Changes of Color Produced by Colorless Liquids.
Make a strong infusion of the leaves of the red cabbage, which will be of a beautiful blue color; drop into it a few drops of dilute sulphuric acid, and the color will change to a bright red; add some solution of carbonate of potash, or soda, and the red color will gradually give way to the original blue; continue adding the alkaline solution, and the fluid will assume a bright green color. Now resume the acid, and as it is dropped in, the color will again change from green to blue, and from blue to red. Now this simple experiment illustrates three points: first, that acids change the color of most vegetable blues and greens to red; second, that alkalies change most blues and reds to green; and third, that when the acid and alkali are united together, they both lose their property of changing color, and become what is called a neutral salt, i.e. a compound possessing the properties of neither of its constituents.