SODIUM AND SODIUM HYDROXIDE 



167 



sis on pp. 139-^40, remains in the solution as sodium hydroxide, 

 which collects around the cathode and flows out into a catch 

 basin. It is purified from residual sodium chloride by fractional 



Copper Bus 



Copper Terminal 

 at End of Cell 





Catch BauSin 

 Caustic Solution 



FIG. 58 



crystallization. Hydrogen is also liberated at the cathode, and 

 is a valuable by-product of the process. 



Physical Properties of Sodium Hydroxide. The substance 

 is & white crystalline solid. Generally it shows the form of the 

 iron drums, into which it is run when melted, or of the sticks into 

 which it is cast. It is exceedingly soluble in water. Its solution 

 gives to objects the smooth, soapy feeling which is characteristic 

 of alkalies. The solution is sometimes called soda-lye, and the 

 solid, caustic soda. 



Chemical Properties. Sodium hydroxide is exceedingly 

 stable, being melted, but not decomposed, by heating. 

 'The aqueous solution possesses the following important prop- 



