Of charcoal and pitcoal (see Carbo) we have spoken at sufficient length, as they are not substances very often employed in medicine. Respecting amber, usually arranged under the inflammables, we have nothing to add. See Amber.

Metals are opaque, brilliant bodies, considerably hard, very frequently malleable in different degrees, though some are flexile and elastic. They make no impression on the organs of smell or taste, except in some instances when rubbed. They are the best conductors of electricity; and during the oxidation of some of these bodies, the Galvanic influence becomes powerfully conspicuous. All may be melted by heat, and the greater number are exhaled in vapour.

Metals are divided into those which, by the addition of oxygen, become acid, and those which are oxidised, without showing any acid properties. Of the former kind arsenic, tungstein, molybdenum, chrome, and columbium. Of the latter, gold, platina, silver, copper, iron, plumbago, lead, tin, zinc, mercury, tellurium (sylvanite of Kirwan), antimony, bismuth, manganese, nickel, niccolanum, cobalt, uranium, titanium, palladium, osmium, and iridium. We shall shortly mention their properties in the same order, excepting only those generally employed in medicine; and their medical effects depend so intimately on their chemical treatment, that it would neither be easy nor advantageous to separate the different parts of the subject.

Tungstein is a semimetal of a gray colour, fusing with great difficulty, oxidisable in the air by heat, and afterwards acidifiable. In the state of an oxide it is yellow; in that of an acid, white. The former gives to glass a blue or brown colour.

Molybdenum has a very slight metallic splendour, and a low specific gravity. It is oxidised by sulphuric, and easily acidified by nitric, acid. The acid is white and styptic. Though the specific gravity of the metal is but 6, that of the acid is 8.4.

Chrome is of a whitish gray colour, very brittle, and with difficulty fused or oxidised. Neither the sulphuric nor muriatic acids dissolve it; but the nitric changes it first into a beautifully green oxide, and afterwards into an orange yellow acid.

Columbium is little known. It was discovered in an American fossil by Mr. Hatchett, and its acid is a white powder, insoluble in water.

Of the oxidisable metals, we shall omit, for the reasons mentioned, gold, silver, copper, iron, lead, tin, zinc, mercury, antimony, bismuth, and manganese.

Platina has not yet found its way into the materia medica, nor is it likely soon to become a medicinal substance. It is of a gray colour, approaching Jo black, when polished. Its specific gravity is about 21, and it yields to gold only in ductility, and to iron in hardness. It is fused in 160° of Wedgewood, 21.877° of Fahrenheit, could Fahrenheit's scale be continued to this point. It is a good conductor of electricity and Galvanism; is oxidised by the former, producing a gray powder. It is oxidised and dissolved by the oxy-muriatic, but more certainly and quickly by the nitro-muriatic, acid.

Plumbago is a carburet of iron, seldom pure, and requiring a high degree of heat for its union with oxygen.

Tellurium, which Mr. Kirwan styles sylvanite, is of a bright lead colour, but brittle and crystallized in lamellae. Its specific gravity is about 6.1. It soon melts and sublimes. It burns with a greenish flame and a white smoke, resembling the smell of radishes. Its oxide melts into a straw coloured radiated glass. It is soluble in sulphuric, nitric, and nitro-muriatic acids.

The colour of nickel is between that of tin and silver, nearly 9 in specific gravity; when pure, extremely ductile and malleable; infusible, and with difficulty oxidisable in the air: yet it yields to the nitrous and nitro-muriatic acid only, tinging them of a brilliant green. It combines with phosphorus, sulphur, and the different metals. Its oxide is of a light clear green, giving to glass a brown and orange, in some instances a red, hue; but reducible by fire only. It is strongly attracted by the magnet, and can assume polarity. Richter. Niccolanum, lately discovered by the same author, very nearly resembles nickel.

Cobalt is a metal so brittle as to be capable of being reduced to powder. Its grain is fine, its colour of a reddish gray, and its specific gravity nearly 7.8. It is oxidated previous to its fusion, and requires a high degree of heat for its melting. It yields to all the acids, and unites with phosphorus and sulphur. Its oxide is of a deep blue, and gives this colour to glass. In the arts it is styled zaffre, or smalt.

Uranium presents a mass of small globules slightly united, of a pale brown, sometimes of a gray, colour. Its specific gravity is 6.44. It is very infusible, but yields to several of the acids, and unites with phosphorus. Its oxide is yellow, colouring glass of a greenish yellow an emerald green, or brown of different shades, and is very soluble in carbonated alkalis.

Titanium occurs in hard friable masses, of a crystalline appearance; internally of a bright red. It is very infusible, and yields only to the principal mineral acids by boiling. Its oxide is a deep red, blue, or white.

Of iridium, osmium, and palladium, three metals, if truly distinct ones, found in platina, we yet know little, and of course shall not enlarge this (already too extensive) article, by enumerating properties imperfectly known. What has been discovered occurs in the Philosophical Transactions for 1804 and 1805.

The Vegetable substances which have claimed the chemists' attention are, sap, mucilage, gum, oils, resins, gum resins, caoutchouc, balsams, foecula (starch), gluten, sugar, albumen, various acids, tanin, alkalis, wax, honey, and aroma. These substances, as we have stated in the beginning of this article, consist of carbon, hydrogen, and oxygen. The tanin, lately introduced to our notice, has been lately examined with peculiar attention in the Philosophical Transactions for 1805, by Mr. Hatchett. He has produced it with a variety of substances artificially, viz. by the action of nitric acid on any carbonaceous substance, vegetable, animal, or mineral; secondly, by distilling this acid from common resin, indigo,dragon's blood, &c; thirdly, by digesting common resin with gum elemi, asafoetida, camphor, etc. which then yield a principle very nearly resembling tanin to alcohol.