215 



with pupils in any/$ the grades. Pupils should provide 

 themselves with pfeces of common window glass, about five 

 Solution and or six incnes squam, Prepare a saturated 

 Crystalliza- solution (one inj| Hi there is as much of 



any given substlp^as will dissolve in the 

 fluid) of common salt, and put a small puddle of it upon the 

 pupils' pieces of glass. If the weather is dry and warm, 

 salt crystals begin to appear in a few minutes. Watch their 

 formation, using low power microscopes or hand magnifiers, 

 if available. For larger crystals pour some of the solution 

 into a glass or small dish and set it away for a few days. 

 When the water has evaporated, discuss the shape and size 

 of the crystals, how trry form, the time required, and many 

 other points noticed. Then try solutions of sulphate of cop- 

 per ("blue stone"), saltpeter, borax, epsom salts, hyposul- 

 phite of soda, or any other crystalline substance soluble in 

 water. 



With older pupils extend the work by considering sub- 

 stances soluble in alcohol, as shellac, camphor gum, or 

 crystals of iodine ; substances soluble in oils, as resin, solu- 

 ble in coal oil or gasoline; paraffin, soluble in turpentine; 

 lime, soluble in dilute sulphuric acid. With these simple 

 experiments as a basis, discuss any crystalline rocks which 

 may be found in the region, such as crystal quartz, granite, 

 marble, calcareous spar, stalactite formations. Call atten- 

 tion to the different forms in which some substances are 

 found, as in the case of carbon, which may be in the form 

 of a gas, common charcoal, mineral coal ; as a part of veg- 

 etable and animal tissues; graphite, of which lead pencils 

 are made ; or the crystalline diamond, which because of its 



