Common frankincense is an ingredient in some ointments and plasters, and on account of its pleasant odour when burned has been used in incense as a substitute for olibanum.
In a scientific definition the compounds of fatty acids with basic metallic oxides, lime, magnesia, lead oxide, &c., should also be included under soap; but, as these compounds are insoluble in water, while the very essence of a soap in its industrial relations is solubility, it is better to speak of the insoluble compounds as " plasters, " limiting the name " soap " as the compounds of fatty acids with soda and potash.
They form excellent decorative plasters on account of their clean white colour and the sharpness of castings made from them, this latter quantity being due to their expansion when setting.
C. Eckel, Cements, Limes and Plasters (New York, 190s); G.
In pharmacy it forms an ingredient in several plasters and ointments.