The Evolution of the Sciences 



chemistry resemble a sketch map drawn by the 

 first explorers of a mountain range ; the principal 

 peaks are already put down with their approxi- 

 mate dimensions. Thus we know, more or less 

 exactly the quantities of heat brought into 

 play by the principal physical or chemical 

 modifications, when they take place under 

 more or less clearly determined conditions, 

 but we cannot follow the undulations of the 

 chain between the peaks; what is wanting is 

 what geographers call the relief of the country. 

 " The quantity of heat called into play by a 

 given reaction or transformation varies with 

 all the circumstances surrounding the reaction 

 or the transformation, such as the temperature, 

 the pressure, the greater or less dilution 

 of the reacting bodies; thermo-dynamics re- 

 quires to know, for all the important reactions 

 of chemistry, the expression of the heat of 

 reaction as a function of all these variables; it 

 demands from the thermo-chemist, who is study- 

 ing a reaction, not a single experiment, but a 

 detailed and frequently exhaustive monograph." 1 



1 " Thermochimie " Revue des questions scientifiques, vol. 

 xii., 1897, p. 361. 



46 



