Lithium is a white metal with silver-like lustre. It remains untarnished in dry air, but a freshly cut surface develops a yellow tinge if moisture is present. In extremely thin layers it is translucent, the transmitted light having a dark, reddish-brown colour. It is harder than caesium, rubidium, sodium, or potassium, but softer than lead, the degree of hardness on Rydberg's scale being 0.6. In ductility it resembles lead, and can be drawn into wire or rolled into thin sheets. It can be welded at the ordinary temperature. It is the lightest of the normally solid elements, Richards and Brink's value for the density at 20° C. being 0.534. An earlier determination by Bunsen and Matthiessen gives the value 0.59. The atomic volume, 13, is lower than those of the other alkali-metals.
According to Kahlbaum, and also Guertler and Pirani, the melting- point of lithium is 186° C., but Masing and Tammann, and also Schukoffsky, give 179° C. In vacuum it volatilizes at red heat. It has the highest specific heat of any element, Regnault's value for the range 26.5° to 99.77° C. being 0.9408. The atomic heat is 6.6.
Both the metal and its compounds colour the flame carmine-red. The spectrum is characterized by a bright red line and a fainter orange line. |