The purpose of experiment 6 is to measure the relative viscosities of a series of alcohols and a series of alcohol water solutions. The reference liquid used for all samples is water. As discussed in class, the relative viscosity is calculated using densities and flow times. Densities of pure substances are tabulated in reference tables. Densities of solutions have to be determined using the appropriate hydrometer. Flow times will be measured using an OST-Wald Viscometer. This video will present the operation of a hydrometer, then it will present the operation of a Viscometer. To measure the specific gravity using a hydrometer, fill one of the extra large test tubes until it is about 3-quarters full. Clamp the test tube with the liquid in a vertical position. Clean the hydrometer with the ionized water. Dry thoroughly. Lower the hydrometer gently into the sample, adding a slight spinning motion to assist the hydrometer, and floating away from the walls of the test tube, and to remove any trapped gas bubbles under it. Keep the rest of the stem dry, as unnecessary liquid on the stem changes the effective weight of the instrument and affects the readings obtained. When the hydrometer has come to rest and is floating freely away from the walls of the sample container, read the hydrometer to the nearest 0.001 unit. The correct hydrometer reading is that point on the hydrometer scale, at which the main surface of the liquid crosses the scale. Determine this point by placing your eye level with the surface of the liquid. Read the scale where the surface of the liquid becomes a straight line crossing the hydrometer scale. Do not read the scale where the meniscus touches the hydrometer. Clean all hydrometers with the ionized water, wipe dry, and place in the box. Remove the viscometer from the detergent bath and rinse it thoroughly with water using a large beaker and a water aspirator. Rinse the viscometer with the solution whose flow time is to be determined. Carefully clamp the viscometer on the wide leg just above the bridge in a vertical position. Using a volumetric pipette, introduce 10 ml of sample into the large bulb of the viscometer. Allow about 3 minutes for the viscometer and sample to reach thermal equilibrium. Use a suction bulb to draw the liquid into the upper bulb of the viscometer. Use a stopwatch to measure the time for the meniscus to drop from the upper line on the viscometer to the lower line. Start the stopwatch when the meniscus touches the upper line. Stop the stopwatch when the meniscus touches the lower line. For the same sample, obtain 2 flow time readings that are in agreement to within 2 seconds. Dispose of the sample into the appropriate waste container. Always rinse the viscometer with the solution whose flow time will be measured next. Remember to determine the flow time of the reference liquid. Put the viscometer into the cleaning bath at the end of the experiment. Make sure the soap solution fills the viscometer.