Journal of the Chemical Society 1872. [antikvár]

JOURNAL OP THE CHEMICAL SOCIETY. PAPERS READ BEFORE THE CHEMICAL SOCIETY. I.—O71 Essential Oils. Part II. By J. H. Gladstone, Ph.D., F.R.S. Eight years ago I communicated a paper on Essential Oils to the Chemical Society, and in concluding it I promised a further communication, with experiments on the oxidised oils, ard a fuller account of the chemical and physical histoiy of some of the hydrocarbons. Shortly after the paper was printed, a series of unforeseen events took me almost wholly away from my laboratory ; other scientific enquiries then engrossed my thoughts ; and so the research on these essential oils was long laid aside. Now, however, I will endeavour to fulfil my promise, though not to carry out my whole design. Before entering on any new observations, I wish to refer to some criticisms on my paper which Mr. Daniel Hanbury kindly sent me. They relate to the plants from which the oils are derived ; and, as I know little of the subject myself, I will just place his statements against those of Mr. Piesse, on whose authority each of the controverted names was given. Oil of calamus is distilled, not from Calamus aromaticus, but from the rhizome of Acorus Calamus. Indian geranium oil is yielded by Andropogon Pachnodes. The wild thyme of our heaths, Thymus Serpyllum, gives an essential oil, but the oil of thyme of commerce is from Thymus vulgaris. During the past spring I was furnished by Mr. Piesse with specimens of some rare essential oils, not previously examined—those of citron, lign aloes, pimento, and vitivert. The following were the determinations of the specific gravity and refraction of these oils as they came into my hands:— VOL. xxv. B GLADSTONE ON ESSENTIAL OILS. Crude oils. Specific gravity. Temp. Cent. Eefractive indices. A. D. H. Citron Lign aloes Pimento 0 -8914 0-8702 1 -0374 1 -0070 10° 18° 10° 19-5° I -4729 1 -4620 1 -5229 1 -5147 1 -4797 1 -4679 1 -5325 1 -5218 1-5011? 1-5660? Citron.—This oil is obtained from the leaves of the lemon, Gitrus Limonum. It was slightly yellow. It began to boil at 156° 0., but the bulk consisted of a liquid having the boiling point 166°—168° ; the specific gravity 0-8549 at 19-5° ; the refractive index for A, 1-4680 ; and the dispersion 0-273. Its odour resembled that of lemon, and it was probably identical with the hydrocarbon found in other parts of the same plant. Lign Aloes.—This is a colourless oil, with a characteristic pleasant odour, believed to be obtained from the wood of a large tree that grows in Mexico.* The principal part distils over at somewhere about 200°, hut it seemed impossible by fractional distillation, even with the aid of sodium, to obtain a body of a fixed boiling point. The specific gravity and optical properties of the best rectified oil are given later on in this paper ; they will be found to resemble closely the properties of citronellole, suggesting the idea that the principal constituent may also have the composition CioHicO. "Pimento.—This pungent oil is derived from the seeds of Myrtus Pimenta. It began to boil at about 197°, and the thermometer rose gradually to 242°, about which temperature the greater portion passed into the receiver. The first portion consists partly of an oil insoluble in potash ; the. second is wholly dissolved by an alkali. When rectified, though perhaps not quite pure, it was found to have the boiling point 243° ; specific gravity at 12-5°, 1-0436 ; refractive index for A 1-6281 ; and dispersion about 0-416. Its odour was that of eugenic acid, and like that body it was freely soluble in potash, giving two salts, of which that which contains the larger proportion of acid will separate from a moderately strong solution in crystalline masses. As the physical properties mentioned above accord Bufiiciently well with those previously determined for eugenic acid,t there can scarcely be a doubt that oil of pimento is substantially the * The Lign aloes of tlie sacred Scriptures is supposed to be the Aqtiilaria Agalloclmm of Northern India. + Phil. Trans., 1863, p. 317.