separated
by analysis they at once revert to their original form. On this
property the analyst depends largely for his results, for in such
matters as food adulteration, etc., the microscope unerringly reveals
impurities by means of the crystals alone, apart from other evidences.
It
is most curious, too, to note that no matter how large a crystal may
be, when reduced even to small size it will be found that the crystals
are still of the same shape. If tin's process is taken still further,
and the subÂstance is ground to the finest impalpable powder, as fine
as floating dust, when placed under the microscope each speck, though
perhaps invisible to the naked eye, will be seen a perfect crystal, of
the identical shape as that from which it came, one so large maybe that
its planes and angles might have been measured and defined by rule and
compass. This shows how impossible it is to alter the shape of a
crystal. We may dissolve it, pour the solution into any shaped vessel
or mould we desire, re-crystallise it and obtain a solid sphere,
triangle, square, or any other form .; it is also possible, in many
cases, to squeeze the crystal by pressure into a tablet, or any form we
choose, but in each case we have merely altered the arrangement of the crystals, so as to produce a differÂently shaped mass, the
crystals themselves remaining individually as before. Such can be said
to be one of the laws of crystals, and as it is found that every
substance has its own form of crystal, a science, or branch of
mineralogy, has arisen, called " crystallography," and out of the
conglomeration of confused forms there have been evolved certain rules
of comparison by which all known crystals may be classed in certain
groups.
