T I N 



473 



T I N 



tin is about a ton and three-quarters. Respecting thi 

 time when this economical fuel was substituted for wood 

 charcoal in the smelting of tin-ores, authorities are at va- 

 riance. Pryce, in his ' Mineralogia Cornubiensis,' p. 282, 

 says that ' Necessity at last suggested the introduction o 

 pit-coal for the smelting of tin-ore, and, among others, to 

 Sir Bevil Granville, of Stow, in this county (Cornwall) 

 temp. Car. I., who made several experiments, though with- 

 out success ;' and he adds that the ' effectual smelting o 

 tin-ore with pit-coal' did not take place till the seconc 

 year of Queen Anne, ' when a Mr. Liddell, with whom 

 Mr. Moult, a noted chemist, was concerned, obtained her 

 majesty's patent for smelting block tin with fossil coal in 

 iron furnaces.' ' The invention of reverberatory furnaces 

 built with brick, stone, sand, lime, and clay, soon followed 

 this discovery ; the form of which,' he states, writing about 

 1778, ' has admitted little improvement to the present 

 time.' Holland, after observing that the commencement 

 of this important substitution is generally supposed to 

 have been about 1680, states that the question as to the 

 discovery of the fitness of pit-coal for the purpose lies 

 between Pryce's account, as above cited, and that of Becher 

 (whose name he incorrectly gives Beecher), an ingenious 

 German who, in consequence of persecutions in his own 

 country, visited England in the reign of Charles II., and 

 introduced several improvements in the art of mining ; and 

 he quotes a passage, but without referring to his authority, 

 in which Becher claims for himself the credit of the in- 

 troduction of coal for smelting tin. Whatever may have 

 been the precise time or manner of this improvement, its 

 importance is indisputable ; and such is the effect of the 

 superior economy of this and other metallurgic operations 

 as performed in England, that experiment has shown the 

 possibility of bringing tin-ore from the Malay countries to 

 this island for the purpose of smelting, and sending the 

 tin back to the East at a lower price than it can be pro- 

 duced 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 

 fim-t 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-fur- 

 naces are employed are commonly called blowing-houses. 

 The furnaces used are about six feet high, from the con- 

 cave hearth to the throat, or commencement of the long 

 narrow chimney, which, after proceeding for some distance 

 in an oblique direction, contains a chamber in which the 

 metallic dust' carried off by the blast is deposited. The 

 furnace is lined with a vertical cylinder of cast-iron, coated 

 internally with loam ; and it has an opening called the 

 liii/f-rc near the bottom, by which the blast is introduced, 

 i ither from large bellows or from cylinders. No substance 

 is added to the ore and charcoal, unless it be the residuary 

 matter of a previous smelting ; and the proportion of char- 

 coal 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 is run off into a large vessel 

 in which it is allowed to settle. The scoriae which run 

 with the metal into the basin of reception are skimmed 

 off, and separated into two portions, one consisting of such 

 as retain tin oxide, and the other of such as have no oxide, 

 but contain tin in a granulated state. The subsequent 

 operations of refining by allowing the mass of metal to 

 rest, and then submitting the upper and purer portion to 

 the refining basin, and re-melting the lower part, and of 

 agitating the tin by the green-wood ebullition, are much 

 the same as with block tin prepared in a reverberatory fur- 

 nace with pit-coal. In order to convert the blocks of tin 

 produced by the blast-furnace process into the form known 

 a* grain tin, or, according to the more appropriate French 

 term, (tain en larmes, ' tears of 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 

 mas of elongated grains. 



From a comparison of the results of the two methods of 

 smelting above described, Dr. Ure shows that the rever- 

 beratory furnace with pit-coal occasions less loss of metal 

 than the blast-furnace, and is by far the most economical. 

 To produce a ton of metal by the former process requires, 

 v before stated, a ton and three-quarters of pit-coal, while 

 a ton and six-tenths of wood-charcoal is consumed in pro- 

 P. C., No. V 



ducing the like quantity of metal by the blast-furnace ; 

 and as one ton of wood-charcoal is about equivalent, in 

 calorific effect, to two tons of pit-coal, the difference in 

 favour of the reverberatory plan is very great. The supe- 

 rior 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 pur- 

 pose. 



Manufacture of Tin-ware. It is unnecessary here to enu- 

 merate the various purposes to which tin is applied in the 

 useful arts, either as an ingredient in many useful alloys, for 

 which its ready fusibility, its cleanliness, and its beautiful 

 appearance render it especially valuable, or as the basis of 

 chemical compounds used in dyeing, &c. It is rarely 

 employed alone in our metalline manufactures, but when 

 laid in a thin coat upon the surface of sheet-iron by the 

 process of TINNING, it produces a material of such exten- 

 sive use in the manufacture of culinary and other articles, 

 that a more detailed notice may be given. Holland ob- 

 serves that in this country the greater portion of the tin 

 used in the manufacture of articles composed exclusively 

 of that metal is that which is expanded by rolling or ham- 

 mering, or by a combination of the two operations into 

 leaves or sheets barely one-thousandth part of an inch in 

 thickness, under the name of tin-foil. This is the sub- 

 stance which is laid upon the back of glass mirrors, and 

 there amalgamated with mercury, so as to form what is 

 called the silvering. 



The art of tin-plate working, or of forming sheets of 

 tinned iron into an almost endless variety of useful vessels 

 and utensils, depends more, observes the author just cited, 

 on the manual dexterity of the workman than upon any 

 peculiarity in the tools which he requires, which are few 

 and simple, consisting of bench and hand-shears, mallets 

 and hammers, steel heads and wooden blocks, soldering- 

 iron and swages. In the formation of a vessel the first 

 operation is to cut the plate to the proper size and form 

 with shears ; and when the dimensions of the article re- 

 quire it, to join them together, which is done either by 

 simply laying the edge of one plate over that of the other, 

 and then soldering them together, or by folding the edges 

 together with laps, and then soldering them. Similar joints 

 are required when gores or other pieces are to be inserted, 

 and also at the junction by which a cylinder is closed in. 

 The usual method of forming laps, bends, or folds for this 

 or other purposes is to lay the plate over the edge of the 

 bench, and to bend it by repeated strokes with a hammer ; 

 but as it is impossible by this means to make the bend as 

 even, or at as true an angle as is desirable, Mr. J. Basset, 

 of Birmingham, contrived a simple and effectual apparatus 

 Tor the purpose, for which he was rewarded by the Society 

 of Arts in 1831. An end view of this apparatus is given 

 in the subjoined cut, in which a a represents a metal block 

 screwed down firmly to a bench, and having a longitudinal 

 cylindrical cavity, within which is laid a long iron cylinder, 

 :he end of which is distinguished in the cut by a tint. The 



liameter of the cylinder is such that it will turn freely 

 upon its axis within the cavity in which it lies, and which 

 las a slit or opening about half an inch wide along the top 

 if the cylinder at b. A squared axis projects from each 

 nd of the cylinder to receive a handle c c , which, when 

 he instrument is at rest, lies in an horizontal position, and 

 s supported by the block d. These handles are not fixed 

 the square axes of the cylinder, but are capable of being 



VOL. XXIV. 3 P 



