ON COLLOID CHEMISTRY AND ITS INDUSTRIAL APPLICATIONS. 51 
loids that form geometric erystals colloid gold, silver, albumen, globulin 
and heemoglobin will all give crystals, while it is possible to obtain * globo- 
morphous * sodium chloride, and many crystalloid solutions pass through 
a jelly-like stage immediately before solidifying into crystals. It is more 
correct to speak of a ‘colloidal state of matter’ than of ‘ colloids’ as a 
sharply defined class. Colloidal solutions are either ‘ suspensoid ’ (7.e., 
having a solid disperse phase) or ‘emulsoid’ (having a finely divided 
liquid disperse phase); the particles or ‘ micelli’ varying in size from 
‘1 pp (crystalloid) to 1 wy (hydrosols) to 100 »p (turbidities) and from 
100 »p to 1 mm. (suspensions fine or coarse). Below 1000 pp the so- 
called Brownian movement is visible, both in true colloid-solutions and 
fine suspensions ; the motion is the more rapid the smaller the particles 
are; it does not vary on admitting or excluding the dark heat-rays ; 
it is independent of the direction of admitted light-rays, or the length 
and intensity of its subjection to these ; it will continue for months and 
even years; it does not depend on the charge upon the particles; it is 
affected by dilution, and the particles appear to influence one another. 
Various theories have been put forward to explain it. Quincke®® considered 
it due to the spreading of liquid layers over the surfaces of the particles ; 
Wiener,* Cantori, Renard, Boussinesq, and Gourg based it upon collisions 
between the particles and the molecules of the solvent ; Einstein,®? von 
Smoluchowski,** Zsigmondy,*! The. Svedberg,®* and Perrin ®® ascribe it 
to kinetic energy. 
The particles migrate, under the influence of the electric current 
(‘ cataphoresis ’), in a direction determined by their charge. The same 
colloidal solution may be positive: or negative—it depends on the 
nature of the continuous phase (‘ intermicellary liquid’) and the 
electrolytes it may contain. The direction can be measured by Coehn’s 87 
apparatus, or that of A. Cotton and H. Mouton,’* or of The. Svedberg 89 ; 
colloidal iron oxide, cadmium hydroxide, titanic acid, &c., and all basic 
dyestuffs, colloid or crystalloid, are positive and wander to the cathode ; 
colloidal gold, silver, platinum, sulphides, mastic, starch, gums, stannic 
acid, molybdenum blue, &c., and all acid dyestuffs, colloid or crystalloid, 
are negative and wander to the anode.®® A trace of added alkali causes a 
neutral colloid (e.g., suspended white of egg in pure water) to become 
negative, added acid causes a cathodic convection.®% The electrical 
8° Verh. d. Ges. d. Naturf. u. Arate, 1898; Beibl. zu d. Annalen d. Phys. 1899, 
23, 934-7. 
81 Poggendorff's Annalen d. Phys. u. Chemie, 1863, 118, 79-94. 
82 Drude’s Annalen d. Phys. (4) 1905, 17, 549-560 ; 1906, 19, 371-381 ; Zeitschr. 
}. Elektrochemie, 1908, 14, 235-239. 
89 Drude’s Annalen d. Phys. (4) 1906, 21, 756-780; 1908, 25, 205-226. 
84 Zeitschr. f. Elektrochemie, 1902, 8, 684-687; Koll. Chemie, p. 38-9; Zur 
Erkenntnis der Kolloide, 1905, S. 106-111, with tables. 
85 ‘Studien zur Lehre von den kolloiden Lésungen,’ 1907, 125-160; Zeitschr. f. 
phys. Chem. 1910, 78, 547-556. 
8° Annales de Chimie et de Phys. 1909, (8) 18, 5-114. 
87 Zeitschr. f. Electrochemie, 1909, 15, 653. 
88 Les Ultramicroscopes, &e., 1906, p. 144. 
89 Loc. cit. 
90 Zsigmondy, Kolloid Chemie, p. 44. 
1 Hardy, Journal of Physiology, 1899, 24, 288-304; Hardy, Zeitschr. f. p. 
Chemie, 1900, 88, 385-400; Perrin, Comptes Rendus, 1903, 186, 1388-1391; 1903, 
137, 513-514, 564-6. 
E2 
