sulphuric acid forms with potash, sulphate of potash, with oxide of iron, sulphate of iron, &c.

343. The different acids, composed of the same base with different proportions of oxygen, form very different salts when combined with the same alkali.

Illus. The salt for instance which the sulphurous acid forms with potash, is very unlike that which it forms with the sulphuric,

344. The proportion of oxygen in the acid of which a salt is formed, is denoted by the termination of the generic name of the salt.

Illus. Thus salts, formed with an acid ending in ous, always ends in ite; as sulphurous acid forms with potash, sulphite of potash. Acids, ending in ic, form salts ending in ate; as sulphuric acid forms sulphate of potash.

345. In most cases the acid and base combine in such proportions, as that neither predominates, and consequently the compound formed is a neutral salt. In a few instances however, a neutral compound is capable of uniting with an additional quantity of acid, or of base, so that one predominates over the other.

Illus. Tartaric acid is capable of uniting with potash in a double proportion, so that the acid greatly predominates over the alkali. Such salts are distinguished by prefixing to their names the Latin preposition super, Thus we have super tartrate of potash, super sulphate of potash, &c.

346. When the base predominates, the deficiency of the acid is denoted by the preposition sub, as sub carbonate of potash, sub borate of soda, &c.

Obs. The pupil will see at once, with what ease the names and composition of a great variety of salts may be remembered, by observing the above rules. By knowing the name of a salt we know its composition. Thus muriate of soda is composed of soda and muriatic acid. If we know the composition of the salt, we also know its name. Thus a combination of muriatic acid and lime would make muriate of lime, and so of all other substances capable of forming salts.

347. The acids admit of being divided into three classes, according to the nature of their bases, or

the kingdoms of nature in which they exist, viz. mineral, vegetable, and animal acids.

MINERAL, AND METALLIC ACIDS.

Obs. These acids are composed of a simple base and oxygen,

Obs. These acids all contain two simple substances as a base, viz. carbon and hydrogen.

oxygen forming acids.

Acetic,

Gallic,

These are combined with

ANIMAL ACIDS.

Obs. Some of these acids, in addition to hydrogen and carbon as a base, contain nitrogen also. Oxygen, as usual, is considered the acidifying principle.

Phosphoric,
Lactic,

Saccholactic,

Formic

Sebacic,

Prussic,

Bombic,

Uric.

Obs. Some of the above acids are both animal and vegetable, Thus the prussic acid is found in plants as well as animals, Several of the mineral acids, as the sulphuric and muriatic, are found among animal bodies, &c.

MINERAL ACIDS.

348. Sulphuric acid is a heavy corrosive liquid, powerfully acid to the taste, but destitute of smell, and free from colour. It is formed by the combustion of sulphur.

Illus. Sulphur, in the open air, burns with a pale blue light and suffocating smell; but by burning it in oxygen gas, at the same time all moisture being excluded from under the vessel, a dense white vapour is produced, resembling snow. This is dry sulphuric acid.

Obs. When sulphur is burned in common air, sulphurous acid is formed. In this case the sulphur has not combined with its full dose of oxygen. When it is burned in oxygen gas it combines with its maximum of oxygen, and becomes sulphuric acid. When water, which has a strong attraction for this acid, is saturated with it, the common liquid sulphuric acid, or oil of vitriol is formed.

In the manufactories of this acid, the sulphur is mixed with a certain proportion of nitre, and the mixture is burned in chambers lined with lead. The nitre supplies the oxygen necessary to form sulphuric acid, which is absorbed as it is formed by water, with which the floor of the chamber is covered. This acid when concentrated by boiling, is about twice as heavy as A bottle of it is soon tinged brown by dropping into it, any vegetable matter. If stopped with a cork, this commonly has the same effect. This is caused by the carbonization of the vegetable matter, by the oxygen of the acid.

water.

When this acid is mixed with water, in the proportion of about four of the former to one of the latter, the temperature of the mixture is raised to about 300 degrees.

349. When sulphuric acid is united to alkalies, earths, or metallic oxides, the compounds are termed sulphates.

Illus. The substance used as a manure, cement, &c. and called plaister of paris, is a compound of sulphuric acid and lime. It is therefore sulphate of lime. The article used in dyeing, and called copperas, is a compound of this acid and oxide of iron, or sulphate of iron.

Obs. Formerly sulphuric acid was obtained by the distillation of copperas, or, as it was also called, green vitriol. Hence this acid was called oil of vitriol.

350. This acid is decomposed by almost every individual of the class of combustibles, especially when assisted by heat.

Illus. When charcoal is immersed in hot sulphuric acid, the charcoal absorbs from it the oxygen which constitutes it sulphuric acid, and it is in consequence converted into sulphurous acid. Several of the metals produce the same effect by absorb

ing the oxygen.

Sulphuric acid is composed, in its dry state, of about 40 parts of sulphur, and 60 of oxygen to the 100. When liquid, and of the density of 1850, it contains 19 parts of water and 81 of the acid.

This

351. Sulphurous acid form of a gas. It is produced burned in common air.

acid exists in the

when sulphur is

Exp. By means of a small spoon, or scoop, plunge some burning sulphur into a wide mouthed bottle filled with common air. As the sulphur burns, sulphurous acid gas is formed, which will soon fill the bottle. It must then be corked up.

352. This gas has a pungent and suffocating smell. It extinguishes burning bodies and destroys animals when they are made to breathe it. It has the property of whitening, or bleaching silk, straw, linen, cotton, &c. Water absorbs about 33 times its bulk of this gas. It is heavier than common air. Exp. 1. Plunge a burning taper into a bottle of this gas, and it will be instantly extinguished.

Remark. It is so much heavier than atmospheric air that a bottle of it may be uncovered for a time without its escape; consequently these experiments are easily made, by covering the bottle with a plate of glass, and removing this whenever any thing is to be introduced.

Exp. 2. Its bleaching property may be shown by permitting any of the substances above mentioned to remain in it for a short time. Coloured flowers are turned white by it. They must be moistened with water before they are introduced.

353. Some of the metallic oxides are revived by the action of this gas.

Exp. Make a solution of acetate of lead in pure water, and with this moisten a piece of silk, or a small plant, às a sprig of mint, and while moist introduce it into a bottle of this gas. The metal

will be revived and will cover the surface of the article with brilliant metallic lead.

Obs. Sulphurous acid has a strong tendency to combine with an additional quantity of oxygen.

Acetate of lead is an oxide
When this is deprived of its

of the metal dissolved in an acid. oxygen, it returns again to the state of a metal. In the obove experiment the oxygen is absorbed by the acid, and consequently the oxide is revived.

354. Nitric acid. This acid is obtained from the salt called nitre, or salt petre. This is composed of nitric acid and potash. It is therefore nitrate of potash. The decomposition is effected by sulphuric acid.

Exp. Put into a glass retort four parts of nitre reduced to a coarse powder, and pour upon it three parts of strong sulphuric acid. Adapt a large tubulated receiver to the retort, and lute the junctures with a mixture of pipe clay, sand, and cut tow. Then apply the heat of a lamp or sand bath. The receiver must be kept cold during the process, and furnished with a tube of safety. The first product which passes over is red and smoking. This gradually diminishes, and the acid drops down pale, or colourless.

355. Nitric acid, made by the above experiment is not perfectly pure, but always contains a portion of muriatic and sulphuric acid.

Obs. Pure nitric acid always exists in the state of a gas. This, however, is found only in the laboratory of the chemist. What is commonly known by this name, contains a quantity of water, and forms what chemists distinguish by the name of hydro nitric acid. As this, however, is so generally known by the name of nitric acid, or aqua fortis, we shall continue to call it so at present.

356. Nitric acid when pure, is a colourless liquid considerably heavier than water. It emits white fumes when exposed to the air. It gives an indelible yellow stain to the skin. It becomes coloured by the sun's light, passing first to a straw colour, and then to a deep orange.

Obs. This change of colour is produced by the union of the light of the sun with the oxygen of the acid, in consequence of which, the acidifying principle suffers some diminution.