296 PROCEEDINGS OF SECTION B. 
The zinc-silver-lead crusts obtained from the second zincing of 
the softened lead in the kettle are also liquated to free them from 
any lead which they may have gathered, and the lead liquated out 
is returned to the zinc kettle. The dry product left behind 
is put into graphite and clay retorts with a percentage of carbon, 
and highly heated. The zinc distils off, and some 50 to 60 per 
cent. of it is recovered in metallic form in the retort condenser, 
the balance being recovered as an oxide known as “ blue powder,” 
some being lost in fume. As scon as the retorting operation is 
finished, which takes twelve to fifteen hours, the zinc condenser is 
removed, and the rich silver-lead bullion, of some 5,000 oz. to 
the ton, is ladled out into moulds. The style of furnace is a 
modification of the Latham retort furnace, and is not so handy as 
the Du-Faur tilting retort furnace, which pours out the lead instead 
of having it ladled out. The retort is thoroughly cleaned, care 
being used because the heat has softened it considerably, and, 
after cleaning, some carbon in the form of charcoal is thrown in 
to keep the little lead left in the retort from forming litharge, 
which would rapidly destroy the retort. The latter is then ready 
for a fresh charge of the zinc-silver-lead crust. A retort Jasts from 
twelve to thirty charges, and then is replaced by a new one. 
The rich lead bullion obtained from the retort is then taken to 
the refining or cupelling furnace. Here it is melted into a test or 
cupel (made of fire-clay, cement, and ground limestone, beaten in 
with a rammer into a cast-iron supporting-frame, being allowed 
four or five weeks to dry before being used), and as soon as the 
lead is hot enough an air blast is turned on to the face of the 
bright red lead, and the operation of refining for silver commences. 
The action of the air is to oxidise the metallic lead into litharge, 
and this flows off in a stream more or less high with silver. As 
the level of the charge falls, fresh bullion is fed in through a small 
hole, but when the charge is almost pure silver, and the cupel 
quite full, thisis stopped. At the finishing part of the cupellation, 
the most beautiful iridescent colours traverse the face of the silver, © 
due to the last traces of lead passing off. The temperature of the 
furnace has to be kept very high to keep the mass of silver molten. 
As the last signs of lead disappear the process is finished. The 
molten silver is then poured into moulds or granulated in water, 
and finally refined in large crucibles with nitrate of soda or potash, 
from whence it is poured into moulds holding about 1,000 oz. of 
fine silver each. The grade of the silver is about 996 fine, the 
remaining four parts usually consist of copper with the very 
smallest trace of lead. 
The gold silver-lead-zine crust got in the first operation of zinc- 
ing in the first kettle, goes through exactly the same process as 
does the second crust just described. After it is made into bars 
it is, however, further treated for the separation of the gold and 
