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Gold has been known from the earliest times. The mummies of Egypt are adorned with it, and medals of it still exist, which are of very high antiquity. Not long ago, our supplies were mostly derived from Siberia, the west coast of Africa, Peru, and Brazil; but the gold-fields of those districts have been completely thrown into the shade by the announcement of successive discoveries in California, Australia, New Zealand, and British Columbia. From these places most of our gold is now obtained. It occurs native, or alloyed with silver, and sometimes also with small quantities of copper and iron, either in veins traversing quartz and similar rocks, or in beds of sand and other alluvial substances that have been washed down by rivers. Its beautiful colour, and the splendid polish it is capable of receiving, have caused it to be largely employed for decorative purposes. Objects of pure gold, however, would not only be too expensive, but too soft to retain their shape; and hence, in Europe at least, it is usually alloyed with copper or some other metal. Fortunately for luxury, the extreme malleability of gold enables us to cover with it all sorts of substances, which thus acquire, externally, the same brilliancy as the metal itself. The gold leaf used for this purpose is said to be, in some cases, a thousand times thinner than paper. Gold is also the most ductile of the metals; one ounce of it may be drawn out into a wire several miles long; and the same quantity is sufficient to gild a silver wire whose length would be measured by hundreds of miles.
Gold is well known to be the symbol of wealth, and the standard of value for other substances. For coinage it is admirably adapted; it has a high intrinsic value, increased by its scarcity; it is also very durable, capable of exact subdivision, and easily distinguished from other substances. The sterling gold, of which sovereigns are made, contains twenty-two parts of pure metal to two of alloy.
Mercury, or Quicksilver, is remarkable as the only metal which remains fluid at the ordinary temperature of the atmosphere. In this, its usual state, it has the brilliant
whiteness of silver, and, when pure, neither rusts nor tarnishes by exposure. It is very heavy, has neither taste nor smell, and feels particularly cold. The most important ore of mercury is cinnabar, a compound of the metal with sulphur. It is found in several localities, of which the most celebrated are Almaden in Spain, and Idria in the south of Austria. Quite recently it has been discovered in great abundance, and of remarkable purity, in California.
The uses of mercury are many and important. Calomel, one of its compounds, is a valuable medicine; another, corrosive sublimate, containing exactly the same elements in a different proportion, is a deadly poison. Mercury is also an ingredient of the beautiful pigment called vermilion, and forms with tin an amalgam used for silvering the backs of looking glasses. Every one has seen the little tube of mercury in the barometer and thermometer, the construction of which will be afterwards described. But perhaps the most important application of this metal is that by which silver and gold are separated from their ores.
SILVER, COPPER, TIN, LEAD.
Silver is so well known as hardly to need description. When pure, it is white and brilliant, but it becomes tarnished by exposure to the air. It is very malleable, flexible, and ductile. Native silver is sometimes found in grains, and sometimes in larger masses, but it is from ores that our supplies of this valuable metal are chiefly obtained. Of these ores, the most important are sulphurets, or compounds of the metal with sulphur. They often contain other metals besides silver. Galena, for example, though considerable quantities of silver are sometimes extracted from it, is properly an ore of lead. Among the principal silver mines may be mentioned those of Mexico and Peru, of the Hartz mountains in Germany, and of Kongsberg in Norway.
A curious plan is adopted for separating this metal from its ores. The ores, after various preparations, are mixed
with mercury, which amalgamates with the silver; the amalgam so formed is then run off, and subjected to fire, which drives off the mercury in vapour, leaving the silver nearly in a state of purity. Silver is never used quite pure, but always alloyed with copper, to render it harder and more durable. It is not affected by any of the substances generally used as food; hence, being at once cleanly and beautiful, it is admirably adapted for culinary and domestic purposes. It is also formed into vases, candelabra, statues, and other ornamental articles. As a medium of exchange it was used as early as the days of Abraham (Gen. xxiii. 15, 16).
Copper, if not the most important of the metals, is unquestionably one of very general utility. It is highly malleable, flexible, and ductile, harder and more elastic than silver, more fusible than iron, and the most sonorous of all the metals. It occurs native in many parts of the world. In America, large masses of native copper are met with, sometimes lying on the surface of the soil. The most abundant ore of this metal is usually known as yellow copper, or copper pyrites, and contains nearly equal quantities of copper, iron, and sulphur. It is found in various localities, both in our own and other countries. A richer but less plentiful ore of copper is the red oxide, which yields four-fifths of its own weight of metal.
Copper and its alloys are applied to purposes innumerable. We cover the hulls of ships with plates of it, and we form it into cauldrons, distilling apparatus, cooking utensils, &c. For the latter purpose it is, to a certain extent, dangerous; one of its salts, called verdigris, which it generates when acted on by certain acids, being a virulent poison. Hence the inside of copper vessels is usually coated with tin. An immense quantity of copper is used for coin, for which purpose it is generally more or less alloyed. Its alloys are, indeed, still more important than the metal itself. It would be impossible to enumerate all the articles, from a pin to a cannon, which are made of alloys of this metal with tin or zinc, or both together, and occasionally with nickel, lead, and iron. These alloys are known under various names,
such as brass, bronze, bell-metal, gun-metal, pinchbeck, German silver, &c.
Tin has long been known and worked in this country. It was the tin mines of Cornwall that first led the Phoenicians, the great merchants of ancient times, to visit our island shores. The only important ore of tin is an oxide, of which the metal forms about three-fourths by weight. It is found in abundance in various countries; the mines of Cornwall alone yield 5000 tons annually. Some of the uses of this metal have been already mentioned. It is, besides, largely employed for covering sheet iron, which, when so covered, is called tin-plate. This tinned iron is manufactured into cheap and useful articles for domestic purposes.
Lead is a well known metal, proverbially heavy, very malleable, but soft and inelastic. It is said to be found native in lava, but it is chiefly procured from a sulphuret called galena, of which (as already stated) some varieties contain silver as well as lead. The lead mines of Britain produce in one year little less than 100,000 tons. It can scarcely be necessary to dwell upon the uses of this metal. Roofs of houses are covered with it, and gutters are made of it to carry off the rain that collects on slates or thatch. Water pipes and tanks, window frames, coffins, bullets for guns and pistols, shot, and many other articles, are also made of lead. It is worth while to add that an alloy of lead and antimony is used for printing-types, to which the civilization of the world is so much indebted.
IRON is by far the most important of all the metals. It pervades, more or less, almost every object in nature. It exists both in plants and animals, and it is the colouring matter of many earths and stones. So extremely various are the forms in which it occurs, and so different the proportions in which it is combined with other minerals, that it is difficult to separate the orcs of iron from those sub
stances in which the metal is merely an accidental or accessary ingredient.
Iron occurs native, but not abundantly. of it are sometimes found lying on the surface of the ground, and are believed to have fallen from the sky; whence they have come it is very difficult to say. The iron of these remarkable productions is called meteoric.
Among the ores of iron, which are numerous and extremely various, there are two important oxides, distinguished as the black oxide, magnetic iron ore, or loadstone, and the red oxide, or hæmatite. The former is remarkable for the possession, in its natural state, of those properties from which the needle of the mariner's compass derives its value. It is the principal ore of iron in Norway, Sweden, and Russia, and the iron manufactured from it, in these countries, is of the very best quality. A beautiful crystallized variety of the red oxide, called specular iron ore, is found in many parts of Europe. The finest specimens are from the island of Elba, in which valuable iron mines have been worked from a remote period. Similar in composition is common hæmatite, which, as the name implies, is usually of a blood-red colour, though the same name is applied, not quite properly, to other varieties of darker hue.
To us in this country, the most interesting ores of iron are carbonates more or less pure. One of these, called spathose iron ore, not only yields the best iron for conversion into steel, but is itself a kind of natural steel. But almost all the iron manufactured in Great Britain is obtained from an impure carbonate, called clay ironstone. It contains from 25 to 40 per cent. of metal, mixed with carbonaceous and clayey substances. The importance of this mineral may be conceived from the fact, that it yields, in Britain alone, from three to four millions of tons of iron every year.
The process by which the iron is manufactured is called smelting. In huge conical kilns of brick, built expressly for the purpose, the smelting fires are kept burning incessantly for years together, their lurid gleams lighting up the sky,