The indigestion tablets are bases. This means universal indicators can determine the pH of a sample quantitatively within a certain range.
The blue dye has been extracted from lichens since the 16th century. In general, litmus paper is red below a pH of 4. As the paper moves along the belt it passes under a mesh or wire cylinder called a dandy roll. You dip the paper into the substance of your choice and it will change colour.
Lichens can be found growing on rocks, trees, and walls, in the soil and even under water in virtually all types of climates. The pH Scale Knowing whether a substance is acidic or basic is only the first step.