A very frequent adulteration consists in an addition of petit-grain oil. Such an addition can only be recognized by the taste and odor. For this purpose add to 3 drops of oil in a small bottle 10 grammes of distilled water, and, after shaking vigorously, test as to the odor and taste. According to Chevalier, pour 1 or 2 drops of the oil upon sugar and stir the latter in water; if the oil is not genuine the water acquires a bitter taste. Hager recommends the following test: Mix 3 drops of the oil in a test-tube with 40 to 50 drops of alcohol; add, after complete solution, about ⅓ the volume of the solution of concentrated sulphuric acid, and effect mixture by careful shaking. Pure oil gives a turbid, reddish, dark-brown mixture (with old oil, dark brown); almost all other oils, which may be substituted, give paler-colored (reddish, red, or ocher-color) mixtures; or, in case the genuine oil is adulterated with non-genuine, the mixture exhibits a considerably less dark-color. When this test has been several times executed with genuine oil, no room for doubt is left. If the mixture be diluted with four times its volume of water, it becomes yellowish and milky. The odor of orange flowers is, according to Soubeiran, due to two volatile oils, of which the one having the most delicious odor is soluble in water. The other volatile oil, of which the neroli oil of commerce chiefly consists, is sparingly soluble in water, and does not possess such a delicious odor. This is the reason why good orange-flower water cannot be prepared by saturating water with neroli oil. The genuine orange-flower water is obtained as a by-product in distilling the oil. Neroli oil is much used for the finer perfumes, it being especially a necessary constituent of _eau de Cologne_. It has to be carefully protected from air and light. For perfuming purposes it is only sufficiently ripe after having been stored for at least one year. If, however, it becomes too old, it inclines towards rancidity, which may be prevented by compounding it with an equal volume of fine spirit. Portugal oil being of inferior quality can only be used for lower grade products. _Petit grain oil_ (_oleum petit grain_) is obtained by distillation from the leaves, young shoots and unripe fruits of different _Aurantiaceæ_. The best oil is that distilled from the leaves of the bitter orange, it possessing an odor similar to that of neroli oil, but, of course, not so fine. Southern France was formerly the chief place for the production of this oil, but considerable quantities of it are now manufactured in Paraguay, and the oil at present brought from there into commerce being of quite a good quality and considerably cheaper than the French oil, has almost entirely supplanted the latter.