Tin
in chemistry, a white, metallic, easily fusible metal, not much affected by exposure to dry or moist air at ordinary temperatures, but becoming oxidized superficially when heated, burning with a brilliant flame if the temperature be raised sufficiently high. It dissolves in hydrochloric acid, with the evolution of hydrogen, forming hydrated chloride of tin. Strong nitric acid acts on it violently, producing an insoluble hydrated binoxide of the metal, a considerable amount of ammonia being formed at the same time by the decomposition of the water and nitric acid present. Cold dilute sulphuric acid has no action on it, but if the concentrated acid be used the metal is converted into the sulphate, while sulphurous acid escapes. Hot dilute sulphuric acid also converts it into sulphate of tin, hydrogen being evolved. The tin which is imported from Banca is nearly pure; that made in England generally contains small quantities of arsenic, copper, iron, and lead. In its chemical characteristics, tin has but few alliances. In some of its properties, however, it seems related to tantalum and titanium.
Its chemical combinations are numerous TIN and important, and its resistance to oxidation and to the action of vegetable acid renders it extremely useful for domestic purposes. Symbol Sn. Prof. Forrest Shepherd, of Missouri, advanced an assertion that tin is not a simple, but a compound metal. His opinion, nevertheless, so far as we know, is not the result of analyses, but of speculation and inconclusive analogies. In metallurgy, tin is a white metal, with a slight yellowish tinge, and a brilliant metallic luster. It is wanting in tenacity, but is extremely malleable at a temperature of 212°. It has a great tendency to crystallize, and its crystalline form may be easily shown by rubbing a piece with a little nitric or hydrochloric acid, when it assumes the appearance known as moiré métallique. By slow cooling it may be procured in octohedral crystals, and on bending a piece of tin backward and forward, a peculiar crackling or grating sound is heard, from the friction of the internal crystals. It fuses at 442° F. F., but it is not sensibly volatilized at that or any higher temperature. If it is stirred while melted till it cools, it may be obtained in a state of powder. Its brilliancy and power of resisting atmospheric changes render it exceedingly useful in the arts as a covering for other metals. What is ordinarily called tin in domestic language, is sheet-iron covered with a layer of tin, a process which is explained further on. Copper is also very well fitted for being coated with this metal. In India, it is applied instead of steel and iron to articles by way of ornament, and there is no reason why our artisans should not take pattern from their more artistic Eastern brethren.
For the manufacture of tin plates, the best soft charcoal iron is obliged to be is obliged used. After it has been rolled and cut to the requisite size, its surface is made chemically clean by immersion for a few minutes in dilute sulphuric acid. The sheets are then heated to a red heat in a reverberatory furnace, withdrawn, allowed to cool, hammered flat, and passed between polished rollers, and then washed in dilute acid. This preparation is needed to free the surface of the iron from the slightest portion of oxide, to which the tin would not adhere. In order to tin them, they are plunged one by one into a vessel of tallow, from which they are transferred to a bath of tin. From this they are taken after a certain time, allowed to drain, and dipped again. The dipped again. superfluous tin at the edge of the plate is removed by dipping it in the melted tin once more, and detaching it by giving the plate a sharp blow. The tin and iron form perfect alloy with each other.
TIN The appearance known as moiré métallique is given by sponging the surface of the tin with dilute nitro-hydrochloric acid, washed with water, and afterward varnished with plain or colored varnish.
Copper is tinned in the same way, but with greater ease, it being so much less difficult to clean the surface of that metal than iron. Tinfoil is made by beating pure tin to the requisite thinness. The alloys of tin are numerous and important principal of these are Britannia metal, consisting of equal parts of brass, tin, antimony, and bismuth; pewter, 4 tin, and 1 lead; Queen's metal, 9 tin, and 1 each of antimony, bismuth, and lead; the various solders; bell-metal, 78 copper, 22 tin; bronze, copper, with 4 to 6 per cent. of tin; gun metal, 78 copper and 22 tin; and several others. Speculum metal, used for the mirrors of reflecting telescopes, is a steel-white, hard, brittle alloy, of 1 part of tin and 2 of cop 1 part of tin and 2 of copper. An amal- gam of tin and mercury is used for silmercury is used for silvering looking glasses. A sheet of tinfoil is laid on an edged slab of stone ayer 1½ inch thick. carefully levelled, and mercury is poured on it till it forms a layer 1/8 inch thick. mercury is poured on it till it forms a layer Glass is laid down on this, and the table is tilted to let the superfluous mercury run off, weights being gradually placed on the glass to facilitate the operation.
Tin ores are met with but in few localities. copper. An amal- Cornwall, Banca, Mexico, and some parts of Australia, are the only important tin yielding districts. The most celebrated tin mines are those of Cornwall, England, which have been worked uninterruptedly from the earliest historic periods. In the United States, crystals of the oxide of tin have been found in localities of Massachusetts, New Hampshire, New York, New Jersey, Virginia, , New California, Missouri, and perhaps in other States. Some of the mines, as Some of the those of Missouri and California, seem promising. Our product in 1916 was 140 short tons, most of which came from Alaska. In 1919, the world produced 125,760 125,76 metric tons of tin, of which the United States imported about 50 per cent .
The only ore of importance is tin stone, a hard dark-brown crystalline body consisting of the binoxide in a crystalline condition. To extract the metal, the ore is first stamped and washed, to get rid of the lighter particles of sand or earth adhering to it. It is then roasted, to free it from arsenic and sulphur, and again washed to carry off the sulphate to carry of copper and oxide of iron. The washed ore is mixed with from one-fifth to oneeighth its weight of powdered anthracite or charcoal, and with a small portion of lime to form a fusible slag with any of TIN the remaining gangue. The charge is placed on the hearth of a low-crowned reverberatory furnace, and the doors are closed up. Heat is applied very gradually 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 being 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 submitted 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 allowed to cool. When just about to set, metals and impurities having sunk into the bottom half, from the tendency that this metal has to separate from its althe upper half is ladled out, the other loys. The finest quality of tin is frequently 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 extent a guarantee of its purity, since impure tin does not become brittle in this English tin generally contains way. small quantities of arsenic, copper, iron and lead.
Chlorides of Tin. - There are two chlorides 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 hydrated 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 TINDAL liquor of Libavius, SnCl2, 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 considerable extent in solution in dyeing. It absorbs sulphuretted and phosphuretted hydrogen, and forms a compound of ammonia. 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 sulphides of tin-the protosulphide, formed by fusing together er metallic tin and gether 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 decorative 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 mercury.