Hydrogen gas is also produced. With very reactive metals such as potassium, the energy of the reaction causes the hydrogen to burn as the reaction takes place.

they have low melting points (increasing up the group from 28°C for Cs to 180°C for Li, whereas typical metals have much higher ... a density that is less than 1 g/cm 3) ...

WHEN these metals are heated in a vacuous tube in such a way as to cause an extremely thin sublimate of the metal to condense upon the glass, the film so obtained will be found to possess a ...