| | | | | | |Cadmium |Dissolves with |Unaltered. |Unaltered.|Melts with | | yellow | evolution of | | |difficulty. | | | sulphuretted | | | | | | hydrogen. | | | | | | | | | | |Zinc |Yellow |Yellow |Unaltered.|Melts with | | yellow |solution. |solution, | |difficulty. | | | |white | | | | | |residue. | | | | | | | | | |Cobalt |Red solution. |Colourless |Unaltered.|Becomes | | yellow | |solution, | blackish | | | |greyish blue | |at high | | | |precipitate. | |temperatures.| | | | | | | |Orpiment |Unaltered. |Colourless |Yellow |Volatilises. | | | |solution. | solution.| | | | | | | | |Turpeth |Dissolves. |Unaltered. |Blackened.|Turns red. | | mineral | | | | | +-----------+---------------+-------------+----------+-------------+ _On Heating on Charcoal_:—Chrome yellow, chrome red, Cassel yellow, massicot and lead iodide give lead beads in the reducing flame. Chrome yellow and red when fused with soda give red masses soluble in water. Naples yellow gives a lead bead and white fumes without smell. Orpiment gives an odour of garlic. Cobalt yellow, when heated with alumina, is turned blue. Cadmium yellow produces a brown incrustation on the charcoal. The examination before the blowpipe serves especially for the recognition of lead, chromium, antimony and arsenic. If a pigment blackens on heating, the presence of an organic colouring matter is indicated, such as Dutch pink, weld lake, etc. The adulteration of pigments free from lead by colours containing that metal is recognised by the blackening produced by ammonium sulphide.