TUNG OIL. Two varieties are known, differing slightly in their physical properties, termed Chinese Tung Oil (China wood oil) and Japanese Tung Oil according to the country of origin. In China the oil is prepared from the seeds of Aleurites cordata; these are roasted in flat dishes over a fire, then coarsely powdered and expressed in primitive wooden presses. The kernels which contain up to 53% of oil yield in practice about 40%. The pale yellow oil for exportation, known as "white tung oil" is ob tained by expressing the seeds in the cold ; the hot-pressed oil— "black tung oil"—is dark brown in colour and possesses a strong, unpleasant odour. Chinese tung oil has the highest specific gravity (0.94o to 0-944) of all known fatty oils, with the exception of castor oil, and the highest refractive index. The characteristic property of Chinese tung oil is the readiness with which it be comes polymerized, setting to a hard jelly on being heated for a short time to a temperature of 25o° Centigrade. Polymerization
is also induced by dropping saturated solution of iodine on to the surface of the oil, which immediately solidifies. The pronounced drying properties of tung oil render it suitable for use in the manufacture of paints and varnishes. In China it is further used for water-proofing paper. Tung-oil trees have been successfully introduced in the United States in the north-central part of Florida where more than 1,50o acres are planted. Up to 1929 all available seed was being used for planting. More than 1oo,000,000 pounds of the oil are imported annually and it is hoped that eventually the domestic supply will meet American needs. (See also OILs, FATS AND WAXES ; and M. Toch, Chemistry and Tech nology of Paints, 1926.) (E. L. ; G. H. W.)