It has been stated that the richer portion of the scoria left by the process of smelting is reserved for further operations. Such as contain email 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 ranch tin are rearmelted without any previous preparation. From these scorke, which are called pillion, an inferior kind of tin is produced by a second smelting.
Of the average quality of tin-ore, as prepared for the smelting furnaces, 20 parts yield from 12i to 13 parts of metallic tin, or from 62i to (35 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 this 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, its importance is indisputable ; and such is the effect of the superior economy of this and other metallurgic operations as performed in England, that experi ment 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 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 blou-ing-houses. 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 the 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 is added to the 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 is run off into a large vessel in which it Is allowed to settle. The scorn which flow 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 sub sequent operations are much the same as with block tin prepared in a reverberatory furnace with pit-coal. In order to convert the blocks of tin produced by the blast-furnace process into the form known as 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 the 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 tho 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 purpose.
Manufacture of Tin-ware.---lt, is unnecessary here to enumerate 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. Sc It is rarely
employed alone in our metalline manufactures owing to its softness, but when laid in a thin coat upon the surface of sheet-iron by the , process of TINNINO, it produces a material of extensive use in the manufacture of culinary and other articles. In this country the greater portion of the tin used in the manufacture of articles composed ex clusively of that metal is that which is expanded by rolling or hammering, or by a combination of the two operations, into leaves or sheets lardy one-thousandth part of an inch in thickness, under the name of tin foil. [Fens] The art of tin.plato working, or of forming sheets of tinned iron into vessels and utensils, depends more on the manual dexterity of the workman than upon any peculiarity in the tools he requires, which are few and simple, consisting of bench and hand-shears, mallets and hammers, steel heads and wooden blocks, soldering-irons, and swages. In the formation of a vessel the first operation is to cut the plates to the proper size and form with shears; and when the dimen sions of the article require it, to join them together, which is done either by simply laying the edge of one plate over that of the other, or by folding the edges together with laps, and then soldering them. Similar joints are required when gores or other pieces are to be in serted, 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. After a tin vessel has been rounded upon a block or mandril, by striking it with a wooden mallet, and the seams finished as above described, all its exterior edges are strengthened by bending a thick iron wire into the proper form, applying it to what would otherwise be the raw edges of the metal, and dexterously folding them over it with a hammer. By this means the appearance of the articles is improved, and their durability and strength are greatly increased. A superior kind of tin-ware, commonly known as block-tin, is carefully finished by beating or planishing with a polished steel hammer upon a metal stake; by which means the surface, which otherwise appears somewhat wavy, is made very smooth and silvery, especially after it has been polished with dry whiting. It is principally in the production of block-tin wares that swaging is resorted to as a ready means of producing grooved or ridged borders or other embossed ornaments. This process consists in striking the metal between two steel dies or swages, the faces of which bear the desired pattern, and are made counterparts to each other. The mouldings round the edges of dish-covers and other similar articles are produced in this way; the swages embossing the pattern in short lengths, and the article being gradually turned round until every part of its circumference has been submitted to their action. The lower die is usually fixed in an appa ratus to which moveable guides are attached to insure the correct position of the article to be operated on, and the upper is made in the form of a hammer, the handle of which is pivoted so as to insure its descent in precisely the right position. Sometimes the power is applied by simply working the upper swage or swage-hammeri itself ; but in other cases the head of the swage-hammer is struck with a mallet. Very many ornamental articles are produced by embossing or stamping tin-plate, in the same manner as other metallic sheets, with a fly-press or other machinery. Cheap coffin-plates are manufactured at Birmingham in this and theme and similar articles are sometimes lacquered, painted, or japanned. A very beautiful method of orna. meriting tin wares by producing a crystallised appearance on the surface was much practised a few years since, under the name of moire metal. lique. It is described under Montg.