Justus von Liebig

Chapter 1 · Expelled, Apprenticed, and a Professor at Twenty-One

Darmstadt to Giessen by way of Paris

1803 – 1824 · Darmstadt · Heppenheim · Bonn · Erlangen · Paris

Justus Liebig was born at Darmstadt in May 1803. His father dealt in pigments, dyes and chemicals, and had a small workshop at the back of the shop where he prepared his own products. Liebig worked in it as a boy.

He was a poor schoolboy. There is a story, which he told himself, that a schoolmaster called him a hopeless blockhead in front of the class and asked what he intended to do with his life; Liebig replied that he intended to be a chemist, and the class laughed.

He was apprenticed to an apothecary at Heppenheim at fifteen and lasted about ten months. Accounts differ as to whether he was dismissed after an explosion in the attic where he had a laboratory.

He studied at Bonn and then Erlangen, where he took a doctorate in 1822 — hurriedly, and possibly to avoid trouble arising from his involvement with a nationalist student fraternity.

Then came the decisive move. With a grant from the Grand Duke of Hesse he went to Paris and was admitted to Gay-Lussac's private laboratory. There he learned analysis at the highest level then practised anywhere. Alexander von Humboldt saw his work on fulminates and recommended him.

In 1824, aged twenty-one, he was appointed extraordinary professor at the small University of Giessen.

He found no laboratory, no equipment and no students worth the name, and set about building all three.

“The composition is the beginning of the question, not the end of it.”

— Attributed to Justus von Liebig, on the limits of combustion analysis

Why this matters

Liebig arrived at Giessen at twenty-one with Parisian analytical training and no facilities, and built the first modern teaching laboratory because he needed one.

You have the blockhead, the explosion and the chair at twenty-one. What would you ask?

Ask Liebig

• “Were you really called a hopeless blockhead?”
• “What did you learn in Gay-Lussac's laboratory?”
• “What did you find when you arrived at Giessen?”
• “What did your father's workshop teach you?”
• “Is twenty-one too young for a chair?”

Chapter 2 · Five Bulbs of Potash

The Kaliapparat, 1831

1831 · Giessen

Determining the composition of an organic compound in 1830 was a week's work for an expert and frequently gave results nobody could reproduce.

Liebig's method was combustion. Burn a weighed sample in a tube with copper oxide, which supplies oxygen and ensures complete oxidation. All the carbon leaves as carbon dioxide; all the hydrogen leaves as water.

Now catch them. The water is absorbed in a tube of calcium chloride. The carbon dioxide is absorbed in a solution of potassium hydroxide.

The problem was absorbing the carbon dioxide *completely*. Gas passing through a simple tube of solution escapes partly unabsorbed.

Liebig's answer, in 1831, is the *Kaliapparat*: a single piece of blown glass in a triangular arrangement, with five bulbs. The gas is forced to bubble through potash solution repeatedly, through bulb after bulb, so that essentially none escapes.

Weigh both absorbers before and after. The gain in the calcium chloride gives the hydrogen; the gain in the Kaliapparat gives the carbon. Oxygen is taken by difference.

A week became a morning. Several hundred organic compounds were analysed at Giessen within a few years, and the technique spread everywhere. The Kaliapparat is still the emblem of the American Chemical Society.

And Liebig was clear about the limitation, more clearly than his followers were. The analysis gives the *ratio* of the elements — the empirical formula — and *nothing else*. It cannot tell you how large the molecule is: CH₂O and C₆H₁₂O₆ give identical analyses. And it cannot distinguish two compounds with the same ratio.

He knew this from his own experience, because he had run straight into it.

Why this matters

Combustion analysis gives the ratio of elements and nothing more, which is the distinction between empirical and molecular formula that every chemistry student now learns first.

You have the five bulbs and the limitation. What is your question?

Ask Liebig

• “Why do you need five bulbs rather than one?”
• “What can combustion analysis never tell you?”
• “Why burn the sample with copper oxide?”
• “How is oxygen determined if you never catch it?”
• “What changed when a week became a morning?”

Chapter 3 · Students at Their Own Benches

Giessen, and the invention of scientific training

1826 – 1852 · Giessen

Liebig's larger invention was institutional, and it changed how every science is taught.

Before Giessen, a chemistry student attended lectures and watched demonstrations. Practical skill was acquired by apprenticeship — attaching yourself to a working chemist as an assistant, if you could find one willing.

Liebig built a laboratory in which *every student had a bench*, apparatus, and a substance to analyse. They worked with their own hands, under supervision, on real problems. As they became competent they were given research problems from the group's programme, and their results were published.

So a student progressed from learning a technique, to using it, to producing new knowledge with it — within the same institution, on a defined path.

That is a *research training*, and it is now the standard structure of a science education everywhere in the world. Giessen is where it starts.

The numbers speak for themselves. Something like seven hundred students passed through, and the roll includes August Wilhelm Hofmann, who founded the British and German dye industries; Charles Gerhardt; Wilhelm Wislicenus; Emil Erlenmeyer; and Kekulé, who came to hear the lectures and stayed.

Hofmann took the method to London in 1845 as head of the new Royal College of Chemistry, where his student William Perkin accidentally made the first synthetic dye, mauveine, in 1856 — founding the modern chemical industry.

Giessen also produced a professional identity. Before Liebig, chemist meant apothecary or manufacturer. After him it meant a person with a training, a laboratory and a publication record.

Why this matters

The Giessen laboratory invented research training — students moving from technique to problem to publication — and it is now the standard structure of every science education.

You have the benches and the seven hundred students. What would you ask?

Ask Liebig

• “How did students learn chemistry before your laboratory?”
• “What does a student learn at a bench that they cannot in a lecture?”
• “How do you move a student from exercise to research?”
• “What did Hofmann take to London?”
• “Did you create a profession as well as a laboratory?”

Chapter 4 · What a Plant Actually Eats

Agricultural chemistry, the law of the minimum, and a failed fertiliser

1840 – 1860s · Giessen · England

In 1840 Liebig published *Organic Chemistry in its Application to Agriculture and Physiology*, and founded a subject.

The prevailing *humus theory* held that plants take their carbon from decayed organic matter in the soil. Liebig demolished it. Plants take their carbon from *carbon dioxide in the air*, their hydrogen and oxygen from water, and their nitrogen and mineral nutrients — potassium, phosphorus, calcium, magnesium, sulphur — from the soil as *inorganic* salts.

The practical implication is enormous: soil fertility can be restored by adding the *specific minerals* a crop has removed, and those minerals can be manufactured.

He also formulated the *law of the minimum*: growth is limited not by the total quantity of nutrients available but by whichever necessary nutrient is scarcest. Supply everything else in abundance and the plant still grows only as far as the missing one allows. It is usually pictured as a barrel made of staves of different heights, which holds water only to the level of the shortest stave.

That principle is general and is applied well beyond agriculture — in ecology, in nutrition, in operations management.

His own first artificial fertiliser failed. He had reasoned that soluble compounds would be washed away by rain and therefore made his phosphates deliberately insoluble; plants could not take them up, and the product was useless. He had to concede it publicly. He was also wrong to believe plants could obtain enough nitrogen from the air; most cannot, and nitrogen fertiliser proved essential.

He also invented a process for concentrating beef into an extract, and Liebig's Extract of Meat Company was founded on it in 1865 — the ancestor of Oxo.

Why this matters

The law of the minimum — growth is limited by the scarcest necessary nutrient, not the total supply — is one of the most widely transferable principles in biology.

You have the barrel with the short stave and the fertiliser that failed. What is your question?

Ask Liebig

• “Where does the carbon in a plant come from?”
• “Explain the law of the minimum to me.”
• “Why did your first fertiliser fail?”
• “Were you wrong about nitrogen from the air?”
• “What does the meat extract have to do with any of this?”

Chapter 5 · The Argument He Lost

Fermentation, Pasteur, and twenty years of being wrong in public

1839 – 1873 · Giessen · Munich · Paris

In 1839 Liebig and Wöhler published, anonymously, a satire in Wöhler's journal, ridiculing the claim that fermentation is caused by living yeast. It described tiny animals shaped like distilling flasks which swallowed sugar and excreted alcohol at one end and carbon dioxide at the other.

The target was Theodor Schwann, Cagniard de la Tour and Kützing, who had independently and correctly shown that yeast is a living organism.

Liebig's own position was that fermentation is a *purely chemical* decomposition: a substance in a state of internal instability communicates that instability to sugar, breaking it down. Yeast, on his account, was a decaying nitrogenous substance whose own decomposition drove the process, not a living agent.

This was not stupid. It was consistent with his whole programme — that biological processes reduce to chemistry — and dragging living organisms into it looked to him like a retreat into vitalism, which he had spent his career attacking.

Louis Pasteur established the living account through the 1850s and 1860s: fermentation requires living cells, different organisms produce different fermentations, and heating kills the agent.

Liebig would not concede. The dispute ran for years, conducted publicly and with personal edge on both sides. Pasteur at one point invited Liebig to come and see the experiments performed; Liebig declined.

He never accepted it, and died at Munich in April 1873, aged sixty-nine, still opposed.

There is a final irony. Eduard Buchner showed in 1897 that a cell-free extract of yeast ferments sugar — the process is carried out by *enzymes*, chemical agents, which is closer to Liebig's picture than to Pasteur's. But the enzymes are made by living cells, so Pasteur was right about the question actually in dispute.

Why this matters

Liebig's objection to living yeast came from his own best principle — that biology reduces to chemistry — and it made him wrong for twenty years in public.

You have the satire and the argument you did not concede. What would you ask?

Ask Liebig

• “Why publish a satire rather than an argument?”
• “What did you think fermentation actually was?”
• “Why did the living account look like vitalism to you?”
• “Why not go and watch Pasteur's experiments?”
• “Buchner's cell-free extract ferments — does that vindicate you?”

What Liebig changed

Every university teaching laboratory descends from Giessen, and combustion analysis remained the standard route to a formula for well over a century. The distinction Liebig's own results forced — between the ratio of atoms in a compound and the actual number in a molecule — is one of the first things a chemistry student learns. He founded agricultural chemistry, and the law of the minimum is applied far beyond it.

A debate that continues

Liebig opposed Pasteur's living account of fermentation for over twenty years and never conceded, and he and Wöhler published an anonymous satire ridiculing Schwann for a claim that turned out to be correct.

Keep exploring — ask Liebig

• “What would you say to Schwann now?”
• “How should a professor treat a student's mistake?”
• “Which of your errors cost the most?”

Related lives

• Friedrich Wöhler — Who Made Urea Without A Kidney
• Louis Pasteur — Father of Germ Theory
• August Kekulé — Who Gave Carbon Four Hands
• Theodor Schwann — Who Said Animals Are Built Like Plants

Related themes

Empirical and molecular formulae · Plant nutrients · Fermentation