45. Tin, when pure, is a metal of whiteness and brilliancy next to silver. It is highly malleable, but inferior in ductility and tenacity to all metals, except lead. Little affected by the atmosphere, at ordinary temperature, it is extensively used in manufacturing tin plate. Tin is not a widely distributed metal; on the contrary it is extremely scarce and very rarely found in the natural or pure state.

Of tin ore there are two kinds, tin stone and tin pyrites. It is found principally in Cornwall, England; Bohemia and Saxony in Continental Europe; in the Malayan Peninsula; Australia; and more recently, in the United States of America.

46. Tin plate is sheet iron or steel coated with tin. The plates of sheet iron are first well cleaned by washing, then dipped in melted tin, and afterwards in a solution of diluted sulphuric acid, this last process being known as pickling. The sheets are then scoured with fine sand and water and afterwards dried. To obtain the proper softness, they are next annealed, sorted, and passed between rollers which impart to them an even thickness. This rolling hardens the plates, after which they are again annealed, sorted, pickled, and trimmed.

The sheets, by this process, go through six different baths: (1) the tinman's pot, containing grease; (2) the tin pot, containing melted tin; (3) the washing pot, containing melted tin, covered with grease in one compartment; (4) the plates are then brushed to remove excessive tin, then dipped in the other compartment containing the purest of tin; (5) the cold pot, containing tallow heated to a low temperature; (6) the list pot, containing tin, in which the edges of the plates are dipped.

Crystalline tin is produced by the application of a mixture of diluted nitromuriatic acid, for a few seconds, to heated tin plate, then washing the plate with water and drying.

47. The tests for tin plate are for ductility, strength, and color. To possess these attributes, the iron must be of the best quality, and the process of tinning must be conducted with skill.

Good tin plate is determined by the following conditions: The sheet should bear cutting into strips of a width equal to ten times the thickness of the plate, both across the fiber and in line therewith, without splitting. These strips must, while hot, stand the strain of being bent on a mold, the circumference of which is equal to four times the width of the strip. The plates when cool must bear bending on a heading machine to such an extent as to form a cylinder whose maximum diameter shall be equal to sixty times the thickness of the plate. If there be any suggestion of lead in the tin, apply to the latter a few drops of pure acetic acid, and a whitish coating will appear. Add to this a few drops of potassium chromate solution. If it turns yellow, the tin has lead in it; the more lead the deeper the yellow.