Bubbler manometer

Fig. 9.5. Apparatus for a tensimetric titration. The bubbler manometer is used to measure aliquots of the reactive gas. 

Fig. 7.2. A versatile bubbler manometer. The bubbler manometer Is securely mounted by the reservoir and attached to the vacuum system. It is then easily filled by the following process. The level of the bottom end of the vertical tube dipping into the reservoir is marked on the outside of the reservoir. Next, a calculated amount of mercury is filtered into the reservoir. With the valve between the two arms open, a vacuum is slowly drawn on the manometer. The mercury level must not drop below the mark on the reservoir, or else bubbles will enter the vertical tube and shoot mercury through the vacuum system. If the mercury level in the reservoir comes close to the mark, the manometer is brought up to atmospheric pressure and more mercury is added. When the proper amount of mercury is present in the fully evacuated manometer, the mercury level should be about 10 mm above the mark on the reservoir, and the upper meniscus should be in a region of the manometer suitable for measurement, as illustrated. Once the manometer is properly filled and evacuated, the valve is closed to isolate the reference arm at high vacuum.

The sequence of operations (assuming the initial solid is not air sensitive) would be to load the sample tube with a weighed amount of reactive compound and the stirrer, to attach this tube to the tensimeter, and to pump out the air in the tensimeter. The sample tube is cooled to liquid nitrogen temperature and solvent is then condensed into the sample tube from a storage container on the vacuum line. The main valve on the tensimeter is then closed and the sample container allowed to warm so the solid may dissolve, perhaps with the aid of the stirrer. A constant temperature slush bath is next placed around the sample tube as illustrated in Fig. 9.5 and an initial pressure measurement is taken on the manometer. Next, the first alloquot of the reactive gas is transferred from a storage bulb elsewhere on the vacuum system into the calibrated bulb using the techniques outlined in Section 5.3.G (the bubbler manometer shown in Fig. 9.5 is used for the pressure determination required for this process). This gas is con-... 

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). 

If the high vacuum working station is used the bubbler/manometer may be accurately used as a manometer since the pools of Hg are interconnected (see Figure 1). 

Caution. It is advisable to incorporate a bubbler manometer into the vacuum line to offset any difficulties arising from sudden expansion of the volatile material. 

The new data given for the lower alkanes and alkenes, the three methylamines, ammonia, bromomethane, and chloroethane, together with my previously reported data on hydrogen sulfide, dimethyl ether, chloromethane, and sulfur dioxide, have been obtained by a bubbler-manometer procedure which is fully described. Not only are these data of significance in many chemical processes, but they have also been vital to the development of the overall essential pattern covering all gases. 

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.

Cold traps must be used if mercury is used in your system (such as manometers, diffusion pumps, bubblers, or McLeod gauges) and if your mechanical pump has cast aluminum parts. Mercury will amalgamate with aluminum and destroy a pump. Even if your mechanical pump does not have aluminum parts, the mercury may form a reservoir in the bottom of the mechanical pump, which may cause a noticeable decrease in pumping speed and effectiveness. Aside from a cold trap between the McLeod gauge and the system, place a film of low vapor pressure oil in the McLeod gauge storage bulb. This oil will limit the amount of mercury vapor entering the system that makes its way to the mechanical pump. In addition, an oil layer should be placed on the mercury surface in bubblers and other mercury-filled components. 

During this operation, stopcock a is closed and stopcock b is opened to the outside. Stopcock a is never opened to the outside unless the manometer indicates an excessive build-up of pressure in the system due to clogging in the traps. To prevent the mercury in the manometer from reacting with the gases in the system, a few milliliters of anhydrous carbon tetrachloride is placed on the surface of the mercury, as indicated in the diagram. A mercury bubbler may be attached to the open end of the manometer to serve as a safety blowout. 

Figure 9. Side view of a manometer and Nujol bubbler of the vacuum line.

The accurate measurement of pressure requires use of a manometer. The bubbler is less accurate since the level of the pool of mercury at the base varies slightly as the column height varies. 

Fig. 2. Diagram of the bubbler-tube (B.T.) and manometer (M) assembly. T1-T5 are taps HV is a high-vacuum pump WTP is a water-tap pump Ci is a cone to fit at V above T2 D (a dewar) is the constant-temperature bath.

By means of the bubbler-tube-manometer procedure/ I determine the mass of n-butane absorbed by a known mass of a liquid S at fC and Pbuh> the pressure of gaseous n-butane. The apparatus constrains me to measure only the total pressure, which is made up of Pbuh and ps- To allow for ps is a protracted operation, as I shall show later but to build up the essential pattern of data for my present purpose, I use liquids which have a low-enough ps to be neglected. Therefore, I take the observed total pressure to be essentially equal to Pbuh- In the conventional terminology the expression partial pressure is used, i.e., Pbuh and ps would be called partial pressures. I do not like this, and see no need for it. To me Pbuh is the pressure due to n-butane, and ps that due to S the measured pressure is Pbuh + Ps ... 

---