Although many variations of a thermometer are documented throughout history, the glass thermometer that is most familiar with what we see today was first invented by the Grand Duke of Tuscany, Ferdinand II, in 1654. Although a significant development, his thermometer was inaccurate and predated a standardised scale.
In 1714, Gabriel Fahrenheit was the first person to make a thermometer using mercury. At this time, mercury expansion was more predictable than spirit and as such combined with an improvement in glasswork, offered a far improved accuracy than all thermometers invented before. Further to this, Fahrenheit was the first inventor to use the discovery of fixed points as the temperature scale for his thermometer, allowing accurate measurements to be taken and recorded for the first time. Even today, Fahrenheit’s scale is widely used.
Throughout history, further temperature scales have been introduced, such as Anders Celsius in 1742 and Lord Kelvin and his absolute temperature scale in 1848, but the basic method of glass thermometer remained consistent with the use of mercury as the expanding medium.
In October 2017 however, the introduction of an EU regulation 2017/852 amended the environmental law and prohibited the manufacture, export and import of a large range of mercury added products, including thermometers. As a result, the common spirit filled thermometer was introduced, using petroleum-based liquids as a direct replacement to mercury.
Spirit filled glass thermometers are the modern-day alternative to mercury in glass thermometers. The use of mercury within thermometers was prohibited within the EU on health and safety grounds due to the toxicity and dangerous characteristics mercury possesses.
Unlike mercury, the liquid in glass thermometers contain expansion media comprising of substances and preparations which present no risk to health, safety or the environment when encased in the glass bulb and capillary, and present minimal risk if the instrument is broken during use.
How does it work?
A glass thermometer typically contains a bulb connected to a hollowed capillary tube. Inside the bulb is a liquid spirit medium. As the temperature rises, the liquid medium expands and rises within the capillary. Similarly, as the temperature cools, the liquid contracts and falls within the capillary. Temperature scales are applied to each thermometer to accurately represent the temperature at varying fixed points. Temperature scales will vary per thermometer as small variations in the tube capillary, such as hollow bore diameter, will need to be accounted for prior to the scale being added.
How do you use it?
Firstly, you will need to set up a thermometer stand to hold the thermometer in place. Place the thermometer in the stand, ensuring any clamp can be closed enough to hold the thermometer in place, but not excessively tightened that unnecessary pressure is placed on the thermometer increasing the possibility of breakage. Using a rubberised clamp is recommended.
Place the thermometer in the material to be tested, at the designated level for the thermometer type. Here at Brannan, we offer two variations of standard lab thermometer; 76mm immersion and total immersion. Ensure the thermometer is not in contact with any container holding the material being tested, as this will influence any results. Allow the thermometer to adjust to the medium temperature before taking any readings. This time period will vary.
To take a temperature reading, ensure your eye line is perpendicular to the thermometer, and mark the point at which the top of the spirit sits.
Brannan sell a comprehensive range of glass thermometers. Our scientific range covers all aspects of laboratory thermometers including general purpose and educational through to specification thermometers such as ASTM and IP. These instruments are used to measure temperatures or temperature changes with a high degree of precision.
All our laboratory thermometers can be supplied with full UKAS. Certification, at an additional charge, on request. Our facilities conform to (BS) EN ISO/IEC 17025:2005 – ‘General requirements for the competence of testing and calibration laboratories’.
For temperature measurement our laboratory can calibrate all types of liquid-in-glass thermometers. Certification is available for test temperatures between -60°C and +250°C.
For more information on any of our laboratory thermometers or calibration services, contact firstname.lastname@example.org