Page:The New International Encyclopædia 1st ed. v. 19.djvu/347

* TIN. 299 TINAMOU. Metric tons on the hearth of the furnace a residuary alloy of England 4.634 tin with iron and other metals. More blocks are Oermany l.*6l added and heated in the same way, till the re- si^'iJr*^-^- ■'^"V::;;:;:;::;;:::;:.v;:.":.':.':::.';;.v.'.':.':.' 793 fining basin contains about sve tons. The un straits Settiements...... 51.339 is then ready for "boilin,';.' In this operation Tasmania ■ ^'^^^ billets of green wood are plunged into the melted -j-g^al 95,058 metal, the disengagement of gas from which produces a constant ebullition, and so causes a METALLOiGT. The Only ore of tin which is scum (chiefly oxide of tin) to rise to the sur- used for the extraction of the metal is tinstone face, which is then easily removed; at the same or eassiterite. The extraction of tin is usually time, impure and dense parts fall to the bottom, performed by dry methods — that is, by a process When the agitation has gone on long encnigh, of calcining and reduction in furnaces, but wet the bath is allowed to settle and cool. The tin methods and electro-metallurgical methods are then separates into zones — the upper consisting also employed to some extent. The ore of the purest portion, the middle being slightly ■when mined from veins has' to be stamped mixed with other metals, and the lower so nuich to a very fine powder before the valuable so that it requires to go tlirough the refining portion can be efl'ectually separated. This process again. The residuary alloy of the separation is performed by an elaborate liquation process has also its tin extracted and series of washings whose effect is to remove the refined again. lighter impurities and to leave the hea^'y par- in former times in Cornw-all tin was smelted tides of tin where they can be collected. Various jn g, blast furnace (see Iron and Steel) instead forms of washing apparatus are employed (see of a reverberatory one; and this is still the case Ore Dressing), but the most common appliance on the Continent. By this method a pure tin is is the puddle. In this device the ore and earthy obtained, but the loss of metal in the process is matters, in the state of a thick mud. are con- greater. It works best where coal is scarce and veyed by square pipes or channels to the eircum- wood abundant. ference of a conical table on which, by the aid of Tin oies which contain the mineral wolfram water, the metallic portion separates, the lighter (tungstate of iron and manganese) are treated stony impurities flowing down toward the centre, by ^ special process, patented by R. Oxland, of and being carried away. There are ahso brushes Plymouth, England. This mineral and tin ore for agitating the ore during the operation. are so nearly the same in specific gravity that The tin ore thus far purified has next to be jio mechanical process of washing will separate deprived of its sulphur and arsenic if these them. Oxland's process consists in roasting the substances should be present; this is done in a dressed tin ore with sulphate of soda, for the reverberatory furnace, the flues of which are purpose of converting the insoluble tungstate connected w'ith large condensing chambers, in of iron and manganese into the soluble tungstate which the arsenic is deposited in a crystalline of soda, which is easily removed by lixiviation. form. The sulphur which is present in the state of The oxides of iron and manganese, which are left sulphide of iron is decomposed by the heat into in a finely divided state, can then, from their sulpliurous acid gas, and the remaining oxide lower density, be readily got rid of by washing. of iron is removed by a subsequent washing. The tungstate of soda procured in the operation Sulphide of copper, when present, is converted has been found to be one of the most valuable by roasting, and afterwards exposing it to the substances for rendering cotton cloths non-inflam- air, into sulphate of copper, and is then easily niable. dissolved out by lixiviation. Tin Plate. A very large proportion of the After this final washing the ore is ready for tin obtained each year is employed in the plating smelting in a reverberatory furnace. The charge of iron and steel sheets which are manufactured consists of from 20 to 25 cwts. of ore mixed with subsequently into cans for preserving and other one-sixth of its -weight of powdered anthracite purposes. The sheets from the rolling mills are or charcoal, and a small quantitv of lime or cleaned in bran-water which has soured and in fluor-spar, to serve as a flux for the siliceous im- dilute sulphuric acid, after which they are purities. Before being put into the furnace, the plunged into baths of molten tallow and tin. mixture is moistened with water, to prevent the The treatment with tallow prevents oxidation finelv powdered ore being carried awav by the of the metal. After the sheets have taken on a draught. When the charge is placed on the sufliciently heavy plate, they are carefully cleaned hearth of the furnace, the doors are closed, and with bran. An inferior quality of plate called the heat gradually raised for about six hours; terne plate is made by dipping sheets in an alloy the oxide'is then" reduced bv the carbon of the of tin and lead. coal. At this stage the furnace door is opened, Bibliographt. For the occurrence and mining and the mass worked with a paddle, to separate of tin, consult The Mineral Industry (^ew York, the slag, which is raked off, and the richer por- annual) ; Charleton, Tin Mining (London. lSb4). tion of it melted over again. The reduced tin For the metallurgy of tin, see Schnabel UandbcKik subsides to the bottom, and is run off into a of ^IcUtUuryy, vol. ii., Eng. ed. (London, 1878). cast-iron pan, from which it is ladled into molds, TINAMOU. The native, and now the pop- to produce blocks or ingots of a convenient size, ular, name for birds of the family Tinamidoe, The tin has still to be purified, first by a proc- inhabiting the tropical portions of South ess of liquation, and afterwards by that of America, having many remarkable features in boiling. 'Liquation' consists in moderately heat- their internal organization, and the striking ing the blocks in a reverberatory furnace till the external character that the tail is exceedingly tin, owing to its comparatively easy fusibility, short or entirely absent. Like partridges in melts and flows into the refining basin, leaving general appearance, and varying in size from Vol. XIX.— i;o.