One of the ironies of scientific word etymologies and histories is that while many words have ancient and clear paths to the modern usage (this week’s neutral and base, for example), many more words and terms have no known or discoverable history. Scientists are often focussed on the scientific task at hand and not the historic, and notes and thoughts leading to definitions are often lost. Today’s term, pH, is an example of this.
Danish chemist Soren Peder Lauritz Sorensen proposed the modern pH scale in 1909 to describe the reactivity of acids and bases. Today the mathematical definition of pH is the negative decimal logarithm of the hydrogen ion activity in a solution. The proposed etymologies for pH are wide ranging: the p stands for the French word puissance or the German word Potenz or the Latin word potentia or pondus, all of which have the same meaning as the English word Power, itself a candidate. P has also been proposed to mean percentage or potential. Some historians of science suggest that Sorensen merely picked two letters out of the alphabet and the coincidences of meaning were accidental. The H at least always stands for Hydrogen.
Photo of Soren Peder Lauritz Sorensen, image in the public domain