M. L'hermite (1854) proposed solutions of alkaloids in oleic acid as substitutes for the oleaginous and glycerinic solutions of these bases. He objected to the oils from their incapability of dissolving the alkaloids, and to the glycerin from its not possessing unctuous properties. His suggestions passed largely unnoticed until the matter was revived, in 1872, by Prof. John Marshall. Oleic acid triturated with the alkaloids dissolves these and their salts perfectly, and the solutions, if desired, may be perfumed. When either alkaloids or metallic oxides are treated with oleic acid, a salt known as an oleate, is produced. The oleates, as employed medicinally, are solutions of these normal salts (true oleates) in an excess of oleic acid. Heat should be avoided where possible, though in many instances a moderate degree of heat is permissible.
Oleates, especially of the metallic oxides, are also prepared by double decomposition between a salt of the base selected and a sodium or potassium oleate or castile soap (sodium oleo-palmitate), with the last-named soap yielding an impure oleate. Prof. J. M. Good (Proc. Mo. Pharm. Assoc., 1891) suggests dissolving the alkaloids in just sufficient oleic acid to effect solution, and then diluting with almond oil or other bland oil.
The oleates possess the properties of their bases, and are employed like the ointments of the same bodies, being, however, more cleanly and finer in appearance, and, on the other hand, more irritating, unless diluted with some bland oil. They should not be applied with friction, but should be gently applied with the finger or brush. (For a short treatise on the oleates, see G. M. Beringer, Amer. Jour. Pharm., 1889, pp. 593-600; also see John V. Shoemaker, The Oleates, Phila., 1885.)