Variations from Mariotte's Law

Abstract

THE universal application of the law enunciated by Mariotte and Boyle, that the “volume of an aëriform body is inversely as the pressure to which it is exposed,” was brought into question at an early date after the publication of the famous experiments on which the principle was based. Oersted and Schwendsen established in 1826 for easily liquefiable gases that the elasticity does not keep pace with the pressure. At about the same time Despretz showed that notable variations took place in the case of air above a pressure of fifteen atmospheres. Arago and Dulong, intrusted by the French Academy with the verification of these observations, carried out a carefully conducted series of experiments on the compressibility of air extending up to twenty-seven atmospheres, but came, however, to the conclusion that Mariotte's law was correct. This opinion was strengthened by Pouillet's researches in so far as it related to the then so-called permanent gases, while confirmatory evidence was brought in favour of Oersted and Schwendsen's experiments on easily liquefiable gases. This view of the correctness of the law for a certain group of gases was held by the scientific world until 1845, when Regnault, by a brilliant series of experiments of the most exact kind, showed that air, nitrogen, and carbonic acid experienced a constant decrease of elasticity when submitted to pressures rising to thirty atmospheres, while under the same conditions a regular increase of elasticity in the case of hydrogen occurred. A few years later Natterer of Vienna published some remarkable experiments on the compressibility of gases, making use for the first time of enormous pressures, reaching in several cases nearly 2,800 atmospheres. While Natterer's methods of measurement were by no means exact, the results of his experiments showed beyond doubt that for pressures above eighty atmospheres oxygen, nitrogen, and carbonic oxide possessed the same peculiar property manifested ordinarily by hydrogen, viz., the volume of the compressed gas being greater than that demanded by Mariotte's law. The verification of Natterer's results was undertaken in 1870 by Cailletet, whose name has been so prominent of late years by his success in liquefying the so-called permanent gases. By making use of one of Desgoffe's manometers he experimented on air and hydrogen up to 600 atmospheres, and obtained figures comparing very closely with those published by Natterer.