812 



SILVER 



back on the silver ; 3, to prevent the escape of the water that must be thrown on the 

 silver at the end of the process. 



When the argentiferous litharge, collected in the above small magazine, is to be 

 removed, it is let out in the form of a jet, by the dexterous use of the iron hook. 



Lastly, after twenty hours, the silver cake is seen to be well formed, and nearly 

 circular. The moment for stopping the fire and the bellows is indicated by the sudden 

 disappearance of the coloured particles of oxide of lead, which, in the latter moments 

 of oxidation, undulate with extreme rapidity over the slightly convex surface of the 

 silver-bath, moving from the centre to the circumference. The phenomenon of their 

 total disappearance is called the lightning, or brightening (Blick). Whenever this 

 occurs, the plate of silver being perfectly clean, there is introduced into the furnace 

 by the door q, iv wooden spout, along which water, previously heated, is carefully 

 poured on tho silver. 



The cupellation of 84 quintals of argentiferous lead takes in general eighteen or 

 twenty hours. The promptitude of the operation depends on the degree of purity of 

 the leads employed, and on the address of the operator, with whom also lies tho 

 economy of fuel. A good workman completes the cupellation of 84 quintals with 

 300 billets, each equivalent to a cubic foot and ^ths of wood (Hartz measure) ; others 

 consume 400 billets, or more. In general, the cupellation of 100 quintals of lead, 

 executed at the rate of 84 quintal charges, occasions a consumption of 790 cubic feet 

 of resinous wood-billets. 



The products of the charge are as follow: 



1. Silver, holding in 100 marcs, 7 marcs and 3 loths of alloy . 24 to 30 marcs. 



2. Pure litharge, containing from 88 to 90 per cent, of lead . 50 60 quintals. 



3. Impure litharge, holding a little silver . . . 2 6 



4. Skimmings of the cupellation 4 8 



5. Floor of the furnace impregnated with litharge . . . 22 30 



The marc is 7 oz. 2 dwts. 4 grs. English troy; and the loth is half an ounce. 16 

 loths make a marc. 100 Ibs. Cologne are equal to 103 Ibs. avoirdupois ; and the above 

 quintal contains 116 Cologne Ibs. 



The loss of lead inevitable by this operation is estimated at 4 parts in 100. It has 

 been diminished as much as possible in the Frankenscharn works of tho Hartz, by 

 leading the smoke into long flues, where the lead- fumes are condensed into a metallic 

 soot. 



Reduction of the litharge. This is sometimes executed in a slag-hearth, with tho 

 aid of wood-charcoal. 



The following is the series of operations : 



1. The fusion of the schlich ; 2, the roasting of the matts under a shed, and their 

 treatment by four successive smoltings ; 3, the treatment of the resulting black cop- 

 per ; 4, the liquation ; 5, the reliquation (ressuage) ; 6, the refining of the copper ; 7, 

 the cupellation of the silver ; 8, the reduction of the litharge into lead. The fifth and 

 sixth processes are carried on at the smelting-works of Altenau. 



The buildings are shown at A, u, c, and the impelling stream of water at D (fy. 

 1803) : the upper figure being the elevation ; the lower, the plan of the works. 



a, is a melting furnace, with n cylinder bellows behind it ; b, c, d, furnaces similar 

 to the preceding, with wooden bellows, such as./fy. 1804 ; c, is a furnace for the same 



