On Sal NitriLtn and Nitro- Aerial Spirit 107 



the particles of any substance when effervescing in un- 

 confined air are so much pressed by the weight and 

 pressure of the incumbent atmosphere that they can- 

 not expand freely ; while yet the same particles, being 

 scarcely burdened at all in a place void of air, will in 

 performing their movements spread out and swell up 

 much more : but this does not come from their more 

 intense action and motion, but from the removal of 

 the hindrance. And hence it is that if water slightly 

 warmed be put in a place void of air, its more agile 

 particles will make the liquid swell and as it were boil, 

 and yet it is not to be supposed that these particles 

 are agitated with a greater force than before. So that 

 clearly, even if the fermentation of a mixture of con- 

 trary liquids in a vacuum were to go on with less force 

 than in free air, still their fermenting particles would 

 spread out to a greater extent than otherwise owing 

 to the withdrawal of the pressure of the atmosphere. 



To this I add that contrary salts, if mixed together 

 in a vacuum and then quickly removed after effer- 

 vescence has gone on for some time, do not appear to 

 have been heated as much as in other circumstances. 

 So that it would appear that even the heat of contrary 

 salts fermenting together, depends to some extent on 

 nitro-aerial particles struck out from the air, as we 

 have already hinted. 



It is besides to be noted that there is a great 

 difference between the fermentation of the blood and 

 that of contrary salts, inasmuch as the effervescence of 

 the latter is due to an internal principle, namely to 

 nitro-aerial particles contained in them, as I already 

 endeavoured to show, while the fermentation of the 

 blood is excited by the nitro-aerial spirit supplied by the 

 air meeting its saline-sulphureous particles. Whence 

 it is, that the access of air is not so necessary for the 



