Preparation of Some Simple Colloidal Systems

It is particularly important in all work on colloids to observe the most stringent precautions to ensure the absolute cleanliness of all apparatus. 

Add I cm3 of a 1% solution of gold chloride (HAuCU SHsO) to 100 cm3 of distilled water, bring to the boil, and add 2.5 cm3 of 1% sodium citrate solution. Keep the solution just boiling. After a few minutes observe the appearance of a blue coloration, followed shortly by the formation of a ruby-red gold sol. 

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