How it began
Theodor von Grotthuss was born in Leipzig in 1785 while his parents were away from their home in the Grand Duchy of Lithuania. After studies in Leipzig, Paris, Rome and Naples, he returned in 1808 to his mother's estate at Gedučiai, now a small village near Žeimelis in the Pakruojis district of Lithuania, and set up a personal laboratory there. In 1817 he found that light affects chemical processes and stated the rule now known as the first law of photochemistry.
Before it existed
Grotthuss was already known for the first theory of electrolysis, which he published in Rome in 1805 in a memoir on the decomposition of water by galvanic electricity. That work, soon translated into English and German, is treated as the first description of the Grotthuss mechanism and belongs to his years abroad. His photochemical work was done after he came back to Gedučiai, where he spent the major part of his life.
How it works
The law, as the Lithuanian Physical Society words it, says that only that light which is absorbed by a system can bring about a photochemical change. Light that passes through a substance or is reflected from it does no chemical work in it. Grotthuss also set out theoretical foundations for luminescence and studied light absorption and phosphorescence.
How it spread
His observations on photochemical reactions were confirmed some 20 years later by John Herschel and John Draper, and the results became known as the Grotthuss-Draper laws of photochemistry. His ideas on luminescence were worked out further in the second half of the 19th century by Becquerel, Brewster and Stokes, and his electrolysis theory influenced Davy, Berzelius, Faraday and Arrhenius.
Where it stands today
The building at Gedučiai where Grotthuss is believed to have done his experiments still exists, and the European Chemical Society has given the Grotthuss Laboratory its Historical Landmarks Award. The Žiemgala museum in Žeimelis plans to rebuild his equipment and open an educational laboratory for visitors and schoolchildren. Lithuanian physicists marked 200 years of the law in 2017.
