The thus purified lye is boiled a second time with flowers of sulphur, added in small doses until saturation is indicated by bubbling and effervescence. The simple (monosulphide) potassium sulphide in this manner takes up four additional atoms of sulphur, and becomes the pentasulphide. The preparation of the vermilion then proceeds in the following manner:--Into a series of large flasks are put 11 lb. of mercury, 5 lb. of the potassium sulphide lye, and 2¼ lb. of sulphur. The contents are subjected to a moderate heat, and the flasks are then agitated in a curious manner by arranging them in pairs in baskets suspended from strings, over a straw mattress, on which the baskets bump each time they descend. Occasionally the flasks are turned about, and after about two hours of this agitation they commence to grow hot, and the contents assume a greenish-brown colour. The lye is robbed of its sulphur by the mercury, and replenishes itself from the excess added. Complete combination of the mercury and sulphur is accomplished in about three and a half hours, when the colour of the mass becomes dark brown. The next step is to cool the compound, an operation which must proceed very slowly, and should occupy about five hours. Development of the colour is effected by heat, for which purpose the flasks are placed in a stove room or water bath, and subjected to a temperature which does not fluctuate beyond 113° and 122° F., under the influence of which the red colour appears. The greatest care is necessary in this heating process, as it determines the success or failure of the colour. It lasts several days, during which the flasks should be shaken three or four times daily. In order to separate the vermilion from the excess of sulphur, water is added to the contents of each bottle, and, after thorough shaking, the whole is turned out into a filter. The clear liquor escapes, and the residual vermilion is mixed with caustic soda lye in stoneware jars, and thus the remaining free sulphur is dissolved out. Subsequently the lye is poured off as completely as possible, and the deposit is repeatedly washed, first by decantation and finally on a filter. The whole operation of filtering and washing cannot be completed in less than two or three days. When this is finished, the drying must be carried on at a very low temperature, till the vermilion can readily be broken and is dry to the touch, when it is put into iron basins and repeatedly stirred, while the temperature is allowed to reach 143° F., but never beyond that. The final desiccation occupies about five hours. Vermilion made in this way is reputed more permanent and less costly than by the usual methods.