have been absorbed it becomes green; and when it has taken up all that it is capable of condensing, it emits an immense quantity of red fumes. The gas thus absorbed may be expelled again by a gentle heat, or by diluting the acid with

water.

Sir H. Davy, in the year 1800, gave the following table, showing the proportion of nitrous gas in nitrous acid of different colours.

Mere dilution with water is sufficient to vary these colours. Thus the dark orange-coloured acid, by dilution, passes through the shades of blue, olive, and bright green. Nitric acid, also, by absorbing nitrous gas, has its specific gravity diminished. Colourless acid, for example, when rendered of pale yellow, becomes lighter in the proportion of 1.51 to 1.502.

Nitro-Muriatic Acid.

This acid may be formed most commodiously by mixing two parts by weight of colourless nitric acid with one of liquid muriatic acid. Proust employs only one of nitric to four of muriatic acid. Though the acids are both perfectly pale, yet the mixture becomes of a deep red colour, a brisk effervescence takes place, and pungent vapours of chlorine are evolved.

Considerable light has been thrown on the nature of this acid by the experiments of Sir H. Davy, who has rendered it probable that its peculiar properties are owing to a mutual

II. Davy 100 parts of nitric acid, when saturated with nitrous gas, hold only 9 or 10 of the latter; and into acid of sp. gr. 1.3, Mr. Dalton could not condense above 20 times its bulk, or a little more than 2 per cent. by weight. Journal of Science, &c. i. 67.

decomposition of the nitric and muriatic acids, the oxygen of the former uniting with the hydrogen of the latter, in consequence of which water, chlorine, and nitrous acid, are the results. For every 101 parts in weight of real nitric acid (equivalent to 118 of hydro-nitric acid) which are decomposed, 67 parts of chlorine, he calculates, are produced. According to this view, it is not correct to say that aqua regia oxidates gold or platinum, since it merely causes their combination with chlorine. By long continued and gentle heat, nitromuriatic acid may be entirely deprived of chlorine, and it then loses its power of acting on gold and platinum.

The nitro-muriatic acid does not form, with alkaline or other bases, a distinct genus of salts, entitled to the name of nitro-muriates; for, when combined with an alkali, or an earth, the solution yields, on evaporation, a mixture of a muriate and a nitrate; and metallic bodies dissolved in it yield muriates only. The most remarkable property of nitro-muriatic acid (that of dissolving gold, from whence it has been called aqua regia) will be described in the chapter on that metal.

Combination of Nitrogen with Chlorine.

Chlorine has no action whatsoever on nitrogen gas, nor on nitrous gas or nitrous oxide, when both gases are perfectly dry; but a compound of chlorine and nitrogen may be formed, by passing chlorine gas through a solution of nitrate of ammonia, or of almost any ammoniacal salt, of the temperature of 80° to 90° Fahrenheit. The chlorine gas is rapidly absorbed, and a film appears on the surface, which soon collects into yellowish drops, that sink to the bottom of the liquor.

Mr. Brande recommends, as the simplest method of forming it, to fill a perfectly clean glass basin with a solution of about one part of sal ammoniac in twelve of water, and to invert into it a tall jar of chlorine gas. The saline solution gradually rises into the glass, a film forms upon its surface, and it acquires a deep yellow colour. At length small globules, resembling yellow oil, collect upon its surface, and successively fall into the basin beneath, from whence they are most conveniently removed by drawing them into a small and perfectly clean glass syringe, made of a glass tube drawn to a

pointed orifice, and having a copper wire, with a little tow wrapped round it for a piston. In this way a globule may be drawn into the tube, and transferred to any other vessel.

This yellowish and oily fluid is the most powerfully detonating compound with which we are acquainted. When gently warmed, it explodes with so much violence, that it is not safe to employ a quantity larger than a grain of mustard seed. Its discoverer, M. Dulong,* was severely wounded in his first experiments on this substance; and Sir H. Davy had a serious injury done to his eyes in repeating them. It is expedient, therefore, to proceed with great caution.

When a globule of this fluid is thrown into olive oil, turpentine or naphtha, it explodes even without heat, and so violently, as to shatter any glass vessel. The same effect ensues when it touches phosphorus, or phosphorized alcohol or ether; but pure alcohol seems to deprive it of its explosive property, and renders it a white oily matter.

The specific gravity of the fluid, Sir H. Davy has determined to be 1.653, water being 1. It is not congealed, by exposure to the cold produced by snow and muriate of lime.

Messrs. Porrett, Wilson, and Kirk, have published an elaborate memoir on this compound in Nicholson's Journal, xxxiv. 180, and have described at great length the appearances attending its formation, and the results of acting upon it with a great variety of substances. These experiments tend to show that it will not explode at any temperature much under 212° Fahr. nor without the contact ofa combustible body; that it may be distilled at or below 160°, and does not become solid at Though the class of bodies termed combustible act upon it most remarkably, yet there are some bodies of that description, camphor for instance, with which it seemed to unite without + Phil. Trans. 1818.

decomposition; nor did the metals, resins, or sugar, cause it to explode. It detonated with the following only, out of 125 substances that were tried.

The products of its detonation are chlorine and nitrogen gases, but it is impossible to determine the bulk of those elements which are afforded by a given weight. The best method of analyzing it, is by its action on mercury, which unites with the chlorine, and sets the nitrogen free. From various experiments of this kind, Sir H. Davy concludes that it is composed of four in volume of chlorine to one in volume of nitrogen, or of

These proportions correspond best with the opinion, that it is constituted of one atom of nitrogen to four atoms of chlorine; it will be represented therefore by 14 + (36 × 4 = ) 144, making together 158; but its analysis is not sufficiently correct to render these numbers worthy of implicit reliance.

Of the Compound of Nitrogen with Iodine.

Iodine cannot be brought to act directly upon nitrogen, but when iodine is kept in a solution of ammonia in water, it is gradually converted into a brownish black substance which is an iodide of nitrogen. This may be collected, and dried at a very gentle heat on bibulous paper.

This compound evaporates spontaneously in the open air. It explodes with great violence when touched or when heated, and is converted into nitrogen gas and iodine, but all attempts to collect the products have failed, and we are ignorant therefore of the proportion of its components.

SECTION III.

Of Carbon, and its compounds with Oxygen, Chlorine, and Iodine.

CHARCOAL, in the form under which it ordinarily occurs, contains several ingredients that are not essential to it; and it is to the pure carbonaceous principle, divested of these impurities, that the term Carbon is alone properly applied. The diamond, which Sir I. Newton had sagaciously inferred to be a combustible body, from its powers of refracting light, was first shown by Guyton to contain carbon,* and his experiments led him to conclude that the diamond is the only form of pure carbon; and that charcoal is a compound of carbon and oxygen, or an oxide of carbon. The experiments of Messrs. Allen and Pepys have, however, gone far towards proving that the diamond and charcoal, though so widely remote from each other in external characters, are, as to their chemical nature, identically the same; and that the difference between them, in all probability, results merely from the respective states of aggregation of their particles.

Some doubts, it must be confessed, were thrown on this conclusion by an experiment of Sir H. Davy, in which an inflammable gas was obtained, by igniting charcoal in a Toricellian vacuum, by a powerful Voltaic battery. But the hydrogen, thus evolved, may reasonably be ascribed to water, from which it is extremely difficult, if not impossible, to free charcoal. The absence of oxygen from charcoal was proved, by heating it with potassium, for no potash was produced; but when potassium was heated with diamond, there was an indistinct appearance of the production of that alkali. The subsequent experiments of the same philosophert tend to es

Annales de Chimie, xxxi.+ Phil. Trans. 1814, p. 557.