certain compounds formed by combining alkalies, earths, or metallic oxides, with an acid. Their great number and variety rendered some method of distinguishing them very desirable; and in this admirable contrivance, the simplicity and ingenuity of the new chemical nomenclature is equally remarkable and important. By this arrangement every salt has a double name, one to indicate the acid, and the other the base of which the salt is formed, so that its appellation shews the ingredients composing it. The words expressive of this class usually end with the syllable ATE: thus all those substances which are compounds and consist of alkalies, earths, or metallic oxides, combined with nitric acid, are called nitrates; those with sulphuric acid, sulphates; with the muriatic acid, muriates; with the carbonic acid, carbonates; with the acetic acid, acetates, &c., &c. In a few instances, however, there are exceptions to this general rule, such as ammoniacal, calcareous, and aluminous salts, &c.; but although the number of this class of compounds at present known may exceed two thousand, their respective composition is immediately recognized by the characteristic terms which are now applied to them.

Sometimes an acid is combined with two bases, and in that case the names of both substances are subjoined to

that of the acid from which they derive their character; as sulphate of alumina and potash; and tartrate of potash and soda.

The advantages attendant upon the new mode of designating different chemical substances will be peculiarly obvious from the following instances :-The medicine formerly called Epsom salt, is now termed sulphate of magnesia, from its consisting of sulphuric acid combined with magnesia; Glauber's salt, is sulphate of soda, being a compound of sulphuric acid and soda; Gypsum, or Plaster of Paris, is sulphate of lime, consisting of sulphuric acid and lime; but the substance which was so improperly called green copperas, is now termed sulphate of iron, for there is no copper in its composition, but it is formed of sulphuric acid and iron. Sulphites, nitrites, phosphites, &c., are salts formed by combining the sulphurous, nitrous, &c., acids with the respective bases by which they are designated.

CARBURETS, SULPHURETS, &c. This class of compounds is distinguished by the termination ET, because carbon, sulphur, &c., form one of their constituent parts, and they consist of carbon, sulphur, &c., combined with alkalies, or metals. Plumbago, the common black lead, is carburet of iron; Ethiop's mineral is sulphuret of mercury; cold short iron is phosphuret of iron, &c. From the brightness of their colour, the sulphurets of some of the metals are used in the naking of pigments for painters; and the sulphuret of lime is employed in bleaching.

OXIDES. This term is used to denote certain mineral, animal, and vegetable substances, combined with such a portion of oxygen as is insufficient to render them acid. The rust of iron is an oxide; and the surfaces of iron, copper, lead, and zinc, become oxides by exposure to the atmospheric air; but several other metals require the assistance of heat or an acid to convert them into oxides; and they acquire an increase of weight in proportion to the quantity of oxygen combining with them. Thus red lead is an oxide of lead, and an instance illustrative of this addition of weight by the combination of the oxygen with the metal. Various metallic oxides, properly prepared, form the pigments employed in the process of enamel painting and staining glass.

"To convert the metals into oxides, there is a degree of heat which is peculiar to each metal, and even to different oxides of the same metal. Mercury, for example, is oxidized at a degeee of heat which produces no change in iron; and lead at one degree of heat becomes minium, at another massicot."-Henry's Chemistry, Vol. I.

OXIDIZE. To oxidize a substance is to combine such a portion of oxygen as shall not produce acidity.

OXYGENIZE. To oxygenize, signifies the re

dering a substance acid by combining oxygen with it.

COMBUSTION. This term is usually employed to denote the act by which combustible bodies, when burning, absorb oxygen from the atmospheric air, and by decomposing the oxygen cause it to give out its caloric, sometimes accompanied with light in the form of flame or the appearance of a red heat.

COMBINATION. By this word the proper chemical union of two or more substances is designated; thus, before the pit coal is decomposed in order to separate it into its constituent parts, the different substances which compose it are chemically united. But mechanical mixture is a different kind of union; and the lime and water employed to purify the gas is an appropriate instance of it; for although both substances are united by means of the water, yet the lime separates of itself, and subsides to the bottom of the vessel when the mixture is not agitated by the motion of the paddle of the machine.

DECOMPOSITION is the operation by which compound bodies are separated into their constituent principles by chemical means. For instance, pit coal is a compound of various sub

stances, which are separated from each other by the application of heat in the process of making coal gas, and this is called decomposing the coal.

ELASTICITY is a term employed to designate that kind of force which some bodies exert to recover their usual size and form when they have been displaced or compressed by external power or pressure. Thus in the portable gas vessels, 30 cubic feet of gas are forced by mechanical means into the space of one cubic foot; but if the pressure be removed, the gas immediately expands, and occupies its original 30 cubic feet of space. The common India rubber is another instance of elasticity.

ELASTIC FLUIDS.

Sometimes both vapours

and gases are so denominated; vapour, or steam, is termed merely an elastic fluid; but the term gas denotes a permanently elastic fluid, and the gases are also called aëriform fluids.

SPECIFIC GRAVITY, is a term used to denote the relative weight which different bodies occupying exactly the same portion of space have to each other; for two bodies may be precisely of the same dimensions, and yet differ greatly in their respective weight; hence that which is the lighter of the two is said to be specifically lighter