102 *Zlnc Desih'erization. 



others being kept in reserve in case of accident or necessary 

 repairs. 



Tlie fuel used was at first coke, which was given up becavise 

 the clinkers attached themselves to the retorts. In trying to re- 

 move them, the men'constantly broke the retorts by poking them, 

 while the cinder was soft, with iron tools, through the opening 

 for the introduction of fuel. Petroleum was then used with 

 great success, but the furnaces were finally abandoned for Faber 

 du Faur's furnace. 



The charge of 380 lbs. of zinc skimmings is introduced with 

 a spoon, immediately after the preceding operation is finished. 

 Two small scoopfuls of small charcoal are added at the same 

 time. The heat is so high that most of the charge melts at once. 

 An allonge, e, Fig. 9, 2 feet long, 4 inches in diameter at the 

 small, and 9 inches at the large end, is then put on and luted. 

 It is partially filled with charcoal. The allonge is covered on the 

 outside with sheet-iron, to jn'otect it against accident. It is sup- 

 ported on a cast-iron shelf, /, which can be raised or low- 

 ered at will by detaching a bar underneath it. This is 

 necessary to prevent the weight of the allonge breaking the re- 

 tort while the furnace is working. When the charge is drawn, 

 it must be let down so as not to interfere with the syphon. Fig. 

 10. 



The zinc commences to distil in about three-quarters of an 

 hour. Metallic zinc collects in the condenser. Some blue pow- 

 der and o.xide of zinc also form there. I'lie object of the 

 charcoal is to prevent the formation of oxide as much as pos- 

 sible. The zinc is allowed to accumulate, and is drawn from 

 time to time with a spoon into a mould placed in front of the 

 allonge. When the zinc is nearly distilled, a small piece of 

 wood is put into the retort to make a reducing atmosphere, to 

 prevent the formation of litharge, Avhich would pierce the sides, 

 and to form a current of gas from the inside to the outside of 

 the retort. The charge of rich silver lead, remaining after the 

 zinc is distilled, is drawn with the iron syphon. Fig. 10 — which 

 must be heated before it is introduced — and the lead is cast into 

 pigs ready for cupellation. 



Before the invention of the Steitz syphon, the neck of the re- 

 tort, which was necessarily built into the masonry of the furnace. 



