The other special reagents of the first and three preceding subdivisions give no characteristic reactions with tungstic salts.

Tungstic salts are chiefly recognized by their oxide and sulphide; but the formation of the indigo-blue oxide by the action of nascent hydrogen is also characteristic, although not peculiar to this metal.

SALTS OF MOLYBDENUM.

This metal bears a considerable resemblance to the preceding; it forms, however, a larger number of compounds with oxygen and other salt-radicals, constituting several series, which are represented respectively by the oxides and chlorides Mo2O and MoCl; Mo, O, and MoCl; Mo, O, and MoCl ̧, while between the two latter oxides there exists one called the blue oxide, which is apparently intermediate or a compound of both (M010 O5?).

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Some molybdenum compounds, as the chlorides, sublime at a gentle heat; those which are fixed, usually yield the oxide Mo2O, when heated in the air. When heated on platinum wire with carbonate of sodium, the oxide Mo, 0, gives a glass which is clear while hot, and becomes milk-white on cooling; if the bead be transferred to charcoal, and heated on it, it sinks in, and if the mass be levigated, a steel-grey powder of the metal is obtained. Molybdenum compounds impart no colour to the blowpipe flame, nor does nitrate of cobalt yield any decisive result. With borax the bead is dark yellow or red in the oxidizing flame whilst hot, and colourless or of a bluish grey opaline appearance when cold, according to the amount of molybdenum present; in the reducing flame the bead becomes brown, with but a minute trace of molybdenum, and quite dark and opaque if a little more be added. With microcosmic salt in the oxidizing flame the bead is yellowish green when hot, and colourless when cold, and if transferred to charcoal, becomes opaque and bright green; in the reducing flame the colour is of as fine a green as that of chromium.

The salts of molybdenum, in which that metal exists as a compound acidradical combined with potassium, sodium, or ammonium (alkaline molybdates), yield with a small quantity of stannous chloride (SnCl) a blue colouration; with a larger quantity of the reagent, a blue precipitate; and with a still larger amount, a green precipitate: the blue and green precipitates dissolve in sulphuric acid, yielding blue or green solutions. There are no combinations of molybdenum known corresponding to the chloroplatinates and chloraurates.

MOLYBDOUS SALTS.

The soluble salts of this series are of a black or deep purple colour, or, if dilute, of a brownish green tint; the insoluble salts are dark grey or black. They are generally obtained from the oxide Mo, O,, by dissolving it in hydrochloric acid and adding zinc: the liquid becomes at first blue, then reddish brown, and finally black; the molybdous chloride (MoCl) formed,

and present in the solution, is separated from the chloride of zinc by excess of hydrate of ammonium, which precipitates it as hydrate. Molybdous salts do not oxidize so readily as those of the next series.

The principal insoluble molybdous salts are the chromate, the hydrate, the sulphide, the ferrocyanide, and the phosphate.

THE CHLORIDE and THE IODIDE are soluble.

THE CYANIDE is unknown.

THE CHROMATE is produced by chromate of potassium.

The Hydrate is obtained by adding the hydrates of potassium or ammonium, or the carbonates of potassium or sodium, to solutions of molybdous salts: it is a brownish black precipitate. Its formula is probably MOHO. It is insoluble in excess of alkaline hydrates, slightly soluble in the carbonates of potassium, sodium, and ammonium. Recently precipitated, it dissolves slowly in acids; but after ignition, by which process it is converted into the oxide (Mo, O), it is quite insoluble in acids.

The Sulphide is produced by the action of hydrosulphuric acid gas, as a brownish black, and by sulphide of ammonium as a yellowish brown precipitate. Its composition has not been ascertained. It dissolves readily in sulphide of ammonium.

THE SULPHATE, formed by dissolving molybdous hydrate in sulphuric acid, is soluble.

THE CARBONATE is not known.

THE OXALATE is a dark grey precipitate, slightly soluble in excess of oxalic acid.

THE FERROCYANIDE is produced by the action of ferrocyanide of potassium, as a dark brown precipitate.

Its composition is unknown.

It is soluble in excess of its precipitant, and also in excess of hydrate of ammonium, yielding dark brown solutions. From its ammoniacal solution it is reprecipitated upon the addition of chloride of ammonium.

THE FERRICYANIDE is produced by the action of ferricyanide of potassium, as a reddish brown precipitate.

THE PHOSPHATE is produced by the action of phosphate of sodium, as a dark grey precipitate, soluble in excess of molybdous chloride.

The action, on solutions of molybdous salts, of the other special reagents of the present and three preceding groups, has not been ascertained in all cases. Molybdous salts are generally recognized by the formation of the insoluble hydrate and sulphide.

MOLYBDIC SALTS.

These salts are prepared by dissolving molybdic hydrate in the various acids. They may also be prepared by digesting excess of metallic molybdenum in a solution of per-molybdic oxide (Mo2O) in that acid whose molybdic salt we desire to obtain. In the anhydrous state these salts are black; but when in solution, or combination with water, red or reddish brown.

The principal insoluble salts are the chromate, the hydrate, the sulphide, the ferrocyanide, and the phosphate.

THE CHLORIDE and THE IODIDE are soluble.

THE CYANIDE is unknown.

THE CHROMATE is produced by the action of chromate of potassium. It is precipitated in greyish yellow flakes, which are insoluble in water.

The Hydrate is obtained by the action of the hydrates of potassium or ammonium, or of the carbonates of potassium or sodium, on solutions of molybdic salts. It is a reddish brown precipitate, which becomes nearly black on drying. The formula is probably MoH, O2. It is insoluble in excess of the alkaline hydrates, but soluble in the carbonates; slightly soluble in water, to which it imparts a yellow or red tint. It is reprecipitated from its aqueous solution by chloride of ammonium and some other salts. It dissolves in acids.

The Sulphide is produced after some time, by the passage of hydrosulphuric acid gas through molybdic salts, as a brown precipitate, or by the addition of sulphide of ammonium, as a yellowish brown precipitate. Its formula is Mo2 S2. It dissolves in sulphydrate of ammonium. It is easily soluble in nitric acid, while it is decomposed by sulphuric acid on ebullition, evolving the gas termed anhydrous sulphurous acid (SO2), and yielding a blue solution.

THE SULPHATE and THE OXALATE are soluble.

THE CARBONATE does not appear to exist.

THE FERROCYANIDE is produced by ferrocyanide of potassium, as a dark brown precipitate insoluble in excess of its precipitant, but soluble in hydrate of ammonium; from this solution it is reprecipitated by chloride of ammonium. THE FERRICYANIDE is produced by ferricyanide of potassium, as a dark brown precipitate insoluble in excess of its precipitant.

THE PHOSPHATE is produced by phosphate of sodium, as a brownish white precipitate.

The action, on bi-salts of molybdenum, of the other special reagents of the present and three preceding subdivisions, has not, in many cases at least, been well ascertained.

The hydrate and the sulphide are the most characteristic salts of the series.

Between the bi-salts and ter-salts of molybdenum, the characteristic BLUE OXIDE of molybdenum occurs: it is obtained by the oxidation of the lower, or the reduction of the higher oxides.

Its formula is doubtful.

It is soluble in water, but reprecipitated from its aqueous solution by chloride of ammonium.

TER-SALTS OF MOLYBDENUM.

The oxide of this series is commonly called molybdic acid; it is really anhydrous molybdic acid, or molybdic anhydride, and yields salts in which

the molybdenum constitutes part of the acid-radical. Other ter-salts of molybdenum exist in addition to the oxide (Mo, O,): they are chiefly formed by dissolving the latter in acids.

The chief insoluble compounds of this series are the oxide, the sulphide, the ferrocyanide, and the ferricyanide.

THE CHLORIDE, THE IODIDE, and THE CYANIDE, if existing at all, are probably soluble.

THE CHROMATE is unknown.

The Oxide is produced by oxidizing one of the lower oxides or hydrates by nitric acid, or by roasting the native sulphide. It is a white crystalline body, which melts at a red heat to a yellow liquid. Its formula is Mo2 O3. It dissolves in the hydrates of potassium and ammonium, forming the molybdates KMOO2, and NH, MoO2. There are several series of molybdatesbasic, normal, and acid; the alkaline molybdates only, such as those just mentioned, are readily soluble in water. The oxide (Mo, O1) dissolves in 500 parts of cold, or 960 of hot water; before ignition it is soluble in many acids.

The Sulphide is produced by saturating a solution of an alkaline molybdate with hydrosulphuric acid gas, whereby an alkaline sulphomolybdate is first formed (KM0O2+2H2S=KMOS2+2H2O); the sulphomolybdate is then decomposed by the addition of hydrochloric acid (2KMOS,+2HCl=Mo, S2 +H2S+2KCl). It is a brown precipitate. Acid solutions of molybdic anhydride (Mo2O) are coloured blue when hydrosulphuric acid is first passed through them after a time, a brown precipitate of the ter-sulphide containing free sulphur occurs; but the molybdenum is never wholly precipitated. The formula of the brown sulphide is Mo, S. It dissolves in the hydrates and sulphides of the first subdivision, forming the sulphomolybdates.

THE SULPHATE, obtained by acting on molybdate of barium with sulphuric acid, is soluble.

THE CARBONATE does not exist.

THE OXALATE is soluble.

THE FERROCYANIDE is produced by adding ferrocyanide of potassium to an acid solution of molybdic anhydride (M, O), and appears as a reddish precipitate, which dissolves in excess of its precipitant, and also (with decomposition) in hydrate of ammonium.

THE FERRICYANIDE is produced by ferricyanide of potassium as a pale reddish brown precipitate, which is soluble in hydrate of ammonium. THE PHOSPHATE is scarcely known.

The other special reagents of the present and three preceding subdivisions are not known to give any decisive results with solutions of ter-molybdic salts, or of the molybdates.

The most characteristic salts of this series are the oxide and the sulphide, together with the derivatives of the oxide known as the "molybdates."

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SALTS OF VANADIUM.

This metal resembles molybdenum in forming a considerable number of different combinations with oxygen and other salt-radicals. The first series, that of vanadious salts, is represented only by the oxide V2O, which is dissolved by nitric acid alone, and which, if exposed to the air, passes into vanadic oxide. The second series, that of vanadic salts, is represented by the oxide V2O2, and the chloride VCI,,—whilst the third series, that of the ter-salts of vanadium, is typified by the oxide V2O, (the anhydrous vanadic acid) and the chloride VCl. Between the oxides of the two latter series there are certain other oxides of a blue or green colour.

The metal zinc precipitates metallic vanadium from its solutions.

VANADIC SALTS, OR BI-SALTS OF VANADIUM.

The anhydrous salts of this series are green or brown, while their solutions are of a blue colour, which varies in intensity with different salts, and which often changes to a green by oxidation. The oxide is prepared by the ignition of vanadite of ammonium; it dissolves slowly in acids.

The principal insoluble salts are the cyanide, the hydrate, the ferrocyanide, and the ferricyanide.

THE CYANIDE is formed by digesting the hydrate in a solution of hydrocyanic acid, as a dark-brown gelatinous mass, which is soluble in cyanide of potassium.

THE CHLORIDE, THE IODIDE, and THE CHROMATE are soluble.

The Hydrate is best produced by precipitating a vanadic salt (through the solution of which hydrosulphuric acid gas has been passed, in order to reduce the vanadic oxide) by slight excess of carbonate of sodium. The precipitate is greyish white: and the liquid should be left perfectly colourless; for if blue, carbonate of sodium enough has not been added, while, if green, vanadic oxide is present. The grey precipitate, if exposed to the air, speedily becomes brown. Its composition has not been ascertained. It dissolves in excess of alkaline hydrates, forming brown solutions containing vanadites; from these solutions it is reprecipitated by more alkaline hydrate. In neutral or acid alkaline carbonates it dissolves, forming pale blue solutions.

Solutions of vanadic salts (also the insoluble hydrate), when mixed with excess of hydrate of ammonium, yield a brown precipitate of vanadite of ammonium, in which the vanadium enters as a constituent of the acidradical. Vanadite of ammonium is insoluble in hydrate of ammonium, but dissolves in water, with a brown colour.

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The Sulphide is not produced by hydrosulphuric acid gas; but by the addition of alkaline sulphydrates (e. g. NH, HS) to solutions of vanadic salts, a brownish black precipitate is obtained. Its composition is V2 S2. It dissolves in excess of its precipitants, forming solutions of a beautiful purplish colour; it dissolves also in a boiling solution of carbonate of sodium, with a brownish yellow colour. It is not affected by hydrochloric or sulphuric