44 REPORTS ON THE STATE OF SCIENCE.—1917. 
acting either as acid or as base under determining conditions, and postu- 
lates a definite acid or basic character both in the fibre and in the dye- 
stuff before true dyeing can take place (dyestuff here being taken to 
mean the system solvent plus solute dye plus mordant). In 1893, 
criticising the new Witt theory, he emphasises the chemical nature of 
his own hypotheses as being far more‘ rational and in accord with facts.’ 
That there is no clearly demonstrable adhesion to the law of multiple 
proportions he considers to be no unanswerable argument; the fibre 
molecules are ‘complicated and Jarge in comparison with those of many 
dyes. Vignon on this and other occasions pointed out the dissociation of 
dye-solutions in presence of the fibre ; the constitution of dyes like Congo 
N. 
red (RC S or=N—N=) that possibly makes them capable of the direct 
abs 
dyeing of cotton by combination with the cellulose. Finally, he admits the 
surface 
volume 
co-efficient being so large that it acts as a porous body. As did Zacharias 
later, he admits of two actions of the fibre : porosity with capillarity, and 
(usually) chemical combination. Knecht®° also showed that hydrolytic 
dissociation played a part in dyeing and that there was an intimate con- 
nection between the dissociation of a colour and its dyeing power. 
L. Hwass and G. Spohn*! adduce experiments in favour of the 
mechanical deposition theory, the latter insisting on deposition pure and 
simple, conditioned by molecular forces, and giving as evidence the micro- 
scopically visible crystals of lead chromate and manganese bistre, which at 
a distance of 60up one from the other give the illusion of homogeneous 
colour to the naked eye, but are separately and sharply deposited, some 
within, some upon, the fibre. He, like von Georgievics, refuses to admit of 
any chemical combination, since inorganic and unaffected matters like 
asbestos can be dyed just like animal and vegetable fibres, but Hwass 
admits the possibility of such combination (e.g., silk saturated with iron 
hydroxides). He looks on dyeing as dissociation phenomena; dyestufis 
readily dissociate, and the fibre acts towards the dissociated solute merely 
as would a thread hung in a saturated alum solution: it receives and 
encourages the deposition of insoluble bodies (the colour radicle or its 
hydrate) and rejects soluble. He is attracted to the solid solution theory 
of Witt (vid. sub.) as being the best statement of such phenomena of selec- 
tion. The appearance of von Georgievics in the arena now so thoroughly 
stated the case for the purely mechanical deposition theorists that no 
further citations need be made from the researches of his disciples to bear 
out his theories. 
Meanwhile, in the hands of C. O. Weber,?2. W. P. Dreaper,?* Rosen- 
stiehl, Gnehm and Rotheli,?4 A. W. Hallitt,?> A. Reychler,3* Prudhomme,3? 
3° Journ. Soc. Dyers and Col. 1898, p. 59. 
31 Joc. cit. 
82 Journ. Soc. Chem. Ind. 1894, p. 120. 
83 Ibid., 1904, p. 111; 1905, pp. 118 and 136. 
84 Journ. Soc. Dyers and Col. 1898, pp. 190 and 215. 
35 Tbid., 1899, p. 30. 
86 Bull. Soc. Chim. de Paris, 1897, p. 449. 
8? Rev. Gen. de Matt. Col. 1900, p. 184. 
great value of the physical structure of the fibre in dyeing, its 
