Soren Sorensen. Portrait of Danish biochemist and inventor, Soren Sorensen (1868-1939). He studied chemistry at Copenhagen. From 1901 he held the Directorship of the Carlsberg Laboratory. Sorensen worked on amino acids, proteins and enzymes. In 1909 he invented the pH scale as a measure of acidity, for which he became famous. This scale is rigorous enough for both chemists and non-chemists alike, and is universally employed. For any solution, a pH from 1 to 7 indicates decreasing acidity; 7 to 14 shows increasing alkalinity; while pH 7 is neutral at 25 degrees Celsius. The value can be measured with a pH meter or with pH indicator paper.