ASTM D2780 Test Method for Solubility of Fixed Gases in Liquids
5. Apparatus
5.1 Ambient Pressure Saturator, suitable for the saturation of liquids with fixed gases at various temperatures at ambient pressure is shown in Fig. 1. The system comprises four parts:
5.1.1 Gas Supply and Pressure Regulator,

5.1.2 Gas Dispersion Element,

5.1.3 Heating Mantle, to fit 1000-mL separatory funnel (Fig. 1), and

5.1.4 Temperature Measurement and Control Devices.

NOTE 1 - In the event that it is desired to saturate a liquid with a toxic or flammable gas, the use of this system is not recommended, unless suitable means are provided for the collection and disposal of the escaping gas.

5.2 Elevated Pressure Saturator, used to saturate liquids with gases at pressures other than ambient. A suitable vessel, usable at pressures up to 608 kPa (6 atm), is illustrated in Fig. 2. The vessel consists of a 2.5 L stainless steel bomb with a thermostatic control jacket. A valve at one end is connected to a pressure gage and gas supply. A valve at the other end is provided with a fitting that connects directly to the gas extraction apparatus.
5.2.1 Thermostatic Control, for jacket of saturator.

5.2.2 Shaker, reciprocating, horizontal.

5.2.3 Vacuum Pump, rotary.

5.2.4 Transfer Line, with two male socket joint 12/2 fittings.

5.3 Gas Extraction System, 6 as shown schematically in Fig. 3. A detailed drawing of the extraction chamber is shown in Fig. 4. The apparatus provides for the separation of dissolved gases from a liquid by repeatedly forcing the liquid containing gas to pass through a narrow annular passage under reduced pressure. Gas removed in this manner is stored and measured in a gas buret. Provision is made for heating the extraction chamber by means of a condensing vapor bath. The gas buret is jacketed. Cooling water may be circulated through the jacket if it is necessary to reduce the temperature of the contents of the buret. A manometer is attached to the manifold connecting the saturation system, gas extractor, and gas buret. Grease-free stopcocks and ball joints are used throughout the system (Note 2). All tubing and connections are 1 mm inside diameter.

NOTE 2 - PTFE stopcocks are satisfactory for most purposes. However, for greatest precision construct the apparatus with stopcocks and joints which are fitted with O-ring seals.

6. Reagents and Materials
6.1 Mercury, triple-distilled, instrument-grade, sufficient amount to fill extraction apparatus, gas buret, and leveling bulbs. (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.)

6.2 Compressed Gases, as required for saturating liquids to be studied. (Warning - Compressed gas under high pressure. Gas reduces oxygen available for breathing. See A1.2.)

7. Sampling
7.1 To obtain specimens for total gas solubility measurements, collect samples in accordance with Practice D4057. For the determination of the concentration of fixed gases in solutions which are not saturated with the gas, take samples in accordance with the procedure described in Section 3 of Test Method D831.