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Joseph Louis Gay-Lussac

Joseph Louis Gay-Lussac was born on December 6th, 1778 in a region of France called Limoges. He was the eldest of five children born to a well respected lawyer, Antoine Gay, who began the habit of calling his family the "Gay-Lussac's" to draw attention to their family property near St. Leonard.

While a young boy he was tutored at home and had a very comfortable upper-middle class existence until the events known as the "French Revolution" broke out and brought the world as he knew it to an end. Fearing for his life, the tutor fled, and his father was imprisoned leaving the family with no option but sending their 14 year old son to Paris to take a set of private lessons and then attend boarding school.

He must have impressed someone in the new order, because young Joseph was eventually selected to become a member of the Ecole Polytechnique, a brand new, revolutionary institution dedicated to sweeping away the old Royal ideas and replacing them with those based on reason, order and discovery.

Here he met and was mentored by Pierre Simon Laplace and Claude Louis Berthollet, both of whom had been pupils and followers of the famous Antonine-Laurent Lavoisier. So they were all interested in oxygen and the chemistry of other gasses. The new, junior assistant, got a chance to see hear all about these discoveries, probably at Berthollet's house near Arcueil, where a group of chemists met regularly to talk over recent events.

a special kind of work

From his writings and the kind of work her carried out over a very productive life time, it is clear that Gay-Lussac was nervous about grand, large, broad new theories of atoms and chemical reactions. He was much more interested in finding out why something happened, and investigating smaller issues very thoroughly and completely until an answer was obvious and irrefutable.

This approach shows itself very clearly in his first major investigation, which he carried out at the age of 24. Berthollet suggested that he clear up a problem of conflicting evidence concerning how gasses expanded as the temperature increased. Unknown to both of them, this problem had already been solved by Jacques Charles 15 years early, but no one knew this as he had not published his work of findings.

So Gay-Lussac was able to write in the Annales de Chimie in 1802 that: For many years physicists have studied the expansion of gases; but the results which they obtained showed such great differences that instead of reaching a definite result they render further examination desirable.


The problem as he saw it was simple: " The expansion of vapors has been given less consideration, although we have known for many years the prodigious effects of water vapor; and although we have made most fortunate applications of these effects, Zeigler and Bettancourt are the only ones, so far as I know, who have tried to measure them. Their experiments cannot give the true expansion of this vapor; for since they always had water in their apparatus, ... "

The problem with all previous experiments was that they were contaminated with water vapor. When he eliminated this problem his results were clear and consistent, and many people now join his name to the "Charles-Gay-Lussac Law" of the effect of temperature on the expansion of gasses. All gasses expand equally through the same increase in temperature.

how high? how far?

Air was all around him, but how far up did it go and was the composition always the same? To answer these a lots of other questions, Gay-Lussac took a record-breaking flight in a hydrogen filled balloon to the incredible height of 23,000 feet in 1804. While aloft he measured everything from the earth's magnetic field to the pressure, temperature and humidity of the air. He also collected lots of samples.

When he returned to earth he felt that he had enough evidence to take on the explorer and scientist, Alexander von Humbolt (who had also published his measurements on the composition of the air). Not angry in the least, von Humbolt became friends with the much younger Gay-Lussac and the two traveled and collaborated together on trips and experiments to find out the percentage of oxygen in the air.

To measure these values, they first needed a way of determining the amount of oxygen in a sample of air. Their method was to become famous and lead eventually to the experiments and results for which Gay-Lussac is most famous.

hydrogen and oxygen

To remove all the oxygen from an air sample, they reacted it with hydrogen to make water. After very careful measurement they found that they needed two volumes of hydrogen to remove one volume of oxygen. This was an important discovery, but it sat in a drawer for almost 4 years while Gay-Lussac and von Humbolt went on their trip to Italy, Switzerland and Berlin, and then did experiments on the specific heats of gasses and their densities.

Using his own results, and combining them with the results previously obtained by Davy, he noticed something; it took two volumes of nitrogen to combine with one volume of oxygen to give the substance nitrous oxide; one volume of nitrogen combined with one volume of oxygen to give "nitrous gas"; and one volume of nitrogen to combine with two volumes of oxygen to give nitric acid. Something was going on here!

law of combining volumes

These are the results which, along with his conclusions, make Gay-Lussac famous, even today. The Law of Combining Volumes, which he announced at a meeting of the Societe Phiolomatique in 1808, presented a clear explanation of how gasses combine. It was logical and showed that this small part of the physical world operated according to regularities and consistencies that could be revealed by application of the scientific method and then applied to many, many other similar situations. It was a triumph of Gay-Lussac's pedantic but irrefutable approach to discovery.

His careful, elegant, painstaking work soon brought him to the attention of others. While at the Mint, he devised a way of determining the purity of the silver used in all coins at that time, he invented a portable barometer that everyone started using, his work was used by Lord Kelvin to find the absolute zero temperature below which it is not possible to go, and by Clausius in the stating of the Third Law of Thermodynamics. Quite an achievement!

At the practical level, in 1827, he refined the lead chamber process used to produce industrial quantities of sulfuric acid (the absorption towers are still called "Gay-Lussac Towers").

everyone but Dalton

But then he ran into "ego" problems. John Dalton started to criticize his famous Law. Speaking and publishing both before and after Gay-Lussac, Dalton had committed himself to a "rule for the combination of atoms" that forced him to conclude that the formula for water was HO, a very different formula than Gay-Lussac was finding. Not only that, but Dalton's own Law of Multiple Proportions could not easily be reconciled with the idea of combining volumes.

Of course, Amedeo Avogadro had already worked out the answer to this one (equal volumes of gasses contain the same number of particles), but he was not appreciated or understood for many years to come, so Dalton continued to fight against Gay-Lussac until the weight of subsequent evidence became so overwhelming he had to grudgingly give in. He never liked Avogadro's work, however.

A common theme in all scientific discoveries is the ego driven stubbornness of scientists like Dalton, Berzelius and even Gay-Lussac to accept a new paradigm or even the inescapable conclusions of the work of others. Very frequently the beauty and genius of a discovery is ignored, hidden or even ridiculed by the owner of the previous beautiful discovery. It seems to be an inescapable fact and frailty of human nature.

Science@a Distance
© 2002, Professor John Blamire