[3]This wonderful copper occurrence has lately been revived by the discovery of rich and strong lode formations outside the formerly worked portions.
[3]This wonderful copper occurrence has lately been revived by the discovery of rich and strong lode formations outside the formerly worked portions.
When water is scarce and the tent has to be retained, much can be done to make the camp snug. I occupied a very comfortable camp once, of which my then partner, a Dane, was the architect. We called it “The Bungalow,” and it was constructed as follows: First we set up our tent, 10 ft. by 8 ft., formed of green baize-lined calico, and covered with a well set fly(Fig. 27).
Next we put in four substantial forked posts about 10 ft. high and 15 ft. apart, with securely fixed cross pieces, and on the top was laid a rough flat roof of brush thatch; the sides were then treated in the same way, but not so thickly, being merely intended as a breakwind.
Fig. 27.Calico Tent With Fly.
The ground plan was as shown inFig. 28.
Fig. 28.
The tent with its two comfortable bunks was placed a little to one side, the remaining space being used as a dining and sitting room all through the summer. Except in occasional seasons of heavy rain, when we were saved the trouble of washing ourdishes, the tent was only used for sleeping purposes, and as a storehouse for clothes and perishable provisions. I have “dwelt in marble halls” since then, but never was food sweeter or sleep sounder than in the old bush bungalow.
To make a comfortable bush bedplace, take four forked posts about 3 ft. 6 in. long and 2 to 3 in. in diameter at the top; mark out your bedplace accurately and put a post at each corner, about 1 ft. in the ground. Take two poles about 7 ft. long, and having procured two strong five-bushel corn sacks, cut holes in the bottom corners, put the poles through, bringing the mouths of the sacks together, and secure them there with a strong stitch or two. Put your poles on the upright forked sticks, and you have a couch that even Sancho Panza would have envied. It is as well to fix stretchers or cross stays between the posts at head and foot(Fig. 29).
Fig. 29.Bush Stretcher.
In malarial countries, sleeping on the ground is distinctly dangerous, and as such districts are usually thickly timbered, the Northern Territory hammock is an admirable device, more particularly where mosquitoes abound.
This hammock, which is almost a standing bedplace whenrigged, is constructed as follows:—To a piece of strong canvas 7 feet long and 2½ feet wide, put a broad hem, say 3½ inches wide at each end. Into this hem run a tough stick, about 2 feet 8 inches long by 1½ inches diameter. Round the centre of the stick pass a piece of strong three-quarter inch rope, 8 to 10 feet long and knot it, so as to leave a short end in which a metal eye is inserted. To each end of the two sticks a piece of quarter-inch lashing, about 6 feet long, is securely attached(Fig. 30).
Fig. 30.Northern Territory Hammock.
To make the mosquito covering take 18 feet of ordinary strong cheese cloth, and two pieces of strong calico of the same size as the canvas bed; put hems in the ends of the upper one large enough to take half-inch sticks, to all four extremities of which 8 feet of whipcord is to be attached. The calico forms the top and bottom of what we used to call the “meat safe,” the sides being of cheese cloth. A small, flapped opening is left on the lower side. When once inside you are quite safe from mosquito bites.
To rig the above, two trees are chosen 7 to 8 feet apart, or two stayed poles can be erected if no trees are available. The bed is rigged about 3 feet from the ground by taking the rope round the trees or poles, and pulling the canvas taut by means of the metal eyelet. Then the lashings at the extremities of the sticks are fixed about 3 feet further up the trees and you have a bed something between a hammock and a standing bed. Themosquito net is fixed above the hammock in a similar manner, except that it does not require the centre stay(Fig. 31).
Fig. 31.Northern Territory Hammock (set up).
An old friend of mine once had a rather startling experience which caused him to swear by the Northern Territory hammock. He was camped near the banks of a muddy creek on the Daly River, and had fortunately hung his “meat safe” about four feet high. The night was very dark, and some hours after retiring he heard a crash among his tin camp utensils, and the noise of some animal moving below him. Thinking his visitor was a stray “dingo,” or wild dog, he gave a yell to frighten the brute away, and hearing it go, he calmly went to sleep again. Had he known who his caller really was, he would not have felt so comfortable. In the morning on the damp ground below, he found the tracks of a fourteen foot alligator, which was also out prospecting, but which, fortunately, had not thought of investigating the “meat safe.”
There is not a more fertile disease distributor, particularly in a new country, than water. The uninitiated generally take it for granted that so long as water looks clear it is necessarily pureand wholesome; as a matter of fact the contrary is more usually the case, except in very well watered countries, and such, as a rule, are not those in which gold is most plentifully got by the average prospector. I have seen foolish fellows, who were parched with a long tramp, drink water in quantity in which living organisms could be seen with the naked eye, without taking even the ordinary precaution of straining it through a piece of linen. If they contracted hydatids, typhoid fever, or other ailments, which thin our mining camps of the strong, lusty, careless youths, who could wonder?
The best of all means of purifying water from organic substances is to boil it. If it should be very bad, add carbon in the form of the charcoal from your camp fire. If it be thick, you may, with advantage, add a little of the ash also.
I once rode forty-five miles with nearly beaten horses to a native well, or rock hole, to find water, the next stage being over fifty miles farther. The well was found, but the water in it was very bad; for in it was the body of a dead kangaroo, which had apparently been there for weeks. The wretched horses, half frantic with thirst, did manage to drink a few mouthfuls, but we could not. I filled our largest billycan, holding about two gallons, slung it over the fire and added, as the wood burnt down, charcoal, till the top was covered to a depth of two inches. With the charcoal there was, of course, a little ash containing bi-carbonate of potassium. The effect was marvellous. So soon as the horrible soup came to the boil, the impurities coagulated, and after keeping it at boiling temperature for about a quarter of an hour, it was removed from the fire, the cinders skimmed out, and the water allowed to settle, which it did very quickly. It was then decanted off into an ordinary prospector’s pan, and some was used to make tea (the flavour of which can be better imagined than described); the remainder was allowed to stand all night, a few pieces of charcoal being added. In the morning it was bright, clear, and absolutely sweet. This experience is worth knowing, as many a bad attack of typhoid and other fevers would be averted if practical precautions of this kind were but used.
The greatest necessity of animal life is water. There are, however, vast areas of the earth’s surface where this most precious element is lamentably lacking, and such, unfortunately, is the case in many rich auriferous districts.
To the practical man there are many indications of water. These, of course, vary in different countries. Sometimes it is the herbage, but, probably, the best of all is the presence of carnivorous animals and birds. These are never found far from water. In Australia the not over-loved wily old crow is a pretty sure indicator of water within reasonable distance—water may be extracted from the roots of the Mallee (Eucalyptus dumosaandgracilis)—the Box (Eucalyptus hemiphloia) and the Water Bush (Hakea leucoptera). To extract it the roots are dug up, cut into lengths of about a foot, and placed upright in a can; the lower ends being a few inches above the bottom. It is simply astonishing how much wholesome, if at times somewhat astringent, water may thus be obtained in a few hours, particularly at night.
Hakea leucoptera.“Pins and needles.”—Maiden, in his work “Useful Native Plants of Australia,” says: “In an experiment on a water-yieldingHakea, the first root, about half an inch in diameter and six or eight feet long, yielded quickly, and in large drops about a wine-glass full of really excellent water.”
This valuable, though not particularly ornamental shrub (for it never attains to the dimensions of a tree), is found, to the best of my belief, in all parts of Australia, although it is said to be absent from West Australia. As to this, I don’t feel quite sure. I have seen it “from the centre to the sea” as far west as Streaky Bay, and believe I have seen it farther west still. Considering the great similarity of much of the flora of South Africa to that of Australia, it is probable that some species of the water-bearingHakeamay be found there. It can readily be recognised by its acicular, needle-like leaves, and more particularly by its peculiarly shaped seed vessel, which resembles the pattern on an old-fashioned Indian shawl(Fig. 32).
If the water found is too impure for drinking purposes and the trouble arises from visible animalculæ only, straining through a pocket-handkerchief is better than nothing; the carbon filter is better still; but nothing is so effective as boiling. A carbon filter is a tube with a wad of compressed carbon inserted, through which the water is sucked. As a rule clay-coloured water is comparatively innocuous, but beware of the bright, limpid water of long stagnant rock water-holes.
Fig. 32.Seed-vessel of Hakea Leucoptera.
Take a nail-can, keg, cask, or any other vessel, or even an ordinary wooden case (well tarred inside, if possible, to make it water-tight). Make a hole or several holes in the bottom, and set it over a tank or bucket. Into the bottom of the filter put (1) a few inches of washed broken stone; (2) about four inches of charcoal; (3) say three inches of clean coarse sand (if not to hand you can manufacture it by crushing quartz with your pestle and mortar), and (4) alternate layers of charcoal and sand until the vessel is half filled. Fill the top half with water, and renew from time to time, and you have a filter which is as effective as the best London made article.But it is better to boil your water whether you filter afterwards or not.
Clear the inside of the water-cask frequently, and occasionally add to the water a little Condy’s fluid, as it destroys organic matter. A useful cement for stopping leaky places in casks is made as follows; Tallow 25 parts, lard 40 parts, sifted wood ash25 parts. Mix together by heating, and apply with a knife blade which has just been heated.
Fig. 33.Canvas Water Bag.
Are easily made, and are very handy for carrying small supplies of drinking-water when prospecting in a dry country; they having the advantage of keeping the water cool in the hottest weather, by reason of the evaporation. The mouthpiece is made of the neck of a bottle securely sewn in(Fig. 33).
Medicine is also a matter well worthy of thought. The author’s worst enemy would not call him a mollycoddle, yet he has never travelled in far wilds without carrying something in the way of medicine. First, then, on this subject, it cannot be too often reiterated that if common Epsom salts were a guinea an ounce instead of a penny the medicine would be valued accordingly, but it is somewhat bulky. What I specially recommend, however, is a small pocket-case of the more commonly known homœopathic remedies, “Mother tinctures,” or first dilutions, which are small, light, and portable, with a small simple book of instructions. Though generally an allopath in practice, I once saved my own life, and have certainly helped others by a little knowledge in diagnosing complaints and having simple homœopathic remedies at hand to be used in the first stages of what might otherwise have been serious illnesses.
Every one has heard, and most believe, that fire may be easily produced by rubbing together two pieces of wood. I have seen it done by aboriginals, but they seldom make use of the operation, which is generally laborious, preferring to carry lighted fire sticks for miles. I have never succeeded in the experiment.
Sometimes, however, it is almost a matter of life or death to be able to produce fire. The back of a pocket knife, or an old file with a fragment of flint, quartz, or pyrites struck smartly together over the remains of a burnt piece of calico, will in deft hands produce a spark which can be fanned to a glow, and so ignite other material, till a fire is produced.
Also it may not be generally known that he who carries a watch has a “burning glass” with which he can, in clear weather, produce fire at will. All that is required is to remove the glass of your watch and carefully three parts fill it with water (salt or fresh). This forms a lens which, held steadily, will easily ignite any light, dry, inflammable substance.
When firearms are carried, cut a cartridge so that only about a quarter of the charge of powder remains. Damp some powder and rub it on a small piece of dry cotton cloth or well-rubbed brown paper. Push a loose pellet of this into the barrel, insert your half cartridge, fire at the ground, when the wad will readily ignite, and can be blown into flame.
The prospector is not usually a business man; hence in dealing with business men who, like Hamlet, are “indifferent honest,” he frequently comes to grief through not having a copy of his correspondence. It is most desirable, therefore, either to carry a carbon paper duplicating book and a stylus, or by adding a little sugar to good ordinary black ink you may make a copying ink; then with the aid of a “yellow back” octavo novel, two pieces of board, and some ordinary tissue paper, you may take a copy of any letter you send.
Buy a couple of cheap small dictionaries of the same edition, send one to your correspondent with an intimation that he is to read up or down so many words from the one indicated when receiving a message. Thus, if I want to say “Claim is looking well,” I take a shilling dictionary, send a copy thereof to my correspondent with the intimation that the real word is seven down, and telegraph—“Civilian looking weird;” this, if looked up in Worcester’s little pocket dictionary, for instance, will read “Claim looking well.” Any dictionary will do so long as both parties have a copy and understand which is the right word. By arrangement this plan can be varied from time to time if you have any idea that your code can be read by others.
Wood ashes from the camp fire are boiled from day to day in a small quantity of water, and allowed to settle, the clear liquid being decanted off. When the required quantity of weak lye has been accumulated, evaporate by boiling, till a sufficient degree of strength has been obtained. Now melt down some mutton fat, and, while hot, add to the boiling lye. Continue boiling and stirring till the mixture is about the consistency of thick porridge, pour into any convenient flat vessel, and let it stand till cool. If you have any resin in store, a little powdered and added gradually to the melting tallow, before mixing with the lye, will stiffen your soap.
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.
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 hundred-weight 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.
Where candles are scarce and kerosine is not, a “slush lamp” is a useful substitute. 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” or honeysuckle tree,Banksia marginata, is often used instead of the cotton wick.
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 be 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 willanswer 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.
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 gold 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.
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 incompetently performed. Sometimes the fuse is notplaced 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.
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.
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 thecentre 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. It is as well to place a piece of paper between the iron and the amalgam to prevent adhesion.
Fig. 34.Smoking-Pipe Retort.
Get two new tobacco pipes similar in shape(Fig. 34), 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.
Multiply the internal diameter of the cylinder by itself and strike off the last figure of the quotient. The diameter is
20” × 20”20-----40ø. The H.P. is 40.
20” × 20”20-----40ø. 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.—Fornon-condensingengines: Multiply the square of the diameter of the cylinder in inches by 7 and divide the product by 80. Forcondensingengines: Multiply the square of the diameter of the cylinder in inches by 7 and divide the product by 200.
To find the Actual Horse-powerof 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.
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 are to be taken from the fire and the gold scraped off. Any part of the plate on which the gold has not blistered shouldbe 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 when it is molten, corrosive sublimate should be put in the crucible till a blue flame ceases to be given off.
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, and 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.
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. When cool, 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.
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 its 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.”
“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 its 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.
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 furtheradvantage 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.”
“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 furtheradvantage 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.
“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 850 lb. stamp, dropping 6 inches 95 times per minute,1·33 h.p.For each 750 lb. stamp, dropping 6 inches 95 times per minute,1·18 h.p.For each 650 lb. stamp, dropping 6 inches 95 times per minute,1·00 h.p.For an 8-inch by 10-inch Blake pattern rock-breaker9·00 h.p.For a Frue or Triumph vanner, with 220 revolutions per minute0·50 h.p.For a 4-feet clean-up pan, making 30 revolutions per minute1·50 h.p.For an amalgamating barrel, making 30 revolutions per minute2·50 h.p.For a mechanical batea, making 30 revolutions per minute1·00 h.p.
“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:
The writer has had small practical experience of the working of that excellent hydraulic motor, the Pelton wheel, but if byhorse-power in the table given is meant nominal horse-power, it appears to be high. Working with 800 cwt. stamps, 80 blows a minute, 1 h.-p. nominal per stamp 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.
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.
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 horse-shoe magnet might probably do just as well, but would require to be re-magnetised from time to time.
To silver copper plates, that is, to amalgamate them on the face with mercury, is really a most simple operation, though many battery men 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 effect the purpose. When the crystals have formed, add sufficient clean quick mercury to form a thick pasty amalgam; moderate heat 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 somewhat dilute 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 copper-plates are coated 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 free sulphuric acid, is being used, the latter plan is preferable.
The copper should be placed smoothly on the wooden table andsecured 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 a glazed 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.
Now have 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 nitrate 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. Then 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 somedays 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 zinco-mercury amalgam 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: eitherutiliseorneutralise. In certain cases, I recommend the former. Some time since I was treating, for gold extraction, material from a mine which was very complex in character. For this ore I coined the term “polysynthetic.” Thiscontained 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.