The packing or insulation must be of some material which is a poor conductor of heat. The following materials may be used and they should be dry: Lint cotton, cotton-seed hulls, wool, shredded newspaper, Spanish moss, ground cork, hay, straw and excelsior.
Sheet asbestos 1⁄8 inch thick and heavy cardboard have proved to be the best lining for the outer container and the wrapping for the nest. Heavy wrapping paper or several sheets of newspaper may be used for the lining of the outer container, but the nest should be wrapped with asbestos or heavy cardboard to prevent the hot stone from scorching or burning the packing.
Fig. 3.—The completed fireless cooker.
1. It is well to have the outside container large enough to permit four inches of packing below and around the sides of the nest. If a cooker is being made with two nests, six inches of packing should be allowed between the nests. Pack into the bottom of the lined outer container four inches of the packing. Place the nest or inside container wrapped with asbestos or heavy cardboard and hold steady while the packing is put around tightly and firmly until it reaches the top of the nest.
2. Make a collar, as shown in the [illustration], of cardboard, sheet asbestos, or wood to cover the exposed surface of the insulating material. This collar should fit tightly.
3. Make a cushion which when filled with packing will be at least four inches thick and will completely fill the space between the top of the nest and the lid of the outside container. It should fit against the top tightly enough to cause pressure when the lid is closed.
4. The outside of the fireless cooker can be made more attractive by staining or painting it. The lid may be held in place by screen-door hooks and eyes. The cooker may be placed on castors so that it can be easily moved.
Selected recipes for preparing food to be cooked in the fireless cooker may be found in Farmer’s Bulletin 771, Homemade Fireless Cookers and Their Use. Write the Department of Agriculture, Washington, D. C.