Take a half-gallon, or larger, tin "billy can," enclose it in a strong cotton handkerchief or cotton cloth, knotting same over the lid, invert, and, taking the knot in the hand, you have a floating appliance which will sustain you in any water, whether you are a swimmer or not. The high silk hat of civilisation would act as well as the can, but these are not usually found far afield.

TO MAKE A HIDE BUCKET

At times when prospecting in an "incline" or "underlay" shaft, particularly where the walls of the lode are irregular, a hide bucket will be found preferable to an iron one. The mode of manufacture is as follows: Procure an ox hide, "green," if possible; if dry, it should be soaked until quite soft. Cut some thin strips of hide for sewing or lacing. Now shape a bag or pocket of size sufficient to hold about a hundredweight of stone, and by puncturing the edges with a knife, marline-spike, or other pointed tool, sew together; make a handle of twisted or pleated hide, and having filled your bucket with dry sand or earth let it stand till the whole is quite dry, when it will be properly distended and will maintain its shape until worn out.

TO MAKE A "SLUSH LAMP"

Where candles are scarce and kerosine is not, a "slush lamp" is a useful subst.i.tute. Take an old but sound quart tin pannikin, half fill it with sand or earth, and prepare a thin stick of pine, round which wrap a strip of soft cotton cloth. The stick should be about half an inch longer than the depth of the pannikin. Melt some waste fat, fill the pannikin therewith, push the stick down into the earth at the bottom, and you have a light, which, if not equal to the electric or incandescent gas burner, is quite serviceable. In Australia the soft velvety core of the "bottle brush," _Banksia marginata_, is often used instead of the cotton wick.

CHAPTER XII

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 ma.s.s. 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 gla.s.s. 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 quant.i.ty 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 QUANt.i.tIES 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 b.u.t.ton 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 QUANt.i.tIES OF MERCURY FOR AMALGAMATING a.s.sAY 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, pa.s.s 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 c.o.ke 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 sc.r.a.ped 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 gla.s.s 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 a.s.sume 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 circ.u.mstances 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 quant.i.ty 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 quant.i.ty 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 quant.i.ty 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 quant.i.ty to be added depends on circ.u.mstances. 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 quant.i.ty, 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 bra.s.s 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 bra.s.s 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.