Søren Peter Lauritz Sørensen (9 January 1868 – 12 February 1939) was a
Danish chemist
A chemist (from Greek ''chēm(ía)'' alchemy; replacing ''chymist'' from Medieval Latin ''alchemist'') is a graduated scientist trained in the study of chemistry, or an officially enrolled student in the field. Chemists study the composition of ...
, known for the introduction of the concept of
pH, a scale for measuring
acid
An acid is a molecule or ion capable of either donating a proton (i.e. Hydron, hydrogen cation, H+), known as a Brønsted–Lowry acid–base theory, Brønsted–Lowry acid, or forming a covalent bond with an electron pair, known as a Lewis ...
ity and
alkalinity
Alkalinity (from ) is the capacity of water to resist Freshwater acidification, acidification. It should not be confused with base (chemistry), basicity, which is an absolute measurement on the pH scale. Alkalinity is the strength of a buffer s ...
.
Personal life
Sørensen was born in
Havrebjerg
Havrebjerg is a village on Zealand (Denmark), Zealand, Denmark. It is located in Slagelse Municipality.
History
Maren Sørensen, considered to be the first female Danish priest, was ordained by Havrebjerg by the independent Grundtvigian priest Nie ...
in 1868 as the son of a farmer. He began his studies at the
University of Copenhagen
The University of Copenhagen (, KU) is a public university, public research university in Copenhagen, Copenhagen, Denmark. Founded in 1479, the University of Copenhagen is the second-oldest university in Scandinavia, after Uppsala University.
...
at the age of 18. He wanted to make a career in medicine, but under the influence of chemist
Sophus Mads Jørgensen
Sophus Mads Jørgensen (4 July 1837 – 1 April 1914) was a Danish chemist. He is considered one of the founders of coordination chemistry, mainly by being one of the pioneers of chain theory, and is known for the debates which he had with Alfred ...
decided to change to chemistry.
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.
Sørensen was married twice. His second wife was Margrethe Høyrup Sørensen, who collaborated with him in his studies.
Work
From 1901 to 1938, Sørensen was head of the prestigious
Carlsberg Laboratory,
Copenhagen
Copenhagen ( ) is the capital and most populous city of Denmark, with a population of 1.4 million in the Urban area of Copenhagen, urban area. The city is situated on the islands of Zealand and Amager, separated from Malmö, Sweden, by the ...
.
While working at the Carlsberg Laboratory he studied the effect of ion concentration on proteins
and, because the concentration of hydrogen ions was particularly important, he introduced the
pH-scale as a simple way of expressing it in 1909. The article in which he introduced the scale (using the notation
) was published in French and Danish as well as in German
described two methods for measuring acidity which Sørensen and his students had refined.
The first method was based on electrodes, whereas the second involved comparing the colours of samples and a preselected set of indicators. (Sørensen, 1909).
:From p. 134: ''"Die Größe der Wasserstoffionenkonzentration ... und die Bezeichnung
für den numerischen Wert des Exponent dieser Potenz benütze."'' (The magnitude of the hydrogen ion concentration is accordingly expressed by the normality factor of the solution concerned, based on the hydrogen ions, and this factor is written in the form of a negative power of 10. By the way, as I refer
o itin a following section (see p. 159), I just want to point out here that I use the name "hydrogen ion exponent" and the notation
for the numerical value of the exponent of this power.)
:From pp. 159–160: ''"Für die Zahl ''p'' schlage ich den Namen "Wasserstoffionenexponent" ... Normalitätsfaktors der Lösung verstanden."'' (For the number ''p'' I suggest the name "hydrogen ion exponent" and the notation
. By the hydrogen ion exponent (
) of a solution is thus understood the
Briggsian logarithm of the reciprocal value of the normality factor of the solution, based on the hydrogen ions, and this factor is written in the form of a negative power of 10).
:Starting on p. 139, ''"4. Meßmethoden zur Bestimmung der Wasserstoffionenkonzentration."'' (4. Methods of measurement for the determination of hydrogen ion concentration.), Sørensen reviewed a series of methods for measuring hydrogen ion concentration. He rejected all of them except two.
:From p. 144: ''"Es gibt noch zwei Verfahrungsweisen, ... bzw. die colorimetrische Methode genannt."'' (There are still two procedures by which the hydrogen or hydroxyl ion concentration of a solution can be determined; namely, gas chain measurement and determination by means of indicators, also called the electrometric or colorimetric method.) On pp. 145–146, Sørensen outlined the electrometric and colorimetric methods:
::From p. 145: ''"Die elektrometrische Methode. Wird eine mit Platin-schwarz bedeckte Platinplatte in eine wäßerige ... von der Wasserstoffionenkonzentration der Lösung abhängt.)"'' (The electrometric method. If a platinum plate that's covered with platinum black is dipped into an aqueous – acidic, neutral, or alkaline – solution and if the solution is saturated with hydrogen, then one finds, between the platinum plate and the solution, a voltage difference whose magnitude depends on the hydrogen ion concentration of the solution according to a law.
::From pp. 145: ''"Die colorimetrische Methode. Der Umschlag des Indicators bei einer gewöhnlichen Titrierung bedeutet ja, wie bekannt, daß die Konzentration der Wasserstoffionen der vorliegenden Lösung eine gewisse Größe von der einen oder der anderen Seite her erreicht oder überschritten hat."'' (The colorimetric method. The sudden change of the indicator during a typical titration means, as is known, that the concentration of hydrogen ions in the solution at hand has reached or exceeded – from one direction or the other – a certain magnitude.)
: p. 146: ''"Die Grundlage ist seit langer Zeit bekannt, ... eine vollständige Reihe Indikatoren mit Umschlagspunkten bei den verschiedensten Ionenkonzentrationen zusammenzustellen."'' (The basis
f the colorimetric methodhas been known for a long time, but the scattered material was first struggled through and perfected at certain points by the beautiful investigations of Hans Friedenthal
870-1942and Eduard Salm,
so that it became possible for them to assemble a complete series of indicators with transition points at the most varied ion concentrations.)
:On pp. 150ff, the electrometric method is detailed; and on pp. 201ff, the colorimetric method is detailed.
References
Notes
{{DEFAULTSORT:Sorensen, S. P. L.
1868 births
1939 deaths
Danish chemists
Carlsberg Laboratory staff
People from Slagelse Municipality
19th-century Danish scientists
20th-century Danish scientists
19th-century chemists
20th-century chemists
Foreign associates of the National Academy of Sciences
Members of the Royal Society of Sciences in Uppsala
Analytical chemists