PROFESSOR IN BERLIN 341 



taken up, by the end-products of the chemical process, when 

 they have returned to the temperature of their initial state, 

 before the chemical process began. The heat-equivalents of 

 any further work that has been done or absorbed (i. e. done 

 negatively) must if necessary be added. 



' By this method is obtained the heat-equivalent of the excess 

 of the whole store of energy which the substances involved 

 contained in their initial state, over that of the final state. 

 This is the foundation of Thermochemistry, firmly established 

 by countless arduous and most valuable investigations, and 

 corresponds to the general Law of the Conservation of Energy. 



'The work done by the chemical forces for the most part 

 appears only in the form of heat, but under special circum- 

 stances we can directly obtain other forms of work, mechanical 

 or electrical, from it. Heat, according to Clausius's stricter 

 interpretation of Carnot's law, plays a peculiar part as com- 

 pared with the other work-equivalents. While the others can 

 be transformed freely and with no perceptible remainder inter 

 se, the convertibility of heat is limited, so long as we are 

 confined to the attainable limits of temperature. At all times it 

 is only a fraction of the heat present that we are able to convert 

 into other forms of work, while the remainder of this part is 

 reduced from a higher to a lower temperature. If we take 

 to denote the lowest absolute temperature (that is, tempera- 

 ture measured from -273 C. as the zero-point) at which we can 

 get our store of heat to flow away, O l being the initial tempera- 

 ture, we must allow the fraction QQ/OI to pass away unconverted, 

 in order to convert the remainder (O l )/0 1 into work. Hence 

 the higher the temperature O lt the larger the fraction of the 

 heat present that can be transformed into mechanical work. 



' In order to describe this antithesis briefly, seeing that it is 

 of essential importance in the question of the efficiency of 

 chemical forces, I have adopted the expression ' free energy ' to 

 describe the work-equivalents of the different natural forces 

 that are freely convertible inter se, with no necessary remainder, 

 denoting the heat store on the other hand as ' bound energy '. 

 To the former, for instance, belong the energy of a raised 

 weight, of a stretched elastic spring, the vis viva of a mass that 

 is moved as a whole, an accumulation of electricity at rest in 

 a conductor, &c. To say that these are interconvertible ' with 



