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Iodine was discovered accidentally in 1813 when seaweed was employed to make saltpetre for gunpowder. It is a nonmetallic element and one of the halogens, chemically similar to the element chlorine. Its shiny black crystals vaporize to form a beautiful violet gas.

It is effective in treating goitre (a disorder of the thyroid gland) and soon replaced the folk remedy of sea sponges. Its relatively mild disinfectant properties makes it suitable for treating minor cuts. Today, rare isotopes of iodine are used in medical diagnosis and radiation therapy.

What does iodine look like when solid? Why is it so important to health? In this video, Dr Andrea Sella takes us through some the many forms of this rare but versatile element.

Read the transcript of this video (PDF, 51KB).