4o6 



Tables 622-524. 



COLLOIDS. 



TABLE 522. — General Properties of Colloids. 



For methods of preparing colloids, see The Physical Properties of Colloidal Solutions, Burton, igi6; for general 

 properties, see Outlines of Colloidal Chemistry, J. Franklin Inst. 185, p. i, 1918 (contains bibliography). 



The colloidal phase is conditioned by sufficiently fine division (i X lo"'' to lo"' cm). Colloids are suspensions (in 

 gas, liquid, solid) of masses of small size capable of indefinite suspension; suspensions in water, alcohol, ben2»le, glyc- 

 enne, are called hydrosols, alcosols, benzosols, glycerosols, respectively. The suspended mass is called the disperse 

 phase, the medium the dispersion medium. 



Colloids fall into 3 quite definite classes: ist, those consisting of extremely finely divided particles (Cu, Au, Ag, 

 etc.) capable of more or less indefinite suspension against gravity, in equilibrium of somewhat the same aspect as the 

 gases of the atmosphere, depending as in the Brownian movement upon the bombardment of the molecules of the 

 medium; 2nd, those resisting precipitation (haemoglobin, etc.) probably because of charged nuclei and which maybe 

 coagulated and precipitated by the neutralization of the charges ; 3rd, colloidal as distinguished from the crystalloidal 

 condition, the colloid being very slowly diffusible and incapable unlike crystalloids of penetrating membranes (gelatine, 

 silicic acid, caramel, glue, white of egg, gum, etc.). 



Smallest particle of Au observed by Zsigmody (ultramicroscope) i . 7 X lo"' cm. 



" " visible in ordinary microscope about 2.5 X io~6 cm. 



" " " " ultramicroscope, with electric arc 15 X 10"' cm. 



" " " " " with direct sunlight i X lo"' cm. 



TABLE 523, — Molecular Weights of Colloids. 



* Formula weight. 



TABLE 524. — Brownian Movement. 



The Brownian movement is a microscopically observed agitation of colloidal particles. It is caused by the bom- 

 bardment of them by the molecules of the medium and may be used to determine the value of Avogadro's number. 

 Perrin, Chaudesaignes, Ehrenhaft and De Broglie found, respectively, 70, 64, 63 and 64 X 10^'' as the value of this 

 constant. The following table indicates the size and the dependence of this movement on the magnitude of the particles. 



The movement varies inversely as the size of the particles; in water, particles of diameter greater than 4jtt show no 

 perceptible movement; when smaller than .ifx, lively movement begins, while at 10 mix the trajectories amount up to 

 aotnfi. 



Smithsonian Tables. 



