Education in Physics Revista Mexicana de F´ ısica E 18, 020210 1–4 JULY-DECEMBER 2021 A note on producing supercooled water in the laboratory I. Amisaday Zarco-Delgado, and H. N. N ´ u˜ nez-Y´ epez Departamento de F´ ısica, Universidad Aut´ onoma Metropolitana, Unidad Iztapalapa, Apartado Postal 55-534, Iztapalapa 09340 CDMX. e-mail: zamisaday@gmail.com; nyhn@xanum.uam.mx A. L. Salas-Brito Laboratorio de Sistemas Din´ amicos, Departamento de Ciencias B ´ asicas, Universidad Aut´ onoma Metropolitana, Unidad Azcapotzalco, Apartado Postal 21–267, Coyoac´ an 04000 CDMX. e-mail: asalasbrito@yahoo.com; asb@azc.uam.mx Received 15 January 2021; accepted 9 March 2021 As we lower the temperature of water at a certain point it changes from liquid to solid. Yet under certain conditions it is possible to keep the water in a non-equilibrium liquid-like phase called supercooled water thus avoiding solidification. In such a state water may freeze under the tiniest perturbation (as stirring it a little). The existence of supercooled water is usually known to students since the introductory courses, but it seems difficult for them to attest such a water state in an undergraduate laboratory. A simple method for supercooling water is, however, readily available. It is this short paper aim to describe such a method in a form that may be performed in any elementary laboratory. Keywords: Supercooled water; undergraduate laboratories; metastable states. PACS: 03.65.Pm; 03.65.Ge DOI: https://doi.org/10.31349/RevMexFisE.18.020210 Introduction Supercooled liquids, in particular water, have a long history dating back perhaps to the work of Joseph Black in the XVIII century [1]. Such liquids have a rich phenomenology which is still far from being completely understood. Water may enter the su- percooled phase, that is, it still may be behaving as a liquid FIGURE 1. Joseph Black shortly before his death in 1799. well below its standard freezing point at 273.15 K (or 0 ◦ C). Instead, it forms a curious substance, supercooled water, oth- erwise called undercooled or subcooled water. In fact, freez- ers can sometimes cool soft drinks to a supercooled state so that when they are opened form a kind of slush. Most people have witnessed this phenomena at home. Supercooling has many uses, for example it has been successfully applied to organ preservation at hospitals: livers that were later trans- planted into recipient animals were preserved by supercool- ing for up to 96 hours (4 days), quadrupling the limits of what could be achieved by conventional methods. For most substances, the melting and freezing points oc- cur at the same temperature. However, certain substances possess differing solid-liquid transition temperatures. For ex- ample, agar (agar, also called agar-agar, a gelatinous sub- stance obtained from various kinds of seaweed and used in biological culture media or in foods) displays hysteresis in its melting and freezing points: it melts at 85 ◦ C (or 358.15 K) and solidifies at 32 ◦ C (or 305.15 K). The properties of super- cooled water may be also used to explain the winter dwellings of aquatic insects [2]. However, we do not address such mat- ters in this work, requiring avanced explanations and a much more elaborate experiment for a basic undergraduate physics course. Though the idea of such a metastable water state is quite analogous to the equilibrium that may be reached by a broom-stick standing upright on the floor for one instant before falling down. The crystallization of pure water usually begins at a lower temperature than the melting point, freezing does not start until the temperature is low enough to allow the formation of nucleation points, that is, small sites in which the freezing