Historical figure · Pearson Edexcel International GCSE revision on Incandio

Justus von Liebig

Portrait of Justus von Liebig

Who Weighed What Burned Away · Chemist · 1803–1873

Who invented the apparatus that made the analysis of an organic compound a morning's work instead of a week's, trained a generation of chemists at Giessen in the first true teaching laboratory, and discovered with Wöhler that two entirely different substances can have exactly the same composition.

Defend these ideas against Liebig

Incandio is a free revision platform for the Pearson Edexcel International GCSE, and on it a topic counts as mastered only once you have learned it, proved it in questions, taught it back and defended it against the person with the strongest claim on it. Justus von Liebig is that person for 2 topics on the course:

Who was Liebig?

Liebig was born at Darmstadt in 1803, the son of a dealer in pigments and chemicals, and was apprenticed to an apothecary before studying at Bonn and Erlangen and then in Paris, where he worked in Gay-Lussac's laboratory. He was made professor at Giessen in 1824, at twenty-one, and there did the thing for which chemistry is most in his debt: he built a laboratory in which students learned by doing analyses with their own hands, and he made those analyses reliable. His method was to burn the substance in a tube with copper oxide, so that all its carbon leaves as carbon dioxide and all its hydrogen as water, then to absorb the water in calcium chloride and the carbon dioxide in a five-bulbed glass vessel of potash solution — the Kaliapparat of 1831 — and to weigh both absorbers before and after. From two weighings came the percentages of carbon and hydrogen, and oxygen was taken by difference. What had been a week of expert labour became a routine determination, and several hundred organic compounds were analysed at Giessen in a few years. The limitation is exactly as sharp as the method. The weighings give the RATIO in which the elements are present, and nothing else; they cannot distinguish a compound from another compound with the same ratio, nor say how large the molecule actually is. Liebig knew this better than anyone, because he had met it head on: his silver fulminate and Wöhler's silver cyanate had, on analysis, precisely the same composition and behaved entirely differently. Berzelius named the phenomenon isomerism. None of the three could say what the difference consisted in. Liebig went on to found agricultural chemistry with his book of 1840, to argue that plants take their nitrogen and minerals from the soil and the air rather than from humus, to formulate the law of the minimum, and to quarrel — long, publicly and unsuccessfully — with Pasteur over whether fermentation is the work of a living organism.

Major achievements

Life in brief

Explore the life of Liebig — five chapters

  1. Expelled, Apprenticed, and a Professor at Twenty-One — Darmstadt to Giessen by way of Paris
  2. Five Bulbs of Potash — The Kaliapparat, 1831
  3. Students at Their Own Benches — Giessen, and the invention of scientific training
  4. What a Plant Actually Eats — Agricultural chemistry, the law of the minimum, and a failed fertiliser
  5. The Argument He Lost — Fermentation, Pasteur, and twenty years of being wrong in public

Read the five-chapter life of Justus von Liebig →

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