PHLOGISTON THEORY IN CHEMISTRY 



University of Halle, who later founded his new theory 

 upon it. Stahl's theory was a development of an 

 earlier chemist, Johann Joachim Becker (1635-1682), 

 in whose footsteps he followed and whose experiments 

 he carried further. 



In many experiments Stahl had been struck with the 

 fact that certain substances, while differing widely 

 from one another in many respects, were alike in com- 

 bustibility. From this he argued that all combustible 

 substances must contain a common principle, and this 

 principle he named phlogiston. This phlogiston he 

 believed to be intimately associated in combination 

 with other substances in nature, and in that condition 

 not perceivable by the senses ; but it was supposed to 

 escape as a substance burned, and become apparent 

 to the senses as fire or flame. In other words, phlogis- 

 ton was something imprisoned in a combustible struct- 

 ure (itself forming part of the structure), and only 

 liberated when this structure was destroyed. Fire, 

 or flame, was free phlogiston, while the imprisoned 

 phlogiston was called combined phlogiston, or combined 

 fire. The peculiar quality of this strange substance 

 was that it disliked freedom and was always striving 

 to conceal itself in some combustible substance. 

 Boyle's tentative suggestion that heat was simply 

 motion was apparently not accepted by Stahl, or 

 perhaps it was unknown to him. 



According to the phlogistic theory, the part remain- 

 ing after a substance was burned was simply the 

 original substance deprived of phlogiston. To restore 

 the original combustible substance, it was necessary to 

 heat the residue of the combustion with something 



VOL. iv. a 



