SALTS OF THE IODIC RADICAL, OR IODATES.

These salts are quite analogous to the bromates, and may be prepared similarly, by the action of iodine on the alkaline hydrates and carbonates. They exist, however, in several closely-related modifications; for, while to the ordinary iodates the formula MIO, is assigned, there are also other salts represented by the formulæ MI011 and MI,O,, all derivable from the action of iodic acid on metallic oxides. A very remarkable series of salts will be found described in the observations upon the phosphates; and we have already had peculiar instances among the sulpharseniates.

Iodates, when heated, are converted either into iodides, with evolution of 3 equivalents of oxygen, or into oxides, with evolution of iodine and of a less proportion of oxygen or formation of periodates; the former decomposition is that which the iodates of the first subdivision of basic radicals suffer, while the latter change is that experienced by the iodates of the second subdivision.

THE HYDROGEN SALT, or iodic acid, may be made directly by heating iodine with nitric acid, or with nitric acid and chlorate of potassium. It is exceedingly soluble in water; and the solution, which is syrupy, is extremely corrosive. Iodic acid, HIO,, when heated to 170° C., yields the iodic anhydride (I2O5), which decomposes at a higher temperature into its constituents.

The most important insoluble salts of this series are the argentic, mercurous, and plumbic iodates.

THE POTASSIUM and AMMONIUM SALTS are soluble.

The Barium Salt is produced by the action of a concentrated solution of a barium salt on a soluble iodate: it is a white granular precipitate. Its formula is BaIO3+aq.

It requires 1746 parts of water at 15°, and 600 parts of boiling water, to effect its solution; it dissolves with difficulty in warm nitric acid.

THE STRONTIUM SALT is soluble.

THE CALCIUM SALT is produced in the same manner as the barium salt: it is a white crystalline precipitate, soluble in 260 parts of cold water, and in 75 of boiling water, but much more easily dissolved by nitric acid.

THE MAGNESIUM SALT is soluble.

THE CUPROUS SALT does not exist.

THE CUPRIC SALT is produced by the action of cupric sulphates on iodate of sodium or iodic acid, and allowing the mixture to stand. If the precipitant were concentrated, the precipitate is bluish green; if dilute, white. It dissolves in 302 parts of water at 15°, or in 145 parts of boiling water, and is readily soluble in hydrate of ammonium.

The Argentic or Silver Salt is obtained by the action of a soluble silver salt on a solution of a soluble iodate: it is a white precipitate. Its formula is AgIO,.

It dissolves in hydrate of ammonium, and sparingly in nitric acid; by hydrochloric acid it is decomposed.

THE MERCUROUS SALT is obtained by the action of a soluble mercurous salt on solutions of iodic acid or iodates: it is a white precipitate, having a pearly lustre.

It is slightly soluble in water, and is dissolved by most acids.

THE MERCURIC SALT is soluble.

THE LEAD SALT is produced by the addition of a soluble lead salt to a solution of an iodate or of iodic acid: it is a white precipitate, which dissolves sparingly in water, and with difficulty in nitric acid.

Most, if not all, of the remaining iodates that are known are comparatively soluble in water.

a. Iodates may be identified, with the same ease as bromates, by the decomposition of their acid constituent. This change is, however, generally effected by the action of a reducing agent, such as sulphurous acid gas (SO2), which separates iodine, this element being subsequently recognized by the usual tests. The strong acids generally liberate iodic acid from the iodates in solution.

B. Iodates detonate when heated with combustible bodies, or when the mixtures containing these bodies are struck; the detonation is not nearly equal in violence to that of the chlorates, bromates, and nitrates when similarly treated.

y. If to a solution of an iodate a soluble iodide be added, and then a strong acid, the hydriodic and iodic acids, at the moment of liberation, act upon one another in the following manner :

7HI+HIO, 4H, 0+81.

The black precipitate, or brown colouration produced in the solution, is an excellent indication of the presence of iodine.

d. Iodates are decomposed by hydrosulphuric acid, a white precipitate of sulphur being formed, and sulphuric and hydriodic acids remaining in the solution.

The iodates are recognized by the precipitation of the barium, silver, and lead salts, and by the tests a, y, and d.

SALTS OF THE PERIODIC RADICAL, OR PERIODATES.

The periodates are, in some respects, similar to the perchlorates. They resemble the iodates in the facility with which they pass into new modifications possessing a different proportion of the basic constituent. The formula of the normal periodates would be MIO; but others are known, to which the formulæ MI, O,, M, IO, M, H, I2012, &c., have been assigned. Most of the insoluble periodates belong either to the second or third of these classes.

Heated on charcoal or with other combustibles, periodates detonate, but not violently; when heated alone, they behave in a similar manner to the iodates.

THE HYDROGEN SALT, or periodic acid, may be obtained in colourless

crystals (HIO,+2aq), which dissolve readily in water; the solution may be boiled without decomposition.

Among the insoluble periodates the sodium, barium, silver, mercurous, mercuric, and lead salts are the most important.

The Sodium Salt is obtained by passing chlorine through an aqueous solution of carbonate of sodium, and adding iodine; also in other ways. It is a pearly, white, crystalline precipitate.

Its formula is Na12 0, +3aq.

It is insoluble in cold, but sparingly soluble in hot water; it is easily soluble in acids. The normal salt (NaIO1) is very soluble in water.

THE POTASSIUM SALTS (KIO, and KI, O,) are soluble.

THE BARIUM SALTS (Ba, IO, and Ba, H, I2012) are produced in several decompositions, generally by the action of the soluble periodates of sodium. They are insoluble in water, but dissolve in dilute nitric acid.

THE STRONTIUM and CALCIUM SALTS are not well known, but are believed to be insoluble.

THE MAGNESIUM and CUPROUS SALTS are unknown.

THE CUPRIC SALT is a light green precipitate, soluble in dilute nitric acid.

The Argentic or Silver Salt is produced by the addition of nitrate of silver to the solution of periodate of sodium in dilute nitric acid, and falls as a light yellow crystalline powder, to which the formula Ag, 12 O, has been given. It is insoluble in water, sparingly soluble in nitric acid.

THE MERCUROUS SALT is said to be produced by the action of mercurous nitrate on the soluble periodate of sodium (NaIO). It is a yellow precipitate, which when warmed becomes reddish brown; it is easily soluble in dilute acids.

THE MERCURIC SALT is said to be produced by the action of mercuric nitrate on the soluble variety of periodate of sodium. It is a white precipitate, which when heated becomes yellow; it is soluble in dilute nitric acid.

THE LEAD SALT is produced by the addition of a solution of plumbic nitrate (PbNO,) to an aqueous solution of the normal periodate of sodium, as a white precipitate, nearly insoluble in water, but soluble in dilute nitric acid.

The PALLADIOUS and PLATINOUS, and several other salts are unknown. Some of the remaining periodates that are known are soluble; a few, chiefly belonging the class MI, O,, are insoluble.

The periodate of sodium (Na, I, O,) is the most characteristic salt of the present series.

SECTION III.-The chlorocadmiates, chloropalladiates, chloroplatinates, chlororhodiates, chlororutheniates, chloriridiates, and chloraurates, &c.

SALTS OF THE COMPOUND ACID-RADICALS WHICH CONTAIN CHLORINE, BROMINE, AND IODINE COMBINED WITH METALS.

The radicals contained in the salts of this section are monobasic; and consequently the general formula of these salts will be MR. The chlorocadmiates are represented by the expression MCdCl2, the chloropalladiates by MPdCl2, the chloroplatinates by MPtCl,, and the chloraurates by MAUCI. The other acid-radicals containing a metal and chlorine have 3 equivalents of the latter element. Many corresponding compounds containing bromine and iodine combined with metals are also formed, but they are as yet but imperfectly known.

SALTS.

Potassium

Cl

Br

I

TABLE OF

F

(see page 254) (see page 256) (see page 260) (see page 263)

These radicals may be recognized best by the insoluble salts which they yield with certain basic radicals, chiefly potassium, ammonium, and the organic compound ammoniums. These insoluble salts are almost all of a yellow, orange, brown, or red colour; and as they have been named or described under their respective metals, they need not be again noticed here.

These radicals may also be identified by their decomposition into new products, &c. When, for instance, a stream of hydrosulphuric acid gas is passed through a neutral or acid solution of chloroplatinate of sodium, one of the products of the reaction is sulphide of platinum. This reaction, described in the appended equation, takes place with all the salts of the acidradicals contained in this section:

2KPtCl ̧+2H2S=2KC1+4HC1+Pt, S ̧.·

(see page 267) (see page 269) (see page 271) (see page 273) (see page 220)