NON-MATHEMATICAL SCIENCES 167 



studied by methods which are not very different 

 from those of the early alchemists. 



After the work of Boyle the next great step 

 in chemical classification came through a study 

 of the phenomenon which we know as reduction 

 and oxidation, but which was first called phlo- 

 gistication and dephlogistication ; and although 

 I have recently shown^ that this classification 

 is not absolute but only convenient, it remains 

 and will remain one of the leading ideas in 

 chemistry. The phlogistonists were not content 

 wdth the idea alone, but must add a mechanism, 

 the hypothetical phlogiston, so that every proc- 

 ess of the type we are discussing was supposed 

 to involve the gain or the loss of this almost 

 imponderable substance. By this mechanism 

 they fell. They had not yet recognized that the 

 air is a chemical reagent, and thought that the 

 process of burning was merely the loss of phlo- 

 giston. When it was found that substances in 

 burning gain in weight they were obliged to 

 retreat before the proponents of the oxygen 

 theory. If they had only thought to say "The 

 substance burning gives up its phlogiston to, 

 and then combines mth, the oxygen of the air," 



1 Lewis, Valence and the Structure of Atoms and Mole- 

 cules. 



