stead of ate, as sulphite, of lime, or phosphite of potass, When a salt is found to contain an excess of acid, the preposition super is generally prefixed to its name; but when it does not contain a sufficiency of acid to saturate the base, the preposition sub is added; thus we may say supertartrate of potass, and sub-borate of soda.

IX. SIMPLE COMBUSTIBLES. 1. Simple substances are those bodies which have never yet been decomposed, mor formed by art. These were very lately said to amount to' about 50 in number; but since the discoveries of Sir Humphry Davy, it is scarcely possible to say what substances are not compound bodies. All the simple substances with which we are at present acquainted, are, light, caloric, oxygen, nitrogen, the metals, some of the earths, and the four simple combustibles, carbon, hydrogen, sulphur, and phosphorus. Carbon, in its purest form, is known only in the diamond; but it may be procured in a state of charcoal by burning a piece of wood covered with sand, in a crucible. Charcoal, the combination with which we are the most familiar, is the coaly residuum of any vegetable that has been burnt in close vessels. It is generally black, sonorous, brittle, very light, and destitute of taste or smell. Charcoal is a powerful antiseptic, has great affinity for oxygen, is unalterable and indestructible by age, and, if air and moisture be excluded, is not affected by the most intense heat. In the preparation of gun-powder, charcoal is a most important ingredient; it is also employed in purifying rancid oils, for decomposing the sulphuric acid, and for many other purposes, by the chemist and the manufacturer. Finely pulverized, it is the best tooth-powder

extant.

2. Sulphur is found in most parts of the world combined with metals, from which it is procured by roasting; it also flows from volcanoes; it is sublimed from the sulphurous grounds in Italy, and is found in many mineral waters, combined with hydrogen. Sulphur, or brimstone as it is sometimes called, is a solid, opaque, combustible substance, of a pale yellow colour, insoluble in water, and very brittle. It is nearly twice as heavy as water, and has various uses in medicine and the arts. Phosphorus is a peculiar substance, chiefly of animal origin. It is generally procured by the decomposition of the

phosphoric acid which is found in bones. This is a solid inflammable substance, which burns at a very low temperature, when in contact with oxygen or atmospheric air: and, when thus saturated with oxygen, it forms a peculiar acid. Its specific gravity is rather more than twice that of water. The other substances, light, caloric, oxygen, nitrogen, the earths, and hydrogen, have already been considered. The metals are the subject of the next division.

X. METALS, The characters by which metals are dis tinguished are, brilliancy, or the metallic lustre ; opacity, fusibility, a superior specific gravity to that of other bodies; a capacity of hardness, elasticity, malleability, and ductility :—but in many metals, some of these properties are wanting. Metals are seldom found in the earth in a pure state, but generally combined with oxygen, sulphur, arsenic, and the acids. The metallic substances now known, (if we include the latest discoveries of SIR IIUMPHRY DAVY), are thirty-eight in number; gold, platinum, silver, mercury, palladium, rhodium, iridium, osmium, copper, iron, nickel, tin, lead, zinc, bismuth, antimony, tellurium, arsenic, cobalt, manganese, chromium, uranium, nolybdenum, tungsten, titanium, columbium, cerium, potassium, sodium, barium, strontium, calcium, magnesium, aluminum, glycinium, zirconium, silicium, and itrium. We shall briefly enumerate twelve of the metals most

in use.

1. Gold is the heaviest of all the metals, except platinum; it is not very elastic, nor very hard; but is so malle-able and ductile, that it may be drawn into very fine wire, or beaten out into leaves, thin enough to be carried away by the slightest wind. Gold is used for jewellery, for plate, and for current coin, but for these purposes it is generally alloyed. It is employed in various ways in the arts. Gold is also used to be spread over other metals to preserve them from tarnishing or rusting, as gold does not become oxydized by exposure to atmospheric air.

2. Platinum is the heaviest of all the metals; it is nearly as white as silver, and is difficultly fusible, though by great labour it may be rendered malleable, so as to be wrought into utensils like other metals. It will resist the strongest heat of our fires without melting, and, like iron, is capable

of being welded when properly heated. Platinum has hitherto been chiefly used for chemical utensils, such as crucibles, spoons, &c. and to make specula for telescopes. It has also been beaten into leaves, and applied to porcelain in the manner of leaf gold, and its oxyd is used in enamel painting.

3. Silver is a heavy, sonorous, brilliant, white metal; exceedingly ductile, and of great malleability and tenacity. It possesses these latter properties in so great a degree, that it may be beaten into leaves much thinner than any paper; or drawn out into wire as fine as a hair, without breaking. Silver is used chiefly 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.

4. Mercury, or quicksilver, is white and brilliant. At the common temperature of the atmosphere it is always fluid, in which respect it differs from other metals, but it becomes solid when exposed to a degree of cold equal to 39 degrees. In this state it may be extended by hammering, without breaking. Mercury combines with most of the metals, and these combinations are called amalgams. It is used in large quantities for silvering mirrors, for water gilding, for making barometers and thermometers, and in the manufacture of vermilion.

5. Copper is of a muddy red colour, with a shade of yellow, and is malleable, flexible, and ductile. Besides its employment to make vessels of capacity, and to sheathe the bottom of ships, it is alloyed with zinc to make brass; it is combined with sulphuric acid to form Roman vitriol; and its oxyds are employed in enamel painting, and in the manufacture of several colours.

6. Iron is universally diffused throughout nature, pervading almost every thing, and is the chief cause of colour in earths and stones. It may be detected in plants and in animal fluids. It is found in great masses, and in various states, in the bowels of the earth in most parts of the world. Every thing we possess is manufactured by means of iron. When converted into steel, it is employed in various ways, especially for edge-tools, all which are formed in part with this metal, from the ponderous pit-saw to the

finest lancet. Its oxyds are used in painting, enamelling, dyeing, and in medicine.

7. Tin is of a fine white colour, like silver, and when fresh is very brilliant. It is the brightest of metals and is very ductile, but at the same time tenacious and flexible. Tin may be combined with most other metals, and its alloys are much used.

8. Lead is of a blueish white colour, and when first melted is very bright. It is the least sonorous, tenacious, and elastic of metals. Lead does not become harder by ham-mering like other metals. It is capable of combination with most other metals.

9. Zinc is a very combustible metal, possessing but a small degree of malleability and ductility, except under certain circumstances. When broken, it appears of a shining blueish white. Zinc is combined with copper or tin, in various proportions, which constitute some of the most useful compound metals or alloys; it is also used in. medicine; it is the base of white vitriol: and its carbonate or oxyd may be advantageously substituted for white lead in house-painting.

10. Antimony is a brilliant, brittle metal, of a dusky white colour, and is destitute of ductility. Though seemingly hard, it may be easily cut with a knife. Antimony is combined with some other metals. in making printers' types, and specula for telescopes.. Its oxyds are employed in medicine, and in colouring glass. In times of mote antiquity, it was used by females as a black pigment, for staining the eye-lashes.

11. Arsenic is generally found in combination with sulphur, oxygen, and many of the metals. When reduced to its pure metallic state, it is a 'friable, brilliant metal, of a blueish white colour, easily, tarnishing, that is, oxydizing, by exposure to the air.. In all its states it is poisonArsenic is used to whiten copper, and it enters into most compositions for the specula of reflecting telescopes and for other optical purposes. Its oxyds are employed in many processer of the dyer, also as fluxes for glass, and in several of the arts. The sulphurets of arsenic form valuable pigments of different colours.

ous.

12. Manganese is a brilliant metal, of a dark grey colour,

of considerable hardness, and difficult fusibility. It is very brittle, and when in powder is attracted by the magnet. The oxyds of manganese are used in bleaching, in purifying glass, and in glazing black earthen-ware. The black oxyd is also much used by chemists for producing oxygen gas, which, by the application of a red heat, it yields in great abundance.

XI. OXYDS. 1. Any one or more of the simple substances, when united to a less quantity of oxygen than is necessary to form an acid, is called an oxyd. The mineral, the animal, and the vegetable kingdoms, all furnish matters which are convertible into oxyds by a union with oxygen. There are several ways in which metallic oxyds are formed, the chief of which are by the access of atmospheric air, by the decomposition of water, and by the decomposition of acids. All metals will not become oxydized by exposure to the air; gold, silver, and platinum, cannot be oxydized, unless in a very high temperature; though iron, copper, and lead, merely by long exposure to the air, will become oxydized in the coldest atmosphere. Manganese, by such exposure, will in a few hours be converted into a perfect oxyd.

2. Besides metallic oxyds, we are acquainted with an oxyd of each of the simple combustibles, sulphur, phosphorus, and hydrogen: with two oxyds of carbon, the other simple combustible; and with two of nitrogen. There are also some other oxyds. Sugar and indigo are vegetable oxyds, and common soap owes its perfection to the absorption of oxygen. Oils, butter, and dried salt meats, become rancid by absorbing, oxygen from the atmosphere. Oxygen not only performs for us an infinite number of valuable and important offices, but appears to be one of the grand agents of decomposition and destruction.

XII. COMBUSTION. 1. This is a process by which certain substances decompose oxygen gas, absorb its base, and suffer its caloric to escape in the state of sensible heat. Those combustible substances that have resisted every attempt to decompose them, are called simple combustibles. Compound combustibles are all such as are formed by the union of two or more of the simple combustibles. Com