Chemical Purity by Dielectric Cryometry.

A consideration of the deficiencies in standard methods used for the cryometric determination of purity has led to a new approach in which the measurement of an intensive rather than an extensive property is the controlling factor. This method, measurement of the dielectric constant as a function of the fraction melted and correlation with the accompanying change in temperature, allows calculation of purity with high precision. The apparatus used and experimental work performed to ascertain the scope of the method are described. Determination of purity for organic compounds with differing polarizabilities and dipole moments indicate a rather wide applicability of the method. The large change in the dielectric constant of a high purity compound as it passes from solid to liquid state, with an accompanying small change in temperature, may allow automatic control of temperature within extremely narrow limits.