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carbonate, obtained by passing a stream of carbonic acid gas through a solution of the foriner.

Soda and potash considerably resemble each other, but the former does not deliquesce so as to liquefy, as potash does; its crystals, however, effioresce or fall to powder. It is used in the manufacture of soap and of glass.

Soda, also, like potash, consists of a metallic base united toxygen. The metal is called sodium. It resenibles potassium in most of its properties. It unites with chlorine, forming chloride of potassium ; this is the common sea-salt so much used in food, and was, till lately, called muriate of soda.

Common salt exists in immense quantities in nature, both in the form of a rock, as rock-salt, which is dug out of the earth in a solid form, and also dissolved in the sea, from which it is obtained by evaporation.

Common salt is decomposed by sulphuric acid. The sodium is converted into soda, by taking oxygen from the water of the sulphuric acid, and the chlorine combines with the hydrogen of the water thus set free, and forms hydro-chloric acid gas, which is the same with what has been called muri. atic acid gas. This gas, absorbed by water, forms muriatic acid. Hence, since muriatic acid was thus procured from sea-salt, it was supposed to exist in it, combined with soda, whence the name muriate of soda.

Soda unites with all the acids, forming neutral salts, the most remarkable of which are the following:

Sulphate of soda, called formerly Glauber's salts, is formed abundantly in the process for procuring the muriatic acid from common salt; the sulphuric acid which is employed uniting to the soda.

Borate of soda, or borax, and
Phosphate of soda, useful as a test.

The fixed alkalies readily combine with oils, and thus form soap.

Soap is soluble in water, and owes its detergent quality to the alkali contained in it. Alkali by itself would be too powerful, and would be apt to destroy the linen and other substances to be cleaned.

Soap when in solution is decomposed by acids, which unite with the alkali; hence if an acid is contained in water, the soap curdles. Neutral salts formed by acids with bases of the earths produce the same effect. Hard waters are such as have earthy salts, and are unfit for washing; soft water is that which is quite free from salts.

Hard soap is made from soda rendered caustic . by lime, and olive-oil, or tallow. Soft soap is composed of potash and whale-oil.

LITHIA.

This alkali was lately discovered by M. Arfvredson, a Swedish chemist.

It is found to be a constituent of certain stones, and has been met with in the petalite, spodumen, and lepidolite. It is of the class of fixed alkalies; is soluble in water, has an acrid taste, and changes vegetable blues to green. It forms neutral salts with the acids.

Lithia, like the other fixed alkalies, has been found by analysis to be the oxide of a peculiar metal, which has been called Lithium. Its decomposition has been effected by the voltaic pile, but the quantity of metal obtained has been extremely small.

AMMONIA.

This substance is known also by the name of the volatile alkali. It is composed of nitrogen and hydrogen. In its purest form it is in the gaseous state. It is then called ammoniacal gas.

Ammoniacal gas is procured by adding dry quicklime to muriate of ammonia, and exposing them in a retort to the heat of a lamp. The muriatic acid, having a stronger attraction for the lime than it has for the ammonia, leaves the latter, which is disengaged, in the state of gas. A pneumatic apparatus is necessary for this purpose, as this gas is rapidly absorbed by water. Ammoniacal

gas has a strong pungent smell, and suffocates animals immersed in it. It changes vegetable blues to green. If water be introduced into the apparatus, in contact with the gas, it absorbs it entirely, and acquires its peculiar smell : this is a solution of ammonia in water, and is called liquid ammonia.

Ammonia exists as a constituent in animal bodies; and it is obtained from bones, horns, &c.

It is a valuable material in manufactures and medicine. Ammonia forms with the acids several valuable compounds.

With carbonic acid it forms carbonate and bicarbonate of ammonia. The carbonate may be obtained by mixing ammoniacal gas with carbonic acid gas over mercury.

The two gases immedi . ately combine and form a solid white body, which still retains some of the pungent smell of the am. monia. This is the common smelling salts. The bi-carbonate is procured by causing a current of carbonic acid gas to pass through liquid ammonia. It has no smell.

Muriate of ammonia was called sal ammoniac from its having been originally brought from the neighbourhood of the Temple of Jupiter Ammon. It is now abundantly prepared in this country by saturating carbonate of ammonia with sulphuric acid, which forms sulphate of ammonia : by decomposing this salt by muriate of soda, muriate of ammonia and sulphate of soda are obtained. Sal ammoniac is employed in many processes,

EARTHS.

At the first view it would seem, from the vast variety of soils on the surface of the globe, and the number of rocks and stony substances, that the different earths of which they are composed were innumerable: nevertheless, their number is very limited, and, by the mixture of these, the greatest part of mineral bodies is composed.

The earths were formerly considered as elementary substances, but late discoveries have shown that most of them are, like the alkalies, metallic oxides. It is found, however, more convenient still to consider them as a separate class.

The earths are of two kinds :

1. Those which have some of the properties of alkalies and which are called alkaline earths.

2. Earths simply so called.

The alkaline earths are, lime, magnesia, barytes, and strontia. They unite with acids forming compound salts as alkalies do : like them they change vegetable blues to green; they have a considerable degree of causticity and taste, and are soluble in water.

The rest of the earths are insipid, and are scarcely at all soluble in water, and have no action on vegetable colours.

LIME.

Lime is one of the most abundant substances in nature. It is the chief constituent in vast mountains and rocks, and is very generally distributed, mixed with other earths. Chalk, marble, calcareous spar, and all those rocks called lime-stones, consist of it.

In these substances, however, the lime is not pure or uncombined. It exists in them united to carbonic acid, constituting carbonate of lime.

To obtain pure lime, these stones are exposed to a white heat, by which the carbonic acid is driven off in the gaseous state. This is called the burning of lime. The stone so treated is then called quicklime ; or, in chemical language, properly lime.

Quicklime, or pure lime, is white; has a hot acrid taste, and is caustic, or corrodes the skin. It changes vegetable blues to green.

Until the discovery of the bases of the alkalies by Sir Humphry Davy, lime, as well as all the other earths, was considered as an elementary substance; but it has been ascertained to be the oxide of a metal to which the name of calcium has been given. From the extreme difficulty, however, in reducing lime to this state, the properties of calcium are but little known. It is white and solid, resembling silver, and soon returns to the state of oxide or lime by attracting oxygen from the air.

When water is thrown on quicklime just burnt, it swells, bursts, and falls to powder; giving out, at

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