We prepared some oil by means of ether, and found it to have a sp. gr. of 0·919 at 23° C.; it solidified at 5° C., becoming rather turbid at some degrees above this temperature. Yet sesame oil is more fluid at ordinary temperatures than ground-nut oil, and is less prone to change by the influence of the air. It is in fact, when of fine quality, one of the less alterable oils.
Chemical Composition—The oil is a mixture of olein, stearin and other compounds of glycerin with acids of the fatty series. We prepared with it in the usual way a lead plaster, and treated the latter with ether in order to remove the oleate of lead. The solution was then decomposed by sulphuretted hydrogen, evaporated and exposed to hyponitric vapours. By this process we obtained 72·6 per cent. of Elaïdic Acid. The specimen of sesamé oil prepared by ourselves consequently contained 76·0 per cent. of olein, inasmuch as it must be supposed to be present in the form of triolein. In commercial oils the amount of olein is certainly not constant.
As to the solid part of the oil, we succeeded in removing fatty acids, freely melting, after repeated crystallizations, at 67° C., which may consist of stearic acid mixed with one or more of the allied homologous acids, as palmitic and myristic. By precipitating with acetate of magnesium, as proposed by Heintz, we finally isolated acids melting at 52·5 to 53°, 62 to 63°, and 69·2° C., which correspond to myristic, palmitic and stearic acids.
The small proportion of solid matter which separates from the oil on congelation cannot be removed by pressure, for even at many degrees below the freezing point it remains as a soft magma. In this respect sesamé oil differs from that of olive.
Sesamé oil contains an extremely small quantity of a substance, perhaps resinoid, which has not yet been isolated. It may be obtained in solution by repeatedly shaking 5 volumes of the oil with one of glacial acetic acid. If a cold mixture of equal weights of sulphuric and nitric acids is added in like volume, the acetic solution acquires a greenish yellow hue. The same experiment being made with spirit of wine substituted for acetic acid, the mixture assumes a blue colour, quickly changing to greenish yellow. The oil itself being gently shaken with sulphuric and nitric acids, takes a fine green hue, as shown in 1852 by Behrens, who at the same time pointed out that no other oil exhibits this reaction. It takes place even with the bleached and perfectly colourless oil. Sesamé oil added to other oils, if to a larger extent than 10 per cent., may be recognised by this test. The reaction ought to be observed with small quantities, say 1 gramme of the oil and 1 gramme of the acid mixture, previously cooled.
Commerce—The commercial importance of Sesamé may be at once illustrated by the fact that France imported in 1870, 83 millions; in 1871, 57½ millions; and 1872, 50 millions of kilogrammes (984,693 cwt.) of the seed.[1734]
The quantity shipped from British India in the year 1871-72 was 565,854 cwt., of which France took no less than 495,414 cwt.[1735] The imports of the seed into the United Kingdom in 1870 were to the value of only about £13,000.
Sesamé is extensively produced in Corea and in the Chinese island of Formosa, which in 1869 exported the exceptionally large quantity of 46,000 peculs[1736] (1 pecul = 133 lb.). Zanzibar and Mozambique also furnish considerable quantities of sesamé, whilst on the West Coast of Africa the staple oil-seed is Ground-nut (Arachis hypogæa L. [p. 186]). The chief place for the manufacture of sesamé oil is Marseilles.
Uses—Good sesamé oil might be employed without disadvantage for all the purposes for which olive oil is used.[1737] As its congealing point is some degrees below that of olive oil, it is even more fitted for cool climates. Sesamé seeds are largely consumed as food both in India and Tropical Africa. The foliage of the plant abounds in mucilage, and in the United States is sometimes used in the form of poultice.