Division 1.2 DEFINITIONS AND UNITS
United Kingdom
The vapour pressure of a substance is defined as the saturation pressure above a solid or liquid substance.
The SI unit of pressure, which is the pascal (Pa), should be used. Other units which have been employed historically are given hereafter, together with their conversion factors:
| 1 Torr | = | 1 mm Hg | = | 1,333 × 102 Pa |
| 1 atmosphere | = | 1,013 × 105 Pa | ||
| 1 bar | = | 105 Pa |
The SI unit of temperature is the kelvin (K). The conversion of degrees Celsius to kelvin is according to the formula:
T = t + 273,15
where, T is the kelvin or thermodynamic temperature and t is the Celsius temperature.
Table 1
| When using a capacitance manometer | |||||
| Measuring method | Substances | Estimated repeatability | Estimated reproducibility | Recommended range | |
|---|---|---|---|---|---|
| Solid | Liquid | ||||
| Dynamic method | Low melting | Yes | up to 25 % 1 to 5 % | up to 25 % 1 to 5 % | 103 Pa to 2 × 103 Pa 2 × 103 Pa to 105 Pa |
| Static method | Yes | Yes | 5 to 10 % | 5 to 10 % | 10 Pa to 105 Pa 10–2 Pa to 105 Paf1 |
| Isoteniscope method | Yes | Yes | 5 to 10 % | 5 to 10 % | 102 Pa to 105 Pa |
| Effusion method: vapour pressure balance | Yes | Yes | 5 to 20 % | up to 50 % | 10–3 to 1 Pa |
| Effusion method: Knudsen cell | Yes | Yes | 10 to 30 % | — | 10–10 to 1 P |
| Effusion method: isothermal thermogravimetry | Yes | Yes | 5 to 30 % | up to 50 % | 10–10 to 1 Pa |
| Gas saturation method | Yes | Yes | 10 to 30 % | up to 50 % | 10–10 to 103 Pa |
| Spinning rotor method | Yes | Yes | 10 to 20 % | — | 10–4 to 0,5 Pa |
Annotations
Footnotes
- f1
-
When using a capacitance manometer