482 Dr. BoUey on the Theory of Dyeing. 



resulting from a more extended knowledge of positive matters of 

 fact. 



Persoz* has made an excellent summary of at least the more 

 ancient learning on this subject ; and it will be quite sufficient for 

 our purpose to take from this source the most essential outlines 

 of some of these various doctrines. 



At first the view found its supporters, that in the group of 

 phsenomena under consideration we had to deal with mechanical 

 adhesion. Hellot was of opinion that the colour of wool de- 

 pended on the intimately divided particles of colouring matter 

 introducing themselves into the pores of the fibres ; and that the 

 distinction between a true and a false dye consisted in this, that 

 in the first case the fibre was covered over with " an astrin- 

 gent substance/' so that the ordinary agents — light, water, 

 &c. — could not get at the colouring matter, whereas in the case 

 of a false dye no such protection existed. In another place he 

 says that the pores must be cleansed, opened, filled, and again 

 closed, so that they may retain the particles of colouring matter 

 as the setting does a diamond. He was aware of the method of 

 forming lakes by the application of certain earthy or metallic 

 salts, and was of opinion that if we could procure the particles 

 of these lakes as small as we pleased, and could open the pores 

 of the fibres sufficiently wide to admit them, the defect of false 

 dye would be removed. 



This too accommodating view, which at the first glance may be 

 seen to be in the highest degree confused and self-contradictory, 

 was soon followed by the more elaborate theory of Le Pileur 

 d^Apligny. He accounted for the different capabilities of wool, 

 silk, cotton, and flax to take up colouring matter, in a manner 

 that clearly showed his extensive acquaintance with the art of 

 dyeing. The observation (true, indeed, only under certain cir- 

 cumstances) that, in a decoction of cochineal of given strength, 

 wool takes a deeper tint than silk, and the latter a deeper tint 

 than cotton or flax, he accounts for on the ground that the pores 

 of the silk fibres, being far smaller than those of the wool, admit 

 fewer particles of lake (formed by the union of the colouring 

 matter of the cochineal with chloride of tin), while the pores of 

 cotton and flax, for a similar reason, admit still fewer. 



Persoz was perhaps the first who maintained, in a thoroughly 

 scientific manner, and without resorting to arbitrai'y hypotheses 

 concerning the constitution of the fibres, the doctrine that the 

 fixing of colour depends on surface attraction. The fundamental 

 idea of his views may be expressed as follows. 



* Theoretical and Practical Treatise on the Printing of Tissues, vol. ii. 

 p. 126. 



