222 METHODS IN TEACHING 



It flashes. Try in the same manner the other two sub- 

 stances. If they fail to ignite in this way, try the flame of 

 a burning taper, and they flash as did the carbon-bisulphide. 

 Place about a teaspoonful of each of the substances in 

 saucers or shallow dishes. By trial, show that each ignites 

 easily and burns with a flame. Extreme care should be 

 used when handling such substances. Only small quanti- 

 ties should be used at a time, and the rest should be kept 

 in tightly closed vessels. Children should also be taught 

 the extremely dangerous character of highly inflammable 

 liquids such as these, and the reasons why they are so. 

 Discuss with them the difference between these liquids, 

 which are very volatile that is, throwing off large quan- 

 tities of inflammable vapors at ordinary temperatures and 

 those liquids which give off such vapors only when heated. 



Place a small quantity of kerosene in a saucer and try to 

 light it by means of a match or taper. It refuses to burn. 

 Now place a small quantity in a beaker and heat until it 

 nearly boils. Try the taper in the air above the mouth of 

 the beaker. It flashes about as gasoline flashes at ordinary 

 temperatures, and continues to burn. Take hold of the 

 two ends of a sheet of paper and bring it down quickly to 

 the mouth of the beaker so as to exclude the air. The 

 flame goes out. Why? Discuss the best means of extin- 

 guishing burning clothing, oil, etc. 



Test various other fats and gums: first, by trying to set 

 fire to them cold; then by melting them and trying the 

 melted form; and finally, by heating until the inflammable 

 gases are given off, when they will flash readily. The fol- 

 lowing can be tested easily by heating in an ordinary tin 

 tablespoon: butter, lard, tallow, paraffin, pitch, and resin. 



