DEVELOPMENT OF HOUSE HEATING 129 



equal ventilation. This will be explained in Chap. VI. 

 The first cost of a hot water system of heating is considerably 

 greater than that of furnace heating and slightly greater than 

 that of STEAM HEATING, which will soon be considered. 



SENSIBLE AND INSENSIBLE HEAT 



148. The Factors of Heat Quantity. We are all more or 

 less familiar with heat changes. If we place a hot iron in a 

 pail of cold water, the water becomes heated and the iron 

 cooled. The temperature of both the iron and the water soon 

 becomes the same. All of the heat which goes out of the iron 

 goes into the water. The change in temperature in each case 

 indicates the change in heat quantity. But we know that, if 

 we use more of the water the change in temperature of the 

 water will be less; or, if we use a larger piece of iron and heat 

 it to the same temperature before placing it in the water, the 

 water will be heated to a much higher temperature. The fact 

 is that heat quantity is made up of three factors. Usually 

 these factors are: (1) Change in temperature; (2) quantity of 

 matter involved; (3) kind of matter (Art. 120). We shall see, 

 however, that the three factors may be: (1) A change in the 

 form or state of the matter; (2) quantity of matter; (3) kind 

 of matter. 



149. Sensible Heat. When the three factors involved in 

 the heat quantity are change in temperature, quantity of 

 matter, and kind of matter we say the heat is SENSIBLE HEAT, 

 because it may be perceived by the senses. The heat units 

 are based upon the measurement of sensible heat. Define 

 1 B.t.u. and show that the last statement is true, likewise 

 show that it is true by defining a Cal. and a cal. (Art. 121). 



150. Heat Necessary to Turn a Liquid into a Vapor. We 

 have seen that by applying heat to the paraffin in the candle 

 wick, to the kerosene in the lamp, to the alcohol and water in 

 the distilling flask we changed these liquids into vapors. In 

 each case we put heat, a certain number of calories, or B.t.us. 

 of heat, into the liquid to turn it into vapor. It takes a large 



