CRYSTALLIZATION 



99 



b. Repeat (a.), using the same amount of water but 

 using three-fourth as much copper 



sulphate as water, in the place of alum. 

 What are your results? Note the 

 shape of the crystals. Are they the 

 same as the alum crystals? A micro- 

 scope, such as is shown in the illu 

 tration will help you, although it is not a necessity. 



c. Make a saturated solution of common salt, one 

 of alum, and one of copper sulphate. Place in separate 

 glasses and in each solution hang a piece of string from 

 a little stick placed across the top of the glasses. Set 

 aside for a few days. The water will evaporate and 

 leave the solids. Are all the crystals the same shape? 

 The crystals of any one substance are always the same 

 where they have formed slowly and have had plenty of 

 room in which to form. Can you tell the difference 

 between a salt crystal and an alum crystal? 



There are many crystals in nature although there 

 are but six different kinds. We may imitate a few of the 

 crystals by cutting out the shapes, as shown in the illus- 



