TIN, BUTTER OF. 



TIN MANUFACTURE AND TRADE. 



2152 



white alloys, which are less fusible than tin ; the potassium alloy burns 

 readily when it contains more than one-fifth of potassium. With 

 arsenic it forma a metallic mass which is whiter, harder, and more 

 sonorous than pure tin. With antimony tin forms a white, hard, and 

 sonorous alloy. Bismuth forms with tin an alloy which ia more fusible 

 than either of the metals separately, a mixture of equal weights melt- 

 ing at 212" ; this compound is hard and brittle. Copper and tin form 

 alloys which are well known and highly useful : they are BELL-METAL 

 and BROSZE. [See, also, BRITANNIA-METAL ; PETVTEB ; SOLDER ; and 

 GUS-MKTAL.] \Vith mercury tin readily amalgamates, and the com- 

 pound is used for silvering mirrors. With iron, tin forms white com- 

 pounds, which are more or less fusible according to the proportion of 

 iron they contain. Tin-plate is of all the alloys of tin the most useful, 

 and the preparation of this and of pewter are the most extensive appli- 

 cations of this very valuable metal. 



In making tin-plate the best iron is employed, and, after being tho- 

 roughly cleansed from oxide and grease, by immersion in dilute sul- 

 phuric acid and scouring, the plates are dipped into a vessel containing 

 melted tin, on the surface of which tallow floats. These and other 

 similar precautions are necessary to secure the uniform adhesion, or 

 rather alloying, of the two metals. Copper may be tinned by a some- 

 what similar process. 



Moirg metaUitjue is tin-plate to which a beautifully crystalline 

 appearance has been given by moistening the warmed plate with a 

 mixture of equal parts of nitric and hydrochloric acids diluted with its 

 own bulk of water. [MoiRlt] 

 TIN, BUTTKR OF. [Tm.] 



TIN MANUFACTURE AND TRADE. Referring to other articles 

 for notices of the mineralogical, chemical, and medical characteristics 

 of tin, we sha^l here treat the metal in its manufacturing and com- 

 mercial aspects. 



Under MINIHO it is explained in what way the orea of tin nre ex- 

 tracted from the mines of Cornwall and other places, and by what 

 processes they are mechanically separated from some of the impurities, 

 and broken into fragments. Wo shall now take up the details from 

 that point. 



Smelling and Refining. After being reduced to a coarse powder, the 

 ore is roasted or calcined in a reverberatory furnace, until it ceases to 

 exhale arsenical vapours. By this, together with some subsequent 

 processes, it is further cleansed from the admixture of foreign matter 

 and prepared for smelting. The ores of tin raised in Cornwall and 

 Devonshire are always smelted within those counties. The smelting 

 work* do not generally belong to the proprietors of the mines, but to 

 other parties who purchase the ore from them. The value is deter- 

 mined by a kind of away. When several bags of ore, of nearly 

 uniform quality, are conveyed to the smelting works, a small sample is 

 taken from each. These samples, after being blended together, are 

 mixed with about four per cent, of ground coal, placed in an open 

 earthen crucible, and heated in an air-furnace until the ore is reduced. 

 The melted metal is poured into a mould, and the drossy substances 

 which remain in the crucible are pounded in a mortar, in order to 

 separate, and to add to the ingot, any minute granules of tin remain- 

 ing among them. The ratio of good tin to crude ore determines the 

 value. 



The smelting of tin-ores is effected by two different methods. In 

 the first and most common, the ore, previously mixed with culm, is 

 exposed to heat upon the hearth of a reverberatory furnace, in which 

 pit-coal is used as fuel ; while in the second, which is applied merely 

 to ttrtam 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, in which wood-charcoal is used for fuel. 



In the former process the prepared ore, called sc/tlich, is mixed with 

 from one-fifth to one-eighth of its weight of powdered anthracite, or 

 culm, to which a little slaked lime is sometimes added as a flux. These 

 substances are carefully blended together, and a little water is added to 

 the mixture to facilitate the operation of charging the furnace, and to 

 prevent the charge from being blown away by the draf t at the com- 

 mencement of the smelting process. From twelve to twenty-four cwt. 

 of the mixture forms a charge. The charge is spread upon the 

 concave hearth of the furnace ; then the apertures by which it is 

 inserted are closed and luted, and the furnace is gradually heated, and 

 kept hot for six or eight hours, by which time the reduction of the 

 ore is complete. When the fusion of the ore is finished, one of the 

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

 to complete the separation of the tin from the scorte. These scorim 

 consist principally of masses of refuse matter from which no more tin 

 can be profitably extracted, and which arc therefore immediately thrown 

 away; but among them are pieces which yet retain a considerable 

 quantity of tin, and which are separated and reserved for further pro- 

 cesses. So soon as these refuse matters are removed, a channel is 

 opened, by which the melted tin flows from the hearth into a large 

 vessel, where it is allowed to rest for some time, in order that the 

 impurities may separate. When it has settled, the tin is ladled into 

 l, so as to form it into large blocks or ingots. These ingots 

 frequently contain portions of iron, copper, arsenic, tungsten, sulphurets 

 and arsetiiuri/t*, unreduced oxide of tin, and earthy matters which have 

 .ssed off with the scoria;. To remove these the tin is exposed to 

 the process of refininy, which commences by placing the blocks or 



ingots on the hearth of a second reverberatory furnace, and applying 

 a moderate heat. This causes the tin to melt and to flow into a basin 

 provided for it, leaving upon the hearth a residuum consisting of a 

 very ferruginous alloy. Fresh blocks are then placed in the furnace, 

 without removing the unmelted remains of the former, until about 

 five tons of tin have flowed into the baain. This part of the process 

 is termed a liquation, and is followed by the actual refining, which is 

 usually effected by plunging billets of green wood into the melted tin 

 in the refining basin, by means of an apparatus erected near it. The 

 heat occasions the disengagement of considerable volumes of gas from 

 the wood, and thus a -kind of ebullition is produced in the tin, which 

 causes the lighter impurities to rise to the surface in a frothy form, 

 and the heavier to fall to the bottom. The scum ia taken off and 

 returned into the furnace ; and when the tin is sufficiently boiled, tho 

 green wood is lifted out, and the whole is allowed to settle, in doing 

 which the purest tin rises to the top, that with a triHing admixture of 

 foreign metals remains in the middle, while the foulest portion sinks 

 to the bottom. When the mass becomes so cool that no further 

 separation can take place, the tin is again ladled into moulds. Tho 

 blocks formed from the lowest part of the tin are usually so impure as 

 to need a repetition of the refining process. A similar effect ia some- 

 times produced by an operation called trsir/ ; in which, instead of the 

 ebullition produced by the green wood, the maaa of melted tin is 

 agitated by a workman repeatedly lifting a quantity of tin in a ladle, 

 and lotting it fall into the basin from a considerable height. After 

 continuing this agitation for some time, the surface is skimmed care- 

 fully ; and if the upper part of the tin be yet too impure for the 

 market, the refining is rendered more perfect by keeping the metal in a 

 fused state, without agitation, until tlio impurities separate spon- 

 taneously. After refining, the tin is cast into blocks of about three 

 cwt. each. The moulds used for this purpose are frequently made of 

 granite ; and the tin thus prepared ia sold as block tin. 



It has been stated that the richer portion of the scoria; left by the 

 process of smelting ia reserved for further operations. Such as contain 

 small grains of tin among the slag 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 

 preparation. From these scoria;, which are called prillitm, an inferior 

 kind of tin is produced by a second smelting. 



Of the average quality of tin-ore, as prepared for the smeltuig- 

 furnaces, 20 parts yield from 124 * 13 parts of metallic tin, or from 

 624 * 65 per cent. ; and the quantity of coal required for producing 

 one ton of tin is about a ton and three-quarters. Respecting the time 

 when thia economical fuel was substituted for wood-charcoal in the 

 smelting of tin-ores, authorities are at variance; but it is generally 

 supposed to have been about the year 1680. Whatever may have been 

 the precise time or manner of this improvement, ita importance is 

 indisputable ; and such is the effect of the superior economy of this 

 and other metillurgic operations as performed in England, that experi- 

 ment has shown the possibility of bringing tin ore from the Malay 

 countries to thia island for the purpose of smelting, and sending the 

 tin back to the East at a lower price than it can be produced for on 

 the spot. 



The smelting or reduction of tin by the blast-furnace, with wood- 

 charcoal, is practised on a limited scale for the production of tin of the 

 greatest possible purity. The finest ores supplied by stream-works, 

 and the finer tin sands, are selected for this operation ; and as these 

 are free from many of the impurities found in other ores, they do not 

 require calcination. The works in which blast-furnaces are employed 

 are commonly called Umcing-hoiuti. The furnaces used are about six 

 feet high ; the long narrow chimney, after proceeding for some dis- 

 tance in an oblique direction, contains a chamber in which the metallic 

 dust carried off by tho blast is deposited. The furnace is lined with a 

 vertical cylinder of cast-iron, coated internally with loam ; and it has 

 an opening near the bottom, by which the blast is introduced, either 

 from large bellows or from cylinders. No substance ia added to tho 

 ore and charcoal, unless it be the residuary matter of a previous smelting ; 

 and the proportion of charcoal consumed is about one ton and six- 

 tenths for every ton of tin produced. The melted tin runs from the 

 furnace into an open basin, whence it ia run off into a large vessel in 

 which it is allowed to settle. The scoriic which flow with the metal 

 into tho basin of reception arc skimmed off, and separated into two 

 portions, one consisting of such as retain tin oxide, and the other of 

 such aa have no oxide, but contain tin in a granulated state. The sub- 

 sequent operations are much tho same as with block tin prepared in a 

 reverbcratory furnace with pit-coal. In order to convert the blocks 

 of tin produced by the blast-furnace process into the form known aa 

 grain tin, they are heated until they become brittle, and made to fall 

 from a considerable height in a semi-fluid state, thus producing an 

 agglomerated mass of elongated grains. 



From a comparison of the results of tho two methods of smelting 

 above described, it appears that the reverberatory furnace with pit- 

 coal occasions less loss of metal than the blast furnace, and is by far 

 the most economical. The superior quality of the tin produced by 

 the other process is attributable partly to the greater purity of the 

 fuel, and partly to the finer quality of the ore selected for the ] 



Mmntfacture of Tin-ware. It is unnecessary here to enumerate tho 

 various purposes to which tin is applied in the useful arts, either as an 



