A new chemistry emerges


In 1766, Englishman Henry Cavendish isolated a gas that he called "inflammable air" because it burned readily. For Lavoisier, combustion meant combining with oxygen; however, until he could explain the combustion of inflammable air, some would still doubt his new chemistry. Priestley noted that when inflammable air and common air were ignited with a spark in a closed vessel, a small amount of "dew" formed on the glass walls. When Cavendish repeated the experiment, he found that the dew was actually water. Cavendish explained the results in terms of phlogiston and assumed the water was present in each of the two airs before ignition. In June 1783, Lavoisier learned of the Cavendish experiment and immediately reacted oxygen with inflammable air, obtaining "water in a very pure state." He correctly concluded that water was not an element but a compound of oxygen and inflammable air, or hydrogen as it is now known. To support his claim, Lavoisier decomposed water into oxygen and inflammable air.

The last objection to discarding phlogiston could now be eliminated. It was known that when a metal dissolved in an aqueous acid solution, it produced a salt and inflammable air:

metal + acid + water --> salt + inflammable air

which Cavendish believed was phlogiston:

metal (calx + phlogiston) + acid --> salt (calx + acid) + inflammable air (phlogiston)

Now that the composition of water was known, Lavoisier offered a different interpretation:

metal + acid + water (inflammable air + oxygen) --> calx (metal + oxygen) + acid + inflammable air --> salt (calx + acid) + inflammable air

For example, when zinc reacts with an acid, it combines with the oxygen of the water to form a calx, which then reacts with the acid to form a salt. The other component of the water, hydrogen, is released as a gas. According to McKie, "This was a new Lavoisier . . . raining down upon the [defender's] heads a destructive fire of incontrovertible chemical fact."

To Lavoisier, it was time "to rid chemistry of every kind of impediment that delays its advance" with a reform that included a new language. Louis Bernard Guyton de Morveau, Claude Louis Berthollet, Antoine François Fourcroy, and Lavoisier adopted the long-neglected idea of an element as originally proposed by Robert Boyle more than a century earlier. "We shall content ourselves here with regarding as simple all the substances that we cannot decompose." They retained the names from the past of many of these simple substances, or elements. But when an element combined with another element, the compound's name now reflected something about its chemical composition. For example, a calx was the combination of a metal and oxygen; therefore, zinc calx became zinc oxide. Lavoisier and his colleagues predicted that if the new system was "undertaken upon sound principles . . . it will naturally adapt itself to future discoveries." Withstanding the test of time, the basic system is still in use today.

Lavoisier's new system of chemistry was laid out for everyone to see in the Traité Élémentaire de Chimie (Elements of Chemistry), published in Paris in 1789. As a textbook, the Traité incorporated the foundations of modern chemistry. It spelled out the influence of heat on chemical reactions, the nature of gases, the reactions of acids and bases to form salts, and the apparatus used to perform chemical experiments. For the first time, the Law of the Conservation of Mass was defined, with Lavoisier asserting that "... in every operation an equal quantity of matter exists both before and after the operation." Perhaps the most striking feature of the Traité was its "Table of Simple Substances," the first modern listing of the then-known elements.

A contentious Lavoisier would later proclaim: "This theory is not, as I hear it called, the theory of the French chemists. It is mine. It is a right that I lay claim to by the judgment of my contemporaries and at the bar of history." Two years later, in 1791, the results were obvious. "All young chemists," he mused, "adopt the theory, and from that I conclude that the revolution in chemistry has come to pass." His legacy endures more than 200 years later.


 

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The chemical heritage of Antoine-Laurent Lavoisier | Combustion and the attack on phlogiston
A new chemistry emerges | Lavoisier's American legacy
The life of Antoine-Laurent Lavoisier (1743-1794) | Landmark designation

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