Mercury(II) bromide or mercuric bromide is the chemical compound composed of mercury and bromine with the formula HgBr2. This white crystalline solid is a laboratory reagent. Like mercury(II) chloride, it is extremely toxic.
It is also used to test for the presence of arsenic, as recommended by the Pharmacopoeia. The arsenic in the sample is first converted to arsine gas by treatment with hydrogen. Arsine reacts with mercury(II) bromide:
The white mercury(II) bromide will turn yellow, brown, or black if arsenic is present in the sample.