castor oil, yellowish oil obtained from the seed of the castor bean. The oil content of the seeds varies from about 20% to 50%. After the hulls are removed the seeds are cold-pressed. Medicinal castor oil is prepared from the yield of the first pressing; this is used as a purgative and laxative. Oil from the second pressing is used as a lubricant for machinery, as a softening agent in making artificial leather, in the dressing of genuine leather, in brake fluids, and in paints and plastic materials. The residue can be used as fertilizer and (after the poisonous substance, ricin, is removed) as cattle feed. Other products having similar properties and uses have been gradually replacing castor oil.