Millimeters of mercury

Drain and Morrison (1) report the following data for the adsorption of N2 on rutile at 75 K, where P is in millimeters of mercury and v in cubic centimeters STP per gram. 

TABLE 5.4 Vapor Pressure of Ice in Millimeters of Mercury For temperatures from —99 to 0°C. 

Atmospheres Millimeters of mercury at 32 F 760 Calories, gram, per gram per degree C. Joules per kilogram per degree Kelvin 4186.8... 

The percent relative humidity is defined as lOOp/P, where p is the actual partial pressure of the water vapor and P is the vapor pressure of water at the same temperature. The total pressure is taken as normal barometric, unless otherwise stated. Note that since the per cent relative humidity is defined as 100(p/Pj) and the per cent absolute humidity equals 100[p/(760-p) -h P,/(760-Pj)], the factor by which the former must be multiplied to convert it to the latter is (760 -P ) / (760-p), where p and Pj can be expressed in units of millimeters of mercury. 

A number of units are used to express a pressure measurement. Some are based on a force per unit area for e.xample, pound (force) per square inch (psi) or dyne per square centimeter (dyne/enr). Otliers are based on a fluid height, such as inches of water (in H O) or millimeters of mercury (iimiHg) units such as these are convenient when tlie pressure is indicated by a difference between two levels of a liquid, as in a imuiometer or barometer. Barometric pressure is a measure of the ambient air pressure. Standard barometric pressure is 1 atm and is equivalent to 14.696 psi and 29.921 in Hg. 

Fcr piping with air in streamline flow at absolute pressures in the range between 50 microns and 1 millimeter of mercury, the following is a recommended method. Calculation procedures in pressure regions below atmospheric are very limited and often not generally applicable to broad interpretations. 

Multiply millimeters of mercury by 0.01934 Multiply inches of mercury by 0.4912... 

Millimeters of mercury — Vacuum (mm Hg Vac) Inches of mercury — Vacuum (in Hg Vac)... 

Inches of mercury — Absolute (in Hg Abs) Millimeters of mercury — Absolute (mm Hg Abs) Pounds per square inch — Absolute (psia)... 

D-1160 is run under vacuum (one millimeter of mercury). The results are converted to atmospheric pressure, using standard cor relations. Some newer apparatuses have built-in software that performs the conversion automatically. D-1160 is limited to a maximum EP temperature of about 1,000°F (538°C) at atmospheric pressure. Above this temperature, the sample begins to crack thermally. 

Because of the way in which gas pressure is measured, it is often expressed in millimeters of mercury (mm Hg). Thus we might say that the atmospheric pressure on a certain day is 772 mm Hg. This means that the pressure of the air is equal to that exerted by a column of mercury 772 mm (30.4 in) high. 

The pressure exerted by a column of mercury depends on its density, which varies slightly with temperature. To get around this ambiguity, the torr was defined to be the pressure exerted by 1 mm of mercury at certain specified conditions, notably 0°C. Over time, the unit torr has become a synonym for millimeter of mercury. Throughout this text, we will use millimeter of mercury rather than torr because the former has a clearer physical meaning. 

The height of the mercury in the system-side column of an open-tube mercury manometer was 10. mm above that of the open side when the atmospheric pressure corresponded to 756 mm of mercury and the temperature was 15°C. What is the pressure inside the apparatus in millimeters of mercury and in pascals ... 

Self-Test 4.2B What is the pressure in millimeters of mercury inside a system when a closed mercury manometer shows a height difference of 10. cm at 15°C ... 

---