ON COLLOID CHEMISTRY AND ITS INDUSTRIAL APPLICATIONS. 45 
and Knecht himself, the chemical theory developed, and widened its 
horizons until it merged into the view that any dyeing process is neces- 
sarily dualistic: that some physical cause of deposition, be it (1) purely 
mechanical adhesion or (2) intermolecular diffusion analogous to the 
interdiffusion of any two solutions, with miscible solvents, until a state of 
equilibrium is reached, or (3) attraction of an electrical nature due to 
contact-difference of potential in the presence of a solute hydrolysed or 
ionised, must accompany any postulated chemical combination of dye and 
fibre. The fundamental theories governing the chemical combination of 
fibre and dye are twofold: (1) All dyestuffs have either acid or basic 
properties or represent salts of acids or bases, (2) these dyestufis combine 
with the animal fibres, especially wool, by virtue of the amphoteric nature 
of the latter. In the case of cotton, although the process is generally 
looked upon as being of a mechanical character, it is quite conceivable that 
a chemical action may sometimes occur.®® 
If cotton be rendered more acid, 7.e., by the formation of oxy-cellulose or 
nitro-cellulose, the fibre shows a marked affinity for basic colours. But 
nitrated or acetylated cotton has lost its affinity for direct colouring- 
matters. More evidence in favour of the Chemical Theory was advanced by 
Fort *® in a series of papers in the “‘ Journ. Soc. Dyers and Col.’ He con- 
structed a theory to explain the taking up of acid dyes by materials which 
are able to effect combination with acids and supported this theory by a 
large number of experiments. 
The first steps towards a clear and adequate explanation other than that 
of chemical combination of the phenomena of absorption by the fibre or a 
dye from its aqueous or alcoholic solution were made by A. Muller Jacobs.*° 
He bases his researches upon the known facts of diffusion of gases, of one 
liquid through another, and of crystalloid solutions through membranes 
that prevent the diffusion of colloids. Researches in the last-mentioned 
diffusions had been first published by Thomas Graham *! in 1861-1864. 
Muller Jacobs divided the ‘ attraction’ between the phases of a disperse 
- system into ‘ hygroscopy,’ ‘ capillarity,’ and ‘ imbibition’ between solids 
and liquids, all based on the phenomena of endosmosis. He is aware that 
even colloids will diffuse if the membrane be suitable (this confirmed in 1912 
with great accuracy by Zsigmondy and Siedentopf) and applies this to 
dyeing. Many dyestuffs, whose colloidal nature is known, will diffuse into 
and colour a parchment membrane, but will not stain the surrounding 
solvent. Some enter into the cell wall, some appear to be fixed upon it. 
Now, in dyeing the aim is either to fix this interpermeated colloid by a 
mordant which will turn it to an insoluble precipitate, still within the 
fibre, or to cause the endosmosis of such large molecules of the colloid 
dyestuff that it will not readily diffuse out. Silk and wool have small 
interstices in their membranous structure : an‘ animalising ’ process is any 
which so closes up the large interstices of the cotton fibre that it will act in 
thesame way. There is no need to postulate any entry into chemical com- 
bination on the part of the fibres (e.g., with the colourless rosaniline solu- 
tion). Heating is of value because it expands the pores of the fibres—here 
he reverts a century to the pure mechanicists of the infancy of the science— 
88 See Knecht, Manual of Dyeing, vol. 1, p. 19. 
89 1913, p. 269; 1914, p. 5; 1915, pp. 80, 96, and 222; 1916, p. 33. 
40 Textile Colorist, 1884 and 1885. 
41 Philos. Transact. 1861-1864. 
