ASTM D2780 Test Method for Solubility of Fixed Gases in Liquids
8. Procedure A
8.1 Procedure A covers the determination of the solubility of fixed gases in liquids at ambient pressure.

8.2 Add to the ambient pressure saturator (Fig. 1) a sufficient amount of the liquid to cover the gas dispersion element with at least 50 to 80 mm of liquid. Bring the cell to temperature equilibrium at whatever temperature is desired for the determination.

8.3 Saturate the liquid with the test gas (Warning - See 6.2) by bubbling the gas through the liquid. Adjust the gas flow rate so that the gas stream causes thorough but not violent agitation of the liquid. If saturation is to be carried out at an elevated temperature, it may be necessary to reestablish temperature equilibrium after the start of gas flow. (Warning - Be certain that the test gas does not react with the sample under the conditions of the test. For example, oxygen may react with certain unsaturated hydrocarbons even at room temperature.)

NOTE 3 - To saturate liquids at higher temperatures, it may be necessary to preheat the saturating gas to avoid cooling the liquid. It may also be necessary to provide the saturating cell with a reflux capability if it is desired to study volatile liquids at elevated temperatures.

8.4 Attach the saturator containing the saturated liquid to the assembled gas extraction system (Fig. 3). Maintain temperature equilibrium of the saturator continuously in order to prevent any change in gas content. Evacuate the system in the following manner:
8.4.1 With stopcock A closed, adjust stopcocks L, M, and N to vent the gas extraction chamber to the atmosphere through S.

8.4.2 Fill the gas extraction chamber with mercury by raising leveling bulb H until mercury level reaches stopcock L. (Warning - Poison can be harmful if inhaled or swallowed. Vapor harmful, emits toxic fumes when heated. Vapor pressure at normal room temperature exceeds threshold limit value for occupational exposure. See A1.1.)

8.4.3 Turn stopcock L to connect the saturator to manifold.

8.4.4 Adjust stopcock M to connect the gas buret P to the atmosphere through S.

8.4.5 Fill the gas buret with mercury by raising leveling bulb Q until mercury level reaches stopcock M.

8.4.6 Turn stopcock M to connect manifold to stopcocks L and N.

8.4.7 Adjust stopcock N to connect the manometer R to the atmosphere through S.

8.4.8 Attach the vacuum pump to S and evacuate the manometer.

8.4.9 Turn stopcock N to connect S with manifold and evacuate the manifold up to stopcock A on the gas saturator.

8.4.10 Close stopcock N and disconnect vacuum pump.

8.5 The following procedure is used to determine the volume of the dissolved gases present in a measured quantity of a liquid suitably presented for analysis (Note 3) or saturated in the manner prescribed in 8.3.

NOTE 4 - An excellent procedure for presentation of such samples is given in Section 3 of Test Method D831.

8.5.1 Lower leveling bulb H until mercury level in the gas extraction chamber falls well below the glass umbrella F.

8.5.2 Adjust stopcock L to connect the gas extraction chamber to the saturator through ball joint B and stopcock A.

8.5.3 Open stopcock A and permit approximately 50 mL of the sample liquid to flow into the gas extraction chamber.

8.5.4 Close stopcock A.

8.5.5 As the liquid flows into the gas extraction chamber some dissolved gas immediately breaks out of solution. To transfer this gas to the buret turn stopcocks L and M so as to connect the gas extraction chamber to the buret, raise leveling bulb H and lower leveling bulb Q.
8.5.5.1 Care shall be taken during the gas transfer process to avoid mercury surges, which can force the sample liquid into manifold or gas buret P.

8.5.6 Close stopcock L. Lower leveling bulb H until the sample liquid is drawn in a thin film through the annular space E between the umbrella F and the wall G of the gas extraction chamber.

8.5.7 Raise the leveling bulb H to force the liquid upward through check valve D.

8.5.8 Repeat 8.5.6 and 8.5.7 several times, and then transfer the liberated gas to the gas buret as described in 8.5.5.

8.5.9 Measure the volume and pressure of the gas collected in the buret with stopcocks M and N turned to connect the buret to the manometer R. For this measurement it is convenient to adjust the pressure as read on manometer R in the buret to 1 atm with leveling bulb Q.

8.5.10 Repeat 8.5.5-8.5.9 until the volume of gas collected is constant.

8.5.11 Close stopcock L and disconnect the extraction chamber from the rest of the system at ball joint C. Allow the extraction chamber to cool if necessary.

NOTE 5 - For studies of the solubility of gases in viscous liquids it may be necessary to heat the gas extraction chamber in order to achieve proper operating conditions. A condensing vapor jacket J together with boiler I and refluxing condenser K are provided for this purpose. Water is a suitable reflux liquid. In most cases, however, no additional heating is necessary.

8.5.12 Tilt the chamber slightly and carefully raise leveling bulb H to force the liquid sample out of the chamber into beaker.

8.5.13 Lower leveling bulb H and allow any excess sample to drain from the chamber walls.

8.5.14 Repeat 8.5.12.

8.5.15 Weigh the collected sample.
8.5.15.1 For studies of the solubility of gases in volatile liquids, provision must be made for that portion of the collected gas which consists of organic vapors. In some cases these can be reduced to a negligible amount by cooling the gas buret by passing a cold fluid through its liquid jacket. If this is not adequate, use the alternative procedure described in 10.3.1.

NOTE 6 - When testing the solubility of gas mixtures, such as air, analysis of the separated gas for the individual constituents by gas chromatography or mass spectroscopy may be desirable to determine the actual percentage of each dissolved gas in the liquid; see Practice E 260.