Definition:Torr
Definition
The torr is an metric unit of pressure.
It is defined as being:
- The amount of pressure equal to exactly $\dfrac 1 {760}$ of a standard atmosphere.
that is:
- $\dfrac {101 \, 325} {760}$ of a pascals.
Conversion Factors
| \(\ds \) | \(\) | \(\ds 1\) | torr | |||||||||||
| \(\ds \) | \(\approx\) | \(\ds 0 \cdotp 99999 \, 98575 \, 33699\) | millimetre of mercury | |||||||||||
| \(\ds \) | \(\approx\) | \(\ds 133 \cdotp 32236 \, 8\) | pascals |
Symbol
- $\mathrm {Torr}$
The symbol for the torr is $\mathrm {Torr}$.
The $\LaTeX$ code for \(\mathrm {Torr}\) is \mathrm {Torr} .
Source of Name
This entry was named for Evangelista Torricelli.
Also defined as
The torr can also equivalently be defined as:
This can be seen to be equivalent to the definition given, as $1$ standard atmosphere is itself defined as exactly $101 \, 325$ pascals.
Older sources may give the definition as $1$ millimetre of mercury, but as the latter is no longer defined in terms of standard atmosphere, and $1$ torr is actually now aproximately equal to $0 \cdotp 99999 \, 98575$ millimetre of mercury.
Historical Note
The torr was originally defined to be the same as one millimetre of mercury, but since that time both definitions have been altered slightly.
Hence the torr and the millimetre of mercury have diverged ever so slightly so they are now different by about $0 \cdotp 00001 \, 5 \%$.
Sources
- 1969: J.C. Anderson, D.M. Hum, B.G. Neal and J.H. Whitelaw: Data and Formulae for Engineering Students (2nd ed.) ... (previous) ... (next): $2.$ Unit Conversion Factors
- 1998: David Nelson: The Penguin Dictionary of Mathematics (2nd ed.) ... (previous) ... (next): torr
- 2008: David Nelson: The Penguin Dictionary of Mathematics (4th ed.) ... (previous) ... (next): torr