Who introduced the pH scale, and in which year?

1. Henderson wrote his equation for the blood buffer system in 1908. 2. The pH scale itself was introduced a year later, in 1909, by the Dane Sorensen. 3. Hasselbalch published measurements of the pH of blood in 1912. 4. In 1916 he recast the earlier equation in logarithmic form to match the pH scale. 5. The Bohr effect paper, which he co authored, dates from 1904. _Source: OpenStax Chemistry (CC BY 4.0), Ch 14 "Acid-Base Equilibria", section 14.6 Buffers_