Litharge is another kind of oxide of lead. This is prepared by exposing calcined lead to a brisk fire for a certain length of time. The substance, on cooling, concretes into a flaky matter. Litharge is used by potters for the glazing of earthenware, but vessels that are glazed with it are thereby rendered unwholesome. It is also employed, in the composition of the finer kinds of glass, for the purpose, not only of giving them greater transparency, but also of rendering them capable of sustaining sudden changes from heat to cold, and of giving to them a susceptibility of being cut without breaking. It, however, adds considerably to the weight of the glass.
Litharge Plaster, or Diachylon Plaster, as it is more frequently called, is prepared by boiling two pints of olive oil with one pint of litharge, adding water, and constantly stirring the mixture till they are duly incorporated. This plaster is applied in excoriations of the skin, slight wounds, and other sores.
Sugar of Lead is a preparation either from the metal itself, or from white lead and distilled vinegar. It is usually observed in the form of small slender crystals, which have a glossy appearance like satin. This substance is employed, in considerable quantity, by dyers and calico printers; and is the basis of a liquid frequently used in medicine, called Goulard, or Goulard’s Extract. Although in itself a most virulent poison, it is often used by unprincipled dealers for correcting the rancidity of oil of almonds and olive oil; and a similar pernicious fraud is practised by dissolving a portion of it in wines which are becoming acid, in order to correct their acidity. These frauds, however, are easily detected by preparations or tests, which are sold by chemists for that purpose. Perhaps the best and simplest test is Harrowgate water: a little of this poured into the suspected compound will discover the presence of lead by giving to the fluid a dark brown or blackish tinge.
The following is a pleasing experiment. Dissolve an ounce of sugar of lead in about a quart of water; filter the solution through a piece of blotting paper, and put it into a glass decanter, suspending in it a piece of zinc by a brass wire. A decomposition will take place; the lead will be set at liberty, and will attach itself to the zinc, forming there a sort of metallic tree.
It has been stated that silver is usually a component part of lead ore. To disengage this, where the quantity is sufficient to repay the expense, the lead, after it has been smelted, is subjected to the action of what is called a refining furnace. A continued blast of fresh air is thrown upon its surface by means of large bellows, while the lead is kept in a state as intensely hot as possible. This by degrees converts the lead into a yellow scaly oxide or dross. The oxide, thus formed, is driven off from the melted metal as it rises, and the silver is left alone at the bottom, in a metallic state. After the operation is complete, the oxide is fused with charcoal, and again reduced to metallic lead.
We must not omit to mention that, in some of the mines of Derbyshire, there is a singular variety of lead ore called slickenside. This is a kind of galena, which presents, to the eye, a smooth and bright surface, appearing as if it were plated. Sometimes it forms the sides of cavities; and it has the extraordinary property, when merely pierced with the miner’s tool, of rending with great violence, and exploding with a crackling noise. Some miners, fearless of danger, venture to scratch it with their tools; and, on coming again to the spot, they often find that, during their absence, the slickenside has exploded, and fallen off in considerable quantity. Sometimes, however, they suffer for their imprudence. Mr. Mawe, in his account of the Mineralogy of Derbyshire, says, that he has seen a man come out of a mine cut violently, as if he had been stabbed about the neck and in other parts of the body, in consequence of the explosion of slickenside which he had pierced. The cause of this extraordinary phenomenon has not been explained.
240. NICKEL, when pure, is a fine white metal, somewhat resembling silver in appearance, but it is attracted by the magnet, and has itself the property of attracting iron.
It is ductile and malleable, difficult of fusion, and about nine times heavier than water. This metal is always mixed with arsenic ([242]) and iron.