CHAPTER XVIII. 



SODIUM AND LITHIUM. 



WE have discussed briefly the non-metal or acid-forming ele- 

 ments that seem of most importance, considering some of their 

 compounds, and we have developed and illustrated some of the 

 principles of chemical action. This work has, however, been 

 somewhat fragmentary and incomplete, because at every step it 

 was necessary to refer to and employ the aid of metallic or base- 

 forming elements, and of salts, that great class of compounds 

 resulting from the combinations of both acid and base-forming 

 elements. In the study of the more important metals, we must 

 at every step invoke the aid of the non-metallic elements in ex- 

 plaining the varied actions and other chemical phenomena that 

 occur. The work will consist, then, in taking new steps in re- 

 viewing and completing many steps already taken, and in the 

 practical application of chemical ideas and principles to the ordi- 

 nary affairs of life. 



Potassium and sodium are typical representatives of the alka- 

 line metals, and from the number of times they have been men- 

 tioned while studying the non-metals we may form some idea of 

 their importance in all lines of chemical phenomena. 



POTASSIUM (K), best known in its hydroxide called potash, is 

 a silver-white metal, lighter than water and so soft that it can be 

 cut and molded like wax. When thrown upon water it unites 

 rapidly with the oxygen, generating heat enough to ignite the 

 hydrogen set free and to vaporize some of the metal, which, burn- 

 ing with the hydrogen, gives the flame the beautiful violet color 

 characteristic of potassium. The oxide formed is dissolved in 

 the water, giving it a soapy feel which is a common property of 

 alkaline solutions. 



Potassium compounds are components of many of the older 

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