ESSAY XVI. 



ON THE QUANTITY OF PURE AIR WHICH IS DAILY 

 PRESENT IN OUR ATMOSPHERE. 1779. 



IT is a known fact that our atmosphere ought not to be 

 considered as a simple fluid substance, for, when freed from 

 all heterogeneous admixture, it is " found, according to the 

 late discoveries, to consist of two very different kinds of 

 air ; the one is called corrupted air, because it is very 

 dangerous and fatal, as well to living animals as vegetables ; 

 it constitutes the greatest part of our atmosphere. The 

 other is called pure air, fire air. This kind of air is 

 salutary, supports respiration, and consequently the circula- 

 tion ; without it we could form no distinct idea either of 

 fire or how it is kindled. It constitutes but the smallest 

 part of the whole atmosphere. Now, as we know that this 

 air is of the most immediate necessity for the support of our 

 health, but as it is uncertain whether there is always the 

 same quantity of it present in the atmosphere, I proposed 

 to make observations upon it through the course of a whole 

 year. 



When this pure air meets with phlogiston uncombined, 

 it unites with it, leaves the corrupted air, and disappears, 

 if I may say so, before our eyes. 1 If, therefore, a given 

 quantity of common atmospheric air be included in a vessel, 

 and meet there with some loosely adhering phlogiston, it 



1 That light arises from this union, I have already proved in my 

 treatise on air and fire. 



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