If a solution of a hypochlorite be mixed with a solution of a lead salt, at first a white precipitate of plumbous chloride (PbCl) is produced (it must be remembered that hypochlorites are almost invariably accompanied by chlorides); this white precipitate, however, speedily becomes brown, being converted, with evolution of chlorine, into the binoxide of lead (Pb,0) :

2PbC1+2CaC10=Pb, 0, +2CaC1+2C1.
brown ppt.

2

d. If a solution of a hypochlorite be mixed with oxide of silver (Ag2O), the latter is rapidly converted into the chloride (AgCl) with violent evolution of oxygen, derived partly from the oxide of silver, and partly from the hypochlorite employed. If the same experiment be performed, only substituting the nitrate for the oxide of silver before used, a black precipitate, formerly believed to be peroxide of silver (Ag, O,), is deposited.

e. The hypochlorites oxidize hydrosulphuric with formation of sulphuric acid and separation of sulphur; by the addition of more hypochlorite, the sulphur is itself oxidized.

The hypochlorites are recognized by the tests a, ß, y, and d, just described, and by their powerful bleaching action on indigo, litmus, and other vegetable colouring matters.

SALTS OF THE CHLOROUS RADICAL, OR CHLORITES.

The chlorites do not occur in the course of analysis. The formula of the anhydrous acid is Cl2O,, and that of the salts MCIO2. Most of the known chlorites are readily soluble in water; the argentic and plumbic chlorites are, however, nearly insoluble: the latter is a beautiful pale yellow precipitate, crystallizing in scales. The chlorites differ from the hypochlorites in the fact that their bleaching power is not destroyed by a solution of arsenious oxide in nitric acid.

SALTS OF THE CHLORIC RADICAL, OR CHLORATES.

These salts are far more stable under ordinary circumstances than the hypochlorites; the most common salt is that of potassium, which is generally prepared by passing chlorine into a solution of hydrate of potassium, and not preventing the consequent rise of temperature:

6KHO+6C1-KC10,+3H,0+5KC1.

The chlorates, when heated on charcoal before the blowpipe, deflagrate with great brilliancy, the charcoal being consumed and converted into carbonic anhydride, and a residue of chloride, oxide, or metal left, according to the nature of the basic radical present, unless indeed complete volatilization occur. The chlorate of barium imparts a green, that of strontium a crimson colour to the blowpipe flame.

When heated alone in the solid state, the chlorates are decomposed, any residue being either a chloride or an oxide, an evolution of oxygen also occurring.

THE HYDROGEN SALT (HCIO,), or chloric acid, is only known dissolved in water; in this state it is decomposed when heated above 40°.

No insoluble chlorates are known; some of the important reactions of acids, &c. upon these salts are given in subsequent paragraphs.

a. The chlorates are easily recognized by the peculiar decompositions which their acid-radical suffers. When a chlorate is mixed with concentrated sulphuric acid, chloric acid (HCIO,) is evolved, thus

2MC10,+H2SO1=2HC10,+M, SO;

as the temperature rises, the chloric acid decomposes, thus

This decomposition is accompanied by a peculiar crackling noise, and the evolution of the greenish yellow gas, hypochloric anhydride (C10), which, if the temperature rises too high, explodes with great violence. This gas has a most peculiar, almost aromatic odour, quite unlike that of chlorine; but no sooner has the explosion and decomposition of the gas into oxygen and chlorine taken place, than the suffocating smell of the latter gas may be directly perceived. Sulphuric acid acts much more readily upon chlorate of potassium when chloride of potassium is also present.

B. When a minute quantity of a chlorate is produced, and then rubbed gently in a mortar with a very small particle of sulphur, frequent and sharp detonations occur.

y. If a chlorate be mixed with an organic substance, such as sugar, the mass placed in a dish, and then a single drop of concentrated sulphuric acid allowed to fall from a glass rod upon the mixture, vivid combustion takes place, due, of course, to the liberation of chloric acid and its oxidizing effect upon the carbon and hydrogen of the sugar.

d. A solution of a chlorate, even if somewhat dilute, when mixed cold with tincture of litmus, and then a few drops of strong sulphuric acid added, bleaches the litmus. This test forms one of the best characteristics by means of which we can distinguish between the chlorates and nitrates.

e. A solution of a chlorate mixed with a solution of indigo in sulphuric acid bleaches the indigo on the application of heat, just as a nitrate would do.

4. Hydrosulphuric acid does not decompose a solution of chlorate of potassium.

The tests a. and d. are among those most usually employed for the recognition of the chlorates.

SALTS OF THE PERCHLORIC RADICAL, OR PERCHLORATES.

The perchlorates are remarkably stable salts; the perchlorate of potassium withstands a higher temperature than the chlorate without decomposition, and is among the first products formed when chlorate of potassium is heated, since it is not itself resolved into chloride of potassium and oxygen, except at a more elevated temperature.

Perchlorates, when fused upon charcoal, explode with violence; but with combustible bodies in general they do not detonate so violently as the chlorates.

THE HYDROGEN SALT (HClO), or perchloric acid, is a white crystalline solid, which melts at 45° C., and is very soluble in water.

The potassic perchlorate is the only salt of the series which may be considered comparatively insoluble.

The Potassium Salt is obtained by the addition of certain soluble potassium salts (e. g. the carbonate [K, CO,]) to an aqueous solution of perchloric acid, or by fusing chlorate of potassium at a gentle heat and for some time, and, after cooling, separating the chloride of potassium formed, from the perchlorate by water. It is a white crystalline powder.

Its formula is KClO4.

It dissolves in 65 parts of water at 15° C., and in a smaller quantity of boiling water: it is quite insoluble in alcohol.

THE AMMONIUM SALT is produced by the addition of hydrate or carbonate of ammonium to aqueous perchloric acid: it is a white crystalline precipitate, very slightly soluble in alcohol, but requiring only 5 parts of cold water for solution.

The barium and all the other known salts of the perchloric radical are soluble in water.

The perchlorates are detected by the precipitation of the insoluble potassium salt, while they are distinguished from the chlorates by not becoming yellow on treatment with sulphuric acid (concentrated) in the cold.

Of the acid-radicals containing bromine combined with oxygen, that existing in the acid (or hydrogen salt) termed bromic acid is the only important one in an analytical point of view.

SALTS OF THE HYPOBROMOUS RADICAL, OR HYPOBROMITES.

From the similarity of bromine to chlorine, and from the peculiar properties of the solution formed when bromine is added to the carbonates or hydrates of potassium or sodium, the alkali being in excess, it is extremely probable that a series of hypobromites exist of the formula MBrO, possessed of bleaching powers like the hypochlorites, and decomposing, when ignited, into bromide of the metal and oxygen. They are of no analytical importance.

SALTS OF THE BROMIC RADICAL, OR BROMATES.

These salts resemble the chlorates in their general characters, and are produced generally by the action of bromine in excess on the hydrates and carbonates of the alkaline metals, with simultaneous formation of bromides.

The bromates, when heated with charcoal or other combustibles, deflagrate or detonate just as the chlorates. They are also decomposed when heated alone.

THE HYDROGEN SALT (HBrO,), or bromic acid, is known as dissolved in water; but it is readily decomposed upon the application of heat.

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

THE POTASSIUM and AMMONIUM SALTS are soluble.

THE BARIUM SALT is produced by the action of a soluble barium salt on a moderately concentrated solution of bromate of potassium: it is a white crystalline precipitate, which requires 130 parts of cold, and 24 parts of boiling water for its solution.

THE STRONTIUM, CALCIUM, and MAGNESIUM SALTS are soluble.
THE CUPROUS SALT does not exist; THE CUPRIC SALT is soluble.

It is a

The Argentic or Silver Salt is produced by the action of a soluble silver salt on a solution of bromic acid or other soluble bromate. white precipitate.

Its formula is Ag BrO3,

This salt is insoluble, or nearly so, in water and in nitric acid, but dissolves in hydrate of ammonium.

THE MERCUROUS SALT is produced by the action of a soluble mercurous salt on solutions of bromates or of bromic acid: it is a yellowish white precipitate.

Its formula is Hg, BrO,.

It is decomposed by washing with water, into bromic acid and a basic salt (Hg, O, Hg, BrO ̧); in hydrochloric acid it dissolves, with formation of mercuric chloride; it is dissolved less easily by nitric acid.

THE MERCURIC SALT is produced by the action of soluble mercuric salts upon solutions of bromic acid or of other bromates: it is a white precipitate. Its formula is HgBrO,+aq.

It is soluble in 650 parts of cold, and in 64 parts of boiling water; it is dissolved by hydrochloric and by nitric acid.

THE LEAD SALT is produced by the action of concentrated solutions only of lead salts on soluble bromates. It is a white precipitate, soluble in 75 parts of cold water; and to it the formula PbBrO,+aq has been assigned.

Nearly all the remaining bromates that are known are insoluble in water. a. The bromates may be recognized, as easily as the chlorates, by the decomposition of their acid constituent; but in their case, bromine, and not an oxide, is liberated. Thus, when sulphuric acid (concentrated), or even a dilute mineral or organic acid (such as acetic), is added to a solution of a bromate, oxygen and bromine are set free, and then the latter may be at once identified by its action on starch.

B. A fragment of a bromate in powder, when rubbed in a mortar with such bodies as carbon, sulphur, or antimony, explodes or detonates. A similar result is obtained on heating the powdered mixture.

y. Bromates mixed with sugar frequently cause the inflammation of the latter when the mixture is moistened with sulphuric acid.

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

The bromates are recognized by the precipitation of the silver, mercury, and lead salts, and by the tests a. and ß.

Of the acid-radicals containing iodine combined with oxygen, those existing in the acids or hydrogen salts, termed iodic and periodic acids are the most important in an analytical point of view.

It is probable that the hypo-iodous (HIO) and iodous (HIO2) acids exist; but nothing definite has as yet been ascertained concerning them.