Final answer:
To remove gas vapor from a container to be abandoned underground, a flow-through process is used where gas may escape after being heated until vaporization and then creating a vacuum in a second flask to distribute the gas, or by condensing the gas back into liquid.
Step-by-step explanation:
When a container is to be abandoned underground, as much of the remaining gas vapor as possible shall be removed through a flow-through process or mechanism. This involves removing the flask from heat as soon as the last bit of liquid becomes gas, ensuring the container is filled with only gaseous sample at ambient pressure. The gas may escape through the hole created for this process, which can be facilitated by creating a vacuum in a second flask and allowing the gas to become evenly distributed between the flasks. Additionally, any remaining gas vapor can be condensed back into a liquid by sealing the flask, allowing the material to condense, and then determining the sample's mass by weighing the flask.