COMBUSTION 71 



into flame. Does the same thing take place when the stick with 

 the spark upon it is held in a bottle of air? 



Hold a lighted match at the mouth of another of the bottles 

 containing oxygen. Does the gas itself burn as illuminating gas 

 does when a match is applied to it ? If the oxygen in the air were 

 increased or decreased, it would have a great effect upon combus- 

 tion. Attach a piece of sulphur to a short piece of picture wire. 

 Ignite it and place the wire in a bottle of oxygen. 



(Figure 31.) Does the sulphur burn strongly? 



How about the wire ? Does it burn too ? fr ' v 



In the experiment just performed, we found 

 that substances burn in oxygen much more 

 fiercely than in air, and that substances FIGURE 31 

 which do not burn in air readily burn in 

 oxygen. Experiments have shown that oxygen, a gas which 

 is in the air about us, must be present where burning 

 occurs. In fact burning is the result of the chemical union 

 of atoms of oxygen with atoms of other substances. 



The paraffin in the candle is a compound that contains 

 both hydrogen and carbon. These two elements are found 

 in all common fuels and are sometimes called fuel elements. 

 Both of them readily unite under proper conditions with 

 oxygen, and the chemical action produces heat. When 

 wood or coal burns, the atoms of the fuel elements in these 

 substances unite with atoms of oxygen. 



Experiment 24. (Teacher's Experiment.) Put a few zinc 

 scraps in a test tube and pour a little hydrochloric acid upon them. 

 Feel the test tube near the zinc. 



Put half an inch of water into another test tube and carefully 

 pour a little strong sulphuric acid down the sides of the tube into 

 the water. Feel the tube. 



Burning is not the only way in which chemical action 

 produces heat. In the preceding experiments, both test 



