6. The mutual action of these stuffs, and neutral compounds not saline.
7. The mutual action of these stuffs, and of one or more definite compounds.
8. Of dyed stuffs considered in reference to the fastness of their colour, under the influence of heat, light, water, oxygen, air, boilings with soap, and reagents.
9. Of dyeing, considered in its connections with chemistry.
10. Of dyeing, considered in its relations with caloric, mechanics, hydraulics, and optics.
1. The preparation of stuffs.
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.
2. Mutual action of stuffs, and simple bodies.
Stuffs chemically considered being composed of three or four elements, already in a state of reciprocal saturation, have but a feeble attraction for simple substances. We know in fact, that the latter combine only with each other, or with binary compounds, and that in the greater number of cases where they exert an action upon more complete compounds, it is by disturbing the arrangement of their elements, and not by a resulting affinity with the whole together.
3, 4. Although stuffs may in a general point of view be considered as neutral in relation to colouring reagents, yet experience shows that they are more disposed to combine with acid than with alkaline compounds; and that consequently their nature seems to be more alkaline than acid. By steeping dry wool or other stuff in a clean state in an alkaline or acid solution of known strength, and by testing the liquor after the stuff is taken out, we shall ascertain whether there be any real affinity between them, by the solution being rendered more dilute in consequence of the abstraction of alkaline or acid particles from it. Wool and silk thus immersed, abstract a portion of both sulphuric and muriatic acids; but cotton and flax imbibe the water, with the rejection of a portion of the acid. The acid may be again taken from the stuffs by washing them with a sufficient quantity of water.