Mercury(II) iodide

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Mercury(II) iodide
Image:Mercury(II) iodide.jpg
General
Other names	mercuric iodide mercury biniodide
Molecular formula	HgI₂
Molar mass	454.40 g/mol
Appearance	scarlet red powder
CAS number	[7774-29-0]
Properties
Density and phase	6.36 g/cm³, solid
Solubility in water	6mg/100g water
Melting point	259°C
Boiling point	350°C (sublimes)
Vapor Pressure	100mm @ 261.8°C
Hazards
EU classification	not listed
NFPA 704
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references

Mercury(II) iodide (Hg I₂) is a chemical compound with an appearance of red-orange crystals.

Conditions/substances to avoid include: heat, light, bromides, chlorides, ammonia, alkalis, cyanides, copper salts, lead salts, iodoform and hydrogen peroxide.

Mercury(II) iodide displays thermochromism; when heated above 126 °C, it undergoes phase transition from the alpha crystalline form to a pale yellow beta form. As the sample cools, it gradually reacquires its original color. It is often used for thermochromism demonstrations. [1]

Mercury(II) iodide is used for preparation of Nessler's reagent, used for detection of presence of ammonia.

Mercury(II) iodide is a semiconductor material, used in some x-ray and gamma ray detection and imaging devices operating at room tmperatures. [2]

In medicine, mercury(II) iodide was formerly used as a treatment for syphilis.

In veterinary medicine, mercury(II) iodide is used in blister ointments in exostoses, bursal enlargement, etc.

Mercury(II) iodide is one of the stated possibilities for the "red mercury".