A2.1.1 Oil Vessel (Fig.A2.1(a)), 5-L equipped with one sidearm septum holder, two sidearm outlets, one egg-shaped TFE-fluorocarbon-coated stirring bar, a cork ring to support the vessel, and a magnetic stirrer.
A2.1.2 Oil-Degassing System (Fig.A2.1(b)), consisting of one 4-L oil reservoir, one 75-mL splash bulb, two high-vacuum stopcocks, one T-type glass connector and a vacuum mechanical pump.
A2.1.3 Mercury Displacement System (Fig.A2.1(c)), to compensate for oil volume variations, consisting of two 500-mL glass bulbs, two high-vacuum stopcocks, and one Y-type glass connector.
A2.1.4 Rigid Stands, with clamps to secure the various elements, and a large plastic tank to contain accidental mercury spills. All connections between these components are of high-vacuum oil resistant flexible tubing.
A2.1.5 Gas-Injection System (Fig.A2.2), consisting of a set of calibrated gas tight syringes of appropriate volumes, a plastic three-way stopcock (standard medical type) modified to minimize dead volumes by inserting pieces of 0.4 mm inside diameter, 1.5 mm outside diameter steel tubing in the inner branches of the barrel and syringe port (filling up with epoxy resin where necessary), a 0.25-mm inside diameter side-port "gas" injecting needle (10 cm long) to go through the rubber septum into the oil vessel, gas cylinders containing the gases or calibrated gas mixtures to be dissolved in the oil equipped with the proper regulators and valves, a length of flexible tubing connecting the cylinder to the stopcock. A 23-gage needle pierced into this tubing to act as a leak, is connected to a water bubbler to check the absence of back diffusion of air.
A2.1.6 Oil-Sampling System (Fig.A2.3), consisting of a 19-gage oil-withdrawing needle (12 cm long), and glass syringes of suitable capacity equipped with two three-way plastic stopcocks.
A2.2 Materials
A2.2.1 Approximately 1L of clean mercury is needed. Oil-contaminated mercury can be cleaned with pentane and filtered through a finely pierced filter paper.
A2.2.2 Gases (H2, O2, N2, CO, CO2, CH4, C2H4, C2H2, C2H6, and so forth) of technical purity, in pressure cylinders, or a mixed commercially prepared primary standard of the gases of interest in appropriate concentrations. The primary standard should have each component prepared gravimetrically.
A2.2.3 High-Vacuum Grease, for stopcocks.
A2.3 Preparation of Apparatus
A2.3.1 Clean all glassware thoroughly, first with detergent, then with a good solvent (methanol, for example), and dry. Pay special attention to the sidearm septum holder. Secure the rubber septum and the flexible connections with pieces of twisted metal wire.
A2.4 Procedure
A2.4.1 Degassing the Oil (Fig.A2.1(b)):
A2.4.1.1 Evacuate the splash bulb and the 5-L oil vessel by opening stopcocks 2 and 4.
A2.4.1.2 Fill the reservoir with oil, and allow oil to flow slowly through stopcock 3 in the 5-L oil vessel with stirrer on, until this vessel is full. Close stopcock 2 and remove the oil-degassing system. If the procedure is followed carefully (filling time, about 4 h), the oil in the vessel will be virtually gas-free.
A2.4.2 Attaching the Mercury-Displacement System (Fig.A2.1(c)):
A2.4.2.1 Turn the oil vessel to bring it into the position, shown in Fig.A2.1(c). Place a wet cloth over the oil vessel to prevent its temperature from rising and attach the mercury displacement system to stopcock 1. Introduce 750 mL of mercury into the system so that the mercury level rises just above stopcock 6, then close the stopcock. From stopcock 5, evacuate sections between stopcock 5 and 1. Open 6 to allow mercury to rise up to stopcocks 1 and 5 and then close stopcock 5. Raise the left bulb so that the mercury level is slightly above the oil and open stopcock 1. Remove the wet cloth. Switch on the stirrer.
A2.4.3 Injection of the Gases (Fig.A2.1(c) and Fig. A2.2) Attach the modified three-way stopcock 7 (in the closed position) to the gas-injecting needle. With the mercury level above the oil vessel, push the needle through the rubber septum into the oil (Fig.A2.1(c)).
A2.4.3.1 Open stopcock 7 to purge the needle and stopcock with oil, then close it (Fig.A2.2). Attach to stopcock the barrel of a gas-tight syringe of appropriate volume and the gas cylinder connection tubing (Fig.A2.2(b)).
A2.4.3.2 Allow a gentle flow of gas to flush the barrel, then slowly push the plunger several times into the barrel, finally down to the volume of gas to be injected, making sure there is continuous bubbling through the needle leak.
A2.4.3.3 Switch stopcock 7 to the inject position (Fig.A2.2(c)), lower the mercury level below the needle tip, and push the plunger to inject the gas volume into the oil.
A2.4.3.4 Switch stopcock 7 to the closed position (Fig.A2.2(d)) and raise the mercury bulb above the oil vessel. Depending on the volume and solubility of the gas injected, it takes from a few minutes to several hours to dissolve completely. As the gas dissolves, the mercury-oil interface resumes its original position.
A2.4.3.5 Repeat the same procedure with each of the gases to be dissolved, changing the gas cylinder connection tube. Instead of adding individual gases, it may be convenient to use calibrated gas mixtures. When all the gases have been injected, remove the gas needle stopcock 7.
A2.4.4 Removal of Oil Samples (Fig.A2.3):
A2.4.4.1 When all the gases are dissolved, switch off the stirrer. Attach two regular three-way stopcocks in the closed position to the oil withdrawing needle and push the needle through the rubber septum (Fig.A2.3(a)). With the mercury level up, switch the two three-way stopcocks to the draw-off position (Fig.A2.3(b)) to purge them with oil.
A2.4.4.2 Attach an oil syringe and draw out a suitable volume of oil (Fig.A2.3(c)). Then switch the two three-way stopcocks to the closed position and remove the syringe leaving the upper stopcock (Fig.A2.3(d)). This oil sample is ready for analysis.
A2.4.4.3 To remove several samples of oil, additional mercury may have to be introduced to the mercury bulb.
A2.5 Calculation
A2.6 Reliability
A2.6.1 The main error comes from the measurement of the volume of gas injected VL which can be obtained with an accuracy of 1 % using calibrated gas-tight syringes. The volume of oil V is obtained more accurately by weighing water in the glass vessel. Correction for dead volume in the injection needle and modified three-way stopcock (approximately 5 mL corresponding to 1 ppm in the dissolved state for the last gas injected) can be made negligible by a last injection of air or nitrogen. The expected overall accuracy therefore is more or less 1 %.