METALLURGY. The act of separat ing metals from their ores with an ore perfectly pure the obtaining a pure metal i is a metallurgic process. It is not con fined however to this, for ores are rarely pure, but contain earthy ingredients, foreign to, and injurious in, the after treatment. The treatment of ores is both mechanical and chemical. The mechan ical processes consist in picking, stamp ing, and washing. Almost all ores are picked by old men, women and children. After the larger lumps are broken by the hammer, then use hand hammers on these broken pieces, and then pick and sort on iron trays the richest lumps of ore. These are at once fit for smelting. The very coarsest are thrown aside as useless, and the intermediate lumps, which contain ore and stone, so inter mixed as not to be separated by hand, are passed on to undergo the process of stamping.
Before describing the refined methods of washing the more valuable ores of copper, silver, lead, &c., it is proper ti point out the means of reducing theta into a powder of greater or less fineness, by damping, so called from the name datope of the pestles employed for that pur pose. Its usefulness is not restricted to preparing the ores ; for it is employed in almost every smelting house for pound ing clays, charcoal, scoria:, &c.. A stamping mill or pounding machine con sists of several movable pillars of wood, placed vertically, and supported in this position between frames of carpentry. These pieces are each armed at their under end with a mass of iron. An arbor or axle, moved by water, and turning horizontally, tosses up these wooden pestles, by means of wipers or cams, which lay hold of the shoulders of the pestles. These are raised in succession, and fall into an oblong trough below, scooped out in the ground, having its bottom covered either with plates of iron, or hard stones. In this trough, beneath these pestles, the ore to be stamped is allowed to fall from a hopper above, which is kept constantly full.
The trough is closed in at the sides by twopartitions, and includes three or four pestles ; which the French miners call a battery. They are so disposed that their ascent and descent take place at equal in tervals of time.
Usually a machine is com posed of several batteries (two, three, or tour), and the arrangement of the wipers on the arbor of the hydraulic wheel is such that there is constantly a like num ber of pestles lifted at a time—a circum stance important for maintaining the uniform going of the machine.
The matter. that are not to be exposed to subsequent washing are stamped dry, that is, without leading water into the trough ; and the same thing is sometimes done with the rich ores, whose lighter parts might otherwise be lost.
Most usually, especially for ores of lead, silver, copper, &c., the trough of the stamper is plated in the middle of a current of water, of greater or less force ; which, sweeping off the pounded sub stances, deposits them at a greater or less distance onwards, in the order of the size and richness of the grain; constituting a first washing, as they escape from be neath the pestles.
After the ore is stamped it undergoes the next process, that of washing. This is a tedious and costly operation, and has for its object the separation of the earthy from the metallic part of the ore, and depends upon the fact that the latter is heavier than the former. Before being washed the ore is generally riddled or sifted by hand or machine.
Sometimes, as at Poulliiouen, the sieves are conical, and held by means of two handles by a workman ; and instead of receiving a single movement, as in the preceding method, the sifter himself gives them a variety of dexterous move ments in succession. His object is to separate the poor portions of the ore from the richer; in order to subject the former to the stamp mill.
Among the siftings and washings which ores are made to undergo, the most useful and ingenious are those practised by iron gratings, called on the Continent grilles anglaises, and the step washings of Hungary, ktveries & grandins. These methods of freeing the ores from the pulverulent earthy matters, consist in placing them, at their out-put from the mine, upon gratings, and bringing over them a stream of water, which merely takes down through the bars the small fragments, but carries off the pulverulent portions. The latter are received in cis terns, where they are allowed to rest long enough to settle to the bottom. The washing by steps is an extension of the preceding plan. To form an idea, let us imagine a series of grates placed succes sively at different levels, so that the water, arriving on the highest, where the ore for washing lies, carries off a portion of it, through this first grate upon a second closer in its bars, thence to a third, &c., and finally into labyrinths or cis terns of In certain mines of the Hartz, tables called a balais, or sweepingtables, are employed. The whole of the process consists in letting flow, over the sloping table, in successive currents, water charged with the ore, which is deposited at a less or greater distance, as also pure water for the purpose of washing the de posited ore, afterwards carried off by means of this sweeping Operation.