Specific heat determinations of pure tantalum were made in the temperature range 53° to 298°K and the entropy was found to beS298.1=9.9±0.1. Tantalum containing hydrogen in amounts ranging from Ta+0.0284 H to Ta+0.0958 H was shown to behave anomalously, the specific heat having a high maximum in the region 220° to 265°K depending on the composition. The height of the maximum and the difference in measureable heat content between hydrogenated and normal tantalum were shown to be approximately proportional to the amount of dissolved hydrogen. The temperature of the maximum increases as the hydrogen is increased. After dehydrogenation, the same specific heat was obtained as for the original unhydrogenated material. The density of the dehydrogenated product also was normal, whereas the hydrogenated materials had lower densities. It is postulated that differences in entropy between hydrogenated and pure tantalum may be attributed to differences in the number of possible ways of arranging the hydrogen particles among the positions in the tantalum lattice available at the higher and lower temperatures.
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