COMPOSITION OF AIR : ATOMIC THEORY 63 



the wax. The wax is a compound containing a great deal of 

 hydrogen and carbon. When the hydrogen is taken away from 

 this compound, when the compound is decomposed, the 

 carbon atoms are left. The small particles of carbon float 

 upward in the flame and are heated red-hot or white-hot. The 

 part of the flame in which the white-hot carbon is present is 

 the part from which the light comes. 



The substance which we call carbon is so familiar to us as 

 electric-light carbons, charcoal, lampblack, soot, etc. that it 

 is not necessary to describe it. If a cold object is held in the 

 flame of a candle a moment, carbon (soot) is deposited upon it. 



Some of the carbon may be seen to pass upward from the 

 tip of the flame as smoke, but if the candle is well trimmed, 

 there should be little or no smoke. Carbon as well as hydro- 

 gen is able to unite with oxygen, and though there is much 

 carbon in the flame, very little of it passes away from the 

 flame in the form of soot. It unites with the oxygen of the 

 air to form a compound made up of carbon and oxygen. We 

 need to make a further study of this compound. 



64. Carbon dioxide formed by the flame. If a candle or 

 other flame is allowed to burn for a time in a bottle of air, the 

 bottle ought then to contain anything that is formed by the 

 flame. If limewater is poured into the bottle and shaken 

 slightly, the limewater will become milky. If we do the same 

 with a bottle of air in which the flame has not burned, the 

 limewater remains clear. This shows that there is something 

 in the bottle that was not there before the flame was put into 

 it. Chemists tell us that the substance which caused the 

 limewater to become milky is a gas composed of carbon and 

 oxygen. Is it an element or a compound ? Taking this sug- 

 gestion, we may burn some charcoal (carbon) in a jar filled 

 with pure oxygen. In that case anything that is formed can 

 contain only carbon and oxygen, since there is nothing else in 

 the jar. If we test the results of this burning, as before, the 

 limewater turns white, showing us the evidence of the same 



