NITROGEN. THE ATMOSPHERE 287 



(Fig. 73), and the water removed by bubbling the gas through sul- 

 phuric acid. 



Skeleton: NH 3 + CuO^ Cu + H 2 + N 2 . 



Balanced: 2NH 3 + 3CuO - 3Cu + 3H 2 O + N 2 . 



A steady stream of nitrogen is most easily made by heating 

 sodium nitrite and ammonium chloride very gently along with a 

 little water in a flask : 



NaNO 2 + NH 4 C1 + NaCl + NH 4 NO 2 - 2H 2 + N t 



The double decomposition is reversible, and the first action might 



be expected to be only partially com- 



pleted. But the ammonium nitrite t =^L-^^mmiu^ &== 



NH 4 N0 2 is unstable, and decomposes FIG. 73 



as fast as it is formed, so that one of 



the substances required to reverse the first reaction is removed, and 



the reversing action does not occur. 



Physical Properties. Nitrogen is a colorless, tasteless, and 

 odorless gas. Its density is indicated in the formula N 2 (mol. wt. 

 2 X 14 = 28). It is very little soluble in water. When liquefied 

 it boils at - 194. 



Chemical Properties. Nitrogen is chemically a rather 

 indifferent gas. It unites easily with a very few elements, notably 

 some of the most active metals, such as calcium and magnesium. 

 When magnesium burns in the air, the white powder which is 

 formed contains some of the nitride of magnesium Mg 3 N 2 , along 

 with much of the oxide : 



N 2 ->Mg 3 N 2 . 



The presence of the nitride may be shown by the odor of ammo- 

 nia, given off when the ash is moistened with water: 



Mg 3 N 2 + 6H 2 -> 3Mg(OH) 2 + 2NH 3 1 . 





