or
at each trip. By these means, the pair of coupled engines raise on an
average 530 tons in twenty-four hours. The skips are furnished with
truck-wheels, which run at an incline to the bottom level, or vice versa; the
tram-road is very well constructed, and is equipped with a single line
of rails of 45 lbs. per yard. Besides this, the engines likewise work
one "blower" and one " air compressor."
At
the 1,000-foot level, their lode is 18 feet in width, and it is a
remarkable circumstance that their bottom level is now in much richer
ore than any had before, and the lode is likewise much more regular.
The stopes exhibit the ore as of a fine streaky and laminated
character, showing in regular bands black sulphurets of silver, native
silver, and some iron pyrites. The average of gold in this mine is
about 35 per cent., and of silver 65 per cent.; but sometimes the gold
exceeds in percentage that of the silver, and the average value per
ton, for some years past, amounted to 26 dollars per ton ; but as high
as 13,000 dollars worth has been obtained per ton, of which ore I
secured specimens, both for the Mining Department and the Bendigo
School of Mines.
Section III.
PUMPING MACHINERY.
At
the new eastern "Combination" shaft of the Virginia Con. and California
United companies, the new pumping engine deserves particular notice, as
being constructed on the " compound" principle, of one to three
expansion, and at present its duty consists in lifting 95 tons of water
per hour from their 1,750-foot level, by means of vertical 12-inch
diameter wrought-iron plated plunger columns. This engine's two
cylinders are bedded on the same bed-plate, " end for end," the first
cylinder nearest the main, shaft receiving the steam direct from the
return multitubular boilers, and instead of passing this steam at the
end of stroke into the exhaust, it is made to supply, by means of a
connecting steam-pipe and valves, the second cylinder, where it acts
expansively, and thus adds nearly two-thirds power to that exerted by
the first cylinder. This first cylinder is 24 inches in diameter, with
a stroke of piston of eight feet; the second cylinder has a
diameter of 40 inches, and of course an exactly like length of stroke.
Automatic (Cornish) valves, on a simple but very ingenious principle,
regulate, in both cylinders, the supply as well as the exhaust of
steam. It has been ascertained, since this engine was set to work, that
more than one-third of the fuel ordinarily consumed whilst pumping with
beam or horizontal engines elsewhere, was saved, which constitutes a
very considerable saving The great difference with compound and
ordinary engines, if used for pumping from great depths, consists,
however, in the saving of all intermediate gear between the cross-head
of the engine and the king-post of the pumping or balance bob at the
surface. The cross-head in these cases being simply connected by means
of a wrought-iron—girder-fashion—sweep-rod, with the top pin at the
king-post, thus securing, at least expense of power, the most direct
action by the engine for the pumps; and the want of vibration when the
plungers take the water evidences the practical utility of this
arrangement.
With
all these large steam engines it becomes a matter of considerable
difficulty to keep their working parts well lubricated without the loss
of time which the attendants use in the usual hand-oiling; therefore
the addition of Cartwright's valve motor is very beneficial; inasmuch
as the requisite lubricants are forced into and distributed amongst all
those parts
