CH. XVI. BECHER AND STAHL—' PHLOGISTON: 135 



In this way, by careful experiments and reasoning 

 Mayow succeeded in proving ihdX fire-air (or oxygen) is 

 the chief agent in combustion and respiration. If he had 

 not died so young he might have become more known, and 

 men might have studied his discoveries, which he pubHshed 

 in 1674. Unfortunately, however, he did not live to spread 

 his knowledge, and a false theory of combustion caused his 

 work to be forgotten for many a long year. 



Theory of * Phlogiston,' 1680-1723.— This mistaken 

 theory was proposed by two very eminent chemists, John 

 Joachim Becher (1625-1682) and Ernest Stahl (i66o- 

 1734). Ernest Stahl in particular was a man of great 

 talent and perseverance, and he did a great deal for the 

 study of chemistry by collecting a great number of facts 

 about the way in which different substances combine to- 

 gether, and by arranging these facts into a system. But his 

 theory of combustion was quite mistaken, and it seems very 

 surprising that it should have been received by the chemists 

 of that day in the face of the facts so carefully proved by 

 Mayow. Stahl imagined that all bodies which would bum 

 contained an invisible substance which he called ^Phlo- 

 giston^ and that when a body was burnt it gave up its 

 phlogiston into the air, and could only regain it by taking it 

 out of the air or some other substance. It would only con- 

 fuse you to try and understand how this theory explained 

 some of the facts of chemistry. You will see at once one 

 which it did not explain, namely, why a body should grow 

 heavier when it is burnt, as Geber, 1,500 years before, had 

 shown it does. This fact alone ought to have been sufficient 

 to prevent the theory gaining ground ; but Stahl's fame was so 

 great, and his imaginary ' Phlogiston ' seemed to answer so 

 well in a great many problems, that chemists believed in it 



