43. Pinate of magnesia. A white powder. When exposed Sect. IX. to a heat of 212° it becomes agglutinated together. It dissolves readily in ether. It is soluble also in alcohol.*

44. Silvate of magnesia. This salt dissolves in absolute alcohol and in alcohol of the specific gravity 0-880. When to one part of this last solution two parts of water are added an alcoate of silvate of magnesia falls down of a tarry consistency. This salt is soluble also in ether, oil of turpentine and naphtha.+

45. Carbazotate of magnesia. Very long but very fine and indistinct needles, of a light yellow colour, very soluble in water and detonating when heated. ‡

46. Urate of magnesia. A white tasteless powder, similar in appearance to uric acid.

47. Aspartate of magnesia. Similar in its properties to aspartate of lime. §

48. Nitrosaccharate of magnesia. A deliquescent salt which does not crystallize, swells much when exposed to heat, and leaves a brown spongy residue like a vegetation. ||

49. Sulphonaphthalate of magnesia. A white salt having a bitterish taste, crystallizing in favourable circumstances, and burning with flame. ¶

SECT. IX. -SALTS OF ALUMINA,

1. Most of the salts of alumina are soluble in water, but Characters. few of them are capable of crystallizing.

2. They are distinguished by a sweet and astringent taste, in which respect they resemble the salts of yttria and glucina. 3. They are not precipitated by oxalate of ammonia nor tartaric acid, which sufficiently distinguishes them from salts of yttria.

4. They are not precipitated by prussiate of potash, nor by tincture of nut-galls, in which respects they differ both from the salts of yttria and glucina.

5. Phosphate of ammonia, when dropped into a salt of alumina, occasions a white precipitate.

6. Hydriodate of potash occasions a white flocky precipitate in a solution of alumina, which speedily becomes yellow and

Class I.

continues permanent. This is not owing to the excess of acid which the salts of alumina usually contain, for the yellow colour does not disappear on the addition of carbonate of ammonia.

7. If sulphuric acid, and then sulphate of potash be added to a salt of alumina, and the mixture be set aside, octahedral crystals of alum speedily make their appearance in it.

8. When nitrate of cobalt is mixed with a mineral containing alumina and the mixture is exposed to the action of the blow-pipe it acquires a fine blue colour, which becomes deeper without losing its colour by an additional quantity of cobalt. The colour is only seen distinctly by daylight and after the assay is cold. This method of proceeding may be followed successfully with most of the salts of alumina.

1. Sulphate of alumina. This salt may be formed by digesting hydrated alumina in dilute sulphuric acid till the acid is completely saturated. A very long continued digestion is necessary for this purpose. When the solution is concentrated in vacuo over sulphuric acid it gradually congeals into a beautiful white, soft, light semitransparent mass, which may be dried on blotting paper, and is not altered by exposure to the atmosphere. It reddens vegetable blues. Its taste is astringent and sour with an impression of sweetness. It is very soluble in water, and the acid and water which it contains may be driven off by heat. Its constituents, by my analysis, are: 1 atom sulphuric acid.

1 atom alumina

7 atoms water

5

2.25

7.875

15.125

2. Trisulphate of alumina. This is a fine white aluminous. looking mineral found in Sussex and near Halle, and distinguished by mineralogists by the name of aluminite. It is tasteless and insoluble in water; but it may be dissolved in acids. Its constituents, as is obvious from the analysis of Stromeyer, are as follows:

3. Subsulphate of alumina. When we precipitate sulphate of alumina by means of ammonia or carbonate of soda, we can

not deprive the alumina, however frequently we wash it, of all Sect. IX. its sulphuric acid. It continues a compound of

1 atom sulphuric acid

30 atoms alumina.

Whether this precipitate be actually a compound of alumina and sulphuric acid in these proportions, or whether it be a mixture of alumina and trisulphate of alumina, we have no means of determining.

4. Sulphite of alumina. This salt was first formed by Berthollet; it has been described by Fourcroy and Vauquelin.

When formed by the usual process it remains in the state of a white powder, and does not crystallize though dissolved in an excess of acid.

It is white and soft, and has an earthy and sulphureous taste. It is insoluble in water. When exposed to the air, it is gradually converted into sulphate. Its solution in sulphurous acid undergoes this change much more rapidly. When heated, its acid is disengaged, and the alumina remains behind, mixed however with a small proportion of sulphate of alumina.

5. Hyposulphite of alumina. Mr. Herschell did not succeed in obtaining this salt. When oxalate of alumina was dropped into hyposulphite of lime no precipitate fell. He assures us that oxalate of alumina occasions no precipitate in muriate or nitrate of lime, any more than in hyposulphite.

6. Hyposulphate of alumina. This salt was obtained by mixing solutions of hyposulphate of barytes and sulphate of alumina. The filtered solution was concentrated in vacuo over sulphuric acid. A white mass was obtained, which, however, when dissolved in water, was copiously precipitated by chloride of barium. It would appear from this, that this salt cannot be brought into a dry state without undergoing decomposition.+

7. Nitrate of alumina. I have not been able to obtain this salt by digesting nitric acid on hydrate of alumina; but it is described by chemists as composed of soft white crystalline plates. Its taste is acid and astringent and it reddens vegetable blues. It dissolves readily in water and alcohol, and deliquesces when exposed to the air. According to Bucholz's analysis, the constituents (abstracting the water). are

Edin. Phil. Jour. i. 21. † Heeren; Poggendorf's Annalen, vii. 180.

But it is doubtful how far we can depend upon the accuracy

of this analysis.

8. Dinitrate of alumina. This salt may be formed by digesting hydrate of alumina in dilute nitric acid till the acid refuses to take up any more. When the solution is concentrated and set aside it concretes into a white solid matter, which may be dried by pressure between folds of blotting paper. Thus prepared it is a white crystalline powder, very soluble in water, and reddening vegetable blues. Its taste is

astringent and sweet, with an impression of acidity. Its constituents, by my analysis, are

9. Trisnitrate of alumina. When the preceding salt is heated on the sand-bath till it loses its liquid form and forms a white dry crust it is converted into trisnitrate. It is nearly insoluble in water, and does not deliquesce when exposed to the air. Its constituents, by my analysis, are

Saussure has shown that water

10. Carbonate of alumina. saturated with carbonic acid is capable of dissolving alumina: but this combination is destroyed by simple exposure to the air. Carbonate of alumina, then, cannot exist in a dry state. What had been considered formerly as a dry carbonate is a triple compound of alumina, carbonic acid, and the alkali employed in precipitating the alumina.

11. Phosphate of alumina. This salt may be obtained by mixing solutions of alum and phosphate of soda in the atomic proportions. No precipitate appears at first; but if the mix

* Jour. de Phys. lii. 28.

ture be heated, a white powder falls, which is the phosphate Sect. IX. of alumina. It is tasteless and insoluble in water; but reddens

12. Biphosphate of alumina. When the preceding salt is dissolved in phosphoric acid, and the solution concentrated, a gummy mass is obtained, which may be fused into a transparent bead, and which is probably a biphosphate.

13. Diphosphate of alumina. The mineral called wavellite, appears, from the analysis of Fuchs and Berzelius, to be a hydrated diphosphate of alumina, composed of

14. Phosphite of alumina. This salt does not crystallize, but forms a gelatinous mass, which, when heated, gives out phosphuretted hydrogen gas, and is converted into phosphate of alumina.

15. Arseniate of alumina. This salt may be obtained by mixing together solutions of alum and arseniate of soda in the atomic proportions. It is a white, tasteless, insoluble powder, not unlike phosphate of lime; but strongly reddening vegetable blues. Its constituents are

16. Binarseniate of alumina. It may be obtained by dissolving the preceding salt in arsenic acid, and concentrating the solution sufficiently. It dissolves in water, and does not crystallize.

17. Borate of alumina. When solutions of alum and borax are mixed, the liquid deposites white, pearly plates, very soft, and scarcely soluble in water. This salt has not been analyzed. Analogy would lead us to consider it as a biborate.

18. Silicate of alumina. No fewer than nine different