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

76 ENAMELS AND ENAMELLING.
are bored through T, around the bottom. The pipe, R, supplies
compressed air which before being discharged into the smelting
fire is heated by passing through a coiled pipe in the same.
The temperature obtainable by the combustion of charcoal
in the hot air blast is so high that the most refractory enamels
can be fused in quantities of 100 grams (3| oz.) and over,
within a few minutes. Hence several tests can be performed
within the hour and therefore a comparatively short time
suffices to reveal the behaviour of a new mixture under
fusion.
ROSSLER'S GAS FURNACE.
Wherever gas is laid on in the works, the enamel-maker
can advantageously employ a gas furnace for making fusion
tests. Such a furnace is represented in section in Fig. 3.
The high, but narrow crucible, A, has a perforated bottom, the
aperture being closed by a ball of porcelain. This crucible
is mounted on a suitable fire-brick block and is covered by a
thin
bell-shaped fireclay vessel, c, which, in turn, is surrounded
by a thick fireclay cylinder, d. The lower part
of the furnace
is formed by an annular block of firebrick, b, containing sundry
small apertures on its inner side. Gas is supplied through a
wide pipe a, to b, where it escapes through the aforesaid small
apertures, and, mixing with air, is ignited. The burning gas
ascends round the crucible, A, makes its way out of the top
of the bell-shaped vessel at c, and descends between the latter
vessel and the outer cylinder to the flue, e, in which a strong
draught is induced by means of a Bunsen burner, /.
As soon as the contents of the crucible, A, have melted, the
porcelain ball floats on the surface and the molten mass falls
down into a basin, g, filled with water. The lid, d, being re-
moved, A can be re-charged, and in this manner several
pounds of enamel can be fused in a very short time. Either
of the furnaces just described can be warmly recommended
for experimental purposes or for preparing very handsome
coloured enamels for artistic work.