41G 



SMELTING PBOCESSES 



'Poling," ok the Production of Type Metal. 



The Abstrioh obtained by scraping oil' the scum which forms in the Lead Refining Process after the men! 

 mechanical impurities of the first fifteen minutes of melting have been removed, is divided into two parts. (1) The 

 Abstrich which is formed during the first half of the time. (2) Abstrich. (Abstrich consists, in general terms, of 

 arseniates and antimoniates of oxide of lead-) 



The dcsilverization of the tst abstrich consists in molting it in a refining furnace, whereby the raw lead which 

 has been mechanically mixed with the abstrich is liquated, while the abstrich itself, remaining unmelted, floats on 

 the surface and can bo scraped through the open door of the furnace into iron pans. 



The lead which is thus separated is drawn off into a hemi-spherical kettle with a long nozzle, and is poured by 

 means of this into a series of radiating lines of iron moulds. The desilverized abstrich is melted in cupola furnace 

 with coke to a load tolerably rich in antimony. In order to get rid of the copper still more completely and to obtain 

 a product in the form desired for commerce, it is again melted gradually in a Pattluson kettle, and the lead is entirely 

 freed from copper by successive formations of "Schlicker," aided by stirring with a pole of green wood. The heat 

 decomposes the wood, and the gases and steam which rise through the molten metal occasion a still further agitation 

 of the particles and bring every part to the surface. In place of poles an iron cage filled with faggots of green wood, 

 and fastened to the end of a long screw fitting into a nut which is supported by two iron rods to uprights in the 

 masonry around the kettle, is employed. Two arms like those of a letter press allow the cage to bo raised and 

 lowered, and at the same time turned round and round in the molten mass. 



CuPELLATION. — This operation consists in a further manipulation of the Kaw Lead from flic Lead, and Load 

 Matt Processes after its refining and concentration. The plau is to separate flic lead and silver by an oxidizing, 

 melting in eontact with flame, on a covered hearth and with tho aid of an artificial draught. Tho air admitted 

 through the tuyeres oxidizes the lead, and the melted oxide being specifically lighter than pure load floats on top and 

 is easily separated from it. In this way the silver, which is with difficulty oxidized, is obtained comparatively free 

 from impurities, and containing from 00 to 05 p.c. of silver. 



The construction of a, cupellation furnace being generally understood needs no mention hero. 



After the melting of the lead the lire in tho furnace is increased. 



Tho fuel consists of split faggots. About 5 to 5} cords are consumed in cupelling 350—380 cwt. of lead in 75 to 

 80 hours, counted from the time the lead was put in the furnace. At the same time tho fire is increased, the blast is 

 increased also. Supposing the lead not, to have been entirely refined, an abstrioh is first formed on tho surface of the 

 molten lead, and is drawn out with the scraper (a small round piece of Wood, inches in length and 1 to 2 inches in 

 diameter, fastened crosswise to flic end of a, long iron bar). 



After these impurities have been removed, tho real litharge formation begins, and the molten oxide is run oil" by 

 means of little cuts made in the dam of clay by the working door. An iron mould in the shape of a rectangular 

 prism lacking 8 sides is placed with one open side against the wall of the furnace immediately under the working 

 door, and in filling, this mould cools, and the litharge is transported in largo blocks of from 10 to 17 centners to an 

 adjoining room, which are broken in pieces in order to separate tho red litharge from the yellow. 



These arc to be distinguished : — 



1. Yellow litharge, with about 0.04 to 0.05 per cent, of silver, is smelted in the cupola furnace. 



2. lied UtJuirge, with very little silver, is found in the interior of the lumps of lil barge obtained from tho cupil- 

 lation. 



:i. Separation litharge, which is produced just before the silver blicks ; i. e. the last portion of the load separates 

 from the silver, and the latter suddenly assumes a bright, clear surface. 



As the surface of the molten lead becomes continually lower, it is necessary to cut the groove for the melted 

 litharge deeper and deeper, and great skill and experience are required to prevent the rich, lead escaping with the 

 litharge. The absorption of the liquid lead into tho solo of the hearth gives rise to the formation of bubbles of car- 

 bonic acid from flic calcareous mass of which it is composed, and this gives tho eupeller a means to guide him in running 

 oil the litharge. The groove is not cut till this border of bubbles is about two inches wide. After so much litharge 



