First, we find Conduction, by which heat passes from one particle to another next to it; as when one end of a poker is warmed by placing the other end in the fire. The bodies which allow this power free course are called conductors, and those which do not are named non-conductors, Metals are good conductors; feathers, wool, and furs are poor conductors; and water, air, and gases are non-conductors.
Another principle of heat is Convection, by which water, air, and gases are warmed. This is, literally, the process of conveying heat from one portion of a fluid body to another by currents resulting from changes of temperature. It is secured by bringing one portion of a liquid or gas into contact with a heated surface, whereby it becomes lighter and expanded in volume. In consequence, the cooler and heavier particles above pressing downward, the lighter ones rise upward, when the former, being heated, rise in their turn, and give place to others again descending from above. Thus a constant motion of currents and interchange of particles is produced until, as in a vessel of water, the whole body comes to an equal temperature. Air is heated in the same way. In case of a hot stove, the air that touches it is heated, becomes lighter, and rises, giving place to cooler and heavier particles, which, when heated, also ascend. It is owing to this process that the air of a room is warmest at the top and coolest at the bottom. It is owing to this principle, also, that water and air can not be heated by fire from above. For the particles of these bodies, being non-conductors, do not impart heat to each other; and when the warmest are at the top, they can not take the place of cooler and heavier ones below.
Another principle of heat (which it shares with light) is Radiation, by which all things send out heat to surrounding cooler bodies. Some bodies will absorb radiated heat, others will reflect it, and others allow it to pass through them without either absorbing or reflecting Thus, black and rough substances absorb heat, (or light,) colored and smooth articles reflect it, while air allows it to pass through without either absorbing or reflecting. It is owing to this, that rough and black vessels boil water sooner than smooth and light-colored ones.
Another principle is Reflection, by which heat radiated to a surface is turned back from it when not absorbed or allowed to pass through; just as a ball rebounds from a wall; just as sound is thrown back from a hill, making echo; just as rays of light are reflected from a mirror. And, as with light, the rays of heat are always reflected from a surface in an angle exactly corresponding to the direction in which it strikes that surface. Thus, if heated are comes to an object perpendicularly—that is, at right angles, it will be reflected back in the same line. If it strikes obliquely, it is reflected obliquely, at an angle with the surface precisely the same as the angle with which it first struck. And, of course, if it moves toward the surface and comes upon it in a line having so small an angle with it as to be almost parallel with it, the heated air is spread wide and diffused through a larger space than when the angles are greater and the width of reflection less.
[Illustration: Fig. 31.]
[Illustration: Fig. 32.]
[Illustration: Fig. 33.]
The simplest mode of warming a house and cooking food is by radiated heat from fires; but this is the most wasteful method, as respects time, labor, and expense. The most convenient, economical, and labor-saving mode of employing heat is by convection, as applied in stoves and furnaces. But for want of proper care and scientific knowledge this method has proved very destructive to health. When warming and cooking were done by open fires, houses were well supplied with pure air, as is rarely the case in rooms heated by stoves. For such is the prevailing ignorance on this subject that, as long as stoves save labor and warm the air, the great majority of people, especially among the poor, will use them in ways that involve debilitated constitutions and frequent disease.
The most common modes of cooking, where open fires are relinquished, are by the range and the cooking-stove. The range is inferior to the stove in these respects: it is less economical, demanding much more fuel; it endangers the dress of the cook while standing near for various operations; it requires more stooping than the stove while cooking; it will not keep a fire all night, as do the best stoves; it will not burn wood and coal equally well; and lastly, if it warms the kitchen sufficiently in winter, it is too warm for summer. Some prefer it because the fumes of cooking can be carried off; but stoves properly arranged accomplish this equally well.
After extensive inquiry and many personal experiments, the author has found a cooking-stove constructed on true scientific principles, which unites convenience, comfort, and economy in a remarkable manner. Of this stove, drawings and descriptions will now be given, as the best mode of illustrating the practical applications of these principles to the art of cooking, and to show how much American women have suffered and how much they have been imposed upon for want of proper knowledge in this branch of their profession. And every woman can understand what follows with much less effort than young girls at high-schools give to the first problems of Geometry—for which they will never have any practical use, while attention to this problem of home affairs will cultivate the intellect quite as much as the abstract reasonings of Algebra and Geometry.,
[Illustration: Fig. 34.]
Fig. 34 represents a portion of the interior of this cooking-stove. First, notice the fire-box, which has corrugated (literally, wrinkled) sides, by which space is economized, so that as much heating surface is secured as if they were one third larger; as the heat radiates from every part of the undulating surface, which is one third greater in superficial extent than if it were plane. The shape of the fire-box also secures more heat by having oblique sides—which radiate more effectively into the oven beneath than if they were perpendicular, as illustrated below—while also it is sunk into the oven, so as to radiate from three instead of from two sides, as in most other stoves, the front of whose fire-boxes with their grates are built so as to be the front of the stove itself.
[Illustration: Fig 35. Model Stove]
[Illustration: Fig 36. Ordinary Stove]
The oven is the space under and around the back and front sides of the fire-box. The oven-bottom is not introduced in the diagram, but it is a horizontal plate between the fire-box and what is represented as the "flue-plate," which separates the oven from the bottom of the stove. The top of the oven is the horizontal corrugated plate passing from the rear edge of the fire-box to the back flues. These are three in number—the back centre-flue, which is closed to the heat and smoke coming over the oven from the fire-box by a damper—and the two back corner-flues. Down these two corner-flues passes the current of hot air and smoke, having first drawn across the corrugated oven-top. The arrows show its descent through these flues, from which it obliquely strikes and passes over the flue-plate, then under it, and then out through the centre back-flue, which is open at the bottom, up into the smoke-pipe.
The flue-plate is placed obliquely, to accumulate heat by forcing and compression; for the back space where the smoke enters from the corner-flues is largest, and decreases toward the front, so that the hot current is compressed in a narrow space, between the oven-bottom and the flue-plate at the place where the bent arrows are seen. Here again it enters a wider space, under the flue-plate, and proceeds to another narrow one, between the flue-plate and the bottom of the stove, and thus is compressed and retained longer than if not impeded by these various contrivances. The heat and smoke also strike the plate obliquely, and thus, by reflection from its surface, impart more heat than if the passage was a horizontal one.
The external radiation is regulated by the use of nonconducting plaster applied to the flue-plate and to the sides of the corner-flues, so that the heat is prevented from radiating in any direction except toward the oven. The doors, sides, and bottom of the stove are lined with tin casings, which hold a stratum of air, also a non-conductor. These are so arranged as to be removed whenever the weather becomes cold, so that the heat may then radiate into the kitchen. The outer edges of the oven are also similarly protected from loss of heat by tin casings and air-spaces, and the oven-doors opening at the front of the store are provided with the same economical savers of heat. High tin covers placed on the top prevent the heat from radiating above the