LATENT AND SPECIFIC HEAT. 331 



lost to thermometric measurement during its lique- 

 faction or vaporization, or the amount of heat that 

 must be communicated to a body to change its 

 condition without changing its temperature. It may 

 be made to reappear during the opposite changes after any 

 interval of time. Many solids may undergo two changes 

 of condition. Such solids have a latent heat of liquefac- 

 tion and a latent heat of vaporization. 



519. Latent Heat of Fusion. We are already 

 familiar with the fact that when ice or any other solid is 

 melted by the direct application of heat, much of the heat 

 is rendered latent. In the case of melting ice we shall 

 show how this latent heat is measured, and that its quan- 

 tity is very great. We may represent the process of lique- 

 faction of ice as follows : 



Water at C. ice at C. + latent heat of water. 



520. Latent Heat of Solution. During the 



process of solution, as well as during fusion, heat is ren- 

 .dered latent. In either case the performance of the icork 

 of liquefaction demands an expenditure of kinetic energy. 

 Hence the solution of a solid involves a diminution 

 of temperature. 



(a.) This loss may in some cases be made good by an equal in- 

 crease, or changed to gain by a greater increase of sensible heat 

 from the chemical changes involved ; but in any case, the act of 

 liquefaction considered by itself produces cold. Thus a cup of 

 coffee is cooled by sweetening it with sugar, and a plate of soup is 

 cooled by flavoring it with salt. 



521. Freezing Mixtures. Ttic latent heat of 

 solution lies at the foundation of the action of 

 freezing mixtures. For example, when ice is melted 

 by salt, and the water thus formed, in turn, dissolves the 



