Tin-stone, or vein tin, as it is called in Cornwall, contains a large proportion of stony matters; it therefore requires considerable care in its preparation, previously to its being reduced. It is first broken by hammers into pieces about the size of a hen's en when it is ready for the operation of stamping, which is performed in the way already described for the ores of gold excepting that there are only three stampers. A tin plate of about a foot square, and pierced with holes, to admit a moderate sized knitting needle, is inserted in front of the trough, and that surface of the plate with the rough extremities of the holes is on the inside, by which the holes are prevented from being plugged up with the ore. As the ore is reduced to the proper fineness, it passes with the water through the holes into the labyrinth where it is collected, and after being washed on a wooden table, it is ready for roasting. In this state it has a considerable proportion of copper and iron pyrites, and is called black, tin; after being calcined, at a low red heat, for several hours in a large rever-beratory furnace, the ore comes out of a bright ochrey red colour, owing to the decomposition and oxidation of some of the metallic substances; but the oxide of tin, when the operation is properly conducted, remains unaltered.
The ore is washed a second time, to separate the remaining impurities, and the water, which is impregnated with sulphate of copper, is retained, and decomposed by means of old iron. The reduction of the ore is the next step in the process; seven cwt. of roasted ore, with one fifth of its bulk of small coal, are introduced into a reverberatory furnace, which is about seven feet long, and three and a half wide - no lime, or, indeed, flux of any kind, is required. A brisk heat is kept up for about six hours, the tin sinking down as it is reduced, and covered with black scoriae. The furnace is now tapped, and the metal flows into a shallow pit; when the whole of the metal has run out, the scoriae are removed from the furnace, and a fresh charge is made. The metal in the pit throws up a slag, rich in metal, which is immediately returned into the furnace, and after the melted tin has cooled a little, it is taken out with ladles, and poured into granite moulds; each charge affords on an average from four to five cwt. of metal, but as the first scoriae are not entirely free from metal, they are again stamped and washed, and mixed with a new parcel of roasted ore.
The pigs of tin are next put into a small reverberatory furnace, where, without any addition, they are subjected to a very gentle heat; the purest part of the tin melts first, and is drawn off, forming what is called common grained tin; the other part contains some copper, arsenic, and iron, which is brought to a state of fusion, and cast into pigs, forming common tin.