The wastefulness of cooking operations, past and present, is due largely to the defects of the apparatus used. The open fireplace for wood, and the open grate for coal, are two arrangements that permit most of the heat to pass up the chimney, and into the room. See Frontispiece and Fig. 14. In Fig. 14 there is illustrated at the right a brick oven with a flue opening into the chimney. This was one of the earliest inventions for saving fuel and heat. This oven was lined with brick or stone, and the fire of wood was built in it, and allowed to remain until it had burned out. The coals and ashes were removed, and when the brick had cooled somewhat cakes and pies were put in to bake. This oven retained its heat for twenty-four hours, and beans put in Saturday afternoon were taken out hot for the Sunday morning breakfast. The method was clumsy, but a good heat saver.
1 These terms perpetuate the names of scientists famous for their work in electricity. Volta was an Italian who invented an electric battery; Ampere was a French electrician; and Watt a Scottish engineer and electrician.
Fig. 14. - A colonial fireplace.
Figure 15 is an American stove, early nineteenth century, wood the fuel; and from this form, modified for using coal, has developed the modern American coal range (Fig. 18). Even the latest types are very wasteful of heat. Stoves like that shown in Fig. 19 have been devised for use with gas. Even with these only a small percentage of the heat generated is available for cooking.
The ideal system is that which gives the largest possible percentage of its heat for cooking, and puts the degree of heat under quick control with the greatest saving of fuel, and of labor in operating. This does not mean that the stove which gives the most intense heat is the best, although some stoves seem to be constructed with that as the aim.
Fig. 15. - An early American stove, 1823.
Let us consider some of the methods of saving heat, and study different kinds of apparatus with this knowledge in mind.
We recall the fact, first, that some substances are good conductors of heat, and others poor.1 If you hold a metal poker in your hand, and place the other end in red hot coals, you will realize that metal is a rapid conductor of heat. If the poker has a wooden handle, the heat of the coals does not readily reach your hand, for the wood is a poor conductor. Moreover, this good conductor is a poor holder of heat, the heat radiating rapidly from it into the surrounding air, but the poor conductor, once thoroughly heated, cools off slowly.
You can think of many illustrations from your daily life. Why do you prefer a woolen blanket on a cool night, rather than a linen sheet, merely? Why do you use a cloth holder in ironing? What is the principle of a hot water bottle? Air is a poor conductor. Can you think of an illustration of this? What is the principle of a thermos bottle?
It is not difficult to see how these facts apply in our cooking apparatus. From an oven with metal sides heat is lost by radiation. In a double oven, with an air space between the inner and outer part, some heat is saved. If the outer cover is of some non-conducting material, even less radiation takes place. This is the principle of the oven devised by Mr. Edward Atkinson. Here the inner oven is of sheet iron, and the outer covering of a non-conducting material, some composition with wood pulp or paper as the basis. If in this way heat can be trapped, as it were, in an oven, it will follow that less heat will have to be supplied, and we can use a smaller amount of fuel. This is the case in the Atkinson oven (Fig. 16), where the source of heat is either a kerosene lamp, or a small Bunsen burner of the rose type, which uses only a small amount of gas.
The teacher of physics can cooperate here, and indeed throughout the whole topic of apparatus and cooking processes.
Another illustration of the conserving of heat by the prevention of radiation is in the fireless cooker. This is a method used in Sweden in simple form, and adapted and improved to suit modern needs. Heat is supplied in the first place by gas or kerosene, and the water in the vessel containing the food is raised to the boiling point, and held there in some cases for a few minutes. The vessel is then placed in the "cooker," which is a box with thick walls of some non-conducting material, and the heat already present is sufficient to finish the cooking process, since the radiation is very slow. In some cookers a heated stone is introduced to raise the temperature slightly. Both of these devices are excellent for the long, slow cooking that seems to mellow the food material and develop the flavors that do not result from rapid cooking.
At the same time, we need rapid processes, such as broiling and toasting, which give characteristic flavors. To meet this double need, a new type of gas stove has been made. See Fig 17.
This is a gas stove, where the oven has thick walls of a non-conducting material. The oven is heated, for a short time only, the gas flame being cut off when the oven has reached the desired temperature. At the left is an attachment where rapid cooking may be accomplished when desired, and there is a device at (1) with the same principle as the fireless cooker, or the tea "cosey." This cover is dropped over the kettle when the boiling point is reached, the flame is turned out, and the heat in the water finishes the process. There is no good reason why stoves embodying this same principle should not be used with kerosene, and with the electric current. Improved stoves of this type will be constructed, and certainly will tend toward great economy of fuel.
Fig. 16. - The Atkinson cooker.
One method of saving fuel is by the use of a steam cooker, which consists of a series of compartments, one above another, containing several kinds of food, all to be cooked over the same burner, either gas or kerosene, or on one section of the top of the coal range when space is being used for the wash boiler or irons.
Fig. 17. - Construction of the duplex gas range.
It requires intelligence to use such devices, and those who lack it cling obstinately to hot fires and violent cooking.