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19 - Lavoisier: Oxygen, Combustion, and Respiration

UNVEILING of the mystery of respiration, probably the most decisive scientific contribution to medicine in the eighteenth century was not the work of a medical man, but of a chemist, Antoine Laurent Lavoisier. After thousands of years of unsubstantiated theories and inaccurate guesses, Lavoisier was first to demonstrate what actually happens during the process of respiration.

Lavoisier’s great discoveries, relating to respiration, represent but one of many facets of his extremely busy life. Through keenly interested in all natural sciences, including meteorology, mineralogy, geology, hydrometry, and illumination, Lavoisier early reveled his great talents for pure scientific research in chemistry’ and for application of scientific knowledge to solution of practical problems. Thus, to medicine and to public health, he not only contributed sound advances to understanding of chemical processes, of combustion, and of gases, but he used his scientific knowledge to help improve water supplies for Paris, ventilation and sanitation in prisons, and to bring about hygienic and procedural reforms in hospitals. Similarly, he served his government on many occasions in solving economic, social, agricultural, chemical, military, and political problems. He brought about an almost complete change in eighteenth century philosophy and theory of chemistry.

Antoine Laurent Lavoisier was born August 26, 1743, in the heart of Paris. His family was middle-class, comfortably situated financially. Lavoisier’s mother died when he was quite young, so that he was reared by a maiden aunt and by his lawyer father. Following his father’s guidance, young Antoine first studied law at Mazarin College, qualifying as a Bachelor of Law in 1763, and as a Licentiate in 1764. However, he had already developed a compelling interest in science, having had some remarkable teachers in astronomy, mathematics, botany, chemistry, and geology. In 1765, Lavoisier published his first paper on a subject in chemistry, wherein he used the quantitative approach, one which he was to make dominant in chemistry later in life. He won a medal from the king in a prize essay contest on metropolitan street lighting, in 1766; and two years later, when he was but 25 years old; Lavoisier was admitted to membership in the Royal Academy of Science. This was the beginning of a long a fruitful association with France’s foremost scientists. Their regard for him is best revealed by the great number of commissions’ findings and to present these to the Academy. Because the French government relied on this scientific body scientific body to investigate a wide variety of subjects and to report its conclusions and advice to the nation’s officials, Lavoisier soon was plunged deeply into service of his country. Among these activities was one that eventually was to cost him his life. In 1768, the same year that he became a member of the Academy, Lavoisier bought a part share in the Ferme Geneale, a much-hated, privately owned organization to which the French monarchy “farmed out” a profitable tax-gathering monopoly in return for guarantees of the government’s financial requirements. Lavoisier seems to have served this organization sincerely and with a fine sense of fairness toward those from whom taxes was collected. However, tax collectors seldom are objects of public admiration; and fate was to prove so to Lavoisier.

Out of his relations with the Ferme Generale came one of the brightest of Lavoisier’s experiences. In 1771, at age 28, he married Marie Paulze, 14-year-old daughter of one of his colleagues in the Ferme. Though a “marriage of convenience” at time it was solemnized, it proved to be a very happy union. Me. Lavoisier, brilliant and talented, took a great interest in her husband’s work and become a devoted collaborator. She translated papers from foreign languages into French for him; made notes of many of his experiments; drew sketches and engraved plates to illustrate some do his publications; and was hostess to a brilliant corps of friends and internationally prominent scientists.

Lavoisier’s greatest accomplishments undoubtedly are to be found in his work on oxygen, which led him to study respiration, and to completely refute long-standing theories of chemistry. Through oxygen had been discovered independently by Scheele, in Sweden, and by priestley, in England, and had been studied by Cavendish, also of England, Lavoisier, stimulated by their reports, carried on further experiments. These enabled him, in 1776, to report on the true nature and role of the gas that was called “dephlogisticated air,” or “respirable air.” And to suggest that it be named “oxygen” (acid-maker). His experiments began with oxidation of metals, and reduction of metallic oxides. In the course of a few years he determined that oxygen makes up only about one-fifth the volume of atmospheric air and is the only gas in air that sustains either combustion or respiration; and that, in combustion, a definite ratio exists between the amount of oxygen consumed and the amount of “fixed air” (carbon dioxide) released. Thus began Lavoisier’s nearly complete reconstruction of the scientific bases of chemistry: overthrow of the ancient theory of four elements-airs, earth, fire and water; and of the phlogiston theory (that substances burned because of escape of an unknown substance called phlogiston). He proved that water is the end product of combining hydrogen and oxygen by combustion, and therefore, is a compound rather than an element. His many chemical experiments and logical conclusions drown there from, and from work done in collaboration with other scientists, including Guyton de Morveau, Fourcroy, and Berthollet, were summed up in his Traile Elementaire de Chimie, published in 1789. This volume included a new system for naming chemical substances, which minor revisions, is still in use.

Most prominent of assignments given Lavoisier by the French government was his appointment in 1777 as head of a committee to direct the Royal Power Factory to remedy a shortage of gunpowder that constituted a threat to the nation’s security. Rapidly, Lavoisier changed the power factory from an inadequate and inefficient operation to one that filled the Royal Arsenal with good quality gunpowder. This placed France in a new position with other nations: as a seller rather than a buyer of gun power. Significantly, this work by Lavoisier made it possible for France to supply the rebellious American colonists with power to sustain their effort toward independence from France’s traditional enemy, Great Britain. Lavoisier was to contribute unknowingly in another way to the growth of the struggling young nation across the Atlantic: the training he gave a young man, Eleuthere Irenee du Pont, who assisted in the power mill and in the research laboratories, was to become basic to founding the great chemical dynasty of E.I. du Pont de Nemours, in Delaware.

It was during his years of residence and work at the Royal Power Factory that Lavoisier carried out his experiments relating to combustion and to respiration. Having proved that in combustion, burning substances combine with oxygen, giving off both heat and carbon dioxide, Lavoisier and Laplace developed methods of measuring oxygen consumed and carbon dioxide formed therein. Then they devised ways of determining oxygen intake, heat output, and carbon dioxide exhalation produced by respiration in a guinea pig during a specific period. By complex comparisons, in which an ice calorimeter was used, they proved that a guinea pig produced approximately the same amount of heat, during consumption of a predetermined amount of oxygen, as was produced by burring charcoal consuming the same amount of oxygen. From these investigations Lavoisier and Laplace concluded that: “Respiration is therefore combustion, admittedly very slow, but otherwise exactly similar to that of charcoal: it takes place in the interior of the lungs, was communicated to the blood, and thereby diffused through the body. Another century was to pass before this bit of biological chemistry was to be thoroughly elucidated. Later, with the cooperation of Armand Seguin, Lavoisier engaged in many other activities. He prepared for the government of France an outstanding memoir on economics including a survey of the nation’s natural resources; he con ducted research into a number of agricultural problems.

The later years of the 1780’s and earlier of the 1790’s, however, were troubled years. The French Revolution was imminent; and Lavoisier’s positions as power commissioner and as a member of the Farmer General brought him into the limelight of unpopularity as a early as 1789. Among the Revolution’s principal targets, after the royal family, was the tax-collecting company, members of which the people considered “bloodsuckers” and “thieves”.

Through he participated moderately in the Revolution, along with Lafayette, Baily, Mirabeau, and Talleyrand, Lavoisier tried to retire from public office abd devote himself entirely too scientific work; but such was not to be his destiny. In 1791, the Ferme Generale was abolished, and he was dropped from the power commission. He continued to work as a member of the Commission on Weights and Measures (which established the metric system) until 1793, In that year, he saw the revolutionary movement become more radical: his beloved for better educational standards came to naught. The menace to Lavoisier and his father-in-law, Paulze, together with their colleagues of the Ferme Generale, were arrested. Through Lavoisier tried to secure release on the basis of his many services to the nation, most of his ever, like Halle and Saint-Hilaire, remained faithful to the end. Lavoisier accepted his fate calmly, remarking: “This probably saves me from the inconveniences of old age.”

Together with 26 colleagues, Lavoisier and Paulze were tried and condemned, May 7, 1794, and executed the following day, May 8, for “plotting against the people of France.”

A Most befitting epitaph was spoken of Lavoisier by Joseph Lagrange, who said: “It took only a moment to sever that head, and perhaps a century will not be sufficient to produce another like it.”

THE PICTURE

Greatest contribution of science to Medicine during the eighteenth century came from experiments relating to the processes of respiration, conducted between 1789 and 1792 by the Parisian chemist, Antoine Laurent Lavoisier, in his laboratory. Together with a young assistant, Seguin, Lavoisier recorded oxygen intake and carbon dioxide exhalation by a man while resting, while working, and while eating. Lavoisier made many scientific, social economic and political contributions before French revolutionary radicals executed him in 1794.