630 TABLES 669-682.— COLLOIDS 



Colloidal science originally dealt with that large field of small particles, but 

 now it has been extended to cover also those materials that are small in one or 

 two of the three dimensions. Thus, this field now includes chain molecules 

 and films as well as the fine particles. 



The diameters of atoms range from 2 to 3 A (angstroms) while diameters 

 of ordinary inorganic molecules extend from about 7 to 10 A. Organic mole- 

 cules are much larger and their dimensions may extend to 20 A or larger. 

 It is sometimes stated that colloid particles range in diameter from 20 A to a 

 much larger value but it must be remembered that it is difficult to fix such 

 dimensions. 



Many of the properties of colloids are due to their relatively very great sur- 

 face as compared with their volumes. Some of the newer experimental tools, 

 i.e., ultracentrifuges, X-rays, and the electron microscopes, have been a great 

 help in studying these particles and their reactions. Several tables follow that 

 give properties and characteristics of colloids and colloidal particles. 



TABLE 669.— BROWNIAN MOVEMENT 



The Brownian movement is a microscopically observed agitation of colloidal particles. 

 It is caused by the bombardment 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 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. 



Diameter 

 Material X 10 B cm 



Dust particles 2.0 



Gold 35 



Gold 1 



Gold 06 



Platinum 4 to .5 



Platinum 4 to .5 



Rubber emulsion 10. 



Mastic 10. 



Gamboge 4.5 



2.13 



The movement varies inversely as the size of the particles ; in water, particles of 

 diameter greater than 4,u show no perceptible movement; when smaller than Afi, lively 

 movement begins, while at IOwm the trajectories amount to up to 20w/x. 



TABLE 670.— PARTICLE SIZES OF SOME INDIVIDUAL DUSTS 2,2a 



Dust Diameter, cm 



Milk powder (by evaporation of fine spray) 1.4X 10~ 2 — .7X 10" 



Fine powder (300 mesh) e.g., cement 1X10" 2 — .7X10" 



Smelter fumes 1X10" 2 — IX 10" 



Atmosphere, fog particles 1.4X10 3 — 3.5X10" 



Cement kiln flue dust 6X10" 3 — .8X10" 



H 2 SC»4 mist from concentrators 1.1X10" 3 — 1.6X10" 



NH«C1 fumes lXlO" 4 - 1X10" 



Oil smoke lXlO" 4 - 5X10" 



Resin smoke lXlO" 4 — 1X10" 



Tobacco smoke l.SXlO" 8 — IX 10" 



**• Alexander, J., Colloid chemistry, vol. 2, Chemical Publishing Co. Used by permission. 



SMITHSONIAN PHYSICAL TABLES 



