1506. To Bleach Vegetable Oils

1506. To Bleach Vegetable Oils. The oils referred to in No. 1504, as well as all other oils and fats, may be rendered perfectly colorless by agitating them with a little chromic acid; or, what is cheaper and more convenient, with a mixed solution of bichromate of po-tassa and sufficient sulphuric acid to seize on the alkali of the bichromate and to liberate its chromic acid. 1 to 2 drachms of the bichromate, mixed with 3 times its weight of oil of vitriol (previously diluted with about twice its volume of water, and allowed to cool), is ordinarily sufficient, when skillfully used, to perfectly bleach 2 or 3 pints of oil. It should be added gradually to the oil, with continued violent agitation, and this should be kept up for some considerable time after the last portion is added. The mixture must be made in a vessel of glass, porcelain, stoneware, or wood, and nothing metallic must touch it.

In some cases a few drops of strong nitric acid (diluted with about twice its bulk of water), if added towards the end of the agitation, will facilitate the process; or, with colza, linseed, nut, and rape oil, instead of the diluted nitric acid, a few drops of hydrochloric acid without dilution. After the final agitation, the oil must be allowed to repose at a temperature of about 60° Fahr. When it has settled, the clear portion should be decanted, thoroughly washed with hot water, again allowed to repose for some time, and then finally decanted for use. If necessary, it may lastly be filtered. (Cooley.)

1507. Berlandt's Method of Bleaching Fixed Oils

1507.    Berlandt's Method of Bleaching Fixed Oils. Shake strongly for some minutes, 300 parts of the oil with 40 parts water containing 1 part permanganate of potassa; allow the mixture to stand in a warm place for some hours, and then filter. This renders the oil colorless.

1508. Dieterich's Method of Bleaching Fixed Oils

1508.    Dieterich's Method of Bleaching Fixed Oils. Dissolve 21/4 pounds (avoirdupois) permanganate of potassa in 311/2 quarts water, in a wooden tub having a faucet in its bottom. Stir into the mixture 521/2 quarts of the oil to be bleached, and keep all well stirred for 2 days. Then add 21 quarts boiling water and 11 pounds commercial hydrochloric acid, and keep the whole stirred for 2 days longer. Draw off the acid water, and wash the oil repeatedly with boiling water until all acid is removed from it.

1509. Engelhardt's Method of Bleaching Palm Oil

1509.   Engelhardt's Method of Bleaching Palm Oil. Heat 1000 parts by weight palm oil in an iron vessel to about 143° Fahr., and let it stand all night, sustaining the temperature. Next day pour it off into a clean vessel and let it cool down to about 100°. Meanwhile, dissolve 15 parts bichromate of potash in 45 parts boiling water; when the solution has cooled a little, pour into it 60 parts hydrochloric acid. Add this mixture to the palm oil, stirring quickly, and in about 5 minutes it will assume a sombre green color; by continued stirring the oil gradually clarifies and becomes quite limpid. It should become quite white after washing it with warm water; but if not entirely colorless, the operation must be repeated, using 1/4 part bichromate of potash, and 1 part hydrochloric acid. This is a quick method, and Engelhardt claims that it produces better results than the means usually employed. (See No. 537 (To Bleach Palm Oil).)