Class A and AS refer always to highest quality grade in accord to the respective standards and 'S' stands for swift delivery only used for volumetric instruments calibrated to deliver, pipettes and burettes (TD, Ex). For volumetric instruments calibrated to contain (TC, In) a swift delivery is not necessary and therefore not defined in the respective standards.
How can the meniscus be read easily?
In case no Schellbach stripe is imprinted the volume of a concave meniscus has to be read at the lowest point of the liquid level. Here the lowest point of the meniscus has to touch the upper edge of the graduation mark. For parallax-free adjustment of the meniscus, the burette is held upright and the observer's eye must be at the same height as the meniscus. In this position the ring mark will appear as a line. The meniscus will appear darker and more easily readable in front of a light background if a piece of dark paper is held behind the instrument immediately beneath the ring or graduation mark.
Is it possible to titrate with a slightly broken tip?
No. Even with a slightly broken tip two effects are obtainable: First, the risk of injury to yourself increases. Second, the flow rate changes through the broken tip so that volumes are false and measure uncertainties increase.
What does "Error limit according to class B, DIN EN ISO 385" mean?
Some burettes contain subdivision marks or a kind of glass which are not prescribed in DIN EN ISO 385. Subsequently these burettes do not meet all specifications of the standard, but they meet the error limits according to class B of DIN EN ISO 385.
How are automatic burettes used in accordance with the Dr. Schilling pattern?
Squeeze bottle for rapid filling, wait for automatic zeroing, and titrate rough by releasing the micrometer screw and pressing the button, or titrate fine by using the micrometer screw. If these burettes are not in use for longer periods they should be drained and the tubing pressure should be released by opening the stopcock.
Is it necessary to lubricate stopcocks?
PTFE valve spindles operate smoothly without any lubrication. Glass keys should be lubricated very slight to operate smoothly.
What does Boro 3.3 or 5.4 stand for?
The abbreviation Boro 3.3 or 5.4 represents the designated borosilicate glass type 3.3 or 5.4, which is used for manufacturing amber burettes.
Is it necessary to take the waiting time into account during titration?
No. Typically, the volume used in a titration is less than nominal volume, and the standard solution is added dropwise when close to the color change to avoid overtitration. In practice the time required for this dropwise addition is the same or even longer than the established waiting time of class AS burets.
How are automatic burettes used following the modular concept?
Attach rubber bellows on glass bottle of modular automatic burette, squeeze rubber bellows for filling, wait for automatic zeroing, and titrate by opening the stopcock.