Dissolve indigo in diluted sulphuric acid, and add to it an equal
quantity of solution of carbonate of potass. If a piece of white cloth
be dipped in the mixture, it will be changed to blue; yellow cloth,
in the same mixture, may be changed to green; red to purple, and blue
litmus paper to red.
Nearly fill a wine-glass with the juice of beet-root, which is of a
deep red colour; add a little lime water, and the mixture will be
colourless; dip into it a piece of white cloth, dry it rapidly, and in
a few hours, the cloth will become red.