[12] Calculated by us from saponification value.
CHAPTER IV.
BLEACHING AND TREATMENT OF RAW MATERIALS INTENDED FOR SOAP-MAKING.
Palm Oil—Cotton-seed Oil—Cotton-seed "Foots"—Vegetable Oils—Animal Fats—Bone Fat—Rosin.
Having described the most important and interesting oils and fats used or suggested for use in the manufacture of soap, let us now consider briefly the methods of bleaching and treating the raw materials, prior to their transference to the soap-pan.
Crude Palm Oil.—Of the various methods suggested for bleaching palm oil, the bichromate process originated by Watts is undoubtedly the best. The reaction may be expressed by the following equation, though in practice it is necessary to use twice the amount of acid required by theory:—
K2Cr2O7 + 14HCl = 2KCl + Cr2Cl6 + 7H2O + 6Cl.
6Cl + 3H2O = 6HCl + 3O.
The palm oil, freed from solid impurities by melting and subsidence, is placed in the bleaching tank, and washed with water containing a little hydrochloric acid. Having allowed it to rest, and drawn off the liquor and sediment (chiefly sand), the palm oil is ready for treatment with the bleaching reagent, which consists of potassium bichromate and commercial muriatic acid. For every ton of oil, 22 to 28 lb. potassium bichromate and 45 to 60 lb. acid will be found sufficient to produce a good bleached oil.