FUSION AND SOLIDIFICATION. 21 



Solution of Solids, &c., in Solvents. 



Besides actions of a purely physical character (like melting ice or 

 evaporating water) where change of state in the narrowest sense 

 takes place, and chemical actions proper where change of state in 

 a wider sense may ensue, as in the last experiment, there are other 

 actions known where solids or gases become apparently transformed 

 into liquids (or separate from liquids under suitable conditions), to 

 which the terms solution and separation from solution are 

 applied : one of the simplest natural examples of which is afforded 

 by the deposition of crystals of salt from pools of sea-water as the 

 water evaporates under a hot sun, and the dissolving again of 

 these crystals to a briny liquid when a shower of rain brings fresh 

 water into the pool. Such actions as this, or the parallel cases 

 where sugar is dissolved in hot tea, or where spirits are mixed 

 with water (solution of liquid in liquid), are generally spoken 

 of as physical changes, no essential alteration being brought about 

 in the nature of the dissolved body, which can be recovered un- 

 changed from the solution by appropriate means, e.g., evaporation 

 of the solution and formation of crystals. In a wider sense, 

 however, the term " solution " includes not only actions of this 

 class but also analogous actions where a body becomes dissolved, 

 a chemical change simultaneously taking place (as when solid 

 zinc is dissolved in dilute hydrochloric acid, Expt. 10), so that the 

 original body dissolved cannot be regained unchanged by such 

 simple processes as evaporation, &c. It will be convenient to 

 study in detail these various kinds of action somewhat systemat- 

 ically. 



2. Physical Changes of State due to Heat and Pressure 

 and not accompanied by Chemical Action 



CHAPTER II 

 FUSION OF SOLIDS AND SOLIDIFICATION OF FLUIDS. 



When a solid substance is sufficiently heated, it melts or fttses ; 

 that is, it loses its tough, rigid texture and acquires the peculiar 

 property of liquids, viz., that of running and flowing spontaneously 

 in all directions unless prevented by means of a hollow containing 



