Dr. Bolley on the Theory of Dyeing. 498 



the dye into the mass of the fibre — is considerably the most 

 common; the second, however — the external adhesion of the 

 colouring matter — is by no means unexampled. On careful 

 investigation of the principal series of specimens of coloured wool, 

 a considerable accumulation of colouring matter may be found in 

 the little pits which occur in the external membrane of the fibre. 

 This may be best shown by treating with dilute caustic soda 

 when the colour is not destroyed by an alkali. I have dyed wool 

 black in the same way as the heavy black dye is produced on silk, 

 and found that considerable quantities of colouring matter ad- 

 hered to the surface of the wool. 



In the case of cotton, and indeed of all cellular vegetable fibres, 

 the question is much more intricate ; hence the contradictory re- 

 sults at which different observers have arrived. Oschatz and Ver- 

 deil declare that, as a rule, the mass of the cell-walls is coloured 

 uniformlythi'oughout; both, however, admit exceptions. Maschke, 

 on the contrary, maintains that cellular fibres take up no colour- 

 ing matter from a solution, — meaning, no doubt, unless previously 

 mordanted. W. Crum adopts the theory of the infiltration of the 

 dye, and its accumulation in the interior of the cells ; and Persoz, 

 as we have seen, only admits the external adhesion of the colour- 

 ing matter to the fibre. 



In this case, that which Oschatz and Verdeil declare to be the 

 rule, namely the penetration of the dye throughout the substance 

 of the cell-walls, cannot be admitted as such. On the contrary, 

 the cases are few in which the penetration of the dye can be 

 clearly recognized ; by far most commonly the substance of the 

 fibre remains uncoloured. 



I shall mention two methods of conducting the investigation*. 

 In the first place, sections were made of bundles of cotton-thread 

 soaked in gum and dried. These were examined with a suitable 

 magnifying power, the precaution being taken, by means of the 

 covering glass of the object-bearer, to turn them about — that is to 

 say, to give them a rotatory motion — so as to be able to compare 

 the effect of the dye on the external and on the sectional 

 surface. 



Only in a few cases in a long series of observations could it be 

 said that the cell-walls appeared to be somewhat coloured through- 

 out their substance. Cotton dyed in a decoction of Brazil wood, 

 after being treated with perehloride of tin, presented this appear- 

 ance ; but even here it was evident that the external sm-face was 

 more strougly coloured than the rest. A similar appearance was 

 presented by cotton dyed with the so-called " Kaliblau " (prus- 



* It was of importance to me (and I mention it here expressly and with 

 thanks), that my oolleagne, Dr. Cramer, had the kindness to repeat and con- 

 firm my observations in certain of the most striking rases. 



