POTASSIUM. 137 



Besides this potassium monoxide, corresponding to water in its 

 composition, two other oxides of the composition K 2 O 2 (corresponding 

 to hydrogen peroxide, H 2 O 2 ) and K 2 O 4 are known. The latter oxide 

 is obtained by the combustion 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 = 138, is ob- 

 tained 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. Crude potash 

 when calcined in a furnace until white is known as pearlash. 



Pure potassium carbonate is obtained by heating the bicarbonate, 

 which is decomposed as follows : 



2KHC0 3 = K 2 C0 3 + H 2 O -f 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. 



Potassium bicarbonate, Potassii bicarbonas, KHCO 3 = 10O. 

 Obtained by passing carbon dioxide through a strong solution of 

 potassium carbonate, when the less soluble bicarbonate forms and 

 separates into crystals : 



K 2 C0 3 + H 2 O + CO 2 = 2KHCO 3 . 



Potassium nitrate, Potassii nitras, KNO 3 =101 (Nitre, Saltpetre). 

 Potassium and sodium nitrate are found as an incrustation upon and 

 throughout the soil of certain localities in dry and hot countries, as, 

 for instance, in Peru, Chili, and India. The formation of these 

 nitrates is to be explained by the absorption of ammonia by the soil, 

 where it gradually is oxidized and converted into nitric acid. This 

 nitrification, i. e., the conversion of ammonia into nitric acid, seems to 

 be due largely to the action of micro-organisms termed the nitrifying 

 ferment. The acid after being formed combines with the strongest 

 base present in the soil. If this base be potash, potassium nitrate 

 will be formed ; if soda, sodium nitrate ; if lime, calcium nitrate. 



Upon the same principle is based the manufacture "of nitre on a 

 large scale, which is accomplished by mixing animal refuse matter 

 with earth and lime, and placing the mixture in heaps under a roof, 

 to prevent lixiviation by rain. By decomposition (putrefaction) of 

 the animal matter, ammonia is formed, which, by oxidation, is con- 

 verted into nitric acid, which then combines with the calcium of the 



