On Sal Nitrum and Nitro-A'erial Spirit 153 



pressure, whether owing to the nitro-aerial and elastic 

 particles struck out of the aerial particles colliding with 

 each other in thunder, or on account of sulphureous 

 exhalations kindled here and there throughout the 

 air ; for aerial particles when deprived of nitro-aerial 

 particles, whether by combustion or in any other way, 

 lose their elasticity, as was previously pointed out. 

 Hence it is that the air, rushing from every quarter, is 

 borne with rapid motion to that place where the 

 pressure of the air is diminished. But these aerial 

 torrents rushing from opposite points produce, in their 

 passage, a sudden and impetuous wind, and when at 

 last they meet and dash against each other they are 

 bent in all directions and driven round in a circle, 

 since the air rushes from all directions and allows no 

 outlet for their escape ; and this seems to be the 

 cause of the violent whirlwinds which suddenly arise. 



I 



CHAPTER XIV 



OF THE HEAT OF QUICKLIME. INCIDENTALLY OF 

 THE COMBINATION OF OPPOSITE SALTS 



Now that we have discussed nitro-aerial spirit in so 

 far as it is the cause of fire and heat, it will not be out 

 of keeping with our plan to treat of quicklime, in 

 which, when it is sprinkled with water, nitro-aerial 

 and igneous particles manifest themselves with very 

 intense heat. With regard to the heat of quicklime, 

 the learned Willis has maintained in his treatise on 

 Fermentation that in consequence of the long-con- 

 tinued calcination of the calcareous stone, igneous 



