CHLOROUS ACID-CHLORITES.

137

decomposes the gas with explosion; arsenicum has a similar effect. Most of the metals-including copper, lead, tin, zinc, and iron-are without action upon it, but mercury absorbs it completely. A solution of the acid (HClO, = 68·5), however, oxidizes all these metals, and they commonly yield a mixture of chlorate and chloride, especially if the acid be in excess; for instance, 2 Zn + 4 HClO2 ZnCl2+ Zn 2 ClO3 + 2 H2O.

=

2

The composition of chlorous anhydride is the following, and its combining volume is anomalous, as appears from the experiments of Millon, confirmed by those of Schiel, the molecule occupying 3 volumes instead of 2:

This gas is soluble in about one-sixth of its bulk of water, and the solution, even when diluted very largely, has a bright yellow colour. The compound is prepared by deoxidizing chloric acid; this object is effected by means of arsenious acid, when the gas is required in a state of purity. Three parts of arsenious anhydride (white arsenic) and 4 of chlorate of potassium are rubbed up into a paste with water, and 16 parts of pure nitric acid, of sp. gr. 1°24, are added; the whole is placed in a small flask, which is filled up to the neck with the mixture, and a very gentle heat is applied by means of a water-bath (Millon, Ann. de Chimie, III. vii. 322). The gas must be collected by displacement in dry bottles, as it is rapidly decomposed by mercury. In this operation the arsenious acid becomes oxidized at the expense of the nitric acid; nitrous acid is formed, and this in turn is reconverted into nitric acid by decomposing the liberated chloric acid: for example—

2 HNO2+ 2 KCIO, = 2 KN→2 + Cl2→3

2

2

Water.

= H2O.

Tartaric acid may be substituted for arsenious anhydride in this operation, but the gas is then mixed with carbonic anhydride.

Chlorous acid (HClO), possesses considerable bleaching power; it acts slowly upon bases, and forms monobasic salts, termed chlorites, with the general formula M'Cle. Chlorite of potassium (KClO)

138

PEROXIDE OF CHLORINE.

is deliquescent: if its solution be slowly evaporated to dryness, it is converted into a mixture of chloride and chlorate of the metal, in equivalent proportions. The chlorites of sodium, barium, and strontium are also deliquescent. The chlorites are decomposed by the feeblest acids, such even as carbonic acid. Nitrate of lead produces a sulphur-yellow scaly precipitate in their solutions, owing to the formation of a chlorite of lead (Pb 2 Cl→2). Chlorite of silver is also yellowish and insoluble.

The chlorites may be distinguished from the hypochlorites by the addition of a mixture of arsenious anhydride with nitric acid, which does not destroy the bleaching power of the chlorites, whilst it destroys that of the hypochlorites. Their solutions deoxidize an acidulated solution of permanganate of potassium.

(385) PEROXIDE of Chlorine (ClO2, or ClO4=67°5); Theoretic Sp. Gr. 2.331, Observed 23227; Boiling-pt. 68°; Mol. Vol. This compound is gaseous at ordinary temperatures, but by slight pressure, or by exposure to a cold of -4° F., it is reducible to a red liquid, which, according to Millon, is liable to explode as powerfully as chloride of nitrogen. The gas is of a colour still deeper than that of chlorous anhydride, and has a similar but less irritating odour. It may be preserved unaltered in the dark, but is gradually decomposed in the sunlight into its component gases. Water dissolves about 20 times its bulk of the gas, and forms a yellow solution, which bleaches powerfully. The gas requires great care in its preparation, as a temperature of 140° or 145° determines its explosion; 2 volumes of this gas furnish a mixture of 2 volumes of oxygen and I of chlorine, its composition being thus represented :

Peroxide of chlorine may be thus obtained :-Fused chlorate of potassium is broken into coarse fragments, and treated with two-thirds of its weight of oil of vitriol, the action being favoured by a very gentle heat. The reaction may be represented by the

This peroxide may also be procured mixed with carbonic anhydride, by mixing chlorate of potassium and crystallized oxalic acid, both finely powdered separately, and gently heating to 150° (Calvert).

CHLORIDE OF NITROGEN.

FIG. 298.

139

Peroxide of chlorine acts rapidly upon mercury, and must therefore be collected by displacement. Mere contact with many combustible matters at once determines its explosion. Place, for instance, 4 or 5 grains of chlorate of potassium at the bottom of a tall glass, and pour upon it a little water; then having placed the glass in a deep plate (fig. 298), add a piece of phosphorus of about the size of a pea, and by means of a long funnel pour slowly in about a teaspoonful of oil of vitriol; flashes of a beautiful green light, attended with a crackling noise, will be immediately produced. If loaf sugar and chlorate of potassium be separately powdered, and mixed in equal proportions with each other on a sheet of paper, by means of a spatula, the addition of a drop of sulphuric acid will liberate peroxide of chlorine, which will be decomposed by the combustible matter, and sufficient heat will be emitted to cause the mass to burst into flame, and to deflagrate with great brilliancy. Peroxide of chlorine is not possessed of acid properties; alkaline solutions, however, absorb it rapidly, but when evaporated, they yield a mixture of chlorite and chlorate of the metal :

Other oxides of chlorine have been obtained; they have a composition which may be explained by considering them as compounds of chlorous anhydride with chloric or with perchloric anhydride; they, however, present but few points of interest. Davy's euchlorine, which is evolved on gently heating a chlorate with hydrochloric acid, is a yellow explosive gas, consisting of a mixture of chlorine with one of these compound oxides, the chloro-chloric acid (2 C1,Cl; Millon).

(386) CHLORIDE OF NITROGEN (HCI,N,CI,N?); Sp. Gr. of Liquid, 1·653.—The attraction existing between chlorine and nitrogen is very feeble; the compound commonly known by the name of chloride of nitrogen is always obtained by indirect means. If a current of ammoniacal gas be directed into a bottle of gaseous chlorine it will take fire spontaneously, burning with a green flame, whilst hydrochloric acid is formed, and nitrogen is set free; dense white fumes being generated by the union of the

140

CHLORIDE OF NITROGEN.

hydrochloric acid with undecomposed ammonia. By modifying the experiment, the reaction may be employed as a means of obtaining nitrogen gas, for when a stream of chlorine gas is transmitted through a solution of ammonia, the hydrochloric acid as fast as it is formed combines with undecomposed ammonia, and nitrogen is liberated: if the solution be concentrated, each bubble of chlorine produces a flash of light. One atom of ammonia, when decomposed by 3 atoms of chlorine, yields 1 atom of nitrogen; 2 H,N+3 Cl,, becoming 6 HCl + N,. The nitrogen is apt to be mixed with a variable quantity of oxygen, a little water being also decomposed at the same time. (A. Anderson.)

But if instead of acting on a solution of free ammonia, a bottle of chlorine perfectly clear from greasy matter be inverted over a leaden dish containing a solution of 1 part of sal ammoniac (H,NCI), in 12 parts of water, drops of a yellow oily-looking liquid gradually collect on the surface of the liquid and fall to the bottom, whilst the chlorine slowly disappears: this liquid is the substance known as chloride of nitrogen. A safer method of obtaining this body consists in suspending a fragment of sal ammoniac (say 20 or 30 grains) in a solution of hypochlorous acid; oily drops of the so-called chloride of nitrogen are gradually formed, and sink in the liquid as the salt is dissolved. The new body remains liquid at -16°, but is very volatile, and possesses a peculiar penetrating odour. It is one of the most dangerous compounds known, for it explodes with tremendous violence when heated to between 200° and 212° F., emitting a flash of light when the detonation occurs. The explosion is so sudden that it invariably breaks any glass or porcelain vessel in which it may be contained hence a leaden saucer is used in preparing the compound. The liquid chloride also explodes violently at ordinary temperatures when brought into contact with many inflammable substances, such as oil of turpentine, phosphorus, and the fixed oils. The alkalies likewise cause its immediate explosion. On the other hand, it does not explode when touched with the resins, the strong acids, with metallic bodies in general, or with sugar.

Little or nothing is known of the cause of these remarkable reactions, or of the light and heat emitted when the chloride explodes by slightly elevating its temperature; in this case and in the analogous instances of the explosion of the oxides of chlorine, light is emitted, not during the act of combination, as is usual, but during the expansion and sudden separation of the two gaseous elements.

The analysis of this body is attended with great difficulty;

CHLORIDES OF CARBON.

141

indeed, considerable doubt exists as to its true composition. It is highly probable that it is not simply a chloride of nitrogen, but a combination of chlorine, nitrogen, and hydrogen (HCI,N, CI,N), somewhat analogous to the corresponding explosive compound which may be formed with iodine (400).

(387) CHLORIDES OF CARBON.*-Chlorine does not unite. directly with carbon, but Faraday succeeded in procuring several compounds between these elements by the decomposition of Dutch liquid, a combination of carbon and hydrogen with chlorine, obtained under circumstances which will be explained when treating of olefiant gas (488).

Acetylene Chloride (formerly Subchloride) of Carbon (ECI) forms fine silky crystals, which may be sublimed in closed vessels without change; it is soluble in ether. This substance is obtained by decomposing the ethylene-chloride of carbon (EC1), by causing it to pass several times through a tube heated to bright redness. If heated in air on platinum foil, it burns with a red smoky flame.

Ethylene Chloride (formerly Protochloride) of Carbon (EC1); Sp. Gr. of Liquid, 1552; of Vapour, 582; Mol. Vol. ; Boiling-pt. 248°. This compound was procured by Faraday from the solid chloride (E,Cl) by subliming it repeatedly through a tube filled with fragments of glass heated to redness. It is a transparent colourless liquid, with an aromatic odour.

Faraday's Chloride (formerly Sesquichloride) of Carbon (ECI); Sp. Gr. of Solid, 20; of Vapour, 8.157; Mol. Vol. ; Melting Pt. 320°; Boiling-pt. 360°.-This chloride was originally procured by the action of chlorine upon Dutch liquid (488) (Faraday); but it has since been obtained by the action of chlorine upon a variety of derivatives from the alcohol series. It is a volatile crystalline solid, with an aromatic odour resembling that of camphor. It is soluble in alcohol, in ether, and in the fixed and volatile oils. An isomeric (556) liquid terchloride, the vapour of which has a density of 4082, and a composition ЄCl, was obtained by Regnault by passing the vapour of tetrachloride of carbon (ECI) through a tube heated to low redness.

Tetrachloride (formerly Bichloride) of Carbon (ECI); Sp. Gr. of Liquid, 1599; of Vapour, 5'30; Mol. Vol. ]; Boiling-pt. 172°. This substance was obtained by Regnault from wood-spirit, from chloroform, and from other derivatives from wood-spirit,

The names of these various chlorides, it will be observed, do not correspond to their formulæ, but they are for the present partially retained, since, though not strictly accurate, they are in general use.