Called also _Mineral Yellow_, has improperly been classed as an orpiment, from which it differs in not being a sulphide, and in containing lead. It is prepared from arsenic fluxed with litharge, and reduced to powder. It is much like orpiment in colour, dries better, and not being affected by lead, is less liable to change in tint. The presence of the litharge, however, renders it subject to be blackened by sulphuretted hydrogen. Of course it is poisonous. 53. _Bismuth Yellow_, Or chromate of bismuth, may be obtained either as a lemon or an orange yellow, sparingly soluble in water. The colour is not permanent, and turns greenish-brown even when excluded from light and air. 54. _Copper Yellow_, Or chromate of copper-potassa, is of a bright yellow tint, not insoluble in water. It is discoloured both by foul gas and exposure. 55. _Gelbin's Yellow_, Or chromate of lime, is a pale whitish yellow, poor in colour, partly soluble, and not at all to be depended on. 56. _Indium Yellow._ Whether the new metal indium will ever be found in sufficient quantity to render it practically useful remains to be seen. The most abundant source at present known is the Freiberg blende, 100,000 parts of which only yield from twenty-five to forty parts of indium. The metal is chiefly interesting in an artistic sense on account of its sulphide, a fine bright yellow resembling cadmium, and best obtained by precipitating an acetic acid solution with sulphuretted hydrogen, or sulphide of ammonium. In the latter, the yellow dissolves on being heated, but deposits again on cooling of a rather paler tint. With one modification, what was said in a former edition of this Treatise concerning cadmium yellow may be repeated of indium yellow. "The metal from which it is prepared being hitherto scarce, it has not been employed as a pigment, and its habits are not therefore ascertained." All we can tell is, that the colour does not suffer from impure air. Indium is likewise distinguished by a straw-yellow oxide. 57. _Iodine Yellow_, Or iodide of lead, is one of those compounds whose presence on the palette should never have been allowed. Exceedingly brilliant, it is also utterly fugitive, destroyed by exposure or foul gas, and useless in admixture. We may state here that, whatever its colour, no pigment containing iodine can in the slightest degree be relied upon. One of the most unstable of substances, being slowly volatile even at common temperatures, iodine is or ought to be quite inadmissible as a constituent. Combined with lead, which is in itself objectionable, it forms a yellow possessing every bad quality. 58. _Iron Yellow_, Or oxalate of protoxide of iron, has very unadvisedly been recommended as a pigment. It is a bright pale yellow, but soon loses the beauty of its tint when submitted to air and light, becoming, by peroxidation, red and buffy. Even in a book the colour changes. 59. _Madder Yellow._