TIN T63 tinually under the front wall and into a re- ceptacle before it, cut in stone and lined with clay and charcoal powder. Here the metal separates and settles, away from the influence the blast. Such a shaft furnace (Saxon) is lown in the accompanying section, in which a is the rough mason- ry of granite or gneiss ; J, the inner wall, of granite ; e, the front wall ; / the hearth ; <7, the tuyere (with two nozzles); A, the "eye," or opening in the breast, through which the molten material escapes ; i, the fore hearth, built with gran- J ite,&, and clay andpow- Saxon Shaft Furnace. dered charcoal, I ; m, the tapping duct, ending in an opening in the iron front plate p; w, the crucible or refining pot. The arrangements for removing the slag from i, and the chambers for saving dust and fumes, placed above the furnace, are not shown in the diagram. The dimensions of the furnace here shown are, in metres: height, 2'83; width at top 0'96, at bottom, front, 0-58, and rear, 0'48 ; depth from front to rear wall at top 0*62, at bottom 0'48 ; inclination of hearth, 26 ; size of " eye," 0-10 high by 0'38 at top and 0;5 at bottom; depth of fore hearth 0'38, of crucible 0*4 ; diam- eter of each, 0'5. The product of the shaft or reverberatory furnace contains more or less of the impurities of the ore. Of iron there are at least traces in all sorts of tin ; 0*5 per cent, injures the silvery color and lustre, and 1 per cent, diminishes perceptibly the softness and smoothness. Of copper, 1 to 1*5 per cent, makes tin harder and less malleable; and as the proportion is increased, the metal becomes more brittle and suffers a change in lustre. Of antimony and bismuth, 0*5 per cent., without affecting the lustre, causes a brittle, crystalline structure. Of lead, 1 per cent, injures color and lustre, and softens the tin. Arsenic to the amount of 0*5 per cent, affects color and lustre; over 1 per cent, of it renders the tin lighter, and gives it a spotted, dull, or darkened ap- pearance. Wolfram and molybdenum in con- siderable proportions diminish rather the fusi- bility than the strength or lustre ; zinc renders the metal harder, more brittle, and whiter; sulphur makes it "short;" tin oxide reduces its brilliancy ; quicksilver, contained in several varieties of East Indian tin, renders it crumbly, and hinders its union with other metals. The refining of crude tin is conducted in England as follows : The blocks of tin are set on the hearth of a reverberatory, and liquated at low temperature, by which process a purer tin is obtained in a kettle, while an alloy consisting mainly of less fusible metals (iron, wolfram, copper, &c.) remains on the hearth. The liquid tin in the kettle is further purified by " poling ;" that is, green wood or damp coal is submerged in it, causing by the generation of gases a vio- lent ebullition, which continually changes the surface of the bath exposed to the air, and promotes the oxidation of the foreign sub- stances. These are skimmed off, and the bath is allowed to settle, when there is a further deposit of heavy metals (iron, copper, &c.) on the bottom. After settling, the tin is drawn off in three portions, the upper layer being re- fined block tin, the middle common tin, and the lowest an impure alloy which is again liquated. Block tin is cast in moulds of mar- ble. The purest metal (containing only O'Ol per cent, of iron) is called grain tin, and is produced by heating the best block tin until it is brittle, and dropping it from a considerable height upon fiat stones. The German process of refining consists in pouring the melted crude tin from a certain height upon an inclined cast- iron plate, coated with loam and covered with a layer of glowing coal about 0-25 metre thick. The less fusible impurities remain among the coals, and the purified tin flows along the plate, to be collected in a sump of cast iron filled with coal. The operation is performed repeat- edly ; the coals are subsequently beaten, to re- move adhering grains of tin, and the residue is returned to the smelting furnace. Care must be taken to cast tin at the right temperature. If too hot, it becomes iridescent and "red- short;" if too cold, it assumes a dull appear- ance, becomes " cold-short," and loses ductil- ity. The proper moment for casting is shown by a mirror-like clearness of the surface of the bath. A special refining of tin in the humid way consists in dissolving the granulated metal in muriatic acid, and precipitation by zinc. The zinc solution is subsequently decomposed with milk of lime, and the precipitate manu- factured by heating into zinc white. The fol- lowing analyses are from Kerl's Metallhutten- (Leipsic, 1873): CON- STITU- ENTS. ' 2. , 4. 5. 6. 95-66 iO-07 1-8 7. 8. 9. 98-18 trace 8n... Fe Pb.... Cu.... 99-961 ! 99'9 0'019i 0'2 0-014'.... 0-006 .... 99-76 trace 6 : 24 9S-64 trace 0-20 0-16 93-50 0-07 2-76 99-9 99-594 tree* 6-406 trace 1-60 trace
- i;
- ;
Sb 8-76 2-34 Bi
.... o-i 1 2. Banca. 3,*4. English. 5,6. Peruvian (Bolivian). 7. Saxon, from ore treated with muriatic acid. 8. Bohemian, refined. 9. Bohemian roll tin, third class.
