Alcohol, usually with a red dye in it
A mercury thermometer is used to measure temperature.
The liquid in which a thermometer is typically dipped is called mercury. Mercury is commonly used in old-style thermometers, but newer thermometers may use alcohol or other liquids instead.
Mercury and alcohol
Mercury rises in a thermometer when the temperature increases because mercury expands as it heats up. This expansion of the mercury column inside the thermometer is used to measure the temperature of the surrounding environment.
A mercury thermometer can go down to -30 deg C
mercury
toxic poison
The liquid in a clinical thermometer is called mercury. It is used to measure body temperature by expanding and rising within the thermometer.
In a mercury thermometer, the mercury expands when it is heated, causing it to rise in the thermometer's narrow tube. This increase in volume is a physical property of mercury known as thermal expansion. The height of the mercury column in the thermometer is then used to measure the temperature.
It could be used to do this - it is capable of doing it. However, Mercury is poisonous and a mercury thermometer is made out of fragile glass. Thus the danger that the thermometer would break releasing mercury into the milk (which would be for a person to drink) means that a mercury thermomiter is not the temperature sensor to use in this instance.
iodine and Mercury
Mercury