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Soap has been made for centuries, but for most of that time nobody knew what happened chemically when fat met alkali. Michel-Eugène Chevreul, a French chemist who lived to the age of 102, worked it out. He showed that fats are built from a sweet substance he called glycerine combined with fatty acids, and names he used, such as stearic and oleic acid, are still in use. This post covers his life, what his 1823 book actually reports, a worked soap calculation, common mistakes, and a habit of his worth copying.
Who was Michel-Eugène Chevreul?
A chapter on his life by his descendant Raoul Chevreul, in a 1997 book from the Muséum national d'Histoire naturelle, gives the essentials. He was born in Angers on 31 August 1786 and died at the Muséum in Paris on 9 April 1889, in his 103rd year. He joined the Muséum in 1810 and later held its chair of chemistry for decades, serving several times as its director. From 1824 to 1883 he directed the dyeing work at the Gobelins tapestry manufactory.
That dyeing job led to his second famous project, an 1839 book on the simultaneous contrast of colours, which the chapter says influenced painters. Most chemistry students know him for fats.
What did Chevreul discover about fats?
His main work was Recherches chimiques sur les corps gras d'origine animale (Chemical Research on Fats of Animal Origin), published in 1823. In it he separated fats into distinct substances, which he named, including stearine and oleine, and studied what alkalis did to each one.
The results are stated plainly. Of stearine he writes that potash "la réduit en glycérine et en acides stéarique, margarique et oléique": it converts it into glycerine and stearic, margaric and oleic acids. Of oleine he writes that potash converts it into glycerine and margaric and oleic acids. In his classification of fatty substances, one group is described as those that alkalis convert into "glycérine (principe doux)", the sweet principle, and fixed fatty acids.
In modern language, a fat is an ester of glycerol with three fatty acid chains, a triglyceride, and boiling it with alkali breaks the ester links.
How does saponification link to your syllabus?
The NCERT Class 10 Science chapter Carbon and its Compounds (2026-27 reprint) describes how an ester treated with sodium hydroxide gives back an alcohol and the sodium salt of a carboxylic acid. It says "This reaction is known as saponification because it is used in the preparation of soap", and that soaps are sodium or potassium salts of long-chain carboxylic acids. The same chapter explains how soap molecules form micelles around oily dirt. Chevreul's experiments are the chemistry underneath that paragraph. For a refresher on the chapter, see our post on carbon compounds in Class 10.
Worked example: how much soap from a kilogram of fat?
Use glyceryl tristearate (tristearin), the triglyceride of stearic acid, and round atomic masses: C = 12, H = 1, O = 16, Na = 23.
The balanced equation is:
C57H110O6 + 3 NaOH → C3H8O3 + 3 C17H35COONa
Molar masses:
Tristearin, C57H110O6: 57 × 12 + 110 × 1 + 6 × 16 = 684 + 110 + 96 = 890 g/mol
NaOH: 23 + 16 + 1 = 40 g/mol
Glycerol, C3H8O3: 36 + 8 + 48 = 92 g/mol
Sodium stearate, C18H35O2Na: 216 + 35 + 32 + 23 = 306 g/mol
Check the mass balance: left side 890 + 3 × 40 = 1010 g; right side 92 + 3 × 306 = 1010 g. It balances.
Now take 1000 g of tristearin:
Moles of fat = 1000 ÷ 890 ≈ 1.124 mol
NaOH needed = 3 × 1.124 × 40 ≈ 134.8 g
Soap formed = 3 × 1.124 × 306 ≈ 1031.5 g
Glycerol formed = 1.124 × 92 ≈ 103.4 g
Check: 1000 + 134.8 = 1134.8 g in, and 1031.5 + 103.4 = 1134.9 g out. The 0.1 g gap is rounding.
What mistakes do students make with fats and soap?
Forgetting the 3. One triglyceride has three ester groups, so it needs three NaOH and gives three soap molecules.
Calling soap the acid. Soap is the salt (sodium stearate), not stearic acid itself.
Losing glycerol. It is a real product, the "sweet principle" Chevreul named, not a by-product to ignore.
Mixing up soaps and detergents. NCERT treats them separately; detergents are not made by saponifying fats.
If ester hydrolysis still feels like memorising rather than understanding, the Fermi Concept Library covers every concept in physics, chemistry, biology, mathematics and computing, with each idea explained on its own.
What can a student learn from how Chevreul worked?
Chevreul did not treat "fat" as one substance. He separated mixtures into individual compounds, named each, and then ran the same test (heating with alkali) on every one, recording what came out. That patient, one-variable-at-a-time comparison is what made his conclusions general. When you study a family of reactions, do the same: write the same reaction for several members side by side and see which parts change.
For the biology side of fats, our post on tests for carbohydrates, fats and proteins shows how they are detected in the lab.
Repeat the worked example with glyceryl trioleate, C57H104O6, and find how much sodium hydroxide 1 kg of it needs.
