27. The theoretical opinions of Hellot were adopted by the celebrated Macquer, whom the French govern ment had appointed his successor for superintending the practice of dyeing, and cultivating such branches of science as had a tendency to promote the improvement 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 llellot's views, but expresses a high admiration of the ingenuity of his theory. Ce sa vant chymiste est le premier qui aft Porte le flambeau de la physique dans Part obscure (le la teinture, et qui aft rassemble et mis cn ordre, suivant les principes d'une theorie ingevieuse, les phenonzenes et les operations bizarres de cet art : it a mis les chynzistes a port(' de voir, (lair dans ce chaos tenebreux. Macquer seems to have held the same sentiments concerning this very absurd hypo thesis, so lately as the year 1766; for, in the eulogium pronounced by him on Ilellot, and inserted in the Me moirs of the Academy for that year, he expresses him self thus strongly, a l'aide de cette theorie si lumineuse, on 11C sera plus trompe dans la Jiratique de cet art, que Tors qu'on vendra Bien 1'etre. Some allowance, indeed, must be made for that studied determination to praise, which characterizes too many of these eulogies.
28. The labours of Alacquer, however, contributed greatly to improve and extend the practical operations of dyeing, particularly of dyeing silk, to which he devoted much of his attention. Ile was the first who ascertained the real nature of Prussian blue, and he endeavoured to make an application of his discovery to the purposes of dyeing. He intended to have published a complete dis sertation 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 design, and he died in 1784 without having accomplished his inten tions. Before his death, Ile abandoned the hypothetical bpinions of Hellot, and embraced the more rational theory of the processes of dyeing, which, before that event, had been suggested by heir, and demonstrated by Bergman and Berthollet.
29. Mr heir, 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; au opinion which, as we have already hinted, was latterly adopted by Macquer himself, and enforced at the article Teitzture of his Dictionnaire de Chymie. 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 hifluence of chemical affinity. He observed that, when wool and side were immersed in a solution of indigo in sulphuric acid, the former attracted the colouring particles more forcibly than the latter ; and that both leaving 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 similar explanation of the phe nomena of dyeing seems to have been proposed, at an earlier period, by Dr Bancroft : In a communication which he made to the Royal Society in 1773, he distinct ly ascribed the pi oduction of ink end 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 ooth Kcir and Bergman.
30. We are indebted to Bergman, however, and more particularly to Bertbollet, for the complete demonstra tion of the truth of these opinions. The latter of these celebrated chemists succeeded Macquer in the place of trust which he held in France under the commercial de partment of administration, and by conjoining extensive observation with enlightened theory, has done more than any of his predecessors to promote the improvement of dyeing, and to raise it from au obscure empirical art, to the rank of a branch of chemical science. Since his ap pointment to the superintendence of the arts connected with chemistry, almost all the investigations which he has inserted in the Memoirs of the Academy, in the Jour nal de Physique, and tile Annalcs de Chymie, relate more or less to the elucidation of toe arts. In 1791, he pub lished his Elements of the Art of Dyeing, in 2 vols. 8vo, a second edition of which, with considerable improve ments, appeared in 1803. This treatise may be regard ed as a standard work on dyeing, since it contains not only a detailed account of the practical operations of the art, but a theoretical view of the principles upon which they are founded. The subject of dyeing has also attract ed the attention of Chaptal, who held, for a considera ble time, the office of minister of the interior, under the French government. This excellent chemist, in his work entitled, Chymie appliquee aux Arts, has introduced many original observations on dyeing, and described the leading processes of the art with much philosophical elegance. He investigated, with great care, the nature of Adrianople red, and published the result of his ex periments and observations on that celebrated colour, in the 26th vol. of the Annales de Chymie. Several other chemists in France have written dissertations on dyeing, which deserve to be noticed in this place. Among these we may mention a small but useful work by M. \Titans of Rouen, entitled Manuel de reinturier sur jil ct sur colon file; a French translation of Scheffer, which first appeared in 1748, and was republished with notes by Bergman ; anodic r of P.7erner from the German; and an original work by Dambourney. The treatise of ScheiTer was chiefly intended for the benefit of Swedish dyers ; that of Pxrner contains an account of many experiments made by the author to ascertain the qualities of different dyes, but these seem to have been guided by no scientific views; and the work of Dambourney is still more defec tive in that respect.