When digested for some time with a caustic alkali it is converted into a basic salt, PbCrO 4 PbO, a pigment known as "chrome red."
A simpler explanation is that the manganese dioxide first gives a normal sulphite which rearranges to dithionate, thus: Mn0 2 +2S0 2 = Mn(S03)2-MnS206, whilst the lead dioxide gives a basic sulphite which rearranges to sulphate, thus: PbO-l-S0 2 = PbOS03 - > PbS04.
Zeit., 1889, 13, p. 1701; 17, p. 1712) adds calcium plumbate to a solution of potassium ferrocyanide and passes carbon dioxide through the mixture: 2K 4 Fe(NC) -f-Ca 2 PbO 4 -} 4C02= K3Fe(NC)6+ K2C03+PbC03+2CaC03.
Of other lead minerals we may mention the basic sulphate lanarkite, PbO PbSO 4; leadhillite, PbSO 4.3PbCO 3; the basic chlorides matlockite, PbO PbC12j and mendipite, PbC1 2.2PbO; the chloro-phosphate pyromorphite, PbC12.3Pb3(P04)2, the chloro-arsenate mimetesite, PbC12.3Pb3(As04)2; the molybdate wulfenite, PbMoO 4; the chromate crocoite or crocoisite, PbCrO 4; the tungstate stolzite, PbW04.
When kept fused in the presence of air lead readily takes up oxygen, with the formation at first of a dark-coloured scum, and then of monoxide PbO, the rate of oxidation increasing with the temperature.