CHARLES D. WINTERS / SCIENCE PHOTO LIBRARY CHARLES D. WINTERS / SCIENCE PHOTO LIBRARY
Heat-sensitive compound. Pile of powdered copper mercury iodide, a heat-sensitive compound. The compound's colour is dependent upon its temperature. The compound is brown (as here) when hot and bright red when cool. The change from one form to the other occurs between 40 degrees celsius (C) and 90 C. The phenomenon of a single chemical compound having more than one physical form is known as allotropy. The difference between the different allotropes may be in the way that the atoms are bonded together or the difference in the structure of the crystals. This compound is made of copper (Cu), mercury (Hg) and iodine (I) and has the formula Cu2HgI4.
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