493 Dr. Bolley on the Theory of Dyeing. 



If we call to miud the method of dyeing with green indigo 

 {vert de Chine, Lo-Kao), which the Chinese make use of, we must 

 admit a deposition of the colouring matter upon the surface of 

 the fibre. It cannot possibly be otherwise with safflovver {Car- 

 thamus), because we here also have to do with colouring matter 

 in a mere state of suspension. 



Fig. ] *, PL III. represents fibres of scoured silk coloured with 

 carthamus. On wetting such silk under a covered object-glass, the 

 loosening and swelling up of the crust of colouring matter ad- 

 hering to the surface is plainly to be observed. The fibre itself 

 indeed is not altogether of its natural tinge, but it is but little 

 discoloured. 



A similar behaviour is to be found, not only in those cases 

 where it might have been expected beforehand, but in a whole 

 series of other colours. 



Brazil-wood red, for example, which has been fixed on scoured 

 silk previously alumed by means of a decoction of Guinea-wood 

 red and chloride of tin (the so-called ^j/iysic of the dyers), ap- 

 peared to me under the microscope altogether similar (fig. 2). 



This phsenomenon showed itself most clearly in the case of 

 black dyes. There is, as is well known to practical dyers, a so- 

 called lieavy black dye used for silk, in which not only is the loss 

 of weight which the silk has undergone in scouring replaced by 

 the dye, but, in the case of unscoured silk, the M'cight is increased 

 sometimes 100 per cent., on account of the thickness of the 

 crust of colouring matter. By far the greater portion of the dye 

 stufi^ (mordant, &c. included) adheres in this case to the surface 

 of the fibre in crusts like strings of pearls (fig. 3). 



The fibre in the parts where still uncovered appears transpa- 

 rent and blackish. By means of a solvent the silk can be removed, 

 the crust of colouring matter scaling off and remaining partly in 

 compressed annular pieces, partly in flat scales (fig. 4). This 

 may be done by means of either caustic soda or solution of oxide 

 of copper in ammonia, which, however, is of greater service in 

 experiments with cotton. 



In the case of many other colours, also, I have observed the 

 very same phsenomenon, penetration of the silk by the dye being 

 nearly always accompanied by an accumulation of colouring mat- 

 ter on the surface : this was so with cochineal-pink, prussiau 

 blue, green, and archil. 



In the case of wool, the first phsenomenon — the infiltration of 



* Figs. 1 to 4, specimens of silk, are represented magnified 160 times by 

 a Keller's microscope. The places on which the colouring matter has been 

 ])recipitated in an external adhesive layer are sho\sn of a darker tinge, 

 without reference to the nature of the colour, which would have required 

 a more complicated lithographic treatment of the plate. 



