Tables 680-682 

 COLLOIDS 



TABLE 680. — General Properties of Colloids 



553 



For methods of preparing colloids, see The Physical Properties of Colloidal Solutions, Burton, 1916; 

 for general properties, see Outlines of Colloidal Chemistry, Journ. Franklin Inst. 185, p. 1, 1918 (con- 

 tains bibliography). 



The colloidal phase is conditioned by sufficiently fine division (ixio"* to 10- 7 cm). Colloids are 

 suspensions (in gas, liquid, solid) of masses of small size capable of indefinite suspension; suspensions 

 in water, alcohol, benzole, glycerine, 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: 1st, 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 (hemoglobin, etc.) 

 probably because of charged nuclei and which may be 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.). 



Lyophile, marked affinity between two phases, c.f., hydrophile. 



Lyophobe, " absent. c.f., hydrophobe. 



Smallest particle of Au observed by Zsigmody (ultramicroscope) i^xio-'cm. 



" " visible in ordinary microscope about 2.5x10-' cm. 



" " " ultramicroscope, with electric arc i5Xio- 7 cm. 



" " " " " with direct sunlight ixio-'cm. 



Viscosity of Lyophile Sols 



Gelatine 20° C, concentration 

 Silicic acid " , 



1, viscosity 0.021 

 1 . 00, " 0.016 

 2.00, " 0.035 



TABLE 681. — Molecular Weights of Colloids 



Determined from diffusion 



Gum arabic 1750 



Tannic acid (322)*... 2730 



Egg albumen 74 2 o 



Caramel 13200 



(Due to Graham) 



Determined from freezing 

 point 



Glycogen (162)* 1625 



Tungstic acid (250)*. 1750 



Gum 1800 



Albumose 2400 



Ferric hj'drate (107)*. 6000 



Egg albumen 14000 



Starch (162)* 25000 



Particle wt. Svedberg 



Egg albumen 34500 



Hemoglobin 68100 



Phycoerthin 20800 



* Formula weight. 



TABLE 682. — 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 io 22 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 4/1 show no 

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

 lomfJL. 



MITHSONIAN TABLES- 



