POTASSIUM. 257 



Antidotes : dilute acids, vinegar, to form salts ; or fat, oil, or milk, to form soap. 

 Liquor potassii hydroxidi is a 5 per cent, solution of potassium hydroxide in 

 water. 



Potassium oxide, K 2 O. This compound can be obtained either 

 by burning potassium in air and subsequent heating of the product 

 to a high temperature, or by fusing together potassium hydroxide 

 and metallic potassium : 



2KOH -f 2K = 2K 2 O + 2H. 



Besides this potassium monoxide, corresponding to water in its composition, 

 two other oxides of the composition K 2 O 2 (corresponding to hydrogen perox- 

 ide, H 2 O 2 ) and K 2 O 4 are known. The latter oxide is obtained by the com- 

 bustion of potassium in oxygen. It is a strong oxidizing agent, and at a high 

 temperature is decomposed into oxide and oxygen. 



Potassium carbonate, Potassii carbonas, K 2 CO 3 = 137.27, is 

 obtained from wood-ashes in an impure state as described above, or 

 from the native chloride by the so-called Leblanc process, which will 

 be described in connection with sodium carbonate. It is also made 

 by passing carbon dioxide into solution of potassium hydroxide, 

 obtained by the electrolytic process. 



Pure potassium carbonate is obtained by heating the bicarbonate, 

 which is decomposed as follows : 



2KHCO 3 = K 2 CO 3 + H 2 O + CO 2 . 



Potassium carbonate is deliquescent, is soluble in about an equal 

 weight of water, insoluble in alcohol, and has strong basic and alka- 

 line properties. 



The strong alkaline reaction of potassium and sodium carbonate in solution 

 is due to hydrolysis of the salts into bicarbonate, which is neutral to litmus and 

 free alkali. (See pages 122 and 201.) 



K 2 C0 3 + H 2 = KHCO 3 + KOH. 



Potassium bicarbonate, Potassii bicarbonas, KHCO 3 = 99.41. 

 Obtained by passing carbon dioxide through a strong solution of 

 potassium carbonate, when the less soluble bicarbonate forms and 

 separates into crystals : 



K 2 CO 3 + H 2 O + CO 2 2KHC0 3 . 



Potassium percarbonate, K 2 C 2 O 6 , also exists as a bluish-white powder, 

 which liberates oxygen when heated, and in dilute acid solution gives off hydro- 

 gen dioxide. It is obtained by electrolysis of a concentrated solution of potas- 

 sium carbonate at about 10 C. (14 F.). It is a good oxidizer. 

 17 



