Reactions of the Red Pigments.

Pigment.Hydrochloric
Acid.		Caustic
Soda.		Ammonium
Sulphide.		On Heating.
Chrome redGreen solution, white
residue soluble on
largely diluting.		Yellow solution and
white residue.		Turns greenish black.Fuses.
Red leadChlorine is evolved,
white residue.		Almost unchanged.Turns black.Turns yellow and
finally melts.
Ferric oxide
pigments		Slowly dissolve to
yellow solution.		Unaltered.Slowly blackened.Become dark
blackish brown.
Antimony
vermilion		Dissolves with
evolution of
sulphuretted hydrogen. 		Dissolves to
colourless solution.		Becomes darker,
partially soluble.		Melts.
Mercury
vermilion		Unaltered.Turns yellowish.Unaltered.Volatilises,
sulphur dioxide
evolved.
Mercuric
iodide		Dissolves to colourless
solution.		Dissolves to
yellowish solution.		Blackened.Fuses and then
volatilises.
RealgarUnaltered.Dissolves to
colourless solution.		Dissolves to
yellow solution.		Volatilises.

On Heating on Charcoal:—Chrome red and red lead give lead beads in the reducing flame. The former gives a red mass when fused with soda, which dissolves to a yellow solution.

Ferric oxide pigments become darker, but give no incrustation.

Antimony vermilion burns with production of sulphur dioxide and white fumes without smell when heated in the oxidising flame; when fused with soda before the blowpipe, it gives a white brittle bead of metallic antimony.

Vermilion volatilises in the oxidising flame and gives a smell of sulphur dioxide.

Mercuric iodide readily fuses and volatilises.

Realgar volatilises. When heated with soda in the reducing flame, white fumes with an odour of garlic are produced.