The Soft Soap Manufacturers' Convention of Holland stipulate that the materials used in soft-soap making must not contain more than 5 per cent. rosin; it is also interesting to note that a patent has been granted (Eng. Pat. 17,278, 1900) for the manufacture of soft soap from material containing 50 per cent. rosin. Fish or marine animal oils--whale, seal, etc., once largely used as raw material for soft soap, have been superseded by vegetable oils. The materials must be varied according to the season; during hot weather, more body with a less tendency to separate is given by the introduction of oils and fats richer in stearine; these materials also induce "figging". The most important material, however, is the caustic potash lye which should average 40 deg. Tw. (24 deg. B.), _i.e._, if a weak solution is used to commence saponification, a stronger lye must be afterwards employed to avoid excess of water in the soap, and these average 40 deg. Tw. (24 deg. B.). The potash lye must contain carbonates, which help to give transparency to the resultant soap. If the lye is somewhat deficient in carbonates, they may be added in the form of a solution of refined pearl ash (potassium carbonate). Caustic soda lye is sometimes admixed, to the extent of one-fourth, with potash lye to keep the soap firmer during hot weather, but it requires great care, as a slight excess of soda gives soft soap a bad appearance and a tendency to separate. The process is commenced by running fatty matter and weak potash lyes into the pan or copper, and boiling together, whilst the introduction of oil and potash lye is continued. The saponification commences when an emulsion forms, and the lye is then run in more quickly to prevent the mass thickening. Having added sufficient "strength" for complete saponification, the boiling is continued until the soap becomes clear. The condition of the soap is judged by observing the behaviour of a small sample taken from the pan and dropped on glass or iron. If the soap is satisfactory it will set firm, have a short texture and slightly opaque edge, and be quite clear when held towards the light. If the cooled sample draws out in threads, there is an excess of water present. If an opaque edge appears and vanishes, the soap requires more lye. If the sample is turbid and somewhat white, the soap is too alkaline and needs more oil. The glycerine liberated during saponification is contained in the soap and no doubt plays a part in the production of transparency.