RATIO OF SPECIFIC HEATS 63 



a part independent of temperature, and a part depending 

 on the latter, and representing the increase in molecular 

 and atomic movements : 



The co-efficient 6 increases with the compositeness of the 

 molecule, thus : 



for H 2 , N,, O 2 , CO b = o-ooi, 



for (C 2 H 5 ) 2 6 - 0-0738, 



in accordance with the high molecular specific heat of such 

 compound gases. 



Finally, it must be mentioned that chlorine, bromine, and 

 iodine have abnormally high specific heats 



C p = 8-8i 8.88 8-53, 



which is perhaps connected with the dissociation occurring 

 in these gases at high temperatures, and indicates a 

 preliminary loosening of the atoms. 



2. Specific Heat of Liquids. 



Whilst in gases, either at extreme dilution or under 

 constant volume, the molecular attractions play no part, 

 this point is the most important with regard to liquids, 

 when heating causes a change of volume. We shall trace 

 this out numerically, and first remark that, in accordance 

 with expectation,, the specific heat of gases at constant 

 volume is not altered by strong compression ; Mallard and 

 Le Chatelier went to the extent of 7,000 atmospheres, so 

 that it is reasonable to suppose that in liquids too the 

 specific heat at constant volume has the same value as in 

 the vapour, to which is to be added the work of expansion 

 when a change in volume occurs ; and in liquids, in which 

 a dissociation of double molecules occurs, that also must be 

 taken into account. 



As the simplest case, we will take liquid mercury, which 

 very possibly consists of monatomic molecules in the liquid 

 form also. According to p. 62, the specific heat of the 



