The operations to which stuffs are subjected before dyeing, are
intended--1. to separate from them any foreign matters; 2. to render
them more apt to unite with the colouring tinctures which the dyer
proposes to fix upon them, in order to give them a more agreeable, or
more brilliant aspect, or to lessen their tendency to assume a soiled
appearance by use, which white surfaces so readily do. The foreign
matters are either naturally inherent in the stuffs, or added to them in
the spinning, weaving, or other manipulation of manufacture. The
ligneous fibres must be freed from the coloured azotized varnish on
their surface, from a yellow colouring matter in their substance, from
some lime and iron, from chlorophylle or leaf-green, and from pectic
acid; all natural combinations. Some of these principles require to be
oxygenized, before alkaline lyes can cleanse them, as I have stated in
the article BLEACHING, which may be consulted in reference to this
subject. See also SILK and WOOL. A weak bath of soda has the property of
preparing wool for taking on a uniform dye, but it must be well rinsed
and aired before being put into the dye-vat.