S62 MORDANT 



tin is retained by it, in virtue of an influence (a condition of capillarity) between the 

 fibre and the salt. There will now be formed a beautiful wine-coloured compound, 

 between the logwood and the tin upon the goods, when they are placed in the logwood- 

 bath, which washing with water will not remove, the compound being insoluble. The 

 tin in this case constitutes the mordant. It is not always essential that the mordant be 

 put upon the fibre previous to being put into the coloured solution ; they may be mixed 

 together, and the goods placed in the mixture, when much of the coloured compound 

 will combine with or adhere to the fibre ; but, in general, this mode of applying the 

 mordant is not so effective. If, as is usually said, the mordant enters into a real 

 chemical union with the stuff to be dyed, the application of the mordant should 

 obviously be made in such circumstances as are known to be most favourable to the 

 combination taking place ; and this is the principle of every day's practice in the dye- 

 house. 



Mordants are in general found among the metallic bases or oxides ; whence they 

 might be supposed to be very numerous, like the metals ; but as they must unite the 

 twofold condition of possessing a strong affinity for both the colouring-matter and the 

 organic fibre, and as the insoluble bases are almost the only ones fit to form insoluble 

 combinations, we may thus perceive that their number may be very limited. It is well 

 known, that although lime and magnesia, for example, have a considerable affinity for 

 colouring particles, and form insoluble compounds with them, yet they cannot be em- 

 ployed as mordants, because they possess no affinity for the textile fibres. 



It will be observed from the above remarks, that the mordant serves a higher pur- 

 pose than the mere bond of union between the colour 'and fibre ; that it, in fact, consti- 

 tutes a principal element in the colour. The colour forming the dye, in the case 

 with the logwood'and tin, is not that of haematoxylin, the colouring-matter of logwood ; 

 but of the compound formed between it and tin, and thus logwood, by different 

 mordant bases, gives a variety of colours, from a grey to a black, and from a light 

 lavender to a deep purple, &c. When an organic colouring-matter is imparted to any 

 fibre without the intervention of a mordant, it can only produce one tint, which cannot 

 be varied except in being light and dark. 



Experience has proved, that of all the bases, those which succeed best as mordants 

 are alumina, tin, and oxide of iron. 



nine-black dye. The mordant. much employed in some parts of Germany for this 

 dye, with logwood, galls, sumach, &c., is Iron-alum, so called on account of its having 

 the crystalline form of alum, though it contains no alumina. It is prepared by dis- 

 solving 78 pounds of red oxide of iron in 117 pounds of sulphuric acid, diluting this 

 compound with water, adding to the mixture 87 pounds of sulphate of potash, evapo- 

 rating the solution to the crystallising point. This potassa-sulphate of iron has a fine 

 amethyst colour when recently prepared ; and though it gets coated in the air with a 

 yellowish crust, it is none the worse on this account. As a mordant, a solution of this 

 salt, in from 6 to 60 parts of water, serves to communicate and fix a great variety of 

 uniform ground colours, from light grey to brown, blue, or jet black, with quercitron, 

 galls, logwood, sumach, &c., separate or combined. The above solution may be use- 

 fully modified by addtng to every 10 pounds of the iron-alum, dissolved in 8 gallons 

 (80 pounds) of warm water, 10 pounds of acetate (sugar) of lead, and leaving the 

 mixture, after careful stirring, to settle. Sulphate of lead falls, and the oxide of iron 

 remains combined with the acetic acid and the potash. After passing through the 

 above mordant, the cotton goods should be quickly dried. 



Colours of the above class are, however, mostly insoluble in water, and have to be dis- 

 solved or extracted by an alkaline solvent : and in this state have no affinity either for 

 the fibre or a mordant. Safflower is an instance of this kind ; the red colouring-matter 

 of this vegetable is extracted by a weak alkaline lye, into which the goods to be dyed 

 are afterwards put ; and the alkali being neutralised by an acid, the colouring-matter 

 is thus rendered insoluble in the liquor, in a state of minute division, and is gradually 

 absorbed by the fibre, which becomes dyed of a red colour in depth according to the 

 quantity of colour absorbed. 



Indigo is another dye of this sort requiring an alkaline solvent, and not dyed with 

 mordants. (See DYKING.) 



The following remarks will illustrate some of the necessary requirements of a mor- 

 dant, which should be attended to by the dyer, in their application. 



In order that a combination may result between two bodies, they must not only be 

 in contact, but they must bo reduced to their ultimate molecules. The mordants tliat 

 are to bo united with stuffs are, as we have seen, insoluble of themselves, for which 

 reason their particles must be divided by solution in an appropriate vehicle. Now 

 this solvent or menstruum will exert in its own favour an affinity for the mordant, 

 which will prove, to that extent, an obstacle to its attraction for the stuff. Hence wo 

 must select such solvents as have a weaker affinity for tlio mordants than the mordants 



