304 PROCEEDINGS OF SECTION B. 
the rocker by a handwheel and screw. The rockers are actuated 
by a lever, which is connected by a rod to an adjustable pin in 
the disc, which is driven by a belt pulley. The belt wheel drives 
the shaft, on which is placed a small dise with an adjustable pin 
in it, to which is attached a rod. One end of this rod is connected 
with the lever which drives the tapping sbafts, and by the aid of 
a ratchet and pawl these shafts are made to rotate very slowly, 
lifting by the cam a rod at the bottom end of which is attached a 
pear-shaped valve or plug. This moticn allows the concentrates 
to pass out through an aperture and on to the proper receptacles 
for this product. By this means the interior compartments of the 
hutch are always kept clear ; the products of the first three com- 
partments are generally sufficiently high grade to sell, while those 
from the next two compartments are, by the aid of an elevator, 
returned to the machine again, the sixth compartment being the 
tailing receptacle. These are drawn off through a tap, with as 
little water as possible. The separator pans are driven with a 
pair of mitre wheels. The jigs are 22 feet long by 9 feet 3 inches 
wide and 4 feet 6 inches deep. The sides and ends are built of 
3 inch Oregon, and the jigs stand on three trestles, made of 8 
inch by 8 inch Oregon, of which two are 11 feet high, with a 
cast-iron girder on the top to carry the gear. <A platform 2 feet 
wide runs along the two sides and tail of the jig. The waste 
water, when the machines are in motion, passes from the tailings’ 
boxes, through the apertures, on to the plungers again, thus 
keeping up a perfect circulation within the jig. 
The capacity of these jigs is given at 8 tons of crude ore per hour. 
It is stated that 75'per cent. to 80 per cent. of the lead con- 
tents of the crude ore is recovered by the Block 10 concentration 
plant, which is certainly the best work that is known yet. The 
plant is capable of treating over 2,000 tons of crude ore weekly. 
The assays of the crude sulphide of lead given earlier are about 
the average value of most of the sulphide ores which are being 
concentrated, if we except the South Mine which is higher in lead 
and lower in zinc and silver. 
Costs vary with the different plants, and from 4s. 6d. to 7s. 6d. 
a ton on the crude ore are about the limits between which the 
costs at the different works lie. The recovery of the silver is the 
weak point in the concentrating process in Broken Hill, seldom 
more than 40 per cent. of the silver contents being recovered in 
the lead concentrate. The reason is, the zinc blende in the ore 
contains about an equal bulk of the silver, and the more successful 
the concentration to get rid of the zine the more successfully the 
silver is removed also. I think close investigation will show that 
this estimate of the distribution of the silver in the ore is a fairly 
accurate one, butit would be interesting to have more information 
on the subject. Hence, in all the concentration plants at work in 
