262 METALS AND THEIR COMBINATIONS. 



second is the most delicate. Some other difficultly soluble salts of 

 potassium arc the picrate, perchlorate and fluosilicate. With the 

 exception of the acid tartrate (cream of tartar) and the picrate, the 

 other difficultly soluble salts of potassium are of a kind not usually met 

 with. 



22. SODIUM (NATRIUM). 



Na i -=23 (22.88). 



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 rock-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, and in double silicates. 



Sodium chloride, Sodii chloridum, NaCl 58.06 (Common salt}. 

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

 material from which the other compounds are directly or indirectly 

 obtained. Common table-salt frequently contains small quantities 

 of calcium and magnesium chlorides, the presence of which causes 

 absorption of moisture, as these compounds are hygroscopic, while 

 pure sodium chloride is not. 



In the animal system, sodium chloride is found in all parts, it 

 being of great importance in aiding the absorption of albuminoid 

 substances and the phenomena of osmose; also by furnishing, 

 through decomposition, the hydrochloric acid of the gastric juice. 



Sodium chloride is soluble in 2.8 parts of cold water, and in 2.5 

 parts of boiling water ; almost insoluble in alcohol ; it crystallizes in 

 cubes and has a neutral reaction. 



Sodium hydroxide, Sodii hydroxidum, NaOH 39.76 (Caustic 

 soda), may be obtained by the processes mentioned for potassium 

 hydroxide, which compound it closely resembles in its chemical and 

 most of its physical properties. 



Experiment 22. Examine the consistency and lustre of sodium metal by 

 cutting a piece the size of a pea. (Do not get water on it while handling it. 

 Why ?) Throw small chips of the metal into a little water in a porcelain dish. 

 When all the metal has disappeared, taste the solution and test its action on 

 red litmus. Add dilute hydrochloric acid to slight acid reaction and evaporate 

 to dryness. Taste the residue. What is it ? Explain all that took place and 

 write reactions. 



