INTRODUCTION.

7

retained all its former whiteness. He appears, however, to have had no con-ception of the other and more important cause of the permanency of adjectivecolours—viz., that which arises from the interposition of a suitable basispossessing a particular attra&ion both for the colouring matter and for thedyed substance, and thereby atting as a bond of union between them ; nor didhis successor, Hellot, ever approach nearer to the truth on this subjedt. He(Hellot) fancied that he could discover in every dyeing process some means bywhich sulphate of potash might be formed; and this neutral salt not beingreadily soluble in cold water, nor affedted by air or light, he conceived the art ofdyeing to consist in first dilating the pores of the substance to be dyed, so asto procure a copious admission of colouring matter, divided by a suitablepreparation into atoms, and then wedging or fastening these atoms within thepores of the dyed substance by the small particles or crystals of this difficultlysoluble neutral salt. Upon this mechanical hypothesis he supposed that alumbecame useful in dyeing, not by the pure clay or alumina which it contains,and which alone contributes to fix any colouring matter, but only by furnishingsulphuric or vitriolic acid to assist in forming the sulphate of potash, whichwas to perform this important fundtion of wedging or fastening the colouringatoms ; though, if he had brought this visionary hypothesis to the test ofexperiment, as might have been easily done, he would have found, not onlythat no sulphate of potash existed in many cases where he supposed it to pro-duce such important effedts, but also that, even if intentionally formed andemployed for this purpose, it possessed no power whatever of fixing anycolouring matter yet known. But, though nothing could be more groundlessthan the theory, the learned in all countries appear to have been satisfied withit for a considerable length of time, it being always less troublesome to believethan to make experiments.

“According to Mr. Henry of Manchester, M. Keir, the ingenious translatorof Macquer’s ‘ “ Chymical Didtionary,” appears to have been the first who sus-pedted that (in dyeing) the earth of alum was precipitated, and in this formattached to the material prepared or dyed.’ Some time after this, Mr. Henrypublished an interesting paper in the third volume of the “ Memoirs of theManchester Society,” “ On the Nature of Wool, Silk, and Cotton as Objedtsof the Art of Dyeing, on the Various Preparations and Mordants requisite forthese Different Substances, and on the Nature and Properties of ColouringMatter, &c.,” a paper replete with useful information and ingenious ideas.”—Bancroft, u On Permanent Colours.”

Trustworthy authorities state that no less than two hundred dye-works existedat Florence about the end of the 14th century. The application of coloursderived from lichens, and more especially the species known as “ Rocella,”was so extensively and successfully carried out that, in order to prevent theprocess being divulged, a guild was formed which obtained the name of“ Rocellarii.”

The discovery of America opens a new era in the progress of dyeing. Manynew dye-stuffs were then brought from that country into Europe, among whichlogwood, cochineal, annatto, and brazil-wood may be mentioned.

The use of tin salts as mordants was discovered about the middle of the17th century by the Dutch chemist, Cornelius Drebbel, who found that theyyielded a magnificent colour with cochineal. Drebbel’s son-in-law, who