Measuring Viscosity

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VISCOSITY

Your instructor will demonstrate to you the mechanics of using a simple viscometer, which is essentially nothing more than a fluid-filled tube down which gravity pulls a plasitc bead. The more viscous the fluid, the slower the bead falls. Thus "timing is everything."


  1. Fig of ViscometerA simple viscometer

    You should be able to make viscometers for about US$0.75 each. From your local hardware merchant purchase meter lengths of transparent, flexible vinyl tubing. (I used 5/16 inch inside diameter.) From your sewing/fabric shop, buy sets of 6 mm and 10 mm diameter spherical beads. Place your beads in boiling water to make sure that they can tolerate that temperature and not get soft. Dry them and fill the needle holes of the beads with waterproof glue. After an hour, dip one end of the tubing into boiling water, and, once softened, push one of the large beads into the end to act as a plug. Using the degassed (boiled) water, fill the tube to the brim. Drop in the smaller bead. Make sure that it can sink all the way to the bottom, and not get "hung up" on a constriction in the tubing. If needed top off the tube with more boiled water, and then insert the other large bead. Try not to trap any air in the tube. (The degassed water should also help prevent later formation of bubbles after the system is sealed.)

    For temperature equilibration, coil the apparatus into a pan and boil the apparatus for a couple of minutes. Using tongs, lift one end out of the hot water, and allow the tubing to hang vertically.

  2. Viscosity measurements. The loose bead will be at the bottom. From the moment you invert the tube, time how long it takes for the bead to sink to the other end. Record your results. Do this twice and average your results along with the fact that the conditions were "boiling".

    Place the tubing in other temperature regimes and allow it to equilibrate to those temperatures. Make the timing measurements and record your data.

  3. Other fluids. Find other viscometers which are labelled as containing other fluids, and make and record readings at various temperatures for each of them.
    1. 5% (w/v) NaCl
    2. 2 drops of dishwashing detergent per liter


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