Experiment: Porosity

Beakers of gravel, sand and silt Solid rock is often not so solid. Sandstone might have started out as a sand dune or a beach, which got buried and compressed. But spaces remain between the particles. These spaces, or pores, are where oil and gas may be found.

If you look at a sponge you can see many open spaces. Sandstone is like that, only the spaces are generally much smaller, so small that they cannot be seen without a microscope.

How much open space is there in rock? In this experiment we check the porosity of gravel, sand and silt, the raw materials that sandstone is made of.

Tools & Materials

Gravel, sand and silt
3 beakers, 500 milliliters each
A 100ml graduated cylinder
Water

Students at Experiment Research Center School in Russia experimenting with porosity.

The Experiment

Fill one beaker to the 350ml mark with gravel, the second beaker with 350ml of sand and the third with 350ml of silt.
Fill the graduated cylinder to the 100ml mark with water.
Slowly and carefully pour the water into the first beaker until the water just reaches the top of the gravel. Record exactly how much water you use. If you need more than 100ml of water, fill the graduated cylinder again.
Follow step 3 again for the beaker with sand, and again for the beaker with silt.

Calculating Porosity:

For each material, calculate the porosity by dividing the volume of water that you were able to pour into it by the total volume of the material. Then express this result as a percentage. For example If you were able to add 90ml of water to 350ml of gravel, the porosity would be

90 ml
----------- = .2571 = 25.71%
350 ml

Use the chart below to record your data and calculations. There are extra spaces if you want to try this with some other materials.

Type of Material	Volume of Material	Volume of Water (pore space)	% Pore Space (porosity)
gravel
sand
silt

After you've tried this you might want to have a look at our results.

Course:

Science

Result/Solution(s)

We used three beakers filled to the 350 ml mark with:

gravel
sand
silt.

The chart below shows our results.

Type of Material	Volume of Material	Volume of Water (pore space)	% Pore Space (porosity)
gravel	350 ml	135 ml	38.57%
sand	350 ml	120 ml	34%
silt	350 ml	186 ml	53%

Calculating Porosity

Here's how we calculated porosity for each material: We divided the volume of water that we were able to pour into it by the total volume of the material. For the gravel the calculation came out like this:

135 ml
----------- = .3857 = 38.57%
350 ml

For sand we calculated:

120 ml
----------- = .3429 = 34.29%
350 ml

For silt we calculated:

186 ml
----------- = .5314 = 53.14%
350 ml

Something else to try:

Fill one beaker with 350 ml of gravel without shaking the beaker. Just leave it still on the table. If you need to level the gravel as it nears the 350 ml mark, just push it gently with your finger or a pencil.

Now fill a second beaker with 350 ml of gravel, but as you fill it, shake the beaker gently and tap it on the table. When it is full to the 350 ml mark, tap and shake some more. If the level then goes below the 350 ml mark, add some more gravel to bring the level up to 350 ml.

How do you expect the porosity of the material in these two beakers compare? Make a prediction and explain why you expect to get the result you predict. Then test the porosities. Did it work out the way you expected?

earth science

ps_nid:

19775

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Experiment