Laboratory Methods of Inorganic Chemistry, 2nd English Ed. 1928

CRYSTALLIZED SILICON. 19

Yield, 30 to 33 g. With smaller amounts of the mixture, a por-

celain crucible (which is, however, very liable to break) may be

used and heated over the blast lamp.

2. Ignite an intimate mixture of 70 g. ignited chromic oxide,
   Cr 2 O 3 , 20 g. of fused and powdered potassium dichromate, K 2 Cr 2 07,
   and 32 g. of aluminium powder in one portion with magnesium
   powder and potassium nitrate paper exactly as described in the
   preparation of manganese (No. 2). Yield, 30-35 g. of chromium
   contained in one large regulus and several smaller globules.
   Dependent preparation, Anhydrous Chromic Chloride, No. 44.


3. Crystallized Silicon.

Heat some pure, sifted sand in a small evaporating dish until

thoroughly dried. Mix together 90 g. of the dried sand, 100 g.

of aluminium powder, and 120 g. of flowers of sulphur in a clay

crucible which is half filled thereby. Cover the mixture with a

little magnesium powder and start the reaction by igniting the

latter. The experiment must be performed out of doors, or

under a hood with a good draft, as considerable sulphur dioxide is

evolved. After cooling, break the crucible and cover the fused

pieces with water in a dish also placed under the hood; hydrogen

sulphide is set free by the hydrolysis of aluminium sulphide.

The aluminium hydroxide and oxide are easily rinsed off from

the regulus of metal. Treat the grayish-black, glistening metallic

regulus, and any smaller globules of metal that can be extracted,

in a beaker with strong hydrochloric acid, keeping it in a warm

place for several days and renewing the hydrochloric acid from

time to time until finally all of the excess of metallic aluminium

has been dissolved away and a loose mass of silicon leaflets re-

mains. Finally boil the crystalline mass with concentrated

hydrochloric acid for some time, cool somewhat and transfer to

a platinum dish. Add hydrofluoric acid in small portions to react

with any silica present. This usually causes considerable evolu-
tion of heat. Heat on the water bath for 45 minutes to remove

the excess hydrofluoric acid, dilute with water and wash by

decantation. Drain the crystals by suction, wash them well with

water, and dry in the hot closet. A further treatment of the metal

with hydrochloric and hydrofluoric acids should have no effect.
Yield, 20 to 25 g. Dependent preparation, No. 51.