How it began
Soren Sorensen (1868 to 1939) held a doctorate from the University of Copenhagen and from 1901 directed the chemical department of the Carlsberg Laboratory, which the brewery's founder J. C. Jacobsen had opened in 1875. In 1909, while studying the effect of ion concentration on proteins, he introduced pH as a convenient way of expressing acidity.
Before it existed
Until Sorensen developed the scale there was no widely accepted way of expressing hydrogen ion concentrations. Chemists were slowly changing over from the old color-change tests for acidity to electrical methods, in which the current produced in an electrochemical cell was measured with a sensitive and delicate galvanometer.
How it works
pH is the negative logarithm of the hydrogen ion concentration of a solution. The scale is usually described as running from 0 to 14 for solutions in water. Values below 7 are acidic, with those nearest 0 the most acidic, and as the number rises toward 14 the solution becomes more basic, or alkaline.
What lasted
Sorensen went on to lead the application of thermodynamics to protein chemistry, assisted by his wife, Margrethe Hoyrup Sorensen. He headed the chemical department at Carlsberg until 1938. The scale became the common way to state acidity, and in 2018 Google marked his work with an interactive game that asked players to sort everyday items into acids and bases.
