Helium 4 has two liquid forms. Helium I, which is a "normal liquid," and Helium II, "He4II," to which it sharply converts at 2.174K. This strange material expands on cooling, has tremendous heat conductivity, a strange viscosity that it will climb up the sides of the container and is the only liquid known which can not be solidified by cooling at ordinary pressures, but will solidify under pressure. With increased pressure the volume of the solid can be decreased more than 30%. A very strange substance indeed, for which there seems to be no explanation in the literature.
There is a possible explanation which would need experimental verification by someone having access to the situation to be able to check it out. The postulated explanation is as follows: At 2.417K. ("K" in this context means "degrees Kelvin, i.e. degrees above Absolute Zero, the He4 nuclei, up to this point consisting of four protons in a tetrahedral array (for the moment we are ignoring the electrons bonding them together) lose the internal vibrational energy necessary to maintain their equal spacing in 3D space and collapse into a 2D, square-planar ground state, with bonding electrons now assuming positions above and below the plane of the "square." This type of activity is unknown for any other nucleus, and would be impossible for almost any other array but corresponds roughly to carbon as a diamond atom changing to carbon of the type found in graphite.
A liquid made up of square-planar atoms would arrange itself automatically into flat plate arrays which could slide over one another and conduct heat easily along the plane of the plates. This would account for the strange viscosity and the heat conduction.
It does not seem to have been noted that, while Helium I, "He4I," would be expected to be an insulator, there is a strong possibility that He4II would be a good conductor of electricity. Solid Helium, which would presumably be "Solid He4II" might add additional evidence in support of the above theory or be able to refute it. Normal Helium would be expected to be a tetrahedral nucleus, resulting in a "ball" atom which would have a "cubic-close-packed" crystal structure. If the above speculations are correct, solid He4II would have a square-planar crystalline structure. The cubic structure would be an insulating dielectric. The structure postulated above would be very likely to show conduction in plane of the square plates which would vary with pressure at right angles to that plane.
A thin film of either of the solid or liquid forms of He4II could very well show colored patterns when viewed with "crossed Polaroids." (This is a technique wherein light is polarized, passed through a substance, then passed through another polarizing lens, films having varying structures within will produce beautiful patterns which can be varied by rotating one of the polarizing lenses.)
Liquid and solid He4II may have some very interesting implications for theoretical chemistry and some very valuable undiscovered uses.
The above ideas need experimental verification or refutation. If this writer's speculations have merit, someone who could verify them would be able to write some very interesting papers. Anyone having a friend working in the field of cryoscopy with liquid Helium is strongly urged to refer their friend to this article. _________ Note: Wouldn't it be great fun if a short article on Helium II published on www.helium.com could spark some advances in chemical theory?!