88 Zinc DesiJverization. 



so often that, at the Germaiiia Works, holes are now bored in the 

 angles of the bottom and sides of the pan, so that the lead cannot 

 collect. The flowing lead warns the men, before any serious 

 accident has happened, that it is time to make repairs. These 

 furnaces should all be placed at the highest point of the works, 

 so that the lead and other products may descend by gravity from 

 one furnace to the other. 



The usual charge at the Germania and Cheltenham Avorks is 

 from 2:2 to 24 tons, de]3i;nding on the purity of the lead. In the 

 works of the Pennsylvania Lead Co., at Mansfield Valle}', they 

 sometimes charge as much as 25 to 26 tons, the charge deiDending 

 on the quantity of crasses that the lead makes. It is ahvays made 

 at Cheltenham so as to produce about 20 tons at the end of the 

 operation, or a quantity sufficient to completely fill one kettle. 

 When the furnace is hot, the whole charge melts in about two 

 hours. It remains in the furnace from 6 to 18 or even 24 hours, 

 depending on the work in the kettles, which must be kept full. 

 During this time it is kept at a low heat, and air is allowed to 

 have free access to the surface of the metal. 



The operation of softening consists in melting at a very low 

 temperature, the object of which is to separate the copper by 

 liquation, as it is much less fusible thiin lead. The scums con- 

 taining the copper are drawn with a tool made of birch wood, so as 

 not to contaminate the lead, as would be the case if an iron tool 

 was used. It is always necessary to endeavor to remove all the 

 copper, whether gold is present or not. The gases in the fur- 

 nace are oxidizing, and crasses containing the oxides of the 

 foreign metals rise to the surface. At the end of three hours 

 the temperature is raised to a dull red heat. The bath is 

 kept for twelve to fifteen hours if necessary, at the same tem- 

 perature, and frequently rabbled to bring the impurities to the 

 surface. If the lead contains from 3 to 4 per cent, of imj)urities, 

 the crasses are only drawn as they form, but if more impure, a 

 steam-jet blast is discharged directly into the bath to produce the 

 oxidation, and the crasses removed several times; but if the lead 

 is moderately pure, the crasses are drawn but once, which will 

 generally be at the end of six to seven hours. The first 

 crasses will amount to from 1.5 per cent, to 2.5 per cent, 

 of the charge, and are taken off at the end of from 5 to 7 



