the extrication of light and heat; and when absorbed into the pores of charcoal, or even blotting paper, by the force of adhesion, this violent separation of the gases takes place. The direct solar rays will also resolve it into its elements without detonation. When mixed with hydrogen it explodes violently by the electric spark. Its analysis shows it to consist of one volume of chlorine, and half a volume of oxygen condensed into one, or one equivalent of each. This would make its equivalent 36 + 8 = 44, but from some of its combinations it is probable that the proportion in which it enters into secondary composition may be double this, or 88. Its formula is ClO2.

The solution of hypochlorous acid is pale yellow; it has a peculiar odour and an acrid taste. It attacks the cuticle more energetically than nitric acid, and stains it of a reddish-brown colour. All the metals which have a strong attraction for oxygen become oxidated by it and evolve chlorine; but silver combines with the chlorine and evolves oxygen.

§ 537. By submitting other oxides to the action of chlorine, it may be made to combine with a higher proportion of oxygen. By passing a current of the gas into a solution of potassa, one portion combines with the metal, forming a chloride of potassium, while another portion unites with the oxygen which is displaced and constitutes an acid, which is called the chloric acid. This, again, combines with some of the unchanged potassa, forming a salt, to which the name of chlorate of potassa has been given. It separates spontaneously, from its little solubility, in brilliant rhomboidal tables.

Chloric acid may also be obtained in the free state, or rather in union with water alone, without which, or a base, it cannot exist, by passing a current of chlorine through oxide of silver suspended in water. Chloride of silver, which is insoluble, is precipitated, and chloric acid remains in solution. It may be freed from any excess of chlorine by boiling. It is a sour, colourless liquid, devoid of bleaching properties; and forms no precipitate in any metallic solution. Hydrochloric acid and chloric acid mutually decompose one another: water is formed, and the chlorine of both set free. Chloric acid consists of,

be

538. The character of the salts of this acid taken from that of the chlorate of potassa. When exposed to a low red heat it fuses, gives off its oxygen, and chloride of potassium remains. We have already mentioned it as a convenient source of pure oxygen (§ 410). It acts very energetically upon most inflammable substances, and when triturated with sulphur, charcoal, or phosphorus, detonates strongly with the evolution of light and heat, owing to the decomposition of the acid.

§ 539. Another compound with a less proportion of oxygen, may be formed by the action of sulphuric acid upon chlorate of potassa. Its preparation should only be attempted in small quantities; as by moistening about 50 grains of the salt with a few drops of strong acid, when a solid mass will be obtained of an orange colour. By introducing this mass into a small retort, and gradually warming it by a water bath kept below the boiling-point, a yellowish-green elastic fluid passes off, which is rapidly dissolved by water, but may be collected in small tubes over mercury. Its odour is peculiar, and not nearly so suffocating as that of chlorine. 100 cubic inches weigh about 72 grains. It explodes at a temperature below 212° with great violence, and the evolution of a bright light. Two volumes are thus expanded in three, two of which are oxygen, and one chlorine, so that its composition must be:

It has been called the chlorous acid; its solution possesses a deep yellow colour, and an astringent corrosive taste. It bleaches very strongly. It combines with the different bases, forming salts, which may be produced by passing the gas into the solutions. They are all soluble and possessed of bleaching properties.

§ 540. From the same source that we obtain the peroxide of chlorine, we may also procure chlorine in a still higher degree of oxidation than in the chloric acid; for, after the oxide has been obtained by the action of the sulphuric acid upon the chlorate of potassa, there remains a white saline mass, which is

a mixture of two salts, namely, bi-sulphate of potassa and perchlorate of potassa, which may be easily separated by solution and crystallization, as the former is much more soluble than the latter.

By distilling the perchlorate of potassa with its own weight of sulphuric acid, diluted with about a fourth part of water, the per-chloric acid separates in white vapours, which condense in the form of a colourless liquid. It is the most stable of all the compounds of the two elements. It may even be obtained in the form of crystals by distillation with sulphuric acid, which abstracts all its water. It is not decomposed by hydrochloric acid. It is constituted of:

§ 541. There is but one known compound of chlorine with nitrogen, which cannot be obtained by the direct action of the two elements; and it is as unstable as its compounds with oxygen which we have just described. It may be formed by the action of chlorine upon any of the salts of ammonia. When gaseous chlorine is passed into ammoniacal gas, it decomposes it with so much energy that the gas inflames: muriatic acid is formed, which combines with another portion of the ammonia, and nitrogen is left. By passing the same gas into an aqueous solution of the alkali, or by mixing the solutions of the two gases, pure nitrogen may be collected. When chlorine, however, is passed into warm solutions of muriate or nitrate of ammonia, the ammonia is still decomposed, but the nitrogen is not given off in the free state, but in combination with another portion of chlorine. The same compound is also formed by suspending a crystal of ammoniacal salt in a solution of hypochlorous acid.

It is an oily-looking liquid which falls to the bottom of the solution in which it is generated, and should not be experimented upon in quantities larger than a grain of mustard seed; even then it should be handled with extreme caution. It is the most powerfully-explosive compound known. Its specific gravity is 1.653, and it does not become solid at great degrees

of artificial cold. At about a temperature of 200° it detonates spontaneously, and the mere contact of some combustible substances causes it to explode. When a globule is touched with olive-oil or turpentine, the concussion which is produced is so great as to shatter any glass or earthenware vessel in which the experiment is made. Metals, resins, and sugar, do not ordinarily cause its decomposition: but most greasy substances, phosphorus, naphtha, potassa, and many others cause it to detonate.

The products of its decomposition are chlorine and nitrogen, and its composition has been inferred to be:

It has been named chloride of nitrogen, and its formula is NCI3.

§ 542. The nature of these detonations, and of the light and heat which are thus given off during the separation of elements which are mostly characterized by having but a feeble mutual affinity, is by no means understood; if, indeed, we can be said to understand the evolution of light and heat at all. At present the usual explanation of the phenomena of combustion does not seem applicable to them. The compounds of nitrogen are particularly liable to such energetic decompositions, which is the more remarkable, as this element appears to be particularly inert in its combining powers.

Compounds of Chlorine with Carbon and Hydrocarbon.

§ 543. When a mixture is made of two parts of chlorine to one of bihydrocarbon by volume, and ignited, muriatic acid is formed, and the whole of the carbon is deposited in the form of a dense black smoke: but if a mixture of equal volumes of the two gases be allowed to remain over water, complete condensation takes place. The result of the combination is a yellow liquid, looking like an oil, but possessing a peculiar odour and sweet taste. It is volatile, and may be distilled without change. It was from the formation of this substance that the bihydrocarbon was formerly called olefiant gas. It possesses, however, very different properties from those of oil, and may

properly be called the chloride of hydro-carbon. Its specific gravity at 45° is 1.22, it boils at 152°, and at 49° its vapour is capable of supporting a column of mercury of 24.66 inches. It burns with a green flame, and gives out copious fumes of muriatic acid and much soot. It is composed of one volume of chlorine and one of olefiant gas, or by weight of :

$544. When the hydrochloride of carbon is exposed in an atmosphere of chlorine to the direct rays of the sun, it is decomposed: muriatic acid is formed by the abstraction of the hydrogen, and the carbon remains in combination with chlorine alone. The per-chloride of carbon thus obtained is a transparent, colourless solid, having very little taste, and possessing an aromatic odour resembling that of camphor. Its specific gravity is 2.4. It is very brittle, and a non-conductor of electricity. It is volatile at common temperatures, and sublimes in very transparent colourless crystals. It melts at 320°, and boils at 360° Fahrenheit. It is scarcely combustible, but when held in the flame of a spirit-lamp it burns with a red flame, and gives off much smoke and fumes of muriatic acid. It is but little soluble in water, but is readily taken up by alcohol, and may be obtained in crystals from that liquid upon careful evaporation. The results of both its analysis and synthesis concur in its being a compound of :

Carbon
Chlorine

$545. This compound may be converted into a protochloride by simply passing its vapour through an ignited glass tube, containing fragments of glass or rock crystal, to increase the heated surface. Chlorine escapes, and a fluid passes over which may be separately condensed.

It is limpid and colourless; does not assume the solid form,