90 ■ Zinc DesUverizaiion. 



kettles. The contract is always made to hare the kettles cast 

 bottom down. 



At the Germanja Works, the tapping is very inconveniently 

 done throngh an iron pipe, 40 feet long and 5 inches in diameter, 

 with holes cut into it at intervals to facilitate the removal of 

 dross which might clog the pipe. It is necessary to heat the 

 whole length of this pipe, to prevent the lead from chilling. 

 This is done with coals suspended in pieces of sheet-iron under 

 it ; but there must be a shield between the fire and the pipe to 

 keep the latter from cracking. 



As the softening-furnace is always above the kettles, it would 

 seem easy to run the lead into the kettles by gravity, in a trough 

 of some kind. The distance, however, would have to be short, 

 or there would be danger of the lead becoming too cool. At the 

 Pennsylvania Lead Works, there are three of these softening- 

 furnaces, each one having three desilverizing kettles. At the 

 Germania Works, there are two, with five kettles each ; at 

 Cheltenham, one, with three kettles. 



The crasses from tlie softening-furnace are first liquated, to 

 remove any excess of lead they may contain. At the Germania 

 Works, this was formerly done in a reverberatory liquation-furnace 

 of peculiar construction. The hearth was 3 feet deep ; 18 inches 

 above it a set of grate-bars was placed; the skimmings were placed 

 on these, and the carcasses remained there while the lead flowed 

 through. The first crasses drawn contain most of the copper. 

 They are always kept sejjarate from the others. The carcasses 

 from the liquation-furnace are put through the blast-furnace 

 at the end of a campaign, with jjyrites, in order to concentrate 

 the copper in a matte. They produce some hard lead, which 

 is treated with the lead of the other crasses. 



At the Germania Works, a copper matte is produced which 

 contains 20 per cent, of copper, 20 to 25 oz. of silver, and a 

 slag containing 10 oz. of silver. The matte is concentrated to 

 40 per cent, of copper, and is sold. 



The assays of three of these concentrated samples contained — 



No. 1. No. 2. No. 3. 



Silver, 113.54 oz. 88. oz. 9466 oz. 



Gold, 1.18 1.03 1.02 



From the dust-chambers connected with this furnace, only a 



