Oil of turpentine, spirit of turpentine, and ordinary or common turpentine are all the same thing. Crude turpen tine is turpentine as it is derived direct from the pine trees. Oil of turpentine really means the essential or volatile oil of turpentine after distillation. Oil of turpentine must not be classed with the ordinary kinds of oils, such as olive oil, etc., which are nonvolatile, and have a different composition altogether. There is an oil of turpentine known as fat oil of turpentine, but this is simply ordinary turpentine that has been exposed to air for some time and has become thickened or partly resinified by oxidation.