TIN-PLATE. The only alloy of iron interesting to the arts is that with tin, in the formation of tin-plate or white-iron. The sheet irorUntended for this manu facture is charcoal instead of coke, subsequently rolled to various de grees of thinness, and cut into rectangles of different sizes, by means of a shearing machine driven by a water-wheel, which will turn out 100 boxes a day, or four times the number cut by hand-labor. The first step towards tinning is to free the metallic surface from every particle of oxide or impurity, for any such would inevitably prevent the iron from allowing with the tin. The plates are next bent separately by hand into a saddle or A shape, and ranged in a reverberatory oven, so that the flame may play freely among then, and heat them to redness. They are then plunged into a bath, com posed of four pounds of mnriatic acid, diluted with three gallons of water, for a few minutes, taken out and drained on the floor, and once more exposed to igni tion in a furnace, whereby they are scaled, that is to say, cast their scales. An ordinary bath will suffice for scaling 1800 plates. When taken out, they are beaten level and smooth on a cast-iron block, after which they appear mottled blue and white, if the scaling has been thoroughly done. They are next passed through chilled rolls or cast-iron cylinders, render ed very hard by being cast in thick iron moulds. After this process of cold rolling, the plates are immersed, for ten or twelve hours, in an acidulous ley, made by fer menting bran-water, taking care to set them separately on edge, and to turn them at least once, so that each may ceive a due share of the operation. From this ley-steep they are transferred into a leaden trough, divided by partitions, and charged with dilute sulphuric acid. Each compartment is called a hole by the work men, and is calculated to receive about 225 plates, the number afterwards packed up together in a box. In this liquid they are agitated about an hour, till they be come perfectly bright, and free from such black spots as might stain their surface at the time of immersion. This process, called pickling, is both delicate and dis agreeable, requiring a good workman, at high wages. The temperature of the last
two steeps should be at least 90° or 100° F., which is kept up by stoves in the apartments. The plates are finally scoured with hemp and sand in a body of water, and then put aside for use in a vessel of pure water, under which they remain bright and free from rust for many months, a very remarkable circumstance. The tinning follows these preparatory steps. A range of rectangular cast-iron pots is set over a fire-flue in an apartment called the stow, the workmen stationing themselves opposite to the narrow ends. The first rectangle in the range is the tin-pot ithe second is the wash-pot, with a partition in it ; the third is the grease pot ; the fourth is the pan, grated at bot tom; the fifth is the list-pot, and is greatly narrower than any of the rest : they are all of the same length.
The prepared plates dried by rubbing bran upon them, are first immersed one by one in a pot filled with melted tallow alone, and are left there for nearly an hour. They are thence removed, with the adhering grease, into the first pot, filled with a melted mixture of block and grain tin, covered with about four inches of tallow, slightly carbonized. This pot is heated by a fire, playing under its bot tom and round its sides, till the metal be comes so hot as nearly to inflame the grease. Here about 840 plates are ex posed, upright, to the action of the tin &or an hour and a half, or more, according to their thickness. They are next lifted out, and placed upon an iron grating, to let the superfluous metal drain off; but this is more completely removed in the next process, called washing.
The plates are then dipped in the pot containing the melted metal: They are then lifted out with tongs, rubbed with a brush, re-dipped in the tin, and then im mersed in the grease-pot. It is dipped a third time, and the rim of tin removed from the under edge of the plate by dip ping the edge in melted metal, when the superfluous metal becomes detached. They are finally rubbed with bran to free' them from tallow, and then packed up in boxes.
Crystallized tin-plate, (see Monies ME