Olive Oil is extracted from the pericarp of the fruit of the _Olea Europea_. When pure, it exhibits a pale yellow or greenish colour, has a specific gravity of 0·9176, and possesses a faint, pleasant odour and a bland and agreeable taste. It is insoluble in water, very slightly in alcohol, but dissolves in about 1½ parts of ether. Olive oil boils at 315°, and begins to deposit white granules at 10°; at 0°, it solidifies to a solid mass which, by pressure, may be separated into tripalmetine and trioleine. Upon saponification, it is decomposed into oleic, palmetic, and stearic acids and glycerine. The best-known varieties of olive oil met with in commerce, in the order of their quality, are--Provence, Florence, Lucca, Genoa, Gallipoli, Sicily, and Spanish.[136] Owing to the high price of the pure article, and perhaps to the difficulty experienced in detecting foreign admixtures, olive oil is probably more extensively adulterated than any substance of general consumption. The oils most employed as adulterants are those of cotton-seed, poppy, pea-nut, sesamé, rape-seed, arachis, and lard. Although the subject of the adulteration of olive oil has received the attention of numerous chemists, including several of exceptionally high standing, the results obtained, while of service in indicating the presence of some foreign oil, are unfortunately often of but little use in the positive identification of the particular adulterant used. Of the many methods of examination that have been suggested, the following are the most satisfactory:-- 1. _Specific gravity._--The density of olive oil is lower than that of the majority of the oils with which it is mixed, and it is sometimes possible to detect the presence of the latter by means of this property, especially when they are contained in a considerable proportion. Cotton-seed oil differs more in specific gravity than the other oils generally employed as adulterants. Donny[137] applies the test by placing in the suspected sample a drop of olive oil of known purity which has been dyed with ground alkanet root, and observing whether it remains stationary. A more satisfactory method is to determine the density by the gravity bottle. The following tabulation gives the densities (at 15°) of olive and several other oils liable to be met with as admixtures:-- Olive oil ·914 to ·917 Poppy oil ·924 „ ·927 Cotton-seed oil ·922 „ ·930 Sweet almond oil ·914 „ ·920 Arachis oil ·916 „ ·920 Colza oil ·914 „ ·916 Sesamé oil ·921 „ ·924 Rape-seed oil ·914 „ ·916 Lard oil ·915 2. _Solidifying point._--Attempts have been made to utilise the fact that some of the oils added to olive congeal at a lower temperature than the pure oil. Thus, cotton-seed oil solidifies at -22°, ground-nut oil at -33°, poppy at -18°.