in-plate Printing
Factory--heated by Perkins' Hot-water Pipes.]

The principle of Perkins' invention has, during the last eighty
years, i.e. since the date of the invention in 1831, been very
extensively applied not only for the heating of buildings of every
description, but it has also been utilized for numerous industrial
purposes which require an atmosphere heated up to 600 deg. F. The
principle lends itself specially to the design of apparatus for
raising and maintaining heat evenly and uniformly, and also very
economically for such purposes as enamelling, japanning, and
lacquering.

The distinctive feature of this apparatus when applied to moderate
temperatures lies in the adoption of a closed system of piping of
small bore, a certain portion of which is wound into a coil and placed
in a furnace situated in any convenient position outside the drying
chamber or hot closet. The circulation is thus hermetically sealed and
so proportioned that while a much higher temperature can be attained
than is possible with a system of pipes open to the atmosphere, yet a
certain and perfectly safe maximum cannot by any possibility be
exceeded.

The efficiency of the apparatus increases within certain limits in
proportion to the pressure employed, which fact explains the
exceedingly economical results obtained, while the fact that, owing to
the high temperature used, a small-bore pipe can be made more
effective than the larger pipes used in any open system, accounts for
the lower first cost of the Perkins' apparatus.

[Illustration: FIG. 8.--Japanning and Enamelling Oven Heated by Single
Hot-water Pipes sealed at both ends with Furnace in Rear.]

[Illustration: FIG. 9--Japanning and Enamelling Oven For Bedstead,
Ironmongery, Cash-box, and Lamp Factories.]

[Illustration: FIG. 10.--Japanning and Enamelling Stove for parts of
Sewing Machines.]

It will be seen from the various illustrations that the articles to be
treated are absolutely isolated from actual contact with the fire or
the fire gases and other impurities which must be an objection to all
methods of heating by means which are not of a purely mechanical
nature. This principle not only recommends itself as scientifically
correct and suited to the purpose in view, but is also a very simple
and practical one. It affords the means of applying the heat at the
point where it is required to do the work without unduly heating
parts where heat is unnecessary; it secures a