This section is from the book "A Treatise On Beverages or The Complete Practical Bottler", by Charles Herman Sulz. Also available from Amazon: A Treatise On Beverages.
From the lavender flower alone or from the flowering tops or the entire plant is obtained by distillation with steam the oil of lavender, yielding about one-half per cent, of the oil; stem and leaves yielding a small portion of less fragrant oil.
Oil of lavender flowers should denote oil of lavender distilled only from the flowers, but more usually the whole plant is distilled and sold under that name or as oil of lavender. It is a very limpid, colorless, yellowish or greenish-yellow liquid of a specific gravity varying between 0.870 and 0.910, commencing to boil at about 185° 0. (365o F.), dissolves in its own weight of alcohol of the specific gravity 0.835 to 0.850, in absolute alcohol in all proportions. Oil of garden lavender is considered a better quality and the English oil is more estimated than the French.
The commercial oil is adulterated with alcohol or turpentine; the latter is detected by the decreased solubility in alcohol. Oil of spike lavender has a deeper green-yellow color, boiling at 175° C. (347° F.). Alcohol is recognized as an adulteration in the distillate obtained, at about 80° C. (176° F.).