By Casey Quackenbush
May 29, 2018

How well do you remember the pH scale from chemistry class?

Today’s Google Doodle presents a small interactive to jog your memory, and more importantly, celebrate Søren Peder Lauritz Sørensen, the even less-remembered scientist behind the pH scale. His work became a foundational concept in chemistry that serves as an important test in many areas of every daily life.

Here’s what you should know about S.P.L. Sørensen.

Who was S.P.L. Sørensen?

Born in Havrebjerg, Denmark in 1868, Sørensen was a Danish chemist who established the pH scale, which tests the acidity or alkalinity of a substance. Sørensen studied at the University of Copenhagen, originally with plans to pursue medicine. After studying under an important chemist named SM Jørgensen, Sørensen pivoted to chemistry. He ran the Carlsberg Laboratory in Copenhagen from 1901 to 1938, where he studied ion concentration on proteins and devised a simple way to express the concentration of hydrogen ions: the pH scale.

What is the pH scale used for?

Introduced in 1909, the pH scale — officially, the power of hydrogen — measures the acidity or alkalinity of a substance. Substances with a pH less than 7 are acidic and those above 7 are alkaline. Water is neutral at 7. The scale is incredibly important for a wide-range of areas in every day life, such as treating soil, reducing tooth decay, medicine, and monitoring the acidity of water.

Sørensen died on Feb. 12, 1939, but his legacy continues to this day.

Tuesday’s animated Doodle depicts a cartoon Sørensen and his pH scale. Viewers must decide if everyday foodstuffs, such as tomatoes, lemons, eggs and broccoli are classed as acidic or alkaline.

Write to Casey Quackenbush at casey.quackenbush@time.com.

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