CHAPTER X 



HEA.T 



Heat. In regarding heat as a form of energy we found it 

 necessary to speak in somewhat vague terms of its nature, but 

 the student will, by studying the properties of heated bodies, and 

 by learning how it is measured, be in a position to form a much 

 clearer conception of what constitutes heat. 



Hot and Cold Bodies. EXPT. 124. Arrange three basins 

 in a row, into the first put water as hot as the hand can bear, 

 into the second put luke-warm water, and fill the third with 

 cold water. Place the right hand into the cold water, and the 

 left into the hot, and after half a minute put both quickly into 

 the luke-warm water. Notice that the left hand feels cold 

 and the right warm while in the same water. 



It will be evident from this experiment that the sense of touch 

 is not to be depended upon for accurately estimating the heat 

 condition of a body. To be able to make an estimate of the 

 temperature, or intensity of heat, of a body we must utilise some 

 effect produced by heat upon an inanimate substance. 



Effects of Heat. The effects of heating a substance may be 

 classed under three heads : 



(1) Change of size. 



(2) Change of temperature. 



(3) Change of state. 



1. The change of size which a body undergoes is spoken of as 

 the amount it expands ; or heat is said to cause expansion in the 

 body. This expansion is regarded in three ways. When we 

 are dealing with solids, we speak of expansion in length or linear 



