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. [Illustration: _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. [Illustration: _Fig._ 41.--Metal lining with rim] THE KETTLE The kettle to be used for cooking should be durable and free from seams or crevices which are hard to clean. It should have perpendicular sides, and the cover should be as flat as possible and be provided with a deep lid fitting well down into the kettle, in order to retain the steam. A kettle holding about six quarts is a convenient size for general use. Tinned iron kettles should not be used in a fireless cooker, for, although cheap, they are very apt to rust from the confined moisture. Enamelware kettles are satisfactory. EXTRA SOURCE OF HEAT Fireless cookers are adapted to a much wider range of cooking if they are provided with an extra source of heat in the form of a soapstone, brick, or an iron plate which is heated and placed underneath the cooking kettle. This introduces a possible danger from fire, in case the hot stove plate should come into direct contact with inflammable packing material such as excelsior or paper. To avoid this danger, a metal lining must be provided for the nest in which the cooking vessels and stone are to be placed. [Illustration: _Fig._ 42.--Tightly fitting lid] COVERING PAD