150 NON-METALLIC ELEMENTS IN BINARY COMPOUNDSbegins to get hot. A white puff of smoke indicates that the re-
action is taking place. If one can see the charge one can see an in-
candescence rapidly spread through it. After this reaction, leave the
crucible in the furnace for 30 seconds, then remove it with the tongs
and pour the liquid contents into the iron pan. Leave the latter
unmoved until the contents have solidified. Then, working in the
furnace room, crack the brittle aluminum sulphide from the lead;
place the latter in the box for scrap lead, and pack the aluminum
sulphide in a 2-ounce common bottle fitted tightly with a cork
stopper. Caution: Aluminum sulphide reacts with the moisture
of the air producing hydrogen sulphide. Do not take any part of
the preparation outside of the furnace room except the well-
stoppered bottle of product. The crucible with adhering alumi-
num sulphide can best be disposed of by putting it in a pail of water
as soon as it is cool, thus getting rid of the hydrogen sulphide all
at once.
QUESTIONS- Experiment. Drop a small lump of aluminum sulphide
(at the hood) into a test tube of water. What is the gas formed,
and what is the insoluble residue left? This is a case of hy-
drolysis. Write the equation in ionized form, and name the acid
and the base. - Lead sulphide does not hydrolyze. Compare the basic
strength of Pb(OH) 2 and A1(OH) 3. Does this fully account for
the difference? Perhaps the relative solubility of PbS and A1 2 S 3
would account for some of the difference. Explain how. Would
this explanation require the solubility of AI2S3 (as such) in water
to be greater or less than that of PbS?
PREPARATION 11
CALCIUM SULPHIDE, CaS
In this preparation an oxy-salt of sulphur, calcium sulphate, is
reduced at a high temperature by means of carbon. Calcium is
too active to be reduced to the metal by this means, but sulphur
is readily reduced from its valence of +6 to its minimum valence
of -2.
The most abundant source of calcium sulphate is the mineral
gypsum CaSO 4 -2H 2 O. We desire anhydrous CaSO 4 as our start-