How Does a Thermometer Work?

When you are sick, your mother takes your temperature with a glass thermometer containing silvery liquid called mercury. This type of thermometer, the mecury-in-glass type, is made in four parts: a sealed glass tube, a glass bulb at the bottom (the part you put in your mouth), a scale of measurements, and a liquid, such as mercury.

Mercury is an ideal filler in a thermometer, for heat causes it to expand and cold causes it to contract. When your temperature is taken and you do have a fever, the mercury responds to that body heat by increasing in volume.

Within minutes, there is too much mercury for the small bulb to hold, and the mercury rises in the tube. When the mercury is heated to the same temperature as your body’s, it stops rising along the tube. The numbered point on the scale of measurements tells your temperature.

Even though the average body temperature of an adult is 98.6°F., in some diseases and in sunstroke, body temperatures have reached as high as 115°F.!