Oil of good quality is a thickish fluid, of a very pale fellow colour (the best now almost limpid), with a slightly nauseous odour, and an oily taste, mild at first, but causing a feeling in the back of the throat which is more or less intense in proportion to the freshness of the specimen. Old or badly prepared oil is rancid and disagreeable. The specific gravity is, at. 55° Fehr., according to Samsun; but according to Geiger it is only It can be solidified only by a very low temperature. It is distin guished among fixed oils by its complete or nearly complete solubility in pure sulphuric tether and in alcohol, thereby approaching the essential oils in its habitudes, and its easy combination with alkaline leys, and consequently its ready saponification, two properties of much importance, the one furnishing a convenient test of its purity, the other facilitating its administration in a form less repulsive than its ordinary state. Its purity may be tested by mixing it with an equal quantity of absolute alcohol, in which it should be entirely dissolved ; the adulterating oil, if there be any, will remain undissolved. Its ultimate composition seems to be— It thus appears to be one of tho most highly oxygenated oils or fats, notwithstanding which, on exposure to the air, it very readily absorbs more oxygen, and quickly becomes rancid ; it is however slow of drying. It is stated to consist of several proximate principles, but whether these are edueta or products is uncertain. Bussy and Lecanu, who have laid great attention to the subject (' Journal de Pharmacie,' xiii. 57) incline to the latter opinion, which is the most probable. "This oil," they state, "cannot be regarded as a simple immediate principle, hut. as a compound organic product resulting from the mixture of at least two different substances." Tho other view is that it is a compound of three fatty adds saturated by glycerin, for in the process of saponification 100 parts of castor-oil yielded—.
For further details respecting tho chemistry of castor-oil, see Pereira's ' Mat. Med.,' ii. p. 1287, edit. of 1350.
Castor-oil is a mild aperient or laxative when pure, operating without griping or other inconvenience, and commonly very soon after Its administration. It is tho most proper laxative for infants, and in many inflammatory states of the abdomen or of the kidneys, bladder, &c. It is also one of the best purgatives in rheumatism, especially in
lumbago, and one of the best means of relieving habitual constipation, az, unlike other purgatives, the dose may be successively reduced without its power being impaired. It is also a most eligible medicine in piles or other affections of the rectum. Alone or with turpentine it is a very elle/Acme means of expelling worms. The chief obstacle to its catenary nse is the repulsive taste which it often possesses. Many expedients have been adopted to remove or lessen this; but no artifice can make bad or old oil good or palatable. Rancid oil may be petrified by ealcined magnesia ; but the careful exclusion of the air, which prevents the rancidity occurring. lapreferable to any process for removing it when it has affected the oil. Mixing the oil, immediately before swallowing it, with hot milk, coffee, or broth, is sometimes a successful means of escaping the unpleasantnees. Besides this the heat not only renders the oil thinner, but quickens its action, so that a less quantity is needed. Thus administered, about ono half the quantav will suffice which is needed when given in any cold vehicle. Brandy and gin are Improper in many cases, owing to their heating properties Syrup of orange and lemon aro beneficial adjuncts, especially if a portion of the orange-peel be masticated immediately after swallowing the mixture. An emulsion with yolk of is some times acceptable, if made Immediately before it is administered. By far the best plan however is to take advantage of the tendency to combine with alkalies, and so form a soapy emulsion, which does not destroy the purgative power, while it completely alters the appearance, and prevents any one recognising the oily object of his aversion. To effect this however requires are and skill, especially as a variable quantity of alkaline Icy is needed, according to the age of the oil, very old oil requiring more ley than fresh oil. In general from fifteen to twenty drops of pure liquor potassm will saponify half an ounce of oil, to which one ounce of distilled water, end one drachin of spirit of pimento or of nutmeg are to be added.
Castor-oil is extensively used in the East, France, Italy, and else where, for burning, and lately to make soap.