The Evolution of the Sciences 



It leads to the following argument: as the 

 heat of formation of sulphuric acid, from its 

 elementary constituents, amounts to 123,000 

 calories, the first member of the equation 

 possesses an energy equal to that of its free 

 constituents, less 123,000 calories; likewise the 

 group forming the second member possesses 

 an energy equal to the energies of the same 

 constituents, less 230,000 calories, which number 

 gives the heat of formation of the zinc sulphate 

 from its elements. Now the difference of these 

 two numbers, 230,000 123,000, corresponds 

 exactly with the 107,000 calories set free in the 

 reaction of the acid on the zinc. Here are, 

 therefore, three numbers which can be obtained 

 by independent measurement, and between 

 which exists a necessary relation; thus the 

 calorimetric study of chemical reactions enables 

 us to establish relations between different 

 quantities of heat and in particular to calculate 

 one of them, if the others are known. 



We can now conceive the possibility of 

 determining experimentally the heat of forma- 

 tion of all compounds, and hence of knowing 



beforehand the thermic effect of any reaction 



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