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Unformatted text preview: ing concentrations, e.g. to prevent the growth
of the particles and consequent precipitation. E.g. sols of various oxides have
been prepared by hydrolysis of salts.
2. Dispersion Methods
Material (bulk) is disintegrated into particles of colloidal dimensions by
(Greek pepticos, promoting digestion), the disintegration is brought
about by the action of a substance known as a peptizing agent. e.g.
cellulose is peptized by the addition of organic solvents, such as ethanolether mixtures, leading to the familiar "collodion" sol. In this case, the
solvent is itself the peptizing agent, but frequently something else must be
added; thus, precipitates of certain metal hydroxides in water can be
peptized by dilute alkali hydroxides.
b) Colloid mill
A method using physical dispersion in which the dispersion medium and
the substance to be dispersed are passed, grinds the material into
c) Electrical disintegration
An arc is struck between metal electrodes under water, with the
production of a metal sol (Brady’s method). 2 L IGHT SCATTERING BY CO LLOIDAL PARTICLES
When light passes through a medium that contains no particles larger than about 10-9
m i n diameter, the pa th of l i g ht cannot be detected and the medi...
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