Manometers

The term manometer refers to any pressure-measuring device. 

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There are a number of relatively simple experiments with soap films that illustrate beautifully some of the implications of the Young-Laplace equation. Two of these have already been mentioned. Neglecting gravitational effects, a film stretched across a frame as in Fig. II-1 will be planar because the pressure is the same as both sides of the film. The experiment depicted in Fig. II-2 illustrates the relation between the pressure inside a spherical soap bubble and its radius of curvature by attaching a manometer, AP could be measured directly. 

When constructing a manometer of the type shown in Fig. 12(c), it is impor tant to apply a very high vacuum (e.g., with a Hy-Vac pump) to the manometer while the mercury in the left-hand (sealed) limb is heated until it boils unless this is done, traces of air will remain in this limb and cause inaccurate readings. During a distillation, the tap I should be kept closed except when a pressure reading is being taken if it is left open indefinitely, a sudden default by the distillation apparatus or by the pump may cause the mercury in the sealed limb of G to fly back and fracture the top of the limb. 

Other similar types of manometer, usually reading over a range of about 10-60 mm., are available in many laboratories. 

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 action of the manostat may be explained with the aid of Fig. II, 23, 6. Mercury is introduced into the container until the disc of the float just makes contact with the oriflce, when the pressure is equalised inside and outside the float. The device is connected to the pump and to the system by way of a large reservoir and a manometer. With the stopcock open, the pressure in the system is reduced by way of a by-pass between the pump and the system until the desired value as read on the manometer is reached, then both the stopcock and by-pass are... 

Apparatus 3-1 rOund-bottomed flask, connected through vacuum tubes to a mercury manometer and a cylinder with oxygen (Fig. 6). 

Monomer emulsions ate prepared in separate stainless steel emulsification tanks that are usually equipped with a turbine agitator, manometer level gage, cooling cods, a sprayer inert gas, temperature recorder, mpture disk, flame arrester, and various nossles for charging the ingredients. Monomer emulsions are commonly fed continuously to the reactor throughout the polymerisation. 

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... 

After World War II, analytical methods for amino acids were improved and new methods were iatroduced. The first was microbial assay usiag lactic acid bacteria which require all of the regular amino acids for growth. Manometric determiaation (by use of a Warburg manometer) of CO2 Hberated by the... 

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. 

Liquid Manometers. Liquid manometers were used extensively by scientists in the seventeenth through the early twentieth centuries to measure pressure. The practice of expressing pressure as a certain height of Hquid evolved from this usage. The typical Hquid manometer consists of a cyclindrical glass U-tube partially fiUed with Hquid. One end is coimected to the process the other can be either open or closed (Fig. 1). 

Fig. 1. U-Tube manometer where h is the height of the ( ) Hquid employed (a) open (b) closed.

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