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#### Updated on Apr 24, 2013

Pores are small openings that allow air and moisture to permeate the surface of a material. Porosity is the measure of these voids relative to the solid structure. Porosity is a significant consideration in many fields, including ceramics, hydrogeology, construction and metallurgy.

The independent variables in this experiment are the kinds of rocks, and the dependent variable is the amount of water they retain. The constants are the containers, the amount of water and the conditions.

### Problem:

The goal of this project is to explore the concept that rocks are not completely solid or exactly alike.Rocks have pores of varying sizes, and water fills these pores seeming to “absorb” the moisture like a sponge.

### Materials:

• Large, clear containers of the same size
• Measuring cup
• Water
• Marker
• Ruler (optional)
• Variety of rocks: granite, sandstone, limestone, shale, clay, etc.

### Procedure

1. Fill the containers with an equal amount of water.
2. Make sure that the water is deep enough to submerge the rock
3. Record the amount of water in the containers. This can be the ounces, the height and/or a line on the outside of the container.
4. Gently place one rock into the center of the containers.
5. Leave the containers undisturbed for at least 30 minutes.
6. Carefully remove the rocks from the containers, letting the excess water drip into the container.
7. Figure out how much water each rock “drank”. This can be done by emptying the water into the measuring cup and calculating the difference from the original amount. Or, the ruler can measure the height and calculate from the original height.
8. Repeat the experiment several time using dry rocks to obtain a more accurate average for each type of stone.
Jane Frances Healey taught for many years at both the college and high school levels. Currently, she's a freelance writer in the San Francisco area, and she enjoys doing research on a wide variety of topics.