218 Domestic Science 



be noted. When the magnesium is strongly heated in 

 air, however, a striking change takes place. 



EXPERIMENT 83. From a coil of magnesium tape, 

 cut off a piece about 2 inches long. Holding this with 

 a pair of crucible tongs, place one end of it in the flame 

 of a match or a Bunsen burner. After a short interval 

 the metal ignites. Remove it from the flame, and note 

 carefully the nature of the light obtained, and of the 

 product left after the burning is over. 



In this case we have a chemical combination taking 

 place. The magnesium combines -with the oxygen of 

 the air to form magnesium oxide. 



Magnesium + oxygen = Magnesium oxide. 



When the combination has once been started it 

 proceeds rapidly with the evolution of great heat and 

 a most vivid light. (Compare the behaviour of phos- 

 phorus with that of magnesium in this respect.) This 

 production of heat, and frequently of light as well, is a 

 general accompaniment of a combination between two 

 substances to form a third. Even when iron rusts in 

 air, heat is produced, but the rate at which it is produced 

 is so slow that we cannot detect it by ordinary means. 



It is interesting to note that by special arrangement 

 of the experiment, magnesium may be made to combine 

 with nitrogen, forming magnesium nitride. This ex- 

 periment, however, is too difficult for us to attempt. 

 By taking advantage of this action, the gas argon was 

 isolated in 1894 by Sir William Ramsay, from nitrogen 

 obtained from the atmosphere. 



EXPERIMENT 84. Place a short coil of bright copper 

 wire in a hard glass tube closed at one end, a rubber 

 stopper, through which passes a short length of glass 

 tubing fitted with a tap, being fixed firmly in the open 



