ALUMINUM SULPHIDE 149PREPARATION OF OTHER BARIUM SALTS
By suitable modification, the procedure used to prepare barium
chloride may be adopted to prepare other barium salts such as the
acetate, bromide, and nitrate. The final volume of the solution
should be adjusted so as to give a nearly saturated solution at
25°. The solubility of these salts will be found on page 365.
PREPARATION 10
ALUMINUM SULPHIDE, AI2S3
Although the obvious method of preparing a binary compound
would seem to be to bring the two elements together, such a
procedure is not very often followed. Aluminum and sulphur
can be made to combine directly, it is true, but when the finely
divided substances are mixed and the mixture is heated, either the
sulphur entirely distils off without any reaction taking place, or if
a reaction starts it is too violent to control. We have, therefore,
selected lead sulphide as a source of the sulphide radical because
this substance is not volatile and cannot escape before it reacts,
and the reaction is not too violent. A part of the energy furnished
by the combination of aluminum and sulphur is expended in sepa-
rating lead and sulphur.
Materials: granulated aluminum, Al, 27 grams = 1 F.W.
pulverized galena, lead sulphide, PbS, 359 grams
(a fairly pure sample of the mineral must be
used to obtain good results).
Apparatus: 30-gram clay crucible without cover.
6-inch sand bath pan.
gas furnace.
Procedure: Mix the powdered galena and granulated alumi-
num. Place the mixture in the clay crucible and put it in the gas
furnace. Place the cover on the furnace and if possible slip it a
little toward the front, so that, by standing on a stool, one can look
down through the hole in the cover and see the charge in the cru-
cible. Light the furnace and heat it as rapidly as possible. Make
sure the iron pan is dry by holding it with the tongs over the
furnace. Caution: If the pan should be wet, the heat of the
molten material poured into it would cause an explosive formation
of steam. Watch the furnace every moment of the time after it