METALLURGICAL METHODS AT BROKEN HILL. 295 
temperature falls below a certain point, the zine, which has alloyed 
with the bulk of the gold present some silver and lead, begins to 
separate out exactlyas cream rises on a dish of milk, and is skimmed 
off and kept for further treatment. The remaining lead and silver 
are then heated up to redness once more, and about 14 per cent. 
of zinc added. The cooling processis repeated, and the zinc-silver- 
lead crust once again skimmed off. This “skimming” or “crust,” 
known as the “silver crust,” in contradistinction to the first one, 
called the “ gold crust,” is kept apart from the latter. The zincing 
operation may have to be repeated once or twice before the lead 
is desilverised ; usually half an ounce left in is considered low 
enough. It is then siphoned off into a lower kettle by means of 
a Steitz siphon, made of ordinary 14 or 2 inch black iron pipe. 
This lower kettle has a movable hood ; and as soon as the tempera- 
ture of the lead has been raised sufficiently dry steam is forced 
into the lead to oxidise the zinc which has remained in from the 
preceding operation of zincing, and also to remove the last traces 
of impurities. When the lead which contains the zine is heated 
to redness it has the power of decomposing the steam, the zinc and 
some lead seizing on the oxygen of the steam to form oxides of 
their metals. These oxides gather on the surface of the lead and 
are skimmed off occasionally. Samples of the lead are taken from 
time to time, and the purity of the lead is judged by its colour and 
the ease with which it can be marked. Good soft lead is easily 
marked with the finger-nail. 
As soon as it is decided that the lead is purified, it is skimmed 
quite clean with wooden rakes, and then allowed to cool consider- 
ably, so that when it is cast into moulds it will set even, and be 
of a silvery-white colour. Moulded at a greater temperature a 
bluish appearance is assumed by the lead, due, probably, to a film 
of oxide forming. When cool enough it is syphoned off into moulds, 
and then is ready for sale in the market as “best refined lead.” 
The Proprietary refined lead is remarkably good, and commands as 
good if not a better price than the English refined lead. This is 
due in great degree to the small amount of impurity which the 
original bullion contained, and, secondly, to the care evidenced 
throughout the refining process. 
We have now to deal with the dross which was obtained at the 
commencement of the process. This is either sent direct to the 
blast furnaces to be smelted up with the charge, or else it is put 
into the liquating or sweating furnaces, where it is heated gently 
to expel any metallic lead which has clung to the actual dross. 
This lead runs out of the furnace into an outside kettle, separately 
fired, to keep the lead obtained in a molten state, and when enough 
has gathered it is moulded into bars, and returned with the next 
charge to the softening furnace. The dry liquated dross is then 
smelted in the blast furnaces with the ordinary ore charge. 
