Page images
PDF
EPUB

SALTS OF THE SELENIOUS RADICAL, OR SELENITES. When selenium is burnt in air, or treated with nitric or nitrohydrochloric acid, the compound Seo, is produced, analogous to the gas 80,; the former compound is, however, a crystalline solid, which vapourizes at about 300° C., yielding a gas of the colour of chlorine. This body yields the salts termed selenites when brought into contact with basic oxides. Selenites easily decompose with reducing agents, giving a deposit of selenium, but are not readily oxidized; nitric acid does not convert them into seleniates.

· When heated alone on charcoal, selenites leave a residue of selenide, or, parting with the whole of their selenium, of metallic oxide.

The HYDROGEN SALT (H, SEO,), or selenious acid, may be obtained from the aqueous solution of the anhydride (Seo,) in crystals resembling those of nitre, and soluble in alcohol: when heated, selenious acid decomposes into water and selenious anhydride (SeO2), which sublimes.

The majority of the normal selenites are insoluble in water; the selenites of the alkaline metals and the acid selenites are, however, soluble. They may thus be recognized not only by products of decomposition, but also by the formation of insoluble salts.

Of the insoluble selenites, the barium, cupric, silver, mercuric, and lead salts are the most remarkable.

THE POTASSIUM and SODIUM SALTs are soluble.

The Barium Salt is produced by the action of a soluble barium salt on a soluble selenite: it is a white precipitate. Its formula is Ba, Seog. It is insoluble in water, but soluble in selenious, hydrochloric, or nitric acid. It is not converted into seleniate by nitric acid, thus differing from the sulphite.

THE STRONTIUM, CALCIUM, and MAGNESIUM SALTS are white precipitates, insoluble, or sparingly soluble, in water.

THE FERROUS, FERRIC, ZINC, CUPROUS, and MANY OTHER SALTS containing metals of the third and fourth subdivisions are white precipitates, insoluble in water.

THE CUPRIC SALT is a crystalline greenish blue precipitate, insoluble in water and selenious acid, but soluble in ammonia water.

THE SILVER Salt is a white crystalline precipitate (Ag, SeO3) sparingly soluble in cold, more so in hot water: it easily dissolves in nitric acid; and from this solution water precipitates it.

THE MERCUROUS SALT is produced by the action of soluble mercurous salts upon solutions of selenites or selenious acid. It is a white precipitate, insoluble in water and selenious acid.

THE MERCURIC SALT is a white precipitate, insoluble in water.

The Lead Salt is precipitated by a soluble lead salt from solutions of selenites or selenious acid: it is a dense white precipitate. Its formula is Pb, SeOg. It is almost insoluble in water or in selenious acid, and but sparingly soluble in hydrochloric or nitric acid ; it dissolves in hot nitric acid without decomposition.

[graphic]

But selenites may also be readily recognized by the decomposition of their acid-radical:

a. Selenites heated on charcoal in the reducing flame give a most powerful odour of horseradish, and often a white incrustation of selenious anhydride.

B. Selenites do not give any characteristic reactions on the addition of strong acids. • 7. Selenites fused with carbonate of sodium on charcoal, and the resulting mass placed on a silver coin and moistened with water, give a brown stain of selenide of silver.

8. Selenites are reduced, giving a red deposit of selenium, by a hydrochlorie solution of stannous chloride, by ferrous salts, and some other reducing agents. · 6. Hydrosulphuric acid passed through the aqueous or acid solution of a selenite of the first and second subdivisions, gives a reddish yellow precipitate of selenious sulphide (SeS2), which is soluble in sulphide of ammonium.

%. If a solution of a selenite containing a metal of the first or second subdivision be acidified with hydrochloric acid, and a plate of iron or zinc immersed in it, the selenium is deposited either as a copper-coloured film, or in red-brown or greyish-black flakes.

n. If sulphurous acid gas be passed through a neutral or acidified solution of a selenite, a red precipitate of selenium is produced in the cold, a grey one if the solution be heated.

6. Selenites ignited in a hard glass tube with chloride of ammonium give a sublimate of selenium. The selenite of ammonium formed in the reaction decomposes in the following manner :

3(NH), Seo,=3 Se+4N+2NH2+9H, O. Selenites may be recognized by the formation of the insoluble barium and and lead salts, and by the tests a, e, %, n, and 0, while they are more particularly discriminated from the sulphites by the tests B, 5, and 0.

SALTS OF THE SELENIC RADICAL, OR SELENIATES.

By the action of fusing nitrate of potassium upon selenium, selenides, or selenites, seleniates are formed ; the action of chlorine on solutions of alkaline selenites also yields the same products. Seleniates greatly resemble the sulphates.

Seleniates thrown on glowing charcoal detonate and evolve the characteristic odour of horseradish, generally leaving a residue of selenide.

The HYDROGEN SALT (H, SeOn), selenic acid, has never yet been obtained in the pure state ; for, as its aqueous solution evaporates, it exhibits a great tendency to decompose into selenious acid and oxygen. From this proneness to change, it has not yet been found possible to obtain the selenic anhydride (SeO3), corresponding to sulphuric anhydride (SO3), since the solution of selenic acid (which has nearly the formula H, Seo,), when heated above 285°, decomposes rapidly into selenious anhydride, water, and oxygen. The concentrated acid evolves nearly as much heat when mixed with water as sulphuric acid ; it also absorbs water from the air.

The great majority of the seleniates are soluble in water. This radical may, however, be recognized not only by its decompositions, but by those few characteristic insoluble salts which it forms.

Of the insoluble seleniates those of barium, strontium, and lead are the most characteristic.

THE POTASSIUM and Sodium SALTs are insoluble.

The Barium Salt is produced by the action of soluble barium salts upon solutions of selenic acid or of seleniates. Its formula is Ba, SeOn. It is insoluble in water, and in hydrochloric or nitric acids; by long boiling, however, with hydrochloric acid, it is gradually decomposed and dissolved, being converted into selenite, thus

Ba, SeO,+2HCl=Ba, SeO,+,0+2C.
THE STRONTIUM Salt is a white powder, nearly insoluble.
The Calcium Salt is unknown ; THE MAGNESIUM Salt is soluble.

THE FERROUS, ZINC, CUPRIC, SILVER, and MANY OTHER SALTS containing metals of the third and fourth subdivisions are soluble.

THE LEAD Salt is a white precipitate, insoluble in water.
Seleniates may be recognized by the following processes of decomposition:-

a, Seleniates heated before the blowpipe on charcoal detonate, emitting an odour of horseradish. The same odour is perceived when these salts are heated with borax or microcosmic salt. Heated with carbonate of sodium, they give the same results as selenites.

B. The strong acids in general exert no apparent decomposing influence upon selenites ; hydrochloric acid, however, long heated with selenic acid or seleniates, gradually reduces the acid to selenious acid, and the salts to selenites.

7. A hydrochloric solution of stannous chloride exerts no decomposing action upon seleniates.

d. Sulphurous acid gas (SO2) or zinc with hydrochloric acid exert no decomposing action upon the selenic radical ; but both selenic acid and the seleniates give reactions of selenites, after their solutions have been boiled for some time with hydrochloric acid.

Seleniates are most readily identified by the formation of the insoluble barium and lead salts, and by the action of boiling hydrochloric acid upon them (8.).

Of the acid-radicals containing tellurium combined with oxygen, only two are known. These bear the closest analogy in composition to the compounds of selenium; their hydrogen compounds are known as tellurious (H, Teo) and telluric (H, TeOw) acids.

SALTS OF THE TELLURIOUS RADICAL, OR TELLURITES.

Tellurium heated in the air or boiled with nitric or sulphuric acid yields a body, tellurious anhydride (Te0,), the analogue of so, and Sen. It is a white crystalline body, volatile at a high temperature, and fusible at a low red heat to a yellow liquid. When brought in contact with water or metallic oxides, saline combinations are formed, many of which are easily decomposed, even by the carbonic acid of the air.

Tellurites, heated with charcoal, generally yield tellurium, and a white incrustation of tellurious anhydride; they also impart a green colour to the

flame.

THE HYDROGEN SALT (H, Teog), or tellurious acid, occurs in white voluminous flakes, which are earthy when dry, redden litmus paper, and have a sharp metallic taste. This acid, when mixed with water, is resolved at 40° into water and the anhydride. The body Teo, partakes much of the character of a metallic oxide; and the corresponding sulphate and nitrate are also known.

The tellurites, with the exception of those of the first subdivision, are insoluble, or very sparingly soluble in water. The insoluble salts are in general dissolved by concentrated hydrochloric acid.

THE POTASSIUM and Sodium Salts are soluble.

The Barium Salt is a white voluminous precipitate, very slightly soluble in water, but soluble in strong acids. It is produced by adding together solutions of chloride of barium and normal tellurite of potassium (K, Te0z).

THE STRONTIUM and CALCIUM SALTS are sparingly soluble; THE MAGNESIUM Salt much more so.

THE FERROUS, FERRIC, ZINC, and MANY OTHER Salts containing the metals of the third and fourth subdivisions are yellow or white insoluble precipitates.

THE CUPRIC SALT is a green precipitate, insoluble in water.

The Silver Salt is a yellowish white precipitate, insoluble in water, but soluble in hydrate of ammonium.

THE MERCUROUS Salt is yellow when freshly deposited, but rapidly becomes brown.

THE MERCURIC Salt is a milk-white precipitate.

THE LEAD SALT is white, and, though nearly insoluble in water, dissolves readily in acids.

Tellurites may be recognized by the following processes of decomposition:

a. When heated before the blowpipe on charcoal in the reducing flame, they impart a green colour to the light.

B. The addition of a few drops of acid, even of the weakest, to a soluble tellurite, decomposes it, liberating and precipitating the acid in white flakes.

y. Most tellurites (the zinc, silver, and some other salts excepted), when fused with carbonate of sodium on charcoal, give a saline mass, which, when dissolved in water, forms a wine-red solution of telluride of sodium.

8. A solution of stannous chloride, added to solutions of tellurites, especially on the addition of hydrochloric acid, produces a brown-black precipitate of tellurium, which, when pressed and rubbed, exhibits a metallic

lustre.

6. Hydrosulphuric acid precipitates, from solutions of tellurites, a black powder of sulphide of tellurium (Tes,), soluble in sulphide of ammonium.

%. The metals zinc, iron, copper, &c. precipitate tellurium from tellurites as a black powder; lead precipitates it in dendritic masses.

7. Sulphurous acid produces a precipitate of tellurium.

0. Tellurite of ammonium does not decompose in the same way as the selenite.

Tellurites may best be recognized by the formation of the barium salt, and by the tests B, y, , e, %, n,-while they may be distinguished from the sulphites by the same experiments, and from the selenites by the test o.

SALTS OF THE TELLURIC RADICAL, OR TELLURIATES. The most common telluriate, that of potassium, is made in the same way as the seleniate, by fusing tellurious anhydride, (Te0,) with nitrate of potassium, or by the action of chlorine on tellurite of potassium.

Heated on charcoal before the blowpipe, many telluriates yield tellurium, the reduction being frequently attended with slight detonation. When heated strongly alone, many telluriates fuse, become yellow or brown, and evolve oxygen, yielding tellurites.

THE HYDROGEN SALT (H, Teo,), or telluric acid, is prepared from the barium salt. It may be crystallized as the hydrated acid (H, Teo,+,0). This, heated to 160°, gives the acid H, TeOm; and this, if more strongly heated, yields the anhydride TeОg, an orange-yellow crystalline mass (the analogue of So, and Sex). The crystallized acid is very soluble in water, but insoluble in alcohol.

The telluriates of the first subdivision are soluble; the rest are insoluble, or nearly so.

THE POTASSIUM and SODIUM Salts are soluble.

The Barium Salt is at first a bulky white precipitate, which gradually becomes denser. Its formula is Ba, Teod. It is slightly soluble in cold water, more so in hot, and easily dissolves, without decomposition, in nitric acid.

THE STRONTIUM, CALCIUM, and MAGNESIUM SALTs are somewhat more soluble in water than the barium salt.

THE FERROUS, FERRIC, and most OTHER Salts containing metals of the third and fourth subdivisions are insoluble, or nearly so, in water.

THE CUPRIC SALT is pale green.
The Silver Salt is deep yellow. It is soluble in hydrate of ammonium.
THE MERCUROUS Salt is yellowish brown.
THE MERCURIC Salt is a bulky white precipitate.
THE LEAD SALT is a white, heavy, somewhat soluble precipitate.

Telluriates may also be recognized by the following processes of decomposition:

[graphic]
« PreviousContinue »