A New Chrome Yellow.

Scientific American, 2.1.1860

Under the above name a yelloa color has been for some time in commerce which is quite certain to find much favor, although its price is far higher than that of the ordinary chrome yellow. It is of a splendid yellow, and differs essentially in its tint from the best samples of chrome yellow. It is pulverulent, of small specific gravity, loses nothing in weight at a red heat, but becomes transitorily reddish brown, and is partially taken up by water without entirely dissolving in that fluid. It dissolves in muriatic and nitric acids; if the acid is poured over it in a concentrated state, a slight effervescence takes place. When prepared with but little acid the solution is somewhat turbid, but does not leave any considerable portion when filtered. When heated with alcohol, the solution in muriatic acid becomes intensely dark green; if more alcohol and then sulphuric acid be added, a white precipitate is produced. Solution of sulphate of lime does not precipitate the solution of the color in muriatic acid, but this is done by sulphuric acid with or without the addition of alcohol. The reddish-yellow color of the solution in nitric acid changes by heating, with the addition of alcohol, into a beautiful blue. If acetate of lead be added to the dilute solution in nitric acid, a heavy precipitate of the color of chromate of lead makes its appearance. If an excess of lead were added, filtered, the excess of lead and the lime precipitated by sulphuric acid, alcohol added, filtered and evaporated, large quantities gave a residue, which, when dissolved in water and mixed with chloride of platinum with the addition of muriatic acid, furnished octahedra of platino-chloride of potassium. The investigation gave no magnesia or other bases except lime and potash. Of acids, besides the chromic acid, which was undoubtedly present from the preceding experiments, there was only a small quanthy of sulphuric acid.

When the author mixed a hot saturated solution of bi-chromate of potash with a saturated solution of chloride of calcium, a precipitate was produced, which, when washed and dried, was undistinguishable from the Steinbuhl yellow.

The substance gave 3-1 per cent to distilled water after short stirring. With nitrate of silver, the yellow filtrate gave a red precipitate of chromate of silver, which was rapidly converted into white chloride of silver on the addition of a few drops of muriatic acid. Sulphuric acid and alcohol produce a strong turbidity in the filtrate. When boiled with reducing organic matters and muriatic-acid, the yellow filtrate loses its color, without, however, acquiring more than a tinge of green. Acetate of lead precipitates the yellow filtrate with the color of chromate of lead. Chloride of platinum produces a very slight turbidity in the original filtrate. Even in 16 hour no precipitate is deposited.

This yellow consists, therefore, of chromic acid, lime and potash; when stirred for a short time with cold water, it parts with chromate of lime.

The poisonous qualities of chromic acid and its soluble salts, and the circumstance that the color parts with perceptible, although not large quantities of chromic acid to cold water, render this yellow and extremely dangerous coloring matter, the employment of which, in confectionery and similar trades, must not be though of.

- London Chemical Gazette

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