THE PATH OF EVOLUTION 



tributed, and the change of one of the four elements 

 for another could give rise to quite another body. 



Robert Boyle (1627-1691) was the first to deny 

 that the composition of matter was dependent either 

 on the four elements above named or upon the Sul- 

 phur and Mercury of Paracelsus, and to suggest that 

 "all substances that could not be chemically sepa- 

 rated into other constituents were elements." This 

 definition of an element is adhered to at the present 

 day. Boyle maintained that Chemistry should be 

 studied not only for its uses in alchemy or in phar- 

 macy, but for its own sake, as a branch of Natural 

 Science. He should be considered as the Father of 

 Chemistry viewed as a true Science. 



The next great forward step was Stahl's (1660- 

 1734) Phlogiston theory, which, although entirely 

 erroneous, and ultimately abandoned, served a useful 

 purpose in holding together for the time facts that 

 were otherwise disconnected, and in affording a work- 

 ing hypothesis, until greater progress disclosed its 

 errors and submitted the true theory of combustion 

 in pjace of the erroneous one. 



Stab 1's theory was, that combustion was caused by 

 the combustible substance parting with its Phlogiston, 

 which was thought to be a constituent of such bodies, 

 the phlogiston escaping in the shape of flame ; in the 

 case of a metallic body leaving behind either a calx, 



162 



