To prepare brown HgCl3·4HgO, a solution of 15.0 g. of borax in 1.5 liters of water is added to a solution of 10.0 g. of mercuric chloride in 2.0 liters of water (both solutions are at 50-55 °C). The desired compound separates on cooling in the form of thin, flexible flakes 0.1-0.8 mm. long. Depending on the thickness of these flakes, the color of the precipitate varies from golden yellow to black-brown. The yield is about 85%, based on the HgCl3 used.
