Søren Peter Lauritz Sørensen (9 January 1868 – 12 February 1939) was a Danish chemist, known for the introduction of the concept of pH, a scale for measuring acidity and alkalinity.

He wanted to make a career in medicine, but under the influence of chemist Sophus Mads Jørgensen decided to change to chemistry.

[1] While studying for his doctorate he worked as assistant in chemistry at the laboratory of the Technical University of Denmark, assisted in a geological survey of Denmark, and also worked as a consultant for the Royal Navy Dockyard.

) was published in French and Danish as well as in German[5] described two methods for measuring acidity which Sørensen and his students had refined.

[6] The first method was based on electrodes, whereas the second involved comparing the colours of samples and a preselected set of indicators.