QUANTITY OF HEAT. SPECIFIC HEAT. 



85 



Compound Gases. 



The last column confirms the result that for less condensable gases the 

 capacity for heat of equal volumes at equal pressures is constant, for 

 the weights of equal volumes of these gases are then very nearly pro- 

 portional to their atomic weights if elements, to their molecular weights 

 if compounds. The heat capacities of these equal volumes are therefore 

 proportional to the numbers in the last column. Dividing the " Mole- 

 cular Heat" for gases of the type AB by 2, and that for gases of the 

 type AB 2 by 3, we get atomic heats 3-3 or 3-4, nearly the same as those 

 found for hydrogen and oxygen, a result indicating that tht- atoms 

 have the same capacity for heat even in combination. It will be noticed 

 that the atomic and molecular heats for the more easily condensable 

 gases are somewhat widely different from those of the more permanent 

 gases. 



E. Wiedemann * has simplified Regnault's method of experiment on 

 gases, and has obtained results in close agreement. His value for air 

 at was 0-2389, and he found no change between C. and 200 C. for 

 air, hydrogen, and carbon monoxide. The capacities for heat of equal 

 volumes of these gases at the same pressure were nearly the same, but 

 the more condensable gases gave very different values from the others, 

 and as their temperature rose the specific heat increased. 



No doubt the specific heat at constant volume is the more appro- 

 priate quantity for comparison, inasmuch as at constant pressure a 

 certain amount of the heat goes to push out the containing surface 

 against the external pressure. As we shall see later, the ratio of 

 the two specific heats is nearly constant for air, hydrogen, oxygen, and 

 nitrogen, so that we may regard the results obtained in the one case as 



* PhU. Mag. (5), 2, p. 81, 1876. The remarks in the footnote on p. 71 apply also 

 to Wiedemann's experiments. 



