SPECIFIC HEAT, ETC 



WHEN we attempt to heat equal quantities of different 

 substances such as brass, copper, and water, we find that 

 it requires different amounts of heat to produce the same 

 rise in temperature. Some substances, like water, change 

 their temperatures slowly when heated ; others, like mer- 

 cury and zinc, change their temperatures rapidly when 

 heated. This difference is due to what we call the Spe- 

 cific Heat of the substances. The amount of heat needed 

 by i gm. of a substance in order that its temperature 

 may be increased i C. is called the specific heat of that 

 substance. The specific heat may also be defined as 

 the amount of heat given out by I gm. of a substance 

 when its temperature falls i C. 



The law of mixtures enables us to determine the specific 

 heat of a substance. Suppose for example we wish to 

 determine the specific heat of zinc. If 20 gm. of zinc at 

 90 C. is put into 60 gm. of water at 10 C., the resultant 

 temperature is 12.41 C. ; and from these facts the specific 

 heat can be determined as follows : 



As a result of the mixture, each gram of zinc had its 

 temperature lowered 77.59 C. If S represents the spe- 

 cific heat of zinc, that is, the number of calories lost by 

 I gm. of the zinc when its temperature falls i C., then 

 the total heat lost by I gm. would be 5 multiplied by 

 77.59, or 77.59 x 5 calories. The heat lost by 20 grams of 

 zinc would be 77.59 x S x 20, or 1551.8 x 5 calories. 



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