CHEMISTRY OF THE EIGHTEENTH CENTURY. 357 



FIG. 173. MACQUER'S EXPERIMENT, WITH PORTRAIT (see page 348). 



to be. In the course of my inquiries I was, however, soon satisfied 

 that atmospheric air is not an unalterable thing ; for that, according 

 to my first hypothesis, the phlogiston with which it becomes loaded 

 from bodies burning in it, and animals breathing it, and various other 

 chemical processes, so far alters and depraves it as to render it alto- 

 gether unfit for inflammation, respiration, and the purposes to which 

 it is subservient ; and I had discovered that agitation, the processes 

 of vegetation, and probably other natural processes, restore it to its 

 original purity. But I own I had no idea of the possibility of going 

 any further in this way, and thereby procuring air purer than the best 

 common air. I might, indeed, have naturally imagined that such 



