Pour the supernatant liquid into the sink and flush with 10 volumes of tap water per volume of supernatant fluid. This is a question without a specific answer. In this case, switching sets of bottles will be effective. When the instructor uses one of the sets at the overhead projector, students who used the other set will probably be provoked to comment. Some students actually will change their report of what they saw.
Surface tension holds the drops in place.
The drops run if the tilt is pronounced. Click here to see a sample data set. Click here to see the second sample data set. Use an overlay on the overhead projector in front of the class. Ask students to provide the observations.