Vacuum manometer

Introduction of Obermiiller Stability Test which consists of heating 1 to 2g NC in a small tube under vacuum at 135—140° and measuring the pressure of evolved gas by vacuum manometer (Ref 38a, pp 87—88) 1904—1905. 2,4,6-Trinitroanisole or Methyl Picrate was patented for use in smokeless proplnts in mixt with an equal amt of Pyrocellulose (Vol... 

All these complications can be avoided when making field measurements by using the vacuum manometer shown in Fig. 6.6. The difference between the two mercury levels is the absolutely correct, inches of mercury absolute pressure, or millimeters of mercury (mm Hg). 

Fine-reading vacuum manometer (Holland and Merten)... 

The key tool in troubleshooting flash-zone pressure problems is a vacuum-tower pressure survey. The time to initiate this survey is just after start-up when the trays, demister, and ejector system are clean and in good condition. Pressures are best measured with a portable mercury-filled vacuum manometer. Using a vacuum pressure gauge will reduce the accuracy of observed pressure drops. Relying on permanently installed gauges for pressure drop data will not give reliable results. 

All these complications can be avoided when making field measurements by using the vacuum manometer shown in Fig. 10.6. 

The specific gravity of baby oil is about 0.9 s.g. The specific gravity of mercury is 13.6. Mercury is 15 times denser than baby oil. Referring to Fig. 23.8, divide the 150 mm of elevation difference in the manometer legs by 15 to determine that the vacuum is 10 mm Hg. For vacuums above 40 mm Hg, the oil-filled vacuum manometer is not practical, as it would be about 30 inches in overall length. 

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. 

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

Gauges. Because there is no way to measure and/or distinguish molecular vacuum environment except in terms of its use, readings related to gas-phase concentration ate provided by diaphragm, McCleod, thermocouple, Pitani gauges, and hot and cold cathode ionization gauges (manometers). 

Fig. 10. The Groth ZG 5 centrifuge. R, rotor R, stationary shaft T, Teflon seal K, K, chambers for gas scoops S, S2, scoops V, gas supply M, manometer Z, Z2, tapping points for enriched and depleted gas P, P2, vacuum chambers E, electromagnet for eddy current heating Tb, Tb2, temperature measuring devices K, cooling coil and D, D2, labyrinth seals.

If the pump is a filter pump off a high-pressure water supply, its performance will be limited by the temperature of the water because the vapour pressure of water at 10°, 15°, 20° and 25° is 9.2, 12.8, 17.5 and 23.8 mm Hg respectively. The pressure can be measured with an ordinary manometer. For vacuums in the range lO" mm Hg to 10 mm Hg, rotary mechanical pumps (oil pumps) are used and the pressure can be measured with a Vacustat McLeod type gauge. If still higher vacuums are required, for example for high vacuum sublimations, a mercury diffusion pump is suitable. Such a pump can provide a vacuum up to 10" mm Hg. For better efficiencies, the pump can be backed up by a mechanical pump. In all cases, the mercury pump is connected to the distillation apparatus through several traps to remove mercury vapours. These traps may operate by chemical action, for example the use of sodium hydroxide pellets to react with acids, or by condensation, in which case empty tubes cooled in solid carbon dioxide-ethanol or liquid nitrogen (contained in wide-mouthed Dewar flasks) are used. 

A flow sheet of the process, as given by Ur banski (Ref 75, his Fig 53), is shown below According to Urbanski To start the nitration, current from the switch (18) is applied to the electromagnet (6), which closes the air inlet to the injector. Mixed acid is admitted by opening the valve under the acid rotameter (4). The injector now comes into operation. The manometer (13) must show full vacuum. The needle valve (7) is then opened and the vacuum adjusted to about 300mm Hg. The glycerine-glycol mixture is sucked in thru the rotameter (3) to the injector from (2)... 

Although a pressure gauge is more commonly used to measure the pressure inside a laboratory vessel, a manometer is sometimes used (Fig. 4.5). It consists of a U-shaped tube connected to the experimental system. The other end of the tube may be either open to the atmosphere or sealed. For an open-tube manometer (like that shown in Fig. 4.5a), the pressure in the system is equal to that of the atmosphere when the levels of the liquid in each arm of the U-tube are the same. If the level of mercury on the system side of an open manometer is above that of the atmosphere side, the pressure in the system is lower than the atmospheric pressure. In a closed-tube manometer (like that shown in Fig. 4.5b), one side is connected to a closed flask (the system) and the other side is vacuum. The difference in heights of the two columns is proportional to the pressure in the system. 

FIGURE 4.5 (a) An open-tube manometer. The pressure inside the apparatus to which the narrow horizontal tube is connected pushes against the external pressure. In this instance, the pressure inside the system is lower than the atmospheric pressure by an amount proportional to the difference in heights of the liquid in the two arms, (b) A closed-tube manometer. The pressure in the adjoining apparatus is proportional to the difference in heights of the liquid in the two arms. The space inside the closed end is a vacuum. 

A reaction is performed in a vessel attached to a closed-tube manometer. Before the reaction, the levels of mercury in the two sides of the manometer were at the same height. As the reaction proceeds, a gas is produced. At the end of the reaction, the height of the mercury column on the vacuum side of the manometer has risen 30.74 cm and the height on the side of the manometer connected to the flask has fallen by the same amount. What is the pressure in the apparatus at the end of the reaction expressed in (a) Torr (b) atm (c) Pa (d) bar ... 

In order to carry out a distillation, the apparatus is completely assembled, the water pump turned on to its maximum capacity, and the screw clip on the capillary tube in the Claisen flask adjusted so that a gentle stream of air bubbles through the liquid (see Section 11,19 for details of the preparation of the capillary tube). The barometric pressiue is read, and if the resulting vacuum determined from the reading on the manometer is satisfactory (as estimated from the temperature of the tap water), the flask may be heated in an air (Fig. II,... 

Figure 4 Schematic of an oxygen uptake device. 1, sample 2, electrical oven 3, Hg manometer 4, intermediate vessel for pressure adjustment 5, drying vessel 6, control thermometer 7, outlet to vacuum pump and 8, inlet for gas feeding. Reproduced with permission from Zaharescu [10]. Springer 2001.

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