thermometry is a branch of physics that related to the measurements of temprature.actually thermometer measures temprature,it just deal with these measurements.there are many types of thermometry i.e
1-vapour-pressure thermometry
2-radiation thermometry
3-thermocouple etc,etc
Probably a cheap one
Mercury's melting point is close to the room temperature, so it is a good indicator of temperature around room temperature.
because in chemistry we have to record the result fast like if we use thermameter and take it quickiy so we can not measure it exactly
A thermometer is considered an instrument, as it is a device used to measure temperature. It is not typically referred to as equipment, which usually implies a larger and more complex set of tools or machinery.
A mercury-in-glass thermometer, invented by German physicist Daniel Gabriel Fahrenheit, is a thermometer consisting of mercury in a glass tube. Calibrated marks on the tube 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 less than atmospheric pressure, which is normally known as a vacuum.
Example of thermal expansion:Spaces or gaps left between rail lines. The reason is that the movement of trains exerts a huge pressure on the rails, this shows up a rise in temp. in the rails made up of Fe .So, the rail expands because of θ. [ rise in temp.= θ]