Into
a charcoal crucible 80 grammes of aluminium is introduced in large
morsels, and 100 grammes of boric acid reduced to fragments. This
crucible is placed with charcoal paste in a crucible of plumbago, and
the whole is subjected to the action of heat in a furnace producing a
heat capable of easily melting pure nickel. This temperature is kept up
for five hours; and when, after the cooling, the crucible is broken
open, it is found to contain two distinct layers. The lower layer is
vitreous, and formed of boric acid and alumina; the other is metallic,
gray, and cavernulous, and is roughened and impregnated throughout its
whole mass with little crystals: this is crystallized boron.
The
mass in which these crystals are distributed is formed principally of
aluminium, but it contains also variable quantities of iron and of
silicon.
The
whole is boiled in a lixivium of soda, of medium concentration, when
the aluminium dissolves. That which remains is boiled with hydrochloric
acid, and the iron is thus removed. The part not yet attacked is
treated by a mixture of hydrofluoric acid and nitric acid, which
removes the last traces of silicon. The boron, which has not
experienced the slightest action under the influence of the preceding
agents, remains as the definitive residue.
The boron thus obtained, however, is not per-
