How to Read Glass Thermometers

Glass thermometers continue to find widespread application.

Glass thermometers are frequently used to measure temperature. While laboratory glass thermometers are often filled with mercury, colored spirits are increasingly used in consumer destined thermometers due to the health concerns associated with mercury. Reading a glass thermometer to detect a fever or find a boiling point may seem straightforward, but careless mistakes are sometimes made when the information presented by the thermometer is ignored or misinterpreted.

Things You'll Need

• Glass thermometer

Instructions

1. Identify the scale of the thermometer. Laboratory glass thermometers are marked in degrees Celsius. In the United States, consumer glass thermometers are often marked in degrees Fahrenheit. Thermometers are typically marked with a C or F corresponding to the scale with which they are marked.

2. Identify the range of the thermometer. Some thermometers have a range extending below the freezing point of water to above the boiling point of water while others have a much narrower range. This implies a target range for the thermometer.

3. Identify the interval of the thermometers markings. Thermometers may be marked in a variety of increments such as 0.5 degrees or 2 degrees. The interval can be determined using the markings from one number to the next. If there are four markings between the 20 degree Celsius mark and the 30 degrees Celsius mark, then the value of each marking is 2 degrees Celsius.

4. Locate the fluid level in the glass thermometer after measuring a temperature. Find the marking closest to the end of the fluid to read the temperature. For instance, if the fluid level reached the second marking after 20 degrees Celsius, then the temperature would read 24 degrees Celsius.

References

• National Science Teachers Association: How to Read a Thermometer
• BBC: Temperature Fact Sheets