Chapter III: Working in Metals (4)

A common horse-shoe magnet, such as can be bought for a mere trifle at any toyshop, will be found very useful for extracting particles of iron from other mineral. Whenever the means of transport will admit, it is well to take a small compact case of simple appliances, tests, and reagents. The whole, by a little ingenuity, may be easily packed in a solid leather case very little larger than an ordinary sandwich box. Its contents should be as follows: Small glass-stoppered and capped bottle of nitric acid, ditto hydrochloric acid, ditto liq. ammonia, ditto quicksilver, small corked bottles of ferrocyanide of potassium, bi-chromate of potash, fused borax, and common salt; a small jointed blowpipe, a pair of forceps, a small pair of scales, fitted for taking specific gravities, and a set of weights, a bit of flint glass, a piece of sapphire, which can be obtained from any lapidary; half a dozen test tubes to nest one within the other; half a dozen old watch glasses, to be obtained for a few pence from any watchmaker; half a dozen narrow strips of window glass, cut to a thickness little greater than stout wire, and 5in. long (these are for stirring up hot acids, &c.); a piece of stout copper wire, shaped like the figure 9, to hold the watch glasses on whilst they are over the lamp or candle flame; a small fine file and a few narrow slips of well burnt light charcoal; a common wire cigar-holder, to hold the test tubes in whilst heated; and a very small bright-faced hammer, such as watchmakers use. It is truly astonishing how much qualitative analysis can be carried out with these comparatively limited means. We will suppose that a little bag of sand has been obtained; that it shows, on being spread out, a number of particles of a glittering yellow substance, as well as black-coloured grains, mixed with common quartz and minute fragments of stone. We first place our sand on a sheet of white paper, and with our pocket lens have a thorough examination of the various constituents. Should any grains of sufficient size and questionable character present themselves, they may be at once taken up on the moistened point of a pin. If one of them should look like gold, place it on some hard substance and give it a blow with your hammer. If it flattens without powdering, drop it into one of your test tubes, pour in a little nitric acid, and hold it in the flame until it boils thoroughly. If your particle gives off a train of minute bubbles and gradually dissolves, pour a little of the contents of your tube into two separate watch glasses placed side by side, add a little water to each. Add a little common salt to No. 1; if the particle is silver, you will at once have a thick white precipitate--chloride of silver. Drop a few drops of your liquor ammonia into No. 2; and if copper, the beautiful and well-marked blue colour of ammonuret of copper will at once appear. Should the particle have crushed under the blow, it is probably either sulphuret of iron or copper ore. To distinguish these two substances when in a minute state of division, proceed with the acid as just described, and test one watch glass with a small fragment of ferrocyanide of potassium, when, if sulphuret of iron or "mundic," you will have a dense cloud of Prussian blue in your watch glass. Treat the other with your liquor ammonia, and you will have the same brilliant ammonuret of copper colour as if the particle had been native or malleable copper. Having satisfied ourselves as to the selected particles--for should the flattened grain resist the action of the hot acid and remain bright, it is surely gold--we place our sand on a shovel, and hold it there until the whole is red hot; it may then be taken from the fire, and allowed to cool on the shovel. The magnet will now take out all the bits of iron. Now with a hammer-face or smooth water-worn pebble proceed to crush all the substances on the shovel fine. Then at the nearest stream of water, or in a large tub, carefully van and wash your sample until all the earthy and worthless matters have been washed away; then the practised eye will instantly distinguish the gold, if any. The utterly inexperienced may, however, be deceived by remaining fragments of mundic or copper ore before referred to; therefore, to make assurance doubly sure, let him dry his washed metal powder on the shovel over the fire, then carefully place it in a small, clean, dry vial-bottle with a little quicksilver. Shake and rattle it well about until all the particles have been brought well in contact with the mercury. Such fragments as it will not take up are not gold; but to find that which it has converted into an amalgam, place the mercury in a piece of clean chamois leather, press it carefully, and the mercury will force its way in minute globules through the leather, leaving the gold in a soft mass within. This, by being heated to redness, throws off the remaining quicksilver, and can be estimated as gold. Silver will also amalgamate with mercury, but can always be distinguished from gold by the nitric acid and salt test before described. Lead ore is rarely mistaken for anything else, its peculiar colour, cubical form of crystallisation, and gravity being generally sufficient to identify it. A small quantity, reduced to a fine powder and mixed with a little fused borax, readily fuses on a charcoal slip before the blowpipe, and is then ordinary lead. The silver often associated with lead ores can alone be estimated by a regular assay, requiring the use of crucibles, cupels, furnace, &c. Sulphuret of antimony, although massive and somewhat lead-coloured, leaves a thick rough deposit on the charcoal, and fuses into a brittle crystalline regulus, in no way resembling lead. Small specimens of galena, or lead ore, should always be preserved for future investigation, as it is at times extremely rich in silver, whilst at others a mere trace only remains. We have analysed lead ore from Cornwall which yielded between 90oz. and 100oz. of silver to the ton, whilst other samples, raised in Wisconsin, although yielding 85 per cent. of lead, did not contain enough silver to render its extraction remunerative. The points of distinction between minerals and metals we have thus been briefly laying down do not properly apply to the investigations of the regular gold-digger, but are mainly intended for the use of those who are engaged in exploration and research. The professed gold-seeker, as a rule, casts all aside save the one great centre of his hopes and pursuit. He, in his prospecting expeditions, makes use of the broad shallow metal pan shown in the illustration which represents "Searching for Gold." The quantity of gold brought to light by its aid guides him in his choice of a locality. If it is considered rich enough, he, with his mates, sinks down to "_the pay dirt_," or deposit containing the gold; this is either washed out at once on the cradle, or piled in heaps for future treatment. With gold quartz-crushing, amalgamation on a large scale, or the washing down of drift by hydraulic power and the use of flumes as practised in California, we cannot deal here, as the appliances are far more complicated and ponderous than the mere traveller could carry with him.

{Base metal, to detect.}

It sometimes happens that imposition is attempted in far-off lands, and imitation gold ornaments offered to the traveller. To test the quality of these, it will be requisite to have a bit of black terra-cotta pot, or a fragment of any hard smooth black stone. Rub the suspected ornament on this until a metallic streak is left, dip one of your bits of glass rod in your nitric acid, and let a drop or two fall on the track left by the metal. If of base material, the particles will rapidly turn green and dissolve; if gold, they will remain unchanged; and if an alloy, the combined metal will be removed, and the gold wall remain stationary on the black surface. The exact standard of mixture or combination can only be arrived at by the use of a set of touch-needles, which are rubbed and compared with the doubtful marks on the stone.

{Stone, to quarry.}

There are many situations in which stone may be advantageously used for the erection of houses, forts, or defensible depôts. On the discovery of a bed of rock adapted for the purpose, the head or covering earth should be removed, either by the agency of water obtained by diverting some neighbouring stream for the purpose, or by digging with the spade or shovel. Careful examination will now generally disclose veins or seams traversing the stone, such of these as run in favourable directions should be selected, and the gads or wedges before described had recourse to. It is well to have, at least, a dozen of these for stone splitting. They should be about 5in. long, 1-1/2in. wide, and 1/2in. thick, tapering to the edge, which should not be too sharp. All gads should be made of the best gad steel, carefully pointed and tempered. In entering the gads, it will be well to insert them in the selected seam at about 1ft. apart; then, with the heavy hammer or pick-head, strike each gad a blow or two in succession, which will serve to open the seam, and not unfrequently detach the required fragment. When large square or oblong blocks are required, it is well to first mark out the size required on the rock with the pick's point, and then with either the borer before described, or a jumping bar (of form shown in the annexed illustration), drill a row of holes about 8in. apart on the line before marked out, in depth proportioned to the intended thickness of the stone, in each hole should be placed a pair of gad cheeks--these are pieces of half-round iron bar. The rounded sides rest against the sides of the holes as the gad is driven between the flat surfaces, thus forcing open the grain of the rock without breaking away the sides of the holes by gad clinching. As in the former case, each gad is gradually driven home until the line of holes run into one long fissure and the block is detached. In breaking out flat slabs of comparatively thin stone, it will be found a good plan, after measuring and marking the size decided on, to sink a shallow groove either with the pick's point or a stonecutter's chisel across the extreme length of the slab; then, by inserting the gads at the outer face or edge of the deposit, the slab will not only be raised but evenly broken off. Fire is a most powerful agent and aid in stone-breaking, especially when assisted by water. The huge and massive boulder of rock which bids defiance to the sledge-hammer may very soon be reduced to fragments by making a strong fire round it, and, when thoroughly heated, throwing buckets of water over it.

{The treatment of stone.}

Some Indians are particularly clever in the art of stone dividing. They build a double wall of clay the whole length of the stone, leaving about six inches of bare rock between them. They then lay more clay on the outsides of the walls, nearly the width of the stone. Then between the walls of clay they make a long line of fire with dry cow dung and chips of hard, dry wood. An incredibly short space of time elapses before the division of the stone is completed, when the fire is carefully extinguished with earth or sand, and the stone allowed to cool. Rocks, so placed as to prevent recourse being had to either of the expedients described, may be split out by the action of a small charge of powder, fired, as before directed, in a hole made by the jumping bar. To drill a hole with this no hammer man is required, but the weight of the protuberance on the instrument, when aided by a jumping and rotatory motion, is sufficient to cut away the rock. Water swab, shell scraper, &c., are used with these implements, just as they are with the miner's borer, which can be used in confined spaces and under outlying works, where the jumper would be useless. A crowbar or two will be found very useful for lifting out broken pieces of stone, &c. There is also an instrument much used in America called a "canthook," which is here represented. It is extremely valuable for moving both stones of large size and logs of unwieldy dimensions. The handle, or lever, is made of tough, well-seasoned timber, and is usually from 6ft. to 7ft. long. The claw is of sound, tough, wrought iron, and proportioned in weight and spread to the bodies it is applied to. Two or three sizes of claws fit one handle, just as a dentist's key is adapted to the size of the tooth it is to grasp. An oblong square hole is cut through the lever for the claw's end to pass through, and a stout iron pin, with a hole in the end for a split stop to go into, keeps the claw at its proper point of adjustment. The boulder claw is another most useful implement. It is used for turning over and rolling out large boulders of rock, lifting out logs, &c. These claws, and the chains and rings to which they are attached, should be made of the best Swedish iron; the claw point should be of gad steel, welded in. The form of the hook or claw is very important, as, if not turned to the exact bend, it will not grip or hold. The above illustrations will serve to show both the form of the claw and its mode of action when in use.

{Miners' pump, to make.}

When water settles in a comparatively shallow pit, too large to be conveniently emptied by the aid of buckets, a very simple form of pump will be found useful. Nail four long planks together in the form of a narrow square box or tube, say 1ft. square; now procure a stout pole a little longer than the box, nail a flat board to one end of it just as a table is attached to its stand, cut away the edges until it fits the box loosely, then nail a bordering of old boot leather or hide round the edges until it fits tight enough to suck; cut a large square hole in it, and fasten over this with tacks a piece of tapping leather or raw hide backed with wood for a valve; bore a hole in the upper end of the pole to put a cross handle through; bore an auger hole through the lower end of your box about 1ft. from the opening, and through this drive a stout stick to keep the sucker from coming too far down; your pump is now complete. Place it in a slightly slanting direction in the pond, and secure it with a crooked stick driven in by its side; push the sucker to the bottom, pour a bucket of water or so in to make it draw, and you will, by working the piston steadily up and down, soon have the water pouring in a flood over the upper edge of the box, where it can be caught in a hollow log or a pit lined with clay. One of these box pumps is shown in the full page illustration "Searching for Gold."

{Charcoal burning.}

The traveller will find it extremely useful to be able to manufacture his own charcoal. There are several methods by which he can do this, all depending on the same general principles. Pieces of wood of suitable length and convenient size are prepared. We show here the most effective arrangements.

The pile, when evenly and completely built up, is covered with turf and a little sand or earth--leaving one fair-sized orifice as a draught hole. Fire is introduced either at the bottom of the pile through a hole left for it, or dropped down through the space left by the withdrawal of the centre post. The orifices of all charcoal pits or chambers should remain open until the fire has become well distributed through the mass of wood, but should be covered with a stopper of turf or clay directly the light grey smoke of active combustion shows itself. The contents of the pile may from time to time be tested by removing a small portion of the stopping or covering turf and inserting a hooked iron rod, by the aid of which a sample of the baking may be withdrawn for examination. Immediately on being satisfied that the charcoal has been sufficiently burned, more earth, turf, sand, &c., should be heaped on the top of the pile, until every crevice is stopped completely. The fire will then soon die out, and the contents of the pile can be removed. We also represent a contrivance for preparing charcoal for gunpowder making. A small cask has one head removed, a stout pole run through the bung-hole, and is then evenly packed with selected billets of light suitable wood. (See "Gunpowder, to make," p. 247.) The head is then replaced, the cask covered with well-worked clay, and then sunk in a pit prepared for its reception. The pole is then withdrawn, and a good quantity of red-hot embers thrown down the hole. The cask, after being used for charcoal making, is very useful for an oven, as will be shown when cookery is under consideration.