



Copper 1 *434 



Zinc 1-401 



Brass 1 -315 



German silver . . 0-936 



Gold 0-834 



Silver 0-810 



Lead "609 



Iron 0-181 



Steel 0*161 



Platinum 0*017 



Carbon 



Zinc 113 



Brass 0'58 



German silver ... "50 



Lead 0*44 



Copper 0*39 



Silver 0*39 



Gold 0-34 



Steel 0-30 



Iron 0-30 



Platinum 0*14 



Carbon 



Several of the metals exhibit maximum electromotive force at an 

 intermediate concentration. 



The following figures were obtained for zinc and copper in solutions 

 of cyanide of varying strengths at 17° C. : — 



Grams per litre. 



E.M.F. zinc. 



E.M.F. copper. 



Difference Z — C. 



2-9 



1-158 



0-948 



+ 0-210 



5 9 



1-167 



0-967 



+ 0-200 





1-184 



1-018 



+ 0-166 





1-221 



1-058 



+ 0-163 





1-269 



1-130 



+ 0-139 



95-5 



1-303 



1-220 



+ -080 





1-355 



1-360 



-0-005 



In a mixed solution of cyanides of zinc and copper there is a 

 neutral condition where the electromotive forces of zinc and copper 

 are equal, and this neutral condition varies with the relative amounts 

 of metal present, with the concentration of the solution, and with the 

 temperature. The neutral temperature for a solution of given con- 

 centration is lowered by adding cyanide of potassium, and is raised 

 by adding ammonia. The neutral point, however, is not well 

 defined, the behaviour of copper being very uncertain ; in general 

 the electromotive force of clean copper in a cyanide solution rises, in 

 some cases as much as 0*06 volt, in a few seconds after immersion,, 

 but is rapidly though temporarily lowered on agitation. 



