222 A Tribute to the Memory of 
demonstrates the futility of those hypotheses, 
that explained the facts by supposed peculia-+ 
rities of mechanical structure in the materials 
to be dyed; and suggests the probability, 
that the unequal powers of absorbing ‘and fix- 
ing colouring matter, manifested ‘by ‘ wool, 
silk, linen, and cotton, depend on the different 
attractions, inherent in those substances as 
chemical compounds, for the various colour- 
ing ingredients. All the preparatory opera- 
tions, though differing for each material, have, 
he apprehends, one common object, viz. the 
removal of some extraneous matter, which, 
being already united with the substance to be 
dyed, prevents it from exertitig 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. ‘I'o explain the prepara- 
tion of cotton for the Turkey-red dye, he en- 
deavours to prove that cotton requires, for 
this purpose, to be approximated, in composi- 
tion, 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 sub- 
