162 Domestic Science 



the same quantity of heat, viz. 8640 calories, to its 

 surroundings. 



103. We may easily find by calculation the tem- 

 perature of the water resulting from the admixture 

 of two quantities of water at different temperatures, 

 if we assume that all the heat supplied by the water 

 at the higher temperature is applied to raising the 

 temperature of the colder water. Suppose that, in 

 Experiment 52, 100 c.c. of water at 60 C. were mixed 

 with 500 c.c. at 15 C. Let n C. be the temperature 

 attained- by the mixture. We have 



Heat given out by hot water = 100 x (60 ri) 

 calories ; 



Heat received by cold water = 500 x (n 15) 

 calories. 



On our assumption, these two quantities must be 

 equal, i.e. 



100 x (60 -n) = 500 x (n - 15). 



Solving this as a simple equation, we have 

 600^ = 13,500, or n = 22' 5 C. 



104. From Experiment 53 we learnt that different 

 substances have different capacities for heat, since 

 bodies of different materials gave out unequal quantities 

 of heat while cooling. The capacity of a given body 

 for heat is called its " thermal capacity " and is measured 

 by the quantity of heat necessary to raise its tempera- 

 ture 1 C. Thus, if 30 g. of mercury have to be supplied 

 with 1 unit of heat in order to cause the temperature 

 of the liquid to rise 1 C., the thermal capacity of the 

 30 g. is said to be 1. When the thermal capacity of 

 unit mass is considered, & new term is introduced, 

 this quantity being known as the " specific heat " of 

 the substance dealt with. Since 1 g. of water requires 



