Chap. 4.] faffing from a folid to a fluid State, 6fr. 119 



folid Hate a quantity of caloric is necefiarily extricated. 

 The heat produced by flacking lime has fomttimes 

 been fo great as to fire wood ; in this cafe it has already 

 been (hewn, that the component particles of the water 

 being abforbed by the lime, the fire which held it in 

 fbfion is expelled. A mixture of the eflential oils 

 with fpirit of vitriol produces the fame effect; the 

 mixture forms itfelf into a folid mafs, and the fire 

 which, the fluids contained is fuddenly extricated. A 

 quantity of water will often continue fluid at fome 

 degrees below the freezing point, but by agitating the 

 water in forms fuddenly into ice, and the caloric which 

 the fluid contained being ft- free, the thermometer 

 will rife fome degrees. The air is often obferved to 

 be peculiarly mild during a fail of fnow ; the reafon 

 is, that the caloric which the water of the fnow con~ 

 tained is difcharged by its patting into a folid Hate, 

 and fen fible heat is produced. The union ofacauf- 

 tic alkali, which contains no fixed air, with an acid, 

 excites great heat, in the fame manner as when water 

 is thrown upon quick-lime j but if the alkali is mild, 

 that is, if it contains a quantity of fixed air, that fub- 

 ftance going off in an aerial form ablbrbs the matter 

 of fire, which it carries off with it, and no heat is ge- 

 nerated *. 



It was dated that expanfion and fluidity are pro- 

 duced by the fame caufe : -there is, however, this dif- 

 ference in the effects, that in expanfion there is a re- 

 gular increafe or extenfion of bulk, according to the 

 degree of heat j whereas the tranfition from a fluid to 

 a folid ftate, or the contrary, is fudden j and below or 

 nbove a particular point of temperature, a body al- 



* See Dr. Higgins's excellent Experiments and Obfervation^ 

 P- 3*9' 



I 4 way* 



