2. Purple litmus test solution can be used to detect the pH of the solution, which turns red in acid and blue in alkali; Red litmus test solution is used for the detection of alkaline solution, which turns blue when it meets alkali; The blue litmus test solution is used for the detection of acidic solution, and turns red when it meets acid.
3. Litmus as a chemical indicator for testing the acidity and alkalinity of solution was first discovered and popularized by British chemist and physicist Boyle (1627- 169 1).