Boyle’s Law: 350th Anniversary

This year marks the 350th anniversary of the publication of Boyle’s law which states that, at constant temperature, the pressure and volume of a gas are inversely related. The hypothesis and the supporting data first appeared in Robert Boyle’s 1662 paper, New Experiments Physico-Mechanical, Touching the Air: Whereunto is Added A Defence of the Authors Explication of the Experiments, Against the Obiections of Franciscus Linus, and, Thomas Hobbes.

Boyle had published a book two years earlier with almost the same title, in which he described the construction of an air pump and a range of experiments performed under reduced pressure. Franciscus Linus had objected that the pressure of the atmosphere was insufficient to raise a mercury column by over 70 cm. To answer this, Boyle designed and made a U-shaped glass tube with one long, open limb of almost 2.5 m and a short, sealed limb of 30 cm. He poured mercury into the long limb and measured the compression of air in the short limb. He showed that the compressed air in the short limb was capable of supporting a long column of mercury, proving Linus wrong. Graphs were not in general use in 1662, but when Boyle’s data are plotted on a standard xy graph, they strongly support his hypothesis that the volume and pressure of a gas are inversely related.

Today the law is commonly expressed as p₁ V₁ = p₂ V₂ and is used to predict the result of a change in the volume (V) or pressure (p) of a fixed quantity of gas. Boyle’s law is ubiquitous in science and nature. For example, it relates to respiration, where the motion of the diaphragm alters the volume of the lungs forcing air in and out to equalize the pressure, and has been combined with Charles’s law and Gay-Lussac’s law as part of the combined gas law.