Fire and Heat 79 



Wind into a tangled mass, about seven inches of a twelve-inch length 

 of very fine iron wire. Hold the mass in a flame until it becomes red 

 hot. Insert in bottle just prepared with sand. What happens? 

 What reason do you find for the sand? Does the iron burn? Will 

 iron burn in the open air, even when heated red hot ? Does this indi- 

 cate that oxygen is a better supporter of combustion than ordinary 

 air ? What does it suggest concerning the importance of nitrogen in the 

 atmosphere ? Fasten a small lump of sulfur on a fine iron wire ; light 

 the sulfur and introduce it into a jar of oxygen. What happens to 

 the iron wire? Why? How was it ignited? Can it be ignited by 

 burning sulfur in the air? Close each bottle immediately after test- 

 ing it. 



4. Put a small lump of sulfur on a deflagrating spoon, light and insert 

 into a bottle. Try the same with a small piece of yellow phosphorus, 

 if available. What is the difference between its burning in air and 

 in oxygen? 



5. Try bottle No. 1, which has failed to support combustion in a 

 glowing splinter or charcoal, with a burning candle. Does the candle 

 burn when introduced? Does this seem to show that oxygen is es- 

 pecially responsible for burning ? 



Physical properties of oxygen. Oxygen, which you collected 

 in bottles, is invisible, and is found by test to have neither 

 taste nor odor. When the bottle is left uncovered for a moment, 

 the gas does not escape ; but if it were lighter than air, it would 

 be forced out as soon as the bottles were opened. It is heavier 

 than nitrogen. Oxygen may be cooled sufficiently to become 

 a liquid, just as water vapor when cooled becomes liquid water. 

 These characteristics of oxygen are sometimes called its physical 

 properties, properties that may be known through our senses, 

 as sight, hearing, touch, taste, muscular sense, smell. 



Chemical properties of oxygen. The tests show something 

 of the behavior and nature of oxygen in combustion. The 

 glowing splinter or charcoal bursts into brilliant flame in oxygen, 

 but by comparison burns faintly in the open air. Iron burns 

 very slowly in the air, or rusts as we commonly describe it ; 

 but in pure oxygen it burns with readiness. Other substances 

 like iron behave in the same way in oxygen. Phosphorus, 

 although it ignites slowly, burns freely in air, but burns with 



