A Mohr Pipet is a graduated pipet that is designd to deliver small portions of a liquid or solution. These portions are determined by recording the difference between the initial and final volume readings. Thus, it is important to note:
Many pipets are labelled TD (to deliver) or TC (to contain), however inspection of the graduations on the pipet should indicate which type of pipet is being used. You should look at the graduations even if the pipet is labelled.
Some pipets are not graduated all of the way to the pipet tip, and the final volume must be read from the pipet. Therefore, the final volume MUST be on the scale - DO NOT allow the bottom of the meniscus to go below the last graduation mark. For a graduated pipet, the volume transferred is determined by calculating the difference between the intitial and final volume in the pipet (the initial and final volume must be recorded).
Other pipets are graduated all of the way to the tip. The graduations near the tip will not be linear. A pipet that is graduated all the way to the tip is designed so that the liquid contained after delivering is calibrated into the graduations. Thus, never attempt to blow the remaining liquid from a pipet. If used correctly, the volume delivered with a pipet that is calibrated in this manner is the same as the initial volume reading.
How can you tell if a pipet is to deliver or to contain?