for common carpenters' pencils: it is sometimes used in manufacturing crucibles, and in compositions for covering cast-iron, and for diminishing friction in machinery.*

Mr. Bakewell was informed at the celebrated mine in Borrowdale, that black-lead, to the amount of one thousand pounds, had been obtained there in one day.

Why is common white-lead made by exposing sheetlead to acetic acid?

Because the fumes of the acid oxidize the metal. Thus, a number of crucibles, holding from three to six quarts each, and nearly filled with vinegar, are placed in hot-beds of tan: upon these crucibles thin sheets of lead, rolled up in coils, are placed, one coil over each crucible. The heat of the bed occasions the vinegar to rise in vapours, and this attaches itself to the lead, and oxidizes its surface to a considerable depth. The oxide which has been thus formed, is scraped off, and the coils of lead replaced: in this manner the operation is repeated, until the whole of the metal is oxidized. This oxide, which contains a portion of carbonic acid, is afterwards washed, and ground for sale. Why does linseed-oil, boiled with red-lead, become drying oil?

Because the oxygen of the metal combines with the oil, imparting to it the property of drying quickly.

ANTIMONY.

Why is antimony important in the arts?

Because, alloyed with lead, in the proportion of 1 to 16, and a small addition of copper, it forms the alloy used for printers' types: with lead only, a white and rather brittle compound is formed, used for the plates upon which music is engraved. With tin, antimony constitutes a kind of pewter, a term, however, applied to an alloy of lead and tin. The finest

*See MECHANICS, page 36.

pewter consists of about twelve parts of tin and one of antimony, with a small addition of copper. A good white metal, (Britannia) used for tea-pots, is composed of 100 tin, 8 antimony, 2 bismuth, and 2 copper.

COPPER.

Why is copper chosen for making trumpets and other musical instruments?

Because of its sonorous property.

Why is copper-wire chosen by wire-dancers?

Because of its great elasticity. Thus a wire 1-10th of an inch in diameter, will support nearly 300lb.

The first copper smelting works were established at Swansea, about a century ago, but the business has so increased, that it is calculated not fewer than 10,000 persons are now employed in the works and the collieries, and the shipping connected with them.

The following is an outline of the process by which ores of copper are reduced, as carried on upon a large scale near Swansea, where the chief part of the Cornish ores are brought to the state of metal. The ore, having been picked and broken, is heated in a reverberatory furnace, by which arsenic and sulphur are driven off. It is then transferred to a smaller reverberatory, where it is fused, and the slag which separates, being occasionally removed, is cast into oblong masses, used as a substitute for bricks. The impure metal collected at the bottom of the furnace, is granulated by letting it run into water; it is afterwards melted and granulated two or three times successively, in order further to separate impurities, which are chiefly sulphur, iron, and arsenic, and ultimately cast into oblong pieces called pigs, which are broken up, roasted, and lastly melted with charcoal in the refining furnace. Malleability is here conferred upon the copper, and its texture improved by stirring the metal with a pole of green wood, generally birch, which causes great ebullition and agitation; assays are occasionally taken out, and

the metal, originally crystalline and granular when cold, now becomes fine and close, so as to assume a silky polish when the assays are half cut through and broken. The metal is now cast into cakes about twelve inches wide, by eighteen in length. Copper for brassmaking is granulated by pouring the metal through a perforated ladle into water; when this is warm, the copper assumes a rounded form, and is called belan shot; but if a constant supply of cold water is kept up it becomes ragged, and is called feathered shot. Another form into which copper is cast, chiefly for exports to the East Indies, is in pieces of the length of six inches, and weighing about eight ounces each: the copper is dropped from the moulds, immediately on its becoming solid, into a cistern of cold water; and thus, by a slight oxidation of the metal, the sticks acquire a rich red colour on the surface. This is called Japan Copper.-Brande.

Sulphate of copper, or Roman vitriol, is much used by dyers, and in many of the arts. Fowling-pieces and tea-urns are browned, by washing them with a solution of this salt. Verdigris is an acetate of copper. Blue verditer, much used in staining paper for hanging rooms, is a nitrate of copper, combined with hydrate of lime. Mineral and Brunswick green, are likewise combinations of copper with potash, &c. At Montpellier, the manufacture of rough verdigris is part of the household business in the wine-farms, and is generally done by the women.

The annual value and produce of the copper and tin from the mines of Cornwall and Devonshire, on an average of several years, may be stated at 75,000 tons of copper ore, value £800,000. sterling; 3,250 tons of metallic tin, value £227,000.-Bakewell's Geology.

According to the tables of the produce of the soft metals raised in Great Britain, as given in a work entitled Records of Mining, the quantity raised in a year

is as follows:-copper, 16,635 tons; lead, 47,000 tons; and tin, 5,316 tons.

Why is the rust advantageous to copper?

Because the corroded part is very thin, and preserves the metal beneath from further corrosion.

Why have small bells a shrill tone?

Because zinc is added to their composition, usually consisting of three parts copper and one of tin.

Why has apparatus been invented for sounding bells without pulling?

Because buildings suffer much from the sounding of bells, especially when they are very heavy. Let one, in fact, only imagine a mass of several tons swinging to and fro, and he will readily perceive how much a building must be shaken by it. In Denmark, Professor Oersted has introduced into a bell a balance; similar to that of a pendulum. An axis, by turning, raises a hammer, which, at each turn, strikes the bell, and produces a sound which cannot be distinguished from that emitted by the bell when tolled.

The largest bells in the world are to be found in Russia. The "Great Bell" of Moscow, cast in the year 1736, weighs 432,000 pounds, is 19 feet high, 21 yards in circumference at the bottom, and at its greatest thickness 23 inches.*

Why should children be cautioned against eating the imitative gold on gingerbread, &c.?

Because it is nothing more than a fine kind of brass, which is supposed to be made by cementation of copper plates with calamine, and hammered out into leaves

* Mirrors are also cast of larger dimensions at St. Petersburgh, than elsewhere. In the Imperial manufactory here, was cast for Prince Potemkin, a mirror, measuring 194 inches by 100. One, of the same proportions, and valued at three thousand guineas, was cast for the Duke of Wellington, a few years since, but was broken to atoms in its conveyanee from St. Petersburgh to England.

in Germany. It is sold very cheap in this country, under the name of Dutch gold or Dutch metal. It is about five times as thick as gold leaf; that is to say, it is about one sixty-thousandth of an inch thick.

Why is tin preferable to other metals for lining copper vessels ?

Because it combines with copper at a much lower temperature than is necessary to fuse the copper alone. When vessels are tinned, they are first scraped or scoured; after which they are rubbed with sal-ammoniac. They are then heated, and sprinkled with powdered resin, which defends the clean surface of the copper from acquiring the slight film of oxide, that would prevent the adhesion of the tin to its surface. The melted tin is then poured in and spread about. An extremely small quantity adheres to the copper, which may perhaps be supposed insufficient to prevent the noxious effects of the copper as perfectly as might be wished.

Why do watchmakers prefer Dutch brass to the English?

Because of its superior ductility, which is owing to the large proportion of copper contained in it; the Dutch being a compound of two atoms of copper and one of zinc, while the English is of equal parts of copper and zinc.--Thomson.

COBALT.

Why is cobalt extremely valuable to the manufacturers of porcelain?

Because it not only produces a beautiful colour, but endures the extreme heat of their furnaces unaltered. This colour is so intense, that a single grain of the pure oxide will give a deep tint of blue to 240 grains of glass. Smalt, or powder-blue, used by laundresses, consists of oxide of cobalt, ground impalpably with flint-glass. This is also used to give a blue tinge to writing and printing papers.