262 A SHORT HISTORY OF SCIENCE 



Boyle found the same fault with the 'Principles' of the 'Vulgar 

 Spagyrists ' as he found with the ' Elements ' of the ' hermetick philos- 

 ophers.' 'Tell me what you mean by your Principles and your Ele- 

 ments,' he cried; 'then I can discuss them with you as working in- 

 struments for advancing knowledge.' 



' Methinks the Chymists in their search after truth are not unlike 

 the navigators of Solomon's Tarshish Fleet, who brought home from 

 their long and perilous voyages not only gold and silver and ivory 

 but apes and peacocks too : for so the writings of several (I say not all) 

 of your hermetick philosophers present us, together with diverse sub- 

 stantial and noble experiments, theories which, either like peacocks' 

 feathers, make a great show, but are neither solid nor useful, or else 

 like apes, if they have some appearance of being rational, are blemished 

 with some absurdity or other that, when they are attentively con- 

 sidered, makes them appear ridiculous.' 



The fact that at the middle of the seventeenth century criticism 

 of this sort seemed to Boyle to be needed shows how little real 

 progress toward modern scientific chemistry had even then been 

 made; and, as often happens, truth had to be reached through 

 further error. 



A FALSE THEORY OF COMBUSTION : PHLOGISTON. Two 

 German contemporaries of Boyle, Becher (1625-1682), and Stahl 

 (1660-1734), as a result of studies on combustion and the calcining 

 of metals, departed from the four elements of antiquity and 

 assumed the participation in these processes of a something dis- 

 pelled by heating. To this something Stahl gave the name 

 phlogiston, " the combustible substance, a principle of fire, but not 

 fire itself." And because from a metallic calx (oxide) the metal 

 could be recovered by burning with charcoal, the metal was held 

 to have absorbed " phlogiston " in the process from the charcoal, 

 which, having mostly disappeared, was regarded as almost pure 

 phlogiston. Conversely, when the metal was calcined (or oxi- 

 dized) by burning without charcoal, it was held to have lost its 

 phlogiston. This theory, which to-day seems bizarre, satisfied 

 the chief requirement imposed on any new theory : viz. that of ac- 

 counting for the facts (as then known), and was therefore naturally 



