Magnesium carbonate is used in Pattison’s process to decompose lead chloride. Dolomite (magnesian limestone) is the raw material for the magnesium carbonate. Coarsely powdered, it is heated at a low red heat, when magnesia is formed, the calcium carbonate remaining almost entirely unaltered, since it requires nearly a white heat for its decomposition. The powder ground in water was, when treated with carbonic acid under a high pressure, soluble, magnesium bicarbonate being formed, the saturated solution of which contains 2·3 per cent. of magnesia, and has a specific gravity of 1·028. The solution of lead chloride contains 1 part of the salt in 126 parts of water; it is mixed with a slight excess of the magnesium carbonate solution as quickly as possible. The liquid is drawn off from the mixing vessel into a large receiver in which a precipitate deposits, consisting of white lead and a little oxychloride. After drying, the precipitate is ground with a small quantity of caustic soda to decompose the oxychloride. A few days afterwards the mass is washed to remove sodium chloride and the product dried. The process of Dale and Milner is similar to the above magnesia process. Litharge, lead hydroxide or insoluble lead salts are mixed with sodium bicarbonate solution, and, with repeated additions of water, ground until the formation of white lead is completed. The lead compound and sodium bicarbonate are used in equivalent proportions. According to the process of P. Bronner (German patent 52,262), 3 molecules of freshly precipitated lead sulphate are heated with a solution of 2 molecules of caustic soda, when the basic sulphate 2 PbSO₄.Pb(OH)₂ is formed according to the equation— 3 PbSO₄ + 2 NaOH = 2 PbSO₄.Pb(OH)₂ + Na₂SO₄. Or 4 molecules of lead sulphate are decomposed by 2 molecules of caustic soda, according to the equation— 4 PbSO₄ + 2 NaOH = 3 PbSO₄.Pb(OH)₂ + Na₂SO₄. This transformation takes place at a temperature of 70° C. The resulting basic sulphate, although pure white, cannot be used as a pigment on account of its lack of covering power; but by heating with a solution of sodium carbonate it is converted into white lead. 2 PbSO₄.Pb(OH)₂ + 2 Na₂CO₃ = 2 PbCO₃.Pb(OH)₂ + 2 Na₂SO₄. 3 PbSO₄.Pb(OH)₂ + 3 Na₂CO₃ = 3 PbCO₃.Pb(OH)₂ + 3 Na₂SO₄. By this process, which is harmless to the workmen, the lead sulphate obtained as a by-product in the preparation of mordants for calico printing, can be converted into good saleable white lead. The lead sulphate may also be obtained from litharge, lead acetate or nitrate. It occasionally happens that white lead has a rose tint, which is clearly perceptible by comparison with a pure white sample. This colouration occurs in white lead made from argentiferous lead. A very small quantity of silver is sufficient to produce the tinge of colour.