AMORPHOUS SULPHUR. 39or obsidian, possess such a viscosity that they appear to be solid bodies.
The amorphous solid condition is, therefore, not distinguished from the
fluid state by any discontinuity, but is so distinguished from the solid
crystalline condition. It is possible by certain expedients, for example by
continued heating at just below the melting-point, to hasten the rate of
crystallization, as in the devitrification of glass. With substances which are
capable of solidifying in either a crystalline or amorphous condition, the
quantity of crystals obtained is for this reason greater, the more slowly the
cooling takes place.- Amorphous Sulphur.
Distil 40 g. of sulphur from the bulb of a small retort and
allow half, as it condenses in the neck, to flow into a mixture of
ice and water, the other half into boiling water. Dry these two
preparations externally with filter paper, then leave them for
several hours at 50° to 60° to dry still further. The next day
extract 5 to 10 g. of each of the samples with carbon bisulphide
in a Soxhlet apparatus, using a weighed extraction-thimble.
Determine, by weighing again, the percentage of each sample of
sulphur which has been dissolved in the carbon bisulphide. The
sample which was slowly cooled dissolves almost completely,
since it has changed into the soluble rhombic form; the sud-
denly cooled sample leaves behind 30 to 50% of amorphous,
insoluble sulphur.
If a mixture of sulphur and ammonium carbonate is distilled,
and the sulphur, as in the first case above, is cooled suddenly in the
freezing mixture, a product is obtained which contains 90% of
the soluble rhombic form, since the presence of ammonia accel-
erates catalytically the transformation.
COLLOIDAL STATE.
A large number of substances are capable of apparently dissolving in water
to form what may be termed pseudo-solutions; such pseudo-solutions are
characterized by an extremely small diffusive power, a low osmotic pressure,
and an inability to undergo dialysis; in these respects they differ from true
solutions of crystalloids, and are thus called colloidal solutions (Graham, 1862).
Colloidal solutions are distinguished, according to the nature of the solvent,
as hydrosols, alcosols, etc. If the dissolved, or, more correctly, the pseudo-
dissolved substance is separated from the solvent, it is often found not to
have lost the power of again passing into colloidal solution (reversible colloids).
On the other hand, there are numerous substances, particularly inorganic ones,