larger portion, and deposits it again on cooling. The crystals effloresce in the air, and are slowly changed into sulphate.

Hypo-sulphite of magnesia may be obtained by boiling a solution of sulphite of magnesia with flowers of sulphur. The salt crystallizes when the solution has cooled. It is intensely bitter, and readily soluble in water, but is not deliquescent. When heated, it burns with a blue flame, and, by a sufficient continuance of the heat, the whole of the acid is expelled, and magnesia remains.

Sulphate of Magnesia.

When highly concentrated sulphuric acid is suddenly added to fresh prepared and pure magnesia, very great heat and vapour are excited, and are accompanied frequently with an extrication of light; an appearance first observed by Westrumb. But if the carbonate of magnesia be added to diluted sulphuric acid, the carbonic acid is expelled, and a solution of sulphate of magnesia is formed, which crystallizes on evapora. tion and cooling. Crystals of sulphate of magnesia may also be procured in the shops, under the name of Epsom salt. These crystals have the following properties:

1. They have the form of small quadrangular prisms, surt mounted by quadrangular pyramids with dihedral summits They undergo no change by exposure to the atmosphere.

2. At the temperature of 60°, this salt is soluble in an equal weight of cold water, and in three-fourths its weight of boiling water, which thus receives an addition of one-fourth of its bulk.

3. When exposed to a low red-heat, it undergoes the watery fusion, but is not volatilized. It loses, however, rather more than one-half its weight, which is water of crystallization, and, according to Berzelius, a very minute portion of acid

escapes.

The crystallized salt is composed* of

Dry sulphate of magnesia.... 48.57
Water

60

51.43

63

or

100.00

123

• Gay Lussac, Ann. de Ch. et Phys. xiii. 308.

or of 1 atom of anhydrous salt, and 7 atoms of water. The dry salt is constituted of

4. Its solution is precipitated by carbonates of potassa and of soda; but not by carbonate of ammonia, unless heat is applied. The carbonate of magnesia of the shops is prepared by mixing together concentrated and hot solutions of carbonate of potassa and sulphate of magnesia. The sulphate of potassa, thus formed, is removed by copious washing with water, and the carbonate of magnesia is then dried. The proportions employed are filtered solutions of 4 parts of the crystallized sulphate, and 3 of the carbonate of potassa. One hundred parts of the desiccated sulphate give about 71 of carbonate of magnesia, or about 33 of the pure earth.

When solution of pure ammonia is added to that of sulphate of magnesia, part of the earth is precipitated. The rest rcmains in solution, and, by evaporation, a triple salt is formed, consisting of sulphuric acid, magnesia, and ammonia, and called ammoniaco-magnesian sulphate.

A compound Sulphate of Magnesia and Soda has been described by Dr. Murray, in a note to his paper on the Analysis of Sea Water. It crystallizes in rhombs truncated on the angles and edges; is soluble in rather more than three times its weight of water at 60° Fahrenheit; is permanent in the air; and does not fuse, but decrepitates on applying heat. It is composed of

• Edinb. Trans.

Sulphate of potassa and magnesia was composed by Link by saturating bi-sulphate of potassa with magnesia. The taste of this triple salt is bitter; in solubility it nearly agrees with sulphate of potassa; its crystals are rhomboidal, and consist of about 3 parts sulphate of potassa, and 4 sulphate of magnesia It has been found by Dr. Marcet to be an ingredient of sea water. (Phil. Trans. 1822, p. 455.)

Seleniate of Magnesia.-Selenic acid unites with magnesia in two proportions, forming a seleniate and a bi-seleniate, but the compounds have no particularly interesting properties.

SECTION VIII.

Glucinum.

We have no experimental knowledge of the base of glucina. When obtained, its proper denomination will be glucinum, The general fact of its existence is proved by igniting glucina with potassium, which is thus changed into potássa.

Glucina.

This earth was discovered by Vauquelin, in the year 1798. He obtained it from the aqua marina or beryl, a precious stone of a green colour, and very considerable hardness, which is found crystallized in Siberia. Glucina has since been detected in the emerald of Peru, and in the gadolinite. The following process may be employed to separate it from the beryl:

Let the stone, reduced to a fine powder, be fused with three times its weight of pure potassa. To the fused mass add a quantity of water, and afterwards diluted muriatic acid; which last will effect a complete solution. Evaporate the solution to dryness, re-dissolve the dry mass, and add carbo

nate of potassa so long as any precipitation ensues. Dissolve the precipitate in sulphuric acid; add a little sulphate of potassa; and, on evaporation, crystals of alum will be obtained. By this process the alumina is detached. The residuary liquor, which yields no more crystals, contains the glucina, and a small portion of alumina. Add a solution of carbonate of ammonia to excess; this will throw down the alumina, and the glucina will remain dissolved by the superabundant carbonate. When this solution is evaporated to dryness, and moderately heated, the alkaline carbonate is expelled, and a carbonate of glucina remains, in the proportion of 16 parts from every 100 parts of the stone.

Glucina has the following properties :

1. It is a fine white and soft powder, resembling alumina in its sensible properties; and, like that earth, adhering to the tongue. Its specific gravity is 2.97.

2. It has no action on blue vegetable colours.

3. It does not harden, or contract, like alumina, by heat; and is infusible.

4. It is insoluble in water, but forms with it a ductile paste. 5. It is soluble in liquid potassa and soda, but not in the solution of pure ammonia. In these respects it agrees with alumina.

6. Glucina is soluble in carbonate of ammonia; a property distinguishing it from alumina.

7. It appears, like alumina, to have an affinity for colouring

matter.

8. With the different acids it forms combinations, which have a sweet and rather astringent taste. Hence its name has been derived from yλuxus, signifying sweet.

9. It is not precipitated by triple prussiate of potassa.

SECTION IX.
Yttrium.

THE base of yttria has not yet been exhibited in a separate form; but the presence of oxygen in yttria is established by

its converting potassium into potassa, when ignited with that metal.

Yttria, or Itria.

This earth was discovered in 1794, by Professor Gadolin, in a stone from Ytterby in Sweden; and its title to the character of a peculiar earth rests, also, on the unquestionable authority of Klaproth and Vauquelin, both of whom have made it the subject of experiment. The following process for obtaining it, is described by Vauquelin in the 36th volume of the Annales de Chimie, p. 150.

Fuse the pulverized stone (called Gadolinite) in the manner already described, with twice its weight of potassa; wash the mass with boiling distilled water, and filter. The filtered solution, which has a beautiful green colour, yields, during evaporation, a black precipitate of oxide of manganese. When this has ceased to appear, allow the liquor to stand; decant the clear part, and saturate with nitric acid. Let the insoluble part be, also, digested with extremely dilute nitric acid, which will take up the soluble earths only, and will leave, undissolved, the silica and oxide of iron. Let the two portions be mingled together, and evaporated to dryness; then re-dissolved and filtered; by which means any remains of silica and oxide of iron are separated. To obtain the yttria from the nitric solution, it would be sufficient, if no other earth were present, to precipitate it by carbonate of ammonia; but small portions of lime, and of oxide of manganese, are still present along with it. The first is separated by a few drops of carbonate of potassa; and the manganese, by the cautious addition of hydro-sulphuret of potassa. The yttria is then to be precipitated by pure ammonia, washed abundantly with water, and dried. It amounts to about 35 per cent. of the stone.

Yttria has the following properties :

1. It is perfectly white; but it is difficult to preserve it free from a slight tinge of colour, owing to its contamination with oxide of manganese.

2. It has neither taste nor smell; and it is smooth to the touch, like alumina.