The Tendencies of Chemistry 



we need only reproduce within a calorimeter all 

 the reactions known to chemistry, and measure 

 the quantity of heat set free in each case. 

 We shall then have a precise and scientific sub- 

 stitute for Bergmann's tables, and our results will 

 act as a check on each other; or better still, from 

 a number of them we can calculate the rest. 



It is, of course, impossible for us to measure 

 the total energy contained in bodies; we can 

 know only the variation of this energy during 

 the act of combination; thus the energy of the 

 molecular weight H 2 = 2 grammes of hydrogen is 

 just as unknown to us as the energy of the 

 molecular weight O = i6 grammes of oxygen; 

 but we do know that when these two weights 

 combine to form aqueous vapour 58,300 calories 

 are released. We are, therefore, entitled to 

 say that a molecule of water vapour has 58,300 

 calories less energy than its constituents, and 

 to complete Lavoisier's chemical equation as 

 follows : 



H 2 +O = H 2 O 4- 58,300 calories. 

 Let us now consider a slightly more complicated 

 reaction, that of sulphuric acid on zinc : 



Zn + H 2 SO 4 = ZnSO 4 + H 2 + 107,000 calories. 

 39 



