Basal temperature thermometer, containing about 2.25 grams of mercury
In a mercury thermometer, a glass tube is filled with mercury and a standard temperature scale is marked on the tube.
changes in temperature, the mercury expands and contracts in a consistent fashion and the temperature can be read from the scale.
A mercury thermometer can be easily identified by the presence of a silver bulb. If the bulb is red, blue, purple, green or any other coluor, it is not a mercury thermometer