I 



On Sal Nitriim and Nitro-Aerial Spirit 49 



of flame when greatly agitated by a very violent blow, 

 but rather that the igneo-aerial particles hidden in 

 the pores of the iron are excited by the violence of the 

 blow into a really fiery motion, and that a little bit of 

 the iron is melted by them and changed into a sort of 

 glass. 



As the rigidity of iron and glass and similar sub- 

 stances arises from nitro-aerial particles imparted to 

 them by fire, so probably the rigidity of frozen water 

 is also caused by nitro-aerial particles which, from 

 being fixed like pegs between the aqueous particles, 

 arrest their fluid movement and press them together. 

 For as in fire nitro-aerial particles whirled round with 

 swiftest motion disturb the particles of the substances 

 in which they exist and break them into minute parts, 

 so on the contrary in the cold, they, set up as 

 spikes, fasten like wedges among the particles of bodies 

 and cause them to become rigid, as has been said 

 above. 



That nitro-aerial and igneous particles in a state of 

 rest produce rigidity and cold may be inferred from 

 the case of nitre itself in which the nitro-aerial particles 

 become extremely cold, and when mixed with vinous 

 liquids almost freeze them, and yet if they are agitated 

 by sulphureous particles they become in fact fiery, as 

 happens in the ignition of nitre. And hence it is that 

 if the hand or other member when stiff with cold be 

 brought near the fire it is hurt as if by fire and 

 even destroyed, for the nitro-aerial particles which 

 freeze as it were the chilly part in which they are fixed, 

 assume also a fiery nature when agitated by the heat 

 of the fire and burn it. So that without doing violence 

 to language cold may properly be said to burn. 



In the foregoing we must seek for the reason why 

 water that has been boiled freezes sooner, as some 



D 



