pplied to general use. I have seen such
doors in division walls where they had successfully resisted the flame
which destroyed four stories of a building filled with combustible
material, without imposing any injury upon the door except the removal
of the tin on the sheet iron; and the doors were kept in further
service without any repairs other than a coat of paint.

The reason for this resistance to fire is that the wood, being a poor
conductor of heat, will not warp and buckle under heat, and cannot
burn for lack of air to support combustion. A removal of the sheet
metal on such a door after a fire in a mill shows that the surface of
the wood is carbonized, not burned, reduced to charcoal, but not to
ashes.

Many fire doors are constructed and hung in such a manner that it is
doubtful whether they could withstand a fire serious enough to require
their services.

The door should be made of two thicknesses of matched pine boards of
well dried stock, and thoroughly fastened with clinched nails. It
should be covered with heavy tin, secured by hanging strips, and the
sheets lock-jointed to each other, with the edge sheets wrapping
around, so that no seam will be left on the edge.

Sliding doors are preferable to swinging doors for many reasons,
especially because they cannot be interfered with by objects on the
floor. But, if swinging doors are used, care should be taken that the
hinges and latches are very strong, and securely fastened directly to
the walls, and not to furring or anything in turn attached to the
walls. The portion of the fixtures attached to the doors must be
fastened by carriage bolts, and not by wood screws.

Sliding on trucks is the preferable method of hanging sliding doors,
inclined two and one half inches to the foot, and bolted to the wall.
The trucks should be heavy "barn door hangers," bolted to the door;
and a grooved door jamb, of wood, covered with tin similar to the
door, should receive it when shut. A step of wood will hold the door
against the wall when closed. A threshold in the doorway retards fire
from passing under the door, and also prevents the flow of water from
one room to another.

These doors are usually placed in pairs, and sometimes an automatic
sprinkler is placed between them.

Fire doors should always be closed at night. In some well ordered
establishments there is a printed notice over each door directing the
night watchmen to close such doors after them. In a stor