Scientists Uncover Mystery Behind Crystal's Dual Melting Points

Researchers have solved a 120-year-old mystery regarding the compound acetaldehyde phenylhydrazone, which exhibits two distinct melting points. The phenomenon is due to a minuscule contamination that causes the compound to form two different liquid structures upon melting, depending on exposure to acid or base. This results in the compound having a lower melting point when exposed to acid, which acts as a catalyst for isomer conversion. The study highlights the compound's sensitivity to acid and the role of isomer configurations in its melting behavior.