DYEING. 



llijtnrr. 





for the improvement of the art. Dufay, who was con- 

 sulted in drawing- up this act, appears to have been the 

 first who entertained just notions concerning the cause 

 of the adhesion of colouring matters to stuff's, particu- 

 larly in those cases in which an immediate affinity 

 subsists between them. Without this affinity, he sta- 

 ted, that the doth in a dyeing bath would never acquire 

 an intensity of colour greater than that of the liquor 

 in wliicli it was immersed, but share the colouring par- 

 ticles, by a mechanical division, equally between itself 

 and tlie bath ; a state of things which is by no means 

 conformable with experience, as the stuff sometimes 

 attracts all the colouring matter, and leaves the liquor 

 in which it was dissolved perfectly limpid. " This 

 seems to indicate," says Dufay, " that the ingredients 

 have less attraction for the water than for the particles 

 of the wool." He also observed the different degrees 

 of attraction which different substances, as wool and 

 cotton, exert upon colouring matters ; but he appears 

 to have had no just opinion concerning the operation of 

 mordants, or those substances which are sometimes ne- 

 cessary to connect the colour with the stuff. His suc- 

 Opinions of cessor Hellot published an excellent practical treatise on 

 Htllot. t ne methods of dyeing wool ; but all his theoretical 

 notions were led astray by a very absurd hypothesis, 

 which he seems to have adopted without the smallest 

 proof. In all the processes of dyeing, he conceived that 

 ii sulphate of potash was formed ; and that this salt, be- 

 ing sparingly soluble in cold water, and little affected 

 by air or light, first dilated the pores of the stuff to be 

 dyed, thus preparing it for the reception of the colour- 

 ing particles, and afterwards wedged tln-se particles so 

 closely together, that it became impossible for them to 

 make their escape. This hypothesis, which was neither 

 supported by fact, nor countenanced by sound reason- 

 ing, was admitted without proof, and regarded for a 

 considerable length of time as a true explanation of the 

 f:iu-e of the adhesion of the colouring matter to the 

 stuff. " I believe," says he, " it may be laid down as 

 .a general principle in the art of which I am now treat- 

 ing, that all the invisible mechanism of dyeing con .-Nt* 

 in dilating the pores of the body to be dyed, in depo- 

 siting in them particles of foreign matters, and retain- 

 ing them there by a kind of covering not liable to be ef- 

 fected by water, rain, or the rays of the sun ; in choos- 

 ing colouring particles of such a degree of fineness as 

 to be rendered sufficiently fixed in the pores of the stuff 

 opened by the heat of boiling water, and again con- 

 stricted by cold, and also coated by the kind of varnish 

 which the salts employed in its preparation had left 

 in those pores ; whence it follows, that the pores of the 

 fibres of the wool which has been wrought, or is to be 

 wrought into cloth, should be cleansed, enlarged, coat- 

 ed over, and then constricted, so that the colouring 

 (articles may be retained in them nearly in the same 

 manner as the diamond is retained in the collet of a 

 ring." Notwithstanding the erroneous views of Hellot, 

 the inferences which he deduced from them were not 

 destitute of practical utility, and many of the processes 

 which he recommended may be followed with the same 

 advantage as if they had been derived from more scien- 

 tific principles. Nor shall we wonder at this, if we re- 

 flect that the most correct theory seldom does more than 

 illustrate the nature of the practical operation which ex- 

 perience has previously discovered to be useful. 



27. The theoretical opinions of Hellot were adopted 

 by the celebrated Macquer, whom the French go- 

 vernment had appointed his successor for superintend- 

 ing the practice of dyeing, and cultivating such branches 



5 



Opinions of 



Macquer. 



of science as had a tendency to promote the improve- 

 ment of the art. In a memoir which is printed among 

 those of the Royal Academy of Sciences for 1749, he 

 not only admits the justness of Hellot's views ; but ex- 

 presses a high admiration of the ingenuity of his theo- 

 ry. Cc savant chymiste cst le premier qui ait ports le 

 flambeau de la physique dans Viirt obicure de la teinturc, 

 et qui ait ra&semble et mis en ordre, snivant les principcs 

 d'une theorie insenictixe, les phenomcnes ct les operations 

 bizarrcs de cet art : il a mis les chymistes a portc de 

 voir, clair dans ce chaos tcnebrenx. Macquer seems to 

 have held the same sentiments concerning this very ab- 

 surd hypothesis, so lately as the year 176t; for, in the 

 eulogium pronounced by him on Hellot, and inserted 

 in the Memoirs of the Academy for that year, he ex- 

 presses himself thus strongly, a Faide de cette theofic 

 si lumineuse, on He sera jitus Irompe dans la pratique de 

 cct art, que lors qu'on vcndra bien I'ftre. Some allow- 

 ance, indeed, must be made for that studied determi- 

 nation to praise, which characterizes too many of these 

 eulogies. 



28. The labours of Macquer, however, contributed 

 greatly to improve and extend the practical operations 

 of dyeing, particularly of dyeing silk, to which he devo- 

 ted much of his attention. He was the first who ascer- 

 tained the real nature of Prussian blue, and he endea- 

 voured to make an application of his discovery to the 

 purposes of dyeing. He intended to have published a 

 complete dissertation on the art, and in 1781 actually 

 drew up a prospectus of the work ; but a continued 

 state of bad health prevented him from prosecuting his 

 de-sign, and he died in 178-1 without having accomplish- 

 ed his intentions. Before his death, he abandoned the 

 hypothetical opinions of Hellot, and embraced the more 

 rational theory of the processes of dyeing which, before 

 that event, had been suggested by Keir, and demon- 

 strated by Bergman and Berthollet. 



29. Mr Keir, the ingenious translator of Macquer's 

 Chemical Dictionary, appears, according to Mr Henry, 

 to have been the first who proposed a true explanation 

 of the cause of the adhesion of the colouring matters to 

 stuffs. He suspected that when the aluminous mordant 

 was employed, the earth of alum was precipitated, and 

 in this state became attached to the cloth ; an opinion 

 which, as we have already hinted, was latterly adopted 

 by Macquer himself, and enforced at the article Teinturc 

 of his Dictionnaire de Chuniie. Berthollet, on the other 

 hand, ascribes the true theory of mordants to Bergman, 

 and affirms that this illustrious chemist first referred the 

 fixing of colours, by dyeing, to the influence of chemi- 

 cal affinity. He observed that, when wool and silk 

 were immersed in a solution of indigo in sulphuric acid, 

 the former attracted the colouring particles more for- 

 cibly than the latter ; and that both having a stronger 

 affinity for the indigo than the solvent, were by this 

 means able to deprive the bath of its colour, and attach 

 it to their own fibres. Upon the same principles he 

 explained why the colours communicated to wool were 

 more durable, as well as more intense, than those 

 communicated by the same process to silk. A simi- 

 lar explanation of the phenomena of dyeing seems to 

 have been proposed, at an earlier period, by Dr Ban- 

 croft : In a communication which he made to the Royal 

 Society in 1773, he distinctly ascribed the production 

 of ink and the black dye to an affinity between iron and 

 the colouring principle of galls, and so far, at least, 

 may be said to have anticipated both Keir and Berg- 

 man. 



30. We are indebted to Bergman, however, and more 



History. 



Benefits 

 which he 

 conferred 

 upon dye- 

 ing. 



True theory 

 of mor- 

 dants, by 

 whom first 

 suggested. 



Researches 

 of Berg- 

 man, 



