iodine and Mercury
The liquid typically used in a Galilean thermometer is colored alcohol.
We still use colored alcohol for our liquid in everyday thermometers.
The two substances used in a liquid column thermometer are mercury and alcohol. Mercury thermometers use mercury as the liquid inside the glass tube, while alcohol thermometers use colored alcohol such as ethanol or dyed ethanol.
A thermometer is used to measure air temperature, or the temperature within a solid or liquid.
Mercury
Liquid is used in a thermometer because it expands and contracts uniformly with changes in temperature, allowing for accurate temperature measurements. The liquid inside the thermometer expands and rises in the capillary tube as it gets warmer, providing a visible indication of temperature.
Temperature is usually measured via expansion/contraction of a liquid (liquid thermometer), differences in expansion/contraction of two metals (bi-metallic strip thermometer), changes in electrical resistance (thermistor or thermocouple) or radiant energy (for example: a pyrometer)
A thermometer is most commonly used to measure the temperature of a liquid. Other methods, such as infrared thermometers or thermocouples, can also be used depending on the specific application and characteristics of the liquid.
A laboratory thermometer is used to check the temperature, or changes in temperature, of an object with precise accuracy.
The liquid in a thermometer does not move when turned upside down because of the properties of the liquid used (usually mercury or alcohol) and the vacuum-sealed tube design of the thermometer. This design prevents the liquid from freely moving when the thermometer is inverted.
The liquid is an antiseptic used to sterilise it. You wouldn't want to be contaminated with any bacteria or viruses from the last person who used the thermometer, would you?
The keyword "what" in a Galileo thermometer is used to indicate the temperature at which the liquid-filled bulbs inside the thermometer are floating.