534 PRINCIPLES OF CHEMISTRY 



whilst chlorine, being a typical non-metal, does not form bases with 

 oxygen. Therefore sodium as an element may be thus characterised : 

 it forms one very stable salt-forming oxide, Na 2 O, having powerful 

 basic properties, its salts are of the general formula, NaX, therefore 

 in saline compounds it is, like hydrogen, a univalent element. 50 



On comparing sodium and its analogues, which will be described later 

 with other metallic elements, it will be seen that those properties, 

 together with the relative lightness of the metal itself and its com- 

 pounds, and the magnitude of the atomic weight of sodium, comprise 

 the most essential properties of this element, clearly distinguishing it 

 from others, and enabling us easily to recognise its analogues. 



50 By heating sodium in dry ammonia, Gay-Lussac and Tlu'nard obtained an olive- 

 green, easily-fusible mass, sodamide, NH 2 Na, hydrogen being separated. This sub- 

 stance with water forms sodium hydroxide and ammonia; with carbonic oxide, CO, it 

 forms sodium cyanide, NaCN, and water H 2 O ; and with dry hydrogen chloride it forms 

 sodium and ammonium chlorides. These and other reactions of sodamide show that the 

 metal in it preserves its energetic properties in reaction, and that this compound of 

 sodium is but little more stable than the corresponding chlorine amide, although it does 

 not show its property of spontaneous decomposition, which is evident from the difference 

 between the properties of metallic sodium and gaseous chlorine. When heated, sodam- 

 ide, NH 2 Na, only partially decomposes, with evolution of hydrogen, the principal part of 

 it giving ammonia and sodium nitride, Na.-^N, according to the equation 8NH 2 Na = 2NH- 

 + NNa 5 . The latter is an almost black powdery mass, decomposed by water into ammonia 

 and sodium hydroxide. 



