A phenomenon by which certain minerals when warmed acquire electrical
properties. (Ganot.) The mineral tourmaline exhibits it strongly. It was
originally observed in this mineral which was found to first attract and
then to repel hot ashes.

The phenomenon lasts while any change of temperature within certain
limits is taking place. In the case of tourmaline the range is from
about 10º C. (50º F.) to 150º C. (302º F.) Above or below this range it
shows no electrification.

The effect of a changing of temperature is to develop poles, one
positive and the other negative. As the temperature rises one end is
positive and the other negative; as the temperature becomes constant the
polarity disappears; as the temperature falls the poles are reversed.

If a piece of tourmaline excited by pyro-electricity is broken, its
broken ends develop new poles exactly like a magnet when broken.

The following minerals are pyro-electric: Boracite, topaz, prehnite,
zinc silicate, scolezite, axenite. The following compound substances are
also so: Cane sugar, sodium- ammonium racemate and potassium tartrate.

The list might be greatly extended.

The phenomenon can be illustrated by sifting through a cotton sieve upon
the excited crystal, a mixture of red lead and flowers of sulphur. By
the friction of the sifting these become oppositely electrified; the
sulphur adheres to the positively electrified end, and the red lead to
the negatively electrified end. (See Analogous Pole-Antilogous Pole.)