RICHARDS. — CHANGING HEAT CAPACITY. 305 



direct measure of the energy of compression. But this additional oscil- 

 lation would signify an evolution of heat.* 



Suppose now that instead of colliding irreversibly, the two imaginary 

 balls were arrested by an outside mechanism, being allowed to attain 

 gently the same united equilibrium, thus utilizing the energy which 

 would otherwise have become manifest in oscillations as outside work. 

 It is conceivable that in this way all oscillation might be prevented, in 

 which case no heat would have been evolved, and the equivalent of the 

 energy which would otherwise have caused the oscillations will have been 

 used for some outside purpose by the mechanism. The Daniell cell, or 

 better, the Ni-Fe cell, may serve as the actual type of such a conception. 



It does not necessarily follow, however, that the mechanism would be 

 capable of using all the attracting energy, or would be able to perform an 

 amount of outside work which would be equivalent to the heat. Indeed, 

 the distortion of both atoms caused by their mutual compression might 

 well be expected to cause an expenditure of energy within the atom ; 

 hence less would be available for outside work. Such distortion would 

 naturally tend to restrict the heat vibration, and hence diminish the heat 

 capacity. Hence one might have predicted that when there is a loss of 

 heat capacity in the system, the free energy could not equal the attract- 

 ing energy, and that some of the attracting energy must inevitably appear 

 as heat, not available for outside work. In symbolic language, according 

 to the first law of energy, C = A' + P> where C represents chemical 

 attracting energy, A' free energy, and P energy needed to effect a dim- 

 inution of heat capacity. 



On the other hand, the vibrational activity of heat energy may be 

 supposed to be continually striving to evercome the restrictions which 

 circumstances impose upon it. Hence when the opportunity of an 

 enlarged heat capacity is offered by the progress of a chemical change, 

 this heat energy may be able to perform outside work in addition to 



* A perfectly symmetrical elastic ball in collision with another symmetrical 

 elastic ball might be supposed to cause this other to rebound reversibly even if 

 attraction existed between them. As a"h illustration of this one may conceive of a 

 perfectly elastic ball bouncing on a perfectly elastic surface under the influence of 

 gravity, — its oscillation would continue forever. If, however, one or both of the 

 atoms under consideration is irregular in shape, it is clear that the shock might be 

 so split up into cross-vibrations as to scatter the energy which would otherwise have 

 been used to cause the rebound. Thus heat would be evolved, and the union would 

 be permanent. It is possible that this need of asymmetry in the atom may be the 

 reason why simple pure substances will not combine, but need the catalytic effect 

 of a third substance such as water. 

 vol. xxxviii. — 20 



