Borrowdale in Cumberland. It is a compound of iron and inflammable matter.

From copper is formed that substance used in painting green colours, called verdigris, which alfo is a strong poifon. The ufe of copper veffels has, in fome inftances, been productive of fatal confequences; whence, unless with particular precautions, they are thought unsafe for culinary purposes.

IRON, the most useful of all metals, is found in greater abundance than any other. It undergoes feveral operations before it is fitted for the purposes of the forge. Two pieces of iron, when heated to a certain degree, in what is called a white heat, will adhere to one another, and may be perfectly united by hammering; which property is peculiar to iron and platina, and called WELDING.

If the pureft malleable iron be bedded in pounded charcoal in a close veffel, and kept for a certain time, longer or shorter according to the thickness of the bars, it is found that by this operation, which is called cementation, the iron has gained a small addition of weight, about the 150th or the 200th part, and is rendered much more brittle and fufible than it was before. After this operation it is called STEEL. It may be welded like bar-iron; but its most useful property is that of becoming extremely hard when made red hot and plunged in cold water. The hardness produced is greater in proportion as the steel is hotter and the water colder.

Artists soften the hardest steel to any degree, by gradually heating it and fuffering it to cool again gradually. This is called tempering.

TIN is very malleable, though not very tenacious. It is extended into plates called tin-foil, and these plates may be beaten into leaves like gold.

A mixture of tin and lead in certain proportions forms the compound called PEWTER, which is much more applicable to certain purposes than tin or lead alone, being much harder, and melted with lefs heat than either of thefe metals in their feparate state; and fometimes to make it harder a little zinc is added. One very remarkable property of pewter is, that by adding bizmuth to it, a mixture is formed which may be melted with less heat than is neceffary to make water boil.

Tin is chiefly found in the county of Cornwall, whence the Phoenicians are faid to have got their tin. WATERS

P 2

WATER S.

NEWTON defines water when pure to be a very fluid falt, vo latile, and void of all favour or tafte. According to others it is nothing but ice diffolved: and all fluidity is fuppofed to be the effect of heat, which exifts to a certain degree in a latent ftate in all bodies, for when part of the heat of water is gone, it becomes fixed and folid.

An important difcovery was lately made by Mr Cavendish in England, and farther confirmed by Monfieur Lavoisier at Paris, that water is a compound of vital and inflammable air, in the proportion of 85 of the former, and 15 of the latter, or as 17 to 3, which fhews the falfehood of the notion formerly entertained, that water is a pure element. Water, however, is fo univerfal an agent in the most important operations of nature, that we need not be surprised at fome ancient philofophers ima gining all things to be derived from it. For not only dew, rain, fnow, and meteors, owe their existence to water, but all animals and vegetables, fays Newton, grow from water, and after putrefaction return (in part) to water again. Its weight is ufed as the measure for determining the fpecific gravity of bodies, one cubic foot of water weighing 1000 ounces Avoirdupois weight; and the boiling point has been affumed as the standard of comparifon of the different degrees of heat in other bodies. Water is the great folvent of all falts, and thefe folutions of falts in water are the folvents of metals, earths, and inflammable fubftances. The difpofition of this globe into parallel strata is supposed to have been the effect of water, from the numerous relicts of aquatic animals and productions found in them. Thus the vast ftrata of marble, limestone, chalk, &c. are entirely compofed of fhells, corals, &c. or of the matter into which thefe animal productions have mouldered and decayed. Vegetable substances, and the relicts of land-animals, are obfervable in the ftrata of free ftone, of some clays, of coal, and of flate, Some have thought, from vari ous experiments, that water is convertible into earth; and others have afcribed to this the diminution they supposed to have taken place in the waters of the fea; but later naturalifts have detected the fallacy of thefe experiments; and we know, that as the fea has funk or receded from fome places, fo it has made encroachments upon the dry land in others,

Water

Water is generally defined to be a fluid that is infipid, colourlefs, and without any flavour. It was alfo faid to be inelaftic, but later experiments have fhewn that it is in fome degree compreffible.

Water is feldom found perfectly pure, but almost always impregnated with fome foreign matter, and to purify it distillation is often ufed.

The varieties of water are, rain or fnow-water, fountain or well-water, river-water, the water of lakes, marshes, and fmall pools, and fea-water. Of these rain-water is the most pure, being in fact water diftilled by nature. It, however, is feldom free from impurities of different kinds; for in defcending it attracts the various volatile fubftances fufpended in the atmosphere. Hence, near great towns, it is found to have a blackish tinge, and a fenfible taste of foot; and in the country, in fummer, when large quantities of the pollen or ftaminal duft of plants are carried up with whirlwinds, the rain falling through this yellow duft is fo much difcoloured by it, as fometimes to have given rise to the popular error of fhowers of fulphur, as a number of certain infects is fuppofed to have occafioned the belief of fhowers of blood.

Fountains or wells are impregnated with various matters, according to the nature of the different ftrata through which the waters pafs in their way to the fprings.

SPRINGS are of feveral kinds. They are in general of the the mean heat of the climate where they occur, but some of them are very hot; as the waters of Bath and Buxton in England, Aix la Chapelle in Germany, Baie in Italy, &c. But the most remarkable hot fprings occur in Iceland. They owe their heat most probably to fubterraneous fires, because the hottest are found in places near volcanoes.

Springs are impregnated with various matters; falts, fulphur, metals, earths, and airs of different kinds. The falts which they contain confift of compounds of the foffil alkali, combined either with vitriolic or muriatic acid, or of different earths or metals with these acids.

Sometimes the earths and metals are diffolved in fpring-water by means of fixed air; as, the calcareous earth in petrifying fprings, and iron in chalybeate fprings. In confequence of the fixed air, which is a very volatile fubftance, evaporating when thefe waters are expofed, the calcareous earth or metals, which had been kept diffolved in the water by this fixed air, is depofited

upon

upon the bottom of the channel in which thefe waters run. And if the waters chance to run over any vegetable or animal fubftance, such substance is gradually covered with calcareous earth, and is then faid to be petrified. Sometimes fprings contain a greater quantity of fixed air than is fufficient for the folution of the different fubftances in the water. The water is then impregnated with a fuperabundant quantity of fixed air, and acquires an agreeable brifk and acid tafte, which waters are called ACIDULE, fc. aque, as the Seltzer waters, and others.

Sulphur, and other inflammable substances, are found diffolved in water. Thefe are called fulphureous springs, as, at Harrowgate in Yorkshire, Springs impregnated with thefe different fubftances are diftinguished, not only by their flavour, but alfo by their medical qualities, hence called medicinal springs.

Water may be confidered as either hard or foft. Soft water is fuch as is pure from any admixture, except alkaline falt; hard water, fuch as is impregnated with an acid, either alone or in a compound falt. The mark of hard water is curdling fope.

The water of rivers or lakes is derived either from rain or fprings, or moft generally from both. The water of rivers is impregnated with a great variety of matter, both mineral and vegetable, according to the nature of the foil through which they pafs. The water of rivers near great cities is replete with fuch a quantity of animal and vegetable substances, that upon ftanding a few days in a veffel it undergoes a putrid fermentation; as is the cafe with Thames water, which is thus purified.

The water of lakes is in general purer than that of rivers. The water of the larger lakes in America is faid to be fo transparent, that ftones and rocks at the bottom may be seen at the depth of feveral hundred feet, as clearly as if no medium intervened.

The water of marfhes and small pools abounds with various impurities, both from vegetable and animal fubftances. In fummer, efpecially, they fometimes abound with such a number of infects and small aquatic animals, that the water appears of the fame colour with thefe infects; and the infects are fo quickly produced as to give rife to a vulgar error, that the water has been fuddenly changed. One fpecies of infects, called monoculus, in particular, of a fcarlet colour, has sometimes made it be believed that water was changed into blood, which the vulgar confider as a portentous omen.

SEA

SEA-WATER is very full of impurities, chiefly of the faline kind. There are three compound falts found in fea-water, viz. 1. common falt, or a compound of muriatic acid and fofil alkali; 2. falited magnesia, or a compound of muriatic acid and magnefia; 3. gypfum, or a compound of vitriolic acid and lime. The proportions of thefe ingredients in fea-water, brought from the Cape of Good Hope, according to Bergman's analyfis, in a thousand parts, 33 of the firft, 9 of the fecond, and I of the third, making about 43 parts in a thousand. How thefe ingredients came to be in the fea-water, can only be explained by fuppofing, that the water meets with these falts either at the bottom of the fea, and diffolves them, or that they are washed down by the rivers from various ftrata, and accumulated in the ocean; for the water evaporated by the fun's heat from the furface of the fea takes up with it no particles of Hence thofe lakes which receive rivers, but have no exit or discharge, are falt; as the lake Afphaltītes, or the Dead fea, in Palestine, into which the river Jordan runs, whofe banks in fummer are encrufted with great quantities of dry falt, of a more pungent nature than the marine falt, having a relish of fal ammoniac. There are very few falt lakes in the world. That furrounding the city Mexico, and the lake Titicaca in Peru, communicating with that of Paria, are faid to be of this kind. Some add the Cafpian fea, which, if considered as a lake, is no doubt the most wonderful in the world. It is reported to be fomewhat less falt than the ocean. Strabo mentions a falt lake in Armenia, xi. p. 529.

falt.

The portion of falt in fea-water is different in different parts of the ocean. The water of the Baltic fea is faid to contain one 64th of its weight of falt; that of the fea between England and Flanders, the 32d part; on the coast of Spain, the 16th part; and between the tropics, from one 11th to one 8th part.

The fea-water in the Ethiopic ocean, over against Guinea, yields white falt as fine as fugar, with once boiling; which cannot be produced from the water of any of the feas in Europe without frequent boilings. The greater faltnefs of feawater in the torrid zone is afcribed to the greater exhalation of the fun, to the heat of the water which diffolves the falt mixed with it, as the fame water or falt-meat taftes falter when hot than when cold; and to the lefs frequency of rain or fnow. In the rainy months the ocean within the tropics is not so falt near the shores as it is in the dry months; and at the mouths

of