xin THE DECOMPOSITION OF THE ALKALIS 275 



and others remained, and were merely tarnished, and finally 

 covered by a white film which formed on their surfaces " 

 (A.C.R. VI. 8). 



To the new metal thus produced, the " basis of potash," 

 Davy gave the name POTASSIUM. 

 Davy describes the physical properties of potassium. 



The new metal at ordinary temperatures is 



" a soft and malleable solid, which has the lustre of polished 

 silver," but " at about the freezing point of water it becomes 

 harder and brittle, and when broken in fragments, exhibits 

 a crystallised texture, which in the microscope seems 

 composed of beautiful facets of perfect whiteness and a 

 high metallic splendour." 



" To be converted into vapour, it requires a temperature 

 approaching that of red heat ; and when the experiment is 

 conducted under proper circumstances, it is found unaltered 

 after distillation." 



" It is a perfect conductor of electricity," and " an 

 excellent conductor of heat." 



" Resembling the metals in all these sensible properties 

 it is however remarkably different from any of them in 

 specific gravity ; I found that it rose to the surface of naphtha 

 distilled from petroleum, and of which the specific gravity 

 was '86 1 and it did not sink in double distilled naphtha, 1 the 

 specific gravity of which was about '770, that of water being 

 considered as i " (A.C.R. VI. 14). 



Gay-Lussac and Thenard (^Physico- Chemical Researches, 

 1811, I. in) who prepared the metal in larger quantities by 

 allowing molten potash to flow on to iron filings heated to 

 whiteness in a gun-barrel jacketed with clay, found that the 

 density of potassium at 15 C. relatively to water at the same 

 temperature was 0*865. They also gave the melting point 

 as 58, the value now accepted being 62-5. 



The chemical properties of potassium, (a) Oxidation 

 Davy had considerable difficulty in preserving the new 



1 This statement made twice by Davy, is remarkable in that it makes 

 the density of sodium less than 077. 



T 2 



