NILERED / SCIENCE PHOTO LIBRARY NILERED / SCIENCE PHOTO LIBRARY
Iodine sublimation and melting. Solid iodine being heated in a laboratory beaker, with a watch-glass used to trap the resulting purple gas. The heating is also melting the iodine. Iodine at room temperature is a grey-black solid. Gentle heating below the melting point drives a solid-gas transition known as sublimation. Further heating results in the iodine melting (at 113 degrees Celsius). The iodine gas deposits on the cooler underside of the watch-glass to form solid iodine crystals. Iodine, found in seaweed and sea water, is an essential part of the diet.
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