1. It furnishes no heat, but conserves the heat which is in the food when it is put into the cooker. 2. It conserves the heat in the food, by surrounding it with substances which are poor conductors of heat. 3. Extra heat may be given the food, after it is put in the cooker, by placing heated stone plates above and below the dish that contains the food. The stone used for this purpose must be a good absorbent of heat. REASONS FOR THE USE OF THE FIRELESS COOKER 1. It saves fuel and is therefore economical. 2. It saves time, because it requires no watching. 3. It conserves the flavour of the food. 4. It obviates all danger of burning the food. 5. It does not heat the room. WAYS OF USING THE FIRELESS COOKER 1. Food cooked in liquid: In all cookers where stone plates are not used, only such foods as are cooked in liquids can be prepared. Examples of foods cooked in this way are, meat soup, beef-tea, meat stews, vegetables, fruit, porridge, cereal, puddings, etc. The prepared food is put into one of the food receptacles belonging to the cooker and is placed over a fire, until it has boiled for a few minutes. The cover is then tightly adjusted, and the dish quickly locked in the cooker, to conserve the heat that the food and liquid have absorbed. 2. Food cooked in dry heat by the use of stone plates: In this method the food is cold when it is placed in the cooker, and all the heat is supplied by stone plates placed above and below the utensil containing the food. These plates are heated for about twenty minutes over a fire, before they are used in the cooker. Examples of food cooked in this way are, roasts of meat; baked fruit, such as apples; baked vegetables, such as potatoes or beans; cakes, such as plain cake or fruit cake; quick bread, such as corn-bread and biscuits. 3. Food cooked in liquid, aided by the heat of one stone plate: In cases where the original heat absorbed by the food is not sufficient to complete the cooking as desired, a heated stone plate may be placed in the cooker below the utensil containing the hot food. The stone may be necessary for one of the following reasons-- (1) Because the amount of food put into the cooker is too small to contain much heat. It is always better to have the food nearly fill the dish. (2) Because the time required is so long that the heat of the food and liquid becomes exhausted before the cooking is completed. (3) Because it is desirable to finish the cooking in less time. A HOME-MADE FIRELESS COOKER Use a large wooden box or a small trunk with a close-fitting cover. Make it as air-tight as possible by pasting thick paper all over the inside.