Litmus paper is available in three colors: purple, red, and blue. A purple litmus paper changes color when exposed to a solution, turning red if the solution is acidic (pH less than 7) and blue if it is basic (pH greater than 7). Blue litmus paper will turn red in acidic conditions, while red litmus paper will turn blue in basic conditions. This simple color change provides a quick and reliable method to assess a solution's pH without the need for complex equipment.
Historically, litmus has been used for centuries as a chemical indicator. Spanish alchemist Arnaldus de Villa Nova reportedly used litmus as early as the 14th century. However, some records suggest that the development of litmus paper in its current form is credited to French chemist J.L. Gay-Lussac in the early 19th century. Gay-Lussac is renowned for his Law of Combining Volumes and made significant contributions to chemistry, including improvements in litmus paper.
The blue dye used in litmus paper has been extracted from lichens since the 16th century, especially in the Netherlands. Lichens, when soaked in distilled water, have a mauve (purple) tint. When an acidic solution is added, the dye turns red, and it turns blue in a basic solution. The word "litmus" originates from Old Norse, meaning "to dye or color."
Today, litmus is primarily sourced from lichen species like Roccella montagnei from Mozambique and Dedographa leucophoea from California. Advances in pH measurement, such as the pH meter developed by Masao Horiba in the 1950s, have refined how we measure acidity and basicity, but litmus paper remains a widely used tool due to its simplicity and reliability.
Litmus Paper: A Simple and Effective pH Indicator
