CH. xvi. THEORY OF ' PHLOGISTON? 133 



proposed by two very eminent chemists, John Joachim 

 Becher (1625-1682) and Ernest Stahl (1660-1734) 

 Ernest Stahl in particular was a man of great talent and per- 

 severance, 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 together, and by arranging these 

 facts into a system. But his theory of combustion was a 

 very misleading one, although it had a germ of truth in it. 

 Stahl imagined that all bodies which would burn contained 

 an invisible substance which he called * Phlogiston] 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 confuse 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, 1500 years before, had shown it does. It seemed, 

 however, to answer so well in a great many problems, that 

 chemists believed in it for nearly a hundred years, and 

 Mayow's true explanation was forgotten till the eighteenth 

 century, when fresh experiments brought it again to the 

 front. 



Chief Works consulted. Brande's 'Manual of Chemistry 'Intro- 

 duction; Rodwell's 'Birth of Chemistry;' Yeats 'On Claims of 

 Moderns to Discoveries in Chemistry and Physiology,' 1798; Birch's 

 'Life of Boyle,' 1744 ; Shaw's ' Philosophical Works of Boyle,' 1725. 



