The Turbith mineral, or subsulphate of the binoxide of mercury, exists
in the form of a bright lemon-yellow, heavy powder. It is soluble in
2000 parts of water, and has an acrid taste.
It may be known by the effects of heat. When heated in a tube, globules
of mercury are sublimed, and at the same time sulphurous acid gas is
disengaged, as may be ascertained by the smell. But a better method of
proving the existence of sulphuric acid in it is to expose it to the
action of a solution of caustic potass: The potass separates from it the
brownish-yellow peroxide, and appropriates the sulphuric acid, which may
be found in the solution by acidulating with nitric acid, and then
adding hydrochlorate of baryta, when a heavy, snow-white precipitate of
sulphate of baryta will form. The nitric acid used in this process must
be quite pure, and free of sulphuric acid, which the acid of commerce
often contains.