Enamels and enamelling; an introduction to the preparation and ...

EAW MATERIALS FOR THE MANUFACTURE OF ENAMELS. 21
particles and to produce an infinite number of cracks, through
which the water gains access to the still glowing interior,
whereby it is converted into steam, which forces the particles
of quartz asunder by its expansion.
This method of sudden cooling is known in practice as
"
quenching," and if a lump of quartz that has been treated in
this way is struck with a hammer, it breaks up into a number
of small fragments easily reducible to a fine powder.
FIG. 1.
The furnaces used for calcining quartz are very simple, a
useful type being shown in Fig. 1. The cylindrical shaft of
fireproof material, about 16-20 inches in diameter and 60 to
80 inches high, is closed at the top by a hinged cover of cast
iron lined with fireclay. Below, at the front of the furnace,
is an aperture of the same width as the internal diameter of
the shaft and about 8 inches high, which can be closed by a
door provided with a damper, and in front of this opening