What is purple litmus? Classification and application

Purple litmus is a filter paper impregnated with a solution of ethanol or water with a pigment extracted from the roots of the lichens Roccella and Dendrographa. Litmus paper is used as a pH indicator in chemical experiments. The advantage of litmus paper compared to other types of pH indicator paper is that the results are quite fast. Litmus paper also has the ability to distinguish gases such as H2S, SO3. Therefore, purple litmus is a tool to measure the quality of water, food or used in laboratories today.