| 摘要 |
<p>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 16 in internal diameter a predetermined distance from an inlet end 12 and a movable valve member such as a lead shot 20 disposed in the tube between the restriction 16 and the opposite end 14, for co-operating with the restriction to retain a column of liquid at the level of the valve member and restriction 16 by surface tension effects. in operation, liquid is drawn into the tube by suction to a level substantially above restriction 16, then the suction is removed and the liquid is allowed to drain out of the end 12, passing the lead shot20 owing to an imperfect seal between the lead shot and the restriction 16. 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.</p> |
