38 'Laruor, Physical Aspect of the Atojnic Theory. 



static type, accompanied by but little energy of intense 

 agitation such as would be partially dissipated into the 

 surroundings. It may thus be the close quarters at which 

 these operations are developed, in the liquid environment, 

 that limit both the occurrence and the diffusion of irregular 

 intense disturbance such as would pass away into sensible 

 heat. In ordinary dissociation of the nearly free molecules 

 of gases, accompanied by comparatively large changes of 

 volume or pressure, or in the cognate phenomena involving 

 osmotic expansion of dilute solutions already formed, a 

 relatively greater degradation of energy is involved, and is 

 indicated by the greater variation of the equilibrium on 

 change of the temperature. 



The history of this problem may be recalled. When 

 Lord Kelvin opened up the subject of availability of 

 chemical energy in 185 1, he found by experiment that in 

 a Daniell cell nearly the whole of the energy of chemical 

 combination was available for mechanical work. Later 

 Gibbs in 1878 and Helmholtz in 1882 pointed out that 

 the change of electromotive force with temperature gave 

 a measure of the proportion of the energy that is not 

 thus available: and the accumulating cases of discrepancy 

 with Kelvin's principle thus became rational. Now the 

 problem is rather why the unavailable part proves to be 

 often so slight, as compared with other chemical processes 

 more thermal in character. Not merely can the opera- 

 tions be conducted in a nearly reversible manner, so that 

 all the available energy is utilized, but in addition nearly 

 all the energy of the chemical change is often actually 

 available so that there is but slight evolution of heat where 

 it occurs. It will be remembered that Professor Nernst 

 devoted his recent Silliman Lectures to this subject. 

 " To enable us to proceed it is necessary to find the 

 conditions under which the principle of Berthelot comes 



