THE ATMOSPHERE 



83 



burned, the limewater will look milky, due to the insoluble solid 

 which is formed by the union of the limewater and the carbon 

 dioxide. Test the limewater with pure oxygen and air. 



Experiment 21. Iron may be burned in oxygen in the follow- 

 ing manner (Figure 84). Put enough sand into one of the bottles 

 of oxygen to cover the bottom 

 well so that the bottle may not 

 be broken. Take a piece of pic- 

 ture wire, tip it with sulphur, and 

 light the sulphur. Then put it 

 into the bottle of oxygen. The 

 burning sulphur heats the wire to 

 its kindling point, after which it 

 will burn rapidly, giving off a very 

 brilliant light. Globules of iron 

 oxide are formed and fall to the 

 bottom of the bottle. 



Experiment 22. The burn- 

 ing of sulphur in oxygen may 

 also be tested. Place the sulphur 

 in a deflagrating or combustion 

 spoon, and after lighting it put it into the oxygen. Sulphur burns 

 with a blue flame in air, but in oxygen it burns with a bright 

 violet flame. 



The nature of oxidation has probably occurred to the 

 student by this time. It is simply the chemical union 

 of a substance with oxygen, usually the oxygen of the 

 air. The uniting of a substance with oxygen is called 

 the oxidation of the substance, and the substance is said 

 to be oxidized. If the oxidation is so rapid that light 

 and heat are evolved, it is called burning or combustion. 

 It was Lavoisier, a French scientist, who first gave to 

 us the explanation of combustion. This was in the same 

 year and shortly after the discovery of oxygen by Priestley. 

 A large number of metals unite with the oxygen of the 

 air to give their oxides. When iron rusts, it oxidizes. 



FIG. 84. Burning Iron Wire in 

 Oxygen. 



