SCIENCE AT THE BEGINNING OF THE CENTURY 



in such profusion during the third quarter of the eigh- 

 teenth century the epoch of pneumatic chemistry. 

 Hydrogen gas, discovered by Cavendish in 1776, and 

 called inflammable air, was thought by some chemists 

 to be the very principle of phlogiston itself. Other 

 " airs " were adjudged " dephlogisticated " or " phlogis- 

 ticated." in proportion as they supported or failed to 

 support combustion. The familiar fact of a candle 

 flame going out when kept in a confined space of or- 

 dinary air was said to be due to the saturation of this 

 air with phlogiston. And all this seemed to tally beau- 

 tifully with the prevailing theory. 



But presently the new facts began, as new facts al- 

 ways will, to develop an iconoclastic tendency. The 

 phlogiston theory had dethroned fire from its primacy 

 as an element by alleging that flame is due to a union 

 of the element heat with the element phlogiston. Now 

 earths were decomposed, air and water were shown to 

 be compound bodies, and at last the existence of phlo- 

 giston itself was to be called in question. The structure 

 of the old chemical philosophy had been completely rid- 

 dled ; it was now to be overthrown. The culminating 

 observation which brought matters to a crisis was the 

 discovery of oxygen, which was made by Priestley in 

 England and Scheelein Sweden, working independently, 

 in the year 1 77i. Priestley called the new element " de- 

 phlogisticated air"; Scheele called it "empyreal air." 



But neither Priestley nor Scheele realized the full im- 

 port of this discovery ; nor, for that matter, did any 

 one else at the moment. Yery soon, however, one man 

 at least had an inkling of it. This was the great French 

 chemist Antoine Laurent Lavoisier. It has sometimes 

 been claimed that he himself discovered oxygen inde- 



31 



