COLOURS VANISHING AND REAPPEARING.
Dissolve brass filings in volatile alkali, which will be a liquid of a blue colour while exposed to the air, but, on corking a phial of it, the colour will disappear.
To nine parts of water in a glass put one part of nitric acid; a red ribbon dipped in this will have its hue “killed,” but it will come again when washed in a solution of fuller’s earth in water.