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The presence of tellurium in its compounds may be readily recognized by several processes of decomposition :
a. A telluride treated with hydrochloric acid evolves telluretted hydrogen, the odour of which is characteristic. Nitric acid converts tellurides into tellurites.
B. A telluride fused with carbonate of sodium on charcoal, transferred to a silver surface, and then moistened with hydrochloric acid, imparts a brown stain to the metal.
y. Sulphurous acid and several other similar reagents produce, in aqueous solutions of hydrotelluric acid, a dark brown precipitate of tellurium.
8. If a telluride be fused with hydrate of potassium, the fused mass dissolved in water, and the solution exposed to the air, tellurium will be precipitated.
SECTION II.—The hyposulphites, sulphites, hyposulphates, tri
thionates, tetrathionates, pentathionates, and sulphates ; the
selenites, seleniates ; tellurites, and telluriates. SALTS OF THE COMPOUND ACID-RADICALS WHICH CONTAIN
SULPHUR, SELENIUM, AND TELLURIUM COMBINED WITH OXYGEN OR AMONG THEMSELVES.
The acid-radicals which contain oxygen, sulphur, selenium, and tellurium are bibasic, like these elements themselves. A sulphate, just like a sulphide, may contain two different basic radicals1 eq. of a metal, for instance, together with 1 eq. of hydrogen. With the sulphurous and several other acid-radicals of the present section, such compound or double combinations are known to occur; and the remainder have not as yet been sufficiently investigated.
Of the acid-radicals containing sulphur combined with oxygen, those existing in the acids or hydrogen salts termed hyposulphurous, sulphurous, and sulphuric are the most important in an analytical point of view.
SALTS OF THE HYPOSULPHUROUS RADICAL, OR HYPOSULPHITES. The hyposulphites of the first and second subdivisions of the basic radicals are best known ; and from them most of the other hyposulphites may be prepared. They may be formed in various ways: when, for instance, an alkaline sulphite is boiled with sulphur, the sulphur is dissolved in considerable quantity, the following reaction taking place :
K, SO, +S=K, S, 03.
The sodium salt is largely prepared, and may be maile by boiling a strong solution of the hydrate with excess of sulphur, and then passing sulphurous acid gas (SO,), evaporating and crystallizing the solution.
Many hyposulphites, when heated on charcoal, yield a large quantity of the corresponding sulphides. When heated alone with access of air, they yield water, sulphurous acid, and sulphates; out of contact of air they are resolved into water, hydrosulphuric acid, and sulphur, which volatilize, while a mixture of alkaline sulphides, sulphites, and sulphates remains.
The hyposulphites of the first and second subdivisions of the basic elements are tolerably stable if kept out of contact of air; but the remainder are exceedingly unstable, and can scarcely be said to exist. Hyposulphurous anhydride (S, 0,) is itself a very unstable substance; but its elements being capable of uniting in other proportions to form compounds of extreme stability, readily yield such products: any excess of sulphur left uncombined with oxygen is either precipitated or, by entering into combination with a portion of the metal present, produces a sulphide. Thus hyposulphite of silver (Ag, 8,03) undergoes the following changes on heating, or by standing :
Ag, S, 0,+H,O=Ag, S+H, SO,
of silver. THE HYDROGEN SALT (H, 8,03), or hyposulphurous acid, is believed to be produced when hyposulphites are decomposed by stronger acids, as when hyposulphite of lead is diffused in water at 0° C., and a stream of hydrosulphuric acid gas allowed to act upon it,--sulphide of lead being precipitated, and hyposulphurous acid obtained in solution. This acid, however, speedily decomposes, thus
H, S, 0,=H, SO, +S.
hypo- sulphurous sulphurous acid.
The hyposulphites may be recognized by the formation of certain insoluble salts, and by the decomposition of their acid-radical.
The hyposulphites of the first and second subdivisions of basic radicals are soluble, with the exception of the barium salt. Nearly all the remaining salts are, as far as known, insoluble in water.
THE POTASSIUM and Sodium Salts are soluble. The latter is much employed in photographic processes, for dissolving iodide, bromide, and chloride of silver.
The Barium Salt is produced by the action of a soluble barium salt on a tolerably concentrated solution of hyposulphite of sodium (Na, S, 0,). Its formula is Ba, S, 02 +aq. It is somewhat soluble in water, soluble in hydrochloric acid, while with nitric acid it is converted into the sulphate.
THE STRONTIUM, Calcium, and MAGNESIUM SALTs are soluble.
metals contained in the third and fourth subdivisions of the basic radicals, are soluble in water.
THE SILVER SALT is a white precipitate, which becomes yellow, red-brown, and finally black, sulphide of silver being produced. Its formula is Ag, S, Og. It is slightly soluble in water, and very soluble in alkaline hyposulphites; if to this solution a soluble chloride be added, it gives no precipitate when excess of alkaline hyposulphite is also present.
The MERCUROUS Salt does not appear to exist, a black precipitate of sulphide being produced. THE MERCURIC Salt is white or yellow, becoming brown or black on boiling, from formation of mercuric sulphide.
THE LEAD SALT is a white precipitate, which becomes black below 100°. Its formula is Pb, S, Og. It is soluble in 3266 parts of water, and easily dissolves in alkaline hyposulphites. By nitric acid it is converted into the sulphate, which is very insoluble.
The hyposulphites may also be recognized by the following processes of decomposition:
a. When an acid is added to a soluble hyposulphite, an immediate precipitation of sulphur occurs, the hyposulphurous acid set free being at once resolved into sulphurous acid and sulphur:
Na, S, 0, +2HCl=2NaCl+H, 0+50,+S.
The sulphurous acid (H, SO2) decomposes instantly into water and sulphurous anhydride, the latter being readily recognizable by its odour.
B. When a hyposulphite is fused with carbonate of sodium on charcoal, a sulphide is obtained which, when treated with an acid upon a silver surface, gives a black stain of sulphide of silver, while hyposulphites previous to fusion give no such result.
7. When a soluble hyposulphite is brought in contact with a hydrochloric solution of stannous chloride, a brown precipitate of stannous sulphide is produced.
This radical is generally recognized by the decompositions which its various combinations so easily undergo. The changes which the hyposulphite of silver suffers, and the tests a, b, and y. are perhaps the most characteristic examples of these methods of identification,
SALTS OF THE SULPHUROUS RADICAL, OR SULPHITES. These salts are bibasic. They are of much easier production than the hyposulphites, and are much more stable. Sulphurous anhydride (SO2) is produced whenever sulphur is burnt in the air; and from it the sulphites may in general be obtained. Sulphites have a tendency to absorb oxygen from the air, especially when kept moist or in solution, and by so doing pass into sulphates :
M, SO3 +0=M, SOZ On account of this property, sulphurous acid and other sulphites are employed as reducing agents.
Heated on charcoal, many sulphites yield the corresponding sulphides, while others are reduced to the metallic state.
THE HYDROGEN SALT (H, SO3), sulphurous acid, is known to exist only in combination with water, the compound having the formula H, 80, +8aq, and occurring in white crystals. It is decomposed with great readiness into the substance known as sulphurous anhydride, or sulphurous acid gas (SO2), and water. This gas has a density of 2.222; its odour is most unpleasant, and produces a painful choking sensation. By a cold of – 12° it may be liquefied, and at a lower temperature it may even be solidified; it may also be rendered liquid by the pressure of from three to five atmospheres at the ordinary temperature.
The sulphites may be recognized not only by the formation of insoluble salts, but also by the transformation and decomposition of their acid-radical.
The majority of the sulphites are insoluble in water and in saline solutions. The sulphites of the alkaline metals and the acid sulphites (MHSO,) are, however, soluble. All sulphites are readily soluble in weak acids, the sulphurous acid being easily displaced. Of the insoluble sulphites the most interesting and characteristic are the barium, cuprous, argentic, and plumbic salts.
THE POTASSIUM and SODIUM Salts are soluble.
The Barium Salt is produced by the action of soluble barium salts on solutions of the alkaline sulphites. It is a white precipitate, having the formula Ba, SOz. It is scarcely soluble in water, but soluble in sulphurous, hydrochloric, and dilute nitric acid, if the sulphite were quite free from sulphate. Upon slightly heating the nitric acid solution, the sulphite of barium it contains is converted into sulphate, which, being very insoluble, is immediately precipitated.
THE CUPROUS Salt is obtained when a cupric salt is mixed with an alkaline sulphite, the cupric sulphite first formed splitting into cuprous sulphite, cupric sulphate, and sulphurous anhydride:
3Cu, 80,=(Cu,), 80,+Cu, 80, +80,.
sulphite. It is a light brown precipitate, scarcely soluble in water, soluble in ammonia water and dilute sulphuric acid, but decomposed by
mosta Argentic or Silve white granular precen deposited, de
The Argentic or Silver Salt is precipitated from silver salts by a soluble sulphite, as a white granular precipitate, which, when boiled in the solution from which it has been deposited, decomposes into metallic silver, and sulphuric acid which remains in solution. The formula of the argentic sulphite is Ag, 80g.
It dissolves in alkaline sulphites, and in ammonia water, but scarcely in sulphurous acid or water.
THE MERCURY Salts do not appear to exist.
THE LEAD Salt is a white precipitate, which has the formula Pb, SO,, and which is insoluble in water, decomposed by strong acids, and by nitric acid especially; with the aid of heat it is converted into sulphate.
Sulphites may also be recognized by the decomposition of their acid-radical :
a. Sulphurous acid, when produced by the action of strong acids (such as hydrochloric acid) upon sulphites, decomposes instantly into sulphurous anhydride (S0,) and water, no sulphur. being precipitated.
B. Sulphites fused with carbonate of sodium on charcoal yield sulphide of sodium, which may be recognized by its action on metallic silver.
. A hydrochloric solution of stannous chloride added to a soluble sulphite produces a gradually increasing precipitate of brown sulphide of tin. But if to the solution of a soluble sulphite some quantity of hydrochloric acid be first added, and subsequently some stannous chloride,—and if, under the glass plate which covers the containing vessel, a slip of lead paper be suspended, this latter will speedily be blackened by the sulphuretted