Measurement of dilute metallic impurity concentration in lead by differential scanning calorimetry

The traditional method for purity determination by analysis of the peak shape of the melting transition has included fitting to a linear relation between sample temperature (T) and the reciprocal fraction molten ($\text{1}\text{7}$). This technique, however, necessitates the use of a series of calibrants to determine the proper choice of limits for $\text{1}\text{7}$ as a function of purity. In this paper, a non-linear relation between T and $\text{1}\text{7}$ is developed and applied to the determination of metallic impurities in Pb in the range of a few to 1000 parts per million. The results are found to be independent of the range of $\text{1}\text{7}$ used. The use of differential scanning calorimety in this determination is discussed, and rate effects are also mentioned.