94 Zinc Desilverization. 



ferred to No. 5, wliere the liquation is completed. All the lead 

 in Nos. 3 and 4 is then put back into Nos. 1 and 2, ready to 

 receive the second addition of zinc. The skimmings from the 

 2d, 3d, and 4th additions of zinc are not liqnated, but are used 

 over again. The amount of labor required is one man to each 

 kettle. The kettle is left until it is full, and is then fired up 

 and partially liquated, which takes about an hour. The kettle 

 must not be heated too hot in this liquation, for there would 

 be danger of oxidizing the zinc, in which case the silver would 

 go back to the lead. The lead separated in liquation is put 

 back into the large kettle, No. 1, before the second addition of 

 zinc. 



At Mansfield, all the skimmings except the first, which con- 

 tains copper and may contain gold, are ladled into the middle 

 kettle, which is kept heated, and are liquated at once, the lead 

 flowing into No. 3. The lead which collects there is put back 

 into No. 1 with the next charge of lead. At Cheltenham, the 

 zinc skimmings are taken from kettle No. 1, and liquated in 

 No. 2. While the second addition of zinc is being made, the 

 liquated lead is removed to No. 3. The six tons in No. 3 are 

 put back into No. 1, after the second addition of zinc. 



The lead remaining in the kettle after the first skimming 

 should not contain more than 20 oz. The zinc for the second 

 and third skimmings is not liquated, but used in the next opera- 

 tions. The skimming is made into the adjacent kettle. After 

 making an assay of the melted lead, to ascertain what is re- 

 quired, the next addition of zinc is made, and the skimming 

 continued about the same time. After the second skimming, 

 there should not be more than 10 to 15 oz. of silver remaining. 

 An addition is made, if the assay shows it to be necessary. The 

 last two charges are placed partly on top of the melted lead and 

 partly in the cage. It is then stirred for three-quarters of an 

 hour and left to cool down. The skimmings are liquated as 

 before. The lead contains from one to one and a half ounces of 

 silver. A new addition of zinc of about 100 lbs. is made. 



At Cheltenham, there is not more than one-sixth of an ounce 

 of silver remaining when the lead is tajDped into the refining 

 furnace. Frequently, the last skimmngs are too poor in silver 

 to admit of treating. They are put to one side, and form 



