Page:Foods and their adulteration; origin, manufacture, and composition of food products; description of common adulterations, food standards, and national food laws and regulations (IA foodstheiradulte02wile).pdf/451

 soap. Palm oil is manufactured in the crudest possible way by the natives, and immense quantities are lost for this reason. By reason of this crude method, which leaves the oil in contact with the putrescible matter, palm oil often comes into the market in a rancid state or at least with a high content of free fatty acid. Appreciable quantities of water are also found in the crude article.

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 The bleaching agents are withdrawn and the oil thoroughly washed with water until all traces of chromate and mineral acid are removed.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