THE MEASURING OF HEAT 69 



cord will burn in oxygen (cf. 51), if tipped with burning 

 sulphur to start the action. A match consists of several 

 substances, each of which is used to kindle another sub- 

 stance having a higher kindling temperature. Friction 

 ignites the phosphorus, the burning phosphorus ignites 

 the sulphur, and the burning sulphur sets the wood on 

 fire. A stick burns from one end to the other, each part 

 giving out enough heat to ignite the part next to it. 



73. The Measuring of Heat. While the thermometer 

 is the instrument for finding the degree of heat of a body, 

 the calorimeter is the instrument by means of which we 

 get the amount of heat in a body (cf. 64). We measure 

 this amount by finding out how much heat 

 the body can give to a certain weight of 

 water. 



The simple calorimeter is a metal vessel 

 (Fig. 60) with polished sides. A covering 

 of felt (a non-conductor) prevents the air 

 from taking heat away from the vessel, or 



adding heat to it. Suppose that we wish to A simple 



1 eter Surrounded 



find out which holds more heat at the same by a Non-con- 



ductor. 



temperature, lead or iron. We put into the 

 calorimeter a known weight of water, at room temper- 

 ature, let us say. We then put into the water 10 g., say, 

 of lead having a temperature of 100 C. The hot lead 

 gives heat to the water, until the water and the lead have 

 the same temperature. A thermometer, kept in the 

 water, tells us how many degrees the temperature of the 

 water has been raised. We now put into the calorimeter 

 another portion of water of the same weight as before, 



