In order that small establishments may put to profit the advantages
derived from the use of annular furnaces heated with gas, smaller
dimensions have been given the baking chambers of such furnaces. The
accompanying figure gives a section of a furnace of this kind, set into
the ground, and the height of whose baking chamber is only one and a
half meters. The chamber is not vaulted, but is covered by slabs of
refractory clay, D, that may be displaced by the aid of a small car
running on a movable track. This car is drawn over the compartment that
is to be emptied, and the slab or cover, D, is taken off and carried
over the newly filled compartment and deposited thereon.

The gas passes from the channel through the pipe, a, into the vertical
conduits, b, and is afterward disengaged through the tuyeres into the
chamber. In order that the gas may be equally applied for preliminary
heating or smoking, a small smoking furnace, S, has been added to
the apparatus. The upper part of this consists of a wide cylinder
of refractory clay, in the center of whose cover there is placed an
internal tube of refractory clay, which communicates with the channel,
G, through a pipe, d. This latter leads the gas into the tube, t, of the
smoking furnace, which is perforated with a large number of small holes.
The air requisite for combustion enters through the apertures, o, in the
cover of the furnace, and brings about in the latter a high temperature.
The very hot gases descend into the lower iron portion of this small
furnace and pass through a tube, e, into the smoking chamber by the aid
of vertical conduits, b', which serve at the same time as gas tuyeres
for the extremity of the furnace that is exposed to the fire.

[Illustration: GAS FURNACE FOR BAKING REFRACTORY PRODUCTS.]