Page:Collier's New Encyclopedia v. 09.djvu/470

LEFT TIN 408 TINDAL the remaining gangue. The chai'ge is placed on the hearth of a low-crowned reverberatory furnace, and the doors are closed up. Heat is applied very gradu- ally for five or six hours, care being taken to raise the temperature high enough to cause the carbon to reduce the tin without melting the siliceous gangue, which would form with the binoxide an enamel troublesome to remove. When nearly all the tin is reduced, the heat is raised considerably, the slags beiiig thus rendered fluid and capable of floating on the top of the melted metal. The tin is then run off into cast iron pans, from which it is ladled off into molds to form ingots. The tin thus procured is far from being pure; it is therefore submit- ted to the process of lignation, which consists in heating the ingots to incipient fusion. By this means the purer tin which fuses at a comparatively low heat separates, running down, and leaving the impure portions behind. The less fusible portion, when remelted, forms block tin and the part which has run out is again melted and agitated with wet stakes. The steam thus formed bubbles up to the surface, carrying with it all other mechanical impurities contained in the tin. The mass is then skimmed and al- lowed to cool. When just about to set, the upper half is ladled out, the other metals and impurities having sunk into the bottom half, from the tendency that this metal has to separate from its al- loys. The finest quality of tin is fre- quently heated to a temperature just short of its melting point. At this heat it becomes brittle, and is broken up into masses, showing the crystals of the metal, and forming what is known as grain tin. The formation of crystals is to some ex- tent a guarantee of its purity, since im- pure tin does not become brittle in this way. English tin generally contains small quantities of arsenic, copper, iron and lead. Chlorides of Tin. — There are two chlo- rides of tin, the protochloride and the per or bichloride. The protochloride, SnCl, may be prepared in the anhydrous state by the action of dry hydrochloric acid on tin at a gentle heat. The hydrat- ed chloride is obtained by dissolving the metal in hydrochloric acid diluted with an equal bulk of water. It crystallizes in transparent needles, containing two equivalents of water. It is a powerful reducing agent, and is much used by dyers for altering reducible coloring matters, such as sesquioxide of iron and peroxide of manganese. It is also used as an antichlore. It forms crystallizable double salts with the alkaline chlorides. The bichloride, perchloride, or fuming liquor of Libavius, SnCU, is made by passing chlorine over an inclined tube^ fitted to a receiver, and containing pieces of tin-foil rolled up. It is used to a con- siderable extent in solution in dyeing. It absorbs sulphuretted and phosphuretted hydrogen, and forms a compound of am- monia. In some respects it plays the part of an acid — chlorostannic acid. Oxides of Tin. — There are two oxides of tin — ^the protoxide and the binoxide. The protoxide is prepared in a variety of ways, too prolix for description here, and is only interesting in a chemical point of view. When heated in air, it burns like tinder, and is converted into the binoxide. The only ore of tin, tin-stone, is a form of the binoxide. Sulphides of Tin. — There are two sul- phides of tin — the protosulphide, formed by fusing together metallic tin and sulphur. The bisulphide, when prepared in the dry way, is known by the name of "aurum musivum," or mosaic gold, and is used as bronze powder in coarse dec- orative works. It is prepared by fusing together seven parts of flowers of sulphur and six of salammoniac with an amalgam of 12 parts of tin and 6 of mer- cury. TINCTURE, in chemistry, the finer and more volatile parts of a substance, separated by a menstruum; an extract of a part of the substance of a body communicated to the menstruum. In her- aldry, the name given to the colors, met- als, or tints used for the field or ground of an emblazoned shield, including the two metals or and argent, or gold and silver, the several colors, and the furs. In pharmacy, a coloi'ed solution of some animal or vegetable principle. Tinctures are very numerous, commencing with the tincture of aconite and the tincture of aloes. Different menstrua are employed ; chiefly rectified spirit, proof spirit, com- pound spirit of ammonia, and spirit of ether. TINDAL, MATTHEW, an English deist; born in Devonshire, England, in 1653; studied at Lincoln and Exeter Col- leges, Oxford; graduated B.A. in 1676; and was elected Fellow of All Souls in 1678. In opinions he was first High Church, then Roman Catholic (1685); next Low Church, and finally Rationalist. His chief work, "Christianity as Old as the Creation, or the Gospel a Republica* tion of the Religion of Nature," was pub- lished anonymously in 1730. The argu- ment of the book is that Christianity, as far as it is true, must be the religion of nature ; for as God is unchangeable, so is human nature. He attacks many of the statements in Scripture, especially those