Preparation of mercury sulfide
Mercury sulfide is conveniently prepared by direct synthesis from mercury and sulfur. Two modifications of this compound are known, one black, which is formed first in this preparation and also by precipitation of mercuric with the ions of sulfide. The other a brilliant red mercury sulfide or vermilion, which is more stable and into which the black form tends to change.
Mercury Sulfide: 20 g of mercury and 8 g of sulfur are placed in a large porcelain mortar and triturated with moistening by sodium sulfide solution. When the globules of metallic mercury seem to have entirely disappeared, 15 ml 6N KOH solution is added and by rinsing as much as possible of the black paste is transferred into the 4-inch dish. Additional 10 ml of water is used to finish rinsing the material into the evaporating dish.
The evaporating dish is covered and left to stand at a temperature of about 50° C. The loss of water by evaporation is replenished by adding some water as often as each day. At the end of about a week, the mass has changed to a pure red color, which is decantated in a 600 ml beaker, where most of the excess of sulfur is floated off.
Mercury Sulfide: The red mercury sulfide is rinsed back into the evaporating dish, leaving behind in the beaker any lumps of black sulfide or globules of mercury. The red sulfide is heated with 50 ml of saturated sodium sulfite solution to remove the last of the uncombined sulfur, then washed by decantation with boiling water and collected the mercuric sulfide on a suction filter. The mercury sulfide is dried on the hot plate and preserved in a stoppered bottle.
Synthetic inorganic chemistry, by A. A. Blanchard, 151-152, 1936
25 g of mercury(II) acetate and 25 g of ammonium thiocyanate are dissolved in 100 ml of hot glacial acetic acid. A steady stream of hydrogen sulfide is passed into the solution until precipitation is complete and then the acetic acid is slowly evaporated with frequent stirring in an air bath (GOOD HOOD HCN!!!). The initially black material turns slowly red as the acid boils away.
To prevent the formation of a discolored product, overheating must be avoided and stirring must be maintained constantly in the final stages of the evaporation. When all the acid has been removed, the mercury(II) sulfide is cooled and 200 ml of distilled water are added. The mercury(II) sulfide is suction-filtered, washed with 95% alcohol, and then dried at 100° C. The yield of mercury(II) sulfide is 25 g.
Inorganic laboratory preparations, by G. G. Schlessinger, 25, 1962
From 13.5 g of mercury(II) chloride in 200 ml of hot water, black mercury(II) sulfide is precipitated completely by hydrogen sulfide. The residue is washed by decantation with boiling water until the rinsings are no longer acid. The mercury(II) sulfide is drained well, then 10 ml of saturated ammonium sulfide solution and 12 g of 20% potassium hydroxide are added to it.
The mixture is transferred to a 50 ml Erlenmeyer flask, stirred well, and the flask is placed in an oven at 50° C for one week, replacing the evaporated water and agitating the reaction vessel daily. At the end of this time the color should be bright red. The mercury(II) sulfide (cinnabar) is washed and suction-filtered, washed with 95% alcohol, and then dried at 100° C. The yield of mercury(II) sulfide is 11.5 g.
Inorganic laboratory preparations, by G. G. Schlessinger, 25-26, 1962