Chemical Effects of Caloric, $c. 67 



diminished, they become solid. It is somewhat 

 remarkable that mixtures of bodies generally 

 melt more easily than the bodies by themselves : 

 of this we have an instance in metals ; but this is 

 only an increase of the disposition to fluidity 

 which depends upon caloric at last. Some bo- 

 dies require the most intense cold for their con- 

 gelation, the smallest is sufficient to freeze others. 

 Before Professor Braun, it was thought that mer- 

 cury was not to be frozen. 



The substances which have shown the greatest 

 repugnancy to become fluid are some earths and 

 stones, but these are few in number, and the 

 number has still been diminished since the em- 

 ployment of the voltaic apparatus and the pre- 

 sent highly improved blowpipes. Those bodies 

 which cannot melt by themselves, melt in mixing- 

 with others; we may therefore reasonably con- 

 clude they would become fluid, if we could apply 

 a sufficient degree of heat, and in a proper 

 manner. 



There is this difference between expansion and 

 fluidity, that in expansion there is a regular in- 

 crease or contraction of bulk, according to the 

 degree of heat ; whereas in fluidity the transition 

 from a fluid to a solid state, or the contrary, is 

 sudden, and below or above a particular point 

 of heat a body always remains fluid or solid. 

 There are, however, some bodies which appear 

 in an intermediate state of fluidity, as wax, sul- 

 phur, pitch, tallow, &c. ; yet every particular de- 

 gree of softness depends upon a particular degree 



