Treats of Tin-Smelting and other Matters.
There is something grand in the progress of a mechanical process, from its commencement to its termination. Especially is this the case in the production of metals, nearly every step in the course of which is marked by the hard, unyielding spirit of vis inertiae on the one hand, and the tremendous power of intelligence, machinery, and manual dexterity on the other.
Take, for example, the progress of a mass of tin from Botallack.
Watch yonder stalwart miner at work, deep in the bowels of the mine. Slowly, with powerful blows, he bores a hole in the hard rock. After one, two, or three hours of incessant toil, it is ready for the powder. It is charged; the match is applied; the man takes shelter behind a projection; the mass is rent from its ancient bed, and the miner goes off to lunch while the smoke is clearing away. He returns to his work at length, coughing, and rubbing his eyes, for smoke still lingers there, unable, it would seem, to find its way out; and no wonder, lost as it is in intricate ramifications at the depth of about one thousand five hundred feet below the green grass! He finds but a small piece of ore—perhaps it is twice the size of his head, it may be much larger, but, in any case, it is an apparently poor return for the labour expended. He adds it, however, to the pile at his side, and when that is sufficiently large fills a little iron wagon, and sends it up “to grass” through the shaft, by means of the iron “kibble.” Here the large pieces of ore are broken into smaller ones by a man with a hammer; as far as the inexperienced eye can distinguish he might be breaking ordinary stones to repair the road! These are then taken to the “stamps.”
Those who have delicate nerves would do well to keep as far as possible from the stamps of a tin-mine! Enormous hammers or pounders they are, with shanks as well as heads of malleable-iron, each weighing, shank and head together, seven hundredweight. They are fearful things, these stamps; iron in spirit as well as in body, for they go on for ever—night and day—wrought by a steam-engine of one hundred horse-power, as enduring as themselves. The stamps are so arranged as to be self-feeders, by means of huge wooden troughs with sloping bottoms, into which the ore is thrown in quantities sufficient to keep them constantly at work without requiring much or constant attendance. Small streams of water trickle over the ore to keep it slowly sliding down towards the jaws, where the stamps thunder up and down alternately. A dread power of pounding have they, truly; and woe be to the toe that should chance to get beneath them!
The rock they have to deal with is, as we have said, uncommonly hard, and it enters the insatiable mouth of the stamps about the size of a man’s fist, on the average, but it comes out from these iron jaws so exceeding fine as to be incapable of thickening the stream of reddish-yellow water that carries it away. The colour of the stream is the result of iron, with which the tin is mingled.
The particles of tin are indeed set free by the stamps from solid bondage, but they are so fine as to be scarcely visible, and so commingled with other substances, such as iron, copper, sulphur, etcetera, that a tedious process of separation has yet to be undergone before the bright metal can be seen or handled.
At the present time the stream containing it is poured continuously on several huge wooden tables. These tables are each slightly raised in the centre where the stream falls, so that all the water runs off, leaving the various substances it contains deposited on the table, and these substances are spread over it regularly, while being deposited, by revolving washers or brushes.
Tin, being the heaviest of all the ingredients contained in the stream, falls at once to the bottom, and is therefore, deposited on the head or centre of the table; iron, being a shade lighter, is found to lodge in a circle beyond; while all other substances are either spread over the outer rim or washed entirely away. When the tables are full—that is, coated with what appears to be an earthy substance up wards of a foot in depth—the rich tin in the centre is carefully cut out with shovels and placed in tubs, while the rest is rewashed in order that the tin still mingled with it may be captured—a process involving much difficulty, for tin is so very little heavier than iron that the lighter particles can scarcely be separated even after repeated and careful washings.
In old times the tin was collected in large pits, whence it was transferred to the hands of balmaidens (or mine-girls) to be washed by them in wooden troughs called “frames,” which somewhat resembled a billiard table in form. Indeed, the frames are still largely employed in the mines, but these and the modern table perform exactly the same office—they wash the refuse from the tin.
Being finally cleansed from all its impurities, our mass of tin bears more resemblance to brown snuff than to metal. An ignorant man would suppose it to be an ordinary earthy substance, until he took some of it in his hand and felt its weight. It contains, however, comparatively little foreign substance. About seventy per cent of it is pure tin, but this seventy per cent is still locked up in the tight embrace of thirty per cent, of refuse, from which nothing but intense fire can set it free.
At this point in the process, our mass of tin leaves the rough hand of the miner. In former days it was divided among the shareholders in this form—each receiving, instead of cash, so many sacks of tin ore, according to the number of his shares or “doles,” and carrying it off on mule or horse back from the mine, to be smelted where or by whom he pleased. But whether treated in this way, or, as in the present day, sold by the manager at the market value, it all comes at last to the tin-smelter, whose further proceedings we shall now follow, in company with Oliver and his friend.
The agent of the smelting company—a stout, intelligent man, who evidently did “knaw tin”—conducted them first to the furnaces, in the neighbourhood of which were ranged a number of large wooden troughs or bins, all more or less filled with tin ore. The ore got from different mines, he said, differed in quality, as well as in the percentage of tin which it contained. Some had much iron mixed with it, in spite of all the washings it had undergone; some had a little copper and other substances; while some was very pure. By mixing the tin of different mines, better metal could be procured than by simply smelting the produce of each mine separately. Pointing to one of the bins, about three yards square, he told them it contained tin worth 1,000 pounds. There was a large quantity of black sand in one of the bins, which, the agent said, was got by the process of “streaming.” It is the richest and best kind of tin ore, and used to be procured in large quantities in Cornwall—especially in ancient times—being found near the surface, but, as a matter of course, not much of that is to be found now, the land having been turned over three times in search of it. This black sand is now imported in large quantities from Singapore.
The agent then conducted his visitors to the testing-house, where he showed them the process of testing the various qualities of tin ore offered, to the House for sale. First he weighed out twenty parts of the ore, which, as we have said, resembled snuff. This, he remarked, contained about five-sixths of pure tin, the remaining one-sixth being dross. He mixed it with four parts of fine coal dust, or culm, and added a little borax—these last ingredients being intended to expedite the smelting process. This compound was put into a crucible, and subjected to the intense heat of a small furnace for about twenty minutes. At the end of that time, the agent seized the crucible with a pair of tongs, poured the metal into an iron mould, and threw away the dross. The little mass of tin thus produced was about four inches long, by half an inch broad, and of a dull bluish-grey colour. It was then put into an iron ladle and melted, as one would melt lead when about to cast bullets, but it was particularly noteworthy here, that a very slight heat was req............