POTASSIUM. 



55 



SECTION I. 

 CLASS I. 

 METALS OF THE ALKALIES. 

 The metals of the alkalies are Fotassium, Sodium, and Lithium, 



POTASSIUM. 



Discovered in 1807 by Davy, by the agency of galvanism. — 

 Prepared by exposing a mixture of carbonate of potash and char- 

 coal to a high heat, in a gun-barrel; the potassium distils over, 

 leaving carbonic oxide, thus : 





1 eq. Carbonate of potassa 



'CO^ ^ 



2 eq. Carbon, 2 C -=^:=^^ 3 CO. 



Prop. — Solid at ordinary temperatures — soft and malleable be- 

 tween the fingers — of a white colour and metallic lustre — brittle at 

 32° — melts at 150° ; sp. gr. -865, — has a powerful affinity for oxygen; 

 — cannot be kept in the air or water; — preserved under naphtha. It 

 takes fire when thrown on water, with the disengagement of hydro- 

 gen, which combines with a portion of the potassium, forming potas- 

 siuretted hydrogen, which also takes fire, increasing the brilliancy 

 of the flame ; — potash is formed as the result. The equivalent of 

 potassium (kalium) is 39 15 ; its Symbol, K. 



It forms two compounds with oxygen, potash, KO, and the 

 peroxide, KOg. 



Protoxide of potassium or potash, is found whenever potassium is 

 exposed to air or water. In the anhydrous form, it is a white solid, 

 very caustic ; has a strong affinity for water, with which it forms a 

 hydrate. 



The hydrate of potassa, KO+HO, also named common caustic 

 Siiid potassa fusa, is prepared by decomposing carbonate of potash, by 

 lime ; the carbonate of lime is thrown down, and the potassa remains 

 in solution ; this is concentrated by heat, and then poured out into 

 moulds. Pure hydrate of potassa is a white solid, very deliquescent, 

 soluble in water and alcohol. The common caustic potash may be 

 purified by dissolving in alcohol. The solution, like lime-water, 

 rapidly absorbs carbonic acid from the air. The solid hydrate, from 

 its affinity for water, is used to free gases from hygrometric mois- 

 ture. 



Peroxide of potassium, KOg, is formed when potassium is burned 

 in dry oxygen, or in the open air ; it is of an orange colour. 



The most important salts of potassa are the nitrates, the carbo- 

 nates, the sulphates, and the chlorate. The impure carbonate {pot 



