Manufacturer and builder 9, 1869
Straw hats which have turned yellow may be bleached by the use of a soap prepared by taking any good soda soap and precipitating it from its solution by means of common salt, and adding to it one fourth the weight of sulphite of soda, previously rubbed into a mass with water, then drying the product. About equal parts, by weight, of water are to be poured upon this, and for every two pounds of soap, half an ounce of spirits of sal-ammoniac (liquid ammonia) is to be added; and after the whole has assumed a gelatinous consistency, one part of the mass is to be dissolved in eight parts of warm crater; smaller proportions of the foregoing will, of course, answer for a few articles. The objects to be bleached are to be washed by means of a brush in this solution, and transferred, while still moist, into water acidulated with hydrochloric acid, (twenty-five parts water to one and a half of acid,) and allowed to remain a few hours in this liquid. They are then to be washed with fresh cold water, and dried. Experiment has proved the results of this method of bleaching to be exceedingly satisfactory. We must, however, add to the recipe just given a caution not to use sulphate of soda for sulphite of soda. Sulphite of soda is composed of soda and sulphurous acid, which latter is the same substance that is produced when sulphur is burned in the air, and the common method of bleaching straw goods is to place them in a box and subject them to the flames of burning sulphur. When hydro-chloric acid is mixed with a solution of sulphite of soda, sulphurous acid is set free, and in this case it is liberated in the very fibres of the material. Such being the rationale of the process, it would obviously be a grave mistake to use sulphate of soda, as was recently recommended by one of our chemical cotemporaries.