Charles Cagniard

Background

Cagniard was born on March 31, 1777, in Paris, France.

Education

Cagniard studied at the École Polytechnique and the École du Génie Géographe.

Career

Because of the great diversity of the subjects he dealt with, it is slightly difficult to present a complete picture of Cagniard’s scientific career. He first worked in mechanics, beginning, in 1809, with a heat engine. Between 1809 and 1815 he produced a new hydraulic engine, a new air pump, a waterwheel mounted horizontally and turned by the current of a river, a portable military mill, and a heat-driven winch. Until 1819 these machines were constantly being improved; after 1820 a curved-cylinder pump was added to the list. Between 1820 and 1823 Cagniard began his research in physics, starting with the discovery of the existence of a critical state in the vaporization of liquids; at the same time he became construction chief of the Crouzoles aqueduct in the Puy-de-Dôme.

Between 1824 and 1827, after the invention of his siren, Cagniard began research in acoustics and the mechanism of voice production and devoted much effort to this field from then on. Between 1828 and 1831 new interests appeared: studies on the crystallization and the effect of acids on carbon; studies on phosphorus; and studies on silica and its crystallization and the hardening of mortar. Between 1832 and 1835 Cagniard worked on adapting the principle of the Archimedean screw to the function of an air pump and then began research on alcoholic fermentation; this work reached its culmination between 1836 and 1838. Toward the end of his career, while still pursuing all his interests, Cagniard contributed to mechanics a dynamometric device giving the average dynamic effect of a machine operating during an interval bounded by two successive observations. The most original aspects of Cagniard’s work include the heat engine, the critical state of vaporization, the siren, the Archimedean screw, and alcoholic fermentation. Both the heat engine machine and the remarks it occasioned are characteristic of this very early period of thermodynamics. About 1822, while attempting to vaporize liquids in a sealed vessel, maintaining a specific ratio between the volume of the liquid and that of the vessel, Cagniard proved that, above a certain temperature, a liquid contained in a hermetically sealed vessel could be completely vaporized. He further determined the temperatures and pressures corresponding to that critical state for a certain number of substances. For sulfuric ether he found, for example, 175° C. and thirty-eight atmospheres; for alcohol, 248° C. and 119 atmospheres. This research was taken up again by Andrews in 1867, but with more effective laboratory equipment and more accurate methods of measurement.

In his lifetime Cagniard’s reputation was made by the acoustical siren. Besides demonstrating the nature of sound, this device, equipped with a speedometer for measuring the rate of revolution, allowed ready determination of the frequency of vibration of any sonorous body: it had only to be put in harmony with the body being studied. According to Cagniard’s original design, there was no auxiliary motor; the apertures were arranged obliquely so that the perforated disk would automatically rotate like a turbine when air under pressure was applied. It had the disadvantage that the pressure had to be increased in order to provide a sharper sound, so that the siren was soft for low notes and shrill for high ones. Furthermore, it was difficult to keep the device at a given pitch, since air pressure was difficult to regulate with such accuracy. The siren was gradually perfected and took final shape in the hands of Helmholtz, who added independent feed (several rings of holes were arranged concentrically on a single disk, thereby allowing variation in the pitch in a known ratio, without changing speed).

The cagniardelle consists of an Archimedean screw partially immersed in a liquid; when rotated, it creates a forced draft or air blast. The first one was set up as early as 1827; however, Cagniard had been using the principle since 1809. This prototype - it was three meters long, two and a half meters in diameter, had four turns, and made six revolutions per minute - produced thirty-five cubic meters of blast per minute at a pressure of twenty-seven millimeters of mercury. This was sufficient to supply twenty-two forges and two cupola furnaces. Later cagniardelles could attain pressures of up to sixty millimeters of mercury. This machine had an excellent yield, but it was cumbersome and ceased to be used when production of compressed air at higher pressure became widespread.

Cagniard’s studies on alcoholic fermentation have unquestionably remained the most valuable of his works. Begun as early as 1835, they led him, toward the end of 1836, to see that there was certainly a living substance in brewer’s yeast. Schwann came to the same conclusion at the same time, but Liebig’s violent attacks forced this point of view into the background for twenty years. Cagniard died on July 5, 1859, in Paris.

Achievements

• Cagniard is best known for his inventions. He was the author of the cagniardelle, a blowing machine, and an improved siren. In 1822, he also discovered the critical point of a substance in his famous cannon barrel experiments.

References

• Annales de Chimie Et de Physique
• Mémoire Sur Le Magnétisme Animal, Adressé À Messieurs Les Membres de l'Académie
  1859
• Naissance et deviation de la theorie cellulaire dans l'oeuvre de Theodore Schwann
  1960