Potassium

(po-ta e-um.) [Same der iv.] (Chem.) A metallic element, compounds of which are very widely diffused. It was first obtained in the metallic state by Davy in 1807, by the electrolysis of its hydrated oxide. It is a bluish-white metal of a pasty consistency, and easily welded when two clean surfaces are kneaded together between the fingers. Sp. gr. 0865; symbol K, from Kalium, a name derived from the Arabic Kali; at. weight 39-1. It melts at 144-5°, and at a red heat distils, forming a beautiful green vapor. The affinity of P. for oxygen is very great. A freshly cut surface instantly tarnishes in the air, and when a small piece of the metal is thrown into water it decomposes it, liberating the hydrogen, and evolving so much heat as to cause the ignition of the gas, which burns with a violet flame, while a globule of the melted metal floats on the surface of the water, and the remaining globule of redhot potash finally disappears with explosion as it unites with the water. Heated with bodies containing oxygen, P. quickly decomposes them. The metal can only be preserved by covering it with mineral naphtha-a hydro-carbon free from oxygen, and sufficiently light to allow the P. to sink in it. P. is obtained by heating a mixture of carbonate of P., carbonate of calcium, and carbon, to whitene in an iron tube arranged as a retort. The P. is set free by the carbon, which takes its oxygen, forming carbonic oxide, and distils over, and is received in ve els containing naphtha. [s. 726]