the late Mr. Henry. 11 



Substances ; and on the Nature and Properties of Colouring 

 Matter." 



After having given a general viev? of the history of the art of 

 Dyeing, Mr. Henry, in this elaborate essay, examines the theo- 

 ries that had been framed to account for the various facility and 

 permanency with which different substances attract colouring 

 matter. He demonstrates the futility of those hypotheses, that 

 explained the facts by supposed peculiarities of mechanical struc- 

 ture in the materials to be dyed ; and suggests the probability, 

 that the unequal powers of absorbing and fixing colouring mat- 

 ter, manifested by wool, silk, linen, and cotton, depend on the 

 different attractions inherent in those substances as chemical 

 compounds, for the various colouring ingredients. All the pre- 

 paratory operations, though differing for each material, have, he 

 apprehends, one common object, viz., the removal of some extra- 

 neous matter, which, being already united with the substance to 

 be dyed, prevents it from exerting its attraction for colouring- 

 matter. The ultimate object of these preliminary steps, he states 

 to be the obtaining a white ground, that may enable the colours 

 to display the full brilliancy of their several tints. To explain 

 the preparation of cotton for the Turkey-red dye, he endeavours 

 to prove that cotton requires, for this purpose, to be approxi- 

 mated, in composition, to the nature of an animal substance. 

 He next offers a classification of the Materia Tinctoria, and 

 some general speculations on the nature of colouring matter. 



In the second part of the Essay, Mr. Henry investigates the 

 mode of action of those substances which, though themselves des- 

 titute of colour, are important agents in the processes of dyeing. 

 Substances of this kind had received, from the French dyers, 

 the name of Mordants, because it was imagined that they cor- 

 roded and removed something, which mechanically opposed the 

 entrance of the colouring matter into the pores of the material 

 to be dyed. To destroy this erroneous association, Mr. Henry 

 proposes that the word basis should be substituted, as a general 

 term, to denote every substance, which, having an affinity both 

 for tlie colouring matter, and for the material to be dyed, is ca- 

 pable of serving as an inlcrmcdium between the two ; and tlial 



