Mercury pressure measurements

Industrial and Control Instruments. Mercury is used in many industrial and medical instmments to measure or control reactions and equipment functions, including thermometers, manometers (flow meters), barometers and other pressure-sensing devices, gauges, valves, seals, and navigational devices (see Pressure measurements Process control Temperature measurement). Whereas mercury fever thermometers are being replaced by... 

Pressure reducing valves should be of steel constmction, designed for minimum and maximum operation conditions. Pressure gauges should be of ak-kon constmction. Pressure rehef valves should be of the spring-loaded type. Rupture disks may be used only as auxkiary equipment. Differential pressure measurements using mercury manometers should be avoided in ammonia service. 

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. 

The following procedure is recommended. The sample solution is de-aerated, then, with the tip of the capillary in the air, the mercury pressure is raised at least 10 cm above the previously found equilibrium height, the capillary is inserted into the cell, and the mercury level is finally adjusted to the desired value. After completion of the measurements the capillary is withdrawn from the cell and washed thoroughly with a stream of water from a wash bottle while the mercury is still issuing from the tip and is being collected in a microbeaker. 

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. 

To reduce deviations in blood pressure measurement in the clinic, the patient and clinician should not talk during blood pressure readings. The measurement arm is supported and positioned at heart level with the blood pressure cuff encircling at least 80% of arm circumference. If a mercury or aneroid device is used, then the palpatory method must be used first to estimate the systolic blood pressure.18 If an automated device is used, this is not necessary. After the patient s cuff is inflated above the systolic pressure, the mercury column should drop at a rate of 2 to 3 mm per second. A stethoscope placed over the brachial artery in the antecubital fossa identifies the first and last audible Korotkoff sounds, which should be taken as systolic and diastolic pressure, respectively. A minimum of two readings at least 1 minute apart are then averaged. If measurements... 

An orifice with a 1 in. diameter hole is installed in a 2 in. sch 40 pipeline carrying SAE 10 lube oil at 100°F. The pipe section where the orifice is installed is vertical, with the flow being upward. Pipe taps are used, which are connected to a manometer containing mercury to measure the pressure drop. If the manometer reading is 3 in., what is the flow rate of the oil, in gpm ... 

Balson, E. W. (1947) Studies in vapour pressure measurement. Part in. An effusion manometer sensitive to 5 x 10 6 millimetres of mercury vapour pressure of D.D.T. and other slightly volatile substances. Trans. Farad. Soc. 43, 54—60. 

Relation 9.77 is usually called the Washburn equation [55,237], One should consider it as a special case of the fundamental Young-Laplace equation [3,9-11], Washburn was the first to propose the use of mercury for measurements of porosity. Now, it is a common method [3,8,53-55] of psd measurements for a range of sizes from several hundreds of microns to 3 to 6 nm. The lower limit is determined by the maximum pressure, which is applied in a mercury porosimeter the limiting size of rWl = 3 nm is achieved under PHg = 4000 bar. The measurements are carried out after vacuum treatment of a sample and filling the gaps between pieces of solid with mercury. Further, the hydraulic system of a device performs the gradual increase of PHg, and the appropriate intmsion of mercury in pores of the decreasing size occurs. 

There are two types of U-tube manometer the open-ended manometer is obviously inconvenient for low pressure measurements if an organic liquid of low vapour pressure is used instead of mercury. The small U-tube with one sealed end is the most common and convenient form. The sealed end is closed whilst the tube is under a good vacuum (p < 10 Torr) and, provided that precautions are taken to preserve the vacuum, the pressure in this reference space (the Torricelli vacuum) can be neglected when calculating the measured pressure. 

Helium and mercury densities were determined on the 6-8 mesh fraction. The larger mesh size was used to avoid the possibility that mercury would not penetrate the space between particles in the mercury density measurements. The coal was placed in a calibrated density tube, evacuated at room temperature for one hour, and then heated at 100°C. in vacuo for 2 hours. The weight of the coal after this treatment was used to compute the densities. Helium densities were determined at 30°C. by the method of Rossman and Smith (11). Mercury densities were determined by admitting mercury at an absolute pressure of 1140 torr to the coal sample after evacuation, following the helium density measurement. 

Conversion factors for various pressure units and flow units are given in Table VI.1. Table VI.2 lists values of the ratio d,/do (the density of mercury at a temperature t divided by the density of mercury at 0°C) over the temperature range 0-99°C. Capillary depression corrections for mercury in glass tubes are given in Table VI.3. The complete set of corrections for a pressure measurement is made as follows ... 

Fundamental knowledge about the behavior of charged surfaces comes from experiments with mercury. How can an electrocapillarity curve of mercury be measured A usual arrangement, the so-called dropping mercury electrode, is shown in Fig. 5.2 [70], A capillary filled with mercury and a counter electrode are placed into an electrolyte solution. A voltage is applied between both. The surface tension of mercury is determined by the maximum bubble pressure method. Mercury is thereby pressed into the electrolyte solution under constant pressure P. The number of drops per unit time is measured as a function of the applied voltage. 

To apply equation (3) for calculation of the equilibrium constant K waves Ia and ic must both be limited by diffusion. To prove this the current is measured under conditions when it is 15% or less of the total limiting current and its dependence on the mercury pressure is followed. A diffusion current must, under these conditions, show a linear dependence on the square root of the height of the mercury column. Whenever possible, polarographic dissociation curves should be compared with data on dissociation obtained by other methods, e.g. potentiometry, N.M.R. or spectrophotometry. In the latter case it is important to show that the species responsible for a given polarographic wave is identical with that responsible for the observed absorption peak. 

Which type of pressure measuring device uses a column of mercury ... 

The beauty of the mercury manometer is that you can assess its accuracy by simply looking at it. If the mercury meniscus is at zero when there is no pressure in the cuff and the column moves smoothly with inflation and deflation it is accurate and can be used as the gold standard for pressure measurement. All other devices must be calibrated against a... 

For laboratory-scale modification, distinction has to be made between static and dynamic adsorption procedures. In a static procedure, the substrate is contacted with a known volume of gas at a well-defined pressure. The modifying gas may be stationary or circulating in a closed loop. Modification in a static gas adsorption apparatus allows the careful control of all reaction parameters. Temperature and pressure can be controlled and easily measured. Adsorption kinetics may be determined by following the pressure as a function of the reaction time. Figure 8.13 displays a volumetric adsorption apparatus, in which mercury is used, as a means to change the internal volume and for pressure measurement. 

Standard high-vacuum techniques8-7 are used since some of the reagents and products are volatile, pyrophoric, and/or toxic. Since F2PI and F2PBr attack mercury, a mercury float-valve system cannot be used, and manometers should be protected with stopcocks until pressure measurements are to be made. ... 

Pressure in the volumetric apparatus was measured by a McLeod gage and by a wide-bore (30-mm.) mercury manometer. Pressures measured with the McLeod gage were corrected for capillary depression of the mercury meniscus. Pressure in the gravimetric apparatus was controlled by regulation of the tempera-... 

Pressure Measurements The term mm Hg used with respect to pressure within an apparatus, or atmospheric pressure, refers to the use of a suitable manometer or barometer calibrated in terms of the pressure exerted by a column of mercury of the stated height. 

The pressure measured by this manometer system is the absolute pressure because the reference (pressure above the mercury) in the vertical tube is a vacuum. 

By the time you finish reading this book, you ll have a very good grasp of just what blood pressure and hypertension are. You ll learn that the ideal level is about 115/75. Those numbers reflect blood pressure measured in millimeters of mercury either in your doctor s office or with a home unit. The top number, the systolic, is the pressure of the major and minor arteries at the time the heart beats. The lower number, the diastolic, is a measurement of pressure while the heart is at rest. 

Transmission electron microscopy (TEM) observations, nitrogen adsorption-desorption and mercury porosimetry measurements indicated that increasing EDAS/TEOS ratio results in (a) a decrease of the building block particle size, (b) an increase of the specific surface area (S ), (c) an increase of mesopore volume determined at saturation pressure of N (Vp) and a decrease of the total pore volume (V,) (d) a general shift of the pore size distribution towards smaller pores, (e) an increase of the pressure of transition (P,), above which mercury can intrude the sample without destroying the pore structure [1-3]. To explain this behaviour... 

Each testing laboratory performed four measurements of each sample Bl, Gl, B2, G2, B3 and G3. The mercury intrusion measurements were carried out according to DIN 66133 [9]. Additionally, the bulk density was determined pycnometrically by mercury immediately after the low-pressure measurement. The experiments were performed according to routine procedures of the participating laboratories and instructions of the test coordinator. 

In mercury penetration measurements, mercury is forced under various pressures into the pores of the material. Due to the large contact angle (0) of mercury in contact with most materials, the pressure required to force mercury into the pores can be expressed as a function of the pore radius ... 

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