both used in the
same wall, they should be carried up at the same time and thoroughly
bonded to each other.

All fire brick should be dry when used and protected from moisture until
used. Each brick should be dipped in a thin fire clay wash, "rubbed and
shoved" into place, and tapped with a wooden mallet until it touches the
brick next below it. It must be recognized that fire clay is not a
cement and that it has little or no holding power. Its action is that of
a filler rather than a binder and no fire-clay wash should be used which
has a consistency sufficient to permit the use of a trowel.

All fire-brick linings should be laid up four courses of headers and one
stretcher. Furnace center walls should be entirely of fire brick. If the
center of such walls are built of red brick, they will melt down and
cause the failure of the wall as a whole.

Fire-brick arches should be constructed of selected brick which are
smooth, straight and uniform. The frames on which such arches are built,
called arch centers, should be constructed of batten strips not over 2
inches wide. The brick should be laid on these centers in courses, not
in rings, each joint being broken with a bond equal to the length of
half a brick. Each course should be first tried in place dry, and
checked with a straight edge to insure a uniform thickness of joint
between courses. Each brick should be dipped on one side and two edges
only and tapped into place with a mallet. Wedge brick courses should be
used only where necessary to keep the bottom faces of the straight brick
course in even contact with the centers. When such contact cannot be
exactly secured by the use of wedge brick, the straight brick should
lean away from the center of the arch rather than toward it. When the
arch is approximately two-thirds completed, a trial ring should be laid
to determine whether the key course will fit. When some cutting is
necessary to secure such a fit, it should be done on the two adjacent
courses on the side of the brick away from the key. It is necessary that
the keying course be a true fit from top to bottom, and after it has
been dipped and driven it should not extend below the surface of the
arch, but preferably should have its lower ledge one-quarter inch above
this surface. After fitting, the keys should be dipped, replaced
loosely, and the whole course driven uniformly into place by means of a
heavy hammer and a piece of wood extending the full length of