Mineral oil, paraffin oil, kerosene, petroleum and petroleum fractions are insoluble in alcohol and can therefore be detected without difficulty in volatile oils; besides, they are often easily recognized by their low specific gravity. Palmarosa oil to which some mineral oil has been added is only partly soluble in 70 percent alcohol. If the insoluble portion is successively treated with 90 percent and absolute alcohol, an oil remains, which in the beginning it is true is colored brown by sulphuric or nitric acids, but in general resists the action of these acids and also of alkalies, and on saponification with alcoholic potassa gives no saponification number.
The mineral oils have different boiling points. The hydrocarbons of illuminating oil boil at about the same temperature as the terpenes. Lower boiling fractions are said to be sometimes used for adulterating turpentine oil. A higher boiling mineral oil, about 250°, has been found in citronella and in gingergrass oils. The petroleum fractions of lower boiling temperatures are easily volatile with water vapor, the higher fractions not at all, or at least to a small degree only.
A method for the quantitative estimation of mineral oils consists in weighing the residue left after having removed the volatile oil by oxidation with fuming nitric acid, as described under turpentine oil. According to Herzfeld1) concentrated sulphuric acid is better adapted to the separation of mineral oil than nitric acid. However, the investigators are very much divided in their opinions on this subject. (For details see under turpentine oil in the second volume). Attention should be called to the fact that some volatile oils, such as rose oil, chamomile oil, orange flower oil and others, contain larger or smaller amounts of paraffins as natural constituents.