Litmus test
Definition
The litmus test uses dyes extracted from lichens to signal acidity or alkalinity through color change. It is simple and fast but profoundly imprecise.
Litmus had existed for centuries and could tell you whether something was acidic but not by how much. Its qualitative nature is exactly the limitation that motivated a quantitative acidity scale. It contrasts with electrode methods that relate hydrogen behavior to measurable voltage.
Related concepts
Part of The Blueprint of Water · 📏 measurement