SODIUM. 141 



not influenced by the presence of alkaline earths, earths, or metals of 

 the iron group.) 



3. Add to a concentrated solution of a neutral potassium salt a 

 freshly prepared strong solution of tartaric acid : a white precipitate 

 of potassium acid tartrate, KHC 4 H 4 O 6 , is slowly formed. Addition 

 of alcohol facilitates precipitation. 



4. Potassium compounds color violet the flame of a Bunsen burner 

 or of alcohol. The presence of sodium, which colors the flame in- 

 tensely yellow, interferes with this test, as it masks the violet caused 

 by potassium. The difficulty may be overcome by observing the 

 flame through a blue glass or through a thin vessel filled with a solu- 

 tion of indigo. The yellow light is absorbed by the blue medium, 

 while the violet light passes through and can be recognized. 



5. All compounds of potassium are white (unless the acid has a 

 coloring effect), soluble in water, and not volatile at a low red heat. 



20. SODIUM (NATRIUM). 

 Nai = 23. 



Occurrence in nature. Sodium is found very widely diffused in 

 small quantities through all soils. It occurs in large quantities in 

 combination with chlorine, as roc]=salt, or common salt, which forms 

 considerable deposits in some regions, or is dissolved in spring waters, 

 and is by them carried to the rivers, and finally to the ocean, which 

 contains immense quantities of sodium chloride. It is found, also, 

 as nitrate, silicate, etc. 



Sodium chloride, Sodii chloridum, NaCl = 58.4 ( Common 

 This is the most important of all sodium compounds, and also is the 

 material from which the other compounds are directly or indirectly 



QUESTIONS. 181. How is potassium found in nature, and from what sources 

 is the chief supply of potassium salts obtained? 182. What color have the 

 salts of the alkali metals, and which are insoluble ? 183. Mention two pro- 

 cesses for making potassium hydroxide, and what are its properties? 184. 

 Show by symbols the conversion of carbonate into bicarbonate of potassium. 

 185. Explain the principle of the manufacture of potassium nitrate, and what 

 is the office of the latter in gunpowder? 186. How is potassium chlorate made, 

 and what are its properties ? 187. Give the processes for manufacturing iodide 

 and bromide of potassium, both in words and symbols. 188. State the com- 

 position .of potassium sulphate and sulphite. How can they be obtained ? 

 189. What is sulphuret of potash? 190. Mention tests for potassium com- 

 pounds. 



