152 NON-METALLIC ELEMENTS IN BINARY COMPOUNDS
Materials: mercury, Hg, 20 grams = 0.1 F.W.
flowers of sulphur, 8 grams.
6iV KOH, 15 cc.
saturated Na2SC>3 solution 50 cc.
sodium sulphide solution.
Apparatus: 4-inch porcelain dish,
large porcelain mortar,
warm closet or plate at about 50°.
600-cc. beaker,
glass spatula,
iron ring and ring stand.
Bunsen burner.
Procedure: Place the mercury and the sulphur in a large porce-
lain mortar, and triturate the mixture, moistening it with sodium
sulphide solution. When the globules of metallic mercury seem
to have entirely disappeared, add the KOH solution and with it
rinse as much as possible of the black paste into the 4-inch dish.
Use 10 cc. of water to finish rinsing the material into the evapo-
rating dish. Cover the dish with a watch glass and let it stand in
some place at a temperature of about 50°. Replace the water lost
by evaporation as often as each day. Stir the mass thoroughly
each time with a glass spatula.
When, at the end of about a week, the mass has changed to a
pure red color, wash it by decantation (see Note 5 (6), page 10)
in a 600-cc. beaker. Most of the excess of sulphur is floated off.
Then rinse the red sulphide back into the evaporating dish, leaving
behind in the beaker any lumps of black sulphide or globules of
mercury. Boil the red sulphide with 50 cc. of saturated sodium
sulphite solution to remove the last of the uncombined sulphur;
wash by decantation with boiling water and collect the mercuric
sulphide on a suction filter. Dry the product on the hot plate and
preserve it in a 2-ounce cork-stoppered bottle.
QUESTIONS
- Red and black sulphides of mercury have exactly the same
composition, as expressed by the empirical formula HgS. Would
you regard them as the same or as different substances? Give
your arguments.
