Manometers: simple mercury

A simple mercury manometer has already been described (see Fig. II, 19, 2). Another type that is frequently employed is the U-tube manometer illustrated in Fig. 7/,2<3,1. It consists of a U-tube filled with mercury and mounted on a wooden stand. The scale B, graduated in... 

The first range can be adequately handled with a simple mercury manometer. ( 1 ) However, absolute pressure transducers, such as the Baratron 200 Series manufactured by MKS Instruments, offer much greater accuracy over a wider pressure range.(8) If accurate and precise pressure measurements are commonly conducted on the vacuum line, the transducers are the sensors of choice. If not, mercury manometers are the economical alternative. 

The vapor-pressure measurements were carried out with hexa sublimed in high vacuum. Pressures of 10 to 10 mm. Hg, corresponding to 20 to 85°, were measured with a quartz filament manometer 2, S). At temperatures of 120 to 210° a simple mercury manometer was used, and the vapor pressures were obtained by extrapolating the pressure-time curves plotted in Fig. 1 to time zero. 

This volumetric method makes no assumptions about particle shape, and indeed is not greatly affected by particle shape except in extreme cases like flaky materials, such as some clays. To count the number of particles in a known volume of suspension, such as for particulate contamination studies or for a blood cell count, the sample volume is accurately metered by means of a calibrated "manometer". Figure 1 illustrates the original, simple, mercury siphon and metering system. 

Wafer flowing at 1500 cm3/s in a 50 mm diameter pipe is metered by means of a simple orifice of diameter 25 nnn. If the coefficient of discharge of the meter is 0.62, what will be the reading on a mercury-underwater manometer connected to the meter ... 

A manometer is similar to a barometer, but in a manometer gases exert pressure on both liquid surfaces. Consequently, a manometer measures the difference in pressures exerted by two gases. A simple manometer, shown in Figure 5 3, is a U-shaped glass tube containing mercuiy. One side of the tube is exposed to the atmosphere and the other to a gas whose pressure we want to measure, hi Figure 5-3. the pressure exerted by the atmosphere is less than the pressure exerted by the gas in the bulb. The difference in heights of mercury (Ah, in mm) between the two sides of the manometer depends on the difference in the pressures. 

A. Mercury Manometers for Routine Work. The pressure-volume-temperature measurement of gases is the backbone of quantitative chemical vacuum line work. For these measurements an error of a few percent is frequently sufficient and may be attained by a simple U-manometer attached to a calibrated volume and read with ah inexpensive cathetometer. 

F. Cleaning Mercury. When it is received, mercury is generally covered with a scum which can foul manometers, Toepler pumps, and similar apparatus. This scum can be removed by a simple filtration procedure. A standard filter paper is folded to fit an appropriate funnel and a pinhole is pierced in the tip. The hole must be large enough so that mercury droplets will run through, but small enough so that the last drop and its associated scum are retained by its surface tension. This type of filtration process is routinely performed before filling an apparatus. 

If gas is to be delivered to a reaction flask which has an unobstructed outlet, a simple flow control valve on the high-pressure cylinder will provide adequate regulation of the gas delivery. In this case a needle valve is attached to the cylinder, or to a pressure regulator which in turn is attached to the cylinder. It also is possible to deliver gas to a closed system, such as a vacuum line, with a flow control valve. In this case the pressure within the apparatus must be carefully monitored by means of a manometer and the system should also be equipped with a means of pressure relief, such as a mercury bubbler manometer (Fig. 7.2). 

Gas pressure inside a container is often measured using an open-end manometer, a simple instrument similar in principle to the mercury barometer. As shown in Figure 9.4, an open-end manometer consists of a U-tube filled with mercury, with one end connected to a gas-filled container and the other end open to the... 

For example, suppose we measure the pressure with a simple U-tube manometer filled with mercury. Suppose the manometer is set up with a 1 cm diameter tube exposed to 1 atm nitrogen at room temperature (298K) on one end, and exposed to vacuum on the other end (which of course will be approximately 760 mm higher). The observed pressure can only change when the column of mercury has time to flow the device (and any other measuring device) will have a nonzero response time. A reasonable estimate for the response time of a manometer might be 0.1 seconds, so the amount the pressure will appear to fluctuate will depend on the number of collisions with the top of the column in that time. 

Mercury Manometers. A U-tube manometer filled with mercury is simple to construct, requires no calibration, and operates over a wide pressure range. It is now less frequently used due to concerns about safety hazards associated with mercury (see Appendix C) and its slow visual readout. However, it is a historically important device and it is directly related to barometers, which are discussed in Chapter XIX. 

A simple manometer, a device for measuring the pressure of a gas in a container, The pressure of the gas is given by h (the difference in mercury levels) in units of torr (equivalent to mm Hg). (a) Gas pressure = atmospheric pressure - h. (b) Gas pressure = atmospheric pressure + h. 

Since these compounds are extremely reactive toward moisture and oxygen, the equipment used to handle them will be discussed briefly. (A high degree of experimental skill and extreme care are required for safe manipulation of these compounds ) A simple vacuum line, consisting of a manifold equipped with a mercury blowout manometer, a gas inlet tube, and several standard-taper joints, is employed. A worthwhile introduction to the use of vacuum-line techniques in synthetic chemistry is given by Jolly and by Sanderson. The sublimation apparatus shown in Fig. 2 and the vacuum filtration apparatus and... 

A simple apparatus used by Regnault and by Magnus for measuring small vapour pressures, which is still applied, consisted (Fig. 2.VIII J) of a siphon tube ab containing mercury and air-free liquid communicating with a mercury manometer c open at the other side to the air. The limb a was first filled with mercury and some of the liquid introduced above it... 

A simple apparatus, the tensimeter (Fig. 8.VIII J),i consists of a U-shaped manometer containing olive oil, paraffin oil, tetralin, bromonaphthalene, or other suitable liquid in which the vapour is insoluble (mercury may have to be used, but on account of its high density is less accurate), connected through... 

It is very important to be able to measure the pressure in a vacuum system, particularly when carrying out a distillation. For low vacuum measurement a simple manometer, such as that shown in Fig. 8.3a, is commonly used and the pressure is taken by subtracting the heights of the mercury levels. Dial gauges are also useful for in-line measurements and they are particularly valuable when used with rotary evaporators. For high vacuum... 

Several types of manometers are conveniently used. A simple U-tube manometer may be purchased with a sliding scale which may be moved to measure the distance between the two arms. The disadvantage of this type is that it is relatively difficult to fill, for in order to avoid getting an air bubble at the top of the U tube, which may make the pre.ssure readings very inaccurate, it is necessary to boil the mercury under reduced pressure while it is being added. 

A convenient arrangement of the manometer and the connections between the pump and the receiver is represented in Fig. 12. A number of forms of manometers are used to register the pressure inside the apparatus. A simple form which can be readily made from a supply of mercury, a meter-stick, and a piece of glass tubing is illustrated in the figure. In order to determine the pressure in the apparatus the readings on the scale opposite the levels of the mercury in the manometer are subtracted, and this difference is subtracted from the height of the barometer. 

A simple U-tube manometer is installed across an orifice meter. The manometer is filled with mercury (specific gravity 13.6). and the liquid above the mercury is carbon tetrachloride (specific gravity 1.6). The manometer reads 200 mm. What is the pressure difference over the manometer in newtons per square meter ... 

A simple technique was used by Wendlandt (113) to record the changes of pressure in a system. The apparatus, which is illustrated in Figure S.46. consisted of a vacuum system whose pressure is determined by a mercury-filled manometer tube containing a resistance wire. This wire is connected as one... 

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