Inasmuch as the natural color of palm oil is somewhat too deep for the taste of the ordinary consumer, ranging from yellow to a dirty red color, it is often bleached in the refining process before being sent into commerce. Ordinary exposure to the air tends to bleach this oil, due probably to the bleaching properties which the air sometimes possesses. Ozone is also employed as a bleaching agent. The bichromate process of bleaching palm oil is very commonly practiced. By this method the oil is freed from its principal impurities and treated with from one to three percent of potassium bichromate and with hydrochloric acid which decomposes the “chrome” liquor, and in the chemical process which attends this reaction decided bleaching effects are produced. The bleaching agents are withdrawn and the oil thoroughly washed with water until all traces of chromate and mineral acid are removed.
Adulterations.
—On account of its great cheapness and the fact that the admixture of other oils of lower melting point would detract from its value, palm oil has not been subjected to any extensive adulteration. The most common adulterations are the impurities which are left in the oil in the slovenly method of manufacture employed by the natives of Africa.
Constituents.
—As would be expected from the name, one of the chief constituents of palm oil is palmitin. If palm oil is saponified and the solid separated from the liquid fatty acid, the former is found to consist almost exclusively of palmitic acid. The specific gravity of palm oil is taken at a high temperature, as much as 50 degrees C. or above. The specific gravity at this temperature is about .893. Palm oil absorbs a little over one half its weight of iodin. The average iodin number may be regarded as varying from 53 to 55. Aside from the limited use of palm oil for human food it is used chiefly in the manufacture of soap and of candles. It is also used extensively in the tin plate industry to spread over the hot iron surface to preserve it from oxidation until it is dipped into the bath of melted tin.
NUTS.
The Acorn.
—Many varieties of acorns are used for human food. All of the nuts of the oak family are edible, but some of the larger and more common varieties contain such a quantity of tannin as to be rather bitter to the taste. The wild acorns were formerly utilized very extensively for the fattening of swine, producing an article of pork of high palatable value but with the production of a fat of a low melting point, unsuitable for the manufacture of lard for summer use. The term applied to the natural nuts eaten by swine for this purpose is “mast,” and formerly “mast-fed” pork was an extensive article of commerce. The disappearance of the oak and beech forests, however, have practically eliminated this variety of pork from the markets, at least to any extent which can be called commercial.
Composition of the Acorn.
—Edible portion, 64.4; refuse, 35.6.