WATER 81 



1.000 for the interval between 0° and 1° 

 centigrade, a number which is due to the 

 choice of water in defining the calorie or 

 fundamental unit of heat. The caloric, small 

 calorie, or gram calorie is that quantity of 

 heat which is required to raise the temperature 

 of one gram of water through 1° centigrade, 

 and it varies slightly with the temperature, 

 having the relative values 1.000 for the in- 

 terval from 0° to 1°, 0.998 for the interval from 

 4° to 5°, 0.992 for the interval from 15° to 

 16°, and its mean value for the interval from 

 0° to 100° is 1.004. The heat capacity of ^ 

 water is then 1.000, in that 1.000 calorie is re- 

 quired to raise the temperature of 1.000 gram 

 of water through 1.000 degree centigrade. 



The approximate specific heats of a variety 

 of important substances are as follows: — 



[liquid .... 1.00 

 Water I solid . . . .0.50 



[gas .... 0.3-0.5 



Lead 0.03 



Iron 0.10 



Quartz 0.19 



Salt 0.21 



Marble 0.22 



Glass 0.20 



Sugar 0.30 



Ammonia, liquid . . .1.23 



Chloroform O.ii 



Hydrogen 3.4 



Alcohol 0.5-0.7 



Hexane 0.50 



It is unnecessary to enter upon an elaborate 

 analysis of the data concerning specific heats, 

 for the magnitude of the specific heat of a 

 substance is dependent upon its chemical 

 nature, as was first made clear b} T Dulong 



