For the outside container a tightly built wooden box, such as that shown
in Figure 39, is satisfactory. The walls should be thick and of some
non-conducting material. An old trunk, a small barrel, or a large butter
or lard firkin or tin will serve the purpose. Another possibility is a
galvanized iron bucket with a closely fitting cover (this has the
advantage of being fire-proof). A shoe box 15 by 15 by 28 inches is
convenient in size, since it may be divided into two compartments. It
should have a hinged cover and, at the front, a hook and staple, or
some other device to hold down the cover tightly; an ordinary clamp
window fastener answers this purpose very well. The size of the
container, which depends upon the size of the kettle used, should be
large enough to allow for at least four inches of packing material all
round the nest in which the kettle is placed.
[Illustration: _Fig._ 39.--Completed fireless cooker]