T I N 



472 



T I N 



in * mortar, in oi.k: to separate, and to add to the ingot, 

 ny minute granules of tin remaining :.mong Hum. Dr. 



In fusing tlir on-, mixed with five per rent, of ground 

 i a crucible liui-il with hard-rammed char- 

 coal. A gentle hi-at should In- applied to the rrurible 

 during the first hour. 11 stronger heat during the m 

 hour, i*d, finally, an intense heat for a quarter of an hour. 

 tit from four to five per edit, more 



tin than tin 1 oilier ; but it is .-tated that it IIILS the incon- 

 \fiiieiiee oi' reducing the iron, if any 1 . which 



, lent solution in nitric 

 aciil. 1 milted, would be too 



.1* for ordinar)- adoption, as the smelter may have 

 .1 samples in one day; and that fust 



.iied. wlulc imperfeet iii a chemical point of view, 



U :i similar result to that nv.Uised by the smelter On a 

 large scale. 



The smelting of tin-ores is effected by two different 

 methods, whieh may be briefly deseribed by staling that in 

 the (ir>t and most common, the ore, previously mixed with 

 I'ulin, is expo>ed to heat upon the health of a icvcrbcratory 

 furuaee. in which ])it-eoal is used as fuel ; while in the 



.1. whieh is applied merely to strriim tin (the tin 

 procured from stream-works \ and which is followed in 

 order to obtain tin of the finest quality, the ore is fused in 

 a blast-furnace, called a blowing-house, in which wood- 

 charcoal is used for fuel. 



In the former process the prepared ore, which is called 



h. is mixed with from one-fifth to one-eighth of its 

 weight of powdered anthracite, or culm, to which a little 

 slaked lime or fluor-spar is sometimes added as a flux. 

 These substances are carefully blended together, and a 

 little water is added to the mixture to facilitate the opera- 

 tion of charging the furnace, and to prevent the charge 

 I: om being blown away by the draft at the commencement 

 of the smelting process. From twelve to sixteen cwt. of 

 the above mixture forms an ordinary charge : but in the 

 smcltiiig-furnaces at St. Austle, or Austell, in Cornwall, of 

 which rcpicsciitations are given by Dr. Ure, each charge 

 amounts to from fifteen to twenty-four cwt. The charge 

 is -;>read ujwn the concave hearth of the furnace, and then 

 the apertures by whieh it is inserted are closed and luted, 

 and tiie furnace is gradually heated, and kept hot for six 

 or eight boms, by which time the reduction of the ore is 

 "omplete. The gradual application of the required tem- 

 peiature i- necessary to prevent the tin oxide from uniting 

 with the quartz of II. or refuse poition of tl 



and forming a kind of enamel. \Vheii the fusion or reduc- 

 tion of the ere is considered to be finished, one of the 

 apertures of the furnace is opened, and the melted mass is 

 I it]) to complete the separation of the tin from the 

 'lieh aie then drawn out by means of an iron 

 rake. These bcoii;r consist principally of masses of lel'use 

 matter from which no more tin can be profitably extracted. 

 and which are therefore immediately thrown awax : but 

 among them are pieces which yet retain a consiuYiablc 

 quantity of tin, and which are separated and resei . 

 further pro So soon as these refuse matters are re- 



moved, a channel is opened, by which the melted tin (lows 

 from the hearth into a large vessel called the basin of 



lion, where it is allowed to rest for some time, in 

 order that the impurities vet remaining with the 



separate, by their different specific gravities. \Vlieii 

 it ha.s si tiled, the tin is ladled into moulds, so as to form it 

 into large blocks or i 



The ingots produced b) the above process frequently 

 contain po iron, copper, .: 



together with small quantities of sulphurets and avsciiiurcl.s 

 that have escaped decomposition, unreduced oxide of tin, 

 and earth-. which have not pa-scd off with the 



corite. To remove these the tin is 



to the process of njnting, whieh conmii ir cs h\ plaeinir 

 the block* or ingots on the hearth of a second revcrbc- 

 ratory furnace, similar to that used ng the 1 me. 



and applxing a moderate heat, which causes the tin to 

 melt, and to flow into a basin provided for it. leaving upon 

 the health a residuum whieh consist, ol a vcix ferruginous 

 alloy. Fresh blocks ar<' then placed in t .with- 



out removing the unmcltcd remains of the foiiuer, until 

 about five tons of tin have flowed into the basin. This 

 part of tl .-i ned a ////H.I//-/H. and is followed 



by Uie actual refining, which is usually effected by plung- 



ing billets Of gfMn WOOd into the melted tin in the refining 



basin, by n;t apparatus erected bx it. The' heat 



us the di- Me vohim 



n the wood, and thus a kind of ebullition is pro- 

 duced in the tin, which causes the lighter impuriti< 



the Mil luce in a trolhy form, and the heavier to fall 

 to the bottom. The froth or scum, which consists chiefly 

 of the oxides of tin and foreign metals, is slummed oil' 

 and returned into the furnace ; and when the 1m is suffi- 



, boiled, the green wood is lifted out. and the v 

 is allowed to settle, ill doing which the purest tin n 

 the top. that with a trifling admixture of 

 remains in the middle, while the foule.st portion 

 to the bottom. \Vlienthc mass 1. iconics so cool that no 

 Imther separation can take place, the tin is again ladled 

 into moulds: the quality of the blocks thus produced 

 varxing according to tin- order in whieh the n 

 filled. The blocks formed from : part of the tin 



aie usually so impure as to need a repetition of the K lining 

 process. The operation as above dcscrib, 

 or six hours; of which the first is occupied in tillim- 

 basin, the three following in boiling the tin with the billets 

 of wood, and the remaining time in subsidence. A Bl 

 effect is sometimes produced by an operation called 

 in'j. in which, instead of the ebullition produced b 

 green wood, the mass of melted tin is agitated by a work- 

 man repeatedly lifting a quantity of tin in a ladle, ar.i: 

 ting it fall iiito the basin fiom a considerable height. 

 After continuing this agitation for some time, the M. 

 is skimmed carefully : and if the upper part of the tin be 

 yet too impure for the market, the refining is ren. 

 more perfect In keeping the metal in a fr.scd slate, wilh- 

 out agitation, until the impurities sej nslx. 



After refining, the tin is cast into blocks of about thicc 

 cwt. each. The moulds used for this purpose aie fre- 

 quently made of granite ; and the tin thus prepared i- 

 as blw-k tin. From avciy remote period, almost to the 

 it time, a duty was paid upon all tin raised in Corn- 

 wall to officers appointed by the duchy, who required all 

 blocks, before being sent to market, to be taken to them 

 for the purpose of being r-jiii<-tl. or marked with a distin- 

 guishing stamp. The mode of collecting the duty on tin 

 was very inconvenient, as it required all tin to be cast inlo 

 blocks ibr coining, although it might have to 

 quently re-cast into some' other form for sale in foreign 

 markets: besides which the miner or smelter had to bear 

 the expense of sending it to one of the places appointed 

 for coining, and the inconvenience of waiting for one of 

 the periodical coinages, xvhieh were usually three months 



These duties weie abolished by 1 Jsi 12 Viet . 

 120, which set lies a peipi-tnal annuity on the duchy of 

 Cornwall equal to the axciuge produce of the. tin i: 

 for ten years previous to its coming into operation. 



It. has been stated that the' richer 



left by the process of smelting; is reserved for further opera- 

 tions. Such as contain small grains of tin among tin 

 or refuse are taken to a stamping-mill, and broken and 

 washed in a similar manner to the ore : while those which 

 contain much tin are re-smelted without any previous pre- 

 paration. From these scoriic. which aie called pri/liun* 

 an inferior kind of tin is produced bx a second smelting. 

 The inferiority of this product max lie readily imagined, 

 observes Dr. I're. since the metal which forms the granu- 

 lations among the scoria' is what, being less fusible than 

 .re tin, solidified quickly, and could not flow off into 

 the metallic bath, or basin Of reception. The < 

 siduiim of the i efining fuinace is fused b\ incrcasii: 

 file alter the removal ol the refined tin. and is then run 

 out into a separate basin, in which it is allowc : 

 The upper poition is then cast into mouM tin, 



which needs a second refilling, and the int. 

 mixli. - deposited on the bottom 



in the form of a brittle white alloy, with 

 line fi act lire, which contains so large a pro; 



ii metals that no use is made of it. 



The average quality of the tin-on'. the 



smelting-turnaccs, is such that 'JO \n\, I from 12J 



to 13 parts of metallic tin. or fiom 

 and the quantity of coal required for producing 



SoDl.rr.-; lull i ,<- ll'.f w linl 



pillion, or jtilliim-ti t ntl't .i. 



I! [ i llu - >!1 ''"-' buiuc/"*i7/ U) ci<]>|>cr ill >. 



