Joseph Louis Gay-Lussac
(born: December 6, 1778 / died: 1850)
||A French chemist and physicist, known for his studies on the physical
properties of gases. He was born in Saint Léonard and educated at the
École Polytechnique and the École des Ponts et Chaussées
in Paris. After holding several professorships he became professor of physics
at the Sorbonne from 1808 to 1832.
In 1804 he made balloon ascensions to study magnetic forces and
to observe the composition and temperature of the air at different altitudes.
In 1809 he formulated a law of gases that is still associated with his name.
Gay-Lussac's law of combining volumes states that the volumes of the gases
involved in a chemical reaction (both reactants and products) are in the
ratio of small whole numbers. In connection with these studies he investigated,
with German naturalist Baron Alexander von Humboldt, the composition of water
and found it forms when two parts of hydrogen and one of oxygen unite.
|In 1809 Gay-Lussac worked on the preparation of potassium and boron
and investigated the properties of chlorine and hydrocyanic acid. In the
field of industrial chemistry, he developed improvements in various manufacturing
and assaying processes. In 1831 he was elected to the Chamber of Deputies
and in 1839 to the Senate.
|The French Revolution affected many of what were to become the French
scientific elite. Gay-Lussac was sent to Paris at the age of fourteen when
his father was arrested. After having had private lessons and attending a
boarding school, the Ecole Polytechnique and the civil engineering school,
Gay-Lussac became an assistant to Berthollet who was himself a co-worker
of Lavoisier. Gay-Lussac thus got the chance to become part of the group
of famous men who spent time at Berthollet's country house near Arcueil.
Here among the Arcueil Society he received his training in chemical research.
|With the encouragement of Berthollet and LaPlace, Gay-Lussac at the
age of 24 conducted his first major research in the winter of 1801-1802.
He settled some conflicting evidence about the expansion properties of different
gases. By excluding water vapor from the apparatus and by making sure that
the gases themselves were free of moisture, he obtained results that were
more accurate than had been obtained previously by others. He concluded that
equal volumes of all gases expand equally with the same increase in temperature.
While Jacques Charles discovered this volume-temperature relationship fifteen
years earlier, he had not published it. Unlike Gay-Lussac, Charles did not
measure the coefficient of expansion. Also, because of the presence of water
in the apparatus and the gases themselves, Charles obtained results that
indicated unequal expansion for the gases that were water soluble.
|Gay-Lussac, like his mentor Berthollet, was interested in how chemical
reactions take place. Working with the mathematical physicist, LaPlace, Gay-Lussac
made quantitative measurements on capillary action. The goal was to support
LaPlace 's belief in his Newtonian theory of chemical affinity. In 1814 this
theoretical bent continued as Gay-Lussac and LaPlace sought to determine
if chemistry could be reduced to applied mathematics. The approach was to
ask whether the conditions of chemical reactions could be reduced simply
to, as LaPlace had suggested, considerations of heat.
|As with his mentor before him, Gay-Lussac was consulted by industry
and supported by the government. "Napoleonic science sharpened the appetites
of young men by holding up the prospects of recognition and reward". Gay-Lussac
and Thenard, the laboratory boy turned professor, isolated the element boron
nine days before Davy's group did (but Davy was the first to publish. Gay-Lussac
led his group into the isolation of plant alkaloids for potential medical
use and he was instrumental in developing the industrial production of oxalic
acid from the fusion of sawdust with alkali. His most important contribution
to industry was, in 1827, the refinement of the lead chamber process for
the production of sulfuric acid, the industrial chemical produced in largest
volume in the world. The tall absorption towers were known as Gay-Lussac
Towers. The process is:
|SO2 (g) + NO2 (g) -------> SO3
(g) + NO (g)
|This reaction was carried out in a lead-lined chamber in which the
sulfur trioxide was then dissolved in water to produce sulfuric acid. Gay-Lussac's
contribution was a process for recycling the nitrogen monoxide after oxidizing
it to NO2. Sulfuric acid was produced this way well into the twentieth
century, when it was replaced by catalytic oxidation of SO2 in
the "Contact Process".
|While Gay-Lussac was a great theoretical scientist, he was also respected
by his colleagues for his careful, elegant, experimental work. Wanting to
know why and how something happened was important to Gay-Lussac, but he preferred
knowing much about a limited subject rather than proposing broad new theories
which might be wrong . He devised many new types of apparatus such as the
portable barometer, an improved pipette and burette and, when working at
the Mint, a new apparatus for quickly and accurately estimating the purity
of silver which was the only legal measure in France until 1881. His work
on iodine is considered a model of chemical research. His precise measurement
of the thermal expansion of gases mentioned above was used by Lord Kelvin
in the development of the absolute temperature scale and Third Law of Thermodynamics
and by Clausius in the development of the Second Law. He and Thenard improved
existing methods of elemental analysis and developed volumetric procedures
for measuring acids and alkalis. His quantification of the effect of light
on the reaction of chlorine with hydrogen elevated photochemistry from mere
artifice into a theoretical science which culminated, fifty years after his
death, in the quantum theory. An example of his dedication to meticulous
experimenting is his decision to undertake a balloon flight to a record setting
height of 23,000 feet to test an hypotheses on earth's magnetic field and
the composition of the air.
|The work for which Gay-Lussac is most remembered in high school and
university courses of general chemistry is his Law of Combining Volumes:
"The compounds of gaseous substances with each other are always formed
in very simple ratios by volume". If we follow the development of this
law we can see the scientific method at work, in all its beauty and nobility,
and with its pitfalls, resting as it does on the frailty of human nature.
Gay-Lussac began with a statement of intent: "I hope by this
means to give proof of an idea advanced by several distinguished chemists--that
we are perhaps not far removed from the time when we shall be able to submit
the bulk of chemical formula to calculation".
|The events that culminated in the presentation of his memoir at Arcueil
began with his balloon flight and measurements of the composition of the
air. These studies led him to criticize a man ten years his elder--the scientist-explorer
Alexander von Humbolt, who had also published measurements on the composition
of the air. But in an illustration of the nobility of science, Humbolt, far
from becoming angry with Gay-Lussac, saw that he had something to learn about
precision in scientific research. The two became collaborators and friends
and, in fact, eventually traveled together throughout Europe for a year in
1805, going to Rome, Switzerland and Berlin(3). Before that trip they worked
on finding the ratio in which hydrogen and oxygen combine to form water.
They needed this fact in order to find the percent of oxygen in the air.
They came up with the remarkably accurate results of a volume ratio of 100
of oxygen to 200 of hydrogen.
|What is surprising is that four years passed before Gay-Lussac published
his now famous results. In the interim, during their trip together, he worked
with Humbolt on measuring the earth's magnetic intensity. In 1807 he worked
on a series of experiments to find out if there is a general relationship
between the specific heats of gases and their densities.
Gay-Lussac looked at some previous data collected by Davy. This
consisted of analysis of the proportions by weight of elements in three different
oxides of nitrogen, as follows:
| Proportions by Weight
|Next Gay-Lussac "reduces these proportions to volumes", using the
specific gravities of the gases relative to hydrogen:
|Proportions by Volume
|Now he can accept (by what today we call the 5% rule) that "the first
and last of these proportions differ only slightly from 100:50 and 100:200",
but he recognizes that the second is significantly different from 100:100.
He also knew that Berthollet had obtained the proportions by volume of H
and N in ammonia, while Gay-Lussac, himself, had obtained those of sulfurous
gas and oxygen in sulfuric acid and that these are indeed simple whole numbers.
So he does an analytical experiment. He reacts 100 volumes of nitrous gas
with "the new combustible substance from potash" (presumably potassium) and
he finds that the volume of the gas decreases by 50% and the remnant is all
nitrogen. The reaction presumably is:
4K (s) + 2NO (g) -------> 2K2O + N2
He can now write:
|Proportions by Volume
|In modern terms these three compounds are N2O, NO, and
NO2. So Gay-Lussac has used the scientific method: Question, Hypothesis,
Experiment (including careful measurement, reproducibility, independent observations
in other laboratories) to devise an explanation of how gases combine--the
resulting Law of Combining Volumes was announced at a meeting of the Societe
Philomatique in Paris on December 31, 1808. For Gay-Lussac,
himself , the law provided a vindication of his belief in regularities in
the physical world, which it was the business of the scientist to discover.
These neat ratios do not, however, correspond exactly to his experimental
results. He deduced his law from a few fairly clear cases... and glossed
over discrepancies in some of the others. The simple reaction between hydrogen
and chlorine, which is often used today as an elementary illustration of
the law, was not discovered until 1809 and was included only as a footnote
when this memoir was printed.
|Now comes the pitfall; not Gay-Lussac's at first but John Dalton's.
In the second part of his "New System of Chemical Philosophy" Dalton criticized
the accuracy of Gay-Lussac's measurements, experiments and generalizations.
This was ironic since Dalton was more speculator than experimentalist, sometimes
accepting large standard deviations, as in the case of the atomic weight
of sulfur, for which he accepted values ranging from 12 to 22 based on his
own experiments. Nevertheless, he had the gall to claim that the ratio of
volumes of H and O in water was 1:1.97 which, he said, was not a simple whole
number ratio, thereby invalidating Gay-Lussac's Law. Thus he was unable to
"admit the French doctrine" as he called it.
|It is instructive to trace Dalton's thought processes. In a paper
read before the Literary and Philosophical Society in Manchester in 1802
(before the Law of Combining Volumes) Dalton stated that: "The particles
of one gas are not elastic or repulsive to the particles of another gas but
only to the particles of their own kind." In his New System of Chemical Philosophy,
Part I (in 1808 after Gay-Lussac's Law), he set out a number of rules for
combinations of atoms: "When only one combination of two bodies can be obtained,
it must be presumed to be a binary one, unless some cause appear to the contrary".
Consequently, hydrogen peroxide not yet having been discovered (it was isolated
by Thenard in 1818), Dalton was forced to conclude that the formula of water
was HO. Although others of his contemporaries, including Berzelius and Avogadro
were quite comfortable with Gay-Lussac's Law and used it to their advantage,
Dalton stubbornly rejected it. Like atoms could not stick together. They would
repel each other as like charges do. Furthermore, atoms combined in simple
proportions by weight according to Dalton's Law of Multiple Proportions, and
Dalton could not see how the same proportions could apply to combining volumes.
Avogadro had the answer: equal volumes of gases at the same temperature and
pressure contain the same number of particles. To the latter, who had used
electricity extensively in his studies of the halogens, it must have seemed
preposterous to believe that gases such as oxygen, hydrogen and chlorine
could be diatomic in nature. Two like atoms and two like charges were bound
to repel each other; even though a cornerstone of Avogadro's work was the
production of two volumes of HCl from one each of hydrogen and chlorine.
So Avogadro's work was consigned to obscurity for fifty years, until his
compatriot, Cannizzaro brought it to light in a pamphlet distributed at the
end of the Karlsruhe Conference in December 1860 after Gay-Lussac, Berzelius
and Dalton were dead.
|In the end Dalton did bow under the weight of the evidence and accept
the Law of Combining Volumes. But neither he nor Gay-Lussac nor Berzelius
ever accepted Avogadro's Law; not even when Gaudin in 1833 clearly showed
how it could be applied to explain the formation of water, not even with
the background of Cavendish eudiometer experiments.
|The stubborn blindness of Dalton and Berzelius and Gay-Lussac is a
clear example of a common pitfall in the practice of science. Roger Bacon
might have recognized it as the third "Cause of Error": popular prejudice,
but it also has elements of Bacon's first cause of error, namely, submission
to faulty and unworthy authority. We see that science has the pitfalls of
human frailty as well as beauty and nobility.