A very singular metal is formed by melting together eight parts of bismuth, five of lead, and three of tin. Tea-spoons formed of this metal surprise all who are unacquainted with their nature: they have somewhat the appearance of common spoons, but they melt as soon as they are put into boiling water.
Bismuth reduced to powder, mixed with the white of eggs and applied to wood, gives it, when gradually dried and rubbed with a polisher, the appearance of being silvered. If this metal be dissolved in aquafortis ([30]), and water be poured into the solution, a white powder precipitates, which is an oxide of bismuth, and which, after being well washed, is used as a pigment, under the name of pearl-white. From its beautiful appearance, this powder is sometimes employed by ladies for painting their skin; a practice which cannot be too much condemned, both on account of the danger with which it is attended, and from its soon injuring both the texture and natural colour of the skin. It has the further disadvantage of turning black when touched by the fumes of fetid and other substances; and ladies, who have used this cosmetic, and have afterwards bathed in the Harrowgate waters, have come from the bath a perfectly tawny colour. It was probably the oxide of bismuth which the Roman ladies used for whitening their skin; for Martial, in speaking of a lady, who made too free an use of cosmetics, describes her as afraid even of the sun. The oxide of bismuth is used in the composition of most of the pomades employed in France for painting the face.
A preparation of bismuth has lately been employed in medicine, as a remedy against spasmodic affections of the stomach.
The following is a pleasing experiment, illustrative of metallic crystallization. Melt a ladleful of bismuth, and allow it to cool slowly and quietly till a thin crust is formed on the surface: then, with a pointed iron, make two small opposite apertures through the crust: and, through one of these, quickly pour out the fluid portion, as carefully and with as little motion of the mass as possible. The air having entered by the other aperture, there will appear, on removing the upper crust by means of a chisel, when the vessel has become cold, a cup-shaped concavity, studded with very brilliant crystals, and more or less regular according to the quantity of metal employed, the tranquillity and slowness with which it has cooled, and the dexterity with which the fluid portion of the mass was poured off before it became solid. The same effect may be produced by melting bismuth in a crucible which has a hole in the bottom, lightly closed by an iron rod or stopper; this is to be drawn out when the mass begins to congeal. By so doing, the upper portion, which is fluid, is made to run off, and a cake studded with crystals will be left.
247. COBALT is a semi-metal of grey colour with a shade of red, brittle, somewhat harder than silver, nearly eight times as heavy as water, is attracted by the magnet, and is itself capable of being rendered permanently magnetical.
The ores of cobalt are not numerous, and are, for the most part, combinations of this substance with other metals, or of its oxides ([24]) with arsenic, or with sulphuric acid ([21]).
The name of this metal implies an evil being, (Kobold, German, goblin) and is said to have been given on account of the vapour of arsenic, which issues from it, tormenting the miners, and making them believe that they are afflicted by wicked spirits. Hence it was once customary in Germany to introduce into the church service a prayer that God would preserve miners and their works from cobalts and spirits.
Cobalt is found in several parts of Europe, but most plentifully in the southern borders of France, and in Saxony; and the cobalt ores of Hesse, although they were formerly used for no other purpose than the mending of roads, are said now to yield a clear profit of nearly 15,000l. a year. Some parts of our own country yield this substance in considerable abundance, particularly the Mendip Hills in Somersetshire, and a mine near Penzance in Cornwall.
After the ore is taken from the earth, it is broken into pieces about the size of a hen’s egg, and the stony parts are picked out. The sorted mineral is then pounded in mills, and sifted through brass-wire sieves. The lighter particles are next carried off by water. After undergoing some other preparations, to rid it of the impurities and foreign matters with which it is connected, it appears in the form of a dark grey oxide. The working of the cobalt ores in Germany is considered so injurious, on account of the arsenic with which they are combined, that much of the labour is performed by criminals who are condemned to it for the commission of crimes which, by the laws of the country, have deserved the punishment of death.
As a metal, cobalt was unknown till the year 1733, when it was discovered by a celebrated Swedish chemist whose name was Brant. In its metallic state it is not employed in the useful arts; but in a state of oxide it is found extremely valuable in the colouring of porcelain, in painting, enamelling, and for other purposes. Cobalt and ultramarine form the most permanent blue colours with which we are acquainted. The old painters generally used them for the representation of the sky and of blue drapery, and this is the reason why these parts in some old pictures have been found so much more durable than any others.