I. DYEING is the art of extracting the colouring princi ple, under its various modifications, from the different substances with which it exists in a state of combination; transferring it to stuffs, heightening its brilliancy, and rendering it as far as possible permanent. It is there fore of the last importance to the dyer to ascertain the nature of the colouring principle, and to determine its relations with the stuffs to which it is to be applied ; as well as the qualities of the chemical agents which may be necessary to give it fixity, and improve its beauty.
2. Before chemistry had attained its present advanced state, the most absurd theories were employed to explain the principles of dyeing. It was long maintained, that the colouring matter was merely deposited in the pores and cavities of the stuffs; and that the various processes to which the latter were exposed, were merely mecha nical operations to open and dilate the interstices of the cloth, or other matter to be dyed, for the reception of the colour. This theory, which was suggested by Ilellot, and adopted by NIacquer, was universally admitted to afford a true explanation of the principles of dyeing, un til Bergman and Berthollet turned their attention to the subject, and demonstrated, by a series of accurate ex periments, that the processes of the art are in reality par ticular exemplifications of the laws of affinity; and that the colouring matter is attached to the stuff by the influ ence of chemical action alone.
3. In some instances, this action is the immediate re sult of a mutual affinity subsisting between the colour ing principle and the stuff; while in others it is so feeble, that recourse must be had to an intermediate substance, having a decided attraction for each, and thus serving as a bond of union between them. These intermediate substances, so very important in the practice of dyeing, received the name of mordants from the earlier French writers, on account of the mechanical action which they were supposed to exert upon the stuff; and they still re tain the same appellation, though the opinions which gave rise to it have been completely disproved.
4. In discussing the subject of dyeing, we propose to begin with a historical sketch of the origin and progress of the art. In the next place we shall take a view of the various kinds of colouring matters employed by the dyer, and describe the processes to which they must be sub jected before they are presented to the stuff. We shall then examine the properties of the different stuffs to which dyes are usually applied; and, after considering the action and preparation of mordants, give an account of the of preparing, by means of them, the stuffs fit; the reception of colouring matters. And, lastly, we shall conclude with a detailed account of the practical methods of dyeing.