SYNTHETIC CHEMISTRY 



For M. Berthelot there are three principles which 

 cover all. The first of these is that the amoxuit of 

 heat developed is a measure of the molecular work 

 done that is to say, of the chemical affinities. 

 Whether the values so obtained afford a clear 

 basis for comparison, free from all confusion, or 

 whether, perhaps, an electrical method may not 

 yield more serviceable results, is still an open 

 question. If chemical affinity turns out to be 

 simply electrostatic attraction, as seems not im- 

 probable, then the thermo- chemical system will 

 probably undergo modification. Until then, M. 

 Berthelot 's principle must hold. 



The second law is that the amount of heat evolved 

 in a given reaction depends solely upon the final 

 state reached, no matter by what route that be 

 attained. If carbon be first burned to carbonic 

 oxide, CO, then to carbon dioxide, CO 2 , the result 

 is the same as if the complete combustion had 

 been reached directly, as in the case of an ordinary 

 wood -fire. This is the principle of Hess, and is 

 useful in calculating the heat reaction where that 

 cannot be done by direct measurement. 



The third principle seems innocent and looks be- 

 guiling enough, but it has caused no end of trouble 

 and dispute. It affirms simply that every chemi- 

 cal change tends towards the production of such 

 compounds as evolve the most heat. If this were 



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