_Soapstock._--This substance is largely imported from America, where it is produced from the dark-coloured residue, termed mucilage, obtained from the refining of crude cotton-seed oil. Mucilage consists of cotton-seed oil soap, together with the colouring and resinous principles separated during the treatment of the crude oil. The colouring matter is removed by boiling the mucilage with water and graining well with salt; this treatment is repeated several times until the product is free from excess of colour, when it is converted into soap and a nigre settled out from it. Soapstock is sold on a fatty acid basis; the colour is variable. FOOTNOTES: [1] Calculated by us from saponification value. [2] Calculated by us from saponification value. [3] Calculated by us from saponification value. [4] Calculated by us from saponification value. [5] Calculated by us from saponification value. [6] Calculated by us from saponification value. [7] Calculated by us from saponification value. [8] Calculated by us from saponification value. [9] Calculated by us from saponification value. [10] Calculated by us from saponification value. [11] Calculated by us from saponification value. [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:-- K_{2}Cr_{2}O_{7} + 14HCl = 2KCl + Cr_{2}Cl_{6} + 7H_{2}O + 6Cl. 6Cl + 3H_{2}O = 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. The best procedure is to act upon the colouring matter of the oil three successive times, using in the first two treatments one-third of the average of the figures just given, and in the final treatment an appropriate quantity which can be easily gauged by the appearance of a cooled sample of the oil.