Pressure of Mercury

To find the correct temperature on a thermometer reading 80°C and that shows a reading of — 0.30°C in a melting ice/water mixture and 99.0°C in steam at 760 mm pressure of mercury ... 

Until the advent of lasers the most intense monochromatic sources available were atomic emission sources from which an intense, discrete line in the visible or near-ultraviolet region was isolated by optical filtering if necessary. The most often used source of this kind was the mercury discharge lamp operating at the vapour pressure of mercury. Three of the most intense lines are at 253.7 nm (near-ultraviolet), 404.7 nm and 435.7 nm (both in the visible region). Although the line width is typically small the narrowest has a width of about 0.2 cm, which places a limit on the resolution which can be achieved. 

The vapor pressure of mercury, P, also behaves kregulatly but may be obtained for temperatures from 0—150 °C by the following ... 

A mixture of 20 g (0.1 mol) of 1 -azaphenothiazine, 4.3 g (0.11 mol) of sodamide and 300 ml of dry toluene is stirred and refluxed for eight hours. A slow stream of dry nitrogen gas is used to sweep out the ammonia as formed. The mixture is cooled and 110 ml of a 1 M solution of 3-dimethylaminopropyl chloride in toluene is added dropwise, with stirring. Subsequently, the mixture is stirred and refluxed for fifteen hours, cooled, and concentrated in vacuo. The viscous residue is refluxed with 500 ml of chloroform and filtered hot. The chloroform filtrate is treated with activated charcoal and again filtered. The filtrate is concentrated and the residue distilled to give about 19.B g (69% yield) of product, an oil distilling at about 195 C to 19B°C (under 0.5 mm pressure of mercury). 

NOTE The standard atmospheric pressure of mercury (Hg) is 760 mm Hg (29.92 in) at 0 °C. Thus, ignoring barometric or temperature differences, it can be seen that the condenser back-pressure is usually in the range of 29 to 29.92 inches down to 26 inches, which equals 1 to 4 in mercury absolute (3.4-13.6 kPa). 

It may be noted that the pressure measuring devices (a) to (e) all measure a pressure difference AP(— Pj — P ). In the case of the Bourdon gauge (0, the pressure indicated is the difference between that communicated by the system to the tube and the external (ambient) pressure, and this is usually referred to as the gauge pressure. It is then necessary to add on the ambient pressure in order to obtain the (absolute) pressure. Even the mercury barometer measures, not atmospheric pressure, but the difference between atmospheric pressure and the vapour pressure of mercury which, of course, is negligible. Gauge pressures are not. however, used in the SI System of units. 

A bottle of mercury at 25°C was left unstoppered in a chemical supply room measuring 3.0 m by 3.0 m by 2.5 m. What mass of mercury vapor would be present if the air became saturated with it The vapor pressure of mercury at 25°C is 0.227 Pa. 

The pore shape affects the pressure of mercury intrusion in ways not contemplated by the usual Washbum-Laplace or Kloubek-Rigby-Edler models. These models have been developed for cylindrical pores and correctly account for the penetration of mercury in the cylindrical pores of MCM-41. The uneven surface of the cylindrical pores of SBA-15 is responsible for a significant increase of the pressure of mercury intrusion and, thereby, for a corresponding underevaluation of the pore size if the classical pressure-size correlations are applied. 

From Appendix E, the molar enthalpy of vaporization of mercury at the normal boiling point is 58.6 kJ/mol. Using the Clausius-Clapeyron equation to find the vapor pressure of mercury at 25°C, we have... 

The data in Table 8.4 [4] represent the vapor pressure of mercury as a function of temperature. Plot In P as a function of 1/T to a scale consistent with the precision of the data. If the resultant plot is linear, calculate AH Iz from the slope obtained by a least-squares fit to the line. If the plot is curved, use a numerical differentiation procedure to obtain the value of AHmjZ as a function of T, and calculate ACpm- See Appendix A for methods. 

TABLE 8.4. Vapor pressure of Mercury as a Function of Temperature... 

In addition to these lines is one measured by Wendt a 3983 A. The structure of this line has been measured by no other observers and as Ruarke points out, his description of source used is rather meager. It was found that this line appeared very faintly in the ordinary Cooper-Hewit arc. In an arc of the type shown in the figure with a quartz window, Q, through which the arc was observed, it was found that the line 3983 A appeared strongly at higher pressures of mercury vapor and at voltages above 25 volts. Since this line has been classified as due to a P — F... 

Mercury diffusion pumps are normally constructed from quartz or heat-resistant glass and are therefore a possible source of hazard should they Sreak, especially whilst they are hot. However, during over 40 years of working with such pumps, the author has neither experienced nor heard of such an accident. The major real disadvantage of mercury pumps is the relatively high vapour pressure of mercury at room temperature (ca. 10 Torr), which makes its necesssary to ensure that the cold traps prevent efficiently the mercury vapour from diffusing forward into the line. 

Fig. 40. Partial pressure of mercury in atmospheres as a function of 103 times the reciprocal absolute temperature along the three-phase curves for the liquids, (Hg . zCd2)yTei The value of z is shown near the bottom, -rich leg of each curve. The circles mark the pressure and temperature where =. ...

Fig. 41. The partial pressure of mercury in atmospheres plotted against 103 times the reciprocal absolute temperature for a traverse across the liquidus surface such that the atom fractions Cd and are always equal. The number near each circle give the atom fraction of mercury in the liquid phase at the pressure and temperature specified by the circle. 

Fig. 42. Partial pressure of mercury in atm along the three-phase curve for the liquid (Hg0 7Cd0 3)JTe1 y is shown as a solid curve. The uppermost line gives the vapor pressure of pure mercury. Each cross along the three-phase curve marks the pressure and temperature where is equal to the value given near that cross. The dashed lines are calculated results for the liquids (Hg0 7Cd0.3),Te, = 0.4,0.5,0.6, and 0.7, for temperatures above the liquidus temperature. The solid symbols are experimental values (Steininger, 1976). Solid circles are for = 0.50 diamonds are for = 0.40.

Fig. 43. Partial pressure of mercury in atmospheres plotted against 103/T for various compositions. Uppermost curve is the calculated result for (Hg0 7Cd0 3)0 0. with the liqui-dus temperature indicated by the open circle. Triangles are experimental results for the same composition. Second highest curve, with the liquidus temperature again indicated by an open circle, is for the composition (Hg07Cd0 3)0 6Te04 and the squares are the experimental values. Lower four lines are the calculated results for various Hg,Te, melts along with the experimental points shown by symbols.

Using data from Table 6.2, calculate the vapor pressure of mercury at 250°C. 

The following table gives the vapor pressure of mercury at various temperatures. Fill in the rest of the table, and use the data to plot curves of Pvap versus T and In Pvap versus 1/T. ... 

Since Kp is defined in units of atmospheres, the vapor pressure of mercury at 25°C is 2.6 X 1CT6 atm (0.0020 mm Hg). Because the vapor pressure is appreciable and mercury is toxic in the lungs, mercury should not be handled without adequate ventilation. 

The normal vapour pressure of mercury at room temperature is many times the CL value of 0.05 mgm 3. 

Standard emf Values for the Cell H2/HCl/AgCl, Ag in Various Aqueous Solutions of Organic Solvents at Various Temperatures Temperature Dependence of the Standard Potential of the Silver Chloride Electrode Standard Electrode Potentials of Electrodes of the First Kind Standard Electrode Potentials of Electrodes of the Second Kind Polarographic Half-Wave Potentials (E1/2) of Inorganic Cations Polarographic E1/2 Ranges (in V vs. SCE) for the Reduction of Benzene Derivatives Vapor Pressure of Mercury... 

The following table provides data on the vapor pressure of mercury, useful for assessing and controlling the hazards associated with use of mercury as an electrode.1... 

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