The value of sulphur as an ingredient of gunpowder is due to the low temperature at which it inflames. It melts at a comparatively low temperature, 115° (293° F.), and inflames at abmit 293° (560° F.). Distilled sulphur, as used in the manufacture of gunpowder, consists of masses of clear yellow crystals in the form of rhombic octahedra, and is readily soluble in bisulphide of carbon.
Figs. 595, 596 show the iron pot or retort in whioh the process is carried on; Fig. 596 is a section through water jacket, and Fig. 595 a section through pipe to subliming dome. The apparatus employed consists of a largo pot of oast iron A, about 1 ft. 8 in. deep, 3 ft. 4} in. in diameter at the mouth, and about 2 ft. 2 in. at bottom. The metal of the pot is very thick, being about 2i in.
thick at the edge, and nearly 6 in. at bottom; round the top edge is shrunk a strong ring or tire ??r wrought iron to prevent splitting by expansion ; this pot is set in brickwork; on the top of it is fitted a large dome-shaped cover, also of cast iron, secured to the pot by three wrought-iron tie rods, which aro secured by screw bolts to a wrought-iron ring passing round the neck of the cover.
At the top of the cover is a circular opening, 1 ft. 6,1 in. in diameter at top, and 1 ft. 3; in. at bottom, fitted with a heavy cast-iron lid, the weight of which is sufficient to keep it in its placo during the refining process. In this lid is a 4 in. iron plug-hole with a considerable amount of taper, through which the pot is charged. The cast-iron plug which closes it fits sufficiently tightly to prevent escape of sulphur-vapour, particularly if a little sand be thrown over it ; but at the same time it acts as valve, being lifted out if an unusual pressure of vapour is exerted inside the pot.
From the dome-shaped cover two pipes proceed at right angles to each other, one D to the sub liming dome E, the other B to the distilling tank or receiving pot O. The first pipe is l ft. 3 in. in diameter, and is furnished with a throttle-valve which can be closed or opened by a handle from without, so as to shut off or open the communication between the pot and the dome when required ; the other pipe is encased in a water-jacket, and can be closed or opened by means of a conical valve worked by a screw. When distilling, a constant flow of water is maintained through tho water
jacket from a cistern overhead, which is filled by a force-pump in the house. There is an escape pipe fitted to the water-jacket, to allow of the escape of water when there is a sudden development of steam, caused by the heat of the sulphur-vapour ; this pipe leads directly into the receiving pot. The receiving pot is a large circular vessel of cast iron, 3 ft. 6 in. in diameter, which is set ou a frame mounted on small trucks, to allow of a slight movement, when the pipe which connects it with the melting pot becomes expanded and lengthened, by the heat of the sulphur-vapour passing through it. There is a large opening through which the melted sulphur can be ladled out when necessary ; this is closed by an iron lid similar to that of the melting pot, in which is also a small plug-holo, through which the depth of melted sulphur in the receiving pot can be gauged with an iron rod. A small pipe leads from another opening in the lid of the receiving pot, into a square wooden chamber lined with lead to receive any non-eondensed vapour, and cause it to deposit its sulphur in the form of flowers. This chamber is provided with a tall chimney, also of wood, con taining a series of steps or traps to catch as much of the flowers as possible.
The subliming dome E is a large dome-shaped building of brick, 10 ft. in diameter at base, and about 12 ft. in height. The pipe from the sulphur pot enters it near the top; the chamber is lined with flag-stones, and the floor is covered with sheet lead ; it is provided with two doors, an inner one of iron, an outer one of wood, lined with sheet lead, both close fitting, through which passes a pipe to allow the escape of air ; this pipe terminates in a vessel of cold water.
In the ordinary course of distilling sulphur for powder-making a small amount must always pass into the subliming dome. Very often distilling and subliming are carried on together ; but in this case the temperature of the dome is not allowed to fall, and it is thus found perfectly prac ticable to obtain both distilled and sublimed sulphur at the same time, but it is better on the whole to carry on the two processes separately.