Zinc white is converted into a green mass when moistened with cobalt solution and heated in the oxidising flame. The more expensive white pigments are frequently mixed with cheaper substances, _e.g._, white lead with finely powdered barytes, chalk or gypsum. Such admixture is distinctly to be regarded as adulteration, since the added substances have not the covering power of white lead. In the case of coloured pigments an addition of a white material is not to be regarded as adulteration, since the addition is made in order to impart a paler shade to the colour. +---------------+--------------+-----------+----------+-------------+ | Pigment. | Hydrochloric | Caustic | Ammonium | On Heating. | | | Acid. | Soda. | Sulphide.| | +---------------+--------------+-----------+----------+-------------+ |Antimony white |Dissolves, |Dissolves. |Turns |Turns yellow | | |solution | | reddish |and melts. | | |on turbid | | yellow. | | | |adding water. | | | | | | | | | | |White lead |Dissolves with|Dissolves. |Turns |Becomes | | |effervescence,| | black. |permanently | | |solution gives| | |yellow. | | |crystalline | | | | | |lead chloride.| | | | | | | | | | |Lead |Dissolves |Dissolves |Turns |Turns yellow.| | oxychloride |without |on boiling.| black. | | | |effervescence.| | | | | | | | | | |Lead sulphate |Insoluble. |Dissolves |Turns |Unaltered. | | | |on boiling.| black. | | | | | | | | |Permanent white|Insoluble. |Insoluble. |Unaltered.|Unaltered. | |(barium | | | | | | sulphate) | | | | | | | | | | | |Bismuth white |Insoluble. |Insoluble. |Turns |Evolves | | | | | black. |reddish | | | | | |brown fumes, | | | | | |which redden | | | | | |litmus paper.| | | | | | | |Zinc white |Dissolves |Dissolves.