Metallurgy. The metallurgy of tin is very simple. The ore, separated as far as possible from earthy materials, is mixed with carbon and heated in a furnace, the reduction taking place readily. The equation is
SnO2 + C = Sn + CO2.
The metal is often purified by carefully heating it until it is partly melted; the pure tin melts first and can be drained away from the impurities.
Properties. Pure tin, called block tin, is a soft white metal with a silver-like appearance and luster; it melts readily (235°) and is somewhat lighter than copper, having a density of 7.3. It is quite malleable and can be rolled out into very thin sheets, forming tin foil; most tin foil, however, contains a good deal of lead.
Under ordinary conditions it is quite unchanged by air or moisture, but at a high temperature it burns in air, forming the oxide SnO2. Dilute acids have no effect upon it, but concentrated acids attack it readily. Concentrated hydrochloric acid changes it into the chloride
Sn + 2HCl = SnCl2 + 2H.
With sulphuric acid tin sulphate and sulphur dioxide are formed:
Sn + 2H2SO4 = SnSO4 + SO2 + 2H2O
Concentrated nitric acid oxidizes it, forming a white insoluble compound of the formula H2SnO3, called metastannic acid: