The open fireplace can, however, be greatly improved by surrounding
its back and sides by an air space, in which air can be warmed and
conveyed into the upper part of the room; and if a special air inlet
is provided for supplying the fire with fresh air to be warmed, we
get a very valuable means of heating. These principles are embodied in
the Franklin and Galton grates. A great many other grates have been
suggested, and put on the market, but the principal objection to them
is their complexity and expense, making their use a luxury not
attainable by the masses.

[Illustration: FIG. 13.

A GALTON GRATE. (TRACY.)]

=Stoves.=--Stoves are closed receptacles in which fuel is burned, and
the heat produced is radiated toward the persons, etc., near them, and
also conducted, through the iron or other materials of which the
stoves are made, to surrounding objects. In stoves seventy-five per
cent of the fuel burned is utilized. They are made of brick, tile, and
cast or wrought iron.

Brick stoves, and stoves made of tile, are extensively used in some
European countries, as Russia, Germany, Sweden, etc.; they are made of
slow-conducting material, and give a very equable, efficient, and
cheap heat, although their ventilating power is very small.

Iron is used very extensively because it is a very good conductor of
heat, and can be made into very convenient forms. Iron stoves,
however, often become superheated, dry up, and sometimes burn the air
around them, and produce certain deleterious gases during combustion.
When the fire is confined in a clay fire box, and the stove is not
overheated, a good supply of fresh air being provided and a vessel of
water placed on the stove to reduce the dryness of the air, iron
stoves are quite efficient.

=Hot-air Warming.=--In small houses the warming of the various rooms
and halls can be accomplished by placing the stove or furnace in the
cellar, heating a large quantity of air and conveying it through
proper tubes to the rooms and places to be warmed. The points to be
observed in a proper and efficient hot-air heating system are the
following:

(1) The furnace must be of a proper size in proportion to the area of
space to be warmed. (2) The joints and parts of the furnace must be
gas-tight. (3) The furnace should be placed on the cold side of the
house, and provision made to prevent cellar air from being drawn up
into the cold-air box of the furnace. (4) The air for the supply of
t