The only possible way to control these stoves is by a device which can cut off air. One of these is a plate-like device with a handle. This fits over the stove and only that portion of the top burns which is exposed to air through the hole in the plate. Making the hole larger or smaller makes the burning surface larger or smaller. To extinguish the fire, cover the entire top with a solid plate to cut off all air. =45. Canned Heat.= Canned heat is alcohol combined with other substances into a cake about the consistency of hard soap. The cover to the can is used to extinguish the fire. It should not be fitted into the top of the can until the flame has been extinguished for two or three seconds. Then it should be fitted on as tight as possible to prevent waste alcohol by vaporization. =46. Acetylene Gas Stoves.= By adjustment of the amount of air that enters the burner, acetylene may be burnt in a gas stove. Usually a cap is placed over the air hole while the gas is being ignited. This is removed as soon as the gas is lighted, so that it will burn with a blue flame. The use of the cap prevents burning back. It is best, however, to use stoves especially designed for burning acetylene. CHAPTER VI FIRELESS AND STEAM COOKERS =47. The Fireless Cooker.= The fireless cooker is a box or can having a diameter somewhat larger than that of the largest vessel to be placed in it. The space left around the vessel is packed with some insulating material to keep in the heat (Fig. 22). In home-made cookers, this material may be hay, feathers, pillows, shredded newspapers, wood shavings or sawdust. In commercially-made cookers, it is felt, asbestos wool, cork, or other insulating material. Because most insulating material will not stay in place and readily absorbs moisture and odors, some kind of lining is put between it and the vessel holding the food. This makes a little nest, into which the vessel fits. In the better made cookers, this lining is made of metal, and the seams are water-tight. The steam from the cooking food is absorbed by the insulating material if this lining is not impervious to water. Enameled or earthen linings, if well glazed, would also serve this purpose as long as they did not chip or crack. The cover, as well as the sides, of the fireless cooker has to be padded with the insulating material. The cover must also fit well so that the steam and heat will not escape thru cracks between it and the body of the cooker.