lity very inferior to the British, so that they are obliged to im port great quantities of the British coal for the use of their mas nufactures.

Coal is found in Strata, not in mountainous fituations, but in places abounding with vallies, moderately rifing hills, and interspersed with plains of confiderable extent. The Atrata of coal are found between ftrata of other substances, usually of ftone of various kinds.

The firata are feldom or never found to be in a horizontal fituation, but ufually having an inclination or defcent, called the dip.

The frata are fometimes interrupted by fiffures, called djkes, hitches, and troubles.

Strata of coal are feldom found dry. They are commonly attended with large fprings of water, which is drawn off sometimes by a drain; but when a level for this purpose cannot be found, by machinery of different kinds, chiefly by fire-engines.

There is often much difficulty in digging for coal. The frata or feams are often of different thicknefs; fometimes there are feveral firata below one another.

Coallieries or coal-pits are expofed to dreadful accidents from what is called a crush or fitt, when the pillars fail by the fuper incumbent weight or otherwise, and from damp or inflammable

air.

There are feveral kinds of coal, as the common Scotch coal, which burns to white afhes; the Newcastle coal, which cakes, and by burning becomes cinders; the blind coal, which barns without flame like charcoal; Kennel coal, which burns with a vivid light, eafily takes fire, and is fo hard as to be capable of receiving a polifh, fo that trinkets of various kinds, fnuff-boxes, buttons, &c. are made of it.

The most remarkable effect of heat in combuftible bodies is when they are brought into contact with nitre.

If nitre touches an inflammable fubftance heated red hot, a violent combustion is produced, accompanied with a kind of crackling noise or explosion, and the body is then said to deflagrate.

If the explofion is almoft inftantaneous, the body is faid to detonate.

This property of nitre gave rife to the compofition of GUNPOWDER, a fubftance which has wholly changed the mili tary fyftem of nations, and which, although in itself most de

ftructive,

fructive, appears to have diminished the slaughter in wars, by repreffing in fome degree the rancour which used anciently to actuate combatants who fought hand to hand. If we fuppofe gun-powder to be divided into 100 parts, 75 parts confift of nitre, 15 of charcoal, and 10 of fulphur; or if we fuppofe it divided into 9 parts, there are 7 parts of nitre, 1 of fulphur, and I of charcoal. Thefe ingredients are intimately blended together by long pounding in wooden mortars, with wooden peitles, and a fmall quantity of water. The mixture is then formed into a fif paste, which being forced through wire fieves is broken into fmall grains, or becomes granulated; and these grains being fhaken or rolled in a barrel with fome powdered black lead, are rounded by their mutual friction against each other, and are glased by the powder of the lead.

The force and explofion of gun-powder, when fet on fire, is occafioned by the fudden expansion of the elaftic aerial matter which it contains.

When three parts of nitre, two of mild vegetable alkali, and one of fulphur, are rubbed together in a warm mortar, they form a compofition known by the name of fulminating powder, from its aftonifhing effects.

When a little of this powder is laid on a plate of iron, and the plate held over a chaffing dish of charcoal, it begins to melt into a blackish dark brown mafs, and as foon as the whole of it is melted, it explodes with a furprisingly loud and fmart noise.

Gun-powder is faid to have been accidentally invented by Schwartz, a German monk, at Mentz, about the year 1330; and fire-arms to have been first used by the Venetians in their war with the Genoese, a. 1376: but historians affirm that great guns were used by the English at the battle of Crefly, a. 1346, and the year following at the fiege of Calais, Rapin. Fol. edit. #743; val. ↳ P. 425.

IV. METALS.

METALS are diftinguifhed from all other known bodies by their weight, the heavieft ftones being not much above four times their weight of water, but the lighteft metal more than feven times heavier than water. Metals are alfo the most opaque bodies, and reflect the rays of light most powerfully.

Thofe

Thofe metals which are moft ductile and malleable, or may be most extended by the hammer, and remain longeft unchanged by fire, are called perfect metals. These are three, gold, filver, and platina, lately discovered in the gold-mines of Spanish America, refembling gold in its properties, but of a white colour. Pure or refined platina is by much the heaviest body known, which gold was reckoned to be before the difcovery of platina. It requires a very strong heat to melt it. Its parts adhere together by hammering, as a plate of heated iron does when doubled and beaten. This property is called welding, and is peculiar to iron and platina.

Such metals as may be destroyed or changed into earth by fire, are called imperfect metals. These are four, copper, iron, lead, and tin. Those metallic fubftances which do not poffefs malleability and ductility are called femimetals, as antimony, bismuth, zine, cobalt, arfenic, nickel, and fome others. Mercury forms a class by itself. All these were known to the ancients except slatina, cobalt, arfenic, and nickel.

By the joint action of fire and air all metals, except gold, filver, and platina, may be reduced to an earthy-like substance called calx, and then they are faid to be calcined.

The pure metallic part of fome of these is called REGULUS, as, regulus of antimony, cobalt, or arfenic.

The calx being mixed with any inflammable fubftance, and expofed to fire in clofe veffels, is reftored by melting into its metallic form, and is then faid to be revived or revivified.

When metals are calcined the calx is found to be heavier than the metal from which it was produced. This fact long puzzled chemifts, and was never fatisfactorily explained, till of late it has been found to be owing to the combination of pure air with the metal during the process of its calcination.

The places where metals are found are called mines, chiefly in mountainous countries. They are feldom found pure, except gold, filver, and quickfilver, then called native or virgin gold and filver, but generally mixed with fulphur, arsenic, or both; in which state the metals are faid to be mineralifed, and the mixture is called an ore.

ORES are frequently found in detached fragments, but most commonly in continued maffes, wholly filling long crevices or cracks in the rocks. Thefe continuations of ore are called veins, and traverse the rock in all directions, fometimes half an inch thick, and other times feveral feet. The rock or ftony matter mixed with the ore in the vein is called the matrix. Sometimes ores are

are found, neither in detached fragments nor in continued veins, but compose the whole fubftance of a mountain, which is particularly the cafe with copper and iron. Thus the mountain of Anglefea in England, and Tahlun in Dalecarlia, confist almoft entirely of copper; Danemora in Sweden, of iron.

Veins are feldom found but in mountains. When they approach the plains they gradually fink under the different ftrata of these plains, fo deep as to be beyond the reach of miners. Hence the inferior ftrata of the earth are fuppofed to contain large quantities of pyritous, fulphureous, and metallic fubftances, which, taking fire, have been thought the cause of fubterranean fires, volcanoes, and earthquakes.

Pyrites is a mineral resembling the ore of metal, and is fometimes fo hard that it has the power of ftriking fparks of fire from steel, whence its name, or rather because it has a great deal of fire in it, Plin. xxxvi. 19. f. 30. It is chiefly of a white, yellowish, or yellow colour.

The operations by which metals are obtained from ores are called the fmelting of ores. A chemical operation to determine the quantity of metal or other matter in minerals, or to difcover the value or purity of any mass of metal, is called an Effay or Affay.

Metals are ranked in the following order: 1. with respect to their weight; platina, gold, mercury, lead, filver, copper, iron, and tin;-2. with refpect to their ductility; gold, filver, copper, iron, tin, lead. The ductility of mercury and platina is not yet determined:-3. with regard to their hardness; iron, platina, epper, filver, gold, tin, and lead:-4. with refpect to their tenacity, or the force with which their parts adhere to one another and refift feparation; which is proved by the weight which wires of the fame diameter, made of the feveral metals, can fustain without breaking; gold, iron, copper, filver, tin, lead. The tenacity of mercury is unknown, and that of platina undetermined and 5. fufibility; mercury, tin, lead, filver, gold, copper, iron, and platina.

By mixing different metals together are formed compound metals. Thus brafs and pinchbeck is formed by a mixture of copper and zinc, or its ore, lapis calaminaris, calamine, in different proportions.

Silver and gold, in their pure ftate, are too soft to be employed for various purposes, and are therefore mixed with fome other metal to harden them, which mixture is called alloy or allay. The alloy for gold is either pure copper, or a mixture of

P

filver

filver and copper, according to the colour defired, whether deep or light. Silver is always alloyed with copper.

Two foft metals mixed together produce a compound much harder than either of them; and in fome cafes, as when copper and tin are mixed together in certain proportions, the mixture becomes the hardest of all metallic fubftances, called bronze or bell-metal. This compound is employed for making cannons, flatues, bells, and parts of heavy machinery which are liable to be much worn. It alfo poffeffes the property of receiving a very fine polish; and is hence used for fpecula or mirrors, and for making reflecting telescopes.

Certain metals eafily mix and combine together; hence the art of foldering. Thus tin is a folder for lead; brafs, gold, or filver are folders for iron, &c. Some metals will not unite at all. This property of uniting, or not uniting, is called the affinity of metals.

When any metal is united with quickfilver, it is faid to be amalgamated, (from aua, together, and yaus, to marry ;) as all the metals may, except iron and platina, and with difficulty, copper and arfenic.

The ufe of this operation is to render metals foft and ductile. Gold is thus drawn over other matters by the gilder. The mixture prepared for this purpofe, commonly confifting of fix parts of mercury and one of gold, is called amalgam or amalga

ma.

Gold is feparated from alloy by the operation called cupellation, from cupel, a fhallow porous crucible, made of burned bones, in which the gold is expofed to a strong heat, together with lead, and is thus purified from the imperfect metals. The operations by which gold is purified from filver are called quartation and parting.

LEAD, by means of heat and air, is formed into minium or red lead; by means of the fteam of the acetous acid or vinegar, into cerufe or white lead.

Thefe are the calces of lead, and are ufed chiefly for paints; as ingredients in colourless or flint-glafs, and for glazing earthen-ware. The calx of lead is a principal ingredient in moft of the modern fine white glaffes.

All the preparations of lead are found to be deadly poisons; hence lead is thought not to be perfectly innocent for waterpipes, and much less fo for any kind of veffels.

There is a mineral fubftance called plumbago or black lead, of which pencils are made; found in different parts, the best at

Borrowdale