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Identification of Dyestuffs

The Identification of Coloring Matters

on Fibres



By Arthur G. Green, M. Sc. F. S. C., F. C. S., assisted by H. Yeoman and J. R. Jones.

The ready identification, by an examination of a textile material, of the dyestuff or dyestuffs with which it has been dyed or printed, is a problem which presents at the present day great difficulties. Twenty or thirty years ago the number of dyestuff's was so small that their identification by an expert was simple enough matter, for the shade alone would usually give a sufficient indication. With the enormous increase both in individual coloring matters and in new groups of coloring matters their detection has been rendered both more necessary and greatly more difficult, since it is now possible to produce any shade in a large variety of ways. The fact that the fastness of such a shade for the purpose in view will depend upon a suitable choice of the dyestuff or dyestuffs renders it particularly important for the dyer in matching a sample submitted, to be able not only to match the shade, but, if necessary, to select the same or similar dyestuff's. It is also a desideratum for the merchant to be able to ascertain whether the color of the material dyed for him is always of constant composition, whether the shade dyed by one firm is or is not a chemical match for that dyed by another, and other similar

problems. Although an extensive series of tables has been published by Lange, Knecht and Loewenthal, Rawson, Lunge, Gnehm. Heermann, and others, giving the reactions of the individual dyestuffs on the fibre towards acids, alkalies, and stannous chloride, there yet exists a want for a systematic scheme of analysis, without which such tables are of little use. A scheme of this kind should be capable of referring the dyestuff to its chemical group, after which the particular brand may, if necessary, be ascertained by comparing the individual reactions with the published tables. In very many cases, however, sufficient information for the practical dyer would be gained by knowing the group to which the dyestuff belongs, the precise identification of the particular individual not being always necessary.

Although for the present moment the identification of mixtures will be left out of consideration, which is often a most difficult and intricate problem, and this limited to the consideration of single dyestuffs or mixtures of dyestuffs of the same class, yet it appears to be an absolute essential for any scheme of analysis that it should also be capable of extension to all the mixtures which may be encountered in practice. For this reason, only such chemical properties can be employed as group reactions as depend not upon individual peculiarities, but upon general differences in chemical structure, so that dyestuffs of the same family shall be grouped together irrespective of shade. Another reason why such a principle can prove satisfactory is that the scheme must be capable of referring to their respective chemical and dyeing groups the many new coloring matters which are constantly appearing and whose individual reactions are still


Dyestuff's may be classified in two ways, either according to their dyeing properties, viz., whether basic, acid, salt, mordant, vat, etc., or according to their chemical structure, that is, according to the chromophor they contain; viz., whether they belong to the nitro, nitroso, azo, triphenylmethane, azine, oxazine, thiazine, acridine, pyrone, anthracene, or other groups. In the scheme of

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