METALS, according to strict defini tion, are inflammable bodies, being all capable of combining with oxygen, and many of them, during this combination, exhibit the phenomena of combustion. Formerly only seven metals were known, but modern discoveries have added to the number about twenty others, which are distinguished by their great specific gravity, considerable tenacity and hard ness, opacity, and property of reflecting the greater part of the light which falls on their surface, giving rise to what is denominated the metallic lustre or bril liancy. See Leaves. To these have been added two others, by Mr. Davy, who has discovered the method of decompos ing potash and soda, and producing there from the new metals, called by that pro fessor Potassium and Sodaium. See Po Tssimiat and SODA117701, which terms a more particular account of these me tals will be given. Of the others, the principal characteristic is their superior specific gravity. In this they etceed all other bodies, the lightest being about six times heavier than water, the common standard, while the specific gravity of the heaviest substance with which we are ac. quainted, that is not metal, is less than five times heavier than water. Opacity is another leading property of metals ; even when beat to the greatest possible thinness, they transmit scarcely any light: from the union of the two qualities, den sity and opacity, arises that of lustre. By their opacity and the denseness of their texture, they reflect the greater part of the light that falls on their stir .
face. From their density they are sus ceptible of a fine polish, by which their lustre is increased. Colour is not a cha racteristic property of metals, but it serves to distinguish them from each other. Their colours are generally shades of white, grey, or yellow. Tena city distinguishes a number of the metals, and is not possessed in any great degree by other bodies ; hence arises their MaL LEAsILITr and DUCTILITY, which see. Some of the metals are neither malleable nor ductile. Metals are less hard than the diamond and many fossils, and their elasticity follows the same order as their hardness. Both these qualities are great
er in combinations of the metals than in the individual metals, and both may be increased by raising the metal to a high temperature, and then suddenly cooling it. Metals are the best conductors of ca loric ; their expansibilities are various, and are probably nearly in the order of their fusibilities. Mercury melts at so low a temperature, that it can be obtain ed in the solid state only at a very low temperature ; others, as platina, can scarcely be melted by the most intense heat which we can excite. In congeal ing, some of the metals expand consider ably, especially iron, bismuth, and anti mony; the others contract, some of them to a great extent, the contraction of mer cury being equal to the of the whole volume. Metals may be volatiliz ed; at the degree of 600 quicksilver may be volatilized ; and zinc and arsenic at a temperature not very remote from this ; many others may be dissipated in the fo cus of a large burning mirror, or by a powerful galvanic battery. Metals are the best conductors of electricity.
Metals are susceptible of combination ; they have an affinity to oxygen, hydro gen, carbon, sulphur, phosphorus, and to each other, and, when combined with oxygen, to all the acids, to the alkalies, and to the earths. The metals, indepen dently of potassium and sodaium, may he thus enumerated and arranged.
//Wm, in heraldry. There are two metals used in heraldry, by way of co lours, viz. gold and silver; in blazon call ed sr and argent. In the common paint ing of arms these metals are represented by white and yellow, which are the natu ral colours of those metals. In engraving, gold is expressed by dotting the coat, &c. all over; and silver, by leaving it quite blank.
It is a general rule in heraldry, never to place metal upon metal, nor colour upon colour; so that if the field be of one of the metals, the bearing must be of some colour; and if the field be of any colour, the bearing must be of one of the metals.