The fluid cocoa-nut oil is stirred in a suitable vessel with half its weight of 71.4 deg. Tw. (38 deg. B.) caustic soda lye at the same temperature, and, when thoroughly mixed, the pan is covered and allowed to rest. It is imperative that the oils and fats and caustic lye should be intimately incorporated or emulsified. The agitating may be done mechanically, there being several machines specially constructed for the purpose. In one of the latest designs the caustic lye is delivered through a pipe which rotates with the stirring gear, and the whole is driven by means of a motor. The agitation being complete, chemical action takes place with the generation of heat, and finally results in the saponification of the fats. At first the contents of the pan are thin, but in a few hours they become a solid mass. As the process advances the edges of the soap become more transparent, and when the transparency has extended to the whole mass, the soap is ready, after perfuming, to be framed and crutched. The admixture of a little caustic potash with the caustic soda greatly improves the appearance of the resultant product, which is smoother and milder. The glycerine liberated during the saponification is retained in the soap. Although it is possible, with care, to produce neutral soaps of good appearance and firm touch by this method, cold-process soaps are very liable to contain both free alkali and unsaponified fat, and have now fallen considerably into disrepute. _Saponification under Increased or Diminished Pressure._--Soaps made by boiling fats and oils, under pressure and _in vacuo_, with the exact quantity of caustic soda necessary for complete combination, belong also to this class. Amongst the many attempts which have at various times been made to shorten the process of soap-making may be mentioned Haywood's Patent No. 759, 1901, and Jourdan's French Patent No. 339,154, 1903. In the former, saponification is carried out in a steam-jacketed vacuum chamber provided with an elaborate arrangement of stirrers; in the other process fat is allowed to fall in a thin stream into the amount of lye required for saponification, previously placed in the saponification vessel, which is provided with stirring gear. When the quantities have been added, steam is admitted and saponification proceeds. (C) _Treatment of Fat with Indefinite Amount of Alkali and no Separation of Waste Lye._--_Soft soap_ is representative of this class. The vegetable fluid oils (linseed, olive, cotton-seed, maize) are for the most part used in making this soap, though occasionally bone fats and tallow are employed. Rosin is sometimes added, the proportion ranging, according to the grade of soap required, from 5 to 15 per cent. of the fatty matter.