Heat
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 ir- HEATING regularly reflected in all directions, it reflection and refraction may also polar- ize its rays, as happens to those of solar reflection and refraction may also polarlight. The heat which falls on a body 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 the quantity required to raise the same weight of water to the same temperature. Heat may be produced by solar radiation, chemical action, friction, prestion; by the conduction of powerful tion; by the conduction of powerful magnets and bodies in motion, etc.
HEATING and VENTILATION. In cold climates, artificial heating and ven- tilation 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 definite- The temperature most conducive to ly 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 tems of heating depend upon radiation or combination of the two. The commonest example of radiation is the open est example of radiation is the open warms the walls and furniture of the room, while leaving the air comparfound in the hot air furnace, which supplies currents of warm air air, which found in the hot air furnace, which tion 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 eleccoal, wood, coke, oil, gas, or some other fuel, but is occasionally obtained elecby water-power. Comparing the relative merits of the different forms of heating the open fireplace is popular because it is cheerful different forms of heating the open fireview it is good because it produces a simple but efficient means of ventilation.
It utilizes, however, only 10-15 per cent. simple but efficient means of ventilation.
HEATING of the heating value of the fuel, and, unless supplemented by other forms of being connected to the chimney by a pipe, is upward of 50 per cent. efficient, The stove which stands out in the room, being connected to the chimney by a pipe, is upward of 50 per cent. efficient, ventilation. The hot-air furnace is of two types. The older type conveys the heated air unless careful attention is given to ventilation. The hot-air furnace is of two parts of the house by means of pipes; air from a central chamber to various parts of the house by means of pipes; house from a single register on the first heat entering the upper part of the house from a single register on the first is supplied with fresh air from the outto 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 probing a dwelling. With the old type of ing 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 overin popularity, and gives satisfaction in in popularity, and gives satisfaction in houses of suitable size and design. The steam furnace generates steam from a over the house by means of pipes conover 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 autoeration of steam, rises, the gas is autotoo 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 HEAVEN 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.