Principle of a mercury thermometer:
Mercury is stored in a ball of mercury at the end. When the mercury is heated, it expands and rises up the very narrow glass tube. So a small change in body temperature causes a large rise in the mercury inside the glass tube. After taking your temperature, you have to shake the thermometer vigorously to get the mercury back inside the mercury bulb.
How to use a mercury thermometer:
When using a thermometer, first look at its range (measuring range), and then look at its smallest divisional value, that is, the value expressed by each small frame. It is important to choose the appropriate thermometer to measure the temperature of the object being measured.
Measurement of the thermometer's bubble should be in full contact with the object to be measured, and the glass bubble can not touch the side walls or the bottom of the object to be measured; readings, the thermometer does not leave the object to be measured, and the line of sight of the eyes should be level with the liquid surface inside the thermometer.
1, should be calibrated before use (can be used to standardize the liquid temperature multi-branch comparison method for calibration or the use of more advanced precision thermometer calibration).
2, does not allow the use of temperature exceeding the maximum scale value of the thermometer's measured value.
3, the thermometer has thermal inertia, should be read after the thermometer reaches a steady state. Readings should be read in the temperature convex curved moon surface of the highest tangent direction, look straight ahead.
4, mercury thermometer should be perpendicular to the measured direction of flow or tilted.
5, mercury thermometer often occurs in the case of mercury column fracture, elimination methods are:
Cold repair method: the thermometer's temperature package inserted into the mixture of dry ice and alcohol (the temperature shall not exceed -38 ° C) for the cold shrinkage, so that all of the mercury in the capillary tube contraction to the temperature package until.
Heat repair method: the thermometer is slowly inserted into the temperature slightly higher than the upper limit of the measurement of the thermostatic bath, so that the mercury broken part of the mercury column with the whole connection, and then slowly remove the thermometer, in the air gradually cold to room temperature.
Ban on mercury thermometers
Considering the mercury hazards of mercury thermometers, many countries have taken measures to ban them. As early as 1992, Sweden banned the sale of all medical devices containing mercury. Britain, France, Denmark and the Netherlands? have also banned their use and sale. In the United States, 13 states and cities, including San Francisco, Boston and Michigan, have banned the sale of mercury thermometers since 2000.
The European Commission has also banned the sale of mercury thermometers since 2005 and their export since 2011, and in December 2008, the Argentine government announced that it would ban the production and import of mercury thermometers. The World Health Organization has also established a Global Mercury Elimination Program, with the goal of reducing demand for mercury-containing thermometers and sphygmomanometers by 70 percent globally by 2017.
But mercury thermometers have not been banned in China. Mercury thermometers are widely used in the medical field and in ordinary households, and are available in some pharmacies. Data from the China Medical Devices Industry Association (CMDIA) show that in 2008, the national production of mercury thermometers consumed 109.25 tons of mercury, equivalent to the amount of mercury used in 21.85 billion standard mercury-containing energy-saving lamps.
According to statistics, about 120 million mercury-containing thermometers are produced in the country each year, and more than 10 tons of mercury are disposed of as waste in China each year due to broken mercury thermometers.
As of August 16, 2017, the Minamata Convention on Mercury came into force for China, which specifies that "the production of mercury-containing thermometers and mercury-containing sphygmomanometers will be banned from January 1, 2026."
Reference for the above: Baidu Encyclopedia - Mercury Thermometer
Reference for the above: Baidu Encyclopedia - Mercury Thermometer