If distillation only is to be oarried on, about 5i cwt. of raw sulphur is placed in the pot each morning ; an extra hundredweight would be put in if both distilling and subliming together.
The Sre being lighted, the conical cast-iron plug is left out of the hole in the lid of the pot, the passage into the dome is opened and that into the receiving pot closed ; the heat is maintained for three hours, till the sulphur is of a proper temperature for distillation. The vapour which first rises from the pot is of a pale yellow colour, and as much of it as passes into the dome falls down con densed as flowers-of-sulphur, but at the end of three hours the vapour becomes of a deep reddish brown colour, showing that the temperature of the melted sulphur has reached the proper point. The plug must then be inserted in the lid, the communication to the dome closed, and that leading to the receiving pot opened, allowing the heavy vapour to pass through the pipe surrounded with the water-jacket, by means of which a constant circulation of cold water is kept up round it ; in this way the sulphur vapour is condensed, and runs down into the receiving pot as a clear orange liquid resembling treacle in colour and consistency. By gauging the depth of the melted sulphur in the receiving pot, it can be ascertained when the of the material has distilled over ; the fire is then lowered, the communication into the dome opened, and that leading to the receiving pot cut off, allowing the remaining sulphur to pass off into the dome as flowers. A low fire is main tained till the whole has been driven off, leaving the earthy residue quite free from it, and conse quently loose like coal ashes, so that it may be easily ladled out next morning before recharging the pot.
When both subliming and distillation are carried on at once, the first part of the process would be the same ; but when the distillation was finished the fire would be maintained for the remainder of the day, but somewhat lower, to drive off the quantity required into the dome, and in this case the subliming process would he carried on for several days, and the pot and dome never suffered to cool down altogether till the required quantity of flowers-of-sulphur had been obtained.
It is of the greatest consequence that the fire should be carefully regulated in all cases, for if the heat becomes too great, and the temperature of the melted sulphur be allowed to rise to 447° (836° F.), the vapour disengaged at that temperature is highly explosive when mixed with common air ; and if the plug be driven out by the pressure of the vapour, or if air be drawn into the pot through some leakage in the pipes, an explosion invariably happens. When the distilled sulphur in the receiving pot has cooled down sufficiently, which it will do in the course of an hour or two, it is ladled by hand into wooden tuba and allowed to solidify. Distilled sulphur immediately after being removed
from the tubs is placed within a boarded-off enclosure, to guard against coming in contact with any fragments of grit or sand, which might thus enter the powder, and is broken up into large lumps, which are sent up to the factory to be ground under a pair of mill-stones. After being ground it is reeled through 32-mesh wire-cloth, and is then fit for the mixing house; its fitness for use as an ingredient of gunpowder may be readily tested :— let. By burning a small quantity on porcelain, when the amount of residuum should not exceed 0.25 per cent.
2nd. By boiling with water and testing with blue litmus paper, which it should only very feebly redden.
As an ingredient of gunpowder, sulphur is invaluable on account of the low temperature at which it inflames, thus facilitating the ignition of the powder. Its oxidation by saltpetre appears also to be attended with the production of a higher temperature than is obtained with charcoal, which would have the effect of accelerating the combustion, and of increasing by expansion the volume of gas evolved.
Before the ingredients can he mixed they must be reduced to a powder sufficiently fine for the purpose. It is true that some manufacturers do not pulverize or mix their ingredients at all, but simply weigh out as much of each as is required in lumps and fragments, and throw them on the bed of the incorporating mill. But this obviously involves a loss of time, as the action of the incor porating mill must he at first merely that of grinding and bringing the three ingredients into juxtaposition, before any incorporation properly so called can be effected. It is important to bear clearly in mind the meaning of the terms mixing and incorporating, as they are used by gunpowder makers. Though gunpowder is really only a mixture, very intimate no doubt, of the three ingre dients, and not a new chemical substance formed out of them, yet by mixing is understood only the stirring together for a few minutes of the saltpetre, sulphur, and charcoal, to get them properly distributed amongst each other ; and by incorporating, the long continued trituration and grinding which the mixture undergoes under heavy edge-runners, by which a mass of the ingredients becomes transformed from a mere mixture of three different substances into gunpowder. A preliminary mixing, such as is employed at most gunpowder works, may he dispensed with ; incorporation, whether performed by pestle and mortar, in the stamping mill, or under edge-runners, never.