PH - History

History

The concept of p was first introduced by Danish chemist Søren Peder Lauritz Sørensen at the Carlsberg Laboratory in 1909 and revised to the modern pH in 1924 to accommodate definitions and measurements in terms of electrochemical cells. In the first papers, the notation had the "H" as a subscript to the lowercase "p", like so: pH.

It has been suggested that the "p" in "pH" stands for "power", others refer to the German Potenz (meaning "power"), others refer to French puissance (also meaning "power", based on the fact that the Carlsberg Laboratory was French-speaking); others refer to "potential". According to the Carlsberg Foundation pH stands for "power of hydrogen". Other suggestions have surfaced over the years that the "p" stands for the Latin terms pondus hydrogenii, potentia hydrogenii, or potential hydrogen. It is also suggested that Sørensen used the letters "p" and "q" (commonly paired letters in mathematics) simply to label the test solution (p) and the reference solution (q).

Current usage in chemistry is that p stands for "decimal cologarithm of", as also in the term pK, used for acid dissociation constants.

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