SPHEROIDAL STATE or CONDI TION, the state of a liquid when it presents spherical phenomena caused by it on a very hot surface; the so-called ecaloric para dox." Leidenfrost observed that a drop of water placed on a very hot surface assumed a spheroidal shape and did not touch the surface. Boutigny made a more thorough study of the subject, and experimented with various liquids. The limit ICJ temperature of the hQt ,surface is the temperature at which the drop of liquid noise.
spreads on it and boils faitha hag Boutigny places the limit for water at 142° C., and at 61 C., for ether. The temperature of a drop of liquid in the spheroidal state is always below that at which the liquid boils, and for this reason the interesting experiment of freezing a small quantity of water on a hot platinum dish may be performed. The dish is heated almost to a white heat, when a small quantity of sul phurous acid is placed upon it, and assumes the spheroidal state ; the boiling point of sulphur ous acid is —10° C., and in the spheroidal state it is a temperature less than 10° C.; a few drops of water added to the sulphurous acid is immediately frozen, and may be thrown out of the dish, a mass of ice. Substituting nitrous oxide for sulphurous acid, and mercury for water, mercury may be solidified in the same manner.
That the liquid does not touch the surface is made evident in various ways, such as that of making the surface a flat plate and observing that light passes between the spheroid and the plate, or letting a conducting point enter the spheroid from above, and seeing if a current of voltaic electricity will pass between the spheroid and the dish. The temperature of the spheroid is kept low by the rapid evaporation which is going on at its surface; the spheroid is kept from touching the dish by a cushion of vapor, and this cushion is non-conducting, so that the heat which affects the spheroid is heat radiated from the dish; as soon as the tempera ture of the dish is less than that component to provide a cushion of vapor sufficiently dense to sustain the spheroid completely from contact with it, the spheroid spreads on the dish and is quickly dissipated by the heat which it now receives by contact. Consult Barker, (Physics) (1893) ; Daniel, (Text-book of the Principles of Physics) (3d ed., 1894) ; Stewart, (Element ary Treatise on Heat) (6th ed., 1895).