Iron filings
Iron filings are very small pieces of iron that look like a light powder. They are very often used in science demonstrations to show the direction of a magnetic field. Since iron is a ferromagnetic material, a magnetic field induces each particle to become a tiny bar magnet. The south pole of each particle then attracts the north poles of its neighbors, and this process is repeated over a wide area creates chains of filings parallel to the direction of the magnetic field. Iron Filings are used in many places, including schools where they test the reaction of the filings to magnets. They are also used in some toys, most famously Wooly Willy, where they serve to mimic hair on a cartoon face.
History
Filings are mostly a byproduct of the grinding, filing, or milling of finished iron products, so their history largely tracks the development of iron. For the most part, they have been a waste product.
Iron filings have some utility as a component in primitive gunpowder. In such a fine powdered form, iron can readily burn, due to its increased surface area.
The primary utility of iron filings is in the study and teaching of magnetism and electromagnetic fields. The substance makes impressive demonstrations when sprinkled on a white card placed on top of a permanent magnet, such as a bar magnet. The filings can be found in toys that allow one to draw with a magnetic pen. By sprinkling fine iron on a magnetic stripe card, it is possible to see the magnetic encoding on the stripe. A semi-viscous fluid in which iron filings are suspended may be poured onto the exposed platter of a hard drive so that the patterns of bits on the platter are revealed by the alignment of the iron filings.
