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of slaves allowed to be employed by those to whom leases of these mines had been granted. The ruby family of minerals is composed of seven species. They are all extremely hard, and several of them highly valued on account of their beauty,

The saline minerals comprehend all the combinations of alkalies with acids which exist in the mineral kingdom: such are salt-petre or nitrate of potash; common rock salt, or muriate of soda; and sal-ammoniac, or the muriate of ammonia. Common salt is found in immense masses under the earth's surface in many countries, particularly in Poland, Hungary, and England. The salt-springs in some parts of the United States owe their origin to beds of fossil salt. The rain-water, which penetrates to their surface, effects the solution of a certain portion of them with which it comes in contact, and thus becomes, in some cases, it is said, ten times salter than the water of the sea. The inflammable minerals comprehend all combustible bodies, except metals and the diamond; and include sulphur, resins, bitumens, and graphite. Among the bitumens are found the several varieties of mineral coal that are used for fuel, gas-lights, and other purposes. At Pittsburgh in Pennsylvania there are inexhaustible quantities of coal of a superior quality; it is found also in other parts of the state, in some parts of New-York, and in Rhode-Island. It not only enhances the value of the lands in which it is found, and through which it must pass, but is a source of national wealth, In England there are vast beds of coal which often lie at the depth of a hundred feet beneath the surface of the earth. Near White-haven there are some coal mines that extend half a mile under the

sea.

The metallic minerals comprehend all the mineral bodies, that are composed either entirely of metals, or of which metals constitute the most considerable and important part. It is from the minerals belonging to this class that all metals are extracted; and for this reason they have been called ores. They are found in a native state, either simple, consisting only of one substance, or compound, when composed of two or more substances. We shall briefly describe a few of the most useful metals. The first is platina. This is the heaviest of metals, and is found among the gold ores of South America in the form of small grains or scales. Its colour is

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between steel-grey and silver-white, and its ductility and malleability are very great. From late improvements in the process of bringing it to a pure and malleable state, its price has been diminished, and its utility is becoming more generally acknowledged. Facts are continually brought to light by means of platina instruments, which, without it, might perhaps ever have escaped notice.

QUESTIONS.-1. What are the four classes of minerals? 2. What are earthy minerals and how are they divided? 3. What is said of the diamond? 4. What are saline minerals? 5. Inflammable? 6. Metallic? 7. To what do salt-springs owe their origin? 8. What is said of mineral coal? 9. What is said of platina? [NOTE. The United States possess abundant sources of some of the most useful minerals, and of the stones used in jewelry.]

LESSON 78.

Gold.

In'got, a mass of metal. Nitro-muriatic acid is formed by mixing one part of nitric and four parts of muriatic acid; it was known to the ancient alchymists, and called aqua regia.

GOLD is never found in a mineralized state; but it occurs native in many parts of the world, generally alloyed with a little silver or copper, and commonly in the form of grains. Most of the gold of commerce is obtained at present from Africa and the continent of America. It is the heaviest of all metals except platina, and although its tenacity is such that a wire of one tenth of an inch in diameter will support a weight of five hundred pounds without breaking, yet it possesses less tenacity than iron, copper, platina, or silver. It is ductile and malleable beyond any known limits. The method of extending it used by gold-beaters, consists in hammering a number of thin rolled plates between skins or animal membranes, upon blocks of marble fixed in wooden frames. A grain of gold has been extended to more than forty-two square inches of leaf, and an ounce, which, in the form of a cube, is not half an inch either high, broad, or long, is beaten under the hammer into a surface of one hundred and forty-six and a half square feet. There are gold leaves not thicker in some parts than the three hundred and sixtythousandth part of an inch; but on the wire used by the

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lace-makers it is still thinner. An ingot of silver, usually about thirty pounds weight, is rounded into a cylinder, an inch and a half in diameter, and twenty-two inches long. Two ounces of gold leaf are sufficient to cover this cylinder, and sometimes it is effected with a little more than one. The ingot is repeatedly drawn through the holes of several irons, each smaller than the other, till it be finer than a hair; and yet the gold covers it, and never leaves the minutest part of the silver bare, even to the microscope. It has been calculated, that it would take fourteen millions of films of gold, such as is on some fine gilt wire, to make up the thickness of one inch: whereas fourteen million leaves of common printing paper would occupy nearly three-fourths of a mile in thickness. The ductility of gold is such, that one ounce of it is sufficient to gild a silver wire more than thirteen hundred miles long.

Gold may be dissolved in nitro-muriatic acid; and it thus becomes muriate of gold, which is obtained in small crystals, and is very soluble in water. If white satin riband, or silk, be moistened with a diluted solution of gold, and, while moist, exposed to a current of hydrogen gas or sulphurous acid gas, the metal will immediately be reduced, and the silk become gilt with a regular coat of gold. The potters dissolve gold to be applied to the common kind of porcelain, and it is used in a state of solution for staining ivory and ornamental feathers. It gives a beautiful purple red, which cannot be effaced; even marble may be stained with it. Mercury and gold form a compound called the amalgam of gold, which is much used in gilding. The amalgam is spread upon the metal which is to be gilt; and then, by the application of a gentle and equal heat, the mercury is driven off, and the gold left adhering to the metallic surface.

QUESTIONS.-1. In what state is gold found? 2. What is said of its weight and tenacity? 3. How do gold-beaters extend it? 4. What surface may an ounce be made to cover? 5. How is silver wire gilt? 6. What calculation has been made respecting the films of gold on gilt wire? 7. What length of silver wire may be covered with an ounce of gold? 8. To what uses may muriate of gold be applied? 9 What is amalgam of gold, and how is it used in gilding?

178

SILVER.

LESSON 79.

Silver and Mercury.

Ful'minate, to explode with a loud report.

SILVER is a heavy, sonorous, brilliant, white metal, only moderately hard, but exceedingly ductile, and of great malleability and tenacity. It is found in various parts of the world, particularly in Peru and Mexico, in a metallic state; also in the state of an alloy, of a sulphuret, of a salt, and in that of an oxyd. It is the most brilliant of metals, and nothing surpasses it in splendour except highly polished steel. It is chiefly used for ornamental work, for domestic utensils, and for current coin: but for these purposes it is generally alloyed with copper, without which it would not have sufficient hardness to sustain much wear. You may know when silver is pure by heating it in a common fire, or in the flame of a candle; if it be alloyed, it will become tarnished; but if it be pure silver, it will remain perfectly white. Of the salts of silver the nitrate is best known, and when melted and run in moulds, it forms the lunar caustic of the apothecary. A solution of it mixed with a little gum water, forms, in conjunction with an alkali, the indelible ink, used in marking linen.

Silvering may be performed on the same substances, and by similar methods with gilding. But as works of this kind are liable to tarnish, they are seldom used. Plating with silver is performed in the following manner: one of the surfaces of an ingot of copper is rendered smooth and clean, and is sprinkled over with a saturated solution of borax; upon this is laid a plate of fine silver, about one twelfth the weight of the copper, and the two are carefully bound together by wire. The mass is now exposed to a full red heat, and the silver adheres to the copper. The ingot is then passed through a rolling-press, and formed into a plate; both the silver and copper extending uniformly during the whole process, at the conclusion of which, the two metals are inseparably united.

Mercury or quicksilver has been known from the earliest ages of the world. In the temperature of our atmosphere, it is a white fluid metal, having the appearance and brilliancy

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of melted silver. When submitted to a sufficient degree of cold, it is similar in appearance to other metals, and may be beaten into plates. At the poles it would probably be always solid. It readily combines with several of the other metals, and forms with them what are called amalgams. Mercury is used in large quantities for separating gold and silver from their ores; for silvering mirrors, for water-gilding, for making barometers and thermometers; by the philosophical chemist for many purposes of the laboratory; and in the manufactory of vermilion. It has also various and important uses in medicine. By dissolving mercury in nitric acid, a fulminating powder is obtained, two or three grains of which, laid on an anvil and struck smartly with a hammer, will explode with a loud report. Four grains will occasion indentation in the hammer and anvil. By exposing mercury to cold of a proper degree of intensity, which may be easily accomplished by certain freezing mixtures, it becomes a solid metal. If a lump of this be dropped into a cup of warm water, the solid metal will immediately become fluid, and the fluid water in the same instant will become solid. If a glass be used for the experiment, it should be infolded within a cloth to prevent accidents; for sometimes it will be shivered in pieces by the rapidity of the action.

The quicksilver mine of Guanca Velica, in Peru, is 170 fathoms in circumference, and 480 deep. In this profound abyss are seen streets, squares, and a chapel. Thousands of flambeaux are continually burning to enlighten it. The mine generally affects those who work in it with convulsions. Notwithstanding this, the unfortunate victims of an insatiable avarice are crowded together, and plunged naked into these abysses. Tyranny has invented this refinement in cruelty, to render it impossible for any thing to escape its restless vigilance :—

For in the dark Peruvian mine confined,
Lost to the cheerful commerce of mankind,
The groaning captive wastes his life away,
For ever exiled from the realms of day;
While all forlorn and sad, he pines in vain

For scenes he never shall possess again. FALCONER. QUESTIONS.-1. What is silver? 2. In what states is it found? 3. For what used? 4. How can you ascertain its purity? 5. What is said of nitrate of silver? 6. Of silvering? 7. Plating? 8. Describe

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