A HISTORY OF SCIENCE 



that burned easily, so that the freed phlogiston might 

 again combine with the ashes. This was explained 

 by the supposition that the more combustible a sub- 

 stance was the more phlogiston it contained, and since 

 free phlogiston sought always to combine with some 

 suitable substance, it was only necessary to mix the 

 phlogisticating agents, such as charcoal, phosphorus, 

 oils, fats, etc., with the ashes of the original sub- 

 stance, and heat the mixture, the phlogiston thus freed 

 uniting at once with the ashes. This theory fitted 

 very nicely as applied to the calcined lead revivified 

 by the grains of wheat, although with some other prod- 

 ucts of calcination it did not seem to apply at all. 



It will be seen from this that the phlogistic theory 

 was a step towards chemistry and away from alchemy. 

 It led away from the idea of a " spirit" in metals that 

 could not be seen, felt, or appreciated by any of the 

 senses, and substituted for it a principle which, al- 

 though a falsely conceived one, was still much more 

 tangible than the "spirit," since it could be seen and 

 felt as free phlogiston and weighed and measured as 

 combined phlogiston. The definiteness of the state- 

 ment that a metal, for example, was composed of 

 phlogiston and an element was much less enigmatic, 

 even if wrong, than the statement of the alchemist that 

 "metals are produced by the spiritual action of the 

 three principles, salt, mercury, sulphur" particularly 

 when it is explained that salt, mercury, and sulphur 

 were really not what their names implied, and that 

 there was no universally accepted belief as to what 

 they really were. 



The metals, which are now regarded as elementary 



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