SPHEROIDAL STATE (from spheroid, from Gk. croatpoct54s, sphairocidrs, like a ball or sphere, from ackaipa, sphaira, ball, globe el8os, eidos, form). The phenomenon observed when a drop of water placed on a highly heated surface remains in its spherical shape and moves about over the surface, evaporating gradually, instead of vaporizing instantaneously. • The ex periment to show this condition of a liquid is gen erally performed by using a metallic disk heated by a lamp or Bunsen burner, on which one or more drops of water are carefully let fall. If the disk is sufficiently heated a layer of vapor will be formed between its surface and the drop, which is known as the `Crookes's layer' The liquid re mains suspended on this vapor and the drop takes the form of an oblate spheroid, the tem perature. however, never rising above the boiling point, being in the ease of water about 206° P. or 96.6° C., while the disk itself must have a temperature of at least 340° F. or 171° C. The explanation of this fact is that the latent heat carried off in the course of vaporization is suf ficient to keep the temperature below the boiling point. The drop does not actually touch the
disk, but is supported on a cushion of vapor, which is evaporating toward the hot plate so rapidly as by its reaction to keep the water from falling. This may be seen by looking at a flame through the intervening space, or by attempting to pass an electric current from the drop of water to the metal disk, using a galvanometer to detect its passage. there being no deflection of the needle unless the two substances are in actual contact. The liquid takes a spherical shape owing to capil lary action. Other liquids and bodies that are solid at ordinary temperatures also show this phenomenon. and instead of a metallic surface. that of a hot liquid can also he used. A striking illustration of this same principle is the immer sion of a, hand in molten metal, o• in liquid air, the thin layer of aqueous vapor preventing the passage of the heat or cold to the hand. Consult: Stewart, Elementary Treatise on Heat (6th ed., Oxford, 1895) ; Barker, Physics (New York, 1893) ;• Daniel, Text-Rook of the Principles of :Physics (3d ed.. New York,.1694).