BLEACHING OF LINEN The bleaching of linen is a much more complicated and tedious process than the bleaching of cotton. This is due in part to the fact that in linen the impurities amount to 2o% or more of the weight of the fibre, whereas in cotton they do not usually exceed 5%. Furthermore, these impurities, which include colouring matter, intracellular substances, and a peculiar wax known as "flax wax," are more difficult to attack than those which are present in cotton, and the difficulty is still further enhanced in the case of piece goods, owing to their dense or impervious character.
The methods used for bleaching of linen resemble those used in cotton bleaching, but require to be frequently repeated, while an additional operation, which is a relic of the old-fashioned process, viz., that of "grassing" or "crofting," is still essential for the production of the finest whites. Considerably more care has to be exercised in linen bleaching than is the case with cotton, and the process consequently necessitates a greater amount of manual labour. The practical result of this is that, whereas cotton pieces can be bleached and finished in less than a week, linen pieces require at least six weeks. Many attempts have naturally been made to shorten and cheapen the process, but without suc cess. The use of stronger reagents and more drastic treatment, which would at first suggest itself, incurs the risk of injury to the fibre, not so much in respect to actual tendering as to the destruction of its characteristic gloss; while if too drastic a treatment is employed at the beginning the colouring matter is liable to become set in the fibre, and it is then almost impossible to remove it. Among the many modern improvements which have been suggested, mention may be made of the use of hypochlorite of soda in place of bleaching powder ; the use of oil in the first treatment in alkali (Cross & Parkes), while de Keukelaere sug gests the use of sodium sulphide for this purpose. With the object of dispensing with the operation of grassing, which, besides necessitating much manual labour, is subject to the influences of the atmospheric conditions, Siemens & Halske, of Berlin, have suggested exposure of the goods in a chamber to the action of electrolytically prepared ozone. Jardin seeks to achieve the same object by steeping the linen in dilute nitric acid.
Since the qualities of linen which are submitted to the bleacher vary considerably, the mode of treatment has to be varied accordingly. Linen is bleached in the yarn and in the piece. Special features of linen bleaching, apart from the repetition of processes, are :—Rubbing between boards with soft soap after kier boiling (scalding) ; exposure of the goods to air during the treatment with bleaching liquor; marking with thread dyed with Turkey red instead of stamping.