Salinity-Density Demonstration

Purpose: to show how salinity affects the density of water. . . a golf ball sinks in fresh water, but floats in very salty water.

1. Dissolve the 150 g. of non-iodized salt (iodine makes the water cloudy) in one of the beakers of water. This is about 135 ml of dry salt.

2. Challenge a student to see if he/she can float a golf ball. Tell them it takes a real soft touch and that few people "have what it takes". Put your golf ball in the salty water and have the student try it in the fresh water. Eventually they will ask to try the water that you used. . . . Now that you've got their attention, you can explain the relationship between salinity and density.

3. Next remove the golf balls and add several drops of food coloring to the beaker of fresh water. Using a spoon to cushion the fall, pour some of the colored freshwater into the beaker containing the salty water. Since it is less dense, the freshwater should float on the salty water.

4. Gently place a golf ball into the beaker near the boundary between the two layers. It should float near that boundary for several days if left undisturbed.