HEAT. 143 



posed to be owing to the tendency which water has in 

 becoming solid, to arrange its particles in one determinate 

 manner, so as to form prismatic crystals. 



Some of the metals have the property, when in a liquid 

 or melted state, of expanding when they become solid ; 

 these are cast-iron, bismuth, and antimony. Hence 

 the use of cast-iron in making castings of a perfect 

 shape, because the iron in the act of cooling, expands 

 and completely fills the mould. Hence likewise, the use 

 of antimony in the composition of types. It should, be 

 remembered however, that these bodies do not constitute 

 an exception to the law of expansion by heat, because 

 the expansion in the above metals is owing to the change 

 of state, from a liquid to a solid, that is, to crystallization. 

 All bodies do not, however, expand.; on changing their 

 state from a liquid to a solid. When liquids become sol- 

 ids they either form crystals or an irregular mass, in 

 which there is no regular arrangement. In the former 

 case, expansion takes place, in the latter contraction. 

 Water and the different kinds of salts are instances of 

 the former ; oils and tallow are examples of the latter. 



Nearly all solid bodies may, by heat, be converted into 

 liquids, and all liquids may be converted into solids by a 

 sufficient degree of cold. Again, all liquids may be con- 

 verted into vapor or elastic fluids, by heat ; and a great 

 number of elastic fluids may, by cold, be condensed into 

 liquids : hence the state of a body depends essentially 

 upon the temperature in which it is placed. 



The following table exhibits the temperature at which 

 a number of bodies melt. 



