XLVII. GLUCINUM.

This metal is derived from the earth glucina, which is an oxide of the metal. This oxide has only been found in a few rare minerals, of which the principal are the emerald and the chryso-beryl. The metallic base is best derived from the metal brought to the state of chloride, and the process for obtaining it is precisely that used for obtaining aluminum. Small pieces of potassium are put into a crucible of porcelain or platinum, and over this an equal bulk of chloride of glucinum. The lid of the crucible being fixed down, a spirit lamp is applied, when decomposition takes place, the crucible becoming red hot. The mass in the crucible is suffered to cool, and then immersed in water, by which means the chloride of potassium is dissolved, and the metal obtained, by filtration, in the state of a dark rubycoloured powder.

Thus glucinum is obtained by the same process, and presents the same external characters, on being reduced, as aluminum. When the scaly matter is burnished, it acquires metallic lustre. Although, having a powerful affinity for oxygen, it may be exposed to air or moisture, or be even boiled in water without being oxidated. When strongly heated in the open air it takes fire, and burns with a vivid flame, and when the combustion takes place in oxygen gas, the splendour of the light is very great. The product in either case is the earthy oxide, which is not at all fused by the intensity of the heat evolved.

Glucinum combines with oxygen, chlorine, and other bodies, in the manner of aluminum, and forms alloys with several of the metals. Its combining weight has been estimated by some at 26.54, by others at 17.7.

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XLVIII. MAGNESIUM.

Magnesium is derived from the oxide. The metal being brought to the state of chloride, is acted upon by potassium, which combining with chlorine, leaves the magnesium free, in the same manner as in the process for obtaining aluminum. The metal had been before obtained by Davy, by means of voltaic action, in one of that series of brilliant experiments which proved so many bodies to be compound, which for ages had been deemed simple. It was first obtained by means of heat and chemical affinities alone by M. Bussey, in the year 1830. Five or six pieces of potassium of the size of peas were put into a glass tube, closed at one end, and bent so as to form a little retort. Upon the pieces of potassium were laid fragments of chloride of magnesium, and these being heated to near the point of fusion, a lamp was likewise applied to the potassium, and its vapour transmitted through the heated chloride. Vivid incandescence took place, and on dissolving the mass, after being cooled in water, the chloride of potassium, with any remaining portion of chloride of magnesium, was dissolved, the pure magnesium subsiding.

This substance possesses a bright metallic lustre, and resembles silver. It is malleable, and fuses at a red heat. In moist air it oxidizes superficially, but undergoes no change in air which is dry, and may be even boiled in water without being oxidated. When strongly heated in air it burns brilliantly, and yields magnesia, and in chlorine gas, it takes fire spontaneously.

Its specific gravity has not been ascertained, but it is heavier than water, sinking quickly in that liquid. Its combining weight was estimated by Berzelius at 12.69.

No subsequent experiments have either proved or disproved the conclusion of the illustrious Swede, yet I cannot but believe that the combining weight of magnesia must exceed 15, so that it may comprehend all the elements which are assumed to enter into the combination of the nearly allied metal calcium.

Of the compounds of magnesia, one, the oxide, enters into the composition of the larger earthly deposites of the globe, and of numerous mineral species, as the precious serpentine, the chrysolite, epsom salt, meerschaum, amianthus, &c. In its separate state, it is an earthy white powder, destitute of taste and smell. It possesses the alkaline property of combining with acids, and producing neutral salts, but it has less action on vegetable colours than the other alkalies, arising, it may be believed, in part from its greater insolubility. It is exceedingly difficult of fusion, having only yet yielded to the flame of the oxyhydrogen blow-pipe, by the action of which it is converted into a white enamel. It is very sparingly soluble in water, and, like lime, is more soluble in cold water than in hot. It seems to be intermediate in its characters between the oxides of alumina and lime, and it has some relations with silica, with which it enters into combination, and with which it is widely associated in the natural state.

XLIX. CALCIUM.

Lime, so largely diffused over the mineral kingdom, was, like the other substances, termed earth, shewn, by the admirable researches of Davy, to be a metal, to which he applied the term calcium. He obtained it by forming the carbonate of the oxide into a paste with water, which he placed upon a disc of platinum, connected with the positive pole of a galvanic battery, while, in the hollow of the paste, he placed a globule of mercury connected with the negative pole. The oxygen of the oxide appeared at the positive pole, while the calcium appeared at the negative, and formed an alloy or amalgam with the mercury; and this being exposed to heat, in the vapour of naphtha, the mercury was volatilized, and the calcium left behind. This method was subsequently improved, but still the quantity of metal obtained has been very small.

Calcium evidently possesses the general characters of the class of metals to which it belongs. It is white, like silver, and highly combustible. When exposed to the air, it attracts oxygen so strongly, that, in a few minutes, it is converted into the oxide, and, when heated, it burns, and lime is in like manner produced. Its combining weight is calculated by Berzelius at 20.52, by Dr Thomson at 20.

It combines with oxygen in two proportions. The protoxide has so great an affinity for acids, that it exists native only in combination with them. Of these salts greatly the most extended is the carbonate, which exists throughout the organic and inorganic kingdoms, forming, in the latter, vast mineral deposites, and entering into all the great series of rock formations. The oxide itself is a white powder, similar in external characters to the corresponding oxides of

the metallic bases of the earths and alkalies. It has an acrid taste, and the characters termed alkaline, in changing vegetable blues to green, and then to yellow. It is amongst the least fusible of known bodies, yielding only, if it yields at all, to the most powerful heat of the oxyhydrogen blowpipe, when it melts into a white enamel. When heated to redness, it becomes vividly phosphorescent. It has a great affinity for water, combining with it in a definite proportion. But it is very sparingly soluble in that liquid, and more soluble in cold water than in hot. It may be regarded as intermediate in its characters between magnesia and the alkalies, and seems to have certain relations with silica, with which it is everywhere associated in the mineral kingdom.