The demonstration of an adulteration with an essential oil is most certain by so-called fractional distillation. Some of the oil to be examined (about four to six fluidrachms) is placed in a small retort with condenser and heated to a temperature a few degrees below the boiling-point of the oil in question. If, for instance, oil of bergamot adulterated with oil of turpentine is to be tested, it is heated carefully to nearly 188° C. (370° F.), the boiling-point of the oil of bergamot; the oil of turpentine which boils at 160° C. (320° F.) passes over completely, while the oil of bergamot remains in the retort. Fractional distillation is also the most reliable way of demonstrating an adulteration with a fixed oil or with paraffin, wax, or spermaceti. An adulteration of oil of lavender with oil of spike-lavender, which is otherwise barely recognizable, is positively shown by this method; even oil of geranium in oil of rose, oil of cassia in oil of cinnamon, etc., may be thus demonstrated. B. ADULTERATION OF ESSENTIAL OILS WITH FIXED OILS. An addition of fixed oils can be easily demonstrated by agitation of the oil with strong alcohol in which the essential oil dissolves, while the fixed oil remains unchanged. Castor oil, however, is likewise soluble in alcohol and for this reason is frequently used for the adulteration of essential oils. Yet the presence of a fixed oil can also be shown in a very simple manner by placing a drop of the suspected oil upon white paper and leaving it for some hours in a warm spot. If the oil was pure, the translucent stain on the paper will disappear completely (also when the oil was adulterated with turpentine); but if it was mixed with a fixed oil, the stain will remain permanently and cannot be removed from the paper even by strong heat. C. ADULTERATION WITH ALCOHOL. This frequent adulteration is demonstrated either by fractional distillation, when the alcohol passes over first between 70° and 80° C. (158° and 176° F.), or by the use of the vessel illustrated in Fig. 31, which is divided into 100 equal parts. [Illustration: FIG. 31.] The vessel is filled to the tenth division with the oil to be tested, and water is added to bring the volume to the 50 mark. If alcohol is present, it is taken up by the water so that the volume of oil appears to diminish. If the oil reaches to the mark 7, it contained three volumes of alcohol, or in other words it was mixed with thirty per cent of alcohol. It is true, essential oils likewise dissolve somewhat in water, but in such minute quantities as not to affect the success of the test. D. ADULTERATION WITH PARAFFIN, SPERMACETI, OR WAX. This mode of adulteration is practised mainly with viscid oils which congeal at rather high temperatures, such as oils of anise, rose, etc., the essential oils being usually mixed at the same time with oil of turpentine or paraffin. The fraud is easily detected by fractional distillation.