106 Zinc Dcsilvenzation. 



shorter time, fo that it is iilvvays desirable to soften tlie metal 

 before ti'eating it with zinc. At Chicago, OAving to careless 

 management in not carefully cleaning the inside, and outside of 

 the retorts, they lasted for only 9 to 10 operations. 



When a new retort is necessary, the furntice must be allowed 

 to cool down, the grate-bars are taken out, and the retort intro- 

 duced from the bottom. 



The Hues leading to the chimney, at Manslield, are made with 

 flaring sides at the bottom, for 18 inches in hight. The sides of 

 the upper part arc vertical and are rounded at the top. Every 

 seven feet, at the bottom, a partition is put in, one-third of the 

 whole hight of the flue. In the brick flues, which are Ave feet 

 high, the partitions are put in every eighteen inches, and further 

 apart. In both the iron and brick flues the most dust is 

 caught near the furnace. Tlie dust settles by gravity in these 

 catches, and as there can be no velocity there, owing to the par- 

 titions, it remains there. Short flues of this construction have 

 been found to be miicli more effective than large condensing 

 chambers. 



The amount of zinc in the skimmings is very variable. If it 

 contained 35 per cent, of zinc, 20 per cent, will be recovei-ed as 

 metallic zinc, and 10 per cent, as oxide, which is afterwards re- 

 duced, and 5 per cent. Avill be lost. This last is either in the 

 lead or volatilized in the dift'erent operations. If the skimmings 

 contained only 10 per cent., 3 per cent, will be recovered as 

 metallic zinc, 5 per cent, will be recovered as oxide, and 3 per 

 cent, will be lost. No lead or silver is found in the distilled zinc. 



This furnace is a very great improvement on all those in which 

 the retort is fixed, as it necessitates the lenst amount of Avork 

 being done on it, and at the same time allows perfect manipula- 

 tion of the furnace. 



The following table, prepared by Mr. E. F. Eukicii, gives the account of 

 two charges in Faber du Faur's furnace, at Manstield : — * 



* Mining Commissioners' Report for 1873. 



