LATENT AND SPECIFIC HEAT. 



339 



FIG. 256. 



the heat expended, to avoid melting of the ice by the heat 



of the surrounding air and making proper 



allowance for the heat expended in warming 



the apparatus itself. Fig. 256 represents a 



form of calorimeter frequently used in such 



experiments. M contains the heated body 



whose weight and temperature are known. 



A contains the ice to be melted, the liquid 



thus produced escaping by D. B is an ice 



jacket to prevent melting of the ice in A by 



the heat of the air. 



532. Definition of Specific 

 Heat. TJie specific heat of a body 

 is the ratio between the quantity 



of heat required to warm that body one degree and 

 the quantity of heat required to warm an equal 

 iveight of water one degree. 



(a.) It is very important to bear in mind that specific heat, like 

 specific gravity, is a ratio ; nothing more nor less. The specific heat 

 of water, the standard, is unity. This ratio will be the same for 

 any given substance, whatever the thermal unit or thermometric 

 scale adopted. 



533. Specific Heat Determined by Mixture. 



One of the simplest methods of measuring specific heat 

 is by mixture. Suppose, e. g., that 3 kilograms of mercury 

 at 100 C. are mixed with 1 kilogram of ice-cold water and 

 that the temperature of the mixture is 9 C. How shall 

 we find the specific heat of mercury ? 



Let x the specific heat of the mercury, or the amount of heat 

 lost by one kilogram of mercury for each degree of change of 

 temperature. Then will 



3.C = the number of heat units lost by the given amount of mer- 

 cury for every degree of change of temperature, and 91 times 

 3x, or 



273ar = the number of heat units lost by the mercury in passing 

 from 100 to 9 C. 



The specific heat of water is 1. This multiplied by the number 

 of kilograms of water taken is 1, which represents the number of 



