Heat 87 







The temperature of a properly heated room, measured by a 

 Fahrenheit thermometer, is about 68 degrees. A centigrade ther- 

 mometer would read 20 degrees under the same conditions. This 

 means that 20 degrees on the centigrade thermometer indicates 

 the same temperature as 68 degrees on the Fahrenheit. To show 

 which scale is meant, it is customary to place an F. after the 

 Fahrenheit reading and a C. after the centigrade reading. 



Physicians and nurses use a clinical thermometer. It is a 

 mercury instrument having a Fahrenheit scale which reads from 

 92 to 110 degrees. Each degree is divided into fifths. In this 

 instrument the mercury remains at the highest temperature 

 recorded until shaken down. The normal temperature of a 

 healthy person is 98.6 degrees; 100 degrees shows that he has 

 some fever; 103 degrees or higher that he is seriously ill'. 



Experiment to Test the Fixed Points of a Thermometer. 

 To show how a thermometer indicates changes of temperature 

 (testing of fixed points) : Boil water in a beaker. Hold a Fahren- 

 heit thermometer with its bulb in the boiling water for three 

 minutes. Read the temperature. Fill a jar with small pieces of 

 ice and a little water. Hold the thermometer bulb in the iced 

 water for three minutes. Read the temperature. What are the 

 fixed points of a Fahrenheit thermometer? 



Effects of Heat. The effects of heat are either physical or 

 chemical. Important physical effects of heat are the causing of 

 matter to expand, to liquefy or melt, and to vaporize or turn to 

 gas. The most important chemical effect is to cause oxidation. 



With rare exceptions, heat will cause matter, whether in a 

 solid, a liquid or a gaseous state, -to expand. Rubber is one 

 exception, for it contracts when heated. Most liquids when 

 heated expand more than solids do. Water, however, is an ex- 

 ception in some respects to the general rule of expansion. As 

 we heat and cool it for daily use, this liquid seems to expand 

 and contract like other forms of matter. But when cooled it 

 contracts until it reaches 39 degrees F., the point at which it 

 begins to expand when heated. At this point it begins to expand 

 again, and continues to expand until it freezes. That this is so 

 may be shown by freezing the water in a full bottle. As you 



