Definition and History
The torr is a unit of pressure equal to 1/760 of an atmosphere. It was named after Evangelista Torricelli, who discovered the principle of the barometer. One torr equals approximately 133 pascals. Historically one torr equaled one millimeter of mercury, but later redefinitions made them slightly different.
The torr, symbol Torr, is a unit of pressure based on an absolute scale. One torr equals exactly 101325/760 pascals, which is about 133.32 pascals. The intention was that one torr would equal one millimeter of mercury, but subsequent redefinitions made them differ by less than 0.000015%.
Since atmospheric pressure is 760 torr, a vacuum of even 1% atmosphere can be written in torr without scientific notation. Over time 760 millimeters of mercury was considered the standard atmospheric pressure.
Practical Application
The torr measures small pressures like in vacuum chambers. We use torr to measure vacuum pressures because it works well for vacuum measurements.
Significance of the Torricelli
The torr was named to honor Torricelli’s discovery. It was defined to equal one millimeter of mercury, reinforcing the connection between the unit and the history of pressure measurement.