Chemical Change and Energy 319 



they leave the heat of the burning hydrogen. That 

 is why kerosene lamps do not smoke when the chimney 

 is on. The chimney keeps all the hot gases together, 

 and this causes a draft of fresh air to blow up the chimney 

 to push the hot gases on up. The fresh air blowing up 

 past the flame gives plenty of oxygen to combine with 

 the carbon. The drum part of an oil heater acts in the 

 same way ; when the drum is open, the heater smokes 

 badly; when it is closed up, enough air goes past the 

 flame to burn up all the carbon. But if you turn either 

 lamp or heater too high, it will smoke anyway; you 

 cannot get enough air through to combine with all the 

 carbon. 



The hottest flames are the blue flames. That is be- 

 cause in a blue flame all the carbon is burning up along 

 with the hydrogen of the fuel both are combining 

 with the oxygen of the air as rapidly as possible. A gas 

 or gasoline stove is so arranged that air is fed into the 

 burner with the gas. You will see this in the following 

 experiment : 



Experiment 96. Light the Bunsen burner in the labora- 

 tory. Open wide the little valve in the bottom. Now put 

 your finger and thumb over the hole in the bottom of the 

 burner. What happens to the flame? Turn the valve so 

 that it will close the hole in the same way. Now hold a 

 white saucer over the flame, being careful not to get it hot 

 enough to break. What is the black stuff on the bottom 

 of the saucer? 



Examine the gas plate (small gas stove) in the laboratory. 

 Light it, and see if you can find the place where the air is 

 fed in with the gas. Close this place and see what happens. 

 Open it wider and see what happens. If the air opening 



