DYEING SUBSTANCES. 305 



two kinds, substantive and adjective, and thus 

 explains the reason for adopting these terms. 

 *' Colouring matter seems to fall naturally under two 

 general classes; the first including those matters 

 which, when put into a state of solution, may be 

 permanently fixed, and made fully to exhibit their 

 colours in or upon the dyed substance, without the 

 interposition of any earthy or metallic basis; and the 

 second comprehending all those matters which are 

 incapable of being fixed, and made to display their 

 proper colours without the mediation of some such 

 basis. The colours of the first class I shall denomi- 

 nate substantive, using the term in the same sense in 

 which it was employed by Bacon, Lord Verulam, as 

 denoting a thing solid by, or depending only upon, 

 itself; and colours of the second class I shall call 

 adjective, as implying that their lustre and perma- 

 nency are acquired by adjection upon a suitable 

 basis *." This beautiful and simple distinction, which 

 is almost generally adopted among the English 

 writers, has not been recognised by the French. 



Adjective colours acquire permanency, and some- 

 times brilliancy also, by the interposition of substances 

 which, having a considerable attraction for the colour- 

 ing matter and the fibres of the fabric about to be 

 dyed, combine with, and serve as a bond of union 

 between them. These intermedia being usually some 

 earthy or metallic substance, employed in a state of 

 solution or combination with the acids, were, from 

 that circumstance, denominated by the French, mor- 

 dants (biters or corroders), and the term has been 

 adopted also in English. Berthollet distinguishes 

 under the title of alteratives those ingredients which 

 are employed merely with a view of changing the 



* Experimental Researches concerning the Philosophy of 

 Permanent Colours, p. 78. 



2 D 3 



