338 HERMANN VON HELMHOLTZ 



in this sense he defines the magnitude of the entropy as the 

 measure of disorganization. 



4 For our instruments (which are coarse in comparison with 

 molecular structure) it is organized motion alone that is freely 

 convertible into other forms of work ; whether such transform- 

 ation is actually impossible in view of the fine structure of 

 living organic tissues appears to me still to be an open 

 question, the importance of which in the economy of nature is 

 plainly obvious/ 



By simple mathematical calculations Helmholtz arrived at the 

 result that in all changes in which the temperature remains 

 constant, work is only done at the expense of the free energy, 

 while the bound energy alters at the expense of the in- and 

 out-going heat. In all adiabatic alterations work is produced 

 at the cost of free as well as of bound energy, so that the 

 entropy remains constant. In all other cases external work is 

 done at the cost of the free energy, all production of heat at the 

 cost of the bound, while with each rise of temperature in the 

 system free energy is transformed into bound. 



Observations on galvanic cells agreed with these general con- 

 clusions. Here too it appeared that the bound energy increases 

 at the cost of the heat supplied, and with rise of temperature at 

 the expense of the free -energy, so that free must always be 

 transformed into bound energy, and not vice versa. Neither 

 is the free work in isothermal changes expressed in irrever- 

 sible processes by the heat developed, when the initial and 

 final temperatures are the same, since this heat is derived 

 from the free and the bound energy, while free work depends 

 upon the former only. The fact that, apart from altera- 

 tions of temperature, the vanishingly small alteration of free 

 energy is not positive, or is nil, may be taken as the condition 

 of the system remaining in its present state, but if a point be 

 reached by rise of temperature, at which this becomes negative, 

 dissociation will ensue. Thus all chemical compounds below the 

 temperature of dissociation give out heat, if they are formed by 

 reversible processes. 



Helmholtz then employed his new concept of free energy in 

 calculating the connexion between the E.M.F. of a cell and the 

 vapour tension. 



In a paper communicated to the Academy (May 3, 1883), ' On 



