The salt required, which, in the example given, would be 1-1/2 cwt., may be added to the solution prior to the addition of rosin or sprinkled in towards the finish of the boiling. When the whole has been sufficiently boiled and allowed to rest, the liquor containing the colouring matter will float over the resinate, and, after removal, may be replaced by another washing.
Many other methods have been suggested for the bleaching, refining and treatment of materials intended for saponification, but the above practical processes are successfully employed.
All fats and oils after being melted by the aid of steam must be allowed to thoroughly settle, and the condensed water and impurities withdrawn through a trap arrangement for collecting the fatty matter. The molten settled fatty materials en route to the soap-pan should be passed through sieves sufficiently fine to free them from suspended matter.
CHAPTER V.
SOAP-MAKING.
Classification of Soaps—Direct Combination of Fatty Acids with Alkali—Cold Process Soaps—Saponification under Increased or Diminished Pressure—Soft Soap—Marine Soap—Hydrated Soaps, Smooth and Marbled—Pasting or Saponification—Graining Out—Boiling on Strength—Fitting—Curd Soaps—Curd Mottled—Blue and Grey Mottled Soaps—Milling Base—Yellow Household Soaps—Resting of Pans and Settling of Soap—Utilisation of Nigres—Transparent Soaps—Saponifying Mineral Oil—Electrical Production of Soap.
Soaps are generally divided into two classes and designated "hard," and "soft," the former being the soda salts, and the latter potash salts, of the fatty acids contained in the material used.
According to their methods of manufacture, soaps may, however, be more conveniently classified, thus:—