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