| 摘要 |
A pipette in which the volume of liquid measured is a function of the stroke of a piston and can be calibrated to vary the volume measured, by varying the stroke. The pipette has a casing formed with a vertically elongate, open ended cavity, part of which cavity threadably engages a threaded portion on an open ended tube disposed in the cavity. A piston actuating rod passes through the tube. A push-button is mounted on the upper end of the rod and projects from the upper end of the tube which is countersunk into the casing. Below the lower end of the tube, a bush is integrally mounted on the rod and urged upwardly by spring pressure towards the lower end of the tube. The stroke of the piston is the distance between the lower end of the tube and the upper face of the bush when the push-button is not being depressed. This distance is variable to calibrate the pipette by rotatably screwing the tube in or out relatively to the casing, using a special key engageable with the upper end of the tube. A friction ring captive between the sleeve and the wall of the cavity prevents inadvertent rotation of the tube with respect to the casing.
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