Litmus paper is a piece of paper that produces a result which can be used as a pH indicator. It is made by treating paper with natural dyes from lichens. Initially, litmus paper is either red or blue.
Litmus paper is available in three different colors which are purple, red and blue. A purple litmus paper turns red if the given solution is acidic and turns blue if the given solution is basic in nature.
The Spanish alchemist Arnaldus de Villa Nova (Arnold of Villanova) is purported to have used litmus in the early 14th century. There is some data that suggest that litmus paper was developed by J.L. Gay-Lussac, a French chemist during the early 1800s. Gay-Lussac is best known for his Law of Combining Volumes.
Originally, the blue dye has been extracted from lichens since the 16thcentury, especially in the Netherlands. In distilled water, lichens have a mauve (purple) tint. It turns red when added to an acidic solution and blue when added to a basic solution.
The word "litmus" comes from the old Norse word for "to dye or color". Today, litmus is prepared mainly from the species Roccella montagnei from Mozambique and Dedographa leucophoea from California.
With the cooperation of two university professors from Kyoto, Masao Horiba developed a suitable pH meter, which was named the “Alligator”. By 1950, he was producing glass electrodes.
History of litmus paper
