CHAPTER VI. 

 QUANTITY OF HEAT. SPECIFIC HEAT, 



Quantity of Heat Unit Quantity: the Calory Specific Heat Water Equivalent 

 and Capacity for Heat Method of Mixtures Regnault's Determinations by 

 the Method of Mixtures Experiments on Solids On Liquids On Gases 

 Specific Heat of a Liquid by Mixture with known Solid Method of Cooling 

 Method of Melting Ice Bunsen's Ice Calorimeter Method of Condensing 

 Steam Joly's Steam Calorimeter Differential Steam Calorimeter Method of 

 Electric Heating Specific Heat of Water General Results Law of Dulong 

 and Petit. 



Quantity of Heat. Specific Heat. When a cold body is put in con- 

 tact with a hot body, the colder rises in temperature, while the hotter 

 is cooled. We describe the rise of temperature of the one by saying 

 that it has gained heat, the fall of temperature of the other by saying 

 that it has lost heat. But we go further than this, and regard the heat 

 gained by the one as identical with the heat lost by the other. That 

 is, we regard the heat as something which we can identify at least in 

 thought, and which has been transferred from the one body to the other. 

 This is no doubt metaphysical ; for all that we are entitled to assert, from 

 actual experiment, is that one body is hotter, the other cooler ; but the 

 conception of the identity of heat enables us to describe the process more 

 shortly, and to think of it much more clearly. 



Let us suppose that we have a number of equal vessels, containing 

 equal quantities of water at the same temperature. Let us plunge into 

 these vessels different hot masses, into one iron, into another copper, 

 into a third stone, and so on, and let us further suppose that the masses 

 and their temperatures are so adjusted that in each case the temperature 

 of the water has risen by the same amount in coming to thermal equi- 

 librium. Since the mass of water is in each case the same, the same 

 amount of heat has been gained by each, and, if we take the view that 

 this heat has passed from the body immersed, we see that we can speak 

 of equal amounts of heat lost by quite different substances, though the 

 effects are very different. The iron, for example, may have fallen 10, 

 the copper 20, the stone 30. We need not then speak of iron heat, 

 copper heat, stone heat, but of heat simply, for all these different sub- 

 stances, on parting with their heat to one chosen substance, have the 

 same kind of effect on it. 



We are thus led to the idea that we may measure quantity of heat 

 by its effect in raising the temperature of a given mass of some chosen 

 substance, and water is the substance which is usually chosen. 



If we make an experiment in which we mix equal quantities of water 

 at different temperatures, we find, after allowing for the heat taken uj> 



