SULPHUR, a non-metallic chemical element, also called "brimstone," has been known from remote times, and, owing to its inflammability, was regarded by the alchemists as the principle of combustion. Sulphur (symbol S, atomic number 16, atomic weight 32.064), is widely and abundantly distributed in nature, both in the free state and in combination. Various forms of free or native sulphur occur in volcanic areas, but they are all related to rhombic sulphur, the monoclinic form being unknown in a natural state. The crystals (see fig.) are of hardness 1-2, and sp.gr. 1.9-2.1; they are transparent or translucent; highly re fractive with strong birefringence, and have a characteristic lustre. Although pure sulphur is yellow, impurities such as selenium or arsenic sulphide give it a reddish tint.
Volcanic sulphur usually occurs as a sublimate on the walls of vents, probably as the result of action between hydrogen sulphide and sulphur dioxide. Natural sulphureous waters, especially if hot, readily deposit sulphur owing to atmospheric oxidation of the sulphuretted hydrogen. Free sulphur may also result from the weathering of pyrites, as in pyritic shales or lignites or from the pyrites of Rio Tinto (Spain). Atmospheric oxidation may affect sulphur itself, producing sulphuric acid, which in the presence of lime produces gypsum, and outcrops of sulphur in Sicily are often covered with this. Important deposits of sulphur in the world occur in Sicily in Miocene marls and limestone, in Transcaucasia and in the Transcaspian steppes, in Japan, Chile, Peru and in many States of the U.S.A., especially in Louisiana. Sulphur is also found occasionally in Carrara mar ble in Calabria, and in carboniferous limestone in Galway.
In combination, the element occurs chiefly in sulphides and sulphates of metals. The former are of great impor tance and value, e.g., copper pyrites, galena (lead), zinc blende, cinnabar (mercury). The sulphates include those of calcium (gypsum and anhydrite), barium (barytes), and magnesium (kies erite). Gaseous compounds occur in vol canic exhalations and in mineral waters. The element is also present in hair, wool, albumen (q.v.) and in certain vegetable
oils, such as those of garlic and mustard.
In Louisiana and Texas the deposits are covered by quicksand and cannot be mined by ordinary methods. The Frasch process was devised for this purpose: four concentric pipes, of diameters 1o, 6, 3 and I inch, are sunk in a bore hole, and superheated steam is forced down the 3-inch pipe to melt the sulphur. Com pressed air is driven down the centre pipe and causes the mixture of water and molten sulphur to rise in the outer pipes; this runs off into settling tanks and yields sulphur of over purity.
Sulphur is also obtained from pyrites either by distilling it in iron or fire-clay tubular retorts, whereby one-third of the sulphur is obtained in the distillate (3FeS2=Fe3S4+2S), or by a modi fication of the Sicilian process. Sulphur from pyrites, however, usually contains traces of arsenic.
Milk of sulphur is produced by boiling sulphur with a sus pension of lime until it has dissolved-5 parts of sulphur require about 2 parts of quicklime—and the solution is clarified, diluted, and nearly neutralised by pure dilute hydrochloric acid; this decomposes the calcium polysulphides, giving a very fine, almost white powder, which is washed and carefully dried. If too much acid is added, the calcium thiosulphate, which is formed together with the polysulphides, is also decomposed, and this gives a yellow, coarser product.