Colloids, freezing reversible

Gaseous isobutene from a cylinder is condensed through the inlet /, into the Kon flask A, degassed, and distilled slowly into A, with T, closed, through trap B. This contains sodium which is heated by the furnace or mantle C to ca. 300 °C. The process is then reversed and the isobutene is distilled back into A, this time rather more rapidly so that it carries some sodium vapour with it which condenses to colloidal sodium, which fairly soon turns from purple to grey. The process is repeated, and this time the purple colour will last rather longer. Finally, the isobutene is distilled very rapidly into A so that it carries a lot of sodium vapour with it. A freeze seal... 

Not affected by presence of electrolytes Equally good in aqueous and non-aqueous dispersions Equally good in dilute and dense colloid systems Often results in reversible flocculation Good stability with temperature changes Electrolytes result in destabilization Effective especially for aqueous colloidal dispersions Best for dilute colloidal dispersions Often irreversible coagulation is obtained Coagulation often upon freezing... 

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