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When a small volume must be removed from a sample containing suspended solids-- for setting up a BOD dilution, for instance-- it is important to get a portion which is representative of the whole sample. Here a rubber bulb is used to draw a few milliliters of wastewater into a graduated pipet. The sample in the beaker is being continuously mixed by means of a magnetic stirrer.
[The base of the stirrer contains a magnet mounted on a motor. In the beaker is a small, Teflon®-coated magnet which is kept spinning at a rate controlled by a dial on the stirrer. This particular stirrer also contains a hotplate.]
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