Heat
3 of the 7 encyclopedias on this shelf carry an entry for Heat. Both are reproduced below, so you can see where they agree and where they differ.
Collier's New Encyclopedia (1921)
in natural philosophy, the term used chiefly to mean, not the sensation which our bodies feel when we say that they are hot, but the particular state or condition of matter which causes this sensation. The accepted hypothesis is that heat is caused by an oscillatory or vibratory motion of the particles of a body. It is thus a condition of matter and not a substance. The hottest bodies are those in which the vibrations move quickest through the widest space. It is called also the Mechanical or Dynamical Theory of Heat. Heat makes bodies, whether solid, liquid, or gaseous, expand, while cold contracts them. Water is a partial exception to the rule. In the case of a solid, heat can produce fusion at a certain definite temperature; in that of liquids vaporization. It is transmitted by radiation or by conduction. Radiant heat is that produced by radiation. Latent heat is that which is absorbed by solid bodies when they are subjected to calorific influence far more than sufficient to make them melt, and when at the very time they are in process of fusion. The heat does not raise the temperature of the solid until it is completely liquefied. There is also a latent heat of vaporization, being heat absorbed by liquids when being converted into vapor. Latent is opposed to sensible heat. Heat may be reflected or refracted, or, by being irregularly reflected in all directions, it may become scattered or diffused heat; reflection and refraction may also polarize its rays, as happens to those of solar light. The heat which falls on a body is called incident heat. Specific heat is the quantity of heat required to raise the temperature of a body of a given weight 1°; the unit of measure being the quantity required to raise the same weight of water to the same temperature. Heat may be produced by solar radiation, chemical action, friction, pressure, percussion, absorption, and imbibition; by the conduction of powerful magnets and bodies in motion, etc. HEATING and VENTILATION. In cold climates, artificial heating and ventilation are both necessary for health and comfort and are equally important. Because the discomfort produced by low temperature is more acutely and immediately felt than that due to foul air, improper ventilation is more common than deficient heating. The two subjects are so closely related, however, that they will be considered together in this article, the question of heating being first dealt with in greater detail. The temperature most conducive to bodily comfort cannot be stated definitely as it is largely determined by climate and personal habit, varying in different countries. A temperature of 68-70° F. is considered necessary in the U. S. A. and Canada, but 62° F. is the temperature most favored in England. All systems of heating depend upon radiation or convection; or, more generally, upon a combination of the two. The commonest example of radiation is the open fireplace which radiates heat, and so warms the walls and furniture of the room, while leaving the air comparatively cool. An example of convection is found in the hot air furnace, which supplies currents of warm air air, which constantly replace the cold air. Radiation and convection combined are found in the ordinary steam or hot water radiator, which heats the air by convection and also radiates some heat to surrounding objects. Heat is most commonly produced by the combustion of coal, wood, coke, oil, gas, or some other fuel, but is occasionally obtained electrically, the electricity being produced by water-power. Comparing the relative merits of the different forms of heating the open fireplace is popular because it is cheerful to see, and from the hygienic point of view it is good because it produces a simple but efficient means of ventilation. It utilizes, however, only 10-15 per cent. Vol. IV-Cyc-FF of the heating value of the fuel, and, unless supplemented by other forms of heating, is quite inadequate for providing sufficient heat in cold climates. The stove which stands out in the room, being connected to the chimney by a pipe, is upward of 50 per cent. efficient, but it has the disadvantage of being dusty, and of quickly producing foul dry air unless careful attention is given to ventilation. The hot-air furnace is of two types. The older type conveys the heated air from a central chamber to various parts of the house by means of pipes; the more modern type is pipeless, the heat entering the upper part of the house from a single register on the first floor, and being carried by convection to all parts of the house. The furnace is supplied with fresh air from the outside, and provided this feature is properly cared for, a hot air system is probably the most healthful method of heating a dwelling. With the old type of furnace, however, it is difficult to obtain uniform heating, the rooms on the windward side of the house being cold, while those on the sheltered side are overheated. The pipeless furnace is growing in popularity, and gives satisfaction in houses of suitable size and design. The steam furnace generates steam from a boiler in the cellar and distributes it over the house by means of pipes connected to radiators. The hot-water furnace is similar, except that hot water instead of steam circulates through the pipes and radiators. Both systems have advantages and disadvantages. Hot water is more difficult and expensive to install but has the advantage that it begins to supply warmth as soon as the water becomes heated, whereas, with steam, the water must boil before heat is supplied. Hot water is also quieter than steam, but high temperatures can be produced more rapidly with the latter and much less radiating surface is needed. A modern development of steam heat is the so-called "vacuum system," " in which the whole system of piping and radiators is maintained under a slight vacuum. One advantage of this system is that the knocking and hissing of the radiators is avoided. Another recent modification is the gas-steam radiator, which is a radiator having a small reservoir of water at the base, heated by gas burners. As the pressure, due to generation of steam, rises, the gas is automatically lowered. Electric heating is too expensive for use on a large scale, but finds application in small heaters for intermittent use, and also in the heating of street cars. Ventilation-A steady supply of fresh air is necessary to the well-being of the animal body, because one-fifth of the air consists of oxygen and it is upon oxygen that the heat and energy of the body depends. When fuel burns, carbonic acid gas is produced. The same gas is contained in the breath from the body, and to produce this carbonic acid, oxygen is absorbed from the surrounding air. An excess of carbonic acid in the air produces headache, depression and even nausea, and anything in excess of six parts per ten thousand is liable to cause discomfort. A gas burner, in a small room, will very quickly pollute the air, and for every cubic foot of gas consumed, eight cubic feet of air are exhausted of their oxygen. It is estimated that one person requires 3,000 cubic feet of air per hour. That is to say, a room 30 feet long, 10 feet high and 10 feet wide contains sufficient air to supply one person for one hour, but it is clear that no one could live in a hermetically sealed room of such a size for that length of time without suffering from poisoning, because throughout the time he would bo polluting the air and the pollution would pass the safe limit very soon. In the ordinary room, of course, there is constant leakage of bad air and admittance of pure air through cracks and in the doors and windows, through the chimney and by other accidental means. In actual practice, it is found that 250- 300 cubic feet per person in dwellings and factories is sufficient.
Aiton's Encyclopedia (1910)
a form of molecular motion. According to the theory of heat, every molecule in a substance is moving to and fro. The hotter a substance, the more violently the molecules bound back and forth. If they begin to subside and swing more quietly in their places, we say that the substance is cooling. The change from a solid to a liquid or to a gaseous condition is thought to be due to the violent jostling of molecules, whereby they get beyond each other's attractive influence. An increase of heat is accompanied by a closely corresponding increase of volume. This increase of volume varies for different substances. Lead and zinc, for instance, increase and shrink more rapidly than iron. The amount of heat required to make, let us say, a pound of a substance too hot to handle varies greatly. Marble and aluminum require the application of seven times as much heat as lead and gold to bring them to the same temperature. Tin heats up ten times as fast as ice, and alcohol nearly twice as fast as water. A proper degree of heat is one of the necessary conditions of all life. So far as the earth is concerned, all heat is derived from the sun. Even the heat obtained from fuel and chemical action comes originally from the sun. Winter clothing is designed to prevent heat from leaving the body. Some substances conduct heat more readily than others. Wool is a poor conductor. Cotton is better. Wool feels warm to the body because it does not carry away heat--really because it remains cold. The heat of the body requires to be maintained by eating food containing fat or some form of carbon. In attempts to investigate heat, scientists have ascertained with reasonable certainty that in freezing air the distance to which a molecule can dart before bumping into another is so short that a quarter of a million such trips, end to end, would make only an inch in length; but that a molecule darts backward and forward often enough to travel over a quarter of a mile per second. The further statement is made that each molecule of air, that is at freezing, is run into at a rate of 5,000,000,000 collisions per second. In the case of heated air, these figures must be increased. According to this theory the amount of heat in a body is the amount of molecular motion. The more a body cools, the less its molecular motion, until at 273 Centigrade degrees below freezing, all molecular motion ceases. This temperature is written-273 deg. C., and is called the absolute zero. This theoretical temperature has never been reached, but scientists claim to have come within fourteen centigrade degrees of it. Prof. Dewar has succeeded in reaching a temperature of-443 deg.F. The highest temperature yet attained is thought to be that of the electric arc, or 3,500 deg. C. Heat may be changed into light and electricity. It is in turn produced by them. Our great source of heat, light, and electricity is the sun. Whether they travel to us separately or whether they are three manifestations of the same energy is not yet understood, but is under investigation. It is believed that solar heat will one day do much of the work now done by coal, wind, and water. Solar mills, constructed somewhat on the windmill plan, but consisting of huge tin mirrors to catch heat, are already in use to drive machinery. Ericsson states that one-half square mile of Arizona sun has energy enough to drive 64,800 steam engines of 100 horse power each. When a substance burns--combines with oxygen--heat is evolved; when iron rusts, heat is evolved; but the amount is too slight for measurement. When a combustible substance burns, it generates a definite amount of heat. Two pounds of petroleum, conditions remaining the same, produce twice as much heat as one pound. A pound of burning petroleum, however, produces more heat than a pound of coal. The unit of measure now in common use is the British Thermal Unit or B. T. U., which may be defined as the quantity of heat required to raise the temperature of one pound of pure water one degree Fahrenheit, at or near its point of greatest density. This point of greatest density is approximately 3.91 deg. F. We can measure the amount of heat produced by means of an instrument called a calorimeter. To secure such a measurement, a definite amount of material is burned in the calorimeter in such a way as to raise the temperature of a surrounding quantity of water. The change in temperature of the water can be accurately determined by means of a very delicate thermometer. By repeated trial with the calorimeter, the amount of heat yielded per pound of fuel has been approximated. The heat for several kinds of fuel is per pound: Fuel. B. T. U. Carbon 14,600 Hard coal 14,900 Soft coal 14,000 Lignite 12,000 Dry peat 10,000 Oak wood 5,000 Long leaf pine. 9,000 Dry tan bark . . 6,000 Dry straw 6,000 Petroleum 20,000 Natural gas 30,000 Hydrogen 62,000 See Clothing ; Food ; Thermometer ; Expansion
The Encyclopedia of Founding (1892)
We experience the sensation of heat when we approach a warm body. The opposite of heat is cold, which merely implies a greater or less deficiency of heat. The two kinds of heat, which are called free, or sensible, and latent, are represented by fire and ice; the free, as in fire, can be felt, while that in ice is latent and cannot be felt. There is heat in all substances, but in those which are called cold it exists in an inferior degree. Some think that heat is not a material substance, but results from the vibrations of the particles of bodies; others believe it to be an exceedingly subtle substance, whose particles repel each other and thus give it a tendency to diffuse itself while they have a strong affinity for other matter. It would appear that heat is closely connected with light, as the one is generally accompanied by the other. That heat has no weight is proved by weighing a piece of ice, and then melting it, the water produced will weigh the same as the ice. The chief sources of heat are the sun, chemical and mechanical action, and electricity. Many speculations have been indulged in as to what composes the sun, that it should continue to give undiminished heat without exhausting the material by which it is supported. That chemical action is a source of heat, may be demonstrated by combining two or more substances to produce a new substance totally different in its nature from either; an increase of temperature alway accompanies such action, as may be proved by mixing sulphuric acid and water in equal quantities; it forms a new substance and gives off heat. Combustion is a chemical union of the oxygen of the atmosphere with the combustible body, or some of its elements. Animal heat is produced by a similar process: when we breathe air is drawn into the lungs, where it comes in contact with the particles of carbon contained in the blood; there is then a chemical union of the carbon with the oxygen of the air inhaled, and, as in the case of combustion, latent heat is evolved. Friction, percussion, and compression are illustrations, showing that mechanical action is a source of heat; and electricity is conclusively shown to be another source of heat, as the heat produced by its action will melt almost any known substance. See COMBUSTION; TEMPERATURE.