A good thermometric liquid should have a few important properties. First, it should have a low freezing point and a high boiling point, so that it remains a liquid over a wide range of temperatures. Second, it should have a high thermal expansion coefficient, which means that it expands and contracts significantly with changes in temperature. This property allows the liquid to be easily seen in a thermometer and to accurately indicate changes in temperature. Finally, the liquid should be non-toxic, non-corrosive, and have a low viscosity, so that it flows easily through the thermometer.
Mercury was once a commonly used thermometric liquid, but it is now considered hazardous due to its toxicity. Alcohol, such as ethanol or isopropyl alcohol, is often used as an alternative because it meets the above criteria and is safe to handle. Other options include mineral spirits, toluene, and kerosene. However, it's important to note that some of these liquids may have a higher viscosity or a lower thermal expansion coefficient than others, which can affect the accuracy of the thermometer.