Gas storage bulbs

The product, which is about 90% bicyclobutane and 10% cyclobutene, is sufficiently pure for most purposes. The purity of the product can be determined by gas chromatography analysis at room temperature, using a 275-cm.-long column containing 20% /3,/3 -oxydipropionitrile on Chromosorb W (45/60). The retention times are 2.7 and 3.8 minutes for cyclobutene and bicyclobutane, respectively. Bicyclobutane (b.p. 8°) can be stored temporarily in the gas storage bulb as a liquid in a dry ice-acetone bath or for longer periods of time in an ampoule, sealed under vacuum, and stored in a freezer. 

The clean, dry, calibrated bulb is attached to a vacuum system, such as site A on the line illustrated in Fig. 5.2, and evacuated to 10-3 torr or lower. Gas may be admitted to the calibrated bulb by isolating the working manifold from vacuum and opening the stopcocks and valves leading to one of the upper gas storage bulbs, C, while the pressure is monitored by manometer D. When the desired pressure is reached, the valve on the storage bulb is turned off, pressure and temperature measurements are made, and then the stopcock on the calibrated bulb is turned off. At this stage we know the pressure, temperature, and volume of the gas in the calibrated bulb, which permits the calculation of the number of moles via the ideal gas equation. 

The manifold is most commonly used for the transfer of a gas from one receiver to another and to measure the quantity of gas which is transferred. The latter use depends on a knowledge of the volume of the manifold. The volume is determined by attaching a gas-storage bulb (Fig. 3-12) of known volume containing air at atmospheric pressure to one of the manifold outlets and evacuating the entire system down to the stopcock of the bulb. The stopcock to the pumping system is then closed, and the air is admitted from the bulb into the manifold. The ratio of the final pressure to the atmospheric pressure is... 

Fractions are changed whenever the vapor temperature, as determined by the thermocouple, changes significantly. After the distillation is completed, the samples are transferred into gas-storage bulbs. The fractions obtained are conveniently analyzed by means of infrared spectroscopy, which is a sensitive method of analysis for gas samples. 

Fig. 31. Apparatus for the study of oxygen exchange with a circulation system. 1, reaction vessel 2, circulation pump 3, valve box 4, cold traps 5, gas sampling ampoule 6, cold trap 1, mano-metric valves 8 to 12, gas storage bulbs 14, gas burette 16, adsorption vessel 24, oxygen purification system. From ref. 245.

Polymerization of acetylene within the microporous pore structure was accomplished on a vacuum line in order to assure absolutely no contact with either oxygen or water. A one-liter gas storage bulb was mounted on a vacuum line manifold and evacuated as much as possible (to less than 10 mm). A stoichiometric excess of acetylene from a cylinder was introduced into the bulb until a pressure (measured by a manometer) of 740 mm Hg was attained. The cold finger of the gas storage bulb was immersed in liquid nitrogen to... 

At this point, the Schlenk tube containing the sample was mounted on the vacuum line and evacuated for about 30 minutes, bringing the pressure down to <10 mm Hg. The vacuum was sealed off from the vacuum manifold, thus leaving a pathway between the mounted gas storage bulb containing acetylene and the Schlenk tube. 

It has been pointed out that appreciable systematic errors might occur in some cases when the pressure-drop method of flow calibration is used, on account of adiabatic expansion which leads to a slight decrease in temperature in the gas storage bulbs. 

The sample preparation vacuum line (often called spray-on line ) should allow for (a) controlled mixing of the host gas with the substrate (or with other components that are added to the matrix) by manometric techniques and (b) the controlled release of the gas (mixture) toward the inlet system of the cryostat. These conditions are met by a vacuum line that incoporates a storage bulb for the gas (mixture), inlets for attachment of evacuable containers that allow degassing of the substrate prior to its mixing with the host gas, pressirre gauges that cover suitable ranges, a needle valve that allows the controlled release of the gas, possibly via a flowmeter, and interfaces to the bottles that contain the host gas(es), and to the inlet system that is attached to the vacuum shroud of the cryostat. 

Before the gas in the calibrated bulb can be dispensed it is necessary to eliminate the gas which fills most of the working manifold and the manometer. This may be accomplished by condensing the excess gas back into the storage bulb and closing off that bulb. The gas which is contained in the calibrated bulb attached at site A can now be condensed into any of the evacuated traps on the line or into an evacuated reaction vessel, which might be attached at site B. 

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 a gas or a low-boiling liquid is to be transferred from a storage bulb to a reaction vessel, both containers are attached to the manifold, the storage bulb is cooled in dr ice-acetone or in liquid nitrogen (depending on the boiling point of the compound), and the entire system is evacuated. The stopcock to the pumping system, as well as the... 

The bulb was sealed off from the vacuum line, and the acetylene was allowed to sublime. The pressure in the bulb went to approximately 600 mm Hg, indicating that dissolved oxygen (or perhaps another gas) indeed was present in the acetylene stream. This procedure was repeated twice to bring the total pressure of acetylene in the storage bulb up to 740 mm Hg. The bulb was left on the vacuum line. 

The mixture was homogenized and a 10-ml charge was placed in the side chamber of the storage bulb. The main compartment of the storage bulb was then charged with 247 Torr of gas mixture I (CH ) As/N2 The final gas phase contained 410 ng As. 

Small traces of X2 [Cl2 or Br2] are added by expanding the X2 gas in a small precalibrated volume (1.1 mL 1/4 in. glass tubing that is part of the storage vessel for the halogen, Fig. 1 j) at room temperature at a known pressure and then condensing it into bulb 1 at - 196°C. 

To find the quantity of gas in a prepared sample. The entire sample is collected in the sample storage tube immersed in liquid nitrogen. The sample is then allowed to warm up to ambient temperature and its volume adjusted to one of the calibrated marks between the bulbs. The pressure, or difference in mercury levels is measured. 

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