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chloride of ammonium, insoluble in water, but soluble in acids, even in acetic.

The neutral meta- and pyrophosphates of barium are insoluble in chloride of ammonium, or water, and the latter also in acetic acid. The same salts of strontium are insoluble in water, and the former also in acids, the latter in acetic acid. The metaphosphate of calcium is a white viscous precipitate; and the pyrophosphate does not dissolve in acetic acid.

THE MAGNESIUM Salt is formed but slowly by the addition of a salt of magnesium alone to a soluble phosphate—the precipitate under such circumstances has the formula Mg, HPO,; if, however, chloride of ammonium and ammonia have been previously added, the subsequent mixture with a magnesium salt gives rise to an immediate crystalline precipitate, which forms more rapidly on stirring: its formula is Mg, NH, POZ.

It is soluble in 7548 parts of chloride of ammonium, in 44,330 parts of hydrate of ammonium, and in 15,627 parts of chloride of ammonium solution containing hydrate of ammonium. It is insoluble in water which contains any phosphate in solution, but dissolves in 15,293 parts of pure water, from which it may be precipitated by the addition of ammonia. It dissolves in acids.

The meta- and pyrophosphates are scarcely produced except in the presence of hydrate of ammonium.

THE FERROUS phosphate and pyrophosphate are white. .

The Ferric Salt is white; its formula is uncertain. It is insoluble in ammonium salts, except the carbonate and sulphite, and it dissolves also in hydrate of ammonium in the presence of phosphate of sodium. It partially dissolves in carbonate of sodium. It is soluble in 1500 parts of water, and is easily dissolved by dilute acids, even by sulphurous, but not by cold acetic acid.

The metaphosphate is white, insoluble in water or dilute acids, but soluble in strong sulphuric acid.

The pyrophosphate is white, and is soluble in hydrate or carbonate of ammonium or in phosphate of sodium; it is insoluble in chloride of ammonium, and in hydrochloric or sulphurous acids.

THE ZINC Salt is a gelatinous precipitate which becomes crystalline on standing. It formula is Zn, POZ. It dissolves in the hydrate and most ammonium salts, is insoluble in water, but soluble in acids.

The metaphosphate is soluble in water. The pyrophosphate is white, soluble in ammonia, but insoluble in water.

THE CUPRIC Salt is bluish green; of the formula Cu, HPOX, slightly soluble in ammonium salts, insoluble in water, but soluble in acids.

The metaphosphate is bluish white, insoluble in water or in dilute acids, but soluble in strong sulphuric acid. The pyrophosphate (Cu, P,0,) is greenish white, soluble in ammonia, phosphate of sodium, and acids.

The Argentic or Silver Salt is yellow.
Its formula is Ag, POZ.

It dissolves easily in the hydrate or carbonate of ammonium, but less so in other ammonium salts; it is insoluble in water, but soluble in most acids.

The metaphosphate is white, decomposed by water, soluble in nitric acid. The pyrophosphate is white, of the formula Ag, P,0q, soluble in hydrate of ammonium, insoluble in water or acetic acid, soluble in nitric acid, which, by boiling, converts it into the ordinary phosphate (Ag3 PO2).

THE MERCUROUS Salt is white, of the composition (Hg.), P,0q, insoluble in water and in many acids. By some acids it is decomposed.

The pyrophosphate is white, and is decomposable by hydrochloric acid.

THE MERCURIC Salt is white, it appears to be the pyrophosphate (Hg, P,0-). It dissolves in many ammonium salts, but very slightly in the hydrate. It is insoluble in water, but soluble in many acids.

THE LEAD Salt is white, and variable in composition, being sometimes Pb, HPO,, and at other times Pb, PO. It dissolves in hydrate of potassium or chloride of ammonium, is insoluble in water or acetic acid, but soluble in nitric acid. This salt exhibits a great peculiarity: when heated on charcoa before the blowpipe even the inner flame fails for some time to reduce it ; and upon removal from the flame, the colourless and transparent bead becomes opaque and crystalline on cooling; the crystalline form is the dodecahedron.

The metaphosphate is white, insoluble in ammonia. The pyrophosphate (Pb, P,0.) is white, soluble in hydrate of potassium or pyrophosphate of sodium, insoluble in hydrate of ammonium and in many acids, but soluble in nitric acid.

Other means of proving the existence of this radical are wanting, owing to its great stability; it may, however, be recognized by adding to the nitric solution of a phosphate (an alkaline phosphate is the best) some molybdate of ammonium (NH, M002), evaporating to dryness, and just redissolving in nitric acid: a yellow crystalline residue is an evidence of the presence of a phosphate.

Of acid-radicals containing arsenic and oxygen, two only are known, those occurring in the arsenites and arseniates.

SALTS OF THE ARSENIOUS RADICAL, OR ARSENITES.

The arsenites are considered bibasic, and have the general formula M, As,0n; they are sometimes colourless, but occasionally of beautiful colours. Most arsenites, when heated alone, decompose and leave the oxide of the basic radical, whilst the anhydride (As, 0) volatiles; some, as the alkaline arsenites, decompose into an arseniate and arsenic.

THE HYDROGEN SALT (H, As, O.) is unknown; for when its supposed aqueous or acid solution is evaporated, the arsenious anhydride (As, 0,) crystallizes out.

THE ALKALINE ARSENITES are soluble in water; but most others are insoluble, although dissolved by acids and frequently by ammonium salts.

THE Barium and STRONTIUM Salts are precipitated only after being allowed to rest for some time.

THE CALCIUM Salt is precipitated immediately on mixing a soluble arsenite, or arsenious acid, with excess of the hydrate or other salt of calcium. It is a white precipitate.

Dried in the air, its composition is Ca, As, 0, +aq.

It dissolves in ammonium salts, but is only slightly soluble in water; in dilute acids, and even in an aqueous solution of arsenious acid, it is soluble.

THE MAGNESIUM and ZINC Salts are scarcely known.

The Cupric Salt is bright green. Its formula is Cu, As, 0,; it dissolves in ammonium salts and in acids.

The Argentic or Silver Salt is lemon-yellow, of the formula Ag, As, Og. It dissolves in ammonium salts and in acids.

THE MERCUROUS, MERCURIC, and LEAD SALTS are white precipitates, insoluble in ammonium salts, but soluble in nitric acid.

In addition to these means of detection, this radical may be recognized by other methods, previously detailed (p. 209), but which may be here briefly recapitulated :

a. By heating the arsenite in a bulb-tube with carbonate of sodium or charcoal, and observing the arsenical mirror.

B. By the action of nascent hydrogen, which produces the gas H, As, by the subsequent decomposition of which the arsenical mirror may also be obtained.

7. By the action of hydrosulphuric acid gas, which, when passed through the hydrochloric solution of an arsenite, yields the arsenious sulphide, which may be further tested by the method of Fresenius and Von Babo (p. 213).

SALTS OF THE ARSENIC RADICAL, OR ARSENIATES.

The arseniates are tribasic, and bear a great resemblance to the phosphates; they are produced by the action of nitric acid or other oxidizing agents on arsenious anhydride or arsenites. The arseniates when heated are not so prone to decompose as the arsenites.

THE HYDROGEN SALT (H, AsO, ?) is known; it occurs in large crystals. By heating this body to fusion, a glassy substance, arsenic anhydride (As, 03), is obtained.

THE ALKALINE ARSENIATES are soluble ; most others are insoluble.

THE BARIUM, STRONTIUM, CALCIUM, and MAGNESIUM Salts are white, insoluble in water, but soluble in acids.

THE ZINC Salt is similar.

THE CUPRIC Salt is bluish green, insoluble in water, but soluble in ammonia water and in the stronger acids.

The Argentic or Silver Salt is dark brick-red; its formula is Ag, AsO,; it is insoluble in water, but soluble in ammonium salts and in many acids.

THE MERCUROUS Salt is white, changing to a fine red, a double salt being at first precipitated. Its composition is (Hg.), HASO,

+aq. It is insoluble in most ammonium salts and in water, but soluble in nitric acid.

THE MERCURIC Salt is yellow, soluble in nitric and arsenic acids.

THE LEAD Salt is white, of the formula Pb, AsO,, insoluble in ammonium salts and in water, but soluble in nitric acid.

This radical may be recognized in precisely the same manner as the preceding one, by processes of decomposition, a few precautions being taken.

a. Arseniates should be mixed with carbon, or carbon and boracic anhydride, before introducing into the bulb-tube in the blowpipe experiment. (See p. 210.)

B. With nascent hydrogen they act as arsenites.

y. But before passing hydrosulphuric acid into their acid solution, the latter should be invariably treated with a current of sulphurous acid gas, in order to reduce the arsenic to an arsenious salt. This is necessary because the arsenic sulphide (As, S3) forms and separates very slowly, whilst the arsenious sulphide (As, S) is much more rapidly produced. The liquid must be boiled until every trace of sulphurous acid gas is evolved, before any attempt is made to pass sulphuretted hydrogen.

Of acid-radicals formed by the union of antimony and oxygen, two only are known-those existing in the antimoniates and metantimoniates; but of their combinations we are almost wholly ignorant. (See p. 207.)

Of acid-radicals formed by the union of arsenic and antimony with sulphur, three are well defined—those existing in the sulpharsenites, in the sulpharseniates, and in the sulphantimoniates ; but they are not of sufficient importance to demand a separate notice. (See pp. 208 and 217.)

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