HIGH TEMPERATURE CALORIMETRY: II. ATOMIC HEATS OF CHROMIUM, MANGANESE, AND COBALT BETWEEN 0° AND 800 °C.

Abstract

The atomic heats of chromium, manganese, and cobalt have been measured up to 800 °C. by the adiabatic method described in Part I of this series. The specific heat of chromium is regular from 0° to 800 °C. The measurements with manganese show the sharp α−β transition at 717 °C., with a latent heat of 450 cal. per mole. Typical supercooling occurs on the reverse transition. Cobalt shows an anomaly due to a gradual transition, which is known to be a change in crystal form. The new data obtained permit a comparative discussion of the atomic heats of the transition metals, chromium to nickel. All these have values C_v > 3R at high temperatures. After allowing for the effects of ferromagnetism, the excess specific heats of cobalt and nickel are accounted for by the conduction electrons. This is not true for chromium and manganese, for which metals there must be some additional source of internal energy. It is tentatively suggested that these two metals may have antiferromagnetic transitions at temperatures above 800 °C.