Helium, the smallest atom on the periodic table, has many interesting properties. For one, it will not solidify unless pressurized to an excess of twenty five atmospheres. At normal pressures, helium will remain a liquid all the way down to zero degrees Kelvin. This is the theoretical lowest possible temperature, and is known as Absolute Zero. Although it will not solidify, liquid helium does go through a phase change at 2.17 degrees Kelvin (-456°F/-271°C). This is known as the lambda point temperature. Above the lambda point liquid helium behaves as any other liquid, but below the lambda point some of its atoms become superfluid. These atoms are in their lowest possible energy state, so they have no entropy and no viscosity, which means that they do not interact at all with other atoms. This allows the atoms to flow freely without any drag or friction. We distinguish these two states by calling the normal liquid helium I, and below the lambda point calling the liquid helium II.

My print depicts one experiment performed with liquid helium, in which a test tube is filled with helium II by dipping it into a large helium bath and then dangling it above the surface of the bath by a fine thread. When this is done, a very thin layer of normal helium atoms (perhaps a few atoms thick at most) will stick to the surface of the test tube. This film creates small channels through which the superfluid helium atoms can flow. They do not stick to the glass because they have no viscosity. The superfluid helium on the outside of the test tube will flow down its surface and drip back into the helium bath (seeking the lowest possible energy level in earth's gravity). As it does this, the small channels act like little siphons. Just as you can siphon the gas out of a car using a small hose, the act of the superfluid helium flowing through these channels pulls more helium up over the edges of the test tube, which in turn drips back down to the helium bath, siphoning more helium, etc. Given enough time the helium will siphon itself completely out of the test tube leaving it empty. If the test tube is left partially submerged in the helium bath, then the fluid will flow out until the liquid level in the test tube is even with the level of the helium bath. Likewise, if the liquid level in the test tube is lower then that of the bath, then the helium will flow into the test tube to equalize the levels.