PROFESSOR IN BERLIN 311 



are equivalent to a large quantity of mechanical work ; the 

 dissociation of the resulting chemical compound requires an 

 expenditure of work corresponding to the amount of the chemical 

 forces lost in the formation of the compound. 



'Oxygen and hydrogen when separated contain a store of 

 energy ; then if they are allowed to burn to form water, they 

 develop a large amount of heat. The two elements are con- 

 tained in the water, and their chemical attraction persists, and 

 keeps them firmly united ; but it can no longer be utilized, nor 

 produce any positive action. We must reduce the united 

 elements to their first state, and separate them from one another, 

 employing to this end a force greater than their affinity, before 

 we can restore to them the power of producing their original 

 effect. The amount of heat produced by chemical association 

 is at least approximately equivalent to the yield of work of the 

 chemical forces brought into play. The same quantity of work 

 must be employed, on the other hand, to dissociate the compound, 

 and reduce the two gases to a free state/ 



In this work 'On Galvanic Currents', Helmholtz was the 

 first to apply the two laws of thermodynamics to electricity. In 

 order to keep up a current of electricity through any conductor 

 it is necessary to expend a certain amount of chemical or 

 mechanical work ; the supply of positive electricity in the 

 positive end of the conductor must be perpetually renewed, in 

 order to oppose the repulsive force of the positive electricity there 

 accumulated, and the same holds for the negative electricity 

 at the negative end. In accordance, therefore, with Faraday's 

 law, the electromotive force of the battery must be proportional 

 to the work which can be obtained by the transformations of one 

 equivalent of each of the substances in question. Here, how- 

 ever, it is not merely the great forces of affinity of the elements 

 that unite or separate in fixed proportions that have to be 

 considered, but, further, the lesser molecular forces of attraction 

 exerted by the water and other components of the solution 

 upon its ions, and Helmholtz set himself the task of detecting 

 influences of this kind (which are too feeble to be found by the 

 calorimetric method) by measurement of the electromotive 

 forces. In order to calculate by means of the mechanical 

 theory of heat what influence the concentration of a solution of 

 salt has upon the E.M.F., a current was led through a salt 



