Lecture Xxvi.

Of Tin.

Tin is a metal of a slightly yellowish cast, though harder than lead, very malleable, but of no great tenacity; so that wires cannot be made of it. It easily extends under the hammer, and plates of it, called tinfoil, are made only one thousandth part of an inch thick, and might be made as thin again.

Tin has less specific gravity than any other metal. It melts long before ignition, at 410 of Fahrenheit, and by the continuance of heat is slowly converted into a white powder, which is the chief ingredient in putty, used in polishing, &c. Like lead, it is brittle when heated little short of fusion, and may be reduced into grains by agitation as it passes from a fluid to a solid state.

The calx of tin resists fusion more than that of any other metal, which makes it useful in making an opaque white enamel.

Tin loses its bright surface when exposed to the air, but is not properly subject to rust; so that it is useful in protecting iron and other metals from the effects of the atmosphere.

Concentrated vitriolic acid, assisted by heat, dissolves half its weight of tin, and yields vitriolic acid air. With more water it yields inflammable air. During the solution the phlogiston of the tin uniting with the acid, forms sulphur, which makes it turbid. By long standing, or the addition of water, the calx of tin is precipitated from the solution. The nitrous acid dissolves tin very rapidly without heat, and yields but little nitrous air. With marine acid this metal yields inflammable air. With aqua regia it assumes the form of a gelatinous substance used by dyers to heighten the colour of some red tinctures, so as to produce a bright scarlet in dying wool.

A transparent liquor, which emits very copious fumes, called, from the inventor, the smoking liquor of Libavius, is made by distilling equal parts of amalgam of tin and mercury with corrosive sublimate, triturated together. A colourless liquor comes over first, and then a thick white fume, which condenses into the transparent liquor above mentioned. Mr. Adet has shewn, that this liquor bears the same relation to the common solution of tin, that corrosive sublimate does to calomel, and has given an ingenious solution of many of its properties.

Tin detonates with nitre; and if the crystals made by the solution of copper in the nitrous acid be inclosed in tinfoil, nitrous fumes will be emitted, and the whole will become red hot. Also if five times its weight of sulphur be added to melted tin, a black brittle compound, which readily takes fire, will be formed.

Another combination of tin, sulphur, and mercury, makes a light yellow substance called aurum musivum used in painting.

Tin is the principal ingredient in the composition of pewter, the other ingredients being lead, zinc, bismuth, and copper; each pewterer having his peculiar receipt. It is also used in coating copper and iron plates, and in silvering looking-glasses, besides being cast into a variety of forms, when it is called block tin.

Tin is sometimes found native, but is generally mineralized with sulphur and arsenic. The latter is thought to be always contained in tin, and to be the cause of the crackling noise made by bending plates of it.

Of the Semi-metals.

Bismuth is a semi-metal of a yellowish or reddish cast, but little subject to change in the air; harder than lead, but easily broken, and reducible to powder. When broken it exhibits large shining facets, in a variety of positions. Thin pieces of it are considerably sonorous.

Bismuth melts at about 460 deg. of Fahrenheit. With more heat it ignites, and burns with a slight blue flame, while a yellowish calx, called flowers of bismuth, is produced. With more heat it becomes a greenish glass. In a strong heat, and in close vessels, this metal sublimes.

Vitriolic acid, even concentrated and boiling, has but little effect upon bismuth; but the nitrous acid acts upon it with the greatest rapidity and violence, producing much nitrous air, mixed with phlogisticated nitrous vapour. From the solution of bismuth in this acid, a white substance, called magistery of bismuth, is precipitated by the affusion of water. This has been used as a paint for the skin but has been thought to injure it.

The marine acid does not readily act upon bismuth; but when concentrated, it forms with it a saline combination, which does not easily crystallize, but may be sublimed in the form of a soft fusible salt, called butter of bismuth.

Bismuth unites with most metallic substances, and in general renders them more fusible. When calcined with the imperfect metals, it unites with them, and has the same effect as lead in cupellation.

Bismuth is used in the composition of pewter, in printers' types, and other metallic mixtures.

This metal is sometimes found native, but more commonly mineralized with sulphur.