86 Zinc Desilverization. 



furnace is lighted all around, and is bright at the tuyeres, they 

 are withdrawn and plugged up. The first charge consists of 

 one scoop of puddle cinder of about twenty pounds, and ten 

 scoops of coke of about eighteen pounds each. The next charges 

 are made with only half the normal charge, until tlie furnace is 

 two-thirds full; the last one-third is put in at tlie normal charge. 

 When the furnace is full, the blast is turned on, and the furnace 

 starts at once with a dark top and in a normal condition. A 

 campaign lasts thirteen months. The concentration of the co])- 

 per matte takes ^jlace on the top of the melted lead. They are 

 enriched up to not less than 40 per cent. They contain 25 to 40 

 ounces of silver, and are sold to Baltimore. 



The process of desilverization, as conducted in the works at 

 Cheltenham, Salt Lake, and Mansfield Valley, consists of — 



1. Softening the lead. 



2. Incorporation of the zinc and sejiaration of tlie zinc scum. 



3. Eefining the desilverized lead. 



4. Treatment of the zinc scum. 



The object of the desilverization, as performed in these works, 

 is to concentrate all the silver into a very small quantity of an 

 alloy of zinc and lead, so rich that the lead resulting from its dis- 

 tillation will contain 8 to 12 per cent, of silver, and to leave 

 behind in the kettles, lead which will contain not over 5 grammes 

 of silver to the 100 kilogrammes, and not more than 0^5 to 0,75 

 per cent. of zinc, and be pure enough to make white lead, and 

 hence command the highest market price. 



1. Softening the Lead. — As the argentiferous lead comes from 

 all sections of the country, and contains a number of impurities 

 in variable proportions, it must be refined or softened before it 

 can be desilverized. The furnace used for this purpose is called 

 the softening-furnace, in most of the works. At the Germania 

 Works it is called the A furnace. It is a large reverberatory, 

 with a cast or tank iron basin, into which the hearth is built. 



The object of this iron basin is to have a furnace so cool 

 that if the lead goes down into the hearth it will chill, or if 

 the furnace is very hot it will be caught. The larger the furnace 

 the better. Made of cast iron, its size is limited ; made of 



