Electrical Resistance and Thermo-Electric Power of the Alkali Metals

Electrical resistance and thermo-electric power of the five alkali metals, -183°C to 250°C.—Pure samples of the metals were fused into glass or quartz tubes, and measurements were made by means of thermo-junctions sealed into each end. Enough points were secured in each case to determine the slopes and the breaks in the curves. In both the resistance and thermo-electric power lines, changes of slope are observed beginning gradually 100 degrees or more below the melting point. These are taken to indicate transformations in each case from an $\alpha$ to a $\beta$ form. These transformations occur at approximately the temperatures, 50°C for Li, -20°C to +20°C for Na, -120°C for K, -35°C for Rb, and -80°C for Cs. In all cases a sharp rise in thermo-electric power and resistance occurs as the melting point is approached. The temperature coefficients of resistance decrease smoothly with increasing atomic weight for all forms.

Atomic heat of electrons in the alkali metals.—The atomic heat of electricity as computed from thermo-electric data is approximately 0.24 cal. for Na and K, and 0.58 cal. for Rb and Cs. The values are too small to account for the observed excess of the atomic heats for these metals above the equipartition value.