CHAPTER XIV 

 SODIUM AND SODIUM HYDROXIDE 



IN our study of common salt we have taken up one of its con- 

 stituents, namely, chlorine, and its commonest derivative hydro- 

 chloric acid. The latter is a good example of an acid. We now 

 turn to the other constituent, sodium, and one of its familiar 

 compounds, namely sodium hydroxide (NaOH). The latter is an 

 example of a different kind of substances, called alkalies or bases. 

 Salt, hydrochloric acid, and sodium hydroxide are examples of the 

 three largest and most important classes of substances known to 

 inorganic chemistry. 



Preparation of the Metal Sodium. Sodium cannot be 

 made by displacement (like hydrogen), because it is close to the 

 top of the activity list (p. 54) of the metals, and 

 no more active, and at the same time easily ob- 

 tained, metal is available to displace it. It was 

 first prepared by Davy (1807) by electrolyzing 

 melted sodium hydroxide, and is still manufac- 

 tured in this way. The aqueous solution of a 

 sodium compound, such as sodium chloride, can- 

 not be used, because, as we have seen (p. 140), 

 hydrogen from the water is liberated in place of 

 the metal. 



The dry sodium hydroxide is melted (about 318) in an iron 

 vessel (Fig. 57), which is connected with the positive wire from the 

 dynamo, and the oxygen is liberated on the iron (anode). The 

 negative wire is connected with rods of carbon which stand up 

 through the bottom of the vessel, and here (cathode) the sodium 

 and the hydrogen are set free. Being lighter than the fused com- 



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