Have you ever broken a mercury thermometer? Maybe as a child, or by mistake while trying to shake it to bring it back to lower temperatures. See that silver liquid flow along the floor or the table, while dividing itself into tiny balls Similar to marbles, it almost gave the impression of being in front of an extraterrestrial substance. Definitely something very fascinating, but also quite dangerous. Since 2009 in Italy it is for sale prohibited of Mercury thermometers, in line with a European directive that aims to reduce the use of this toxic metal.
Mercury, in fact, is volatile and its vapors are harmful to the nervous and respiratory system, as well as representing a great risk for pregnant women. Yet, for years it has been used precisely for its physical properties: expands with heat, allowing you to measure body temperature in a simple and precise way.
For many years, these thermometers have been the most popular on the market: today they have been replaced by digital or infrared ones.
The danger of mercury
That silver liquid that was inside the thermometers was precisely metal mercury, a chemical element very particular: from the whole periodic table, it is the only metal found in liquid form at room temperature.
Just this feature also involves a risk: mercury is highly volatile, therefore it tends to evaporate easily, releasing vapors that can be inhaled. Once you enter the body, mercury can cause serious respiratory damage (such as tracheitis or bronchitis) and the nervous system, both central and peripheral. In addition, being able to overcome the placental barrier, mercury represents a great risk for pregnant women and for the child they carry on their womb. Not surprisingly, theWorld Health Organization (WHO) has inserted the mercury between the ten chemicals that cause greater concerns about the effects on citizens.
The Ministry of Labor, Health and Social Policies In 2008 a European directive (2007/51/EC) implemented in 2008 which prohibits the sale of the thermometers containing mercury to the public. The ban entered into force on April 3, 2009 and from that date It was no longer possible to market these tools in the pharmacy or in other shops. This decision aims to gradually eliminate mercury from common products, in line with international agreements such as the Minamata Convention, then signed in 2013.
Why was Mercury used?
Equipped with Thermometric properties, The metal mercury expands or contracts with the temperature variations, which made it a perfect component for the functionality of the old thermometers: when heated, the atoms of Mercury vibrate and move faster, so much so as to increase the distance between them and increasing the volume of metal mercury overall.
This phenomenon is called thermal dilationand is literally the basis of the operation of a thermometer: the mercury contained in the glass tubicino, if subject to an increase in heat, expands and dates back to the capillary. The height reached corresponds to a certain temperature, indicated on the graduated scale. As soon as the temperature lowers, the mercury particles move less, the volume narrows and we saw the mercury “go back” to the initial position in the glass tubicino.
It is not difficult to think how comfortable it was to be comfortable for the functioning of thermometers, without the use of batteries or electric current, but taking advantage of a simple physical phenomenon.
