The common onion, Allium Cepa, L, owes its pungent, persistent odor to a volatile oil which, when distilled from the entire plant, is obtained with a yield of 0,046 p. c.8).
1) An interesting compilation of the occurrence of sulphur-containing oils of the vegetable kingdom has been published by C. Hartwich (Apotheker Ztg. 17 , 339). This list not only includes the oils in which the presence of sulphur has been proved but also those the garlic-like odor of which leads to the supposition of its presence.
2) According to Parry (The chemistry of essential oils. London 2nd ed. 1903, p. 191) the statement in the Jahresber. d. Chem. 1876, 398 that Beckett and Wright [Journ. chem. Soc. 1 (1876), 1] found a sesquiterpene in garlic oil is due to an error in translation, since oil of cloves was translated as "Knoblauchol" (oil of garlic).
3) Schimmel's Bericht April 1889, 44.
It is dark brown in color and rather viscid. d847o 1,041c1), or d19o1,036'-); aD - 5°.
An oil obtained by H. Hasnsel3) from common onions (0,015 p. c.) was concrete; d35o 0,9960; aD - 3° 40'; soluble with difficulty in ordinary solvents.
Oil of onion4) is decomposed when distilled under ordinary pressure; under 10 mm. pressure it passes over almost completely between 64 and 125°.
According to Semmler1), the principal constituent is a disul-phide C6H12S2 (b. p. 75 to 83° under 10 mm.; d12o 1,0234), which upon reduction with zinc dust is changed to a substance C6H12S (b. p. 130°). Nascent hydrogen reduces it to the disulphide C6H11S2 (b. p. 68 to 69° under 10 mm.).
Onion oil also contains a higher sulphide with the same radicles which zinc dust reduces to C6H12S. Finally, the oil contains still another sulphur-containing substance which, probably is identical with one of the higher boiling constituents of asafetida oil.
Neither allyl sulphide nor terpenes are contained in oil of onion any more than in garlic oil.