1. ChemistryA universal indicator is a pH indicator made of a solution of several compounds that exhibit various smooth colour changes over a wide range pH values to indicate the acidity or alkalinity of solutions. A universal indicator can be in paper form or present in a form of a solution. == History == Although there are several commercially available universal pH indicators, most are a variation of a formula patented by Yamada in 1933. == Composition == A universal indicator is usually composed of water, 1-propanol, phenolphthalein, sodium hydroxide, methyl red, bromothymol blue, sodium bisulfite, and thymol blue. The colours that indicate the pH of a solution, after adding a universal indicator, are: The colors from yellow to red indicate an acidic solution, colors blue to violet indicate an alkaline solution and a green colour indicates that a solution is neutral. Wide-range pH test papers with distinct colours for each pH from 1 to 14 are also available. Colour matching charts are supplied... from wikipedia.org