The arrangements of the works for the manufacture of vermilion in the dry way consist of:—One sulphur stamp battery. One amalgamating plant with eighteen small barrels; both pieces of apparatus being driven by a two horse-power water-wheel. Four sublimation furnaces, each with six retorts of cast iron. Four vermilion mills, each driven by a water-wheel of 2·5 horse-power. Kettles and vats for heating, digesting, and refining the ground cinnabar. One drying hearth. The preparation of vermilion as an article of commerce, falls into several separate operations, viz.:
1. Amalgamation; i. e. preparation of the raw mohr.
2. Sublimation; i. e. preparation of the cake cinnabar.
3. Grinding of the cake cinnabar, refining and drying of the vermilion.
For the preparation of the raw mohr, for each charge of eighteen kegs there are taken 80·64 kg. (117½ lb.) powdered and sifted sulphur, and 423·36 kg. (731½ lb.) of quicksilver.
The amalgamating kegs each contain 28 kg. (61½ lb.) of the charge, and are given intermittent rotating motion by a rack and pinion driven by a water-wheel. After an average of two and three-quarter hours, the amalgamation is complete, and the raw mohr is taken from the casks.
For the sublimation, four furnaces are used, each with six pear-shaped cast-iron retorts of considerable thickness. Each is charged with 58 kg. (127½ lb.) of mohr, the mouth covered with a loosely placed sheet-iron helmet, the furnace being slowly fired; the combination of the sulphur and the quicksilver then results in about fifteen minutes, with a detonation. As soon as this operation (das Abdampfen) is over, a clay helmet is placed over the retort, and the firing is increased, so that after two hours and twenty minutes the excess of sulphur evaporates from the tube. The condenser is now added (Stückperiode—Cake-period) and luted, then the firing is still more urged, whereupon the cinnabar volatilises and deposits itself upon the glazed earthenware condensation apparatus (tube, helmet, &c.). After four hours, the sublimation is complete, and there is furnished by the helmet 69 per cent., by the tubes 26 per cent., by the condenser (Vorlage) 2 per cent., cinnabar.
The grinding of the cake cinnabar takes place in four mills driven by an undershot water-wheel. These mills have a fixed under and upper movable stone, and the grinding is done with water. The vermilion which leaves the spout and runs into glazed clay vessels has a temperature of about 100° F., that of the air being 59° F. The millstones make forty revolutions per minute, and after each passage of the charge are placed nearer together.
(2) A German chemist named Fleck has discovered that when a warm solution of hyposulphite of soda is added to a double salt of mercury, such as chloride of mercury and sodium, the solution becomes acid, and black sulphide of mercury is deposited. But if the hyposulphite solution is added in excess, and the temperature is not allowed to rise beyond 140° F., the solution remains neutral, and red sulphide of mercury, or vermilion, is deposited. The least quantity of acid causes the production of the black sulphide. The presence of a salt of zinc facilitates the production of the vermilion. The best method is as follows:—To four equivalents of hyposulphite of soda mixed with four equivalents of sulphate of zinc in diluted solution, is added, drop by drop, a solution containing one equivalent of corrosive sublimate. The whole is gently heated for 60 hours, at a temperature of 112° to 130° F.
(3) The following account of vermilion manufacture in China appeared over the initials T. I. B., in the Chemical News.