Checking the Calibration of Thermometers by Using Ice and Boiling Water

Section 1: Concept of Calibration

Calibration: A crucial process to ensure the accuracy of scientific instruments like thermometers. It involves comparing the readings of an instrument against a known standard.
Importance: Correct calibration ensures the validity of experimental data, minimising errors and improving the reliability of results.

Section 2: Using Ice and Boiling Water

Ice Point Calibration: This method uses melting ice to calibrate the lower end (0 °C) of a thermometer’s range. The thermometer should read 0 °C when fully immersed in the melting ice.
Boiling Point Calibration: Used to calibrate the upper end (100 °C) of a typical thermometer’s range. The thermometer should read 100 °C when fully immersed in boiling water.

Section 3: Practical Procedure

Step 1: Prepare the calibration environments – a container of melting ice for the low point and boiling water for the high point.
Step 2: Fully immerse the thermometer in the melting ice. Allow it to stabilise before taking a reading.
Step 3: Repeat the same process in the boiling water.
Step 4: Note down the actual readings at both points. If these do not match the expected values, the thermometer might require recalibration or replacement.

Section 4: Considerations and Safety Precautions

Waiting Time: Allow sufficient time for the thermometer to equilibrate in each environment before taking readings.
Safety: Be cautious when dealing with boiling water to prevent burns and scalds.
Parallax Error: To avoid this, always read the thermometer at eye level.

Section 5: Interpreting Calibration Results

Calibration Curve: A plot of how thermometer readings deviate from known standard values. This provides a basis for correcting future readings.
Calibration Certificate: On successful calibration, a thermometer may be issued with a certificate indicating its accuracy over its operational range.