Chap. II

COMPOSITION AND USE OK MINERALS.

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rather less than 9 parts in 100; if it is pulverised too finely, which is difficult to present,especially when it is not very hard, there is a chance of loss in smelting, from the particlesbeing carried up the chimney by the force of the draughts. For this reason copper ore, whichlias been pulverised in the stamping mill, generally sells rather lower than the other ores.

In tin and lead ores there is also danger from the same cause as well as some loss, asthey contain about two-thirds of their weight of metal when they are put into the fur-nace. The other ores of copper are found in comparatively such small quantities that thelarge operation in preparing them for sale scarcely applies. T lie Grey Ore , chiefly asulphuret with a small admixture of iron, is the second in importance, but relatively of rareoccurrence. It requires no difference of treatment from that of the richer portionsof the bisulphuret. The black ores, of which but a very small quantity is found (usuallyoxide of copper), are permitted to touch the water as little as possible, as they are oftenfound in particles so fine as easily to be carried oft’by a small stream.

There is probably no metal which exists in so few varieties as tin: except a littlesulphuret, which has been found in combination with sulphuret of copper, all the tin ore isin the state of oxide. The tin and copper are sometimes so intimately mixed in theore, and it is so difficult to separate them, that it becomes a subject of debate whether itshould be sampled as copper ore, or carried to the smelting-house as tin. The tin oresraised in the west of England are smelted there, and the metal is brought to differentdegrees of purity for various purposes.

The richest stream tin is not taken to the stamping mill, as it merely requires some re-duction of size to prepare it for the furnace. Parcels may he frequently seen, the greatestpart of which consist of small pebbles, just as they were found in the stream, whichrequire little or no calcination. Put with this exception tin ore is all subjected to thestamping mill. The ore is in itself so rich, and consequently so heavy, that it is easilyseparated from the stony particles by the power of gravity.

This mode would not be advantageous for the copper ores, as the trouble of effectingtheir separation would l>o far too great; none therefore of these ores are subjected to thestamping mill, except some of the halvans, which have been thrown aside from the otherprocesses, to separate which pulverisation and subsequent dressing by water must beemployed.

The tin ore, which has connected with it the largest quantity of copper and iron pyrites,naturally yields the greatest proportion of arsenic. Copper ore is calcined by partial de-composition, to get rid of the sulphur and arsenic contained in it, and tin ore to decomposethe ores of other metals connected with it, and to expel the* sulphur and arsenic theycontain ; afterwards the tin oies are taken to the stamps, and a series of washings succeed,sometimes 100, before they are prepared for the calcining furnace. The portion of copperores subjected to similar processes is comparatively very small, simple selection and pulver-ising being the only preparation necessary.

In the preparation or dressing of the copper ores, the first step is the separation of thelarger pieces raised from the smaller by a sieve called riddle or griddle . When tills has beendone, the process of picking the valuable portions of the latter from the worthless succeeds ;ami this is the work which female children are first employed upon, whilst some of theyoungest boys are engaged in washing up, or cleansing the stones previously to this selection :this is done in wooden troughs, through which a stream of water flows immediately infront of the pickers. The girls are seated or half recline on a table, and a small heapof the mineral being thrown before them, they select and it put into a basket, or otherwiseseparate the valuable pieces, and throw hack the others into what are called the boxes,w'henee they are wheeled by boys to a large heap, which is again subjected to examination.This picking is carried on under a shed {hutch), open on both sides, for the convenienceof washing in front, and of the carrying away the rejected portion at the hack.

The Riddling, mentioned as the first part of the separation of the larger from the smallerpieces of ore, is performed by girls of sixteen years old or more: the very large massesare broken or ragged by men; those somewhat smaller are spalled by stout girls withlong-haiulled hammers, much in the way in which the larger pieces of stone are bioken forthe repair of roads. The riddling and spalling are performed in the open air.

The fragments are next to be cubbed; this process is performed by girls, who areseated a little above the ground with an iron anvil at their side; they break the stoneswith a short-handled hammer, to about the size usual in the repair of roads, rejectingas they proceed the worthless and very inferior parts. The stones of ore are now takento he bruised or bucked, where the further reduction of sizes is effected by the mill,called a crusher or grinder, now employed in pulverising of probably full half the copper oresraised. The manual process of bucking consists of pulverising by a sort of combined move-ment of percussion and trituration the pieces of ore already reduced to the weight of anounce or two, being chiefly those brought from the cobbers ; tins is done with a broadsquare hammer 2 or 3 pounds in weight, worked with both hands, or sometimes with oneonly, whilst the otlu-r is employed in sweeping the ore within convenient range ; the bucker

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