SUBDIVISION IV.

SALTS OF NITROGEN, PHOSPHORUS, ARSENIC AND ANTIMONY, AND OF THE CHIEF COMPOUND ACIDRADICALS INTO THE COMPOSITION OF WHICH THEY ENTER.

The three latter members of this subdivision present a remarkable similarity in properties; nitrogen, although closely allied to them in many respects, exhibits, as we shall presently see, important differences, which may nevertheless be cleared away by future observations. In the preliminary observations made upon each section, we shall enter more into detail concerning the chemical peculiarities of the radicals considered, since, although not strictly important in an analytical point of view, their knowledge will be of extreme use and interest to the student. This subdivision is divided into two sections :—

SECTION I.-SALTS OF NITROGEN, PHOSPHORUS, ARSENIC, AND

ANTIMONY.

The nitrides, phosphides, arsenides, and antimonides.

SECTION II.-SALTS OF THE ACID-RADICALS WHICH CONTAIN NITROGEN, PHOSPHORUS, ARSENIC, AND ANTIMONY COMBINED WITH OXYGEN OR SULPHUR.

The nitrites, nitrates, hypophosphites, phosphites, phosphates, arsenites, arseniates, antimoniates; sulpharsenites, sulpharseniates, and sulphantimoniates.

SECTION I.-The nitrides, phosphides, arsenides, and antimonides. SALTS OF NITROGEN, PHOSPHORUS, ARSENIC, AND

ANTIMONY.

The elements considered in this group have the property of combining with many basic radicals, and are usually found to be triatomic, uniting with 3 equivalents of a monatomic molecule; a few circumstances have, however, raised great obstacles to these combinations being considered truly saline. Their hydrogen compounds, in the first place, are not possessed of manifestly

acid properties-they do not redden litmus; this may, nevertheless, be accounted for by supposing that hydrogen, when combined in the proportion of 3 equivalents with the weak acidradicals, nitrogen, phosphorus, or arsenic, forms a basic radical sufficiently powerful, in its counteraction, entirely to mask the acid properties of the nitrogen, phosphorus, or arsenic. These hydrogen compounds are also all gaseous bodies at common temperatures; this is a great barrier to the perfect investigation of the properties of a substance; and, what is more perplexing, they all (and the compound NH, in the most marked manner) have a tendency to unite with a fourth equivalent of hydrogen to form a compound base, which again combines with acidradicals to form stable saline compounds. With regard to the compounds produced by the union of these acid-radicals directly with metals, little is known; and (as might be readily conjectured from the fact that hydrogen saturates their acid tendency so completely) those are the most stable, in which the weaker basic radicals exist combined.

SALTS OF NITROGEN, OR NITRIDES.

These bodies have not been hitherto obtained by the action of ammonia (H,N) either as gas or in solution upon saline bodies at ordinary temperaratures; the only method which has successfully resulted in their production is that of passing the dry gas (H,N) over the heated metal, the molecules of which we desire to substitute for those of hydrogen in the body H ̧N. This, as might be expected when the triatomic character of nitrogen is considered, does not always result in the formation of the substance M,N; but occasionally, as in the case of potassium, a compound is obtained, the formula of which represents a partial replacement. The olive-green substance which potassium yields when gently heated in ammonia gas, has the composition H, KN; it is known as amide of potassium, a name given by chemists who believed its constitution to be K(NH2),-NH, being a hypothetical acid-radical which they called amidogen. This body, when heated to redness in a close vessel, decomposes into nitride of potassium and nitride of hydrogen, with the consequent separation of the latter (ammonia):

3H, KN=K,N+2H, N.

When, again, dry ammonia gas is passed over iron wire heated to redness in a tube for six or eight hours, a white brittle substance is obtained, the composition of which nearly corresponds to the formula Fe, N2, that is, to a mix

ture of equivalents of nitride and dinitride of iron; for Fe, N2 = Fe, N+ (Fe), N: this has no analogue among the combinations of iron with other acid-radicals, although the probable existence of a disulphide of iron (Fe)2 S or Fe, S, and the well-known tendency of iron salts of different series to combine together, removes the improbability of its existence. The di- or subnitride of copper may be made by heating the precipitated oxide in dry ammonia gas; its formula is Cu N, that is, (Cu), N. Mercuric nitride is similarly produced; it is a brown powder having the composition Hg, N, which explodes with great violence when struck or heated,

THE HYDROGEN COMPOUND of nitrogen (H, N), or ammonia, is almost always found in combination or union with water: its great source is the decomposition of nitrogenized organic matters; any such compounds, when heated with the hydrates of potassium or calcium, yield the whole of their nitrogen in the form of ammonia. The analogous compounds of phosphorus, arsenic, and antimony will be seen to be produced by the action of nascent hydrogen upon the element under experiment. This is not the case when the same agent meets with already eliminated nitrogen; the gaseous condition of the latter body is, however, perhaps unfavourable to the success of the reaction. The gas ammonia has a very pungent odour, but is not corrosive; it is slightly combustible, burning when a candle is applied to it, but the combustion ceasing upon the removal of the ignited body: when intensely heated it decomposes into its elements. It may be condensed to the liquid and even to the solid state by cold and pressure. The solid is colourless and crystalline, and melts at 75° C. the liquid is colourless and very mobile, of specific gravity 0.76; it boils at -33°.7 C. at about the ordinary pressure (0.7493m). The gas is absorbed by water with the greatest rapidity; and, according to Ure, when the specific gravity of the solution is 0.8914 it holds 27.94 per cent. of H, N in solution.

No decomposition with formation of nitrides takes place when ammonia gas is passed into saline solutions, or when its aqueous solution is added to them this may, perhaps, be accounted for by the change which is very generally believed to occur whenever H,N meets with H2O, and which certainly takes place when it meets with more powerful acids-namely, its direct union with the acid, and formation of the corresponding salt of the basic radical ammonium :

H_N+H,O=NH HỌ;

H2N+HCl=NH, Cl.

SALTS OF PHOSPHORUS, OR PHOSPHIDES.

These are more numerous than the analogous compounds of nitrogen, and may be more readily obtained by reason of the occurrence of phosphorus in the solid, liquid, and gaseous forms within a convenient range of temperature, which is a circumstance most favourable for a full investigation of the chemical properties of a body. The phosphides may be produced similarly with the nitrides; but some are also formed by the action of phosphuretted hydrogen, H, P (the ammonia of this series), upon saline solutions. The potassium salt is formed when its components are gently heated in an atmosphere of nitrogen; it is a substance of a chocolate-brown colour. The calcium salt is produced, together with hypophosphite of calcium, when the vapour of phosphorus acts on lime (Ca, O). Others, again, as the phosphides of iron, copper, and lead, are prepared by throwing phosphorus on the melted or red-hot metal, or by igniting the filings of the metal with glacial phosphoric acid (HPO2). These compounds may also be formed by heating the metal in the gas H, P; and in some cases, by the passage of that gas through the aqueous solution of the metallic salt, the phosphide is slowly formed: thus cupric salts yield black phosphide of copper (Cu, P), mercuric salts a whitish yellow precipitate of a basic salt, and lead salts a brown precipitate. One thing is to be remarked in the phosphides, viz. that two distinct series of them are known, in one of which phosphorus plays the part of a bibasic, in the other of a tribasic radical; thus we have two series of salts :

It is interesting to know that whilst the majority, if not all, of the tribasic phosphides are produced by the vapour of a phosphorus (ordinary phosphorus, see p. 34) upon metals, the bibasic cupric phosphide (Cu2 P) is obtained by the reducing action of hydrogen gas at a high temperature upon the bibasic cupric phosphate (Cu, P2O): it may be, that in the bibasic phosphides the ẞ variety of phosphorus occurs.

THE HYDROGEN COMPOUND (H, P), or phosphuretted hydrogen, is usually obtained by the action of solution of hydrate of potassium upon phosphorus, or by the decomposing influence which water exerts upon the calcium salt (Ca, P); it is not obtained by the action of nascent hydrogen on solid phosphorus. As usually prepared, it is spontaneously inflammable in the air. In addition to this gaseous body, there is another which is liquid, having the composition H, P: this latter it is which is said to result from the action of water or other acids on the phosphide of calcium (Ca, P); but by the agency of light it almost imme

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diately splits up into the gas H, P, and a yellowish solid body, insoluble in water, which has the formula HP2: this decomposition is as follows:

5H, P=HP2+3H, P.

The liquid HP possesses an intense spontaneous inflammability in the air; and the presence of a small portion of it is said to impart its inflammability to the gas H, P, which is prepared from the phosphide of calcium: this is by no means improbable, since, when mixed with any combustible gas, it renders it spontaneously inflammable when exposed to the air. The gas H, P is very slightly absorbed by water, but sufficiently so to impart to it a disagreeable smell and taste. The liquid HP is insoluble in water.

Solutions of MANGANESE, ZINC, or IRON SALTS are not precipitated by solution of phosphuretted hydrogen; but this liquid does. precipitate solutions of the salts of COPPER, SILVER, MERCURY, LEAD, and GOLD.

SALTS OF ARSENIC, OR ARSENIDES.

These also are both a numerous and important class of salts, although they have not yet been much studied; together with the phosphides, silicides and other similar compounds, they are of the utmost importance to the metallurgist, since their presence in minute quantity so much affects the character of the metals he produces. Arsenic occurs frequently combined with metals in nature; and these compounds begin to partake more of the characters of metallic alloys than those previously mentioned. The arsenides may be produced artificially, just as the phosphides — namely, by heating the acid-radical itself or its oxygen compound As, O with the metal,—by heating the metal under experiment with the gaseous hydrogen compound H, As, or by passing the latter into solutions of some metallic salts. The constitution of the arsenides varies even more than that of the phosphides; and they may be grouped into three series, in which a molecule of arsenic of the same atomic weight plays the part of a monobasic, a bibasic, or a tribasic radical respectively. Our surprise at such peculiarities is prevented by the remarkable instances of allotropy occurring among the elements, and of isomerism and polymerism among compound bodies. A few examples of arsenides may be given, the whole of which here quoted occur as minerals in nature—