I just purchased The Aromatherapy Encyclopedia and it's exactly the kind of book I was looking for. It has detailed information about 385 plant oils, there origin, history, and practical uses. It also has documented properties for some of the oils, and the best method for use. It even has a chapter on vegetable oils, butter, and waxes. Both writers Carol, and David Schiller are recognized experts with over 5 internationally published books on the use of essential oils.
If your a soapmaker you will really appreciate this book, I can't live without it.