ON COLLOID CHEMISTRY AND ITS INDUSTRIAL APPLICATIONS, 49 
having been furnished by Zacharias). He now places the dyeing process 
in close relation to that of solution, with its phenomena of hydrolysis 
and ionisation, on the border-line between chemistry and physics. The 
cohesion between fibre and dye he now conceives to be possibly electrical 
in character, comparable to the combination of ions.  Kssentially, 
dyeing is the coagulation of a colloid in or upon another colloid, in such 
a form as to be insoluble; the electrolyte present in the bath causes such 
coagulation by its electrical effects on the colloid solute and its solvent. 
He does not now deny the possibility of subsequent chemical combination 
a the cohering fibre and dye, particularly in the case of animal 
res. 
W. P. Dreaper also did something to bring the observed dyeing pheno- 
mena into line with the evolving colloid theory. In his earlier papers 
his theory is one of endosmosis, proportional to pressure and to the absolute 
temperature, coupled with chemical combination; he also inclines to 
the solid solution theory, applying Linder and Picton’s idea of ‘ pseudo- 
solution ’ to the phenomena of dyeing. Finally he rejects both the chemi- 
eal and the solid solution theories, upholding one of pure adsorption by 
the fibre, acting as a more or less dry gel, of the hydrosols of the various 
dyes. Dyeing is always carried on in the wet condition, so that the fibre 
may be snfficiently hydrated to act as a hydrogel of the gelatine type ; the 
state of hydration Dreaper finds to influence the amount of any solution 
adsorbed. His text book (1906) ‘Chemistry and Physics of Dyeing’ 
gives a very broad and somewhat indecisive theory of ‘ the phenomena 
which take place in dyeing,’ including: (1) ‘ A solution state of the dye, 
within certain limits of aggregation, determined by the laws of size’ ; 
(2) ‘a fibre state corresponding to this state of aggregation, and of a 
permeable nature ’ ; (3) ‘ effective localisation of the dye within the fibre 
area, due to surface concentration phenomena’; (4) ‘localisation of 
salts, acids, &c., within the fibre area’; (5) ‘ indirect entrance of dye 
aggregate by molecular migration with subsequent re-formation of aggre- 
gates within the fibre area, according to the laws of size’ ; (6) ‘ de-solution, 
due to secondary attraction between the fibre substance and the dye, 
or by reduced surface energy phenomena, or concentration effects’; (7) ‘in 
some cases, primary or chemical action may play some part at this stage ; 
this may even, in some cases, take the place of de-solution phenomena’ ; 
(8) ‘ dissociation effects in the case of basic dyes which may lead to the 
production of very basic salts in a high state of aggregation within the 
fibre area.’ He is aware of the electro-positive or electro-negative nature 
of all colloids, but does not connect this with the coagulating (he calls 
it “ degrading ’) influence of crystalloids in the dissolved colloid. 
A similar cognition of the diverse and seemingly irreconcilable nature 
of the dyeing processes was published by Grehm and Rotheli,®* who, after 
an exhaustive criticism of all existing theories and evidence, conclude 
that each existent theory can find place in the final and adequate one. 
They were the first to show that cotton takes up direct cotton colours in 
an unchanged condition. Later Gnehm and Kiufler performed the 
following experiment: a skein of cotton dyed with benzopurpurin was 
boiled with two undyed skeins in a small beaker. After drying, all three 
skeins were alike. This observation is in direct opposition to Krafit’s 
58 Zeitschr. f. angewandte Chemie, 1898, pp. 482, 501. 
1917. E 
