OXYGEN AND LIFE 



51 



FIG. 45. 



Burning Iron Wire in 

 Oxygen. 



Sand is put into one of the bottles of oxygen, so that the bottom is 

 completely covered. Then a bundle of fine iron wires (picture cord) 

 is tipped with a little sulphur, or with a splinter of wood. The sulphur 

 (or wood) is lighted, and the wire is put into the 

 bottle of oxygen. The burning tip heats the iron 

 to its "kindling temperature," so that it burns 

 brilliantly in the oxygen. Iron oxide is formed, 

 as in rusting. The melted oxide collects as a drop 

 upon the end of the wire, or falls into the bottle. 

 The sand is used to protect the bottle from the 

 hot iron oxide. 



(3) Sulphur, which burns with an almost invis- 

 ible, blue flame in the air, burns with a brilliant, 

 violet flame in oxygen. The sulphur is held in a 



"combustion spoon" (Fig. 46), and is melted and 

 lighted lii a burner before being put into the oxygen. 

 The product formed is sulphur dioxide, the same 

 choking gas that results when sulphur burns in air. 



(4) Charcoal burns in air with a faint glow; but in 

 oxygen it TSurns vigorously, giving off a brilliant light. 

 The charcoal is held by means of a copper wire, or in a 

 combustion spoon, and is ignited in a flame before 

 being put into the oxygen. The product is the color- 

 less gas, carbon dioxide. If we put " lime water " 

 (cf. 127) into the bottle in which charcoal has been 

 burned, the lime water and carbon dioxide unite to form a white, 

 insoluble solid which makes the lime water look "milky." In a bottle 

 of pure oxygen or air, lime water is not changed. 



Oxygen dissolves slightly in water. Like air, of which 

 it forms a part, oxygen has no color, odor, or taste. 



52. Oxygen and Life. Oxygen forms a part of all 

 living things, and an abundant supply is needed to main- 

 tain life. The process of getting oxygen in contact with 

 the tissues of an animal or plant is called respiration. 



FIG. 46. 



Burning Sulphur 

 in Oxygen. 



