On Sal Nitrnm and Nitro- Aerial Spirit 77 



and a sky almost constantly wrapped in clouds pre- 

 vented me from repeating the experiment. It is 

 probable, however, that air which is unsuitable for 

 supporting life is also incapable of producing flame, 

 since a greater quantity of aerial particles is needed 

 for the burning of a lamp than for sustaining life. But 

 it is to be noted here that although flame and life are 

 sustained by the same particles it is not on that 

 account to be supposed that the mass of the blood is 

 really on fire, as will be shown in the next chapter. 



But assuredly difficulties by no means slight occur 

 in connection with what has been said. For, in the 

 first place, how should it be that an animal or a lamp 

 enclosed in these glass vessels is unable to survive while 

 a sufficient abundance of air is contained in them ? 

 For the water underneath ascends into a part only of 

 these glasses and the remaining space is filled with air, 

 and that air although diminished in volume is yet 

 able to resist the pressure of the surrounding air. 



Further, in what way shall we suppose that the air 

 in the aforesaid glasses loses its elastic force ? For we 

 must believe that air is contained in them in undi- 

 minished quantity after the extinction of the flame 

 and the death of the animal. For the aerial particles 

 are not annihilated by the burning of the flame or the 

 breathing of the animal. Nor are they driven out of 

 the glass, for neither air nor any other elastic matter 

 mixed with it is able to penetrate glass, as we have 

 indicated above ; for otherwise the pressure of the air in 

 the glass could not be removed or diminished by any 

 suction, inasmuch as the air or the elastic matter would 

 immediately enter the glass from which the air had 

 been exhausted and fill the space left by the air, especi- 

 ally since the pressure of the surrounding air assists 

 towards their entrance. 



