It should have a hinged cover and, at the front, a hook and staple, orsome 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.
THE INSULATING MATERIAL
For packing or insulating material a variety of substances may be used. Asbestos and mineral wool are the best, and have the additional advantage that they cannot burn. Ground cork (used in packing Malaga grapes), hay, excelsior, Spanish moss, wool, and crumpled paper may also be used satisfactorily. Of these materials crumpled paper is probably the best, as it is clean and odourless and, if properly packed, will hold the heat better than the others. It is wise to line the box with one thickness of heavy paper or with several thicknesses of newspaper, to make it as air-tight as possible. Asbestos sheeting may be used instead. To pack the container with paper, crush single sheets of newspaper between the hands and pack a layer at least four inches deep over the bottom of the outside container, pounding it in with a heavy stick of wood.
Place the inside container for the cooking kettle or the lining for the inside of the nest in the centre of this layer, and pack more crushed paper about it as solidly as possible. The method of packing with paper is shown in Figure 40. If other material is used it should be packed in a similar way.
Where an extra source of heat is to be used, it is much safer to use some non-inflammable material such as asbestos or mineral wool. A cheap substitute and one which is easily obtained are the small cinders sifted from coal ashes, preferably those from soft coal. However, the cinders from hard coal burned in the kitchen range will do. If a fire-proof packing material is not used, a heavy pad of asbestos should be placed at the bottom of the metal lining, and a sheet or two of this paper should be placed between the lining of the nest and the packing material. Whatever is used should come to the top of the inside container, and the box should be filled to within about four inches of the top.
Fig. 40.—Fireless cooker, showing method of packing with paper
THE INSIDE CONTAINER
The inside container for the cooking kettle or the lining for the nest in which it is to be placed should be cylindrical in shape, should be deep enough to hold the cooking kettle and stone, if one is used, and should fit as snugly as possible to the cooking kettle, but at the same time should allow the latter to be moved in and out freely. For this purpose a galvanized iron or other metal bucket may be used, or, better still, a tinsmith may make a lining of galvanized iron or zinc which can be provided with a rim to cover the packing material, as shown in Figure 41. In case no hot stone or plate is to be used, the lining may be made of strong cardboard.
