SOLUTION. 275 



also an attraction for these particles. In the case of 

 many substances, it overcomes the force of cohesion 

 and distributes them throughout its own volume. 

 Such a distribution, in which the solid form of the 

 solid is entirely lost, is called solution. Different 

 liquids are employed, as solvents for different sub- 

 stances. A solution is said to be saturated when no 

 more of the solid will dissolve in it. 



688. PRECIPITATION. In solution, the 



Have the par- 

 ticles lost their particles of bodies have not lost their 



TractionThoio property of cohesive attraction. It is only 

 may they be overcome by a superior force. As soon as 



precipitated ? 



this is weakened, they unite again to form 

 a solid. The solvent power of alcohol for camphor, is 

 thus diminished when water is added to the solution. 

 As a consequence, the camphor immediately re- 

 assumes the solid form. When a solid is thus 

 re-produced as a liquid, it is called a precipit- 

 ate. The above experiment is made, by ad- 

 ding water to an ordinary solution of camphor. 



689. One case of precipitation is men- 



Mention two . i i T 



general mcth- tioned m the preceding paragraph. But it 

 ods of precip- mav ^ e effected by various methods. All 



ttation f * 



of these may be arranged under two heads ; 

 precipitation by changing the character or quantity of 

 the solvent, and precipitation by changing the sub- 

 stance dissolved. 



Mention three 690. CHANGE OF SOLVENT. The three 



'b' cases in whic h precipitation is effected by 

 ye of sol- changes in the solvent, are, mixing, cooling, 

 and evaporation. The first has just been 



