On Sal Nitrum and Nitro-Aerial Spirit 47 



in order to produce in substances the more sluggish 

 movement of fermentation, so, on the other hand, 

 for an effervescence exceedingly intense and igneous, 

 it appears to be necessary that nitro-aerial spirit 

 should exist in a somewhat fixed condition, but the 

 sulphureous particles in a state of vigour and 

 motion, as we have indicated above. 



CHAPTER VI 



OF NITRO-AERIAL SPIRIT IN SO FAR AS IT PRO- 

 DUCES RIGIDITY IN BODIES, AND THE POWER 

 OF RESILIENCE. ALSO OF THE CAUSE OF ELAS- 

 TICITY. INCIDENTALLY OF THE BREAKING OF 

 GLASS DROPS 



Thus far we have treated of nitro-aerial spirit in its 

 state of motion and vigour ; it remains to contemplate 

 it in a state of rest. As the nitro-aerial particles in 

 a state of motion are the cause of nearly all natural 

 movements — so, on the other hand, they are the 

 cause, I think, of rigidity and the power of resil- 

 ience, when quiescent and securely fixed in the pores 

 of bodies. 



For in order that glass or iron and the like may 

 become rigid and acquire the power of resilience 

 they must be made to glow in a very hot fire, and 

 then be quickly cooled by being plunged at once 

 into cold water, that so the nitro-aerial particles 

 conveyed by the fire to the said substances may 

 be obstructed in their movement by encountering 

 cold, and secured more firmly in the structure of 

 these substances. For the same nitro-aerial par- 



