Page:Collier's New Encyclopedia v. 09.djvu/469

LEFT TIN 407 TIN and important, and its resistance to oxi- dation and to the action of vegetable acid renders it extremely useful for do- mestic purposes. Symbol Sn. Prof. For- rest Shepherd, of Missouri, advanced an assertion that tin is not a simple, but a compound metal. His opinion, neverthe- less, so far as we know, is not the result of analyses, but of speculation and incon- clusive analogies. In metallurgy, tin is a white metal, with a slight yellowish tinge, and a bril- liant metallic luster. It is wanting in tenacity, but is extremely malleable at a temperature of 212". It has a great ten- dency to crystallize, and its crystalline form may be easily showrw by rubbing a piece -with a little nitric or hydrochloric acid, when it assumes the appearance known as moiri metallique. By slow cool- ing it may be procured in octohedral crys- tals, and on bending a piece of tin back- ward and forward, a peculiar crackling or grating sound is heard, from the fric- tion of the internal crystals. It fuses at 442° F., but it is not sensibly vo?atilized 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 atmos- pheric 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 ex- plained 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 or- nament, 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 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 The sheets are then heated to a red heat in a reverberatory furnace, withdrawn, al- lowed to cool, hammered flat, and passed between polished rollers, and then washed in dilute acid.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, al- lowed to drain, and dipped again. The 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 a perfect alloy with each other. The appearance known as moir^ metaU lique 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. The principal of these are Britannia metal, consisting of equal parts of brass, tin, an- timony, and bismuth; pewter, 4 tin, and 1 lead; Queen's metal, 9 tin, and 1 each of antimony, bismuth, and lead ; the vari- ous 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 copper. An amal- gam of tin and mercury is used for sil- vering looking glasses. A sheet of tin- foil is laid on an edged slab of stone carefully levelled, and mercury is poured on it till it forms a layer % inch thick. Glass is laid down on this, and the table is tilted to let the superfluous mercury run oflF, weights being gradually placed on the glass to facilitate the operation. Tin ores are met with but in few lo- calities. Cornwall, Banca, Mexico, and some parts of Australia, are the only impor- tant tin yielding districts. The most celebrated tin mines are those of Corn- wall, 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 Hamp- shire, New York, New Jersey, Virginia, California, Missouri, and perhaps in other States. Some of the mines, as 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 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 con- sisting 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 of copper and oxide of iron. The washed ore is mixed with from one-fifth to one- eighth its weight of powdered anthracite or charcoal, and with a small portion of lime to form a fusible slag with any of