What is a Thermometer?
Thermometers measure 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.Daniel Gabriel Fahrenheit was the German physicist who invented a alcohol thermometer in 1709, and the mercury thermometer in 1714. In 1724, he introduced the standard temperature scale that bears his name - Fahrenheit Scale - that was used to record changes in temperature in an accurate fashion.
In 1742, the Celsius scale was invented by Swedish Astronomer Anders Celsius. The Celsius scale has 100 degrees between the freezing point (0°C) and boiling point (100°C) of pure water at sea level air pressure.
The liquid used in laboratory thermometer can be pure ethanol or toluene or kerosene, depending on manufacturer and working temperature range. Since these are transparent, the liquid is made more visible by the addition of a red or blue dye.The space above the liquid is a mixture of nitrogen and the vapour of the liquid.The range of usefulness of the thermometer is set by the boiling point of the liquid used.
