ON COLLOID CHEMISTRY AND ITS INDUSTRIAL APPLICATIONS. 41 
From his experiments Georgievics considers he has proved beyond doubt 
that the dyeing process takes place according to a definite physical law 
in the case of acid colours on animal fibres and salt colours on cotton. 
He uses Henry’s law very indiscriminately and alters it to fit his figures. 
The earliest mechanical theorists had been content with the theory 
that the dye particles from the solution wandered by endosmosis into 
the ‘ pores’ of the fibres and were there fixed by the formation of an 
insoluble ‘lake’ with the mordant. This being done in a hot bath. the 
contraction of the pores on cooling, aided by a possible astringent action 
of the various mordants, held the dye particles fast. The first investigator 
to suggest adhesion of dye particles to the surface of the fibre was Macquer 
in 1768, followed by Berthollet,* Thomas Henry, Bancroft,” and finally 
Walter Crum,‘ the greatest of von Georgievics’ predecessors, who defined 
this (purely physical) adhesion as ‘ catalytic force’ and insisted on the 
analogy between the dyeing process and the absorption of gases, salts 
dissolved in liquids and colouring matters, in an unchanged torm, by 
wood-charcoal and bone-black. Crum also points out the capillary 
attractive force of fibres, in common with other porous bodies. So well 
reasoned were his theories that the upholders of the then extremely vague 
and nebulous chemical theory felt themselves impelled to greater clarity 
and more logical statement of their point of view. 
The title of ‘ first chemical theorist’ is given to Bergmann,'’ who, 
in an essay on indigo, suggests that the wool extracts the whole of the 
indigotine disulphonic acid trom the bath because it has a greater ‘ affinity 
for it than the latter. This vague ‘ affinity ’ satisfied Berthollet, Henry, 
and Chaptal, but it was left to Chevreul,'* the head of the Gobelin Dye- 
works in Paris, to speak the first clear words on the nature of this ‘ affinity ’ 
in his “ Mémoire’ of the year 1834. He divides dyes into chemical com- 
on simple mixtures and substances that_partake of the nature of 
oth. Then, investigating those dyeing processes which appear to lead 
to chemical combinations, he says: ‘Chemical combination is analogous 
to salt formation,’ but the combinations between fibre and dyestuff are 
looser and evolve less heat than is observed in the case of acid reacting 
with base, and the combining proportions are not always constant. In 
dyeing, moreover, he recognises a ‘ contact-effect,’ adhesion, which he 
places in a position next to affinity in importance, and calls ‘ capillary- 
affinity °; his conclusion is that there are molecular forces at work between 
bodies in contact, which slowly combine. Dyeing will not take place 
unless there is a greater affinity between the fibré and the dye than between 
the dye and its solvent, and in judging of the probable result it is necessary 
to take into consideration the water, with dissolved acids, bases, or salts ; 
dyestuff ; fabric, and one or more mordants of more or less complex 
character. That one fibre dyes better than another in the same bath 
he explains by the principle of * elective affinity,’ which at that time so 
greatly exercised the minds of the students of the infant science of chemistry. 
12 Dictionnaire de Chemie, article ‘ Teinture.’ 
13-1791, 1804, Hléments de l’ Art de la Teinture. 
_ 14-1790, Nature of Colouring Matters. 
19 1794, 1813, Philosophy of Permanent Colours. 
16 loc. cit. : 
17 1776, Mémoires des Savants Etrangers, t. 9. 
18 Mémoires de l’ Académie des Sciences, 1853, 1861. Cours de Chemie appliquée 
a la Teinture, 2° partie, 1838-1864. 
