The hues of the real otto, are also those of the adulterated; the presence of the sandal wood may be detected by the simple sense of smelling; but in order to discover the union of a grosser oil with the essential, drop a very little otto on a piece of clean writing paper, and hold it to the fire; if the article is genuine, it will evaporate without leaving a mark on the paper, so ethereal is the essential oil of roses!