RULES OF THUMB
MINING APPLIANCES AND METHODS
A TEMPORARY FORGE
What prospector has not at times been troubled for the want of a forge?
To steel or harden a pick or sharpen a drill is comparatively easy,
but there is often a difficulty in getting a forge. Big single action
bellows are sometimes bought at great expense, and some ingenious
fellows have made an imitation of the blacksmith's bellows by means of
sheepskins and rough boards.
With inadequate material and appliances to hand, the following will
be found easier to construct and more lasting when constructed. Only
a single piece of iron is required, and, at a pinch, one could even
dispense with that by using a slab of talcose material, roughly shaping
a hearth therein and making a hole for the blast. First, construct a
framing about the height of an ordinary smith's forge. This can made
with saplings and bark, or better still, if available, out of an empty
packing case about three feet square. Fill the frame or case with
slightly damped earth and ram it tight, leaving the usual hollow hearth.
Then form a chamber below the perforated hearth opening to the rear.
Now construct a centrifugal fan, such as is used for the ventilation of
shallow shafts and workings. Set this up behind the hearth and revolve
by means of a wooden multiplying wheel. A piece of ordinary washing line
rope, or sash line rope, well resined if resin can be got--but pitch,
tar, or wax will do by adding a little fine dust to prevent sticking--is
used as a belt. With very rough materials a handy man can thus make a
forge that will answer ordinary requirements.--N.B. Do not use clay for
your hearth bed unless you can get a highly aluminous clay, and can give
it full time to dry before the forge fire is lit. Ordinary surface soil,
not too sandy, acts well, if damped and rammed thoroughly. Of course,
if you can get an iron nozzle for your blower the whole operation is
simplified.
SIMPLE WAY OF MAKING CHARCOAL
Dig a pit 5 feet square by 3 feet deep and fill with fuel. After
lighting, see that the pit is kept full. The hot embers will gradually
sink to the bottom. The fuel should be kept burning fiercely until the
pit seems almost full, when more fuel should be added, raising the heap
about a foot above the level of the ground. The earth dug out of the pit
should then be shovelled back over the burning mass. After leaving it to
cool for 24 hours the pit will be found nearly full of charcoal. About
one-quarter the weight of the dry fuel used should be recovered in
charcoal.
ROUGH SMELTING ON THE MINE
Rough smelting on the mine is effected with a flux of borax, carbonate
of soda, or, as I have often done, with some powdered white glass. When
the gold is smelted and the flux has settled down quietly in a liquid
state, the bulk of the latter may be removed, to facilitate pouring into
the mould, by dipping an iron rod alternately into the flux and then
into a little water, and knocking off the ball of congealed flux which
adheres after each dip. This flux should, however, be crushed with a
pestle and mortar and panned off, as, in certain cases, it may contain
tiny globules of gold.
MISFIRES IN BLASTING
One of the most common sources of accident in mining operations is due
either to carelessness or to the use of defective material in blasting.
A shot misses, generally for one of two reasons; either the explosive,
the cap, or the fuse (most often the latter), is inferior or defective;
or the charging is incompletely performed. Sometimes the fuse is not
placed properly in the detonator, or the detonator is not properly
enclosed in the cartridge, or the fuse is injured by improper tamping.
If several shots have been fired together, particularly at the change
of a "shift," the men who have to remove the broken material may in so
doing explode the missed charge. Or, more inexcusable still, men will
often be so foolish as to try to clear out the drill hole and remove
the missed cartridge. When a charge is known to have missed all that
is necessary to do in order to discharge it safely is to remove a few
inches of "tamping" from the top of the drill hole, place in the bore
a plug of dynamite with cap and fuse attached, put an inch or two of
tamping over it and fire, when the missed charge will also be exploded.
Of course, judgment must be used and the depth of the drill taken into
consideration. As a rule, miners use far more tamping than is at all
requisite. The action of the charge will generally be found quite as
effective with a few inches of covering matter as with a foot or more,
while the exploding of misfire cartridges is rendered simple, as no
removal of tamping is required before placing the top "plug" in case of
misfire.
TO PREVENT LOSS OF RICH SPECIMENS IN BLASTING
When blasting the cap of a lode, particularly on rich shutes of gold,
the rock is apt to fly, and rich specimens may be thrown far afield and
so be lost. A simple way of avoiding this is to procure a quantity
of boughs, which tie into loose bundles, placing the leafy parts
alternately end for end. Before firing, pile these bundles over the
blast and, if care is used, very few stones will fly. The same device
may be used in wide shallow shafts.
A SIMPLE MODE OF RETORTING SMALL QUANTITIES OF AMALGAM
Clean your amalgam and squeeze it as hard as possible through strong
calico or chamois leather. Take a large sound potato, cut off about a
quarter from one end and scoop out a hole in the centre about twice as
big as the ball of amalgam. Procure a piece of flat iron--an old spade
will do as well as anything--insert the amalgam, and, having placed the
potato, cut side downwards, thereon, put the plate of iron on the forge,
heat up first gently, then stronger, till separation has taken place,
when the gold will be found in a bright clean button on the plate
and the mercury in fine globules in the potato, from which it can be
re-collected by breaking up the partly or wholly cooked tuber under
water in an enamelled or ordinary crockery basin.
TO RETORT SMALL QUANTITIES OF MERCURY FOR AMALGAMATING ASSAY TESTS
Get two new tobacco pipes similar in shape, with the biggest bowls and
longest stems procurable. Break off the stem of one close to the bowl
and fill the hole with well worked clay (some battery slimes make the
best luting clay). Set the stemless pipe on end in a clay bed, and fill
with amalgam, pass a bit of thin iron or copper wire beneath it,
and bend the ends of the wire upwards. Now fit the whole pipe, bowl
inverted, on to the under one, luting the edges of both well with clay.
Twist the wire over the top with a pair of nippers till the two bowls
are fitted closely together, and you have a retort that will stand any
heat necessary to thoroughly distil mercury.
A SIMPLE MODE OF ASCERTAINING THE NOMINAL HORSE-POWER OF AN ENGINE
Multiply the internal diameter of the cylinder by itself and strike off
the last figure of the quotient. The diameter is
20" X 20"
20
____
400. The H.P. is 40.
The following rules will be found more professionally accurate from
an engineering standpoint, though the term "horse-power" is not now
generally employed.
_To find the Nominal Horse-power_.--For _non-condensing_ engines:
Multiply the square of the diameter of the cylinder in inches by 7 and
divide the product by 80. For _condensing_ engines: Multiply the square
of the diameter of the cylinder in inches by 7 and divide the product by
200.
_To find the Actual Horse-power_ of an engine, multiply the area of the
cylinder in square inches by the average effective pressure in pounds
per square inch, less 3 lb. per square inch as the frictional allowance,
and also by the speed of the piston in feet per minute, dividing the
product by 33,000, and the quotient will be the actual horse-power.
"SCALING" COPPER PLATES
To "scale" copper plates they may be put over a charcoal or coke fire
to slowly sublimate the quicksilver. Where possible, the fireplace of
a spare boiler can be utilised, using a thin red fire. After the entire
evaporation of the quicksilver the plates should be slowly cooled,
rubbed with hydrochloric acid, and put in a damp place overnight, then
rubbed with a solution of sal ammoniac and nitre in equal parts, and
again heated slowly over a red fire. They must not be allowed to get red
hot; the proper degree of heat is indicated by the gold scale rising
in blisters, when the plates should be taken from the fire and the gold
scraped off. Any part of the plate on which the gold has not blistered
should be again rubbed with the solution and fired. The gold scale
should be collected in a glass or earthen dish and covered with nitric
acid, till all the copper is dissolved, when the gold can be smelted in
the usual way; but after it is melted corrosive sublimate should be put
in the crucible till a blue flame ceases to be given off.
_A Second Method_
The simplest plan I know is to have a hole dug nine inches deep by about
the size of the plate to be scaled; place a brick at each corner, and
on each side, halfway between, get up a good fire; let it burn down to
strong embers, or use charcoal, then place the plate on three bars of
iron extending between the three pairs of bricks, have a strong solution
of borax ready in which soak strips of old "table blanket," laying these
over the plate and sprinkling them with the borax solution when the
plate gets too hot. After a time the deposit of mercury and gold on
the plate will assume a white, efflorescent appearance, and may then be
readily parted from the copper.
_Another Method_
Heat the plate over an open fire, to drive off the mercury; after which,
let it cool, and saturate with dilute sulphuric acid for three hours,
or longer; then sprinkle over the surface a mixture of equal parts of
common salt and sal ammoniac, and heat to redness; then cool, and the
gold scale comes off freely; the scale is then boiled in nitric or
sulphuric acid, to remove the copper, previous to melting. Plates may be
scaled about once in six months, and will under ordinary circumstances
produce about one ounce of clean gold for each superficial foot of
copper surface employed. I always paint the back of the plate with
a mixture of boiled oil and turpentine, or beeswax dissolved in
turpentine, to prevent the acid attacking the copper.
HOW TO SUPPLY MERCURY TO MORTAR BOXES
I am indebted for the following to Mr. J. M. Drake, who, speaking of his
experience on the Wentworth Mine, N.S.W., says:
"Fully 90 per cent of the gold is saved on the outside plates, only a
small quantity remaining in the mortar. The plates have a slope of 2
in. to 1 ft. No wells are used, the amalgam traps saving any quicksilver
which may leach off the plates. The quicksilver is added every hour
in the mortar. The quantity is regulated by the mill manager in the
following manner: Three pieces of wood, 8 in. wide by 12 in. long by 2
in. thick, have 32 holes 1 in. deep bored in each of them. These holes
will just take a small 2 oz. phial. The mill manager puts the required
quantity of quicksilver in each bottle and the batteryman empties one
bottle in each mortar every hour; and puts it back in the hole upside
down. Each block of wood lasts eight hours, the duration of one man's
shift." This of course is for a 20-head mill with four mortars or
"boxes."
I commend this as an excellent mode of supplying the mercury to the
boxes or mortars. The quantity to be added depends on circumstances. A
careless battery attendant will often put in too much or too little
when working without the automatic feeder. I have known an attendant
on suddenly awaking to the fact half through his shift, that he had
forgotten to put in any mercury, to then empty into the stamper box two
or three pounds weight; with what effect may be easily surmised.
HOW WATER SHOULD ENTER STAMPER BOXES
The following extract which relates to Californian Gold Mill practices
is from Bulletin No. 6 of the California State Mining Bureau. I quite
agree with the practice.
"The battery water should enter both sides of the mortar in an even
quantity, and should be sufficient to keep a fairly thick pulp which
will discharge freely through the grating or screen. About 120 cubic
feet of water per ton of crushed ore may be considered an average, or 8
to 10 cubic feet per stamp per hour.
"Screens of different materials and with different orifices are used;
the materials comprise wire cloth of brass or steel, tough Russian sheet
iron, English tinned plate, and, quite recently, aluminium bronze. The
'aluminium bronze' plates are much longer lived than either of the other
kinds, and have the further advantage that, when worn out, they can be
sold for the value of the metal for remelting; these plates are bought
and sold by the pound, and are said to contain 95 per cent of copper and
5 per cent of aluminium. Steel screens are not so much used, on account
of their liability to rust."
I have had no experience with the aluminium bronze screen. I presume,
however, that it is used only for mills where mercury is not put in the
mortars, otherwise, it would surely become amalgamated. The same remark
applies to brass wire cloth and tinned plate. Unless the metal of which
they are composed will not readily amalgamate with mercury, I should be
chary of using new screen devices. Mercury is a most insidious metal
and is often found most unexpectedly in places in the battery where
it should not be. Probably aluminium steel would be better than any
substance mentioned. It would be hard, light, strong, and not readily
corrodible. I am not aware if it has been tried.
Under the heading of "Power for Mills" the following is taken from the
same source.
POWER FOR MILLS
"As the Pelton wheel seems to find the most frequent application in
California, it may be convenient for millmen to have the following rule,
applicable to these wheels:
"When the head of water is known in feet, multiply it by 0.0024147,
and the product is the horse-power obtainable from one miner's inch of
water.
"The power necessary for different mill parts is:
For each 850lb. stamp, dropping 6 in. 95 times per minute,
1.33 h.-p.
For each 750lb. stamp, dropping 6 in. 95 times per minute,
1.18 h.-p.
For each 650lb. stamp, dropping 6 in. 95 times per minute,
1.00 h.-p.
For an 8-inch by 10-inch Blake pattern rock-breaker
9.00 h.-p.
For a Frue or Triumph vanner, with 220 revolutions per min.
0.50 h.-p.
For a 4-feet clean-up pan, making 30 revolutions per min.
1.50 h.-p.
For an amalgamating barrel, making 30 revolutions per min.
2.50 h.-p.
For a mechanical batea, making 30 revolutions per min.
1.00 h.-p."
The writer has had small practical experience of the working of that
excellent hydraulic motor, the Pelton wheel, but if by horse-power in
the table given is meant nominal horse-power, it appears to be high.
Working with 800 cwt. stamps, 80 blows a minute, one horse-power nominal
will be found sufficient with any good modern engine, which has no
further burden than raising the stamps and pumping the feed water. It is
always well, however, particularly when providing engine power, to err
on the right side, and make provision for more than is absolutely needed
for actual battery requirements. This rule applies with equal potency to
pumping engines.
TO AVOID LOSS IN CLEANING UP
The following is a hint to quartz mill managers with respect to that
common source of loss of gold involved in the almost inevitable loss
of mercury in cleaning up operations. I have known hundreds of pounds'
worth of gold to be recovered from an old quartz mill site by the simple
process of washing up the ground under the floor.
If you cannot afford to floor the whole of the battery with smooth
concrete, at all events smoothly concrete the floor of the cleaning-up
room, and let the floor slope towards the centre: where a sink is
provided. Any lost mercury must thus find its way to the centre, where
it will collect and can be panned off from time to time. Of course an
underground drain and mercury trap must be provided.
IRON EXTRACTOR
When using self-feeders, fragments of steel tools are especially liable
to get into the battery boxes or other crushing appliance where they
sometimes cause great mischief. I believe the following plan would be a
practicable remedy for this evil.
By a belt from the cam or counter shaft, cause a powerful electric
magnet to extract all magnetic particles; then, by a simple ratchet
movement, at intervals withdraw the magnet and drop the adhering
fragments into a receptacle by automatically switching off the electric
current. A powerful ordinary horseshoe magnet might probably do just as
well, but would require to be re-magnetised from time to time.
TO SILVER COPPER PLATES
To silver copper plates, that is, to amalgamate them on the face with
mercury, is really a most simple operation, though many batterymen make
a great mystery of it. Indeed, when I first went into a quartz mill the
process deemed necessary was not only a very tedious one, but very dirty
also.
To amalgamate with silver, in fact, to silver-plate your copper without
resort to the electro-plating bath, take any old silver (failing that,
silver coin will do, but is more expensive), and dissolve it in somewhat
dilute nitric acid, using only just sufficient acid as will assist the
process. After some hours place the ball of amalgam in a piece of strong
new calico and squeeze out any surplus mercury.
About an ounce of silver to the foot of copper is sufficient. To apply
it on new plates use nitric acid applied with a swab to free the surface
of the copper from oxides or impurities, then rub the ball of amalgam
over the surface using some little force. It is always well when coating
copper plates with silver or zinc by means of mercury to let them stand
dry for a day or two before using, as the mercury oxidises and the
coating metal more closely adheres.
Only the very best copper plate procurable should be used for battery
tables; bad copper will always give trouble, both in the first "curing,"
and after treatment. It should not be heavily rolled copper, as the
more porous the metal the more easily will the mercury penetrate and
amalgamate. I cannot agree that any good is attained by scouring the
plates with sand and alkalies, as recommended in some books on the
subject; on the contrary, I prefer the opposite mode of treatment, and
either face the plates with nitrate of silver and nitrate of mercury,
or else with sulphate of zinc and mercury, in the form of what is
called zinc amalgam. If mine water, which often contains a little free
sulphuric acid, is being used, the latter plan is preferable.
The copper should be placed smoothly on the wooden table and secured
firmly thereto by copper tacks. If the plate should be bent or buckled,
it may be flattened by beating it with a heavy hammer, taking care to
interpose a piece of inch-thick soft wood between hammer and plate.
To coat with mercury only, procure some nitrate of mercury. This is
easily made by placing mercury in an earthenware bowl, pouring somewhat
dilute nitric acid on it, and letting it stand till the metallic mercury
is changed to a white crystal. Dense reddish-brown fumes will arise,
which are injurious if breathed, so the operation should be conducted
either in the open air, or where there is a draught.
Having your silvering solution ready, which is to be somewhat diluted
with water, next take two swabs, with handles about 12 inches long, dip
the first into a basin containing dilute nitric acid, and rub it rapidly
over about a foot of the surface of the plate; the oxide of copper will
be absolutely removed, and the surface of the copper rendered pure and
bright; then take the other swab, wet with the dilute nitric of mercury,
and pass it over the clean surface, rubbing it well in. Continue this
till the whole plate has a coating of mercury. It may be well to go
over it more than once. Now turn on the water and wash the plate clean,
sprinkle with metallic mercury, rubbing it upwards until the plate will
hold no more.
A basin with nitrate of mercury may be kept handy, and the plates
touched up from time to time for a few days until they get amalgamated
with gold, after which, unless you have much base metal to contend with,
they will give no further trouble.
It must be remembered, however, that an excessive use of nitric acid
will result in waste of mercury, which will be carried off in a milky
stream with the water; and also that it will cause the amalgam to become
very hard, and less active in attracting other particles of gold.
If you are treating the plate with nitrate of silver prepared as already
mentioned, clean the plate with dilute nitric acid, rub the surface with
the ball of amalgam, following with the swab and fairly rubbing in. It
will be well to prepare the plate some days before requiring to use
it, as a better adhesion of the silver and copper takes place than if
mercury is applied at once.
To amalgamate with zinc amalgam, clean the copper plate by means of a
swab, with fairly strong sulphuric acid diluted with water; then while
wet apply the zinc-mercury mixture and well rub in. To prepare the
zinc-amalgam, clip some zinc (the lining of packing cases will do)
into small pieces and immerse them in mercury after washing them with
a little weak sulphuric acid and water to remove any coating of oxide.
When the mercury will absorb no more zinc, squeeze through chamois
leather or calico (as for silver amalgam), and well rub in. The plate
thus prepared should stand for a few days, dry, before using. If, before
amalgamation with gold takes place, oxide of copper or other scum should
rise on this plate a little very dilute sulphuric acid will instantly
remove it.
Sodium and cyanide of potassium are frequently used in dressing-plates,
but the former should be very sparingly employed, as it will often
do more harm than good by taking up all sorts of base metals with the
amalgam, and so presenting a surface which the gold will pass over
without adhering to. Where water is scarce, and is consequently used
over and over again, lime may be added to the pulp, or, if lime is not
procurable, wood ashes may be used. The effect is two-fold; the lime
not only tends to "sweeten" sulphide ores and keep the tables clean,
but also causes the water to cleanse itself more quickly of the slimes,
which will be more rapidly precipitated. When zinc amalgam is used,
alkalies would, of course, be detrimental.
When no other water than that from the mine is available, difficulties
often arise owing to the impurities it contains. These are various,
but among the most common are the soluble sulphates, and sometimes free
sulphuric acid evolved by the oxidisation of metallic sulphides. In the
presence of this difficulty, do one of two things; either _utilise_ or
_neutralise_. In certain cases, I recommend the former. Sometime since
I was treating, for gold extraction, material from a mine which was very
complex in character, and for which I coined the term "polysynthetic."
This contained about half a dozen different sulphides. The upper parts
of the lode being partially oxidised, free sulphuric acid (H2SO4) was
evolved. I therefore, following out a former discovery, added a little
metallic zinc to the mercury in the boxes and on the plates with
excellent results. When the free acid in the ore began to give out in
the lower levels I added minute quantities of sulphuric acid to the
water from time to time. I have since found, however, that with some
water, particularly West Australian, the reaction is so feeble (probably
owing to the lime and magnesia present) as to make this mode of
treatment unsuitable.
HOW TO MAKE A DOLLY
I have seen some rather elaborate dollies, intended to be worked with
amalgamating tables, but the usual prototype of the quartz mill is
set up, more or less, as follows: A tree stump, from 9 in. to a foot
diameter, is levelled off smoothly at about 2 ft. from the ground; on
this is firmly fixed a circular plate of 1/2 in. iron, say 9 in. in
diameter; a band of 3/16 in. iron, about 8 or 9 in. in height, fits
more or less closely round the plate. This is the battery box. A beam
of heavy wood, about 3 in. diameter and 6 ft. long, shod with iron,
is vertically suspended, about 9 in. above the stump, from a flexible
sapling with just sufficient spring in it to raise the pestle to the
required height. About 2 ft. from the bottom the hanging beam is pierced
with an augur hole and a rounded piece of wood, 1 1/2 in. by 18 in.,
is driven through to serve as a handle for the man who is to do the
pounding. His mate breaks the stone to about 2 in. gauge and feeds the
box, lifting the ring from time to time to sweep off the triturated
gangue, which he screens through a sieve into a pan and washes off,
either by means of a cradle or simply by panning. In dollying it
generally pays to burn the stone, as so much labour in crushing is thus
saved. A couple of small kilns to hold about a ton each dug out of a
clay bank will be found to save fuel where firewood is scarce, and will
more thoroughly burn the stone and dissipate the base metals, but it
must be remembered that gold from burnt stone is liable to become so
encrusted with the base metal oxides as to be difficult to amalgamate.
ROUGH WINDLASS
Make two St. Andrew's crosses with four saplings, the upper angle being
shorter than the lower; fix these upright, one at each end of the shaft;
stay them together by cross pieces till you have constructed something
like a "horse," such as is used for sawing wood, the crutch being a
little over 3 feet high. Select a leg for a windlass barrel, about 6 in.
diameter and a foot longer than the distance between the supports, as
straight as is procurable; cut in it two circular slots about an inch
deep by 2 in. wide to fit into the forks; at one end cut a straight slot
2 in. deep across the face. Now get a crooked bough, as nearly the shape
of a handle as nature has produced it, and trim it into right angular
shape, fit one end into the barrel, and you have a windlass that will
pull up many a ton of stuff.
PUDDLER
This is made by excavating a circular hole about 2 ft. 9 in. deep and,
say 12 ft. in diameter. An outer and inner wall are then constructed of
slabs 2 ft. 6 in. in height to ground level, the outer wall being thus
30 ft. and the inner 15 ft. in circumference. The circular space between
is floored with smooth hardwood slabs or boards, and the whole made
secure and water-tight. In the middle of the inner enclosure a
stout post is planted, to stand a few inches above the wall, and the
surrounding space is filled up with clay rammed tight. A strong iron pin
is inserted in the centre of the post, on which is fitted a revolving
beam, which hangs across the whole circumference of the machine
and protrudes a couple of feet or so on each side. To this beam are
attached, with short chains, a couple of drags made like V-shaped
harrows by driving a piece of red iron through a heavy frame, shaped as
a rectangular triangle.
To one end of the beam an old horse is attached, who, as he slowly walks
round the circular track, causes the harrows and drags to so puddle
the washdirt and water in the great wooden enclosure that the clay is
gradually disintegrated, and flows off with the water which is from time
to time admitted. The clean gravel is then run through a "cradle," "long
Tom," or "sluice," and the gold saved. This, of course, is the simplest
form of gold mining. In the great alluvial mines other and more
intricate appliances are used but the principle of extraction is the
same.
A MAKESHIFT PUMP
To make a temporary small "draw-lift" pump, which will work down to
a hundred feet or more if required, take a large size common suction
Douglas pump, and, after removing the top and handle, fix the pump as
close to the highest level of the water in the shaft as can be arranged.
Now make a square water-tight wooden column of slightly greater capacity
than the suction pipe, fix this to the top of the pump, and by means
of wooden rods, work the whole from the surface, using either a longer
levered handle or, with a little ingenuity, horse-power. If you can
get it the iron downpipe used to carry the water from the guttering of
houses is more easily adapted for the pipe column; then, also, iron pump
rods can be used but I have raised water between 60 and 70 feet with a
large size Douglas pump provided only with a wooden column and rods.
SQUEEZING AMALGAM
For squeezing amalgam, strong calico, not too coarse, previously soaked
in clean water, is quite as good as ordinary chamois leather. Some gold
is fine enough to escape through either.
MERCURY EXTRACTOR
The mercury extractor or amalgam separator is a machine which is very
simple in construction, and is stated to be most efficient in extracting
quicksilver from amalgam, as it requires but from two to three minutes
to extract the bulk of the mercury from one hundred pounds of amalgam,
leaving the amalgam drier than when strained in the ordinary way by
squeezing through chamois leather or calico. The principle is that
of the De Laval cream separator--i.e., rapid centrifugal motion.
The appliance is easily put together, and as easily taken apart. The
cylinder is made of steel, and is run at a very high rate of speed.
The general construction of the appliance is as follows: The casing or
receiver is a steel cylinder, which has a pivot at the bottom to receive
the step for an upright hollow shaft, to which a second cylinder of
smaller diameter is attached. The second cylinder is perforated, and
a fine wire cloth is inserted. The mercury, after passing through the
cloth, is discharged through the perforations. When the machine
is revolved at great speed, the mercury is forced into the outside
cylinder, leaving the amalgam, which has been first placed in a calico
or canvas bag, in a much drier state than it could be strained by hand.
While not prepared to endorse absolutely all that is claimed for this
appliance, I consider that it has mechanical probability on its side,
and that where large quantities of amalgam have to be treated it will be
found useful and effective.
SLUICE PLATES
I am indebted to Mr. F. W. Drake for the following account of sluice
plates, which I have never tried, but think the device worth attention:
"An addition has been made to the gold-saving appliances by the placing
of what are called in America, 'sluice plates' below the ordinary table.
The pulp now flows over an amalgamating surface, 14 ft. long by 4 ft.
wide, sloping 1 1/2 in. to the foot, and is then contracted into a
copper-plated sluice 15 ft. long by 14 in. wide, having a fall of 1 in.
to the foot. Our mill manager (Mr. G. C. Knapp) advocated these sluice
plates for a long time before I would consent to a trial. I contended
that as we got little or no amalgam from the lower end of our table
plates there was no gold going away capable of being recovered by copper
plates; and even if it were, narrow sluice plates were a step in the
wrong direction. If anything the amalgamating surface should be widened
to give the particles of gold a better chance to settle. His argument
was that the conditions should be changed; by narrowing the stream and
giving it less fall, gold, which was incapable of amalgamation on the
wide plates, would be saved. We finally put one in, and it proved
so successful that we now have one at the end of each table. The
per-centage recovered on the sluice plates, of the total yield, varies,
and has been as follows:--October, 9.1 per cent; November, 6.9 per cent;
December, 6.4 per cent; January, 4.3 per cent; February, 9.3 per cent."
MEASURING INACCESSIBLE DISTANCES
To ascertain the width of a difficult gorge, a deep river, or
treacherous swamp without crossing and measuring, sight a conspicuous
object at the edge of the bank on the farther side; then as nearly
opposite and square as possible plant a stake about five feet high, walk
along the nearer margin to what you guess to be half the distance across
(exactitude in this respect is not material to the result), there plant
another stake, and continuing in a straight line put in a third. The
stakes must be equal distances apart and as nearly as possible at a
right angle to the first line. Now, carrying in hand a fourth stake,
strike a line inland at right angles to the base and as soon as sighting
over the fourth stake, you can get the fourth and second stakes and
the object on the opposite shore in line your problem is complete. The
distance between No. 4 and No. 3 stakes is the same as that between No.
1 and the opposite bank.
TO SET OUT A RIGHT ANGLE WITH A TAPE
Measure 40 ft. on the line to which you wish to run at right angles, and
put pegs at A and B; then, with the end of the tape held carefully at
A, take 80 ft., and have the 80 ft. mark held at B. Take the 50 ft. mark
and pull from A and B until the tape lies straight and even, you will
then have the point C perpendicular to AB. Continue straight lines by
sighting over two sticks in the well-known way.
_Another method_.--Stick a pin in each corner of a square board, and
look diagonally across them, first in the direction of the line to which
you wish to run at right angles, and then for the new line sight across
the other two pins.
A SIMPLE LEVELLING INSTRUMENT
Fasten a common carpenter's square in a slit to the top of a stake by
means of a screw, and then tie a plumb-line at the angle so that it
may hang along the short arm, when the plumb-line hangs vertically
and sights may be taken over it. A carpenter's spirit-level set on an
adjustable stand will do as well. The other arm will then be a level.
Another very simple, but effective, device for finding a level line is
by means of a triangle of wood made of half-inch boards from 9 to 12
ft. long. To make the legs level, set the triangle up on fairly level
ground, suspend a plummet from the top and mark on the cross-piece where
the line touches it. Then reverse the triangle, end for end, exactly,
and mark the new line the plumb-line makes. Now make a new mark exactly
half way between the two, and when the plumb-line coincides with this,
the two legs are standing on level ground. For short water races this is
a very handy method of laying out a level line.
TO MEASURE THE HEIGHT OF A STANDING TREE
Take a stake about your own height, and walking from the butt of the
tree to what you judge to be the height of the timber portion you want,
drive your stake into the ground till the top is level with your eyes;
now lie straight out on your back, placing your feet against the stake,
and sight a point on the tree. AB equals BC. If BC is, say 40 ft., that
will be the height of your "stick of timber." Thus, much labour may be
saved in felling trees the timber portion of which may afterwards be
found to be too short for your purpose.
LEVELLING BY ANEROID BAROMETER
This should be used more for ascertaining relatively large differences
in altitudes than for purposes where any great nicety is required.
For hills under 2000 ft., the following rule will give a very close
approximation, and is easily remembered, because 55 degrees, the assumed
temperature, agrees with 55 degrees, the significant figures in the
55,000 factor, while the fractional correction contains _two fours_.
Observe the altitudes and also the temperatures on the Fahrenheit
thermometer at top and bottom respectively, of the hill, and take the
mean between them. Let B represent the mean altitude and b the mean
temperature. Then 55000 X B - b/B + b = height of the hill in feet for
the temperature of 55 degrees. Add 1/440 of this result for every degree
the mean temperature exceeds 55 degrees; or subtract as much for every
degree below 55 degrees.
TO DETERMINE HEIGHTS OF OBJECTS
_By Shadows_
Set up vertically a stick of known length, and measure the length of its
shadow upon a horizontal or other plane; measure also the length of
the shadow thrown by the object whose height is required. Then it will
be:--As the length of the stick's shadow is to the length of the stick
itself, so is the length of the shadow of the object to the object's
height.
_By Reflection_
Place a vessel of water upon the ground and recede from it until you see
the top of the object reflected from the surface of the water. Then it
will be:--As your horizontal distance from the point of reflection is
to the height of your eye above the reflecting surface, so is the
horizontal distance of the foot of the object from the vessel to its
altitude above the said surface.
_Instrumentally_
Read the vertical angle, and multiply its natural tangent by the
distance between instrument and foot of object; the result is the
height.
When much accuracy is not required vertical angles can be measured by
means of a quadrant of simple construction. The arc AB is a quadrant,
graduated in degrees from B to A; C, the point from which the plummet P
is suspended, being the centre of the quadrant.
_When_ the sights AC are directed towards any object, S, the degrees
in the arc, BP, are the measure of the angle of elevation, SAD, of the
object.
TO FIND THE DEPTH OF A SHAFT
_Rule_:--Square the number of seconds a stone takes to reach the bottom
and multiply by 16.
Thus, if a stone takes 5 seconds to fall to the bottom of a shaft--
5 squared = 25; and 25 X 16 = 400 feet, the required depth of shaft.
DESCRIPTION OF PLAN FOR RE-USING WATER
Where water is scarce it may be necessary to use it repeatedly. In a
case of this kind in Egypt, the Arab miners have adopted an ingenious
method which may be adapted to almost any set of conditions. At a is a
sump or water-pit; b is an inclined plane on which the mineral is washed
and whence the water escapes into a tank c; d is a conduit for taking
the water back to a; e is a conduit or lever pump for raising the
water. A certain amount of filtration could easily be managed during the
passage from c to a.
COOLING COMPOUND FOR HEATED BEARINGS
Mercurial ointment mixed with black cylinder oil and applied every
quarter of an hour, or as often as expedient. The following is also
recommended as a good cooling compound for heavy bearings:--Tallow 2
lb., plumbage 6 oz., sugar of lead 4 oz. Melt the tallow with gentle
heat and add the other ingredients, stirring until cold.
CLEANING GREASY PLUMMER BLOCKS
When, through carelessness or unpreventable cause, plummer blocks
and other detachable portions of machinery become clogged with sticky
deposits of grease and impurities, a simple mode of cleansing the same
is to take about 1000 parts by weight of boiling water, to which add
about 10 or 15 parts of ordinary washing soda. Keep the water on the
boil and place therein the portions of the machine that are to be
cleaned; this treatment has the effect of quickly loosening all grease,
oil, and dirt, after which the metal is thoroughly washed and dried. The
action of the lye is to form with the grease a soap soluble in water. To
prevent lubricating oil hardening upon the parts of the machinery when
in use, add a third part of kerosene.
AN EXCELLENT ANTI-FRICTION COMPOUND
For use on cams and stamper shanks, which will be harmless should it
drop into the mortar or stamper boxes, is graphite (black-lead) and
soft soap. When the guides are wooden, the soft soap need not be added;
black-lead made into a paste with water will act admirably.
TO CLEAN BRASS
Oxalic acid 1 oz., rotten stone 6 oz., powdered gum arabic 1/2 oz.,
sweet oil 1 oz. Rub on with a piece of rag.
A SOLVENT FOR RUST
It is often very difficult, and sometimes impossible, to remove rust
from articles made of iron. Those which are very thickly coated are
most easily cleaned by being immersed in a nearly saturated solution
of chloride of tin. The length of time they remain in this bath is
determined by the thickness of the coating of rust. Generally from
twelve to twenty-four hours is long enough.
TO PROTECT IRON AND STEEL FROM RUST
The following method is but little known, although it deserves
preference over many others. Add 7 oz. of quicklime to 1 3/4 pints
of cold water. Let the mixture stand until the supernatant fluid is
entirely clear. Then pour this off, and mix with it enough olive oil
to form a thick cream, or rather to the consistency of melted and
re-congealed butter. Grease the articles of iron or steel with this
compound, and then wrap them up in paper, or if this cannot be done,
apply the mixture somewhat more thickly.
TO KEEP MACHINERY FROM RUSTING
Take 1 oz. of camphor, dissolve it in 1 lb. of melted lard; mix with
it (after removing the scum) as much fine black-lead as will give it an
iron colour; clean the machinery, and smear it with this mixture. After
twenty-four hours rub off and clean with soft, linen cloth. This mixture
will keep machinery clean for months under ordinary circumstances.
FIRE-LUTE
An excellent fire-lute is made of eight parts sharp sand, two parts good
clay, and one part horse-dung; mix and temper like mortar.
ROPE-SPLICING
A short splice is made by unlaying the ends of two pieces of rope to a
sufficient length, then interlaying them, draw them close and push the
strands of one under the strands of the other several times. This
splice makes a thick lump on the rope and is only used for slings,
block-straps, cables, etc.