Substances. 127 



both are cool again, rub one upon the other to see which is 

 hardest. It will be found that the one cooled quickly is 

 harder. Why ? Why does the blacksmith plunge his hot 

 iron into cold water? Ask him. 



What will it do to a needle to heat it red-hot ? Why will 

 it soften the needle ? Because heating destroys the temper. 

 This answer is not scientific, but it is sufficient for children. 

 We must ignore those things which the child is too young 

 to understand. 



IV. Iodine. 



Procure one or two scales of iodine ; one cent's worth is 

 plenty. Place them upon a card and pass them around 

 among the pupils. Tell them not to touch it. After all 

 have seen it place it in a test-tube or a large piece of glass 

 tubing having one end closed. Heat gently in the flame. 

 See the beautiful purple (violet) vapor. Cool the tube and 

 see the fine frostlike crystals all over the inside of the tube 

 where the violet vapor has changed back to the solid form. 

 Now add a drop or two of alcohol or ether. See the brown 

 tincture of iodine formed. This experiment alcne is enough 

 for one lesson. 



Second Lesson on Iodine. 



Take a potato, carrot, parsnip, beet, radish, turnip, apple, 

 and any other fruit or root in market. Cut them in thin 

 slices. The best results are obtained if they are cooked. 

 Give small pieces of these vegetables to each child. Take 

 a broom-splint and wet the end in the iodine tincture and 

 touch the slice of potato, carrot, etc. Some will turn blue. 

 Even an apple when unripe will show blue spots scattered 

 through it. Ripe apples will not. What makes these things 

 turn blue ? We will find out. 



Take a number of small bottles ; into the first put sugar 

 and water, into the second salt and water, into the third a 

 little starch which has been cooked. Add a drop of iodine 

 tincture to the first, second, and finally to the third bottle. 

 What happens ? When anything contains starch iodine 



