| 摘要 |
A sample tube for obtaining a column of liquid of predetermined height in laboratory applications comprises a simple and effective construction, with a local restriction in internal diameter a predetermined distance from an inlet end and a movable valve member such as a lead shot disposed in the tube between the restriction and the opposite end, for co-operating with the restriction to retain a column of liquid at the level of the valve member and restriction by surface tension effects. In operation, liquid is drawn into the tube by suction to a level substantially above restriction, then the suction is removed and the liquid is allowed to drain out of the end, passing the lead shot owing to an imperfect seal between the lead shot and the restriction. When the liquid reaches the level of the lead shot and restriction, it is retained at this level by surface tension effects interacting with the lead shot and restriction.
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