ed mixture becomes slowly transformed into
its two separate components--the brilliant yellow sulphur, and the
equally brilliant red-lead. These particles form in lines and waves
around the respective poles in beautiful symmetry, their positions
corresponding with the directions of the lines of magnetic force,
exactly as will iron filings round the two poles of a magnet.

From this it will clearly be seen how simple a matter it is to isolate
the topaz, tourmaline, and all the pyro-electric stones from the
non-pyro-electric, for science has not as yet been able to give to
spurious stones these same electric properties, however excellent some
imitations may be in other respects. Further, almost all minerals lose
their electricity rapidly on exposure to atmospheric influences, even to
dry air; the diamond retains it somewhat longer than most stones, though
the sapphire, topaz, and a few others retain it almost as long again as
the diamond, and these electric properties are some of the tests which
are used in the examination of precious stones.

Those stones which show electricity on the application of pressure are
such as the fluorspar, calcite, and topaz.

With regard to magnetism, the actual cause of this is not yet known with
certainty. It is, of course, a self-evident fact that the magnetic iron
ore, which is a form of peroxide, commonly known as magnetite, or
lodestone, has the power of attracting a magnet when swinging free, or
of being attracted by a magnet, to account for which many plausible
reasons have been advanced. Perhaps the most reasonable and acceptable
of these is that this material contains molecules which have half their
substance positively and the other half negatively magnetised.

Substances so composed, of which magnets are an example, may be made
the means of magnetising other substances by friction, without they
themselves suffering any loss; but it is not all substances that will
respond to the magnet. For instance, common iron pyrites, FeS_{2}, is
unresponsive, whilst the magnetic pyrites, which varies from 5FeS,
Fe_{2}S_{3}, to 6FeS, Fe_{2}S_{3}, and is a sulphide of iron, is
responsive both positively and negatively. Bismuth and antimony also are
inactive, whilst almost all minerals containing even a small percentage
of iron will deflect the magnetic needle, at least under the influence
of heat. So that from the lodestone--the most powerfully magnetic
mineral known--to those minerals possess