Part 14

221. _BOVEY COAL, BROWN COAL, or BITUMINOUS WOOD, is of brown colour, and in shape exactly resembles the stems and branches of trees, but is usually compressed. It is soft, somewhat flexible, and so light as nearly to float when thrown into water._

The greatest abundance of this coal occurs at Bovey, near Exeter, from which place it derives its name. The lowest stratum is worked at the depth of seventy─five feet beneath the surface of the earth. It is also found in Scotland, Ireland, and Germany.

As fuel, the Bovey coal is used only by the poorest classes of the community, as, notwithstanding its burning with a clear flame, it emits a sweetish but extremely disagreeable sulphureous gas, which is injurious to the health of the inhabitants. It is principally used for the burning of lime, and for the first baking of earthen ware.

222. _JET, or PITCH COAL, is a solid, black, and opaque mineral, harder than coal, and found in detached_ _masses from an inch to seven or eight feet in length, having a fine or regular structure, and a grain resembling that of wood._

_It has sometimes been confounded with cannel coal (219), but it is easily distinguished by its superior hardness: Jet cannot without difficulty be scratched with a knife, whilst cannel coal may be marked by the simple pressure of the nail._

The name of jet has been derived from Gages, a river of Lycia, whence the ancients are said to have obtained this substance. It is frequently cast ashore on the eastern coasts of England, together with pieces of amber and curious pebbles, particularly near Lowestoft in Suffolk, and in some parts of Yorkshire, where many persons employ their leisure in searching for it, and forming it into various kinds of trinkets. Jet is found in several countries of the Continent.

It is stated that in the district of Aude, in France, there are more than 1,000 persons constantly employed in the fabrication of jet into rosaries, buttons, ear─rings, necklaces, bracelets, snuff─boxes, and trinkets of different kinds. Near fifty tons weight of it are annually used for this purpose; and articles to the value of 18,000 livres are said to be sold in Spain alone. In Prussia the amber diggers call it _black amber_, because it is found accompanying that substance; and because, like amber, it is faintly electric, or attracts feathers and other light objects when rubbed. They manufacture it into various ornamental articles, and sell these to ignorant persons, as black amber, at a great price.

In different parts of the globe the trunks of trees, which have been long buried, have passed into the state of jet; and, in almost all these trees may be traced the distinctive characters of the species to which they belong. They are more or less brittle, more or less unctuous, according to the species, the degree of alteration, and the nature of the soil. All of them have a smooth and glassy fracture, but all are not adapted for the tool of the workman. When, for instance, the texture of the tree presents only a mass of dry fibres, the jet obtained is dry and brittle; and cannot be used in the forming of trinkets. But, if the texture be unctuous the fibre acquires a considerable degree of softness, is susceptible of being properly wrought, and receives a perfect and beautiful polish.

A fictitious kind of jet is made of glass; and several varieties of mineral pitch, and cannel coal, are imposed upon ignorant purchasers for jet.

When jet is once set on fire it burns with a green flame, and continues to burn for a considerable time, exhaling a strong bituminous smell. If the heat be rendered greater, it melts.

GRAPHITE FAMILY.

223. _BLACK LEAD, or PLUMBAGO, is an inflammable mineral, which consists of carbon, or charcoal (48), combined with iron, in the proportion of about nine parts of the former to one of the latter._

_It is of dark iron─grey colour, with a strong metallic lustre, and so soft that it is easily scratched with a knife. To the touch it is soft and greasy; and, when handled, it stains the fingers. In weight it is about twice as heavy as water._

The name of black lead has very improperly been given to this substance from its appearance only, as it has no alliance whatever with lead. It is usually found in kidney─shaped lumps of various size, and occurs in several countries of Europe, but no where of such excellent quality as in Borrowdale, Cumberland, where it has the name of _wadd_. The vein of black lead lies between strata of slate, and is from eight to nine feet thick. This mine is not opened more than once every three or four years, the quantity thus obtained being found fully sufficient for the demand. The only other mine of black lead in Britain is in Ayrshire, Scotland.

Artists in water─colours, if deprived of this mineral, would find great difficulty in making their sketches; as the marks that are erroneously made with it are more easily expunged than those of almost any other substance. Hundreds of thousands of pencils are every year formed of black lead. For this purpose the mineral is sawed into slender square pieces. These are fixed into grooves, of the same shape, cut in cedar, or some other soft wood; another piece of wood is then glued upon this, and the whole is worked into a circular form. The finer kinds of black lead are prepared for use by being boiled in oil before they are cut. The coarser kinds, and the refuse of the sawings, are melted with sulphur, and then cast into coarser pencils for carpenters. These may, in general, be easily distinguished by their sulphureous smell. The pencils that are manufactured in England are more esteemed on the Continent than any others.

The powder produced in the sawing of pencils is employed for numerous purposes. It is used for giving a bright gloss to cast─iron grates and stoves, and defending them from rust, and from the action of fire. It may also be advantageously applied to the inner surface of wooden screws, to packing presses, the axles of various sorts of machines, to slides, and other wood work, which are subject to friction. In this respect it is far superior either to grease or soap. The makers of razor─strops occasionally employ black lead in the composition which they spread upon leather for the sharpening of razors; and, on the Continent, it is sometimes used for blackening the hair. A coarser kind of black lead is used for making the vessels that are used by chemists, called crucibles.

RESIN FAMILY.

224. _AMBER is a substance usually of golden yellow colour, semi─transparent, and of shining and somewhat resinous lustre. It is occasionally seen of yellowish white colour, and nearly opaque._

The origin of amber is unknown. From the ants and other insects which it frequently contains, there can be no doubt that it has once been in a fluid state: and some writers have thought that it is a resinous juice, gradually modified by the action of sulphuric acid (24); but this is entirely conjecture. The ancients called it _electron_, and attributed its formation to the sisters of Phaëton, who, lamenting the death of their brother, were converted into poplar trees; these, it was said, instead of tears, yielded every year this substance; which, issuing from them in a fluid state, ran into the river, and there became hardened.

Amber is usually found in rounded and detached pieces, on the south coast of the Baltic, on the eastern shores of England, and in small quantity, on those of Sicily and the Adriatic; and a substance greatly resembling it is occasionally found in gravel pits near London. The only mines of amber at present known are in Prussia. These are worked in the usual way, by shafts and galleries, to the depth of about 100 feet. The amber is imbedded in a stratum of fossil wood, and occurs in rounded pieces, from a few grains to three and even five pounds in weight. The largest piece of amber ever known to be discovered in a detached state was found near the surface of the ground, in Lithuania, about twelve miles from the Baltic Sea. It weighed more than eighteen pounds, and was deposited in the cabinet of the King of Prussia at Berlin. Very lately a mass of amber, weighing thirteen pounds, was also found in Prussia. For this piece 5000 dollars are said to have been offered; but the Armenian merchants assert that it might have been sold in Constantinople for more than 30,000 dollars.

Anterior to the discovery or general dispersion of precious stones from India, amber was considered of great value as a jewel, and was employed in all kinds of ornamental dresses. The ancient Romans were so partial to this substance that Pliny, reprobating the great demand for it, says, the Roman females would give larger sums for a puppet or figure in amber, resembling a man or woman, however small its size, than they would for the finest man or the most valiant soldier. Under the Emperor Nero, persons were sent from Rome, for the purpose of collecting and purchasing amber; and so much of it was at length obtained, that it was used for ornamenting the nets and cordage employed in the theatres for preventing the wild animals from approaching the populace there assembled. It was likewise used to ornament the armour, the biers, and funeral apparatus of such persons as were killed.

Amber is now chiefly in request by Greek and Armenian merchants, but it is uncertain where they dispose of it. Some persons conjecture that it is purchased by pilgrims previously to their journey to Mecca; and that, on their arrival in that place, they burn it in honour of Mahomet.

The kind most in esteem is of a bright golden yellow colour. This is occasionally manufactured into snuff─boxes, small vases, necklaces, bracelets, cane─heads, and other ornamental articles, many of which are purchased by the Turks, Russians, and Poles; but the general demand for them has of late very much decreased. Some years ago the German artists paid great attention to this substance; and many experiments were made for the purpose of discovering means of removing its defects, and improving its beauty. It is said that they possessed the art of liquefying it to such a degree, that it could be run into moulds without injuring its beauty; and that specimens of this liquefied amber are preserved in the Electoral Cabinet at Dresden. There are still considerable manufactories of amber at Stolpen, Konigsberg, Dantzic, and Lubeck.

Amber, when wrought into ornaments, is first split on a leaden plate, and then turned on a particular kind of whetstone. The polishing of it is performed with chalk and water, or chalk and oil; and the work is finished by rubbing the whole with clean flannel. Without great attention it becomes very hot, and either flies into pieces, or takes fire during the operation.

After having been roasted or melted, amber is readily soluble in oil, and, in this state, constitutes the basis of several kinds of varnish. It was formerly much used in medicine, but, in this respect, it is now almost wholly neglected. Some persons, however, have still an absurd notion that a collar or necklace of amber, tied round an infant’s neck, will enable it to cut its teeth in safety. Oil of amber combined with liquid ammonia constitutes a white soapy liquor called _eau─de─luce_.

It has already been mentioned that insects are occasionally found in amber. These are generally in a very perfect state, and consist of flies, small moths, &c. Grains of sand, pieces of iron pyrites, and the leaves of plants, are also sometimes found in it. Insects, sand, and other substances, are likewise remarked in a species of gum, called _gum animè_, which, in colour, appearance, and qualities, so nearly resembles amber, that it is almost impossible to distinguish the two substances from each other. Large productions, which were formerly supposed to have been made of amber, such as a column ten feet high in the Florentine Museum, are now usually considered to have been formed of this gum; and many of the large beads of what are sold as amber necklaces are made of it.

If a piece of amber be fixed on the point of a knife and lighted, it will burn entirely away, emitting at the same time a white smoke, and a somewhat agreeable though sickly odour. When rubbed it has the property of attracting light bodies; hence one of the ancient Greek philosophers attributed to it a certain kind of life. From the name of _electron_, which was given to it by them, in consequence of this property, we derive our word electricity.

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CLASS IV.–METALLIC SUBSTANCES.

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OF METALS IN GENERAL.

225. METALS, in a perfect state, are easily distinguished from other minerals, by a peculiar brilliancy which pervades their whole substance, and which has the name of _metallic lustre_; by their complete opacity, and their great weight in proportion to that of other mineral substances.

When taken from the earth they are found in one or other of the four following states: 1. In a native or metallic state, 2. Combined with sulphur, 3. In a state of oxide (21) 4. Combined with acid.

Metals, when found in a state of combination with other substances, have the name of _ores_. They are in general deposited in veins (4), of various thickness, and at various depths in the earth. The mode of obtaining them is to penetrate from the surface of the earth to the vein, and there to follow it, in whatever direction it may lie. The hollow places thus formed are called _mines_, and the men employed in them are denominated _miners_. When the veins are at a great depth, or extend to any considerable distance beneath the surface of the earth, it is necessary, at intervals, to make openings, or _shafts_, to the surface, for the admission and circulation of the air; and also to draw off the water which collects at the bottom, by drains, pumps, or steam─engines, as the situation or circumstances require.

After the metallic ores are drawn from the mine, they, in general, go through several processes before they are in a state fit for use. Some of them are first washed in running water, to clear them from earthy particles. They are then piled with combustible substances, and burnt or roasted, for the purpose of ridding them of the sulphur or arsenic with which they may happen to be combined, and which rises from them in a state of fume or smoke. Thus, having been freed from impurities, they undergo the operation of melting, in furnaces constructed according to the nature of the respective metals, or the uses to which they are to be subsequently applied.

The knowledge of metals is a subject of great importance to mankind. Their use in trade is so frequent, and in the arts so various and so interesting, that few objects can be more worthy of attention than these.

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ORDER I.—MALLEABLE METALS;

OR, SUCH AS ARE CAPABLE OF BEING FLATTENED OR ELONGATED BY THE HAMMER, WITHOUT TEARING OR BREAKING.

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226. _PLATINA, the most ponderous of all the metals with which we are acquainted, is, when purified, about twenty times heavier than water. It is also one of the hardest and most difficult to be melted, is of white colour, but darker and not so bright as silver, and is found only in small blunted and angular grains or scales in the sands of some of the rivers in South America._

If platina could be obtained in sufficient quantity, it would perhaps be the most valuable of all metals. The important uses to which it is applicable may easily be imagined when we state that it is nearly as hard as iron, and that the most intense fire and most powerful acids have scarcely any effect upon it. Platina is not fusible by the heat of a forge, but requires either the concentrated rays of the sun in a burning mirror, the galvanic electricity, or a flame produced by the agency of oxygen gas.

It is admirably adapted for the uses of the philosophical chemist: although vessels made of it must always be found expensive, from its being necessary to solder them with gold; and although it has the disadvantage of being subject to corrosion by the application or use of caustic alkalies. Vessels made of it are not liable to be broken, and are as indestructible as those made of gold. When properly refined, its colour is somewhat betwixt that of silver and iron. Not being liable to tarnish like silver, platina is manufactured into several kinds of trinkets.

Its ductility is so great that it may be rolled into plates, or drawn into wire; and platina wire, for strength and tenacity, is considered much preferable to that either of gold or silver of equal thickness. Platina is also made into mirrors for reflecting telescopes, into mathematical instruments, pendulums, and clock─work; particularly where it is requisite that the construction of these should be more than usually correct, as platina is not only free from liability to rust, but is likewise subject to very little dilatation by heat. It is sometimes beaten into leaves and applied to porcelain, in the same manner as leaf gold; and its oxide (21) is used in enamel painting, and might be used, with great advantage, in the painting and ornamenting of porcelain. The platina employed for all these purposes is repeatedly melted with arsenic, as without the aid of this it could only be obtained in very small masses, owing to the intense heat that is required for its fusion.

This extraordinary metal was unknown in Europe until about the year 1735, when it was first brought from South America by Don Antonio Ulloa.

227. _GOLD is a metal distinguished by its yellow colour; by its being next in weight to platina, softer than silver, but considerably more hard than tin; and being more easily melted than copper._

_It is found in various states, massive, in grains, small_ _scales, and capillary, or in small branches. It cannot be dissolved in any acid except that called aqua regia (207), and is more than nineteen times heavier than water._

The countries of hot climates are those chiefly in which gold is discovered. It abounds in the sands of many African rivers, and is very common in several districts both of South America and India. The gold mines of Lima and Peru have had great celebrity; but, since the late commotions in the Spanish colonies, the working of them has been much neglected. It is from Brazil that the greatest part of the gold which is seen in commerce is brought. The annual produce of the various gold mines in America has been estimated at nearly 9,500,000_l._ sterling.

The principal gold mines in Europe are those of Hungary, and next to them those of Saltzburg. Spain is probably very rich in gold. Considerable mines were worked there in former times, particularly in the province of Asturia; but, after the discovery of America, these were given up or lost. Gold has been found in Sweden and Norway, and also in several parts of Ireland, but particularly in the county of Wicklow.—Among the sands of a mountain stream in that county, and among the sand of the valley on each side, lumps of gold are occasionally found. Pieces have been discovered which weighed twenty─two ounces, but they are generally much smaller, from two or three ounces to a few grains. It is said that lumps of gold, of large size, have been used as weights in some of the common shops, and that others have been placed to keep open the doors of cottages and houses in some parts of Ireland, the owners not knowing what they were. Gold is also occasionally found in Cornwall, and some other counties of England. Wherever it occurs it is commonly observed in a state of alloy with copper or silver, and in the form of grains, plates, or small crystals.

Gold was formerly obtained in Scotland. It is asserted that, at the marriage of James V. there were covered dishes filled with coins made of Scottish gold, and that a portion of these was presented to each of the guests by way of dessert. Very extensive operations for the discovery of gold were carried on during the reign of Queen Elizabeth, at Leadhills, in Lanarkshire, under the direction of an Englishman whose name was Bulmer. The trenches, the heaps of soil that were turned up, and other marks of these operations, are yet visible near the road between Leadhills and Elvanfoot. It is said that 300 men were then employed; and that, in the course of a few years, a quantity of gold was collected, equal in value to 100,000_l._ sterling. Not many years ago similar operations were commenced under the superintendence of a celebrated manager of the Scottish lead mines. The gold was found immediately under the vegetable soil; and the method of obtaining it was to direct a small stream of water, so as to carry the soil along with it, to basins or hollow places, where the water might deposit the matters carried down by the force of its current. The matter thus deposited was repeatedly washed, till the whole of the earthy substances were carried off. The gold, being heaviest, sunk to the bottom, and remained behind. The soil still furnishes gold; but the produce would by no means be equal to the expense of collecting it. Searching for gold, therefore, is now regarded only as an amusement, and not as a source of profit. Grains of this metal are sometimes found, after great floods, among the sand of brooks in different parts of Scotland.

The mode of extracting gold from its ore is by reducing it into a fine powder, and mixing this powder with quicksilver (228). The latter having the quality of uniting with itself every particle of the precious metal, but being incapable of union with the other substances, extracts it even from the largest portions of earth. The quicksilver, which has absorbed the gold, is then separated by means of heat; it flies off in vapour, and leaves the other metal in the vessel used for the operation.

Gold has been known, and in request, from the very earliest ages of the world. By the assent of civilized nations, it has become the representative of wealth under the form of money; and it is now an universal circulating medium for the purchase of all kinds of commodities. It has been chosen to occupy this important place on account of its scarcity, its weight, and other valuable properties.

As gold is not liable to tarnish or rust, it is frequently employed for ornaments of dress. But, beyond its use in the coinage, its most important uses are for goldsmith’s work, in jewellery, and for gilding. In each of these its standard or purity is different. That denominated _coinage_, or _sterling gold_, consists of an alloy of about twenty─two parts of gold with two parts of copper; whilst gold of the _new standard_, of which gold plate, watch─cases, and many other articles are made, consists of only eighteen parts of gold, and six parts of copper. Each of these is stamped at Goldsmiths’ Hall; the former with a lion, a leopard’s head (the mark of the goldsmith’s company), a letter denoting the year, the king’s head, and the manufacturer’s initials; the latter is stamped with the king’s head, letter for the year, a crown, the number 18 to designate its quality, and the manufacturers initials. The coinage gold of Portugal and America is of the same standard as our own; that of France is somewhat inferior; and Spanish gold is inferior to the French. The Dutch ducats and some of the Moorish coins are of gold unalloyed. _Trinket gold_, which is unstamped, is in general much less pure than any of the above; and the _pale gold_ which is used by jewellers is an alloy of gold with silver.