The oil of the large-seeded variety is occasionally extracted by the cold process, but most commonly by a combination of roasting and boiling. The seeds are first partially roasted over a charcoal fire, both to coagulate the albumen and liquefy the oil ; they are then pounded, and boiled in water till the oil rises to the surface. The yield is about 33 per cent, of a very impure oil having a deep-red colour, and an ompyreumatic odour, which is often very offensive during ite combustion in lamps ; it is thick and viscid, and soon grows rancid. It is produced only for home consumption, forming the common "lamp-oil "of the bazars, and being very extensively used for dressing articles of leather.
Most of the Indian oil is extracted in and exported from Calcutta, the crushed seed being eent up from Madras for the purpose—an inexplicable proceeding. The exports from Calcutta in 1870-1 were 654,917 gal., of which, 214,959 gal. were for the United Kingdom ; in 1877-8, the total Indian export had grown to the very large figure of 1,411,216 gal. It is sent to the United Kingdom, Mauritius, the Straits Settlements, Ceylon, and Australia, chiefly, it would seem, for lubricating purposes, much of it being obtained from the large-seeded kind, and extracted by the roasting and boiling process.
The manufacture of castor-oil is actively carried on in the United States, especially at St. Louis, the seeds being largely produced in S. Illinois. In 1875, Kansas had 24,145 acres under this crop, producing 361,386 bush. of seed. Other states participate in the industry. The land is prepared as for other crops, and the seeds are planted much the same as maize, except that only one seed is put into each bill, and that every fourth row is missed to afford space for the harvesting. Ripening commences in August ; the yield varies from 15 to 25 bush. an sere, 20 being considered fair. The oil is generally extracted in the following manner. The seeds, having been thoroughly cleansed from the dust and particles of the pod with which they are always contaminated, are placed in an iron tank, and heated to such a degree as will liquefy the oil without any risk of scorching. They are then pressed, the oil escaping being known as " lst quality." The pressed seed is heaped up and left for a day ; on the following day, it is again heated and pressed, and gives a " 2nd quality " oil. The yield from 1 bush. of seed is 12 lb. of 1st quality, and 4 lb. of 2nd quality oil ; sometimes a 3rd expression is made, giving 1-3 lb. of a very much coloured oil. Occasionally too, the cake from the 2nd pressing is treated with bisulphide of carbon, which extracts a small additional quantity of thick, dark, common oil. All qualities need purifying and clarifying. This is usually effected by boiling first with a large quantity of water, and skimming off the impurities as they rise, while the mucilage and starch are dissolved, and the albumen is coagulated. The clear oil is
removed[and boiled with a very little water, which clarifies it, and drives off volatile acid matters. The chief point to be noticed is to expose the oil as little as possible to the air, or it quickly becomes rancid. The let quality oil is used medicinally, the 2nd for burning, lubricating, leather dressing, &c. In America, the cake is frequently used as fuel.
Italian castor-oil has lately attracted some notice. It is principally expressed from the seed of plants grown in the province of Verona, especially the district of Legnago, in N. Italy ; the produce is now 400,000 kilo. of seed yearly, but all Italian-pressed oil is not from Italian-grown seed, as Genoa imports considerable quantities of the seed from India. Two varieties are cultivated in Italy, the black-seeded Egyptian and the red-seeded American ; the former yields the lesser percentage, but of a paler colour. The seeds are very carefully peeled, and after crushing, are placed in hydraulic presses, standing in a room which is heated to 21° (70° F.) in winter. The exudation of the oil is promoted by warming the press-plates to 32°-38° (90°-100° F.). The yield of oil is about 40 per cent. on the peeled seeds.
The castor-oil-plant grows as a weed in the Bahamas, but the little oil which is extracted by boiling is never met with in commerce. A supply of the best Indian seed has been sent to these islands, and is found to afford three times as much oil as the native plant, besides being quite as readily cultivated. Hopes are entertained that the colony will soon be an important producer of the oil. The plant has been introduced into Brazil from India, and attains an immense size; in 1879, an attempt was made to export castor-oil direct from Maceio to Europe, and probably large quantities will eventually be seut, as it is most extensively produced in the province of Alagoas, and locally used in lamps; the value of the shipments coastwise from Maeeio rose from 16/. in 1877 to 117/. in 1879. In Angola (W. Africa), the dry sandy beds of the rivers in the hot season are often completely covered with a magnificent growth of the castor-oil plant. Among other countries, China may be mentioned as yielding considerable quantities of castor-oil ; the exports from Newchwang were 581 piculs (of 133* lb.) in 1877, and 1664 in 1878; Shanghai exported 555 piculs to other Chinese ports in 1878, and 3 piculs to Chinese ports, and 76 pieuls to foreign countries, in 1879. In France, the fresh seeds are bruised and pressed in the cold, and the albumen and mucilage are separated by long standing and filtering ; the product is 33 per cent. of the seeds, but is much weaker (less purging) than that obtained from the tropics. This remark applies also to the Italian oil. Rarely, the bruised seed is macerated in cold alcohol, 1 lb. of seed then giving 6 oz. of oil. Algeria and Egypt are large producers.