of the rivers Oronooco, of the Amazons, and de la Plata, the ocean lofes its falt taste for several leagues from the shore.

The fea-water is heavier than fresh in proportion to its faltnefs. It was the opinion of the Peripatetics that falt water would freeze fooner than fresh, as being lefs pure. But the contrary is the cafe; owing to this, that in falt there is a certain spirit which refifts coagulation, and which, being feparated from the falt, will not congeal in the hardest froft. See Varenius, vol. I. p. 220. This, however, is not altogether confiftent with the opinions at prefent entertained.

Salt is extracted from fea-water, or from any water which contains it, (for there are many falt springs in various parts of the earth), by evaporating the water. That is done in this country by means of large fhallow iron boilers, called falt pans, and the crystals of falts are taken out in baskets. In Ruffia, and other northern parts, the fea-water is exposed to freeze; and the ice, which is almost entirely fresh, being taken out, the remaining brine, thus rendered much stronger, is evaporated by boiling.

In the fouth of Europe falt is made by fpontaneous evaporation in flat pieces of ground near the fea, which are banked round; and the water made to pass from one shallow pond to another, till the falt is formed. This is called Bay falt, from its being found in large quantities formed by nature on the Bay of Bifcay.

Common falt is found in large maffes, or in pits below ground, as in England and elsewhere. This is called rock-falt.

The island of Ormus is nothing but white hard falt, of which they make the walls of their houses, and there is not one spring of fresh-water in the whole ifland.

Sea-water, if taken up near the furface, contains alfo the remains of animal fubftances, which render it naufeous, and in long continued calms cause the fea to emit a disagreeable smell.

Solution, Fufion, Distillation, &c.

1. When a body is fo diffufed through any liquor as to be invifible, that is, when the mixture is perfectly tranfparent and homogeneous, then that body is faid to be diffolved in the liquor; and the mixture is called a folution; the body diffolved is called the folvend; and the liquor which diffolves it, the fol vent or menftruum.

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A body may be feparated from the body in which it is dif folved by the addition of a third fubftance, which is taken up by the folvent, and the body which was before diffolved is fet loofe, and falls to the bottom of the veffel in the form of very fine powder. Thus, if lime be diffolved in muriatic acid, and an alkali falt be added to the folution, the lime will fall down to the bottom of the veffel in the form of a white powder; this operation is called precipitation. The substance used to produce it is called the precipitant, and the powder which falls down, the precipitate.

Fufion is the reducing of a folid body to a fluid state, by the application of heat.

The veffels for fufion are either iron ladles or crucibles, fo called, because formerly they used to be marked with a cross. Crucibles are veffels compofed of earthern ware of a peculiar kind. Those in common ufe are called Hian crucibles, becaufe originally brought from that country; but for certain purposes, which require a more intenfe heat, crucibles are made of a mixture of clay and black lead, commonly called black-lead crucibles, or blue pots.

Filtration or firaining, is when a fluid is purified by making it pafs through different fubftances.

Evaporation is the feparating of the more volatile parts of a body from the more fixed; but the term evaporation is more ftrictly confined to the diffipating of fluids by heat. When the volatile parts of a body that are diffipated are folid, the operation is called roafting. Thus water is feparated from fome falts, which are diffolved in it by evaporation; and fulphur is separated from the ores of metals by roafting.

When the evaporation is fo performed that the volatile parts are preferved, it is called diftillation if the volatile parts are fluid; and fublimation if they are folid.

Diftillation is of three kinds, technically called per defcenfum, ad latus, and per afcenfum. The first is when the vapour is made to defcend, and is received into a veffel below; but this method is feldom ufed. The fecond is, when the vapour is made to pass out of the veffel, which contains the materials, at one fide, and is received into a veffel properly adapted to it. In this kind of diftillation, which is in frequent ufe, the veffel containing the materials is called a retort; and the veffel fixed to its fide, in which the vapour is condenfed, is called a receiver. The retorts are made of iron, earthen ware, or more commonly of glafs. The receivers are generally of glafs, but fometimes of earthen ware. In the third, namely the diftilla

tion per afcenfum, the vapours are fuffered to take their natural courfe upwards, and are condenfed in a cavity above the vessel which contains the materials.

Formerly the veffels used in this operation were called a cu curbit for holding the materials, and an alembic for condensing the vapour. Thefe vefels are ufually made of glafs or earthen ware. But for general ufe they are found inconvenient, and their place is fupplied by the common fill, which is generally made of metal, and confifts of a body for holding the materials, a head or cavity above the body for receiving the vapour, a beak or pipe iffuing from the head, and terminating in a long tube that paffes through a veffel conftantly filled with cold wa ter, called the refrigeratory. The vapours paffing through this pipe are condenfed into a fluid before they arrive at its extremity, whence they drop into vcffels placed below. The more effectually to condenfe the vapours in the pipe paffing through the refrigeratory, the pipe is bent fpirally like a cork fcrew, and thus makes feveral circumvolutions among the cold water, This fpiral pipe is commonly called the worm of the still.

The fluids obtained by diftillation are generally called Spirits, or difilled waters; and what remains in the ftill is called the refiduum, which, from its often having a blackish appearance, is called a caput mortuum. And as it is frequently of no ufe, the ancient chemifts fometimes called it terra damnata. When fpirits undergo a second diftillation, they are faid to be rectified.

The veffels used for fublimation are chiefly the cucurbit and alembic, above defcribed, or fometimes aludels, which are globular veffels, either of glafs or earthen ware, with two openings diametrically oppofite to each other. Thefe aludels are pla ced one above another, the neck of the undermoft into the mouth of the uppermoft; fo that if any vapour be not conderfed in the first, it may pafs to the fecond to be there condenfed, fo to the third, the fourth, &c. The product of the fublimation is called fublimate, which, from its pulverifed light state, is fometimes called flowers; as, flowers of fulphur, &c.

Both in diftillation and fublimation the different veffels are fixed to one another by means of certain paftes, most commonly made of clay (lutum), hence called lutes.

In fome diftillations, especially in retorts, the retort itself is not expofed to the naked fire; but another fubftance is placed between them; thus, an iron pot is placed above the fire, and filled with fand, afhes, water, or fome other fubftance in which the retort is placed. Thefe are called baths, (balnea,)

as;

as, balneum arena, maris, vaporis, &c. fand-baths, water-baths, vapour-baths, &c. The use of these baths is to convey an equal heat to every part of the retort, to moderate the degree of heat, and to prevent the retorts, which are generally made of glafs, from being broken by a fudden expofure to the fire.

General DIVISIONS of the TERRAQUEOUS GLOBE.

WHAT part of the earth is covered with water is not exactly known. It is fuppofed to exceed the land at least by one third.

The whole collection of water is called the ocean, or the fea. It is commonly divided into three parts; the Atlantic, which feparates Europe and Africa from America, about 3000 miles broad; the Pacific, which feparates America from Afia, 10,000 miles broad; and the Indian ocean, which separates the Eaft Indies from Africa, 3000 miles broad: all of them communicating with one another. To thefe may be added the Northern and Southern oceans.

Certain parts of the ocean are called feas, and have their names from the countries they border on, as, the Irish fea, the German fea.

A part of the sea running up into the land is called a gulf, as, the Arabian gulf or Red fea, the Perfian gulf, &c. If it be of great extent it is called an inland fea, as, the Mediterranean, the Baltic: If it do not go far up into the land, it is called a bay, as, the bay of Biscay, the bay of Bengal, &c. If it be of very fmall extent, it is called a creek, haven, ftation, or road for thips. A narrow communication between two feas is called a ftrait or ftraits, as, the ftraits of Gibraltar, the ftraits of Dover and Ca lais, &c.; if fo fhallow as to be founded, a found, as the found of Denmark, the found of Mull, &c. The Capian fea in Afia communicates with no other.

A great body of fresh water, furrounded by land, is called a lake, as, the lake of Geneva, the lake of Conftance, &c. In Scotland and Ireland lakes are usually called lochs or loughs, as loch Ness, lough Neagh, &c. which name is alfo applied to arms of the fea. A fmall quantity of ftanding water is called a pool, or, efpecially if it be artificial, a pond. Standing water having earth raifed and appearing above it here and there,

or having earth or mud mixed with it, is called a morafs, a marfh, a bog, a fen, or favamp.

A large ftream or body of running water is called a river; a fmall ftream, a brook or rivulet; a violent flux of water from the top of a mountain, or down any steep declivity, is called a torrent. A river on which veffels may fail is called a navigable river. But rivers are ufually distinguished fimply by their largenefs or rapidity. The hollow or cavity in which a river runs between its banks is called its channel or bed; a place where two rivers meet, a confluence or conflux. When a river runs over a precipice it is called a cataract or fall: if the quantity of water be small, a cafcade. The streams or smaller rivers which run into a great one are called its branches; which name is likewife given to the divifions of a river, when it separates or divaricates into two or more channels. Thefe are fometimes called arms, and when they run into the fea, mouths. let of the fea into the land is properly termed an arm; and when the fea runs up a river, a frith or eftuary. The fources from which a river flows are called its fprings, The fprings of most rivers are upon mountains, but feveral flow from lakes. A place where water rifes when the earth is dug up, but does not run out, is called a well, (puteus, Plin. ii. 97.. 100.) but this word is sometimes put for a spring or fountain.

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A great extent of land, containing many countries not separated by water, is called a continent. A country entirely furrounded by the fea, is called an island: a country almost furrounded by the fea, a peninfula, or, by a Greek word, Cherfo nefus. That neck of land which joins a peninsula to the continent, is called an ifthmus; as the Ifthmus of Suez, between Afia and Africa: the Ifthmus of Darien, between North and South America. When the land projects far into the fea it is called a promontory, (quod in mare prominet), and the end of it a cape; as, Cape Tanurus or Metapan, the most southern part of Europe; the Cape of Good Hope, the moft fouthern part of Africa; Cape Horn, the most fouthern part of Ame rica; Cape Comorin, the moft fouthern part of Indoftan, &c, If the part of land which projects be small or not high, it is called a point, a head-land, naze, nefs, or mull; as the Lizard point, the Naze of Norway, Buchan-nef, the Mull of Galloway or Cantire.

When the land rifes to a very great height above the level country, it is called a mountain, or a chain of mountains; as, the Alps, in Europe; Taurus and Imaus, in Afia; Atlas, and the Mountains of the Moon, in Africa; the Andes, in South

America.