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former, as that again was from the one preceding it, by the increased number of insoluble salts which its members formed. In addition to the carbonates, oxalates and phosphates, which are as a general rule insoluble in water and in neutral saline solutions, both in this and the second subdivision we find that the hydrates and sulphates of the metals and basic radicals belonging to this group are almost equally insoluble. A well-marked distinction is thus seen between the members of the present subdivision and those of the two preceding ones; and their separation may be readily effected by taking advantage of this difference.

To the oxides of the first eight of the above metals the conventional expression "the earths" is frequently applied, and their salts are spoken of in general as "the salts of the earths," while to the last three the term "alkaloids" is applied, and their salts are called "the salts of the alkaloids."

The really important members of this group, to the reactions of which only the beginner need at first attend, are the salts of aluminium, chromium, uranium, iron, manganese, nickel, cobalt and zinc; the remainder, viz. the salts of yttrium, thorinum, cerium, lanthanium, didymium, zirconium and glucinum, are of very rare occurrence. They form a kind of link between the second and third subdivisions, resembling the salts both of magnesium and of aluminium in many particulars. Neither need the reactions of the compound bases, morphine, quinine, and strychnine, be studied by the beginner; it may be remembered, however, that they are all decomposable by ignition. One characteristic of certain oxides of this group deserves to be mentioned: they are, after ignition, soluble only in hot sulphuric acid.

There are several reactions by means of which this group may be divided into smaller sections: this division is perhaps most easily, and, for practical purposes, most effectively accomplished by the action of excess of hydrate of ammonium in the presence of chloride of ammonium. The group divides thus:

SECTION I.-SALTS OF YTTRIUM, THORINUM, CERIUM, LANTHANIUM, DIDYMIUM, ZIRCONIUM, GLUCINUM, ALUMINIUM, CHROMIUM, URANIUM, TITANIUM, TANTALUM, NIOBIUM, AND PELOPIUM.

Not volatilized by heat, but precipitated as hydrates by excess of hydrate of ammonium (NH, HO) in the presence of chloride of ammonium (NHCl); ferric salts behave in a similar manner.

SECTION II.-SALTS OF MANGANESE, COBALT, NICKEL, AND ZINC.

Non-volatile, and not precipitated by the addition of excess of hydrate of ammonium (NH, HO) in the presence of chloride of ammonium (NHCl); ferrous salts behave in a similar manner.

SECTION III.-SALTS OF THE COMPOUND BASES, MORPHINE, QUININE, AND

STRYCHNINE.

Volatilized and destroyed by heat.

The group-test is a soluble sulphide-a salt chosen because it precipitates every member of this group, but produces no precipitate in either of the preceding groups. Of the soluble sulphides, sulphide of ammonium ([NH,], S) is selected, for reasons which will be evident presently.

SECTION I.-Salts not volatilized by heat, but precipitated as hydrates by excess of Hydrate of ammonium (NH, HO) in the presence of Chloride of ammonium (NHCl)

SALTS OF YTTRIUM, THORINUM, CERIUM, LANTHANIUM, DIDYMIUM, ZIRCONIUM, GLUCINUM, ALUMINIUM, CHROMIUM, URANIUM, TITANIUM, TANTALUM, NIOBIUM, AND PELOPIUM.

SALTS OF YTTRIUM.

The salts of this metal are but of rare occurrence in nature; and it has been shown that they consist of a mixture of the salts of three metals, to which the names Yttrium, Erbium, and Terbium have been assigned; their separation is, however, very difficult, on account of the small quantity in which they occur, and the great similarity of their chemical characters; the mixed salts are therefore generally called the salts of yttrium, and recognized by the reactions given below: these salts are believed to be proto-salts.

The colour of the salts is' white, unless the acid-radical introduces colour. The taste of pure yttrium salts is at first sweet, and then astringent. Heated

before the blowpipe, the oxide is generally produced, and remains infusible. The oxide of erbium is said to be of an orange-colour, while the salts of terbium are said to acquire a reddish colour on drying. Yttrium salts give no peculiar reaction with borax before the blowpipe, nor do they impart any colour to the flame; with nitrate of cobalt, oxide of yttrium (Y,2O) gives a greyish-blue colour.

The principal insoluble salts which this metal forms are these,—the hydrate, the double sulphate of yttrium and potassium, the carbonate, the oxalate, the ferrocyanide and the phosphate.

THE CYANIDE is soluble.

The Hydrate is a white powder, and is produced when the hydrates of potassium or ammonium are added to solutions of yttrium salts: it is also formed by the action of the sulphides of potassium or ammonium, its precipitation being accompanied by the evolution of hydrosulphuric acid, according to the following equation :

2YC1+(NH4)2S+2H2O=2YHO+2NH ̧Cl+H2 S.

The composition of the precipitate is not always exactly YHO; for occasionally it contains a little of the original salt of yttrium employed, if that salt were the sulphate or nitrate. This hydrate is insoluble in excess of the precipitants; it dissolves somewhat in salts of ammonium, and if boiled with them dissolves entirely, displacing the ammonium. It is insoluble in water, but soluble in acids.

THE DOUBLE SULPHATE OF YTTRIUM AND POTASSIUM forms when a saturated solution of sulphate of potassium is added to a somewhat concentrated solution of a salt of yttrium. It is a crystalline powder. Its formula is said to be YKSO. It is soluble in 10 parts of the precipitant, in 16 parts of cold water, and in a less quantity of a solution of an ammonium salt, or of acids. THE CARBONATE is produced by the action of the carbonates of potassium or ammonium on solutions of yttrium salts; it is also formed by exposure of the hydrate to the air. It is a white powder, occasionally crystalline. Its composition is Y2 CO2+3aq.

The Oxalate is produced by the action of oxalic acid or oxalate of ammonium. It is a white powder. Its composition is Y2 C2O4+3aq. The three salts (those of yttrium, erbium, and terbium) of which this precipitate is composed are of different degrees of solubility in acids, the yttrium salt being more soluble than the others: a method of separation has been founded on this fact. It is insoluble in water, also in oxalic and in dilute hydrochloric acid, but is soluble in nitric or concentrated hydrochloric acid. The action of oxalate of potassium on yttrium salts produces the double oxalate of yttrium and potassium YKC2 04.

THE FERROCYANIDE is produced by the addition of ferrocyanide of potassium to any salt of yttrium except the acetate. The precipitate is at first white, changing to a pearl-grey. Its composition is Y, Cfy. It is insoluble in excess of the precipitant, in water, and in acetic acid, but soluble in hydrochloric acid.

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THE PHOSPHATE is formed by the addition of phosphate of sodium to salts of yttrium. It is a white powder. Its formula is probably Y, HPO. It is very slightly soluble in water, but dissolves in hydrochloric or nitric acids: on boiling these solutions the salt Y, PO, is deposited, while this precipitate, by exposure to the air, becomes converted into a mixture of Y, CO, and Y, HPO Y, PO, occurs in nature as the mineral Xenotime.

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The Silicofluoride is insoluble in water, but soluble in hydrochloric acid. The other reagents of the preceding groups produce no characteristic precipitates with solutions of yttrium salts.

The characteristic reactions by means of which the metal yttrium is distinguished, are the absence of colour in the borax bead, and the insolubility of the hydrate in the hydrates of potassium or ammonium, coupled with the great solubility of its double sulphate.

SALTS OF THORINUM.

The salts of thorinum are even rarer than those of yttrium. The mineral Thorite is the chief source of this metal. Its salts are believed to be protosalts: they are white, unless the acid-radical introduces colour. When these salts are heated before the blowpipe, the oxide (Th, O) is generally produced, and remains infusible; it imparts no tinge to the flame, and gives with borax a colourless bead. It yields no characteristic reaction with nitrate of cobalt.

The principal insoluble salts which this metal forms are these,—the hydrate, the sulphate of thorinum and potassium, the carbonate, the oxalate, the ferrocyanide and the phosphate.

THE CYANIDE is soluble.

The Hydrate is formed by the action of the hydrates or sulphides of potassium or ammonium on solutions of thorinum salts. It is a white gelatinous precipitate. Its formula is probably ThHO. It is soluble in excess of the precipitants, and in water. It is readily dissolved when moist by hydrochloric and nitric acids, but with difficulty when dry.

The Double Sulphate of Thorinum and Potassium is most perfectly precipitated by adding a boiling concentrated solution of sulphate of potassium to a solution of sulphate of thorinum. It is a white crystalline powder. The formula of the salt is ThKSO. It dissolves slowly in cold water, but very easily in hot water; it is, however, perfectly insoluble in a cold saturated solution of sulphate of potassium, and is thereby distinguished from the corresponding salt of yttrium. The sulphate of thorinum is insoluble in hot water, but redissolves on cooling; this reaction is not observed with the double sulphate. THE CARBONATE is produced by the action of the carbonates of potassium or ammonium. It is produced also by exposing the hydrate to the air. Its formula is that of a basic carbonate. It is soluble in excess of the precipitant, and in acids with decomposition.

THE OXALATE is precipitated by the addition of oxalic acid. It is a heavy white precipitate. Its formula has not been ascertained. It is insoluble in

water or oxalic acid, and but sparingly soluble in other dilute acids. The oxalate of potassium produces a double salt of potassium and thorinum.

THE FERROCYANIDE is produced by the action of ferrocyanide of potassium, and is precipitated as a heavy white powder. Its composition has not been ascertained. It is insoluble in water, but soluble in acids.

THE PHOSPHATE is produced by the action of phosphate of sodium, and is precipitated in white flakes. Its composition has not been ascertained. It is insoluble in water and in phosphoric acid.

The special reagents of the first and second groups produce no characteristic effects in solutions of thorinum salts. Chromate of potassium produces a yellow precipitate.

The reactions characteristic of thorinum salts are-the absence of colour in the borax bead, the insolubility of the hydrate in the hydrates of potassium or ammonium, and the great insolubility of its double sulphate in a saturated solution of sulphate of potassium.

SALTS OF CERIUM.

The salts of this metal are met with in many minerals; they are nevertheless of rare occurrence. Like yttrium, it is always accompanied by two other metals; these are lanthanium and didymium; and although the salts of the two latter elements have not been examined very minutely, yet sufficient is known about them for us to furnish a slight account of each. The reactions which follow must therefore be understood to be those of cerium, although, from the great similarity in the chemical properties of the three metals, the descriptions of salts of cerium will apply to a considerable extent to the salts of lanthanium and didymium also.

Cerium forms two classes of salts,—the cerous or protosalts (such, for instance, as the protochloride [CeCl], and the protoxide [Ce, O]), and the ceric or sesqui- or per-salts (such, for instance, as the sesquichloride [Ce2 Cl2] and the sesquioxide [(Ce2), O,]): the proto-salts are generally colourless, the others frequently red or yellow. The proto-salts when heated before the blowpipe are converted into sesquioxide, which, if pure, is an infusible powder of a lemon-yellow colour, but if containing didymium, of a brownish red. It does not tinge the flame, nor does it give any reaction with nitrate of cobalt: but with borax on the platinum wire it forms a glass which is orange or dark yellow while hot, and a paler yellow when cold; this is the effect of the oxidizing flame, the colour being of course due to the presence of sesquioxide of cerium. If the bead be subsequently brought into the reducing flame, it is decolorized by reason of the reduction of the sesquioxide into the protoxide.

CEROUS SALTS.

The principal insoluble cerous salts are the hydrate, the double sulphate of cerium and potassium, the carbonate, the oxalate, the ferrocyanide, and the phosphate.

THE CYANIDE is produced by the action of cyanide of potassium. It is a

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