Chemical Composition—The most important constituent of the seed is the fixed oil, called Castor Oil, of which the peeled kernels afford at most half of their weight.
The oil, if most carefully prepared from peeled and winnowed seeds by pressure without heat, has but a slightly acrid taste, and contains only a very small proportion of the still unknown drastic constituent of the seeds. Hence the seeds themselves, or an emulsion prepared with them, act much more strongly than a corresponding quantity of oil. Castor oil, extracted by absolute alcohol or by bisulphide of carbon, likewise purges much more vehemently than the pressed oil.
The castor oil of commerce has a sp. gr. of about 0·96, usually a pale yellow tint, a viscid consistence, and a very slight yet rather mawkish odour and taste. Exposed to cold, it does not in general entirely solidify until the temperature reaches -18° C. In thin layers it dries up to varnish-like film.
Castor oil is distinguished by its power of mixing in all proportions with glacial acetic acid or absolute alcohol. It is even soluble in four parts of spirit of wine (·838) at 15° C., and mixes without turbidity with an equal weight of the same solvent at 25° C. The commercial varieties of the oil however differ considerably in these as well as in some other respects.
The optical properties of the oil demand further investigation, as we have found that some samples deviate the ray of polarized light to the right and others to the left.
By saponification castor oil yields several fatty acids, one of which appears to be Palmitic Acid. The prevailing acid (peculiar to the oil) is Ricinoleic Acid, C₁₈H₃₄O₃; it is solid below 0° C., does not solidify in contact with the air by absorption of oxygen, and is not homologous with oleic or linoleic acid, neither of which is found in castor oil. Castor oil is nevertheless thickened if 6 parts of it are warmed with 1 part of starch and 5 of nitric acid (sp. gr. 1·25), Ricinelaïdin being thus formed. From this Ricinelaïdic Acid may easily be obtained in brilliant crystals.
As to the albuminoid matter of the seed, Fleury (1865) obtained 3·23 per cent. of nitrogen which would answer to about 20 per cent. of such substances. The same chemist further extracted 46·6 per cent. of fixed oil, 2·2 of sugar and mucilage, besides 18 per cent. of cellulose.
Tuson in 1864, by exhausting castor oil seeds with boiling water, obtained from them an alkaloid which he named Ricinine. He states that it crystallizes in rectangular prisms and tables, which when heated fuse, and upon cooling solidify as a crystalline mass; the crystals may even be sublimed. Ricinine dissolves readily in water or alcohol, less freely in ether or benzol. With mercuric chloride, it combines to form tufts of silky crystals, soluble in water or alcohol. Werner (1869) on repeating Tuson’s process on 30 lb. of Italian castor oil seeds, also obtained a crop of crystals, which in appearance and solubility had many of the characters ascribed to ricinine, but differed in the essential point that when incinerated they left a residuum of magnesia. Werner regarded them as the magnesium salt of a new acid. Tuson[2119] repudiates the suspicion that ricinine may be identical with Werner’s magnesium compound. E. S. Wayne of Cincinnati (1874) found in the leaves of Ricinus a substance apparently identical with Tuson’s ricinine; but he considers that it has no claim to be called an alkaloid.
The testa of castor oil seeds afforded us 10·7 per cent. of ash, one tenth of which we found to consist of silica. The ash of the kernel previously dried at 100 C. amounts to only 3·5 per cent.
Production and Commerce—Castor oil is most extensively produced in India, where two varieties of the seeds, the large and the small, are distinguished, the latter being considered to yield the better product. In manufacturing the oil, the seeds are gentry crushed between rollers, and freed by hand from husks and unsound grains. At Calcutta, 100 parts of seed yield on an average 70 parts of cleaned kernels, which by the hydraulic press afford 46 to 51 per cent. of their weight of oil; the oil is afterwards subjected to a very imperfect process of purification by heating it with water.[2120]