AMMONIUM COPPER TETRASULPHIDE. 139
combined filtrates to crystallization and proceed as in Method 1
with the recrystallization, etc. Yield, about 60 g.
1- Potassium Ferric Sulphide, K[FeS 2 ].
Place an intimate mixture of about 30 g. iron powder, 180 g.
flowers of sulphur, 150 g. potassium carbonate, and 30 g. anhydrous
sodium carbonate in a Hessian crucible, and heat the mass in a
charcoal furnace until it is melted to a thin liquid. This takes
about an hour. Close the furnace and let the melt cool slowly;
break the crucible and digest the lumps of the melt with warm
water in a porcelain dish until they are completely disintegrated.
From time to time replace the resulting green solution with fresh
water until nothing more dissolves and pure, glistening, dark
needles remain behind. Wash the product with water and alcohol
and dry it in the steam closet. Yield, about 70 g. Confirm the
composition by a quantitative analysis. The experiment can be
performed on a smaller scale using about one-sixth as much of
each substance. In this case a porcelain crucible and a blast lamp
or Meker burner should be used.- Ammonium Copper Tetrasulphide, NHJCuSJ.
It is known from qualitative analysis that copper sulphide dissolves appre-
ciably in ammonium or sodium polysulphide. Alkali salts of thio-copper acids
are thereby formed of which the one under consideration has been best in-
vestigated.^2
Place a mixture of 200 c.c. of concentrated ammonia and 50 c.c.
of water in a closed flask, and while keeping the liquid cooled with
tap water, pass in hydrogen sulphide until it is saturated. Dis-
solve in one-half of the solution as much finely powdered sulphur
as possible at 40° (about 60 g.), then filter this and add it to the
other half of the solution.
While rotating this solution in a flask, add a 10% solution of blue
vitriol little by little until a permanent precipitate of copper sul-
phide just begins to form; filter immediately through a plaited
filter into an Erlenmeyer flask; the latter should be filled almost
completely with the liquid. On standing, best in an ice-box,
(^1) The yield corresponds closely with the reaction as given by Mitscherlich:
8 Sb 2 S 3 + 16 S + 18 Na 2 CO 3 + 3 H 2 O = 10 Na 3 SbS 4 + 3 H 2 Na 2 Sb 207 + 18 CO 2.
(^2) H. Biltz and P. Herms, Ber. 40, 977 (1907).