A second retort at these works measured 7 ft. 4 in. deep, and was elliptical in form, the greater axis being 4 ft.1 in. diameter, and the smaller 3 ft. 2 in. This made about 10 cwt. of bisulphide per twenty-four hours; but its great size was found inconVenient, as tho heating was rendered uneven and spasmodic, causing considerable waste of sulphur. When using unrefined sulphur, the retorts need cleaning every two weeks; but with clean sulphur, they may safely run two months. This cleaning is a very troublesome operation, causing much loss of time and material, and exer eisiug an injurious effect upon the workmen. The cast-iron retorts, when well built in, and thoroughly protected by fire-lumps, last about tweuty-two weeks.
Sidot has proved that temperature has a most important bearing on the product of bisulphide of carbon. He experimented with 40 grms. sulphur and 10 grms. purified charcoal, at three different temperatures, with the following results :— I. Dull red heat .. .. 5 gr. charcoal gave 17 gr. bisulphide.
2. Red heat 6.3 „ „ „ 29 „ „ 3. Blight red . 7.5 „ „ „ 19 „ „ The figures show the extent to which tho charcoal is consumed in each operation. They show incontestably that a red heat is the one best suited, and that great care should be taken to avoid exceeding it, ospeoially as there is danger of the bisulphide becoming divided up again at a high temperature, the carbon being redeposited, and the liberated sulphur distilling over with the bisnlphide. With every precaution, there is certain escape of sulphur in this way, giving the bisulphide the yellow colour peculiar to its crude state, and necessitating a precess of purification, to be described farther on.
The very poisonous aed inflammable characters of this substance render it one of the most dangerous chemical compounds, and necessitate tbe most rigid precautions in its manufacture, to prevent the least escape of the vnpour. The inhalation of tbe vapour produces, on the workmen employed, symptoms of depression, weakness, and loss of memory, which is sometimes followed by coma. A solution of ferrous carbonate in carbonic acid water is found to be partially effectual in relieving these symptoms; but attention must be devoted to prevention rather than cure, as besides the evil effect produced by the vapour, its escape represents a direct monetary loss.
The crude bisulphide always contains a considerable proportion of sulphur—sometimes as much as 10 per eent.,—besides various hydrogen compounds, formed, during the preparation of the
substance, by the action of nascent hydrogen on it, nnd producing the peculiar disagreeable odour which characterizes it. This crude bisulphide has then to uudergo purification, to fit it for the market. At Swoszowice, recourse is had to simple distillation in a water bath, and condensing the distillate in an unusually long cooling worm ; the product is a colourless bisulphide, but it always retains some sulphur, and loses but little of its bad smell. Numerous plans are adopted for securing more perfect rectification. According to one method, it is first washed several times with distilled water, and then transferred to a retort containing quicklirne. After twenty-four hours' contact, the bisulpbide is distilled off from the lime, and caught in a. receiver, partially filled with copper turnings, previously roasted to remove all trace of fatty matter, and afterwards reduced by hydrogen. The lime remaining in the retort is strongly coloured by the impurities eliminated from the bisulphide, whose disagreeable smell will be found to have departed. Another way of performing the operation is to mix the bisulphide with Pb2NO3, and a small quantity of metallic lead ; when the salt turns dark, tho liquid is transferred to another vessel with a fresh quantity of lead salt, and 80 on till the salt remains nearly white after contact with the liquid. The latter is then placed in a retort, and distilled over. Friedburg recommends the following process. The crude bisulphide is first distilled, then poured into fuming nitric acid, agitated, and left for twenty-four hours. The bisulphide becomes saturated with peroxide of nitrogen, and this solution, which is brown, remains unaltered for weeks. The addition of cold water causes the bisulphide to separate as a rose or violet-coloured liquid, which is distilled at 50°-60° (122°-140° F.), again agitated with cold water, and, after another distillation, is perfectly pure. Other proposed means of purification are :— 1. Agitation with mercury. 2. Agitation with 5 per cent. sublimate, and distillation with 2 per cent. colourless fat. 3. Distillation with soda hydrate solution chlorine in water, and solution chloride lime. 4. Distillation with solution chloride lime. 5. Several distillations with pure oil, the oil extracting each time some of the impurities.