# Calibrating liquid thermometers

The calibration of a thermometer involves marking the thermometer so that the temperature can be read accurately. The scale is based on the thermometric property used by the thermometer.

In a certain mercury thermometer, the mercury column is 3 cm long when the temperature is $$0^{\circ}\text{C}$$. If the thermometer was accurately calibrated, there should be a $$0^{\circ}\text{C}$$ marking at the 3 cm point.

To calibrate a thermometer using the **Celsius scale** without using another thermometer:

- Place the thermometer next to
**melting ice**and record the length of the liquid column, $$\Tblue{x_{1}}$$. - Place the thermometer in
**boiling water**and record the length of the liquid column, $$\Tred{x_{2}}$$.

Only record the length of the liquid column once it has reached a steady level.

The temperature of an unknown source T (in $$^{\circ}\text{C}$$) can then be calculated: $$$\Tgreen{\text{temperature}} = \frac{\Tgreen{x_{3}} - \Tblue{x_{1}}} {\Tred{x_{2}}-\Tblue{x_{1}} } \times 100$$$