METALLURGICAL METHODS AT BROKEN HILL. 293 
made out on the basis of the assays which were obtained from 
the samples, every little item being brought into account each 
week to the last fraction of a penny, to get at the cost per ton of 
ore treated. These latter were correct enough, but the statement 
of the recovery of the silver and lead was not worth the paper it 
was written on, inasmuch as the basis of the whole thing, the assay 
of the ore, was the result of incorrect sampling. The samples were 
just as likely to show a greater value in the ore than it contained, 
or vice versa. Hence you would see that for one week the total 
extraction of lead was 70 per cent., silver, 120 per cent. The next 
week the figures would show a recovery of, lead, 47 per cent., silver, 
65 per cent. These discrepancies can only be attributed to the 
incorrect method of sampling. Apparently more silver was re- 
covered in the first instance than was in the ore, showing immedi- 
ately the valuelessness of the whole return. <A reliable statement 
of the extraction of silver and lead from Broken Hill furnaces 
generally is not to be obtained, but my opinion is that about 90 
per cent. to 92 per cent. of silver and 65 per cent. to 70 per cent. 
of the lead actually in the ore were recovered in marketable pro- 
ducts. The loss in slag was great, because the proportion of slag 
made to ore smelted was from 1} to 14 to 1, due to the silicious 
character of the ore. The average lead assay of the ore smelted in 
later years was not more than 15 per cent., and the average lead 
assay of the slags was about 4 per cent. If 14 tons of slag were 
made for each ton of ore smelted, the loss of lead must have been 
5 units out of the 15 units of lead in the ore, or 33 per cent. Other 
losses of lead take place in fumes and escaping flue dust, but are not 
so extensive as has been assumed. ‘The flue dust recovered is equal 
to from 0°80 per cent. to 1$ percent. on the weight of ore charged 
into the furnace. 
The following determinations give some idea of its principal 
constituents :— 
Flue Dust. 
Head, per cent.” ....16.0.00005 25 37 23 30 30 
IIWENMIO ZA are Sitisioeesddcocivcns 20 24 30 21 21 
FANG, PEV-CENE, s4.6)checccsecass 11 13 10°8 10°7 10 
The usual method adopted with this material is to moisten it 
with water and return it to the furnace. Necessarily a great 
percentage of it rapidly dries, and is carried out of the furnace by 
the strength of the blast back into the flues. 
No particular effort has been made to make a better collection 
of the flue dust, the flues being designed simply to carry off the 
smoke and fumes, and accordingly the lighter particles of dust 
(and these are always rich in lead) are carried off by the force of 
the draught into the stack, and fall outside on the surrounding 
