SODIUM AND SODIUM HYDROXIDE 165 



pound, the hydrogen rises in bubbles, and the sodium in melted 

 globules, to the surface. Here they collect under an iron cylinder. 

 Tha latter is made of wire-gauze at the lower part, to permit cir- 

 culation of the liquid, but prevent the escape of the globules of 

 sodium. It is closed at the top, to prevent the heated sodium 

 from burning, as it would do if air could reach it. The melted 

 sodium is ladeled into cylindrical moulds, and the sticks of the 

 metal are preserved in air-tight tin boxes. 



Physical Properties of Sodium. Sodium is a silver-like 

 metal, of specific gravity 0.97. It is soft and can be cut with a 

 knife. It melts at 95.6 and boils at 742. The gram-molecular 

 volume of sodium vapor weighs 23 g., the same as the atomic 

 weight, so that the molecular formula is Na. 



Chemical Properties. Sodium burns in chlorine, giving 

 sodium chloride NaCl. It burns also in oxygen (or air) to form 

 sodium peroxide Na^CV It acts violently on water, as we have 

 seen (p. 50), displacing hydrogen and forming sodium hydroxide. 



Skeleton: Na + H 2 - NaOH + H 2 . 



Balanced: 2Na + 2H 2 O - 2NaOH + H 2 . 



For this reason it tarnishes quickly in moist air. In the labora- 

 tory small amounts are kept under kerosene, which contains no 

 compounds of oxygen. 



Uses. Sodium is used in the manufacture of many complex 

 organic compounds. By contact action, it converts isoprene 

 (C 5 H 8 ) into caoutchouc (Ci Hi 6 ) n or raw rubber (see p. 480). 

 This is a method of making rubber artificially. It cannot yet be 

 carried out so cheaply as to compete with the natural product 

 under ordinary circumstances, but in Germany during the war, 

 when the supply of natural rubber was cut off entirely, consider- 

 able quantities were manufactured by this synthetic method. 



