Dissolve indigo in diluted sulphuric acid, and add to it an equal quantity of solution of carbonate of potash. 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 color; add a little lime water and the mixture will be colorless; dip into it a piece of white cloth, dry it rapidly, and in a few hours the cloth will become red.