THE CUPROUS SALT is white; it is soluble in hydrate of ammonium.

THE CUPRIC SALT is a greenish blue precipitate. Its formula is Cu C,O,+aq. It is soluble in neutral alkaline oxalates, and in hydrate, carbonate, and succinate of ammonium, but not in other ammonium salts. It is insoluble in water, in oxalic acid, and in warm dilute nitric acid. It dissolves in warm concentrated hydrochloric acid.

THE SILVER SALT (Ag,C,O,) is a white precipitate. It dissolves in hydrate and carbonate of ammonium, and in warm solutions of other ammonium salts. It is scarcely soluble in water, but dissolves in nitric acid.

THE MERCUROUS SALT is precipitated by the action of mercurous nitrate on oxalic acid or soluble oxalates: it is a white precipitate. Its formula is (Hg.),C,O,+aq. It is but slightly soluble in water or in dilute acids.

THE MERCURIC SALT is a white precipitate. Its formula is Hg,C,O,+aq. It is soluble in solutions of chloride and nitrate of ammonium, insoluble in water and dilute acids, somewhat soluble in sulphuric acid, and dissolved easily by other strong acids.

THE LEAD SALT is a white precipitate. Its formula is Pb,C,O (dried at 140°). It is soluble in most ammonium salts, the hydrate and carbonate excepted; it is insoluble in water and in acetic acid, but soluble in nitric acid; it is somewhat soluble in oxalic acid.

The oxalates may be detected by the decomposition of their acid-radical.

a. When to an oxalate some strong sulphuric acid is added, and the mixture warmed, the oxalic acid thus liberated undergoes instant decomposition, partly from the tendency of sulphuric acid to form a hydrate :

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H.C,O,+HSO.=H,SO, H,O+CO+CO,. Considerable effervescence ensues from the escape of the carbonic anhydride and carbonic oxide gases; and the latter gas will be found to burn with a blue flame. This action of sulphuric acid,

without any blackening of the substance under examination, points decisively to the presence of oxalic acid; for though the salts of some of the more complex acid-radicals yield carbonic oxide also, they blacken simultaneously, the ferrocyanides excepted.

B. If, instead of sulphuric acid alone, a mixture of binoxide of manganese (Mn,O,) and sulphuric acid be made to act upon oxalic acid, the sole gaseous product of the reaction is carbonic anhydride (CO2).

SALTS OF THE BORACIC RADICAL, OR BORATES.

These salts are by no means of such frequent distribution in nature as the carbonates; they occur in some few minerals, and in greater abundance in the hot lakes or boracic lagoons of Tuscany, into the waters of which the vapours are conveyed which rise from the volcanic bottom. These vapours, which are charged with boracic anhydride (Bo̟,0), yield it to the water, with which it combines to form boracic acid. It is generally met with in commerce combined as borax, the biborate of sodium.

Most borates may be heated on charcoal without decomposition. The use of borax as a blowpipe reagent is well known.

THE HYDROGEN SALT crystallizes from a hot aqueous solution; but if these crystals be heated, they evolve water, and yield a fused glassy substance, which is the so-called anhydrous acid (Bo20). This body bears the same relation to boracic acid as chromic anhydride does to chromic acid. When dissolved to saturation in hot water, it separates on cooling, in the form of hexagonal laminae having a pearly lustre and the formula HBOO,+aq. It may be considered as the representative of what are called the monoborates, which have the formula MBOO,+naq. If these crystals be heated to a temperature considerably above 100°, they part with the elements of water, and another hydrogen compound is obtained (H, Bo,O,), which, when written without its 2 eqs. of accidental water, becomes H, Bo, O,, and may then be considered as the type of the biborates. The biborates may

also be viewed (like the bichromates) as combinations of the anhydride (Bo2O,) with the monoborates; thus we have the following equation when we disregard water of crystallization:

The rationale of the process whereby the biborates are produced may be as follows::-we may suppose that, under the influence of heat, 1 molecule of the anhydride (Bo20 ̧) is formed from 2 equivalents of boracic acid, thus:

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2(HBOO,, H2O)=Bo, 0, +3H,0;

the body, Bo, 03, thus formed, then unites with 2 equivalents of undecomposed acid to form the biborate of hydrogen. Or we may merely express the change as follows:

:-

4(HB002, H2O)=H, Bo ̧0,, 2H, 0+3H20.

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Borates, then, may be of at least two classes, borates and biborates. The latter salts are much more stable than the formerso much so, indeed, that even the potassium salt of the former series, by mere exposure to the air, absorbs carbonic anhydride, and becomes converted into the carbonate and biborate, thus—

4KB002+CO2=K2CO2+K2 Bo ̧O..

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Nor are these the only classes of borates. Just as boracic anhydride combines with borates to form biborates, so additional proportions of this body yield salts which have been called ter-, quadri-, and sex-borates. The formulæ of the sodium (or potassium) salts of these compounds are—

Quadriborate Na, Bo, O,,=2NaBo0,+3B0,0 ̧.

Sexborate

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Na, Bo12019=2NaBoO,+5B0,0 ̧.

The borates, biborates, and sexborates are pretty well known ; but not so the others.

The boracic radical may be recognized both by the formation of sparingly soluble salts, and by processes of decomposition.

The normal borates are more soluble in water than the others. Of the biborates, which are the most common boracic salts,

almost all, excepting those of the first subdivision, are insoluble in water.

THE POTASSIUM SALT (K, Bo ̧0,+5aq) is soluble.

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THE SODIUM SALT (Na, Bo ̧0,+10aq), or borax, is soluble. THE BARIUM SALT is produced by the action of soluble barium salts on a solution of borax. It is a white precipitate. Its formula is Ba, Bo ̧0,+2aq. It is soluble in excess of chloride of barium, also in ammonium salts; it dissolves in 100 parts of cold water, and in a smaller quantity of boiling water; it is soluble in acids. Before the blowpipe it fuses to a grey glass.

THE STRONTIUM SALT is produced by the action of a soluble strontium salt on a solution of borax: it is a white precipitate. It dissolves readily in cold solutions of chloride or nitrate of ammonium; 1 part is soluble in 130 parts of boiling water.

The Calcium Salt is produced by the action of a soluble calcium salt on a solution of borax. Its formula is Ca ̧ Bo ̧O,+aq after having been air-dried. It is scarcely soluble in water, but dissolves in acids. Before the blowpipe it fuses to a glass.

THE FERROUS, FERRIC, and MANY OTHER SALTS of the third and fourth subdivisions are yellowish or white precipitates, insoluble in water.

THE CUPRIC SALT is a pale green precipitate, slightly soluble in water, and dissolved easily by a solution of boracic acid. Before the blowpipe it fuses to a green opaque glass.

THE SILVER SALT is white: its formula, under all circumstances, is AgBoO,. It is sparingly soluble in water.

THE MERCUROUS and MERCURIC SALTS do not appear to exist; the biborates precipitate basic mercury compounds.

The Lead Salt is obtained by the action of soluble lead salts on a solution of borax: it is a white precipitate. Its formula is Pb, Bo,O,. It is insoluble in excess of its precipitant, but slightly soluble in pure water.

This acid-radical is also detected by the following experiments. a. When sulphuric acid is added to the aqueous solution of a borate, boracic acid separates in characteristic crystalline scales (HBoO2+aq). If the boracic acid be then dissolved in alcohol,

and the solution kindled, the flame produced will have a dark green edge, best seen against a black background. In this experiment, the presence of chlorides and of copper salts should be avoided.

3. The most characteristic reaction of boracic acid is the action of its aqueous solution on turmeric paper. All other acids exert no influence upon ordinary yellow turmeric paper, or, if it has been browned by an alkali, they simply restore its original colour; but boracic acid behaves like an alkali, turning the yellow of the paper to a reddish brown. The suspected borate is mixed with hydrochloric acid, and into the mixture a small piece of turmeric paper is placed. The test is applied in a white porcelain dish.

7. Sulphuretted hydrogen and ferrocyanide of potassium produce no characteristic actions upon boracic acid or soluble borates.

SALTS OF THE SILICIC RADICAL, OR SILICATES.

These salts are of universal distribution in nature they form a very large proportion of the rocks constituting the earth's crust, and enter into the composition of many minerals.

Heated before the blowpipe, most silicates fuse to a colourless or coloured glass.

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THE HYDROGEN SALT (HSiO), or silicic acid, is not very well known; it is believed that the body termed gelatinous silica has, when air-dried, this formula, but when dried at 100° the formula H, Si,O,, i. e. 2HSiO,+Si,O,: at a higher temperature it is resolved into water and silicic anhydride (Si,O,). This body (Si,O,), which bears the same relation to silicic acid (HSiO) as boracic anhydride (Bo,O,) bears to boracic acid (HBOO), is of very common occurrence, and is familiar to every one under the forms of quartz, amethyst, siliceous sand, flint, and chalcedony. Silicates are as various in their constitution as they are great in number; but, as we have seen in the tungstates, chromates, and especially in the borates, a number of acid-radicals may be built up by the assimilation of successive additions of the body which has been termed the anhydride,