oxide of chromium. Its composition may be expressed by the formula G1,0.SiO ̧ Al,O,.SiO..

The beryl is a pale green variety of emerald.

Euclase is another mineral containing glucinum; its formula is 2G1,O,.SiO,, 2A1,0, SiO..

Chrysoberyl has the composition A10.G10.

Glucinum may be prepared by decomposing the sesquichloride with potassium, in exactly the same way as aluminum was obtained. Glucinum is very similar to aluminum; it is not oxidized by dry air, and does not decompose water at the ordinary temperature. When heated in air or oxygen, it is converted into glucina (G),0,).

This metal decomposes water in presence of acids or alkalies.
Only one oxide of glucinum is known.

GLUCINA, GI,O,

Preparation. This oxide is generally prepared from the mineral termed emerald of Limoges, which contains silicates of alumina and glucina, together with lime and sesquioxide of iron.

The mineral, in a state of fine powder, is mixed with about three times its weight of carbonate of potassa and fused in a platinum crucible; the fused mass is digested with dilute sulphuric acid, which leaves a quantity of silica undissolved; the filtered solution is evaporated to a small bulk, and allowed to cool, when crystals of alum are deposited; the liquor separated from the crystals is now mixed with excess of ammonia, which precipitates the sesquioxide of iron and the glucina, together with a little alumina; this precipitate is digested with a saturated solution of carbonate of ammonia, which dissolves only the glucina, and deposits the carbonate of this base on ebullition; the precipitated carbonate is washed, dried, and ignited, when pure glucina is left.

Properties.-Glucina much resembles alumina, being white, infusible, and insoluble in water. Unlike that base, however, it absorbs carbonic acid when exposed to air, and expels ammonia from its salts. Glucina is soluble in acids; the salts thus produced have a sweet astringent taste (hence its name, from yauxús); they are acid to test-papers. It is also soluble in solutions of potassa and soda, and is reprecipitated when these solutions are diluted with water and boiled.

Glucina is considered by some chemists as a protoxide, but its analogy with. alumina favors the view which we have taken above, that it is a sesquioxide. Glucina is precipitated from its solutions in the form of hydrate.

The Neutral Sulphate of Glucina, crystallizes in octohedra of the formula GI,O,.3SO,+12Aq. It is very soluble in water.

Other sulphates of glucina exist, but it does not form an alum.

A basic Carbonate of Glucina, GIO.CO,+5Aq, is obtained by precipitation; it is soluble in alkaline carbonates.

Sesquichloride of Glucinum, GI,Cl, may be prepared in the same way as the corresponding aluminum-compound, which it much resembles.

Sesquisulphide of Glucinum, Gl,S,, may be obtained by the direct combination of glucinum with sulphur; it is precipitated as a white gelatinous hydrate, on adding a hydrosulphate of an alkaline sulphide to a solution of glucinum.

The compounds of glucinum have at present received no practical application. REACTIONS OF GLUCINA.-Potassa, soda, and their carbonates produce, in solutions of glucina, white precipitates soluble in excess.

Ammonia and Sulphide of Ammonium also give a gelatinous precipitate, insoluble in excess, but soluble in carbonate of ammonia, and reprecipitated by boiling.

Phosphate of soda precipitates phosphate of glucina.

When a hot solution of fluoride of potassium is added to a hot solution of glucina until a precipitate begins to appear, and the solution then cooled, a crystalline precipitate of a double fluoride is produced.

Fixed organic matters interfere with the precipitation of glucina. Glucina does not yield a blue compound with nitrate of cobalt before the blowpipe.

THORINUM OR THORIUM.

Sym. Th. Eq. 59.6.

§ 216. This is a very rare metal, found in the minerals rite. The former contains about 57 per cent. of thorina.

thorite and pyrochloThe metal itself may

be prepared by the same process as aluminum, which it resembles in most of its properties.

It is not easily dissolved by acids, with the exception of hydrofluoric acid; alkalies are said to have no action upon it.

We are acquainted with only one oxide of thorinum.

OXIDE OF THORINUM, THORINA, ThO.

Preparation. This oxide is prepared from thorite, in which it is associated with silica, lime, magnesia, and the oxides of iron, manganese, uranium, lead, and tin. The mineral is boiled with hydrochloric acid, the solution evaporated to dryness, the residue extracted with water, the lead and tin precipitated by sulphuretted hydrogen, and the solution mixed with excess of ammonia, which throws down the thorina, together with the oxides of iron and uranium; the precipitate is dissolved in sulphuric acid, and the solution rapidly boiled down, when sulphate of thorina, being sparingly soluble in hot water, is precipitated; this is collected on a filter, washed with boiling water, and ignited, when pure thorina is obtained as a white powder.

Properties. This earth is remarkable for its great density (sp. gr. 9.4). It combines with water, forming a hydrate (ThO.HO), which is insoluble in the alkalies, soluble in the acids and in alkaline carbonates. After ignition, however, thorina is soluble only in sulphuric acid.

REACTIONS OF THORINA.-Potassa, soda, ammonia, and sulphide of ammonium produce, in solutions of thorina, gelatinous precipitates, insoluble in excess. The carbonates of potassa and of ammonia produce a precipitate soluble in excess.

Phosphate of soda precipitates phosphate of thorina.

Soluble salts of thorina are decomposed at a red heat.

Solutions of some of these, e. g. the sulphate, yield precipitates upon boiling, which redissolve very slowly as the solution cools. This peculiar reaction does not take place when the solution contains any base capable of forming a doublesalt with thorina.

YTTRIUM, ERBIUM, AND TERBIUM.

Sym. Y. Sym. E. Sym. Tb.

§ 217. These metals are exceedingly rare, and possess no practical interest. They are found in the minerals gadolinite, orthite, and yttrotantalite.

Yttrium is obtained by decomposing its chloride with potassium; it is very similar to aluminum.

The oxides of these metals, viz. yttria (YO), erbia (EO), and terbia (TbO) are obtained together from the mineral gadolinite.

By digesting the mixed precipitate in very dilute sulphuric acid, the yttria is dissolved, and may be reprecipitated from the solution by potassa. The residue of erbia and terbia is dissolved in nitric acid, and the solution saturated with sulphate of potassa, which yields a sparingly soluble double-salt with the sulphate of erbia. The solution yields terbia upon addition of potassa.

Pure Yttria is a white powder of great density; it dissolves more easily in dilute than in concentrated acids. The hydrate, obtained by precipitation, resembles hydrate of alumina.

The solutions of salts of yttria are sweet and astringent; they have an acid reaction.-Nitrate of Yttria is white, crystallizable, and deliquescent.-The sulphate forms colorless crystals, which are sparingly soluble.-Chloride of Yttrium is volatile, crystalline, and deliquescent.

Erbia has a dark yellow color, which it loses when ignited in a current of hydrogen, and regains when gently heated in air. It dissolves in acids, forming colorless salts.

The sulphate is crystallizable, and does not effloresce on exposure to air at 176° F. (80° C.)-Nitrate of Erbia is not deliquescent; its solution is colorless, even when concentrated.

The Salts of Terbia acquire a reddish color upon desiccation.—The sulphate is efflorescent at 122° F. (50° C.)

REACTIONS OF YTTRIA, ERBIA, AND TERBIA.-Potassa, soda, ammonia, and sulphide of ammonium, yield bulky precipitates of the hydrates, insoluble in

excess.

Alkaline carbonates; a white precipitate, soluble, though with difficulty, in a large excess.

Phosphate of Soda; a white precipitate, soluble in hydrochloric acid, reprecipitated by boiling.

CERIUM, LANTHANIUM, DIDYMIUM.

Sym. Ce. Eq. 47. Sym. La. Eq. 47. Sym. D. Eq. 50.

§ 218. Cerite is the chief mineral from which these metals are extracted; they exist in it as silicates. They are also contained in gadolinite, orthite, and yttrocerite. Cerium forms two basic oxides, the oxide (CeO) and sesquioxide (Ce,O,).

In order to extract the oxides of cerium, lanthanium, and didymium, the powdered cerite is ignited and extracted with aqua regia; the solution is evaporated to dryness, and the residue treated with dilute bydrochloric acid, which leaves the silica undissolved; the filtered liquid is precipitated by ammonia, and the precipitate boiled with an excess of oxalic acid, which dissolves the sesquioxide of iron, and leaves the three oxides in the form of oxalates; this residue is ignited, and the oxides thus obtained are dissolved in concentrated nitric acid; the solution is evaporated to dryness, and the residue ignited, when the oxides are left in a very finely divided state. By boiling these with a large quantity of very dilute nitric acid, the oxide of lanthanium is then dissolved, and may be precipitated, as carbonate, by carbonate of ammonia. To separate the didymium and cerium, the residue left by nitric acid is boiled with hydrochloric acid, which dissolves the oxide of didymium, and leaves sesquioxide of cerium.

Cerium, Lanthanium, and Didymium are obtained by reducing their chlorides with potassium; they form gray powders, which become lustrous when burnished; they are very infusible, and non-volatile. These metals oxidize rapidly when exposed to air; they readily decompose water at the boiling-point.

Oxide of Cerium (CeO) is obtained by heating the carbonate in a current of hydrogen. The hydrate, obtained by precipitation, is white at first, and becomes yellow when exposed to air, or when treated with chlorine (oxide of lanthanium is not turned yellow by chlorine).

The Salts of Oxide of Cerium are colorless, and have an acid reaction. The nitrate is soluble and crystallizable.-The sulphate crystallizes in hydrated prisms; it forms a nearly insoluble double salt with sulphate of potassa.-The carbonate is insoluble in water.

Sesquioxide of Cerium (Ce,O,) is obtained by heating the metal in air or oxygen. It has a yellow color, which is darkened by ignition. The sesquioxide is slowly acted upon by hydrochloric acid, which forms chloride of cerium, with evolution of chlorine. Sulphuric acid (conc.) dissolves it easily with the aid of heat.

The hydrated sesquioxide forms a yellow gelatinous precipitate. The neutral sulphate forms a yellow double salt with sulphate of potassa, which is sparingly soluble in water.

Chloride of Cerium (CeCl) is white; soluble in water and alcohol; its solution in the latter burns with a green flame.-Sulphide of Cerium has a yellow or red color, and is easily dissolved by acids.

Only one Oxide of Lanthanium (LaO) is known; it is a white powder, soluble in acids, and in ammoniacal salts, from which it expels the ammonia. The hydrate, obtained by precipitation, rapidly absorbs carbonic acid from the air. The salts of oxide of lanthanium have a sweet astringent taste. The nitrate crystallizes in deliquescent prisms.-Sulphate of lanthanium forms six-sided prisms of the formula LaO.SO,+3Aq, which are soluble in 6 parts of cold water and in 120 of boiling water. A solution of this salt, saturated at a low temperature, deposits the greater part of the sulphate when heated to ebullition.-Carbonate of lanthanium has been found native. The chloride is very soluble.

The Oxide of Didymium (DO) has a dark color. The hydrate has a violet color, and absorbs carbonic acid from the air. It dissolves readily in acids, and expels ammonia from its salts, but is a weaker base than oxide of lanthanium. Its salts have a pink or violet color. The nitrate crystallizes with difficulty, and is deliquescent; its solution has a deep red color. The sulphate forms red crystals, which are more soluble in cold than in hot water. It yields a double-sult with sulphate of potassa.

REACTIONS OF (OXIDES OF) CERIUM, LANTHANIUM, AND DIDYMIUM.— Potassa, soda, ammonia, and sulphide of ammonium; a white hydrate, insoluble in excess. The alkaline carbonates; precipitate, very sparingly soluble in excess.-Phosphate of soda; a white precipitate.-Sulphate of potassa; a crystalline precipitate. With a borax-bead, in the outer blowpipe-flame, a reddishyellow, which fades on cooling, and vanishes in the inner flame.

The reactions of lanthanium closely resemble those of cerium, but the former metal is not precipitated from its solutions by sulphate of potassa.

The solutions of didymium, as stated above, have a violet color. Sulphide of ammonium precipitates them with difficulty in the cold. Sulphate of potassa gives an amethyst-colored double-salt. With a bead of phosphorus-salt, in the inner flame, a red glass with a shade of violet.

ZIRCONIUM.

Sym. Zr. Eq. 22.4.

§ 219. This rare metal exists in the minerals zircon and hyacinth, which are chiefly composed of silicate of zirconia (Zr,O,.SiO1).

The metal, which is prepared by the action of potassium upon the double fluoride of zirconium and potassium, is a black powder, capable of assuming a metallic lustre. When heated in air, it is converted into zirconia.

Alkalies, their carbonates, and even borax, are capable of oxidizing this metal, but it is not attacked to any extent by acids, except hydrofluoric.

The only oxide of this metal, zirconia (Zr,O,), is, in many respects, similar to alumina.

In order to extract this base from hyacinth, the mineral is fused with hydrate of potassa; the fused mass is decomposed with hydrochloric acid, and the silica separated in the usual manner; the solution freed from silica is treated exactly as in the extraction of cerium from cerite (see p. 324).

Zirconia is a white powder, slightly soluble in carbonate of ammonia and in the alkaline bicarbonates. After ignition, it can be dissolved only by sulphuric acid. A hydrate of zirconia has been obtained. The neutral salts of zirconia redden litmus. The nitrate does not crystallize, and is very soluble. The neutral sulphate is crystalline and soluble; other sulphates exist. The carbonate is insoluble. Anhydrous sesquichloride of zirconium is not volatile; the hydrated chloride crystallizes.

REACTIONS OF ZIRCONIA.-Potassa, soda, ammonia, and sulphide of ammonium; a white precipitate, insoluble in excess. Alkaline carbonates; precipitate, soluble in large excess. Phosphate of soda; white precipitate. Sulphate of potassa; a double sulphate, sparingly soluble in water and acids, when precipitated from hot solutions.

CHROMIUM.

Sym. Cr. Eq. 26.7. Sp. Gr. 5.9.

§ 220. Chromium is moderately abundant in nature, but not in the free state. It is found in chrome-iron (a compound of the oxides of chromium and iron), and as chromate of lead.

The ruby also contains chromic acid, to which its color is due; this gem contains 82.5 per cent. alumina, 8.9 per cent. magnesia, and 6.2 per cent. chromic acid.

As already stated, the green color of the emerald is due to sesquioxide of chromium.

Preparation.-Chromium may be prepared by exposing to a very high temperature, in a crucible lined with charcoal, an intimate mixture of sesquioxide of chromium and charcoal; the spongy mass thus obtained is powdered in an iron mortar and mixed with a little more sesquioxide of chromium (to oxidize as much of the carbon as possible); the mixture is again exposed to a very high temperature, in a porcelain crucible, when a coherent mass of metal is obtained. The chromium thus prepared always contains more or less carbon.

It may be obtained in a purer state by the action of potassium upon sesquichloride of chromium.