1006 TIN 



of the crucible (concave hearth) to the Liu-oat, which is placed at the origin of a long 

 and narrow chimney, interrupted by a chamber, where the metallic dust carried off by 

 the blast was deposited. This chamber was not placed vertically over the furnace ; 

 but the lower portion of the chimney had an oblique direction from it. The furnace 

 was lined with an upright cylinder of cast iron, coated internally "with loam, with an 

 opening in it for the blast. This opening, which corresponds to the lateral face 

 opposite to the charging side, receives a tuyere, in which the nozzles of two cylinder 

 single bellows, driven by a water-wheel, were planted. The tuyere opens at a small 

 height above the sole of the furnace. On a level with the sole, the iron cylinder 

 presents a slope, below which was the hemispherical basin of reception, set partly 

 beneath the interior space of the furnace, and partly without. Near the corner of 

 the building there was a second basin of reception, larger than the first, which could 

 discharge itself into the former, by a sloping gutter. Near this basin there was 

 another, for the refining operation. These were all made either of brick or cast iron. 

 Such blast-furnaces are now entirely superseded in this country by the roverberatory 

 furnace. 



The quality of the average ground tin ore prepared for smelting is such that 20 

 parts of it yield from 12 to 13 of metallic tin (62J to 65 per cent.) The treatment 

 consists of two operations, smelting and refining. 



First operation ; deoxidisation of the ore, and fusion of the tin. Before throwing the 

 ore into the smelting furnace, it is mixed with from one-fifth to one-eighth of its 

 weight of blind coal, in powder, called culm ; and a little slaked lime is sometimes 

 added, to render the ore more fusible. These matters are carefully blended, and 

 damped with water to render the charging easier, and to prevent the draught from 

 sweeping any of it away at the commencement. From 20 to 25 cwts. are introduced 

 at a charge ; and the doors are immediately closed and luted, while the heat is pro- 

 gressively raised. Were the fire too strong at first, the tin oxide would unite with 

 the quartz of the gangue, and form an enamel. The heat is applied for 6 or 8 hours, 

 during which the doors are not opened ; of course the materials are not stirred. By 

 this time the reduction is in general finished ; the door of the furnace is removed, and 

 the melted mass is worked up to complete the separation of the tin from the scoriae, 

 and to ascertain if the operation be in sufficient forwardness. When the reduction 

 seems to be finished, the scoriae are taken out at the same door, with an iron rake, and 

 divided into three sorts : those of the first class A, which constitute at least three- 

 fourths of the whole, are as poor as possible, and may be thrown away ; the scoriae of 

 the second class B, which contain some small grains of tin, are sent to the stamps ; 

 those of the third class c, which are last removed from the surface of the bath of tin, 

 are set apart, and re-smelted, as containing a considerable quantity of metal in the 

 form of globules. These scoriae are in small quantity. The stamp-slag contains fully 

 5 per cent, of metallic tin. 



AB soon as the scoriae are cleared away, the channel is opened which leads to the 

 basin of reception, into which the tin consequently flows out. Here it is left for some 

 time, that the scoriae which may be still mixed with the metal may separate, in 

 virtue of the difference of their specific gravities. When the tin has sufficiently 

 settled, it is lifted out with ladles, and poured into cast-iron moulds, in each of which 

 a bit of wood is fixed, to form a hole in the ingot, for the purpose of drawing i out 

 when it becomes cold. 



Refining of Tin. The object of this operation is to separate from the tin, as com- 

 pletely as possible, the metals reduced and alloyed along with it. These are, prin- 

 cipally, iron, copper, arsenic, and tungsten ; to which are joined, in small quantities, 

 some sulphides and arsenides that have escaped decomposition, a little unre- 

 duced oxide of tin, and also some earthy matters which have not passed off with the 

 scoriae. 



Liquation. The refining of tin consists of two operations ; the first being n, 

 liquation, which, in the interior, is effected in a reverberatory furnace similar to that 

 employed in smelting the ore (figs. 1989, 1990). The blocks being arranged on 

 the hearth of the furnace, near the bridge, are moderately heated ; the tin melts, 

 and flows away into the refining-basin ; but, after a certain time, the blocks cease 

 to afford tin, and leave on the hearth a residuum, consisting of a very ferruginous 

 alloy. 



Fresh tin-blocks are now arranged on the remains of the first ; and thus the liqua- 

 tion is continued till the refining-basin be sufficiently full, when it contains about 5 

 tons. The residuums are set aside, to be treated as shall be presently pointed out. 



Refining proper. Now begins the second part of the process. Into the tin-bath 

 billets of green wood are plunged, by the aid of the gibbet above described. The dis- 

 engagement of gas from the green wood produces a constant ebullition in the tin ; 

 bringing up to its surface a species of froth, and causing the impurest and densest 



