THE REVIVED THEORY OF PHLOGISTON. 567 



ed, more adapted to the needs of the time, than the partial truth 

 which it displaced. To him chemists are indebted for their present 

 conception of material elements ; and especially for their knowledge 

 of the part played by the air in the phenomena of combustion, where- 

 by oxygenated compounds are produced. The phlogistians, indeed, 

 were not unaware of the necessity of air to combustion, but, being 

 ignorant of the nature of air, were necessarily ignorant of the func- 

 tions which it fulfilled. To burn and throw off phlogiston being 

 with them synonymous expressions, the air was conceived to act by 

 somehow or other enabling the combustible to throw its phlogiston 

 oiF; and a current of air was conceived to promote combustion by 

 enabling the combustible to throw its phlogiston off* more easily. 

 Moreover, contact of air was not essential to combustion, provided 

 there was present instead some substance, such as nitre, which, 

 equally with or even more effectively than air, could enable the com- 

 bustible to discharge itself of phlogiston. But, while the phlogis- 

 tians, on the one hand, were unaware that the burnt product differed 

 from the original combustible otherwise than as ice differs from water, 

 by loss of energy, Lavoisier, on the other hand, disregarded the no- 

 tion of energy, and showed that the burnt product included not only 

 the stuff of the combustible, but also the stuff of the oxygen it had 

 absorbed in the burning. - But, as well observed by Dr. Crum-Brown, 

 we now know " that no compound contains the substances from which 

 it was produced, but that it contains them minus something. We 

 now know what this something is, and can give it the more appro- 

 priate name of potential energy ; but there can be no doubt that this 

 is what the chemists of the seventeenth century meant when they 

 spoke of phlogiston." 



Accordingly, the phlogistic and antiphlogistic views are in reality 

 complementary and not, as suggested by their names and usually 

 maintained, antagonistic to one another. It has been said, for exam- 

 ple, that, according to Stahl, the product of combustion is simple, and 

 the combustible a compound of the product with imaginary phlogiston 

 which is false; w^hereas, according to Lavoisier, the combustible is 

 simple, and the product a compound of the combustible with actual 

 oxygen which is true. But in this case, as in so many others, every- 

 thing turns upon the use of the same word in a different sense at dif- 

 ferent periods of time. When Lavoisier spoke of red lead as being- 

 metallic lead combined with oxygen, he meant that the matter or stuff 

 of the red lead consisted of the matter or stuff of lead jt??ws the matter 

 or stuff of oxygen. But, when the Stahlians spoke of metallic lead be- 

 ing burnt lead combined with phlogiston, they had the same sort of 

 idea of combination in this instance as others have expressed by say- 

 ing that the weight of a body is compounded of its matter and its 

 gravity ; or that steam is a compound of water and heat ; or, to use a 

 yet more Lavoisierian expression, that oxygen gas itself is a compound 



