OF SILVER BETWEEN ZINC AND LEAD. 13 



and kept in it for about one hour, when most of the zinc 

 separated out as scum. The scum was separated by filtering off 

 the melted mass through closely packed glass wool under the 

 pressure of about ten inches of mercury. The scum and the 

 filtrate were analysed separately. The former contained most of 

 the silver, and not a small quantity of lead which adhered to 

 the particles of zinc-silver alloy. The latter contained such 

 minute quantities of silver that its exact determination was 

 difficult. This was accomplished by dissolving the mass in nitric 

 acid and concentrating the solution (when the greater part of 

 the lead separated out as nitrate and was removed) and then 

 titrating it with a dilute solution of thiocyanate. 



In three experiments the concentration of silver in solid 

 zinc varied from Ü.171 to 0.2339^ and the partition coefficient 

 from 1300 to o700. The discrepancy is no doubt due to the 

 contamination of the liquid phase by solid particles which passed 

 through the glass wool. But whether the highest value be near 

 the truth or not can not be decided ; for in this case the deter- 

 mination of the silver retained in the melted lead is very 

 uncertain. Yet it is quite clear that the partition coefficient of 

 silver between solid zinc and liquid lead is enormously large, 

 and this fact explains the practical completeness with which the 

 lead is desilverised in practice. 



I very much regret that I must leave this investigation in 

 this unsatisfactory form ; for the time at my disposal is nearly 

 over, and I can neither repeat nor extend the determinations. 



