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Common Science 



FIG. 148. Alum crystals. 



In both of the above experiments, the hot water was 

 able to dissolve more of the alum than the cold water 

 could possibly hold. So when the water cooled it could 

 no longer hold the alum in solution. Therefore part 

 of the alum turned to solid particles. 



When the string was in the cooling liquid, it attracted 

 the particles of alum as they crystallized out of the 

 solution. The force of adhesion drew the near-by mole- 

 cules to the string, then these drew the next, and these 

 drew more, and so on until the crystals were formed. 

 But when you kept stirring the liquid while it cooled, 

 the crystals never had time to grow large before they 

 were jostled around to some other part of the liquid or 

 were broken by your stirring rod. Therefore they were 

 small instead of large. Stirring or shaking a solution 



