THE SILVER SALT is a white curdy precipitate. Its formula is Ag, Cocy. It is insoluble in water and acids.

THE MERCUROUS SALT is a white precipitate.

THE MERCURIC SALT is soluble.

THE LEAD SALT is readily dissolved by water, but is insoluble in alcohol. Cobalticyanide of potassium gives with manganese and stannous salts white precipitates, and with cadmium salts a brown precipitate which becomes white. It does not yield any results with titanic, uranic, and chromic salts.

Cobalticyanogen may be recognized by its decomposition in a similar manner to the two preceding acid-radicals.

Of acid-radicals containing carbon, oxygen, and hydrogen, a very large number is known; we shall, however, describe the salts of those only which are likely to come in the way of the student, viz. the acetates, benzoates, lactates, succinates, tartrates, citrates, gallates, and tannates.

SALTS OF THE ACETIC RADICAL, OR ACETATES.

The radical under consideration is an exemplar of a new class or order of compounds: it is a member of what is called " a homologous series." Some approach to this form of combination has already been noticed in the case of the borates; but among the compounds of carbon with hydrogen and oxygen, it is more completely and extensively developed. An immense number of acid-radicals has been discovered by degrees, each requiring the same amount of base for its saturation, and each differing, from the term of the series next above or below it, only by the molelecule CH,. The following list shows a few of the hydrogen compounds or acids of these radicals:—

HC,H,O,=HCHO,+3CH,.

Valerianic acid HC,H,O,=HCHO2+4CH,.

The series of which acetic acid is a member, is called "the series of fatty acids," because, as the amount of CH2 increases in them, they no longer exhibit the limpidity and perfect miscibility with water characteristic of formic and acetic acids, but

become more and more oily, until, finally, the higher terms of the series reach the condition of solid fats. All these acids have certain features in common: they are volatile without decomposition; their boiling point increases regularly with each increment of CH,; they all yield similar products of decomposition, which vary only by CH,; and they may all be formed by the same agencies from a series of "alcohols" containing basic radicals, which bear a fixed and constant relation to the radicals of the acids.

The acid of the acetic series is produced by the imperfect combustion of most organic bodies; as "vinegar" it is produced by the slow oxidation of alcohol, and as " pyroligneous acid" by the distillation of wood at a high temperature in iron retorts.

The acetates of the first and second subdivisions, when heated, yield carbonates, and, if out of contact of air, a volatile liquid of peculiar odour, called acetone (C, H,O). Alkaline acetates, if mixed with excess of alkaline hydrate and heated, are completely decomposed into the combustible gas known as marsh-gas"

and alkaline carbonates.

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THE HYDROGEN SALT (HC, H2O2), or acetic acid, is a colourless crystalline solid at temperatures below 15° C.; on this account it has received the name of glacial acetic acid.* It boils at 120° C. It has the well-known taste and smell of vinegar in a most marked degree, and acts as an acrid poison.

The normal or neutral acetates are almost without exception soluble in water; the basic acetates are for the most part insoluble.

THE POTASSIUM, SODIUM, BARIUM, STRONTIUM, CALCIUM, and MAGNESIUM SALTS are soluble.

THE FERROUS and Ferric Salts are soluble; the latter, however, if produced by adding a drop of ferric chloride to the solution of an alkaline acetate, imparts a distinct brownish red colour to the liquid. If the coloured solution be then boiled, the neutral ferric acetate will be decomposed, a mixed hydrate The hydrate of this acid, having the formula C, HO2, H2O, boils at 104° C.

and acetate, or basic acetate, being produced, and the solution becoming gradually colourless.

THE ZINC and CUPRIC SALTS are soluble.

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THE MERCUROUS SALT is obtained by adding mercurous nitrate to acetic acid or a soluble acetate: it is a white, scaly, crystalline precipitate. Its formula is Hg, C, H,O,. It dissolves readily in excess of its precipitant: it is slightly soluble in water or acetic acid, especially on warming; but a slight decomposition of the salt into mercuric acetate and mercury then occurs.

The Silver Salt is produced by the action of soluble silver salts on the solution of an acetate: it is a white, beautifully crystalline precipitate, which becomes discoloured by exposure to light.

It is soluble in hydrate of ammonium, but dissolves very sparingly in cold water or acetic acid, although it dissolves more abundantly in these liquids when hot, crystallizing out again on cooling.

THE MERCURIC SALT is soluble.

THE LEAD SALT (PbC, H,O,) is soluble. THE BASIC LEAD SALT is soluble, and is remarkable for having an alkaline reaction. Its formula is PbC, H,O,, Pb,O.

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This acid-radical may also be detected by the following special processes:

a. When an acetate is warmed with dilute sulphuric acid, acetic acid is liberated, and, being volatile without decomposition, may be recognized by its peculiar odour and inflammability.

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B. If an acetate be mixed with a small quantity of alcohol (C, H, HO or EHO, the hydrate of the compound basic radical ethyle) to which an equal bulk of sulphuric acid has been previously added, a true salt will be formed, containing a compound basic and a compound acid-radical: this product is termed acetate of ethyle, or acetic ether, and may be at once recognized by its peculiar and agreeable aromatic odour. The reaction is as follows:EHO+HÃ=H,O+EA.

y. When an acetate of the first or second subdivision is

heated in a test-tube, acetone, remarkable for its odour and inflammability, is evolved; the reaction is as follows:

The acetic radical is generally recognized by the formation of the silver salt, and the test ẞ.

SALTS OF THE BENZOIC RADICAL, OR BENZOATES.

Just as acetic acid is the representative of the series of fatty acids, so benzoic acid is the type of "the series of aromatic acids." This group is by no means so numerous as the former; but its members present the same regular differences of composition, and the same relations to other groups of connected bodies. Benzoic acid, though itself somewhat rare, is the member of this series most commonly met with.

Benzoates when heated decompose, generally giving rise to the formation of a volatile solid body termed benzophenone, which is in reality the benzoate of phenyle (C, H5, C, H, O2).

This radical may be recognized by the formation of insoluble salts, and by processes of decomposition.

THE HYDROGEN SALT (HC, H2O2), or benzoic acid, is generally obtained by exposing "gum benzoin" and several other resins to heat, or by boiling them with an alkaline hydrate. It crystallizes in plates, and has an aromatic odour. At 120° C. it fuses, sublimes at 145°, and boils at 239°. Its vapour, if inhaled, provokes coughing. It is but slightly soluble in cold, more readily in hot water. In alcohol it is soluble.

Nearly all benzoates are soluble in water; the ferric salt is the most characteristic insoluble benzoate.

THE POTASSIUM, SODIUM, BARIUM, STRONTIUM, CALCIUM, MAGNESIUM, and FERROUS SALTS are soluble.

The Ferric Salt is produced by the action of ferric chloride upon solutions of benzoates. It is of a reddish yellow colour, and has the composition of a basic salt. It is dissolved by most acids.

THE ZINC SALT is soluble. THE CUPROUS SALT is unknown.

THE CUPRIC SALT is produced by the action of soluble cupric salts upon solutions of benzoates, as a blue precipitate. Its composition is CuC, H, O2 with some water of crystallization. It is soluble in many acids.

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THE SILVER SALT is produced by adding a soluble silver salt to a solution of a benzoate, as a white curdy precipitate. Its formula is AgC, H, O2. It dissolves in boiling water and in many acids.

THE MERCUROUS SALT is a curdy precipitate. THE MERCURIC SALT is a white curdy precipitate, slightly soluble in water and alcohol.

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THE LEAD SALT is a white precipitate of the formula PbC, H, O2 with water of crystallization.

This acid-radical may also be detected by the following methods:—

a. When an acid is added to a soluble benzoate, a precipitate of benzoic acid is produced, which, if boiled in water, dissolves, and crystallizes out again on cooling. The acid, when separated, may be recognized by its fusibility, volatility, and remarkable odour.

B. The dry cupric benzoate, when heated in a test-tube, decomposes, with the formation, among other products, of the benzoate of phenyle (C ̧ H¿, C, H, O2), which is a body possessing an odour resembling that of the geranium.

SALTS OF THE LACTIC RADICAL, OR LACTATES.

This radical is bibasic; and the lactates known belong to the two series of acid and neutral salts: for the most part they dissolve sparingly in water or alcohol, and are insoluble in ether.

THE HYDROGEN SALT, or lactic acid, occurs in sour milk, in which it is produced by a fermentive action upon the milk-sugar that liquid naturally contains, thus

It is produced by the fermentation of other kinds of sugar. Its formula is H2 C H10 O. It is a colourless syrupy liquid, which does not solidify at 24° C. It is inodorous, but has a biting acid taste. In presence of platinum it volatilizes without decomposition at about 200° C. Heated alone, it decomposes at about 130° C. into water and lactic anhydride (C12 H20 010). The latter is a pale yellow, bitter, and easily fusible solid. At high temperatures, lactic acid decomposes into a great variety of products. Lactic acid dissolves in water in all proportions.

The lactates of the first subdivision are very soluble in water; those of the second subdivision require from 20 to 30 parts of water for solution, while the majority of the remaining salts dissolve easily.

THE POTASSIUM, SODIUM, BARIUM, STRONTIUM, CALCIUM, and MAGNESIUM SALTS are soluble.

THE FERROUS SALT is a nearly white precipitate. Its formula is Fe, L. It is soluble in 48 parts of water at 10° C., or in 12 of boiling water; it is insoluble in strong alcohol.

THE FERRIC SALT is brown and soluble.

THE ZINC SALT is white, and crystallizes in four-sided prisms belonging to the right prismatic system. Its formula is Zn, L. It is soluble in 58 parts of cold, or 6 of boiling water; it is insoluble in alcohol.

THE CUPRIC SALT is very soluble.

THE SILVER SALT is soluble in 20 parts of cold water, nearly insoluble in cold, but very soluble in hot alcohol.

THE MERCUROUS SALT is a white precipitate consisting of fine needles. Its formula is (Hg2) L+aq. It is sparingly soluble in cold, and is decomposed by boiling water.

THE MERCURIC SALT is soluble.