206 CHEMISTRY. 



CHAPTER XVI. 



GROUP I. POTASSIUM AND SODIUM. 



282. Potassium and Sodium. These metals have so great 

 an attraction for oxygen that they are never found native. 

 They occur only in combination, usually as salts. They de- 

 compose water at ordinary temperatures, setting hydrogen 

 free ; this is of itself a sufficient reason for their not existing 

 native. Their oxides and hydrates are exceedingly soluble 

 in water, forming intensely alkaline caustic solutions. They 

 form important compounds with the non-metals and with 

 the principal acids. 



283. How Potassium is Obtained. Potassium was origi- 

 nally obtained by Davy by decomposing the hydrate, by 

 means of a galvanic battery. But it is now commonly ob- 

 tained by decomposing potassium carbonate by a process 

 which we will describe. The carbonate and some charcoal 



.finely pulverized and well mixed are exposed to a white 

 heat in an iron retort, a, Fig. 85 (p. 207). Observe now what 

 the chemical changes are. Potassium carbonate is composed 

 of K 2 CO 3 . This is decomposed, the oxygen uniting with 

 the carbon to form carbonic oxide. We have then formed 

 two things, carbonic oxide and the metal potassium : 

 Potassium carbonate. Carbon. Potassium. Carbonic oxide. 



K 2 CO 3 + 2C K 2 + SCO 



Now the heat is so great that the metal is in the state of 

 vapor, and this vapor and the carbonic oxide gas pass out 

 together through the tube, , into the copper receiver, h. 

 The upper part of this receiver is surrounded by a wire 



