In order to determine whether any structural change takes place when a liquid is supercooled, measurements have been made on the viscosity of pure phenyl ether, which by its melting point (26.85° c.) is suitable for accurate work. It has been found that in both the ordinary and the supercooled state the liquid obeys a formula of the type η=A exp (b/T), but that the value of b in the supercooled state, which was investigated down to 17° c. below the melting point, is significantly larger than the value of b for liquid above the melting point. It is shown that an accurate value for the melting point can be obtained from viscosity measurements without the liquid ever becoming solid. The temperature coefficient of density shows no detectable change in passing through the melting point.