It frequently occurs, that substances of different colours, or even without colour, by coming in contact, produce colours very different from that of either of the ingredients when separate; thus, if a sheet of paper be striped in one direction with a hair pencil dipped in a solution of sub-carbonate of potass; and then crossed with a solution of sulphuric acid, diluted with five times as much water, it will be colourless; but dip it in a mixture of a weak solution of sulphate of iron, and infusion of nut galls, and it will instantly become a beautiful plaid; the ground being purple, striped one way with black and crossed with white. If a similar paper be striped with sub-carbonate of potass, and crossed with infusion of galls, and afterward dipped in a solution of sulphate of iron, it will become purple, yellow, black and white. Dip a piece of white calico in a cold solution of sulphate of iron and let it dry. Then imprint any figures upon it with a strong solution of colourless citric acid, and let this dry also. If the piece be then well washed in warm water, and afterwards boiled in a decoction of log-wood, the ground will be dyed either a slate or a black colour, according to the strength of the metallic solution, while the printed figures will remain beautifully white. Stain some parts of a sheet of paper a purple brown, with a mixture of infusion of galls and sulphate of iron; stain other parts green with a mixture of tinctures of turmeric and litmus; stain other parts purple with juice of red cabbage; other parts red with tincture of litmus and muriatic acid; other parts yellow with tincture of turmeric; wash the remainder of the sheet with a solution of sulphate of iron, which will remain white. Then print, or draw with a camel-hair pencil, any figure or figures on every part of the paper, with a solution of sub-carbonate of potass. On the purple brown, the figure will be black; on the green it will be purple; on the purple it will be green; on the red it will be blue; on the yellow, red; and on the white, it will take a yellow colour. Thus the figure will appear in colors different from the ground in every part. Immerse a piece of white cotton in a solution of sulphate of iron—it will remain white; dip another piece in tincture of turmeric, it will take a yellow; wet another piece with juice of red cabbage, containing also, a few drops of muriatic acid,—it will be red; dye another piece green, by immersing it in a mixture of tincture of turmeric and litmus; and another, purple by a mixture of infusion of galls and sulphate of iron. Let them dry; then immerse them all together in a solution of sub-carbonate of potass. The white will be changed to a yellow; the yellow to a red; the red to green; the green to purple; and the purple to black; and it is not improbable that some black might be materially changed or bleached by the same simple solution.