Have in one vessel some sulphuric acid, and in another an infusion of nut-galls; they are both colourless and transparent; mix them, and they will become black and opaque. TWO COLOURLESS FLUIDS MAKE A COLOURED ONE. Put into a wine-glass of water, a few drops of prussiate of potash; and into a second glass of water, a little weak solution of sulphate of iron in water: pour the colourless mixtures together into a tumbler, and they will be immediately changed to a bright deep blue colour. Or, mix the solution of prussiate of potash with that of nitrate of bismuth, and a yellow will be the product. Or, mix the solution of prussiate of potash with that of sulphate of copper, and the mixture will be of a reddish brown colour. CHANGE OF COLOUR BY COLOURLESS FLUIDS. Three different colours may be produced from the same infusion, merely by the addition of three colourless fluids. Slice a little red cabbage, pour boiling water upon it, and when cold, decant the clear infusion, which divide into three wine-glasses: to one, add a small quantity of solution of alum in water; to the second, a little solution of potash in water; and to the third, a few drops of muriatic acid. The liquor in the first glass will assume a purple colour, the second, a bright green, and the third a rich crimson. Put a dram of powdered nitrate of cobalt into a phial containing an ounce of the solution of caustic potass; cork the phial, and the liquid will assume a blue colour, next a lilac, afterwards a peach colour, and lastly a light red. TO CHANGE A BLUE LIQUID TO WHITE. Dissolve a small lump of indigo in sulphuric acid, by the aid of moderate heat, and you will obtain an intense blue colour: add a drop of this to half a pint of water, so as to dilute the blue; then pour some of it into strong chloride of lime, and the blue will be bleached with almost magical velocity. VERITABLE “BLACK” TEA. Make a cup of strong green tea; dissolve a little green copperas in water, which add to the tea, and its colour will be black. RESTORATION OF COLOUR BY WATER. Water being a colourless fluid, ought, one would imagine, when mixed with other substances of no decided colour, to produce a colourless compound. Nevertheless, it is to water only that blue vitriol, or sulphate of copper, owes its vivid blueness; as will be plainly evinced by the following simple experiment. Heat a few crystals of the vitriol in a fire shovel, pulverize them, and the powder will be of a dull and dirty white appearance. Pour a little water upon this, when a slight hissing noise will be heard, and at the same moment, the blue colour will instantly re-appear. Under the microscope, the beauty of this experiment will be increased, for the instant that a drop of water is placed in contact with the vitriol, the powder may be seen to shoot into blue prisms. If a crystal of prussiate of potash be similarly heated, its yellow colour will vanish, but re-appear on being dropped into water.