b 



254 REPORT — 1901. 



the discovery and development of colouring matters of the rosaniline or 

 triphenylmethane group, such as Magenta, Aniline Blue, Hofmann 

 Violet, Methyl Violet, Acid Magenta, Acid Violets, Phosjahine, Victoria 

 Blues, Auraniiue, Malachite Green, and Acid Greens. Individual 

 members of other groups had already been discovered, but the latter had 

 not yet attained to the importance which they were destined later to 

 occupy. This is especially the case with the class of colouring matters 

 containing the double nitrogen radical known as ' azo ' colours. This 

 group of compounds has, during the fifteen years which we have to con- 

 sider, attained to such enormous dimensions and importance that this 

 interval may fairly be termed the ' azo period.' The number of individual 

 compounds belonging to this class, which have either been prepared or are 

 at present preparable, runs into many millions and far exceeds the 

 members of all other groups of colouring matters put together. In com- 

 mercial importance also they occupy a position at present far in advance 

 of any other group, the employment of some of them (e.y., the ' azo ' blacks) 

 amounting to many thousands of tons annually. A great stimulus to the 

 investigation of the azo compounds was given by the discovery by 

 Bottiger in 1884: of the first colour possessing a direct affinity for cotton 

 (Congo Red), which was followed within a few years by a rapidly 

 increasing series of colours of all shades having similar dyeing properties. 

 The azo colours knowii prior to this time were either basic colours 

 (Aniline Yellow, Chrysoidine, Bismarck Brown, &c.) or acid wool colours 

 (Xylidine Scarlet, Crocoine Scarlet, etc.). The great simplification of 

 cotton dyeing brought about by the introduction of the new group of azo 

 colours — ' Benzo ' or 'Diamine' coloui's as they were called — led to a 

 rapid increase of their number, and compounds containing two, three, 

 four, or more double-nitrogen groups, linking together the residues of 

 various paradiamines (benzidine, tolidine, dianisidine, azoxytoluidine, 

 paraphenylenediamine, naphthylenediamine, Arc.) to various naphthol-, 

 amidonajihtliol-, and naphthylamine sulphonic acids made their appear- 

 ance in quick succession. Simultaneously therewith proceeded the dis- 

 covery and investigation of the various isomeric derivatives of naphthalene 

 required as raw products for the pi'eparation of these colours, an investiga- 

 tion which was largely aided by the classical research on the isomerism 

 of naphthalene compounds carried out in this country by Armstrong and 

 Wynne. 



Another mctliod of applying azo colours to cotton, by which much faster 

 shades ore obtained, was introduced by Messrs. Read Plolliday, of 

 Huddersfield, in 1880, and consisted in producing unsulphonated azo 

 compounds on the fibre by direct combination. Owing to the technical 

 difficulties which were at first encountered in applying this process it has 

 only reached its full development during the last few years and at other 

 hands than those of its discoverers. The most important colour produced 

 by this method is Paranitraniline Red, for which over two hundred tons 

 of chemically pure paranitraniline are manufactured annually. 



The search for direct cotton colours led the author in 1887 to the 

 discovery of Primuline. This compound, having a direct affinity for 

 cotton and containing at the same time a diazotisable amido group, could 

 be used for the synthesis of various azo colours on the fibre which were 

 remarkable for great fastness to washing. It has had a large employment 

 for the production of fast reds, and the n'&w pi"inciple of dyeing which it 

 intr'o'duc'ed has been cbusiderably extended in other so-called ' diaz'o ' 



J 



