336 HERMANN VON HELMHOLTZ 



quantity of tensional force, the analytic development of dynamics 

 had been essentially simplified and generalized. As a rule, 

 however, alterations of temperature had not been taken into con- 

 sideration in the application of this conception, either because 

 the forces of which the work-equivalent was to be calculated, 

 e. g. the force of gravity, did not depend on temperature at all, 

 or because the temperature during the processes under in- 

 vestigation might be regarded as constant, or as a function 

 of definite mechanical alterations, viz. in sound-waves, as 

 a function of the density of the gas. But if the physical 

 constants occurring in the value of the potential energy, such 

 as density, and the like, vary with the temperature, which 

 would make that energy a function of the temperature, then the 

 integration constants comprised in the value of such potential 

 energy would require a purely arbitrary determination for 

 each new temperature ; the transition from one temperature to 

 the other would not be possible. 



Previous investigations of the work-equivalent of chemical 

 processes referred almost exclusively to the quantities of heat 

 that appear or vanish when compounds are formed or decom- 

 posed, whereas most changes are connected with alteration 

 of the state of aggregation and density of the bodies. These, 

 however, produce or consume work under two forms, as heat, 

 and as unrestrictedly transformable work. A supply of heat is 

 not unrestrictedly convertible into other work-equivalents, but 

 can only be partially transformed, and only on the condition of 

 a simultaneous transference of the remainder of the uncon- 

 verted heat to a body of lower temperature. Since in most 

 chemical processes the changes of melting, evaporating, &c., 

 also attract heat out of the environment, it is necessary to 

 inquire in what proportions mechanical and thermal energy 

 are obtained in these cases also. When we further consider 

 that chemical energies per se may produce not merely heat but 

 other forms of energy as well, without any alteration of tempera- 

 ture in the combining bodies being required, proportional to 

 the work done, as e.g. in the work produced by galvanic 

 batteries, it is evident that there must in chemical processes 

 also be a distinction between that portion of their forces of 

 affinity which is capable of free conversion into other forms 

 of work, and the portion which is manifested as heat only. 



