SECTION I.-SALTS OF CHLORINE, BROMINE, IODINE, AND FLUORINE.

The chlorides, bromides, iodides, and fluorides.

SECTION II.-SALTS OF THE ACID-RADICALS WHICH CONTAIN CHLORINE, BROMINE, AND IODINE COMBINED WITH OXYGEN.

The hypochlorites, chlorites, chlorates, perchlorates, hypobromites, bromates, iodites, iodates, and periodates.

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

The chloropalladiates, chloroplatinates, chlororhodiates, chlororutheniates, chloriridiates, and chloraurates.

SECTION I.-The chlorides, bromides, iodides, and fluorides. SALTS OF CHLORINE, BROMINE, IODINE, AND FLUORINE. The radicals of this Section are monobasic, and when combining with monatomic basic radicals yield compounds having the general formula MR. They are detected by both the methods described in the preliminary observations to the present Chapter, i.e. both by presenting to a soluble chloride, bromide, iodide, or fluoride a soluble salt of some basic radical known to form, with the acid element sought for, an insoluble salt of easily recognizable properties, and also by submitting the chloride, bromide, or iodide to such decomposing influences as are calculated to eliminate their acid-radical.

SALTS OF CHLORINE, OR CHLORIDES.

These salts are for the most part soluble in water, sparingly soluble in alcohol, and nearly insoluble in ether. Their formulæ vary according to the atomic nature of the combined basic constituent; but the following are the most usual:

M2CI, MCI, M, Cl,, MC1, and MCI,.

When heated before the blowpipe on charcoal, the deportment

of chlorides differs according to the nature of the combined basic radical: if the metal belongs to Subdivision I., the compound fuses, and sinks into the charcoal; if to Subdivision II., it fuses and generally remains as a molten mass upon the charcoal: the chloride of magnesium is the exception here; for, as it cannot exist in the presence of aqueous vapour, it suffers decomposition, and leaves a white residue of oxide. Some of the remaining chlorides, such as those of silver and lead, fuse without change; others again, as those of tin, antimony, and arsenic, volatilize, whilst others, such as those of platinum and gold, decompose into chlorine and the metal.

If a bead of microcosmic salt be fused upon a platinum wire, and cupric oxide (Cu,O) added to it until the bead is saturated, if a chloride be then introduced, and the bead submitted to the heat of the blowpipe jet, a blue colour will be imparted to the flame.

THE HYDROGEN SALT (HCl), or hydrochloric acid, is a transparent colourless gas at ordinary temperatures, which, at 45°.3 C., and under the pressure of 40 atmospheres, becomes a colourless liquid, highly dispersive of light. 1 volume of water dissolves 480 volumes of the gas.

The principal insoluble salts of this acid-radical are-as the student will readily recollect-the cuprous, argentic, plumbic, mercurous, and platinous chlorides.

THE CUPROUS SALT is produced by the action of a soluble cupric salt on a solution of stannous chloride. Its formula is CuCl. It is insoluble in water, but soluble in most acids.

The Argentic or Silver Salt is produced by the action of a soluble silver salt on hydrochloric acid or any other soluble chloride: it is a white curdy precipitate, which assumes a grey tinge on exposure to light.

Its formula is AgCl.

It is insoluble in water, soluble to a slight extent in solutions of certain chlorides and in concentrated acids, and easily dissolves in hydrate of ammonium, in cyanide of potassium, and in hyposulphite of sodium.

THE MERCUROUS SALT is produced by the action of a soluble

mercurous salt (e. g. mercurous nitrate [Hg, NO,]) on hydrochloric acid, or a soluble chloride. It is a dense white precipitate. Its formula is Hg, Cl. It is but slightly soluble in water.

THE LEAD SALT is produced by the action of a soluble lead salt on hydrochloric acid or any soluble chloride. It is a white crystalline precipitate. Its formula is PbCl. It is dissolved by a large quantity of cold water, but is soluble in a much smaller amount of boiling water.

The platinous and other insoluble chlorides are not employed in testing for chlorine.

Many of the remaining chlorides are soluble either in water or in dilute hydrochloric acid.

The other methods by which this acid-radical is identified are the following:

a. Concentrated sulphuric acid and peroxide of manganese (Mn, O2) are added to a chloride, and the mixture warmed: the sulphuric acid liberates hydrochloric acid

2MnCl+H, SO=2HC1+Mn, SO1;

the peroxide then acts upon the hydrochloric acid—

4HCl + Mn202=2MnCl+2H2O+2C1.

It is believed that bichloride of manganese (MnCl2) is first formed, and then decomposed into the protochloride (MnCl) and free chlorine.

The free chlorine thus produced is recognized by its odour and bleaching properties, while it is distinguished from bromine and iodine by the absence of any coloured reaction with starch.

B. When 1 part of chromate of potassium and 3 parts of oil vitriol are mixed with 1 part of the supposed chloride, and the resulting pasty liquid heated in a test-tube, to which a dry cork and bent tube have been fitted, the other end of the bent tube dipping into a test-tube free from any trace of water, and kept cool, a blood-red liquid distils over, to which the name chlorochromic acid, and the formula CrCl,, Cr, O,, have been given :*3KCrO2+3NaCl+3H, SO=CrCl,, Cr,O,+3KNaSO,+3H,0.

* Possibly this reaction is more simple,—

KCrO2+NaCl+H, SO, CrO Cl+KNASO,+H2O.

In this case the product usually termed chlorochromic acid might be con

If to this red distillate a few drops of ammonia-water are added, a yellow liquid is obtained, which is a solution of chromate and chloride of ammonium,——

CrCl, Cr,O,+6NH HO=3NH C1+3NH_CrO,+3H,0;

2

4

and if into this solution, after the addition of a slight excess of acetic acid, a few drops of nitrate of silver be introduced, a beautiful crimson precipitate will be obtained, thus

NH,CrO,+AgNO,=NH_NO,+AgCrO,.

crimson ppt.

SALTS OF BROMINE, OR BROMIDES.

The bromides bear the closest resemblance to the chlorides; they are isomorphous with them. They are for the most part soluble in water, but sparingly soluble in alcohol, and nearly insoluble in ether. Bromine is monobasic; but when combined with biatomic acid-radicals, it yields salts having the formulæ already given as those of the various chlorides.

Heated before the blowpipe on charcoal, the bromides exhibit the same deportment as the corresponding chlorides. They colour the flame green when fused with a bead of microcosmic salt saturated with cupric oxide.

THE HYDROGEN SALT (HBr), or hydrobromic acid, is a transparent colourless gas at ordinary temperatures, which, however, liquefies at 33°-3 C., and solidifies at -37.7. Hydrobromic acid is very soluble in water, the solution possessing the property of dissolving a large quantity of bromine, forming a red liquid.

The insoluble bromides are those which contain the same basic radicals as the insoluble chlorides, viz. the cuprous, argentic, mercurous, and plumbic bromides. The platinous bromide is unknown.

sidered the chloride of a compound basic radical chromyle (Cro), thus CrO, Cl. The reaction of this body with hydrate of ammonium will be thus expressed in an equation :

CrO,C1+2NH, HO=NH_C1+NH,CrO,+H.,O. 3(CrO,C1)=CrCl, Cr, Og.

THE CUPROUS SALT is obtained by the action of a solution of a cuprous salt on a soluble bromide. It is a white precipitate. Its formula is Cu, Br. It is insoluble in water, but soluble in hydrate of ammonium, and in hydrochloric and hydrobromic acids. In nitric acid it dissolves with decomposition; but boiling sulphuric acid does not decompose it.

The Argentic or Silver Salt is produced by the action of a soluble silver salt on hydrobromic acid or other soluble bromides. It may also be obtained by adding the silver solution very cautiously to a mixture of hydrochloric and hydrobromic acids, when the bromide is first removed from the solution. It is a yellowish white curdy precipitate.

Its formula is AgBr.

It is slowly dissolved (but in considerable proportion) by a concentrated solution of ammonia; it is but very slightly soluble in other ammonium salts; it dissolves, however, to some extent in a boiling solution of chloride of ammonium. It is slightly soluble in a concentrated solution of an alkaline bromide; and when boiled with an alkaline iodide, it is wholly converted into iodide of silver (AgI). Bromide of silver dissolves slightly in concentrated hydrochloric or hydrobromic acid; boiling nitric acid has no decomposing action on it, but boiling sulphuric acid alters it slightly.

THE MERCUROUS SALT is obtained by the action of a soluble mercurous salt (e. g. Hg, NO,) on a soluble bromide: it is a yellowish white precipitate. Its formula is Hg, Br. It is insoluble in ammonium salts, but, on ebullition with some of them, undergoes decomposition into mercuric bromide and mercury.

THE LEAD SALT is obtained by adding a soluble lead salt to hydrobromic acid or other soluble bromide. Its formula is PbBr. It is soluble in solutions of some ammonium salts, especially on warming; it is almost insoluble in cold water, and but sparingly soluble in hot. It is somewhat more soluble in dilute acids.

The other insoluble bromides are not employed in testing for bromine. Many of the remaining bromides are soluble either in water or in hydrobromic acid.