THE CHEMISTRY OF COMBUSTION 83 



latter part of (a) using a piece of smoldering candle wicking or a 

 piece of burning punk and a fresh bottle of oxygen. 



(c) Effect of Pure Oxygen on Gloicing Charcoal. Wrap a small wire 

 around a piece of charcoal the size of a lead pencil and an inch in 

 length. Heat the charcoal in the flame until it glows. Quickly lower 

 it into another bottle of oxygen and notice what takes place. When 

 the charcoal ceases to burn, remove it from the bottle and close the 

 mouth of the bottle. Compare the rate at which the charcoal burns 

 in the oxygen with that in the air. Charcoal is chiefly carbon, and the 

 compound resulting is carbon dioxide, a gas, which remains in the 

 bottle. CAUTION. Quench the charcoal by putting it into water. 



(d) Effect of Pure Oxygen on a Burning Candle. Twist a small wire 

 around a short piece of candle or taper, light the candle and observe 

 the rate at which it burns in the air ; then plunge it into a fresh bottle 

 of oxygen. Observe the rate of burning in the oxygen. 



(e) Burning Iron in Oxygen. Slightly unravel the end of a piece 

 of iron picture wire. Heat the unraveled end in the flame; then 

 quickly dip it into a little powdered sulphur and at once plunge it 

 into a bottle of oxygen. Does the iron burn? It may be necessary 

 to make several trials before the iron burns brilliantly. Do not use 

 too much sulphur, just enough to kindle the iron. Can you make 

 iron burn in the air? 



(/) The Limewater Test for Carbon Dioxide. Place a tablespoonful 

 of fresh, clear limewater in each of the bottles used above. Place 

 the palm of the hand over the mouth of each bottle in turn and shake 

 well. In which cases does the limewater become milky in color and 

 in which does it not? Ihere may be several dark-colored specks in 

 some of the bottles, but disregard them. The milky color of the lime- 

 water is a test for carbon dioxide. 



93. Discussion of the Experiment. The union of oxygen 

 with the substances burned in this experiment is termed 

 OXJDATION. The products arising from the union of the 

 oxygen with the elements burned are called OXIDES. Thus 

 the carbon in the wood, candle wicking, charcoal, and candle 

 united with the oxygen to form carbon dioxide. The hydrogen 

 in the wood, the candle wicking, and the candle united with 

 the oxygen to form water. This was in the form of steam 

 when made. The iron of the picture wire formed iron oxide. 



Carbon dioxide causes limewater to become milky. Oxygen 

 does not change limewater. 



