METALLURGICAL METHODS AT BROKEN HILL. 301 
satisfactory solution of the difficulty is adding oxide of lime to the 
solution and precipitating the lead and silver in that way as oxide ; 
the bye-product of chloride of calcium can be Jet go to waste. It 
is a matter of expense only, for the reactions are perfectly satis- 
factory. 
AMALGAMATION, 
This process was discontinued some twelve months ago. The 
extraction of silver was very satisfactory, but the specific gravity 
of the ore was high enough to always interfere with the separation 
of the mercury in the settling pans, and you would see masses of 
manganic iron slime that were full of mercury in the finest state 
of division—of course carrying silver—with which nothing could be 
done, economically, to extract the locked-up mercury. It soon 
resolved itself into a matter of the cost of mercury ; but, if an ore 
of about 20 to 22 oz. of silver had been obtained steadily for the 
amalgamation work, there was no doubt of its superiority to the 
leaching plant ; because the loss remained the same, whether on 
14 oz. or on 20 oz. ore, a rule which did not act so well with the 
leaching. As the grade of ore necessary, low in lead, could not 
be obtained in large enough quantities to keep the whole of the 
plant going, it was stopped. Its capacity was about 1,000 tons 
weekly. There were 60 stamps erected, with a drop of 6 inches, 
weighing 850 lb. each, and 95 drops a minute. The remainder of 
the plant consisted of 24 grinding and 24 Howell amalgamating 
pans, each 4 feet 6 inches in diameter and 3 feet 4 inches deep— 
the first-named pans running 40 revolutions a minute, and the 
latter 75 to 80 revolutions. There were also 12 settling pans, 
running 14 revolutions a minute, each being 8 feet in diameter 
and 3 feet 6 inches deep, the whole of the pans being cast-iron. 
Towards the latter end of the operations it was found that blue- 
stone (sulphate of copper) was not necessary for the successful 
extraction of the silver in the amalgamating pans ; and it was not 
an uncommon thing to have the retorted bullion from this plant, 
after the use of the blue-stone stopped, running 996 to 999 fine in 
silver. 
CONCENTRATION. 
The first attempts at concentration were made on the low-grade 
carbonate ores. The evil day of sulphide treatment had not yet 
come. The ore sent to the concentration department was highly 
silicious, low in lead and silver ; and if the ore had been specially 
mined for the purpose of concentrating it, there is no necessity to 
hesitate over the fact that it was not a payable proposition. But, 
like the low-grade ores which are chloridised and leached, this 
ore had to be taken out, whatever use was made of it afterwards. 
The cost of mining it was borne by the smelting ore necessarily, 
and placing the matter on a common, ordinary, bookkeeping footing 
