92 



Zinc Desilverizution. 



for every 0.2 oz. of silver. This will usually amount to betAveen 

 250 and 550 lbs. to each kettle. In general, with ores varying 

 from 100 to 300 oz. of silver, 1.4 to 3 per cent, of zinc is added. 

 It is not all added at once, but sometimes in two and sometimes 

 in three additions, the proportions being determined by assay in 

 each case. These additions should be so regulated as to make the 

 richest possible alloy at first, in order to shorten the process as 

 much as practicable, and to diminish the liability to oxidation 

 when it is liquated. 



At Mansfield, the lead contains from 50 to 400 ounces of sil- 

 ver. To this, from one and one-tenth to two per cent, of zinc 

 is added, in four additions. The zinc is thrown in on the top 

 of the melted lead, and then is stirred into it by a tool, five by 

 ten inches, with a long handle. After the first addition, it is 

 stirred for half an hour. The scum is then allowed to rise and 

 cool, until there is a ring of 31 inches around the outside. It is 

 then skimmed with a perforated skimmer until the lead is 

 bright. The other additions are made in the same way. 



At the Germania works, for a charge containing 60 oz. of 

 silver and 3 oz. of gold, 1.85 per cent, of zinc was added. For a 

 charge containing 140 oz. of silver, and 3.8 oz. of gold, 2.3 per 

 cent, of zinc was used. Of this, 0.5 was added in the first addi- 

 tion, 0.4 in the second, and 0.1 in the third. For a charge 

 containing 350 oz., 2.6 per cent, of zinc was used. 



The following Table, prepared by Mr. A. V. Weisse, of the Germania 

 Works, gives the amount of zinc used in two charges. 



Example. 



Total weight 



of softened 



lead. 



Silver contained in 



grammes to the 



1000 kilos. 



Gold contained in 



grammes to the 



1000 kilos. 



Zinc used. 



No. 1. 

 No. 2. 



402.442 lbs. 



402.224 



4300. 

 4256.7 



125. 

 127 45 



2.3 per ct. 

 2.6 per ct. 



To be sure of lead at 5 grammes from lead containing 1,000 

 to 1,400 ounces of silver, at least 1^ per cent, of zinc must be 



