A gas that sinks in a liquid—the first helium experiment published by Kamerlingh Onnes**Official Contribution of the National Institute of Standards and Technology; not subject tocopyright in the United States.

Abstract

The year 1906 was a year of many remarkable achievements in the laboratory ofKamerlingh Onnes and his staff. They put into operation a hydrogen liquefier producing4 l h−1, followed by a liquid-hydrogen cryostat for work below 21 K. They prepared their firstsample of 2 l of helium gas. Pressure–volume–temperature measurements down to 54 K werein progress for hydrogen, and initiated for helium, in order to obtain an estimate for thecritical temperature of helium; this estimate was urgently needed for design of a heliumliquefier. Towards the end of 1906, Kamerlingh Onnes performed the first heliumexperiment at liquid-hydrogen temperature: a test of the phase behaviour of a mixture ofhydrogen and helium. In the process, he discovered what he termed the barotropic effect: atincreasing pressure, the helium-rich vapour phase sank to the bottom, having becomeheavier than the hydrogen-rich liquid phase. This paper describes the experiment andthe resulting flurry of activity by Van der Waals, Kamerlingh Onnes, Keesomand Van Laar, all trying to understand and model the curious phase behaviour,as well as earlier relevant work by Van der Waals, Korteweg, Kuenen and VanLaar.