A beautiful scarlet-red pigment. It is usually obtained from mercury, being the red sulphuret of that metal. It is said, by some authors, that the Chinese vermilion is a sulphuret of arsenic: others, on the contrary, assert that it is prepared from the cinnabar of the East, which being an ore of mercury, already combined with sulphur, renders it an obvious and an easily conducted process. Large quantities of vermilion are manufactured by the Dutch. Their process consists in grinding together 150 pounds of sulphur, and 1000 of quicksilver, and then heating the AEthiops mineral thus produced, in a cast-iron pot, two feet and a half in diameter, and one foot deep. If proper precaution is taken, the AEthiops does not take fire, but merely clots together, and requires to be ground. Thirty or forty pots, capable of holding twenty-four ounces of water each, are then filled in readiness with this AEthiops.
The sublimary vessels are earthen bolt heads, coated two-thirds of their height with common fire-lute, and hung in the iron rings, at the top of three pot furnaces, built in a stack under a hood or chimney, so that the fire has free access to the coated part; each sublimer has a flat iron plate, which covers the mouth of it occasionally. The fire being lighted in the evening, the sublimers are heated gradually to redness. A pot of AEthiops is then flung into each sublimer; the AEthiops instantly takes fire, and the flame rises from four to six feet high; when the flame begins to diminish, the sublimer is covered for some time. By degrees, and in the course of thirty-four hours, the whole of the AEthiops is put into the sublimers, being 410 pounds into each. The sublimers being thus discharged, the fire is kept up, so that on taking off the covers every quarter or half-hour, to stir the mass with an iron poker, the flame rises about three or four inches above the mouth of the sublimer. The sublimation usually takes thirty-six hours, and when the sublimers are taken out of the furnace, cooled, and broken, 400 pounds of vermilion are obtained from each.
Kirchoff first showed, that by commingling and triturating mercury, sulphur, and potash together, and applying heat, cinnabar might be obtained; but the process was uncertain, and gave variable quantities of vermilion. The following is a process recommended by M. Bruner:-
Mercury . . .. . . . . . . . . . . . . . . . . .
Sulphur . .. . . . . . . . . . . . . . . . . .
Caustic potash . .. . . . . . . . . . . . . . . .
Water . .. . . . . . . . . . . . . . . . . . .. . .
400 to 450
The mercury and sulphur are first triturated together, from three hours to a whole day, according to the quantites used. When the mixture is homogeneous, the solution of potash is added, the trituration continued, and the mixture heated in an earthen vessel or porcelain, or, if on a large scale, of iron. At first, the stirring must be constant, afterwards, from time to time. The heat should be sustained 113°; it should never pass 122°. The liquid should not be allowed to diminish by evaporation, but be made up. After some hours, the mixture will acquire a reddish brown colour, and then great care is required: the mixture must not pass 113°. If it becomes glutinous, a little water should be added; the mixture of sulphur and mercury should always be in a pulverent form in the liquid. The colour becomes more and more brilliant, and at times increases with astonishing rapidity: when it has attained its highest intensity, the vessel is to be taken off the fire, but still to be retained warm for several hours. The time necessary for the application of heat, appears to be directed as the quantity operated upon.
If the proportion above be in grammes, (about 15 1/2 grains each,) the red colour will appear in about eight hours, and the operation be finished in about twelve hours.
The cinnabar is then to be washed, and the small quantity of metallic mercury that may be present, separated; from 328 to 330 parts of vermilion will be obtained, of a colour, equalling that of the native cinnabar, and far surpassing that of cinnabar obtained by sublimation. The mercury and the potash should be quite pure.