Determination of The Melting Points of Organic Compounds Making Use of β-Ray Backscattering

Abstract

A new method of determining the melting points was devised using the principle that the β-rays backscattered by the organic compounds placed on the heated metal disk increase rapidly at the melting point because the scattering area of the compounds becomes small by the effect of capillary action in the melting and the metal disk surface covered with the compounds is partly exposed. Carbon-14 and platinum plate were used as the β-ray source and the disk, respectively. The measured melting points of powdered azobenzene, sulfanilamide, dicyandiamide and phenol phthalein agreed with the correct melting points within an accuracy of ±2°C. The quantities of sample necessary for measurements are about 1 mg. This method is free from error due to visual observation and is also free from the β-ray source contamination.