litmus paper /lit″məs/ [ONorse, litmosi, coloring herb; L, papyrus, paper] , absorbent paper coated with litmus, a blue dye, that is used to determine pH. Acid substances or solutions turn blue litmus to red. Alkaline substances or solutions do not cause a color change in blue litmus. The pH range is 4.5 (red) to 8.5 (blue).
