Perfumes and their preparation

by George William Askinson

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.

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.

Oil of bitter almonds is often adulterated with oil of mirbane; this can be demonstrated by shaking 1 volume of the oil with 17 volumes of alcohol of 45%, and setting the mixture aside to settle. The nitrobenzol (oil of mirbane) will then collect at the bottom. Oil of Rose may be tested as follows: Mix the oil with an equal quantity of concentrated sulphuric acid. Neither the color nor the odor of the oil should be changed, but if oil of geranium was present a disagreeable odor and a darker color is produced.

It has been proposed, too, to test the oils by heating with iodine or nitric acid and determining the purity by the reaction; but the results with the different oils are so similar that the test is almost worthless. We have had the same experience with the test by nitro-prusside of copper which on being heated with essential oils gives colored precipitates differing with various oils, but still so similar that they cannot be relied upon. We have found in all cases that a comparison of an oil with a sample of known purity is the best, or else the tests given in the preceding pages.