McClintock, Peter V. E. (1987) Science of helium in technology. Nature, 326 (6111). p. 340.
Full text not available from this repository.Abstract
Liquid helium is something of an oddity. Its existence as a liquid at all is rather marginal, as shown by the ease with which it can be vaporized by tiny influxes of heat - just one watt is enough to evaporate about a litre of liquid in an hour. For temperatures below 2.17K, it behaves as though it were an interpenetrating mixture of two completely miscible fluids: a (relatively ordinary) normal fluid component, and a superfluid component which carries no entropy and whose viscosityis identically zero. It is the latter component that gives rise to liquid helium's celebrated frictionless-flow properties, enabling it, for example, to climb out of any open vessel in which it is placed.