4 PROCESS FOR REFINIXG LEAD, 



litharge is re- *hc test until the hollow part be nearly filled, the opera- 

 movcdfromthe tor closes the feeding aperture, and increases the heat of 

 lead, put into *^® furnace until the surface of the lead is well covered 

 the test, &c. with litharge ; he then removes the door from the feeding 

 hole, and with an iron rod, which has one end bent down 

 at right angles about 3 inches and made flat or chissel- 

 shaped, scrapes the small gutter or channel o until the 

 litharge just flows into it , the blast from a pair of double 

 bellows is then directed from tlie back part over the sur- 

 . face of the test, the litharge is urged forward, and flows 

 from the gutter upon the floor of the refinery ; the ope- 

 ration now goes forward, gradually adding lead as the 

 escape of litharge makes necessary, until the gutter is so 

 worn down that the test does not contain more than an 

 inch in depth of lead, the blast is then taken off, the 

 gutter filled up with moistened ashes, and a fresh one 

 made on the other side the breast ; the test is again tilled, 

 though not so full as at first, and the operation carried on 

 until this gutter also is worn down and the test contain 

 from about 50 to 70 lbs. of alloy. This quantity is run 

 into an iron pot, and set by until a sufficient number of 

 pieces have been collected to make it worth while to take 

 off^ a plate of pure silver from them. 

 Alloy left be- '^^^ quantity of alloy left in the working oflf each test 

 hind. ' must depend in a great measure upon the quantity of sil- 



ver it by estimation is supposed to contain. A sufficient 

 quantity of lead should always be left in the alloy to make 

 it fuse easily in the iron pot. 

 Some litharge When the test is removed from the furnace and broken 

 soaks into the yp^ the litharge" will be found to have penetrated to an 

 inconsiderable but equal depth in the ashes; that part 

 not impregnated with litharge may be pulverised, mixed 

 with fresh ashes, ^nd 4gain used for another test. 

 The silver is The operation of taking off" the silver pure differs in 

 refined by oii- no respect from the foregoing, only more care is observed 

 BtilfcontaTns/^ ^" *^^ Working, not to sijfler the escape of any metallic 

 particles with the litharge, as that would occasion con- 

 siderable waste of.silvcr. As the process advances, and 

 the' proportion of silver to lead, increases, the litharge 

 assumes a darker colour, a greater heat becomes neces- 

 sary, and at last tlie brightening takes place; the interior 

 2 of 



