Testing for melting point depression is a common diagnostic method used in chemistry to check for impurities. Pure compounds melt at known temperatures, and ty

Testing for melting point depression is a common diagnostic method used in chemistry to check for impurities. Pure compounds melt at known temperatures, and typically do so within a narrow range (+/- 0.5 °C). Impurities almost always lower the melting point and widen this band. I spent a lot of my undergrad chem courses packing my products into capillary sized test-tubes and watching them slowly melt. https://www.mt.com/us/en/home/applications/Application_Browse_Laboratory_Analytics/Thermal_Values/melting-point-determination.html https://www.mt.com/us/en/home/applications/Application_Brows... Some companies leverage this effect to make non-reversible temperature indicators that change color at specific temperatures. https://www.mcmaster.com/temperature-indicating-stickers/ https://www.mcmaster.com/temperature-indicating-stickers/