e therein by leaving void spaces as described further on for the
fireclay heating apparatus. Behind this wall the iron flue-pipe should
be placed, turning back upon itself, as described above, for perhaps
half-a-dozen times, and ending in the vertical brick flue. The furnace
itself should be of fire-clay, and so designed that its utmost heating
power may be economically employed in warming the incoming air, which
should pass over the furnace and iron flues, through the holes in
partition wall, and thus into the hot rooms. The flue, if of wrought
iron, should be rectangular in section, but if of cast-iron it should be
round.

The most economical way of obtaining a high temperature in a small,
inexpensive, and unpretentious private bath is by means of a common
laundry stove, with a longer or shorter length of iron flue in the
apartment. This is the cheapest and quickest method of raising the
temperature of a room for sudorific purposes.

[Illustration: FIG. 10.

A Fireclay Heating Apparatus.]

To turn to methods of heating from a radiating surface of firebrick, at
Fig. 10 I have given the plan, elevation, and sections of a fireclay
heating apparatus. It is constructed wholly of fireclay--fireclay
bricks, quarries, and cement. In the main it consists of a long flue of
firebricks and slabs, which coils backwards and forwards over itself
till the desired amount of radiating surface is gained. Between the
coils are spaces for super-heating the air already warmed by passing
over the actual furnace and into the warm air chamber, the air passing
through by means of perforated bricks. The illustration shows a simple
furnace; but it would be an easy matter to improve upon this by
providing iron air-tight doors lined with fireclay, for cleansing flues
and air-chambers. The example given is only suited to heat a small
public bath. For a large set of hot rooms, a compound apparatus could be
constructed by placing an additional furnace in a sub-basement, the one
on the level of the sudatory supplying radiant heat, and the lower one
hot air. Two such apparatus might be placed one behind the other, end to
end, or might form the _sides_ of the laconicum; the last plan, however,
being the least to be recommended, as in such positions they would not
directly radiate their heat into the adjoining hot rooms.

The advantage of such a furnace as that shown is that it supplies
radiant heat of a most exhilarating kind, besides a proportion