Mercury-in-glass thermometer
A basic mercury thermometer is a precisely crafted piece of tube-shaped glass enveloping a mercury-filled reservoir connected to an extremely thin channel, called the capillary bore, that provides a chamber the mercury from the reservoir can expand into.
[1] As the temperature of the surrounding environment changes, the mercury thermally expands and contracts, causing it to move out of, or into, the reservoir and, at the same time, rise or fall through the bore.
This design feature results in clearly visible movement of the mercury up or down the scale, enabling precise temperature readings.
In principle, thermometers made of different material (e.g., coloured alcohol thermometers) might be expected to give different intermediate readings due to different expansion properties; in practice the substances used are chosen to have reasonably linear expansion characteristics as a function of thermodynamic temperature, and so give similar results.
[3]: 23 Later, in the 1650s, failed experiments were run to determine if mercury might be a superior substitute for spirits in an enclosed glass thermometer.
In 1659, the astronomer Ismael Boulliau abandoned using mercury when he determined that it was not as responsive to changes in temperature as spirits.
When the temperature falls, the column of mercury breaks at the constriction and cannot return to the bulb, thus remaining stationary in the tube.
To avoid this, some weather services require that all mercury-in-glass thermometers be brought indoors when the temperature falls to −37 °C (−35 °F).
As of 2012[update], many mercury-in-glass thermometers are used in meteorology; however, they are becoming increasingly rare for other uses, as many countries banned them for medical use due to the toxicity of mercury.
[7][8] Swallowing this amount of mercury would pose little danger but the inhaling of the vapour could lead to health problems.
There was a voluntary take-back action for thermometers containing mercury based on the Federal Waste Management Plan 2006, and carried out in close cooperation between the Austrian Chamber of Pharmacists (Österreichische Apothekerkammer), the Federal Ministry of Environment, a private waste disposer, a producer of electronic thermometers and a pharmaceutical distributor.
The Federal Ministry supported each sold thermometer (covering about 30% of the direct costs) and advertised the project.
The country was the first one to make a step to ban mercury from its health care system in Southeast Asia and they used non-mercury digital thermometers instead.
[13][14] Since European Union directive 2007/51/EC came into force on 3 April 2009, the UK Health Protection Agency (HPA) reported that mercury thermometers could no longer be sold to the general public.
The purpose of these restrictions is to protect the environment and public health by decreasing the amount of mercury waste released.
