234 ON CHEMICAL ENERGY. 



versely, tliat wheu two substances act on each other tlieh' potential 

 mast bo difterent. 



That general law whicli can be regarded as expressive of the Second 

 Theorem holds also for the chemical potential, namely: Two potentials 

 which individually are equal to a third are equal to each other. This 

 proposition seems quite self-evident, and therefore equally meaning- . 

 less. Yet we can draw from it conclusions tliat are very far reaching. 

 It says that two bodies or groups of bodies which are in equilibrium 

 with each other, can mutually replace each other at pleasure towards 

 a third system in every reaction in which this third system (towards 

 which ecpiilibrium has been established) can react. Thus, for example, 

 every soluble body can be replaced by its saturated solution, every 

 liquor by its saturated vapor, every solid body at its fusing ])oint by the 

 melted body withoutcausiugany alteration in tlie equilibrium depending 

 upon the former. Among other things this shows that while the heat 

 of solution, fusion, and evaporation, change the evolution of heat dur- 

 ing a cliemical process, they do not thus affect the equilibrium. The 

 thermal theory of affinity, which is even to-day championed by Berthe- 

 lot and others, is by this circ-umstauce proved to be quite untenable. 



It is natural in the case of such a far-reaching proposition to require 

 proofs. This proof is found in the fact that it is impossible to create a 

 peiyotuuni mobile. To have a perpetuum mobile it is not necessary to 

 create energy from nothing, but only to transform potential energy into 

 kinetic. If it were for instance i)ossil)le to transform the constant heat 

 which is })resent in enormous amounts in the ocean into work which 

 then could change biick into heat, we would require no more coal to 

 propel our steamshi}>s, since all the work which we re(|uired for their 

 propulsion would be transformed into heat by friction and could return 

 to the ocean in unchanged amounts. Such 'A perpetuum mobile will be 

 instantly ))ossible when two substances which individually are in equi- 

 librium with a third are not in e(|uilibrium with each other. If we 

 assume that a substance .1, when in contact with a large body B (the 

 ocean), assumes a temperature which is difterent from that imi)arted to 

 a body i>, sinuiltaneously in contact and e(piilibrium with the ocean, 

 we w(mld cause a transmission of heat between A and B which would 

 be capable of driving a machine. This proof is equally true for every 

 other form of Ciiuilibrium and for every form of energy, and thus we 

 also prove our chemical proposition. 



When we have thus recognized the conditions under which energy is 

 in equilibrium or at rest, we can directly reason that energy can not be 

 at rest when its potentials are different. A process must then take 

 place by means of which they become equal. This is the most common 

 phenomenon with which we are acquainted; everything which takes 

 place is based, m the last instance, upon an e(jnalization of energies of 

 different potentials. 



Since however energy, as is a fact, has a never-ceasing teudenc3' to 



