20 THE ELEMENTS.- " Crystallized Boron."^1
Mix 50 g. of anhydrous boron trioxide, 75 g. of sulphur, and
100 g. of granulated or powdered aluminium in a crucible and
bring the charge into reaction in the same manner as in No. 4.
After cooling break the crucible and the solidified melt, treat the
latter with water and rinse away the aluminium hydroxide, formed
by hydrolysis, as well as the microscopic, crystalline needles of
aluminium oxide. Pick out the lumps of regulus and free them
completely from the last traces of slag both mechanically and by
long continued boiling with water. Treat the 30 to 40 g. of
purified regulus particles thus obtained with concentrated hydro-
chloric acid, adding only a little at a time, and after the first
violent action is over let stand in a warm place several days
until all of the aluminium has dissolved away. A heavy, black,
shining mass of crystals is left. Remove the lighter impurities
by repeated decantation with water; boil with concentrated
hydrochloric acid, placing a round flask filled with cold water
over the beaker in order to condense the acid vapors; then warm
with hydrofluoric acid in a platinum dish for several hours, wash
again, and finally allow to stand in a warm place with dilute
hydrochloric acid until no more bubbles of gas are given off.
The last traces of aluminium dissolve very slowly.
About 7.5 g. of small, compact, mostly opaque, black crystals
are obtained which have a luster resembling that of hematite.
The thinnest crystals, which are most often six-sided, show a
deep dark-red color by transmitted light. The crystals scratch
glass. They were formerly taken to be pure crystallized boron;
their composition, however, corresponds to the formula A1B 12.
REDUCTION WITH POTASSIUM CYANIDE.- Tin from Cassiterite; Melting-point Determination.
Native stannic oxide, SnC>2, in spite of the fact that tin is closely related
to the noble metals, can be reduced by carbon only at a very high heat.
The reduction takes place far more readily with potassium cyanide, the
latter being oxidized thereby to potassium cyanate :^2
KCN + O = KCNO.(^1) H. Biltz, Ber. 41, 2634 (1908). According to the advice of Dr. K. Schaefer
it is well to add a little ignition mixture (barium peroxide and aluminium) to
the charge.
(^2) Some samples of cassiterite are not reduced readily.