10 SCIENCE OF HOME AND COMMUNITY 



wise the direct-indirect method explained above may be 

 used. 



The source of the heat in the steam is due not merely to 

 the fact that the steam is hot, but largely to the fact that 

 when steam condenses it gives off a large amount of heat. 

 When water is boiled, it takes a large amount of heat to 

 change it into steam. When we wish to measure the amount 

 of heat, we use a standard called the calorie, as we use the 

 pound to measure weight. A calorie represents the amount 

 of heat necessary to raise the temperature of one gram of 

 water one degree Centigrade. It requires over five hundred 

 calories to change one gram of water into steam, that is, 

 over five times the amount of heat needed to heat water 

 from the freezing point to the boiling point. This heat is 

 stored up in the steam, and when the steam condenses, 

 the heat is given out to surrounding objects. It is the 

 condensing of steam that furnishes most of the heat. Pro- 

 vision is made for pipes to take the water thus formed 

 back to the furnace. 



DEMONSTRATION 3 



Purpose. To learn the source of heat in the steam-heating 

 system. 



Apparatus. Flask, rubber stopper with one hole, piece of 

 glass tubing about eighteen inches long, beaker, ringstand, 

 thermometer. 



Directions. Bend the tubing twice at right angles so that the 

 two arms are parallel and point in the same direction. One of 

 these arms should be about three inches long, and the other arm 

 about eight inches long. Fill the flask a third full of water and 

 insert a rubber stopper with one hole. Push the short arm of 

 the tubing through the hole in the stopper. Support the flask 

 on a ringstand. Fill a beaker with cold water and place it so 

 that the long arm of the tubing dips below the surface of the 

 water in the beaker. Take the temperature of the water. Heat 

 the water in the flask. After it has boiled five minutes, take 



