camber," and the
brick arch built upon it naturally takes the same curve. Each end is
"caulked," that is, split longitudinally and turned up and down. The
interior of a chimney breast behind the stove should always be filled in
solid with concrete or brickwork. The flooring in the chimney opening is
called the "hearth"; the back hearth covers the space between the jambs of
the chimney breast, and the front hearth rests upon the brick "trimmer
arch" designed to support it. The hearth is now often formed in solid
concrete, supported on the brick wall and fillets fixed to the floor
joists, without any trimmer arch and finished in neat cement or glazed
tiles instead of stone slabs.

Tall furnace chimneys should stand as separate constructions, unconnected
with other buildings. If it is necessary to bring other work close up, a
straight joint should be used. The shaft of the chimney will be built
"overhand," the men working from the inside. Lime mortar is used, cement
being too rigid to allow the chimney to rock in the wind. Not more than 3
ft. in height should be erected in one day, the work of necessity being
done in small portions to allow the mortar to set before it is required to
sustain much weight. The bond usually adopted is one course of headers to
four of stretchers. Scaffolding is sometimes erected outside for a height
of 25 or 30 ft., to facilitate better pointing, especially where the
chimney is in a prominent position. The brickwork at the top must,
according to the London Building Act, be 9 in. thick (it is better 14 in.
in shafts over 100 ft. high), increasing half a brick in thickness for
every additional 20 ft. measured downwards. "The shaft shall taper
gradually from the base to the top at the rate of at least 21/2 in. in 10 ft.
of height. The width of the base of the shaft if square shall be at least
one-tenth of the proposed height of the shaft, or if round or any other
shape, then one-twelfth of the height. Firebricks built inside the lower
portion of the shaft shall be provided, as additional to and independent of
the prescribed thickness of brickwork, and shall not be bonded therewith."
The firebrick lining should be carried up from about 25 ft. for ordinary
temperatures to double that height for very great ones, a space of 11/2 to 3
in. being kept between the lining and the main wall. The lining itself is
usually 41/2 in. thick. The cap is usually of cast iron or terra-cotta
strengthened with iron bol