=Cadmium Chrome Yellow.=—When a solution of cadmium sulphate, or any other cadmium salt, is mixed with a solution of potassium chromate, a precipitate of cadmium chromate, CdCrO₄, is formed. This pigment has a beautiful, deep yellow colour, in no way inferior in shade to the finest lead chromes, and having the great advantage over the latter of being entirely unaltered by the atmosphere; it is thus to be highly recommended for artistic purposes. The high price at which it is sold prevents its general use, though now that cadmium compounds are to be obtained at so much lower prices than formerly, the price of cadmium chromate appears to be excessively high. =Cadmium Yellow= is cadmium sulphide, CdS; in nature it occurs as the somewhat rare mineral greenockite. Cadmium yellow is obtained by dissolving metallic cadmium in sulphuric acid, and precipitating the solution with sulphuretted hydrogen. The solution of cadmium sulphate must be digested for some time with excess of cadmium, in order to separate the foreign metals present as impurities; the colour is not so fine when a quite pure cadmium solution is not used. Cadmium yellow is a very bright yellow. Several shades are obtained according as the solution of cadmium sulphate used in its precipitation is neutral or acid. The reason of this difference in shade lies apparently in the different size of the crystals of which the precipitate is composed. The deep, pure yellow colour becomes still deeper by fusion, which takes place at a white heat. Weak alkalis, acids and sulphuretted hydrogen do not alter cadmium yellow; it is thus to be regarded as a durable artists’ colour. It can be mixed with ultramarine without decomposition, when a fine green is formed; but mixed colours cannot be made from cadmium yellow and blue copper pigments, since these would blacken in the light. =Lead Iodide.=—On precipitating a solution of lead nitrate with potassium iodide, lead iodide is formed. This is but slightly soluble in water, and, when dry, has a handsome, deep yellow colour. Unfortunately it is not permanent, but is decomposed on exposure to light. It can be used for bronzing, but other and cheaper pigments are available for this purpose. On account of the great solubility of lead iodide in a solution of potassium iodide, it is prepared in another way, and accurately weighed quantities are used. Calcium iodide may be used instead of the potassium salt; 100 parts of iodine, 15 parts of fine iron filings and 25 parts of lime are mixed with sufficient water to form a thin paste, which is warmed until all the iodine is dissolved, when water is added, the liquid filtered, and the residue washed in order to extract all the calcium iodide. The solution and wash waters are united, then a solution of 152 parts of lead acetate is added, when all the iodine is precipitated as lead iodide.