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The improved method of purifying it is to submit it to distillation in alarge cast-iron still: the receiver , which is made of iron, is kept cool byimmersion in water. The sulphur obtained by this process is calledrefined sulphur. When cast in wooden moulds it constitutes stick, roll,or cane'sulphur (sulphur in baculis, — s. rotundum, — s. in rotulis). If it berequired to obtain the sulphur in a pulverent form, the above process ofdistillation is modified, thus:—The communication between the still andthe iron receiver is shut off, while another is opened with a large chamberor sulphur-house, on the walls of which the sulphur condenses in a pulverentform : in this state it constitutes sublimed sulphur, or flowers of sulphur{sulphur sublimatum, seu flares sulphuris). When washed with water toseparate a little adhering acid, it is termed washed sulphur (sulphur lotum).The method of purifying sulphur adopted at Marseilles , as described byDumas {op. cit.), is somewhat different to that now described, and which1 have seen practised in the neighbourhood of London .
(b.) Decomposition of metallic sulphurets. —In some places sulphur isprocured by the decomposition of metallic sulphurets (iron or copper).In Anglesea it is (or was) prepared by roasting copper pyrites, by whichpart of the sulphur is burned, while the remainder is volatilized and col-lected in chambers connected with the domes of the furnaces by meansof horizontal flues {Aikin's Diet, of Chem. vol. ii.)
The dregs remaining after the purification of sulphur are called horsebrimstone {sulphur vivum; sulphur caballinum; sulphur griseum).
Properties.— At common temperatures, pure sulphur is a brittle,crystallizable solid, of a yellowish green colour, without smell, and witha very weak and almost imperceptible taste. The specific gravity ofordinary sulphur is about T99, but, when free from air-bubbles, 2'087.It is a bad conductor of electricity, and, therefore, by liiction becomespowerfully electric. It is a bad conductor of heat, and when grasped inthe warm hand crackles, and sometimes breaks to pieces. It is fusible,volatilizable, and combustible. In atmospheric air it burns with a paleblue flame, and emits a large quantity of fumes having a peculiar suffo-cating odour {sulphurous acid.)
It is called dimorphous because it has two distinct primary forms. Theprimary form of the crystals of native sulphur, or of those deposited fromits solution in bisulphuret of carbon, is a right rhombic octahedron;while that of the crystals obtained by the fusion and slow cooling ofsulphur, is an oblique rhombic prism. Now these two forms are incom-patible, and cannot be derived the one from the other : the first belongsto the rectangular or rhombic right prismatic system ; the second to therectangular or rhombic oblique prismatic system.
When sulphur is heated to 340°, it becomes viscid ; and by increasingthe heat the viscidity increases, until the temperature arrives at between400° and 500°. If while in this state it be suddenly cooled, as by throw-ing it into water, it remains quite soft, so that it may he drawn out intothreads. The cause of this change, which seems to be merely physical,is not understood. The atomic weight of sulphur is about 16.
Characteristics. —Sulphur is easily distinguished from other bodies,by its colour, its fusibility, its volatility, and its burning with a blueflame, and the evolution of sulphurous acid gas, the odour of which canbe easily recognized.
Impurities. —Rough sulphur is always mixed with variable quantities
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