Mercury Thermometer



Invented by : Daniel Gabriel Fahrenheit
Invented in year : 1714

Thermometer is an instrument which is used to measure temperature. It measures temperature by using materials that change in some way when they are heated or cooled. In a mercury or alcohol thermometer the liquid expands as it is heated and contracts when it is cooled, so the length of the liquid column is longer or shorter depending on the temperature. Modern thermometers are calibrated in standard temperature units such as Fahrenheit or Celsius. Mercury Thermometer is actually a mercury-in-glass thermometer. There are Calibrated marks on the tube which allow the temperature to be read by the length of the mercury within the tube, which varies according to the heat given to it. To increase the sensitivity, there is usually a bulb of mercury at the end of the thermometer which contains most of the mercury; expansion and contraction of this volume of mercury is then amplified in the much narrower bore of the tube. The space above the mercury may be filled with nitrogen or it may be a vacuum.

The predecessor to the thermometer were called Thermoscopes. It was Galileo Galilei who is known to be the inventor of the first Thermometer. He invented a rudimentary water thermometer in 1593 which merely indicated temperature differences. Many several inventors invented a version of the thermoscope at the same time but it was Italian inventor Santorio Santorio who put a numerical scale on the instrument in 1612. Daniel Gabriel Fahrenheit (1686-1736) was the German physicist who invented the Alcohol Thermometer in 1709, and the Mercury Thermometer In 1714. In 1724, he introduced the temperature scale that bears his name - Fahrenheit Scale. The key to Fahrenheit's thermometer was a new method for cleaning mercury that enabled it to rise and fall within the tube without sticking to the sides. Mercury was an ideal substance for reading temperatures since it expanded at a more constant rate than alcohol and is able to be read at much higher and lower temperatures.

Fahrenheit based his scale on three reference points of temperature. The zero point was determined by placing the thermometer in brine: a mixture of ice, water, and ammonium chloride, a salt, was used. This was a type of frigorific mixture. The mixture automatically stabilized its temperature at 0 °F. The thermometer was placed in the mixture and the liquid in the thermometer was allowed to descend to its lowest point. The second point was 32 degree found by putting the thermometer in still water as ice is just forming on the surface. The third point, the 96 degree, was the level of the liquid in the thermometer when held in the mouth or under the armpit. Fahrenheit noted that, using this scale, mercury boils at around 600 degrees. Later, other scientists observed that water boils about 180 degrees higher than the freezing point and decided to redefine the degree slightly to make it exactly 180 degrees higher. It is for this reason that normal body temperature is 98.6 on the revised scale while it was 96 on Fahrenheit's original scale.

Development in the Invention Mercury Thermometer


In 1731 the Frenchman, René Antoine Ferchauld de Réamur (1683-1757) proposed a thermometer scale on which the freezing point of water was 0° and the boiling point was 80°. But it the Réamur scale is not in use today.

In 1742 a Swedish scientist named Anders Celsius (1701-1744) devised a thermometer scale dividing the freezing and boiling points of water into 100 degrees. Celsius chose 0 degrees for the boiling point of water, and 100 degrees for the freezing point. A year later, the Frenchman Jean Pierre Cristin (1683-1755) inverted the Celsius scale to produce the Centigrade scale used today (freezing point 0°, boiling point 100°). By international agreement in 1948 Cristin's adapted scale became known as Celsius and is still in use today.

In 1848 Sir William Thomson, Baron Kelvin of Largs, Lord Kelvin of Scotland (1824 - 1907) proposed the absolute temperature scale with zero degrees being the theoretical lowest temperature possible where molecular motion ceases. Kelvin defined 1 Kelvin degree as being equal to one Celsius degree. The Degree Kelvin is the current Standard Unit of temperature measurement.

Role of Mercury Thermometer in the Improvement Of Human Life
  • Because of the Mercury thermometer scientists came to know that mercury has better thermoconductiity and they have a greater range of readings
  • Clinical Thermometers made diagnose and treatment of various diseases easy
  • Mercury started to become widely used in Meteorology and Electrical instruments
  • It lead to the invention of other types of thermometers which were used for varios purposes
  • It also encouraged the glass industry
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