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.