50 REPORTS ON THE STATE OF SCIENCE.—1917, 
theory of colloidal precipitation, for if the colour in the dyed skein is due 
to the formation of a colloid precipitate, it cannot be conceived that in 
one case solution should ensue and in another precipitation. 
Wilhelm Ostwald,5? M. van Bemmelen,®° H. Freundlich,® G. Losev,® 
L. Pelet-Jolivet,® and W. Biltz “ investigated the laws governing adsorp- 
tions by solids such as charcoal, of crystalloids and colloids, and the 
dyeing of mineral substances by dyestuffs. The associated phenomena 
of contact-electrification were also studied by Perrin,® who formulated 
laws,®* and by Pelet-Jolivet and Grand,®? Miolati,®* Gee and Harrison,®® 
and Knecht.?° Further work in the same fields—by Svante Arrhenius 7 
(diffusion of hydrosols and adsorption isotherms), O. Biitschli ” (structure 
of gels, and influence of hydration on a dried gel), Wolfgang Ostwald 
(classification of disperse systems, conductivity of metal hydrosols, electrical 
coagulation of suspensions, &c.), A. Lottermoser “ (metallic hydrosols, 
solid sols, freezing of metallic hydrosols, mutual precipitation), W. Pauli * 
(electric charge and coagulation of albumen, precipitation by electrolytes, 
internal friction of albuminous sols, structure of jellies, turgescence of the 
same and conditions governing its rapidity), P. P. von Weimarn’® 
(emulsoids and suspensoids, the formation of jellies from crystalloid 
solutions and the crystallisation of colloids, laws governing surface tension 
in two-phase systems), Emil Hatschek*? and Zsigmondy,’* working with 
Siedentopf, Ambronn, Heyer, Kirchner, Schultz and Wilke Dorfurt—has 
resulted in a comprehensive theory of colloidal systems, which many 
of the investigators have themselves applied to the dyeing process. 
The idea of ‘ solution’ is to be widened to embrace all possible com- 
binations of a solid, liquid or gaseous disperse phase with a solid, liquid 
or gaseous continuous phase.*® The most common solutions still are 
those having a liquid continuous phase, and the most common solvent 
is water—tfew, if any, substances refusing to go into colloid, if not crystal- 
Joidal, solution in water. Now, the obvious method of differentiating 
between crystalloids and colloids is by means of dialysis, whether it be 
carried out by the Graham dialyser or the far more complicated and efficient 
ones of Kiihne, Jordis, or Zsigmondy and Heyer. But a substance may 
be colloid in some solvents and crystalloid in others ; nor is it only crystal- 
59 Zeitschr. f. phys. Chemie, 1890, 6, 71-82; Lehrbuch der allgem. Chemie, 1 Aufl, 
1, 778-791 (1885), 2 Aufl. 2, 3, 217 et seq. (1906). 
6 Zeitschr. f. anorg. Chemie, 1903, 28, 238, 18, 114-7, 18, 350. 
61 * Kapillar Chemie,’ 1909, Zeitschr. f. phys. Chemie, 1909, 44, 129. 
62 Zeitschr. f. phys. Chemie, 1907, 59, 284-312, &e. 
63 ‘Theorie des Farbeprozesses’ (1910), Kolloidzeitschr. 1909, 5, 238-243. 
64 Berichte, 1904, 37, 1095-1116; van Bemmelen, Gedankboek, 1910, 108-20. 
65 Annales de Chim. 1909, 18, 5-114; Comptes Rendus, 1903, 136, 1388-1391, 
187, 513, 564. 
66 Journal de Chim. Physique, 1904, p. 619, and 1905, p. 100. 
6? Rev. Gen. 1907, p. 225; Koll. Zeitschr. 1907, 2, 41. 
68 Berichte, 1893, 26, 1788. 
69 ‘The electrical theory of dyeing,’1910, Journ. Soc. Dyers and Col. 1911, p. 279. 
79 Journ. Soc. Dyers and Col. 1909, 25, No. 7. 
71 Immuno Chemie, 1907, p. 17. 
7275 See Zsigmondy, Kolloid Chemie. 
76 ‘Zur Lehre von den Zustanden der Materie’ in Koll. Zeitschr. 1907-9, 2-5. 
‘Grundzuge der Dispersoid Chemie’ (1911), Chemikerzcitung, p. 725. 
77 Introduction to the Physics and Chemistry of Colloids, 1916. 
78 Kolloid Chemie, 1912. 
79 Zsigmondy, ibid. p. 25. 
