Is Dirt Just Dirt?

K–12 Online Activity

Contents

 

 

Purpose of our experiment:

Soil is one of the most important links between people and the natural environment. We want to know all about dirt; how it is supposed to work when it is healthy, and how it can help us clean up spills. We are going to look closely at several types of dirt by doing four experiments: (1) sieve, (2) sand/silt/clay, (3) fizz, and (4) bleach.

 

Vocabulary

Disaggregate

Archival

Dilute

Clay fraction

 

Collect your sample

Label everything with your name and the place and depth at which your sample was collected.

Materials you will need:

  • data sheet
  • bag of dirt
  • jar
  • 2 small bags

Put a nice piece of your dirt in a small bag. This is your archival sample (to show later).

Sand/silt/clay test -first day

Disaggregate (smash to powder) your sample and put it in your jar. Do a little at a time until you have 300 ml.

Fill your jar with water, put on the lid, and shake it for 5 minutes. Don't drop it!

Sieve your sample. Put the wet mud back in your jar. Rinse, dry, and examine the material you collected in the sieve. What did you get?

Shake the jar again, and let it stand undisturbed for 1 day. Look closely the next day, what has happened as it stood?

 

Fizz test for caliche

Disaggregate a little of your sample into a jar lid.

Add a tiny drop of dilute acid. What happens? Write down your result on your data sheet.

 

Bleach test for organics

Disaggregate a little of your sample into a jar lid.

Add a capful of bleach and let stand several minutes.

What has happened to the color? Write down your result on your data sheet.

If nothing happens on these tests, visit a group who got an effect and check your sample again. No change is a good scientific result.

Sand/silt /clay test - second day

Without shaking,examine the dirt in the jar closely. Can you see several layers? On your data sheet, draw what you see in your jar. Use your ruler to make your drawing to scale.

Carefully siphon the water out of your jar. (Instructions on how to siphon from a jar are at the bottom of this page.)

Spoon out the very top of your sample into a jar lid. This is your clay fraction.

Now you can spoon out some of the other layers in your jar. What can you see?

Pour out most of the material in your jar keeping only the bottom part (you can recycle the dirt back outside). Wash the material in the bottom of the jar by adding water, swirling it in the jar, and then pouring out most of the muddy water. The washed material in the bottom is your sand fraction.

 

Record your data

Glue some of your sand and clay fractions to the circles on your data sheet.

Put your sieve fraction in a bag and staple it; staple your archival sample to your data sheet. You now have a record of what was in your dirt.

 

Analysis

Each group should report its own results of the four tests.

We will make a large graph comparing how dirt is the same and different in several parts of Texas and at different depths below the ground surface.

Equipment needed

  • Shovel and trowel for sampling
  • Gloves (if desired)
  • Large plastic bags - 1 for each team
  • Small plastic bags - 2 for each team
  • Quart canning jars - 1 for each team
  • "Sharpies" or other permanent markers that will write on glass
  • Jar lids or other small, flat dishes - 2 for each team
  • Sidewalk and lightweight tool for hammering (4 inches long, 2 x 2 pieces)
  • Broom for clean up
  • Hose or large bucket of water
  • 10% HCl in small squeeze bottle
  • Goggles for lab safety
  • Household bleach
  • Small jars for disposal
  • Sieve and catch basin
  • Rulers
  • Siphon (2 ft of 3/8-inch tubing), bench and catch basin
  • Data sheets
  • Camera to document experiment

 

How to siphon from a jar:

Put the jar on a bench or off the ground above a catch basin.

Immerse the tube and fill with water. Put your thumb tightly over the opening in one end while the tube is underwater, it should stay full when you remove it from the bucket. Still holding your thumb over one end of the tube, put the other end of the tube into the water in the jar. Lower the end of the tube in your hand below the jar toward the catch basin, and release your thumb. Water should start flowing out of the tube into the catch basin. Watch to keep the supply end of the tube that is in the jar in the water but above the top of the mud. The exhaust end of the tube has to stay lower than the supply end. Put your thumb over the end of the tube to stop.

Updated November 11, 1999

Send questions or comments to Sue Hovorka or Sigrid Clift.

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