Vacuum mercury manometer

Above 30 or 40 mm Hg of vacuum, an ordinary digital battery powered vacuum gauge is sufficient. However, only a vacuum mercury manometer is accurate in the 5 to 15 mm Hg range. As long as the mercury was dry, such a gauge gave excellent results. But few of my clients now permit the use of mercury in the field. 

I have developed an alternate method that works almost as well as the vacuum mercury manometer. It s really the same idea (see Fig. 23.8). Fill the closed end of the tubing with baby oil and mineral oil. Make sure you get the last bubble of air out of the closed end of the tubing. Always use fresh oil to prevent moisture... 

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

Figure 1. Diagram of apparatus (M) monomer reservoir (F) flow meter (VG) vacuum gage (mercury manometer) (E) electrode (T) liquid nitrogen trap (P) mechanical pump (V,) needle valve (Vt) stop valve (Vs) pressure control valve (OSC) discharge frequency oscillator (AMP) amplifier (1MC) impedance matching circuit...

Figure 1. Apparatus for the synthesis of borazine. (A) nitrogen supply from tank (B) oil bubbler (C) valve (D) 2-L, three-necked, round-bottomed flask (E) thermometer (F) distilling column (G) vacuum tubing (H) mercury manometer (I) four traps for the collection of the borazine product (J) valve to mechanical vacuum pump.

Mercury manometer (a) Atmospheric pressure in both tubes (b) Gas pressure in flask, and vacuum in righthand tube. 

The mechanical fore pump is a heavy item which sets up considerable vibration. This vibration disrupts the menisci of mercury manometers and is otherwise undesirable. To minimize the transfer of vibrations to the vacuum line, the fore pump generally is mounted on the floor (rather than on the bench of the vacuum rack) and the connection between the fore pump and the vacuum system is made with heavy-walled vacuum tubing or flexible corrugated metal tubing. 

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. 

In the following procedures a standard glass vacuum line with high-vacuum stopcocks (lubricated with Kel-F-90 grease ) is used. Because of the reactivity of many of the compounds with mercury, it is convenient to use a null-point pressure device, such as a Booth-Cromer16 pressure gage or spiral gage. A mercury manometer covered with Kel-F-3 oil can be used. 

Figure 1. Schematic of apparatus A, calibrated variable-volume mercury burette B, reference volume C, main chamber D, mixing pump E, adsorption chamber F, reference chamber G, constant temperature baths H, mercury manometer J, cold-cathode gauge P, Pirani vacuum gauge R, mercury reservoir...

A tensiometer consists of a small porous cup which is inserted into a soil or packing and connected to a suitable mercury manometer. When the porous cup is partly filled with water and the soil in which it is inserted is dry, water will leave the porous cup and cause a slight vacuum. For a given type of porous cup, the amount of decrease in pressure is indicative of the moisture conditions in the soil. Figure 77 shows the essential features of a tensiometer. 

Second only to the mechanical gauge as the easiest device to measure and read a vacuum (and decidedly easiest in construction) is the liquid manometer (see Fig. 7.37). A well-made mercury manometer, kept very clean, can measure vacuums of up to 10 3 torr. This sensitivity can be increased by up to 15 times if a liquid with less density, such as diffusion pump oil, is used. However, diffusion pump oil is far more difficult to keep clean and can require either (a) a very tall (and thereby impractical) column or (b) a manometer of very limited range. In addition, because of the strong surface tension between diffusion pump oil and glass, long waiting periods between readings are required as the oil settles into place. 

Mercury Manometer. An open-end U-tube mercury manometer, known historically as the Torricelli barometer, can typically be read to 0.05 mmHg, but should be corrected for the capillary depression of mercury in glass and for residual gases in the "vacuum" above the column these two small effects are usually corrected for by the manufacturer s scale next to the column. The isoteniscope is just a fancy term for a U-tube of the Torricelli type, containing a liquid, which measures pressure differences by different heights of the liquid in the two arms, one open to the system under study, the other open to air. 

Moderate-Temperature Reaction. Gas-kinetics apparatus as shown in Fig. 2, including vacuum line with greaseless stopcocks, sample reservoir bulb, reaction vessel, heated mercury manometer regulated oil bath thermometer 500-mL beaker 1-qt Dewar stopwatch or other timer. 

Vacuum Absolute Water Pump Mercury Manometer Manometer... 

The standard Pyrex vacuum line used in these syntheses was equipped with glass stopcocks and mercury manometers covered with Kel-F oil. 

The pressure of gas being pulled though a line by a vacuum pump is measured with an open-end mercury manometer. A reading of -2 in. is obtained. TOat is the gas gauge pressure in inches of mercury What is the absolute pressure if Paim = 30 in. Hg ... 

HF is supplied in steel compressed-gas cylinders. Because the boiling point of HF is 19 °C, most of the HF in the cylinder is liquid, and the pressure is low (about SOOTorr). When HF cylinders are stored for a long time, pressure in the cylinders can build up due to reaction of HF with iron to form hydrogen. Newly purchased cylinders have been received with high pressure open such cylinders very cautiously the first time. If there is high pressure in the cylinder, mercury in the vacuum-line manometer can be blown out of the top and scattered about the hood. ... 

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