84 THE PRODUCTION AND USE OF HEAT 



In each part of the experiment, probably a part of the com- 

 bustible substance was left unburned. One might infer that 

 burning ceased because the oxygen was all used up, but it is 

 not likely that such was the case in any part of the experiment. 

 The reason for this will be apparent in the discussion which 

 follows. 



94. Concentration of the Oxygen. It was observed that 

 the burning was much more vigorous in the bottle of oxygen 

 than in the air. This is because the air is but 21% oxygen 

 while the gas in the bottle was 100% oxygen. Therefore, the 

 burning particles would meet oxygen particles much oftener 

 in the bottle of oxygen than in the air, and hence the union 

 of the combustible material with oxygen was more rapid in 

 the pure oxygen. This factor which influences the rate of 

 oxidation is known as CONCENTRATION. If our atmosphere 

 contained 100 per cent, oxygen or even 80 per cent, oxygen, 

 iron would be a poor metal of which to make stoves, because 

 the iron would burn in such an atmosphere just as soon as it 

 became hot enough. Iron will burn in the air but not with 

 sufficient rapidity to injure it much when used for stoves. 

 When fuels containing carbon are burned, they, of course, pro- 

 duce carbon monoxide or carbon dioxide. These substances, 

 being gases, mix with the unused oxygen and thus dilute it or 

 decrease its concentration. The effect is the same as if the 

 fuel were burning in an atmosphere containing less oxygen. 

 It becomes necessary, then, to remove these gases of combus- 

 tion as fast as formed so as to keep them from decreasing 

 the concentration of the oxygen. This is exactly what is 

 done in a stove or furnace by means of the draft (Arts. 136 

 and 137). The draft serves to remove, from the stove or 

 furnace, the gases produced by combustion, and also to intro- 

 duce fresh air into the fire. Both of these ends serve to 

 maintain the concentration of the oxygen about the fire. 



95. Temperature and Oxidation. Another' factor which 

 influences the rate of oxidation is TEMPERATURE. At ordinary 

 temperatures the rate of oxidation is very slow for most 



