Dr. Bolley o?i the Theory of Dyeing. 491 



Lastly, the group of substances consisting of cellulose is con- 

 sideredj and the following observations made thereon : — 



"These substances, consisting altogether of cellulose (and 

 also that substance consisting entirely of vascidar or vesicular 

 membrane, which I am inclined to regard as corticular sub- 

 stance, that is, as the substance of which the peel of potatoes 

 and the cuticle of plants consists), as well as amylaceous matter, 

 sugar, and mucilage, gave altogether negative results. 



"We have therefore two groups of organic substances, of 

 which the one unites with colouring matter, while the other 

 does not appear to the microscope to do anything of the kind. 

 Both groups are of the greater importance, that all the members 

 of the proteine family belong to the one, those of the cellulose 

 to the other, and that almost all the members of these families 

 nearly exclusively compose the substance of plants." 



From this summary it is most evident that, on the two ques- 

 tions mentioned at the commencement of this essay, on which 

 the whole subject turns, there is no kind of unanimity amongst 

 the different authors whose names we have mentioned. 



We shall first take a general view of those observations which 

 relate to the deposition of the colouring matter on the fibre. 



While Persoz contends for external adhesion as the most 

 general, W. Crum (who, however, only concerns himself with 

 cotton fibre) considers the storing up of the colouring matter 

 in the interior of the cells as the true state of the case. Oschatz 

 and Verdeil declare for the uniform penetration of the dye 

 throughout the mass of all fibres, but allow some exceptions. 

 Finally, Maschke denies that cellulose possesses the property of 

 penetrability by dyes, while on the other hand he claims the pro- 

 perty of attraction for fibres of an animal nitrogenous constitution. 



With regard to wool and silk, we find a certain agreement of 

 opinion among the three last authors. Persoz's view, however, 

 which indeed is not grounded on any special observations, but 

 rather on considerations of general plausibility, is entirely opposed 

 to them all. One point is certain : if the question whether wool 

 and silk are penetrated by the dye is to be decided by the micro- 

 scope, it must be answered in the affirmative, provided only that 

 fibres are not examined which have been dyed by colouring mat- 

 ter in a mere state of suspension. In numerous and manifoldly 

 varied experiments, I have always found this to be the case. Wc 

 cannot, however, in all cases admit the truth of what Verdeil 

 says, viz. that silk is only in some exceptional cases coloured by a 

 crust adhering to the surface of the fibre. Against this asser- 

 tion, arguments may be urged derived from the nature of certain 

 dyeing processes, as well as a scries of observations which we 

 shall mention directly. 



