A thermometer is a device used to measure temperature that works by detecting changes in a sensor as temperature varies. A mercury-in-glass thermometer was invented by Daniel Gabriel Fahrenheit and consists of a bulb reservoir containing mercury whose volume changes with temperature, and a stem containing a measuring scale. Mercury is well-suited for thermometers as it easily changes between liquid and solid and has a low freezing point. While inexpensive, accurate, and easy to use, mercury thermometers are also fragile, toxic if broken, and pose environmental hazards.

1.  Thermometer is a device that measures temperature gradient using
variety of different principles .
 It is thermo + meter i.e. thermo means heat and meter means measure .
 A thermometer is used in health care to measure and monitor body
temperature .

2.  There are markings on thermometer which are in the form of Celsius or
Fahrenheit .
 The invention of the thermometer is generally credited to the Italian
mathematician-physicist Galileo Galilei .
 A thermometer has two important elements:
1. a temperature sensor in which some physical change occurs with
temperature
2. some means of converting this physical change into a numerical value .

3. Mercury-In-Glass thermometer
 It is also known as mercury thermometer.
 The mercury-in-glass thermometer was invented by Daniel Gabriel
Fahrenheit in Amsterdam .
 It consists of two basic parts :- (a) The Bulb (b) The Stem.
(a) The Bulb :-
 It acts as a reservoir holding the mercury whose volume changes with
change in temperature .
 The bulb also acts as a sensor or gauge which is inserted in the body .
 Mercury is perfect to measure temperature because it changes from solid

4. to liquid very easily and also it has low freezing point .
(b) The Stem :-
 It contains the scale that is measuring the temperature and a capillary
through which the liquid can accordingly expand and contract.
Advantages of mercury thermometer
 Inexpensive .
 Readily available .
 Easy to use .
 Accurate enough for clinical use .
 Able to be chemically sterilized .
 Available with a measuring range suitable for clinical use .

5.  Mercury is a naturally opaque liquid . This means that it can be directly
utilized in its pure form
 Mercury does not wet glass. When it moves up and down in the narrow
tube, strong cohesive properties of mercury do not allow it to leave any
traces on the inside of the narrow tube .
Disadvantages of mercury thermometer
 Fragile, toxic, rigid .
 Mercury possess a potential toxic hazard if the glass container is
ruptured.
 Range : -38 °C to 356 °C