By Felicia Cherry
Product Developer

Magnetism is a physical property of certain metals. A particular alignment of their atoms may produce a magnetic field. Within a magnetic field, lines of force can be detected and measured. These lines seem to flow through and around a magnet, out from the north pole, then back through the south pole.

Figure 1  Bar magnet with lines of force.

The word magnet comes from the Greek word meaning "the stone of Magnesia." In a region once known as Magnesia, the Greeks found a magnetic iron ore (lodestone) that attracted iron-containing materials. These naturally occurring rocks can be found in various parts of the world. In addition to occurring naturally, magnetism can be induced in ferromagnetic metals (iron, nickel, and cobalt).

Magnets are not just for attaching things to refrigerators. They are all around us—in computer hard drives, speakers, medical equipment, toys, and motors. One peculiar use of magnets involves cows. A special long, cylindrical magnet is administered like a pill to a cow. The fairly heavy magnet remains in the bottom of the cow’s stomach, where it attracts and holds bits of steel and iron that the cow accidentally ingests while grazing (e.g., barbed wire, fence nails). This lessens the likelihood that sharp metal will churn through the stomach until it pokes through and damages another organ (often the heart), causing a condition called hardware disease. Note: Humans should never eat magnets! They can stick together through intestinal walls, causing damage and requiring surgery to remove.

Magnets are made from different materials. Alnico magnets are so-named because they are made from aluminum, nickel, and cobalt. Ceramic magnets contain iron oxide particles embedded in a ceramic matrix. Neodymium magnets are among the rare-earth magnets. See Fig. 2 for some of the comparative features of various types:

Figure 2  Magnet comparison chart.

Iron is a magnetic metal and an essential nutrient (e.g., our oxygen-carrying hemoglobin contains iron). Many processed foods are fortified with iron to provide this nutrient, sometimes in the form of iron salts (ferrous salts) and sometimes in the form of superfine particles of elemental iron. Elemental iron, also known as reduced iron, is used when iron salts may attract moisture that would cause a product to spoil. Common iron-enriched products include breakfast cereal, instant oatmeal, and infant cereal. "Iron powder" or "reduced iron" is listed as an ingredient.

To demonstrate both the magnetic properties of iron and the presence of added iron in foods, the following activity guides you through the extraction of iron from cereal with a magnet. Your students may be surprised to find that they are eating actual metal in their cereal. A document camera or similar device may help the class view the extraction of iron.

National Science Education Standards

Grades 5–8
Science as Inquiry

• Abilities necessary to do scientific inquiry
• Understandings about scientific inquiry

Physical Science

• Properties and changes of properties in matter

Science and Technology

• Understanding about Science and Technology

Grades 9–12
Science as Inquiry

• Abilities necessary to do scientific inquiry
• Understandings about scientific inquiry

Physical Science

• Structure and properties of matter

Materials

• Iron-enriched Breakfast Cereal, 1 c, (Total® is a popular brand to test)
• Laboratory Blender (option: mortar and pestle, large beaker, stir plate and stir bar)
• Warm Water, 1 c
• Clear Container (large enough to hold water/cereal mixture)
• Strong Magnets (neodymium magnets work well)
• Plastic Wrap or Resealable Bag

Preparation and procedure

1. Add 1 cup of water and cereal to the blender. Blend for 60 seconds.
   Option: If you do not have a blender, then crush the cereal into smaller particles with the mortar and pestle. To the beaker, add crushed cereal, water, and the stir bar. Set the beaker on the stir plate and allow it to stir for several hours. You may want do this the day before lab.
2. Transfer the cereal/water mixture to the container.
3. Cover a magnet with plastic wrap or place it in a resealable bag. (It is very difficult to remove fine iron particles from an uncovered magnet, especially a neodymium magnet.)
4. Immerse the covered magnet into the mixture and swirl for 30 seconds.
5. Remove the magnet from the mixture. You should see small black specks on the plastic

Here are 2 additional magnet tests that students enjoy:

Currency
US bills are printed with magnetic ink. The Federal Reserve Banks remove worn paper currency from circulation, shred the bills, and sell the shredded currency. Shredded currency may contain all denominations of bills. In the above procedure, substitute 1 cup of shredded currency for breakfast cereal. Compare the amount of iron found in each. Note: You may want to cut the currency into short pieces. Long pieces may entangle the blender blade.

Fingernail polish
Many stores carry fingernail polish that contains iron particles. Paint a fingernail (or other surface) with polish and, before it dries, quickly position the magnet (found on the product’s cap) close to but not touching the wet polish for 10 to 15 seconds. A pattern will appear. Explore how different types of magnets affect the polish. Challenge the class to explain why the manufacturer’s magnet makes a pattern. Note: Be sure to wrap the magnets with plastic to protect them from the polish. Also, be aware that a neodymium magnet is strong enough to remove iron particles from the polish.