Chap. 2,] Phenomena on flacking Urns. 105 



city of which keeps their particles remote from each 

 other, and prevents their fixing into a folid mafs. All 

 bodies, therefore, in patting from a fluid to a folid ftate, 

 emit a quantity of fire or hear. When water is thrown 

 upon quick-lime, it is abforbed by the lime, and in 

 this ftate it is capable of retaining a much fmaller quan- 

 tity of caloric than in its natural ftate ; on the flacking 

 of lime therefore a very intenfe heat is produced, the 

 matter of fire which preferved the water fluid being 

 difengaged and detached. If fpirit of vitriol is added 

 to ftrong oil of turpentine, they will condenfe into a 

 foiid mafs, and a great quantity of heat will be fen- 

 fibly emitted. If water is expofed to freeze, and a 

 thermometer applied to it, during the act of freezing, 

 or parting from a fluid to a folid ftate, it will be found 

 feveral degrees warmer than the air which furrounds 

 it, which is owing to the caloric or fire emitted by that 

 part of the water which is converted into ice. This 

 effect is ftill more apparent from the condenfation of 

 the elaftic fluids, which, from their rarity, contain a 

 greater proportion of the matter of fire,. 



Upon the fame principle it will be found, on the 

 other hand, that when any body pafles from a folid to 

 a fluid ftate, the adjacent bodies will be deprived of a 

 quantity of their natural heat. Thus if a quantity of 

 aqua-fortis is poured upon folid ice, the ice immedi- 

 ately liquifies, and an aftonifhing degree of cold is in- 

 ftantly produced, even by the fire -fide : this effect is 

 altogether owing to the quantity of caloric which is 

 abforbed by the congealed water reafluming its fluid 

 form. This experiment will ferve to explain the fact 

 that a thaw is generally colder than the commence- 

 ment of a froft. The abfbrption of the matter of fire 

 is further exemplified in the inftance of bodies pafling 

 from the ilate of a common fluid to that of vapov.r, or 



an 



