Liquid, measurement graduated pipettes

Amount of material required. It is convenient to employ an arbitrary ratio of 0 10 g. of solid or 0 20 ml. of liquid for 3 0 ml. of solvent. Weigh out 0 10 g. of the finely-powdered solid to the nearest 0 01 g. after some experience, subsequent tests with the same compound may be estimated by eye. Measure out 0-20 ml. of the liquid either with a calibrated dropper (Fig. 11,27, 1) or a small graduated pipette. Use either a calibrated dropper or a graduated pipette to deliver 3 0 ml. of solvent. Rinse the delivery pipette with alcohol, followed by ether each time that it is used. 

Graduated Pipettes They have graduated stems and are used to deliver different small volumes as needed. However, they are not normally used for measuring very exact volumes of liquids. 

Pipettes are used for the exact measurement of a definite volume of a liquid. They are narrow cylindrical glass tubes with still narrower top and bottom ends (Fig. 4a). The upper part of an ungraduated pipette has a mark showing up to what level it must be filled to obtain the volume indicated on it. Pipettes with a volume of 10 or 20 ml are used the most. Graduated pipettes are also used (Fig. 45). 

Volume measuring means the exact determination of a defined volume of a liquid (or of a powder mixture in the case of preparing capsules). Devices for measuring of volumes for pharmacy preparations include graduated pipettes (traditional or automatic), syringes and graduated cylinders. Beakers, Erlenmeyer flasks and medicine bottles are not fit for volume measurement, even if they are... 

Liquids may be measured and transferred using a graduated pipette and a pipette pump. The style of pipette pump shown in Figure 5.3A is available in four sizes. The 2-mL size (blue) works well wifh the range of pipettes previously indicated. To fill the pipette, one simply rotates the knurled wheel forward so that the piston moves upward. The liquid is discharged by slowly turning the wheel backward until the proper amount of liquid has been expelled. The top of the pipette must be inserted securely into the pump and held there with one hand to obtain an adequate seal. The other hand is used to load and release the liquid. 

Figure P2.3 Volumetric and graduated pipettes are used to transfer accurate volumes of liquid. Volumetric pipettes give greater accuracy than graduated pipettes, due to the single line to measure to on the thin section above the bulge.

An important general rule in the quantitative handling of liquids is that the graduated vessel or pipette should be of a size appropriate to the volume being measured it is certainly not sensible to measure out a few ml of liquid in a 100 ml measuring cylinder, nor a few pi with an adjustable pipette that holds 100 pi. 

Experiment 33. — a) Measure into a test tube 10 cc. of w ater from a graduate or a pipette. If a pipette is used, proceed as follow s Rinse out the pipette with water, dip the pointed end into w ater and suck up the liquid nearly to the top, then remove the pipette from the mouth and quickly close the top with the forefinger, as shown in Fig. 40 now cautiously lessen the pressure of thq finger enough to allow the liquid to sink slowly to the mark around the stem, then press down tightly, lower the end of the pipette into a dry test tube, and remove the finger. 

Measuring Liquids and Gases. — Liquids are measured in graduated cylinders, or graduates, tubes, burettes, and pipettes. Vessels of various capacities are used, depending upon the volume of liquid to be measured. A... 

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