GB690207A - Improvements in the manufacture of soap - Google Patents

Abstract

Hydrosulphite-bleached soap is freed of its objectionable odour and also whitened by adding to the soap, before or after the hydrosulphite treatment, a small proportion of a water-soluble zinc compound. The zinc compound is most effective if added to the soap in the presence of water and is preferably added at a stage up to and including the finishing stage; it may be added with the perfume or other ingredients. The zinc compounds specified comprise zinc sulphate, chloride, acetate, borate, bromide, bromate, carbonate, chromate, nitrate and thiocyanate. The zinc compound is preferably added in an amount sufficient to provide 0.25 to 0.75 gram equivalents of zinc ion per gram equivalent of hydrosulphite ion used in the bleaching treatment, which latter is normally used in an amount of between 0.1 and 0.2 per cent by weight of the mass to be bleached. The soaps may be the usual ammonium, sodium or potassium soaps of C12 to C24 fatty acids and abietic acid. In an example sodium hydrosulphite was added during the washing of the soap with brine, the soap mass then acquiring a greyish colour and an objectionable odour. After withdrawal of the lyes, the mass was boiled prior to finishing. The specified quantity of zinc sulphate crystals was then added and the soap boil lost its greyish colour, became white, and also lost its odour. After addition of a small quantity of caustic soda to restore the original alkalinity, the soap was finished in the usual manner.