AIR AND OXYGEN 43 



3. Why does a forced draft make a fire burn more rapidly? 



4. Why does a naked flame sometimes cause an explosion in a 

 mine, when the air of the mine is filled with coal dust? 



5. The substances, like phosphorus and sulphur, which burn 

 rapidly in ordinary oxygen, combine very, very slowly with oxygen 

 which has been freed from moisture by careful drying. How is 

 this effect of water to be classified? 



6. Air is 20 per cent oxygen. Why does iron burn brilliantly 

 in pure oxygen, but not in air? 



$. What weight of copper would be required to combine with 

 the amount of oxygen contained in 100 grams of mercuric oxide? 



{ i * cZL-v-'C- ' : 





