298 PROCEEDINGS OF SECTION B. 
labour, salt, repairs, assay expenses, water, light, stores, &e., of 
12s. to 13s. a ton on the gross ore crushed. 
The following analysis of the chloridised ore may be of 
interest :— 
1 2 
Silica 78:40 @ cent 78:00 @ cent 
PbO... 376 ~ 5, Or 
ieiC .... 042 =~, 044 ,, 
Na OP’ 7 | 2a C20" =e 
Hess's. > Sero2 200 es 
AUG Oe: O1d= 
MnO, Ons, sie, ted aaah Lae eis 
ZnO P20 * a ete ae oO nee 
Trace of Antimony. 
99-762 
99-894 
From the cooling floors the chloridised ore is hauled to the 
lixiviating works and there dropped into leaching vats, of which 
there are 12, arranged in two rows, with footways between them 
and tramways over them. Each vat is circular, made of 3-inch 
thick timbers, the bottom timbers being tongued and grooved and 
the sides simply butt joints, the whole stayed with wrought-iron 
straps passing around the vats. The diameter is 16 feet and the 
depth 7 feet, and with a 5-inch false or filter bottom, made of 
rough cobble stones about 4-inch ring size, covered with a layer 
of straw. The vats are filled up within about 12 to 15 inches of 
the top, and hold about 49 to 50 tons of the roasted ore. 
The vat of ore is first washed with hot water at the rate of 16 
inches an hour for one and a half to two hours. This dissolves out 
a very considerable quantity of the lead chloride and salt in the 
ore. The wash-water runs into depositing pits outside the building, 
where the metallic contents are precipitated by scrap-iron, the 
after liquor running to waste. 
After washing, a 1 per cent. solution of sodium hyposulphite is 
run on the ore, and of a temperature as nearly as possible about 
100° Fahrenheit. The speed of the leaching is from 4 to 6 inches 
per hour, and it usually takes forty to fifty hours to finish a vat. 
Ten hours after the leaching liquor is put on; 360 tb. of carbonate 
of soda are put on to the top of the ore under the stream of hypo- 
sulphite of soda, which dissolves it up. This is added for the 
reason that the lead chloride not extracted by the first wash-water 
attacks the solution of hyposulphite of sodium, decomposing por- 
tions of it, and forming lead hyposulphite. If carbonate of soda 
is added to the hyposolution, it, in turn, decomposes the lead 
hyposulphite and forms carbonate of lead, and regenerates the 
