water is heated the salt then becomes more and more insoluble as the temperature increases, till it is completely insoluble.
If
a super-saturated solution of this Glauber's Salt is made in a glass,
at ordinary atmospheric temperature, and into this cold solution,
without heating, is dropped a small crystal of the same salt, there
will be caused a rise in temperature, and the whole will then
crystallise out quite suddenly; the water will be absorbed, and the
whole will solidify into a mass which exactly fits the inner contour
of the vessel.
We have now formed what might be
a precious stone, and no doubt would be, if continuous pressure could
be applied to it for perhaps a few thousand years; at any rate, the
formation of a natural jewel is not greatly different, and after being
subjected for a period, extending to ages, to the washings of moisture,
the contact of its containing bed (its later matrix), the action of the
changes in the temperature of the earth in its vicinity, it emerges by
volcanic eruption, earthquake, landslip and the like, or is discovered
as a rare and valuable specimen of some simple compound of earth-crust
and water, as simple as Glauber's Salt, or as the pure crystallised
carbon.
It
is also curious to note that in some cases the stones have not been
caused by aqueous deposit in an already existing hollow, but the
aqueous infusion has acted on a portion of the rock on which it rested,
absorbing the rock, and, as it were, replacing it by its own substance.
This is evidenced in cases where gems have been found encrusted on
their matrix, which latter was being slowly transformed to the
character of the jewel encrusted, or "scabbed " on it.
